Digital Dentistry 2018 by Professional Dentistry

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Contents...

1 Breaking down the choices of all ceramic crowns and bridges....................................................... 4

4 3D and 4D printing in dentistry*......................................................... 34

Materials............................................................................................... 4

Overview of additive manufacturing............................................... 37

Pressed or milled?................................................................................ 6

General description of the workflow using

What is monolithic or veneered?....................................................... 6

additive manufacturing technologies.............................................. 38

Singles or bridges................................................................................. 8

Multi-layered dental structures.......................................................... 39

Adhesive single wing bridges............................................................. 10

3D multi-material-printing of replicas of natural teeth.................... 39

Prep colour........................................................................................... 10

Applied materials................................................................................ 40

Incisal area........................................................................................... 40

Evaluation of printing results............................................................... 41

Summary............................................................................................... 10

2 Digital photography as an aid to shade matching.................................................................. 12

Description of the technology........................................................... 35

5 Digital radiography................................................................................ 42

Chief complaint................................................................................... 14

Examination.......................................................................................... 14

Historical background......................................................................... 42

Types of digital radiography.............................................................. 43

Advantages of digital radiography.................................................. 45

Disadvantages of digital radiography.............................................. 46

Other considerations........................................................................... 46

Discussion and treatment plan.......................................................... 14

Digital photography and shade-mapping...................................... 16

Laboratory discussion.......................................................................... 22

Tooth preparation................................................................................ 22

Stump shades....................................................................................... 24

Review of provisionals......................................................................... 24

6 Research updates in digital dentistry............................................. 48

Fit appointment................................................................................... 24

Lab study questions cast accuracy.................................................. 49

Try-in paste............................................................................................ 24

Orthodontic applications................................................................... 50

Porcelain treated................................................................................. 25

Full arch implant care......................................................................... 51

Adhesive and cement........................................................................ 25

Single implants digitalised................................................................... 51

Clean-up............................................................................................... 26

Occlusal splint benefits from the digital revolution.......................... 52

References........................................................................................... 53

Review appointment.......................................................................... 26

3 Minimal intervention dentistry and caries detection.......................................................... 28

The CariScreenÂŽ.................................................................................. 29

DIAGNOdent........................................................................................ 30

The Midwest Caries I.D.â&#x201E;˘................................................................... 31

Spectra................................................................................................. 31

Soprolife................................................................................................ 32

The Canary System.............................................................................. 32

CarieScan............................................................................................. 32

CariVu................................................................................................... 33

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Chapter 1

Breaking down the choices of all ceramic crowns & bridges By Ashley Byrne

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As well as helping to solve some problems, technology can also create some of its own. In this article laboratory owner and technician Ashley Byrne discusses some of the dilemmas spawned by materials in the digital age. The term â&#x20AC;&#x2DC;All ceramic crownâ&#x20AC;&#x2122; has been around for well over 25 years and whilst there used to be only a couple of types available, there are now literally dozens of types of these restorations on the market, with multiple ways of producing them. This laboratory production method and materials have various advantages and disadvantages that should influence your choice of all ceramic relevant to the restoration type.

Materials The main two materials that all ceramic falls into is press-able materials like Lithium Disilicate and milled and sintered materials like Zirconia. Lithium Disilicate is available from multiple companies and usually around the 450Mp strength. Zirconia is available in many more types with strength ranging from 550Mp all the way up to 1400Mp. The variety comes from the various different types of Zirconia but as a rule of thumb, the more translucent the Zirconia, the weaker the material is. This has its own advantages and disadvantages as the stronger Zirconia options are ideal for larger span bridges but will not look as natural as their weaker translucent counter parts. If we look at these materials in more depth with regards to production and use, we have in summary three major all ceramic materials - Lithium Disilicate and the two extremes of Zirconia, that being the translucent weaker material and the opaque stronger material.

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Pressed or milled? The terms pressed or milled are manufacturing procedures used in dental laboratories. Pressed is a derivative of the lost wax method when a wax design is made, encased in investment and then the wax is burnt out and metal poured in. With modern pressing the wax is still invested and burnt out but then a Lithium Disilicate ingot is pressed into the cavity under pressure. It is only Lithium Disilicate type materials that have these liquid under temperature properties. Lithium Disilicate can also be milled in its solid state. This ‘post processed’ hardened material is not very easy to mill as is prone to micro chipping around the margins. As it is milled in its hard state, this can be costly on burs which in turn, drives the price of the restoration up. Most Llithium Disilicate is pressed because of this reason. Zirconia is not a material that can be pressed and can only be milled. Zirconia is bought in a blank or disc form and has to be milled in its soft state, which is a chalk like appearance. This soft state means there is less wear and tear on the burs and additionally, considerably less chipping. The other advantage of soft state materials is they can be stained before the sintering process, which allows technicians to put deep colours into the neck and occlusal areas and enhance the restorative result. The material is milled at percentage larger size as the milled soft state Zirconia is then sintered over night and shrinks into its final state. The final sintered material now takes on its colour from either the impregnated blank or the stains applied.

What is monolithic or veneered? Monolithic literally means ‘formed from a single block’, meaning the crown is made solely from the same material. This can be achieved in all types of all ceramic crowns and due to the solid block, is considered stronger as there is no material to chip off. However the downside of monolithic can be the lack of aesthetics due to it being milled in a solid block. Modern digital CAD-CAM materials are changing this with layered blocks going from dentine to enamel in the same disk. The crown is then milled with the cusps in enamel and, with careful staining, the crown can look very natural. It is not ideal however, for restorations like a single central where the multiple colours and effects are needed to match the tooth adjacent. This is when a veneered all ceramic crown is used. The process of veneering is like a porcelain fused to metal crown but instead of a metal coping, a coping is milled or pressed from one of the all ceramic materials. The process of design is the same as the monolithic material but then the crown is cut back to allow space for the veneering

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ceramic. The coping is then milled or pressed and then instead of just glaze being used, multiple colours of ceramic are built and fired onto the coping to achieve optimum aesthetics. This material may be prone to a risk of chipping or fracture due to the multiple layers but modern materials have dramatically reduced the risk of fractures.

Singles or bridges As patients push for â&#x20AC;&#x2DC;metal freeâ&#x20AC;&#x2122; restorations, bridge options have had to improve in the all ceramic market but they are not without complications and compromises. Ceramic is not only weaker than metal sub structures but also considerably more brittle. This limits its use in many cases, especially where the jaw is flexing like in the cross arch bridge in the mandible. The flex of the jaw on opening and closing can cause these full arch bridges to crack and shatter. In large full arch cases we generally advise to break up the bridges into smaller spans. For single units, both Lithium Disilicate and Zirconia can be used but the main consideration is the bonding of these units. Lithium Disilicate can be acid etched and bonded but Zirconia cannot. Therefore, when using minimal preps, veneers or inlays, it would be a contradiction to use Zirconia and it is likely to debond. Modern cements are now claiming to assist in the bonding of Zirconia but there is almost no data on the bond strengths. When bridges are being designed, the material choices become a lot problematic. Lithium Disilicate can be used in bridges but it is the weakest of all the all ceramics so great care must be taken when selecting the materials. Bruxists, posterior units and patients with a strong bite would all be contraindications. In many labs, including ours, we actively discourage any bridges in Lithium Disilicate and default to Zirconia. The problem with Zirconia bridges is the choice of Zirconia used. If we use the high strength material in monolithic we create a near unbreakable bridge but looks chalky and opaque. A small compromise is to veneer the strong material which gives it the ideal all ceramic strength to aesthetics ratio. In high aesthetic cases in the anterior zone, then the translucent Zirconia can be used but like with Lithium Disilicate, we avoid bruxists and strong bite cases.

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Adhesive single wing bridges Adhesive bridges (commonly known as Marylands) are one of the most conservative ways to restore missing teeth, especially missing laterals. The problems of restoring cases like this using the traditional metal is the greying of the teeth the metal wing can give the patient. Using all ceramic is a method that can work but material choice and the patient has to be ideal. These little bridges need to bond to the central or the canine which can be an issue for Zirconia as the bond strength is not as high as etched Lithium Disilicate. It is essential there is no occlusal force on these bridges and certainly no bruxing. If the patient looks to be in a situation where low force will be on the all ceramic single wing bridge, these can be an incredible restoration which can disappear in the mouth.

Prep colour Another deciding factor on the all ceramic we use depends on the prep colour. If we plan to use a translucent Zirconia or Lithium Disilicate, then a prep which is black, very dark or contains a post and core, is not ideal and will discolour the crown. In this case we would use one of the stronger opaque zirconia materials. To help your technician with this part of the process, we would always suggest sending a photograph of the preparation to assist in material choice.

Summary Choosing the right all ceramic material can be challenging and working with your dental technician on team treatment planning is vital for the correct result for your patient. With a choice of over 100 different all ceramics - varying on translucency, strength, and the ability to bond, it can be a challenge. As patients become more health focused and the demand for â&#x20AC;&#x2DC;metal freeâ&#x20AC;&#x2122; restorations continues to rise, it is vital that we understand how these materials work from both a functional and an aesthetic point of view. With the growth of CAD-CAM methods in both chair side and laboratory, companies are investing heavily in developing new all ceramic materials and our choices are only likely to increase.

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Chapter 2

Digital photography as an aid to shade matching By Ken Harris

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The task of trying to mimic natural tooth tissue with an aesthetic synthetic alternative has always been difficult and becomes more so when fabricating indirect restorations. Working with a laboratory technician, who may never actually meet the patient in the flesh is a major challenge and communication between the clinician and the laboratory is of utmost importance. The most popular method to determine shade is still the subjective eye of the clinician even though the clinicianâ&#x20AC;&#x2122;s interpretation of traditional shade tabs is notoriously unreliable; not forgetting that the effects of different light sources upon the perception of colour can also be significant. The skill of the clinician in imparting the information required to the lab technician is therefore a key factor. Furthermore, the skill of the technician in carrying out the instructions provided by the clinician is equally important. There have been many attempts made to simplify this process from increasingly sophisticated lab tickets to actually attempting to draw in great detail, the maverick colours and characteristics of a particular tooth even to the use of sophisticated computerised colour scanners, yet the problem still persists. It is all too easy for us as clinicians to blame the laboratory technician when there is a mismatch in colour, yet often the problem is due to a breakdown in communication. Ultimately it is the responsibility of the clinician to provide what is required because it is the clinician who has to actually fit the restoration and also deal with any embarrassing errors that may only manifest themselves for the first time at chairside. There are many ways to communicate with our labs, and it is not unusual these days, to use a combination of tools to get our message across. Obviously, photography can be a key tool, especially when coupled with sophisticated image management software such as Photoshop there are also more sophisticated shade tab systems, which are attempting to deal with the problem by dealing with hue, chroma and value as separate entities.

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Chief complaint A 62-year-old, recently retired gentleman in excellent health, and possessing significant dental awareness attended the practice to enquire about the possibility of cosmetic improvement to his teeth. Initially, he felt that a complete smile makeover was what he required, but when he realised the financial implications he decided that perhaps compromise would be the way forward. He left the practice promising to think things over and it was almost a year before he contacted us again. In the meantime, his regular dentist had replaced a gold crown upper left premolar with a porcelain crown but had not felt competent enough to deal with the challenges of more anteriorly placed porcelain work given the dramatic colouration of his natural teeth. For this reason, the patient had returned; believing we could deliver a successful outcome and match the shades.

Examination He was a regular patient at another practice and stated he intended to return there for his regular treatment, and so we addressed only his cosmetic interests. A routine examination revealed nothing of note, and upon examining his occlusion felt we could work within his current occlusal pattern and decided upon a ‘conformative’ occlusal approach despite the posterior wear, as we were only working with two teeth. The teeth themselves were vital despite large restorations in place, and radiographs revealed no areas of concern apically. Medically he was taking anti hypertensives, but nothing else.

Discussion and treatment plan It is relatively easy to shade match when providing porcelain work for an entire upper arch, which was what I expected the patient to request after his visit last year, however, he had actually decided his cosmetic goals could be achieved by working with just two teeth. The teeth in question were the in-standing upper lateral incisors, which he wanted bringing forward into the arch, and of course he wanted them to match his other teeth perfectly. His natural teeth, were exactly as we might expect for a gentleman in his 60s with chips, cracks and staining producing what might charitably called a ‘lived-in look’. I explained a great deal of laboratory communication would be necessary to satisfy his needs, especially given his heightened dental awareness, and he agreed to proceed with treatment.

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We tested the idea of bringing the laterals forward by adding composite resin freehand to their labial services and the resulting appearance was acceptable. At this stage I suggested we could produce the result he required with direct composite resin, however, he felt a more long term solution was what he required and so we agreed to fit all ceramic porcelain restorations to both upper lateral incisors.

Digital photography and shade-mapping He returned for a shade mapping appointment where photographs were taken and shade comparisons noted. The light in my treatment room is from fluorescent tubes, which are not ideal for shade-matching and the process was therefore carried out in the waiting room, which has full length windows facing north, as a source of natural light, and with all the lights turned off. Optimum light quality to distinguish subtle colour differences is Cloud-Diffused North Noon Daylight because it provides a uniform spectral power distribution and a colour temperature of 5000 K. Photographs of the anterior teeth were taken from directly in front but also from oblique angles and above and below, in an attempt to gather as much information as possible; a procedure known as ‘Vectoring’. Teeth were also photographed both wet and dry to show surface texture variations. Extra close-up photography was utilised in an attempt to see all the subtle details within the enamel of the adjacent teeth. Shade selection was narrowed down to a small selection of possible shades by using the Vita pan 3D shade matching system. Final shade selection (Hue) was aided by using a selection of photographs, taken each with a different shade tab held next to the teeth for comparison. Using Photoshop, all the photographs were then ‘improved’ by adjusting the histogram to provide for full chromatic range, and sharpened to varying degrees to highlight individual nuances of detail. We were able to once again use Photoshop to take out the colour altogether, creating black and white photographs. Consulting a selection of black and white photographs of the teeth with differing shade tabs adjacent to the tooth in each picture is an ideal way to check the ‘value’ without the complications of hue to distract us. Eventually, I was able to draw a detailed plan for the shade, including the cracks and surface texture required for the lab to make a realistic attempt at colour matching. All the photographs were then e-mailed to the lab and an appointment scheduled to talk to the technician before any work was begun. It is important that the lab actually see the digital photographs on their screen in the same way as you see them on yours so it is best to ensure that both screens have the same resolution and are calibrated to the same colour range. 16

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MAKE IT RETRIEVABLE! ANGLED SCREW CHANNEL TECHNOLOGY FOR IMPLANT RESTORATIONS Winner of the â&#x20AC;&#x2DC;Most Innovative Labâ&#x20AC;&#x2122; at the Dental Lab Awards London 2016: Stephen Green is a big fan of Angled Screw Channel Technology for Implant Restorations

How Stephen Green Dental Studio utilise the benefits of CADCAM technology to support the dentist tephen Green Dental Studio opened in 1988, and has developed a reputation based on the labs expertise in CADCAM dental technology through education and innovation. Stephen Green Dental Studio was an early adopter of digital technology. Now all our work is digitally manufactured on a variety of CADCAM systems and milled in-house. We use angled screw channel components daily, a large part of the CADCAM work we manufacture are implant restorations so milling in-house is essential for us to provide an efficient service to the dentist. We have Angled Screw Channel digital libraries which fit perfectly with my continued drive to manufacture all our work through a digital workflow!

Angled CAD-CAM screw channel 18

SOLUTIONS WITH ANGLED ABUTMENT SYSTEMS At Stephen Green Dental Studio, we use the Angled Screw Channel Technology for many cases where there is either little bone and the implant has been placed in what could be considered a compromising position to restore or cases where there is plenty of bone but not in the most ideal situation, where once a Titanium custom abutment would have been used with a cemented crown we can now achieve screw retention and retrievability. This CADCAM technology allows us to give our dentists a screw-retained crown almost every time.

The difference between the emergence for a straight & angled abutment Ti-base

DOES ANGLED SCREW CHANNEL TECHNOLOGY COST MORE? Angled channel technology costs only slightly more as there is a small premium on the components and it takes a little more time to design however our digital technology helps keep the costs down with proven efficiencies through CADCAM.

TECHNICAL INFORMATION FOR ANGLED SCREW CHANNEL TECHNOLOGY You will need another screw driver as these systems are very specific regarding screw torque. This is part of the USP of Angled Screw Channel technology as a â&#x20AC;&#x2DC;cupâ&#x20AC;&#x2122; in the screw accepts the driver which has a round head allowing variation in angle for tightening. Manufacturers of Angled Screw technology make abutments to fit a range of the leading implant systems and the driver is unique to individual systems.

WHY WOULD WE CHOOSE ANGLED SCREW CHANNEL TECHNOLOGY? A difficult situation sometimes for Dentists to appreciate is just how out of alignment an implant has been placed; this could be for many reasons unbeknown to the technician. What we do know is that we are being asked in the lab to restore the case and preferably with screw retention. At Stephen Green Dental Studio we pride ourselves on finding a solution and often the answer is a correction through CADCAM and Angled Screw Channel Technology.

ISSUES RESOLVED WITH ANGLED SCREW CHANNEL TECHNOLOGY One of the simple examples can be a molar implant crown where if the implant is at a difficult angle, and the screw hole is straight, the emergence angle can be in such a way that itâ&#x20AC;&#x2122;s not aesthetically pleasing. Angled Screw Channel Technology allows us to centralise the screw hole making the screw hole easier for the dentist to close and making a stronger crown as the hole has more material around it. Perhaps the most benefit for Stephen Green Dental Studio, its clients and patients is how Digital technology along with Angled Screw Channel Technology systems help us to communicate with our dentists. When we have a restoration that we consider may need an angled screw channel we can scan the model, design the restoration by utilising the comprehensive library of Ti-bases which we can then design our restoration on. Once this has been done we have a virtual design to full contour to send as a screenshot via secure email to the dentist to review, my clients like this simple opportunity to review their case before anything has been manufactured helping to avoid any misunderstanding or incorrect design of the frameworks. Once this has been approved we can continue the manufacturing process. 20

Comments from our dentist clients regarding Angled Screw Channel Solutions

‘The use of the Angled Screw Channel Technology has helped us get out of a number of difficult situations where the use of an Angled Screw Channel has meant we can screw retain a crown or bridge in a compromised position’. ‘We don’t want to cement crowns at all anymore if possible and the Angled Screw Channel means we can choose screw-retained crowns when we need to achieve this’. ‘Cemented crowns with a Custom Titanium abutment are not always suitable if we need to retrieve the crown, previously this could mean cutting the crown off but the Angled Channel System means we can screw retain and achieve a retrievable situation’. ‘The way Stephen’s team design the work on CADCAM so we can review before the manufacturing has started is the ideal way for us (the dentist) to review a case, it is an essential part of what we like about Stephen Green Dental Studio’s commitment to digital technology in order to help and support the dental practice’. ‘The technology at Stephen Green Dental Studio which allows the predictability of CADCAM combined with the use of the latest bio-compatible materials makes this system hard to beat’!

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Laboratory discussion Following discussions with the lab, we decided to use Authentic pressed porcelain (Jensen Industries) to fabricate the restorations as the lab felt they had more than enough space labially to achieve a good shade. However, the laboratory still felt further shade investigation was necessary before building the final restorations so they fabricated a few trial ‘Tabs’ of porcelain across a range of shades and sent them to the practice, and the patient then returned for shade comparisons with these trial ‘Tabs’ to be made. A similar shade likeness was chosen from the ‘Tabs’ and a further range of colour corrected and black and white photographs with the selected ‘Tab’ in place were taken for the laboratory. The patient was then scheduled for his preparation appointment.

Tooth preparation Both lateral incisors were in-standing and as the aim was to bring them forward into the arch we anticipated very little labial reduction would be necessary during our preparation, yet still be able to leave space for adequate thickness of porcelain for the technician to create a lifelike restoration. One tooth also had a significantly sized composite resin filling with the other way out of line we had to concede that perhaps simple veneers would not suffice. Both teeth were mocked-up with composite once again to bring them into the required position in the arch, and using depth cutters3 the labial surfaces were prepared. It turned out that only margin preparation was required labially and that almost all the labial enamel was left intact. Upon removal of the old composite restorations, however it was decided that the upper left lateral incisor would best be served by placing a full coverage crown. Equally, significant porcelain wrap-around was indicated for the upper right lateral incisor veneer, so our ideal of minimal preparation was somewhat compromised. The restoration margins were then refined with a Kavo sonic-flex handpiece respectful of biologic width, and all sharp angles within the preps rounded off with soflex discs (3M). The exposed dentine was ‘Hybridised’ to seal the tubules, and following gingival retraction, major impressions and opposing arch impressions were taken with silicone (Express; 3M), as well as interocclusal record (Futar). Having already examined the patient’s occlusion, it was not deemed necessary to use an articulator (other than the basic average value model) and so no face-bow recording was taken. Provisional restorations were fabricated and shaped freehand to an acceptable contour using multi-fluted carbide birds and soflex discs.

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Provisional restorations were abdicated freehand with reference to contact point placement and again, considering biologic width.

Stump shades When using all ceramic restorations it is important for the lab to be aware of the underlying colour of the preparation stumps to deal with any modifying influence they may have upon the final shade, so the shade of the stumps were recorded and again extensively photographed before the Provisionals were fitted.

Review of provisionals The patient attended two days later without the numb lip, for further refining of the shape of the provisionals, and then silicone impressions were taken of the final acceptable provisionals. Further photographs were also taken and everything was sent to the lab. Further detailed discussions took place with the lab, and it was decided that two different-shaded sets of restorations should be fabricated rather than just the one as we felt unsure which of to final shade designs would be best. The decision which set to use would be made at chairside.

Fit appointment Three weeks later the patient attended for fitting. The porcelain restorations were first shown to the patient, and his approval was sought, and agreement was reached to fit the restorations before any LA was administered or any Provisionals removed.

Try-in paste LA was then administered, the Provisionals were removed, and the preps gently sandblasted and cleaned with Chlorhexidine (Consepsis scrub; Ultradent), and the porcelain restorations were tried on to check fit. They were then both tried on with water in lieu of a transparent cement to see what effect the stump shades would have on the final shade. As is often the case in older patients who have reduced

thickness of enamel, their natural teeth have a relatively lower ‘value’ than a younger person’s teeth. So, perhaps as might be expected in this case, it was felt after try in with water that the value of the restorations would be too high if we used a transparent cement. So after experimenting with try-in pastes of different shades, we were able to select a coloured try in paste which would help us achieve a good match. Once tried in with the correct try-in paste, the porcelain restorations were again shown to the patient, and his approval was sought, and agreement was reached to actually fit the restorations.

Porcelain treated The fit surface of the porcelain was then etched at chairside with HF acid (ultradent), and then each placed in a separate test tube of distilled water and then into an ultrasonic bath for cleaning. They were then removed and dried with suction; can we trust our air supply to be oil free? Multiple coats of Silane coupling agent (Monobond-S; Ivoclar) were then applied and sequentially evaporated with warm air for 5 minutes using a hairdryer.

Adhesive and cement Rubber dam (split dam technique) was then placed and the preps were cleaned again with chlorhexidine, and using 35% phosphoric acid, the total-etch system was used and care was particularly taken to avoid over-etching. The etched preps were rinsed thoroughly and kept hydrated with an aqueous based desensitising agent (Aquaseal; Aquamed Industries). A 4th generation bonding system (Optibond FL; Kerr) was applied to the preps as directed by the manufacturer, with separate primer and adhesive components used. Light cured resin cement (Appeal; Ivoclar) with a ‘Low value’ shade (shade -2) was applied to the porcelain and to the preps and the restorations were fitted. The restorations were spot cured using the 2.0 mm curing tip to tack them down, and excess resin cement removed before thorough, final curing with the wide diameter 11.0 mm light tip.

Clean-up If the restorations fit correctly there is no need to use rotary instruments to refine the gingival margins, and a curved scalpel (Swann Morton no 12) was all that was needed to clear excess resin. Contact points were also cleared and the areas polished with diamond strips (Visonflex; Brassler Komet) and checked for smoothness with dental floss. Finally, occlusion was checked and found to be fine, so there was no need to adjust the porcelain, and consequently no need to polish the porcelain either. Photographs were taken and the patient was dismissed to return the following week for final review.

Review appointment The patient rang to cancel his review appointment the day he was due to return for final checks and to offer feedback. He reported that he was delighted with the results and so were his family and friends. Consequently we were unable check final results or take final radiographs or indeed any other photos. A report was sent to his dentist outlining which treatment had been carried out, however, he did suggest he may consider further cosmetic work with us in the future if the need should arise. *A modified version of this case report appeared in the International Journal of Cosmetic Dentistry 2012 3: 1-10.

Figure 1 a and b Retracted images before and after

Figure 2 a-f Various images before and after

f) 27

Chapter 3

Minimal intervention dentistry & caries detection

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One of the main influences of digital dentistry has been to support and enhance knowledge and techniques already in existence. This is particularly true of its role in caries diagnosis where early detection is th key to more holistic patient care.

The guiding principles in restorative dentistry have for many years been those the Black classification of cavity design, originated over one hundred years ago and based on the maxim of extension for prevention. While in this regard not a great deal changed for at least the first half of the twentieth century, for the last few decades various factors have come to bear on the subject which have caused what is now a significance shift in the prevention and treatment of caries. The understanding of the role of fluoride in caries prevention and its adoption for inclusion in toothpastes and other forms of professionally applied products has brought down the prevalence of caries in western societies, eliminating it for many more people and either reducing or arresting its rate of progress in others. This in turn has dictated a change in the way in which caries can be detected and treatment if necessary. In tandem with this change in the disease patterns has been the advent of new dental materials which has meant that there are now many options from which to choose other than the â&#x20AC;&#x2DC;traditionalâ&#x20AC;&#x2122; dental amalgam which has served so many and so well for so long. The newer materials also have the advantage of not requiring mechanical retention, being instead retained by acid etch and bonding technologies which in turn mean that it has been possible to completely revise the approach to cavity design that influenced Blackâ&#x20AC;&#x2122;s thinking in the 1900s. This provides the background to the evolving philosophy and practice of Minimal Intervention Dentistry (MID). The aim behind this approach is to preserve dental tissues whenever possible and restore them only when absolutely indicated. As such it is rather more than a change to merely cutting smaller cavities and involves the need to assess the process of demineralisation and remineralisation of initial

(non-cavitated) caries lesions as an integral part of caries management. Central to this is the need to be able to diagnose the earliest signs of carious change. Traditionally visual examination, with or without probing, and radiographs have provided the diagnostic tools. Vision remains key and the development of sophisticated loupes to enhance accuracy has allowed improvements in this respect, especially as their use is being embraced by an increasing number of clinicians. Massive technological developments in digital radiology (see the separate article on this subject in this e-book) now mean that greater accuracy than ever can be achieved by using digitally created radiographs. Together, the skill and experience of the practitioner in visual examination and the use of radiographs will continue to be the main methods of diagnosis in the medium term. However, technology has also provided an further new adjunct to the detection process in the form of caries screening tests. Here we mention some of those currently available and their modes of action. The CariScreen® (Oral Biotech, Albany, OR) (Figure 1) is a caries susceptibility screening system using bioluminescence which determines the level of a patient’s caries risk at the chairside. It uses the CariScreen meter and the CariScreen Swab to measure the adenosine triphosphate (ATP) level in the oral biofilm. ATP is found in and around living cells and as such gives a direct measure of biological concentration, in this case as a measure of actively growing microorganisms. The amount of ATP is quantified by measuring the light produced through its reaction with the naturally occurring firefly enzyme luciferase using a luminometer. The amount of light produced is directly proportional to the amount of ATP present in the sample and therefore the degree of bacterial presence. The higher the level, the higher the patient’s risk.

Figure 1 The CariScreen® 29

The CariScreen swab is used to collect samples from a patient’s teeth, which are then placed in the CariScreen testing meter. The digital screen shows the ATP level and in a matter of seconds searches the biofilm for all aciduric/acidogenic bacteria that are known to cause dental caries. The CariScreen will give a score between 0 and 9,999. A score under 1,500 is considering relatively healthy, while above that shows considerable risk for decay. This technology not only allows measurement of patients’ risk for decay at the time of the first test but also helps measure their progress as they follow the recommended protocols for reducing risk. These numbers, in combination with other diagnostic technologies, provide important information for accurate caries diagnosis and treatment. As a non-invasive technology it is also one which is easily accepted by patients. For several years DIAGNOdent classic (KaVo Dental Corporation, Lake Zurich, IL) and DIAGNOdent pen (KaVo Dental) (Figure 2) have used diode laser technology to provide high accuracy in detecting occlusal lesions (not detectable with a probe or radiographs). In addition, this technology enables providers to eliminate doubt as to whether caries is actually present at a specific occlusal site. The small, hand-held battery operated DIAGNOdent probe is placed on the dry surface of the tooth to be evaluated using either a tip for smooth surfaces or occlusal surfaces. It emits a red laser light at a wavelength of 655 nm that measures laser fluorescence within the tooth structure. Healthy, non-carious tooth structure exhibits little to no fluorescence. When caries is present, the light is absorbed and released back (fluoresces) at a higher level, 680 nm.

Figure 2 DIAGNOdent

Figure 3 Midwest Caries I.D.™ caries detection handpiece

There are two reasons for this, firstly the tooth stimulates fluorescence due to the porosity associated with demineralisation and secondly cariogenic bacteria such as Streptococcus mutans, release metabolites known as porphyrins, which can absorb the energy and release it back at a higher wavelength. This infrared fluorescence corresponds to a numerical value between zero and 99. A score between five and 10 signifies enamel caries, while a value between 10 and 20 indicates early dentine caries and a value higher than 20 denotes advanced dentine caries. While the

DIAGNOdent detects dentine caries, it does not detect enamel demineralisation. It needs to be calibrated in the patientâ&#x20AC;&#x2122;s mouth before it is used for caries detection and it is necessary to continually move the device around the surface to obtain the highest value. A signal sounds as values change throughout the exam. A newer version of the product is the DIAGNOdent pen, which can be used for interproximal areas. Fluorescence is the process where light of a short wavelength is first absorbed and then emitted back at a longer wavelength. This reflected light can be measured and caries risk assessed because the light absorption and reemission is different for carious tooth structure than for it is for healthy tooth structure. The technology works because carious tooth structure will fluoresce, while healthy tooth structure will not. The disadvantage of using fluorescence technology is that any plaque, calculus, stain, or residual prophy paste can interfere with the caries detection, causing the areas to fluoresce when caries is not present. This is known as a false positive. To prevent false positives from occurring, the tooth must be thoroughly cleaned with either sodium bicarbonate or pumice and rinsed thoroughly. The Midwest Caries I.D.â&#x201E;˘ caries detection handpiece (DENTSPLY Professional Division, Des Plaines, IL) (Figure 3) uses LED and fibre optic technology in the detection of caries in pits, fissures and interproximal areas of posterior molars and premolars that have not been restored. It can be used in both a wet and dry environment and is not hampered by fluoride, making it particularly useful on children. Because light reflects off an altered enamel prism, when this handpiece light penetrates natural tooth structure (up to 3 mm), it detects changes in the mineral density of the enamel. The speed of the signal corresponds to the depth of the lesion; a fast signal indicates a deep lesion. If no caries is detected, a green light will appear on the handpiece. If caries is present, a red light, as well as a beeping sound, will indicate that result. Research has shown that the Midwest Caries I.D. is 92% effective in detecting occlusal decay and 80% effective in detecting interproximal decay in unrestored molar teeth. Spectra- The Spectra Caries Detection Aid System (Air Techniques, Inc., Melville, N.Y.) is another fluorescence-based caries detection system. The technology used is similar to that of the DIAGNOdent but it uses six light-emitting diodes (LEDs) to project a blue-violet wavelength of 405 nm. The system connects to a computer via a USB port and uses software analysis to determine the level of caries involvement. There are two modes: detection, displayed in colour (healthy enamel is green while caries appears as red) and analyse in which the software provides numerical values: 1.0 indicates early enamel caries, 1.5-2.0 denotes deep enamel caries, 2.0-2.5 indicates 31

dentine caries, and 2.5 and higher signifies deep dentine caries. The Spectra wand is handheld and portable, and an autoclavable rubber spacer fits over the lens. The spacer must be in contact with the tooth to produce consistent images. Images can be saved for monitoring. The device is self-calibrated, but the tooth must be dried thoroughly. Spectra can detect recurrent decay around existing amalgam and composite restorations. Soprolife- Soprolife (Acteon Imaging, La Ciotat, France) is a light-induced fluorescence intraoral camera system. This uses two types of LEDs to illuminate the tooth and evaluate changes in mineral density. Images can be captured in three different modes: daylight, which uses a high-level magnification intraoral camera illuminated with white LEDs, diagnosis, and treatment. The diagnosis and treatment modes use fluorescence via four blue LEDs at a 450 nm wavelength and this second light is directed at the tooth surface to produce a superimposed image over the white light image, a phenomenon known as autofluorescence. Green fluorescence is considered an indicator of healthy tissues, and red fluorescence indicates a carious lesion. The treatment mode can be used as a guide during cavity preparation and images can be saved for future comparisons. The Canary System- The Canary System (Quantum Dental Technologies Inc., Ontario, Canada) uses a combination of laser light-induced luminescence and heat. The changes between emitted and absorbed energy from the tooth are converted into unique thermal and light signatures. The Canary System measures both the reflected light and the released heat from the tooth to examine the crystal structure of the tooth, thereby detecting the presence and/or the severity of decay. The science behind this technology is called Photothermal Radiometry and Modulated Luminescence (PTR-LUM) which makes it possible to detect caries under sealants and around the margins of existing restorations. Additionally, the Canary System does not require a dry field and is not hampered by stain. The handheld wand and console are connected to a computer and can be transported to and from different locations. Using a scoring system from 0-100, 0-20 indicates a healthy tooth, 21-70 denotes an early carious lesion and 71-100 signifies advanced decay. CarieScan- The CarieScan (Dundee, Scotland) is another handheld, batteryoperated device that uses multiple electrical frequencies to measure the mineral density of the tooth, thereby detecting the presence and severity of caries. The technology is called the Alternating Current Impedance Spectroscopy Technique (ACIST). Healthy or sound enamel exhibits high electrical resistance (impedance) and demineralised areas have lower resistance. Numerical values are as follows; 1-20 indicates sound enamel, 21-90 denotes enamel caries, 91-99 signifies early dentine

caries, and a score of 100 is considered established dentine caries. As it relies on electrical current it is not affected by staining. A low-voltage electrical current is delivered to the dried tooth and a lip hook is used to close the ACIST electrical circuit. The current is undetectable to the patient; however, due to the nature of the CarieScan, it cannot be used on patients with a pacemaker. The device is equipped with a test sensor to confirm that the device is working correctly. CariVu- The CariVu (Dexis, Hatfield, Pa.) uses a different approach called near infrared (NIR) transillumination to detect early occlusal and interproximal carious lesions. Also able to detect cracks, NIR uses longer wavelengths allowing deeper penetration into the tooth. In the NIR range, enamel appears translucent and carious lesions appear dark due to a scattering effect. An advantage to using this technology is that it does not require a clean tooth surface or calibration. The black and white images look similar to a radiograph and can be captured, saved, and stored to compare present and past images. Whatever system is chosen and used the adjunctive benefits to the classic visual and radiographic evidence mean that caries detection will provide a more definitive answer in the vast majority of cases. The earlier a confirmed diagnosis of caries, the more conservative the treatment required and if decalcification of natural tooth structure is diagnosed before decay begins, the most conservative treatment of all can be initiated: prevention or remineralisation. All important foundations for MID. Digital caries detection technology can remove the doubt from treatment decisions, whether restorative or preventive, with respect to hidden caries, questionable stained grooves, or any other suspicious-looking tooth surfaces.

Chapter 4

3D and 4D printing in dentistry*

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This article describes possible technological approaches to capture and digitise the outer and inner structure of human teeth; and to printing natural-looking teeth and dental restorations. Manufacturing of high-aesthetic restorations from tooth-coloured restorative materials is currently dominated by manual manufactur¬ing procedures and the aesthetic outcome is highly dependent on the knowledge and skills of the dental technician and the mastering of the ‘2D-3D-4D approach’ to dental morphology. Due to this the highly technique-sensitive procedure which requires a considerable amount of experience, several steps are often necessary to achieve pleasing aesthetic outcomes. In all fields of industrial fabrication additive manufacturing processes currently arouse great interest. In the dental field, additive approaches have been applied for over a decade, such as the stereo-lithographic manu¬facturing of implant-drill-guides for guided surgery-procedures and laser-sintered alloys, which have paved the way for additive fabri¬cation technologies. Nowadays, even the full digital workflow, starting with intraoral-scanning, requires the use of com¬puter-aided manufactured physical models on the basis of digital data. Consequently, additive technologies are increasingly used, especially stereo-lithography, laser-sintering and 3D-printing, as well as digital light pro¬cessing (DLP). Until recently, mainly monolithic restorations have been used in dentistry. Since 2014, printers have been capable of processing multiple materials in one single manufacturing cycle. This enables new approaches for dental applications. This is especially true for the combination of 3D-multipart and multicolour printing, further allowing the relentless pursuit of the biomimetic emulation of teeth. In this regard, a key element for the optical integration and aesthetic appearance of dental restorations is the thorough understanding of the histo-anatomic structures and dynamic light interaction of the natural dentition.

This is especially true of the tri-dimensional form of the dentine core, as defined by the dentine-enamel junction (DEJ) and the sigmoid curve distribution (convex enamel/concave dentine) as these seem to be decisive for the optical appearance of a tooth and a restora¬tion respectively. The DEJ and the outer enamel surface (OES) are essential three-dimensional structures of the tooth that substantially influence its optical appearance. Hence, a prerequisite for the so-called ‘4D-printing’ (multi-layered 3D-printing) of teeth or dental restorations are tooth-structure databanks containing the threedimensional information about the outer and also inner architecture of natural teeth. Such databanks already exist and are patented including connected technologies, providing the basis for 3D multi-material printing of teeth and restorations. The tooth structure databank is loaded with several datasets for each tooth (OES, the DEJ and pulp geometry). The DEJ may contain significant informa¬tion about the outer surface of a tooth. Inversely, this might allow the determination of the inner architecture (DEJ) from the outer surface. Furthermore, outer and inner layer-geometries may be dynamically connected to each other. This implies that virtually modifying the outer surface of a tooth in the CAD-software would automatically lead to an alteration of the cor¬responding inner structure. One basic challenge in this approach is the capturing of the inner structures of each type of intact natural tooth, in order to learn more about the specific relation of DEJ and OES.

Description of the technology 3D capturing of outer and inner tooth-structures Digitising and displaying the outer and inner tooth-structures three-dimensionally, espe¬cially the DEJ, can be currently achieved using hybrid analogue-numerical or numerical-only techniques. Additional technologies are presented that might be able to capture the inner tooth structure in the near future but are still under development. Analogue-numerical capturing – chemical removal of enamel and 3D-digitalisation A destructive method used in the 1950s and 1960s to expose the DEJ was the chemical removal of the enamel layer using 37% phos¬phoric acid. Before this irreversible loss of the OES, it first needs to be captured by con¬ventional impressions or nowadays digitally by scanning the crown with mechanical (for example, Procera

forte, Nobel Biocare, Sweden), light optical lasers – or stripe-light-based detectors. After the chemical removal of the enamel layer the same technologies are used to scan the exposed dentine core. Digital capturing – computed tomography/cone beam computer tomography The numerical capturing of the three-dimen¬sional geometry of the OES and DEJ can be conducted by X ray methods using computed tomography (CT) or cone beam computed tomography (CBCT). The resolution and accuracy can vary significantly between the systems. This might lead to limitations in receiving data with sufficient accuracy and resolution for further processing. Using 3D data-processing software two-dimensional data from the CBCT are converted into DICOM-data (DICOM = digital imaging and communications in medicine) as a first step. Subsequently STL-data (STL = Standard Tesselation Language) for each inner structure can be generated from the DICOM data based on the voxel density of the different (human) tissues using a segmentation software (for example, Mimics, Materialize, Belgium etc). Digital capturing – micro computed tomography The most accurate data of the OES and DEJ can be generated using microcomputed tomogra-phy technology. Although a better resolution than with CT and CBCT can be achieved, the technology cannot be used in vivo due to the radiation level. This limits its application to extracted or cadaver teeth. This technology was used to digitise the teeth that were used as a reference template for the 3D-mulitmaterial printing approach that is described below. Future acquisition perspectives – ultrasonic acquisition A further physical acquisition method for inner tooth structures is based on ultrasonic technology. Within the frame of a scientific research project at the RheinischWestfälische Technische Hochschule Aachen (RWTH, Germany) an ultrasonic-based acquisition device is under development. Because acoustic waves penetrate gingiva, saliva and blood, tooth areas below the gingiva can be detected and captured without invasive resection. Further on, the scanner can capture the surface of prepared teeth, as well as the outer enamel surface (OES) of intact teeth. Due to the underlying physical principle of the ultrasonic acquisition it might be also possible to acquire deeper layers of natural teeth, like the DEJ. Future acquisition perspectives – light-optical acquisition Most of the current 3D intraoral scanning devices are based on light-optical principles. Within this group are systems based on the tri¬angulation principle and

with parallel light projection. Using the triangulation principle, structural light or non-structural light can be used. Stereo-photogrammetry works without structural light, whereas in laser-light-cut and stripe-light-scanners a light-projection is used. In addition, so-called ‘stochastic patterns’ can be applied during light-projection. Enamel is transparent for light with long wavelengths. Therefore, this kind of light penetrates and is reflected at the DEJ, whereas light with shorter wavelength is reflected right at the OES.

Overview of additive manufacturing In common usage the expression ‘3D-printing’ is often used generically for all additive manufacturing technologies and proce¬dures. However, technically, it can be divided into two major groups:

Binder jetting Here the object is built layer by layer - each layer of material (liquid, powder, solid) being placed onto a platform. The binding agent is selectively deposited to join powder particles appropriately in accord¬ance to the contours of the object to be built, examples are: •

Stereolithography (SLA)

•

Selective laser sintering (SLS)

•

Indirect 3D-printing (powder bed printers)

•

LOM-Technologies (laminated object manufacturing).

Material jetting In this deposition method, the material is dispensed through a nozzle or print head con¬tinuously or in single drops and placed layer by layer as a point or line-pattern. Examples are: Fused deposition modelling-technologies (FDM) •

Direct 3D-printing

•

3D-material-extrusion of pastes

•

Polyjet-technologies, where photo-sensitve polymers

are placed drop-like over a print head.

General description of the workflow using additive manufacturing technologies In general all additive technologies follow the same workflow including the following steps: Computer aided design (CAD) of components During the CAD process the virtual design of the object is conducted in specific software. Subsequently to the CAD process, the con¬struction dataset can be saved in different possible formats. Mostly the STL-format is used, which describes the surface of the object with the help of multiple small triangles. Slicing of the CAD dataset With the help of another software, for example, Objet Studio (Stratasys, Eden Prairie, MN) or CAMbridge, (3Shape, Copenhagen, DNK) the STL dataset is sliced into single layers similar in thickness. Layer-by-layer build-up of the object in accordance to the ‘sliced’ data On the basis of the sliced STL dataset the object is built layer-by-layer. The accuracy in the direction of build-up (Z-axis) is mainly dependent on the thickness of each single layer. The single layers are always visible in the resulting object. Even with high resolution, thin slices and high precision of the outlines, thin striations remain recognisable and lead to a rough surface of the object, which might require a postprocessing surface polishing. This undesirable effect is called Z stepping.

Fig. 1 STL-data of multi-layered structure (DEJ and OES) of a natural upper incisor extracted from DICOM datasets generated by micro-computed tomography (Micro-CT). These data were used as form-models for 3D-replication by multi-material 3D-printing 38

Multi-layered dental structures Printing dental restorations by additive manu¬facturing with different materials of different properties and colours is now possible in one build-up process called ‘multimaterial-3D-printing’, which could be simplified as ‘4D printing’. This technology makes processes that were to date conducted in multiple steps or assemblies, achievable in one single process. Several makers of additive manufacturing systems offer this tech¬nology. Here FDMtechnology, as well as direct and indirect 3D-printing (powder) is applied. Current examples of direct multi-material 3 D-printers are PolyJet-3D-printing (Stratasys), MultiJet-Printing (MJP; 3D Systems) and MultiJet Fusion–3D-printing (Hewlett Packard). Within the group of indirect multi-material-printers, WZR-Multimaterial-3D-printing (WZR ceramic solutions GmbH, Rheinbach) is the only system available. This procedure is patented by WZR.

3D multi-material-printing of replicas of natural teeth The following section describes the digital manufacturing process of multilayered anterior teeth using 3D multi-material-print¬ing. Replicas of extracted intact natural teeth were produced and subsequently evaluated.

Fig. 2 From natural tooth to 3D-printed replica: a) extracted natural upper anteriors; b) STL-data of DEJ and OES filtered from micro computed tomography; c) 3D-multi-material-printed replicas of natural teeth (incident light); d) 3D-multi-material- printed replicas of natural teeth (transmitted light) 39

For the aquisition of datasets, extracted teeth were scanned using micro-computed tomog¬raphy (exaCT S Desktop-CT S60 HRE; Wenzel Volumetrik GmbH, Singen, D) with a voxel-size of 45 μm. The aquisition software ‘exaCT Control Analysis’ (Wenzel Volumetrik GmbH, Singen, D) was used to generate STL-data of the enamel (including OES and DEJ), as well as data of the dentine core including the root and pulp cavity (Fig. 1). The post-processing of the data, especially the optimisation of the surface quality used the software Sensable Freeform (3D Systems, Rock Hill, US). In the next step the STL-data were analysed with the software Magics RP (Materialise, Leuven, Belgium), to detect and eliminate possible errors within the dataset, that could negatively influence the structure and homoge¬neity of the future object. On the basis of the sliced datasets the teeth were additively build up using the direct-3D-printing-system ‘Objet260 Dental Selection’ (Stratasys); the most current 3D dental printer with triple-jetting-technology. Realistic colours as well as detailed surface structures can be printed with three different materials in one process.

Applied materials Dentine core For the root and dentine-core the material ‘Objet VeroGlaze MED620’ was used in shade A2. This material exhibits sufficient strength and form stability and a translucency compa¬rable to natural dentine. VeroGlaze is currently approved for temporary intraoral application of maximum 24 hours. Therefore it can be applied for diagnostic try-ins and mock-ups.

Incisal area The incisal area was printed using the trans¬parent and strong material ‘Objet MED610 Biocompatible, Clear’. Both materials were printed simultaneously. For the outer surface, an automatic surface finish was used with the so called ‘glossy-mode’, which created a clear finished surface.

Evaluation of printing results The first results seem very promising. Evaluation included the ‘aesthetic appearance’ and the ‘surface quality’. The aesthetic result can be described as excellent. The additively produced teeth show light dynamic effects that are similar to those seen in the natural model teeth. They are likely caused by the scattering of the light on the dentine-core, leading to several specific effects in the incisal area. The threedimensional form of the dentine-core therefore has instantaneous influence on the overall aesthetic result of the printed teeth. Due to the nature and organic optical behaviour of the materials used (resins), it can be assumed that beautiful biomimetic reproductions of teeth can be generated with a very simple build-up scheme and a simple bilaminar approach (dentine and enamel) (Fig 2 a–d). Under incident and transmitted light the printed teeth show extreme light dynamics that are even more pronounced than in natural teeth. In the feasibility study, the buccal surfaces of the anterior teeth were positioned upwards with regards to the build-up direction. Therefore, the tooth surface exhibited different qualities, as the most upper surfaces were produced in glossy-mode. These surfaces showed a very smooth, homogeneous and shiny surface, whereas the side and lower surfaces showed a rougher surface with z stepping, due to the supporting structures. This shortcoming can be easily resolved by manual finishing using silicone polishers (Silico, Heraeus Kulzer, Hanau) and natural bristle brush with polishing pastes (Acrypol and Abraso Starglanz, Bredent, Senden) even though the degree of gloss was superior in the automatically generated ‘high-gloss’ areas. Currently the drawback of additive materials is that the photopolymers have only been approved for intraoral use for 24 hours; which is at least sufficient for an aesthetic evaluation of the planned restora¬tion in the form of a mock-up. However, future material developments can be expected, both polymers and ceramics with appropriate stability in the oral environment. The biocompatibility of restorations fabricated with the subtractive approach from homogeneous blocks is a golden standard and benchmark for future 3D-printed restorations.

*Adapted from: Schweiger J et al. Histo-anatomic 3D printing of dental structures. Br Dent J 2016; 221: 555-559, with permission.

Chapter 5

Digital radiography

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Digital radiography is a relatively new technology for dentistry but one which brings many benefits that increasing numbers of practices are discovering. Here we look at the differences between digital and conventional radiography. One common misunderstanding is that digital radiography uses different equipment to conventional radiography. Although the technology of the processing of the image is different the use of x-rays remains the same, as does the x-ray generating equipment (often known as the x-ray tube or machine) although at a lower dosage, which is described later in this article. This means that the safety requirements also remain the same. They are contained in the Ionising Radiation Regulations 1999 (IRR99) and the Ionising Radiation Regulations 2000 (IR(ME)R) and are concerned with the protection from exposure to ionising radiation as a result of activities to, in this instance, dental team members and the public and are focussed on minimising patient exposure during medical procedures. The regulations are administered by the Health and Safety Executive (HSE) as part of the Health and Safety at Work Act 1974.

Historical background The German physicist Wilhelm Conrad Roentgen discovered X-rays in 1895 and the first dental radiograph was taken only two weeks later by dentist Otto Walkoff. He placed small photographic plates which he wrapped in rubber dam into his mouth and exposed them for what we would now regard as a terrifying long period of 25 minutes. It is perhaps surprising that the first digital x-ray sensors were introduced as long ago as the 1980s by Francis Mouyen but this early first digital system only acquired the image, not having the ability to store it. It was Per Nelvig and his colleagues who

then soon developed a more comprehensive system which was improved upon by manufacturers to provide the basis of todayâ&#x20AC;&#x2122;s systems. The key to the successful development was the parallel advances in computers and computer software and these in particular have improved the quality of the resolution of the images obtained. Technically, these are now described as being captured at 12-16 bit depth. More recently 3-D reconstruction and rendering of radiographic image data has been introduced in the form of cone beam computed tomography (CBCT), together with CT which offer a higher resolution with much lower doses of radiation to the patient.

Types of digital radiography Indirect digital radiography Indirect images are captured by using a digital camera or by scanning and digitalising a film captured image. It is more time consuming and requires the taking and processing of conventional x-ray film. This method does not increase the information available from the original radiograph but works by turning the image into one that can be read and analysed by a computer. However, once the image has been digitalised possibilities exist for it to be contrast enhanced and it can be shared electronically with ease.

Fig. 1 Corded digital radiography film

Fig. 2 Cordless digital radiograph film

Direct digital radiography Direct images can be are divided into two types both of which are available to use with intra-oral systems and extra-oral systems: â&#x20AC;˘

Real time, or corded

â&#x20AC;˘

Photostimulable Phosphor Storage Plate (PPSP), or cordless.

Real time or corded In these systems conventional film generating equipment is used but instead of the conventional film a solid-state sensor is substituted. This is constructed around an electronic chip which contains x-ray sensitive elements called pixels. The solid-state systems are called charge coupled devices (CCD) or complementary metal oxide silicon sensors (CMOS) depending on the type of technology used to create the chip. The pixels within the sensors are sensitive to both x-ray photons and light photons which allows a layer of luminescent crystals to be placed on top of the pixels, producing light when they are struck by x-ray photons. The sensor is connected to the computer by a cable and the electronic information produced by the pixels is transferred through the cable to the computer. PPSP, or cordless Based on a different technology, these sensors consist of a thin plate of synthetic material coated with a layer of phosphor crystals. They then store some of the energy from the x-ray photons in the phosphor layer during radiographic exposure. With this system a scanner is required to read the image information from the plate. It does so by scanning the plate with a laser beam of near-red wavelengths which releases the energy from the phosphor layer and converts it into a digital image which is then stored on a computer. All formats film can be used, just as with conventional films, and using existing film holders: periapical, bitewing, occlusal, panoramic and cephalometric and the well practised surgery procedures are easily transformed from film based to image plate technology. In some systems, the exposed image plate is transferred to a cassette that holds up to two plates. The cassette is then placed in a scanner unit which can accommodate usually up to four cassettes and therefore eight images at any one time. Scanning the plates follows, a process that then records the data, stores the images, deletes the information from the plates and returns them for re-use all in one step. The process, which is fully automatic, takes approximately 30 seconds from the touch of a button, although the first image appears on the screen after just eight seconds.

Advantages of digital radiography Lower dose Although arguably a by-product of the digital systems in that the technology merely requires a lower dosage to produce an image, the consequent lower exposure to radiation is a huge plus for both the patient and for dental team members when compared to conventional radiography. Because the intraoral sensors are sometimes smaller than conventional x-ray films it may be necessary to take more radiographs but the reduced dosage means that this is still of benefit in comparison. Also, the positioning of the digital detectors can occasionally be more difficult which may result in more retakes. Image quality and manipulation Once captured the images can be manipulated, stored, shared and compared is a way that is just not possible with a conventional radiograph. This provides great diagnostic and information advantages to aid in efficient and accurate patient management and treatment. Not only can the contrast and density of the image be enhanced with computer software to improve the quality of a digital image, subtraction can be undertaken for comparison with previous images of the same site or tooth. By this method of superimposition the rate of caries development or arrest can be estimated as can the growth or resolution of a periapical area, periodontal bone defect and many other diagnostic applications. Similarly, magnification of an image can help yield a far greater amount of information than has ever been possible previously. Storage and referrals The radiographic images are far more easily stored than the rather more clumsy and unquestionably space-consuming options with conventional radiographic film. There is no danger of the physical films being separated from the patientâ&#x20AC;&#x2122;s notes and the chances of them being damaged or lost are equally reduced. The images can be conveniently shared with other colleagues either within the practice or with other practices and referral services. Obviating the need to post radiographs and notes, the electronic transfer of images by email provides a safe, convenient and efficient method of communicating the patientâ&#x20AC;&#x2122;s condition quickly and accurately. Similar capture by the receiving colleague also confers the same advantages of manipulation upon them.

Time saving That the images are available so quickly is a great asset in a busy practice. No longer will the patient need to be asked to wait or be re-appointed while the radiographs are developed, as the images are all but instantly viewable. This saves valuable surgery time otherwise spent transferring the patient backwards and forwards to the waiting room as well as administration time in making further appointments. Processing Conventional processing with chemicals in a dark room are no longer needed. This not only frees up precious space in a practice it also gets rid of the need for smelly and toxic chemicals together with the problems of their storage and disposal. Additionally it avoids faults that can occur with conventional film processing such as under or overexposure due to either chemical degradation, timing errors or operator experience or variation.

Disadvantages of digital radiography Security As with all electronically stored data, digital images need to be securely held and regularly backed-up. Breaches of this are serious and data protection regulations need to be closely adhered to. Capital cost The initial cost of installing a digital system and software can be high but the immediate and longer term benefits are considered to substantially outweigh this.

Other considerations Training Companies that sell digital systems will almost always provide training and ongoing support for dental team members but time will need to be set aside for this. Adjustment to a new way of working with the imaging equipment as well as the computer hardware and software will also be needed. Computer screens A computer monitor in a suitable position and of an appropriate size and screen resolution will be required in order for the clinician to gain maximum diagnostic value

from the images created by the system. Careful accommodation of this is crucial as reflection of lights on the screen needs to be avoided so as not to affect the quality of the image during viewing. Patient friendly As well as feeling that they are in safe hands in an efficient practice, patients also appreciate the greater comfort of the image plates compared to conventional films and being able to see clear images more quickly of their teeth and jaws. A talking point and great practice builder. Economy Savings in consumables are very welcome nowadays and while the speed and efficiency of image delivery are in themselves great for practice profitability, the added benefit of reduced bills is a big plus. Developing and fixing chemicals are no longer required, nor are conventional films. The now redundant dark room space can be utilised for other practice purposes plus all the mess and headache of chemical disposal is also dispensed with. Where used, image plates can be reused tens, if not hundreds, of times being made quickly re-available by the scanner there are additional longer term efficiencies built into the system. Located at any convenient point in the practice, the compact scanning unit can be placed anywhere from chairside to a central site for multi-surgery access allowing digitisation of the entire practice while still using existing x-ray units. Overall, the future of digital radiography is assured in dental practice. It is highly unlikely that any new practice would be set up without including it and as old conventional equipment requires replacement then digital is the obvious choice. As with so much in life. Image is everything.

Chapter 6

Research updates in digital dentistry

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The introduction of any new technology, material or technique spawns a whole set of applications and research opportunities. Here we review a few recent papers from the research literature which help to show the increasing ways in which digital technology is being tested and applied. The accuracy of digital impressions is naturally going to greatly influence their clinical viability in implant restorations and other applications. In a study by Lee et al.1 the aim was to compare the accuracy of gypsum models originated from conventional implant impressions with digitally milled models created from direct digitalisation, by three-dimensional analysis. Thirty gypsum and 30 digitally milled models, impressed directly from a reference model, were prepared. The models and reference model were scanned by a laboratory scanner, and 30 surface tessellation language (STL) datasets from each group were imported to an inspection software program. The datasets were aligned to the reference dataset by a repeated best-fit algorithm, and 10 specified contact locations of interest were measured in mean volumetric deviations. The areas were pooled by cusps, fossae, interproximal contacts, horizontal and vertical axes of implant position and angulation. The pooled areas were statistically analysed by comparing each group to the reference model to investigate the mean volumetric deviations accounting for accuracy and standard deviations for precision. The results showed that milled models from digital impressions had comparable accuracy to gypsum models from conventional impressions. Although differences in fossae and vertical displacement of the implant position from the gypsum and digitally milled models compared to the reference model exhibited statistical significance, the authors concluded that milled models from digital impressions are comparable to gypsum models from conventional impressions.

Lab study questions cast accuracy While Lee et al.â&#x20AC;&#x2122;s study confirmed the accuracy of milled and scanned models, which is reassuring for the future of digital impression taking, other studies have presented conflicting results. For example, the accuracy and reproducibility of digitally fabricated casts compared to conventional non-digital methods was also studied recently by Cho and co workers2. They also conducted an in vitro study to compare the accuracy and reproducibility of both types of casts by using conventional impressions in a one-step single viscosity technique with vinyl siloxanether material of a typodont master model, and creating conventional casts in dental stone. Digital impressions were obtained with a digital scanner, and digital stereolithographic models were printed. The typodont and fabricated casts were digitised with a structured light scanner and saved in STL format. All STL records were superimposed via a best-fit method. The two types of impression taking and cast fabrication were compared for discrepancy, accuracy, and reproducibility and statistically analysed. No significant statistical difference was found between the digital and conventional casts in the internal area or finish line area. In addition, there was no statistically significant difference between the two techniques for a fixed dental prosthesis or single crown. However, statistically significant differences were observed for overall areas of the casts in terms of accuracy and reproducibility. Digital impression and cast fabrication were less accurate and reproducible than conventional impression and cast fabrication methods. This led the researchers in this study to conclude that as far the reproducibility and accuracy of the entire cast area was concerned, the conventional cast was significantly better than the digital cast. But then againâ&#x20AC;Ś To add to the uncertainty, a further study by Rajshekar et al3 into intra-oral 3D scanning of dentitions broadly concurred with Lee et al.1 that is has the potential to provide a fast, accurate and non-invasive method of recording dental information. The aim of this study was to assess the reliability of measurements of human dental casts made using a portable intra-oral 3D scanner appropriate for field use. Two examiners each measured 84 tooth and 26 arch features of 50 sets of upper and lower human dental casts using digital hand-held callipers, and secondly using the measuring tool provided with the Zfx IntraScan intraoral 3D scanner applied to the virtual dental casts. The measurements were repeated at least one week later.

Reliability and validity were quantified concurrently by calculation of intra-class correlation coefficients (ICC) and standard errors of measurement (SEM). The measurements of the 110 landmark features of human dental casts made using the intra-oral 3D scanner were virtually indistinguishable from measurements of the same features made using conventional hand-held callipers. The difference of means as a percentage of the average of the measurements by each method ranged between 0.030% and 1.134%. The inter-method SEMs ranged between 0.037% and 0.535%, and the inter-method ICCs ranged between 0.904 and 0.999, for both the upper and the lower arches. The inter-rater SEMs were one-half and the intramethod/rater SEMs were one-third of the inter-method values. This study demonstrates that the Zfx IntraScan intra-oral 3D scanner with its virtual onscreen measuring tool is a reliable and valid method for measuring the key features of dental casts.

Orthodontic applications Impression taking is not confined only to restorative dentistry, where the accuracy of reproduction of a single tooth or several teeth in the arch is required. In orthodontics impressions are required of full-arches. How do digital impressions fare in this situation? Zimmemann et al.4 studied the precision of guided scanning procedures compared to conventional impression techniques in vivo for this purpose. Two intraoral scanning systems with implemented full-arch guided scanning procedures (Cerec Omnicam Ortho; Ormco Lythos) were included along with one conventional impression technique with irreversible hydrocolloid material (alginate). Full-arch impressions were taken three times each from five participants (n = 15). Impressions were then compared within test groups using a point-to-surface distance method after best-fit model matching (OraCheck). The conventional impression technique with alginate showed the lowest precision for full-arch impressions with 162.2 Âą 71.3 Âľm. Both guided scanning procedures performed statistically significantly better than the conventional impression technique (p < 0.05). The in vivo results showed that the precision of guided scanning procedures exceeded conventional impression techniques with the irreversible hydrocolloid material alginate. Consequently this research concluded that guided scanning procedures may be highly promising for clinical applications, especially for digital orthodontic workflows.

Full arch implant care Papaspyridakos et al.5 in their research aimed to illustrate a digital workflow in fullarch implant rehabilitation with minimally veneered monolithic zirconia and to report the outcomes including technical complications. Three patients (with five edentulous arches) received full-arch fixed implant rehabilitation with monolithic zirconia and mild facial porcelain veneering involving a digital workflow. The incisal edges and occluding surface areas were milled out of monolithic zirconia to reduce the possibility of chipping. Porcelain veneering was applied on the facial aspect to improve the aesthetic result. Outcomes and technical complications were reported after two years of clinical and radiographic follow-up. The implant and prosthesis survival rates were both 100% after this short-term followup although technical complications were encountered in one patient. They did not adversely affect prosthesis survival or patient satisfaction and were easily addressed. The results suggest that a digital workflow for the design and fabrication of full-arch monolithic zirconia implant fixed implant prostheses has benefits, but that caution is necessary during CAD planning of the prosthesis to ensure a successful outcome. Long-term clinical studies are needed to corroborate the findings discussed in this report.

Single implants digitalised In this technique involving placement of a single dental implant, a stent made of autopolymerised acrylic resin was used to transfer the implant position to the laboratory6. Once the implant position was transferred, the stone cast was scanned, and a computer-aided design and computer-aided manufacturing (CAD-CAM) interim implant-supported crown was milled from a poly(methyl methacrylate) (PMMA) block. A titanium insert, in contact with the implant platform and not the PMMA material, was used to support the crown. The interim prosthesis was then placed intraorally. The soft tissues were sutured, and the interim prosthesis was left for a period of at least three months to confirm osseointegration and allow the soft tissue to heal. A CAD-CAM titanium impression coping was made and used for the definitive impression. The contours of the impression coping were identical to the contours of the interim restoration. The data of the digital design of the interim prosthesis were saved, and the definitive prosthesis was fabricated with contours identical to those of the interim prosthesis meaning that the resulting accuracy was clinically acceptable.

Occlusal splint benefits from the digital revolution Finally in this research round up we feature a case report by Aslanidou et al.7 in which they describe the procedure of fabricating a customised occlusal splint, through a revolutionary software that combines cone beam computed tomography (CBCT) with jaw motion tracking (JMT) data and superimposes a digital impression. The treatment was conducted on a 46-year-old female patient diagnosed with a temporomandibular disorder. A CBCT scan and an optical impression were obtained. The range of the patient’s mandibular movements was captured with a JMT device. The data were combined in the SICAT software (SICAT, Sirona, Bonn, Germany) which enabled the visualisation of patient-specific mandibular movements and provided a real dynamic anatomical evaluation of the condylar position in the glenoid fossa. After the assessment of the range of movements during opening, protrusion, and lateral movements all the data were sent to SICAT and a customised occlusal splint was manufactured. Thus the SICAT software provided a three-dimensional real-dynamic simulation of mandibular movements relative to the patient-specific anatomy of the jaw opening up new possibilities and potentials for the management of temporomandibular disorders.

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References 1.

Lee SJ, Betensky RA, Gianneschi GE, Gallucci GO. Accuracy of digital versus

conventional implant impressions. Clin Oral Implants Res 2015; 26: 715-719. doi:

10.1111/clr.12375. Epub 2014 Apr 10.

Cho SH, Schaefer O, Thompson GA, Guentsch A. Comparison of accuracy

and reproducibility of casts made by digital and conventional methods. J

Prosthet Dent 2015; 113: 310-315. doi: 10.1016/j.prosdent.2014.09.027. Epub

2015 Feb 11.

Rajshekar M, Julian R, Williams AM, Tennant M, Forrest A, Walsh LJ, Wilson

G, Blizzard L. The reliability and validity of measurements of human dental

casts made by an intra-oral 3D scanner, with conventional hand-held digital

callipers as the comparison measure. Forensic Sci Int 2017; 13: 198-204. doi:

10.1016/j.forsciint.2017.07.009. [Epub ahead of print]

Zimmermann M, Koller C, Rumetsch M, Ender A, Mehl A. Precision of guided

scanning procedures for full-arch digital impressions in vivo. J Orofac Orthop

2017; doi: 10.1007/s00056-017-0103-3. [Epub ahead of print]

Papaspyridakos P, Kang K, DeFuria C, Amin S, Kudara Y, Weber HP. Digital

workflow in full-arch implant rehabilitation with segmented minimallyveneered

monolithic zirconia fixed dental prostheses: 2-year clinical follow-up. J Esthet

Restor Dent 2017; doi: 10.1111/jerd.12323. [Epub ahead of print]

Proussaefs P, AlHelal A. A technique for immediately restoring single

dental implants with a CAD-CAM implant-supported crown milled from

a poly(methyl methacrylate) block. J Prosthet Dent. 2017 Jul 7. pii: S0022-

3913(17)30288-3. doi: 10.1016/j.prosdent.2017.03.025. [Epub ahead of print]

Aslanidou K, Kau CH, Vlachos C, Saleh TA. The fabrication of a customized

occlusal splint based on the merging of dynamic jaw tracking records, cone

beam computed tomography, and CAD-CAM digital impression. J Orthod Sci

2017; 6: 104-109. doi: 10.4103/jos.JOS_61_16.

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