DIAGNOSTIC AIDS IN ORTHODONTICS-2
INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
DIAGNOSTIC AIDS IN ORTHODONTICS-2 • • • • • •
Kesling diagnostic set up. Xeroradiography. Electromyography. Occlusograms. Holograms. Digital- 1)cameras, 2)models
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KESLING DIAGNOSTIC SET UP • Proposed by H.D.Kesling. • Individual
teeth
&
their
associated
alveolar
processes are sectioned off and replaced on model base in the desired position. • Helps in simulating various tooth movements.
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. • Horizontal cut-using fretsaw blade 3mm apical to gingival margin. • Vertical cuts to separate teeth.
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Uses 1) Visualizing and testing effects of complex tooth movements and extractions on the occlusion. 2) Patient motivation. 3) Tooth size - arch length discrepancy can be visualized.
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Xeroradiography • Developed by Chestor.F.Carlson in 1937. • Records images without the need of film. • Dry non chemical process which makes use of electrostatic process. • 2 typesa) Medical 125-in general radiography. b) Denta 110 – Dental xeroradiography. www.indiandentalacademy.com
Technique • Made on selenium coated aluminium plates. • Selenium when given a positive or negative charge is photosesnsitive ant the charge is altered by exposure to x-rays-Latent image • Development is by blowing fine electrically charged powder over exposed plate. • Image is then transferred from plate to paperVisible image • If selenium is positive charged-areas of greatest density are displayed as dark blue, • Negative charged-light blue or white • Can be reused aswww.indiandentalacademy.com many as 1000 times
Advantages 1) It can be viewed without transillumination. 2) Serial xeroradographic tracings can be applied directly over original head film thereby reducing tracing error. 3) Edge enhancement effect-intraosseous detail &soft tissue boundary definitions are superior. 4) Teeth are more readily visualized in negative mode,intraosseous structures in positive mode.Soft tissues are represented equally in both. 5) Cephalometric landmarks are easily identified. 6) Reconstruction of cephalometr planes &points can be made directly. www.indiandentalacademy.com
Disadvantage • Because of expense of leasing the processing system use of xeroradiographic head film is not practical in orthodontic office.
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ELECTROMYOGRAPHY • Defined as recording of &study of intrinsic electrical properties of skeletal muscle by means of surface or needle electrodes. • Quality better with needle electrodes. • Surface electrodes are non invasive & decreased risk of infections. • Robert & Moyers-first to use E.M.G. • Pancherz (1980) found decreased E.M.G. activity of masseter &temporalis muscle during chewing in class II divI subjects-attributed to diverging dentofacial morphology &unstable occlusal contact www.indiandentalacademy.com
• Moyers (1949)studied E.M.G.s of children with class II div I –found temporalis muscle dysfunction in habitual occlusion &at rest. • Winders et al (1958)studied forces exerted on the dentition by perioral &lingual musculature during swallowing &found increased muscle activity in tongue thrust group. • E.M.G. is a valuable diagnostic toola) determine etiology of malocclusion, b) response of orofacial musculature to orthodontic therapies c) helps in research www.indiandentalacademy.com
OCCLUSOGRAMS • It is a 1:1 reproduction of the occlusal surfaces of plaster models on a sheet of acetate tracing paper. • A central groove cut into backs of both models can be used for orientation.
Grooves can be cut by a custom made dental cast scriber or a triangular file.
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• Dr.Charles Burstone developed an occlusogram camera assembly-4“x 5“box camera,a dental cast stage,2 flood lights&a hinged plexiglass plate. • A 210 mm lens is used to produce 1:1 magnification • Disadvantage-Expensive & scarce equipment
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• Another technique to produce occlusalgrams was by orthoscan camera. • The depth of field of this camera is almost nil, and the central orientation groove on the backs of the models is apt to be distorted and inaccurate. • Third technique: Use of a copying machine to copy the occlusal surfaces of the dental casts. Disadvantage: Images are enlarged by as much as 10% depending on the machine used, so clinical accuracy may be seriously undermined with this technique. www.indiandentalacademy.com
• The most premitive technique for making occlusal grams is to trace the occlusal surfaces of the teeth onto a clear 1/8” plastic sheet. • Since the eye of the viewer is the camera, the viewer’s head must not be moved while tracing both sides of the model. www.indiandentalacademy.com
Procedure • To make standard photographs of the occlusal aspects of the dental casts, the occlusogram camera assembly consists as a 4 by 5 inch box camera, a dental cast stage, two 375-watt floodlights, and a hinged Plexiglas plate. • To produce 1:1 magnification, a 210 mm lens is found to be satisfactory. • Each dental cast is placed on dental stage and is brought up to the leading edge of the stage. • Registration dots which are located in the leading edge of the stage will also be recorded on the occlusogram. www.indiandentalacademy.com
• With a fine-grain positive film placed into the film cassette, and with both floodlights focused on the dental cast, a typical exposure of 4 seconds at f45 is made. • Processed according to manufacturer’s directions, maxillary
and
mandibular
occlusograms
produced at 1:1 magnification.
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are
Tracing of occlusal gram • Acetate paper is placed over the occlusograms and the maxillary and mandibular teeth are outlined, showing the gingival tooth contours, incisal edges, buccal cusp ridges, central grooves, and cusp tips. Also traced are the palatal rugae, the midpalatal raphe, the fovea palatinus, and the registration dots. www.indiandentalacademy.com
Orientation of occlusogram
• Midsaggital and transverse registration lines are constructed. • Midsagittal – by connecting the incise papilla. • Transverse – Is constructive distal to the last molar in the arch and perpendicular to the midsagittal registration line. www.indiandentalacademy.com
• The maxillary and mandibular occlusogram tracings are then separated. • Assembled using the registration dots and the maxillary registration lines are duplicated on the mandibular occlusogram tracing. • Both pieces of tracing paper, when oriented can be thought of as the maxillary and mandibular denture bases in centric relation at the beginning of orthodontic treatment. www.indiandentalacademy.com
Typical ideal normal Class I occlusogram
1) The biting edge of the upper anterior teeth lies in front of the biting edge of the lower anterior teeth by an averaged of .7mm (anterior overjet). 2) The upper posterior teeth extend beyond the lower posterior teeth by an average of 2.3mm on each side (posterior overjet) 3) The upper bicuspids are wider than the lower bicuspids by an average of 1.9mm on each each side (bicuspid lateral overjet). 4) The upper molars www.indiandentalacademy.com are wider than the lower molars by an average of1.4mm on each side (lateral molar overjet)
Clinical significant of Occlusograms 1) Individualised arch forms 2) Arch length Discrepancy Measurement: By superimposing the idealized lower arch form on the original. 3) Occlusal simulations: It permits the orthodontists to quickly see if the maxillary teeth even have the possibility of occluding with the lower correctly. • Also to judge if the teeth will fit together without mesiodistal alteration. Tuverson (1980) and Andrews (1976) have suggested that improper torque and / or tip on the anterior teeth will limit available arch length, space for proper www.indiandentalacademy.com occlusion is lost.
•
So when ideal occlusograms are designed with 1mm of anterior overjet, one is assuming correct tip and torque for the incisors too.
4) Evaluation of Various Treatment Plans: • With occlusograms, the orthodontist can try any alternative he can think of without risk of harm to the patient. • Since the anteroposterior position of the denture bases is influenced by growth, facial growth rotations, changes in the cant of the occlusal plane, and/or surgery, these positions should be anticipated for the period of treatment and incorporated into the occlusogram tracings. www.indiandentalacademy.com
Holograms: • Holography is a photographic technique for recording and reconstructing images in such a way that 3D aspect of an object can be attained. • The recorded image is called a “Hologram. • The theory of holography was first developed by Garbor in 1948, and the first hologram was produced by Leith and Upatnieks in 1964. • Holography is a wave front reconstruction process in which two coherent beams converge to produce constructive and destructive intereference pattern which is recordedwww.indiandentalacademy.com in film.
• Laser is needed to produce a hologram • A hologram can record all the information contained by dental casts and also can be used for direct measurement. The storage of many dental casts for several years can be eliminated if a working duplication of all the information from the casts can be put on a single holographic film. • A developed hologram contains all of the target information. If the hologram is cut in half, each half contains a complete image; if subdivided further, each small piece still contains a complete image but at some sacrifice of resolution and image quality. www.indiandentalacademy.com
Recording of Hologram
• The laser beam passes through the film first, thus acting as the reference beam and is then reflected back on to the film as the object beam. • Laser beam used is helium-neon of 25mW power • The Holographic film used is 4 x 5 inch Kodak holographic film with high resolution. • A film is held within two optical quality glass plates of 2.5mm thick which keeps the film absolutely flat and firm. • The orthodontic study models are placed beneath these glass plates and as close as possible to them but www.indiandentalacademy.com without touching.
• It is important not to have any external or internal vibrations affecting the system, as a movement of even half the wavelength of light will affect the quality or ever totally destroy the image. • It can be minimized by keeping all the components of the system on the one optical bench so that such movement is then applicable to each component and is thus negated.
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Processing Technique of Hologram • The films are exposed in semi-darkness and are best developed by treating immediately as the latent image may fade within 24 hours. • They have special emulsions whose particle size has been refined down to one-twentieth the wavelength of light – 30 nm. • Film is immersed in a dish of developer (Kodak DX80), with the emulsion side uppermost for 45 seconds at about 20oC • Removed from the developer and rinsed briefly under a tap and immersed in fixer/bleach until clear. • Washed in running water for about 1 minute and www.indiandentalacademy.com then dried in methanol.
Orthodontic applications • Storage of study models • Measurement of incisor intrusion • Study of the effects high pull head gear traction in human children skulls. • Effect of class-II elastics on bone displacements. • Effect of cervical pull head gear on maxilla • Determine centres of rotation produced by orthodontic forces. • Lower incisor space analysis • Prognosis in Franke, theory patients. • To assess facial and dental arch symmetrics. www.indiandentalacademy.com
Advantages 1) Scratches / dost covering does not interfere with the latent image. 2) Serial superimposition allows to visualize tooth movement. 3) The virtual image of holographic record can be measured accurately in 3D. 4) Reconstruction of images for clinical purpose may be done using a simple light source. 5) Vast reduction in storage space and used for medicolegal requirement, where films are stored with normal medical record. 6) Cost of production is similar to conventional radiography. 7) Images are clinically reliable and errors are not clinically significant. www.indiandentalacademy.com
BuscAang et al (J.C.O. 90) in his study compared cast and occlusal view of hologram. Errors were found to be consistently greater for the holograms than for the cast, and the disparity can be minimized by taking measurements parallel and closer to the hologram reference plane.
To ensure accuracy
separate hologram from various perspectives would be required.
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• Mc Guinners et al (B.J.O. 1993) found that errors in the hologram readings were found to be 3 times as great for study models and when individual components of PAR were compared significantly smaller scores were obtained for lower incisor crowding and midline discrepancy and goes an indication that PAR index tends to underestimate the severity of malocclusion when assessed from holograms as opposed to study models. www.indiandentalacademy.com
• Most of the study shows greater errors in holographic images than in study cast, so better refinement is needed to decrease errors and there by
improving
precision
and
holographic images.
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reliability
of
DIGITAL CAMERAS AND ORTODONTICS • The technique dates back to 1981 – Sony produced the Mavica, the first consumer level electronic camera. • Initially, the quality of images was poor. • The rapid advancements in digital improvements in image quality, and in the capacity of computer hardware to store these images. • It’s widely used now a days compared to conventional film photography as 1) Whole process of storage and retrieval is demanding in both time and space. 2) Risk of pictures being misfiled www.indiandentalacademy.com 3) Deteriorating in quality over time.
Working of Digital Camera • The image to be recorded to focused onto a grid on a charge-coupled device (CCD). • Each cell of the grid is assigned a numerical value, determined by the average shade and intensity of colour of the light falling on that cell (pixel). • Images taken on a digital camera stored within the memory card analogues to the film in a conventional camera • Memory cards can be slotted into a Personal Computer Manufacturer Interface Adaptor (PCMIA) or 3.5 inch floppy disk adaptor of a PC for direct downloading onto the hard disk. www.indiandentalacademy.com
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Once downloaded the image is usually stored as a compressed file using one of a number of internationally agreed standards.
•
The images are then normally stored as JPEG files (Joint Photographic Experts Group).
•
The size of standard JPEG images – 200-600kB.
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A single floppy disk will hold approximately 2 to 7 images
•
A CD with 650 MB capacity will hold over 100. www.indiandentalacademy.com
Types of Digital Camera 3 Types 1) Low resolution – these are no longer available 2) Mid-range- generating a file size of approximately 350kB 3) Megapixel – producing files of approximately 600 kB. The greater the number of pixels, greater the detail recorded. But increasing the number of pixels requires more memory. The camera may also have in LCD color display, enabling the operator to preview the image before storage. www.indiandentalacademy.com Eg: Kodak 120, Nikon Coolpix 900, Olympus C-
•
Quality of Digital photos at present is limited by following factors. 1) The
optical
resolution
of the
digitizing
mechanism 2) The amount of memory in the camera 3) Resolution of the final output device (eg. Printer Projector).
If it is less than that
recorded by the camera, then the final quality of the image will be determined by the resolution of www.indiandentalacademy.com printer.
Advantages 1) The images can be instantly reproduced and poorly composed pictures can be retaken immediately. 2) Inexpensive 3) No chemical processing is required. 4) Storage and filing is easy 5) Images are immediately ready to transmit electronically or project using a display tablet or video projector, no scanning of negatives or prints is necessary. www.indiandentalacademy.com
Image manipulation • It is possible to alter the brightness, intensity, colour tint and sharpness of the image, as well as adding to add deleting parts of the picture. • Image manipulation may be accidental or intentional but innocent, or deliberately fraudulent • New encryption systems have been developed to detect tampering with images, where changes in the image are identified as changes in a superimposed coding added at the time of the original image capture. www.indiandentalacademy.com
Digital Models • The recent technological advances have allowed the general of digital dental models that can be saved and viewed three-dimensionally on a computer. • The alginate impressions are shipped overnight to one of the companies offering digital models. • A traditional plaster model is fabricated and using CAD-CAM technology, is transformed into a digital, 3D image of the dentition. • Within few days a electronic file is available to be downloaded from the internet to a desired computer • Once downloaded, the software enables the digital models to be viewed and manipulated. www.indiandentalacademy.com
Advantages over plaster models 1) Not subject to physical damage 2) Require negligible storage space – 1 set of models is less than 1 MB in size. A typical 700MB CD-R holds over 700 cases. 3) Retrieval is fast and efficient 4) No expense of model duplication. 5) Digital models are also in excellent presentation tool. 6) Simultaneous view of models at one time is possible. www.indiandentalacademy.com
• The two major computerized model systems creating digital models are OrthoCADTM (Cadenrt, Inc, Fairview, NJ) and emodelsTM (GeoDigm, Corp, Chanbassen, MN) OrthoCADTM • First company to introduce a digital model service in 1999. • The startup software for OrthoCADTM is free of charge and is about 8 megabytes in size. • The cost is approximately same as for a laboratory charge for a set of trimmed study casts. • OrthoCAD’s – 3-D browser software allows the clinician five simultaneous views of the models. www.indiandentalacademy.com
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• It can also make measurement in any plane of space. E.g., Bolton analysis, Tanaka Johnson analysis • It also features of crosssectional tool (Jaws Alignment Tool) that can slice the digital models in any vertical or horizontal plane • It also has a occlusogram feature www.indiandentalacademy.com
OrthoCAD’s Virtual Set-Up enables the clinician to simulate and visualize any desired treatment option including virtual extractions, interproximal reduction, expansion leveling, and to apply various fixed appliances.
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• The new innovation introduced by OrthoCADTM is their Bracket Placement System • The clinician places each bracket in desired position virtually in the digital model using bracket placement wand • It has a miniature video camera, that transmites high resolution images of the intra oral environment www.indiandentalacademy.com
• The system determines the relative position of the want versus the actual tooth and gives the practitioner a positioning target and signals when the virtual placement coincides with the actual placement • One of the new innovation currently tested is centric occlusion – centric relation (CO-CR) feature in their software
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emodelsTM • Founded in 1996 by GeoDigm as interactive reflective imaging system • Software size 12MB compare to 8MB of OrthoCAD • More expensive • Has the facility of simultaneous viewing, tooth measurement in any plane of space, cross sectional tool • The most useful feature is eplanTM – virtual diagnostic setup www.indiandentalacademy.com
References
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