Treatment planning of implants in posterior quadrants
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To sum up series number 1… “rationale for dental implants”
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Recap…..
Dental implants are a more conservative long term option than long span bridges
Placement of dental implants serves to preserve bone
Dental implants can provide long term posterior support than RPD’s
Dental implants are resistant to disease www.indiandentalacademy.com
Introduction The risk of FPD’s reduced with the introduction of implants in the posterior quadrants. From 1993 till now, single tooth implants are considered the most successful method of tooth replacement, which are shown by multiple studies done by Schmitt (1993), Carlson (1994), Becker (1995) and Henry (1996) Dental implants does not depend on the abutment teeth and allowed segmentation of the restoration. www.indiandentalacademy.com
The advantages of segmentation includes ď Ž Easier fabrication ď Ž Improved marginal fidelity ď Ž Retrievability When it comes to the treatment planning of posterior quadrants, decision must be made on a long term basis & whether to use conventional treatment procedures or implants. Buser (1996) and Volgel (2000) stated that no limits exists to placement of implants due to advances in the surgical procedures like bone augmentation procedures, sinus lift procedures and distraction osteogenesis. www.indiandentalacademy.com
There are many advantages of implant retained restorations over RPD’s. They include: Improved support Preservation of bone More stable occlusion Simplification of the prostheses Improvement of the long term oral health Use of implants in the posterior quadrants is not entirely dependant on the long term reports but also on other factors like biomechanical advantages and availability of prefabricated components. www.indiandentalacademy.com
The success of implants in the posterior quadrants depends on the following factors: 1. Available space 2. Implant number and position 3. Occlusal considerations 4. Type of prostheses 5. Overall treatment plan
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Available space The space available should be considered in three directions: a) b) c)
Mesiodistal Buccolingual Occlusogingival
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Mesiodistal Although esthetics is not the prime concern while replacing the posterior teeth, care should be taken with the implant position such that it develops proper occlusion and comfort. Mesiodistal space is evaluated in 2 dimensions. The required MD space depends on the type and number of teeth which is being replaced.
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The natural maxillary first and second premolar and molar have an average MD size of 7.1, 6.6 and 10.4mm. Hebel (1997) and Woelfel (1990) stated that the dimensions of these teeth at the CEJ are 4.8, 4.7 and 7.9mm and at a distance of 2mm from the CEJ they measure 4.2, 4.1 & 7.0mm.
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Hence while deciding with the implant size, the following guidelines can be used. ď Ž The implant should be at least 1.5mm away from the adjacent teeth. ď Ž The implant should be at least 3mm away from the adjacent implant. ď Ž A wider diameter implant should be selected for a molar teeth. Similar guidelines are followed for the mandibular teeth. When planning for a premolar restoration the implant is placed 1.5mm away from the adjacent root, and for a molar its about 2.5mm away from the adjacent tooth. (as molar teeth are wider mesiodistally) www.indiandentalacademy.com
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Buccolingual If a 4mm diameter implant is used, then 6mm of bone is required buccolingually. If 5mm diameter implant is planned, then 7mm of bone is required. The fixture must be contained within the crown. The screw access must be positioned towards the centre of the occlusal surface. Mandibular fixture – exit angle – inner inclines of palatal cusp Maxillary fixture – exit angle – inner inclines of buccal cusp www.indiandentalacademy.com
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Occlusogingival It is also considered in 2 dimensions. The parameters include: ď Ž
Adequate space for restoration
ď Ž
Adequate osseous volume for implant placement www.indiandentalacademy.com
Adequate space for restoration: Sufficient space must be present between the residual ridge and the opposing occlusal plane. Ideally 7 – 10 mm of space is required. ď Ž
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Adequate osseous volume for implant placement:
One of the FAQ is “what is the minimal height of the implant required to support a posterior restoration?” Initially it was thought that the unfavorable implant : suprastructure resulted in crestal bone loss. But studies conducted by Nedir(2001) and Ten Bruggengate(1998) showed that the unfavorable ratio did not produce any crestal bone loss. Ideally, 7.5mm of bone height is required for a 6mm long fixture and 8.5mm is required for a 7mm long fixture. www.indiandentalacademy.com
Critical structures like maxillary sinus, inferior alveolar nerve canal, mental foramen should be evaluated by a CT scan. There should at least 2mm of bone between the apical end of the implant and the neurovascular structures. The diameter of the implant is also important in Occlusogingival placement. Studies done by Graves & Jansen(1990) stated that the wider diameter implants more closely replicate the emergence profile. Balshi(1990) advocated the placement of 2 implants in molar positions which had a poor bone quality. www.indiandentalacademy.com
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The advantages of double implants includes: It resembles the anatomy of the roots It increases anchorage Eliminates antero-posterior cantilever Reduces the rotational forces Reduces screw loosening The disadvantage includes the maintenance of daily oral hygiene.
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Implant number and position There is no scientific evidence to decide on the number of implants required to rehabilitate the patient with multiple missing posterior teeth. It can be derived from traditional prosthodontic experience. When three posterior teeth are missing , 2 or 3 implants may be required. In the maxilla where the bone is less dense, placement of one implant per tooth is preferred. www.indiandentalacademy.com
The choice between using 2 or 3 implants depends on the how the load is distributed. With 3 implants it is possible to offset the implant and position them for a tripod effect. Rangert & Langer(1995) stated that this arrangement gives more bone support than linear arrangement.
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If the osseous volume is reduced, bone augmentation procedures can be done. But if the patient is not willing for sinus lift procedures then implants can be placed in the tuberosity area. This technique was described by Bahat(1992).
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Occlusal considerations Carr & Laney(1987) stated that masticatory forces with an implant supported restoration is equal to that of a natural dentition. General assessment of the likely load to be placed on implants should be made, because complications with dental implants occurs due to improper treatment planning.
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Occlusion for implants should be that there is an anterior guidance and disclusion of the posterior teeth on lateral excursion. Initial occlusal contact should occur on the natural dentition. The cuspal inclinations should be shallower on the implant supported restorations. The author also prefers to splint the teeth. www.indiandentalacademy.com
Type of prostheses Screw retained / cemented: The author of the present article prefers the use of screw retained restorations. It has the advantage of retrievability. It helps in: individual implant evaluation soft tissue inspection and any necessary prostheses modifications.
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Certain practitioners prefer cement retained prostheses, as it is more esthetic and screw holes can be avoided. The choice for screw retained or cemented restoration is dependent on the tooth that is replaced. For instance, the occlusal surface of a premolar is small and patients may object to occlusal holes, in such cases cement retained restoration can be used.
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ď Ž
Splinted (or) non – splinted: Cibirka & Razoog(1997) stated that stress distribution can be manipulated by splinting.
Splinting offers the following advantages: 1. Increases retention 2. Reduces the risk of screw loosening 3. Fewer proximal contacts to adjust 4. Delivery made easy
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ď Ž
Abutment level vs. implant level restoration, segmented vs. non segmented:
Screw retained abutments are only used when the implants are placed deeply or soft tissue depth is excessive. When cement retained restorations are used the abutments placed should have proper contours and must be retentive. The cement margin should not be placed more than 1mm sub mucosal to facilitate cement removal. When cement retained restorations are planned there must be sufficient inter occlusal space. www.indiandentalacademy.com
Overall treatment plan ď Ž
The difficulty with implant treatment essentially lies in the ability to detect risk patients.
ď Ž
A risk patient is a patient in which the strict application of the standard protocol does not give the expected results.
ď Ž
The clinician has to decide whether to retain the compromised tooth versus an implant. www.indiandentalacademy.com
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1. Single tooth planning for molar replacements: (implants in clinical dentistry – Richard N Palmer)
Two – implant solutions
Single implant solutions with wide - diameter implants
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The author states that if space and economics allow, choose the two implant option. In other cases ensure that the Buccolingual width will accommodate a wider diameter implant (assuming the MD space is inadequate). Advantages: 1. Better force distribution 2. Reduction of leverage forces 3. Implant is stronger and less likely to fracture 4. The abutments and abutment screws are usually bigger and stronger 5. The surface area of the abutment is usually larger and provides more retention. www.indiandentalacademy.com
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2. Treatment sequence & planning protocol: (Risk factors in implant dentistry – Franck Renouard) The author states that it is important to distinguish between available bone volume, necessary bone volume & useful bone volume. Available bone volume: represents the total amount of bone in which it is theoretically possible to place an implant in a certain region Necessary bone volume: represents the minimum amount of bone required for placement of an implant that will function in the given clinical situation www.indiandentalacademy.com
Useful bone volume: represents the amount of bone that can be utilized in a given clinical situation, considering the prosthodontic parameters (esthetic as well as functional). Summing up: Available bone volume = surgical evaluation Necessary bone volume = prosthetic evaluation Useful bone volume = surgical + prosthetic evaluation Note: If only the available bone volume is considered during the preoperative examination, the prosthetic result may suffer www.indiandentalacademy.com
Summary
Based on long term treatment options implants must be considered for every treatment plan. The implants are the choice of treatment for the missing posterior teeth because it: Improves support Provides more stable occlusion Preserves bone Improves long term oral health www.indiandentalacademy.com
Next article the next article in this series will focus on “treatment planning of implants in the esthetic zone�
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