By UNCLLS payday loans
Written by Stephen M. Parel, DDS, FACD Friday, 01 February 2002 00:00
The classic approach to placing osseointegrated implants in the edentulous mandible requires a period of undisturbed healing of 4 to 5 months before loading.1 This concept was unchallenged from its inception in the middle 1960s until the 1990s when the prospect of immediate loading began to have some visibility in the literature.2-11 Schnitman reported on an early (1990) and eventually a 10-year follow-up (1997) of implants loaded immediately in the anterior mandible with encouraging results, but with success rates somewhat less than the approximate 96% expected using the classical approach.2,3,12 Others have reported improved success with immediate load variations, which include overdentures initially followed by a definitive restoration at a later time.7,10 Tarnow, using implants from four different manufacturers over a 5-year period, reported equivalent immediate load success rates compared with the classical approach with a similar pattern of bone remodeling for both.4 Based partly on emerging surface technology and short-term clinical experience, it appears that the standard protocol for providing implant restorations for the edentulous mandible may be shifting towards immediate loading for many patients.
One of the most appealing aspects of immediate loading in the edentulous lower jaw is the potential for a “same-day” functioning restoration.13 Even with an accelerated clinical schedule, however, conventional technology to create a casting with subsequent resin processing will require several days to complete a final fixed bridge. The best result that can be anticipated from this approach is a functioning provisional prosthesis from an existing denture or prefabricated provisional restoration. At some future time, these patients will then require construction of a final restoration.
There is an alternative to this provisional concept in the form of the Novum system (Nobel Biocare), which will allow the delivery of a true “definitive” restoration on three precisely placed single-stage implants within a single day. To accomplish this, premachined titanium bar components are employed, which eliminate the time required for conventional impressions and a casting. This concept was introduced more than 5 years ago in Sweden, with published results for 150 patients indicating a 98% success rate for implants and their associate restorations over a 2-year period.14 This compares favorably with the approximately 96% success reported in long-term studies on mandibular implants loaded after a conventional healing period and exceeds the published success rates of several non-Novum immediate load studies.1,2,5,10,12
As with any surgical or implant procedure, the systemic health of any individual must be thoroughly evaluated, and the patient must be judged as a good candidate for what is planned. A comprehensive radiographic analysis is needed, because the Novum system requires a minimum of 12 mm of vertical bone after reduction for implant placement. Some long-standing edentulous patients with moderate to severe atrophy will not be candidates for this approach. Patients with a failing natural dentition, or individuals who have been edentulous for a relatively short period of time, may be better candidates since significant atrophy and resorption from denture wear has not yet occurred. A minimal horizontal bone width platform of approximately 6 mm is also required for implant placement, which may eliminate patients with thin superior ridge anatomy. Patients with significant lingual concavities, or those with severe class II jaw relationships, are generally not good candidates for the Novum system. Poor medullary bone density may also be a limiting factor for initial implant stability unless it is possible to engage the cortical plates.
The clinical examination is essentially the same as that for any edentulous patient who is a candidate for restoration with mandibular implants. Soft tissue ridge form, occlusion, jaw relationships, vertical dimension of occlusion, and general oral health are all evaluated conventionally. Panoramic films are valuable, but anterior occlusal and lateral cephalometric films are more helpful in assessing bone contour, medullary density, and cortical plate relationships (Figure 1). Surgical guide stents are generally not required, so mounted casts are not routinely necessary. A repeatable centric jaw relationship and a recordable vertical stop at the correct vertical dimension of occlusion are necessary for bridge construction following surgery (Figures 2 and 3). Prior to implant surgery, the maxillary occlusal plane must be appropriate for the correct restoration of the mandibular arch. If this is not the case, measures to establish the correct plane, such as constructing a new maxillary denture or restoring the existing dentition, must be undertaken prior to implant placement.
|Figure 1. The panoramic film demonstrates generalized periodontal disease in both the maxilla and mandible. The maxillary treatment plan includes extraction and immediate denture with implants to follow after healing. Additional lateral cephalometric and occlusal films are necessary to verify sufficient bone height, width, and medullary density for the Novum procedure for the mandible.||Figure 2. Failing existing dentition, which demonstrates sufficient tooth contact for accurately recording the patient’s vertical dimension of occlusion.|
|Figure 3. Presurgical measurement of the patient’s vertical dimension of occlusion is recorded, and these marks are preserved throughout the surgical procedure by covering them with clear adhesive tape.||Figure 4. Following extractions, the vertical bone height is reduced to the point where a horizontal table of at least 6 mm of bone is present.|
|Figure 5. Preliminary implant position is determined using the guide template. This template is secured with guide pins, which help determine the relationship of the distal implants to the inferior alveolar canal or anterior extension of the canal.||Figure 6. The evaluation template is then secured using the guide pins to observe the relationship between the proposed lower bar position and the existing occlusal plane. It is critical to have an accurate opposing occlusal plane to ensure the correct positioning of the lower Novum bar.|
|Figure 7. The evaluation template is replaced with the positioning template, and the midline fixture site is prepared using a series of drill guides. Once final sizing has been completed, the site can be tapped using the appropriate size guide with a titanium surface.||Figure 8. The Novum fixture has thread lengths ranging from 11.5 to 13.5 mm, and is available in widths of 4.5 and 5 mm. The collar is smooth and varies in height depending on fixture length. This single-stage implant is driven to place with an external hex connection to the fixture mount in the same manner as other hex head osseointegrated implants.|
|Figure 9. The final placement of the midline fixture is accomplished with profuse irrigation and slow drill speeds using a depth-limiting fixture mount.||Figure 10. The positioning template is then removed and replaced with a V-template that is anchored securely to the new midline implant, and provisionally to the two distal sites using the guide pins. Here the V-template is further stabilized using two temporary threaded pins between the implants in sites prepared with a 2-mm twist drill.|
|Figure 11. The distal implant sites are prepared using the same series of drill guides that were utilized in the placement of the anterior implant. These distal implants are also delivered with the same depth-limiting fixture mount so that all three implants will terminate in the same horizontal plane.||Figure 12. The final template is then removed revealing the precise placement of the three Novum implants in the mandible. The lower and upper bars are placed provisionally to determine that enough distal bone has been removed to allow bar seating, after which the tissues are then sutured around the implant collars.|
|Figure 13. The lower bar is delivered initially using compression screws with nylon washers to bring the upper implant surface to the lower bar surface, creating an intimate fit.||Figure 14. This diagram illustrates the crimping effect against the thin lip of the superior implant surface created when the compression screws are slowly hand torqued against the upper bar.|
|Figure 15. The compression screws are removed and are replaced individually with titanium lower bar screws that can be torqued to 45 Ncm. This creates a very rigid and intimate fit of the bar structure to the implants, ensuring cross arch stabilization.||Figure 16. The upper bar is the basis for the prosthetic reconstruction. It is shown here in its final position prior to collection of jaw relation records and transfer of this information to the laboratory.|
|Figure 17. This diagram demonstrates the step-by-step procedures where, after final delivery of the lower bar, jaw relation records are recorded and the case is sent to the laboratory for mounting. This is followed by a wax try-in and delivery of the final prosthesis, which has been processed using a rapid-cure technique.||Figure 18. The completed mandibular Novum fixed bridge is delivered with three or four screws and is torqued to a clamping force of 45 Ncm. This essentially creates a rigid single-beam structure on top of the individual implants. The entire process, from surgery to delivery of the finished bridge, was completed in 1 working day.|
|Figure 19. Periapical films at 18 months reveal what appears to be successful osseointegration of each implant. The bridge was stable and the patient was asymptomatic.||Figure 20. At 22 months, the maxillary fixed bridge on conventional and zygoma implants was completed and continues to function well against the mandibular Novum prosthesis.|
Much of the success of the Novum system is dependent on patient selection and a precise surgical approach. The implants must be placed in an exact relationship to each other in order for the premachined bar components to fit passively. Any variation in parallelism or spatial relationship can cause unfavorable stress to develop in one or several fixtures, possibly leading to implant failure. Proper attention to surgical procedure, therefore, is critical to a successful outcome.
Once properly aligned in bone, the three Novum implants are joined with a rigid premachined titanium bar, which provides immediate cross-arch splinting and stabilization. In this stable environment, the implants have been shown to integrate with a high degree of success, while immediately restoring the functional equivalent of first molar occlusion.14
The key to ideal surgical implant placement is the series of templates designed for precise drilling and insertion. The first template is basically diagnostic to determine crestal bone reduction relative to the ideal horizontal plane, and to determine if the width of the surgically created bone platform will allow implant placement (Figure 4). Three pilot holes are then drilled with this guide template using a 2-mm twist drill (Figure 5). A second evaluation template simulates the final mandibular bar and, when stabilized with guide pins in the pilot holes, allows for visualization of the interarch relationship relative to the available vertical space and the occlusal plane (Figure 6).
The positioning template is used to place the center implant through a series of sizing and tapping (if required) steps (Figure 7), all of which are controlled by the use of precision drill guides (Figures 8 and 9). These guides fit precisely into the positioning template creating a vertical channel that virtually eliminates the possibility of oversizing or improperly angulating the osteotomy site during preparation. Once in place, this midline fixture will be the stabilizing reference point for the placement of the two distal implants using the final “V” template. This template is further stabilized with two temporary screws prior to initiating drilling procedures for the two distal implants (Figure 10). All sizing and tapping is done with the same surgical drills and precision stainless steel guides. Implant placement requires the use of a titanium guide to avoid metal contamination on the implant surface for all three implants (Figure 11).
When all implants are finally positioned (Figure 12), the temporary stabilizing pins are removed, the tissue is closed, and the initial (lower) premachined bar is positioned with specialized nylon compression screws (Figures 13 and 14). These screws are slowly torqued by hand to provide an even pressure on the bar against the superior surface of the implant, bringing the two titanium surfaces together for a final intimate and passive fit. As each of the nylon compression screws is removed, it is replaced by the final bar abutment screw, which is machine torqued to 45 Ncm (Ncm = Newton-centimeters, an international torque measurement for screw tightening; Figure 15).
Prosthesis construction now begins with placement of a precisely fitting second (upper) premachined bar that is attached to the lower bar with similar titanium screws. A jaw relation record, based on the preoperative measurement of the vertical dimension of occlusion is then made using either a wax rim or silicone putty registration material (Figure 16). After mounting on an articulator, the titanium upper bar is reduced where necessary to make room for denture teeth. A wax try-in is completed after the teeth have been preliminarily set to determine proper appearance, position, occlusion, and vertical dimension (Figure 17). With in-house or close approximation of laboratory support, the elapsed time from the start of surgery to completion of the intraoral wax verification of tooth position is approximately 4 to 4.5 hours.
While the patient is resting, the wax-up is completed and the teeth are processed to the upper bar using a rapid heat-cure technique. This may require 2.5 to 3 hours, allowing the finished restoration to be completed within a normal working day (Figure 18).
The delivery protocol requires attaching the upper bar with processed teeth to the lower bar using screws designed to withstand torque of 45 Ncm. When joined together, the intimate fit of the upper and lower bars essentially forms a structural beam that transmits occlusal forces as a single unit and immediately provides a splinting effect during loading.
A cotton pledget is placed over the screw head and temporary restorative material is used in the screw access holes for an observation period of several months. A more permanent seal is then created using a new pledget over the screw head, which is then covered with composite resin. This will create a smooth surface, which can remain uninterrupted during long-term follow-up. Periapical radiographs are taken annually to monitor the bone-implant relationship, but the bar is not routinely removed for inspection unless an emergency situation arises (Figures 19 and 20).
It is important to emphasize that the Novum approach is not universally adaptable to every edentulous mandibular jaw. Contraindications include inadequate bone depth or cross-sectional width, an unfavorable position of the inferior alveolar nerve, or some class II jaw relationships. Furthermore, patients should be informed prior to surgery that limitations to implant placement may be encountered during surgery, and an alternate approach may be required once this determination has been made.
While the Novum system does not offer a solution for immediate loading and restoration of mandibular implants in all patients, it is a valuable treatment option for many individuals. Although the surgery is precise and labor intensive, the fact that no additional (stage 2) surgery is necessary, and that a definitive restorative outcome is possible in a single working day, makes this an appealing treatment option. Current results with this technique in the United States are favorable but short term. Experience in Europe, however, appears to validate this technique, with results that are comparable with the well-documented 2-stage approach.
1. Adell R, Lekholm U, Rockler B, et al. A 15-year study of osseointegrated implants in the edentulous jaw. Int J Oral Surg. 1981;10:387-416.
2. Schnitman PA, Wöhrle PS, Rubenstein JE. Immediate fixed interim prostheses supported by two-stage threaded implants: methodology and results. J Oral Implantol. 1990;16:96-105.
3. Schnitman PA, Wöhrle PS, Rubenstein JE, et al. Ten-year results for Brånemark implants immediately loaded with fixed prostheses at implant placement. Int J Oral Maxillofac Implant. 1997;12:495-503.
4. Tarnow DP, Emtiaz S, Classi A. Immediate loading of threaded implants at stage 1 surgery in edentulous arches: ten consecutive case reports with 1- to 5-year data. Int J Oral Maxillofac Implant. 1997;12:319-324.
5. Piatellii A, Paolantonio M, Scarano A. Immediate loading of titanium plasma-sprayed screw-shaped implants in man: a clinical and histological report of two cases. J Periodontol. 1997;68:591-597.
6. Hermans M, Durdu F, Herrman I, et al. A single-step operative technique using the Brånemark system. A prospective study in the edentulous mandible. Clin Oral Implants Res. 1997;8:437(abstract).
7. Henry P, Rosenberg J. Single-stage surgery for rehabilitation of the edentulous mandible. Preliminary results. Pract Periodontics Aesthet Dent. 1994;6:1-8.
8. Nicolopoulos C. Immediate loading vs. delayed loading of non-submerged implants in 20 consecutive mandibles. Presented at: Academy of Osseointegration: March 1999; Palm Springs, Calif.
9. Randow K, Ericsson I, Nilner K, et al. Immediate functional loading of Brånemark dental implants. An 18-month clinical follow-up study. Clin Oral Implant Res. 1999;10:8-15.
10. Gatti C, Haefliger W, Chiapasco N. Implant retained mandibular overdentures with immediate loading: a prospective study of ITI implants. Int J Oral Maxillofac Implant. 2000;15:383-388.
11. Balshi TJ, Wolfinger GJ. Immediate loading of Brånemark implants in edentulous mandibles. A preliminary report. Implant Dent. 1997;6:83-88.
12. Esposito M, Hirsch JM, Lekholm U, et al. Biological factors contributing to failures of osseointegrated oral implants. Eur J Oral Sci. 1998;106:527-551.
13. Balshi T, Wolfinger G. A new protocol for immediate functional loading of dental implants. Dent Today. 2000;20:60-65.
14. Brånemark PI, Engstrand P, Öhrnell LO, et al. Brånemark Novum: a new treatment concept for the edentulous mandible. Preliminary results from a prospective clinical follow-up study. Clin Implant Dent. 1999;1:2-16.
Disclosure: Dr. Parel is a consultant to Nobel Biocare.
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