Written by Robert A. Lowe, DDS, FAGD, FICD, FADI Sunday, 29 February 2004 19:00
Dental implants have been used with great success as root replacements in oral reconstruction. Due to the high predictability of osseointegration,1,2 clinicians are now seeing patients who have prosthetic components in need of replacement, because of either functional wear or the patients desire for a more aesthetic restoration. The withdrawal of certain implant systems from the market may create difficulty in finding prosthetic replacement parts for well-integrated and clinically successful implants. In addition, some of the earlier implant reconstructions were fabricated with the prosthetic components splinted to natural teeth, and now the natural teeth are failing. This situation has been shown to lead to early failure of the restoration due to differences in occlusal stress tolerance between the natural teeth and implants.3
Advances in implant prosthetics and materials now allow the dentist and laboratory technician to create aesthetic restorations that are totally implant-borne. Most clinicians recommend that the implant segments of the reconstruction be separate and free standing from remaining natural teeth to allow for retrievability and/or replacement of both implant and tooth-borne segments.4 In cases where this is not possible, a stress breaker such as a semiprecision male-female connector can be integrated into the design of the case to allow the natural tooth abutments to move independently of the osseointegrated implant segments.5
Preexisting implant abutments can pose clinical problems, however. These problems include: (1) improper position in the mesio-distal, or bucco-lingual, direction, (2) improper angulation, leading to problems in prosthetic tooth position for aesthetics and function, and (3) if damaged while removing the existing prosthesis, implant components can be irreplaceable if the implant system is old and no longer available.
When replacement prosthetic parts are not available for the original implant system that was used, one solution is to re-prepare directly the existing implant abutments and use a superstructure with a cemented prosthesis. This approach may allow the reconstruction of the restorations to proceed more easily for the dentist and the patient, with a higher degree of predictability, compared to trying to replace the implant abutments, which may not be of the same system. Further, if a system is no longer available, replacing the entire implant with a current system would be necessary.
DIRECT PREPARATION OF IMPLANT ABUTMENTS
Many older implant reconstructions used titanium or titanium/metallic abutments that were stock and not specifically angulated or shaped like prepared teeth. As a result, prosthetic reconstruction of the implants was often an aesthetic and functional challenge for the dentist. UCLA type custom abutments were developed to correct some of these problems.6 However, many times they were not used because of the increased laboratory costs. When they were used, they often were not prepared at the restorative margin to allow for a sufficient thickness of ceramic to create an aesthetic emergence at the gingival-restorative interface. The restorative dentist would be required to reshape the metal implant abutments intraorally to correct these shortcomings.
Some of the challenges that occur when preparing abutments directly in the mouth are: (1) heat generation that could possibly be transferred to the implant cylinder and interfere with the osseointegrated surface,7 (2) control of the handpiece in preparing the margins, and (3) creating a smooth, polished surface after preparation is complete.
|Figure 1. Two stock cylinder implant abutments after removal of the restorations. Note the supragingival position of the restorative margins and the thin gingival tissue associated with the implant in the No. 12 position.||Figure 2. Repreparing the restorative margin at a more aesthetic level. A connective tissue graft will be placed after the provisional restoration is fabricated, creating a more aesthetic restorative gingival emergence.|
|Figure 3. After gross preparation, a 30 mm rounded cylinder diamond is used to smooth the metal surface. Axial reduction should be 1.5 mm for porcelain-fused-to-metal implant restorations, which is the same as for natural teeth.||Figure 4. Rubber porcelain abrasives are used to polish metal abutments to a fine luster. The smoother the preparation, the better the fit.|
Gross preparation of metal implant abutments can be accomplished in a controlled fashion using a No. 2S Great White Bur (SS White) in a high-speed or electric handpiece. The geometric design of the blade (sharp dentated surface) cuts metal smoothly without skipping or gouging the metallic surface. Once the gross preparation is completed, an 8855-014 rounded cylinder 30-um finishing diamond (Brasseler USA) is used to begin the polishing by removing the abrasions left by the carbide bur. Final polishing of the abutment is accomplished using rubber porcelain abrasive points (Brasseler USA). A smooth abutment will yield a more precise fit to the superstructure that will be fabricated for the new porcelain-to-metal restoration (Figures 1 through 4).
The following case reports demonstrate a current technique for direct preparation of existing implant abutments in order to achieve the desired aesthetic and functional result.
CASE REPORT NO. 1: SPATIAL REPOSITIONING OF TEETH IN THE AESTHETIC ZONE INVOLVING MALPOSITIONED PREEXISTING IMPLANT ABUTMENTS
|Figure 5. A preoperative view showing a patient with multiple clinical problems. Both incisal and gingival planes exhibit a left-to-right superior-inferior cant, creating aesthetic and functional problems. Other problems include color mismatches, proportional discrepancies, and overlap of the maxillary central incisors.||Figure 6. Maxillary arch preoperative view. Note the labial position of the implants, which could prove problematic for achieving an aesthetic restoration.|
|Figure 7. Radiograph showing existing implants in the No. 10 and 11 positions. Although not in the ideal position to be restored aesthetically, they are well integrated.|
The patient presented with a request for correction of her crooked smile (Figure 5). She also wanted straighter and whiter teeth. Upon examination, the patient had implant restorations replacing teeth Nos. 10 and 11. The gingival margins on the right side of her mouth were more incisal when compared to the left side due to the more apical placement of the implants in teeth positions 10 and 11, thus making her smile appear unbalanced from left to right in terms of gingival height. Minor supereruption and crowding of the maxillary right anterior region further complicated the aesthetic and functional challenge (Figure 6). For this patient, the implants that were placed 12 years previously were well integrated, but prosthetic replacement parts were no longer available for the system that was used (Figure 7).
It became apparent that the position of the implants was contributing to the aesthetic problems in this case. The recommendation to the patient was to recover the implants, place bone grafts in the removal sites, and replace the implants with an updated system in a prosthetically more desirable location. However, the patient did not wish to undergo replacement of the implants. The treatment plan that was developed involved restoration of teeth Nos. 4 to 13. Teeth Nos. 4 and 5 had occlusal and proximal caries and were to be restored with inlay veneer restorations. Teeth Nos. 6 through 9 required all-ceramic "mini-crowns" (less than 1.0 mm of reduction). These teeth were to be reduced incisally, and the crown restorations would eliminate the crowding. The implants (Nos. 10 and 11 positions) would be restored with porcelain to Captek (Precious Metals, Inc) restorations, splinted for retention but separate from the adjacent teeth. Teeth Nos. 12 and 13 would require porcelain veneers for proper color, rotational correction, and closure of the diastema.
The plan for the periodontal tissues was to perform crown lengthening with osseous recontouring for teeth Nos. 4 through 9. The goal was to have the cervico-incisal height of the central incisors be slightly more apical than the lateral incisors, and the cervico-incisal height of the canines to be slightly more apical than the central and lateral incisors. The area where this was most difficult to achieve was in the region of the implants due to the apical and labial position of the fixtures. Therefore, a connective tissue graft was planned to obtain as much coverage of the implant/restorative surfaces as possible and to thicken the alveolar ridge facially to help create better emergence profiles.
|Figure 8. The soft-tissue plan with the incisal edges marked to indicate where they need to be reduced to correct the incisal-occlusal plane. This situation requires correction of the functional (incisal) aspect as well as the tissue (apical) aspect to correct the slant of the teeth without increasing tooth length.|
The surgical plan was outlined using a disposable, extra-fine felt marker. This is critical in visualizing the end result prior to surgical intervention. The gingiva was marked at the appropriate level with the height of contour for each dental unit located at the distolabial line angle. Where the biologic dimension would be violated, osseous recontouring was anticipated. The implant restorations were marked at the gingival area to assess how much additional soft-tissue coverage would be needed to provide balance with the height of the gingival tissue on the contralateral teeth. The ideal incisal edges were marked to correct the incisal plane discrepancy. The incisal edges can be reduced if excessive overlap exists, but only if there is no interference with protrusive disclusion and canine guidance. It is desirable that the maxillary central incisors be 10 and 12 mm in length, with a 0.75:1 to 0.80:1 width-to-length ratio (Figure 8).
|Figure 9. Soft-tissue correction has been accomplished with a diode laser, and the incisal edge has been reduced with rotary instrumentation.||Figure 10. View showing how a combined approach corrects the aesthetically undesirable cant in the smile zone. Areas where biologic width has been violated will require reduction of the osseous crest to create a healthy biologic zone.|
A diode laser (Twilight, Biolase Technologies) was used to perform a gingivectomy at the marked areas. The incisal edges of the teeth were shortened using a high-speed diamond bur (Figures 9 and 10). The teeth were then prepared for the appropriate restorations at the new gingival margins. Margin placement was to be in the final position for desired aesthetics. In this case, the osseous correction (crown lengthening) was to be accomplished at the time of grafting soft tissue. At the time of surgery (reflection of the gingival tissues), the periodontist will only have to follow the restorative margins and place the crest 3 mm apical to that line, which was established by the restorative dentist with the provisional restorations.8,9 This is an excellent way to communicate aesthetic parameters to the periodontist.
|Figure 11. The ceramic and metallic superstructure is removed to the cement layer of the restoration. At this point, the old restoration can be removed from the implant abutments.||Figure 12. The diode laser is used to modify the soft tissues surrounding the nonanatomic implant abutments so that the ceramic restorations can have a more natural emergence profile.|
|Figure 13. The surgical provisional restoration in place. The patient is then referred to the periodontist for connective tissue grafting and osseous reduction. The provisional restoration helps identify the crestal height.|
As tooth preparation begins, the existing implant restorations must be carefully removed, since the type and spatial position of the abutments may not be known. A No. 2S Great White carbide (SS White) was used to remove the superficial ceramic and then the metal superstructure until the cement layer was seen (Figure 11). Once the cement seal was broken, the superstructure was removed with a hemostat. After modification and polishing of the abutments in the manner previously described, the diode laser was used to shape the soft tissue around the abutments to create a normal emergence profile for the ceramo-metallic restoration (Figure 12). The provisional restoration (bisacrylic) was fabricated using a preoperative mockup and a clear stent (Figure 13). As noted, this provisional restoration serves as a guide for the periodontist when performing the osseous surgery.
After the connective tissue graft and osseous surgery were complete, the surgical area was allowed to heal for 4 months. This allows for tissue maturation and stabilization of the graft. The gingival tissues of the teeth that underwent osseous surgery will generally mature to the provisional margins if the surgeon contoured the alveolar crest to a level 3 mm apical to the restorative margins.
|Figure 14. Final impressions of the implant abutments are taken using conventional mechanical tissue displacement (retraction cord) in a similar fashion to the natural tooth abutments.||Figure 15. Intraoral view showing the maxillary reconstruction after cementation. The area of the connective tissue graft will continue to mature for several months.|
|Figure 16. Compare this postoperative view with the preoperative view in Figure 5.|
When healing was complete, final impressions were taken using a double cord technique. For the natural abutments, one wrap of No. 00 cord (Ultrapak, Ultradent) was placed followed by a single wrap of No. 1 cord. A No. 2 cord was used for the implant abutments due to the increased depth of the peri-implant sulcus. Care must be taken not to force the cord too deeply into the sulcus. The No. 2 cord should not be placed below the restorative margin of the implant abutment (Figure 14). The final impression (Honigum, Zenith/DMG) should capture the marginal detail plus 0.5 mm of apical root (implant abutment) surface so that the ceramist can develop proper emergence profiles. Figures 15 and 16 show the retracted view and smile of the patient after completion of treatment. Compare these to the preoperative view (Figure 5). A more aesthetically pleasing smile has been created for this patient using appropriate planning that included utilization of preexisting implant abutments.
CASE REPORT NO. 2: CORRECTION OF EXISTING IMPLANT ABUTMENTS TO ALLOW FOR CREATION OF ANATOMIC TOOTH FORM
|Figure 17. Full arch view of a patient who presented with existing provisional restorations. This restoration was a full arch splint on natural teeth and implant abutments.|
The patient presented with an existing maxillary full arch prosthesis (Figure 17). Teeth Nos. 2, 6, 7, and 8 were present and in good condition. Implants with cemented gold abutments were present in the Nos. 10, 12, and 13 positions. The laboratory-fabricated prosthesis splinted the natural teeth on the patient's right side to the implants on the left side. The patient was never comfortable with the prosthesis.
|Figure 18. Removal of the provisional restorations demonstrates implant abutments that are underprepared and need to be reshaped to allow completion of the new restoration.|
Upon examination, the implant abutments (primarily Nos. 12 and 13) appeared excessive in length and were not prepared in a proper two-plane fashion on the facial and lingual surfaces. Implant abutments (as well as natural teeth) should be prepared in 2 planes, reflecting the natural anatomy of the tooth. This will ensure that there is enough space for a sufficient thickness of restorative material when creating an aesthetic and functional tooth replacement to proper physiologic contour. As a result of improper preparation, there was insufficient space for metal and porcelain to recreate proper tooth contours. Therefore, the restoration was bulky and not comfortable for the patient (Figure 18).
|Figure 19. Full arch view showing the prepared and polished implant abutments.|
A No. 2S Great White carbide (SS White) was used to correct the preparations. The abutments were shortened and reduced in the central groove areas to allow for adequate space to create proper occlusal anatomy with a desired thickness (1.5 to 2.0 mm) of ceramic material. The preparations were then polished as previously described using a 30 m rounded cylinder diamond (Brasseler USA) and porcelain polishing abrasives (Brasseler USA) (Figure 19).
|Figure 20. Completed maxillary reconstruction at delivery.|
A new restoration was fabricated at the same vertical dimension of occlusion as the original restoration. Although the existing abutment restorations were overcontoured buccal-lingually and mesio-distally, and thus were uncomfortable for the patient, the existing vertical dimension of occlusion was comfortable, thus it was not altered. The plan for the new prosthesis included a semiprecision stressbreaker between teeth Nos. 9 and 10 to allow physiologic movement of the natural abutments yet create the cross-arch stabilization gained from a full-arch splint (Figure 20).
Two cases have been presented that illustrate the re-use and preparation of implant abutments for new restorations. Intraoral preparation of metallic structures demands instrumentation that can be used efficiently and produce the required result without damage to the supporting structures, whether they are natural teeth or implants. Metallic abutments on well-integrated implants, when in the proper position, can often be modified, polished, and reused, much like previously prepared teeth in a new reconstruction. This approach can save time and expense.
1. Buser D, Ingimarsson S, Dula K, et al. Long-term stability of osseointegrated implants in augmented bone: a 5-year prospective study in partially edentulous patients. Int J Periodontics Restorative Dent. 2002;22:109-117.
2. Becker W, Becker BE, Alsuwyed A, Al-Mubarak S. Long-term evaluation of 282 implants in maxillary and mandibular molar positions: a prospective study. J Periodontol. 1999;70:896-901.
3. Hosny M, Duyck J, van Steenberghe D, Naert I. Within-subject comparison between connected and nonconnected tooth-to-implant fixed partial prostheses: up to 14-year follow-up study. Int J Prosthodont. 2000;13:340-346.
4. Laufer BZ, Gross M. Splinting osseointegrated implants and natural teeth in rehabilitation of partially edentulous patients. Part II: principles and applications. J Oral Rehabil. 1998;25:69-80. Review.
5. Naert IE, Duyck JA, Hosny MM, Van Steenberghe D. Freestanding and tooth-implant connected prostheses in the treatment ofpartially edentulous patients. Part I: An up to 15-years clinical evaluation. Clin Oral Implants Res. 2001;12:245:237-244.
6. Vigolo P, Majzoub Z, Cordioli G. Measurement of the dimensions and abutment rotational freedom of gold-machined 3i UCLA-type abutments in the as-received condition, after casting with a noble metal alloy and porcelain firing. J Prosthet Dent. 2000;84:548-553.
7. Gross M, Laufer BZ, Ormianar Z. An investigation on heat transfer to the implant-bone interface due to abutment preparation with high-speed cutting instruments. Int J Oral Maxillofac Implants. 1995;10:207-212.
8. Kois JC. The restorative-periodontal interface: biologic parameters. Periodontol 2000. 1996;11:29-38.
9. Kois JC. Altering gingival levels: the restorative connection part 1: biologic variables. J Esthet Dent. 1994;6:3-9.
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