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Transitional Custom Abutments: Aesthetic Treatment in Implant-Supported Restorations

Traditionally, limitations at the restorative/implant connection have posed obstacles in the achievement of superior treatment outcomes with osseointegrated implants. Complications often resulted in aberrant contours that were unaesthetic and difficult to maintain--particularly in the management of compromised fixture placement.1,2 Several prosthetic components have been developed in an effort to optimize the emergence profile of implant-supported restorations by improving the relationships at the tissue-restorative interface.3-5

The development of alternative implant diameters has allowed individualized fixture selection to specifically match the cervical widths of the replaced teeth.6-8 In addition, various restorative components have been designed to guide the healing of the supraimplant soft tissue contours.9-12 Despite their efficacy, however, it is impossible for any prefabricated abutment system to compensate for the infinite variations in gingival topography that may be encountered intraorally.

The use of customized abutments has been suggested as an alternative to circumvent the limitations of prefabricated components.13,14 Although this technique represents a significant improvement, the design of the custom abutment remains confined within the supraimplant soft tissue contours generated through the use of prefabricated healing abutments and subsequently transferred with standard impression posts. This article introduces the transitional custom abutment technique as a prosthetic adjunct to increase restorative flexibility and improve emergence profiles--particularly in the presence of compromised fixture placement, angulation, or selection.

Treatment Rationale

Optimum emergence profiles can be predictably achieved only through the use of techniques that allow maximum manipulation of the available supraimplant soft tissue contours. One frequently employed method utilizes a provisional fixed prosthesis that is gradually modified to develop the soft tissue contours.15,16 This technique, however, is limited to patients where implant placement is adequate. Its application in areas where compromised fixture angulation is present will often cause the screw access to exit through the buccal surface or at the incisal edge of the provisional restoration.

The use of transitional custom abutments may provide enhanced restorative flexibility and emergence profiles in situations where mesiodistal positioning, buccolingual angulation, or fixture diameter selection have been compromised. This technique allows simple and controlled modification of the abutment profile to optimally manipulate the supraimplant tissue contours. The tissue resistance generated by gingival expansion during seating of the abutment is effectively overcome by the screw-retained transitional custom abutment. In addition, excessively subgingival restorative margins are avoided and can instead be placed according to aesthetic and functional demands. A significant advantage of the transitional custom abutment technique is its ability to compensate for inadequate implant angulation as a result of rotational deviation from the optimal axial orientation either in a mesiodistal or buccolingual direction.

               

Clinical Technique

On a diagnostic model, a fully contoured waxup of the teeth to be restored is developed with the desired functional and aesthetic anatomy. A vacuum-formed stent and a silicone index are fabricated from a duplicate of the diagnostic waxup (Figures 1 and 2). A pickup impression is made at the implant level utilizing internally hexed UCLA-type impression copings. This is followed by the fabrication of a master model that incorporates laboratory implant analogs.

Internally hexed UCLA-type temporary cylinders are connected to the implant analogs and modified until they resemble full-coverage crown preparations. Coarse- or medium-grit diamonds and carbide burs are recommended to increase surface roughness and mechanical retention. The vacuum-formed stent is utilized as a guide throughout the preparation, while the silicone index aids in verifying adequate reduction at the incisal third (Figure 3). Exposure of the screw access cavity will occur depending on the degree of angulation to be corrected. Nevertheless, longitudinal exposure of the screw access cavity as a result of excessive axial wall reduction should be avoided.

Once the preparation is completed, the temporary cylinders are washed and dried. A 35% phosphoric acid gel is applied for 10 seconds as a cleansing agent. The prepared surfaces are primed and a coat of bonding agent is applied and light cured. This is followed by the incremental addition of a light-cured hybrid composite with low flow characteristics until the preliminary emergence profile is developed for the core. A layer of opaque composite may be used to mask the metal surface prior to core buildup in aesthetically demanding situations (Figure 4). The composite core is modified through reduction or addition of material until the desired contours are achieved. A flowable composite may also be used at this stage. The vacuum-formed stent and silicone index enable development of optimum implant angulation and position, and can be used to verify the existence of adequate space for the definitive restorative materials within the confines of the diagnostic waxup.

The transitional custom abutments are then transferred to the mouth, where additional modifications are performed as necessary. Once all tissue-borne surfaces have been polished, the transitional custom abutment is installed. Complete seating is achieved by gradually tightening the retaining screw. A chamfer or shoulder finish line--which generally follows the gingival margin topography--is subsequently established according to the site-specific aesthetic demands of the area being treated. Once installed intraorally, the transitional custom abutments may be progressively modified until the optimum supraimplant tissue contours and emergence profiles are established (Figures 5-6-7).

In order to fabricate the definitive prosthesis, the finalized tissue-restorative contours must be reproduced. The accurate transfer of the optimally developed soft tissue topography requires that collapse of the peri-implant sulcus be prevented. A soft tissue model is then poured with the transitional custom abutments in situ, which yields an exact replica of the prosthetically induced peri-implant sulcus topography (Figures 8 and 9).

Next, wax can be flowed into the peri-implant sulci and around UCLA castable abutment patterns to fabricate cast metal custom abutments that replicate the contours of the transitional custom abutments (Figure 10). Once the custom abutments are tried in, the final restoration can be fabricated.

Although certain high-strength nonmetallic crowns may be a consideration in single-unit applications as a result of their ability to conceal the underlying metal abutment, caution must be exercised since temporary cement, which is traditionally recommended to preserve the retrievability of implant-supported restorations, may not adequately support the nonmetallic substrate. Composite-gold alloy frameworks are an excellent alternative in aesthetically demanding regions, as they offer a balance between strength and aesthetics (Figures 11 and 12). More extensive splinted prostheses require the use of traditional metal-ceramic materials.

(Continued from page 1 )

Treatment Sequence and Surgical Considerations

Transitional custom abutments perform optimally when generated from an integrated treatment approach where the definitive prosthetic outcome has been preestablished. This would encompass prosthetically driven site development, augmentation, and implant placement.17

An initial transfer impression must be taken prior to fabrication of the transitional custom abutments. Although this procedure may be performed simultaneously with implant placement or at exposure, it is advantageous to delay until adequate healing has occurred. This allows stable gingival margins to be transferred and reproduced, which improves the accuracy of the transitional custom abutment and, therefore, the adaptation of the attendant provisional prosthesis.

Prosthetic modeling of the supraimplant tissues requires the presence of sufficient attached gingiva. It is therefore necessary to adopt a surgical protocol that will yield maximum quantities of tissue. Generally speaking, any required soft tissue augmentation procedures should be performed prior to implant exposure. Conservative second-stage surgical techniques are subsequently utilized and complemented with the use of undersized healing abutments.

Installation of the transitional custom abutments is accomplished in the presence of sufficient mature attached gingiva that is amenable to stretching. Gradual expansion of the tissues will be accomplished through pressure generated by tightening of the retaining screw as the abutment is seated. At this stage, procedures that involve flap elevation are contraindicated. The increased circumference of a transitional custom abutment is difficult to adequately overcome regardless of flap design and seldom results in primary flap closure without excessive pressure and compromised soft tissue contours.

Conclusion

The term transitional custom abutment accurately describes the progressive contour modifications and gingival remodeling required to achieve an aesthetic emergence profile. The aforementioned technique is not limited to the development of an adequate emergence profile, but may also include aesthetic enhancements to the tissue-restorative interface, eg, control of gingival margin position, creation of interdental papillae, and camouflage of compromised mesiodistal as well as buccolingual implant placement (Figures 13 through 19). Adequate position and proper fixture selection are essential in achieving predictable implant-supported restorations. The utilization of transitional custom abutments further enhances restorative flexibility while allowing the optimization of emergence profiles in situations that involve compromised fixture position, angulation, and selection. The technique's versatility allows its application in simple as well as extensive restorations.

*Private Practice, Bryn Mawr, PA

 

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