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Soft Tissue Integration With Natural Tooth-Shaped Abutments

When first introduced, implant dentistry achieved great success in the treatment of completely edentulous patients.1-4 The technique was eventually utilized to successfully replace missing teeth in partially dentate patients.5,6 The development of abutment connections was pioneered to enhance aesthetics while maintaining the hygiene of the peri-implant tissues. Replacement of a single missing tooth in the anterior maxilla is one of the most challenging procedures, since soft tissue aesthetics, location and volume of available bone, prosthetic aesthetics, phonetics, and occlusion must be considered.

The use of traditional abutment / prosthetic connections in the replacement of a single missing tooth has been restricted by inadequate interarch distance. The “UCLA” abutment was introduced to address the difficulties in space restriction and axial alignment.7,8 Customization of the abutment with either metal or porcelain allowed the development of the desired emergence profile and provided an option of segmented or nonsegmented restoration.9 Cementable restorations seemed to be more appropriate to maximize aesthetics in the anterior maxilla. However, they required the use of the available abutments, which had a round cross-section with a relatively straight emergence that caused a disparity between the widest diameter of the intended restoration and the diameter of the implant platform.

The dimensional disparity between the implants and the postextraction sockets resulted in the development of abutments fabricated in a shape similar to that of natural teeth.10 Abutment systems have been recently introduced that are fabricated to the configuration of natural teeth in the anterior maxilla. The systems permit the development of an aesthetic emergence profile and contours that facilitate hygiene maintenance of maxillary anterior implant-supported single-tooth restorations.

Since a considerable tissue deficiency frequently accompanies the loss of a tooth in the anterior maxilla, grafting of the area may be required. The extent of bone resorption indicates whether the implant should be placed concomitantly with a bone graft or delayed until the bone graft has healed.11 Due to the potential loss of papillae and other soft tissue profiles, soft tissue replacement in these areas may be required. When optimal soft tissue aesthetics around single-tooth implant restorations is the treatment objective, techniques of regeneration with interpositional,12 subepithelial connective tissue,13 soft tissue onlay grafts,14 and a three-stage approach15 have offered varying degrees of success.

A proper treatment plan must include the selection of an appropriate design for retrieval, from which the orientation of implant placement can be verified with a radiographic stent/template and concurrent tomogram or similar digital image of the site. Strict adherence to the surgical stent can be accomplished by providing the surgeon with a serial drill guide.16 Since the concentricity of the original twist drill can be preserved in the final tap drill, its use prevents the osteotomy site from migrating during placement. The 2-mm pilot drill is used to initiate the procedure and to bur to the appropriate depth. Since the prosthetic design dictates the orientation and position of the implant, a system that allows abutment try-in at the time of placement aids the surgeon in correct placement and angulation.

These important planning features are important when one is selecting the appropriate implant and anatomical abutment system. The try-in body for the respective abutment is selected at this stage to determine which abutment configuration is most appropriate. The try-in may also have a role in determining the extent of countersinking required  (Figure 1). Serial-sized osteotomes may be used in specific clinical circumstances to widen the osteotomy site while preserving buccal cortical plate.17 The site is widened almost to the final tap drill, for which only minimal bone is removed, promoting stabilization of the implant fixture and the architecture of the facial gingival complex (Figures 2 and 3).

Once the implant is in place, the 1.5-mm guide pins can be inserted in the abutment try-in body and placed inside the fixture. The selection of the most appropriate abutment can now be determined, particularly if surgical indexing is used. Recording the position of the implant is helpful in the development of soft tissue profiles following second-stage surgery. If stability of the implant is acceptable at placement, recording of the implant position with autopolymerizing resin can be performed carefully prior to grafting and/or closure (Figure 4). The flat side of the hex should be oriented to the facial aspect when utilizing the depicted anatomical abutment system.

Following polymerization, the surgical index can be attached to the diagnostic cast with an adjoining implant analog to preserve the position of the newly placed implant. A recess is created in the diagnostic cast to approximate the shape of the implant body (Figure 5); it allows placement of the surgical index / implant analog complex on the diagnostic cast. Either resin or stone is used to anchor the implant analog in place. If the try-in body configuration was determined at implant placement, abutment selection will allow preparation of the abutment and the provisional fabrication in the laboratory (Figure 6).

Indications and Contraindications

These specialized techniques can be utilized with single or multiple missing teeth in any region. However, since these abutments are available only for maxillary anterior dentition, the use of a customized abutment may be necessary in other regions. It must also be determined whether bone and/or soft tissue grafting will be required in order to anticipate replacement resulting from future aesthetic and hygienic complications. This technique should not be used with implants that are countersunk to greater depths, since the removal of cement in these cases may be difficult, if not impossible. The use of a nonsegmented screw-retained restoration or a ceramic abutment may be an alternative in these circumstances.

Clinical Procedure

The clinical procedure should be preceded by the evaluation of any existing deficiencies. To determine the quantity of missing or malposed keratinized tissue, soft tissue of the implant site is compared with that of the adjacent dentition. Tomograms or similar digital imaging alternatives may provide a clearer indication as to the extent of bone missing from the facial cortical plate. A waxup will determine the position of the incisal edge, cingulum form, cementoenamel junction, lingual concavity, and axial emergence. The waxup is subsequently duplicated in stone, and a surgical stent/template is fabricated.

It should be determined whether the intended restoration will be cemented or screw-retained. Depending upon the size of the restorative space for anterior teeth, a screw access may have to be placed in the cingulum for aesthetic demands. If screw retention is required, the ideal access hole is positioned between the incisal edge and the cingulum. Due to alveolar resorption, an implant is often placed palatally. This frequently occurs in the lateral incisor region because of its labial concavity. If a screw-retained restoration is desired, the resultant prosthesis should be fabricated with a ridge lap to simulate the free gingival margin.18 To achieve uniform contours with the definitive restoration, a modified ridge-lap has to be created, which complicates patient hygiene procedures (Figure 7). To retain the external contours of the prosthesis in physiological and aesthetic limits, cement-retained restorations are considered to be the norm for the anterior maxilla.

Cemented restorations are preferable to screw-retained restorations in the establishment of aesthetic contours and favorable gingival profiles. If an alteration in the emergence profile is desired, a screw-retained restoration requires a different abutment and the fabrication of a new master model, while the cemented restoration may be adapted without the recording of a new impression.19,20

The primary surgical procedure should be based on an atraumatic flap design that preferentially excludes the papillae, yet allows adequate visibility of the underlying bone. The stent should allow access from the lingual aspect for adequate instrumentation and retain the facial surface intact with the estimated position of the cementoenamel junction. When position of the 2-mm pilot drill has been determined, the try-in abutment may be placed to determine the appropriate configuration and countersinking. In the depicted system, five abutment configurations are available--three for incisors and two for cuspids and bicuspids.

Once the implant fixture is placed, its position can be verified with the abutment try-in and a 1.5-mm guide pin. This assembly fits within the implant body and gives a clear indication of the exact implant position with respect to abutment selection. The level of countersinking can also be verified prior to surgical indexing, grafting, and flap closure. The abutment configuration is recorded, and an abutment can be fabricated in time for the second-stage surgery without the need for an extensive inventory. If the implant is mobilized or if residual material is allowed to remain in the surgical site, surgical indexing may pose a risk to the success of implant surgery. If a surgical index is made, however, the fabrication of a provisional restoration is a time-efficient alternative to placement of a tissue-contouring abutment. The indirect abutment is fabricated with a finish line 4 mm superior to the implant platform, which may require preparation to retain the metal surface below the tissue, since the balance of the emergence profile can be created in the provisional restoration (Figure 8).

Discussion

Single-tooth implant-supported restorations in the anterior maxilla are planned with an appropriate diagnostic waxup. The timing of surgical procedures should be strategically arranged to include concomitant bone grafting, if required, and appropriate implant placement. Cases of this type frequently require soft tissue grafting, particularly if the tooth has been missing for a considerable length of time. The soft tissue grafting should be performed following at least 3 to 4 months of integration. The implant should essentially be integrated at this time, and split-thickness dissection allows the placement of an interpositional connective tissue graft. If the graft is performed following or simultaneously with the uncovery procedure, interferences may be present and become a nidus for bacteria and potential infection. In addition, the external tissue contours may be used to obtain an improved aesthetic result.

The grafting technique utilized is dependent upon the type and/or quality of tissue required--keratinized, interpositional bulk, attached, etc. Soft tissue architecture is of crucial importance for the aesthetic success in these cases, and grafting will have a limitation of volume based on its blood supply.

Titanium abutments have demonstrated to be predictable, durable, and biocompatible connections. The use of anatomical abutments is helpful when the clinician is attempting to create a natural emergence with porcelain restorations, due to the close approximation of these abutments with the cervical shape of natural teeth. By using prefabricated healing abutments and components, the uncertainties of soft tissue modification following uncovering is restricted to a minimum. Retrieval techniques in cementable prosthetics may rely on the use of an auxiliary tap screw to engage the abutment through the existing tissues. This secures the restoration and, if a provisional restorative cement is used, effectively seals any potential internal void.

Conclusion

Maxillary anterior single or multiple tooth implant supported restorations create high aesthetic and hygienic demands for the patients and the surgical/restorative team (Figures 9-10-11-12-13-14-15-16-17-18-19-20). Appropriate implant selection and placement in this area is crucial for restorability and patient hygiene maintenance. Provided the placement is optimal, titanium abutments have demonstrated superb biocompatibility with soft tissues and implant surfaces. However, the use of titanium restricts the aesthetic potential of porcelain restorations, due to the dark metallic abutments that are visible through the gingival tissue. In these cases, the subgingival emergence of the tooth-shaped titanium abutments may be created and finalized with porcelain to an anatomical shape. Since the configurations are identical with healing abutments, impression posts, and definitive abutments, only minimal or no soft tissue modifications are required following second-stage surgery. Porcelain is a biocompatible substance, and utilization of subgingival porcelain is the key to the health of periimplant tissues. The highly glazed surface and the exceptional marginal adaptation of an all-ceramic system further promote the health of the surrounding gingiva.

*Assistant Professor, Department of Prosthodontics, Louisiana State University School of Dentistry, New Orleans, Louisiana.

 

References

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