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Compendium
April 2017
Volume 38, Issue 4
Peer-Reviewed

7. Palatal SCTG for ‘Biotype Conversion’

The last of the surgical keys is often overlooked. In their IIPP study (mean 4 years) of the esthetic zone without bone grafting the buccal gap or using a SCTG, Kan et al61 reported significantly greater facial gingival level (FGL) changes in the thin gingival biotype group (–1.50 mm) compared to the thick gingival biotype group (0.56 mm) (Figure 9 and Figure 10). This finding supported the results of 2 previously mentioned studies.45,46 Facial gingival recession is common after immediate tooth replacement. The amount of recession is approximately –0.5 mm to –0.8 mm of FGL.45,62,63,64 When SCTG was added to the IIPP protocol, no significant difference was observed in the FGL change at a mean follow-up of 2.15 years between thick (8 patients) and thin (12 patients) gingival biotypes (0.23 mm vs. 0.06 mm, respectively).65 This may suggest a thin gingival biotype can be converted to a thicker gingival biotype morphologically and behaviorally—thus the term “biotype conversion.” The mean mesial and distal marginal bone level changes and the mean FGL changes in this study also showed no significant differences at a mean follow-up of 2.15 years, demonstrating well-preserved peri-implant papilla.65 This agrees with a study by Fenner et al,66 in which cases that received SCTG (baseline facial tissue thickness of <2 mm) had stable papilla height after an observation time of 8 years, whereas the cases that did not obtain SCTG saw a decrease of the papilla between year 1 and year 8.

In a 1-year prospective study in nonesthetic sites in humans, Linkevicius et al67 found the initial gingival thickness at the alveolar crest may be considered a significant influence on marginal bone stability around implants. If the tissue thickness was 2.5 mm or less, crestal bone loss of up to 1.45 mm occurred within the first year of function, despite a supracrestal position of the implant–abutment interface. They also recommended thickening of thin mucosa before implant placement, converting a thin-tissue biotype into a thicker one.

The results of the study by Linkevicius et al67 are consistent with an animal study by Berglundh et al68 who reported the correlation of thin tissues with crestal bone loss during biologic width formation if a minimum dimension of the biologic width was not preexisting. Bone resorption would follow to allow for the reformation of the biologic width. Linkevicius et al69 found that platform switching in a 1-stage implant placement approach does not prevent crestal bone loss if, at the time of implant placement, mucosal tissue is thin (2 mm or less). However, in thick soft tissue (>2 mm), use of a platform-switch implant maintained crestal bone level with minimal remodeling at 1 year. In a 2-stage implant placement approach with a platform switch, Puisys et al70 found similar results. Thin tissues (≤2 mm) lost significant crestal bone, whereas thick tissues (>2 mm) or thin tissues augmented with acellular dermal matrix had similar crestal bone maintenance with minimal bone loss at 1 year.

The use of SCTG in conjunction with bone-grafting the implant–socket gap with IIPP in the esthetic zone and 3D placement has been evaluated in several other case studies.8,71-75 Rungcharassaeng et al74 examined the facial gingival tissue thickness (FGTT) with IIPP on maxillary anterior teeth with the placement of SCTG (n = 31) and without SCTG (n = 24). In a study by Jung et al,76 at 1.5 mm of gingival tissue thickness all materials tested (titanium, titanium-ceramic, zirconia-ceramic, and zirconia) caused visible tissue color change. It was determined that 3 mm of gingival thickness was necessary to sufficiently mask all test materials, while with 2-mm-thick gingival tissue, only zirconia did not induce visible color change using spectrophotometric analysis. In the study by Rungcharassaeng et al,74 patients who did not receive SCTG had a FGTT mean measurement of 1.42 mm, which seemed inadequate to mask any type of underlying restorative material, as Jung et al76 also noted. The mean for the SCTG cases was significantly greater at 2.61 mm. Rungcharassaeng et al74 concluded that performing IIPP in conjunction with a connective tissue graft will more likely result in sufficient peri-implant tissue thickness to conceal the underlying implant restorative materials compared to nongrafted sites.

Cosyn et al77 evaluated immediate screw-retained restorations in 22 patients who presented with thick gingival biotypes (patients with thin biotypes were excluded); the platform-switch concept was used with all implants. All implant–socket gaps were grafted with DBBM. At 3 months, 5 cases demonstrated alveolar process remodeling (1 mm or more) and received SCTG using the pouch technique. In addition, 2 cases showed advanced midfacial gingival recession (1.5 mm to 2 mm) and were also grafted with SCTG. Thus, 7 cases (31.8% of cases) were grafted at 3 months because of esthetic complications. SCTG use resulted in a steady improvement of the pink esthetic score (PES) after 3 months. The authors found similar PES post-treatment (PES: 11.86) compared to presurgery (PES: 12.15). They concluded preservation of pink esthetics is possible following immediate tooth replacement; however, to achieve this, SCTG is necessary in about one-third of the patients (who presented with a thick gingival biotype). Similarly, in the study by Chen et al,45 midfacial mucosa recession of 1 mm to 3 mm was noted in 10 (33%) of 30 sites within the first year.

Several recent clinical studies have shown highly acceptable esthetic outcomes resulting from grafting the buccal gap (freeze-dried cortical bone allograft or DBBM) without the use of SCTG. These sites were managed by preserving the gingival contours at the time of implant placement using a customized contoured healing abutment (polyether-ether-ketone [PEEK]) or a custom-contoured immediate provisional (IIPP) restoration for immediate support of the gingival tissues.7,9-19

To summarize, treatment strategies recommended to reduce the risk for facial mucosal recession when using type 1 implant placement include placing low-substitution bone fillers in the buccal gap, utilizing flapless surgery, using SCTGs, and immediately managing gingival contours at the time of immediate placement.

8. Management of Emergence Profile

Emergence profile management is performed with a flat or under-contoured customized anatomical screw-retained provisional restoration or a customizable PEEK abutment to mold and sculpt the soft tissues (ie, the transition zone) (Figure 11 through Figure 18). This first of the restorative-related keys begins with collecting patient data and treatment planning. After diagnosis, the team confers to generate a plan, which results in fabrication of an ACSGT to ensure correct tridimensional position of the dental implant. This is crucial in developing the transition zone with the provisional restoration.5,7,8,19-21,23,24,29,30,43,44 No clear advantage seems apparent for either screw retention or cement retention of the final restoration. The previously reported high incidence of screw loosening associated with older retention screw materials and external hexagon butt-joint designs has largely been resolved through the use of genuine (original equipment manufacturer) components, which have precise tolerance, control of machined interfaces, or internal connections.78,79 Cement retention can be associated with biologic/infection complications possibly because of operator error in controlling excess cement.80-88

Recommendation of a screw-retained restoration is based, in part, on the risk for excess cement potentially causing complications to adjacent tissues. A screw-retained provisional also facilitates the opportunity to apply pressure against the soft tissue when developing the transition zone during site optimization and tissue conditioning. As previously discussed, soft-tissue thickness around implants is important for long-term esthetic results. The shape of the provisional is fundamental in achieving good esthetics. The facial contour on the implant prosthesis can be quite different from that of a natural tooth. Undercontoured or flat facial design allows the soft tissue to occupy the space without pressure and proliferate coronally. Excessive or undesirable provisional pressure on the facial soft tissue can cause thinning of the mucosa and possible facial recession. The provisional can be adjusted to the correct height of the proposed mucosal margin without causing blanching of the tissue for a prolonged period (empirically 5 minutes). Typically, an immediate provisional will be initially undercontoured, and tissue maturation and shaping can be corrected after several appointments of adjustments (Figure 13 through Figure 18.).

The implant-retained provisional can be fabricated by either a direct method intraorally or an indirect method in the laboratory. With the indirect technique, a presurgical cast is modified after the intraoral index (impression) of the dental implant is made. Different abutment types, including titanium or PEEK, and materials—such as polymethyl-methacrylate (PMMA), bisphenol A-glycidyl methacrylate (bis-GMA), denture teeth, or the patient’s previous crown or tooth—can be used for fabrication of the provisional. Based on research, controlling the emergence contour in the esthetic zone has immediate benefits. This is most easily done with a screw-retained, custom-contoured abutment in unprovisionalized cases (Figure 11 and Figure 12) or a custom-contoured, screw-retained provisional (Figure 13 through Figure 18) when restored.

Use of the customized PEEK abutment allows the tissues to begin achieving the desired transition zone shape. This is done prior to insertion of a screw-retained, laboratory-processed provisional 12 weeks later (Figure 13 and Figure 14). This temporary titanium abutment usually needs to be adjusted to improve esthetics by opaquing the grayness of the titanium with a light-cured opaque resin material to prevent darkening the peri-implant mucosa. The provisional is shaped with the correct or undercontoured emergence profile, and the gingival embrasure is designed following the adjacent teeth even if a black triangle is present at insertion. The transition zone can be further modified with the provisional by adding or removing subgingival restorative material and allowing the gingiva to mature. Full papillary height may not be appreciated for several months following provisionalization.

Choquet et al89 showed when papilla is filling the space between an implant and a natural tooth, the average distance between the gingival portion of the proximal contact and the interproximal bone is approximately 3.8 mm. However, this number is merely an average of the patients in the study, and the papilla can be longer. The gingival embrasure ideally should be opened initially in the provisional to allow for papilla maintenance or regrowth. The provisional should eventually be reevaluated and a decision to close spaces or modify shapes should be considered. A provisional restoration in the esthetic zone may be worn for an extended period. Determining the optimal time to make a final impression for fabrication of the final restoration is a clinical decision, as interproximal tissues can continue to mature and increase in height for 1 year or longer.

9. Custom Impression Coping Technique

After the implant has osseointegrated and the clinicians are satisfied with the soft-tissue architecture and transition zone that has materialized in the provisional phase, the position of the implant and transition zone is communicated to the laboratory technician (Figure 19 through Figure 23). Once the provisional is removed, the tissue noticeably collapses immediately due to the circular peri-implant connective tissue fibers. In almost all esthetic-zone cases, a stock impression coping will not prevent the soft tissues from collapsing, nor will it hold the tissues in a proper shape. This prevents the transition zone from being duplicated accurately. Under these conditions, the laboratory technician will design the emergence profile according to his or her knowledge of the dental anatomy.

To provide the technician with an accurate representation of the transition zone and avoid having to estimate its shape, Hinds90 proposed a technique to produce a custom impression coping. Patras and Martin91 modified the technique by using photopolymerizing materials such as flowable composites. The provisional restoration contains the developed transition zone shape and, by default, the support for the transition zone (Figure 17 and Figure 18). A polyvinyl siloxane (PVS) material is used to copy the shape of the provisional on an implant analog (Figure 19 and Figure 20). Once the material is set, the provisional is removed from the analog and the stock impression coping (open tray or closed tray) is adapted to the analog. The space between the impression coping and the PVS (ie, the transition zone) is filled with flowable composite and light cured. The custom impression coping is then removed from the analog and placed in the implant site intraorally. The custom impression coping now supports the surrounding tissues identically to the provisional for the final impression92 (Figure 20 and Figure 21). Once the impression is removed, an analog is attached to the impression coping and a soft-tissue model is made (Figure 22 and Figure 23).

10. Final Restoration

The restorative doctor and/or dental laboratory have many materials from which to choose for laboratory fabrication of the final implant restoration (Figure 24 through Figure 29). Historically, ceramic fused to metal utilizing a “cast to” abutment has shown excellent long-term results and superb esthetics. Dentistry’s pursuit of even more predictable esthetics and greater manufacturing efficiencies has led to metal-free restorations and milled ceramic/titanium abutments.

Concerns regarding zirconia abutments with titanium implant interfaces focus on long-term survival and possible complications, including fracture of zirconia at the titanium implant connection and wear of the titanium walls of the implant adjacent to the abutment. The wear can result in micromovement of the abutment connection and eventual fracture of the zirconia abutment or tattooing of the soft tissues due to fretting.93 This complication can be avoided by using a titanium bonding base, which provides a titanium interface in contact with the dental implant and a retention portion for cementation of a ceramic abutment complex. This can be accomplished with the “Ti base” concept, whereby a titanium interface connection is milled in titanium (as in our case presentation) as a one-piece abutment, and the ceramic crown is cemented extraorally by the laboratory, and then screwed into place intraorally (“screw-ment” design). Alternatively, the abutment can be milled in zirconia and bonded to the Ti base. If done as a zirconia abutment, porcelain can be applied directly, thereby avoiding cementing the crown to the abutment. The firing of the porcelain would be performed before bonding to the Ti base.

When using final restorations that are cemented on custom abutments intraorally, there is no statistical difference in success for single-unit restorations. Clinicians should be aware of the risk for excess cement being left subgingivally due to the inability to detect or remove cement at tissue depths greater than 1 mm.83-88 Linkevicius et al84 demonstrated how difficult it can be to remove excess cement when the abutment margins are subgingival.

To avoid these clinical situations, a correct 3D custom abutment should be fabricated. The contours should follow the gingival margins equal to or no more than 1 mm subgingival. Also, when cementing is necessary, the amount of excess cement must be controlled.85-88 Resin and other radiolucent cements should be avoided because excess cement cannot be detected radiographically and because of the bacteriophyllic properties of the material. In addition, removing resin cement can be difficult due to the formation of a thin layer subgingivally along the abutment interface. Radiopaque cements, such as those containing zinc, are recommended for their ability to be seen radiographically and their bacteriostatic properties.86,88

Conclusions

The 10 keys for esthetic-zone success for single immediate implants are intended to be a guide for clinicians and aid them in the treatment planning and execution of these types of cases. Each key can be critical in achieving the final, predictable long-term esthetic outcome. Treatment in the esthetic zone is a complex SAC procedure for both the surgical phase (key Nos. 3 through 7) and prosthetic phase (key Nos. 8 through 10); therefore, the team approach should be considered when treatment planning in the esthetic zone.

Keys that have emerged in the past few years for immediate placement of implants at the time of extraction include: treatment planning, including facial buccal bone assessment and recognition and management based on the sagittal position of the tooth to be extracted using CBCT analysis; palatal placement of the implant leaving a 2-mm to 3-mm gap between the facial surface of the implant and the buccal plate; use of smaller-diameter implants to leave a larger buccal gap; placement of a mineralized bone graft in the buccal gap; placement of SCTG with a small envelope or tunneling incision facial to the buccal plate to compensate for anticipated buccal remodeling (this is particularly important for patients with thin- or medium-thickness gingival phenotype); and immediate contour preservation with either a custom provisional restoration or a custom healing abutment.

More traditional keys include: dedication to a team approach with open communication and each member having expertise in his or her own therapeutic area and knowledge of other aspects of treatment; optimization of the subgingival contours with accurate provisional restorations; accurate transfer of contours to the dental laboratory using a customized impression coping; and selection of final restorative materials and techniques recognizing possible limitations and complications of implant–abutment interfaces, cementation issues, and biologic parameters.

Short- and medium-term studies now show equivalent results between immediate placement and provisionalization compared with delayed placement with conventional healing when the 10 keys are followed.7-19,38,94 Long-term studies are needed that compare the procedures for optimal timing of implant placement in the esthetic zone, because contour changes of the soft and hard tissues may continue for many years post-implant placement.38,61

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