Crown shape
The crown shape influences the esthetics around implant-supported crowns. Tooth shapes can be categorized as square, ovoid, or triangular. The portion of the tooth coronal to the free gingival margin will influence the volume and height of the gingival embrasure, while the portion apical to the free gingival margin will support the soft tissue facially and interproximally. Triangular-shaped embrasure forms are at great risk for “black triangles” because they create large embrasure spaces that require greater volume of soft tissue to fill. Square-shaped crowns, due to their longer proximal contact, are at lower risk. A restorative modification of the crown shape may be preferred to achieve improved esthetic results.104
Additional Implant-Related Considerations
Implant position
Ideal three-dimensional placement of the implant results in optimal support and stability of the hard and soft tissues. This, in turn, will allow for an esthetically pleasing implant-supported restoration. In regard to the buccolingual position of the implant, the buccal extent of the implant platform should be positioned 1 to 2 mm lingual to the proposed free gingival margin. Alternative references can be lingual to an imaginary line connecting the emergence profile of the adjacent teeth or 1 to 2 mm lingual to the labial position of the proposed CEJ of the future restoration. It should be no more than 2 mm lingual to that point of reference.137,153,193
Free gingival margin position
Evaluation of the initial level of the free gingival margin prior to immediate implant placement allows for prediction of the future gingival symmetry. Sites with free gingival margins coronal to the contralateral tooth resulted in similar gingival levels after the therapy. However, sites in which gingival levels were initially leveled or apically positioned in relation to the contralateral tooth failed to achieve gingival symmetry following therapy.105
Flapless surgical approach
Patients presenting with intact facial bone and a thick gingival phenotype are less prone to advanced recession (> 1 mm) when treated by flapless implant surgery and an immediate implant crown.136 One study evaluated peri-implant soft tissue alterations following immediate and conventional implant placement in 39 patients with intact socket walls and a thick gingival phenotype. The impact of a flapless versus a flapped approach was analyzed. It was shown that a flapless approach had less soft tissue recession compared with a flapped approach, with a mean difference of 0.89 mm at 52 weeks.194
Immediate provisionalization and soft tissue
In addition to providing instant esthetics and comfort for the patient, one of the greatest benefits of implant-supported provisional restorations delivered at the time of implant placement is the preservation of soft tissue architecture.146 In immediately placed implants, recession around a delayed provisional restoration was 2.5 to 3 times higher than those with immediate provisionalization (1.16 vs 0.41 mm, respectively). For both immediate and delayed implant placement protocols, placement of an immediate fixed provisional restoration at the time of implant placement had a positive impact on the maintenance of the soft tissue architecture. It preserved 1 mm more facial gingival tissue for the immediate group compared with the delayed group.145 The fabrication of an immediate provisional restoration is recommended to limit the amount of marginal soft tissue recession in cases where good primary stability of the implant is achieved.144
Clinicians should expect about 1 mm of soft tissue recession, with the majority of recession occurring within 3 to 6 months.121,122,135,154 One study suggested to wait at least 3 months prior to making a master impression and/or selecting a definitive implant abutment,135 while another study recommended use of an implant-supported provisional restoration for at least 6 months prior to placing the definitive restoration.121 Some studies report longer evaluation periods (1 to 3 years) of peri-implant soft tissue. They demonstrate continuing remodeling of soft tissue in certain patients, up to 1.7 mm after placement of the definitive restoration. These findings suggest potential esthetic complications over time, as there is a certain subset of patients who experience recession. This should be taken into account when treatment planning for esthetic outcomes with implant-supported restorations, particularly when initial recession is seen.158,195,196
Materials Biocompatibility
General concepts
Adhesion of bacteria in the mouth to different hard surfaces— teeth, restorative material, and dental prostheses—is one of the mechanisms for accumulation of bacterial plaque. It is influenced by two material-related factors: surface roughness and surface free energy. Surface roughness tends to promote formation and maturation of the bacterial plaque. Surface free energy (wettability) is related to how strongly the bacteria and the surface of the restorative material can bond. For the supragingival environment, it is desirable to have a smooth surface with low levels of surface free energy to prevent or minimize supragingival plaque formation. In the subgingival environment, the influence of surface roughness is negligible and of minor importance when comparing two different types of implant abutments (machined titanium vs highly polished ceramic). This is due to the ability of bacteria to prosper in that subgingival environment.197–199
Type of restorative material
Soft tissue health may also be related to the biocompatibility of the material at the margins of crowns and fixed dental prostheses when the finish line is placed at or below the free gingival margins. Various types of ceramics and noble and high-noble dental alloys are considered safe for use in the oral environment from a biocompatibility perspective.200,201 Several types of ceramics have demonstrated different levels of cytotoxicity,202 and different types of metal alloys demonstrated continuous corrosion.200 Little is known on the specific effects of metal alloys and ceramic materials on the gingiva. One study demonstrated severe gingival histologic reaction to copper-based alloy compared with gold-based alloy crowns.203 Inclusion of several elements was detected in histologic sections of gingiva in contact with casting alloys.204
One clinical study evaluated the relationship between periodontal health and three different subgingival restorations (amalgam, glass-ionomer cement, and composite resin). At the 1-year follow-up, the clinical parameters were similar among the experimental groups, but the bacterial count and the shift in subgingival flora to more gram-negative microbiota were noted in the composite resin group. Restorations made of this type of composite resin (and perhaps others) may have a negative impact on the quality of subgingival plaque.205
The implant abutment material can influence the stability of the peri-implant seal, characterized by the presence or absence of alveolar bone loss and/or peri-implant mucosa recession.206 For abutments made of titanium and alumina-based ceramics, the mucosal healing was similar for both materials, with a formation of 2.0 mm of epithelial attachment and 1.0 to 1.5 mm of connective tissue attachment. In contrast, no proper attachment formed around gold or feldspathic porcelain abutments, resulting in recession and bone resorption.62 Histologic evaluation of healing between 2 and 5 months revealed formation of a stable dimension of soft tissue barrier around titanium and zirconia abutments. Apical migration of the junctional epithelium and marginal bone was noted around gold alloy abutments. Lesser amounts of collagen, fewer fibroblasts, and large numbers of inflammatory cells were noted in the connective tissue around gold alloy abutments. This suggests better soft tissue response to titanium and zirconia abutments.63 Titanium and the once-used alumina ceramic are highly biocompatible. These materials are stable and resistant to corrosion in living tissue with direct and strong adhesion to the surrounding tissues.62 More importantly,