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Optimal Implant Positioning for Soft Tissue Aesthetics

The single-unit implant-supported restoration is a reliable means of replacing a missing tooth.1 In order to be considered successful, an implant-supported restoration must achieve a harmonious balance between functional, aesthetic, and biological imperatives. This concept has resulted in the development of "restoration-driven implant placement,"2 in which implants are positioned in relation to the anticipated requisites of the restorative phase rather than the availability of bone.

 

Implant Selection, Position, and Angulation

Prior to implant placement, the following factors should be analyzed:

  • Smile type;
  • Quality and quantity of keratinized gingiva;
  • Osseous topography of the edentulous ridge;
  • Anticipated form, position, and type of the restoration; and
  • Surgical procedures involved in ridge augmentation.

Failure to consider these factors will compromise the aesthetic result.3 As the objective of implant treatment is the accurate replication of the natural dentition,4 it is also critical to possess an understanding of crown and root anatomy (Figure 1). Since implant placement within the edentulous space significantly impacts the functional, periodontal, and aesthetic result, the implant must be aligned with the anticipated restoration, adapted to the site, and positioned in the tridimensional space.

 

Implant Selection

To determine the shape and width of the crown to be replaced, the dimensions of the contralateral tooth, root size, and anatomy at the level of implant placement should be evaluated. Implant diameter is dictated by the corresponding root anatomy at the crest of bone. Under normal conditions, the crest of bone appears to be 1.5 mm to 2 mm below the crest of the cementoenamel junction (CEJ) of the extracted tooth or adjacent teeth. Following the determination of crown/root size, interdental crest width, and periodontal prerequisites, an implant of corresponding dimensions can be selected to provide a natural emergence profile (Table).

 

Angulation

In order to ensure proper implant angulation, a surgical template should be utilized to transfer prosthetic parameters (eg, tooth position, emergence profile, gingival margin, arch form, vertical dimension) to the surgical site.

Mesiodistal Placement

According to Adell et al,5 an implant with a diameter of 4.1 mm requires a minimum mesiodistal space of 7 mm between two adjacent teeth (ie, 4.1 mm for the implant and 1.5 mm of clearance on each side). The mesiodistal position also depends on the coronal and cervical width of the replaced tooth, the proximity of the adjacent roots, and the presence or absence of diastemata. Moreover, a direct relationship exists between the height of the interproximal bone and the height and shape of the papillae.6

A distance of 2 mm is required at the cervical implant level to ensure development of interdental papillae between the implant and the adjacent teeth; this distance should be a minimum of 3 mm between two implants. If the interproximal distance between tooth/implant and two implants is less, horizontal bone loss will occur and the aesthetic result will be compromised (Figure 2).

 

Faciolingual Placement

This orientation varies with the type of restoration connection (ie, screwed or cemented). Faciolingual placement determines the proximal dimensions of the crown and its anticipated aesthetic appearance. Occlusally, the collar of the implant should remain inside the virtual line that connects the incisal borders of the adjacent teeth (Figure 3).

If the implant axis is aligned with the axis of the restoration, the crown height is the same as that of the tooth it replaces (Figure 4). In order to achieve an acceptable aesthetic result, a palatally positioned implant should generally be placed to a greater apical extent.7 If the implant axis is facially inclined, the emergence is located coronally to the cervical contour of the adjacent teeth. This results in an excessively long crown, and the collar is misaligned with that of the adjacent contralateral tooth.8 In order to prevent a buccal angulation, it is recommended to orient the implant palatally and to place the implant closer to the palatal cortical aspect.

 

Apicocoronal Placement

The apicocoronal location of the implant shoulder depends on the cervical bone resorption morphology, the diameter of the implant, the size discrepancy between the root and the diameter of the implant, the thickness of the marginal gingiva, and the proximal tissue. The implant collar should be 2 mm apical to the line of CEJ of the neighboring tooth if no gingival recession is evident and 3 mm from the gingival margin when gingival recession is present. Consequently, the optimal reference line in all instances is not the CEJ, but the buccogingival contour.9 The implant should be at a maximum of 3 mm from the gingival margin displayed in the surgical guide or on the adjacent teeth (Figure 5) to allow the crown to emerge from a round implant to a triangular emergence profile.10 If the discrepancy between the tooth and the implant diameter increases, the implant shoulder must be placed more apically to achieve an aesthetic emergence profile.

The height of soft tissues determines the length available for the emergence profile, and the sulcus should remain shallow. While soft tissue heights of less than 2 mm are challenging for aesthetic restoration, a height of more than 4 mm establishes a satisfactory aesthetic result but will present a deep sulcus with long-term soft tissue complications.11

If the position is too apical, it will result in the formation of an infrabony defect, a peri-implant pocket, complications in the second phase, difficulty at abutment connection, and excess cement at seating of the restoration. If the position is too occlusal, the biologic width can be violated. A more ideal emergence profile can be obtained when the diameter of the implant is similar to the diameter of the tooth to be replaced.12  

Since the biological height in submerged implants is approximately 3 mm and the sulcus depth 1 mm,13 it is critical to position the platform of the implant in relation to these biological dimensions. It is also important to consider that the majority of the submerged implants lose approximately 0.9 mm to 1.6 mm of crestal bone during the first year of function.14 Care should also be taken to maintain or reestablish a minimum of 2 mm of buccal bone thickness. The hard and soft tissues may require augmentation and placement of the implant platform at 3 mm to maintain the 4 mm of soft tissue required (Figure 6).

 

Occlusal Considerations

Obtaining and maintaining a nontraumatic occlusal relationship with the opposing dentition is a decisive factor in preserving osseointegration and, consequently, the aesthetics of the implant prosthesis. If the occlusal forces developed between the prosthetic occlusal surfaces are excessive axially or laterally, they may induce cervical bone loss around the implant collar, increase the gingival recession, or compromise the gingival level and the definitive aesthetic result.15

The implant axis should be aligned close to the one of the opposing teeth. The palatal orientation of a maxillary anterior implant is more favorable than a buccal position, which considerably increases the lateral forces to be dissipated on a thin buccal bone. In addition, an appropriate accommodation for axial forces can be made by avoiding an unfavorable vertical ratio between the prosthetic crown and the osseointegrated portion of the implant by limiting the prosthetic overbite and overjet and by establishing a nontraumatic occlusal relation during maximum intercuspidation, incision, and mastication. This correct axis could be achieved by reestablishing the normal bone morphology.

(Continued from page 1 )

 

Soft Tissue Management

In order to achieve natural soft tissue aesthetics, the contour, height, and width of the gingiva at the implant site must correspond to the gingivae of the adjacent natural teeth. The status of the gingiva must be evaluated for the diagnosis and treatment planning in order to determine its quantity, quality, color, texture, and biotype (ie, scalloped or flat). It is also a prerequisite to measure the thickness of the gingiva that encompasses the maxilla (ie, buccal 1 mm to 2 mm; palatal 3 mm to 4 mm) and the mandible (ie, buccal and lingual 1 mm). This examination allows the restorative team to decide if keratinized peri-implant gingiva is adequate for a single-unit implant restoration in the aesthetic zone.

Although the elimination of inflammation around the implant does not appear to be required for long-term osseointegration,5 the presence of a band of keratinized gingiva appears to be conductive to the establishment and maintenance of aesthetics. Recession can be prevented by keratinized gingiva, which is less likely to recede due to its thickness, which can also conceal the metallic appearance of an abutment.

The presence of keratinized gingiva is not sufficient in itself to ensure an aesthetic result postoperatively, but it is a prerequisite to achieve this objective. Sufficient hard tissue must be present, however, to support the 4 mm of soft tissue that is required to develop and maintain the biologic width around implants. It is necessary to overcontour the soft tissues by a minimum of 2 mm to 3 mm, as they tend to recede by 1 mm during surgical and restorative procedures.16 The guideline for this level is an imaginary line drawn from the papillary height to the papillary height of the proximal teeth.17  

In certain instances, orthodontics may be utilized to provide an alternative solution (Figures 7-8-9). This can be achieved when the root socket is moved coronally to allow bone regeneration in the defect. The resultant modification in soft tissue topography is concomitant with the change in the osseous configuration.

The proximal papilla can be preserved at implant placement by excluding them from the flap design using two proximal divergent incisions or by immediate implant placement after extraction without flap elevation through sulcular incision. Uncovering the implant can be accomplished by using the palatal flap design or by using a soft tissue punch to minimize tissue reflection when adequate keratinized attached gingiva and intact papillae are present to achieve optimal soft tissue architecture.18 Gradual tissue expansion can be performed with a small abutment and then the provisional restoration at the subsequent treatment stage to transfer the gingival margin to the master model. The expansion ensures that restorative dimensions are increased progressively below the gingival tissues to provide for a proper emergence profile and to establish contours that are aesthetic and conducive to hygiene procedures.19

Immediate placement of the implant in a single stage should be considered when the tooth to be replaced is still in the socket because the potential of successful peri-implant tissue management is optimal. The implant and a contoured healing abutment can also be placed in a single-stage approach to facilitate margin closure, maintain ideal soft tissue morphology, and prevent soft tissue collapse (Figures 10-11-12-13).20

 

Provisionalization and Prosthetic Stage

Placement of a customized provisional restoration allows the tissue to heal in the exact cervical contour and emergence profile of the definitive prosthesis. When the soft tissues are not adapted to the provisional restoration, the incision should facilitate delicate exposure to provide for any necessary augmentation or adjustment of soft tissue defects (Figures 14-15-16). All biological, functional, and aesthetic objectives must be achieved in the provisional phase prior to the placement of the definitive restoration.

Once the soft tissues have been molded by the refined provisional crown and have become stable following 6 months of healing, the subgingival peri-prosthetic envelope is transferred to the final laboratory model using the "prototype duplication concept."19 A well-adapted cervical contoured metal-ceramic abutment is subsequently screwed to the implant, and the definitive ceramic restoration is cemented (Figures 17 and 18).

 

Conclusion

The development and maintenance of the aesthetic hard and soft tissue complex are important—particularly when implant treatment is performed in the aesthetic zone. The site selected for the implant must be guided in the mesiodistal, apicocoronal, and buccolingual dimensions by the anticipated restoration. The volume of the osseous support must allow the implant to be placed in the ideal situation, while the soft tissue morphology must mimic that of the adjacent teeth following the anticipated recession.

Implant selection and the interdental papilla volume (height and width) are determined by the implant's mesiodistal position. The length of the crown restoration is indicated by its buccopalatal orientation. The emergence profile and peri-implant pocket depth are influenced by the apicocoronal location. The cervical contour of the provisional restoration determines the shape of the buccal gingiva and height of the interdental papillae. Finally, the ceramic restoration must possess a form that complements the surrounding tissues, facilitates proper plaque control and occlusal function, and presents a harmonious natural appearance.

 

*Private practice, Paris, France.

† Editor-in-Chief, Practical Procedures & Aesthetic Dentistry, and private practice, Paris, France.

 

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