2.2.1General Aspects and Biological Considerations

The use of dental implants in the esthetic zone is well documented in the literature. Numerous controlled clinical trials have shown that the overall implant survival and success rates are similar to those reported for other indications. However, most of these studies did not include well-defined esthetic parameters (Belser and coworkers 2004a; Belser and coworkers 2004b; Grütter and Belser 2009).

Implant therapy in the esthetic zone is considered an advanced or complex procedure that requires comprehensive preoperative planning and precise surgical execution based on a prosthetically driven approach (Buser and coworkers 2004). In general, the esthetic zone is defined as any dentoalveolar segment that is visible in full smile. Subjectively, the esthetic zone can be defined as any dentoalveolar area of esthetic importance to the patient (Higginbottom and coworkers 2004). (Note: For the purpose of this text, the esthetic zone has been defined as the portion of the dentition that is predominantly visible when facing an individual, encompassing the maxillary anterior teeth from right to left canine.)

There is convincing evidence that the replacement of single teeth with implant-supported restorations in the esthetic zone will be successful both esthetically and functionally if the hard and soft tissues at the adjacent natural teeth are intact and if the guidelines for correct three-dimensional implant placement for the respective indication are properly followed (Garber and Belser 1995; Buser and coworkers 2004).

Conversely, the esthetic result when replacing multiple adjacent missing teeth in the anterior maxilla with fixed implant-supported restorations is not as predictable (Kan and Rungcharassaeng 2003; Mitrani and coworkers 2005). The main problem is that vertical as well as horizontal bone and soft-tissue volumes in the affected area are often deficient in these cases. When deficiencies are present, appropriate grafting procedures are required (Buser and coworkers 2004).

A major concern in the presence of multiple adjacent missing teeth in the esthetic zone is the lack of interimplant soft tissue. The height of a papilla between two implant crowns is dictated by the interimplant bone level (Tarnow and coworkers 2000, 2003; Kourkouta and coworkers 2009). Frequently, the interimplant crestal bone presents at a lower level than next to a tooth with intact periodontal bone height. This can be due to a preexisting condition (i.e. reduction of or flattening of the alveolar ridge after a previous extraction) or to inadequate interimplant distance. If two implants are placed extremely close (3 mm or more, according to Tarnow and coworkers 2000), a loss of interimplant crestal bone height must be expected. This is caused by the configuration of the biologic width around dental implants (Cochran and coworkers 1997), which will lead to a circumferential vertical bone loss of approximately 2 mm from the level of the implant-abutment or implant-restoration interface. The width of this peri-implant “bone defect” is up to 1.5 mm circumferentially (Hermann and coworkers 1997, 2000; Tarnow and coworkers 2000; Cardaropoli and coworkers 2006). If two implants are too close, the adjacent interproximal resorption defects will overlap, resulting in a reduction in interimplant bone height and, consequently, in a shortened papilla (Hermann and coworkers 1997; Tarnow and coworkers 2000, 2003; Kourkouta and coworkers 2009). The result will be a black triangle (or several), which can only be managed by accepting a prosthodontic compromise—square teeth with long proximal contacts or prosthetic papillae in pink ceramic (Mitrani and coworkers 2005).

Due to the biologic changes in crestal bone, one of the main rehabilitative goals in the esthetic zone must be to preserve the peri-implant bone at the optimal vertical height as much and as diligently as possible. For adjacent implants, this means that an interimplant distance of at least 3 mm at the level of the alveolar crest needs to be respected. This can be difficult if the missing adjacent teeth in the maxillary anterior segment are a canine and a lateral incisor or a lateral and a central incisor, since the interdental space is often too narrow to meet this requirement even when implants with reduced diameters or restorative platforms are used (Tymstra and coworkers 2011).

More recently, it has been suggested that implant-abutment interfaces with a horizontal offset (platform switching) will minimize crestal bone resorption and improve the chances of achieving more favorable interimplant bone levels (Rodriquez-Ciurana and coworkers 2009). Clinical reports have been promising, so this may be a valid recommendation. However, conclusive evidence from comparative outcome studies is still unavailable at this time (Bateli and coworkers 2011).

Attempts have also been made to use implants with a scalloped top for better preservation of the proximal peri-implant bone height. Clinical outcomes with this design have not found to have any advantages over flat-top implants; instead, more extensive bone loss has been reported than for conventional implant designs (den Hartog and coworkers 2011).

Consideration has to be given to alternate implant-supported restorative units with pontics or cantilevers if the interimplant distance is limited. A prosthodontic mock-up helps evaluate implant locations and interimplant distances. Today, with the help of cone-beam computed tomography and three-dimensional modeling of implant positions via treatment planning software, these parameters can be previsualized even more accurately at the planning stage. In contrast to the potential consequences of implants, pontics or cantilevers will not adversely affect the crestal bone height. In a recent prospective comparative pilot study, Tymstra and coworkers (2011) evaluated peri-implant tissue levels in patients with both a central and a lateral maxillary incisor missing, treated either with one implant supporting a cantilever restoration or with two implants supporting solitary restorations. Implant survival, pocket probing depths, papilla index, marginal bone levels, and patient satisfaction were assessed during the 1-year follow-up. No implants were lost; the mean peri-implant probing values were comparable in both groups. Papillary index scores were relatively low in both groups, pointing toward a compromised papilla. Marginal bone loss was minimal and comparable in both groups. Patient satisfaction was very high in both groups. The authors concluded that, based on this 1-year prospective comparative study, no substantial differences in hard- and soft-tissue levels were demonstrable in patients with a central and a lateral maxillary incisor missing, who were treated either with one implant supporting a crown with a cantilever or with two implants supporting solitary crowns.

Biologically interesting but clinically not well documented (not by any comparative outcome studies) is the “root submergence technique” (Salama and coworkers 2007). By preserving a natural dental root below the local keratinized mucosa in areas where adjacent teeth need to be replaced, the surrounding tissues can be predictably maintained, as the periodontal attachment apparatus will preserve the surrounding alveolar bone. In situations of periodontal bone loss, orthodontic extrusion will need to be performed before submerging the roots to bring the local tissues back to a desirable level (Zuccati and Bocchieri 2003).

2.2.2Treatment Planning and Risk Assessment

As stated earlier, implant therapy in the esthetic zone is considered an advanced or complex procedure that requires comprehensive preoperative planning and precise surgical execution based on a prosthetically driven approach (Buser and coworkers 2004). Appropriate patient selection and information is essential in achieving esthetic treatment outcomes that are acceptable to both the patient and the dentist. The patient’s expectations, attitude, and smile line are important determinants in predicting treatment success subjectively (in the patient’s view) or objectively (in the dentist’s view). Similarly, there is a need to identify patients with significant systemic risks (compromised medical status, periodontal susceptibility, smoking, lack of compliance) because esthetic outcomes are less consistent here (Weber and coworkers 2009). The SAC Assessment Tool, freely available at no cost on the ITI website (iti.org), is helpful in determining the complexity (SAC = Straightforward, Advanced, Complex) of specific treatment cases (Dawson and Chen 2009).

2.2.3Surgical Procedures

Correct three-dimensional implant placement is essential to esthetic treatment outcomes. If the comfort zones in all three dimensions are respected, the implant shoulder will be located in an ideal position, allowing for an esthetic implant-supported restoration with stable, long-term peri-implant tissue support (Buser and coworkers 2004). Implant type and dimensions should be selected based on site anatomy and on the planned restoration. An inappropriate implant body or restorative platform may result in tissue complications.

As mentioned above, an adequate horizontal and vertical bone volume is essential to the long-term stability of esthetic soft tissue. Where deficiencies exist, appropriate augmentation procedures are required (Buser and coworkers 2004). A number of effective surgical approaches are available for the augmentation of deficient edentulous ridges to allow placement of implants. However, most relevant studies in the literature have been retrospective in nature, with small sample sizes and short follow-up periods. No direct comparisons should therefore be made between those studies, and caution must be exercised in drawing any definitive conclusions (Chiapasco and coworkers 2009).

A variety of techniques and grafting materials are available to increase the width of the alveolar ridge effectively and predictably. Autologous bone blocks for grafting, used with or without membranes, achieve greater horizontal bone gains and involve lower complication rates than particulate materials used with or without a membrane (Jensen and Terheyden 2009).

Different techniques to increase the height of the alveolar ridge have been described. Overall, they are much less predictable and involve a substantially higher complication rate than procedures for horizontal ridge augmentation. Generally, autologous bone blocks, used with or without membranes, result in greater vertical bone gains than particulate materials used with or without a membrane (Jensen and Terheyden 2009).

Given the limited predictability of vertical augmentation, it is important to consider orthodontic extrusion of prognostically unfavorable teeth with periodontal bone loss prior to their extraction. This will allow the regeneration of deficient hard and soft tissues in the vertical dimension before the teeth are removed (Zuccati and Bocchieri 2003; Brindis and Block 2009).

Some clinicians use alveolar distraction osteogenesis to augment vertically deficient alveolar ridges in selected cases. But this procedure has a high complication rate, including changes of the distracting vector, incomplete distraction, fracture of the distracting device, and partial relapse of the initial bone gain, and must therefore be considered a complex procedure that is highly technique-sensitive and has limited applicability and predictability (Chiapasco and coworkers 2009).

In summary, vertical bone deficiencies continue to be a challenge and often lead to esthetic shortcomings. The use of pink ceramic or resin materials to replace missing soft tissues will often be necessary in these indications (Salama and coworkers 2009; Coachman and coworkers 2009). In the phase of treatment planning, it is important to discuss with the patient the option or need for “artificial gingiva” as a non-invasive alternative to overcome the problem (Mitrani and coworkers 2005).

Regarding the actual surgical placement of dental implants, techniques and biomaterials continue to develop and have facilitated the expansion of clinical indications for implant therapy (Chen and coworkers 2009c). The variety of procedures and biomaterials available may offer a confusing picture for the implant surgeon, who is responsible for recommending the best surgical approach with the lowest risk of complications and morbidity to the patient (Chen and coworkers 2009c). Some of the important aspects relevant to the objectives of this treatment guide are summarized in the paragraphs that follow.

Timing of implant placement after tooth extraction

At the 3rd ITI Consensus Conference in 2003, a classification system for the timing of implant placement after tooth extraction was proposed (Hämmerle and coworkers 2004). This system is based on desired levels of healing following tooth extraction rather than on descriptive terms or rigid time frames. Type 1 refers to placement of an implant into a tooth socket at the time of extraction (“immediate implant placement”); type 2 refers to the placement of an implant after completion of soft-tissue healing but before clinically significant bone fill within the socket has occurred; type 3 refers to placement of an implant following significant clinical or radiographic socket bone fill (types 2 and 3 fall in the category of “early implant placement”); and type 4 refers to placement of an implant into fully healed alveolar bone (“late implant placement”).

Advantages and disadvantages of implant-placement times

The survival rates of implants placed immediately or early after extraction are high and comparable to those of implants placed in healed sites (Grütter and Belser 2009; Chen and coworkers 2009c). All of these approaches have specific advantages and disadvantages, which should be carefully considered at the time of treatment planning (Chen and coworkers 2004; Chen and Buser 2008). As for immediate implant placement (type 1), the combined approach to extracting the tooth and inserting the implant reduces the number of surgical procedures that the patient needs to undergo. Extraction socket defects will normally feature two or three walls, and this renders simultaneous bone augmentation highly predictable. Also, this protocol offers an opportunity to attach a provisional restoration to the implant immediately or soon after implant placement. This may prevent the patient from having to wear an interim removable prosthesis. However, these advantages are counteracted by the technical challenges inherent in preparing intrasocket implant sites such that the implant exhibits good primary stability in the desirable prosthodontic position.

An increased risk of mucosal recession is also associated with immediate implant placement (Chen and coworkers 2007; Evans and Chen 2008), which can compromise the esthetic outcome. Mucosal recession is mostly associated with the resorption of labial bone after extraction (Araújo and coworkers 2006a; Araújo and coworkers 2006b; Chen and coworkers 2007; Evans and Chen 2008). This may even be more pronounced when multiple adjacent teeth are extracted (Al-Askar and coworkers 2011). Additional tissue augmentation procedures are usually required to overcome this risk, further increasing the technical complexity of the procedure. While the grafting of peri-implant defects with particulate bone or bone substitutes is readily achieved, grafting of the external surfaces of the facial bone is more demanding due to the convexity of the bone wall. If primary soft-tissue closure is required, the lack of soft tissue increases the difficulty of attaining tension-free closure, and flap advancement may alter the mucogingival line (Chen and coworkers 2009c).

Bone modeling following tooth extraction is unpredictable and may lead to suboptimal bone-regenerative outcomes and seemingly random dimensional changes. With early implant placement (type 2), healing of the soft tissues increases the volume of mucosa at the site. This facilitates manipulation of the surgical flaps, and flap advancement for partial implant submersion or primary closure can be more readily achieved. In areas of high esthetic importance, the increased soft-tissue volume of may enhance soft-tissue esthetic outcomes.