Treatment Planning

Treatment Planning for Success: Wise Choices for Maxillary Single-Tooth Implants

Belinda L. Gregory-Head, BDS, MS; Alex McDonald PhD, DDS; and Eugene LaBarre DMD, MS

Copyright 2001 Journal of the California Dental Association.

The purpose of this article is to demonstrate to general practitioners who have no experience with dental implant treatment the esthetic limitations of such treatment. The criteria for wise case selection will be described so that esthetic excellence can be predictably achieved in general practice. A checklist of criteria will be provided as a treatment-planning tool to determine if a patient is likely to have an esthetically successful outcome.

While the anterior implant patient may come into the office fixed on the notion of having an implant, further questioning often reveals that his or her chief concern is to have a missing tooth replaced with something that looks good, feels good, and works like a real tooth. The challenge of treatment planning is to fulfill these goals. If any of these criteria cannot be satisfied, then the treatment may be considered a failure.^1-3

California dentists may very well face a greater challenge than most in satisfying the esthetic demands of their patients. Practitioners here must satisfy an extremely esthetically aware population. Unreasonable demands from patients and unrealistic promises by practitioners can led to unsatisfactory experiences for all parties. A clear understanding of the esthetic limitations of dental implants and the practitioner’s own expertise in this area will reduce the risk of unforeseen problems.

Long-term data on the success of implant-supported single-tooth restorations in the anterior maxilla have been available since 1996⁴ and have been corroborated in many more-recent studies.^5-7 Success rates of between 90 percent and 98 percent have been consistently reported. Early papers documented complications as being mainly mechanical in nature, including screw loosening, component fracture, and loss of integration. Studies seeking to define success in the anterior region have, until recently, focused on retention and not on esthetic success.

The push for better function and esthetics has led to a growing appreciation of the biomechanical limitations of implants. Wider-diameter implants have been introduced.^8,9 This addition to the armamentarium along with better engineering of the components and screw-tightening systems^10,11 have brought us to a time when a dental implant can be a predictable and functional success. Advances in determining the ideal position of the implant and more-accurate surgical techniques have greatly enhanced esthetic outcomes.¹² These have been significant improvements, but they may never be enough to allow a dental implant to be the treatment of choice for all edentulous spaces in the anterior region.

Functional Success With Esthetic Failure

The purpose of this article is to demonstrate that there are some esthetic limitations to dental implant treatment. It is aimed at practitioners with no experience with implant treatment. The criteria for wise case selection will be described so that esthetic excellence can be predictably achieved in general practice.

The following checklist of nine issues will be discussed. The checklist provides a treatment-planning tool to determine if a patient is likely to have an esthetically successful outcome:

* Assessment of patient expectations;

* Assessment of gingival display;

* Gingival thickness;

* Papilla presence or absence;

* Morphology of adjacent teeth (crown-to-root ratio);

* Size and shape of contact areas of adjacent teeth;

* Available bone height;

* Available bone width; and

* Studies appropriate for final decision making.

Assessment of Patient Expectations

Patients’ desires are often overlooked in guides to treatment planning, yet they may be the most important criterion assessed by the dentist. An experienced practitioner will be better able to judge a patient’s esthetic demands, but in any case a clear understanding of the patient’s wishes must be established before any treatment recommendations are made. It is possible to satisfy some demanding patients, but significant co-operation is required of them. It is critical that the patient be involved and educated as to the risks, esthetic or otherwise, that may be inherent in the treatment. The patient will be expected to maintain rigorous dental hygiene and deal with various provisional restorations as treatment progresses. For this reason, an emphasis on the team approach is recommended. The patient should become an integral member of the treatment team along with the laboratory technician, hygienist, and dentists.^13,14 Pretreatment intraoral photographs and carefully selected patient-education videos can help bring the patient’s level of understanding up to that required for an esthetic case.¹⁵ For a practitioner’s first anterior implant case, it is recommended that he or she choose a co-operative patient with realistic expectations.

Assessment of Gingival Display

After initial assessment of patient expectations, the evaluation of the smile line or gingival display will provide the best indicator as to the esthetic risk of the case. Excessive gingival display may be due to a number of factors, including vertical maxillary excess, short clinical crowns, and hypermobility of the upper lip.¹⁶ Whatever the underlying etiology, it is important to evaluate the patient’s ability to display gingiva.^17,18 Being asked to smile can result in a forced or half smile and may be misleading. It is recommended that the patient be asked to sneer or lift his or her upper lip as high as possible so the dentist can assess the situation. If a "gummy" smile is presented, the patient should be fully informed of the difficulties ahead. Additional periodontal procedures such as crown lengthening of remaining maxillary dentition may be considered.¹⁹ If the patient is unable to display gingival tissue, it is still important to discuss the risks, but it is also possible to reassure the patient that any gingival esthetic compromise will be hidden from view. The single most important factor for esthetic success in anterior implants is the smile line. It is highly recommended that the first few patients treated in a practice have a low lip line.

Gingival Form

The morphology of gingival tissue has been discussed extensively in the periodontal literature. It is relevant to esthetic success with anterior implants since gingival recession has been identified as a significant complication in these cases.²⁰ The forms of periodontium can be broadly divided into two distinct "biotypes," which have been correlated to specific tooth forms.²¹ Thin, highly scalloped gingival tissues are associated with long, narrow, and tapered tooth forms. The second important biotype is the thick, flat more fibrous form associated with a shorter, wider, and squarer tooth shape. The two tissue types are associated with different responses to inflammatory stimuli. The thin, highly scalloped type tends to respond with marginal recession and loss of papillary height, while the thick, fibrous type tends to develop a chronic inflammatory response that may result in periodontal pocketing.²² An ideal first implant patient would have an abundance of thick, flat, fibrous gingival tissue and therefore be more resistant to gingival recession around the restoration. This biotype also allows for the use of metal abutments with less chance of show-through at the gingival margin. This gingival form is also associated with a favorable square tooth form.

Papilla Presence or Absence

The existence of papillae filling the interdental spaces is a key indicator for future success. If the remaining dentition exhibits "black triangles" due to lack of complete fill of the spaces, then the risk of similar incomplete fill around the implant restoration is high. "Black triangles" may be pre-existing for a number of reasons, including gingival recession, highly tapered triangular tooth form, and previous periodontal surgery. The problem is difficult to resolve, and the patient should be educated as to the esthetic risks involved. Attempts have been made to classify loss of papillae and provide prognostic indicators.²³ Surgical techniques aimed at regenerating lost papillae have been developed.^24,25 Such regeneration remains challenging, and it may be unwise for a general dentist who is new to implants to treatment plan a first case anticipating the need for additional periodontal plastic procedures.

The position of the osseous crest is a critical indicator for potential loss of papillae after a surgical intervention such as extraction or implant placement.²⁶ The greater the distance from the free gingival margin to the osseous crest, the greater the esthetic risk. A sounding depth of greater than 3 mm at the midfacial aspect or 4 mm at the interproximal position would indicate an esthetic risk.²⁷ An ideal patient would therefore have excellent periodontal health and a high, flat bone profile.

Adjacent Tooth Morphology

Complete papillary fill of the interdental space after implant restoration is also closely related to tooth form, particularly the position and shape of the contact areas.

It has been determined that if the apical limit of the contact area is 5 mm or less from the osseous crest, then a papilla will be present almost 100 percent of the time in the natural dentition. An additional 1 mm distance drops the likelihood of a papilla being present to only 56 percent.²⁸ While the position of the osseous crest may be difficult to adjust, the position of the contact areas may be changed by the restorative dentist. A careful evaluation of the patient’s natural tooth morphology should be made. Long, narrow tapered teeth tend to have short incisally positioned contact areas (Figure 1) likely to be further from the osseous crest and therefore likely to have incomplete fill of the interdental space. The triangular shape (Figure 2) is also associated with thinner highly scalloped gingival tissue that tends to recede. More predictable anterior esthetics will be gained with patients who have broader tooth forms and longer, more cervically positioned contact areas (Figures 3 and 4). Pretreatment photographs are an essential tool for evaluation of tooth shape and educating the patient as to potential risks.

Crown shape is related to root form. Ironically, unfavorable clinical crowns with a triangular morphology taper into a narrow neck and narrow, tapered root form with more interdental bone. This would be a favorable variable providing for more bone between the titanium implant and the adjacent natural roots. This makes placement easier and reduces the risk of root proximity issues. It is generally believed that at least 1.5 mm of healthy bone should exist between the dental implant and the adjacent root surface. Recent work on treatment-planning criteria for multiple implant restorations has suggested that at least 3 mm should separate neighboring implants to reduce interimplant crestal bone loss and hence preserve vital osseous support for the interimplant papillae.²⁹

Adjacent tooth morphology has an additional effect on treatment planning a single dental implant. The length of the adjacent clinical crowns will have biomechanical consequences for the implant restoration regardless of tooth shape. Neighboring long clinical crowns must be replicated in the final restoration and may result in a long lever arm acting on the dental implant itself. Unless excellent bone height is available to facilitate the placement of a long implant, an unfavorable crown-to-implant ratio will result for most implant systems available.

In relation to adjacent tooth morphology, the ideal implant patient would have short, wide clinical crowns with long contact areas and existing papillae.

Available Bone Height

Occlusal forces act obliquely on anterior teeth. Likewise, an anterior implant restoration will be loaded nonaxially. Longer implants resist nonaxial loading better and have been associated with higher success rates. Implants of 11 mm or longer have proven to be successful in the anterior maxilla.³⁰ If the replacement being proposed is for a single tooth only, there is often adequate remaining bone height to facilitate fixture placement. However, the osseous crest may be positioned apical to ideal. Ideal placement of a dental implant will result in the top of the fixture being placed 2-4 mm apical to the cementoenamel junction of the adjacent teeth (Figure 5). The exact ideal distance will be modified by the diameter of the chosen implant, the desired emergence profile of the final crown, and the tissue biotype. If the top of the implant closely replicates the diameter of the missing tooth, the placement will be more coronal. If the top of the implant is narrower, then placement will be deeper to facilitate harmonious broadening of the crown form as it emerges from the tissue. Implant placement in a patient with thin, highly scalloped tissue would also be deeper to accommodate the tendency to recede and to reduce the risk of metal show-through.

Available bone height can be evaluated with periapical radiographs and clinical examination. The ideal patient would have adequate height to house a long implant (13 mm or more) with the crest of the residual ridge 2 mm below the cementoenamel junction of the adjacent teeth (Figure 6).

Available Bone Width

Successful placement of dental implants depends on adequate osseous housing in all dimensions. At least 1.5 mm of healthy bone is required between the implant and neighboring root surfaces and the "standard" implant from most manufacturers approximates 4 mm in diameter. Therefore the minimum mesiodistal space that can accommodate an implant between two teeth is 7 mm. Replacement of a central incisor or cuspid would not usually present a problem in this dimension, but loss of a small lateral incisor could present risk. In such a case, a narrower implant may be considered or orthodontic correction carried out.

The implant must also be fully encased in bone in the labiolingual dimension. Again, a minimum of 7 mm is required for a standard diameter implant. It is this requirement that presents the most common complication of treatment planning for the anterior maxilla. The labial plate of cortical bone is often missing and remodeled before implant treatment planning begins. This may be due to previous periodontal or periapical infection, traumatic loss, or loss during extraction. Even if an atraumatic extraction technique is employed, the labial plate will inevitably remodel and become positioned lingually within three to six months. A distinct labial concavity will be evident when the site is viewed from the occlusal aspect (Figures 7 and 8).

A significant labial defect that would result in the facial aspect of the implant being located entirely outside the osseous structures should be considered for hard tissue augmentation prior to implant placement. A less-significant defect may be accommodated by slightly deeper and more lingual placement of the fixture to allow for good osseous contact while maintaining the proper emergence profile (Figure 9).

Determining Available Bone

Assessment of available bone in the mesiodistal and buccolingual dimensions can be achieved with a thorough clinical examination, or measuring directly from study casts. Anesthesia and "sounding" of the osseous structures is also a useful technique. The most accurate diagnostic aid is the CT scan (Figure 10). Unlike Panorex films, where measurements have to be corrected for varying magnification, the CT film can be measured directly and is accurate to within 0.1 mm. Dental CT scans have become economic (as low as $275 to $350 per arch). They should be considered if there is a question as to whether bone augmentation will be required.

Completing the Case

After thorough treatment planning and ideal fixture placement, there is still opportunity for esthetic excellence or mediocrity in the restoration phase. Several months of provisionalization allows for maturation of the gingival tissues to an appropriate (noncylindrical) emergence profile. The tooth form generated through excellent provisionalization must be carried through to the final restoration so that crown and papilla form is maintained (Figures 11 through 13).

Conclusion

Restoring dental implants in the esthetic zone can be fun if wise choices are made. If the factors discussed above are carefully considered, patients who present significant esthetic risks will be screened out and patients with predictably good prognoses will be taken on. While much emphasis has been placed on the anatomic features of the ideal first patient (Figure 14) possibly more important is the patient’s desire to cooperate with the team and have realistic expectations. A thorough understanding of the esthetic limitations of dental implants by all members of the team will result in a rewarding and satisfying experience.

Authors

Belinda L. Gregory-Head, BDS, MS, is an associate professor and director of dental implants at the University of the Pacific School of Dentistry.

Alex McDonald, PhD, DDS, is an associate professor and surgical coordinator at the Implant Clinic at UOP School of Dentistry.

Eugene LaBarre, DMD, MS, is an associate professor and chair of removable prosthodontics at UOP.

References

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To request a printed copy of this article, please contact/Belinda L. Gregory-Head, BDS, MS, UOP School of Dentistry, 2155 Webster St., San Francisco, CA 94115, or bhead@sf.uop.edu.

Legends

Figure 1. The tapered crown form results in a short, incisally positioned contact area. A small interdental space is visible in this natural dentition.

Figure 2. The triangular crown form is associated with thin, highly scalloped gingival tissues.

Figure 3. Shorter, broader tooth forms have longer contact areas and better prognosis for fill of the interdental space

Figure 4. The broader, squarer tooth form is associated with thicker, flatter gingival tissue.

Figure 5. Ideal vertical placement of implant 3 mm apical to the cementoenamel junction of adjacent teeth allows for appropriate emergence of crown form (Nobel Biocare implant with a custom abutment).

Figure 6. Example of a patient with excellent bone height and favorable tooth form, note long contact areas.

Figure 7. Occlusal view of potential implant site showing significant labial concavity. Hard tissue onlay grafting will idealize the site prior to implant placement.

Figure 8. The same patient as Figure 6. Excellent ridge width in both edentulous lateral incisor sites.

Figure 9. Graphic illustration of placement lingually and apically from ideal due to loss of labial cortex. This technique can be used to avoid grafting but should be employed with caution since significant deviation from ideal position can result in unfavorable cantilevers and maintenance problems (Illustration by Annette Kramer).

Figure 10. CT scans can significantly increase accuracy in determining available bone for fixture placement (Image made with GE Lightspeed Plus, Advanced Imaging Center, Sacramento, Calif.).

Figure 11. Ideal placement and provisionalization of implant #5 site results in excellent emergence profile.

Figure 12. Morphology of provisional is accurately duplicated in final restoration.

Figure 13. Final restoration in place.

Figure 14. Key anatomic features of an ideal anterior implant patient: low smile line; abundance of attached keratinized tissue (thick, flat biotype); papillae preserved after extraction; wide, square-shaped teeth with long contact areas; and excellent bone height and width (Illustration by Annette Kramer).