Objective Criteria: Guiding and Evaluating Dental Implant Esthetics

The evolution of dental implant therapies is fully apparent. From the introductory concepts of the tissue integrated prostheses with remarkable functional advantages, innovations have resulted in dental implant solutions spanning the spectrum of dental needs. Current discussions concerning the relative merit of an implant versus a three-unit fixed partial denture fully illustrate the possibility that single implants represent a bona fide choice for tooth replacement.1 Interestingly, when delving into the detailed comparisons between the outcomes of single-tooth implant versus fixed partial dentures or the intentional replacement of a failing tooth with an implant instead of restoration involving root canal therapy, little emphasis has been placed on the relative esthetic merits of one or another therapeutic approach to tooth replacement therapy.2 An ideal prosthesis should fully recapitulate or enhance the esthetic features of the tooth or teeth it replaces. Although it is clearly beyond the scope of this brief article to compare the various methods of esthetic tooth replacement, there is, perhaps, sufficient space to share some insights regarding an objective approach to planning, executing, and evaluating the esthetic merit of single-tooth implant restorations. Therapeutic success for dental implants has largely been described in terms of implant survival. Anterior single-tooth implant survival is high.3 Further documentation provides implant success criteria, defined by the reporting of marginal bone level data.4 Occasionally, prosthetic or restorative outcomes have been reported. Here, marginally less favorable data are reported for abutment complications of loosening or screw fracture.3 Less often, biologic data concerning the peri-implant mucosal responses are provided. A biologic width develops around implant crowns, and the associated peri-implant connective tissue inflammatory cell infiltrate reacts to plaque accumulation.5 The incidence of peri-implantitis and its effect on implant esthetics may not be fully appreciated. Recently, two different esthetic scoring systems have been described.6,7 These or possibly other esthetic evaluations have not been widely deployed. Although Chang and colleagues8 examined patient-based outcomes for anterior single-tooth implants, there remain many unanswered questions regarding the esthetic requirements and related patient satisfaction concerning anterior single-tooth implants. In 2008, esthetic concerns dominate discourse surrounding dental implants. An objective approach to planning, executing, and evaluating therapy is warranted. Meeting the goal of providing a single-tooth implant crown that equals or exceeds the esthetic value of the tooth it replaces requires identifying and addressing easily recognized anatomic constraints. The hypothesis underscoring an objective approach to single-tooth dental implant esthetics is that the majority of unresolved esthetic problems are because of the discrepancies of implant crown dimension and orientation. Most often, these reflect improper clinical management of peri-implant and peri-coronal soft tissue architecture.9 The application of time-proven and well-documented objective criteria for dental esthetics to the anterior single-tooth implant scenario can guide planning and assure execution of implant placement, abutment design, and crown formation to achieve the highest and most reproducible esthetic goals of the clinician and patient. The aim of this report was to describe how objective criteria can guide planning and execution of implant therapy and, importantly, how a single aspect of dental implant planning and placement can negatively impact half of these objective criteria and lead to unacceptable implant-supported restorations. In a classic (now out of print) textbook entitled Esthetic Guidelines for Restorative Dentistry,10 Dr. Urs Belser described the objective criteria for dental esthetics. More recently, an updated list and illustration of these criteria were published as a chapter in the textbook Bonded Porcelain Restorations in the Anterior Dentition.11 These criteria (Table 1), together with the additional significance of identifying the midline and plane of occlusion as a prerequisite for ideal anterior dental esthetics, can provide an indelible guidance system for dental esthetics. In the process of evaluating single-tooth dental implant restorations in prospective and retrospective studies,11–14 it became apparent that these criteria were equally valid to the dental implant restoration. The form of the dental implant-supported tooth requires careful consideration of these objective criteria (Figure 1). Tooth form is objectively defined. The objective criteria for dental esthetics (Table 1) help to guide decisions concerning ideal tooth form. The clinical photo of this implant crown replacing the central incisor #8 reveals the significance of the many soft tissue items present as criteria defining dental esthetics. Note that much of the crown form is defined by the peri-implant mucosa. The lack of symmetry between the central incisors is due to the incorrect depth of implant placement and the 1-mm apical location of the gingival zenith. The incorrect soft tissue contour is represented by a more oval or triangular tooth form and a longer clinical crown when compared with the left central incisor. The more mesial location of the zenith has been compensated by the enhancement of the line angles and tooth character to correct the appearance of the tooth long axis. The loss of attachment at tooth #7 results in the absence of gingival closure and cannot be accommodated by modifications of the implant procedure or the crown #8. These objective limitations reduce the overall esthetic value of this tooth display. Dental implant placement is neither fully intuited from the anatomy of the residual alveolar ridge nor can it be divined from the existing volume of bone. Desired tooth position dictates implant placement and informs the clinician regarding potential requirements for tissue augmentation. In considering the role of the objective criteria in planning for dental implant placement and recognizing that the depth of implant placement can dramatically affect one-half of these criteria, a potential objective strategy to esthetic planning for dental implant placement emerges. That strategy requires the evaluation of the edentulous alveolar ridge and adjacent teeth in the context of the objective criteria for dental esthetics. Simply stated, dental implant placement can be guided by the location of the gingival zenith. The gingival zenith represents the most apical part of the clinical crown. It also represents both the faciolingual and the mesiodistal location of the crown in relationship to the edentulous ridge. As such, it has a remarkable influence on the morphology of the planned restoration. The gingival zenith affects other objective criteria, including the balance of gingival levels (too inferior or superior), the tooth axis (too distal or mesial), the tooth dimension (too inferior or superior), and the tooth form (triangular becomes ovoid if too inferior). Without the control of the gingival zenith, the clinician's ability to define dental implant esthetics is vastly diminished (Figure 2). In the left (A) and right (B) views, the retained c and f teeth reflect the absence of permanent cuspid teeth. The retained deciduous teeth have aided in the preservation of alveolar bone, but the location of the gingival contours are not correct and are unattractive. Using the present bone and gingival locations to guide implant placement would result in short clinical crowns. Redefining the gingival zeniths of the permanent cuspid teeth is required. At least four factors affect the gingival zenith. One is, of course, the relative location of the tissues to the planned gingival zenith. Second is the depth of the dental implant placement. Third is the response of the buccal bone and mucosa to the implant procedure and components. The fourth is the prosthodontic management of the gingival zenith architecture. Ideally, the planned gingival zenith is symmetric with the contralateral tooth and harmonious with the gingival levels of adjacent teeth. Unfortunately, most residualalveolar ridges are significantly resorbed.15 Important objective classification16 is useful and a diagnostic waxing permits the exact determination of the extent of resorption and permits planning to the key esthetic parameters. Interproximal tissue contours (papillae) appear to be supported by adjacent teeth connective tissue contacts, but peri-implant facial tissue contours are dependent on facial bone and co-dependent soft tissue morphology. Decisions concerning the depth of implant placement should be based on the biologic understanding of the tissue responses to the implanted device. Assuming a steady state peri-implant bone level, it is well known that a biologic width forms at the dental implant17 and that the buccal dimension of the biologic width formed at an abutment is approximately 3 mm.18 The ideal depth of the implant placement is suggested to be 3 mm apical to the planned gingival zenith. The implant/abutment interface should also reside 2 mm palatal to the zenith to assure that there is adequate thickness of bone and mucosa to support tissue form.19 This “three/two” rule further suggests to the clinician when bone grafting or soft tissue augmentation should be performed. If bone is not present at approximately this position from the gingival zenith, bone grafting procedures should be considered in preparation for ideal esthetics (Figure 3). The location of the gingival zenith should be symmetrical with the contralateral tooth and in harmony with the adjacent teeth. As revealed in this illustration, the gingival zenith should be located approximately 3 mm from the implant/abutment interface. This permits a subgingival crown margin at the facial aspect of the implant and provides at least 2.5 mm for the development of the biologic width in a supercrestal position. Placement of the implant/abutment interface in a deeper location will result in loss of bone and facial peri-implant mucosal recession. Without apology for the following circular logic, controlling the depth of placement is achieved by defining the gingival zenith. Managing the gingival zenith at the time of implant placement sets the stage for ideal anterior single tooth esthetics. Whether or not William's theory of tooth form has merit,20 the characterization of teeth as square, ovoid, or triangular is based on the peri-coronal architecture. An often unrecognized truth about dental implant esthetics is that tooth form is largely defined by the peri-implant mucosal architecture. A reproducible procedure should be imposed onto the artistic philosophy of each clinical exercise. For the single tooth dental implant, this process begins with an esthetic diagnosis. The diagnosis is nothing more than the assessment of the objective criteria as displayed by the preoperative condition of the patient. Suggested is the use of clinical digital photographs upon which simple evaluations can be superimposed (Figure 4). A simple photograph (representing the situation illustrated in Figure 2) can be used to objectively evaluate the clinical situation to make a complete esthetic diagnosis. Note that the mirror image of the right and left gingival contours do not match. Note also that the orthodontist has provided good spacing for the central and lateral incisors; it is clear that relative to #10, tooth #7 is distal in its location. The gingival zenith on tooth #11 has been marked to indicate how its position guides overall esthetic value of the implant restoration, presently represented by provisional crowns without occlusion. Perhaps, the most prognostic indicator of eventual esthetic success through symmetry is gained by evaluation of the connective tissue attachment at the adjacent teeth. Careful assessment using a periodontal probe and diagnostic peri-apical radiographs are needed. Loss of attachment of greater than 1.0 mm is clinically discernible and difficult to regenerate. This step is essential because interproximal peri-implant mucosal contours (papillae) are greatly dependent on adjacent tooth contours. Together with study casts indicating the extent of alveolar ridge resorption, a thorough prognosis and treatment plan can be provided to the patient. For the situation of the single anterior missing tooth, it is not possible to fully appreciate these criteria unless a fully contoured crown is waxed in the edentulous space (Figure 5). Following the diagnostic waxing, it is then possible to understand the relationship between the proposed gingival zenith location and the existing mucosa. The relationship of the gingival zenith to the underlying bone can only be determined by bone sounding with a diagnostic template in place or, preferably by use of volumetric imaging (e.g., cone beam computed tomography) with a radiopaque image of the gingival zenith in place (Figure 6). This assessment is critical. Without underlying bone to support the buccal contour in full dimension, the esthetic volume of the edentulous space ultimately will be deficient (Figure 7). Based on the location of the planned gingival zenith, therefore, decisions regarding the need for bone augmentation, socket preservation, and/or soft tissue augmentation procedures can be prudently accessed. Study casts of the interim situation and the diagnostically waxed cast. The location of the gingival zenith is directed by the process of diagnostic waxing. This is confirmed by the evaluation of the intraoperative study cast. A, Detailed evaluation of the diagnostically waxed cast reveals that the concepts revealed by the objective esthetic evaluation have been translated to the cast. This includes the harmonious arrangement of the gingival zeniths and the proper location of the cuspid zenith in the buccolingual as well as the apicoincisal direction. Bone should be present 3 mm apical to the gingival zenith. B, An unrelated cone beam computed tomography image of a canine site exemplifies the examination of the required gingival zenith/bone relationship. In this example, insufficient bone for an esthetic restoration exists. The planned restoration's zenith is 8 mm from the alveolar crest. The resulting crown would be approximately 14 to 15 mm in length (versus the average of 10–11 mm). Bone augmentation would be indicated. A, Intervening veneer preparations for teeth #7 to #10 were performed in the enamel only. The provisional crowns are removed and impression copings are placed for fixture level impressions of the AstraTech dental implants. B, ZirDesign abutment delivery in the well-formed residual alveolar mucosa. The provisional crown should aid in the creation of the gingival contours. The form of the provisional crown should reflect both the clinical crown marginal contours as well as provide ideal submucosal transition contour. In most cases, the interproximal surfaces of the abutment and crown should be concave or flat, whereas the buccal contours are slightly convex in support of the buccal architecture. The interproximal contours must accommodate sufficient interproximal tissue mass to support contours. C, Provisional crowns reflect the contours of the diagnostic waxing and have been used to direct soft tissue changes at the implants as well as the mesial aspects of tooth #7 and #9. With an implant positioned properly in the alveolus, the control of peri-implant tissues is enhanced morphologically by enforcing the remodeling of tissues using properly contoured abutments and provisional crowns (Table 2). To assure proper healing and to limit inflammation, properly polished abutments of titanium or zirconia should be sculpted to support the soft tissue form, and thus, the cervical contour of the crown. Typically, the abutment will possess concave features with the possible exception being a convexity of the buccal surface. This is particularly important in developing the contours of any provisional restoration for a dental implant. Morphologic refinement is established using the provisional crown and again, the submucosal contours should be refined to be more root-like (concave interproximally) to support ideal tissue form. No particulate materials should be introduced into the sulcus and all debris should be carefully washed from the implant and sulcus prior to the delivery of the abutment and crown. The provisional crown should be highly polished, well adapted to the abutment margin, and free of extruded cement (Figure 7). Excellent esthetics frequently involves iterative processes. For implant crowns, attempts to provide highly esthetic crowns to properly contoured peri-implant mucosa directly from a fixture level impression is not likely to achieve great expectations. It is important to provisionalize implants with provisional or definitive abutments and achieve the planned tissue architecture described earlier. After a period of tissue healing (6–8 weeks) or adaptation (3–4 weeks), objective assessment should be performed. Only after reviewing potential opportunities for refinement should the final impression of the implant or abutment be made. Several suggestions for capturing the form of the peri-implant mucosa include the placement of rigid materials into the sulcus. This is not recommended if the peri-implant tissues display little inflammation and tissue prolapsed (Figure 8). Regardless of the method chosen, the sulcus should be carefully examined and debrided after the impression is made. The provisional restoration should be replaced with little or no displacement or disruption of the peri-implant mucosa. A, Facial view of final restorations on implants #6 and #11, and teeth #7 to 10. All ceramic crowns were bonded to ZirDesign implant abutments and veneers were bonded to #7 to #10. The photograph was made 3 months after delivery of the definitive prostheses. B, One-year evaluation of the restoration/tissue relationships #6 to #8 and (C) #9 to #11. The form and color of the peri-implant mucosa is in part due to the choice of the zirconia abutments and modification of the tissues during the immediate provisionalization period. The thick biotype contributes to the predictability of tissue responses illustrated here. The definitive restorations were artfully produced by Mr. Lee Culp, CDT. The goal of the laboratory procedures includes the preservation and possible directed enhancement of the peri-implant mucosal form created by the clinician, maintenance of the designated incisal edge position and incisal embrasures, and the creation of the designated abutment and crown. The prepared abutment and crown may be delivered to complete the restorative procedure. With a major goal being to preserve the peri-implant mucosal architecture with the gingival zenith as a reference point, it is important to evaluate possible tissue displacement when a final abutment is placed. Only modest, if any, blanching should be evident using this protocol following a careful provisionalization process. If tissues are displaced it suggests that the abutment is contoured and is most likely convex in form. The abutment can be and the tissue contours can be delivery is, therefore, a step in the control of the peri-implant mucosal form. the crown can be in the and the objective criteria for dental esthetics, is a useful for this It will beyond the of an implant and it the maintenance of peri-implant mucosal architecture. of the concepts that for all anterior implants, there is a of procedures that can assure esthetic success (Table 3). The process begins with an esthetic diagnosis to the limitations present and to to esthetic limitations implant The key features to include adjacent tooth connective tissue Further evaluation requires that a diagnostic waxing is performed to the ideal restorative form. The designated gingival zenith can then be used to the using volumetric imaging If the ideal gingival zenith is greater than 3 mm incisal and 2 mm buccal from the existing bone then the bone augmentation procedures may be The gingival zenith, therefore, becomes the therapeutic reference A esthetic result is suggested when the adjacent tooth attachment levels are and there is adequate bone relative to the reference Using a the implant can be positioned to the zenith reference At the time immediate placement, or an abutment can be placed to the formation of biologic width the abutment and to to properly contour the peri-implant The provisional crown should be used to direct proper development of the peri-implant mucosa and control the form. the definitive restoration should and that or the adjacent and contralateral anterior teeth. An objective approach to dental implant therapy is warranted. application of objective criteria suggests that further control of the anterior dental esthetics be For example, the level of the peri-implant margin to or 2 mm of the reference tooth in no more than of the implant-supported The color of the peri-implant soft tissue that of the reference tooth in no more than of More recently, and reported that only of crowns in were by a patient This may be the result of soft tissue For example, the apical displacement of facial soft tissue was mm after crown placement on abutments at dental implants and In and reported the of the facial soft tissue contour at implant/abutment a period following dental implant placement and It may be possible to clinical control the facial soft tissue contours that control esthetics. the limitations and treatment planning by the use of the objective criteria for dental esthetics are essential to this process. the clinical and biologic factors affect these criteria, the buccal tissue contour may implant esthetics. The influence of is suggested but the controlling depth of implant placement, peri-implant mucosal by inflammation, and peri-implant mucosal morphology through ideal abutment and provisionalization the clinical control of single-tooth dental implant esthetics.