Knowledge of the periodontal-restorative interface is critical in the fabrication of restorations that are functional and esthetic. Understanding biological principles allows the clinician to predict how the periodontium will respond to restorative therapy. Factors that influence the response to therapy in the periodontal-restorative interface are periodontal biotype, gingival architecture, alveolar crest position, gingival margin position, and gingival zenith.
Key points
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Knowledge of biological principles allows the clinician to predict periodontal response to restorative therapy.
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Factors that influence the periodontal-restorative interface in both implant and tooth-borne restorations include periodontal biotype, gingival architecture, alveolar crest position, gingival margin position, and gingival zenith.
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Identification of alveolar crest position is critical in determining the location of the restorative margin.
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Resolution of periodontal inflammation before restorative therapy is paramount in predicting the periodontal response.
Introduction
Understanding the periodontal-restorative interface allows for fabrication of restorations that are both functional and esthetic. Diagnosis and treatment planning, which integrates biological and mechanical principles, allows the clinician to predict the periodontal response to therapy in both implant and tooth-borne fixed prosthodontics. Factors that influence the periodontal-restorative interface are periodontal biotype, gingival architecture, alveolar crest position, gingival margin position, and gingival zenith.
Periodontal Biotype and Gingival Architecture
Periodontal biotype has been evaluated and discussed throughout the dental literature from its relation to anatomy to its effect on therapy. Periodontal biotype plays a critical role in gingival esthetics and treatment outcomes in the periodontal-restorative interface.
Hirschfield first observed a thin alveolar contour and made the clinical observation that a thin bony contour was accompanied by a thin gingival form. Ochsenbein and Ross classified the gingival anatomy as flat or pronounced scalloped, relating a flat gingiva to a square tooth form and pronounced scalloped gingiva to a tapering tooth form. Weisgold demonstrated an increased susceptibility to recession in individuals with a thin, scalloped gingival architecture. This theory was further supported by studies demonstrating that central incisors with a narrow crown had a greater prevalence of recession than incisors with a wide, square form.
De Rouck and colleagues illustrated the presence of 2 distinct gingival biotypes. The first, which occurred in one-third of the study population and was most prominent among women, was classified as having a thin gingival biotype, slender tooth form, narrow zone of keratinized tissue, and a high gingival scallop. The second, which occurred in two-thirds of the study population and mainly among men, was classified as having a thick gingival biotype, quadratic tooth form, broad zone of keratinized tissue, and a flat gingival margin.
Cook and colleagues demonstrated that clinically there are 2 distinct periodontal biotypes. A thin periodontal biotype is associated with a thin labial plate and an apical alveolar crest when compared with a thick/average periodontal biotype. An accurate tool to diagnosis periodontal biotype is the ability (thin periodontal biotype) or inability (thick/average periodontal biotype) to visualize the periodontal probe through the gingival sulcus.
Diagnosis of periodontal biotype influences the treatment planning of many esthetic procedures. Periodontal biotype evaluation can be a valuable tool in establishing patient expectations in many complex esthetic procedures by allowing the clinician to predict therapeutic outcomes.
Alveolar Crest Position
Becker and colleagues used human skulls to measure the vertical distance between the interproximal bony crest and the buccal crest of bone at the midfacial point on the same tooth and developed the following classification system: flat with a mean distance 2.1 mm (standard deviation of 0.51 mm); scalloped with a mean distance 2.5 mm (standard deviation of 0.56 mm); and pronounced scalloped with a mean distance 4.1 mm (standard deviation of 0.60 mm).
Kois suggested a classification system related to periodontal biotype involving the relationship between the cementoenamel junction (CEJ) and the crest of the bone:
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Normal crest: midfacial alveolar crest is 3 mm and proximal alveolar crest is 3 to 4.5 mm apical to the CEJ—85% of population.
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High crest: midfacial alveolar crest is less than 3 mm and proximal alveolar crest is 3 mm apical to the CEJ—2% of population.
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Low crest: midfacial alveolar crest is greater than 3 mm and proximal alveolar crest is greater than 4.5 mm apical to the CEJ—13% of population.
Position of the Gingival Margin
Gingival margin position is critical when determining ideal gingival esthetics. There are 2 categories of ideal gingival esthetics: strong and soft. In the strong configuration, the gingival margins of the maxillary center incisors, lateral incisor, and canines coincide on a horizontal plane ( Fig. 1 ). In the soft configuration, the gingival margins of the maxillary center incisors and canines coincide, whereas the gingival margin of the lateral incisors is slightly below this horizontal line ( Fig. 2 ). Other factors such as maxillary/mandibular lip position, tooth form (tapered, square), and gender may play a role in gingival margin position.
Gingival Zenith
Gingival zenith location is an important aspect of gingival esthetics because it establishes the visional illusion of the tooth’s long axis. The gingival zenith is located distal to the long axis of the maxillary central incisors and canines. Maxillary lateral incisors display a symmetric gingival height of contour and a gingival zenith at the mesial-distal midline. Lateral incisors can display the most gingival zenith variation (0.4 mm).
Implant Restorations and the Periodontal-Restorative Interface
The diagnosis and treatment planning of maxilla anterior implant restorations is a complex process involving the merger of form, function, and esthetics. Successful treatment outcomes require clinicians to pay close attention to the periodontal-restorative interface during diagnosis and treatment planning to ensure restorations mimic natural dentition. This detailed thought process is evident when evaluating anterior implant restorations, where the difference between treatment success and failure may be tenths of millimeters. Understanding how the periodontium responds to therapy is critical to achieving a successful esthetic outcome.
Diagnosis and treatment planning of anterior implant restorations involves evaluation of the 4 Ps:
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Periodontal biotype
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Position of the gingival margin and gingival zenith
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Placement of implant
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Position of the alveolar crest
Periodontal biotype
Diagnosis of periodontal biotype allows clinicians to predict clinical outcomes by relating the soft tissue morphology to the underlying bony anatomy. Patients with a thin periodontal biotype differ from patients with a thick/average periodontal biotype in that they present with a thinner labial plate ( Fig. 3 ) and an alveolar crest position that is located more apical in relation to the CEJ ( Fig. 4 ). Periodontal biotype can be diagnosed by the ability to visualize the periodontal probe ( Fig. 5 ) through the gingival sulcus in thin biotype and the inability to visualize the probe ( Fig. 6 ) in a thick biotype. Periodontal biotype has been shown to affect soft tissue esthetic outcomes around anterior implants. Patients with a thin periodontal biotype have more interproximal and midfacial recession postimplant placement than a patient with a thick periodontal biotype. Diagnosis of periodontal biotype is essential in treatment planning of anterior implant restorations. Patients with a thin periodontal biotype can be challenging due to their clinical presentation. Patients who present with a thin periodontal biotype may require additional therapy such as hard and soft tissue augmentation.
Position of the gingival margin and gingival zenith
Evaluation of the preexisting gingival margin position is critical in the diagnosis and treatment planning of anterior implant restorations. Ideal gingival esthetics is associated with the gingival margins of the maxillary central incisors and canines being on the same horizontal plane as if an imaginary line connected them. The lateral incisors are either along the same horizontal line or 0.5 to 1.0 mm inferior ( Fig. 7 ). If a vertical line bisected the midline of the maxillary anterior teeth, the location of the gingival zenith position would be found 1.0 mm distally for central incisors, 0.4 mm distally for the lateral incisors, and 0 mm for canines ( Fig. 8 ). The gingival zenith level in an apical-coronal direction of lateral incisors relative to the gingival tangential zenith line joining adjacent central incisor and canine is approximately 1 mm.
When evaluating the gingival margin position in anterior implant restorations, it is pertinent to compare the adjacent and contralateral teeth. With this in mind, the proposed implant gingival margin can be classified as being superior, equal or inferior to the adjacent or contralateral tooth ( Fig. 9 ). Diagnosis of the existing gingival margin position assists the clinician in sequencing the treatment plan.
Placement of the implant
Planning the position of an anterior implant is critical to the esthetic and functional prognosis. Diagnosis and treatment planning begins with a conventional or digital full-contour wax-up. A diagnostic wax-up allows the clinician to diagnose the amount of restorative space and interimplant space, and establish the proposed gingival margin position.
Adequate horizontal and vertical space between teeth and implants is essential to achieve an esthetic outcome. The horizontal space needed between a tooth and an implant is 1.5 to 2 mm ( Fig. 10 ) and between 2 adjacent implants is 3 mm ( Fig. 11 ). The vertical distance from the alveolar crest to the restorative contact position between a tooth and an implant will be 4.5 mm ( Fig. 12 ) and between 2 adjacent implants is 3.4 mm ( Fig. 13 ).
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