Ashman Department of Periodontology and Implant Dentistry, New York University College of Dentistry, New York, NY, USA
Review of the Esthetic Parameters
When considering the natural aesthetics in patient treatment, there are a number of components to be considered. These include extra‐oral, intra‐oral, and indirect components. Extra‐oral components are comprised of the face and smile line. An adequate facial analysis will address issues such as any midline deviations and occlusal plane discrepancy. It has been noted that the mean threshold for acceptable dental midline deviation was 2.2 ± 1.5 mm (Beyer and Lindauer 1998). Furthermore, natural and subtle asymmetry is often unimportant in judging the facial attractiveness, so much so that beautiful faces may be functionally asymmetrical (Zaidel and Cohen 2005). In addition to a midline analysis, the planes of the inter‐pupillary line and frontal occlusal plane are assessed. In an ideal situation these two lines are parallel to one another and perpendicular to the midline. Phonetics is also addressed. The second portion of the extra‐oral evaluation is the smile line. Tjan et al. (1984) evaluated the smiles of 454 dental hygiene students 20–30 years old and defined a standard of normalcy for the esthetic smile. A high smile line (10.57%) was defined as revealing the total cervico‐incisal length of the maxillary anterior teeth and a contiguous band of gingiva. Average smiles (68.94%) revealed 75–100% of the maxillary anterior teeth and only interproximal gingiva. Low smiles (20.48%) displayed less than 75% of the anterior teeth (Tjan et al. 1984). In addition to evaluating the amount of maxillary teeth and gingiva showing, they also assessed the curvature of the incisal edges in relationship to the lower lip finding that 84.8% had a parallel curve, 13.88% showed a straight curve, and only 1.32% have a reverse curve.
Intraorally, the esthetic components are comprised of the teeth and dento‐gingival complex. Restoratively driven implant placement dictates taking teeth size and proportion into account. For example, the average mesio‐distal dimension of a maxillary central incisor is 8.45 mm, while the lateral is only 6.44 mm. When assessing teeth, the shape or relative dimensions must also be considered. In 1999 Snow described and published what they determined to be the “Golden Percentages” of esthetics in relation maxillary anterior tooth size. In this ratio, the centrals take up 25% of the width respectively followed by the lateral incisors with 15% and the canines with 10%. This equates to a proportion of 1.618 : 1.618. The authors suggest that this proportion be used as a striating point, but not a definitive methodology due to anatomical and soft tissue variations that inherently exist. Assessment of the maxillary anterior teeth can also be made with respect to the axial alignment. Rufenacht (1990) described that the general mesial inclination is more pronounced from the central incisors to the canines. He went on to elaborate and describe the contact points of these teeth as descending from the incisal to cervical third as we move laterally towards the canines. The last component of tooth related esthetics is the gingival zenith, or rather, the most apical point of gingival tissue. The gingival zenith was noted to be 1 mm distal to the tooth midline on central incisors, 0.4 mm distal on lateral incisors, and coincident with the midline on the canines.
The dento‐gingival complex is comprised of the periodontium (and its subsequent biotype), the gingival line, and the dimension of the supracrestal tissue. Generally speaking, there are two gingival biotypes: thick/flat and thin/scalloped. A thick gingival biotype is related to square teeth and bulbous convexities in the cervical third of the tooth. It often correlates to a gingival margin at the cementoenamel junction (CEJ) and has thicker and more fibrotic tissue, thicker bone, increased quality and quantity of keratinized attached gingiva, and greater contact areas between adjacent teeth. The thin/scalloped biotype is associated with a triangular tooth form has delicate soft tissue, presence of scalloped osseous form with dehiscence or fenestration, reduced keratinized tissue, and often lack of interproximal tissue fill (Olsson and Lindhe 1991; Weisgold 1977). Biotype will dictate response to bacteria and treatment. For example, a thick biotype is more resilient and therefore prone to pocket formation. In the same scenario with a thin biotype, recession is the most common outcome (Müller et al. 2000). Additionally, tissue biotype dictates the phenomenon known as creeping attachment. Thick biotypes demonstrated significantly more creeping attachment than thin biotypes (Pontoriero et al. 2001).
The gingival line, or junction between hard and soft tissue, is considered to be the key to esthetic harmony. This scallop is created by the confluence of the periodontium and teeth. The level of the gingival line on the central incisors is ideally the same as the canines, with the laterals being 1 mm coronal. It must harmonize bilaterally with the smile line, the facial midline, and axial inclination of the teeth (Smukler and Chaibi 1997). Schluger (1949) stated that the form of the underlying bone dictated soft tissue results and that the difference between the levels and shapes of osseous tissue and the soft tissue caused recurrent pocketing and recurrent periodontal disease. In contrast, Doza De Bastos (1977) found that the degree and configuration of osseous scalloping is determined by the surface topography of the tooth. Gingival form is dictated both by the osseous configuration and the surface anatomy of the tooth. In health, bone and tissue are adjacent to one another and consistent with each other in form. In periodontal disease, the hard and soft tissues are no longer consistent with or adjacent to each other, creating disharmony and a poor esthetic result. Overall, the contour or shape of the gingiva varies considerably and depends on the shape of the teeth, their alignment in the arch, the location and size of the area of proximal contact, and the dimension of the facial and lingual gingival embrasures.
The final component of the dento‐gingival complex is the interdental papilla. The lateral borders and tip of the interdental papilla are formed by the free gingiva from adjacent teeth. The center portion is formed by attached gingiva. Filling of the interproximal contact space was noted in 98% of sites with 5 mm or less measured from the peak of bone to the contact point. If this distance was greater than 5 mm, a black triangle was evident (Tarnow et al. 1992