SMILE LINE

SMILE LINE

Mid - line

Heartwell defines the dental mid-line as vertical imaginary line that doesn’t necessarily coincide with the facial mid-line which runs vertically from the nasion, subnasal point, interincisal point & pogonion, perpendicular to the interpupillary line. Ideally the papilla between the maxillary centrals acts as a placement landmark & coincides with the mid-line of the face. In 75% of cases maxillary & mandibular midlines doesn’t coincide which is not esthetically unpleasant as mandibular teeth are not usually exposed while smiling. It demonstrates that the lower mid-line is not reference for the maxillary midline placement in cases of lost midline (premature tooth extraction).In any unrestored dentition slanting is an unacceptable major flaw.

Incisal length

The position of incisal edge of the maxillary central incisor is the important determinant in the creation of smile which sets a parameter upon which rest of the treatment is built. Elongation of incisal edge is often indicated to correct incisal wear, inadequate tooth display while shortening of incisal edge is required to compensate for unaesthetic elongation by periodontal recession. The visibility of central incisor while smiling rather than lips at rest tends to render an older appearance to the dentition. Therefore the visibility of the teeth when the mandible and lips are at rest is one of the most important factors in dental esthetics. In case of compromised incisal edges the upper and lower lips, exposed portion of the teeth are used as the reference points. When the mouth is slightly open, approximately 3.5mm of the incisal portion of the maxillary teeth is visible in a young person while mandibular teeth are barely visible. As age increases, the muscles become lax and slowly diminish the display of the maxillary incisors, while the visibility of mandibular incisors increases. The pronunciation of F and V sounds should also be used to determine the superior/inferior length of the incisal edges & buccolingual placement of the upper maxillary incisors is evaluated. For the veneers the S sound is used to determine the vertical height of dimension i.e the mandibular incisors should be in gentle touch with the palatal surfaces of the mandibular incisors being 1mm behind and 1mm below.

Zenith points

Zenith points are the most apical points of the clinical crowns i.e height of contour. They are located distal to a line drawn vertically through middle of each anterior tooth dictated by the root form anatomy, cementoenamel junction, osseous crest where the gingiva is scalloped the most. In Diastema closure the zenith points should be repositioned distally to avoid mesially tilted appearance. The extreme distal positions of the gingival zeniths will result in an exaggerated triangular form. In order to avoid this zenith points should be moved mesially to create an illusion of bodily shifted central incisors towards the mid-line. Zenith points are moved apically through elongation in cases of shorter teeth. Zenith points can enhance the perception of the tooth axis as well as the length and the gingival shapes, achieved by horizontal or vertical alterations.

Gingival health and embrasures

Ideally interdental papillae should be thin and terminate on the tooth in a knife-edged contour forming a pyramid-shaped confluence of the gingival margin of the adjacent teeth. Healthy gingiva lies about 3 mm away from the intact bone on the facial aspect and tip of the stable papilla is at a distance of 5mm from the intercrestal bone. The gummy smile is corrected by placing the gingival tissues apically.

Gingival levels and harmony

The gingival line runs parallel to the canine line with a tangent through the incisal edges of both canines. The tips of the papilla gradually follow a pattern in the apical direction proceeding from the anterior towards the posterior teeth, thus the volume of the gingival embrasures gets smaller. The zenith points of the lateral incisors are 0.5 to 1mm below those of central incisors and canines, while that of canines and central incisors remain on the same horizontal drawn imaginary line. This relationship of zenith points forms a type of imaginary triangle. In cases of gummy smile by maxillary overgrowth with gingival display more than 10mm, only periodontal means will result into nonproportional crown root ratios hence orthognathic surgery, orthodontics or periodontal osseous surgery is advocated.

Tooth axis

In an esthetic smile the direction of the anterior teeth and the long axis follow a progression as the teeth are viewed from the mid-line towards the posterior area. The axis of the central incisors is usually slightly tilted distally towards the apex of the tooth when compared to the mid-line, perpendicular to the interpupillary line. The lateral incisors are somewhat inclined distally towards the apical than the central aspect. The canine tends to be even more distally inclined viewed facially & follows a parallel line drawn from the corner of the mouth to the corner of the eye while smiling

Interdental contact areas and points

The broad zone in which two adjacent teeth appear to touch is called as interdental contact area. Observation suggests that the 50-40-30 rule indicating the relationship between the anterior teeth i.e the interdental contact points (where incisal & distal surfaces of the tooth begin to converge at the incisal edges) moves apically as the teeth proceed from the central incisors towards the posterior area.

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Incisal embrasures

A dark area or negative space seen in the anterior region between the incisal edges creates a contrast which enhances the appearance of the incisal embrasures. As the dentition progress away from the midline, the size and the volume of the incisal embrasures increase. The incisal embrasure is the smallest and sharpest in the central incisors. The incisal embrasures between the central and lateral incisors are larger than the incisal embrasures between the centrals with a relatively wide angle. The largest of the incisal embrasures exists between the lateral incisors and canine. The embrasures may also affect the perception of the length, width and the incisal edge. In an aged or worn dentition caused by the incisor loss of length, the incisal embrasures becomes small or may even disappear, to create a youthful smile ,these teeth have to be lengthened and the embrasures recreated.