Anterior aesthetics part 4: Anterior tooth forms

Anterior tooth forms are simple to design when broken down into parts. As covered in previous blog posts we start the design with a rectangle. The length of the tooth is determined when considering the incisal edge and gingival margin positions. From this, the mesial-distal dimension can be judged when considering the ideal ratio of the tooth as it sits in the mouth. Once the position and size of the central incisor is defined, the other teeth can be designed more posteriorly. Canines are narrower than canines anatomically but tend to be the same length. Therefore then appear thinner in proportion.

The rectangle defines the border of the tooth as viewed from the labial. From here, defining certain points on the borders of the rectangle will allow you to join the dots and define the form of the tooth (Figure1) . These points are:
-Mesial and distal contact points which also define the incisal embrasures (the negative space that is formed between the incisal edge and interproximal surface). The positions of the contact points starts quite incisally at the midline but move more towards the gingiva the further distal you go. By extesion the height of the papilla becomes shorter and the base become broader the further distal you go.
-Incisal edge/cusp tip: which defines the occlusal extension of the tooth. Generally the most occlusal point of the tooth is slightly to the mesial of the centre of the crown. This is true for the lateral incisor and canine cusp tip but the central incisor tends to be quite flat with the lower edge of the rectangle.
-Gingival zenith: which is the highest point of the gingival margin. This lies slightly distal to the centre of the crown in general. The mesial position of the highest incisal point and distal position of the gingival zenith gives the appearance of mesial tilt of the teeth. It is never a sharp peak but a gentle curve.
-the gingival height of the canine is higher than the lateral incisor and the canine. Often times the gingival height of the canine is equal to or slightly below the central. However, our eye tends to draw a line between the central and canine gingival zenith which exaggerates the position of the lateral and makes it appear much shorter than the central.

Figure 1: Anterior tooth forms

These four points define the borders of the tooth form. The lines joining these points have their own set of rules.
-Incisal corners: formed between the incisal edge and the interproximal contact. The mesial corner is always sharper than the distal which tends to be more rounded. As the mesial corner is sharper it therefore causes the mesial incisal embrasure to be smaller than the distal but it is never completely closed i.e the mesial corners of the two centrals are never touching. The distal corner of the central incisor tends to mirror the mesial corner of the lateral incisor corner. The same goes for the distal corner of the lateral incisor and mesial corner of the canine. It is important that the distoincisal corner of the lateral incisor is very rounded and not just smaller versions of the central incisor. The importance of this is that in class 1 occlusions, the lower canine tip travels through this embrasure in lateral excursion. If the corner is made too bulky it will clip the canine tip in excursion and will fracture off.
-Lateral incisors are narrower and shorter than central incisors. The proportion should appear narrower than central incisors but this is open to creativity.
-The mesial interproximal surface is always straighter than the distal. It starts quite straight on the mesial of the central incisor and gets more rounded the further distal you go.
-A line drawn from the central incisal edge and canine tip should show the lateral incisor tip slightly gingival to the line.
-The incisal edge of the canine is quite smooth and gradual mesial to the cusp tip but the distal incisal edge has a defined "turn" about 2/3 of the way to the contact point. This is important in a natural appearance of the canine.
-As previously mentioned, the anterior teeth should appear to be tilting mesially. The distal as a more severe tilt than the central as its zenith is further distal to the midline. The canine has a less severe tilt when viewed purely from the labial but its position and angulation in the arch makes it appear to have a more severe mesial tilt when viewed from the front of the face.
-The gingival margins tilt gradually from the contact points, down the papillae to the zenith point. Due to the position of the zenith point to the distal, the distal part of the gingival margin tends to be steeper than the mesial which tends to be straighter in slope.

Focussing on the teeth themselves can cause you to develop tunnel vision and miss details. Instead, focussing on the negative space i.e the outline of the teeth can help with details. This means noting the increase in depth and width of the incisal embrasures as you move distally, noting the shift of the gingival margins moving posterior to anterior and noting the shape of the incisal edges.

As you continue more distally from the midline, the teeth tend to transition to resemble their more posterior counterparts. Lateral incisors tend to be between the form of a central and a canine in that the incisal zenith is more defined than a central which has a flatter incisal edge. Laterals are rounder than centrals as they transition to a canine. The facial surface of laterals tend to be rounder than centrals whereas canines are even more rounded than laterals. The buccal surface of premolars tend to continue that of the canines when viewed from the mesial. Premolars tend to appear shorter and wider in proportion than canines and the palatal cusps become more defined (compared to the cingulum of the canine) as they more towards becoming grinding molar teeth.Said another way, lateral incisors are the transition tooth between central incisors and canines and premolars are the transition teeth between canines and molars.