It is well documented that tooth shape and size, and other disparities are more easily recognized and scrutinized by dentists and non-dentists alike, as opposed to color or cant. Even so, it can be difficult for dentists to see what or how the shape and size actually needs to be changed. Symmetry: The first step should be to assess the symmetry of the tooth with the teeth on either side. A nice way to assess the general symmetry is to identify the highest points by using the side of a pencil to mark the highest spots, also known as the transitional line angles (Figure 1). You can see in Figure 1 that the provisional on one central is clearly not symmetrical with the other. What aspects should you evaluate with the pencil lines? Location of transitional line angles: Is the mesial pencil mark on the provisional crown skewed towards the middle of the tooth or towards the adjacent tooth? Is it more rounded or straighter? What about the distal pencil mark? Again, if we just notice the differences in pencil marks, we can begin to clarify what we saw when we noticed the lack of symmetry. Proximal embrasures: The more space that exists on the mesial side of the mesial line, the larger the facial embrasure. The longer horizontal lines (that have been drawn in), the larger the embrasure space must be (Figure 2). Additionally, a view from the incisal (Figure 3) will also reveal the lack of symmetry of proximal embrasures that you see from the facial and why the longer horizontal lines exist. Gingival embrasures: The less space that exists on the mesial side of the mesial line, the smaller the facial embrasure. The smaller the horizontal lines, the smaller the embrasure (Figure 4). Perceived Width/Distance Between Transition Line Angles:  We cannot change the outline of the tooth (the actual space between teeth); however, the space between the transition line angles on one tooth can make a tooth look wider or thinner. This can be used in our favor when we are attempting to make two non-symmetrical teeth look more symmetrical, but it can be a key indicator when trying to make teeth that are the same width look symmetrical. Even when most of the line looks fairly symmetrical, a small segment of asymmetry can drastically change what we see, as with the incisal 1-2 mm in Figure 5, making the provisional look wider than the other central. The provisional in Figure 6 looks much wider do to the distance between line angles, as was also the case in Figure 4. Tracing the lines using the side of a pencil to mark the highest points on teeth, which are by default the transitional line angles, is an easy way to help identify why teeth are not looking symmetrical. This technique works equally well on composite and enamel and can become a routine part of contouring teeth in the mouth for any procedure.  


Comments

Commenter's Profile Image Gerald Benjamin
January 24th, 2014
If dentists were more competent at direct veneers, they would have a better understanding of the anatomy of anterior teeth. Most clinicians would rather destroy tons of beautiful natural tooth structure by placing full crowns than conserve tooth structure with fabulous direct layered resins. The by product of conserving tooth structure would be that their temporaries would look like teeth rather than a dental freshman wax up. Sad
Commenter's Profile Image Arnie Mirza
January 25th, 2014
Kevin, thank you for the nicely explained and illustrated article.