Positioning Maxillary Central Incisal Edges: Laboratory Use of Go-By Models

In previous articles in this series, I discussed how to finalizethe desired incisal edge position, whether it is the use of a bonded composite mock-up, or provisional restoration. In this article I'll illustrate a very simple example of how a lab can use a go-by model made from an impression of your desired incisal edge position to know they are producing the correct tooth position.

The patient seen in figure 1 is interesting because he can easily afford to have his anterior teeth treated, but is afraid if he does they will look too straight, white and artificial. In other words he has some very specific requests concerning tooth contour, arrangement and color. He is an artist and is more aware of such things than perhaps the average patient. After explaining to him that something needs to be done due to the decay present under the restorations on the anterior teeth, he agreed to restore the four incisors. But it is clear he wants them done to a very specific contour and arrangement.

Due to the severity of the decay and size of the old restorations I prepared the teeth for full crowns; some of them required composite build-ups. Figure 2 shows a model of the final preparations after sectioning and trimming the dies. Imagine you are now the laboratory technician and have to decide where to place the incisal edges. The logical thing to do is to make the centrals level with the canines; however, the problem is the left canine is significantly more apical than the right in his smile. Unless we provide our technicians with a model of what we want for the desired incisal edge position, any errors at the time of seating are on our shoulders not theirs.

In this case, after consultation with the patient it was clear he wanted the left central slightly shorter than the right and more to the facial. I used composite on a model of his existing teeth to create a quick and inexpensive mock-up, just improving the edge of the left central and shortening the long right lateral. I made a clear matrix of this model to use in the fabrication of his temporaries.

Figure 3 shows a model of his temporaries, the go-by model, and silicone-putty being used to make a simple impression of the incisal edge position on the model. The putty needs to be extended far enough posterior so that when it is placed on the prep model there is no question about it being correctly positioned by the unrestored teeth. This case is easy as I'm only restoring the four incisors and there are plenty of posterior teeth and the canines to index the putty. When doing a more complicated restoration such as a full arch, different techniques need to be used.

Figure 4 shows a solid model of this patient's preps seated into the silicone-putty. You can now imagine the clarity the technician has about how to position the incisal edges. They can use the silicone index to aid in the fabrication and position of the final restorations. The final restorations typically won't fit the silicone putty exactly, which is fine, but it should be within a few tenths of a millimeter of your desired incisal edge position from the model.

Figure 5 shows the final restorations closely replicating the position of the go-by model this patient desired. Taking the time to insure your technician has some reference for incisal edge position doesn't need to be difficult, it may be a simple pre-operative model if you like the existing tooth position. But a failure to provide your technician guidance on where the teeth need to be positioned can produce an esthetic nightmare that also may turn out be very expensive.