Outcome-Based Preparation Design of Anterior Teeth Part II: Single Dimension Problems

In Part I of this series, I outlined the five dimensions that should be considered when developing your preparation design. After a clear vision of the outcome of treatment is formed and the five dimensions are evaluated to determine the current conditions of the existing dentition, the restorative approach (technique) and material choice should be determined. The primary factors influencing whether a direct or indirect restoration will be used are the severity of the existing conditions, the changes required to accomplish the outcome, and the desire to complete treatment using the least invasive procedures. 

The first consideration in determining which restorative approach will be used is assessment of the current condition of the teeth. Is there only one dimension that is a problem, or is there a combination of several or all that will influence the preparation design? This will determine the type of restoration, the most appropriate restorative material to use for the case, the restorative process required (direct or indirect technique), and the invasiveness of the tooth preparation.

The least invasive restorative procedure to accomplish the goals of treatment should be used whenever possible. If there is a one-dimension problem to be solved requiring an additive process, a direct restorative technique should be considered. A direct restoration will require the least invasive preparation and is less costly to the patient than an indirect restoration, as there are fewer appointments needed and no laboratory fees are involved. The following are examples where only one problem needs to be addressed in the preparation design.

Tooth Length

An example of a single problem in this dimension is when the anterior tooth length is too short from an incisal edge perspective. The least invasive preparation would be to do a direct composite restoration that would require only a bevel of the enamel.

Great esthetic outcomes can be achieved, especially if a layering technique is implemented using a nano-fill composite resin. The esthetic outcome is comparable to ceramic if dentin and enamel composite materials are layered. The predictability of the esthetic outcome can be higher than indirect techniques because the clinician is working directly on the tooth, providing a high degree of predictability for shade and translucency matching.

(Click here for more on shade selection in the anterior.)

There are many additional variables if an indirect technique is pursued. The one with the most influence is if the technician cannot accurately replicate the appearance of the prepared tooth or the adjacent teeth in the laboratory. The esthetic outcome cannot be evaluated until the try-in appointment when other factors can influence the result, such as the predictability of the try-in paste esthetically matching the final resin cement. In addition to the esthetic and conservative aspects of a direct versus indirect restoration, it is easier and more predictable to repair composite than ceramic if fractures occur.

​Esthetics

An example of a single problem in the esthetic dimension would be making a simple shade change. Using a direct labial composite veneer would be a good non-invasive restorative option. If you are not changing labial position and you are looking to make a shade change with a direct veneer, a similar approach to tooth reduction will need to be followed as when preparing teeth for indirect veneers. There must be space created for the opacified resin needed to mask the underlying tooth in addition to the space required for the dentin and enamel layers of composite to recreate the appearance of a natural tooth. Dealing with other esthetic issues related to color and value, as well as the amount of tooth reduction required to accomplish the esthetic goals, will be discussed in detail in Parts III and IV of this series.

(Click here for all of our Esthetics articles.)

Labial Aspects of Tooth Morphology and Position

An example of a single problem involving labial tooth morphology would be a noncarious cervical lesion or cases in which there is loss of labial tooth structure from erosion or abrasion. An additive technique such as a direct labial composite restoration would accomplish the restorative goal.

(Click here for important considerations when treating cervical lesions.)

Another example of a single problem would be making a labial position change. If the tooth is retroclined and you want to change the position of the facial aspect by moving it labially, a direct composite facial veneer may be possible without reducing the tooth. If the tooth is in an ideal position and no tooth reduction is done, you risk creating an over-contoured tooth using a direct restoration.     

Interdental Issues

An example of a single problem or issue in the interdental region would be when the patient presents with diastemas or open gingival embrasures. Using a direct restorative approach can be highly predictable long term because it is in a non-stress bearing area of the tooth, but can be more challenging clinically when trying to create the desired morphology to close the interdental space, develop the interdental contact, and establish the proper convex contour to support the papilla. The clinician must work subgingivally to establish the convex contour. Isolation of the area, use of matrix bands to create the desired restorative contours, and finishing the restoration by trimming and polishing can be difficult.

If there is only one interdental area that needs to be treated, a direct approach is recommended. If there are interdental issues between all of the anterior teeth, most clinicians will prefer an indirect approach as the dental technician can typically manage these areas more easily when working on a stone cast of the teeth and tissue. 

Palatal/Lingual Morphology

A single problem related to the palatal/lingual aspect of a tooth could occur as a result of attrition, erosion, tooth fracture or carious lesion. If the problem was caused by tooth fracture or carious lesion, the tooth could be restored most conservatively with a direct restoration. The tooth preparation can be conservative by keeping the finish line bevels in enamel.

If the tooth structure loss is caused by attrition or erosion, the key factor to consider is managing the possible loss of space due to the loss of tooth structure and the subsequent movement (tooth eruption) to maintain opposing tooth contact. The most conservative approach to regain space for the restorative material and minimize tooth preparation is to orthodontically intrude the tooth to its ideal position. An additive restorative technique can then be performed. The tooth preparation for a direct restoration could be limited to beveling the enamel margins.

The photos above show an application of direct composite restorations to solve a one-dimension problem. This case involves only the incisal edges of the teeth. There were no other concerns with these teeth relative to facial tooth morphology and the overall esthetic aspects of the appearance of the teeth, and the lingual morphology did not need to be altered. 

As noted above, Part III will discuss esthetic issues related to color, value and translucency as well as the amount of tooth reduction required to accomplish the esthetic goals.

(If you enjoyed this article, click here for more clinical insights by Dr. Bob Winter.)

Bob Winter, DDS, Spear Faculty and Contributing Author