Solving Esthetic Problems - Indirect Veneer Preparations

Indirect veneer preparationsPart I in this series outlined the five dimensions that should be considered to determine the preparation design that will be used. Part II discussed preparation design for cases in which the patient presents with a problem or need in only one dimension. 

Now, we will explore how to determine the preparation design for anterior indirect veneer restorations when the restorative outcome is related to the esthetic dimension. We will also define the three types (depths) of reduction needed to address specific esthetic scenarios. 

The extent of facial reduction required is determined by assessing the current appearance of the tooth and ascertaining the changes needed to meet the desired outcome. The depth of tooth reduction needs to take into consideration the restorative material selection, the laboratory fabrication technique (monolithic versus laminated ceramic), the degree of masking required to achieve the desired shade and value, and whether it is an additive or a subtractive restoration

The three factors that determine the depth of reduction on the facial aspect of the teeth for indirect veneers are:

  1. The degree of change in color/color saturation desired (e.g. chroma change from A4 to A1, 5 shades)
  2. The degree of change in value/brightness desired (e.g. a value change from C2 to A1)
  3. The degree of relative translucency versus opacity required to achieve the outcome (i.e. masking required to hide underlying tooth discoloration)

The following recommendations are based on the average enamel thickness of teeth and the thickness of ceramic material needed to make the required color and value changes. The average enamel thickness is 0.3 to 0.4 mm at the CEJ, 0.8 to 1.0 mm in the middle third, and 1.1 to 1.3 mm in the incisal third of a maxillary central incisor.  The recommended technique to follow, especially when greater tooth reduction is required to accomplish the required shade change, is one that is additive. An additive wax-up is completed, an intraoral mockup is placed on the teeth and then the depth cuts are made through the mockup. This process creates the space necessary for the ceramic and preserves more enamel on the labial surface of the tooth.

An additive restorative technique would be preferred when greater depth of reduction is required in order to keep the preparation in enamel in the incisal half of the tooth. As the number of shade changes increases, the greater the depth of tooth reduction required. The base layer of ceramic must become more opacified in order to mask the underlying tooth. This requires additional space for the overlying dental and enamel ceramic to re-establish the translucency of the ceramic to match the natural dentition. A minimum thickness of ceramic is needed to predictably accomplish the shade changes, and the thinner the ceramic, the greater the risk of preparation “show through” in the final restoration. The goal is to have the preparation remain within tooth enamel because bonding to enamel is the most predictable way to retain the restoration compared to bonding to dentin. 

depth limiting burs

Minimal Veneer

  1. Indications: 0 to 1 shade/value change
  2. Depth: 0.3/0.5/0.7 mm tapered depth from gingival margin to incisal third (Depth Limiting Bur: RW Min .3/.5/.9 Brasseler USA)
  3. Material choices:
    1. Feldspathic or glass ceramic (flexural strength 80 MPa – ex: Ivoclar d.SIGN)
    2. Leucite reinforced glass ceramic (flexural strength 160 MPa – ex: Ivoclar Empress)
    3. Monolithic only
    4. Lithium Disilicate (flexural strength 360-400 MPa – ex: Ivoclar e.max)
      1. Recommended as monolithic or 0.3 mm microlayer of enamel glass ceramic in the incisal third

This preparation depth is the most conservative I would recommend – less than this and the outline of the tooth preparation will show through the ceramic, making it difficult to make a change in shade if required.

Conventional Veneer

  1. Indications: 1 to 2 shade/value changes and moderate morphology changes
  2. Depth: 0.5/0.7/0.9 mm tapered depth from gingival margin to incisal third (Depth Limiting Bur: RW Conv .5/.7/.9 Brasseler USA)
  3. Material choices:
    1. Feldspathic or glass ceramic
    2. Leucite reinforced glass ceramic
      1. Monolithic or 0.3 mm micro layer of enamel glass ceramic in the incisal third
    3. Lithium Disilicate
      1. Monolithic or 0.5 mm layer of enamel glass ceramic in incisal one-half

A layered restoration is preferred because there is some masking required to make the necessary shade/value change. Space for the dentin layer allows the necessary material thickness to make the shade change, and the layering of enamel creates the translucency required for a natural tooth appearance. A monolithic restoration has all of the shading characteristics applied on the surface. Simulation of translucency is achieved by using violet or blue stains. A glaze ceramic is then applied over the surface characteristics to achieve a smooth and shiny appearance.

Extensive Veneer

  1. Indications: 2 to 3 shade/value changes
  2. Depth:  0.8/1.0/1.2 mm tapered depth from gingival to incisal third (Depth Limiting Bur: RW Ext .8/1.0/1.2 Brasseler USA)
  3. Material choices:
    1. Feldspathic or glass ceramic
    2. Leucite reinforced glass ceramic
      1. Monolithic or 0.5 mm layer of enamel glass ceramic in the incisal half of the restoration
    3. Lithium Disilicate
      1. Monolithic or 0.5 mm layer of enamel glass ceramic in the incisal half of the restoration

As with the conventional veneer, a layered restoration is preferred over monolithic to improve the esthetics, because a relatively opacified ceramic must be used to mask the underlying tooth. In this case, because of the shade change expected, if a monolithic ceramic is used it is more difficult to overcome the opacity of the ceramic required to mask the underlying preparation. Surface stains can be applied to simulate the natural translucency of a tooth, but it will appear more artificial. 

This article outlined the rational for selecting the depth of tooth preparation based on the shade/value changes required to meet the esthetic outcome. To achieve a predictable result and achieve the most life-like appearance of a restoration, a layered veneer is recommended.

Part four in this series discuss preparation design for crown restorations when the desired restorative outcome is related to the esthetic dimension.