COLOR CONTROL OF

ANTERIOR COMPOSITES

INTRODUCTION

Perception aesthetics is a philosophy which expresses an understanding of how smiles and consequently how results of aesthetic dentistry are perceived. It further studies what influences the perception of size, color and shape of teeth. This article will review concepts to maximize perception of color using light cured composite restorations.

CONCEPT

Restoration with light cured composite resin is the most demanding of any technique in restorative dentistry. Materials are used which are different than tooth structure to achieve a perception that it is tooth structure. The dentist is responsible for smile design, tooth reduction, color analysis and selection of color, material and technique. Restoration includes composite build up, sculpture and finish. The result of this artistic interpretation is solely a dentist's responsibility. While artistic ability is important, often, the biggest limitation is a lack of knowledge of specific materials and techniques.

Presently dentists learn about the composites they use by trial and error. There are many brands of light cured composites and each brand has different esthetic characteristics. Generalizations can be made about microfills, hybrids, macrofills, opaquers and composite stains but these generalizations do not provide a dentist with enough information to deliver consistent results. It is impossible to set specific guidelines to reflect all composites, however, analysis of specific brands of light cured composite materials, their interaction and analysis of restorative situations allow for predictable results.

RESTORATIVE THEORY

The theory for achieving proper color with composite restorations is to match composite color to tooth color. This may involve matching composite material to existing tooth structure or to change the color of tooth structure. There is a varying degree of opaqueness and translucency in composites. For purposes of explanation of this restorative theory, an opaque or dentin replicating composite and a translucent enamel replicating composite is used. When color change of tooth structure is required, a layer of dentin or opaque composite is first placed onto the colored tooth structure. Dentin or opaque composite is used because it is a more opaque composite and can block out underlying color. If underlying color shows through a this layer, an opaque layer is painted over it. A translucent enamel composite layer is then applied to achieve translucency, a high polish and color blending. There are times when only a translucent enamel composite or only a dentin or opaque composite will provide excellent results. The question arises when to use what, how and how much?. A logical systematic approach of analyzing tooth defects and composite materials is necessary.

RESTORATIVE DEFECTS

Restoration of tooth defects can be divided into two major categories including those which have no tooth structure background and those which have a tooth structure background. Defects include areas of loss, apparent loss or incorrect color of tooth structure. Restorations which have no tooth structure background, such as class IV or some class III defects, show darkness from the back of the mouth causing composites to look darker. These defects occur as a result of acute trauma such as a blow to the mouth, chronic trauma such as attrition, caries, and congenital abnormalities. The amount of darkness depends upon the translucency of the composite material. Situations which present with a tooth structure background such as class I, II, V, and some class III defects may show the color of the remaining tooth structure through the material. These defects occur as a result of acute trauma, caries, chronic trauma such as attrition and abrasion, and congenital abnormalities. The effect of remaining tooth structure as a background will vary with the depth, degree of darkness and color of the defect.

COMPOSITE ANALYSIS

Color and translucency of specific composite materials can be analyzed by judging the amount of hue, chroma, value and translucency at thicknesses of .5 millimeter, 1.0 millimeter, 1.5 millimeter and 2.O millimeter. Analysis can be done by simple experimentation.

A simple technique of composite analysis places a specific shade of material on a tooth defect one layer at a time without bonding. Each layer should be approximately .5mm, cured and evaluated for color. When complete block out of background tooth color and the shade of the restorative material is achieved, the material thickness is measured and recorded. It is now known that this particular shade at the recorded thickness will block out that color. As different degree of darkness and color defects are tested, they are recorded on a Composite Color/Depth Chart.

A faster and more deliberate technique to construct a Composite Color/Depth Chart, can be done by placing composite onto surfaces of materials with similar colors to those seen in restorative situations such as shade tabs. This produces a nice reference because the shade of the defect may be taken with a shade guide and referenced to the chart.

An an example, an A2 shade translucent enamel composite is applied to a moderately dark orange defect without bonding. The material is applied in increments of .5mm and light cured. When the material shows its original color, a thickness has been achieved which is compatible with restoring this defect. The material is removed and the thickness measured (1.5mm for our example). In the future, when a moderately dark orange defect occurs, it is known that if the defect is 1.5 millimeter deep, an A2 translucent enamel composite will properly restore the defect.

The same defect is then tested with an A2 dentin or opaque composite. The color of the defect is blocked out with .5 millimeter of the dentin or opaque composite material. This implies that a moderately dark orange defect can be restored with a minimum of .5mm of the dentin or opaque composite material to achieve proper color. To further apply this information, a l millimeter defect would not be effectively restored with an A2 translucent enamel composite because it requires a depth of 1.5 millimeter but it could have .5 millimeter of dentin or opaque composite applied first to bring the underlying color to an acceptable range. A .5 millimeter translucent enamel composite layer is then applied over it therefore maintaining the esthetic advantages of a translucent enamel composite.

To completely understand the A2 dentin or opaque composite and translucent enamel composite composites, the same testing is done for light, moderately dark and dark orange, brown, yellow, gray, white, or silver and gold and entered in the Composite Color/Depth Chart. In the future, when a restorative situation occurs which requires an A2 result, information will be available to make an intelligent decision about which materials and at what thickness is required.

RESTORATIVE TECHNIQUES

Restorative techniques apply composite and defect analysis with the Composite Color/Depth Chart to various restorative situations. Evaluation of a defect should include the following: 1. Tooth Structure or No Tooth Structure Background 2. Color (orange, brown, yellow, gray, white, silver and gold) 3. Degree of Darkness (light, moderate, dark) 4. Depth of Defect 5. Translucency of Defect

RESTORATION WITH NO BACKGROUND TOOTH STRUCTURE

Restoration of teeth with no background tooth structure requires special attention. Normally the back of a mouth is dark because limited light enters. In a dental office, a dental light and overhead lights eliminate darkness in the back of a mouth so the effects of darkness may not be shown while a patient is in a dental chair. It must be assumed that darkness will occur so a dentin or opaque composite layer which has increased opacity is placed as a backing and a translucent enamel composite layer applied over it. If a dentin or opaque composite has much translucency at the required thickness, an opaque layer is placed on it prior to a translucent enamel composite layer.

RESTORATION WITH BACKGROUND TOOTH STRUCTURE

Defects with background tooth structure are classified and analyzed for correct restorative color perception by color, degree of darkness and the desired shade of the restoration. The translucent enamel composite Color/Depth Chart is referred to first by selecting the desired shade on one axis and the defect color on the other. The resulting x and y coordinates provide the depth required to block out underlying color and achieve the desired shade. If the defect is deeper than the depth required on the chart, translucent enamel composite alone may be used.

If the depth of a defect is less than the depth required on the translucent enamel composite chart, an analysis is done on the dentin or opaque Composite Color Chart. If the depth of the defect is more than the depth required on the dentin or opaque composite chart, a dentin or a layered dentin/enamel composite may be used. As a point of interest, if the defect depth is equal to the depth required from the dentin or opaque composite chart, there will be no room for a translucent enamel composite over the dentin or opaque composite. In reality, placing slightly less dentin or opaque composite would produce a lighter defect which would be blocked out further by an overlying translucent enamel composite layer thus yielding a successful perception.

If the defect cannot be restored with a dentin or opaque composite and/or a translucent enamel composite, an opaque layer or increase in the depth of the defect is required. This is common with composite veneering and restoration of metal defects on crowns or amalgams.

COLOR ANALYSIS AND COLOR BLENDING

Color analysis is critical to successful composite color perception. Color analysis through selection of color and understanding of normal color variation within a tooth is an art form beyond the scope of this article. It should be noted, however, that there is great inaccuracy in shade guides. Analysis of a dentist's shade guide accuracy must be done and custom guides made or direct shade matching done if required.

Color blending is the art of making a transition from composite material color to tooth structure color. Color blending is a technique which utilizes the translucency of translucent enamel composites to show through underlying tooth structure in a gradual transition. Transition is accomplished with bevels which vary in length depending on the amount of color change. A tooth which is almost the same color as a translucent enamel composite would require only a .5mm bevel but a greater color transition may use bevels which extend most of the tooth. Transition occurs as the material gets thinner further out on the bevel while continually and increasingly showing through underlying tooth color.

For example, if a tooth color is between an A2 and A3 and a deep defect occurs at the gingiva, it may be possible to restore the defect with an A3 microfill material. Normally enamel gets thinner in the gingival third resulting a darker color so a tooth which appears to be an A2 may have an A3 gingival third. The top of the defect is beveled with a long bevel and because a microfill has great translucency, an acceptable gradual blending of color from A3 to A2 is achieved.

In advanced color blending, if the defect were dark and shallow, A2 microfill could yield a similar result. For example, if the defect were .8mm and moderately dark orange, A2, which would require 1.5mm for complete block out, would show through the underlying tooth structure making it appear between A2 and A3 shades which is desired. This is based on the knowledge from the Composite Color/Depth Chart that any defect with depth less then the indicated value will show through color.

In an alternative technique of color blending, a dark area is lightened by placing layers of light translucent enamel composite until the desired shade is reach. A final layer of the correct shade translucent enamel composite is then applied over this initial layer resulting in a restoration with maximum translucency and the perception of proper color. In a similar process for posterior teeth, a layer of lighter hybrid is placed first, then the correct shade on top.

THINGS TO CONSIDERATION

1. Not all tooth colors match composite colors. If the shade of a tooth is not the same color as the shade guide, two composite shades or composite stains may be mixed. This presents the problem of air incorporation and porosity so color blending is preferred.

2. There may be great color variation, including characterization, within the same tooth.

3. There are other factors which are critical to proper perception of color including proper surface texture, tooth shape and the light source.

4. Defects occur in many variations or combinations of colors which may not be described on the Composite Color/Depth Chart.

SUMMARY

Perception esthetics and the Composite Color/Depth Chart presents a logical pattern for color control with composites. It has limitations but dramatically improves the present thought process to restore teeth with composites. It is as important to understand the use, properties and techniques of materials as it is to write down a Composite Color/Depth Chart. Hopefully, in the future, companies will include a Composite Color/Depth Chart with their composites.