Direct Restorations in the Anterior
At the beginning of our career we are often interested in technical details that distract us from the true challenge of the case we are handling. For instance, it is much more difficult to motivate a patient to adopt a low–caries risk lifestyle than it is to prepare a cavity. After many years of practice, however, one of the technical aspects in the field of restorative dentistry—either direct or indirect—that is still challenging involves reproducing tooth shades, especially when restoring single teeth. Indeed, although reproduction of tooth shade is based on scientific principles, there is also a strong element of personal interpretation.
The principle of cosmetic restoration is still dominated by too many individual parameters, and, despite the many attempts to systematize knowledge, protocols are subject to strong and personal influences. Indeed, one technique is not necessarily better than another, and some may even be used together. In this chapter I will try to propose a rational and standardized protocol for direct restoration in the anterior, with due regard for scientific principles.
Figure 7-2 Large lesions may be treated with direct techniques even in elderly patients or those undergoing supportive periodontal therapy, and on a more general level in all cases that require a waiting period, as long as they are limited to a few teeth.
Figure 7-3 A, Large lesions (entire buccal surface), the number of teeth involved, the patient’s age and esthetic needs, and the difficulties in restoring morphology and function (many therapeutic goals) make the placement of direct restorations unadvisable except for diagnostic or temporary reasons—for example, if a waiting period is involved. B, Checkup after 4 years.
Figure 7-4 A, In this case tooth 9 is nonvital and dyschromic. B, Owing to the partial results obtained with the internal bleaching procedure, the direct restoration did not satisfy the patient’s esthetic needs. C and D, Therefore a partial-coverage indirect ceramic restoration was placed (the dental laboratory work was done by Mario Svanetti, Brescia, Italy).
Figure 7-5 Fracture of these teeth (A) necessitated root-canal treatment of teeth 9 and 10 (B), followed by internal bleaching. The severe involvement of some of these teeth might suggest indirect treatment, but the good chromatic results, the type of function, and the patient’s young age and esthetic needs permitted direct treatment (C).
Figure 7-6 A, Dyschromic nonvital incisors. In this case the evaluation criteria point to indirect treatment. Based on the patient’s requirements and occlusion permitting, direct restoration (B and C) can be used as a medium-long–term provisional restoration or for buildup purposes (preprosthetic restoration).
In the case of Black Class IV restorations, the most logical way to control the thickness of the material is to prepare a diagnostic wax-up of the missing portion on a plaster cast mounted in the articulator, and then in the dental laboratory fabricate a silicone tray (Shore hardness about 95) that will be used as a template for the palatal side (Figure 7-7). Thickness control on the buccal aspect is achieved through precise shaping without a great deal of excess material.
• Reproduction of the enamel is considered a high-definition aspect because color, opacity, and shape are equally important; its realization requires the operator’s close attention in order to grasp every detail to be reproduced.
In 1969 Henry Munsell introduced parameters based on visual and cognitive perception that, translated into dental terms, mean hue, chroma, and value; the last of these is the most significant for dental purposes (Figures 7-8 to 7-10).
Figure 7-8 Value: the amount of gray in a shade.
Figure 7-10 Chroma: degree of saturation or depth of the shade. The left glass contains red wine (pure color at maximum saturation); the right one contains the same wine, but it has been watered down (diluted to achieve less color saturation). In the Vita shade guide it is indicated by numbers—for example, for shade A the chroma ranges from 1 to 4.
In dentistry, shade means the basic color of the tooth. In the Vita shade guide the different shades are indicated by the following letters: A, red-brown; B, yellow; C, gray; and D, gray-pink. Given today’s composite market, maintaining this four-color classification makes little sense, because one of the main problems with these materials is excessive transparency compared with the Vita shade guide. Transparency corresponds to grayness. Consequently, gray shades are obtained automatically by using a composite material (C and D masses are unnecessary, and there is little difference between A and B). Currently a shade can be modified toward gray simply by applying a more transparent enamel (the shade is not changed by the dentin mass). We can hope that in the future for each shade there will be specific dentin masses that are sufficiently opaque and colored (already a feature of all ceramic materials).
Value corresponds to brightness—that is, the amount of light that is reflected, refracted, or absorbed by a surface—and it is influenced by the type of surface finish. As shown in Figure 7-8, the interaction between light and a glass object produces dark and clear areas with a low value, alternating with clearer and more reflective high-value zones, depending on the surface finish: smooth, orange peel, or sanded. In short, analysis of a tooth value can be compared with a black-and-white photograph and can be divided into two parts:
Shade can be assessed in mathematical terms—that is, spectrophotometric parameters. The shade can be found within the color space, represented by three numbers (spatial coordinates) that identify it unambiguously: hue, chroma, and value.
In Figure 7-11 we can see that the inner layers of dentin (close to the pulp) have a high value, whereas in the outer layers (toward the enamel) chroma increases and the value is lower. The inner enamel layer (toward the dentin) has a low value, whereas the outer one has a high one.
The most important parameters in shade reproduction with composite materials are opacity, shape, and shade for the dentin, and opacity, thickness, and surface texture for the enamel (Figures 7-12 to 7-14).
Figure 7-11 Assessment of chroma and value in natural teeth.
Figure 7-12 Analysis and reproduction of dentin.
Figure 7-13 Natural enamel varies greatly, and opacity must be assessed in order to reproduce it. For a schematic approach it is helpful to classify opacity by reducing the number of possible variables to transparent (7.25a), opaque (7.25c) and intermediate (7. 25b) (slightly yellow and white).
• There is no agreement among composite manufacturers concerning the level of opacity, shade depth, and amount of masses required for a line of composite materials—that is, there are very simple lines with a single opaque composite, and others that offer three or more.
• Masses are usually too transparent, which means that they have a low value and look gray. This makes the choice of shade even less important; the value is further lowered after curing, especially for the more transparent masses.
In general, transparent composite materials are characterized by a dominant yellow-gray shade owing to the high percentage of vitreous-like filler. On the contrary, white masses lose their transparency almost completely because they are obtained by adding a large amount of white-opaque pigment. Therefore yellow-gray and white-opaque masses are readily available, whereas the white-transparent masses are poorly represented.
Figure 7-15 shows machine-made enamel samples with the same thickness and polishing, although they differ in opacity. We can observe more transparent samples with a low value and others that are more opaque with a high value.
Figure 7-15 Value: brightness and opacity.
The samples shown in Figure 7-16 were obtained by overlapping cores of dentin (approximately 2.5 mm) on thick enamel shells (approximately 1.5 mm). In Figure 7-16 the left sample is obtained with chroma dentin 7 (very deep shade) and NT enamel (Neutral Transparent with a low value); the sample on the right side is made with chroma dentin 1 (diluted color) and WB enamel (White Opaque with a high value). The shades of the sample teeth obtained with these layerings are logical and consequential, whereas the color of the sample on the left side of Figure 7-16—obtained with chroma dentin 1 and NT enamel—cannot be grasped immediately. Using a low-chroma dentin one would expect a light-colored tooth, but its association with a thick layer of NT enamel lowers the value drastically, overpowering the dentin in the final result. This demonstrates that overlaying completely different enamel composite shades on the same dentin affects value.
Figures 7-17 and 7-18 exemplify the behavior of several composite materials layered over a thick core to reproduce dentin, over which thin vertical columns differing in opacity, chroma, and hue were applied. Given the />