Shape or Form

The shape of teeth largely determines their esthetic appearance. To achieve optimal dental esthetics, it is imperative that natural anatomic forms be achieved. A basic knowledge of normal tooth anatomy is fundamental to the success of any conservative esthetic dental procedure.

When viewing the clinical crown of an incisor from a facial (or lingual) position, the crown outline is trapezoidal. Subtle variations in shape and contour produce very different appearances, however. Rounded incisal angles, open incisal and facial embrasures, and softened facial line angles typically characterize a youthful smile. A smile characteristic of an older individual having experienced attrition secondary to aging, typically exhibits incisal embrasures that are more closed and incisal angles that are more prominent (i.e., less rounded). Frequently, minor modification of existing tooth contours, sometimes referred to as cosmetic contouring, can effect a significant esthetic change (see section on alterations of shape of natural teeth). Reshaping enamel by rounding incisal angles, opening incisal embrasures, and reducing prominent facial line angles can produce a more youthful appearance (Fig. 12-2).

Significant generalized esthetic changes are possible when treating all anterior teeth (and occasionally the first premolars) visible in the patient’s smile. This fact is particularly true when placing full-coverage facial restorations such as veneers (see the section on Veneers). With this treatment method, the dentist can produce significant changes in tooth shapes and forms to yield a variety of different appearances.

Although less extensive, restoring an individual tooth rather than all anterior teeth simultaneously may require greater artistic ability. Generalized restoration of all anterior teeth with full facial veneers affords the dentist significant control of the contours generated. When treating an isolated tooth, however, the success of the result is determined largely by how well the restored tooth esthetically matches the surrounding natural teeth. The contralateral tooth to the one being restored should be examined closely for subtle characterizing features such as developmental depressions, embrasure form, prominences, or other distinguishing characteristics of form. A high degree of realism must be reproduced artfully to achieve optimal esthetics when restoring isolated teeth or areas.

Illusions of shape also play a significant role in dental esthetics. The border outline of an anterior tooth (i.e., facial view) is primarily two-dimensional (i.e., length and width). The third dimension of depth is crucial, however, in creating illusions, especially those of apparent width and length.

Prominent areas of contour on a tooth typically are highlighted with direct illumination, making them more noticeable, whereas areas of depression or diminishing contour are shadowed and less conspicuous. By controlling the areas of light reflection and shadowing, full facial coverage restorations (in particular) can be esthetically contoured to achieve various desired illusions of form.

The apparent size of a tooth can be changed by altering the position of facial prominences or heights of contour without changing the actual dimension of the tooth. Compared with normal tooth contours (Fig. 12-3, A), a tooth can be made to appear narrower by positioning the mesiofacial and distofacial line angles closer together (see Fig. 12-3, B). Developmental depressions also can be positioned closer together to enhance the illusion of narrowness. Similarly, greater apparent width can be achieved by positioning the line angles and developmental depressions further apart (see Fig. 12-3, C).

Although more difficult, the apparent length of teeth also can be changed by illusion. Compared with normal tooth contours (Fig. 12-4, A), a tooth can be made to appear shorter by emphasizing the horizontal elements such as gingival perikymata and by positioning the gingival height of contour further incisally (see Fig. 12-4, B). Slight modification of the incisal area, achieved by moving the incisal height of contour further gingivally, also enhances the illusion of a shorter tooth. The opposite tenets are true for increasing the apparent length of a tooth. The heights of contour are moved farther apart incisogingivally, and vertical elements such as developmental depressions are emphasized (see Fig. 12-4, C).

Used in combination, these illusionary techniques are particularly valuable for controlling the apparent dimension of teeth in procedures that result in an actual increased width of teeth, such as in diastema (i.e., space) closure (see the section on Correction of Diastemas). By contouring the composite additions in such a way that the original positions of the line angles are maintained, the increased widths of the restored teeth are less noticeable (Fig. 12-5). If full facial coverage restorations are placed in conjunction with a diastema closure, vertical elements can be enhanced and horizontal features de-emphasized to control further the apparent dimension of teeth.

Symmetry and Proportionality

The overall esthetic appearance of a human smile is governed largely by the symmetry and proportionality of the teeth that constitute the smile. Asymmetric teeth or teeth that are out of proportion to the surrounding teeth disrupt the sense of balance and harmony essential for optimal esthetics. Assuming that the patient’s teeth are aligned normally (i.e., rotations or faciolingual positional defects are not present), dental symmetry can be maintained if the sizes of contralateral teeth are equivalent. A dental caliper should be used in conjunction with any conservative esthetic dental procedure that would alter the mesiodistal dimension of teeth. This recommendation is particularly true for procedures such as diastema closure or other procedures involving augmentation of proximal surfaces with composite. By first measuring and recording the widths of the interdental space and the teeth to be augmented, the appropriate amount of contour to be generated with composite resin addition can be determined (Fig. 12-6). In this manner, symmetric and equal tooth contours can be generated (see the section on Correction of Diastemas). When dealing with restorations involving the midline, particular attention also must be paid to the incisal and gingival embrasure forms; the mesial contours of both central incisors must be mirror images of one another to ensure an optimally symmetric and esthetic result.

In addition to being symmetric, anterior teeth must be in proper proportion to one another to achieve maximum esthetics. The quality of proportionality is relative and varies greatly, depending on other factors (e.g., tooth position, tooth alignment, arch form, configuration of the smile). One long-accepted theorem of the relative proportionality of maxillary anterior teeth typically visible in a smile involves the concept of the golden proportion.² Originally formulated as one of Euclid’s elements, this theorem has been relied on through the ages as a geometric basis for proportionality in the beauty of art and nature.³ On the basis of this formula, a smile, when viewed from the front, is considered to be esthetically pleasing if each tooth in that smile (starting from the midline) is approximately 60% of the size of the tooth immediately mesial to it. The exact proportion of the distal tooth to the mesial tooth is 0.618 (Fig. 12-7, A). These recurring esthetic dental proportions are based on the apparent sizes of teeth when viewed straight on and not the actual sizes of individual teeth. An example of an esthetically pleasing smile that meets the golden proportion can be seen in Figure 12-7, B.

Although the golden proportion is not the absolute determinant of dental esthetics, it does provide a practical and proven guide for establishing proportionality when restoring anterior teeth, especially if these teeth are considered long. However, according to a study by Preston, only 17% of the population naturally exhibits smiles that meet the golden proportion as the recurring esthetic dental proportion.⁴ According to a survey of dentists by Ward, a recurring esthetic dental proportion of 70% (as opposed to 61.8 % as with the golden proportion) is preferred when teeth are of normal dimension.⁵

Little scientific information is available regarding the proper proportions of individual anterior teeth. A study by Sterrett et al. revealed that the average width-to-length ratio for a maxillary central incisor in men was 0.85 and in women was 0.86.⁶ The actual width-to-length ratios found in this same study for maxillary lateral incisors in men and women were 0.76 and 0.79, respectively. Another study by Magne et al. reported average width-to-length ratios of 0.87 for worn maxillary central incisors and 0.78 for unworn maxillary central incisors.⁷ An accepted theorem for achieving esthetically pleasing central incisors maintains that the ideal width-to-length ratio should be 0.75 to 0.80.⁸ This ratio represents the ideal proportions needed to optimize the esthetic result and can help guide the treatment planning process. Considering the range of recommended width-to-length ratios, 0.80 seems to be a good benchmark for achieving optimally esthetic results when restoring maxillary central incisors and 0.75 for maxillary lateral incisors.

A good example can be seen in Figure 12-7, C through F. Because of altered passive eruption, this teenaged patient exhibited a preoperative width-to-length ratio of 1 : 1 for her maxillary central incisors (see Fig. 12-7, C). She revealed excessive gingival tissues relative to the display of her anterior teeth. To achieve a more esthetic appearance, it was determined that a width-to-length ratio of 0.80 would be desirable. After a periodontal surgical crown-lengthening procedure, a more esthetic width-to-length ratio of 0.80 was attained (see Fig. 12-7, D). After placement of eight etched porcelain veneers for the treatment of fluorosis discoloration, the same 0.80 width-to-length ratio can be seen (see Fig. 12-7, E). A 7-year postoperative photograph reveals the long-term esthetic result (see Fig. 12-7, F).

Because central incisors are the dominant focal point in dental composition, the dentist must avoid narrow, elongated, or short-and-wide contours. Adequate treatment planning and a fundamental knowledge of the importance of the ideal width-to-length ratios can optimize the final esthetic outcome. The importance of interdisciplinary treatment involving orthodontics, periodontics, or both cannot be underestimated.

Position and Alignment

The overall harmony and balance of a smile depend largely on proper position of teeth and their alignment in the arch. Malposed or rotated teeth disrupt the arch form and may interfere with the apparent relative proportions of teeth. Orthodontic treatment of such defects always should be considered, especially if other positional or malocclusion problems exist in the mouth. If orthodontic treatment is either impractical or unaffordable, however, minor positional defects often can be treated with composite augmentation or full facial veneers indirectly made from composite or porcelain. Only problems that can be treated conservatively without significant alteration of the occlusion or gingival contours of teeth should be treated in this manner.

Minor rotations can be corrected by reducing the enamel in the area of prominence and augmenting the deficient area with composite resin (Fig. 12-8, A and B). Care must be taken to restrict all recontouring of prominent areas to enamel. If the rotation is to be treated with an indirectly fabricated composite or porcelain veneer, an intra-enamel preparation is recommended, with greater reduction provided in the area of prominence. This preparation allows subsequent restoration to appropriate physiologic contours.

Malposed teeth are treated in a similar manner. Teeth in mild linguoversion can be treated by augmentation with full facial veneers placed directly with composite or made indirectly from processed composite or porcelain (see Fig. 12-8, C and D). Care must be exercised in maintaining physiologic gingival contours that do not impinge on tissue or result in an emergence profile of the restoration that is detrimental to gingival health. A functional incisal edge should be maintained by appropriate contouring of the restoration (an excessively thick incisal edge should be avoided). If the occlusion allows, limited reduction of enamel on the lingual aspect can be accomplished to reduce the faciolingual dimension of the incisal portion of the tooth. Lingual areas participating in protrusive functional contact should not be altered, however. Individual teeth that are significantly displaced facially (i.e., facioversion) are best treated orthodontically.

Surface Texture

The character and individuality of teeth are determined largely by their surface texture and existing characteristics. Realistic restorations closely mimic the subtle areas of stippling, concavity, and convexity that are typically present on natural teeth. Teeth in young individuals characteristically exhibit significant surface characterization, whereas teeth in older individuals tend to possess a smoother surface texture caused by abrasional wear. Even in older patients, however, restorations that are devoid of surface characterizations are rarely indicated.

The surfaces of natural teeth typically break up light and reflect it in many directions. Consequently, anatomic features (e.g., developmental depressions, prominences, facets, perikymata) should be examined closely and reproduced to the extent that they are present on the surrounding surfaces. The restored areas of teeth should reflect light as in the unrestored adjacent surfaces. In addition, as alluded to earlier, by controlling areas of light reflection and shadowing, various desired illusions also can be created.

Color

Color is the most complex and least understood artistic element. It is an area in which numerous interdependent factors exist, all of which contribute to the final esthetic outcome of the restoration. Although complex, a basic knowledge of color is imperative to producing consistently esthetic restorations.

Three fundamental elements of color are hue, value, and chroma. Hue is the intrinsic quality or shade of the color. Value refers to the relative lightness or darkness of a hue. It is determined by the amount of white or black in a hue. Chroma is the intensity of any particular hue. Some current shade guides are based first on value because of the importance of this element of color.

Dentists also must understand the coloration of natural teeth to select the appropriate shades of restorative materials accurately and consistently. Teeth typically are composed of a multitude of colors. A gradation of color usually occurs from the gingival region to the incisal region, with the gingival region being typically darker because of thinner enamel. Use of several different shades of restorative material may be required to restore a tooth esthetically. Exposed root surfaces are particularly darker (i.e., dentin colored) because of the absence of overlying enamel. In most individuals, canines are slightly darker than are incisors.

Young individuals with thick enamel characteristically exhibit lighter teeth. Individuals with darker complexions usually appear to have lighter teeth because of the contrast that exists between teeth and the surrounding facial structures. Women can enhance the apparent lightness of their teeth simply by using a darker shade of makeup or lipstick. By increasing the contrast between teeth and the surrounding facial tissue, the illusion of lighter teeth can be created.

Color changes associated with aging also occur, primarily owing to wear. As the facial enamel is worn away, the underlying dentin becomes more apparent, resulting in a darker tooth. Incisal edges are often darker because of the thinning of enamel or the exposure of dentin because of normal attrition. Cervical areas also tend to darken because of abrasion.

An understanding of normal tooth coloration enhances the dentist’s ability to create a restoration that appears natural. Several clinical factors also must be considered, however, to enhance the color-matching quality of the restoration. Many shade guides for composite materials are inaccurate. Not only are they often composed of a material dissimilar to that of the composite, but they also do not take into consideration color changes that occur from batch to batch or changes caused by aging of the composite. Accurate shade selection is best attained by applying and curing a small amount of the composite restorative material in the area of the tooth that may need restoration. Shade selection should be determined before isolating teeth so that color variations that can occur as a result of drying and dehydration of teeth are avoided.

Problems in color perception also complicate selection of the appropriate shade of restorative material. Various light sources produce different perceptions of color. This phenomenon is referred to as metamerism.⁹ The color of the surrounding environment influences what is seen in the patient’s mouth. Color perception also is influenced by the physiologic limitations of the dentist’s eye. On extended viewing of a particular tooth site, eyes experience color fatigue, resulting in a loss of sensitivity to yellow-orange shades.⁷ By looking away at a blue object or background (i.e., the complementary color), the dentist’s eyes quickly recover and are able to distinguish subtle variations in yellow-orange hues again. Because of the many indirect factors that influence color perception, it is recommended that the dentist, the assistant, and especially the patient all be involved in shade selection.

Translucency

Translucency is another factor that affects the esthetic quality of the restoration. The degree of translucency is related to how deeply light penetrates into the tooth or restoration before it is reflected outward. Normally, light penetrates through enamel into dentin before being reflected outward (Fig. 12-9, A); this affords the realistic esthetic vitality characteristic of normal, unrestored teeth. Shallow penetration of light often results in loss of esthetic vitality. This phenomenon is a common problem encountered when treating severely intrinsically stained teeth such as teeth affected by tetracycline with direct or indirect veneers. Although opaque resin media can mask the underlying stain, esthetic vitality is usually lost because of reduced light penetration (see Fig. 12-9, B). Indirect veneers of processed composite or porcelain fabricated to include inherent opacity also may have this problem.

Illusions of translucency also can be created to enhance the realism of a restoration. Color modifiers (also referred to as tints) can be used to achieve apparent translucency and tone down bright stains or to characterize a restoration. Figure 12-10 shows a case in which the maxillary right central incisor with intrinsic yellow staining caused by trauma to the tooth warranted restoration. When bleaching treatments were unsuccessful because of calcific metamorphosis, a direct composite veneer was used in this patient. After an intra-enamel preparation and acid-etching, a violet color modifier (the complementary color of yellow) was applied to the prepared facial surface to reduce the brightness and intensity of the underlying yellow tooth. Additionally, a mixture of gray and violet color modifiers was used to simulate vertical areas of translucency. The final restoration is shown in Figure 12-10, B. Color modifiers also can be incorporated in the restoration to simulate maverick colors, to check lines, or to surface spots for further characterization. Color modifiers always should be placed within a composite restoration, not on its surface.

Alterations of Shape of Natural Teeth

Some esthetic problems can be corrected conservatively without the need for tooth preparation and restoration. Consideration always should be given to reshaping and polishing natural teeth to improve their appearance and function (Fig. 12-11). In addition, the rounding of sharp angles can be considered a prophylactic measure to reduce stress and to prevent chipping and fractures of the incisal edges.

Treatment

Consultation and examination are necessary before any changes are made to the shapes of teeth. Photographs, study models, line drawings, and esthetic imaging devices enable the patient to envision the potential improvement before any changes are made.

As noted earlier, cosmetic contouring to achieve youthful characteristics often includes rounding incisal angles, reducing facial line angles, and opening incisal embrasures. The opposite characteristics typically are considered more mature features. Cosmetic reshaping to smooth rough incisal edges and improve symmetry is equally beneficial to women and men.

The patient must understand what is involved and must want to have the alteration made. If reshaping is desired, it is helpful to mark, by using a pencil or alcohol-marking pen, an outline of the areas of the teeth to be reshaped (see Fig. 12-11, B). By marking the anticipated areas for enamel reshaping, the patient is provided some indication of what the post-operative result may look like (see Fig. 12-11, C). If available, esthetic computer imaging also can be used to illustrate the possible result before treatment.

Because all reshaping is restricted to enamel, anesthesia is not required. A cotton roll is recommended for isolation. Diamond instruments and abrasive disks and points are used for contouring, finishing, and polishing (see Fig. 12-11, D and E). Through careful reshaping of appropriate enamel surfaces, a more esthetic smile (characterized by youthful features) is attained. Rounded incisal edges also are less likely to chip or fracture (see Fig. 12-11, F).

A second example involves the irregular, fractured incisal surfaces of maxillary central incisors (Fig. 12-12, A). An esthetic result can be accomplished by slightly shortening the incisal edges and reshaping both teeth to a symmetrical form. Photographs, line drawings, esthetic imaging, or marking the outline on the patient’s teeth enables the patient to envision the potential improvement before any changes are made. Protrusive function always should be evaluated to prevent inadvertent elimination of this occlusal contact. Conservative treatment consists of using diamond instruments and abrasive disks and points for contouring and polishing the central incisors. The finished result is illustrated in Figure 12-12, B.

As some patients grow older or have the habit of bruxism, the incisal surfaces often wear away, leaving sharp edges that chip easily. This is also accompanied by loss of the incisal embrasures (Fig. 12-13, A). To lessen the chance of more fractures and to create a more youthful smile, the incisal embrasures are opened, and the incisal angles of teeth are rounded (see Fig. 12-13, B).

Anterior teeth can have embrasures that are too open as a result of the shape or position of teeth in the arch. When the permanent lateral incisors are congenitally missing, canines and posterior teeth may drift mesially, or the space may be closed orthodontically. The facial surface and cusp angle of some canines can be reshaped to appear like lateral incisors. In many instances, the mesio-incisal embrasures remain too open (Fig. 12-14, A).

The presence of diastemas between anterior teeth is an esthetic problem for some patients (Fig. 12-15). Before treatment, a diagnosis of the cause is made, including an evaluation of the occlusion. Probably the most frequent site of a diastema is between maxillary central incisors. A prominent labial frenum with non-elastic fibers extending proximally often prevents the normal approximation of erupting central incisors.¹¹ Other causative factors include congenitally missing teeth, undersized or malformed teeth, interarch tooth size discrepancies (i.e., Bolton discrepancy), supernumerary teeth, and heredity. Diastemas also may result from other problems such as tongue thrusting, periodontal disease, or posterior bite collapse. Diastemas should not be closed without first recognizing and treating the underlying cause, as merely treating the cause may correct the diastema.

Treatment

Traditionally, diastemas have been treated by surgical, periodontal, orthodontic, and prosthetic procedures. These types of corrections can be impractical or unaffordable and often do not result in permanent closure of the diastema. In carefully selected cases, a more practical alternative is use of the acid-etch technique and composite augmentation of proximal surfaces (see Figs. 12-5 and Fig. 12-6). All treatment options (including no treatment) should be considered before resorting immediately to composite augmentation. Line drawings, photographs, computer imaging, models with spaces filled, and direct temporary additions of ivory-colored wax or composite material on natural teeth (unetched) are important preliminary procedures.

The correction of a diastema between maxillary central incisors is described and illustrated in Figure 12-15. After the teeth are cleaned and the shade selected, a Boley gauge or other suitable caliper is used to measure the width of the diastema and the individual teeth (see Fig. 12-15, B and C). Occasionally, one central incisor is wider, requiring a greater addition to the narrower tooth. Assuming the incisors are of equal width, symmetrical additions can be ensured by using half of the total measurement of the diastema to gauge the width of the first tooth restored. Cotton rolls, instead of a rubber dam, are recommended for isolation because of the importance of relating the contour of the restoration directly to the proximal tissue. Usually, the restoration must begin slightly below the gingival crest to appear natural and to be confluent with the tooth contours.

With cotton rolls in place, a gingival retraction cord of an appropriate size is tucked in the gingival crevice of each tooth from midfacial mesially to midlingual (see Fig. 12-15, D). The cord retracts the soft tissue and prevents seepage from the crevice. In some instances, the retraction cord may need to be inserted for one tooth at a time to prevent strangulation of interproximal tissue during preparation and restorative procedures. To enhance retention of the composite, a coarse, flame-shaped diamond instrument is used to roughen the proximal surfaces, extending from the facial line angle to the lingual line angle (see Fig. 12-15, E). More extension may be needed to correct the facial or lingual contours, depending on the anatomy and position of the individual tooth. The enamel is acid-etched approximately 0.5 mm past the prepared, roughened surface. The acid should be applied gingivally only to the extent of the anticipated restoration. After rinsing and drying, the etched enamel should display a lightly frosted appearance (see Fig. 12-15, F). A 2 × 2 inch (5 × 5 cm) gauze is draped across the mouth and tongue to prevent inadvertent contamination of the etched preparations by the patient. After both preparations are completed, the teeth are restored one at a time.

A polyester strip is contoured and placed proximally, with the gingival aspect of the strip extending below the gingival crest. Additional contouring may be required to produce enough convexity in the strip. In most cases, a wedge cannot be used. The strip is held (with the index finger) on the lingual aspect of the tooth to be restored, while the facial end is reflected for access. A light-cured composite is used for the restoration. After the bonding agent is applied, the composite material is inserted with a hand instrument (see Fig. 12-15, G). Careful attention is given to pressing the material lingually to ensure confluence with the lingual surface. The matrix is gently closed facially, beginning with the gingival aspect (see Fig. 12-15, H). Care must be taken not to pull the strip too tightly because the resulting restoration may be under-contoured faciolingually, mesiodistally, or both. The light-cured composite material is polymerized with the light directed from the facial and lingual directions for an appropriate amount of time. Note that curing times may vary according to the type of light source, the composite used, and the thickness of the material (see Fig. 12-15, I). Initially, it is better to over-contour the first restoration slightly to facilitate finishing it to an ideal contour.

When polymerization is complete, the strip is removed. Contouring and finishing are achieved with appropriate carbide finishing burs, fine diamonds, or abrasive disks (see Fig. 12-15, L). Finishing strips are invaluable for finalizing the proximal contours (see Fig. 12-15, J and M). Final polishing is deferred until the contralateral restoration is completed. It is imperative for good gingival health that the cervical aspect of the composite addition be immaculately smooth and continuous with the tooth structure. Overhangs must not be present. Removal of the gingival retraction cord facilitates inspection and smoothing of this area. Flossing with a length of unwaxed floss verifies that the gingival margin is correct and smooth if no fraying of the floss occurs (see Fig. 12-15, P). It is important that the correct mesiodistal dimension of the first tooth be established before the second tooth is restored.

After etching, rinsing, and drying, the second restoration is completed. A tight proximal contact can be attained by displacing the second tooth being restored in a distal direction (with the thumb and the index finger) while holding the matrix in contact with the adjacent restoration (see Fig. 12-15, K). Contouring is accomplished with a 12-fluted carbide bur and finishing strips (see Fig. 12-15, L and M). Articulating paper should be used to evaluate the patient’s occlusion to ensure that the restorations are not offensive in centric or functional movements; adjustments can be made with a carbide finishing bur or abrasive disks. Final polishing is achieved with rubber polishing points or polishing paste applied with a Prophy cup in a low-speed handpiece (see Fig. 12-15, N and O). Unwaxed floss is used to detect any excess material or overhang (see Fig. 12-15, P). The final esthetic result is seen in Figure 12-15, Q.

Multiple diastemas among the maxillary anterior teeth are shown in Figure 12-16, A. Closing the spaces by orthodontic movement was considered in this patient; however, because the patient’s teeth were under-contoured mesiodistally, the diastemas were closed by etching the teeth and bonding composite to the proximal surfaces. The teeth after treatment are shown in Figure 12-16, B. In the presence of defective Class III restorations or proximal caries, it is recommended that the teeth be restored with the same composite used for closing the diastema. Often, these restorations can be performed at the same time the diastema is closed with composite additions (Fig. 12-17).

Occasionally, diastemas are simply too large to close esthetically with composite augmentation alone (Fig. 12-18, A). Closing a large space of this magnitude with composite would merely create an alternative esthetic problem, that is, excessively large central incisors, which would further exacerbate the existing discrepancy in proportionality among anterior teeth. In such cases, large spaces are best redistributed orthodontically among anterior teeth so that symmetric and equal composite additions can be made to the central and lateral incisors (see Fig. 12-18, B and C). This approach that involves space distribution results in improved proportionality among anterior teeth (see the earlier section on Artistic Elements). The final result, immediately after completion, is shown in Figure 12-18, D.

Stains on the external surfaces of teeth (referred to as extrinsic discolorations) are common and may be the result of numerous factors. In young patients, stains of almost any color can be found and are usually more prominent in the cervical areas of teeth (Fig. 12-19, A). These stains may be related to remnants of Nasmyth’s membrane, poor oral hygiene, existing restorations, gingival bleeding, plaque accumulation, eating habits, or the presence of chromogenic microorganisms.¹² In older patients, stains on the surfaces of teeth are more likely to be brown, black, or gray and occur on areas adjacent to gingival tissue. Poor oral hygiene is a contributing factor, but coffee, tea, and other types of chromogenic foods or medications can produce stains (even on plaque-free surfaces). Tobacco stains also are observed frequently. Existing restorations may be discolored for the same reasons.

An example of one of the most interesting and unusual types of external staining is illustrated in Figure 12-19, B. In Southeast Asia, some women traditionally dye their teeth with betel nut juice to match their hair and eyes as a sign of beauty.¹³ Slices of lemon are held in contact with the teeth before applying the betel nut juice to make the staining process more effective. This example was probably one of the first applications of the acid-etch technique. A weak acid, such as that found in citrus fruits, is known to cause rapid decalcification of enamel.

Treatment

Most surface stains can be removed by routine prophylactic procedures (Fig. 12-20). Some superficial discolorations on tooth-colored restorations and decalcified areas on teeth, however, cannot be corrected by such cleaning. Conservative correction may be accomplished by mild microabrasion or by surfacing the thin, outer, discolored layer with a flame-shaped, carbide finishing bur or diamond instrument (i.e., macroabrasion), followed by polishing with abrasive disks or points to obtain an acceptable result. (See subsequent sections on Microabrasion and Macroabrasion for details of clinical technique.)

Intrinsic discolorations are caused by deeper (not superficial) internal stains or enamel defects; these stains are more complex to treat than are external types. Teeth with vital or non-vital pulps as well as root canal–treated teeth can be affected. Vital teeth may be discolored at the time the crowns are forming, and the abnormal condition usually involves several teeth. Causative factors include hereditary disorders, medications (particularly tetracycline preparations), excess fluoride, high fevers associated with early childhood illnesses, and other types of trauma.¹² The staining may be located in enamel or dentin. Discolorations restricted to dentin still may show through enamel. Discoloration also may be localized or generalized, involving the entire tooth.

Various preparations of the antibiotic drug tetracycline can cause the most distracting, generalized type of intrinsic discoloration (Fig. 12-21, A).¹⁴ The severity of the staining depends on the dose, the duration of exposure to the drug, and the type of tetracycline analogue used. Different types of tetracyclines induce different types of discoloration, varying from yellow-orange to dark blue-gray. Dark blue-gray, tetracycline-stained teeth are considerably more difficult to treat than are teeth with mild yellow-orange discolorations. Staining from tetracycline-type drugs most frequently occurs at an early age and is caused by ingestion of the drug concomitant with the development of permanent teeth. Studies indicate that permanent teeth in adults also can experience a graying discoloration, however, as a result of long-term exposure to minocycline, a tetracycline analogue.¹⁴

The presence of excessive fluoride in drinking water and other sources at the time of teeth formation can result in another type of intrinsic stain called fluorosis. The staining usually is generalized. Localized areas of discoloration may occur on individual teeth because of enamel or dentin defects induced during tooth development. High fevers and other forms of trauma can damage the tooth during its development, resulting in unesthetic hypoplastic defects. Additionally, localized areas of dysmineralization, or the failure of the enamel to calcify properly, can result in hypocalcified white spots. After eruption, poor oral hygiene also can result in decalcified white spots. Poor oral hygiene during orthodontic treatment frequently results in these types of decalcified defects. White or discolored spots with intact enamel surface (i.e., surface not soft) are often evidence of intraoral remineralization, however, and such spots are not indications for invasive treatment (unless for esthetic concerns). Additionally, caries, metallic restorations, corroded pins, and leakage or secondary caries around existing restorations can result in various types of intrinsic discoloration.

As noted earlier, aging effects also can result in yellowed teeth. As patients grow older, the tooth enamel becomes thinner because of wear and allows underlying dentin to become more apparent. Also, often, continuing deposition of secondary dentin occurs in older individuals, resulting in greater dentin thickness. This deposition results in a yellowing effect, depending on the intrinsic color of dentin. Additionally, the permeability of teeth usually allows the infusion (over time) of significant organic pigments (from chromogenic foods, drinks, and tobacco products) that produce a yellowing effect.

Nonvital teeth also can become discolored intrinsically. These stains usually occur in individual teeth after eruption has taken place. The pulp may become infected or degenerate as a result of trauma, deep caries, or irritation from restorative procedures. If these teeth are properly treated by root canal therapy, they usually retain their normal color. If treatment is delayed, discoloration of the crown is more likely to occur. The degenerative products from the pulp tissue stain dentin, and this is readily apparent because o/>