Oral Health Group
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Dentistry’s Esthetic Mt. Everest: Undetectable Restoration of a Single Discolored Maxillary Central Incisor

April 1, 2003
by Robert L. Nixon, DDS


Restoration of a single discolored maxillary central incisor to a near mirror image of the contralateral tooth, in all esthetic, functional, biological, and material dimensions, is a very formidable task at best and an exercise in utter frustration at worst. The reasons for this supreme challenge are both obvious and subtle:

The maxillary central incisor is the largest, most visible, most centrally-located, and most important anterior tooth in the esthetic zone. Therefore, variations in the central incisors are generally perceived more readily than with any other tooth pair.

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By definition, a single tooth restoration limits the degree of modification that can be imposed on all remaining adjacent teeth. Since the more common dental treatment, multiple esthetic restorations altering several teeth, is not possible in this context, the contralateral tooth to be matched dictates very precisely the parameters of the entire restoration. Hence, the single discolored central incisor tooth doesn’t conform to the usual restorative pattern of greater esthetic latitude characteristic of a multiple restoration case.

For many single tooth procedures such as a Class V restoration, a unilateral space closure, or elimination of a white-spot hypocalcification, the clinical approach is relatively patterned and consistent from patient to patient. By contrast, a single discolored maxillary central incisor correction has little standardization from case to case, at least from the perspective of the laboratory technician. Consequently, the degree of difficulty in attaining an acceptable match rises considerably, because each case is essentially a unique artistic endeavor. This often necessitates the fabrication of two or three slightly different restorations to hopefully achieve the optimal color gradient, opacity/translucency proportion, and surface anatomy/texture from one of them.

There is no universally agreed upon restorative material, so expertise is fragmented between such restorative options as direct or indirect bonding with a state-of-the-art composite, a ceramic laminate veneer, an all-ceramic crown, a ceramic-metal crown, and, under certain conditions, tooth whitening. Additionally, a single discolored maxillary central incisor tooth restoration has nowhere near the frequency of occurrence of many other indirect, laboratory-based procedures. As a result, refinement of the art and science of a single discolored incisor tooth correction, to match a contralateral tooth, undoubtedly suffers to a degree from lack of repetition of the procedure.

Some of the more subtle reasons for the immense difficulty of matching a single maxillary central incisor are the predilection for dehydration-induced tooth lightening, when the contralateral tooth is isolated for inspection, and the variable color of photographed teeth sent to the technician, as a result of the film type e.g. Kodachrome, Ektachrome, Fuji Color, etc. Also, the nature, degree, and angle of the photographic lighting can significantly influence the tooth detail for better or for worse. The treatment fee, which must factor in extra chairtime, multiple restorations to achieve an acceptable match, and the increased difficulty of the provisional restoration, may dissuade the patient from even initiating treatment. Some have reasoned that it is less expensive, less time-consuming, less stressful and more predictable to simply restore both central incisors. The inherent drawback in this solution is that a completely sound tooth must be irreversibly reduced, a consequence that is perceived as unnecessary by many patients.

The purpose of this case study is to describe a treatment approach for optimal restorative correction of a single discolored maxillary central incisor, with the aid of a recently introduced, digital shade mapping device.

CASE STUDY

A twenty-nine-year-old male patient with a discolored maxillary right central incisor (Figs. 1-5) presented for treatment, with the request that it be altered to “look as much as possible like my other front tooth.” The maxillary right central incisor had been fractured due to an accident, when the patient was ten-years old. The traumatic event resulted in discoloration of the tooth, calcific obliteration of the pulp chamber and root canal, and placement of several subsequent composite resin restorations to replace the missing incisal segment. The patient’s dentition was complete, with the exception of four extracted 3rd molars, and was uneventful other than exhibiting generalized gingivitis and progressive tooth wear due to deficient oral hygiene and bruxism, respectively. Initial periodontal preparation, intensified oral hygiene instruction, and a nocturnal orthotic were provided for the patient prior to initiating restoration of the maxillary right central incisor.

Due to the amount of missing tooth structure and the progressive tooth wear from bruxing, a bonded, hand-stacked all-ceramic crown was selected by the patient and the author as the preferred esthetic restoration, after several alternative restorative options were considered. Close-up photographs of the tooth to be matched, the maxillary left central incisor, were taken from three different angles (Figs. 3-5) for laboratory communication, as well as full-face and smile photographs.

The body shade of the maxillary left central incisor was approximated by photographing a shade guide reference (2M-2 from the Vitapan 3-D shade guide system, Vident, La Brea, CA) (Fig. 6). To enhance further the communication between the patient and the laboratory technician, the ShadeScantm (Cynovad, Montreal), a computerless, digital shade-taking device that simulates human vision, was used to generate a precise, comprehensive visual report (Fig. 7). Using an ergonomic handpiece with an LCD screen, the entire tooth image to be communicated (the maxillary left central incisor) is captured with a single click (Fig. 8). Voice commentary can be recorded for precise clinical information. Detailed color analysis can be readily communicated to the dental laboratory by either e-mail or by a portable flashcard.

A sophisticated color printout permitting complete evaluation of hue, chroma, and value from a variety of shade guides is rendered (Fig. 9). Shade mappings can be observed at different resolutions in greater or lesser detail. An extra dimension of considerable value is the translucency/ opacity mapping, as well as the highlight/texture topography image of the tooth (Fig. 10). At the dental laboratory end, the completed restoration can be imaged with the ShadeScantm and a validation of its accuracy accomplished, compared to the original tooth mapping.

In a single-tooth, full-coverage restoration case it is necessary to scrutinize the tooth to be matched, to determine if any preliminary alterations of a conservative nature are indicated. Such alterations might consist of enamel reshaping of the incisal edge, replacement of an aging partial tooth resin restoration, or recontouring of a slight rotation for better alignment. In this case, the pretreatment taper of the mesial wall of the maxillary left central incisor invited either a “dark triangle” at the midline or an overbulked crown contour on the maxillary right central incisor restoration. To overcome these undesirable effects, a mesial microfill resin contour augmentation (Renamel Microfill, Cosmedent, Inc., Chicago, IL) was placed on the maxillary left central incisor to enhance its bulk. Additionally, to resolve a generalized gingivitis, a variety of oral hygiene measures were introduced, including the daily utilization of an electric toothbrush with extremely fine bristles (Rotadent, ProDentec, Batesville, AK).

The decided improvement in soft tissue health is evident at the time of full crown tooth preparation of the maxillary right central incisor (Fig. 11). As part of the thorough laboratory communication, the full crown tooth preparation shade or “stump” shade is conveyed to the laboratory technician via a photograph or slide (Fig. 12), especially if the tooth is discolored. A full-arch, final impre
ssion was taken with a cutting-edge polyvinyl siloxane impression material (Affinity, Clinician’s Choice, London, ON, Canada). The full crown tooth preparation was then provisionalized with a bis-acryl material with a lower modulus of elasticity (more flex) than other bis-acryl provisional materials to resist fracture (Temptation, Clinician’s Choice, London, Ontario, Canada) (Fig. 13). The provisional crown was cemented with a dual-curing, resin-based provisional cement (Temp-Bond, Clear, SDS/Kerr, Orange, CA) after desensitization with a potassium oxalate desensitizer (Super Seal, Phoenix Dental, Fenton, MI).

Two slightly different all-ceramic crowns were subsequently fabricated by the laboratory technician, primarily from the definitive color analysis provided by the ShadeScantm (Cynovad, Montreal). After a try-in of both all-ceramic crowns, the more accurately color-matched crown was selected, and adhesively cemented with a fourth generation dentinal adhesive (Optibond — FL, SDS/ Kerr, Orange, CA) and a dual-curing resin cement (Insure-Lite, Cosmedent, Inc., Chicago, IL) using a total-etch technique.

The all-ceramic crown on the maxillary right central incisor was very well received by the patient, who described it as a “nearly perfect match” (Figs. 14-16).

DISCUSSION

Electronic shade scanning, a newly-emerging technology that objectively refines the traditional subjective methods of color communication, provides a promising avenue for improving and simplifying the methodology for matching a single maxillary central incisor. It is likely that digital shade mapping devices will become standard equipment in numerous dental offices and dental laboratories in the foreseeable future. This technology will undoubtedly be utilized in color-mapping composite restorations, as well as color-evaluating the composite resins themselves in the days ahead.

Just as Mt. Everest has been climbed, so the difficult maxillary central incisor single tooth color match is also being conquered, due to break-through technologies in combination with talented laboratory technicians that permit very close simulation of the natural dentition.OH

Dr. Nixon is co-director, Center for Esthetic Excellence, Chicago, IL.

Acknowledgments

The author would like to express his profound gratitude to John Hunsicker, CDT, for the outstanding ceramic restoration in this case.

Oral Health welcomes this original article.


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