by James Fondriest, DDS; Matt Roberts, CDT
No- or minimal-preparation veneers offer both benefits and limitations.
No synthetic restorative material used to reproduce natural tooth structure can match the combination of ideal qualities of functional strength and optical or esthetic display that exists in nature. Maintaining as much natural tooth structure as possible is a goal when doing restorative dentistry, especially when done for elective purposes. While less tooth reduction is a desirable goal, there are times when more reduction better serves the overall restorative agenda.
Evaluation Process for Minimum Preparation Veneer Candidates
It is critical to carefully appraise the patient’s pre-existing condition, tooth position, and dentition color as well as functional envelope, phonetic components, and the patient’s perceived goals of treatment before deciding the possible modalities of treatment. A comprehensive examination with a complete set of records and photographs should be taken to evaluate the interaction of function and determine the esthetic result desired. Mounted models can be compared with the facial photographs to analyze the desired changes to be made.
Additive vs Subtractive Dentistry
The functional and esthetic components of restoring teeth include planning the ideal alignment, shape and contour, surface morphology, incisal edge positions, and the opposing functional surfaces. The existing teeth can either be moved orthodontically into position or the tooth contours are modified by subtraction or addition. There has been a trend in restorative dentistry toward less invasiveness by means of tooth reduction and more common partnering with orthodontists with the goal of less tooth reduction or subtractive dentistry. Orthodontic and periodontal solutions to biologic and esthetic problems should be accomplished before planning definitive restorative solutions.
The patient’s models and photographs are used to evaluate any supplemental restorative repositioning of teeth beyond orthodontics necessary to achieve the treatment goals (Figure 1 and Figure 2). The photographs are faithfully oriented relative to the facial midline to properly assess the occlusal plane and tooth axial alignment issues. Line drawings of the proposed restorative treatment are created on the photographs (Figure 3), which assist the technician in choosing landmarks for a wax rendering of the treatment agenda. An “additive-reductive wax-up” is done (Figure 4) where contour is added in wax or removed from the stone models of the patient’s existing dentition using the facial photographs to orient the procedure. This process produces a template of the ideal esthetic form for the patient, and from this an intraoral silicone matrix can be fabricated for use in provisional fabrication and intraoral mock-up evaluation. If reductive changes have to be made to reach the ideal tooth position, those areas at least will require some tooth preparation, without which the patient is forced to accept a compromised treatment outcome.
Mock-Up Evaluation of Additive-Only Esthetic Outcome
For patients who visually may be candidates for no-preparation veneers, an additive-only wax-up can be done; after a silicone matrix of this wax-up is created, the shape and position of this wax-up can be tested in the patient’s mouth by filling the matrix with a material such as Luxatemp® (DMG, http://www.dmg-dental.com) and placing it over the existing dentition to create an intraoral mock-up (Figure 5). An intraoral mock-up may also be accomplished with direct bonding. If an esthetically pleasing outcome can be accomplished by additive procedures only, the case is one step closer to qualifying for very conservative veneers with little or no preparation.
Functional and Phonetic Evaluation of Mock-Up
If the mock-up results are esthetically pleasing, then a phonetic evaluation should be undertaken. After an evaluation of “f,” “v,” and “s” sounds is completed, the overall form of the teeth should be looked at. Excessive incisal thickness of maxillary anterior teeth is quite common after an additive mock-up, which may lead to the necessity of lingual preparation in some cases. Most esthetic changes in the anterior incisors will have functional ramifications as well. Canine guidance, crossover, and protrusive positions must be evaluated while the patient is wearing the mock-up. Changes in the incisal-edge positions of the maxillary incisors almost always create the need for modifications to the mandibular incisors to maintain a comfortable and atraumatic guidance.