Benefits of pre-restorative orthodontic treatments on veneer preparations
Sung E, Chang T-L, Shah K, et al. J Dent Res (Special Issue, AADR-CADR Abstracts). 2010;89: Abstract no. 1076.
OBJECTIVE: The benefits of pre-restorative alignment has been well documented. These characteristics are of particular interest in cases for patients with mal-aligned dentition who are seeking prosthetic rehabilitation. The question arises whether complete or partial orthodontic alignment is necessary when managing these cases. The purpose of this investigation was to measure the impact of pre-restorative orthodontic treatment on veneer preparation depth and the amount of orthodontic movement necessary to maximize outcome.
METHODS: 30 arches class I crowding cases requiring 12 months of orthodontic treatment for complete alignment of the anterior teeth were simulated in ClinCheck. Little's index of irregularity was determined on the 3D models to quantify crowding. Models were created from each case at 0, 6, and 12 month of orthodontic treatment for crowded dentition using set-ups. Diagnostic wax up for six anterior veneers was made for each time point, and silicone preparation guides were fabricated. Four different clinicians then prepared the study models for veneers for each time point. A total of 540 teeth were prepared. All prepared arches were scanned and the amount of tooth reduction was determined by 3D software.
RESULTS: There was a significant direct correlation between Little's index of irregularity with the percent of teeth being over prepared.
CONCLUSIONS: Orthodontic treatment time reduced crowding and amount of variance of labial preparation. Little's index of irregularity is a significant predictor of preparation depth and coefficient of variance in preparation depth.
Since the introduction of porcelain veneers as a treatment modality to esthetically change the appearance of teeth, especially anterior teeth, there has been some controversy concerning the amount of tooth reduction recommended to restore these teeth. One specific indication for porcelain veneers has been to correct tooth position and alignment through tooth preparation. The most predictable adhesion interface between veneer and tooth is with intra-enamel preparations. For some cases where anterior teeth are rotated or crowded, tooth preparation in critical areas can end in dentin, which can compromise the durability of the veneer. It is not unusual for patients desiring a change in the appearance for their smile to select porcelain veneers for esthetic treatment to avoid orthodontic treatment.
This well-designed and executed research study investigated whether complete or partial orthodontic alignment will significantly preserve enamel allowing for a more minimally invasive porcelain veneer preparation design. The results reflect significant data collection and evaluation to draw a conclusion. For any given patient, a clinician must ask the question: Is it prudent to wait one year to correct anterior crowding to preserve tooth structure and minimize over-preparation for veneers? From this study, the conclusion supports orthodontic treatment to preserve enamel. Clinicians should evaluate each patient on a case-by-case basis to make recommendations for pre-treatment orthodontic evaluation.
About the Authors
Howard E. Strassler, DMD
Professor, Division of Operative Dentistry
Department of Endodontics, Prosthodontics and Operative Dentistry
University of Maryland Dental School