title: Dentin exposure in tooth preparations for porcelain veneers: a pilot study.
abstract: BACKGROUND
  The various clinical techniques available for even reduction of a tooth surface to receive a porcelain veneer restoration do not produce a consistently even conservative reduction. In addition, it is not known which technique is most conservative of enamel.
  
  
  OBJECTIVE
  The purpose of this pilot study was to assess the effectiveness of 3 clinical techniques, namely, dimple, depth groove, and freehand, in producing an intraenamel preparation. The relation between overpreparation beyond the commonly accepted depth of preparation of 0.5 mm and dentin exposure was also examined.
  
  
  METHODS
  A single operator prepared 3 groups of 5 extracted maxillary central incisors to a depth of 0.5 mm using dimple, depth-groove, and freehand methods of tooth preparation. The prepared teeth were scanned using an x-ray microtomography scanner. The reconstructed images were studied using software that provided a volume-rendering routine so that, by choosing suitable x-ray linear attenuation coefficient thresholds, enamel (2.78 cm(-1) at 40 keV) and dentin (1.63 cm(-1) at 40 keV) surfaces could be viewed. The percentage area of enamel conserved was analyzed from these images. Coordinate metrology was used to produce color-coded images depicting the depth of preparation. The Kruskal-Wallis test was used to determine the statistical significance (alpha=.05) in the difference between the mean percentage area of enamel conserved in the 3 technique groups. The coordinate metrology and x-ray microtomography images were visually compared to study the correlation between overpreparation and dentin exposure.
  
  
  RESULTS
  The Kruskal-Wallis test did not demonstrate significant difference (P=.07) between the 3 techniques in conserving enamel. However, the dimple technique showed a greater trend to retaining a larger mean percentage area of enamel (77.5% +/- 14.2) compared to depth-groove (50.1% +/- 17.5) and freehand (76.8% +/- 24.4) techniques. Preparation depth in the range of 0.4 to 0.6 mm was largely seen to be intraenamel, except in the cervical region.
  
  
  CONCLUSIONS
  Within the limitations of this pilot study, the 3 different techniques tested did not differ significantly in conserving enamel.
authors.affiliation: Centre for Adult Oral Health, Queen Mary's School of Medicine and Dentistry, London, UK. g.p.cherukara@qmul.ac.uk
authors.forename: George P
authors.initials: GP
authors.lastname: Cherukara
authors.forename: Graham R
authors.initials: GR
authors.lastname: Davis
authors.forename: Kevin G
authors.initials: KG
authors.lastname: Seymour
authors.forename: Lifong
authors.initials: L
authors.lastname: Zou
authors.forename: Dayananda Y D
authors.initials: DY
authors.lastname: Samarawickrama
mesh_terms: D003776:Dental Porcelain; D003801:Dental Veneers; D003804:Dentin; D006801:Humans; D007180:Incisor; D010865:Pilot Projects; D018709:Statistics, Nonparametric; D014056:Tomography, X-Ray / Q000379:methods; D019231:Tooth Preparation, Prosthodontic / Q000009:adverse effects* / Q000379:methods*
chemical_list: D003776:Dental Porcelain