title: Measurement of total occlusal convergence of 3 different tooth preparations in 4 different planes by dental students.
abstract: BACKGROUND
  Total occlusal convergence of crown preparation is an important didactic and clinical concept in dental education.
  
  
  OBJECTIVE
  The purpose of this study was to compare the discrepancy between the total occlusal convergence of dental students' typodont crown preparations and the ideal range (4 to 10 degrees) in 3 different regions of the mouth and in 4 different planes of the teeth.
  
  
  METHODS
  The dental students of the Class of 2012 at Harvard School of Dental Medicine were asked to prepare typodont teeth for crowns on 3 different teeth, the maxillary left central incisor (ceramic), mandibular left first molar (complete metal), and mandibular left first premolar (metal ceramic), during their third year preclinical summative examination and the Comprehensive Clinical Examination in their fourth year. Eighteen students prepared 3 teeth in their third and fourth years, whereas 19 students participated only in their fourth year, for a total of 55 sets of 3 teeth. By using custom fit die bases to reproduce the position, a novel procedure of measuring each tooth was accomplished in 4 different planes: the faciolingual, mesiodistal, mesiofacial-distolingual, and mesiolingual-distofacial. The total occlusal convergence of each image was measured with a computer screen protractor. The gingival 2 mm of the axial wall was used to determine the taper of each wall. Linear mixed model analysis was used to estimate and compare the total occlusal convergences of different teeth and planes (α=.05). Bonferroni corrections were used to adjust for post hoc multiple comparisons.
  
  
  RESULTS
  The mean total occlusal convergence varied by tooth and plane (2-way interaction; P<.001). For the first molar, dental students excessively tapered in all 4 planes; the model-predicted 99% CIs for the total occlusal convergence were as follows: faciolingual (12.7, 19.4), mesiodistal (14.0, 19.3), mesiofacial-distolingual (13,4, 19.4), and mesiolingual-distofacial (13.7, 19.1). For the central incisor, 99% CIs for the total occlusal convergence were (15.9, 24.4) for the faciolingual measurement, providing strong evidence of excessive tapering, and (4.1, 8.0) for the mesiodistal measurement, which was within the ideal total occlusal convergence range. The mesiofacial-distolingual and mesiolingual-distofacial planes in the central incisor and all 4 planes in the first premolar had mean total occlusal convergences that exceeded 10 degrees; however, excessive tapering could not be statistically established, because their CIs included values within the ideal range.
  
  
  CONCLUSIONS
  The present study found significant evidence of excessive tapering in a study comparing the total occlusal convergence values of crown preparations with those of the ideal preparation for 3 different teeth in 4 different planes. The total occlusal convergence for the molar preparations had the highest mean values.
authors.affiliation: Resident, Department of Orthodontics, University of California-San Francisco, San Francisco, Calif.
authors.forename: Stephan S
authors.initials: SS
authors.lastname: Yoon
authors.affiliation: Resident and Post-doctoral Fellow, Department of Prosthodontics, Harvard School of Dental Medicine, Boston, Mass.
authors.forename: Chan
authors.initials: C
authors.lastname: Cheong
authors.affiliation: Research Professor, Department of Biostatistics, School of Public Health, University of North Carolina at Chapel Hill, Chapel Hill, NC.
authors.forename: John
authors.initials: J
authors.lastname: Preisser
authors.affiliation: Assistant Professor, Department of Oral and Maxillofacial Surgery, Korea University Anam Hospital, Seoul, South Korea.
authors.forename: Sangho
authors.initials: S
authors.lastname: Jun
authors.affiliation: Section Head of Maxillofacial Prosthodontics, Cleveland Clinic Foundation, Cleveland, Ohio.
authors.forename: Brian M
authors.initials: BM
authors.lastname: Chang
authors.affiliation: Professor and Chairman, Department of Prosthodontics, School of Dentistry, University of North Carolina at Chapel Hill, Chapel Hill, NC. Electronic address: robert_wright@dentistry.unc.edu.
authors.forename: Robert F
authors.initials: RF
authors.lastname: Wright
mesh_terms: D001641:Bicuspid; D003442:Crowns / Q000706:statistics & numerical data*; D003722:Dental Alloys / Q000737:chemistry; D003776:Dental Porcelain / Q000737:chemistry; D004497:Education, Dental; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D007180:Incisor; D008348:Manikins; D016876:Metal Ceramic Alloys / Q000737:chemistry; D008963:Molar; D010781:Photography / Q000379:methods; D011476:Prosthodontics / Q000193:education; D013335:Students, Dental; D019231:Tooth Preparation, Prosthodontic / Q000706:statistics & numerical data*; D014093:Tooth, Artificial
chemical_list: D003722:Dental Alloys; D016876:Metal Ceramic Alloys; D003776:Dental Porcelain