title: Impact of interproximal groove placement and remaining coronal tooth structure on the fracture resistance of endodontically treated maxillary anterior teeth.
abstract: OBJECTIVE
  This in vitro study investigated the effect of grooves, remaining tooth structure, and their combination on tooth fracture resistance of endodontically treated anterior teeth with cast dowel and cores.
  
  
  METHODS
  Sixty extracted maxillary anterior teeth of similar dimensions were endodontically treated and then randomly divided into three groups of 20 teeth each. The teeth in the first group were cut horizontally at the widest part of their anatomical crowns. Three hundred and sixty degree 1 and 2 mm axial walls for ferrule effect were provided for the teeth in the second and the third groups, respectively. Cast dowel and cores were fabricated for all teeth. Each group was then subdivided in two groups: one with no grooves and another with mesial and distal grooves. Hence, six groups were created as follows: (1) teeth with no remaining coronal tooth structure and no grooves (group A-control); (2) teeth with no remaining coronal tooth structure, with mesial and distal grooves (group B); (3) teeth with 1 mm remaining coronal tooth structure, with no grooves (group C); (4) teeth with 1 mm remaining coronal tooth structure, with mesial and distal grooves (group D); (5) teeth with 2 mm remaining coronal tooth structure and no grooves (group E); and (6) teeth with 2 mm remaining coronal tooth structure, with mesial and distal grooves (group F). Complete cast crowns were then fabricated for all teeth. A universal testing machine applied controlled loads to the teeth at a crosshead speed of 2.54 mm/min at an angle of 130 degrees to the long axes of the teeth until failure occurred. The loads were applied 2 mm lower than the incisal edges of the specimens. Descriptive statistics, one-way ANOVA (alpha= 0.05) and Tukey's honestly significant difference (HSD) tests were used to determine the effect of failure loads among the tested groups (alpha= 0.05).
  
  
  RESULTS
  The mean failure loads were (N): group A (control), 151.21 +/- 38.18; group B, 221.53 +/- 107.03; group C, 295.35 +/- 81.92; group D, 270.20 +/- 76.01; group E, 491.70 +/- 180.36; group F, 432.67 +/- 193.83. Group E presented the highest failure load and group A (control) the lowest.
  
  
  CONCLUSIONS
  The inclusion of interproximal grooves on the cast dowel and cores of endodontically treated anterior teeth with 1-2 mm of remaining coronal tooth structure does not significantly lower the failure threshold.
authors.affiliation: Division of Graduate and Postgraduate Prosthodontics, Tufts University School of Dental Medicine, Boston, MA, USA.
authors.forename: Hyunki
authors.initials: H
authors.lastname: Cho
authors.forename: Konstantinos X
authors.initials: KX
authors.lastname: Michalakis
authors.forename: Yeongjeong
authors.initials: Y
authors.lastname: Kim
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hirayama
mesh_terms: D002484:Cementation; D003735:Dental Casting Technique; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D005899:Glass Ionomer Cements; D006801:Humans; D007180:Incisor / Q000503:physiopathology*; D011176:Post and Core Technique; D019228:Tooth Crown / Q000473:pathology; D014082:Tooth Fractures / Q000517:prevention & control*; D019231:Tooth Preparation, Prosthodontic; D019553:Tooth, Nonvital / Q000503:physiopathology*
chemical_list: D005899:Glass Ionomer Cements