title: Fracture resistance of root filled premolar teeth restored with direct composite resin with or without cusp coverage.
abstract: OBJECTIVE
  To evaluate the fracture resistance and fracture patterns of root filled maxillary first premolar teeth (with mesio-occlusal cavity preparation) restored with several composite restoration designs.
  
  
  METHODS
  One hundred extracted sound human maxillary first premolars were randomly divided into five groups. Group 1 remained untreated (negative control). Conventional root canal treatment with additional mesial-occlusal cavity preparation was carried out on teeth in groups 2-5. In group 2, the teeth were restored intra-coronally with direct composite resin (positive control). In group 3, the palatal cusps of the teeth were reduced, and the cavities were restored with composite resin covering the palatal cusp (partial coverage). In group 4, the buccal and palatal cusps along with the distal marginal ridges were reduced; the cavities and cusps were restored with composite resin (conventional full coverage). In group 5, the buccal and palatal cusps were reduced but the distal marginal ridges were conserved. The cavities and the cusps were restored with composite resin (modified full coverage). All teeth were subjected to a progressive compressive loading parallel to their longitudinal axis until fracture. Fracture resistance was analysed using the one-way ANOVA and Fisher's LSD test. Fracture patterns were analyzed with chi-square test. The significance level was set at 0.05.
  
  
  RESULTS
  The fracture resistance (mean ± SD) of groups 1-5 was 1131 ± 207N, 904 ± 184N, 927 ± 224N, 1095 ± 289N and 1085 ± 243N, respectively (groups 1, 4, 5 > groups 2, 3; P = 0.004). Cusp fractures were recorded as the fracture pattern in 20 (100%), 19 (95%), 16 (80%), 8 (40%) and 12 (60%) premolars in groups 1-5, respectively (groups 1, 2 > groups 4, 5; group 3 > group 4; P < 0.001).
  
  
  CONCLUSIONS
  When direct composite resin was used to restore root filled maxillary first premolar teeth involving a proximal surface, those restored with full-coverage designs had greater fracture resistance.
authors.affiliation: Department of Cariology and Endodontology, Peking University School and Hospital of Stomatology, Beijing, China.
authors.forename: K X
authors.initials: KX
authors.lastname: Xie
authors.forename: X Y
authors.initials: XY
authors.lastname: Wang
authors.forename: X J
authors.initials: XJ
authors.lastname: Gao
authors.forename: C Y
authors.initials: CY
authors.lastname: Yuan
authors.forename: J X
authors.initials: JX
authors.lastname: Li
authors.forename: C H
authors.initials: CH
authors.lastname: Chu
mesh_terms: D001641:Bicuspid / Q000473:pathology / Q000503:physiopathology*; D003188:Composite Resins / Q000737:chemistry*; D003737:Dental Cavity Preparation / Q000145:classification; D003764:Dental Materials / Q000737:chemistry*; D017267:Dental Prosthesis Design; D003793:Dental Restoration, Permanent / Q000145:classification*; D017220:Dentin-Bonding Agents / Q000737:chemistry; D005899:Glass Ionomer Cements / Q000737:chemistry; D006801:Humans; D008437:Maxilla; D019279:Resin Cements / Q000737:chemistry; D012117:Resins, Synthetic / Q000737:chemistry; D012389:Root Canal Obturation / Q000379:methods; D013314:Stress, Mechanical; D019228:Tooth Crown / Q000473:pathology*; D014082:Tooth Fractures / Q000145:classification / Q000503:physiopathology*; D019553:Tooth, Nonvital / Q000503:physiopathology / Q000628:therapy*
chemical_list: D003188:Composite Resins; D003764:Dental Materials; D017220:Dentin-Bonding Agents; C079765:Fuji II LC cement; D005899:Glass Ionomer Cements; D019279:Resin Cements; D012117:Resins, Synthetic; C084018:Scotchbond Multi-Purpose; C121818:Tetric ceram