title: Effects of different cusp coverage restorations on the fracture resistance of endodontically treated maxillary premolars.
abstract: BACKGROUND
  Cusp coverage restorations for the restoration of endodontically treated teeth represent a conservative approach in terms of function and esthetics. However, limited scientific data are available regarding the optimum reduction design and thicknesses.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to evaluate the fracture resistance and fracture patterns of cusp coverage restorations with different cusp reduction designs and reduction thicknesses on endodontically treated maxillary premolars (ETMPs) with mesio-occluso-distal (MOD) cavities.
  
  
  METHODS
  One hundred sixty-five extracted intact human maxillary premolars were divided into 11 groups: G1-10 (test groups) and G11 (intact group). In the test groups, all of the teeth were restored with composite resin after canal treatments with MOD cavities. However, the cusps of the G1-9 teeth were reduced with combinations of different thicknesses (1.5, 2.5, and 3.5 mm) and designs (beveled, horizontal, and anatomic). The specimens were subjected to 10(5) cycles of 50 N mechanical loading. Next, the specimens were subjected to a compressive load at a crosshead speed of 0.5 mm/min until fracture. The fractured specimens were analyzed to determine the fracture pattern. Two-way ANOVA followed by the Fisher least significant difference (LSD) test was used to analyze the interaction between groups.
  
  
  RESULTS
  The fracture resistance values increased with increases in the cusp reductions. The fracture resistance values of the G6 (2.5 mm, anatomic) and G9 (3.5 mm, anatomic) groups were significantly greater than that of the MOD group. However, the G6, G8 (3.5 mm, horizontal), and G9 groups were comparable with G11. The highest restorable fracture rates were observed in G6 and G9.
  
  
  CONCLUSIONS
  Cusp reduction design and thickness influenced the fracture resistance and fracture patterns of cusp coverage restorations of ETMPs with MOD cavities. The teeth restored with anatomic cusp reduction designs with reduction thicknesses of at least 2.5 mm exhibited greater fracture resistance and more frequent restorable fractures.
authors.affiliation: Research Assistant, Department of Restorative Dentistry, Faculty of Dentistry, Karadeniz Technical University, Trabzon, Turkey. Electronic address: tugbaserinkalay@hotmail.com.
authors.forename: Tugba
authors.initials: T
authors.lastname: Serin Kalay
authors.affiliation: Professor, Department of Restorative Dentistry, Faculty of Dentistry, Karadeniz Technical University, Trabzon, Turkey.
authors.forename: Tahsin
authors.initials: T
authors.lastname: Yildirim
authors.affiliation: Associate Professor, Department of Restorative Dentistry, Faculty of Dentistry, Selcuk University, Konya, Turkey.
authors.forename: Mustafa
authors.initials: M
authors.lastname: Ulker
mesh_terms: D001641:Bicuspid / Q000601:surgery*; D003737:Dental Cavity Preparation / Q000379:methods; D019232:Dental Restoration Failure; D003793:Dental Restoration, Permanent / Q000379:methods*; D003799:Dental Stress Analysis; D006801:Humans; D066298:In Vitro Techniques; D008437:Maxilla; D019553:Tooth, Nonvital / Q000601:surgery*