title: The impact of endodontic access on the biaxial flexure strength of dentine-bonded crown substrates - an in vitro study.
abstract: OBJECTIVE
  To investigate how preparation of a simulated access cavity into ceramic materials suitable for the manufacture of dentine-bonded crowns (DBCs) impacted on biaxial flexural strength (BFS) determined as a monolithic structure and in a more clinically representative resin-cemented form.
  
  
  METHODS
  One hundred and twenty feldspathic and 120 leucite-reinforced ceramic disc-shaped specimens were divided into eight groups (n = 30). All groups received 'fit' surface treatments representative of pre-cementation modifications and of cementation prior to preparation of a representative endodontic access cavity through the sample. BFS was determined for both 'intact' and the 'annular' disc-shaped specimens which had received simulated endodontic access. Newly reported analytical solutions were used to calculate BFS of the 'annular' specimens. Statistical analysis included two-way anovas (α = 0.05) and Weibull analysis. Fractographic examination provided insight into the fracture mechanisms.
  
  
  RESULTS
  A two-way anova identified a significant impact of material (P < 0.01) and of resin coating (P < 0.01) on the mean BFS of intact specimens. For the annular ceramic specimens, the substrate material significantly impacted on mean BFS (P < 0.01), but the effect of resin coating was dependent on the substrate type (P < 0.01).
  
  
  CONCLUSIONS
  Endodontic access cavity preparation modified the critical defect population of the all-ceramic restorative materials investigated. The strength of a predominantly glassy ceramic following endodontic access can be maintained if adhesive cementation was used; however, the beneficial effects of adhesive cementation on ceramic reinforcement were lost on leucite-reinforced ceramics following access cavity preparation. Replacement restoration for these materials would be recommended clinically following endodontic access as opposed to repair of the access cavity using a direct restorative material.
authors.affiliation: Biomaterials Unit, College of Medical and Dental Sciences, University of Birmingham School of Dentistry, Birmingham, UK.
authors.forename: R D
authors.initials: RD
authors.lastname: Kelly
authors.affiliation: Biomaterials Unit, College of Medical and Dental Sciences, University of Birmingham School of Dentistry, Birmingham, UK.
authors.forename: W M
authors.initials: WM
authors.lastname: Palin
authors.affiliation: Biomaterials Unit, College of Medical and Dental Sciences, University of Birmingham School of Dentistry, Birmingham, UK.
authors.forename: P L
authors.initials: PL
authors.lastname: Tomson
authors.affiliation: Biomaterials Unit, College of Medical and Dental Sciences, University of Birmingham School of Dentistry, Birmingham, UK.
authors.forename: O
authors.initials: O
authors.lastname: Addison
mesh_terms: D002516:Ceramics; D003442:Crowns; D003804:Dentin; D004708:Endodontics / Q000379:methods*; D066298:In Vitro Techniques
keywords: biaxial flexure strength; dental ceramic; dentine-bonded crown; endodontic access