title: Impacts of Contracted Endodontic Cavities on Instrumentation Efficacy and Biomechanical Responses in Maxillary Molars.
abstract: BACKGROUND
  Recently, we reported that in mandibular molars contracted endodontic cavities (CECs) improved fracture strength compared with traditional endodontic cavities (TECs) but compromised instrumentation efficacy in distal canals. This study assessed the impacts of CECs on instrumentation efficacy and axial strain responses in maxillary molars.
  
  
  METHODS
  Eighteen extracted intact maxillary molars were imaged with micro-computed tomographic imaging (12-μm voxel), assigned to CEC or TEC groups (n = 9/group), and accessed accordingly. Canals were instrumented (V-Taper2H; SSWhite Dental, Lakewood, NJ) with 2.5% sodium hypochlorite irrigation, reimaged, and the proportion of the modified canal wall determined. Cavities were restored with bonded composite resin (TPH-Spectra-LV; Dentsply International, York, PA). Another 28 similar molars (n = 14/group) with linear strain gauges (Showa Measuring Instruments, Tokyo, Japan) attached to mesiobuccal and palatal roots were subjected to load cycles (50-150 N) in the Instron Universal Testing machine (Instron, Canton, MA), and the axial microstrain was recorded before access and after restoration. These 28 molars and additional 11 intact molars (control) were cyclically fatigued (1 million cycles, 5-50 N, 15 Hz) and subsequently loaded to failure. Data were analyzed by the Wilcoxon rank sum and Kruskal-Wallis tests (α = 0.05).
  
  
  RESULTS
  The overall mean proportion of the modified canal wall did not differ significantly between CECs (49.7% ± 12.0%) and TECs (44.7% ± 9.0%). Relative changes in axial microstrain responses to load varied in both groups. The mean load at failure for CECs (1703 ± 558 N) did not differ significantly from TECs (1384 ± 377 N) and was significantly lower (P < .005) for both groups compared with intact molars (2457 ± 941 N).
  
  
  CONCLUSIONS
  In maxillary molars tested in vitro, CECs did not impact instrumentation efficacy and biomechanical responses compared with TECs.
authors.affiliation: MSc Endodontics Program, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Brent
authors.initials: B
authors.lastname: Moore
authors.affiliation: Division of Endodontics, School of Dental Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania.
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Verdelis
authors.affiliation: Discipline of Endodontics and Dental Research Institute, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Anil
authors.initials: A
authors.lastname: Kishen
authors.affiliation: Discipline of Prosthodontics, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Thuan
authors.initials: T
authors.lastname: Dao
authors.affiliation: MSc Endodontics Program, University of Toronto, Toronto, Ontario, Canada. Electronic address: shimon.friedman@dentistry.utoronto.ca.
authors.forename: Shimon
authors.initials: S
authors.lastname: Friedman
mesh_terms: D001696:Biomechanical Phenomena; D003188:Composite Resins; D003737:Dental Cavity Preparation / Q000295:instrumentation / Q000379:methods*; D003786:Dental Pulp Cavity; D003793:Dental Restoration, Permanent / Q000379:methods; D003799:Dental Stress Analysis; D006801:Humans; D008422:Materials Testing; D008437:Maxilla; D008963:Molar / Q000033:anatomy & histology*; D012388:Root Canal Irrigants / Q000627:therapeutic use; D018915:Root Canal Preparation / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods*; D012973:Sodium Hypochlorite / Q000627:therapeutic use; D013314:Stress, Mechanical; D019227:Tooth Apex / Q000033:anatomy & histology; D019228:Tooth Crown / Q000033:anatomy & histology; D014082:Tooth Fractures / Q000209:etiology*; D014092:Tooth Root / Q000293:injuries; D055114:X-Ray Microtomography / Q000379:methods
chemical_list: D003188:Composite Resins; D012388:Root Canal Irrigants; D012973:Sodium Hypochlorite
keywords: Endodontic cavity; fracture strength; instrumentation efficacy; minimally invasive; root strain