title: Histological evaluation of the effectiveness of increased apical enlargement for cleaning the apical third of curved canals.
abstract: OBJECTIVE
  To evaluate the influence of apical size on cleaning of the apical third of curved canals prepared with rotary instruments.
  
  
  METHODS
  Forty-four mesiobuccal canals of maxillary molars teeth were instrumented to different apical sizes (30, 0.02; 35, 0.02; 40, 0.02; 45, 0.02) using a crown-down technique. After canal preparation, the apical thirds of the roots were submitted to histological processing and examination. The specimens were analysed at 40× magnification and the images were submitted to morphometric analysis with an integration grid to evaluate the percentage of debris and uninstrumented root canal walls. The action of the instruments on the root canal walls was assessed based on the surface regularity, abrupt change on the continuity of root canal walls, and partial or total pre-dentine removal. The results were statistically compared using one-way anova with post hoc Tukey test. Pearson's correlation was performed to identify potential correlations between values.
  
  
  RESULTS
  The percentage of uninstrumented root canal dentine was higher when apical enlargement was performed with instruments 30, 0.02 taper (55.64 ± 4.62%) and 35, 0.02 taper (49.03 ± 5.70%) than with instruments 40, 0.02 taper (38.08 ± 10.44%) and 45, 0.02 taper (32.65 ± 8.51%) (P < 0.05). More debris were observed when apical enlargement was performed with instruments 30, 0.02 taper (34.62 ± 9.49%) and 35, 0.02 taper (25.33 ± 7.37%) (P < 0.05). There was a significant correlation between the amount of remaining debris and the perimeter of uninstrumented root canal dentine (r = 0.9130, P < 0.001).
  
  
  CONCLUSIONS
  No apical enlargement size allowed the root canal walls to be prepared completely. Apical third cleanliness could be predicted by instrument diameter.
authors: Department of Endodontics, Faculty of Dentistry, University of Ribeirão Preto, Ribeirão Preto, São Paulo, Brazil.
authors: V J
authors: VJ
authors: Fornari
authors: Y T C
authors: YT
authors: Silva-Sousa
authors: J R
authors: JR
authors: Vanni
authors: J D
authors: JD
authors: Pécora
authors: M A
authors: MA
authors: Versiani
authors: M D
authors: MD
authors: Sousa-Neto
mesh_terms: D003722:Dental Alloys / Q000737:chemistry; D003754:Dental High-Speed Equipment; D003786:Dental Pulp Cavity / Q000473:pathology*; D003804:Dentin / Q000473:pathology; D004867:Equipment Design; D006801:Humans; D008422:Materials Testing; D008963:Molar / Q000473:pathology; D009532:Nickel / Q000737:chemistry; D012388:Root Canal Irrigants / Q000627:therapeutic use; D018915:Root Canal Preparation / Q000295:instrumentation / Q000379:methods*; D016369:Smear Layer; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry; D019227:Tooth Apex / Q000473:pathology*
chemical_list: D003722:Dental Alloys; D012388:Root Canal Irrigants; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium