title: Fracture resistance of weakened bovine teeth after long-term use of calcium hydroxide.
abstract: OBJECTIVE
  In some parts of the world, revascularization may not be the most feasible treatment option for necrotic immature teeth. Therefore, apexification remains the most widely utilized treatment option for these cases. This study aimed to evaluate the fracture resistance of weakened bovine tooth roots treated with various irrigant solutions as well as long-term application of calcium hydroxide intracanal medication (ICM).
  
  
  METHODS
  One hundred seventy bovine teeth were randomly divided into three experimental groups (n = 50) and two control groups (n = 10). Group SS was irrigated with physiologic solution; group CHX was treated with 2% chlorhexidine gel and group NaOCl was irrigated with 1% sodium hypochlorite. After instrumentation, root canals were dressed with calcium hydroxide and evaluated at different periods (15, 60, 90, 180, and 360 days). The specimens were loaded at a 45° angle to measure fracture resistance through the use of an EMIC test machine.
  
  
  RESULTS
  A decrease in fracture resistance was observed during the time of ICM dressing. The highest values of fracture resistance were observed in group SS with 15 days of ICM, not differing from the control group. Irrigation with NaOCl associated with ICM for 15 days presented the lowest fracture resistance; however, a statistically significant difference was not observed when compared with SS and CHX in the same time period. In longer periods of exposure to ICM (180 and 360 days), root canals irrigated with NaOCl and CHX showed significantly lower fracture resistance than SS (P < 0.05).
  
  
  CONCLUSIONS
  Apexification with periodic changes of calcium hydroxide medicament leads to weakness of the teeth independent of the irrigation solution used.
authors.affiliation: São Jose dos Campos Dental School, São Paulo State University, UNESP, São Paulo, Brazil.
authors.forename: Marcia Carneiro
authors.initials: MC
authors.lastname: Valera
authors.affiliation: São Jose dos Campos Dental School, São Paulo State University, UNESP, São Paulo, Brazil.
authors.forename: Maria Tereza Pedrosa
authors.initials: MT
authors.lastname: Albuquerque
authors.affiliation: Piracicaba Dental School, State University of Campinas, UNICAMP, São Paulo, Brazil.
authors.forename: Mayra Cristina
authors.initials: MC
authors.lastname: Yamasaki
authors.affiliation: São Jose dos Campos Dental School, São Paulo State University, UNESP, São Paulo, Brazil.
authors.forename: Flávia Nicolle Stefani
authors.initials: FN
authors.lastname: Vassallo
authors.affiliation: São Jose dos Campos Dental School, São Paulo State University, UNESP, São Paulo, Brazil.
authors.forename: Denise Almeida E Silva Alves
authors.initials: DA
authors.lastname: da Silva
authors.affiliation: Dentistry Department, Endodontics Area, Federal University of Sergipe, Lagarto, Brazil.
authors.forename: Juliana Yuri
authors.initials: JY
authors.lastname: Nagata
mesh_terms: D000818:Animals; D056624:Apexification; D002126:Calcium Hydroxide / Q000494:pharmacology*; D002417:Cattle; D002710:Chlorhexidine / Q000494:pharmacology; D003799:Dental Stress Analysis; D066298:In Vitro Techniques; D011897:Random Allocation; D012387:Root Canal Filling Materials / Q000494:pharmacology; D012388:Root Canal Irrigants / Q000494:pharmacology*; D018915:Root Canal Preparation / Q000379:methods*; D012973:Sodium Hypochlorite / Q000494:pharmacology; D014082:Tooth Fractures / Q000517:prevention & control*
chemical_list: D012387:Root Canal Filling Materials; D012388:Root Canal Irrigants; D012973:Sodium Hypochlorite; D002126:Calcium Hydroxide; D002710:Chlorhexidine
keywords: calcium hydroxide; fracture resistance; irrigant solution; permanent tooth; prognosis; root fracture