title: The impact of post preparation on the residual dentin thickness of maxillary molars.
abstract: BACKGROUND
  The oval-shaped palatal roots of maxillary molars usually have smaller cross-sectional diameter in the buccolingual direction. However, the effect of parallel-sided post preparation on the remaining dentin thickness of root canal walls is unknown.
  
  
  OBJECTIVE
  The purpose of this study was to investigate, in vitro, the residual dentin thickness (RDT) of palatal roots in maxillary molars after various intracanal procedures for post placement, and to determine the risk of root canal perforation or weakening on different root canal walls at 2 levels, coronal and apical.
  
  
  METHODS
  Fifteen extracted first maxillary molars exhibiting radiographic mesiodistal root canal widths ranging from 3.8 to 4.2 mm, measured at 5 mm from the apex, were selected from a pool of teeth. The teeth were horizontally sectioned at 2 levels, coronal and apical, after being embedded in acrylic resin with the aid of a metal index, allowing identical repositioning of the sectioned parts throughout the study. Each sectioned surface was photographed with a digital camera coupled to a microscope. The palatal roots were subsequently prepared for post placement as follows: endodontic preparation up to file K50, Largo 3 and 4 drills, and ParaPost 4.5 and 5.0. Cross-sections were rephotographed after each step. Image J software was used to measure the RDT of each root wall at both levels, and data were further analyzed with a 3-way ANOVA/General Linear Model (GLM) for repeated measures. The post-hoc Tukey's range test was used to calculate differences in RDT among the 4 root walls at each root level (α=.05).
  
  
  RESULTS
  A significant difference was observed among the intracanal procedures (P<.001). At the apical level, RDT was significantly lower after ParaPost preparation than at the coronal level (P=.009). Buccal and palatal walls displayed significantly lower RDT than the mesial and distal walls at both levels (P=.004).
  
  
  CONCLUSIONS
  Intracanal preparation up to ParaPost 5.0 increased the risk of perforation or weakening of the buccal and palatal walls, especially at the apical level.
authors: Post Graduation Department, School of Dentistry, University Center of Maranhão-UniCeuma, São Luís, MA, Brazil. erickmsouza@uol.com.br
authors: Erick Miranda
authors: EM
authors: Souza
authors: Luciano Maurício
authors: LM
authors: do Nascimento
authors: Etevaldo Matos
authors: EM
authors: Maia Filho
authors: Cláudia Maria Coelho
authors: CM
authors: Alves
mesh_terms: D000704:Analysis of Variance; D017267:Dental Prosthesis Design; D003786:Dental Pulp Cavity / Q000033:anatomy & histology / Q000601:surgery; D003804:Dentin / Q000033:anatomy & histology* / Q000601:surgery; D006801:Humans; D008437:Maxilla; D008963:Molar / Q000033:anatomy & histology* / Q000601:surgery; D011176:Post and Core Technique / Q000009:adverse effects / Q000295:instrumentation*; D018915:Root Canal Preparation / Q000009:adverse effects / Q000379:methods*; D014092:Tooth Root / Q000033:anatomy & histology / Q000293:injuries / Q000601:surgery*