title: Parallel post-space preparation in different tooth types ex vivo: deviation from the canal centre and remaining dentine thickness.
abstract: OBJECTIVE
  To determine the deviation of parallel-sided twist-drills during post-channel preparation and relate this to tooth type and position.
  
  
  METHODS
  Human teeth with single root canals were selected: maxillary second premolars (group i); maxillary lateral incisors (group ii); mandibular canines (group iii); mandibular first premolars (group iv; all groups n = 16). The teeth were reduced to 17 mm length by sectioning the crown, and the root canals prepared and filled. Microradiographs were made in two directions. The teeth were individually embedded in a gypsum jaw and placed in a phantom head. Two operators performed parallel post-space preparation (12 mm length, 1.25 mm diameter) to the following protocol: gutta-percha removal with Gates Glidden drills numbers 2 and 3 and post-space enlargement with parallel drills numbers 3, 4 and 5, consecutively. Subsequently, microradiographs were re-exposed. The original and post-operative microradiographs were digitized and superimposed, and deviation of the post-space from the filled canal and remaining dentine thickness measured.
  
  
  RESULTS
  Overall, the mean deviation was 0.07 mm to the mesial (95% CI: 0.01-0.12), and 0.27 mm to the buccal (95% CI: 0.18-0.35). Group ii had significantly more buccal deviation than other groups (P = 0.004-0.008). A remaining dentine thickness of <0.5 mm occurred 16 times in 14 teeth, and of <1 mm occurred 97 times in 52 teeth.
  
  
  CONCLUSIONS
  Deviation during parallel post-preparation was common, predominantly in mesial and buccal directions, especially in maxillary incisors. This deviation increased the risk of perforation considerably.
authors: Academic Center Oral Health Groningen, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands. m.c.d.n.j.m.huysmans@med.umcg.nl
authors: M C D N J M
authors: MC
authors: Huysmans
authors: M H J
authors: MH
authors: Klein
authors: G F
authors: GF
authors: Kok
authors: J M
authors: JM
authors: Whitworth
mesh_terms: D000704:Analysis of Variance; D003786:Dental Pulp Cavity / Q000000981:diagnostic imaging; D003804:Dentin / Q000033:anatomy & histology / Q000601:surgery; D006801:Humans; D008852:Microradiography / Q000379:methods; D011176:Post and Core Technique; D018915:Root Canal Preparation / Q000295:instrumentation / Q000379:methods*; D012390:Root Canal Therapy / Q000295:instrumentation / Q000379:methods; D018709:Statistics, Nonparametric