title: Evaluation of the friction force generated by monocristalyne and policristalyne ceramic brackets in sliding mechanics.
abstract: OBJECTIVE
  To evaluate and compare "in vitro" the maximum friction force generated by three types of esthetic brackets, two types of polycrystalline conventional ceramic brackets (20/40 and InVu) and one type of sapphire monocrystalline bracket (Radiance) in dry and artificial saliva wet settings. Also, to evaluate the influence exerted by artificial saliva on the friction forces of those brackets.
  
  
  METHODS
  Tests were performed in dry and artificial saliva wet setting (Oral Balance) by using an EMIC DL 10000 testing machine, simulating a 2 mm slide of 0.019 x 0.025-in rectangular stainless steel wires over the pre-angulated and pre-torqued (right superior canine, Roth prescription, slot 0.022 x 0.030-in) brackets (n = 18 for each bracket). In order to compare groups in dry and wet settings, the ANOVA was used. For comparisons related to the dry versus wet setting, the student t test was used for each group.
  
  
  RESULTS
  The results showed that in the absence of saliva the Radiance monocrystalline brackets showed the highest friction coefficients, followed by the 20/40 and the InVu polycrystalline brackets. In tests with artificial saliva, the Radiance and the 20/40 brackets had statistically similar friction coefficients and both were greater than that presented by the InVu brackets. The artificial saliva did not change the maximum friction force of the Radiance brackets, but, for the others (20/40 and InVu), an increase of friction was observed in its presence.
  
  
  CONCLUSIONS
  The InVu brackets showed, in the absence and in the presence of saliva, the lowest friction coefficient.
authors.affiliation: Dental Clinic, UFJF.
authors.forename: Roberta Ferreira
authors.initials: RF
authors.lastname: Pimentel
authors.forename: Roberto Sotto Maior Fortes
authors.initials: RS
authors.lastname: de Oliveira
authors.forename: Maria das Graças Afonso Miranda
authors.initials: Md
authors.lastname: Chaves
authors.forename: Carlos Nelson
authors.initials: CN
authors.lastname: Elias
authors.forename: Marco Abdo
authors.initials: MA
authors.lastname: Gravina
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry*; D000704:Analysis of Variance; D002516:Ceramics / Q000737:chemistry*; D003481:Cuspid; D003799:Dental Stress Analysis / Q000295:instrumentation / Q000379:methods*; D017276:Friction; D006801:Humans; D008422:Materials Testing / Q000295:instrumentation / Q000379:methods*; D016910:Orthodontic Brackets; D009969:Orthodontic Wires; D012464:Saliva, Artificial / Q000737:chemistry*; D013193:Stainless Steel / Q000737:chemistry; D013499:Surface Properties
chemical_list: D012464:Saliva, Artificial; D013193:Stainless Steel; D000537:Aluminum Oxide
keywords: Biomechanics; Biomedical and dental materials; Friction; In vitro; Orthodontic brackets