title: Evaluation of several protocols for the application of ultrasound during the removal of cast intraradicular posts cemented with zinc phosphate cement.
abstract: OBJECTIVE
  To evaluate several protocols for the application of ultrasound during removal of cast posts with varying core configurations cemented with zinc phosphate.
  
  
  METHODS
  Sixty maxillary canines were distributed into three groups (n = 20): group 1 - core with 5 mm diameter/height and post diameter of 1.3 mm; groups 2 and 3 - core with the same diameter as the post (1.3 mm) and heights of 5 mm and 3 mm, respectively. Posts/cores were cemented using a standard technique with zinc phosphate cement. Each group was divided into two subgroups according to the ultrasonic vibration mode: point vibration - ultrasonic vibration applied to the core surface for 5 s, on each face totalling 25 s; alternate vibration - intermittent application of ultrasonic vibration for 10 s to the labial and lingual surfaces, 10 s to the mesial and distal surfaces and 5 s to the incisal surface, totalling 25 s. The specimens were submitted to the tensile test using an Instron machine (1 mm min(-1)) and results were analysed by anova and t-test. The failure type was also analysed.
  
  
  RESULTS
  Statistical analysis showed significant differences between groups relating to the core preparations (P < 0.05). The lowest mean values of traction force were obtained for group 3 (46.1 +/- 7.7 N), followed by group 2 (89.0 +/- 2.7 N) and group 1 (160.4 +/- 7.5 N). Regarding ultrasonic vibration, the lowest mean was observed with alternate vibration (81.1 +/- 10.1 N), which was significantly lower than the point vibration (115.9 +/- 9.5 N) (P < 0.05). Cohesive failure occurred in all cases.
  
  
  CONCLUSIONS
  A reduction in core diameter/height and intermittent ultrasonic application improved the removal of cast posts cemented with zinc phosphate.
authors.affiliation: School of Dentistry, Federal University of Amazonas-UFAM, Manaus, AM, Brazil.
authors.forename: A D B
authors.initials: AD
authors.lastname: Garrido
authors.forename: A G
authors.initials: AG
authors.lastname: Oliveira
authors.forename: J E V
authors.initials: JE
authors.lastname: Osório
authors.forename: Y T C
authors.initials: YT
authors.lastname: Silva-Sousa
authors.forename: M D
authors.initials: MD
authors.lastname: Sousa-Neto
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry; D002484:Cementation; D002858:Chromium Alloys / Q000737:chemistry; D003481:Cuspid / Q000473:pathology; D017005:Dental Debonding / Q000379:methods*; D017267:Dental Prosthesis Design; D003799:Dental Stress Analysis / Q000295:instrumentation; D006801:Humans; D008422:Materials Testing; D011176:Post and Core Technique / Q000295:instrumentation*; D018915:Root Canal Preparation / Q000295:instrumentation / Q000379:methods; D013314:Stress, Mechanical; D013499:Surface Properties; D014465:Ultrasonics; D014732:Vibration; D015036:Zinc Phosphate Cement / Q000737:chemistry*
chemical_list: D002858:Chromium Alloys; D015036:Zinc Phosphate Cement; D000537:Aluminum Oxide