title: Effect of frequency and amplitude of vibration on void formation in dies poured from polyvinyl siloxane impressions.
abstract: BACKGROUND
  Numerous factors are involved in making a void-free dental stone cast from a polyvinyl siloxane impression.
  
  
  OBJECTIVE
  The aim of this study was to determine whether frequency and amplitude of vibration had any effect on the formation of voids on the cast surface poured from polyvinyl siloxane impression with a mechanical model vibrator.
  
  
  METHODS
  Impressions were poured in dental stone with a mechanical model vibrator that was set at vibration frequency 3000 cycles/min (low) and 6000 cycles/min (high) by a knob. The amplitude of vibration is provided in 5 steps and remained constant for the step set on the instrument. A total of 240 casts were prepared. The vibrator was set at low frequency and 30 impressions were poured for each of the 5 steps of amplitude. The vibrator was then set at high frequency and 30 impressions were poured for each of the 5 steps of amplitude. The resultant casts were examined for the presence of surface voids under 10 x magnification.
  
  
  RESULTS
  Means for voids in all cast groups calculated for low and high vibration frequencies indicated that an increase in the amplitude of vibration caused an increase in the number of voids on the die surface.
  
  
  CONCLUSIONS
  Use of high frequency of vibration 6000 cycles/min and 0.40 mm amplitude produced significantly fewer voids (P < .0001) compared with steps 4 (0.45 mm) and 5 (0.80 mm) amplitude.
authors.affiliation: College of Dentistry, King Saud University, Riyadh, Kingdom of Saudi Arabia.
authors.forename: M A
authors.initials: MA
authors.lastname: Abdullah
mesh_terms: D000704:Analysis of Variance; D002133:Calcium Sulfate / Q000737:chemistry*; D003734:Dental Casting Investment / Q000737:chemistry*; D003735:Dental Casting Technique / Q000295:instrumentation; D003760:Dental Impression Materials / Q000737:chemistry*; D003761:Dental Impression Technique / Q000295:instrumentation*; D005069:Evaluation Studies as Topic; D011145:Polyvinyls / Q000737:chemistry*; D012833:Siloxanes / Q000737:chemistry*; D013499:Surface Properties; D014732:Vibration
chemical_list: D003734:Dental Casting Investment; D003760:Dental Impression Materials; D011145:Polyvinyls; D012833:Siloxanes; C034183:vinyl polysiloxane; D002133:Calcium Sulfate