title: Dimensional accuracy of two rubber base impression materials as a function of spacer design and techniques in custom trays for fixed partial dentures.
abstract: BACKGROUND
  A prostheses can't be better than the cast over which it has been fabricated. To make accurate casts, accurate impressions are mandatory. To get an accurate and dimensionally stable impression, various techniques and materials have been advocated. This study compares the most commonly used techniques and materials for dimensional accuracy. Two types of spacers were designed to compare the addition silicon and polyether and their techniques.
  
  
  METHODS
  A metal die was used to make the impressions. A total of 60 impressions were made using multiple mix and monophasic techniques for addition silicon and polyether in custom trays. A travelling microscope was used to measure the dimensional accuracy of die stone casts retrieved from impressions.
  
  
  RESULTS
  The results were compared using paired t test and SPSS software. The study was highly significant (p < 0.001). The polyether was more accurate than the addition silicon and spacer design I (adapted to the edentulous area) was more accurate than the design II (spacer over the abutments, not adapted to edentulous area). The multiple mix technique was more accurate than the monophasic for addition silicon.
  
  
  CONCLUSIONS
  The combination of multiple mix technique with spacer design I for addition silicon gave the best accurate results.
authors: Graded Specialist (Prosthodontics), Department of Dental Surgery, Armed Forces Medical College, Pune 40, India.
authors: Pankaj
authors: P
authors: Kaushik
authors: Associate Professor, Department of Dental Surgery, Armed Forces Medical College, Pune-40, India.
authors: R K
authors: RK
authors: Dhiman
authors: Associate Professor, Department of Dental Surgery, Armed Forces Medical College, Pune-40, India.
authors: Dinesh
authors: D
authors: Kumar
keywords: Addition silicon; Dimensional accuracy; Polyether; Rubber base