title: A clinical trial to compare double-arch and complete-arch impression techniques in the provision of indirect restorations.
abstract: BACKGROUND
  Anecdotal reports of use of double-arch impressions for indirect restorations suggest time and materials savings, but there is little clinical evidence to support their use.
  
  
  OBJECTIVE
  To establish whether a double-arch impression technique could produce restorations comparable with those produced by use of the complete-arch technique and to investigate reported time and material savings.
  
  
  METHODS
  Five practitioners each recruited 10 adult patients requiring a single complete veneer crown into the study. Two sets of impressions, 1 complete-arch in a stock metal tray, and 1 double-arch in a plastic double-arch tray were made for each patient in addition-polymerized silicones in a random order. The time taken for each impression was recorded along with patient's assessment of comfort, taste, and overall acceptability. One technician, who selected the impressions for the fabrication of each crown according to a predetermined scheme of randomization, fabricated all crowns. Equal numbers of crowns were made from the complete and double-arch impressions. At the time of crown placement, the accuracy of fit, occlusal harmony, and the time taken for try-in were also recorded. The weight of impression material used was measured for each impression. Data were analyzed by use of computerized statistical software (t test for equality of means) at a significance level of 95%.
  
  
  RESULTS
  The double-arch technique was faster (222 seconds [SD, 57 seconds] vs 445 seconds [SD, 87 seconds], P=.000), more comfortable (P=.025), better tasting (P=.001), and preferred by 80% of the patients (P=.000). No significant differences were found between the 2 groups for accuracy of fit, occlusion, or time taken for try-in of the restorations. The mean weight of impression material used was 39 g (SD, 10 g) for complete-arch and 20 g (SD, 7 g) for double-arch impressions, a mean difference of 19 g (P=.000).
  
  
  CONCLUSIONS
  Within the limitations of this study, double-arch impressions were found to take less time, to use less material, and to be preferred by patients. Under the conditions of this study, the resulting restorations were no less accurate than those made from complete-arch impressions.
authors.affiliation: Unit of Operative Dentistry and Odontology, University Dental Hospital of Manchester, Manchester, United Kingdom. lane@vtsurvey.com
authors.forename: D Andrew
authors.initials: DA
authors.lastname: Lane
authors.forename: Rosalind C
authors.initials: RC
authors.lastname: Randall
authors.forename: Natalie S
authors.initials: NS
authors.lastname: Lane
authors.forename: Nairn H F
authors.initials: NH
authors.lastname: Wilson
mesh_terms: D000328:Adult; D000368:Aged; D003442:Crowns; D003760:Dental Impression Materials; D003761:Dental Impression Technique; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017060:Patient Satisfaction; D011787:Quality of Health Care; D013997:Time Factors
chemical_list: D003760:Dental Impression Materials