The effect of sulcular width on the linear accuracy of impression materials in the presence of an undercut.
OBJECTIVE
This study examined the effect of gingival sulcular width, in the presence of an undercut, on the accuracy of dies poured from impressions made with different impression materials.


METHODS
Three polyvinyl siloxanes (Examix, Elite, and Express), one polyether (Permadyne), and one polysulfide (Permlastic) were used to make impressions of six metal dies. The dies were machined to simulate teeth with a chamfer preparation, root convergence, and sulci of varying widths (0.10 to 0.40 mm). The impressions were poured with type IV stone, and the resulting dies were measured under a traveling microscope at the level of the finish line. The distortion of each die was calculated.


RESULTS
The distortion ranged from 0.01% to 0.89%. All materials showed similar behavior: At the narrowest sulcular width (0.10 mm), the distortion was considerably larger (0.43% to 0.89%) than at the wider sulci (up to 0.20% in most cases). Examix (polyvinyl siloxane), Permlastic (polysulfide), and Permadyne (polyether) gave the most accurate dies for sulci 0.15 mm and wider. Express (polyvinyl siloxane) showed greater deformation than other materials in most sulcular widths under the conditions of this study.


CONCLUSIONS
Accurate impressions can be expected in sulci > or = 0.15 mm in width at the level of the finish line coronal to an undercut. Impressions with 0.10-mm sulci widths are not predictable. The physical properties of the impression materials used cannot be anticipated based on their chemical group.
Baharav
Haim
H
Department of Oral Rehabilitation, The Maurice and Gabriela Goldshleger School of Dental Medicine, Tel Aviv University, Israel.
Kupershmidt
Irit
I
Laufer
Ben-Zion
BZ
Cardash
Harold S
HS
D000704:Analysis of Variance; D003735:Dental Casting Technique; D003760:Dental Impression Materials; D005881:Gingiva / Q000033:anatomy & histology*; D006801:Humans; D008422:Materials Testing; D003765:Models, Dental; D011145:Polyvinyls; D015203:Reproducibility of Results; D012833:Siloxanes; D018709:Statistics, Nonparametric; D013440:Sulfides; D019231:Tooth Preparation, Prosthodontic
D003760:Dental Impression Materials; C495447:Permadyne; D011145:Polyvinyls; D012833:Siloxanes; D013440:Sulfides; C034183:vinyl polysiloxane; C032915:polysulfide