Document Type : original article
Authors
1
Associate Professor and Director of Postgraduate Education Program, Dept. of Prosthodontics, Dental School, Mashhad University of Medical Sciences, Mashhad, Iran
2
Assistant Professor, Dept. of Prosthodontics, Dental School, Mashhad University of Medical Sciences, Mashhad, Iran
3
Assistant Professor, Dept. of Prosthodontics, Dental School, Ghazvin University of Medical Sciences, Ghazvin, Iran
Abstract
Introduction and objective:
One of the most important laboratory procedures in crown and bridge construction is preparing the wax pattern. A restoration is predictable when its marginal gap is minimum, which depends on the marginal fitness of wax pattern. Since a lot of studies related to marginal distortion of the wax pattern have been done after removing it from the working model ( die ), this study was designed to evaluate marinal fintess using different time intervals and temperatures while the wax pattern remains on the die.
The purpose of this study was to assess the marginal wax pattern fitness on the working model in different temperatures and time intervals with two types of hard and soft waxes.
Materials and Methods:
In an experimental study, 30 wax patterns were made on 30 truncated cone shape brass models using dipping wax technique.
A brass cap was used to control the thickness of the wax, and marginal fitness. The dimensions of the brass models were 6mm × 6mm with an 8 degree convergence and a shoulder finishing line of 1mm width.
15 wax patterns were prepared from hard wax (Ramin) and 15 from soft wax (Renfert). Each type of wax was divided into third groups: The first group was immersed in the water with 23oc temperature, the second group in water with 32oc temperature and the third group was stored in refrigerator at 8oc. In order to protect the wax patterns from the direct contact with the water, they were located in a brass container. This also helps in properly heat transition.
The storage times for each group were 2h, 5h and 22h. The marginal vertical discrepancy was determined by a scanning electron microscope with magnification of 200 at 3 determined points.
The data were analyzed with 3 way, 2 way and one way ANOVA and Duncan test.
Results:
1) The maximum mean gap for soft wax (Renfert) occurred during 0-2 hours (15.23mm±4.52) and for hard wax (Ramin) during 2-5 hours (1.23mm±0.67).
2) Soft wax (Renfert) showed more marginal gap at the temperature of 32°c and time interval of 0-22h compard with 8oc temperature and the time interval of 0-22 hour.
3) Hard wax (Ramin) showed no significant difference in marginal gap at temperatures of 23oc, 32oc and 8oc even after 22h interval.
Conclusions:
1) The best storage temperature for sofwax (Renfert) is 8°c.
2) The best wax for marginal fitness is hard wax (Ramin) .
3) The marginal discrepancy in hard wax (Ramin) was not significant clinically even after 22h.
Keywords
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