The Relationship Between the Marginal Integrity, Surface Adaptation of Cast Base Metal Crown and Storage Time & Conditions of investing
Mostafa Gomaa* and Ali Fahmy**
* Lecturer of Fixed prosthodontics, Faculty of Dentistry Misr International University.
**Assistant professor of fixed prosthodontics, Faculty of Dentistry Misr International University.
Corresponding author: email@example.com
ABSTRACT: The conventional investing technique is used most commonly for casting. Conventional casting techniques require considerable time, typically one hour for bench set (generally judged as the time taken for the investment to reach its maximum exothermic setting reaction temperature) for the investment and 1 to 2 hours for the wax elimination. It has been traditional either to cast invested waxpatterns immediately after the investment has set or to store the invested patterns in a humidor for casting later. Sometimes, due to unexpected conditions, the bench set may extend to many hours. The purpose of this study was to evaluate different storage conditions effect and time before wax elimination on the marginal fit & surface adaptation (cement space) of base metal alloy crowns invested in phosphate-bonded investment material. This study compared the marginal fit , surface adaptation (cement space) of base metal alloy crowns to parent dyes after 1 hour following the setting of the investment in air, storage in a humidor for 12, 24 and36 hours, and storage in air for the same period of time before wax elimination. Material and Methods : A total of 35wax patterns were made simulating the artificial crown from the master dye (for investigation of surface adaptation and marginal accuracy) ,divided into three groups ; Group A (control group ;n=5) 1hour bench set. Group B divided into 3 subgroups B1(n=5),B2(n=5) &B3(n=5) ,rings stored in a humidor for 12, 24 & 36 hours respectively.. Group C divided into 3 subgroup C1(n=5),C2 (n=5),C3 (n=5) rings stored in air for 12,24 &36 hours respectively. Wax burnout was carried out for all rings followed by casing using base metal alloy (Wiron Light) following the manufacturer instructions. Marginal discrepancy and surface adaptation of Groups A, B, and C were determined using measuring microscope .The obtained values of Groups A, B, and C were subjected to statistical analysis using student's "t" test. Results: The study showed that as regard to marginal discrepancy there were significant differences between the control group A and each of tested groups (at P<0.05) .But for surface adaptation, the only significant difference were observed between point 2 in group A 138.8(±13.8), and point 2 in subgroup B2, 226,3 (±8.7). Also significant difference was observed between all measuring points in group A and that in all measuring points in subgroup B3. Conclusions: Increasing storage time of the invested wax pattern in humidor or air, adversely affects the marginal integrity. Invested wax patterns that had been stored for 36 hours in a humidor were demonstrated remarkable changes in surface adaptation in comparison with the control group especially at occlusal area. Storing the wax patterns in air for different periods had no statistical difference from control group.
[Mostafa Gomaa and Ali Fahmy. The Relationship Between the Marginal Integrity, Surface Adaptation of Cast Base Metal Crown and Storage Time & Conditions of investing. J Am Sci 2012;8(10):76-82]. (ISSN: 1545-1003). http://www.jofamericanscience.org. 13
Key words: Marginal discrepancy- Surface adaptation- Bench set- Humidor- Master dies- Counter die Full Text 13