The Relati
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 protected]
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
