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Abstract
Retention is an important factor affects the long-term
serviceability of cast restorations.
This study was designed to evaluate the retention of Nickel-
Chromium and Cobalt-Chromium crowns luted with zinc phosphate,
resin-modified glass ionomer and adhesive resin cement on teeth
restored with pin retained amalgam or silver-reinforced glass
ionomer cores.
Sixty upper posterior molars were selected and aligned in
acrylic blocks then subjected to uniform reduction using a lathe
machine to be simulating full metal crown preparation with the
following dimensions 2.5 mm height, ten degrees axial convergence
and 0.3 mm chamfer finish line.
Pin retained amalgam or silver-reinforced glass ionomer cores
were fabricated for each tooth using a specially designed core
former to have standardized preparation with five mm height.
Direct wax patterns were fabricated for each tooth then cast in
Nickel-chromium or Cobalt-Chromium alloy. Each casting divided
into three groups, each group cemented with one of the three tested
cements.
The retention of the cemented restorations was measured
using universal testing machine. The results were recorded in
Newton, all the data collected, tabulated and statistically analyzed.
Summary & Conclusions
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Based on the previous results the following conclusions could
be submitted.
• Type of metal alloy used for construction of extracoronal
restoration had limited role in crown retention. Using either
Nickel-Chromium or Cobalt-Chromium alloy offered
insignificant effect.
• The proper choice of cement type is a decisive factor in crown
retention. Adhesive resin cement enhanced significantly crown
retention than did resin-modified glass ionomer cement while
zinc phosphate cement recorded the least retentive value.
• Type of core material had a direct effect on crown retention.
Amalgam core increased significantly the retention of cast
metallic restorations than did silver-reinforced glass ionomer
core.
Clinical significance
from the previously proven and discussed results we could
conclude that: one of the best treatments for badly mutilated vital
tooth is through pin retained amalgam cores which restored with
either Nickel-Chromium or Cobalt-Chromium crowns cemented with
adhesive resin cement. If adhesive resin was not available the resin
-modified glass ionomer cement can be used successfully with the
previously mentioned combinations.