چكيده لاتين :
Introduction: Base metals are being increasingly used in casting procedures in dentistry. Since recasting these alloys in laboratory might have negative effects on marginal fitness, it seems necessary to study the effect of recasting procedures more carefully. The goal of this study was to study the effect of recasting base metals on vertical marginal fitness of crowns with different marginal configurations with different percentages of alloys.Material and Methods: In this study, two dies made up of brass with dimensions of prepared premolars and marginal configurations of shoulder bevel 45° and shoulder 135° were prepared by CNC machine. Total of 30 copings were waxed and cast, 15 copings for each die. Copings were further subdivided in to three groups A, B and C. Group A consisted of 100% new alloy, group B consisted of combination of 50% new alloy and 50% old alloy, group C consisted of 100% recast alloy. After copings were seated, vertical distance from margin of the restoration to margin of the die was measured by metric microscope with Moticam camera at four points of buccal, lingual, mesial and distal. Data were analyzed by two- and one-way ANOVA and t- test. Results: Group A/ (135 shoulder finishing line cast with 100% new alloy): 156.11 micron. Group A2 (45 shoulder bevel finishing line cast with 100% new alloy): 99.74 micron. Group Bl (135 shoulder finishing line cast with 50% new alloy and 50% recast alloy): 273.38 micron. Group B2 (45 shoulder bevel finishing line cast with 50% new alloy and 50% recast alloy): 123.07 micron. Group C1 (135 shoulder finishing line cast with 100% recast alloy): 369.40 micron. Group C2 (45 shoulder bevel finishing line cast with 100% recast alloy): 106.97 micron. There were statistical differences between groups A, B and C in vertical gap when three different percentages of alloys (100% new with average gap of 127.93 micron, 50% new+50% recast with average gap of 198.22 micron, 100% recast with average gap of238.18 micron) were used (p value = 0.036). There were statistical differences in mean vertical gap distance between different preparations (shoulder bevel 45, shoulder 135 ) within each group (100% new, 50% new + 50% recast, 100% recast). Discussion: When three different percentages of alloys were used (100% new alloy, 50% new + 50% old, 100% old), 100% new alloy showed the least mean vertical gap compared to other two groups. In shoulder 135 there were statically differences between group A and C only and in shoulder bevel preparation there were no statically differences between groups A, B and C. In group C (100% recast) there were significant differences between two preparations (shoulder bevel 45 and shoulder 135).
