The popularity of base metal alloy for porcelain fused to a metal crown and bridges has increased recently because of lower price, superior yield strength and modulus of elasticity (rigidity). The use of these alloys give them the potential advantage of thinner coping with less material and the required rigidity for long-span fixed partial dentures. The addition of beryllium to base metal alloys increases fluidity and improves casting fit. Beryllium also controls surface oxidation and bonding strength. Oxidation heat treatment of the metal is used to remove entrapped air, eliminate organic material and form the metal oxidized layer. The bonding agent and gold bonding agent also affect the bonding strength between porcelain and metal alloys. Four commercially available ceramic base alloys (two alloys contain beryllium element, another two do not) are studied. The purposes of this investigation are to test the shear bond strength between porcelain and metal alloy under different conditions (oxidized layer removed or not, gold bonding agent and uniseal bonding agent used in combination, separately or not at all). The following results were obtained: 1. Whether the oxidized layer was removed or not did not have a significant effect on the bond strength of porcelain (p > 0.05). 2. When different metal alloys was used, Wiron 88 alloy showed significantly the best bond strength of all alloys tested (p < 0.05). 3. When different bonding agent were used, the combination of bonding agent and gold bonding agent showed the best bond strength of all bonding agents tested. It showed a significantly higher bonding strength than opaque layer and gold bonding agent. 4. Vita porcelain powder showed a significantly higher bond strength than did Unibond porcelain (p < 0.05). 5. When opaque layer was used and when no bonding agent was used, the porcelain powder significantly affected the bond strength (p < 0.0001). The Vita porcelain showed a significantly higher bond strength than did Unibond porcelain. Wiron 88 alloy showed significantly the high bond strength than Rexillium III alloy (p < 0.05). 6. When bonding agent was used, the porcelain powder and alloy significantly affected bond strength. The Vita porcelian showed a significantly higher bond strength than did Unibond porcelain. Wiron 88 alloy showed significantly the best bond strength than other alloys Wiron (p < 0.05). 7. When bonding agent and gold bonding agent were used, the porcelain powder significantly affected the bond strength (p < 0.05). The Vita porcelain showed a significantly higher bond strength than did Unibond porcelain (p < 0.05). 8. When gold bonding agent was used, there was not any bond strength between metal and powder.
Crowns Dental Alloys