Introduction
The base metal ceramic restorations are one of the most popular restorations in the world. No research has been done about the porcelain metal junction on the occlusal surface yet.
The main purpose of this study was to find the best location for porcelain metal junction with regard to occlusal contact in base metal- ceramic crown.
Materials &Methods
75 Porcelain Fused to Metal (P.F.M) crowns were made for metal dies. Crowns were cemented on the respective die with zinc phosphate cement and were divided into three groups of 25 samples.
Occlusal contact in each group was as follows:
First group (A): On the porcelain metal junction.
Second group (B): 2mm away from the porcelain metal junction on the porcelain.
Third group (C): 2mm away from the porcelain metal junction on the metal.
All of the samples were prepared for compressive force with Instron machine.
Data were analyzed with one way ANOVA and Duncan tests.
Results: 1) The average force was different in each of the 3 groups significantly.
2) Group B had the lowest amount of force (290kgF) and group C had the greatest amount (713kgF).
3) Group A developed a force between B& C (529kgF).
Conclusions
1- The best location for occlusal contact in the porcelain metal junction restorations is on the metal.
2- When the occlusal contact is on the porcelain metal junction, It needs more force for porcelain fracture than when it is  on the porcelain.