Crown retention for non-retentive preparations using adhesive resin cements.

This study examines the effect of preparing teeth with six varying convergence angles (ranging between 12 and 120 degrees) and height (1 and 2 mm) on the retention of cast gold crowns. Six groups of 4 human premolar teeth were prepared to give a flat occlusal surface in dentine with very short axial wall heights (1 or 2 mm) and variation in axial wall convergence (between 12 and 120 degrees). Impressions were recorded of the prepared teeth and custom castings made using a high copper content precious metal alloy.

Bonding of adhesive resin luting agents to metal and amalgam.

The shear bond strength of three adhesives, Panavia 21, Superbond, All Bond C&B Cement, and a dual cure resin (Variolink), to Ni-Cr-Be (Rexillium III), Midigold (Type III gold) and Amalgam (Sybraloy) were determined. Fifteen samples were prepared using 800 grit abrasive papers for Ni-Cr and Midi-Gold, and 100 grit papers for amalgam. Ni-Cr-Be and Midi-Gold samples were sandblasted for 30 s and steam cleaned for 10 s.

Bonding of crown and bridge adhesive resins to dentine.

The shear bond strength of three adhesives, Panavia 21, Superbond, All Bond C&B Cement, and Variolink (a dual cure resin) to various dentine depths were determined. Fifteen human fully erupted permanent first and second molars were wet ground using 500 and then 800 grit abrasive papers to expose the superficial, middle and the deep dentine, for each adhesive tested. Five samples were prepared for each dentine depth.

Polymerisation shrinkage of luting agents for crown and bridge cementation.

The volumetric contraction of a variety of luting agents, including Panavia 21, All-Bond C&B Cement, Superbond., Variolink and zinc phosphate cement, was assessed and compared using a minimal transducer The contraction among the materials tested was determined from the post-gel linear displacement of a deflecting coverslip resting on 4 silicone rubber spacers between which a mixed material was centrally located. Finally, the rate and duration of shrinkage over a period of 60 minutes from the moment of rigid contraction for all materials were investigated, and the final shrinkage values among the materials tested were compared.

Film thickness and rheological properties of luting agents for crown cementation.

The film thickness and rheological properties [viscosity and tan sigma], of different resin based crown and bridge luting agents, including Panavia 21, Superbond, All Bond C&B Cement, Variolink were compared with zinc phosphate cement. A modification of the method in ISO 9917 (1991) and a controlled stress rheometer were used to monitor the changes in the film thickness and rheological properties respectively. For each material, the film thickness and rheological characteristics were determined at 60s after start of mixing and then made at regular intervals until immediately before the material was set.