The effect of seating force and die spacing on pulpward cementation pressure transmission: a laboratory study

Pulpward pressure transmission during crown cementation occurs via the dentinal tubules. The present study investigated the effect of crown seating forces and the effect of increasing the die spacing on pulpward pressure transmission. Twenty upper premolars were prepared with 1 mm shoulder margins for non-precious metal full crowns. A 0-104 kPa pressure transducer (Mediamate EA, Data Instruments, Baltimore, MD, USA) was connected, via the sectioned root of the premolar, to the pulp chamber which was perfused with saline at 83 kPa driven by nitrogen gas, for two hours prior to cementation. Crowns with 2 or 6 layers of die-spacing were seated with 25 N or 100 N force using zinc-phosphate cement. The pressure transducer was connected to a Wheatstone bridge (Measurements Group, Instruments Division) and the extent of crown seating and output from the pressure transducer was recorded. Results indicate that 25 N seating force produced a lower mean pulpward pressure (41 +/- 54 Pa) compared to the 100 N seating force (251 +/- 276 Pa). Seating was significantly improved with 6 layers of die-spacing (seating discrepancy 18 +/- 12 mm) compared with 2 layers (139 +/- 111 mm). It is concluded that a higher seating force increases pulpward pressure transmission. Increasing die spacing improved crown seating but did not affect the amount of pressure transmitted.