Comparing the Fracture Resistance of Two Different Amalgam Bonding Agents

Objectives: Currently, VCU School of Dentistry uses Adper^TM Scotchbond^TM Multi-Purpose Plus (SMPP) for all extensive amalgam restorations requiring additional retention. The objective of this in vitro study was to evaluate the fracture resistance of extensive amalgam restorations retained by two different amalgam bonding agents [SMPP (control), and 3M ESPE Scotchbond ^TM Universal Adhesive (U)].
Methods: Twenty extracted posterior molar teeth were randomly divided into 2 groups (n=10) and mounted in a phenolic ring using Self-Cure Orthodontic Resin. A diamond blade was used to produce a flat dentin surface 2mm coronal to the cemento-enamel junction (CEJ). Surface area was measured using aluminum foil to account for different molar sizes. Copper bands were tightly adapted to each tooth to prevent ledging of amalgam during restoration. Teeth were etched (32% H₃PO_4, 15s), bonded (SMPP or U) according to the manufacturer’s instructions, restored (Valiant, PhD), adjusted to a uniform height of 5mm with a 1mm bevel, stored (37°C, 7d), tested in the Instron machine (0.5mm/min, 45° angle), and statistically analyzed (T-test, p≤0.05).
Results: SMMP had a mean bond strength of 14.177±5.31 MPa. U had a mean bond strength of 23.48±7.67 MPa. Unequal variance t-test found that SMPP had a significantly higher stress to break than U (p=0.007, 95% confidence interval 0.77 to 3.93).
Conclusions: SMMP provides statistically greater fracture resistance compared to U.