In vitro bond strengths of amalgam added to existing amalgams.
This study determined if a standardized condensation force and dwell time per condensation pressure point could reliably bond new amalgam to older amalgam without applying extrinsic Hg. A stabilization jig was created to hold 15 friction-fit 1-inch diameter (25 mm) cylindrical resin specimen blocks face up with cavities drilled to contain the condensed primary amalgam (Valiant PhD-XT). Freshly mixed secondary amalgam (Valiant PhD-XT) was condensed against the primary amalgam surfaces through the 3.5-mm-diameter central holes of specially fabricated split-ring molds. The 15 disks fit snugly within the holes of the stabilization jig tray. Condensation was with a consistent, calibrated force of 22.5 MPa (4 lbs/0.79 mm2) applied with a spring-loaded amalgam carrier custom adapted with a 1-mm-diameter stainless steel condenser tip. Secondary amalgam additions were built up in three 1-mm thick increments with a pattern of eight 22.5 MPa two-second condenser strokes per incremental layer. Shear-bond testing with a 1-mm/minute crosshead speed occurred 24-hours post-condensation. One-way analysis of variance statistical analysis was conducted to analyze the results. The mean shear-bond forces (MPa, N = 15) found were: Control 28.1 +/- 5, 15 minutes 31 +/-5, one hour 10.7 +/-4 (N = 30), one day 25.5 +/- 4, one week 25.2 +/- 4, two months 25.1 +/- 5 and seven years 24.7 +/- 4. Under the condensation pressures used in the current study, the addition of new amalgam to smooth previously set amalgam surfaces, not including the one-hour group, up to seven years old, resulted in shear-bond forces not statistically different (p = 0.05) from the intact control. Virtually all (94%) of the bonds tested, except for the one-hour sample, resulted in cohesive rather than adhesive failures except those of the one-hour sample. Forty percent bond strengths of the controls were achieved when only 5.6 MPa (1 lb/0.79 mm2) and 14 MPa (2.5 lb/0.79 mm2) condensation pressures were used.
Loma Linda University School of Dentistry, Loma Linda, CA, USA. croggenkamp@llu.edu
Clyde L
CL
Roggenkamp
Frederick A
FA
Berry
Huan
H
Lu
D055598:Chemical Phenomena; D003300:Copper / Q000737:chemistry; D003722:Dental Alloys / Q000737:chemistry; D003723:Dental Amalgam / Q000737:chemistry*; D001840:Dental Bonding; D017269:Dental Prosthesis Repair; D005240:Feasibility Studies; D006801:Humans; D008422:Materials Testing; D008628:Mercury / Q000737:chemistry; D010165:Palladium / Q000737:chemistry; D011312:Pressure; D033081:Shear Strength; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors
D003722:Dental Alloys; D010165:Palladium; D003300:Copper; D003723:Dental Amalgam; C072894:Valiant PhD; D008628:Mercury