Applicability of Hertzian “Ball-on-Disk” Method as Standard Test-Method for Amalgam

Objectives: The objective of this work was to investigate the suitability of the Hertzian-“ball-on-disk”(HBOD) test-method as a standard test-method to evaluate the strength-development and corrosion of dental-amalgam.
Methods: Laboratory testing was performed on 2-amalgam-brands, Dispersalloy(DA) and Megalloy-EZ(MEZ), according to standard and non-standard test-methods: ANSI/ADA-No.1 and the HBOD-method. To determine the corrosion-induced-strength-reduction(CISR) effect that dental-amalgam exhibits, for both DA and MEZ-alloys, HBOD-testing was performed on 10specimens stored in artificial-saliva and compared to 10specimens stored-dry, with both sets of 10specimens maintained at 37°C for 30days. Additionally, for strength-development-testing(SDT), HBOD-testing was performed at 2 and 24hrs for specimens maintained at 37°C. The HBOD-method is described in the literature(Dental Materials-28,2012). SDT-results from the HBOD-method were compared to results from compression-testing performed according to ANSI/ADA-Standard-No.1 with all-testing performed on n=5specimens.
Results: The corroded test-specimens displayed a 21.5% and 10.2% decrease in average loading failure, in relation to their dry-controlled counterparts, for MEZ and DA, respectively. Under uniaxial-compression, MEZ had average compressive-strengths of 205(±10) and 451(±39)MPa for setting-times(ST) of 1 and 24hrs, respectively; furthermore, DA averaged 102(±8) and 399(±14) MPa for ST of 1 and 24hrs, respectively. Both amalgams surpassed the ANSI/ADA compressive-strength-requirements of 80 and 300MPa for ST of 1 and 24hrs, respectively. For the HBOD-method, MEZ had mean loads at failure of 1147(±74) and 1404(±222)N for ST of 2 and 24 hours, respectively; furthermore, DA had mean loads at failure of 995(±117) and 1363(±59)N for ST of 2 and 24 hours, respectively. The results for both of these alloys compare favorably to the proposed early(2hr) and late(24hr) minimum-loads at failure of 400 and 800N, respectively, suggested in the literature.
Conclusions: This study verified the CISR effect that amalgam exhibits when placed into an artificial-saliva-solution compared to a dry-environment, both maintained at 37°C for 30days. Additionally, SDT of amalgam using the HBOD-method was compared to results of the compression-test specified in ANSI/ADA-No.1.