Development of metal-resin composite restorative material. Part 3. Flexural properties and condensability of metal-resin composite using Ag-Sn irregular particles.

Powder-liquid type metal-resin composites, using Ag-Sn irregular particles as the filler, 4-META as coupling agent and UDMA + TEGDMA as resin matrix, were experimentally prepared under 9 different conditions (three different particle sizes and three different filler contents). The flexural strength and flexural modulus were measured. Three different irregular particle size MRCs without redox-initiator at 94% filler content, as well as amalgam, conventional hybrid composite and Ag-Sn spherical particle MRC were evaluated for condensability. The flexural strength of the Ag-Sn irregular particle MRC was significantly influenced by both the filler particle size and filler contents (p < 0.01). It increased when either the filler content increased or the particles size decreased. The highest flexural strength (97.6 MPa) was obtained from the condition of particles size < 20 microns and 94% filler content. The flexural modulus was significantly influenced by filler content and it increased with increasing filler content. The condensability of the Ag-Sn irregular particle MRC was lower than that of amalgam but much higher than presently available conventional composites and spherical particle MRC.

Development of metal-resin composite restorative material. Part 2. Effects of acid and heat treatments of silver-tin filler particles on flexural properties of metal-resin composite.

The effects of acid and heat treatments of silver-tin filler particles on the flexural properties of metal-resin composite restorative materials were investigated. Five metal-resin composite restorative materials containing different silver-tin filler particles treated under different conditions were experimentally prepared. The conditions of the alloy particles were; 1) as atomized (NT), 2) 1.8% HCl acid-treated (AT), 3) heat-treated at 150 degrees C for 5 min after AT (A15), 4) heat-treated at 200 degrees C for 5 min after AT (A20) and 5) heat-treated at 250 degrees C for 5 min after AT (A25). The flexural strength and the flexural modulus of elasticity were measured for the five metal-resin composites to evaluate the effects of the acid and heat treatments. The flexural strength of the prepared composites was significantly influenced by the surface condition of the filler particles (p < 0.01), and increased significantly when the as atomized particles (NT) were acid-treated (AT) or acid- and heat-treated at 150 degrees C (A15), but then significantly decreased as the heat treatment temperature increased (A20 and A25). The strength of the A15 composite was significantly higher than those of the other composites, and exceeded that (about 60 MPa) of the previous composite with no treatment. No significant difference was found in the flexural modulus of the composites.

Development of metal-resin composite restorative materia. Part 1. Experimental composite using silver-tin alloy as filler and 4-META as coupling agent.

Metal-resin composites, using metal particles instead of inorganic particles as the filler and 4-META as the coupling agent, were experimentally prepared under 20 different conditions (five different concentrations of 4-META, and four different contents of metal particles). The flexural strength of the prepared metal-resin composites was in the range of about 14.5-61.3 MPa. The flexural strength was significantly influenced by the 4-META concentration, the metal particle content and their interaction. The highest strength was estimated at 2-3 mass% of 4-META concentration and 92.0-93.5 mass% metal filler content. The flexural modulus of the metal resin composite ranged approximately from 7.8 GPa to 15.5 GPa. The flexural modulus of the metal resin composite significantly increased with the metal particle content. The effect of the 4-META concentration on the flexural modulus was not significant.

Early compressive strength and phase-formation of dental amalgam.

The compressive strength of five different amalgams was measured at one hour, six hours, 24 hours, and seven days, and X-ray diffraction analysis was carried out for each amalgam at the same times in order to investigate the early strength characteristics of the amalgams in relation to the formation of different phases. At 24 hours all tested amalgams reached about 90% or more of their seven-day compressive strength, but the increase in the early compressive strength from one hour to 24 hours varied between different amalgams. Two of the five amalgams tested reached about 90% of their seven-day compressive strength at six hours. A significant correlation was found between the ratio of early compressive strength to seven-day compressive strength, and the X-ray diffraction intensity ratio (ratios of one-, six- and 24 hour intensity to seven-day intensity) for the gamma 1 phase, indicating that the increases in early compressive strength are mainly dependent upon the formation of gamma 1.