Pin-and-disc wear and Knoop Hardness measurements were made on three commercial glass-ionomer cements having slightly different compositions. The specific objective was to determine whether these cements have potential for use in posterior teeth, and, if not, what modifications in composition and structure would be appropriate to enhance their performance. The specimens were pre-conditioned in air, water, or lactic acid at 37 degrees C for one week prior to being wear-tested. Although differences among the samples were noted, some common trends were observed. From changes in hardness, before and after storage, two opposing trends were observed. One trend involved continued cross-linking and possible dehydration, resulting in a substantial increase in hardness. The other trend involved softening from penetrant liquid absorption and a concomitant decrease in hardness. The wear resistances compared favorably with those for resin-based composites except for the lactic-acid-stored specimens, for which changes in microstructure were revealed by SEM. All specimens were very brittle, and catastrophic failure during wear was frequent. Although our conclusion is that glass-ionomer cements with composition similar to those evaluated here are not acceptable for posterior occlusal application, some compositional changes may enhance their performance in stress-bearing applications.

The effectiveness of acrylic-based visible light curable composites with amorphous calcium phosphate (ACP) as the filler phase to release Ca 2+ and phosphate (PO 4 ) ions in aqueous media was enhanced with the incorporation of zirconyl dimethacrylate (ZrM) or 3-methacryloxypropyltrimethoxysilane (MPTMS) as coupling agents. Relatively hydrophobic resin-based composites formulated with these coupling agents were found to more rapidly release these ions over a longer period to establish solution Ca 2+ and PO 4 concentrations much higher than those obtained from similar composites without these coupling agents. The increased effectiveness of the former composites was comparable to that observed with more hydrophilic composites formulated with 2-hydroxyethyl methacrylate. In addition, composite strength was not compromised by the incorporation of MPTMS or ZrM. These results suggest that coupling agents make ACP-filled composites even more effective as bioactive dental materials for use in clinical applications where preventing demineralization or promoting remineralization of tooth structures is desirable.Because of their excellent biocompatibility with both soft and hard tissue, crystalline calcium orthophosphates, especially hydroxyapatite (HAP) and those capable of converting to HAP are finding increasing use as prophylactic, prosthetic, adhesive and restorative materials in dental and other biomedical applications (7-J). Polymeric calcium phosphate composites and cements have also been developed (6-11) in an effort to enhance the toughness, strength and handling properties of these materials.By contrast, amorphous calcium phosphate (ACP), which has an approximate compositional formula of Ca 3 (P0 4 )2 3H 2 0 (12) and is an important intermediate in This chapter not subject to U.S.

Knoop Hardness and pin-and-disc-wear measurements were made on a commercial silver-sintered glass-ionomer cement. The objective was to determine whether the incorporation of a bonded-metal-to-glass filler would enhance durability as determined by the above measurements. As with the previous work on conventional (non-metalized) glass-ionomer cements, the specimens were preconditioned at 37 degrees C in air, water, 0.02 mol/L lactic acid (pH 2.67), and heptane. The influence of these media on the microhardness of the silver-sintered material was about the same as that on the conventional materials. Storing in air produced dehydration, which increased the hardness considerably. Heptane storage increased the hardness less, but this increase is attributed to continued curing during storage. After storage in water, the hardness was essentially unchanged; the influence of increased cure is believed to be offset by softening or plasticization from water uptake. Lactic acid produced a decrease in hardness from chemical dissolution as seen from the SEM observations. In most cases, in particular for the air-stored specimens, the wear resistance was enhanced markedly over that of the conventional materials evaluated previously. The exception was the lactic acid-stored specimens for which little, or no, improvement was observed during early periods of wear. The incorporation of silver appeared to provide lubrication, thus reducing wear. However, catastrophic failure from brittle fracture was still a problem, but its occurrence was less frequent.

This study explored how resin type affects selected physicochemical properties of complex methacrylate copolymers and their amorphous calcium phosphate (ACP)-filled and glass-filled composites. Two series of photo-polymerizable resin matrices were formulated employing 2,2-bis [p-(2'-hydroxy-3'-methacryloxypropoxy)phenyl]propane (Bis-GMA) or an ethoxylated bisphenol A dimethacrylate (EBPADMA) as the base monomer, Unfilled copolymers and composites filled with a mass fraction with 40 %, 35 % and 30 %, respectively, of ACP or the un-silanized glass were assessed for biaxial flexure strength (BFS), water sorption (WS) and mineral ion release upon immersion in HEPES-buffered saline solution for up to six months. Substituting EBPADMA for Bis-GMA significantly reduced the WS while only marginally affected the BFS of both dry and wet copolymers. Independent of the filler level, both dry and wet ACP composites formulated with either BTHM or ETHM resins were mechanically weaker than the corresponding copolymers. The BFS of ACP composite specimens after 1 month in saline did not further decrease with further aqueous exposure. The BFS of glass-filled composites decreased with the increased level of the glass filler and the time of aqueous exposure. After 6 months of immersion, the BFS of glass-filled BTHM and ETHM composites, respectively, remained 58 % and 41 % higher than the BFS of the corresponding ACP composites. Ion release data indicated that a minimum mass fraction of 35 % ACP was required to attain the desired solution supersaturation with respect to hydroxyapatite for both the BTHM and ETHM derived composites.

Calcium phosphate cements (CPC) have proven successful in the repair of small, non-stress bearing skeletal defects. These cements do not have sufficient tensile strength or fracture toughness to allow their use in stress-bearing applications. It was hypothesized that a bioresorbable fiber mesh would improve the load-bearing behavior of shell structures fabricated of CPC. This study used a biaxial flexure fixture to compare the work-to-fracture values of discs made of: (1) CPC; (2) CPC reinforced with a bioresorbable two-dimensionally oriented poly(glactin) fiber-mesh; and (3) poly(methyl methacrylate) (PMMA) that were immersed in a serum-like solution for 0-28 days. CPC-mesh and PMMA discs were indistinguishable at 0, 1 and 7 days, based on work-to-fracture data. CPC and CPC-mesh discs were indistinguishable at day 28, because of fiber hydrolysis. The knitted fiber-mesh was effective in improving load-bearing behavior of a calcium phosphate cement for potential structural repair of bone defects.