The International Journal of Prosthodontics, 01/1997

This study examined the compatibility of nine popular gypsum products with three more recently developed irreversible hydrocolloid impression materials, some of which were disinfected before pouring. A test die and evaluation procedure conforming to ANSI/ADA specification no. 18 standards were used to evaluate detail reproduction of the impression materials and detail transfer and roughness of the resultant die. Statistical evaluation of the data revealed that there continue to be deleterious surface interactions between specific irreversible hydrocolloid materials and gypsum products. Analysis also confirmed that the phenolic disinfectant used in this study did not influence the surface interaction between materials nor alter the resultant dimensional properties of the gypsums used.

Dentists in practice from 3 to 5 years who were exposed to an integrated fixed and removable prosthodontic curriculum as students at the university of British Columbia responded to a survey on the relevance of their prosthodontic education to current dental practice. The majority of the respondents reported that the integrated curriculum prepared them adequately for general dental practice, although many felt that they would have benefited from a greater emphasis on specific treatments, most notably cast metal inlays and onlays, all-ceramic restorations, and implant-supported prostheses.

This study used three-dimensional finite element analysis to investigate the effect of three different occlusal surface materials (resin, resin composite, and porcelain) and four different framework materials (gold, silver-palladium , cobalt-chromium, titanium alloys) on the stress distribution in a six-implant-supported mandibular fixed prosthesis and surrounding bone. A total of 172 N vertical load was distirbuted over the entire occlusal surface of the finite element model. Generated stress values were calculated in the occlusal surface material, framework, prosthesis retaining screws, implants, and surrounding cortical and spongy bones. The results obtained demonstrated that using a prosthesis superstructure material with a lower elastic modulus (1) did not lead to substandial differences in stress patterns nor in values at the cortical and spongy bones surrounding the implants; and (2) concentrated stresses in the retaining scres for the prosthesis and thus increased the potential risk of prosthesis failure. For the single loading condition ivestigated, the optimal combination of materials was found to be cobalt-chromium for the framework and porcelain for the occlusal surface

This in vitro study evaluated the wear resistance of a high-strength resin posterior denture tooth against eight opposing dental materials. The tooth specimen was cusp shaped and the opposing materials were formed as a 10 X 10 X 5 mm plate. All material combinations were tested using a machine desinged to produce sliding contact 20 x 10 to the fourth power times at 60 cycles per minute and a 4-mm sliding distance per stroke in the buccolingual direction under a load of 1 kg. Wear analysis was meaured as the total height loss of each material combination and the volume loss of each material. Wear against human enamel was evaluated as a control. The least loss was observed opposing a gold-silver-palladium-copper alloy, and the greatest loss was observed opposing porcelain. The volume loss of high-strength resin against gold-silver-palladium-copper alloy was as small as that against human enamel. High-strength resin wear was more signif icant against castable ceramics and porcelain. Teh volume losses of high-strength resin against high-strength resin, polycarbonate, or cobalt-chromium alloy were significantly larger than those against polyethersulfone, poly(methyl methacrylate), gold-silver-palladium-copper alloy, or human enamel. These findings suggest that tyhe wear resistance of high-strength resin is influenced considerably by opposing dental materials, and that the best combination was high-strength resin-gold-silver-palladium-copper alloy, and the poorest combination was high-strength resin-porcelain.

This study examined the influence of thickness on changes (lin ear dimensions, warpage, and water uptake) in a denture base resin following two processing methods (heat polymerization and microwave activation). Changes were influenced by both processing method and thickness. These findings suggested that the processing method and denture base resin thickness are important factors in the dimensional change of acrylic resin dentures, and that the overall dimensional denture base changes are the result of localized changes.

This study examined the intraoral changes of the elastic properties and roughness of a tissue conditioner after treatment with a fluorinated copolymer coating agent developed by the authors. The surface of the conditioner was t reated with the agent on half of the internal surface of five maxillary complete dentures and was compared with the untreated half on the other side. The cushioning effects of the conditioners were evaluated by measuring the creep compliance strain-to-stress ratio. The value of compliance on the treated half was significantly greater than that on the untreated half. There was significantly less roughness on the treated side than on the untreated side. It was found that the coating provides an improved, glossy surface to the conditioner and may increase its useful life.

The effect of different polymerization temperatures on the bond strength and the type of bond failure between denture base polymers and polymer teeth were investigated using two autopolymerized and one heat-polymerized denture base material. For this purpose, a peel test and a shear test were used. The strongest bond strengths occurred between the heat-polymerized denture base polymer and the polymer teeth. Autopolymerized denture base polymers showed lower bond strengths. With increasing temperatures, the bond strength of the autopolymerized systems increased and the bonding characteristics changed from adhesive to cohesive failure, particularly at temperatures above 50 degrees C.

The cushioning effect of soft denture lkiners was evaluated by using a free drop test with an accelerometer. Materials tested included SuperSoft (Coe Laboratories, Chicago, IL), Kurepeet-Dough (Kreha Chemical, Tokyo), Molteno Soft (Molten, Hirshima, Japan), and Molloplast-B (Molloplast Regneri, Karlsruhe, Germany). All materials were found to reduce the impact force when compared to acrylic denture base resin. A 2.4-mm layer of soft denture material demonstrated good impact absorption, and Molloplast-B and Molteno had excellent impact absorption. When the soft denture liner was kept in an accelerated aging c hamber for 900 hours, the damping effect recorded increased for all materials tested. Aging of all materials also affected the cushioning effect.

The ideal denture adhesive demonstrates a neutral or slightly basic pH, minimal toxicity to the oral mucosa, and sa tisfactory adhesive bond strength for 12 to 16 hours. Three brands of commercially available denture adhesives 9Fixodent Fresh, Procter and Gamble, Cincinnati, OH; Super Poli Grip, Block Drug, Jersey City, NJ; and Super Wernet's, Block Drug, Jersey City, NJ), and a complex ma nnose carbohydrate (Acemannan, Carrington Laboratories, Irving, TX) were evaluated in vitro to determine significant differences in pH, cytotoxicity, and adhesive bond strength. Super Poli Grip and Super Wernet's remained above the critical pH for hydroxyapatite (pH 6.5) throughout the study, while Acemannan and Fixodent Fresh did not. Fixodent Fresh exhibited significant cytotoxicity to human gingival fibroblasts. Acemannan demonstrated significantly greater overall mean adheisve bond strength in both dry and simulated oral conditions. The generally favorable in vitro performance of the Acemannan material compared to commercially available denture adhesive formulations indicates that complex carbohydrates may be ef ficacious denture adhesives.

This in vitro study examined the effect of eluate from heat-ac tivated, chemically activated, and microwave-activated denture base resins on cell viability of primary cultures of human gingival fibroblasts. Eluates corresponding to 24, 48, 72, and 96 hours of resin disk immersion were prepared. Fibroblasts were plated at a density of 3 x 10 to the fourth power cells in 96-well plates and exposed to a medium containing eluate. After 24 hours, the cytotoxic effect was determined by cellular mitochondrial function. The effect of eluates was compared to control cultures containing culture medium without eluate. Results indicated that at all time periods tested, all three resins leached materials that were cytotoxic to the fibroblasts. Eluate from chemically activated resin disks was more cytotoxic than eluate from heat-activated and microwave-activated disks. In general, cytotoxicity appeared to diminsh as disk immersion time was increased. The greatest cytotoxic effect on cell viability was observed with eluates recovered after 24 hours of disk immersion, and the least cytotoxic effect was observed with eluates recovered after 96 hours of immersion.

The occlusal curvature should be harmonized with stomatognathic function, but excessive occlusal curvatures are found in some craniomandibular disorder patients. Forty healthy subjects and 95 patients with craniomandibular d isorder (50 with clicking, 25 with locking, and 20 with myofascial pain dysfunction syndrome) were evaluated to investigate the functional significance of the occlusal curvature. Anteroposterior and lateral occlusa l curvature were measured using the least-square approximation of the mandibular buccal cusps in a second-order quadratic and modification of Monson's 4-inch sphere. Clicking and locking groups had significantly greater occlusal curvatures than healthy subjects. There appeared to be a relationship between occlusal curvature and craniomandibular disorders.

This study evaluated the effects of chemical disinfectants on the color of denture base materials. Materials tested included Paladon 65 (Kulzer, Friedrichdorf, Germany), Triad VLC (Dentsply Int, York, PA), and ProBase Cold (Ivoclar, Schaan, Liechtenstein). The disinfectants were Klinex (Lever Hellas, Athens, Greece), Cidex-7 (Johnson & Johnson, East Windsor, NJ), Hibitane (Imperial Chemical, Macclesfield, UK), and Cabadol (Detax Karl Huber, Ettlingen, Germany. Denture material samples were placed in the various disinfectants and evaluated for color changes (AE*) at intervals of 10 minutes, 10 hours, and 7 days. Changes in color were measured using a tristimulus colorimeter on 10 samples for each denture material and disinfectant combination. It was concluded that if the recommended disinfecting times are followed, no observable color changes should be anticipated for the denture materials tested. Even the long-term (7-day) immersion caused observalbe color changes only with Cabadol, a phenol-based disinfectant, and ProBase and Triad denture materials.