Adaptation of acrylic dentures reinforced with metal wire.

The aim of this study was to reveal the effect of metal wire on the adaptation of the denture reinforced with it. Forty maxillary dentures were made with two polymerization systems (DS system and SR-Ivocap system). The dentures were divided into two groups: (1) the unreinforced dentures (control) and (2) the dentures reinforced with metal wire 1.0 mm in diameter. Discrepancies between the denture base and the stone cast were measured at five points immediately after polymerization and after a 30-day immersion in water. The data were analysed using a two-way or one-way ANOVA test. Dentures reinforced with metal wire exhibited significantly lower adaptation to the stone cast than the unreinforced ones for each polymerization system. Immersion in water did not affect the adaptation of dentures reinforced with metal wire for each polymerization. Unreinforced dentures made by the DS system had significantly smaller discrepancies compared with the dentures processed with the SR-Ivocap system. The adaptation of the dentures reinforced with metal wire decreased in comparison with the unreinforced ones regardless of the polymerization method. This should be considered when metal wire is used clinically as reinforcement.

Controlled polymerization system for fabricating precise dentures.

STATEMENT OF PROBLEM: Most processed resin denture bases do not fit the cast accurately because of polymerization changes in the resin. The fit is more noticeable in the palate between the denture base and the cast. Therefore, development of a polymerization system that will improve the fit of a denture base to the cast is lack of worth considering to improve the fit and retention of the denture. PURPOSE: A newly developed polymerization system for dentures is presented that results in excellent adaptability of the denture base to the cast when compared with 2 other polymerization systems. MATERIAL AND METHODS: Forty-five maxillary dentures were made with 3 resins and 3 polymerization systems (a new polymerization system, SR-Ivocap system, original microwave polymerization system). Each denture and cast was sectioned through the second molar area parallel to the posterior border. Discrepancies between denture base and stone cast were measured at several points immediately after polymerization and after 30 days of immersion in water. In addition, disks of 3 materials processed in each system were examined for absorption of water and hardness at 2 measurement stages. Data were analyzed with the split-plot or 2-way ANOVA test. RESULTS: Dentures made with the new polymerization system had significantly smaller discrepancies, compared with dentures processed with the SR-Ivocap system and the microwave method. The amount of water absorption of the resin disks processed by the new system was less than the disks made by the other 2 systems. Dentures made with the new system exhibited significantly better adaptation to the cast than those made with the other 2 systems. CONCLUSION: The new polymerization system produced a more accurate method of processing dentures when fit was compared with the fit of dentures made with the other 2 denture base resins.

Dimensional changes and pressure of dental stones set in silicone rubber impressions.

OBJECTIVES: A high expansion stone has been used for improving the adaptation of dentures. Although the method is based on the idea to compensate for the processing shrinkage of the denture base resin with the high expansion stone, there are few studies on the expansion behavior of stones in an impression. The purpose of this study is to clarify the dimensional changes of stones set in silicone rubber impressions using two types of impression tray. METHODS: Impressions of a master model that represents the alveolar ridge were taken using a silicone impression material and the dimensional changes in the stone casts were measured in different directions (x, y and z-axes). Two types of impression tray were used, one with an open surface and the other with a closed surface. In order to evaluate the setting expansion of the stones and the pressure against the impression, stones were poured in other impressions that were taken from a cubic master model. The thickness of the impression was set at 2 mm. RESULTS: A statistical analysis showed that there were significant differences in the dimensional change in the vertical direction (z-axis) and horizontal directions (x- and y-axes) of any stone casts set in the open tray. However, there were no significant differences in the dimensional changes in any direction of each stone cast set in the closed tray. SIGNIFICANCE: The impression tray influences the setting expansion of stones. Stones do not uniformly expand in the open tray and the dimensional changes in the stone casts in the three-dimensions increases, when used with a high expansion stone.

Resin pattern material with low polymerization shrinkage.

PURPOSE: The purpose of this study was to develop a material with low polymerization shrinkage for resin patterns to improve the fit of a long superstructure to implants. MATERIALS AND METHODS: Three different chemical substances were added at 1, 2, 3, 5, 10, and 20 wt% to the liquid component of a self-curing acrylic resin. Specimens for measuring shrinkage during self curing were prepared in a metal mold that took the form of a conical cavity with slightly tapered walls. The specimens were prepared using three different methods: (1) a brush-on technique, (2) an injection method, and (3) an injection-press method. The percentage of linear shrinkage was calculated from the protrusion of the specimen from the bottom of the cavity. RESULTS: The injection-press method and the brush-on method gave the lowest polymerization shrinkage results (P < 0.05). The standard deviation of the former method was smaller than that of the latter. The linear shrinkage in the injection-press method decreased with the increase of the powder-to-liquid ratio (P < 0.05). All three additives reduced shrinkage to about 1/3 of the shrinkage of the basic resin using the injection-press method and a 2.00:1.00 powder-to-liquid ratio. CONCLUSION: The addition of three different chemical substances to liquid reduces linear shrinkage to about 1/3 of the shrinkage of the original self-curing acrylic resin.

A development of visible light cured FRP plate denture.

A FRP denture base, which was made from visible light curing prepreg, was developed. The visible light cured FRP denture base had advantages with respect to an adequate strength, bonding strength of acrylic base resin, esthetic properties and ease to manipulation. The matrix resin of Bis-GMA/UDMA/3 G at 48/48/4 was determined from the results of the bending test and manipulation processing. The sateen weave's glasscloth was used for the reinforcement of the prepreg. The adaptability of the FRP plate denture was better than that of the resin base denture constructed with microwave heating.

[Fatigue properties of junction of crown and bridge resin and metal frame. 1. Effects of retention beads and adhesive].

The bending fatigue test of crown and bridge resin facing metal frame was carried out under a scanning electron microscope, and the fracture and propergation behavior of junction was studied. The resin facing metal frame with retention beads had a static breaking stress of about 100 kgf/mm2. The resin facing metal frame, when bonded with adhesive, had the stress of about 36 kgf/mm2. The specimens with retention beads and bonded with adhesive were not destroyed at cycles of 10(6) under the bending fatigue stress of below 40% and 50% of the static breaking stress, respectively. Marginal micro gaps between resin and metal frame with retention beads were observed before the fatigue test, and were increased with the number of cycles. Then fracture of the specimen occurred from the resin of the retention beads side. In the specimen bonded with adhesive, marginal micro gaps between resin and metal frame were observed during the fatigue test, and the partially cohesive fracture occurred.

[A development of FRP frame for crown and bridge resin. (2) Rigidity and adaptability of FRP frame].

Retainer and pontic of FRP frame for crown and bridge resin were constructed with two different prepregs, used glass cloth and roving as reinforcement. Rigidity and adaptability of the FRP frame and bonding strength of jointing of retainer and pontic were investigated. The glass content was about 50 wt% for both kinds of prepregs. Bonding strength and modulus of FRP plate reinforced with glass roving were about 1.5 times larger than that of the FRP plate reinforced with glass cloth. Bonding strength of FRP specimen constructed by curing the prepreg put on the FRP plate was about 3 kgf/mm2. However, the bonding strength of specimen constructed by curing simultaneously the two prepregs was about 12 kgf/mm2. Though discrepancy of the FRP frame to stone cast of abutment tooth was proportional to the length of pontic, that of the FRP frame with a 50 mm pontic was less than 0.05 mm.

[Application of microwave for dental technique. 5. Injection molding system for resin base denture].

An injector and FRP denture flask were developed for injection molding and the fit of the denture base constructed with this injection molding system was evaluated. In addition, the flow and pressure of the dough, that is polymer-monomer mixture, in the mold space were investigated. The monomer of 10 mg/cm2 in the dough vaporized during the 5 minutes it took for the flash to be removed. When pressure of more than 55 kgf/cm2 was exerted to the dough, the dough was completely packed in the mold space. Fastening of the sprue with a bolt within 2 minutes after injection of the dough made the pressure of the dough increase to about 30 kgf/cm2. The dough in the mold space was maintained at a pressure of above 20 kgf/cm2 for microwave heating time. The adaptability of the resin base denture constructed with a combination of injection molding and microwave polymerization was 2 or 3 times greater than that of the denture constructed with microwave heating from the tissue side of the denture base.

[Development of denture base resin. 2. Manufacturing of visible-light cured prepreg and physical properties of FRP].

To develop the visible light-cured FRP denture base, we investigated the physical properties and the warp of FRP plate by using various combinations of matrix resin and reinforcement. From the results of the bending test, hardness test and manipulation processing, the matrix resin of Bis-GMA/UDMA/3 G at 48/48/4 wt% was determined. The sateen weave's glasscloth as the reinforcement of the prepreg was used. The maximum plies included FRP of 0.5 mm, 0.8 and 1.0 mm thickness have the same maximum bending strengths of 45 kgf/mm2, which is about 5 times larger than that of conventional acrylic resin. The warp of these FRP plates were not found.

[Production of denture by preform compression molding method. Part 3. Retentive strength of artificial teeth].

A preform compression molding method to make a polysulfone denture has been reported. Retentive strength of artificial teeth to the denture base was examined to select artificial teeth for the compression molding method. Ceramic teeth with metal pins and polysulfone teeth heated at above 140 degrees C were retained to the denture base by useful retentive strength. Acrylic teeth on which the adhesive was used were also retained by useful strength. Each of the teeth, acrylic teeth, ceramic teeth and polysulfone teeth, could be used in the compression molding method.

[The production of denture by preform compression molding method. Part 2. Model material and fittability].

A preform compression molding method to make polysulfone denture was reported previously by paper. Properties of the mold, adaptability of the molded denture to master model and the movement of artificial teeth were examined. It was necessary to raise the temperature of the crystbalite-stone model above 270 degrees C to obtain stable expansion. Mold made using 22 wt%-colloidal silica showed strong compressive strength under the compression molding condition. Displacement of artificial teeth between wax denture and polysulfone denture was independent of the mold expansion, and the displacement was equal to that of heat-curing acrylic denture. Adaptability of the molded denture to the master model was associated with expansion of the model. Good adaptability was obtained under the expansion of the model, such as setting expansion about 0.30% and total expansion 1.05-1.10%, with about 0.2 mm average discrepancy.