Bond strength of six soft denture liners processed against polymerized and unpolymerized poly(methyl methacrylate).

The bond strength of six commercial soft denture liners was evaluated by a two-phase tensile test. The soft denture liners investigated were VinaSoft, Prolastic, Flexor, Molloplast-B, Novus, and SuperSoft. The samples were fabricated by processing them (1) against polymerized poly(methyl methacrylate), and (2) against unpolymerized poly(methyl methacrylate). The soft denture liners were processed according to the manufacturers recommendations. The samples were tested using an Instron Universal Testing Machine. The mode of failure, adhesive or cohesive, was also recorded. The bond strength when processed against unpolymerized poly(methyl methacrylate) ranged from 0.48 to 2.60 MPa, and when processed against polymerized poly(methyl methacrylate) the bond strength ranged from 0.94 to 2.56 MPa. A two-way analysis of variance (P = .05) revealed a significant increase in bond strength when the liners were processed against polymerized poly(methyl methacrylate), except for Novus, which had no change, and VinaSoft, which decreased. The Tukey interval between materials was .22 and between methods of polymerization was .08. Four of the six liners investigated demonstrated increased bond strength when processed against polymerized poly(methyl methacrylate). It was concluded that bonding can be influenced by the processing method.

Effect of mixed silanes on the hydrolytic stability of composites.

A filler for a urethanedimethacrylate composite was silanated with mixtures of fluoroalkyl-, aminoalkyl-, phenyl-, vinyl-, bis silyl ethane- and 3-methacryloxypropyltrimethoxysilane (MAOP) in an attempt to increase the hydrophobicity of the coupling agent layer. Diametral tensile strength was used to evaluate composites stored for (1) 24 h in 23 degrees C (RT) air; (2) 24 h in RT air plus 24 h in 100 degrees C air; (3) 24 h in RT air plus 24 h in 100 degrees C water; and (4) 24 h in RT air plus 24 h in 100 degrees C air plus 24 h in 100 degrees C water. Water sorption and solubility of composites was also determined on samples stored for 24 h in RT air. Heating composites for 24 h in 100 degrees C air increased the tensile strength in eight of 13 silane treatments, while heating in 100 degrees C water for 24 h caused decreases for five silane treatments, no change for six and increases in tensile strength for two silane treatments. When composites that had been stored for 24 h at RT plus heated for 24 h in 100 degrees C air were then heated for 24 h in 100 degrees C water, only one silane treatment, the vinyltriethoxysilane at 25% (25% V), showed no significant decrease in tensile strength. Also, the composite silanated with 25% V had the highest value for tensile strength after storing for 24 h at RT air plus 24 h in 100 degrees C air plus 24 h in 100 degrees C water. These data indicate that the use of vinyltriethoxysilane increases the hydrolytic stability of the composite. Water sorption and solubility of the silanated composites were not satisfactory tests for evaluating hydrolytic stability of composites.

In vitro comparison of parameters affecting the fixation strength of sagittal split osteotomies.

PURPOSE: The goal of this study was to determine how different parameters affect the bending strength of human cadaver mandibles that have undergone a sagittal split osteotomy. MATERIALS AND METHODS: The effects of screw material (titanium [Ti] vs polylactic acid/polyglycolic acid [PLA/PGA]), screw configuration (linear vs inverted L-shape), screw diameter (2.0 mm vs 2.7 mm), material into which screws were inserted (human mandible, bovine rib, synthetic polymer), and loading rate (1.0 mm/min vs 10.0 mm/min) were quantified. Also, biomechanical principles were used to model shear stress and displacement. Variable lever arms, screw material, screw diameter, screw configuration, distance between screws, and bone properties were all evaluated in this model. RESULTS: Accounting for variable mandible geometries and differentiating between deflections (and shear stresses) due to bending and due to torsion, in vitro mechanical testing revealed that there was a statistically significant difference in total shear stress at 3 mm of deflection depending on screw material (Ti > PLA/PGA), screw diameter, and material into which screws are inserted (mandibles > ribs = synthetic polymer). There was no significant difference in total shear stress depending on screw configuration or strain rate. CONCLUSION: Total shear stress and deflections are important and more viable parameters than load to assess parameters of clinical importance in osteotomy or fracture fixation.

Mechanical properties of laser-welded cast and wrought titanium.

This study evaluated the mechanical properties of laser-welded cast and wrought titanium base and compared them with those of a brazed type IV casting gold alloy. Ultimate tensile strength, 0.2% yield strength, and percent elongation were recorded for joined and unjoined bars of the previously mentioned materials. Sections of titanium bars were laser-welded, and gold alloy bars were brazed. Both joining methods significantly reduced the ductility of the material. The strength of the cast gold alloy was superior to that of titanium. However, the strength of the laser-welded titanium equaled that of the brazed gold alloy, which suggests that dental restorations made of cast and wrought titanium would satisfy ordinary clinical requirements.

Dynamic viscoelastic properties of processed soft denture liners: Part II--Effect of aging.

The proper functioning of soft denture liners depends to a great extent on their mechanical properties. As with many polymers these materials are affected by aging. Twelve soft denture liners were processed by a laboratory according to the manufacturers' directions. Five specimens of each material were tested without aging. Five additional specimens of each material were subjected to 900 hours of accelerated aging in a Weather-Ometer instrument. These were tested with a dynamic viscoelastometer at three frequencies and two temperatures, and data for 37 degrees C and 1 Hz was obtained. Two of the ethyl methacrylate resins demonstrated the largest increases in storage (E') and loss moduli (E") after aging. These materials also showed the greatest overall E' and E". One denture liner material exhibited 673% and 488% increases in E' and E", and other materials showed smaller increases. The effects of aging on the damping factor (tan delta) were varied and five materials showed increased tan delta. Only two ethyl methacrylate resins developed lower tan delta. All the silicone and polyphosphazine rubbers showed small changes after aging and had the lowest tan delta values. Significance of differences between materials and treatments was tested with ANOVA, Scheffé intervals, and t-tests at a = 0.05. The ethyl methacrylate soft denture liners were affected the most by accelerated aging, and the silicones and polyphosphazine were least affected. The ethyl methacrylate resins also had the greatest values of E', E", and tan delta after aging.

Dynamic viscoelastic properties of processed soft denture liners: Part I--Initial properties.

This research evaluated the dynamic viscoelastic properties of 12 laboratory-processed soft denture liners. Specimens, 1.4 x 3 x 40 mm, were prepared according to the manufacturer's instructions. Five specimens of each material were tested under applied strain frequencies of 1, 5, or 10 Hz and temperatures of 23 degrees C and 37 degrees C. The values at 37 degrees C and 1 Hz were judged most important because they closely approximate the service environment; therefore material comparisons were made for these conditions. Samples were tested with a custom-made dynamic viscoelastometer. The statistical significance of the results was tested by ANOVA and Scheffe's intervals test. Large differences in the storage modulus (elastic stiffness) were found. One acrylic resin, Verno-Soft, showed significantly higher storage moduli than the other materials. The viscous behavior of the materials was reflected by the loss modulus; here large differences were also found. Verno-Soft again exhibited much higher values than all of the other materials. Three other acrylic resins (Super Soft, Soft-Pak, and Justi Soft) also showed significantly higher loss moduli than the other materials. Significant differences were found in the damping factor between many of the materials. Most of the acrylic and vinyl resins had higher damping factors than the silicone and polyphosphazine rubbers. The values of the storage moduli, loss moduli, and the damping factor were affected by temperature and by applied strain frequency with some materials.

Sorption and solubility of 12 soft denture liners.

The long-term stability of a soft denture liner depends to a large extent on the sorption and solubility of the liner. Because sorption and solubility are accompanied by a volumetric change, bacterial infestation, hardening, and color change, it is a physical property of importance. The purpose of this investigation was to determine the sorption and solubility of 12 soft denture liners (Verno-Soft, Super Soft, ProTech, Soft-Pak, Flexor, Novus, Molloplast-B, Durosoft, Justi Soft, Velvesoft, VinaSoft and Prolastic). They include nine copolymers, two silicones and one polyphosphazene fluoroelastomer. The sorption and solubility test was performed as outlined in American Dental Association (ADA) specification 12 for denture base polymers. Five specimens of each material were tested and data were collected at 1 week, 1 month, 3 months, 6 months, and 1 year. Sorption data varied from 0.2 to 5.6 mg/cm2 at 1 week; 0.3 to 12.5 mg/cm2 at 1 month; 0.1 to 22.0 mg/cm2 at 3 months; 0.1 to 13.6 mg/cm2 at 6 months; and 0.1 to 35.7 mg/cm2 at 12 months. Solubility data varied from 0.0 to 0.4 mg/cm2 at 1 week; 0.1 to 0.8 mg/cm2 at 1 month; +0.1 to 1.2 mg/cm2 at 3 months; 0.0 to 1.9 mg/cm2 at 6 months; and +0.2 to 2.3 mg/cm2 at 1 year. A statistical analysis of the data by two-way ANOVA and calculated Tukey intervals showed significant differences between materials at all time intervals. The results of this study have clinical implications because the sorption and solubility may affect the long-term life expectancy of the soft denture liner.

Physical properties of three maxillofacial materials as a function of accelerated aging.

This study compares the tensile strength, elongation, Shore-A hardness, and tear resistance of three silicone maxillofacial materials before and after aging to provide comparative data for evaluation of new or experimental elastomers. The materials evaluated were MDX-4-4210, Factor II (A-2186), and Cosmesil. Tests were conducted 24 hours after specimen preparation and were repeated after aging for 900 hours in a Weather-Ometer device. Five samples were made for each material under all test conditions. After testing, mean values were calculated for all materials under all test conditions and were compared by two-way analysis of variance and Tukey intervals at p < or = 0.05.

Physical property comparison of 11 soft denture lining materials as a function of accelerated aging.

Soft denture-lining materials are an important treatment option for patients who have chronic soreness associated with dental prostheses. Three distinctly different types of materials are generally used. These are plasticized polymers or copolymers, silicones, or polyphosphazene fluoroelastomer. The acceptance of these materials by patients and dentists is variable. The objective of this study is to compare the tensile strength, percent elongation, hardness, tear strength, and tear energy of eight plasticized polymers or copolymers, two silicones, and one polyphosphazene fluoroelastomer. Tests were run at 24 hours after specimen preparation and repeated after 900 hours of accelerated aging in a Weather-Ometer device. The data indicated a wide range of physical properties for soft denture-lining materials and showed that accelerated aging dramatically affected the physical and mechanical properties of many of the elastomers. No soft denture liner proved to be superior to all others. The data obtained should provide clinicians with useful information for selecting soft denture lining materials for patients.

Comparison of bond strength of six soft denture liners to denture base resin.

The bond strength of six commercial soft denture liners was evaluated using a modified tensile test. The soft denture liners investigated were Prolastic, VinaSoft, Flexor, Molloplast-B, Novus, and Super-Soft. The samples were processed according to the manufacturers' instructions to cured denture base resin (polymethyl methacrylate; PMMA). The soft denture liners were 10 x 10 x 3 mm and were processed between two PMMA blocks. The samples were placed in tension until failure. The mode of failure, cohesive or adhesive, was also recorded. The results of this study showed that the bond strength is related to the components of the materials. Prolastic, VinaSoft, and Flexor had the lowest bond strength to cured PMMA and ranged from 9.6 to 11.3 kg/cm2. Super-Soft, Novus, and Molloplast-B demonstrated better bond strengths and ranged from 16.7 to 17.6 kg/cm2. The bond strength of Novus could be improved by using the recommended bonding agent and bonded Novus at 26.1 kg/cm2 had the highest bond strength of all materials tested.

Comparison of the physical properties of 11 soft denture liners.

Soft denture liners are an important treatment option for patients who have chronic soreness associated with their prostheses. The objective of this study is to determine the tensile strength, elongation, hardness, tear strength, and tear energy of eight plasticized polymers or copolymers, two silicones, and one polyphosphazene fluoroelastomer. Tests were made on samples that were stored in a humidor for 24 hours before testing. The range of data is as follows: tensile strength, 8 to 85 kg/cm2; percent elongation, 150% to 542%; hardness, 25 to 95 Shore-A units; tear energy, 1.43 x 10(6) to 40.4 x 10(6) ergs/cm2; tear resistance, 2.6 to 26.3 kg/cm. It can be concluded that (1) the data obtained can be useful in characterizing the performance of soft denture liners, (2) there is considerable variability in the physical/mechanical properties of soft denture liners, and (3) the required essential properties for soft denture liners are as yet not known.