Indentation modulus and hardness of whisker-reinforced heat-cured dental resin composites.

OBJECTIVES: Recent studies showed that ceramic whisker reinforcement imparted a two-fold increase in the strength of dental composites. The aim of this study was to investigate the indentation response and measure the elastic modulus, hardness, and brittleness of whisker-reinforced heat-cured resin composites as a function of filler level, heat-cure temperature, and heat-cure duration. METHODS: Silica particles were fused onto silicon nitride whiskers to facilitate silanization and to roughen the whiskers for improved retention in matrix. Whisker filler mass fractions of 0, 20, 40, 60, 70, 74 and 79% were tested. Heat-cure temperature ranged from 100 to 180 degrees C, and duration from 10 min to 24 h. A nano-indentation system enabled the measurement of elastic modulus. Fracture toughness was measured and composite brittleness index was calculated. An inlay/onlay composite and a prosthetic composite were tested as controls. RESULTS: Whisker filler level and heat-cure duration had significant effects on composite properties, while heat-cure temperature had non-significant effects. The whisker composite with 79% filler level had a modulus in GPa (mean (SD); n = 6) of 26.9 (1.0), significantly higher than 15.1 (0.2) of an inlay/onlay control, and 16.1 (0.3) of a prosthetic control (Tukey's multiple comparison test; family confidence coefficient = 0.95). The fracture toughness in MPa.m1/2 was 2.22 (0.26) for the whisker composite, higher than 0.95 (0.11) for inlay/onlay control, and (1.13 +/- 0.19) for prosthetic control. The brittleness index was (0.49 +/- 0.07) for whisker composite, lower than (1.02 +/- 0.12) for inlay/onlay control and (0.63 +/- 0.13) for prosthetic control. SIGNIFICANCE: Whisker filler level had a profound influence, heat-cure duration had significant effects, while temperature did not have significant effects, on the properties of whisker composite. The whisker composite had significantly higher elastic modulus and fracture toughness, and lower brittleness than the inlay/onlay and prosthetic controls.     

Effects of different whiskers on the reinforcement of dental resin composites.

OBJECTIVE: Whiskers were recently used to reinforce dental composites to extend their use to large stress-bearing restorations. The aim of this study was to investigate the effects of different types of whiskers on composite properties. METHODS: Silicon nitride and silicon carbide whiskers were each mixed with silica particles at whisker/silica mass ratios of 0:1, 1:5, 1:2, 1:1, 2:1, 5:1, and 1:0, and thermally treated. The composite was heat-cured at 140 degrees C. Strength and fracture toughness were measured in flexure, while elastic modulus and hardness were measured with nano-indentation. RESULTS: Both whisker type and whisker/silica ratio had significant effects on composite properties (two-way ANOVA; p<0.001). Silicon nitride whiskers increased the composite strength and toughness more than did silicon carbide. Silicon carbide whiskers increased the modulus and hardness more than silicon nitride did. The silicon nitride whisker composite reached a strength (mean+/-SD; n=6) of 246+/-33 MPa at whisker/silica of 1:1, while the silicon carbide whisker composite reached 210+/-14 MPa at 5:1. Both were significantly higher than 114+/-18 MPa of a prosthetic control and 109+/-23 MPa of an inlay/onlay control (Tukey's multiple comparison test; family confidence coefficient=0.95). Fracture toughness and work-of-fracture were also increased by a factor of two. Higher whisker/silica ratio reduced the composite brittleness to 1/3 that of the inlay/onlay control. SIGNIFICANCE: Whisker type and whisker/silica ratio are key microstructural parameters that determine the composite properties. Reinforcement with silica-fused whiskers results in novel dental composites that possess substantially higher strength and fracture toughness, and lower brittleness than the non-whisker control composites.     

Wear and mechanical properties of nano-silica-fused whisker composites

Resin composites must be improved if they are to overcome the high failure rates in large stress-bearing posterior restorations. This study aimed to improve wear resistance via nano-silica-fused whiskers. It was hypothesized that nano-silica-fused whiskers would significantly improve composite mechanical properties and wear resistance. Nano-silicas were fused onto whiskers and incorporated into a resin at mass fractions of 0%-74%. Fracture toughness (mean +/- SD; n = 6) was 2.92 +/- 0.14 MPa.m(1/2) for whisker composite with 74% fillers, higher than 1.13 +/- 0.19 MPa.m(1/2) for a prosthetic control, and 0.95 +/- 0.11 MPa.m(1/2) for an inlay/onlay control (Tukey's at 0.95). A whisker composite with 74% fillers had a wear depth of 77.7 +/- 6.9 mum, less than 118.0 +/- 23.8 microm of an inlay/onlay control, and 172.5 +/- 15.4 microm of a prosthetic control (p < 0.05). Linear correlations were established between wear and hardness, modulus, strength, and toughness, with R = 0.95-0.97. Novel nano-silica-fused whisker composites possessed high toughness and wear resistance with smooth worn surfaces, and may be useful in large stress-bearing restorations.     

Three-body wear of dental resin composites reinforced with silica-fused whiskers.

OBJECTIVE: Recent studies used silica-fused whiskers to increase the strength and toughness of resin composites. This study investigated the three-body wear of whisker composites. It was hypothesized that the whisker composites would be more wear resistant than composites reinforced with fine glass particles, and the whisker-to-silica filler ratio would significantly affect wear. METHODS: Silica particles were mixed with silicon nitride whiskers at seven different whisker/(whisker + silica) mass fractions (%): 0, 16.7, 33.3, 50, 66.7, 83.3, and 100. Each mixture was heated at 800 degrees C to fuse the silica particles onto the whiskers. Each powder was then silanized and incorporated into a dental resin to make the wear specimens. A four-station wear machine was used with specimens immersed in a slurry containing polymethyl methacrylate beads, and a steel pin was loaded and rotated against the specimen at a maximum load of 76 N. RESULTS: Whisker-to-silica ratio had significant effects (one-way ANOVA; p < 0.001) on wear. After 4 x 10(5) wear cycles, the whisker composite at whisker/(whisker + silica) of 16.7% had a wear scar diameter (mean +/- sd; n = 6) of (643 +/- 39) microm and a wear depth of (82 +/- 19) microm, significantly less than a wear scar diameter of (1184 +/- 34) microm and a wear depth of (173 +/- 15) microm of a commercial prosthetic composite reinforced with fine glass particles (Tukey's multiple comparison). SEM examination revealed that, instead of whiskers protruding from the worn surface, the whiskers were worn with the composite surface, resulting in relatively smooth wear surfaces. SIGNIFICANCE: Silica-fused whisker reinforcement produced dental resin composites that exhibited high resistance to wear with smooth wear surfaces. These properties, together with the strength and fracture toughness being twice those of current glass particle-reinforced composites, may help extend the use of resin composite to large stress-bearing posterior restorations.     

Effects of whisker-to-silica ratio on the reinforcement of dental resin composites with silica-fused whiskers

Resin composites need to be strengthened to improve their performance in large stress-bearing restorations. This study aimed to reinforce composites with whiskers and to investigate the effects of the whisker:silica ratio. It was hypothesized that changing the whisker-silica ratio would affect the whisker-matrix bonding and the filler's distribution, and hence alter the composite properties. Silica particles and whiskers were mixed at various whisker:silica mass ratios, thermally fused, and combined with a dental resin at filler mass fractions of 0-65%. Whisker:silica ratio and filler level had significant effects on composite properties. At 60% filler level, the silica composite (whisker:silica = 0:1) had a flexural strength (mean +/- SD; n = 6) of 104 +/- 21 MPa; that at a whisker:silica ratio of 1:0 was 74 +/- 36 MPa. However, that of the silica-fused whisker composite (whisker:silica = 5:1) was 210 +/- 14 MPa, compared with 109 +/- 23 MPa and 114 +/- 18 MPa of two prosthetic controls. Mixing silica with whiskers minimized whisker entanglement, improved filler distribution in the matrix, and facilitated whisker silanization and bonding to the matrix, thus resulting in substantially stronger composites.     

Ceramic whisker reinforcement of dental resin composites

Resin composites currently available are not suitable for use as large stress-bearing posterior restorations involving cusps due to their tendencies toward excessive fracture and wear. The glass fillers in composites provide only limited reinforcement because of the brittleness and low strength of glass. The aim of the present study was to reinforce dental resins with ceramic single-crystalline whiskers of elongated shapes that possess extremely high strength. A novel method was developed that consisted of fusing silicate glass particles onto the surfaces of individual whiskers for a two-fold benefit: (1) to facilitate silanization regardless of whisker composition; and (2) to enhance whisker retention in the matrix by providing rougher whisker surfaces. Silicon nitride whiskers, with an average diameter of 0.4 microm and length of 5 microm, were coated by the fusion of silica particles 0.04 microm in size to the whisker surface at temperatures ranging from 650 degrees C to 1000 degrees C. The coated whiskers were silanized and manually blended with resins by spatulation. Flexural, fracture toughness, and indentation tests were carried out for evaluation of the properties of the whisker-reinforced composites in comparison with conventional composites. A two-fold increase in strength and toughness was achieved in the whisker-reinforced composite, together with a substantially enhanced resistance to contact damage and microcracking. The highest flexural strength (195+/-8 MPa) and fracture toughness (2.1+/-0.3 MPa x m(1/2)) occurred in a composite reinforced with a whisker-silica mixture at whisker:silica mass ratio of 2:1 fused at 800 degrees C. To conclude, the strength, toughness, and contact damage resistance of dental resin composites can be substantially improved by reinforcement with fillers of ceramic whiskers fused with silica glass particles.     

Long-term water-aging of whisker-reinforced polymer-matrix composites

Long-term water exposure may degrade polymer-matrix composites. This study investigated the water-aging of whisker composites. It was hypothesized that whiskers would provide stable and substantial reinforcement, and that whisker type would affect water-aging resistance. Silica-fused Si(3)N(4) and SiC whiskers were incorporated into a resin. The specimens were tested by three-point flexure and nano-indentation vs. water-aging for 1 to 730 days. After 730 days, SiC composite had a strength (mean +/- SD; n = 6) of 185 +/- 33 MPa, similar to 146 +/- 44 MPa for Si(3)N(4) composite (p = 0.064); both were significantly higher than 67 +/- 23 MPa for an inlay/onlay control (p < 0.001). Compared with 1 day, the strength of the SiC composite showed no decrease, while that of the Si(3)N(4) composite decreased. The decrease was due to whisker weakening rather than to resin degradation or interface breakdown. Whisker composites also had higher moduli than the controls. In conclusion, silica-fused whiskers bonded to polymer matrix and resisted long-term water attack, resulting in much stronger composites than the controls after water-aging.     

Dental composite resins containing silica-fused ceramic single-crystalline whiskers with various filler levels.

Currently available direct-filling composite resins are susceptible to fracture and hence are not recommended for use in large stress-bearing posterior restorations involving cusps. The glass fillers in composites provide only limited reinforcement because of the brittleness and low strength of glass. The aim of the present study was to use ceramic single-crystalline whiskers as fillers to reinforce composites, and to investigate the effect of whisker filler level on composite properties. Silica particles were fused onto the whiskers to facilitate silanization and to roughen the whiskers, thereby improving retention in the matrix. The composite flexural strength, elastic modulus, hardness, and degree of polymerization conversion were measured as a function of whisker filler mass fraction, which ranged from 0% to 70%. Selected composites were polished simulating clinical procedures, and the surface roughness was measured with profilometry. The whisker composite with a filler mass fraction of 55% had a flexural strength (mean +/- SD; n = 6) of 196+/-10 MPa, significantly higher than 83+/-14 MPa of a microfill and 120+/-16 MPa of a hybrid composite control (family confidence coefficient = 0.95; Tukey's multiple comparison). The composite modulus and hardness increased monotonically with filler level. The flexural strength first increased, then plateaued with increasing filler level. The degree of conversion decreased with increasing filler level. The whisker composite had a polished surface roughness similar to that of a conventional hybrid composite (p>0.1; Student's t). To conclude, ceramic whisker reinforcement can significantly improve the mechanical properties of composite resins; the whisker filler level plays a key role in determining composite properties; and the reinforcement mechanisms appear to be crack pinning by whiskers and friction from whisker pullout resisting crack propagation.     

Nano DCPA-whisker composites with high strength and Ca and PO(4) release

The main challenges facing composite restorations are secondary caries and bulk fracture. The objective of this study was to develop nano DCPA (dicalcium phosphate anhydrous)-whisker composites with high strength and Ca and PO(4) ion release to combat caries. Flexural strength for the nano DCPA-whisker composites at a nano DCPA:whisker mass ratio of 1:2 ranged from (148 +/- 9) MPa to (167 +/- 23) MPa, significantly higher than the (103 +/- 32) MPa of an inlay/onlay commercial control composite without Ca-PO(4) release. The nano DCPA-whisker composite released PO(4) to a concentration of (1.95 +/- 0.13) mmol/L and Ca of (0.68 +/- 0.05) mmol/L. Compared with previous conventional Ca- and PO(4)-releasing composites, the nano DCPA-whisker composites had strengths two-fold higher, and released comparable or higher levels of Ca and PO(4). In conclusion, combining nano-DCPA with whiskers yielded novel composites that released high levels of Ca and PO(4) requisite for remineralization. These high-strength composites may provide a unique combination of stress-bearing and caries-inhibiting capabilities.     

热处理时间对钛酸钾晶须增强牙用复合树脂的抗弯强度的影响

目的：研究不同热处理时间对钛酸钾晶须增强的复合树脂抗弯强度的影响。方法：将3%硅烷偶联剂处理过的钛酸钾晶须按照60%质量分数的填充量与树脂基质手工搅拌混合后制备复合树脂三点弯曲测试标准试件四组,每组6个。四组标准试件分别经120℃热处理30min、45min、1h、2h后按照ISO-10477的标准进行三点弯曲测试。结果：热处理时间1h的复合树脂抗弯强度（123.90±15.90）MPa明显高于热处理时间为30min时的抗弯强度（98.82±15.84）MPa。结论：钛酸钾晶须增强复合树脂经120℃热处理30min-1h时,随着热处理时间的增加,抗弯强度逐渐增大。     

Single-crystalline ceramic whisker-reinforced carboxylic acid-resin composites with fluoride release

Currently available glass-ionomer, resin-modified glass-ionomer, and compomer materials have relatively low strength and toughness and, therefore, are inadequate for use in large stress-bearing posterior restorations. In the present study, ceramic single-crystalline whiskers were mixed with fluorosilicate glass particles and used as fillers to reinforce experimental carboxylic acid-resin composites. The carboxylic acid was a monofunctional methacryloxyethyl phthalate (MEP). Five mass fractions of whisker/(whisker + fluorosilicate glass), and corresponding resin (resin + MEP), were evaluated. Four control materials were also tested for comparison: a glass ionomer, a resin-modified glass ionomer, a compomer, and a hybrid composite resin. Flexural specimens were fabricated to measure the flexural strength, elastic modulus, and work-of-fracture (an indication of toughness). Fluoride release was measured by using a fluoride ion selective electrode. The properties of whisker composites depended on the whisker/(whisker + fluorosilicate glass) mass fraction. At a mass fraction of 0.8, the whisker composite had a flexural strength in MPa (mean +/- sd; n = 6) of 150 +/- 16, significantly higher than that of a glass ionomer (15 +/- 7) or a compomer control (89 +/- 18) (Tukey's multiple comparison test; family confidence coefficient = 0.95). Depending on the ratio of whisker:fluorosilicate glass, the whisker composites had a cumulative fluoride release up to 60% of that of a traditional glass ionomer. To conclude, combining ceramic whiskers and fluorosilicate glass in a carboxylic acid-resin matrix can result in fluoride-releasing composites with significantly improved mechanical properties.     

Hardness and fracture toughness of four commercial visible light-cured composite resin veneering materials

summary Four commercial visible light (VL)-cured composite resin veneering materials with a dentine shade were examined for their Knoop hardness and fracture toughness. Composite specimens were classified into three groups. The first group was cured by VL only, the second group was cured by VL and postcured by VL and the third group was cured by VL and post-cured by heat. It became evident that one composite containing four-functional urethane monomer had both hardness and fracture toughness greater than those of the other three composites containing two-functional urethane monomer. The filler content (vol%) in the composite tended to be linearly proportional to both hardness and fracture toughness. Post-curing by VL and heat were proven to effectively increase both hardness and fracture toughness of once light-cured composites. These results suggest that the clinical performance (e.g. wear resistance and colour stability) of VL-cured composite resin veneering materials might be improved with the aid of post-curing.     

Dental resin composites containing ceramic whiskers and precured glass ionomer particles.

OBJECTIVES: Glass ionomer, resin-modified glass ionomer, and compomer materials are susceptible to brittle fracture and are inadequate for use in large stress-bearing posterior restorations. The aim of this study was to use ceramic single crystal whiskers to reinforce composites formulated with precured glass ionomer, and to examine the effects of whisker-to-precured glass ionomer mass ratio on mechanical properties, fluoride release, and polishability of the composites. METHODS: Silica particles were fused onto silicon nitride whiskers to facilitate silanization and to improve whisker retention in the matrix. Hardened glass ionomer was ground into a fine powder, mixed with whiskers, and used as fillers for a dental resin. Four control materials were also tested: a glass ionomer, a resin-modified glass ionomer, a compomer, and a hybrid composite. A three-point flexural test was used to measure flexural strength, modulus, and work-of-fracture. A fluoride ion-selective electrode was used to measure fluoride release. Composite surfaces polished simulating clinical procedures were examined by SEM and profilometry. RESULTS: At whisker/(whisker + precured glass ionomer) mass fractions of 1.0 and 0.91, the whisker composite had a flexural strength in MPa (mean (SD); n = 6) of (196 (10)) and (150 (16)), respectively, compared to (15 (7)) for glass ionomer, (39 (8)) for resin-modified glass ionomer, (89 (18)) for compomer, and (120 (16)) for hybrid composite. The whisker composite had a cumulative fluoride release of nearly 20% of that of the glass ionomer after 90 days. The whisker composites had surface roughness comparable to the hybrid resin composite. SIGNIFICANCE: Composites filled with precured glass ionomer particles and whiskers exhibit moderate fluoride release with improved mechanical properties; the whisker-to-glass ionomer ratio is a key microstructural parameter that controls fluoride release and mechanical properties.     

The effect of filler loading and morphology on the mechanical properties of contemporary composites

STATEMENT OF PROBLEM: Little information exists regarding the filler morphology and loading of composites with respect to their effects on selected mechanical properties and fracture toughness. PURPOSE: The objectives of this study were to: (1) classify commercial composites according to filler morphology, (2) evaluate the influence of filler morphology on filler loading, and (3) evaluate the effect of filler morphology and loading on the hardness, flexural strength, flexural modulus, and fracture toughness of contemporary composites. MATERIAL AND METHODS: Field emission scanning electron microscopy/energy dispersive spectroscopy was used to classify 3 specimens from each of 14 commercial composites into 4 groups according to filler morphology. The specimens (each 5 x 2.5 x 15 mm) were derived from the fractured remnants after the fracture toughness test. Filler weight content was determined by the standard ash method, and the volume content was calculated using the weight percentage and density of the filler and matrix components. Microhardness was measured with a Vickers hardness tester, and flexural strength and modulus were measured with a universal testing machine. A 3-point bending test (ASTM E-399) was used to determine the fracture toughness of each composite. Data were compared with analysis of variance followed by Duncan's multiple range test, both at the P<.05 level of significance. RESULTS: The composites were classified into 4 categories according to filler morphology: prepolymerized, irregular-shaped, both prepolymerized and irregular-shaped, and round particles. Filler loading was influenced by filler morphology. Composites containing prepolymerized filler particles had the lowest filler content (25% to 51% of filler volume), whereas composites containing round particles had the highest filler content (59% to 60% of filler volume). The mechanical properties of the composites were related to their filler content. Composites with the highest filler by volume exhibited the highest flexural strength (120 to 129 MPa), flexural modulus (12 to 15 GPa), and hardness (101 to 117 VHN). Fracture toughness was also affected by filler volume, but maximum toughness was found at a threshold level of approximately 55% filler volume. CONCLUSION: Within the limitations of this study, the commercial composites tested could be classified by their filler morphology. This property influenced filler loading. Both filler morphology and filler loading influenced flexural strength, flexural modulus, hardness, and fracture toughness.     

Effect of novel filler particles on the mechanical and wear properties of dental composites.

OBJECTIVES: The purpose of this study was to investigate the method of producing pre-polymerized fused-fiber filler modified composite (PP-FFMC) particles and the effectiveness of incorporating these novel filler particles into dental composites. METHODS: Fused-fiber filler (FFF) blocks were impregnated with composite by two different methods. Three-point flexure tests were utilized to determine which was more effective. In order to assess the effect of the addition of PP-FFMC particles, two Bis-GMA/TEGDMA based conventional composite compositions were utilized as baselines, to which the novel particles were added. Mechanical and wear tests were performed to determine the fracture toughness, biaxial flexure strength, and in vitro wear of the materials. RESULTS: Mechanical testing showed that the addition of PP-FFMC particles decreased the strength and toughness of the conventional composites. Wear tests indicated that addition of the same particles improved the wear behavior of the conventional composites. SEM analysis of the fracture surfaces indicated that the PP-FFMC particles were incorporated without creating porosity, and that fracture was transgranular through the reinforcing particles. Microscopic flaws observed in the novel particles are the likely explanation for the observed strength and toughness values. SIGNIFICANCE:The results indicate that PP-FFMC particles have the potential to improve the wear properties of dental composites, however, they adversely affect the fracture behavior. Existing processing techniques for these particles, which introduce imperfections, limit their current usefulness.     

Fracture toughness of nine flowable resin composites

STATEMENT OF PROBLEM: Flowable composite is used in a variety of clinical applications; however, the capacity of these materials to resist crack propagation is not well understood. PURPOSE: The purpose of this investigation was to compare the resistance to crack propagation of 9 flowable composites as measured by the fracture toughness. MATERIAL AND METHODS: The composites studied include AeliteFlo, Crystal Essence, Flow-it, FloRestore, Permaflo, Revolution, Tetric Flow, VersaFlo, and Wave. Ten specimens of each composite were formed with a brass mold with a 3-mm preformed notch. The final dimensions of each specimen were 2 x 4.2 x 20 mm. All specimens were light-polymerized to manufacturer specifications and stored in air for 24 hours. The fracture toughness value, K(IC) (MNm(-3/2)), for each specimen was measured by use of a 3-point bending mode and a single-edge notched beam at a crosshead speed of 0.125 mm/min until fracture. The data were analyzed statistically by use of 1-way analysis of variance, t tests (P<.05), and regression analysis. RESULTS: The flowable composites tested showed a spectrum of fracture toughness values ranging from 1.15 +/- 0.10 MNm(-3/2) for Wave to 1.65 +/- 0.13 MNm(-3/2) for Permaflo (significantly different, P<.05). The remaining materials formed 1 group with intermediate K(IC) values not different from each other (P>.05) but significantly different from Wave and Permaflo. Comparisons of fracture toughness to the filler content by volume of each composite revealed no correlation. CONCLUSION: This in vitro study concluded that there was no significant difference among 7 of the 9 composites tested in their resistance to fracture. Permaflo showed the greatest resistance to crack propagation. There was no correlation between the filler content by volume and the fracture toughness of these flowable composites.     

Nanocomposites with Ca and PO4 release: Effects of reinforcement, dicalcium phosphate particle size and silanization

OBJECTIVES: Nanoparticles of dicalcium phosphate anhydrous (DCPA) were synthesized in our laboratory for the first time and incorporated into a dental resin. Our goal was to develop a mechanically strong dental composite that has Ca and PO(4) ion release to combat tooth caries, and to investigate the effects of whisker reinforcement, DCPA particle size and silanization. METHODS: DCPA nanoparticles and two larger DCPA particles were used with nano-silica-fused whiskers as fillers in a resin matrix. Composite mechanical properties were measured via three-point flexure, and the release of Ca and PO(4) ions were measured versus time. RESULTS: Using DCPA nanoparticles with a diameter of 112nm, the composite at a DCPA:whisker mass ratio of 1:1 had a flexural strength (mean+/-S.D.; n=5) of (112+/-17)MPa, not significantly different from (112+/-14)MPa of a commercial non-releasing composite; both were higher than (29+/-7)MPa for the composite at DCPA:whisker of 1:0 (p<0.05). The composite with DCPA particle size of 112nm released Ca to a concentration of 0.85mmol/L and PO(4) of 3.48mmol/L, higher than Ca of 0.67mmol/L and PO(4) of 1.11mmol/L using DCPA with 12microm particle size (p<0.05). Silanization of DCPA increased the composite strength at DCPA:whisker of 1:0 compared to that without silanization, but decreased the Ca and PO(4) release (p<0.05). Increasing the DCPA particle surface area increased the Ca and PO(4) release. SIGNIFICANCE: Decreasing the DCPA particle size increased the Ca and PO(4) release; whisker reinforcement increased the composite strength by two- to three-fold. The nano DCPA-whisker composites, with high strength and Ca and PO(4) release, may provide the needed, unique combination of stress-bearing and caries-inhibiting capabilities.     

Physical and mechanical properties of an experimental dental composite based on a new monomer.

OBJECTIVE: The purpose of this study was to investigate the physical and mechanical properties of a dental composite based on BTDMA, a new dimethacrylate monomer based on BTDA (3,3',4,4'-benzophenone tetracarboxylic dianhydride), and to compare these with the properties of a composite based on commonly used Bis-GMA monomer. METHODS: Experimental composites were prepared by mixing the silane-treated filler with the monomers. The prepared pastes were inserted into the test molds and heat-cured. Light-cured composites were also prepared using camphorquinone and amine as photoinitiator system. Degree of conversion of the light-cured and heat-cured composites was measured using FTIR spectroscopy. The flexural strength, flexural modulus, diametral tensile strength (DTS), water sorption, water contact angle, microhardness and thermal expansion coefficient of the prepared composites were measured and compared. Water uptake of the monomers was also measured. RESULTS: The results showed that the mechanical properties of the new composite are comparable with the properties of the Bis-GMA-based composite but its water sorption is higher. BTDMA as a monomer containing aromatic rings and carboxylic acid groups in its structure gives a composite with good mechanical properties. There is a close relation between the contact angle, water sorption of the cured composite and water uptake of their monomers. SIGNIFICANCE: Finding new monomers as alternatives for Bis-GMA have been a challenge in the field of dental materials and any investigation into the properties of new composites would be beneficial in the development of dental materials.     

Effects of calcium phosphate nanoparticles on Ca-PO4 composite

Nano-particles of dicalcium phosphate anhydrous (DCPA) were synthesized for the first time. The objectives of this study were to incorporate DCPA nano-particles into resin for Ca-PO(4) release to combat dental caries, and to investigate the filler level effects. Nano-DCPA and nano-silica-fused silicon nitride whiskers at a 1:1 ratio were used at filler mass fractions of 0-75%. The flexural strengths in MPa (mean +/- SD; n = 6) of DCPA-whisker composites ranged from (106 +/- 39) at 0% fillers to (114 +/- 23) at 75% fillers, similar to (112 +/- 22) of a non-releasing composite (TPH) (p > 0.1). The composite with 75% fillers in a NaCl solution (133 mmol/L, pH = 7.4, 37 degrees C) yielded a Ca concentration of (0.65 +/- 0.02) mmol/L and PO(4) of (2.29 +/- 0.07) mmol/L. Relationships were established between ion-release and DCPA volume fraction V(DCPA): Ca = 4.46 V(DCPA)(1.6,) and = 66.9 V(DCPA)(2.6). Nano-DCPA-whisker PO(4) composites had high strength and released high levels of Ca-PO(4) requisite for remineralization. These new nano-composites could provide the needed combination of stress-bearing and caries-inhibiting capabilities.     

Properties of heat-treated composites after aging in water

Objectives. Post-cure heat treatments have been shown to increase the fracture toughness and elastic modulus of composites. The objective of this study was to determine if the increase remained after the composites were aged in water.Methods. The fracture toughness (K_Ic), flexural modulus and flexural strength of four experimental and one commercial composite (Z-100, 3M Dental Products) were tested after 1, 7, 30, 60 and 180 d of aging in 37°C water. The four experimental composites were made with a BisGMA/TEGDMA resin and were characterized as follows: Micro = 38 vol% silane-treated silica, Fine = 65 vol% silane-treated quartz of 1–2 μm average size, Hybrid = 65 vol% silane treated quartz of a mixture of 1–2 μm average and 8 μm average size, and Large = 65 vol% quartz of 8 μm average size (of which only 75% were silane-treated). All specimens were light-cured (normal-cured; Triad II-80 s). One set of each composite was further heat-cured at 120°C for 10 min (heat-cured). A third set of the Hybrid was heat-cured with simultaneous light exposure (Elipar, Espe) for the first 3 min.Results. By 30 d, normal-cured and heat-cured specimens showed significant (ANOVA/Tukey's test; p ≤ 0.05) reductions in fracture toughness (avg. 16% and 22%, respectively), flexural modulus (avg. 11% and 11%, respectively) and flexural strength (avg. 25% and 29%, respectively). Further aging had little effect. The use of additional light-curing during heating did not affect the properties more than heat-curing alone.Significance. The improvements in some of the properties of composites produced by heat-treating are of only short-term benefit, and are for the most part negated due to an alteration of the resin matrix as the composite equilibrates with water.