Ionic Dimethacrylates for Antimicrobial and Remineralizing Dental Composites.

Two ionic dimethacrylates (IDMA1 and IDMA2) intended for utilization in multifunctional, antibacterial and remineralizing dental resins and composites were synthesized by nucleophilic substitution reactions. Crude IDMAs were purified by multi-step extraction from ethanol-diethyl ether-hexane solvent system. Their structures were validated by nuclear magnetic resonance and mass spectrometry. As evidenced by the water contact angle measurements ((63.2-65.5)0), IDMAs did not affect the wettability of urethane dimethacrylate (UDMA)- based copolymers (average contact angle ((60.8±5.1)0).The attained degrees of vinyl conversion increased from 88.1% (no-IDMA control) up to 93.0% (IDMA2 series). Flexural strength (FS) of copolymers was reduced from 94.8 MPa (control) to (68.9-71.8) MPa (IDMA counterparts) independent of monomer type and/or its concentration. This reduction in FS should not disqualify IDMAs from consideration as viable antibacterial agents in multifunctional restoratives. Tested at concentrations exceeding the expected leachability of unreacted monomers from cured copolymers and/or composites, IDMAs had no deleterious effect on viability and/or metabolic activity of fibroblasts. The remineralization potential of amorphous calcium phosphate IDMA/UDMA composites was confirmed by calcium and phosphate ion release kinetic experiments. Results of this study warrant in-depth biological, physicochemical, mechanical and antibacterial assessments of IDMA resins and composites to identify prototype(s) suitable for clinical testing.

Chipping fracture resistance of dental CAD/CAM restorative materials: part I--procedures and results.

OBJECTIVE: The edge chipping test was used to measure the fracture resistance of CAD/CAM dental restoration ceramics and resin composites. METHODS: An edge chipping machine was used to evaluate six materials including one feldspathic porcelain, two glass ceramics, a filled resin-composite, a yttria-stabilized zirconia, and a new ceramic-resin composite material. Force versus edge distance data were collected over a broad range of forces and distances. Data were analyzed by several approaches and several chipping resistance parameters were evaluated. The effects of using different indenter types were explored. RESULTS: The force versus distance trends were usually nonlinear with good fits to a power law equation with exponents usually ranging from 1.2 to 1.9. The order of chipping resistance (from least to greatest) was: feldspathic porcelain and a leucite glass ceramic (which were similar), followed by the lithium disilicate glass ceramic and the two resin composites (which were similar), and finally the zirconia which had the greatest resistance to chipping. Chipping with a Vickers indenter required 28-45% more force than with the sharp conical 120° indenter. The two indenters rank materials approximately the same way. The power law exponents were very similar for the two indenters for a particular material, but the exponents varied with material. The Rockwell C indenter gives different power law trends and rankings. SIGNIFICANCE: Despite the variations in the trends and indenters, simple comparisons between materials can be made by chipping with sharp conical 120° or Vickers indenters at 0.50mm. Broad distance ranges are recommended for trend evaluation.

Chipping fracture resistance of dental CAD/CAM restorative materials: part 2. Phenomenological model and the effect of indenter type.

UNLABELLED: The edge chipping resistances of six CAD/CAM dental restoration materials are analyzed and correlated to other mechanical properties. A new quadratic relationship that is based on a phenomenological model is presented. OBJECTIVE: The purpose of this study was to further analyze the edge chipping resistance of the brittle materials evaluated in Part 1. One objective was to determine why some force-distance trends were linear and others were nonlinear. A second objective was to account for differences in chipping resistance with indenter type. METHODS: Edge chipping experiments were conducted with different indenters, including some custom-made sharp conical indenters. A new force - distance quadratic expression was correlated to the data and compared to the linear and power law trends. RESULTS: The new quadratic function was an excellent fit in every instance. It can account for why some materials can be fit by a linear trend, while others can be fit by the power law trend. The effects of indenter type are accounted for variations in crack initiation and by the wedging stresses once an indentation hole is created. SIGNIFICANCE: The new quadratic force - edge distance function can be used with edge chipping data for all brittle materials, not just those evaluated in this study. The data trends vary from linear to nonlinear depending upon the material's hardness, fracture toughness, and elastic modulus.

Chipping fracture resistance of denture tooth materials.

OBJECTIVE: The applicability of the edge chipping method to denture tooth materials was assessed. These are softer materials than those usually tested by edge chipping. The edge chipping fracture resistances of polymethylmethacrylate (PMMA) based and two filled resin composite denture tooth materials were compared. METHODS: An edge chipping machine was used to chip rectangular blocks and flattened anterior denture teeth. Force versus edge distance data were collected over a broad range of forces and distances. Between 20 and 65 chips were made per condition depending upon the material, the scatter, and the indenter type. Different indenter types were used including Rockwell C, sharp conical 120(o), Knoop, and Vickers. The edge toughness, Te, was evaluated for different indenter types. RESULTS: The edge chipping data collected on the blocks matched the data collected from flattened teeth. High scatter, particularly at large distances and loads, meant that many tests (up to 64) were necessary to compare the denture tooth materials and to ascertain the appropriate data trends. A linear force-distance trend analysis was adequate for comparing these materials. A power law trend might be more appropriate, but the large scatter obscured the definitive determination of the precise trend. Different indenters produce different linear trends, with the ranking of: sharp conical 120(o), Rockwell C, and Knoop, from lowest to highest edge toughness. Vickers indenter data were extremely scattered and a sensible trend could not be obtained. Edge toughness was inversely correlated to hardness. SIGNIFICANCE: Edge chipping data collected either from simple laboratory scale test blocks or from actual denture teeth may be used to evaluate denture materials. The edge chipping method's applicability has been extended to another class of restorative materials.

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.

[Studies on bonding interfaces of two dentin adhesives by scanning electron microscopy].

OBJECTIVE: To purpose of this study was to investigate the microstructure and bonding mechanism of bonding interfaces of two current one-bottle dentin bond systems(Prime & Bond NT, PBNT; Prime one Mirage, P-One). METHODS: Fifteen extracted, caries-free human molars were prepared according to a modified method used for microtensile bond strength measurement. Each crown was divided into nearly equal halves with a 5 mm deep slot for accepting treatment of the two dentin bond systems, respectively. After 24 h storage in distilled water at 37 degrees C, the bonded teeth were subjected to two treatments: 5 teeth were observed by and tested for microtensile bond strengths without further treatment and 10 teeth were thermocycled(2400 cycles, between 5 degrees C and 55 degrees C) prior to SEM observation and bond strength testing. Hour-glass shaped microspecimens with a thickness of approximately 0.5 mm were cut from each tooth and used for SEM observation and microtensile bond strength measurement. RESULTS: A typical resin-infiltrated zone (hybrid layer) with a thickness of 3-5 microns and well-formed cone shaped resin tags that penetrated the dentinal tubules were clearly observed at the resin-dentin interfaces in the two bond systems. There were multiple lateral branches of tubular resin tags that interconnected to form a micro-network of resin. No evident differences in SEM images between the two bond systems as well as between thermocycling and without thermocycling in each bond system were found. CONCLUSION: PBNT and P-One provided good resin infiltration, producing a three-dimensional interlocking micro-network of resin tags in the dentin tubules with multiple lateral branches that penetrate the intertubular dentin, which positively influenced the adhesion between dentin and the two bond systems.

[The studies on microtensile bond strength measurements of two dentin adhesives].

OBJECTIVE: The purpose of this study was to investigate the feasibility of a modified microtensile method used to test bond strengths of two current one-bottle dentin bond systems (Prime & Bond NT, PBNT; Prime one Mirage, P-One) with a parallel match design. METHODS: 15 extracted, caries-free human molars were cut to expose occlusal dentin. A 5 mm deep slot was prepared in each crown to divide the crown into nearly equal halves for accepting treatment of the two dentin bond systems, respectively. After 24 h storage in distilled water at 37 degrees C, the bonded teeth were subjected to two treatments: 5 teeth were tested without further treatment and 10 teeth were thermocycled (2400 cycles, between 5 degrees C and 55 degrees C) prior to bond strength testing. Hour-glass shaped specimens with a distance of approximately 1.0 mm at the narrowest portion were cut from each tooth and tested in tensile mode. RESULTS: Bond strengths (mean MPa) were: for PBNT: 42 & 31, and for P-One 64 & 38 without and with thermocycling, respectively. Two-way ANOVA revealed a significant difference in bond strengths(P < 0.001) between the two systems and when thermocycled. However, a pairwise multiple comparison (Tukey test) showed that after thermocycling the difference between the two systems was not significant (P > 0.05). Regression analysis showed that a correlation existed between the two systems' tensile bond strength values grouped by tooth (correlation coefficient r = 0.575, P < 0.05). CONCLUSION: The modified microtensile method with a parallel match design is feasible and suitable for evaluating two different bonding systems or dentin treatments.

Reinforcement of a self-setting calcium phosphate cement with different fibers.

A water-based calcium phosphate cement (CPC) has been used in a number of medical and dental procedures due to its excellent osteoconductivity and bone replacement capability. However, the low tensile strength of CPC prohibits its use in many unsupported defects and stress-bearing locations. Little investigation has been carried out on the fiber reinforcement of CPC. The aims of the present study, therefore, were to examine whether fibers would strengthen CPC, and to investigate the effects of fiber type, fiber length, and volume fraction. Four different fibers were used: aramid, carbon, E-glass, and polyglactin. Fiber length ranged from 3-200 mm, and fiber volume fraction ranged from 1.9-9.5%. The fibers were mixed with CPC paste and placed into molds of 3 x 4 x 25 mm. A flexural test was used to fracture the set specimens and to measure the ultimate strength, work-of-fracture, and elastic modulus. Scanning electron microscopy was used to examine specimen fracture surfaces. Fiber type had significant effects on composite properties. The composite ultimate strength in MPa (mean +/- SD; n = 6) was (62+/-16) for aramid, (59+/-11) for carbon, (29+/-8) for E-glass, and (24+/-4) for polyglactin, with 5.7% volume fraction and 75 mm fiber length. In comparison, the strength of unreinforced CPC was (13+/-3). Fiber length also played an important role. For composites containing 5.7% aramid fibers, the ultimate strength was (24+/-3) for 3 mm fibers, (36+/-13) for 8 mm fibers, (48 +/-14) for 25 mm fibers, and (62+/-16) for 75 mm fibers. At 25 mm fiber length, the ultimate strength of CPC composite was found to be linearly proportional to fiber strength. In conclusion, a self-setting calcium phosphate cement was substantially strengthened via fiber reinforcement. Fiber length, fiber volume fraction, and fiber strength were found to be key microstructural parameters that controlled the mechanical properties of CPC composites.

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.

Edge-bevel fracture resistance of three direct-filling materials.

Edge strength is defined in this study as the resistance to fracture of the beveled extension normally located at the cavosurface margin of a dental restoration. The edge strength of direct-filling alloy restorations plays an important role in maintaining the integrity of margins at tooth-alloy interfaces during functional loading. The purpose of this study was to determine the relative strength of an experimental consolidated silver material in comparison to other direct filling materials. The method used was designed as a simulation for relative edge-strength clinical properties. Stainless steel dies were formed from disks 5 mm thick, each with a centered hole tapered (1/48) toward the bottom side of the disk. A 41 degrees bevel, 0.5 mm wide as viewed from above, was placed on the top-side of the disk. Dispersalloy (D) or Unison (U) amalgam, Z-100 composite (C), hand-consolidated silver powder (HAg), or pneumatically consolidated silver powder (PAg) was used to fill the die opening. Excess was polished from both sides of the disk with 600-grit abrasive paper. The sample was loaded from the beveled side with a 3 mm-in-diameter flat-ended plunger at a rate of 1.0 mm/minute until failure. Failure load and total energy to failure were recorded and compared. Tukey's multiple comparison test (p < 0.05) ranked the materials (U) > (HAg) > (D) > (PAg) > (C) for fracture strength and (HAg) > (D) > (U) > (PAg) > (C) for fracture energy.

Microleakage of a consolidated silver direct filling material.

Microleakage of an experimental direct filling material comprised of a chemically precipitated silver powder that had been surface treated with a dilute acid to promote cold welding upon consolidation was evaluated. Microleakage was compared to both dispersed-phase and spherical amalgam by use of an in vitro gas-diffusion method and in class 5 restorations placed in extracted human teeth. The effect of two cavity varnishes and two dentin adhesives as cavity liners on microleakage was also evaluated using extracted teeth. Microleakage of silver powder consolidated with dental instruments was less than that found with dental amalgam. The use of copal or polyamide cavity varnish resulted in the lowest combination of microleakage on dentin and enamel margins.

Three-body wear of a hand-consolidated silver alternative to amalgam.

Recent studies have investigated a mercury-free silver alternative to amalgam, but the silver powders required a relatively high compaction pressure to consolidate. The aim of the present study was to consolidate a precipitated silver powder into a cohesive solid using an air-driven pneumatic condenser fitted with an amalgam plugger at a clinically realistic load, and to study the mechanisms and rates of three-body wear of the consolidated silver in comparison with that of an amalgam. The silver powder was annealed, rinsed with a dilute acid, and consolidated either in a prepared tooth cavity or in a specimen mold at a load of 15 N. A four-station wear machine was used where each specimen was immersed in a slurry containing polymethyl methacrylate beads, then a steel pin was loaded and rotated against the specimen at a maximum load of 76 N. The flexural strength in MPa (mean +/- SD; n = 10) was 86 +/- 20 for amalgam, 181 +/- 45 for silver with a polished surface, and 202 +/- 21 for silver with a burnished surface. After 4 x 10(5) wear cycles, the wear scar depth in microm was 134 +/- 54 for amalgam, 143 +/- 8 for polished silver, and 131 +/- 9 for burnished silver, which were not significantly different (Tukey's multiple comparison test; family confidence coefficient = 0.95). SEM examination revealed cracks and fracture pits in the worn surface of amalgam, in contrast to a smooth surface in silver. Wear and material removal in amalgam occurred by microfracture and dislodgement of cracked segments, while wear in the silver occurred by ductile deformation and flow of materials. To conclude, the consolidated silver possesses a three-body wear resistance similar to that of amalgam, and a higher resistance to wear-induced damage and cracking than amalgam. The mechanism of wear in amalgam is microfracture and material dislodgement, while that in consolidated silver is ductile deformation and flow of material.

Two-body sliding wear of a direct-filling silver alternative to amalgam.

OBJECTIVE: This study investigated the wear resistance of a mercury-free silver direct-filling material and a dental amalgam. METHOD AND MATERIALS: A precipitated silver powder was rinsed with dilute fluoboric acid and consolidated into a cohesive solid. For tooth cavity restoration and flexural testing, the silver was consolidated with a dental amalgam plugger at a load of 15 N. For wear testing, because of the relatively large specimen size, the silver was pressed at a pressure of 150 MPa, yielding a density similar to that obtained by hand consolidation. RESULTS: The silver had a flexural strength twice that of amalgam. Pin-on-disk wear resulted in a smooth surface and hardening in silver, as measured by indentation inside the wear tracks, in contrast to the damage that was found in amalgam. The wear track cross-sectional area (n = 12) at 10(6) revolutions was not statistically significantly different among amalgam, polished silver, and burnished silver. CONCLUSION: The consolidated silver exhibited work hardening and surface densification during wear and, as a result, was more resistant to wear-induced damage than amalgam.

Cyclic contact fatigue of a silver alternative to amalgam.

OBJECTIVE: To purpose of this study was to compare the cyclic contact fatigue resistance of a novel mercury-free silver direct filling material to that of a dental amalgam (Dispersalloy). METHODS: The silver specimens were made by pressing a precipitated powder at room temperature with a pressure of 150 MPa, which can be achieved in clinical hand-consolidation. To simulate clinical contact of restorations against enamel cusps, a cyclic contact fatigue methodology was employed. A spherical indenter was used to repeatedly indent the specimen, while the accumulation of deformation and damage was examined as a function of the number of cycles up to 5 x 10(5). Student's t test, analysis of variance (ANOVA) and Duncan's multiple range test were used to compare the specimen groups for significant differences in flexural strength, indentation impression diameter, and hardness. A type I error of alpha = 0.05 was considered as significant. Subsurface damage was examined by using a bonded-interface technique. RESULTS: As a result of cyclic indentation, microcracks were produced in the amalgam, but no cracks were found in the silver filling material. At fewer numbers of cycles, indentation produced larger impressions in silver (e.g., diameter = [450 +/- 31] microns at 10(2) cycles) than in amalgam ([145 +/- 20] microns) due to a lower hardness of the former. However, with increasing number of cycles, damage accumulated more rapidly in the amalgam, while the silver beneficially work-hardened in repeated indentations. At 5 x 10(5) cycles, the difference in impression diameter between silver and amalgam ([582 +/- 20] microns vs. [568 +/- 42] microns) become insignificant (p > 0.1, Student's t test). SIGNIFICANCE: The mercury-free silver direct filling material is more resistant to microcracking and to cyclic contact fatigue than amalgam, and the indentation impression sizes in the consolidated silver and dental amalgam are not statistically different at large numbers of cycles.

Compatibility of ceramic-ceramic systems for fixed prosthodontics.

This study evaluated dilatometric data for predicting ceramic-ceramic compatibility for porcelains fired on central incisor copings (n = 72) of high expansion colored IPS-Empress porcelain. Nine body porcelains (leucite 0 wt% to 51 wt%) were each fired onto eight copings. Cracks were detected at 10 x magnification using transilluminating light. Failure was defined as the presence of at least one crack and probability of failure (Pf) as the ratio of failed to total crowns. Thermal contraction coefficients (alpha) were determined using four bars of each porcelain following the protocol of ISO 9693. Absolute differences in thermal contraction, magnitude of delta alpha, between core and test porcelains were plotted against Pf and curve fit. Significant differences in alpha were found among the porcelains tested (ANOVA, 95% Tukey); the alpha values ranged from 7.92 to 17.83 x 10(-6)/degree C; Pf ranged from 0 to 1. Compatible porcelains (no cracks during any firing of all eight crowns) had magnitude of delta alpha values less than 1 x 10(-6)/degree C. Absolute values (magnitude of delta alpha) were surprisingly predictive of Pf given the very different cooling rates (dilatometry versus dental lab) and the relatively complex crown shape. Standard dilatometry may be useful for predicting the compatibility of ceramic-ceramic systems. Three porcelains, IPS-Empress dentin, Duceram, and Will-Ceram were successfully used for veneering IPS Empress cores.

Consolidation conditions for a cold-welded mercury-free alloy.

Alloys being investigated as possible direct-filling materials rely upon a cold-welded, deformable silver matrix phase for cohesion and strength. The silver matrix is formed by direct consolidation of comminuted silver under an oxide-removing acid. The object of this study was to determine the effect of conditions such as load, increment thickness, and concentration of oxide-removing acid on the properties of the silver matrix. Results indicate that the addition of higher impact loads significantly improved yield strength and specimens built up by using thinner increments were significantly stronger and denser.