Bacterial penetration along different root canal filling materials in the presence or absence of smear layer.

AIM: To study the effect of the smear layer on the penetration of bacteria along different root canal filling materials and to examine the dentine/sealer and sealer/core material interfaces for the presence of bacteria. METHODOLOGY: A total of 110 human root segments were instrumented to size 80 under irrigation with 1% sodium hypochlorite. Half of the roots were irrigated with a 5-mL rinse of 17% EDTA. Roots with and without smear layer were filled with gutta-percha (GP) and AH Plus sealer (AH), GP and Apexit sealer (AP), or RealSeal cones and sealer (RS). Following storage in humid conditions at 37 degrees C for 7 days, the specimens were mounted into a bacterial leakage test model for 135 days. Survival analyses were performed to calculate the median time of leakage and log-rank test was used for pairwise comparisons of groups. The level of significance was set at P = 0.05. Selected specimens were longitudinally sectioned and inspected by scanning electron microscopy for the presence of bacteria at the interfaces. RESULTS: In the presence of the smear layer, RS and AP leaked significantly more slowly than in its absence. In the absence of the smear layer, AH leaked significantly more slowly than RS. SEM results indicated a differential pattern of bacterial penetration among the sealers. CONCLUSIONS: Removal of the smear layer did not impair bacterial penetration along root canal fillings. A comparison of the sealers revealed no difference except that AH performed better than RS in the absence of the smear layer.

Survival of Enterococcus faecalis in infected dentinal tubules after root canal filling with different root canal sealers in vitro.

AIM: To investigate the ability of different endodontic sealers and calcium hydroxide to kill bacteria in experimentally infected dentinal tubules. METHODOLOGY: Fifty-six human root segments were enlarged to size 2 (ISO size 090) Largo Peeso Reamer. After treatment with 17% EDTA and 5% NaOCl for 4 min each, the specimens were infected with Enterococcus faecalis for 3 weeks. The roots were divided into eight groups and filled with gutta-percha and AH Plus (AH); Grossman's sealer (GS); Ketac-Endo (KE); Apexit (AP); RoekoSeal Automix (RSA); or RoekoSeal Automix with an experimental primer (RP), or calcium hydroxide (CH) only. One group of specimens was left unfilled for control (CT). Following storage in humid conditions at 37 degrees C for 7 days, the root canals were re-established with new sterile Largo size 2. Dentine samples from each canal were then collected using a sterile size 5 (ISO size 150) Largo Peeso Reamer. The number of colony-forming units (CFU) was determined for each sample. RESULTS: The mean log10 CFU in all test groups was significantly lower (P < 0.05) than that in the CT group. Root filling with AH and GS killed bacteria (mean CFU = 0) in the dentinal tubules. The mean log10 CFU for the CH group (0.53) was lower than that of RSA, AP, RP and KE (1.36, 1.40, 1.46 and 1.94, respectively), but only the difference between the CH and the KE groups was statistically significant (P < 0.05). CONCLUSION: Root fillings in vitro with gutta-percha and AH or GS were effective in killing E. faecalis in dentinal tubules. Other endodontic sealers, as well as CH, were less effective.

The effects of dentine pretreatment on the adhesion of root-canal sealers.

AIM: The adhesion of five root-canal sealers to dentine and gutta-percha was studied. The effects of various dentine pretreatments on adhesion were also investigated. METHODOLOGY: Root dentine cylinders, 4 mm in diameter, were prepared from human teeth. The dentine surfaces were conditioned with either 37% H(3)PO(4) for 30 s, 25% citric acid for 30 s, 17% EDTA for 5 min or a rinse with 10 mL distilled water (control). Gutta-percha cylinders, 4 mm in diameter, were prepared and their end surfaces polished flat. The dentine and gutta-percha surfaces were coated with freshly mixed sealer: Grossman's sealer (GS), Apexit (AP), Ketac-Endo (KE), AH Plus (AH), RoekoSeal Automix (RS) or RoekoSeal Automix with an experimental primer (RP). The surfaces were pressed together and the sealers allowed to set. The test specimens were subjected to a tensile force in a universal testing machine. RESULTS: Mean tensile bond strengths (MPa +/- SD) ranged from 0.07 +/- 0.01 (AP) to 1.19 +/- 0.47 (AH). Pretreatment with EDTA showed no effect or produced weaker bonds than controls. Phosphoric and citric acid pretreatments increased adhesion of GS. A primer used with RoekoSeal significantly enhanced its adhesion to untreated dentine. Inspection of fractured surfaces indicated failure of adhesion to dentine for GS and RS and to gutta-percha for KE and RP. The failure appeared to be mainly cohesive within the sealer for AH and AP. CONCLUSIONS: Removal of the smear layer may impair sealer adhesion to dentine. Different sealer types require different dentine pretreatments for optimal adhesion.

Water sorption and solubility of dental composites and identification of monomers released in an aqueous environment.

Water sorption and solubility of six proprietary composite resin materials were assessed, and monomers eluted from the organic matrix during water storage identified. Water sorption and solubility tests were carried out with the following storage times: 4 h, 24 h and 7, 60 and 180 days. After storage, water sorption and solubility were determined. Eluted monomers were analysed by high performance liquid chromatography (HPLC). Correlation between the retention time of the registered peak and the reference peak was observed, and UV-spectra confirmed the identity. The results showed an increase in water sorption until equilibrium for all materials with one exception. The solubility behaviour of the composite resin materials tested revealed variations, with both mass decrease and increase. The resin composition influences the water sorption and solubility behaviour of composite resin materials. The HPLC analysis of eluted components revealed that triethyleneglycol dimethacrylate (TEGDMA) was the main monomer released. Maximal monomer concentration in the eluate was observed after 7 days. During the test period, quantifiable quantities of urethanedimethacrylate (UEDMA) monomer were observed, whereas 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)-phenyl]propane (Bis-GMA) was only found in detectable quantities. No detectable quantities of bisphenol-A were observed during the test period.

Changes in appearance of silicone elastomers for maxillofacial prostheses as a result of aging.

PURPOSE: The purpose of this study was to investigate the influence of certain defined variables on color and opacity of silicone elastomers for maxillofacial prostheses. MATERIALS AND METHODS: Three condensation-type and five addition-type silicone elastomers were tested for their changes in color and opacity as a result of aging. The specimens were aged under a xenon light source, dry or wet, and in darkness, also dry (control specimens) or wet. The aging times were 24, 96, 168, 336, 504, 840, 1176, and 1512 hours. The changes in appearance were measured with a spectrophotometer. RESULTS: The condensation-type polymers increased in opacity in an aqueous environment, while the addition-type polymers, as a group, showed the smallest color changes. Although the addition-type polymers generally had a higher filler content than the condensation types, they had a lower opacity. However, because of their higher viscosity, the condensation-type polymers offer better possibilities for intrinsic coloring of the prosthesis. CONCLUSION: Under the experimental conditions studied, significant differences between the silicone elastomers regarding color and opacity changes were demonstrated. However, for a proper choice of material in a given case, these factors have to be related to biologic and mechanical properties of the material.

Effect of water storage on the flexural properties of E-glass and silica fiber acrylic resin composite.

PURPOSE: The aim of this study was to determine the effect of water on the flexural properties of fiber-reinforced denture base polymers. MATERIALS AND METHODS: Continuous woven silanized electrical glass, or E-glass, fibers and woven silica fibers were used to reinforce heat-cured and autopolymerized denture base polymers. Fibers were oriented at a 45-degree angle to the long axis of the test specimens. Control specimens were unreinforced. Dry test specimens and those stored in water for up to 48 weeks were tested with a three-point loading apparatus. The surfaces of the fibers of the test specimens stored dry or 48 weeks in water were analyzed with a scanning electron microscope to evaluate the degree of adhesion between fibers and polymer matrix. RESULTS: The ultimate transverse strength of unreinforced and reinforced denture base polymers decreased during 48 weeks' storage in water (P < 0.05, one-way analysis of variance, n = 5), and most of this reduction occurred during the first 4 weeks of storage in water. The flexural modulus of the unreinforced test specimens decreased significantly (P < 0.001), whereas there was less, if any, change in the flexural modulus of the fiber-reinforced test specimens. Scanning electron microscopic examination revealed no differences in adhesion of E-glass fibers to the polymer matrix when the specimens stored in water were compared with those stored by. Reduced adhesion between the silica fibers and matrix was observed after 48 weeks' storage in water. CONCLUSION: The results of this study suggest that the ultimate transverse strength of the E-glass fiber-reinforced test specimens decreased 14% and that of the silica fiber-reinforced test specimens decreased 36% after 48 weeks of storage in water.

Effect of polymerization temperature and time on the residual monomer content of denture base polymers.

The aim of this study was to investigate the effect of polymerization time and polymerization temperature on the residual methyl methacrylate (MMA) content of two heat-cured and two autopolymerized denture base polymers. Gas chromatography was used to determine the residual MMA content of three test specimens of each type of polymer. Increasing the polymerization temperature for the autopolymerized denture base resins from 30 degrees C to 60 degrees C decreased the residual MMA content of the polymer from an average of 4.6 wt% to 3.3 wt%. With the heat-cured denture base resins, a curing cycle at a polymerization temperature of 70 degrees C followed by a period at 100 degrees C significantly reduced the residual monomer content of the polymer when compared with a resin cured at 70 degrees C only. Polymerizing the heat-cured denture base resin at 100 degrees C only for various lengths of time significantly affected the residual MMA content of the polymer. The lowest residual MMA content (0.07 wt%) was obtained by polymerizing the heat-cured denture base resin at 100 degrees C for 12 h. The results of this study suggest that the polymerization temperature and polymerization time considerably affect the residual MMA content of denture base polymers.

How different curing methods affect mechanical properties of composites for inlays when tested in dry and wet conditions.

The purpose of this investigation was to evaluate the differences in the mechanical properties of 3 composite materials in relationship to the intraoral and extraoral curing techniques of direct and indirect (inlay) restorations, and how the mechanical properties are affected by water sorption. Creep characteristics in compression as well as the stress-strain relationship at a constant loading rate both in compression and flexure, were determined. A secondary aim was to investigate the influence of filler content and monomer composition on the mechanical properties. The results are presented as creep curves and as values for elastic moduli, ultimate strength, and ultimate strain. The materials were cured with 2 curing methods. Method A was light curing with a handheld curing unit, and method B was curing in light curing ovens. Water sorption increased the creep values for all types of specimens. Curing in light ovens (method B) gave significantly lower creep values at high stresses than curing with a handheld curing unit (method A). Water sorption decreased the modulus and ultimate strength values for specimens cured with method A. The ultimate strength values also differed for dry and wet specimens cured with method B. There were no general differences in compressive and flexural stress-strain properties between specimens cured according to the methods A and B.

The swelling phenomenon of acrylic resin polymer teeth at the interface with denture base polymers.

PURPOSE: This study examined the interface between acrylic resin polymer teeth and denture base polymers. MATERIAL AND METHODS: An autopolymerized denture base polymer was cured either at 30 degrees C, 50 degrees C, or 70 degrees C, and a heat-cured denture base polymer was cured at 100 degrees C in contact with acrylic resin polymer teeth. The specimens were ground wet and polished to a thickness of 0.21 mm for the examination of the interface with a light microscope. The surface of the specimens was then treated with the solvent tetrahydrofuran, and the specimens were examined with a scanning electron microscope (SEM). RESULTS: As a result of grinding, the inner parts of the beads at the interface of the teeth were exposed to the denture base polymer. The inner part in these polymer beads of the polymer teeth swelled to a depth of 3 microns when the autopolymerized polymer was cured at 30 degrees C. When cured at 70 degrees C, the thickness of the swelled layer was 21 microns (p < 0.001). Microscopically, the interface between the heat-cured denture base polymer and the polymer teeth appeared diffuse in the region of the interpenetrating polymer networks (IPN) and the matrix. The IPN appeared as a separate zone in the outer parts of the beads of the teeth, both with the light microscope and with the SEM. CONCLUSIONS: The results suggest that by increasing the polymerization temperature, the monomers of the denture base polymers diffused more effectively into acrylic resin polymer teeth. This increases the bond strength between the polymer teeth and the denture base polymer.

Swelling of poly(methyl methacrylate) resin at the repair joint.

This study investigated the thickness of a swollen layer between heat-activated and autopolymerized denture base polymer based on poly(methyl methacrylate) and autopolymerized repair acrylic resin. The repair surfaces of polymerized poly(methyl methacrylate) resin specimens (n = 5) were wet with methyl methacrylate liquid for 0, 0.5, 3, 30, or 60 minutes before the mixed repair resin was applied and polymerized to the surface of the specimen. The specimens were wet ground to a thickness of 0.15 mm, and the repair joint was examined using a light microscope. The thickness of the layer of swollen poly(methyl methacrylate) at the repair joint was measured from the micrographs. Both the type of polymer, ie, heat-activated or autopolymerized, and the wetting time of the repair surface with methyl methacrylate had a significant effect on the thickness of the swollen layer (P < .001). Prolonged wetting time of the repair surface of the autopolymerized poly(methyl methacrylate) increased the thickness of the swollen layer (r = .944, P = .000), but had less effect on the thickness of the swollen layer of heat-activated poly(methyl methacrylate) (r = .391, P = .005). This study suggests that methyl methacrylate diffuses more easily into an autopolymerized poly(methyl methacrylate) than into heat-activated poly(methyl methacrylate) during the repair of denture base polymer.

The effects of polymerization temperature on the acrylic resin denture base-tooth bond.

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.

Quantitative determination of type A and type B carbonate in human deciduous and permanent enamel by means of Fourier transform infrared spectrometry.

Caries progression has been shown to be faster in the deciduous than in the permanent dentition. Several factors influence caries progression. Among these are variations in the chemical composition of the two enamel types. The carbonate ion is known to occupy two different positions in the hydroxyapatite structure of the enamel, the hydroxide position (A) and the phosphate position (B). Carbonate may be of different chemical importance in the two lattice positions. In the present study, a quantitative determination of the carbonate in the two different positions (type A and type B) in deciduous and permanent enamel was performed by FTIR spectrometry. Calibration curves, made with synthesized hydroxyapatites with carbonates in either position, were used to determine the quantity of type A and type B carbonates in both enamel types. The deciduous enamel contained significantly more type A carbonate than permanent enamel. The total carbonate content (sum of type A and type B carbonates) was also significantly higher in deciduous than in permanent enamel. TG analysis of enamel samples confirmed the quantitative carbonate determinations by FTIR spectrometry. The difference in carbonate content between deciduous and permanent enamel may be one of several factors contributing to faster caries progression in deciduous teeth.

Tissue reaction and material characteristics of four bone substitutes.

The aim of the present study was to qualitatively and quantitatively compare the tissue reactions around four different bone substitutes used in orthopedic and craniofacial surgery. Cylinders of two bovine bone substitutes (Endobon and Bio-Oss) and two coral-derived bone substitutes (Pro Osteon 500 and Interpore 500 HA/CC) were implanted into 5-mm bur holes in rabbit tibiae. There was no difference in the amount of newly formed bone around the four biomaterials. Interpore 500 HA/CC resorbed completely, whereas the other three biomaterials did not undergo any detectable biodegradation. Bio-Oss was osseointegrated to a higher degree than the other biomaterials. Material characteristics obtained by diffuse reflectance infrared Fourier transform spectrometry analysis and energy-dispersive spectrometry did not explain the differences in biologic behavior.

How different curing methods affect the degree of conversion of resin-based inlay/onlay materials.

The purpose of this investigation was to measure the conversion of five inlay materials with different curing methods. In particular, the influence of secondary curing in light ovens--that is, additional curing with light and heat simultaneously--was evaluated. The conversion was determined by infrared multiple internal reflection spectroscopy. The inlays were cured with three curing methods (A, B, and C). The conversion was recorded immediately after ended curing and after an additional storage period (postcuring). The mean conversion with method A, using a handheld curing unit, was 42.1% and increased significantly to a mean of 55.4% during the storage period at (37 +/- 1) degrees C. Both curing methods B and C, including the use of light ovens, gave a mean conversion of 65%, which did not increase significantly during the storage period. This investigation demonstrated that the degree of conversion depends on the curing method used.

Color stability of denture base polymers.

One light-polymerized, three heat-polymerized, and three autopolymerized denture base polymers were exposed to coffee, tea, water at 50 degrees C +/- 1 degree C, as well as artificial sunlight and water, and evaluated for color stability. The color characteristics were determined using a computer-controlled spectrophotometer. Water sorption and solubility were assessed, and the materials were also chemically characterized. Coffee and tea stained the denture base materials superficially. Brushing with toothpaste and moderate grinding reduced discoloration to an acceptable level. All materials were relatively color stable when immersed in water at 50 degrees C +/- 1 degree C. The materials behaved differently when exposed to artificial sunlight and water.

Allergenic potential of two orthodontic bonding materials.

The sensitization potential of two orthodontic bonding materials, one conventional premix product and one nonmix product, was evaluated by a modified guinea pig maximization test. The nonmix product, consisting of a liquid to be applied to the tooth surface and a paste which was placed on the bracket base, caused reaction in 50% of the tested animals. This material should be considered to be a possible cause of allergy in patients or professionals handling it.

Hydroxyapatite coatings on Ti produced by hot isostatic pressing.

Plasma spraying is a technique currently used in the production of HA-coated titanium implants. These coatings have been shown to be porous; they dissolve and have a weak bond to the substrate. The long-term interface strength has been questioned in particular. The aim of the present work was to produce HA coatings without the shortcomings of those produced by plasma spraying. Hot isostatic pressing (HIP) at 850 degrees C and 1000 bar with no holding time was applied for this purpose. Initially, the HA powder was mixed with water and air sprayed on the Ti substrate. The Ti specimens were then cold-pressed, enclosed by a protective Pt foil, and encapsulated in an evacuated glass ampulla. Subsequent to HIP, the glass and the Pt foil were removed. These coatings were denser than those produced by plasma spraying. The bonding was measured to be > 62 MPa, which is considered to be satisfactory. The structure of the coating was checked by X-ray diffraction and IR spectroscopy, and was found to correspond to that of HA. Some cracks were observed in the coating running predominantly vertical to the surface. Whether these are acceptable has to be verified by in vivo experiments.

Chemical, physical, and histologic studies on four commercial apatites used for alveolar ridge augmentation.

The purpose of this study was to evaluate four commercial apatite products. Subperiosteal alveolar ridge augmentation was performed on the maxilla of rats by implantation of granules of two dense products and of two porous products, and the tissue response was compared with the material characteristics obtained by chemical analysis and infrared spectrometry. None of the apatites caused osteoinduction or osteoconduction; fibrous encapsulation with multinuclear giant cells was observed around all four types. One of the apatites was fluorapatite and not hydroxylapatite, as claimed by the manufacturer. The tissue response to this implant material was dominated by multinuclear giant cells.

Types of resin-based inlay materials and their properties.

The composition of 'chairside' resin-based inlay materials is similar to that of direct resin-based filling materials. The handling and curing procedures vary for the different inlay materials. Some systems involve precuring inside the oral cavity and a final cure at elevated temperature outside the oral cavity. Others are only cured extra-orally. The advantage of the inlay technique is that polymerisation shrinkage of the composite occurs before bonding to tooth structure. After cementation, therefore, the inlay gives good marginal adaptation in occlusal restorations. Some of the curing procedures for inlays give good conversion. The systems with good conversion also show better mechanical properties than the equivalent resin-based material cured according to the direct filling technique.