Incorporation of bacterial inhibitor into resin composite.

Attempts to produce resin composite with antibacterial properties by incorporation of an antibacterial agent such as chlorhexidine have been reported, but problems can arise due to release of the inhibitory agent from the composite. Such problems may include toxic effects, influence on mechanical properties, and loss of effectiveness. A new monomer, methacryloyloxydodecylpyridinium bromide (MDPB), was synthesized by combining an antibacterial agent and methacryloyl group. The monomer was incorporated into resin composite to develop a non-releasing antibacterial composite. The ability of composite incorporating MDPB to inhibit growth and plaque accumulation by Streptococcus mutans in vitro was assayed, elution of antibacterial components from the material was investigated, and the influence of incorporation of MDPB on the mechanical properties of composite was studied. Uncured MDPB revealed antibacterial activity against S. mutans and six other species of oral streptococci, with the minimum inhibitory concentration for S. mutans being comparable with that of triclosan. After composite incorporating MDPB was cured, no elution of the antibacterial components was observed from the material, even after 90 days' immersion in water or other solvents. Growth of S. mutans on agar under specimens of MDPB-containing composite was inhibited compared with controls. In a bacterial accumulation study, S. mutans accumulated to a lesser degree on the surface of composite incorporating MDPB (p < 0.05) than on control. Incorporation of MDPB had no significant influence on the mechanical properties of the composite.

Appearance of neuropeptide Y-like immunoreactive cells in the rat trigeminal ganglion following dental injuries.

The effects of these injuries on the presence and distribution of neuropeptide Y (NPY)-immunoreactive (-IR) neurones were examined immunohistochemically. In the normal trigeminal ganglion: some perivascular nerves displayed NPY-IR but there were no NPY-IR ganglionic cells. Fourteen days after extraction or pulp exposure of the upper first molar, NPY-IR cells appeared in the maxillary region of the trigeminal ganglion. About 90% of the injury-evoked NPY-IR cells had medium to large diameters (more than 300 microns2 in cross-sectional area). Shallow cavity preparation, however, did not induce the appearance of NPY-IR cells in the trigeminal ganglion. These results indicate the dental injuries alter the primary sensory neurones in the trigeminal ganglion.

Marginal adaptability and fit of ceramic milled inlays.

The authors investigated the marginal adaptation and internal fit of ceramic inlay made by a ceramic milling system. The study's results indicated that the mean marginal and internal gap size of the ceramic inlay restorations was less than 100 microns, making the fit clinically acceptable.

6-year clinical evaluation of fired ceramic inlays.

The purpose of the present study was to evaluate the quality of fired ceramic inlay restorations consisting of a feldspathic porcelain system (G-Cera Cosmotech II) after 6 years in vivo. A total of 49 fired ceramic inlays (for 27 premolars and 22 molars: class 1 in 11 teeth, class 2 in 36 teeth, and onlays in two teeth) were placed in 29 patients, and all restorations were evaluated at the time of placement, at 6 months, and 1, 2, 4, and 6 years after placement using modified USPHS criteria. Replicas made of the restorations were observed using a scanning electron microscope (SEM) to assess the state of the marginal area and wear of the restoration. Favorable color match was noted, and no bulk fracture, tooth fracture, or missing restorations were detected. Longevity was observed in 92% of the fired ceramic inlay restorations at 6 years (Kaplan-Meier method); however, marginal fracture was detected in six restorations (13%) and marginal discoloration in 11 (23%). SEM evaluation disclosed marginal microfracture in 49% of the restorations, wear in 19%, and wear of resin cement along margins in 36% at 6 years. No significant difference was observed in the incidence of each of these three characteristics between molars and premolars. This longitudinal 6-year clinical observation suggested that fired ceramic inlay restorations made by the G-Cera Cosmotech II system are aesthetic, durable, and clinically acceptable. Further follow-up is needed for the restorations showing marginal degradation and fracture from a microscopic and macroscopic perspective.

Inhibition in vitro of caries around amalgam restorations by bonding amalgam to tooth structure.

Class 5 preparations in human molars were restored with amalgam. In half of the restorations, an experimental resin liner capable of bonding amalgam to tooth structure was used. The restored teeth were incubated in a bacterial medium containing sucrose and a culture of Streptococcus mutans. Artificial carious lesions were produced around all restorations. The experimental liner inhibited penetration of the lesions along the cavity wall. This inhibition was more effective at the occlusal side.

Eight-year clinical evaluation of fired ceramic inlays.

This study evaluated the quality of fired ceramic inlay restorations consisting of a feldspathic porcelain system (G-Cera Cosmotech II, GC Co, Tokyo, Japan) after eight years in vivo. Forty-five fired ceramic inlays (for 26 premolars and 19 molars; Class I in 12 teeth, Class II in 31 teeth and onlay in two teeth) were placed in 25 patients. All restorations were evaluated at the time of placement and at 6 months, 1, 2, 4, 6 and 8 years after placement using modified USPHS criteria. Replicas of the restorations were observed with a scanning electron microscope (SEM) to evaluate the degradation of the marginal area and wear loss of the restoration. Longevity was observed in 80% of the fired ceramic inlay restorations at eight years (Kaplan-Meier method), although it was 92% at the six-year observation. Marginal fracture was detected in 11 restorations (22%), including bulk fracture in five (11%), which had first occurred during the last two years. Recurrent caries was observed in three (7%) cases and marginal discoloration in 14 (31%). SEM evaluation disclosed marginal microfractures in 77% of the restorations, wear in 36% and wear of the resin cement along the margin in 74% at eight years. No significant difference was observed in each of these three characteristics between molars and premolars. This longitudinal eight-year clinical observation suggested that fired ceramic inlay restorations made by the G-Cera Cosmotech II system are clinically acceptable. However, critical failure as bulk fracture may become a future problem since marginal disintegration was detected in 77% of the restorations from microscopic and macroscopic perspectives.

Shear bond strength of amalgam adhesives to dentin.

This study compared the bond strength of resinous adhesives used to bond amalgam to dentin. The adhesives were: All-Bond 2 (AB), Liner-F (LF), SuperBond C&B (SB), Amalgambond (AM), Photo Bond (PB), and Panavia (PA). Occlusal surfaces of non-carious molars were ground wet to 600 grit finish, exposing dentin. The dentin surfaces were conditioned and the adhesives were applied according to manufacturers' instructions. Dispersalloy amalgam (D) was condensed onto the adhesive immediately. For comparison, resin composite, Photo Posterior (PO) and Bis-Fil (BIS) were used. After 24 hours of storage in 100% humidity at room temperature, shear bond strengths were determined with a shear testing jig in an Instron testing machine at a crosshead speed of 0.5 mm/minute. The data were compared using ANOVA, P < 0.01. AB, LF, D had significantly higher bond strengths than other amalgam adhesives. There was no significant difference between SB, D and PB, PO. Bond strength of PB, PA, D was significantly higher than PA, D. Thus, there were significant differences among adhesives for bonding amalgams. Amalgam to dentin and composite to dentin bond strength were comparable except for the All-Bond groups. Fracture patterns at the dentin/restoration interfaces were examined by scanning electron microscopy (SEM).

Effect of particle variation on wear rates of posterior composites.

PURPOSE: To evaluate the relationship between filler size, shape, mechanical properties and wear resistance of posterior resin composite was evaluated. MATERIALS AND METHODS: Six UDMA/TEGDMA-based experimental resin composites consisting of different types of filler particles were investigated. These included four sized spherical fillers, (9.88 microns, 2.01 microns, 0.62 micron, 0.20 micron) and two irregular, (9.46 microns, 1.97 microns). Property measurements consisted of hardness and compressive strength. Wear resistance was evaluated by a three-bodied in vitro wear test. RESULTS: The composites containing the smallest sized spherical particle exhibited maximum mechanical strength and maximum wear resistance. The composites containing the largest spherical particle exhibited minimum wear resistance. There were no significant differences amongst those containing similar sized fillers regardless of particle shape. However, differences between the 0.20 microns spherical filled composite and other composites were statistically significant. SEM analysis showed that only the larger sized filler exhibited some exfoliation after wear testing. The smaller size spherical filler exhibited better mechanical strength and substantially higher wear resistance.

Relationship between particle size of barium glass filler and water sorption of light-cured composite resin.

The reaction of barium glass filler with water was determined by investigation of the effects of the particle size of barium glass filler on the water sorption rate and the mechanical properties of composite resin. Barium glass and quartz were milled to obtain powders with different average particle sizes. These powders were silanized and used as inorganic filler in composite resin. Photoactivated base monomer was loaded at 65% (w/w) with these fillers to prepare the composite resin paste. The water sorption of barium glass filled resin was always more than that of quartz filled resin. The amount of sorbed water obtained by barium glass filled resin increased as the particle size decreased. The particle size of the quartz filler did not affect the water sorption. The flexural strength of barium filled resin decreased after water immersion more than that of the quartz filled resin as the particle size decreased. These results suggest that the water durability of barium glass is low and the surface of barium glass filler is damaged by water. Water would be retained in the interface between the barium glass filler and the matrix resin.

Relationship between the degree of conversion and internal discoloration of light-activated composite.

In order to elucidate the relationship between the degree of conversion and internal discoloration of light-activated composite, four experimental composites which contained different amounts of Bis-GMA and TEGDMA were prepared, and the degree of conversion and discoloration of each composite, with or without annealing, were determined. The degree of conversion was measured by Fourier transformation infrared spectroscopy and the color change was determined after 1, 2, 3 and 4 weeks of immersion in water at 60 degrees C. The non-annealed composites demonstrated a greater degree of conversion and less discoloration as the amount of TEGDMA was increased. Annealed composites showed a significantly greater degree of conversion and less discoloration compared with the non-annealed composites. The results indicate that the greater the degree of conversion, the less the discoloration of composite, and the correlation between the two factors was significant for light-activated composite.

Comparison of two methods for measuring generalized wear of dental materials.

The object of this study was to analyze two measuring methods for determining the amount of generalized wear of dental materials. Using a recently developed three-body wear testing machine, generalized wear defect was produced on the surface of various dental materials. Although the generalized wear was defined as the depth of the enamel exposed at the cavity margin for both methods, this depth was measured with two different devices. One is an image-analyzer and the other was a profilometer. From the results of this study, it was confirmed that measurement by means of profilometer gave almost the same wear values with those by image-analyzer. In addition, the measurement by profilometer seemed to be more precise and not very much sophisticated.

In vitro quantitative assessment of generalized wear of dental composites.

The purpose of this paper was to compare generalized wear resistance of eleven proprietary posterior dental composites and one amalgam using a recently developed in vitro wear testing apparatus. Upon completion of the in vitro wear testing process the wear area of occlusal surface was replicated and the depth of enamel exposed at the cavity margin was measured by a traveling microscope. Based upon the results of this study it was demonstrated that there were significant differences amongst materials included in this study. Also this wear test not only reproduced the microstructure of worn oclusal surface, but also predicted wear rates which correlated somewhat well with clinical performances.

Localized three-body wear of resin composites.

Localized wear tests have been performed on six resin composites using a recently developed three-body wear testing machine. After repeated loading to the composites, the worn surface was replicated. Then the wear values of the respective resin composites were determined from the surface area of the worn defect using an image-analyzer. In addition, the microstructure of the worn area was analyzed with a scanning electron microscope (SEM). This study revealed that a fine particle hybrid composite exhibited the greatest localized wear resistance of all resin composites investigated in this study. SEM of the microfilled resin composites showed some degradation between filler and matrix.

Effects of resin composite components on glucosyltransferase of cariogenic bacterium.

The aim of our study was to investigate the effect of resin composite components on glucan synthesis by glucosyltransferase (GTase) derived from a cariogenic bacterium, Streptococcus sobrinus B13. The eluates from cured composites stored in 0.05 mol/L potassium phosphate buffer (KPB) (pH 6.8) for 2 weeks at 37 degrees C stimulated the formation of water-insoluble glucan, whereas those from amalgam inhibited it. This finding suggests that the eluates from the resin composites enhance GTase activity and contribute to plaque formation. In the individual resin components, a diglycidyl methacrylate and triethylene glycol dimethacrylate significantly enhanced GTase activity. However, most polymerization inhibitors and accelerators were potent inhibitors of enzyme activity. Thus, GTase stimulation by eluates from resin composites is hypothesized to be heavily dependent on the effect of the eluated resin monomers, even though the other eluting components had inhibitory effects on GTase.

[Inhibition of water insoluble glucan formation by eluate from amalgams].

The effect of the eluate from amalgam on glucan synthesis was investigated in this study in order to elucidate the mechanisms by which plaque accumulation is inhibited on amalgam but not on enamel or composite. Glucosyltransferase (GTase) was prepared from a cultured supernatant of Streptococcus mutans B 13 by the ammonium sulfate precipitation method. Five commercial amalgams were tested. The eluate from amalgams was prepared by immersing the amalgam discs (10 mm dia. x2 mm thick.) into distilled water for 2 weeks. A glucan synthesizing system was compounded using GTase (50 microliters), [14C]-sucrose (100 microliters), distilled water, and the eluate (350 microliters). After 18 h incubation at 37 degrees C, the formed water insoluble glucan was collected on glass fiber filters and its radioactivity was counted. Moreover, concentrations of zinc (Zn) and copper (Cu) in the eluates were determined by atomic absorption spectrophotometry. The eluates from Dispersalloy and Fluor alloy, which eluted Zn, were the most inhibitory for glucan synthesis. Sybraloy, which released Cu to a much greater degree than the other amalgams and its eluate showed intermediate antienzymatic activity. The other amalgams, Hi-atomic M and Spherical-D, did not effect GTase at all. The results indicated that various amalgams strongly impact inhibition rates of glucan formation.

Effect of several resin monomers on water insoluble glucan formation by glucosyltransferase of Streptococcus sobrinus.

The cause or mechanism by which more plaque tend to accumulate on composite resins than on any other restorative materials has yet to be sufficiently explained. The purpose of this study was to investigate a possible mechanism by clarifying the effects of several monomers on the glucosyltransferase activity from Streptococcus sobrinus. The following results were obtained. In the individual resin monomers, di-, tri- and tetra-ethylene glycol dimethacrylate (2G, 3G and 4G), Bis-GMA and UDMA showed a stimulatory tendency of water insoluble glucan (WIG) formation. However, ethylene glycol dimethacrylate (IG), polyethylene glycol dimethacrylate (9G and 14G), and MMA diminished the synthesis of water soluble glucan as the concentration of monomers was increased. In addition, the eluate from experimental resin consisted of IG and Bis-GMA decreased the production of WIG when compared to that from 3G and Bis-GMA based resin. These results indicated that it was possible to develop a composite resin which inhibits plaque accumulation by using some antienzymatic monomers.

Antibacterial effect of composite incorporating Triclosan against Streptococcus mutans.

It has been shown that composite incorporating the antibacterial agent Triclosan (Irgasan DP 300, which is sparingly soluble in water, inhibited in vitro plaque formation by Streptococcus mutans, although the release of the agent was much less than the minimum inhibitory concentration for the bacterium. In this study, the inhibitory effect of the composite incorporating 1% Triclosan against growth and adherence of S. mutans was investigated. S. mutans was inoculated on the surface of a specimen made of control or Triclosan-incorporated composite and the number of bacteria was compared after 3, 6, 12 and 24 hr of incubation. The adherence of S. mutans to the control and experimental composite, with or without saliva treatment, was also examined by scanning electron microscopy. The composite incorporating Triclosan demonstrated significant inhibition of growth of S. mutans after 6, 12 and 24 hr of incubation. Adherence of S. mutans to the Triclosan-incorporated composite was less compared with control for both non-treated and saliva-treated specimens. It is concluded that the antiplaque effect of composite incorporating Triclosan depends upon its ability to inhibit bacterial growth and adherence, and Triclosan-incorporated composite is able to exhibit the antibacterial activity even after being treated with saliva.

Basic study of fluoride-releasing adhesive resin for prevention of root caries: 1. Transfer of fluorine from the resin to dentin.

Release of fluoride ion from a newly-developed fluoride-releasing resin (F-resin) into phosphate buffer and incorporation of fluorine by the dentin were studied in vitro. The rate of fluoride release (amount of daily release) from a pellet of cured F-resin showed rapid decrease to 1/2 of the initial value by day 6, and then moderate decrease to 1/4 of the initial by day 30. However, the pellet continued to release fluoride at a low but constant rate for more than 520 days. In the first 30 days after F-resin was applied to the dentin surface, large amount of fluorine was concentrated within 100 mu of the subsurface dentin. With longer incubation period, the peak concentration of fluorine at the dentin surface decreased but the depth of penetration increased to about 180 mu by day 180.

Basic study of fluoride-releasing adhesive resin for prevention of root caries: 2. Enhancement of acid resistance of the dentin.

The human root dentin was covered with a fluoride-releasing resin (F-resin) and incubated for various periods up to 180 days in phosphate buffer. After removal of the F-resin, resistance of the dentin to decalcification by acetic acid--sodium acetate buffer was assessed by measuring both the amount of calcium dissolved during decalcification and the knoop hardness of dentin after decalcification. The acid resistance progressively increased for 90 days when assessed by measurement of calcium dissolution and for 30 days by measurement of the knoop hardness. The percent inhibition of calcium dissolution achieved by 30 days of incubation was about 90% of the maximal inhibition obtained by incubation in concentrated sodium fluoride solution (2.4 x 10(-2) M). The enhancement of acid resistance was not induced by the resin infiltrated layer of the surface dentin but by the fluoride released from the F-resin into the dentin.