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Biomedical subjects

B I Suh

Publications and source records attributed to B I Suh.

17 recordsLinked to original sources
PubMed2006

The effect of curing modes on polymerization contraction stress of a dual cured composite.

Although a lower curing rate is often cited as the reason why a chemical cured (CC) dental composite produces lower polymerization contraction stress (PCS) than a light cured (LC) composite, the exact mechanism is still unclear. In addition, the comparison is often made by using different brands of composites. The comparison's fairness is questionable because the two composites have different compositions and preparation procedures. The goal of the present work was to determine if the curing mode alone can produce different PCS. We formulated a dual cured composite and prepared it the same way for both CC and LC modes. We measured PCS by a strain gauge method, shrinkage by a video-imagining technique, degree of conversion (DC) by infrared spectroscopy, and flexural modulus by the three-point bending test. The CC specimens showed lower PCS and lower flexural modulus than the LC specimens, although both possessed an identical chemical composition and physical texture before cure. This finding indicates that the curing mode alone can affect PCS. Because the CC and LC specimens produced a similar shrinkage and DC, the lower modulus is considered to be one of the reasons for the lower stress. Using a structural inhomogeneity model, we explained how a resin composite with an identical DC can have different physical properties such as the modulus.

Dental Materials↗
PubMed2006

A mechanism on why slower polymerization of a dental composite produces lower contraction stress.

It has been well documented that the rate of polymerization of a dental composite often affects its polymerization contraction stress. In most cases, a slower cure produces a lower stress. To investigate the mechanism behind this, we prepared an unfilled dimethacrylate resin sample and photocured it using two light irradiances, both with the same total irradiation energy. We measured the polymerization-induced shrinkage from the unbonded surface of a class I restoration, contraction stress, extent of polymerization, and flexural modulus. The resin specimens cured under the two irradiances achieved the same extent of polymerization and developed an identical amount of shrinkage from the unbonded surface. But those cured under the lower irradiance possessed a lower contraction stress and a lower flexural modulus than those cured under the higher irradiance. We demonstrated that the stress level did not respond to the extent of viscous flow of the curing resin because the slower polymerization did not produce more shrinkage from the unbonded surface. Instead, the lower stress is likely due to a lower modulus of the cured resin. To explain why the cured resin with an identical extent of polymerization can have different moduli, we proposed that slower polymerization produces a higher level of structural inhomogeneity, which reduces the rigidity of the cured resin.

Calorimetry, Differential Scanning↗
PubMed2005

Incompatibility of oxalate desensitizers with acidic, fluoride-containing total-etch adhesives.

The use of oxalate desensitizers on acid-etched dentin prior to adhesive application can result in subsurface tubular occlusion by calcium oxalate crystals. However, the solubility of calcium oxalate increases in acidic solution. We hypothesized that total-etch adhesives can, depending upon their pH, interact with oxalate-desensitizer-treated dentin in an adverse manner. Acid-etched human dentin treated with 2 oxalate desensitizers (BisBlock and Super Seal) was bonded with 4 simplified total-etch adhesives: One-Step (OS), Single Bond (SB), OptiBond Solo Plus (OB), and Prime&Bond NT (PB). Composite-dentin beams were examined by SEM and TEM, both of which revealed numerous spherical globules on OB- and PB-bonded, desensitizer-treated dentin, but not in OS or SB samples. Bond strengths produced by OB and PB were significantly lower in oxalate-treated specimens than those produced by OS or SB. These surface globules may have interfered with hybridization of demineralized dentin with OB and PB resins and caused compromised bond strengths.

Analysis of Variance↗
PubMed2004

Effect of resin hydrophilicity and water storage on resin strength.

This study evaluated the change in the ultimate tensile strength (UTS) of five polymerised resin blends of increasing hydrophilicity, after ageing in distilled water or silicon oil. Resin blocks were prepared from each resin blend by dispensing the uncured resin into a flexible, embedding mould, containing multiple cavities. The resins were polymerised in the moulds under nitrogen at 551.6 kPa and light-activated at 125 degrees C for 10 min. After dry ageing for 24 h at 37 degrees C, the middle third of each resin specimen was trimmed into an 'I' shape. Fifteen control specimens were randomly selected from each resin blend for baseline UTS evaluation. The UTS of the experimental specimens were determined after 1, 3, 6 and 12 months of ageing in water or oil. The UTS of each group of resins at different storage periods in water or oil were analysed using the Friedman multiple ANOVA on ranks and Dunn's multiple comparison tests at 95% confidence level. Significant reduction (p < 0.01) in UTS was observed in Groups II-V resins after 12-month storage in water, while the most hydrophobic Group I resin showed no significant change (p > 0.05) in the same period. The percentage reduction in UTS increased with the hydrophilicity of the resin blends. Long-term water storage of hydrophilic resin blends such as those employed in dentine adhesives, resulted in a marked reduction in their mechanical strength that may compromise the durability of resin-dentine bonds.

Absorption↗
PubMed2003

Integrating oxalate desensitizers with total-etch two-step adhesive.

Compromised bonding of total-etch adhesives to dentin treated with oxalate desensitizers results from the interference of a surface layer of acid-resistant crystals of calcium oxalate. We hypothesize that effective tubular occlusion and dentin bonding may be simultaneously achieved by depleting dentin surfaces of calcium with acids before desensitizer application. Dentin specimens treated with 4 oxalate desensitizers before or after being acid-etched were bonded with a two-step adhesive. Microtensile bond strengths ( micro TBS) were significantly lower, compared with the control, when oxalates were used before the specimens were acid-etched; in contrast, when oxalates were used after acid-etching. micro TBS were similar to nonoxalate-treated controls. Dentin surfaces and tubular orifices were covered with a surface layer of crystals when desensitizers were applied to fractured dentin and smear-layer-covered dentin before specimens were acid-etched. However, when the dentin was acid-etched prior to the application of oxalate desensitizers, the crystals were largely limited to the subsurface of dentinal tubules, where they did not interfere with subsequent resin bonding.

Acid Etching, Dental↗
PubMed2001

Determining the direction of shrinkage in dental composites by changes in surface contour for different bonding configurations.

PURPOSE: To determine if polymerization shrinkage of a light-cured composite is directed toward the light source, and if a relationship exists between C-factor and magnitude of deflection. MATERIALS AND METHODS: Either a self-cured composite or light-cured composite each was placed in an experimental model of composite cured in a glass ring. Changing the surface area prepared for bonding within the cavity preparation produced three different C-factors (the ratio of bonded to unbonded surface areas): 0, 1.9, and 4.8. Profilometer tracings were obtained, and the largest deviation from the height of the glass ring was reported. An uncured control sample also was evaluated and showed a linear tracing with fluctuations of less than 0.5 micron. The specimens were then cut in half and examined by scanning electron microscope. RESULTS: The top (unbonded) surface exhibited a concave shrinkage profile with the greatest deflection at the center. The magnitude of deflection at the center increased as the cavity's C-factor increased from 31 microns (C = 0) to 57 microns (C = 4.8). The bottom (unbonded) surface, similarly formed a concave surface. When the composite was bonded to the glass, fractures in the glass wall near the glass-composite interface were observed.

Bisphenol A-Glycidyl Methacrylate↗
PubMed2001

Effect of delayed activation of light-cured resin composites on bonding of all-in-one adhesives.

PURPOSE: This study examined the effect of delayed activation of light-cured resin composites on the microtensile bond strengths of two all-in-one adhesives to sound dentin. MATERIALS AND METHODS: Flat dentin surfaces prepared from caries-free third molars were bonded with either Prompt L-Pop (ESPE) or One-Up Bond F (Tokuyama). Each adhesive was divided into 6 subgroups containing three teeth each. A hybrid composite was left to contact the cured adhesive surfaces for 0, 2.5, 5, 10 or 20 min before light activation. In the 6th subgroup, the cured adhesive was covered with a layer of nonacidic bonding resin before contacting the composite for 20 min. Composite-dentin beams, with average cross-sectional areas of 0.85 mm2 were prepared for microtensile bond testing. Representative fractured beams from the 0, 10- and 20-min delay subgroups were prepared for SEM examination. Additional specimens were prepared in the 0- and 20-min delay subgroups by replacing the hybrid composite with either a flowable composite or a composite liner to facilitate TEM preparation and examination. RESULTS: Kruskal-Wallis ANOVA and Dunn's multiple comparison tests showed that significant differences existed among the subgroups of each adhesive. Regression analyses showed that for each adhesive, there was an exponential decline in mean bond strength with increasing delay in light activation, and the correlation was highly significant (r = -0.99, p < 0.005 for Prompt L-Pop; r = -0.96, p < 0.01 for One-Up Bond F). SEM examination of fractured interfaces in the immediately light-cured subgroups revealed the absence of voids within the fractured composite. However, voids were consistently observed in the 10 min- and 20 min-delay subgroups. They corresponded to soapsuds-like blisters that were observed with TEM in the 20 min-delay subgroups. CONCLUSION: Adverse interactions between acidic adhesive resin monomers and tertiary amines in light-cured composites normally do not occur because of the fast rate of free-radical generation in photochemical redox reactions. However, such interactions can occur in all-in-one adhesives on prolonged contact of light-cured composites with the cured adhesive layer.

Composite Resins↗
PubMed2000

Effects of prism orientation on tensile strength of enamel.

PURPOSE: This study tested the hypothesis that the tensile strength of enamel varies according to prismatic orientation. MATERIALS AND METHODS: Eight extracted, caries-free human third molars were thoroughly cleaned with pumice and water. The entire enamel surface was conditioned with 37% phosphoric acid for 30 s, air dried, and bonded with Single Bond adhesive system. Several layers of composite (Z-100) were incrementally applied to the crown to build up a "cube-like" resin structure approximately 5 mm thick covering the entire crown of the teeth. The teeth were stored for 24 h in water at 37 degrees C, and then the crown was serially, vertically sectioned in a mesio-distal direction to obtain several slices approximately 0.7 mm thick. The slices were sectioned into halves, and each half was gently trimmed from both sides with a diamond bur to reduce the cross-sectional area to a "neck" located in enamel, either on the external slope or functional slope of the cusps. The specimens were trimmed to permit testing of enamel with its prisms either oriented parallel (PL) or perpendicular (PD) to the applied load. The trimmed specimens were glued to the fixtures of a Vitrodyne tester and stressed in tension at 0.5 mm/min. SEM images were taken from the fractured surfaces to examine the site of failure and confirm the prism orientation. RESULTS: Mean tensile strength of enamel was 24.7 +/- 9.6 MPa (n = 22) for PL and 11.4 +/- 6.3 MPa (n = 22) for PD oriented enamel prisms (t value = -5.45, p < 0.05). There was no significant difference between specimens originating from different slopes of the cusps (p > 0.05). CONCLUSION: The results showed that tensile strength of enamel is dependent on the prismatic orientation.

Acid Etching, Dental↗
PubMed1999

Pulse activation: reducing resin-based composite contraction stresses at the enamel cavosurface margins.

PURPOSE: To evaluate the effect of pulse activation light-curing of resin-based composites on the stress reduction at the enamel surface. MATERIALS AND METHODS: The rate of polymerization of a resin-based composite known to be accompanied by high contraction stress was examined by its surface hardness. The effects of polymerization stresses were examined with the use of dye penetration along enamel margins in cavities with a C-factor of 5. The occlusal-most layer of resin-based composite was polymerized at different power densities and time intervals; 40 s@600 mW/cm2, 40 s@100 mW/cm2 and pulse activation; 2 s@300-350 mW/cm2, followed by additional exposure of 10 s@600 mW/cm2. Diametral tensile strengths were measured for each parameter. RESULTS: The surface hardnesses of both the 40 s@600 mW/cm2 group and the 40 s@100 mW/cm2 group developed at nearly the same rate. The surface hardness of the pulse activated group developed appreciably slower. The diametral tensile strengths of all three groups were not significantly different. There was significantly less dye penetration with the use of the lower power density but there was very little leakage noted with the pulse-activated group. It is believed that this is the result of a prolonged gel state, which allowed flow to occur in the resin-based composite. There is significant clinical potential for the use of pulse activation of light-cured resin-based composite materials.

Composite Resins↗
PubMed1999

Controlling and understanding the polymerization shrinkage-induced stresses in light-cured composites.

The shrinkage of composites induces stress in the final restoration when the composite is bonded to the tooth surface. The amount of stress can be controlled by the method of pulse-delay cure used. The development of new composites has changed the energy requirements for obtaining polymerization. The total energy required for optimal polymerization has been reduced and the rate at which the energy is delivered can have a strong effect on the final properties of the restoration. Newer composites may employ different photoinitiators, making the spectral emission from the curing light an important factor for properties of the final restoration. It is proposed that labels for composites carry: (1) indications for the total energy required; (2) specification of the pulse-delay cure if applicable; and (3) the required spectral bandwidth of the curing lamp light emission.

Composite Resins↗
PubMed1999

The effect of the pulse-delay cure technique on residual strain in composites.

Polymerization-induced shrinkage of composites leads to residual stress in the final restoration. For composites with a high modulus of elasticity, the level of stress can have significant clinical consequences, including crack formation in the enamel or microscopic separations at the preparation/restoration interface. The pulse-delay cure technique cures composites by providing low-energy pulse initially (e.g., 200 mW/cm2 for 3 seconds), followed by a waiting period of 3 to 5 minutes for strain relief, during which the composite can be finished and polished. The final cure is obtained by exposure to a high-intensity light source of 500 mW/cm2 for the recommended time. In vitro data obtained by strain gauges show that the pulse-delay cure technique can reduce residual strain in the composite by as much as 34%.

Composite Resins↗
PubMed1998

Adhesive bonding of fractured anterior teeth: effect of wet technique and rewetting agent.

PURPOSE: To compare the fracture strength of intact teeth with that of fractured crowns bonded with adhesive and a resin material on either wet or dry dentin, or dried dentin rewetted with a rewetting agent for various periods of time. MATERIALS AND METHODS: Sheep central incisors were divided into seven groups, each of 10 teeth. Group 1: Intact teeth tested for fracture strength in an Instron testing machine and used as controls. Groups 2-7 were sectioned in a vice equipped with sharp blades, 2.5 mm away from and parallel to the incisal edge. The two fracture surfaces were etched with 37% phosphoric acid for 15 s and rinsed with water for 5-6 s. Group 2: The surfaces were air-dried for 2 s. Group 3: As for Group 2 but the surfaces were rewetted with Aqua-Prep for 2 s and immediately air-blasted to remove excess. Group 4: As for Group 3, but the rewetting agent was applied for 10 s before air-blasting. Group 5: As for Group 4, but the rewetting agent was applied for 20 s. Group 6: As for Group 4, but the rewetting agent was applied for 30 s. Group 7: As for Group 2, but the surfaces were left moist after etching and rinsing by gently shaking the specimens twice. The fracture surfaces of Groups 2-7 were rebonded with All-Bond 2 adhesive system and Aeliteflo composite. After 48 hrs the restored teeth were debonded in the Instron testing machine. Fracture strengths were calculated and compared with the fracture strength of intact teeth (control group). RESULTS: Newman-Keuls' multiple range test revealed that there was a statistically significant difference between the control mean and the means of Groups 2 and 3. All other means were not significantly different. Drying of the dentin surface decreased the bonding strength, and rewetting of the dried dentin for 2 s was not sufficient to rewet the collapsed collagen fibers, as indicated by a decrease of fracture strength.

Acid Etching, Dental↗
PubMed1994

A 4th generation universal bonding system.

This paper reviews the fourth generation universal bonding system and highlights its supremacy over the earlier bonding systems. This new system has the ability to bond to all dentally related surfaces and its hydrophillic nature allows the advantage of bonding in a naturally moist environment. The effect of acid on dentine and the role of hydrophillic primers in the formation of a collagen-resin complex are described in relation to obtaining good bonding and adhesion. A new fourth generation universal bonding system. ALL-BOND 2, is discussed in the light of these developments and its features compared to those of the ideal bonding system.

Dental Bonding↗
PubMedDate not supplied

Optimization of hybrid composite properties.

Hybrid composites have been a popular class of a wear-resistant posterior composite restorative material. The purpose of this study was to determine the effect of hybridization on the physical properties of a composite with different amounts of submicron silica (0.04 microns) with semiporous strontium glass (1.4 microns ave. by number/5 microns ave. by volume) in a Bis-GMA based resin system. As the submicron content increases, the total filler loading in the composite was increased. At the 25 percent submicron silica level, the filler loading was highest and the physical strength measurements were highest, except for DTS results, which were fairly steady throughout the 5-40 percent level.

Composite Resins↗
PubMedDate not supplied

All-Bond--fourth generation dentin bonding system.

The All-Bond system is a unique development in the field of adhesive dentistry. It is a universal bonding system that will bond composite to all dental-related surfaces: dentin, enamel, metal alloy (precious and nonprecious), amalgam, porcelain, and composite. It is also the only system that allows use of both the conservative and all-etch techniques. The main purpose of this paper is to explain the features of the All-Bond system. Its chemistry and a working hypothesis are shown as well.

Composite Resins↗
PubMedDate not supplied

Shear bond strength to dentin and Ni-Cr-Be alloy with the All-Bond universal adhesive system.

The shear bond strength of the All-Bond system to dentin and a nonprecious alloy was evaluated. Eighty human molar teeth (10 per group) were used in the dentin bonding phase of the study. A bond site was prepared in dentin, and both the succinic anhydride modified HEMA and 10 percent phosphoric acid dentin conditioning techniques were evaluated under both wet and dry conditions. Eighty Rexillium III specimens were used in the metal bonding phase of the study. All-Bond primer and opaquer were applied to the metal surface, followed by a visible light-cured composite restorative material. Dentin bond strengths were determined at 24 hours, while metal bond strengths were evaluated both at 24 hours and after thermocycling (2,500 cycles). Separate groups were established for adhesion to both dentin and metal with the composite placed in a plastic matrix or a gelatin capsule. The highest mean shear bond values to dentin were obtained in the groups with the gelatin capsule bonding procedure, where the dentin was treated with 10 percent phosphoric acid and then blotted dry (wet technique) before the bonding procedure (39.99 MPa). These values were higher than the succinic anhydride modified HEMA-treated group with gentle air drying (wet technique-29.56 MPa). There was essentially no difference in mean shear bond strengths to dentin when a succinic anhydride modified HEMA dentin conditioner was used with aggressive (dry technique) or gentle air drying (wet technique) [29.56 versus 29.08 MPa]. High bond strengths to Rexillium III were obtained when the All-Bond adhesive system was used in combination with a dual-care opaquer and a composite restorative material.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid Etching, Dental↗