Biomedical subjects

F A Rueggeberg

Publications and source records attributed to F A Rueggeberg.

At least 19 recordsLinked to original sources

PubMed2006

Polymerization kinetics of pre-heated composite.

Temperature affects the polymerization behavior of dimethacrylate-based materials. This study describes the influence of pre-polymerization temperature and exposure duration on polymerization kinetics of a commercial dental photo-activated composite at the top and at 2-mm depth. We used the temperature-controlled stage of a diamond-attenuated-total-reflectance unit to pre-set composite temperature between 3 degrees and 60 degrees C. Composite was light-exposed by a conventional quartz-tungsten-halogen curing unit for 5, 10, 20, or 40 sec. Real-time conversion, maximum conversion rate (R(p)(max)), time to achieve R(p)(max), and conversion at R(p)(max) were calculated from infrared spectra. Composite pre-warming enhanced maximal polymerization rate and overall monomer conversion (top significantly greater than 2 mm). Time when R(p)(max) occurred did not change with temperature, but occurred sooner at the top than at 2-mm depth. Conversion at R(p)(max) increased with temperature, allowing more of the reaction to occur prior to vitrification than at room temperature.

Composite Resins↗

PubMed2005

Monomer conversion of pre-heated composite.

The potential for maximizing conversion of room-temperature, photoactivated resin composite in the oral environment is limited. Pre-heating composite prior to light-curing is hypothesized to increase monomer conversion and reduce the duration of light exposure. Composite temperature was controlled at between 3 degrees C and 60 degrees C prior to exposure with a conventional quartz-tungsten-halogen curing unit: 5, 10, 20, or 40 sec. Monomer conversion was calculated from infrared spectra at 0 mm (top) and 2-mm-deep surfaces 5 min after light initiation. A strong, positive correlation existed between temperature and monomer conversion: top r(2) = 0.999, 2 mm r(2) = 0.998. Conversion ranged from 31.6% (3 degrees C) to 67.3% (60 degrees C). The duration of light exposure, reduced by 50 to 75% with pre-heated composite, yielded the same or significantly higher conversion (p = 0.001) than with control (22 degrees C, 20 sec). Both hypotheses were accepted: Pre-heating composite prior to photoactivation provides greater conversion requiring reduced light exposure than with room-temperature composite.

Analysis of Variance↗

PubMed2005

Tubular occlusion prevents water-treeing and through-and-through fluid movement in a single-bottle, one-step self-etch adhesive model.

Water entrapment occurs at resin-dentin interfaces of one-step self-etch adhesives. We hypothesized that by preventing water fluxes from dentin, any water entrapment would be attributed to incomplete removal of adhesive solvents. We tested this hypothesis by bonding to transparent carious dentin containing occluded dentinal tubules. An experimental single-bottle, one-step self-etch adhesive was applied to flat surfaces of caries-affected dentin surrounded by sound dentin, with or without pulpal pressure. Resin-dentin interfaces were examined with TEM after silver-impregnation. Although caries-affected dentin was highly porous, adhesive layers were devoid of silver deposits when tubules were occluded. Conversely, variable extents of water-treeing and water-droplets were identified from adhesive layers in bonded sound dentin. Water-treeing and water-droplet formation, being manifestations of evaporative and convective water fluxes, can be eliminated during bonding to occluded transparent carious dentin. However, the highly porous nature of this clinically relevant substrate after bonding may lead to potentially undesirable consequences.

Acid Etching, Dental↗

PubMed2004

Blue light differentially modulates cell survival and growth.

Previous studies have reported that blue light (400-500 nm) inhibits cell mitochondrial activity. We investigated the hypothesis that cells with high energy consumption are most susceptible to blue-light-induced mitochondrial inhibition. We estimated cell energy consumption by population doubling time, and cell survival and growth by succinate dehydrogenase (SDH) activity. Six cell types were exposed to 5 or 60 J/cm(2) of blue light from quartz-tungsten-halogen (QTH), plasma-arc (PAC), or argon laser sources in monolayer culture. Post-light SDH activity correlated positively with population doubling time (R(2) = 0.91 for PAC, 0.76 for QTH, 0.68 for laser); SDH activity increased for cell types with the longest doubling times and was suppressed for cell types with shorter doubling times. Thus, light-induced exposure differentially affects SDH activity, cell survival, and growth, depending on cell energy consumption. Blue light may be useful as a therapeutic modulator of cell growth and survival.

Animals↗

PubMed2003

Dimensional changes in acid-demineralized dentin matrices following the use of HEMA-water versus HEMA-alcohol primers.

Although dried acid-etched dentin can be reexpanded by hydroxyethyl methacrylate (HEMA)/water primers, the primed dentin collapses when the water is evaporated. Experimental HEMA/alcohol primers should stiffen the matrix and permit less shrinkage when the solvent is evaporated. The purpose of this study was to test the hypotheses that matrix shrinkage induced by solvent evaporation from HEMA primers is inversely related to solvent-induced matrix stiffness. Dentine discs were prepared from midcoronal dentine of unerupted human third molars. After demineralization in 37% phosphoric acid, the specimens were placed in the well of a linear variable differential transformer instrument, which measures changes in the matrix height and stiffness by load displacement after the application of weights. This was done in their hydrated state after water had been applied, after drying with dry nitrogen gas, and after the application of 35 vol % HEMA-water, HEMA-methanol, HEMA-ethanol, or HEMA-propanol primers. The degree of reexpansion after the application of the primers to the dentine in the dried state was found to be highest using the HEMA-water primer, followed by HEMA-methanol and HEMA-ethanol, with the HEMA-propanol primer producing no expansion. However, when the solvents were evaporated the HEMA-water-treated specimens shrank the most, the HEMA-ethanol-treated specimens shrank an intermediate amount, and the HEMA-methanol-treated specimens shrank the least. The net result of expansion minus shrinkage produced by evaporation determines how much HEMA remains in the hybrid layer just prior to polymerization.

Acids↗

PubMed2001

Solvent-induced dimensional changes in EDTA-demineralized dentin matrix.

The purpose of this study was to test the null hypothesis that the re-expansion of dried matrix and the shrinkage of moist, demineralized dentin is not influenced by polar solvents. Dentin disks were prepared from midcoronal dentin of extracted human third molars. After complete demineralization in 0.5M of EDTA (pH 7), the specimens were placed in the well of a device that measures changes in matrix height in real time. Dry, collapsed matrices were created by blowing dry N(2) on the specimens until they shrank to a stable plateau. Polar solvents [water, methanol, ethanol, n-propanol, n-butanol, formamide, ethylene glycol, hydroxyethyl methacrylate (HEMA), or mixtures of water-HEMA] as model primers then were added and the degree of re-expansion measured. These same solvents also were applied to moist, expanded matrices and the solvent-induced shrinkages measured. Regression analysis was used to test the correlations between matrix height and Hansen's dispersive, polar, hydrogen bonding, and total solubility parameters (delta(d), delta(p), delta(h), delta(t)). The results indicate that water-free polar solvents of low hydrogen bonding (H-bond) ability (e.g., neat HEMA) do not re-expand dried matrices and that they shrink moist matrices. When HEMA was mixed with progressively higher water concentrations, the model water-HEMA primers expanded the dried matrix in proportion to their water concentrations and they produced less shrinkage of moist matrices. Solvents with higher H-bonding capacities (methanol, ethanol, ethylene glycol, formamide, and water) re-expanded the dried matrix in proportion to their solubility parameters for H-bonding (delta(h)). They also induced small transient shrinkages of moist matrices, which slowly re-expanded. The results require rejection of the null hypothesis.

Biocompatible Materials↗

PubMed2001

Examination of the implant-abutment interface after fatigue testing.

PURPOSE: This study examined potential differences in detorque values of abutment screws after fatigue testing when the dimensions between external implant hexagon and internal abutment hexagon were altered or the implant external hexagonal shape was eliminated. MATERIAL AND METHODS: Three subsets (N = 10) of NobelBiocare implants were assessed: (1) standard external hexagon (R), (2) modified hexagon (M), and (3) circular (C) platform geometry. Thirty Procera machined abutments with 25-degree angulated loading platforms were manufactured. Abutments were retained with gold Unigrip abutment screws tightened to 32 N/cm with an electronic torque controller. Vertical scribes across the implant-abutment interface allowed longitudinal displacement evaluation. A carousel-type fatigue testing device delivered dynamic loading forces between 20 and 200 N for 5,000,000 cycles, or the approximate equivalent of 5 years in vivo mastication, through a piston to the abutment platform. Macroscopic and radiographic examination of the implant/abutment specimens was performed. The abutment screws were removed and the detorque values recorded. Bearing surfaces were examined microscopically. RESULTS: No abutment looseness or longitudinal displacements at the implant-abutment interface were noted. Radiographic examination demonstrated no indication of screw bending or displacement. The mean detorque values for R, M, and C were 14.40 +/- 1.84 N/cm, 14.70 +/- 1.89 N/cm, and 16.40 +/- 2.17 N/cm, respectively. The analysis of variance demonstrated significant differences between only designs R and C (P=.031). CONCLUSION: Increasing the vertical height, or degree of fit tolerance, between the implant external hexagon and the abutment internal hexagon or completely eliminating the implant external hexagon did not produce a significant effect on the detorque values of the abutment screws after 5,000,000 cycles in fatigue testing, or the equivalent of 5 years' of mastication for the implant/abutment specimens evaluated.

Analysis of Variance↗

PubMed2001

Curing potential of dual-polymerizable resin cements in simulated clinical situations.

STATEMENT OF PROBLEM: Little is known about the ability of dual-polymerizable resin cements to polymerize when they are used in various clinical scenarios. PURPOSE: This study was conducted to determine whether any of 6 commercially available dual-polymerizable resin cements should be classified as an "all-purpose" resin cement. MATERIAL AND METHODS: . Chemical conversion values (C=C converted to C-C, or the extent of the curing reaction) of 6 commercially available dual-polymerizable resin cements were determined with infrared spectroscopy in 5 clinically relevant scenarios. Scenarios included: using each cement in a dual-polymerizable mode (mixing of 2 pastes); light polymerizing curing through Mylar sheets (dual-Mylar), which served as the control; light polymerizing through 3-mm porcelain (dual-3 mm); and no exposure to light (dual-no light). The single-component light-polymerizable product was also tested as follows: exposed directly through Mylar (light-Mylar) or exposed through 3 mm of porcelain (light-3 mm). Results. For each product, dual-Mylar treatment yielded the highest conversion value of all treatments (control for each product). For all products, dual-3 mm conversion was at least 97% of control and equivalent to control, with the exception of Lute-It!. Dual-no light conversion was less than control treatment but at least 86% of control for all products except for Variolink II (62% of control). For all products in dual-no light mode, except Choice and Variolink II, conversion was at least equal to the light-Mylar values. Only 1 product (Variolink II) did not demonstrate increased conversion values for dual-Mylar compared with light-Mylar treatments. For most other products (Calibra, Insure, and Lute-It!), conversion values for light-3 mm were significantly less than for light-Mylar. Conversion values for Nexus, Choice, and Variolink II were equivalent between light-Mylar and light-3 mm treatments. CONCLUSION: The choice of a dual-polymerizable cement should be based on its intended use because not all products polymerize adequately in every clinical situation. Although no cement met the stated criteria for an "all-purpose" cement, those tested did produce a range of product-specific results.

Analysis of Variance↗

PubMed2001

Curing potential of dual-polymerizable resin cements in simulated clinical situations.

STATEMENT OF PROBLEM: Little is known about the ability of dual-polymerizable resin cements to polymerize when they are used in various clinical scenarios. Purpose. This study was conducted to determine whether any of 6 commercially available dual-polymerizable resin cements should be classified as an "all-purpose" resin cement. MATERIAL AND METHODS: Chemical conversion values (C=C converted to C-C, or the extent of the curing reaction) of 6 commercially available dual-polymerizable resin cements were determined with infrared spectroscopy in 5 clinically relevant scenarios. Scenarios included: using each cement in a dual-polymerizable mode (mixing of 2 pastes); light polymerizing curing through Mylar sheets (dual-Mylar), which served as the control; light polymerizing through 3-mm porcelain (dual-3 mm); and no exposure to light (dual-no light). The single-component light-polymerizable product was also tested as follows: exposed directly through Mylar (light-Mylar) or exposed through 3 mm of porcelain (light-3 mm). RESULTS: For each product, dual-Mylar treatment yielded the highest conversion value of all treatments (control for each product). For all products, dual-3 mm conversion was at least 97% of control and equivalent to control, with the exception of Lute-It!. Dual-no light conversion was less than control treatment but at least 86% of control for all products except for Variolink II (62% of control). For all products in dual-no light mode, except Choice and Variolink II, conversion was at least equal to the light-Mylar values. Only 1 product (Variolink II) did not demonstrate increased conversion values for dual-Mylar compared with light-Mylar treatments. For most other products (Calibra, Insure, and Lute-It!), conversion values for light-3 mm were significantly less than for light-Mylar. Conversion values for Nexus, Choice, and Variolink II were equivalent between light-Mylar and light-3 mm treatments. CONCLUSION: The choice of a dual-polymerizable cement should be based on its intended use because not all products polymerize adequately in every clinical situation. Although no cement met the stated criteria for an "all-purpose" cement, those tested did produce a range of product-specific results.

Analysis of Variance↗

PubMed2001

Effect of light-enhanced bleaching on in vitro surface and intrapulpal temperature rise.

PURPOSE: This study investigated the effect of the presence, absence, and aging of a heat-enhancing compound (colorant) added to bleaching gel on the temperature rise of the gel itself, as well as the temperature rise within the pulp chamber, when a tooth was exposed to a variety of light-curing units in vitro. MATERIALS AND METHODS: An extracted human upper central incisor was fitted with thermocouples placed in the pulp chamber as well as on the facial tooth surface. A temperature-controlled simulated intrapulpal fluid flow was provided to the tooth, and bleaching agent (Opalesence XTRA, Ultradent) containing heat-enhancing colorant, aged colorant, or no colorant was applied to the facial surface. The tooth and light-curing unit were placed in a thermostatically controlled oven at 37 degrees C, and real-time gel and intrapulpal temperature values were recorded digitally. Light-curing units used were a plasma arc light (PAC) (PowerPac, ADT), a conventional quartz tungsten halogen source (QTH) (Optilux 501, Demetron/Kerr), the QTH light used in high-power (bleaching) mode, and an argon ion laser (AccuCure 3000, LaserMed). An exposure scenario simulating light-enhanced bleaching of 10 upper teeth was developed. Temperature rise over the pre-exposure, baseline value associated with the last light exposure in the bleaching sequence was calculated for each curing and bleaching combination. Five replications for each test condition were made. Temperature rise values were compared using analysis of variance (ANOVA) at a preset alpha of 0.05. RESULTS: When fresh colorant-containing bleach was used, the PAC light increased bleach temperature 39.3 degrees C above baseline. With no added colorant, temperature rise was 37.1 degrees C. The QTH light in bleach mode resulted in gel temperature 24.8 degrees C above baseline, whereas the temperature increase was only 11.5 degrees C when no colorant was used. Conventional QTH light use increased fresh bleach temperature by 17.7 degrees C, whereas an increase of only 11.1 degrees C was measured without colorant. The argon ion laser produced equivalent temperature rise regardless of the presence or freshness of the colorant, approximately 9.4 degrees C. Intrapulpal temperatures were all significantly lower than those recorded in the bleaching gel and ranged from 5 degrees to 8 degrees C. As a rule, the presence of fresh heat-enhancing colorant in the bleaching gel resulted in a significant intrapulpal temperature increase (approximately 1 degrees C) over that reached using other lights. The PAC and the QTH light used in bleach mode induced greater intrapulpal temperature rise than the laser. CLINICAL SIGNIFICANCE: Freshness of bleaching agent incorporating light-activated, heat-enhancing colorant influences temperature rise of bleaching gel and also may increase intrapulpal temperature values. Use of intense lights does elevate bleach temperature and also results in increased intrapulpal temperature that may further impact on patient sensitivity and pulpal health resulting from this treatment.

Analysis of Variance↗

PubMed2000

Effect of dentin desensitizers and cementing agents on retention of full crowns using standardized crown preparations.

STATEMENT OF PROBLEM: Past research has not controlled preparation surface area when examining the influence of dentin desensitizers on the retentive strength of cemented cast crowns, leading to inconsistent results. PURPOSE: This research controlled crown preparation surface area and evaluated the effect of various dentin desensitizers and conventional cementing agents on the in vitro retentive strength of cast crowns. METHODS AND MATERIAL: Freshly extracted human molars were prepared for a standardized crown preparation (26 degrees total convergence, 4 mm axial height) with a custom-made pantograph. Dentin desensitizers included none (control), a polymerizable material (All-Bond 2), and a nonpolymerizable desensitizer (Gluma Desensitizer). Cementing agents included zinc phosphate (Fleck's), glass ionomer (Ketac-Cem), resin-modified glass ionomer (Fuji II), and resin cement (Panavia 21). Twelve teeth were prepared for each test condition (144 teeth total). Individual castings were made from a base metal alloy (Rexillium III). Crowns were removed after storage at 26 degrees C for 48 hours at 100% relative humidity using a universal testing machine at a crosshead speed of 1.27 mm/min. The proportion of cement retained on the tooth and casting after debonding was quantified according to treatment. Statistical treatment included 1- and 2-way ANOVAs, followed by the Tukey-Kramer post hoc test at a preset alpha of 0.05.Results. Resin cement exhibited the highest retentive strength and all dentin treatments resulted in significantly different retentive values (All-Bond 2 (5.68 +/- 0.70 MPa) > control (4.67 +/- 0.48 MPa) > Gluma (4.12 +/- 0.37 MPa)). Retention of resin-modified glass ionomer was between the resin cement and glass ionomer groups: All-Bond 2 (3.46 +/- 0.26 MPa) > Gluma (2.81 +/- 0.15 MPa) = control (2.96 +/- 0.18 MPa). Conventional glass ionomer values were between those of Fuji Plus and zinc phosphate groups: All Bond 2 (2.23 +/- 0. 20 MPa) = control (2.36 +/- 0.20 MPa) > Gluma (1.98 +/- 0.23 MPa). Zinc phosphate had the lowest retention values: control (1.68 +/- 0. 08 MPa) > Gluma (0.81 +/- 0.11 MPa) > All-Bond 2 (0.67 +/- 0.14 MPa). The majority of cement was retained on the debonded tooth surface versus the casting, with the exception of zinc phosphate when used with dentin pretreatments. CONCLUSION: Controlled crown surface areas reduced the variation in strength values permitting high discrimination among retention values of desensitizer/cement combinations. In all but 1 combination, Gluma desensitizer significantly decreased crown retention. With resin cement and resin-modified glass ionomer, use of All-Bond 2 desensitizer significantly increased crown retention values.

Analysis of Variance↗

PubMed2000

The effect of post-cure heating on residual, unreacted monomer in a commercial resin composite.

OBJECTIVES: This paper examined the influence of post-cure temperature on the amount of unreacted monomer remaining in a commercial light-cured resin composite restoration following initial light-curing and subsequent post-cure heating. METHODS: Discs of composite were light-cured and then subjected to immediate post-cure heating (50, 75, 100, or 125 degrees C for 7 min) or were left unheated (control). They were then placed in a solvent for two weeks at 37 degrees C to extract the unreacted monomer. HPLC analysis was used to determine the amounts of TEGDMA, BIS-GMA, and ethoxylated BIS-GMA remaining after the different treatments. The amounts of each monomer leaching were compared using ANOVA with respect to the different curing treatments. RESULTS: Even the lowest post-cure heat treatment (50 degrees C) resulted in 80% reduction in remaining, unreacted TEGDMA, 75% reduction in BIS-GMA, and 77% lower ethoxylated BIS-GMA than the light-cured only control. Post-cure heating at 75 degrees C and above resulted in the lowest amount of each type monomer remaining uncured in the polymer and did not significantly decrease with an increase in post-cure temperature for the most part. SIGNIFICANCE: One of the main benefits of post-cure heating of resin composite restorations could be the enhancement of biocompatibility of these restorations as a result of the significant decrease in potentially leachable, unreacted monomer.

Analysis of Variance↗

PubMed2000

Changes in cell phospholipid metabolism in vitro in the presence of HEMA and its degradation products.

OBJECTIVES: Diacylglycerol-kinase (DAG-kinase) is an enzyme that phosphorylates diacylglycerol (DAG) to phosphatidic acid (PA), which serves as a precursor to phosphoglycerides involved in cell signaling or as cell membrane structural components. DAG-kinase can be inhibited by diacylethylene glycols (DAEG). We hypothesize that 2-hydroxyethyl methacrylate (HEMA) may alter phosphorylation of DAG to PA following intracellular formation of DAEG. METHODS: Cultured rabbit kidney (RK13) epithelial cells were treated with HEMA, EG, or known inhibitors of DAG-kinase for 24 h, then exposed to [32P]O4- in the presence of a synthetic diacylglycerol for 2 h. Other cultures were radiolabeled with [3H]-oleic acid for 24 h, then exposed to HEMA for an additional 24 h. The cells were harvested and the lipids extracted. Radioactive lipids were separated by thin layer chromatography, located by autoradiography, and quantitated as cpm/ug protein. Cell cultures treated with HEMA were homogenized and the DAG-kinase activity was assayed and expressed as cpm/ug protein. Data were analyzed by one-way ANOVA and Newman-Keuls Multiple Comparison Test. RESULTS: Cultures exposed to HEMA or known DAG-kinase inhibitors exhibited reduced incorporation of radioactivity in the PA fraction compared to control cultures. Direct assays of DAG-kinase activity from cells exposed to HEMA demonstrated decreased enzyme activity. Evaluation of cell phospholipid synthesis showed altered formation of phosphatidylethanolamine and phosphatidylcholine. SIGNIFICANCE: Results suggest that HEMA impairs formation of PA, possibly by acylation of EG released by hydrolysis of the HEMA and resultant production of the inhibitor DAEG. The decreased availability of PA may alter PA-dependent cell structural lipid pathways and lipid-dependent signaling pathways, altering cell growth.

Analysis of Variance↗

PubMed2000

Effect of stepped light intensity on polymerization force and conversion in a photoactivated composite.

PURPOSE: This study evaluated the effect of stepped light intensity on the polymerization shrinkage forces and degrees of conversion of a hybrid composite. MATERIALS AND METHODS: Composite specimens were bonded between two steel rods (5.00 mm diameter, 1.25 mm apart, configuration factor = 2) mounted in a universal testing machine using a constant displacement mode. Polymerization contraction force was recorded for 300 seconds under four light exposure conditions: group 1: 40 s x 800 mW/cm2; group 2: 10 s x 100 mW/cm2 + 30 s x 800 mW/cm2; group 3: 60 s x 800 mW/cm2; group 4: 10 s x 100 mW/cm2 + 50 s x 800 mW/cm2. Maximum curing force (N300 s) and maximum force rate of the four groups were compared using one-way analysis of variance (ANOVA) (alpha = 0.05) and the Tukey test. Degree of conversion in all groups was evaluated at two depths (top surface and 2 mm) using Fourier transform infrared spectroscopy (FTIR). RESULTS: Mean maximum shrinkage forces and standard deviations (SD) were: group 1, 177 N (SD = 23); group 2, 172 N (SD = 11); group 3, 213 N (SD = 15); group 4, 197 N (SD = 17). Mean maximum forces for stepped and standard groups with the same duration (1 and 2; 3 and 4) were not statistically different; means for groups 2 and 3 were statistically different. Maximum force rates were not significantly different (p = .1548). Force:time curves were S-shaped. Specimens exposed to stepped curing exhibited longer delays before force was recorded. Mode of curing was shown not to contribute to overall cure, but both duration of cure and the depth (top surface vs. 2.00 mm) were significant with an interaction effect.

Analysis of Variance↗

PubMed2000

Effect of ramped light intensity on polymerization force and conversion in a photoactivated composite.

PURPOSE: This study evaluated the effect of ramped light intensity on the polymerization shrinkage forces and degrees of conversion (DC) of a hybrid composite. MATERIALS AND METHODS: Composite samples were bonded between two steel rods (2.50 mm diameter, 1.25 mm apart, configuration factor = 1.0) mounted in a universal testing machine using a constant displacement mode. Polymerization contraction force was recorded for 250 seconds under four light exposure conditions: group 1, STD: (40 s x 800 mW/cm2); group 2, EXP: (150 mW/cm2 logarithmic increase to 800 mW/cm2 over 15 s) + (25 s x 800 mW/cm2); group 3, 2-STEP: (10 s x 150 mW/cm2) + (30 s x 800 mW/cm2); group 4, MED: (80 s x 400 mW/cm2). Maximum curing force (N250s) and maximum force rate of the four groups were compared using one-way analysis of variance (ANOVA) (alpha = 0.05) and the Tukey test. Degrees of conversion obtained with STD, EXP, and MED cure modes were evaluated at three depths (top surface, 1 mm, and 2 mm) using Fourier transform infrared spectroscopy (FTIR). RESULTS: Maximum rates of polymerization shrinkage force development and standard deviations (SD), in ascending order, were group 4, MED: 0.33 +/- 0.03 N/s; group 2, EXP: 0.35 +/- 0.06 N/s; group 1, STD: 0.44 +/- 0.03 N/s; and group 3, 2-STEP: 0.46 +/- 0.07 N/s. Maximum rates of polymerization shrinkage force development of group 2, EXP and group 4, MED were statistically equivalent and lower than those of group 1, STD and group 3, 2-STEP. Maximum shrinkage forces (+/- SD), in ascending order, were group 2, EXP: 20.4 +/- 2.5 N; group 4, MED: 25.8 +/- 1.0 N; group 3, 2-STEP: 27.4 +/- 5.8 N, and group 1, STD: 30.5 +/- 2.7 N. Maximum force of the EXP mode was statistically lower than MED, 2-STEP, and STD curing modes. The EXP ramp was successful in reducing the conversion rate at the top surface and at 1.0-mm depth, but it did not affect the total conversion compared to the STD 40-second cure mode. There was no difference in DC at the top surface and 1-mm depth with mode of cure. The MED cure mode resulted in a higher DC than the EXP mode at a depth of 2 mm. CLINICAL SIGNIFICANCE: Maximum shrinkage force and force rate exhibited during the first 250 seconds of polymerization were significantly lower using a ramped light intensity exposure. Ramped light intensity decreased conversion rate at the top surface and at 1.0-mm depth and did not affect the total extent of conversion compared to a standard 40-second, single-intensity cure mode. The slower conversion rate resulting from ramped light intensity helped to reduce the rate and maximum polymerization stress, but would not be expected to compromise the physical properties for the restorative material, since similar degrees of conversion were obtained.

Analysis of Variance↗

PubMed2000

Polymerization depths of contemporary light-curing units using microhardness.

PURPOSE: This research investigated composite depths of cure using a variety of light-curing units and exposure protocols. MATERIALS AND METHODS: Composite (Herculite XRV, shade A2, Kerr, Orange, California) was exposed in opaque compules to conventional quartz tungsten halogen (QTH) units, soft-start units, high-intensity QTH and plasma arc (PAC) curing lights, and one argon laser. Cured compules were sonicated to remove uncured composite and were sectioned and polished along the long axis to expose cured composite. Knoop hardness was measured 0.5 mm from the irradiated, top surface and then at 1.0 mm and in 1.0-mm increments until reliable readings could no longer be obtained. Hardness values were compared by analysis of variance at similar depths within a specific curing-light classification, using the hardness of the standard 40-second conventional QTH exposure as comparison (Dunnett's t-test). Depth of cure was defined as the deepest hardness value found equivalent to that at 0.5-mm depth for a specific curing light and scenario. RESULTS: Conventional QTH lights provided similar hardness profiles. At 2-mm depth, use of a different unit or curing tip made no difference in hardness compared with the standard. At this depth, soft-start (pulse-delay and step-cure) methods yielded hardness similar to that of the standard. High-intensity QTH lights provided similar hardness at 2-mm depth in 10 seconds to that of the standard 40-second exposure. Plasma arc exposure for less than 10 seconds produced inferior hardness compared with the standard. A 10-second PAC and a 5-second laser exposure gave hardness at 2-mm depth equivalent to that of the 40-second standard. Depth of cure for almost all curing scenarios was not greater than 2 mm. CLINICAL SIGNIFICANCE: Similar-type conventional QTH lights with different tip diameter (8 and 12 mm) provide similar composite cure characteristics. Soft-start techniques provide similar cure profiles to those achieved with conventional QTH technique when used according to manufacturer's recommendations. High-intensity QTH units and the argon laser can reduce exposure time while providing composite with similar hardness to that of conventional QTH curing. Plasma arc exposure should be at least of 10 seconds duration to provide hardness equivalent to that achieved with conventional 40-second QTH exposure. Even with consideration of high-intensity curing units, composite increments should still be no greater than 2 mm to provide homogeneous hardness.

Analysis of Variance↗

PubMed2000

H+-induced tension development in demineralized dentin matrix.

Recent atomic force microscopy studies have shown that acid-etching dentin causes the surface to recede. The purpose of this work was to test the hypothesis that acidic solutions can cause contraction of demineralized dentin matrix. Small beams of dentin were cut from extracted human third molars. The central region of each specimen was completely demineralized in EDTA. Specimens held in a tester were immersed in acidic solutions, and the amount of tension was recorded. Test variables included gauge length, cross-sectional area, pre-strain, and pH. The results showed that immersion of demineralized dentin in acidic solutions caused tension that was directly related both to H+ concentration at pH < 2 and to pre-strain. The contractile stress development (ca. 0.2-0.4 MPa) was sufficient to cause a collapse of demineralized dentin matrix. The mechanism for this effect probably involves H+-induced conformation changes in the collagen matrix.

Acid Etching, Dental↗

PubMed1999

Identification and characterization of estrogen-like components in commercial resin-based dental restorative materials.

Recently, resin-based dental restorative materials have been targeted as potential sources of xenoestrogens, specifically bisphenol A (BPA) and bisphenol A dimethacrylate (BAD), which could contribute to overall estrogen load and result in deleterious side effects. The present study used high-pressure liquid chromatography (HPLC) to analyze twenty-eight different commercially available dental resins for the presence of BPA and/or BAD. In addition, sublines of the MCF-7 human breast tumor cell line were cultured in the presence of eluates from eleven of the dental resins and assessed for proliferative responses using the sulforhodamine B assay. Only one resin, Delton II, had detectable levels of BPA or BAD that could be verified by Fourier transform infrared spectrometry. Likewise, eluates from Delton II were the only samples that elicited a significant proliferative response in two of the MCF-7 sublines tested. Therefore, we conclude that dental resins in general do not represent a significant source of BPA or BAD exposure.

Benzhydryl Compounds↗