Remineralization of Natural Human Carious Dentin Lesions with an Experimental Whisker-Reinforced Atraumatic Restorative Treatment Composite.

PURPOSE: To evaluate the remineralization of natural human dentin caries with an experimental whisker-reinforced Atraumatic Restorative Treatment (ART) composite. MATERIALS AND METHODS: Teeth with moderate active dentin caries were prepared with caries-disclosing dye and hand instruments, restored with ART or resin-modified glass ionomer cement (RM-GIC), and then wet sliced into 120-µm sections with 15 sections in each group. After taking transverse microradiographs and implementing digital image analysis to determine the "mineral-loss-before," each section was incubated in artificial saliva solution (pH = 7.0) for 4 weeks and 8 weeks with 1 hour each workday in demineralization solution (pH = 4.3). Transverse microradiographs of each section were retaken, and the "mineral-loss-after" was determined. The remineralization was calculated from [1-("mineral-loss-after"/"mineral-loss-before")] × 100%. Results were statistically analyzed with a repeated-measures ANOVA with one within-subject factor (time: 4 and 8 weeks) and one between-subject factor (material: ART and RM-GIC) (α = 0.05). RESULTS: The statistical analysis indicated that ART composite resulted in significantly higher remineralization than the RM-GIC (p ≤ 0.05). For the remineralization of each material, there was a statistical difference between 4 weeks and 8 weeks (p ≤ 0.05). CONCLUSIONS: This experimental ART composite remineralized natural human dentin caries better than the RM-GIC.

Remineralization of human natural caries and artificial caries-like lesions with an experimental whisker-reinforced ART composite.

This paper compares the remineralization of human natural caries and artificial caries-like dentin lesions treated with a novel whisker-reinforced experimental composite resin (ART composite) with a resin-modified glass ionomer cement (RM-GIC) as control. Ten molars with moderate natural dentin caries were prepared (N). Artificial caries-like dentin lesions were prepared in occlusal dentin of 10 caries-free molars and demineralized at pH 4.3 for 48 h (A). The cavities were restored with ART composite or RM-GIC. All restored teeth were sliced into 120 µm sections. Transverse microradiography combined with digital image analysis was performed to analyze the change in mineral density at the same position in the specimens before and after 4 and 8 weeks remineralization/demineralization treatment. The mean percent remineralization ± standard deviation after 4 and 8 weeks are: N with ART composite, 27 ± 9 and 46 ± 14, respectively; N with RM-GIC, 18 ± 6 and 36 ± 11, respectively; A with ART composite, 48 ± 9 and 66 ± 11, respectively; A with RM-GIC, 50 ± 13 and 62 ± 11, respectively. There was a significant difference between the ART composite and RM-GIC for the remineralization of natural caries (P<0.05). For both restoratives there were significant differences between the remineralization of natural and artificial caries (P<0.001). The ART composite and RM-GIC remineralized natural and artificial caries differently, most likely due to differences in the microstructure and composition of the caries dentin.

A chemical phosphorylation-inspired design for Type I collagen biomimetic remineralization.

OBJECTIVES: Type I collagen alone cannot initiate tissue mineralization. Sodium trimetaphosphate (STMP) is frequently employed as a chemical phosphorylating reagent in the food industry. This study examined the feasibility of using STMP as a functional analog of matrix phosphoproteins for biomimetic remineralization of resin-bonded dentin. METHODS: Equilibrium adsorption and desorption studies of STMP were performed using demineralized dentin powder (DDP). Interaction between STMP and DDP was examined using Fourier transform-infrared spectroscopy. Based on those results, a bio-inspired mineralization scheme was developed for chemical phosphorylation of acid-etched dentin with STMP, followed by infiltration of the STMP-treated collagen matrix with two etch-and-rinse adhesives. Resin-dentin interfaces were remineralized in a Portland cement-simulated body fluid system, with or without the use of polyacrylic acid (PAA) as a dual biomimetic analog. Remineralized resin-dentin interfaces were examined unstained using transmission electron microscopy. RESULTS: Analysis of saturation binding curves revealed the presence of irreversible phosphate group binding sites on the surface of the DDP. FT-IR provided additional evidence of chemical interaction between STMP and DDP, with increased in the peak intensities of the PO and P-O-C stretching modes. Those peaks returned to their original intensities after alkaline phosphatase treatment. Evidence of intrafibrillar apatite formation could be seen in incompletely resin-infiltrated, STMP-phosphorylated collagen matrices only when PAA was present in the SBF. SIGNIFICANCE: These results reinforce the importance of PAA for sequestration of amorphous calcium phosphate nanoprecursors in the biomimetic remineralization scheme. They also highlight the role of STMP as a templating analog of dentin matrix phosphoproteins for inducing intrafibrillar remineralization of apatite nanocrystals within the collagen matrix of incompletely resin-infiltrated dentin.

Preclinical effectiveness of a novel pulp capping material.

INTRODUCTION: The purpose of this study was to evaluate the direct pulp capping response to a novel resin-based calcium phosphate cement (RCPC). METHODS: The RCPC was placed in contact with the exposed healthy pulps of dog teeth and in a follow-up study on the healthy or inflamed pulps of ferret teeth. The inflamed ferret teeth had reversible pulpitis induced with Salmonella typhimurium lipopolysaccharides. After direct pulp capping with RCPC or visible light-curing resin-modified calcium hydroxide material (VLCCH) as a control, the restorations were bonded using a composite resin. The pulp responses and dentin repair were evaluated histologically in dog teeth after 7, 28, or 90 days and in ferret teeth after 45 days. RESULTS: Most of the RCPC-treated healthy pulps and 75% of the RCPC-treated inflamed ferret teeth had dentin healing and repair, whereas those teeth treated with VLCCH had minimal healing and dentin repair. CONCLUSIONS: The direct pulp capping of ferret and dog teeth with RCPC was associated with superior healing in comparison to VLCCH.

Effects of adhesive, base and diluent monomers on water sorption and conversion of experimental resins.

OBJECTIVES: To establish the relationship of resin composition and resin hydrophilicity (indicated by solubility parameters and logP) to water sorption (WS), solubility, and degree of double bond conversion (DC) of resin mixtures designed for adhesive restoratives by varying the concentration of pyromellitic glycerol dimethacrylate (PMGDM) and various co-monomers. METHODS: Sixteen resin mixtures were prepared with (30-70) mass fraction % PMGDM. At given PMGDM concentrations there were up to five compositions with increasing logP. Polymer disks (13 mm x 0.7 mm) were exposed to 96% relative humidity (RH) to determine water sorption in humid atmosphere (WSH) and subsequently immersed in water for immersion water sorption (WSI) and solubility. DC was assessed by near infrared spectroscopy. RESULTS: WSI was somewhat higher than WSH, which ranged from (2.1 to 5.3) mass fraction %. Both data were positively correlated to PMGDM concentrations [Pearson correlation, p<0.02; R(2)=0.74, 0.73 (WSI)] and solubility (R(2)=0.64), but not to logP. When grouped by structural similarities, i.e., base resins with bisphenol A core (Group B), Group O containing diluent monomers, or Group U containing urethane dimethacrylate, WS within each group was inversely correlated to logP with R(2)=0.98, 0.81, 0.95, and WS/solubility correlation improved with R(2)=0.88, 0.92 and 0.75, respectively. Solubility ranging from 0.3% to 2.3% was inversely related to DC (r=-0.872). Conversion ranging from 41% to 81% was lower for resins with high base monomer concentrations and highest in mixtures with UDMA. SIGNIFICANCE: LogP was a good predictor of WS after grouping the resins according to functional, compositional and structural similarities. WS and conversion were reasonably well predicted from Hoy's solubility parameters and other physical resin properties.

Effect of a bonding agent on in vitro biochemical activities of remineralizing resin-based calcium phosphate cements.

OBJECTIVES: To test whether fluoride in a resin-based Ca-PO4 ion releasing cement or coating with an acidic bonding agent for improved adhesion compromised the cement remineralization potential. METHODS: Cements were formulated without fluoride (Cement A) or with fluoride (Cement B). The treatment groups were A=Cement A; A2=Cement A+bonding agent; B=Cement B; B2=Cement B+bonding agent. The calcium, phosphate, and fluoride ion release in saliva-like solution (SLS) was determined from hardened cement disks without or with a coating of bonding agent. For the remineralization, two cavities were prepared in dentin of extracted human molars and demineralized. One cavity received composite resin (control); the other received treatment A, A2, B or B2. After 6 week incubation in SLS, 180 microm cross-sections were cut. The percentage remineralization was determined by transverse microradiography comparing the dentin mineral density under the cement to that under the control. RESULTS: The percentage of remineralization (mean+/-S.D.) was A (39+/-14)=B (37+/-18), A2 (23+/-13), B2 (14+/-7). Two-way analysis of variance (ANOVA) and Holm-Sidak test showed a significant effect from the presence of bonding agent (p<0.05), but not from fluoride (p>0.05). The ion solution concentrations of all groups showed undersaturation with respect to dicalcium phosphate dihydrate and calcium fluoride and supersaturation for fluorapatite and hydroxyapatite suggesting a positive remineralization potential. SIGNIFICANCE: Compared to the control all treatments resulted in mineral increase. The remineralization was negatively affected by the presence of the bonding agent.

Degree of cure and fracture properties of experimental acid-resin modified composites under wet and dry conditions.

OBJECTIVE: Evaluate the effects of core structure and storage conditions on the mechanical properties of acid-resin modified composites and a control material by three point bending and conversion measurements 15min and 24h after curing. METHODS: The monomers pyromellitic dimethacrylate (PMDM), biphenyldicarboxylic-acid dimethacrylate (BPDM), (isopropylidene-diphenoxy)bis(phthalic-acid) dimethacrylate (IPDM), oxydiphthalic-acid dimethacrylate (ODPDM), and Bis-GMA were mixed with triethyleneglycol dimethacrylate (TEGDMA) in a 40/60 molar ratio, and photo-activated. Composite bars (Barium-oxide-glass/resin=3/1 mass ratio, (2mmx2mmx25mm), n=5) were light-cured for 1min per side. Flexural strength (FS), elastic modulus (E), and work-of-fracture (WoF) were determined in three-point bending after 15min (stored dry); and after 24h under dry and wet storage conditions at 37 degrees C. Corresponding degrees of conversion (DC) were evaluated by Fourier transform infrared spectroscopy. Data was statistically analyzed (2-way analysis of variance, ANOVA, Holm-Sidak, p<0.05). RESULTS: Post-curing significantly increased FS, E and DC in nearly all cases. WoF did not change, or even decreased with time. For all properties ANOVA found significant differences and interactions of time and material. Wet storage reduced the moduli and the other properties measured with the exception of FS and WoF of ODPDM; DC only decreased in BPDM and IPDM composites. SIGNIFICANCE: Differences in core structure resulted in significantly different physical properties of the composites studied with two phenyl rings connected by one ether linkage as in ODPDM having superior FS, WoF and DC especially after 24h under wet conditions. As expected, post-curing significantly contributed to the final mechanical properties of the composites, while wet storage generally reduced the mechanical properties.

Light-emitting diode curing light irradiance and polymerization of resin-based composite.

BACKGROUND: Light-emitting diode (LED) curing lights are becoming popular; however, questions about their efficiency remain. The authors performed a comprehensive analysis of the properties of resin-based composites cured with LED lights. METHODS: The authors evaluated seven LED lights and one quartz-tungsten-halogen light (control). They measured intensity, depth of cure (DOC), degree of conversion (DC), hardness and temperature rise. They used three shades of a hybrid resin-based composite and a microfill composite, as well as one shade of another hybrid composite. RESULTS: Two LED lights required additional cure time to reach a DOC similar to that of the control light. DC at the top of the samples was independent of the light used. At 2.0 millimeters, the DC for several LED lights was significantly lower than that for the control light and was correlated strongly to the light's intensity. The bottom-to-top ratio for hardness of resin-based composites cured by all but one light was greater than 0.80. All LED lights except one had smaller temperature rise than did the control light. CONCLUSIONS: Six of the seven LED curing lights performed similarly to a quartz-tungsten-halogen curing light in curing resin-based composites. Clinical Implications. While LED curing lights and a quartz-tungsten-halogen light could cure resin-based composites, some resin-based composites cured with LED lights may require additional curing time or smaller increments of thickness.

In vitro cytotoxicity of a remineralizing resin-based calcium phosphate cement.

UNLABELLED: Recently, a resin-based calcium phosphate cement (RCPC) has been reported as a remineralizing pulp-capping or lining cement. RCPC consists mainly of tetracalcium and dicalcium phosphates, ethoxylated bisphenol A dimethacrylate and pyromellitic glycerol dimethacrylate monomers and photo- and chemical initiators. OBJECTIVES: Here, the cytotoxic effects of RCPC were evaluated. The hypothesis was that RCPC induced only minor cytotoxic response in immortalized murine odontoblast and pulp cells, comparable to that produced by similar dimethacrylates due to unpolymerized dimethacrylate monomer present after curing. METHODS: Cytotoxicity was determined following the changes in cell succinate dehydrogenase activity after 24 h exposure to the cement components and after a 24 h recovery period. A fourfold range of concentrations was tested of the monomers, the eluate of cured RCPC leached in Dulbecco's modified Eagle's medium, and crushed cured cement in dimethyl sulfoxide. RESULTS: The monomers themselves had cytotoxicities similar to those reported for other dimethacrylates, although they are significantly less toxic than Bis-GMA. Differential cell sensitivity was demonstrated, with the pulp cells having greater sensitivity to the unpolymerized monomer than the odontoblast-like cells. The leached components have cytotoxicity similar to that of the free monomers. The crushed material demonstrated no apparent cytotoxicity at the dilutions tested. SIGNIFICANCE: These data demonstrate that RCPC has an in vitro cytotoxicity that is comparable to other materials containing dimethacrylate monomers and suggest that the material may be suitable for use in dental restorations. The data also indicate that the pulp cells appear more sensitive to dimethacrylates than the odontoblasts.

Network structure of Bis-GMA- and UDMA-based resin systems.

OBJECTIVES: The commonly used dental base monomers 2,2-bis[p-(2'-hydroxy-3'-methacryloxypropoxy)phenylene]propane (Bis-GMA) and 1,6-bis(methacryloxy-2-ethoxycarbonylamino)-2,4,4-trimethylhexane (UDMA) require the use of a diluent monomer, such as triethylene glycol dimethacrylate (TEGDMA). The aim of this study was to measure double bond conversion of UDMA/TEGDMA and Bis-GMA/TEGDMA polymeric systems, determine the leachable portion, and analyze network formation by evaluating crosslinking and pendant double bonds. METHODS: UDMA or Bis-GMA was combined with TEGDMA in systematic increments and irradiated to form light cured polymers. Fourier transform infrared spectroscopy in the near-infrared region was used to measure double bond conversion. The leachable sol fraction was analyzed by 1H NMR. Resin composites were formulated. Flexural strength was measured by three-point bending and volumetric shrinkage was determined with a mercury dilatometer. RESULTS: The amount of base monomer greatly influenced double bond conversion, sol fraction, and crosslinking. Increasing base monomer concentration decreased double bond conversion, increased the leachable fraction, and decreased crosslinking and network formation. At mole fractions higher than 0.125, the UDMA polymers had significantly higher conversion than the Bis-GMA polymers. Bis-GMA polymers had higher leachable amounts of unreacted monomer, while UDMA mixtures had more crosslinking than the Bis-GMA mixtures. In regards to the physical properties of resin composites, increasing the base monomer improved flexural strength and decreased volumetric shrinkage. SIGNIFICANCE: This systematic study for the evaluation of conversion, leachability, crosslinking, and network structure along with physical properties, like volumetric shrinkage and flexural strength, are required for the optimization of competing desirable properties for the development of durable materials.

Evaluation of dental restorative composites containing polyhedral oligomeric silsesquioxane methacrylate.

OBJECTIVES: The aim of this study was to explore novel polymeric dental restorative composites, in which polyhedral oligomeric silsesquioxane methacrylate monomer (POSS-MA) was used to partially (or completely) replace the commonly used base monomer 2,2'-bis-[4-(methacryloxypropoxy)-phenyl]-propane (Bis-GMA). METHODS: The composites were cured (hardened) by photo-initiated free radical polymerization. Mechanical properties (i.e. flexural strength, Young's modulus and diametral tensile strength) of the composites were tested by a universal mechanical testing machine; photopolymerization induced volumetric shrinkage was measured using a mercury dilatometer; and near infrared (NIR) technique was used to study the degree of methacrylate double bond conversion and photopolymerization rate. RESULTS: Small percentage POSS-MA substitution of Bis-GMA (i.e. mass fraction of 10% or less) in the resin system improved the mechanical properties of the composites; while large amount substitution led to less desirable mechanical properties, lower methacrylate double bond conversion, and slower photopolymerization rate. Statistical examinations showed the maximum flexural strength of the composites occurred when 10% (mass fraction) of Bis-GMA was replaced by POSS-MA, while the highest modulus occurred when the mass fraction of POSS-MA was 2%. SIGNIFICANCE: Polymeric dental restorative composites with improved mechanical properties may be designed by judicious choice of monomer (POSS-MA, Bis-GMA and TEGDMA) compositions.

Interpretation of bond failure through conversion and residual solvent measurements and Weibull analyses of flexural and microtensile bond strengths of bonding agents.

OBJECTIVES: An inverse correlation between initial acetone content of bonding agents and microtensile bond strength (MTBS) has previously been reported. Here it was investigated whether the inferior MTBS of acetone-rich bonding agents was caused by flaws and low adhesive layer strength, insufficient to resist polymerization shrinkage stresses of the overlying composite. METHODS: Bonding solutions with (27-67) mass fraction% acetone were dried for 10 s or 30 min. Specimens for infrared (IR) spectroscopy and flexural strength (FS) were cured for 10 s (cure mode 1) to represent the adhesive layer properties when polymerizing the composite resin or for 10 s plus an additional 60 s through composite resin (cure mode 2) to represent adhesive layer properties when testing the bond strength. Degree of conversion (DC) and residual acetone content were evaluated for films by mid-IR and bulk specimens by near-IR spectroscopy. FS and MTBS data using these bonding solutions were interpreted by Weibull statistics and ANOVA (alpha = 0.05). RESULTS: In bulk specimens, initial and residual acetone content were positively correlated (P = 0.003). FS in cure mode 1 was significantly lower than in cure mode 2 and decreased with increasing initial acetone content, while DC remained consistent, suggesting pores from acetone evaporation as flaw initiating sites affecting the mechanical adhesive properties. SIGNIFICANCE: From DC and Weibull analyses of MTBS and FS, early low strength of the adhesive layer and shrinkage stresses acting on pre-existing flaws are suggested as critical factors affecting the dentin/adhesive bond strength.

Properties of eight methacrylated beta-cyclodextrin composite formulations.

OBJECTIVES: Methacrylated beta-cyclodextrins (MCDs) are novel candidate dental monomers if all or some of the hydroxyl groups of beta-cyclodextrin are substituted with methacrylate groups. The main objective of this study was to evaluate mechanical properties of a number of composite formulations having MCDs as novel dental comonomers. The properties determined were flexural strength (FS), volumetric shrinkage (VS), and degree of conversion (DC). METHODS: A mass fraction of 50% of MCD monomers was mixed with a mass fraction of 50% each of a series of dimethacrylate or monomethacrylate diluent comonomers to produce consistent formulations of a workable viscosity. For comparison a resin mixture of a mass fraction of 50% Bis-GMA and a mass fraction of 50% triethyleneglycol dimethacrylate (a typical dental resin mixture) was also studied. The mixtures were activated with camphorquinone and ethyl 4-dimethylamino benzoate. One part by mass of each activated resin formulation was mixed with three parts by mass of glass filler. Samples for the FS tests were prepared in (2 x 2 x 25) mm3 molds by light-curing the composites for 2 min on each side. The cured samples were immersed in 37 degrees C water for 24 h, and FS was measured with an Instron machine at a crosshead speed of 0.5 mm/min. VS was measured by a computer-controlled mercury dilatometer. DC was measured by near-infrared spectroscopy. RESULTS: The properties of the MCD-based composites depended on the kind of diluent used. With these MCD monomers, diluents of triethyleneglycol dimethacrylate, 1,10-decamethylenediol dimethacrylate, or benzyl methacrylate yielded the best composite properties. SIGNIFICANCE: Although not yet fully optimized, MCD-based composite formulations containing triethyleneglycol dimethacrylate, 1,10-decamethylenediol dimethacrylate, or benzyl methacrylate yielded flexural strength and volumetric shrinkage values were comparable to those of the Bis-GMA/triethyleneglycol dimethacrylate controls. These findings lend support for further development and evaluations of polymerizable cyclodextrin derivatives for use in dental materials.

Shear bond strength of experimental methacrylated beta-cyclodextrin-based formulations.

Previous studies have shown that methacrylated beta-cyclodextrins (MCDs) can be used as comonomers in resin-based dental composites. These MCDs by virtue of having several polymerizable methacrylate groups and hydrophilic hydroxyl groups, may also promote bonding of dental composites to dentin. This study evaluated MCDs as adhesive comonomers, and optimized comonomer and polymerization initiator concentrations for maximum shear bond strength (SBS). Experimental MCD-based bonding formulations in acetone were prepared by mixing 33 mass fraction % MCDs with (10, 20, 30, 40, or 50) mass fraction % of 2-hydroxyethyl methacrylate (HEMA). The MCD/HEMA-based solutions were activated with varied amounts of camphorquinone (CQ) and ethyl 4-dimethylamino benzoate (4E). Samples for SBS were prepared by bonding a composite resin to acid-etched dentin surfaces of extracted human molars with the experimental bonding solutions. The specimens were immersed in 37 degrees C water for 24 h and bond strengths were determined in shear mode. With increasing HEMA concentration, the SBS values of MCD-bonding solutions increased to 16 MPa at a composition of 33% MCD, 30% HEMA, and 37% acetone by mass. Also, SBS values of MCD-bonding solutions varied as a function of the CQ and 4E concentrations and passed through a maximum SBS at 21 MPa, which was comparable to that of a commercial control. This preliminary study indicated that nonacidic MCD monomers could be used as an adhesion-promoting comonomer. Additional modification of MCDs having both polymerizable groups and anionic ligand groups, e.g., polymerizable acidic cyclodextrin derivatives should increase the SBS even further.

Chemistry of Silanes: Interfaces in Dental Polymers and Composites.

The performance and service life of glass-or ceramic-filled polymeric composites depend on the nature of their resin, filler and interfacial phases as well as the efficacy of the polymerization process. The synergy that exists between the organic polymer matrix and the usually inorganic reinforcing filler phase is principally mediated by the interfacial/interphasial phase. This latter phase develops as a result of the dual reactivity of a silane coupling agent, (YRSiX3), a bifunctional molecule capable of reacting with the silanol groups of glass or ceramic fillers via its silane functional group (-SiX3) to form Si-O-Si- bonds to filler surfaces, and also with the resin phase by graft copolymerization via its Y functional group, usually a methacrylic vinyl group. In this paper, we explore some of the chemistry of organosilanes, especially that of functional organosilanes (or silane coupling agents as they are commonly known) that are used to mediate interfacial bonding in mineral reinforced polymeric composites. The chemistry of organosilanes can be quite complex involving hydrolytically initiated self-condensation reactions in solvents (including monomers) that can culminate in polymeric silsesquioxane structures, exchange reactions with hydroxylated or carboxylated monomers to form silyl ethers and esters, as well as the formation of silane derived interfaces by adhesive coupling with siliceous mineral surfaces.

Dentin adhesion and microleakage of a resin-based calcium phosphate pulp capping and basing cement.

An experimental resin-based bioactive calcium phosphate cement, intended as a pulp capping and basing material, was evaluated for dentin shear bond strength and microleakage. The interfacial morphology was examined by scanning electron microscopy (SEM). For microleakage, dentin cavities without (Group A) or after (Group B) acid etching were restored with the calcium phosphate cement. A resin-based calcium hydroxide (VLC Dycal; Group C) was used as control material according to the manufacturer's instructions. After water storage and thermocycling, the microleakage was scored using a AgNO(3) staining procedure. For the shear bond strength, flat exposed dentin surfaces were treated as for the microleakage test. Metal irises pressed against the dentin surface were filled with the cements, which were photocured. Both tests were carried out after 1 wk. While acid etching did not result in significantly greater microleakage, it led to higher shear bond strength, and allowed, as shown by SEM, the formation of a hybrid layer and resin tags. Both groups treated with the calcium phosphate cement had significantly lower microleakage scores and higher mean shear bond strength values than the groups treated with the control material.

Probing the origins and control of shrinkage stress in dental resin composites. II. Novel method of simultaneous measurement of polymerization shrinkage stress and conversion.

This study probes the interrelationships between polymerization shrinkage stress development and the polymerization progress with a novel experimental technique. This technique is capable of real time, simultaneous measurement of double-bond conversion and shrinkage stress with the use of a noninvasive near-infrared fiber-optic system, along with a cantilever beam-based tensometer. The results from both filled and unfilled bis-GMA/TEGDMA (70:30 mass ratio) systems showed that the shrinkage stress buildup was concentrated in the latter stages of polymerization, with its dramatic increase linked to the asymptotic approach of conversion to its limiting value. The monotonic increase of shrinkage stress with conversion in the vitrified state is attributed to the dramatic increase of the sample's elastic modulus during the vitrification stage and a certain amount of cooling stress as the sample cools down from the temperature rise caused by the exothermic polymerization and light absorption. Excellent reproducibility of both the polymerization kinetics assessment and the shrinkage stress measurement has been achieved.

Effects of polymerization initiator complexation in methacrylated beta-cyclodextrin formulations.

OBJECTIVES: Methacrylated beta-cyclodextrin (MCD) is a candidate dental monomer that can complex molecules within its hydrophobic cavity. This study determined the effects of complexation of polymerization initiators such as camphorquinone (CQ) and ethyl-4-dimethylaminobenzoate (4E) with MCD on the flexural strength (FS) and degree of conversion (DC) of resulting dental composite formulations. METHODS: Complexation of CQ and 4E with MCD was studied by thin layer chromatography. A mass fraction of 44% 2-hydroxyethylmethacrylate or triethyleneglycoldimethacrylate was mixed separately with a mass fraction of 56% MCD to produce a workable formulation. The mixture was activated with varied amounts of CQ and 4E. One part by mass of the activated resin formulation was mixed with three parts by mass of glass filler. Specimens for FS were prepared by filling molds with composites and curing for 2 min. The cured specimens were immersed in 37 degrees C water for 24 h and FS was measured with an Instron machine at a crosshead speed of 0.5 mm/min. DC in MCD-based resin formulations was measured with a differential photocalorimeter under nitrogen. RESULTS: MCD appears to form inclusion complexes with CQ and 4E. As a result, FS and DC of MCD-based composites vary significantly as a function of the concentration of polymerization initiators used in the formulations. SIGNIFICANCE: Complexation of polymerization initiators with MCD can influence the FS and DC in MCD-based dental formulations and should be taken into consideration when evaluating MCD as a dental monomer.

Effects of the acetone content of single solution dentin bonding agents on the adhesive layer thickness and the microtensile bond strength.

OBJECTIVES: This study investigated the hypothesis that varying the acetone content of single solution dentin bonding agents may affect the adhesive layer thickness and microtensile bond strength (MTBS) of the bonded complex, and explored whether the adhesive layer thickness is a valid predictor for MTBS. METHODS: Experimental dentin bonding agents containing (27, 37, 47, 57, or 67) mass fraction% acetone were used to bond composite resin onto occlusal dentin surfaces of extracted human molars. The adhesive layer thickness was determined by digitized image analysis. MTBS was measured after 48 h. The fracture surfaces were observed using SEM. RESULTS: With increasing acetone content, MTBS varied from 38 MPa (67% acetone) to the highest MTBS of 64 MPa (37% acetone), while the adhesive layer thickness decreased linearly. Both dependent variables demonstrated moderate inverse correlation with the acetone content (p<0.0001), but were not correlated with each other (p>0.05). Ninety-four percent of the specimens showed fractures within the adhesive layer extending toward the interfaces with the hybrid layer or the composite resin. In the groups containing 57 and 67% acetone, cracks were observed at these interfaces. SIGNIFICANCE: Rather than the adhesive layer thickness, interfacial cracks in specimens with acetone-rich bonding agents may have caused lower MTBS. Within the scope of this investigation, lower acetone concentrations, as could be anticipated from solvent evaporation during clinical use of the bonding agent, did not seem to lower MTBS, but rather improved the integrity of the dentin/adhesive bond.

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

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