Relation of dental composite formulations to their degradation and the release of hydrolyzed polymeric-resin-derived products

Relationship between the degree of conversion, solubility and salivary sorption of a hybrid and a nanofilled resin composite

This study analyzed the relationship between the degree of conversion (DC), solubility, and salivary sorption of a hybrid (Filtek P 60) and a nanofilled resin composite (Filtek Supreme), and evaluated the influence of the light-activation mode on these properties. Two light-activation modes were used: Conventional (C; 850 mW/cm² for 20 s) and Soft-start (SS; 100-1,000 mW/cm² for 10 s + 1,000 mW/cm² for 10 s). The DC (%) was evaluated by FT-Raman spectroscopy. The solubility and salivary sorption were measured after immersion in artificial saliva for 7 days. Data were analyzed by ANOVA and Student-Newman-Keuls' test and linear regression analysis (α = 0.05). The DC varied from 50.52% (nanofilled composite) to 57.15% (hybrid composite), and was influenced by the light-activation mode: C > SS. The solubility (0.45 μg/mm³) and salivary sorption (8.04 μg/mm³) of the nanofilled composite were greater than those of the hybrid composite (0.40 μg/mm³/ 6.87 μg/mm³), and were influenced by the light-activation mode: SS > C. Correlation was found between DC and solubility (r = - 0.89, p<0.05), as well as between solubility and salivary sorption (r = 0.95). These findings suggest that nanofilled composites may present higher degradation in the oral environment than hybrid ones. Soft-start light-activation mode may increase the solubility of resin composites.

Cytotoxicity and genotoxicity of glycidyl methacrylate

Methacrylates are used in the polymer form as composite restorative materials in dentistry. However, the polymers can release monomers and co-monomers into the oral cavity and pulp, from where they can migrate into the bloodstream reaching virtually all organs. The local concentration of the released monomers can be in the millimolar range, high enough to induce adverse biological effects. Genotoxicity of methacrylate monomers is of a special significance due to potential serious phenotypic consequences, including cancer, and long latency period. In the present work, we investigated cytotoxicity and genotoxicity of glycidyl methacrylate (GMA) in the human peripheral blood lymphocytes and the CCR-CM human cancer cells. GMA at concentrations up to 5mM evoked a concentration-dependent decrease in the viability of the lymphocytes up to about 80%, as assessed by flow cytometry. This agent did not induce strand breaks in the isolated plasmid DNA, but evoked concentration-dependent DNA damage in the human lymphocytes evaluated by the alkaline and neutral comet assay. This damage included oxidative modifications to the DNA bases, as checked by DNA repair enzymes Endo III and Fpg as well as single and double DNA strand breaks. The lymphocytes exposed to GMA at 2.5 microM were able to remove about 90% of damage to their DNA in 120 min. The ability of GMA to induce DNA double-strand breaks was confirmed by pulsed field gel electrophoresis. The drug evoked apoptosis and induced an increase in the G2/M cell population, accompanied by a decrease in the S cell population and an increase in G0/G1 cell population. Due to broad spectrum of GMA genotoxicity, including DNA double-strand breaks, and a potential long-lasting exposure to this compound, its use should be accompanied by precautions, reducing the chance of its release into blood stream and the possibility to induce adverse biological effects.

Two-year Water Degradation of Self-etching Adhesives Bonded to Bur Ground Enamel

All the adhesives tested showed no difference in bond strength after 24-hours of water storage. After two years of water storage, the bonds produced by some self-etch adhesives were significantly reduced.

In vitro bonding performance of self-etch adhesives: II--ultramorphological evaluation

OBJECTIVE

To study the interfacial ultra-morphology formed by "all-in-one" self-etch adhesives.

METHODS

Forty-nine extracted molars were assigned to one of five all-in-one adhesives: Adper Prompt L-Pop (AP, 3M ESPE); Clearfil S3 Bond (S3, Kuraray); G-Bond (GB, GC America); iBond (iB, Heraeus Kulzer) and Xeno IV (XE, Dentsply Caulk). Adper Single Bond Plus (SB, 3M ESPE), a two-step etch&rinse adhesive, and Clearfil SE Bond (SE, Kuraray), a two-step self-etch adhesive, were used as controls. Dentin, unground enamel and ground enamel were used as bonding substrates. Dentin specimens were processed for FESEM and TEM analyses. Enamel specimens were processed for FESEM.

RESULTS

Dentin: GB, iB, S3, SE and XE resulted in a submicron-thick hybrid layer (0.2-0.7 microm), but only S3 and SE did not result in interfacial gaps. AP resulted in the thickest hybrid layer (1.7-2.9 microm) among the self-etch adhesives. SB resulted in a 3.4-5.2 pm thick hybrid layer. Unground enamel-GB, iB and SE resulted in a mostly featureless morphology resembling that of untreated enamel with areas in which the superficial enamel layer was removed without dissolving the subsurface enamel. XE resulted in areas of intra-prismatic etching and areas without any etching pattern. S3 resulted in frequent shallow intra-prismatic etching, while AP was able to unveil the enamel crystallites across the entire enamel surface. Phosphoric acid in SB resulted in the deepest intra- and inter-prismatic demineralization. Ground enamel--AP resulted in a well-defined inter-prismatic etching pattern. iB, GB, SE and S3 resulted in islands of superficially dissolved enamel within areas without evidence of enamel dissolution. XE resulted in etched enamel areas with mild intraprismatic exposure of crystallites. Phosphoric acid in SB resulted in deep enamel etching.

CONCLUSIONS

Only AP, an aggressive self-etch adhesive, showed enamel morphological features that resemble those created by etch & rinse adhesives. S3 and SE were the only self-etch adhesives that did not result in dentin interfacial debonding.

Analysis of the degradation of a model dental composite

Dental composites undergo material property changes during exposure to the oral environment and may release compounds of potential toxicity, such as bisphenol A. Degradation of dental composites was studied in a simplified overlayer model in which bisphenol A diglycidyl methacrylate (BisGMA) was covalently bound to a porous silicon oxide surface. It was hypothesized that the chemical structure of this overlayer would allow release of bisphenol A, BisGMA, and the decomposition products thereof, upon exposure to water for an extended period. Liquid chromatography mass spectrometry found leaching of intact BisGMA and several degradation products that contained the bisphenol A moiety from the overlayer into distilled water after 2 wks of aging. The absence of bisphenol A release from the overlayer reduces concerns regarding its potential health risk in dental composites. Nevertheless, health concerns might arise with respect to BisGMA and the leached degradation products, since they all contain the bisphenol A moiety.

ABBREVIATIONS

BisGMA, bisphenol A diglycidyl methacrylate; HPLC, high-performance liquid chromatography; LCMS, liquid chromatography mass spectrometry; MA, methacrylic acid; MPS, 3-(trimethoxysilyl) propyl methacrylate; m/z, mass-to-charge ratio; and TIC, total ion chromatogram.

Four-year water degradation of a total-etch and two self-etching adhesives bonded to dentin

OBJECTIVES

To evaluate effect of direct and indirect water storage on the microtensile dentin bond strength of one total-etch and two self-etching adhesives.

METHODS

The adhesive materials were: one total-etch adhesive; 'Admira Bond' and two self-etch adhesives; 'Clearfil SE Bond' and 'Hybrid Bond'. Freshly extracted human third molar teeth were used. In each tooth, a Class I cavity (4mmx4mm) was prepared in the occlusal surface with the pulpal floor extending approximately 1mm into dentin. The teeth were divided into three groups (n=18). Each group was restored with the resin composite 'Clearfil APX' using one of the tested adhesives. For each experimental group 3 test procedures (n=6) were carried out: Procedure A: the teeth were stored in water for 24h (control), then sectioned longitudinally, buccolingually and mesiodistally to get rectangular slabs of 1.0-1.2mm thickness on which a microtensile test was carried out. Procedure B: the teeth were also sectioned; however, the slabs were stored in water at 37 degrees C for 4 years before microtensile testing (direct water storage). Procedure C: the teeth were kept in water at 37 degrees C 4 years before sectioning and microtensile testing (Indirect water storage). During microtensile testing the slabs were placed in a universal testing machine and load was applied at cross-head speed of 0.5mm/min.

RESULTS

For the 24h control, there was no significant difference in bond strength between the three tested adhesives. After 4 years of indirect water storage, the bond strength decreased but the reduction was not significantly different from those of 24h. After 4 years of direct water storage, the bond strengths of all tested adhesives were significantly reduced compared to their 24h results.

CONCLUSION

All the tested adhesives showed no reduction in bond strength after indirect water exposure for 4 years. After 4-year direct water exposure, the bond produced by all tested adhesives was unable to resist deterioration.

Durability of enamel bonding using two-step self-etch systems on ground and unground enamel

This study examined the early and long-term microtensile bond strengths (MTBS) and interfacial enamel gap formation (IGW) of two-step self-etch systems to unground and ground enamel. Resin composite (Filtek Z250) buildups were bonded to proximal enamel surfaces (unground, bur-cut or SiC-treated enamel) of third molars after the application of four self-etch adhesives: a mild (Clearfil SE Bond [SE]), two moderate (Optibond Solo Plus Self-Etch Primer [SO] and AdheSE [AD]) and a strong adhesive (Tyrian Self Priming Etchant + One Step Plus [TY]) and two etch-and-rinse adhesive systems (Single Bond [SB] and Scotchbond Multi-Purpose Plus [SBMP]). Ten tooth halves were assigned for each adhesive. After storage in water (24 hours/37 degrees C), the bonded specimens were sectioned into beams (0.9 mm2) and subjected to microTBS (0.5 mm/minute) or interfacial gap width measurement (stereomicroscope at 400x) either immediately (IM) or after 12 months (12M) of water storage. The data were analyzed by three-way repeated measures ANOVA and Tukey's test (alpha=0.05). No gap formation was observed in any experimental condition. The microTBS in the Si-C paper and diamond bur groups were similar and greater than the unground group only for the moderate self-etch systems (SO and AD). No reductions in bond strength values were observed after 12 months of water storage, regardless of the adhesive evaluated.

Assessment of in vitro methods used to promote adhesive interface degradation: a critical review

One factor that has a great influence on clinical performance of dental restorations is their resistance to degradation. Morphological changes in the structure of tooth-restoration interface aged in the oral environment have been reported. However, even though the in vivo performance is the ultimate testing environment for predicting the behavior of restorations because of the complexity of intraoral conditions, in vitro models such as thermocycling, mechanical loading, pH cycling, and aging of materials in distilled water, NaOCl, and food-simulating solutions may provide important information about the fundamental mechanisms involved in resin-tooth interface degradation. Most recently, the effect of host-derived enzymes and the storage in deproteinizing solutions (such as aqueous NaOCl) on the degradation of resin-dentin bonds has also been described. This review considers the importance of these in vitro methods on bond durability interface in an attempt to understand the behavior of restoratives over time. The first section is focused on the mechanism of in vivo biodegradation, whereas the second looks at studies that have described the influence of water storage, NaOCl storage, host-derived matrix metalloproteinases, thermocycling, mechanical loading, pH cycling, and food-simulating solutions on the degradation of the adhesive interface. It is obvious that these methodologies do not occur separately in the oral cavity, but that each one has a specific importance in the mechanisms of bond degradation.

CLINICAL SIGNIFICANCE

The in vitro methods used to simulate bond degradation may describe important points related to the clinical performance of restorations. This article evaluates the mechanism of the in vivo biodegradation of adhesive interfaces as well as the influences that various testing methods have on these bonds.

Dental adhesion review: Aging and stability of the bonded interface

OBJECTIVE

Most of current dental adhesive systems show favorable immediate results in terms of retention and sealing of bonded interface, thereby counteracting polymerization shrinkage that affects resin-based restorative materials. Despite immediate efficacy, there are major concerns when dentin bonded interfaces are tested after aging even for short time period, i.e. 6 months.

METHODS

This study critically discusses the latest peer-reviewed reports related to formation, aging and stability of resin bonding, focusing on the micro and nano-phenomena related to adhesive interface degradation.

RESULTS

Most simplified one-step adhesives were shown to be the least durable, while three-step etch-and-rinse and two-step self-etch adhesives continue to show the highest performances, as reported in the overwhelming majority of studies. In other words, a simplification of clinical application procedures is done to the detriment of bonding efficacy. Among the different aging phenomena occurring at the dentin bonded interfaces, some are considered pivotal in degrading the hybrid layer, particularly if simplified adhesives are used. Insufficient resin impregnation of dentin, high permeability of the bonded interface, sub-optimal polymerization, phase separation and activation of endogenous collagenolytic enzymes are some of the recently reported factors that reduce the longevity of the bonded interface.

SIGNIFICANCE

In order to overcome these problems, recent studies indicated that (1) resin impregnation techniques should be improved, particularly for two-step etch-and-rinse adhesives; (2) the use of conventional multi-step adhesives is recommended, since they involve the use of a hydrophobic coating of nonsolvated resin; (3) extended curing time should be considered to reduce permeability and allow a better polymerization of the adhesive film; (4) proteases inhibitors as additional primer should be used to increase the stability of the collagens fibrils within the hybrid layer inhibiting the intrinsic collagenolytic activity of human dentin.

A semi-empirical computational model for the inhibition of porcine cholesterol esterase

Cholesterol esterase significantly contributes to cell membrane structure. It also facilitates transfer of cholesterol and phospholipids across membranes. Inhibition of this enzyme by a number of xenobiotics has been reported. This research sought to confirm if a widely used methacrylate monomer, bisphenol A dimethacrylate, inhibits porcine cholesterol esterase since this and other methacrylates are known to leach from various biomaterial preparations. A quantum mechanically developed computational chemistry model is presented. Specific chemical information linking potential mechanisms of cholesterol esterase inhibition to chemical structure is shown. Model chemical descriptors identified the importance of maximum oxygen valency and molecular shape/size to cholesterol esterase inhibition. A porcine cholesterol esterase inhibition mechanism is inherent in bisphenol A dimethacrylate which mimics chemical properties of reported cholesterol esterase inhibitors. This predictive semiempirical quantum mechanical model can be used to design new cholesterol esterase non-inhibitors for biocompatible biomaterials used in an aqueous environment.

Impact of adhesive application to wet and dry dentin on long-term resin-dentin bond strengths

This study compared the effects of moisture and rubbing action on the immediate and one-year microtensile bond strength (BS) of an ethanol/water-based adhesive system (Single Bond [SB]) and an acetone-based system (One Step [OS]) to dentin. A flat superficial dentin surface on 60 human molars was exposed by wet abrasion. Two coats of the adhesives were applied on either a dry (D) or rewetted surface (W) with no (NRA), slight (SRA) or vigorous rubbing action (VRA). After light curing (600 mW/cm2/10 seconds), composite buildups were constructed incrementally and the specimens were stored in water (37 degrees C/24 hours). They were longitudinally sectioned in the "x" and "y" directions to obtain bonded sticks (0.8 mm2) to be tested in tension at 0.5 mm/minute. The sticks from each tooth were then divided, stored in water at 37 degrees C and tested immediately and after 12 months (12 M) at 0.5 mm/minute. The bond strength values of sticks from the same hemitooth were averaged for statistical purposes. The prematurely debonded specimens were included in the hemi-tooth mean. The data from each adhesive was analyzed by three-way ANOVA and Tukey's multiple comparison tests (alpha = 0.05). In the dry groups, high bond strength values were obtained under VRA. When the dentin was kept moist, both SRA and VRA provided high resin-dentin bond strength values. Reductions in bond strength values after one year of water storage were not observed for the SB adhesive or were less pronounced for the OS adhesive when it was vigorously rubbed onto the dentin surface.

Effect of water storage and surface treatments on the tensile bond strength of IPS Empress 2 ceramic

PURPOSE

The aim of this study was to evaluate the effect of water storage (24 hours and 1 year) on the tensile bond strength between the IPS Empress 2 ceramic and Variolink II resin cement under different superficial treatments.

MATERIALS AND METHODS

One hundred and eighty disks with diameters of 5.3 mm at the top and 7.0 mm at the bottom, and a thickness of 2.5 mm were made, embedded in resin, and randomly divided into six groups: Groups 1 and 4 = 10% hydrofluoric acid for 20 seconds; Groups 2 and 5 = sandblasting for 5 seconds with 50 microm aluminum oxide; and Groups 3 and 6 = sandblasting for 5 seconds with 100 microm aluminum oxide. Silane was applied on the treated ceramic surfaces, and the disks were bonded into pairs with adhesive resin cement. The samples of Groups 1 to 3 were stored in distilled water at 37 degrees C for 24 hours, and Groups 4 to 6 were stored for 1 year. The samples were subjected to a tensile strength test in an Instron universal testing machine at a crosshead speed of 1.0 mm/min, until failure. The data were submitted to analysis of variance and Tukey's test (5%).

RESULTS

The means of the tensile bond strength of Groups 1, 2, and 3 (15.54 +/- 4.53, 10.60 +/- 3.32, and 7.87 +/- 2.26 MPa) for 24-hour storage time were significantly higher than those observed for the 1-year storage (Groups 4, 5, and 6: 10.10 +/- 3.17, 6.34 +/- 1.06, and 2.60 +/- 0.41 MPa). The surface treatments with 10% hydrofluoric acid (15.54 +/- 4.53 and 10.10 +/- 3.17 MPa) showed statistically higher tensile bond strengths compared with sandblasting with 50 microm(10.60 +/- 3.32 and 6.34 +/- 1.06 MPa) and 100 microm (7.87 +/- 2.26 and 2.60 +/- 0.41 MPa) aluminum oxide for the storage time 24 hours and 1 year.

CONCLUSIONS

Storage time significantly decreased the tensile bond strength for both ceramic surface treatments. The application of 10% hydrofluoric acid resulted in stronger tensile bond strength values than those achieved with aluminum oxide.

Tensile strength and durability of bovine dentin

This study investigated the effects of thermal cycling on the tensile strength of dentin. Bovine dentin were divided into 10 groups, which were then subjected to various conditions: intact after preparation, thereby serving as a control; heating in boiling water for 45 minutes; 10,000 thermal cycles in water; 10,000 thermal cycles in PBS; storage in water at 5, 23, or 55 degrees C for two weeks; and storage in PBS at 5, 23, or 55 degrees C for two weeks. Subsequently, bovine dentin were trimmed into dumbbell-shaped specimens and the tensile test performed in distilled water at 37 degrees C. Mean tensile strengths were compared statistically by one-way ANOVA and Fisher's PLTD test (p<0.05). Fracture surfaces were observed by scanning electron microscopy, and reliability of the results was analyzed with Weibull distribution. Tensile strength did not significantly change after thermal cycling or storage in water and PBS at all temperatures tested (71.2-77.0 MPa) but decreased after treatment with boiling water (65.5 MPa).

New developments in dental adhesion

Numerous simplified adhesives have been introduced to the dental market within the last few years, sometimes without comprehensive testing to validate the performance claimed by the respective manufacturers. Mild self-etch adhesives are unable to etch enamel to provide adequate retention for bonded restorations. Although high early resin-dentin bond strength values can be achieved with some self-etch adhesives, their resistance to thermal and mechanical stresses over time is disappointing. In light of the current drawbacks attributed to all-in-one self-etch adhesives, etch-and-rinse adhesives are still the benchmark for dental adhesion in routine clinical use. This article summarizes current issues and factors related to the performance of adhesives.

Influence of water-storage time on the sorption and solubility behavior of current adhesives and primer/adhesive mixtures

This study evaluated the effects of water-storage on the water sorption and solubility behavior of five commercially available dental adhesive systems and two primer/adhesive mixtures. The adhesives comprised three different approaches to bonding to hard tooth tissues: a one-step self-etching adhesive (One-up Bond F), two two-step self-etching primers (Clearfil SE Bond and Clearfil Protect Bond) and two etch-and-rinse systems: a water/ethanol-based (Single Bond) and an acetone-based filled adhesive (Prime&Bond NT). The bonding agents and primers of the two-step self-etching systems were mixed in a 1:1 volume ratio. Water sorption and solubility values were determined after 1, 7, 30, 90 and 180 days. The results showed that, except for SB, all adhesives presented increased water sorption with increased storage time. The one-step self-etching adhesive and self-etching primer/adhesive mixtures presented the highest water sorption and solubility values. Equilibrium in the water sorption values was observed for all adhesives after 90 days of water-storage. However, solubility values continued to increase for some materials until 180 days. The sorption and solubility behavior of the materials tested seem to be related to hydrophilicity of the adhesive resin solution and might influence the long-term performance of resin-based composite restorations.

Apical sealing ability of Resilon/Epiphany versus gutta-percha/AH Plus: immediate and 16-months leakage

AIM

To compare the long-term apical sealing ability of gutta-percha/AH Plus and Resilon/Epiphany.

METHODOLOGY

The root canals of 90 single-rooted human mandibular premolars with single narrow root canals were prepared with ProFile 0.4 taper instruments to apical size 40. After each instrument, the canals were irrigated with 1% sodium hypochlorite. Subsequently, the teeth were randomly divided into four groups containing 20 teeth each. Additionally, 10 prepared premolars served as positive and 10 counterparts with intact crowns as negative controls. The root canals were filled with gutta-percha/AH Plus or Resilon/Epiphany using lateral or vertical compaction. Specimens were allowed to set for 7 days at 37 degrees C and 100% humidity. Subsequently, the root fillings were removed down to the apical 4 mm. Fluid movement was then assessed using a fluid transportation model and re-evaluated after 16 months of water storage. Leakage within and between groups was compared using nonparametric tests.

RESULTS

Negative controls revealed no fluid movement and positive controls displayed gross fluid movement at both times of observation. At the immediate measurement, there were no significant differences between the experimental groups (Kruskal-Wallis, P > 0.05). Gutta-percha/AH Plus fillings retained their seal after 16-months storage (Wilcoxon, P > 0.05), whilst the Resilon/Epiphany groups lost their sealing capacity (Wilcoxon, P < 0.001). In these groups, 29 of the 40 specimens exhibited gross leakage similar to positive controls.

CONCLUSION

Initially, Resilon/Epiphany root fillings prevented fluid movement to the same degree as gutta-percha/AH Plus counterparts, but showed more fluid movement when tested at 16 months.

In vitro cytotoxicity of dental composites based on new and traditional polymerization chemistries

The biological response to dental restorative polymer composites is mediated by the release of unpolymerized residual monomers. Several new composite formulations claim to reduce unpolymerized residual mass. The current study assessed the cytotoxic responses to several of these new formations and compared them with more traditional formulations. Our hypothesis predicted that if these new polymerization chemistries reduce unpolymerized residual mass, the cytotoxicity of these materials also should be reduced relative to traditional formulations.

METHODS

Materials (HerculiteXRV, Premise, Filtek Supreme, CeramxDuo, Hermes, and Quixfil) were tested in vitro in direct contact with Balb mouse fibroblasts, initially, then after aging in artificial saliva for 0, 1, 3, 5, or 8 weeks. The toxicity was determined by using the MTT assay to the estimate SDH activity. Knoop hardness of the materials also was measured at 0 and 8 weeks to determine whether surface breakdown of the materials in artificial saliva contributed to cytotoxic responses.

RESULTS

Materials with traditional methacrylate chemistries (Herculite, Premise, Filtek Supreme) were severely (>50%) cytotoxic throughout the 8-week interval, but materials with newer chemistries or filling strategies (Hermes, CeramXDuo, and Quixfil) improved over time of aging in artificial saliva. Hermes showed the least cytotoxicity at 8 weeks, and was statistically equivalent to Teflon negative controls. Hardness of the materials was unaffected by exposure to artificial saliva.

CONCLUSIONS

Newer polymerization and filling strategies for dental composites show promise for reducing the release of unpolymerized components and cytotoxicity.

Effect of Pulp Pressure on the Micropermeability and Sealing Ability of Etch & Rinse and Self-etching Adhesives

Etch & rinse adhesives are much more micropermeable and affected by pulp fluid compared with self-etching adhesives. Pulp pressure reduces dentin sealing with etch & rinse adhesives but not with self-etching adhesives. Pulp pressure has no effect on enamel sealing, which is lower when self-etching adhesive is used.

An overview of treatment considerations for esthetic restorations: a review of the literature

Controversy persists regarding the treatment planning criteria for esthetic restorations. This article reviews the literature regarding the biocompatibility, marginal adaptation, color matching, patient selection, technique sensitivity, and mode and rate of failure of tooth-colored restorations. A Medline search was completed for the period from 1986 to 2006, along with a manual search, to identify pertinent English peer-reviewed articles and textbooks. The key words used were amalgam, posterior composite resin, ceramic inlays/onlays, CEREC, porcelain laminate veneers, all-ceramic crowns, and all-ceramic fixed partial dentures.

Determination of elastic modulus of demineralized resin-infiltrated dentin by self-etch adhesives

The purpose of this study was to determine ultrasonically the changes in elastic modulus of demineralized adhesive-infiltrated dentin. Dentin disks were obtained from bovine incisors and shaped into a rectangular form. The specimens were immersed in single-step self-etch adhesives, then stored in distilled water and run through thermal cycles between 5 and 60 degrees C. The longitudinal and shear wave sound velocities and the elastic modulus were determined using ultrasonic equipment composed of a pulser-receiver, transducers, and an oscilloscope. After 24 h of storage, the elastic modulus of mineralized dentin was 16.9 GPa and that of demineralized dentin was 2.1 GPa. The immersion of demineralized dentin in adhesives significantly increased the elastic modulus to 3.3-5.9 GPa. After 30,000 thermal cycles, the elastic modulus of dentin was 32.4 GPa, whereas that of demineralized adhesive infiltrated dentin was 3.1-4.1 GPa. Thermal stresses did not cause adhesive-infiltrated demineralized dentin to deteriorate, as measured by elastic modulus.

An in vivo evaluation of bonding ability of comprehensive antibacterial adhesive system incorporating MDPB

OBJECTIVES

This study examined the in vivo bonding ability to sound dentin of antibacterial adhesive systems incorporating an antibacterial monomer MDPB based on morphological evaluation of the resin-dentin interface.

METHODS

Class V cavities were prepared on the buccal surfaces of the teeth of a beagle dog and a composite filling performed using (1) commercial self-etching system Liner Bond 2 (LB primer+LB bond), (2) experimental primer containing 5% MDPB and LB bond, (3) LB primer and experimental bonding-resin containing 2.5% MDPB, or (4) combination of experimental primer and bonding-resin. After 7 days, the tooth crown was cut and fixed in half-Karnovsky's solution, and the sectioned surface observed under scanning electron microscopy (SEM) after treatment with phosphoric acid and NaOCl. The ultrastructure of the bonding interface was also examined by transmission electron microscopy (TEM). Microtensile bond strengths (microTBS) of each group were measured using extracted teeth.

RESULTS

SEM demonstrated that all groups produced a 1-2microm thick hybrid layer with funnel shaped resin tags, although the length of tags was shorter for the group in which MDPB-containing bonding-resin was used. TEM examination supported good adhesion of the comprehensive adhesive system employing MDPB-containing primer/bonding-resin, showing integrity between resin and dentin. There were no significant differences in microTBS among the four groups tested (p>0.05, ANOVA).

SIGNIFICANCE

This study confirmed that the experimental antibacterial adhesive systems employing MDPB-containing primer or/and bonding-resin could produce an effective bond under in vivo conditions.

FDI report on adverse reactions to resin-based materials

Resin-based restorative materials are considered safe for the vast majority of dental patients. Although constituent chemicals such as monomers, accelerators and initiators can potentially leach out of cured resin-based materials after placement, adverse reactions to these chemicals are rare and reaction symptoms commonly subside after removal of the materials. Dentists should be aware of the rare possibility that patients could have adverse reactions to constituents of resin-based materials and be vigilant in observing any adverse reactions after restoration placement. Dentists should also be cognisant of patient complaints about adverse reactions that may result from components of resin-based materials. To minimise monomer leaching and any potential risk of dermatological reactions, resin-based materials should be adequately cured. Dental health care workers should avoid direct skin contact with uncured resin-based materials. Latex and vinyl gloves do not provide adequate barrier protection to the monomers in resin-based materials.

Influence of different light curing units on the cytotoxicity of various dental composites

OBJECTIVES

To evaluate the dependence of the toxicity of various dental composites on the use of high- and low-power light curing units (LCUs).

METHODS

The composites Filtek Z 250, Durafill VS, Solitaire 2 and Grandio were polymerized using different light densities from three LCUs, namely Heliolux II, Swiss Master Light (SML) and a prototype LED. The toxicity of polymerized samples was tested by exposing them to the cell culture medium up to 28 days. The extracts of the composites were collected daily and used for incubation in human gingival fibroblasts cultures.

RESULTS

Slow, low-intensity curing using the LED or the Heliolux II showed similar characteristics for all four composites, regarding the cell viability rate of human gingival fibroblasts. After 1 day of storage suboptimal results could be observed for the SML/Durafill and optimal results for SML/Grandio combination (approximately 100% cell viability). In addition, the composite Solitaire the SML yielded significantly better results than the other LCUs (cell viability, p < or = 0.001: SML 60.5%, Heliolux 44.5%, LED 44.2%). Furthermore, the combination of the SML with Z 250 composite showed, after the first day and up to day 28, statistically significantly higher cell viability rates than the combination with the LED or Heliolux II.

SIGNIFICANCE

This study shows that the combination of a high power LCU with some composites positively influences the HGF cell viability effected by the investigated composite extracts. Moreover, there is further indication that a reduction of composite toxicity is possible if the curing mode is adapted to the used composite.

Resin-based dentin restorative materials under accelerated ageing: bio-functional behavior

OBJECT

The aim of the present study was the evaluation of the effect of different polishing and finishing procedures on Filtek Z250 FZ ESPE restorative material. Particularly, the consequence of artificial aging (UV-irradiation) on this resin-based dental material was investigated determining also its outcome on cell behavior.

METHODS

96 specimens of restorative material were prepared using a light emitting diode curing unit and randomly divided into four finishing and polishing groups: (I) No treatment (FZ); (II) Identoflex rubbers (ID); (III) Enhance System (EN) and (IV) Sof-Lex Pop-on XT discs (SF). The surface morphology of native and artificially aged materials was assessed with Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). FTIR and biological (biocompatibility and bacterial adhesion) analyses were also performed.

RESULTS

Among all, the ID procedure represented an acceptable compromise for efficiency of polymerization and biocompatibility both before and after artificial ageing. SF and EN techniques showed better interactions with the biological environment.

CONCLUSION

UV artificial ageing of the tested specimens has shown an acceleration of the surface degrading processes, favoring a possible decrease in the mechanical properties and the release of toxic free radicals. Finishing and polishing procedure seemed to affect the photodegrading pathways, even though no differences among the techniques were observed. As the cytotoxicity of materials undergoing accelerated aging is relevant, further improvement of dental restorative materials are required to limit the long-term biological damage.

Genotoxicity evaluation of five different dentin bonding agents by chromosomal aberration analysis

Dentin bonding agents became unavoidable in today's aesthetic restorative dentistry. Nevertheless, more and more evidences on their possible cytotoxicity and/or genotoxicity emerge. Still, only limited number of studies has been published on that issue. In our work we evaluated possible genotoxicity of five different adhesives: Adper Single Bond, Adper Single Bond 2 with nanofiller, Excite, OptiBond Solo Plus and Prompt L-pop. Genotoxicity assessment was carried out on human lymphocytes in vitro, using chromosomal aberration analysis. Polymerized adhesives were tested at three different dilutions of the 0.5 g mL(-1) eluate stock (2.5 x 1:10(6), 1:10(6) and 1:10(5)) after 1 h, 24 h and 5 days of elution. Slight but significant increase in the number of chromatid breaks was observed after 24-h elution period, for adhesives Adper Single Bond 2, Excite, and OptiBond Solo Plus at dilutions of 1:10(6) and 1:10(5), and for other two only at dilution of 1:10(5). First three adhesives also appeared to be slightly genotoxic after 1 h of elution but only at 1:10(5). As a bonding agent remains in close contact with living dental tissue over a long period of time, information on their possible genotoxicity and carcinogenicity should be more clearly clarified in the near future.

NaOCl degradation of a HEMA-free all-in-one adhesive bonded to enamel and dentin following two air-blowing techniques

OBJECTIVE

Phase-separation within HEMA-free all-in-one dental adhesives may result in the entrapment of droplets within the adhesive resin. Strongly air-blowing prior to polymerization, can remove most of these droplets. The objective of this study was to evaluate the effect these droplets may have on the resistance of the adhesive-tooth interface to NaOCl degradation.

METHODS

The micro-tensile bond strength (microTBS) to enamel and dentin was determined when a HEMA-free all-in-one adhesive was applied either following a mild or strong air-blowing technique. The bonds were also exposed to an aqueous sodium hypochlorite (NaOCl) solution for 1h, following a recently introduced methodology to mimic in vivo bond degradation.

RESULTS

This study revealed that strong air-blowing of the adhesive only resulted in a significantly higher micro-tensile bond strength (microTBS) to dentin, but not to enamel. Likewise, NaOCl only reduced the microTBS to dentin for both the mild and strong air-blowing technique, but again not the microTBS to enamel. Failure analysis by SEM clearly revealed that strong air-blowing is less effective in droplet removal when the adhesive was applied in small and narrow class-I cavities, as compared to when it was applied to flat surfaces.

CONCLUSIONS

NaOCl did preferentially dissolve the hybrid layer at dentin, and more for the mild than for the strong air-blowing technique. A strong air-blowing procedure resulted in a more NaOCl-resistant hybrid layer, so that it can be concluded that a HEMA-free one-step adhesive definitely benefits from a strong air-blowing technique.

Influence of enamel border and regional variability on durability of resin-dentin bonds

OBJECTIVES

To evaluate the influence of enamel border on regional resin-dentin microtensile bond strength (muTBS) over time.

METHODS

Thirty human third molars had a flat dentine surface exposed. Two adhesive systems (Single Bond [SB] and ScotchBond Multi Purpose Plus [SBMP]) were applied and composite resin crowns (Filtek Z250) were constructed. Teeth were divided into three groups (n=5). Group A, specimens were sectioned to obtain sticks to be tested in tension (0.5mm/min) immediately. Group B specimens were stored without outer enamel in water for 6 months, before sectioning and testing. Group C, specimens were stored with outer enamel in water for 6 months, before sectioning and testing. In all groups, the origin of the sticks, periphery and inner regions was controlled. The data for each adhesive were subjected to a two-way repeated measure ANOVA (location versus storage conditions) and Tukey's test.

RESULTS

No significant degradation in muTBS was observed for SBMU in all conditions. For SB, a significant reduction on muTBS was observed in the specimens without enamel border (group B). The degradation was more pronounced in the specimens from the periphery.

CONCLUSIONS

The three-step etch-and-rinse system is less susceptible to water degradation effects; stable resin-dentin bonds can be achieved with two-step etch-and-rinse systems as long as there is a bonded enamel border.

Genetic and cellular toxicology of dental resin monomers

Monomers are released from dental resin materials, and thus cause adverse biological effects in mammalian cells. Cytotoxicity and genotoxicity of some of these methacrylates have been identified in a vast number of investigations during the last decade. It has been well-established that the co-monomer triethylene glycol dimethacrylate (TEGDMA) causes gene mutations in vitro. The formation of micronuclei is indicative of chromosomal damage and the induction of DNA strand breaks detected with monomers like TEGDMA and 2-hydroxyethyl methacrylate (HEMA). As a consequence of DNA damage, the mammalian cell cycle was delayed in both G1 and G2/M phases, depending on the concentrations of the monomers. Yet, the mechanisms underlying the genetic and cellular toxicology of resin monomers have remained obscure until recently. New findings indicate that increased oxidative stress results in an impairment of the cellular pro- and anti-oxidant redox balance caused by monomers. It has been demonstrated that monomers reduced the levels of the natural radical scavenger glutathione (GSH), which protects cell structures from damage caused by reactive oxygen species (ROS). Depletion of the intracellular GSH pool may then significantly contribute to cytotoxicity, because a related increase in ROS levels can activate pathways leading to apoptosis. Complementary, cytotoxic, and genotoxic effects of TEGDMA and HEMA are inhibited in the presence of ROS scavengers like N-acetylcysteine (NAC), ascorbate, and Trolox (vitamin E). Elevated intracellular levels of ROS can also activate a complex network of redox-responsive macromolecules, including redox-sensitive transcription factors like nuclear factor kappaB (NF-kappaB). It has been shown that NF-kappaB is activated probably to counteract HEMA-induced apoptosis. The induction of apoptosis by TEGDMA in human pulp cells has been associated with an inhibition of the phosphatidylinositol 3-kinase (PI3-K) cell-survival signaling pathway. Although the details of the mechanisms leading to cell death, genotoxicity, and cell-cycle delay are not completely understood, resin monomers may be able to alter the functions of the cells of the oral cavity. Pathways regulating cellular homeostasis, dentinogenesis, or tissue repair may be modified by monomers at concentrations well below those which cause acute cytotoxicity.

Controlled release of chlorhexidine from UDMA-TEGDMA resin

Chlorhexidine salts are available in various formulations for dental applications. This study tested the hypothesis that the release of chlorhexidine from a urethane dimethacrylate and triethylene glycol dimethacrylate resin system can be effectively controlled by the chlorhexidine diacetate content and pH. The filler concentrations were 9.1, 23.1, or 33.3 wt%, and the filled resins were exposed to pH 4 and pH 6 acetate buffers. The results showed that Fickian diffusion was the dominant release mechanism. The rates of release were significantly higher in pH 4 buffer, which was attributed to the increase of chlorhexidine diacetate solubility at lower pH. The higher level of filler loading reduced the degree of polymerization, leading to a greater loss of organic components and higher chlorhexidine release rates.

Inhibition of TEGDMA and HEMA-induced genotoxicity and cell cycle arrest by N-acetylcysteine

OBJECTIVES

Dental resin monomers like triethylene glycol dimethacrylate (TEGDMA) and 2-hydroxyethyl methacrylate (HEMA) are able to cause an imbalance of the redox state in mammalian cells. The resulting oxidative stress originating from reactive oxygen species (ROS) has been associated with cytotoxicity. We hypothesized that ROS might contribute to the generation of genotoxicity by TEGDMA and HEMA as well. Therefore, we examined the formation of micronuclei in V79 cells by both resin monomers in the presence of the antioxidant N-acetylcysteine (NAC), which scavenges ROS. In addition, we analyzed the effects of TEGDMA and HEMA on the normal cell cycle in the presence of NAC.

METHODS

V79 fibroblasts were exposed to increasing concentrations of TEGDMA and HEMA in the presence and absence of NAC for 24h. Genotoxicity was indicated by the formation of micronuclei. The modification of the normal cell cycle was analyzed by flow cytometry (FACS).

RESULTS

A dose-related increase in the number of micronuclei in V79 cells-induced by TEGDMA and HEMA indicated genotoxicity of both chemicals. However, the formation of micronuclei was reduced in the presence of 10 mmol/L NAC, indicating its protective role. A cell cycle delay in G2 phase caused by TEGDMA was absent when cells were co-treated with NAC. Similarly, the presence of NAC led to a reversion of the cell cycle delay in HEMA-treated cell cultures.

SIGNIFICANCE

Our results suggest that genotoxic effects and the modification of the cell cycle caused by TEGDMA and HEMA are mediated, at least in part, by oxidative stress.

Adhesive systems and secondary caries formation: Assessment of dentin bond strength, caries lesions depth and fluoride release

OBJECTIVES

The present study evaluated the microtensile bond strength and caries formation on adhesive/dentin interfaces before and after dynamic chemical formation of secondary caries.

METHODS

Restorations were prepared on the dentin surface of 80 bovine incisors using four adhesive systems: two fluoride-free (Single Bond and Clearfil SE Bond) and two fluoride containing (Optibond Solo Plus and Clearfil Protect Bond). The restored teeth were then sectioned into multiple slabs that were further trimmed at the bonded interface to a cross-sectional area of 1 mm2. Half of the slabs were subjected to secondary caries formation using a pH cycling model (treated groups); while the other half was used as the control group (no pH cycling). The specimens designated for bond strength evaluation were subjected to microtensile bond strength test (muTBS). Caries lesions formation was assesses by polarized light microscopy at different depths from the adhesive-dentin bonded interface. The fluoride ion concentration was evaluated using the de/remineralization solutions (De/Re).

RESULTS

No differences in muTBS were observed among the adhesive systems in both the control and treated conditions. Secondary caries significantly reduced the values of muTBS for all adhesives (p<0.05). Optibond Solo Plus presented the lowest caries formation at 5 microm depth. Fluoride concentrations present in the De/Re were less than 0.03 ppm, regardless of the adhesive system tested.

SIGNIFICANCE

Bond strength values significantly decreased after in vitro secondary caries formation. Fluoride present in adhesive systems is not capable of inhibiting secondary caries or maintaining bond strength values following caries formation.

Hygroscopic and hydrolytic effects in dental polymer networks

OBJECTIVES

The objective of this manuscript is to outline the factors associated with hygroscopic and hydrolytic effects in dental polymer networks, and to review the literature generated over the past thirty years or more in this area.

METHODS

Information was gathered from nearly 90 published articles or abstracts appearing in the dental and polymer literature. Studies were predominantly identified through a search of the PubMED database.

RESULTS

Studies were included that provided direct evidence for the uptake of solvent by a polymer network and its subsequent physical or chemical effect, or the loss of molecular species into solvents. An attempt was made to select articles that spanned the timeframe from approximately 1970 to today to ensure that most of the classic literature as well as the latest information was included.

CONCLUSIONS

Dental polymer networks have been shown to be susceptible to hygroscopic and hydrolytic effects to varying extents dependent upon their chemistry and structure. The importance of these effects on the clinical performance of polymer restoratives is largely unknown, though numerous investigators have alluded to the potential for reduced service lives.

SIGNIFICANCE

While the physical and mechanical properties of these materials may be significantly altered by the effects of solvent uptake and component elution, what may constitute the greatest concern is the short-term release of unreacted components and the long-term elution of degradation products in the oral cavity, both of which should be strongly considered during restorative material development.

Determination of bisphenol diglycidyl ethers in topical dosage forms

A method involving extraction and LC-ESI-MS-MS detection of BADGE, BFDGE, BADGE*H2O, BADGE*2H2O, BADGE*HCl, BADGE*H2O*HCl, BADGE.2HCl and BFDGE*2HCl in aqueous cream was developed and validated. Initially, empty internally lacquered aluminum container closure systems were extracted with isopropanol as an attempt to estimate the upper limit of extractable bisphenol diglycidyl ethers present in lacquer. Six of the eight potential bisphenol diglycidyl ethers were quantified. In an accelerated experiment, on aqueous cream stored in lacquered aluminum tubes at 70 degrees C, all derivatives except BADGE*2HCl and BFDGE*2HCl were extracted from cream samples and quantified as an attempt to estimate the upper limit of compounds leaching to the cream. Detection limits were from 0.3+/-0.2 to 3.4+/-0.7 microgl(-1). Recoveries were determined for all compounds at three concentration levels (mean 63+/-6%). Mean inter-day and mean intra-day precision was 7+/-2 and 13+/-6%, respectively. Three commercially available creams were obtained from a local community pharmacy and analysed for bisphenol diglycidyl ethers. BADGE, BADGE*H2O, BADGE*2H2O and BADGE*H2O*HCl were detected and quantified. In conclusion, the developed method allows for the extraction and detection of bisphenol diglycidyl ethers originating from the epoxy phenol lacquer used in aluminum tubes. This study does not indicate that they leach into aqueous cream in significant amounts under normal storage conditions.

Water sorption/solubility of dental adhesive resins

OBJECTIVES

This study evaluated the water sorption, solubility and kinetics of water diffusion in commercial and experimental resins that are formulated to be used as dentin and enamel bonding agents.

METHODS

Four commercial adhesives were selected along with their solvent-monomer combination: the bonding resins were of Adper Scotchbond Multi-Purpose (MP) and Clearfil SE Bond (SE) systems, and the "one-bottle" systems, Adper Single Bond (SB) and Excite (EX). Five experimental methacrylate-based resins of known hydrophilicities (R1, R2, R3, R4 and R5) were used as reference materials. Specimen disks were prepared by dispensing the uncured resin into a mould (5.8mm x 0.8mm). After desiccation, the cured specimens were weighed and then stored in distilled water for evaluation of the water diffusion kinetics over a 28-day period.

RESULTS

Resin composition and hydrophilicity (ranked by their Hoy's solubility parameters) influenced water sorption, solubility and water diffusion in both commercial and experimental dental resins. The most hydrophilic experimental resin, R5, showed the highest water sorption, solubility and water diffusion coefficient. Among the commercial adhesives, the solvated systems, SB and EX, showed water sorption, solubility and water diffusion coefficients significantly greater than those observed for the non-solvated systems, MP and SE (p<0.05). In general, the extent and rate of water sorption increased with the hydrophilicity of the resin blends.

SIGNIFICANCE

The extensive amount of water sorption in the current hydrophilic dental resins is a cause of concern. This may affect the mechanical stability of these resins and favor the rapid and catastrophic degradation of resin-dentin bonds.

Identification of organic extractables from commercial resin-modified glass-ionomers using HPLC-MS

Elution of organic compounds from resin-based dental fillings during their application in the human mouth environment may have a potential impact on the human health. Ethanol, water and other solvents very often present in the human mouth have the ability to penetrate dental fillings placed in the human tooth. Penetration of liquids into the tooth may lead to the liberation of unreacted dental filling ingredients or their degradation products. Determination of these compounds is necessary for better knowledge from possible harmful effects caused by dental fillings. The aim of this study was the isolation and identification of compounds released from resin-modified glass-ionomer cements (RMGICs), resin-based dental materials applied in dentistry. Compounds were extracted from fillings by using four solvents (40% ethanol, water, 1% acetic acid and artificial saliva). Liquid samples containing eluted compounds were then extracted, evaporated and analyzed by using of HPLC-MS (high-performance liquid chromatography-mass spectrometry) and HPLC-DAD (high-performance liquid chromatography-diode array detection) techniques. Almost thirty components (monomers and additives) of RMGICs were identified. The main identified extractables were: Bis-GMA (bisphenol A glycidyl dimethacrylate), Bis-EMA (ethoxylated bisphenol A dimethacrylate), UDMA (urethane dimethacrylate), TEGDMA (triethylene glycol dimethacrylate), HEMA (2-hydroxyethyl methacrylate) as monomers and diphenyliodonium chloride, camphorquinone (initiators), BHA (inhibitor), 4-(dimethylamino) ethyl benzoate (co-initiator) as additives.

Degradation of Methacrylate Monomers in Human Saliva

This study assessed the effect of the molecular structure of newly synthesized methacrylate monomers on their chemical stability in human saliva, whereby these monomers can be used as dental composite resins. Six model monomethacrylates and two urethane-modified BisGMA monomers were added to human saliva, and their change in concentration after 24, 48, and 72 hours were measured by high-performance liquid chromatography. Degradation of the six model monomethacrylate monomers was found to be influenced by the molecular structure, such as steric hindrance and presence of urethane bond in chemical backbone. Based on the degradation test results of these six monomers, urethane-modified BisGMA derivatives--in which the hydroxyl groups in original BisGMA monomer were substituted with alkyl isocyanate--were synthesized and subjected to degradation test. The urethane-modified BisGMA monomers showed a particular resistance to salivary hydrolysis. Results of this study thus suggested that urethane groups should be considered when designing new monomers for dental composite systems as they demonstrated improved resistance to hydrolysis.

Identifying enzyme activities within human saliva which are relevant to dental resin composite biodegradation

Esterase activities similar to those of cholesterol and pseudocholine esterases (CE and PCE, respectively) have been detected within whole human saliva. Since commercial CE has been shown to possess distinct activity relative to PCE for select components in dental composites, it is hypothesized that esterases isolated from human saliva will also show selectivity towards specific monomer elements within the composites. The objective of this work was to carry out the isolation of these activities from whole human saliva and study their individual effects on resin monomers such as Bis-phenyl glycidyl dimethacrylate (aromatic structure) and triethylene glycol dimethacrylate (hydrophilic structure), and on cured composites containing the latter monomers. Human saliva samples were processed, fractionated on a gel filtration column and assayed for CE and PCE-like activity. Selected fractions were incubated at 37 degrees C with the above monomers and select commercial composites. Degradation was monitored using high-performance liquid chromatography. The fraction with the highest cholesterol esterase-like character preferentially degraded the aromatic monomer and significantly degraded more of the composite's material relative to a fraction containing low amounts of the cholesterol esterase activity but elevated pseudocholine esterase-like activity. Hence, it was concluded that select salivary esterases had preferences for distinct composite resin components.

Interleukin-1 levels in gingival crevicular fluid adjacent to restorations of calcium aluminate cement and resin composite

OBJECTIVES

The aim of this clinical study was to intra-individually compare Class V restorations of a calcium aluminate cement (CAC), resin composite and enamel with respect to the adjacent levels of interleukin (IL)-1alpha, IL-1beta and IL-1 receptor antagonist (IL-1ra) in gingival crevicular fluid (GCF). The hypothesis was that there are higher IL-1 levels adjacent to resin composite, compared with CAC and enamel.

MATERIALS AND METHODS

In 15 subjects, at least one set of two Class V restorations with subgingival margins, one CAC and one universal hybrid resin composite, and one control surface of enamel were included. In a cross-sectional study and on days 0, 3 and 7 of an experimental gingivitis study, GCFs were collected with Periopaper for 30 s. The GCF concentrations of IL-1alpha, IL-1beta and IL-1ra were quantified with enzyme linked immunosorbent assays.

RESULTS

Neither the cross-sectional study nor the experimental gingivitis study showed any significant differences in the levels of IL-1alpha, IL-1beta and IL-1ra between CAC, resin composite and enamel sites (p>0.05). In the cross-sectional study, low IL-1 concentrations were observed. The IL-1 levels increased significantly during the experimental gingivitis.

CONCLUSION

Regardless of CAC or resin composite, the restorations per se did not affect the GCF levels of IL-1 and IL-1ra, neither at healthy gingiva, nor at initiation of plaque-related gingival inflammation.

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.

Mechanical stability of resin-dentin bond components

OBJECTIVES

To evaluate the effects of long-term storage on the mechanical properties of the components of resin-dentin bonds, that is, resin composite, adhesive system, demineralized and mineralized dentin.

METHODS

Specimens of resin composite (Z250) and adhesive systems (Single Bond-SB; One-Step-OS and Clearfil Liner Bond 2V-CL) were cast in molds. Dentin specimens were prepared from dentin discs obtained from the crowns of extracted human molars. Specimens of demineralized dentin were obtained by immersion of dentin discs for 6 days in 0.5 mol/l EDTA (pH 7.0). Both dentin and resin-based substrates were shaped to hourglass or I-beam specimens that were used to determine the true stress (TS) or apparent modulus of elasticity (E), respectively. Control specimens were subjected to tensile testing at 0.6 mm/min after 24 h of immersion in distilled water. Experimental specimens were stored at 37 degrees C in either distilled water or mineral oil and tested after 12 months. The data of each group were individually analyzed by ANOVA and Tukey's test.

RESULTS

Both TS and E of the resin-based materials decreased significantly after 12 months of storage in water (p < 0.05) except the TS of SB (p > 0.05). No changes were observed for specimens of mineralized dentin, regardless of storage condition (p > 0.05). Storage of demineralized dentin in water did not cause any significant effect in either TS or E (p > 0.05), however, significant reductions of TS and E of demineralized dentin occurred after storage in oil for 1 year (p < 0.05).

SIGNIFICANCE

Storage time and medium may be deleterious to the mechanical properties of the resin-dentin bond components, which ultimately could compromise the durability of resin-dentin bonds.

Influence of specimen size and regional variation on long-term resin–dentin bond strength

OBJECTIVES

Verify whether the dimension of a bonded specimen stored prior microtensile testing and its regional variation may affect the resin-dentin bond strength (BS) over time.

METHODS

Thirty human third molars had a flat dentin surface exposed and all peripheral enamel removed. Two adhesive systems (Single-Bond and One-Step) were applied and composite resin crowns (Z250) were constructed. Teeth were divided into three groups (n = 5). Group A specimens were sectioned to obtain sticks to be tested in tension (0.5 mm/min) immediately. Group B specimens were stored in water for 6 months, before sectioning and testing. Group C specimens were sectioned; the sticks were stored for 6 months and tested. In groups A and B, the origin of the sticks, periphery and inner regions was controlled. Bond strength (BS) was expressed as an index that considers cohesive failures and estimated values of premature debonded specimens. One-way ANOVA and Tukey's test (alpha = 0.05) were used to compare groups A, B and C, and a second analytical approach (A and B) employed a two-way ANOVA (time versus regional differences) for each adhesive system.

RESULTS

For Single-Bond (SB), the BS for specimens in group A was higher than for groups B and C. For One-Step (OS), the BS in group A was higher than for B, which was in turn higher than for C. In the second group approach, no difference was found when the test was performed immediately; however, after 6 months, the inner sticks from group B showed significantly higher BS.

SIGNIFICANCE

(1) The amount of decrease in BS is dependent on the specimen size; (2) the decrease in BS was greater for peripheral specimens than more centrally located specimens.

Effect of smear layer thickness and acidity of self-etching solutions on early and long-term bond strength to dentin

OBJECTIVES

To evaluate the effect of smear layer thickness (SL) on early and 6-month bond strength (BS) of self-etching adhesives to dentin and to measure the ultimate microtensile strength (UTS) of the adhesives.

METHODS

Clearfil SE Bond; Optibond Solo Plus Self-Etch Primer; Tyrian Self Priming Etchant (TY) and as controls, Single Bond (SB) and Scotchbond Multi-Purpose Plus (SBMP) were applied on flat superficial dentin surface with thick and thin SL thicknesses. After adhesive's application (n=6) a resin build-up was made. After 24h, resin-dentin beams (0.8mm(2)) were prepared to be tested immediately and after 6-month (6M) at 0.5mm/min. For the UTS measurement, hour-glass specimens were prepared with the bonding resin alone or after mixing (1:1). BS values were analyzed by three-way repeated measures ANOVA and Tukey's multiple comparison tests. Two-way ANOVA (bonding resin and bonding resin+self-etching primer) and Tukey's test were used for the UTS values. The bonding resins were re-evaluated separately by a one-way ANOVA and Tukey's test, since Single Bond is a one-bottle adhesive (alpha=0.05).

RESULTS

The SL thickness was not significant (p=0.64). BS values were reduced after 6M, except for the SBMP. TY provided the lowest BS mean while SB and SBMP the highest BS. The UTS of the SBMP was the highest. TY yielded the lowest UTS. Regression analysis revealed a linear and significant relationship between the UTS of self-etch systems and the mean BS (R=0.95, p=0.02).

CONCLUSIONS

The performance of a self-etching system does not seem to be dependent on the SL thickness. The total-etch, three-step system provided the highest BS to dentin and maintained the BS stable over 6 months. The performance of the self-etching systems can be envisaged by their UTS.

Effect of cavity configuration and aging on the bonding effectiveness of six adhesives to dentin

OBJECTIVES

The purpose of this study was to determine the effect polymerization contraction stress may have on bond durability.

METHODS

Bonding effectiveness was assessed by micro-tensile bond strength testing (muTBS) and electron microscopy. The muTBS to flat dentin surfaces and in standardized cavities was determined (this after 1 day as well as 1 year water storage). Six adhesives representing all current classes were applied: two etch-and-rinse (OptiBond FL, Kerr; Scotchbond 1, 3M ESPE), two self-etch (Clearfil SE Bond, Kuraray; Adper Prompt, 3M ESPE) and two glass-ionomer (Fuji Bond LC, GC; Reactmer, Shofu) adhesives.

RESULTS

The conventional 3-step etch-and-rinse adhesive OptiBond FL bonded most effectively to dentin, and appeared insensitive to polymerization shrinkage stress and water degradation. The 2-step self-etch adhesive Clearfil SE Bond most closely approached this superior bonding effectiveness and only slightly lost bond strength after 1-year water exposure. The 2-step etch-and-rinse adhesive Scotchbond 1 and the 'strong' 1-step self-etch adhesive Adper Prompt appeared very sensitive to cavity configuration and water-aging effects. The 2-step resin-modified glass-ionomer adhesive Fuji Bond LC only suffered from shrinkage stress, but not from 1-year water-exposure. Remarkable also is the apparent repairability of the 'mild' 1-step glass-ionomer adhesive Reactmer when stored for 1 year in water, in spite of the very low 1-day muTBS.

SIGNIFICANCE

Simplified bonding procedures do not necessarily imply improved bonding performance, especially in the long term.

Mutual influence of cholesterol esterase and pseudocholinesterase on the biodegradation of dental composites

It has been demonstrated that human saliva contains cholesterol esterase (CE)- and pseudocholinesterase (PCE)-like hydrolase activities. While PCE has been shown to preferentially degrade triethylene glycol dimethacrylate (TEGDMA) and its derivatives, CE has a greater catalytic effect on the breakdown of bis-phenol-A-diglycidyl dimethacrylate (bisGMA) components in composite dental resins. The current study seeks to determine if there is a mutual influence between the different esterases with respect to the biodegradation of resin composite. Photopolymerized model composite resin samples (containing 60% by weight fraction of silanated barium glass filler) based on bisGMA/TEGDMA (bis) or urethane-modified bisGMA/TEGDMA/bisEMA (ubis) monomers were incubated in buffer, CE and/or PCE solutions (pH=7.0, 37 degrees C) for 8 and 16 days. The incubation solutions were analyzed for degradation products using high-performance liquid chromatography, UV spectroscopy and mass spectrometry. In the bis system, higher amounts (p<0.05) of a bisGMA derived product, bishydroxy-propoxyphenyl-propane (bisHPPP), were detected in the combined enzyme group as compared to the sum of the two individual enzyme groups. In the ubis system, similar comparisons showed that higher levels (p<0.05) of bisHPPP were detected in the combined group at 8 days while higher amounts (p<0.05) of a bisEMA derived product, ethoxylated bis-phenol A, were detected in the combined group at 16 days. The study concluded that CE and PCE act synergistically to increase the biodegradation of both composite resin materials.