Contraction Stress in Dentin Adhesives Bonded to Dentin

Adhesives cured under constrained conditions develop contraction stresses. We hypothesized that, with dentin as a bonding substrate, the stress would reach a maximum, followed by a continuous decline. Stress development was determined with a tensilometer for two total-etch systems and two systems with self-etching primers. The adhesives were placed in a thin layer between a glass plate and a flat dentin surface pretreated with phosphoric acid or self-etching primer. After an initial maximum shortly after light-curing, the stress decreased dramatically for the total-etch systems (70%) and, to a lesser extent, for the adhesives with self-etching primers (30%). The greater stress decrease for the total-etch systems was ascribed to water and/or solvents released into the adhesives from the fully opened dentinal tubules by the pulling/sucking action of the contraction stress. This happened less with the adhesives with self-etching primers, where the tubules remained mainly closed.

Effect of Nd:YAG laser on the solvent evaporation of adhesive systems

OBJECTIVE

This study evaluated the influence of Nd:YAG laser on the evaporation degree (ED) of the solvent components in total-etch and self-etch adhesives.

MATERIALS AND METHODS

The ED of Gluma Comfort Bond (Heraeus-Kulzer) one-step self-etch adhesive, and Adper Single Bond 2 (3M ESPE), and XP Bond (Dentsply) total-etch adhesives was determined by weight alterations using two techniques: Control--spontaneous evaporation of the solvent for 5 min; Experimental--Nd:YAG laser irradiation for 1 min, followed by spontaneous evaporation for 4 min. The weight loss due to evaporation of the volatile components was measured at baseline and after 10 s, 20 s, 30 s, 40 s, 50 s, 60 s, 70 s, 80 s, 90 s, 100 s, 110 s, 2 min, 3 min, 4 min, and 5 min.

RESULTS

Evaporation of solvent components significantly increased with Nd:YAG laser irradiation for all adhesives investigated. Gluma Comfort Bond showed significantly higher evaporation of solvent components than Adper Single Bond 2 and XP Bond. All the adhesives lost weight quickly during the first min of Nd:YAG laser irradiation.

CONCLUSION

The application of Nd:YAG laser on adhesives before light curing had a significant effect on the evaporation of the solvent components, and the ED of Gluma Comfort Bond one-step self-etch adhesive was significantly higher than with Adper Single Bond 2 and XP Bond total-etch adhesives.

CLINICAL RELEVANCE

The use of the Nd:YAG laser on the uncured adhesive technique can promote a greater ED of solvents, optimizing the longevity of the adhesive restorations.

Influence of ceramic thickness and type on micromechanical properties of light-cured adhesive bonding agents

OBJECTIVE

The aim of this study was to evaluate the micromechanical properties of different adhesive bonding agents when polymerized through ceramics.

MATERIALS AND METHODS

Sixty sound extracted human third molars were selected and the crowns were sectioned perpendicular to the long axis in order to obtain dentin slices to be bonded with one of the following adhesives: Syntac/Heliobond (Ivoclar-Vivadent) or Adper-Scotchbond-1XT (3M-ESPE). The adhesives were cured by using a LED-unit (Bluephase®, Ivoclar Vivadent) with three different curing times (10 s, 20 s and 30 s) under two ceramics (IPS-e.max-Press, Ivoclar-Vivadent; IPS-Empress®CAD, Ivoclar-Vivadent) of different thicknesses (0 mm, 0.75 mm, 2 mm). Thirty groups were included, each containing 60 measurements. Micromechanical properties (Hardness, HV; indentation modulus, E; and creep, Cr) of the adhesives were measured with an automatic microhardness indenter (Fisherscope H100C, Germany). Data were statistically analyzed by using one-way ANOVA and Tukey's post-hoc test, as well as a multivariate analysis to test the influence of the study parameters (SPSS 18.0).

RESULTS

Significant differences were observed between the micromechanical properties of the adhesives (p < 0.05). The ceramic type showed the highest effect on HV (Partial-eta squared (η(2)) = 0.109) of the tested adhesives, while E (η(2) = 0.275) and Cr (η(2) = 0.194) were stronger influenced by the adhesive type. Ceramic thickness showed no effect on the E and Cr of the adhesives.

CONCLUSIONS

The adhesive bonding agents used in this study performed well by curing through different thicknesses of ceramics. The micromechanical properties of the adhesives were determined by the adhesive type and were less influenced by ceramic type and curing time.

Effects of prolonged light exposure times on water sorption, solubility and cross-linking density of simplified etch-and-rinse adhesives

PURPOSE

This study evaluated the effects of light exposure times on water sorption, solubility, and polymer cross-linking density of simplified etch-and-rinse adhesives.

MATERIALS AND METHODS

Four commercial adhesives (XP Bond, Adper Single Bond 2, Tetric N-Bond, and Ambar) were selected, and resin disks 5 mm in diameter and 1.0 mm thick were prepared and light cured for 20, 40, or 80 s using an LED light-curing unit at 1200 mW/cm2. Water sorption and solubility were evaluated over a 28-day period. For polymer cross-linking density, additional specimens were prepared and their Knoop hardness measured before and after immersion in 100% ethanol. The data from each test were evaluated using a two-way ANOVA and Tukey's test (α = 0.05).

RESULTS

The XP Bond adhesive showed higher water sorption (similar to Adper Single Bond 2) and solubility (p < 0.05) than did the other materials. Prolonged exposure times did not reduce the water sorption but did reduce the solubility of all tested materials (p < 0.05). For Ambar, the increase in the exposure time resulted in a significantly lower percent reduction in hardness.

CONCLUSION

Water sorption, solubility, and cross-linking density of the materials selected in this study seem to be mainly influenced by the adhesive composition. Prolonged light exposure times reduced the solubility of the materials.

Influence of photopolymerization parameters on the mechanical properties of polymer-ceramic composites applied in the conservative dentistry

In this paper, the results of study of mechanical properties for four commercial polymer-ceramic composites applied in the conservative dentistry are presented, including one new silorane based composite and three standard composites based on methacrylate compounds. Influence of the type of light of diode and halogen polymerization lamps on the microhardness, flexural strength and elasticity were studied. Both exposed and unexposed specimens were taken into account. An exposure time was also differentiated (40 sec and 60 sec). Basic statistics of the analysed material parameters were determined. A post hoc test (Newman-Keuls) was performed in order to evaluate differences between microhardness of the materials studied, as well as Kruskal-Wallis test to evaluate differences in flexural strength and elasticity modulus of the material. It has been indicated that there is an impact of the type of lamp on the microhardness and flexural strength of composites with methacrylate matrix and lack of such impact in the case of composites containing siloranes. Additionally, it has been found that an increase of photopolymerization time has a significantly different impact on the mechanical properties depending on the type of irradiated material.

Temperature changes in the pulpal chamber and the sealing performance of various methods of direct pulp capping of primary teeth

AIM

To compare changes in pulpal chamber temperature during the visible-light curing of direct pulp capping compounds and various modes of diode laser irradiation without prior placement of a pulp capping compound and the resultant seals.

MATERIALS AND METHODS

Pulp exposure holes were made in 100 extracted human primary first molars, which were randomly assigned to ten equal groups. The holes were sealed by (a= Group 1, 2, 3, 4, 5, 6 and 7) different pulp capping compounds which were cured using various types of visible-light curing units or (b=Group 8, 9 and 10) diode laser irradiation without prior application of a pulp capping compound. Pulpal chamber temperatures were recorded during the procedure, and the resultant seals were examined under a scanning electron microscope.

RESULTS

Visible-light curing of the pulp capping compounds and diode laser irradiation at a 0.7 W output power can cause non-injurious temperature rises in the pulpal chamber. At higher output powers of the diode laser, the temperature rises are sufficient to cause thermal injury. The seals were complete when pulp capping compounds were used for direct pulp capping, but were incomplete when laser irradiation without prior placement of a pulp capping compound was used for the identical purpose.

CONCLUSION

The visible-light curing of pulp capping compounds is not harmful to vital pulp, and provides an effective seal of the pulp exposure hole. Laser irradiation is not an effective sealant, and can cause thermal injury to vital pulp at high output powers.

Influence of shade and light-curing distance on the degree of conversion and flexural strength of a dual-cure core build-up resin composite

PURPOSE

To investigate the influence of shade and light-curing distance on the degree of conversion (DC) and flexural strength (FS) of a dual-cure core build-up resin composite.

METHODS

135 specimens were prepared and divided into three main groups according to the shade of the composite core material; dentin, blue and white shades. Each group was further subdivided into three subgroups according to the light-curing distance; 0 mm, 3 mm and 5 mm. The DC was measured using FTIR spectrometer. For testing the FS, the mini flexural test specimens were prepared and subjected to three point bending test in a universal testing machine. The results were analyzed using two-way and one-way ANOVA followed by Duncan's Multiple Range Test. The significance level was set at P = 0.05.

RESULTS

Both the DC and FS of the dual-cure core build-up material used in this study were influenced by the shade of the material and the light-curing distance. The blue shade exhibited the highest percentage DC values while the white shade revealed the lowest percentage DC. The dentin shade at 0 mm light-curing distance exhibited the highest mean FS value; however the 3 mm and 5 mm light-curing distance of the white shade showed the lowest mean FS values.

Effect of cement shade and light-curing unit on bond strength of a ceramic cemented to dentin

PURPOSE

To evaluate the effect of cement shade, light-curing unit, and water storage on tensile bond strength (σ) of a feldspathic ceramic resin bonded to dentin.

MATERIALS AND METHODS

The dentin surface of 40 molars was exposed and etched with 37% phosphoric acid, then an adhesive system was applied. Forty blocks of feldspathic ceramic (Vita VM7) were produced. The ceramic surface was etched with 10% hydrofluoric acid for 60 s, followed by the application of a silane agent and a dual-curing resin cement (Variolink II). Ceramic blocks were cemented to the treated dentin using either A3 or transparent (Tr) shade cement that was activated using either halogen or LED light for 40 s. All blocks were stored in 37°C distilled water for 24 h before cutting to obtain non-trimmed bar-shaped specimens (adhesive area = 1 mm2 ± 0.1) for the microtensile bond strength test. The specimens were randomly grouped according to the storage time: no storage or stored for 150 days in 37°C distilled water. Eight experimental groups were obtained (n = 30). The specimens were submitted to the tensile bond strength test using a universal testing machine at a crosshead speed of 1 mm/min. The data were statistically analyzed using ANOVA and Tukey's posthoc tests (a = 0.05).

RESULTS

The mean bond strength values were significantly lower for the corresponding water stored groups, except for the specimens using A3 resin cement activated by halogen light. There was no significance difference in mean bond strength values among all groups after water storage.

CONCLUSION

Water storage had a detrimental effect under most experimental conditions. For both cement shades investigated (Tr and A3) under the same storage condition, the light-curing units (QTH and LED) did not affect the mean microtensile bond strengths of resin-cemented ceramic to dentin.

Temperature rise during photo-polymerization for onlay luting

PURPOSES

(1) To measure the temperature rise during long-time irradiation needed to lute adhesive indirect restorations, with one halogen and five LED high-power lamps, in a simulated oral environment, and (2) to propose a technique to reduce heat.

METHODS

Temperature within the pulp chamber of an extracted human molar in a 35 degrees C water bath, before and after restoration with a ceramic onlay, was continuously recorded during 3 x 120 seconds of irradiation for different curing regimens, with and without cooling by compressed air, water and water spray. Temperature rise in a thermo-insulated well was also measured during 120 seconds of irradiation with LEDemetron II and TuTu.

RESULTS

Maximal temperature rise of 6.2 degrees C/7.7 degrees C on intact/onlay restored tooth was found after 3 x 120 seconds of irradiation. Compressed air application reduced the temperature by 4 degrees C for LEDemetron II, while water spray increased the temperature by 15.1 degrees C for TuTu. Temperature decreased with irradiation distance, except for LEDemetron II. Air was heated up to 65 degrees C after 120 seconds of irradiation in an insulated well with TuTu.

Influence of the interaction of light- and self-polymerization on subsurface hardening of a dual-cured core build-up resin composite

OBJECTIVE

To investigate the influence of time delay and duration of photo-activation on subsurface microhardness of a dual-cured resin composite.

MATERIAL AND METHODS

A commercially available dual-cured core build-up resin composite (Rebilda DC) was filled in cavities (diameter: 4.0 mm; height: 6.0 mm) of polystyrene molds and light-cured for 20 or 60 s either immediately after the filling procedure (time delay 0 s) or after a time delay of 30, 90, 180 or 300 s. Non-irradiated self-cured specimens served as a control group (n = 15). Specimens were stored in complete darkness and at 100% relative humidity at 37°C for 2 weeks and cross-sectioned. Knoop Hardness Numbers (KHNs) were measured six times per depth and averaged at distances of 0.25, 0.50, 1.00, 2.00, 3.50 and 5.50 mm from the light-exposed surface. Data were statistically analyzed using one- and two-way ANOVA followed by Scheffé's post-hoc test at a level of significance of 0.05.

RESULTS

Mean hardness values in all experimental groups ranged between 54.3 ± 2.1 and 58.1 ± 2.3 KHN. Light-curing did not significantly increase composite KHN at any depth measured. Delaying light exposure had no influence on KHN, irrespective of depth. A longer light-exposure time (60 versus 20 s) resulted in significantly higher KHN only at depths of 3.50 and 5.50 mm.

CONCLUSION

Photo-activation of the tested dual-cured resin composite provided no clinically relevant benefit compared to self-curing regarding the degree of hardening.

Comparison of shear bond strength of orthodontic brackets bonded with light emitting diode (LED)

Light-emitting diode (LED) light curing units (LCU) have recently been used to polymerize resin-based orthodontic adhesives and preliminary studies indicate their use has been successful. The objectives of this study were to evaluate the shear bond strength (SBS) oforthodontic brackets bonded to enamel with a LED LCU (LEDMAX 4, Hilux, Kulzer comp.) at 10, 20 and 40 seconds and comparing them with that of 40 seconds light exposure from a conventional halogen-based LCU (Hilux unit, Heraeus Kulzer comp.). Also to assess the amount of adhesive remaining on the tooth after debonding using Adhesive Remnant Index (ARI). 120 extracted human premolars were divided into 4 groups of 30 each. After photo polymerization, all the samples were stored in distilled water at 37 degrees C for 24 hours and then subjected to a shear force with universal testing machine until bracket failure. All the recordings were evaluated statistically ANOVA and Turkey tests revealed that, no statistically significant differences were found among the shear bond strengths of 40 sec halogen (10.15 +/- 1.55), 20 sec LED (9.58 +/- 1.71) and 40 sec LED (10.34 +/- 1.83) cured groups; but the bond strength of 10 sec cure LED group (7.56 +/- 1.47) showed significantly lower than the other groups. Chi-square comparisons indicated that there were no significant differences in the ARI scores between the 4 groups tested. The results of this study are promising for orthodontic application of LED curing units in clinics, but further in vivo trials should be performed before validation.

Effect of X-ray radiation dose on the bond strength of different adhesive systems to dentin

PURPOSE

To investigate the influence of different x-ray radiation doses on the bond strength of adhesive restorations to dentin using different bonding strategies.

MATERIALS AND METHODS

Flat dentin surfaces on human molars were obtained and cylinder-shaped specimens for the microshear bond test were built up with a composite (Z250, 3M ESPE), using three adhesive systems: a two-step etch-and-rinse (Single Bond 2--SB2, 3M ESPE), a two-step self-etching (Clearfil SE Bond--CSE, Kuraray), or a single-step self-etching (Adper Prompt--ADP, 3M ESPE). The specimens were assigned to 4 groups (n = 10), according to the x-ray dose: 0 (control), 5, 35, or 70 Gy. Radiation was directed to the surface of the resin cylinders. Microshear testing was conducted after 24 h, and the failure modes classified under magnification (200X). Data were submitted to two-way ANOVA and Holm-Sidak's test (p < or = 0.05). A nonlinear regression analysis was carried out with bond strength as dependent variable.

RESULTS

Bond strength results were dose and material dependent. SB2: control > 5 = 35 > 70; CSE: control = 5 > 35 = 70; ADP: control = 5 = 35 = 70. Generally, SB2 > CSE > ADP. The nonlinear regression plots showed that in general, an increase in radiation dose may predict a decrease in bond strength (R2 > or = 0.905). Failure modes were dependent on the bonding system, generally with no significant influence of radiation.

CONCLUSION

X-ray radiation might present a dose-dependent detrimental effect on the bond strength of resin composite restorations to dentin.

Effect of Er:YAG laser on dentin bonding durability under simulated pulpal pressure

PURPOSE

To evaluate the effects of Er:YAG laser ablation on the microtensile bond strength and the nanoleakage of Er:YAG-lased dentin bonded to a self-etching adhesive system with and without pulpal pressure.

MATERIALS AND METHODS

Twenty flat dentin surfaces were obtained from extracted molars. Ten specimens were irradiated by Er:YAG laser, other specimens (control group) were ground using #600 SiC paper. Direct communication to the pulp chamber was created by cutting at a level approximately 1 mm below the cementoenamel junction and parallel to the occlusal surface. The experimental groups were exposed to a simulated pulpal pressure of 15 cm H2O. Each specimen was restored using an adhesive and a photocured composite. The specimens were then sectioned vertically to obtain dentin/adhesive slabs. Ninety-six slabs were prepared for microtensile bond testing. Sixty-four slabs were immersed in ammoniacal silver nitrate tracer solution for 18 h, then rinsed thoroughly, and immersed in photodeveloping solution for 6 h prior to their examination by FE-SEM.

RESULTS

The method of dentin preparation and the pulpal pressure storage condition significantly affected the microTBS, while the storage duration did not (p < 0.05). The nanoleakage patterns observed in the dentin/bond interface differed depending on whether the dentin was conventionally prepared or ablated by Er:YAG laser.

CONCLUSION

Er:YAG laser ablation to dentin adversely affected the microTBS and the sealing ability of SE Bond bonded to dentin under simulated pulpal condition.

Effect of radiotherapy on the microleakage of adhesive systems

PURPOSE

The aim of this in vitro study was to evaluate the effect of radiotherapy on the microleakage of three adhesive systems: a one-step self-etching, a two-step self-etching, and an etch-and-rinse system.

MATERIALS AND METHODS

Box-shaped Class V cavity preparations were prepared on the buccal surfaces of 84 extracted human molars. The molars were randomly assigned into 6 groups (n = 14) according to the irradiation and adhesive system as follows: G1, Clearfil S3 Bond (irradiated); G2, Clearfil SE Bond (irradiated); G3, Prime & Bond NT (irradiated); G4, Clearfil S3 Bond (nonirradiated); G5, Clearfil SE Bond (nonirradiated); and G6, Prime & Bond NT (nonirradiated). The cavities were restored with composite resin (Filtek Z 250). After restoration of the samples, a total dose of 60 Gy was delivered in 2 Gy/d fractions for 5 days per week for 6 weeks for the related groups. All specimens were thermocycled for 200 cycles between 5 degrees C and 55 degrees C using a dwell time of 60 s in each bath and then placed in 0.5% basic fuchsin solution for 24 h at room temperature. Specimens were then rinsed and sectioned; the dye penetration at the enamel and dentin margins was examined using a stereomicroscope, and a score of 0 to 3 was assigned. Data were analyzed using the Kruskal-Wallis and Mann-Whitney U-tests.

RESULTS

No statistically significant difference existed between the irradiated and nonirradiated groups (p > 0.05). Significant differences in microleakage were observed between enamel and dentin (p < 0.01). The microleakage at the dentin margins was greater than at the enamel margins. Prime & Bond NT revealed statistically significantly (p < 0.05) higher leakage scores in dentin than did ClearfilS3 Bond and Clearfil SE Bond.

CONCLUSION

Within the limitations of this study, irradiation application did not affect the microleakage of dental adhesive systems.

Influence of Nd:YAG laser irradiation on microtensile bond strength of adhesive systems to sound or carious dentin

OBJECTIVE

To evaluate the microtensile bond strength of 2 adhesive systems (Adper Single Bond Plus [3M ESPE] and Clearfil SE Bond [Kuraray]) to carious or normal dentin, with or without previous treatment with Nd:YAG laser or Nd:YAG laser associated with fluoride.

METHOD AND MATERIALS

Dentin surfaces of 60 human third molars were exposed. Teeth were divided into 12 groups; groups 1 to 6 were submitted to pH cycling for artificial caries, and groups 7 to 12 remained with normal dentin. Dentin surfaces received 3 treatments: laser Nd:YAG irradiation (60 mJ, 15 Hz, and 0.9 W) for 1 minute; laser Nd:YAG irradiation associated with fluoride in gel; and no treatment (controls). In experimental groups, adhesive systems were applied in accordance with the manufacturers' instructions, and a composite resin block (Filtek Z250, 3M ESPE) was made incrementally for the microtensile bond strength test. The teeth were sectioned serially in both x and y directions, and sticks were submitted to microtensile bond strength testing in a universal testing machine.

RESULTS

According to ANOVA and Tukey (P < .05), the highest mean bond strengths were obtained in groups of normal dentin treated with Clearfil SE Bond (40.65 MPa) and Single Bond (34.2 MPa). The presence of carious dentin significantly decreased the mean bond strengths of the 2 adhesive systems whether or not they were previously laser irradiated. Nevertheless, Clearfil SE Bond presented the best microtensile bond strength on an irradiated surface. Moreover, laser irradiation associated with fluoride also decreased the bond strength values of the 2 adhesive systems.

CONCLUSION

After excavating a cavity with caries-affected dentin, the use of Nd:YAG laser followed by a self-etching adhesive system is the best clinical choice when considering bond strength, compared with the total etching- based system and laser.

Effects of light exposure time on composite resin hardness after root reinforcement using translucent fibre post

OBJECTIVES

The purpose of this in vitro study was to evaluate the Vickers hardness (VHN) of a Light Core (Bisco) composite resin after root reinforcement, according to the light exposure time, region of intracanal reinforcement and lateral distance from the light-transmitting fibre post.

METHODS

Forty-five 17-mm long roots were used. Twenty-four hours after obturation, the root canals were emptied to a depth of 12 mm and the root dentine was artificially flared to produce a 1mm space between the fibre post and the canal walls. The roots were bulk restored with the composite resin, which was photoactivated through the post for 40s (G1, control), 80 s (G2) or 120 s (G3). Twenty-four hours after post-cementation, the specimens were sectioned transversely into three slices at depths of 2, 6 and 10mm, corresponding to the coronal, middle and apical regions of the reinforced root. Composite VHN was measured as the average of three indentations (100g/15 s) in each region at lateral distances of 50, 200 and 350 microm from the cement/post-interface.

RESULTS

Three-way analysis of variance (alpha=0.05) indicated that the factors time, region and distance influenced the hardness and that the interaction timexregion was statistically significant (p=0.0193). Tukey's test showed that the mean VHN values for G1 (76.37+/-8.58) and G2 (74.89+/-6.28) differed significantly from that for G3 (79.55+/-5.18).

CONCLUSIONS

Composite resin hardness was significantly lower in deeper regions of root reinforcement and in lateral areas distant from the post. Overall, a light exposure time of 120 s provided higher composite hardness than the shorter times (40 and 80s).

Influence of ceramic thickness on mechanical properties and polymer structure of dual-cured resin luting agents

OBJECTIVE

To investigate the influence of ceramic thickness on the mechanical properties and polymer structure (degree conversion and cross-linking density) of three dual-cured resin luting agents.

METHODS

Three dual-cured resin luting agents [Linkmax HV (GC), Nexus 2 (Kerr), and Variolink IIHV (Ivoclar-Vivadent)] were polymerized with or without 800 mW/cm2 irradiation through 0-3-mm-thick GN-I (GC) machinable ceramic. Bar-shape specimens were subjected to three-point bending to determine flexural strength (FS) and elastic modulus (EM) after dry storage at 37 degrees C for 24 h. Knoop hardness was measured on the irradiated surface of disk-shaped specimens before (KHN1) and after (KHN2) storage of 100% ethanol solution at 37 degrees C for 24 h. KHN1 and KHN2 were estimated as indirect indicators of degree of conversion (DC) and cross-linking density, respectively. Data were analyzed by one-way ANOVA and Student-Newman-Keuls test for each luting agent, and four mechanical properties were subjected to regression analysis.

RESULTS

For three resin luting agents with dual-cured mode, FS, EM, KHN1, and KHN2 decreased with the increase of ceramic thickness. FS except for Nexus 2 and EM for three resin luting agents had a positive linear relationship with both KHN1 and KHN2.

SIGNIFICANCE

The variables tested behaved differently. When the ceramic thickness increased, the chemical cured components of dual-cured resin luting agents did not produce significant compensation for all variables. Mechanical properties and polymer structure of dual-cured resin luting agents was dependent on the intensity of light irradiation.

Adhesive procedures in daily practice: essential aspects

Adhesive procedures are essential to most restorative protocols used in modern dentistry. Increasing demand and constant interest in new products have stimulated dental manufacturers to produce new adhesive systems and marketing campaigns that announce fast and easy bonding. However, laboratorial and clinical studies show that, usually, ease of application of an adhesive system does not relate to its competence in creating a quality, long-term adhesive interface. This article will present relevant data from the scientific literature to help clinicians understand quality adhesion and achieve excellent results with the current adhesion systems.

Effect of solvent type and content on monomer conversion of a model resin system as a thin film

OBJECTIVE

The purpose of this study was to examine the effect of solvent concentration on the degree of conversion of a model photo-activated resin formulation when placed as a thin film in ambient air.

METHODS

A photo-activated co-monomer mixture (ethoxylated bis-GMA/TEGDMA) (Bisco Inc.) was diluted into six concentrations (from 1.0 to 13.0M) with either acetone or ethanol. A controlled volume of diluted, uncured resin was placed on the horizontal surface of an attenuated reflectance unit and the infrared (IR) spectrum obtained. A light emitting diode light-curing source (Bluephase, Ivoclar/Vivadent) then immediately irradiated the specimen for 10s (n=5). Five minutes after exposure, IR spectra of the cured material were obtained, and monomer conversions were calculated using standard methods that monitored changes in aliphatic-to-aromatic CC absorbance ratios in the uncured and cured states.

RESULTS

In the acetone/model resin system, maximum conversion occurred with 2.5-5.0M solvent. In the ethanol/model resin system, conversion peaked at 2.5M solvent. Above 5.0M solvent, conversion values declined rapidly for both solvents. A 13.0-M solution resulted in near 0% conversion for both solvents. At 2.5 and 5.0M acetone, conversions exceeded those of equivalent concentrations of the ethanol-based system.

CONCLUSIONS

For both an acetone- and ethanol-solvated model resin system, conversion did not immediately decrease with addition of solvent, but instead increased over that of the model resin alone. At higher solvent content (greater than 2.5M ethanol and 5.0M acetone), conversion rapidly declined, with ethanol causing less conversion at equal-molar solvent concentrations.

Precuring of self-etching bonding agents and its effect on bond strength of resin composite to dentin and enamel

OBJECTIVES

To evaluate and compare shear bond strength of 3 self-etching bonding agents to enamel and dentin when the bonding agent is light cured before the application of resin composite or co-cured together with the resin composite.

METHOD AND MATERIALS

One hundred twenty extracted teeth were wet ground to create a flat bonding area on enamel and dentin. Three bonding agents (Adper Prompt-L-Pop, Clearfil SE Bond, and Xeno III) were applied to either dentin or enamel according to the manufacturers' directions. In half of the specimens, bonding agents were light cured immediately after their application (Group PRC). The other half were not light cured until resin composite application (Group COC). Resin composite was placed into a Teflon tube and light cured over the adhesive. Specimens were stored in deionized water for 24 hours at room temperature before being loaded in shear until failure with an Instron testing machine. Shear bond strength (in megapascals) was analyzed with 2-factor ANOVA, separate single-factor ANOVA models for cure and material, and Tukey's Honestly Significant Differences multiple comparison procedure. All testing was performed at the 5% significance level (n=10).

RESULTS

Light-curing the adhesive separately produced significantly higher bond strengths to dentin (P <.001) than did the co-cure method. Group PRC did not produce significantly different bond strengths to enamel (P = .420).

CONCLUSIONS

Pre-curing of self-etching adhesives before curing of the resin composite produces greater bond strength to dentin. The curing technique has no significant effect on enamel bond strength of self-etching adhesives.

Extent of polymerization of dental bonding systems on bleached enamel

PURPOSE

To analyze the extent of polymerization of four adhesive systems on whitened enamel immediately after bonding or delayed for 24 hours and 2 weeks. The effect of prolonged light-curing was also analyzed.

METHODS

One adhesive of each class was investigated: Adper Scotchbond Multi-Purpose (three-step etch-and-rinse), One-Step (two-step etch-and-rinse), Clearfil Protect Bond (two-step self-etching) and Xeno III (one-step self-etching). Enamel fragments were treated with Opalescence Xtra Boost for 30 minutes, powdered and pressed into aluminum pans. Specimens were bonded immediately after bleaching, after 24 hours or after 14 days of storage in 100% humidity at 37 degrees C. Unbleached enamel powder was prepared as control. Extent of polymerization of bonded interfaces was obtained with differential scanning calorimetry (DSC) at 20, 40 and 60 seconds and data were statistically analyzed with 3-way ANOVA and Tukey's post-hoc test.

RESULTS

The extent of polymerization obtained from DSC exotherms of adhesives applied immediately after bleaching was significantly lower compared to controls. Increased extent of polymerization after storage was confirmed for all adhesives and no difference with controls was found after 14 days. Prolonged irradiation time increased curing rate for all the tested adhesives. This study supported the hypothesis that polymerization of the adhesive is reduced after enamel bleaching and delayed adhesive application reverses the polymerization inhibition. Prolonged polymerization intervals may counteract the inhibition of polymerization due to the bleaching procedure; nevertheless further clinical studies should validate this hypothesis.

Dentin bond strength of composites with self-etching adhesives using LED curing lights

AIM

The purpose of this study was to investigate the effect of light-emitting diode (LED) light curing units (LCUs) compared with halogen LCUs on the shear bond strength (SBS) of one nanofill composite (Filtek Supreme) and one microhibrid composite (Artemis) with self-etch adhesives.

METHODS AND MATERIALS

The buccal surfaces of 60 non-carious extracted human molars were flattened to expose dentin and, subsequently, polished for 60 seconds with 600-grit wet silicon carbide abrasive paper. Specimens were assigned into six groups (n=10) according to composite material, self-etch adhesive, and curing light used as follows: Group 1: Adper Prompt L-Pop (AP) and Filtek Supreme (FS) using an Elipar Free Light (EFL); Group 2: AP and FS using an Elipar Free Light 2 (EFL2); Group 3: AP and FS using a Hilux Expert (HE) light, Group 4: AdheSE (AS)+Artemis (AR) using an EFL; Group 5: AS+AR using an EFL2; and Group 6: AS+AR using a HE light. The specimens were thermocycled for 500 cycles (5 masculineC-55 masculineC) and then loaded to failure in a Zwick universal testing machine at a crosshead speed of 5 mm/minute. SBS values were calculated as megapascals (MPa) and statistically analyzed using the one-way analysis of variance (ANOVA) test at a significance level of 0.05.

RESULTS

Mean SBS (+/- standard deviations) values were as follows: Group1: 15.99+/-5.18; Group 2: 18.76+/-6.71; Group 3: 17.70+/-5.04; Group 4: 16.93+/-3.99; Group 5: 18.01+/-5.19, and Group 6: 17.46+/-5.40. There were no statistically significant differences for SBS to dentin among the groups tested.

CONCLUSION

The LED curing lights used in the study seem to be comparable with the halogen curing light for nanofill and microhybrid composites used in conjunction with self-etching systems in dentin. The EFL2 reduces curing time, which can be considered as an advantage.

Effect of LED light-curing time for the adhesive resin on the modulus of elasticity

PURPOSE

To evaluate the elastic modulus of successive layers where an adhesive resin was cured by different light-curing times.

METHODS

Eighty dentin discs which were 2 mm thick were prepared from 40 sound third molars. The dentin discs were further divided into four groups and bonded with 3M Single Bond 2 and cured with an LED for 5, 10, 15 and 20s. Bonded specimens were restored with a microhybrid resin composite. Specimens were cut perpendicular to the resin dentin interface, embedded in epoxy resin, and polished. Polished specimens were evaluated for the elastic modulus at the layer of dentin, hybrid layer, adhesive resin, and resin composite at 24 hours after preparation.

RESULTS

Light-curing times influenced the elastic modulus of hybrid layer and adhesive resin. The significant differences of elastic modulus among successive layers were found. The results suggested that extension of light-curing times of adhesive resin from 5 to 20 seconds increased the mechanical properties of the resin dentin interface.

Effect of polymerization accelerator on dentin bonding of one-step bonding agent

The aim of this study was to enhance the bond strength of one-step bonding agents to dentin. In particular, the focus was on using Catabrush the applicator system of AQ Bond Plus. Catabrush was supplemented with N-phenylglycine and aromatic sulfinate as polymerization accelerators, as N-phenylglycine was reportedly beneficial in improving the bond strength to dentin. The results indicated that the bond strength to dentin was significantly augmented and the photo-polymerization as well as the chemical polymerization were both improved even in the moistened dentin when 1.0 wt% N-phenylglycine was added to AQ Bond Plus agent, hence implying significantly higher bond strength to dentin. It was therefore concluded that N-phenylglycine is useful as a polymerization accelerator to be adopted in the applicator system for one-step bonding agents.

The Effect of Modifying the Self-etchant Bonding Protocol on the Shear Bond Strength of Orthodontic Brackets

OBJECTIVE

To compare the shear bond strength (SBS) of orthodontic brackets when the self-etching primer (SEP) and the bracket adhesive are light cured either separately or simultaneously.

MATERIALS AND METHODS

Seventy-five human molars were randomly divided into five equal groups. Brackets precoated with Transbond XT composite adhesive were used. The five protocols were: Group 1 (control), the SEP Transbond Plus was applied, brackets placed, and adhesive light cured for 20 seconds; Group 2, SEP Adper Prompt L-Pop was applied, light cured, brackets placed, and light cured; Group 3, the same SEP as in Group 2 was used, however, the SEP and bracket adhesive were light cured together; Group 4, SEP Clearfil S3 Bond was applied, light cured, brackets placed, and light cured; and Group 5, the same SEP as in group 4 was used, however, the SEP and the adhesive were light cured together. The teeth were debonded using a universal testing machine, and the enamel was examined for residual adhesive. Analysis of variance was used to compare the SBS.

RESULTS

The SBS of Clearfil S3 Bond after one light cure and two light cures were significantly greater than the bonds of brackets using Transbond Plus. Brackets bonded using Adper Prompt L-Pop after one light cure and two light cures were not significantly different from the other groups. The groups did not differ significantly in their bracket failure modes.

CONCLUSION

Only one light curing application is needed to successfully bond brackets when using SEPs and adhesives. This approach can potentially reduce technique sensitivity as well as chair time.

Influence of light-curing units on dentin bond strength after bleaching

PURPOSE

The aim of this in vitro study was to comparatively evaluate the influence of three different light curing units (QTH Hilux, LED SmartLite, PAC Plasmaster) on shear bond strength of an adhesive system (Clearfil SE Bond ) after bleaching.

MATERIALS AND METHODS

Sixty molars were used for this study. Carbamide peroxide was applied to the floor and wall of the dentin surfaces in bleached groups for 3 weeks. Each week the paste was renewed for the bleached group. Teeth were sectioned mesiodistally. The roots of the sectioned teeth were mounted in a cylindrical mold using chemically cured acrylic resin. Composite resin was added to the center of flattened dentin surfaces with an internal diameter of 3 mm and height of 3 mm. The bonding procedure was performed in the bleached test groups as follows: G1: immediately/QTH; G2: after 1 week/QTH; G3: after 2 weeks/QTH; G4: immediately/LED; G5: after 1 week/LED; G6: after 2 weeks/LED; G7: immediately/PAC; G8: after 1 week/PAC; G9: after 2 weeks/PAC. The non-bleached groups (control group) were G10: QTH; G11: LED; G12: PAC. Specimens were mounted in a universal testing machine and shear load was applied at a crosshead speed of 1 mm/min until failure. Bond strength values were calculated as MPa and the comparisons were made statistically using one-way ANOVA with light source and bleaching treatment) as the two factors.

RESULTS

The mean values of shear bond strength in MPa were: G1 (12.23), G2 (19.18), G3 (23.08), G4 (13.07), G5 (21.01), G6 (25.27), G7 (12.55), G8 (19.06), G9 (25.41), G10 (24.54), G11 (26.99), G12 (25.97). No statistical difference was found between the control group and groups bonded two weeks later. The bond strength values of the control group and those bonded 2 weeks later were higher than other groups. Statistically significant differences were found between the immediate and 1-week groups (p < 0.01). Immediately bonded groups had the lowest bond strength compared to the others (p < 0.05). No significant differences in bond strength were observed among three lightcuring units (p > 0.05).

CONCLUSION

It was concluded that different light-curing units had no effect on shear bond strength of bleached dentin. A 2-week delay in restoration after bleaching improved the reduced bond strength of resin composite.

Characterization of photopolymerization of dentin adhesives as a function of light source and irradiance

Manufacturers have attempted to address the limitations associated with dentin bonding by eliminating as many steps as possible in the bonding protocol. Theoretically, this approach increases the efficiency of the procedure and reduces technique sensitivity. These trends are reflected in the introduction of all-in one, single-step adhesive systems; the increased concentration of acidic resin monomers in these systems allows for simultaneous etching and priming of the prepared dentin surface. Ideally, the degree of monomer conversion would be high enough that the acidic reaction would be self-limiting. The purpose of this study was to investigate the effect of light irradiance and source on the photopolymerization of three commercial dental adhesives by monitoring the double bond conversion as a function of time during and after irradiation. The photopolymerization curing efficiency of the commercial adhesives investigated in this study varied as a function of light source and distance. The use of LED performed better than the halogen light in terms of polymerization rate and degree of conversion for the commercial single-step, sixth generation adhesive, Adper Prompt. In contrast, polymerization of commercial single-bottle, fifth generation adhesive, Single Bond and One-Up Bond F, was mainly a function of exposure time, irrespective of the two light units or intensities.

Nd:YAG laser influence on microtensile bond strength of different adhesive systems for human dentin

OBJECTIVE

The purpose of this study was to investigate the influence of Nd:YAG on microtensile bond strength (microTBS) of different adhesive systems for human dentin.

BACKGROUND DATA

Lasers have been widely used in dentistry. New adhesive systems with different chemical compositions are introduced every year, and it is important to investigate the bonding of new adhesive systems to dentin irradiated with laser.

METHODS

The occlusal surfaces of third molars were removed to obtain flat dentin surfaces. The teeth were randomly divided into six groups. Each adhesive system was applied, according to manufacturers' instructions, to surface dentine with and without Nd:YAG laser irradiation (0.9 W, 15 Hz, 60 mJ per pulse). A block of composite resin was built over the adhesive layer. The specimens were sectioned to obtain 0.70 x 0.70 mm of transversal section. Twenty test specimens were selected for each group, and were then submitted to microTBS on a universal testing machine.

RESULTS

According to Student's t-test, for Single Bond, there was no statistically significant difference without (49.32 MPa) and with (47.34 MPa) laser application (p = 0.60). For the Tyrian SPE/One Step Plus, microTBS value with laser (27.09 MPa) was statistically higher than without laser (19.13 MPa), as well as for Adper Prompt L-Pop (22.85 and 13.78 Mpa; p < or = 0.01).

CONCLUSION

The application of Nd:YAG laser to dentin provided an increase in the bond strength values for the Tyrian SPE/One Step Plus and Adper Prompt L-Pop adhesive systems, but did not influence the bond strength values of the Single Bond adhesive system.

Water sorption and solubility of dentin bonding agents light-cured with different light sources

OBJECTIVE

The aim of this study was to compare water sorption (WS) and solubility (WSB) of different dentin bonding agents (DBA) as regards classification and light-activation system. The null hypotheses were: (1) there is no difference among DBA with respect to water sorption and solubility; (2) there is no effect of light-curing source on water sorption and solubility of DBA.

METHODS

The tested materials were: three-step etch-and-rinse (ScotchBond multi-purpose and Heliobond-control groups), two-step etch-and-rinse (Excite, Adper Single Bond, Adper Single Bond 2), self-etching (Adhse) and all-in-one (Xeno III) systems. For each material, six specimens were prepared (0.8mmx5.5mm) for each light-activation device: halogen lamp (control) or light-emitting diodes (LED). They were transferred to desiccators until a constant mass was obtained (m(1)), subsequently immersed in deionized water until no alteration was obtained (m(2)). Following, the specimens were reconditioned to constant mass in desiccators (m(3)). The volume (V) of each specimen was calculated (mm(3)). WS and WSB were determined using the equations (m(2)-m(3)/V) and (m(3)-m(1)/V), respectively. Data were subjected to one-way analysis of variance and Tukey test (p<0.05). The influence of photo-activation units was analyzed by t-test.

RESULTS

Higher values of WS and WSB were observed for the two-step etch-and-rinse and all-in-one systems. The employed light-activation unit also affected the tested characteristics. Thus, the anticipated null hypotheses were rejected.

CONCLUSIONS

Simplified systems were more susceptible to water adverse and they may become more prone to degradation over time regardless of the type of light-activation source.

Effect of light curing type on cytotoxicity of dentine-bonding agents

AIM

To compare the cytotoxic effects of dentine-bonding agents (DBAs) polymerized with two different curing units at 24 h and 72 h on L-929 cells.

METHODOLOGY

Disc-shaped test samples of light-activated DBAs were prepared according to manufacturers' instructions and cured with either conventional quartz tungsten halogen or light-emitting diode light curing units (LCUs). After curing, the samples were transferred into a culture medium for 24 h. Eluates were obtained and pipetted onto L-929 mouse fibroblast cultures (3 x 10(4) cells per well), incubated for evaluation after 24 and 72 h. After both incubation periods, measurements were performed by an dimethylthiazol diphenyltetrazolium assay. The degree of cytotoxicity for each sample was determined according to the reference value represented by the cells with a control (culture without sample). Statistical significance was determined by a three-way analysis of variance followed by the Mann-Whitney U-test.

RESULTS

No significant three-factor interaction occurred amongst LCUs, DBAs and time factors (P = 0.955). LCUs and DBAs had a significant two-factor interaction (P < 0.001). In general, the test materials cured with the light-emitting diode LCU demonstrated higher cell survival rates when compared with the those cured with the quartz tungsten halogen.

CONCLUSIONS

Differential toxic effects of the DBAs cured with the quartz tungsten halogen or the light-emitting diode on the fibroblast cells may prove to be very important when suitable DBAs or LCUs are used for operative restorations.

Influence of light-curing sources on polymerization reaction kinetics of a restorative system

PURPOSE

To determine the effect of using a variety of commercial light-curing units on polymerization of a dentin-bonding agent (Adper Single Bond) and of a resin composite (Filtek Z250).

METHODS

Infrared (IR) spectra were obtained kinetically at one scan/second at 2 cm(-1) resolution for a period of 5 minutes and were analyzed for: maximum conversion rate (%/s), time into exposure when maximum rate occurred (seconds), conversion at maximum rate (%), and total conversion (%) at 300 seconds by comparison of aliphatic-to-aromatic absorption IR peak ratios, before and after polymerization. Light units used were: QTH 540 mW/cm2 (XL3000); LED 750 mW/cm2 (Elipar FreeLight 2); PAC 2,130 mW/cm2 (ARC II). Exposure followed manufacturers' recommendations: dentin bonding agent for 10 seconds, RC for 20 seconds (QTH), and 10 seconds (LED and PAC). Polymerization kinetics was evaluated at the bottom surface (2.5 mm thick) for the resin composite and as a thin film for the dentin bonding agent on the diamond surface of an attenuated total reflectance accessory in the IR spectrometer. Values (n = 5) were compared using ANOVA and Tukey's pairwise post-hoc test: pre-set alpha 0.05.

RESULTS

PAC produced the highest total conversion and conversion rate for the resin composite (P < 0.05). Total conversion was lower for dentin bonding adhesive using PAC than with LED or QTH (P < 0.05). LED provided the highest proportion of conversion at the maximum rate with respect to conversion at 300 seconds for both materials. QTH demonstrated the lowest maximum rate value that occurred at a longer time into exposure (P < 0.05). Polymerization kinetic parameters varied greatly between the restorative materials as well as among light-curing unit types when compared to values observed when using a QTH light as control.

Effect of two light-emitting diode (LED) and one halogen curing light on the microleakage of Class V flowable composite restorations

AIM

The disadvantages of light cured composite resin materials with respect to microleakage are predominantly a result of polymerization shrinkage upon curing. It has been shown curing methods play a significant role in polymerization shrinkage of light-cured composite resins. The purpose of this study was to investigate the effect of light-emitting diode (LED) light curing units (LCUs) compared with a halogen LCU on microleakage of three different flowable composites using self-etch adhesives.

METHODS AND MATERIALS

A total of 63 extracted human premolars were prepared with standardized Class V cavity preparations on the buccal and lingual surfaces of each tooth. The occlusal margin of the cavities was located on the enamel and the gingival margin was on dentin. Teeth were randomly assigned to three groups of 21 teeth each as follows: Group 1: Adper Prompt L-Pop + Filtek Flow (3M ESPE); Group 2: AdheSE + Tetric Flow (Ivoclar, Vivadent); and Group 3: Clearfil Protect Bond + Clearfil Protect Liner F (Kuraray Medical Inc.). All the groups were subdivided into three groups according to the curing lights used (n=7). Two LED LCUs, Elipar FreeLight and Elipar FreeLight 2 (3M ESPE), and one halogen-based LCU, Hilux Expert (Benlioglu ), were used. All teeth were then immersed in 0.5% basic fuchsin dye solution for 24 hours after thermocycling (500 cycles; between 5 degrees C to 55 degrees C). The teeth then were longitudinally sectioned and observed under a stereomicroscope (40X magnification) by two examiners. The degree of dye penetration was recorded separately for enamel and dentin. Data were analyzed with the Kruskal-Wallis and Mann-Whitney tests with the Bonferroni correction.

RESULTS

No statistically significant differences in microleakage were observed between groups either on enamel or dentin (p>0.05).

CONCLUSION

With the limitation of this in vitro study, the differences in microleakage between LCUs used were not statistically significantly different. Elipar Free Light 2 reduces curing time which can be considered as an advantage.

The effect of application sustained seating pressure on adhesive luting procedure

OBJECTIVES

To evaluate the effect of short versus long application seating pressure on the bond strength of resin blocks, luted with a dual-cured resin cement (Panavia F) to pre-coated or non pre-coated dentin with an hydrophobic light-cured adhesive (Clearfil Protect Bond).

METHODS

Sixteen non-carious human third molars were randomly divided into six Groups (four teeth each). Cylindrical composite blocks were luted with Panavia F (Group Ia) and with Clearfil Protect Bond with Panavia F (Group IIa) and seating pressure was applied for 5s. In Groups Ib and IIb, the two bonding procedures were respectively repeated, but the resin cylinder was maintained under constant pressure during the entire 3min polymerization period for the resin cement. After storing in distilled water for 24h, 0.9mmx0.9mm sticks were produced from these luted specimens for microtensile bond testing and SEM examination.

RESULTS

The use of Clearfil Protect Bond with Panavia F produced higher bond strengths than the use of Panavia F (p<0.05). Extending the time of pressure application up to 3min increased the bond strength (p<0.001) and improved the integrity of the interfacial quality.

SIGNIFICANCE

The application of sustained seating pressure during luting procedures and the additional use of a hydrophobic light-cured adhesive both improve the final bond strength of the resin cement.

Shear Bond Strength of Dual-cured and Self-cured Resin Composites to Dentin Using Different Bonding Agents and Techniques

When using resin composites as core buildup materials, dual-cured resin composites show higher shear bond strength to dentin than self-cured resin composites. Light activation of bonding agents prior to applying a resin composite core can improve the shear bond strength of resin composites to dentin.

Influence of Light Irradiation Condition on Microshear Bond Strength of Dual-cured Resin Luting Agents

The purpose of this study was to evaluate the microshear bond strength and bond durability between ceramic and two dual-cured resin luting agents irradiated by different light intensities. Ceramic specimens were bonded with two resin bonding systems: Ceramic Primer and Linkmax HV (CP/LMHV) and Monobond S and Variolink IIHV (MBS/VLIIHV), and were either irradiated by 800, 310, 160, 80, and 40 mW/cm2 light or not irradiated. Bond strength was measured after 24-hour water storage at 37 degrees C and after subsequent 10,000 times of thermal cycling. Failure modes were determined by stereomicroscopy. After 24-hour water storage, there were no significant differences among the various irradiation conditions for both MBS/VLIIHV and CP/LMHV. However, regardless of light intensity, MBS/VLIIHV showed higher bond strength than CP/VLIIHV at each thermal cycling, except for no irradiation condition at 10,000 thermal cycles. In conclusion, thermal cycling significantly reduced the bond strength for all groups.

Dentin bonding of light- and self-curing resin composites using simplified total- and self-etch adhesives

OBJECTIVE

The purpose of this study was to evaluate the influence of (1) the curing mode of resin composites and (2) activators for dual curing of the bonding on dentin bond strength.

METHODS

The light-curing resin composite Brilliant (B) and the self-curing resin composite Brilliant MH were bonded with the following adhesives (n = 10): OptiBond FL, Excite, Prime&Bond NT, OptiBond Solo Plus, Adper Prompt L-Pop, Clearfil SE Bond, Xeno III, and AdheSE. Excite, Prime&Bond NT, and OptiBond Solo Plus were also used in combination with activators for dual curing. Tensile bond strengths were measured after 24 hours of water storage (37 degrees C), and fractured surfaces were analyzed in the scanning electron microscope.

RESULTS

Except for Excite/dual curing and Prime&Bond NT/dual curing, bond strengths with Brilliant MH were significantly lower than with Brilliant. Activators significantly increased bond strengths in Excite/Brilliant MH, but not in Prime&Bond NT/Brilliant MH and OptiBond Solo/Brilliant MH.

CONCLUSIONS

This study confirms the incompatibility between self-curing resin composites and simplified bonding systems containing acidic components. Activators for dual-curing the bonding eliminated this chemical incompatibility only in 2 of 3 bonding systems. The use of these activators in combination with light-curing resin composites must be avoided.

Polymerization kinetics of dental adhesives cured with LED: correlation between extent of conversion and permeability

OBJECTIVES

The aim of this study was to analyze the polymerization kinetics of different adhesive films in relation to their permeability after exposure to different LED curing units.

METHODS

One adhesive from each class was analyzed: a three-step etch-and-rinse (OptiBond FL; Sybron-Kerr), a two-step etch-and-rinse (One-Step, Bisco), a two-step self-etch (Clearfil Protect Bond, Kuraray) and a one-step self-etch adhesive (Xeno III; Dentsply DeTrey). Adhesive films were prepared and cured with SmartLite IQ (Dentsply) or L.E. Demetron I (Demetron Kerr) up to complete curing. Polymerization kinetic curves of the tested adhesives were obtained with differential scanning calorimetry (DSC). In particular, total reaction time and extent of polymerization (Ep) at 20, 40 or 60s were compared. Permeability of the adhesive films was evaluated on flat dentin surfaces of human extracted teeth connected to a permeability device and statistically analyzed.

RESULTS

Total reaction time differed among the adhesives tested: OptiBond FL<Clearfil Protect Bond<One-Step<Xeno III with both curing units (p<0.05). At 20s OptiBond FL showed the highest Ep, while the lowest values were obtained with One-Step and Xeno III (p<0.05). E(p) increased when curing time was prolonged (40 and 60s) for all adhesives tested (p<0.05), however, on simplified adhesives, incomplete polymerization took place even after prolonged exposure intervals. An inverse correlation was found between Ep of the adhesives and their permeability using LED curing units.

SIGNIFICANCE

This study supports the hypothesis that, longer curing times than those recommended by the respective manufacturer decrease permeability of the bonded interfaces.

Bond strength of resin-based restorations polymerized with different light-curing sources

PURPOSE

To evaluate the influence of different light-curing units on microtensile bond strength of resin composite restorations.

MATERIALS AND METHODS

Standardized Class I preparations (6.0 x 4.5 mm, 2.5 mm deep) were made in extracted human third molars after abrading the cusps. Resin was inserted in bulk using a 3M ESPE restorative system [Adper Single Bond (DBA)/ Filtek Z250 (RC)]. Both materials were polymerized using different light-curing units: QTH at 540 mW/cm(2) (XL 3000, 3M ESPE); LED at 750 mW/cm(2) (Elipar FreeLight2, 3M ESPE); PAC at 2130 mW/cm(2) (Arc Light II, Air Techniques). Nine different light combinations were developed to polymerize both DBA and RC: QTH/QTH; QTH/LED; QTH/PAC; LED/LED; LED/QTH; LED/PAC; PAC/PAC; PAC/QTH; PAC/LED. Restored teeth were stored in distilled water for 24 h at 37 degrees C and then sectioned, yielding stick-shaped specimens with a bonded area of approximately 0.9 mm(2). Specimens were assessed in a testing machine at a crosshead speed of 1 mm/min. The results were analyzed using two-way ANOVA and Tukey's test at a pre-set alpha = 0.05.

RESULTS

The combinations PAC/QTH and QTH/QTH presented the highest bond strength values, and LED/QTH the lowest (p < 0.05). Significantly lower values were observed in combinations when the LED light was used to polymerize DBA compared to QTH and PAC lights, irrespective of the light source used to polymerize RC (p < 0.05). Same light combinations presented similar bond strength values.

CONCLUSIONS

Different light sources influence restoration bond strength. Bond strength is more dependent on the light source used for DBA than for curing RC.

Step-cure polymerization: effect of initial light intensity on resin/dentin bond strength in class I cavities

This in vitro study assessed the effect of a step-cure light curing method on resin/dentin bond strength on the buccal wall of Class I cavities in human teeth. Occlusal enamel was removed to expose a flat dentin surface. Twenty four box-shaped cavities (C-factor = 4.5) were prepared in dentin. Prime&Bond 2.1 was applied and TPH Spectrum (Dentsply) was inserted using a bulk-filling increment. The composite was light-cured using either a step-cure photoactivation technique or a one-step continuous curing method. For step-cure polymerization, the initial cure intensity was varied by changing the distance between the light source and the resin surface. The light-cured resins were cured using four low light intensities: 150(G1), 200(G2), 250(G3) and 300(G4) mW/cm2. In the continuous exposure curing method, the samples were light-activated for 40 seconds at 740 mW/cm2 and irradiation was applied in a box-shaped cavity and a flat cavity (exposed buccal wall, C-factor = 0.22). Samples were prepared for TBS testing by creating bonded beams (of approximately 0.8 mm2) obtained from the buccal wall. The data were analyzed using one-way ANOVA, Tukey Test and Dunnett's Test at a significance level of 0.05. The mean TBS values for the continuous exposure group in the flat and box-shaped cavities were 24.31 and 10.23 MPa, respectively. The corresponding TBS for step-cure polymerization was 23.13 (G3), 18.83 (G2), 14.87 (G1) and 13.26 MPa (G4). Bond strength values to the cavity wall were lower in the three-dimensional cavities and dependent on the light curing method (p < 0.05). The use of a low initial light intensity (200-250 mW/cm2) for 10 seconds followed by high irradiation intensity provided the best bond strengths, similar to bonding in a flat cavity.

Influence of radiation on bond strength

PURPOSE

The aim of this in vitro study was to evaluate the shear bond strength of two adhesive systems--Prime & Bond NT (PBNT) and Clearfil SE Bond (CSEB)--to dentin irradiated before or after adhesive application.

MATERIALS AND METHODS

Thirty extracted molars were sectioned mesiodistally with a diamond bur. The inner surface of each tooth's dentin was ground flat with SiC abrasive papers. The roots of the sectioned teeth were mounted in a cylindrical mold using chemically cured acrylic resin. In groups A1 and B1, a radiation dose of 60 Gy (R) was applied to the dentin surfaces at this point. In all groups, adhesives were applied according to the respective manufacturer's instructions. Cylindrical composite resin restorations (CRR; internal diameter 3 mm, height 4 mm) were then placed on the center of the flattened dentin surfaces. At this point, groups A2 and B2 received 60 Gy of radiation, and groups C1 and C2 remained as nonirradiated controls. Thus, the test groups were: A1: R + PBNT (Primed Bond NT) + CRR; A2: PBNT + CRR + R; B1: R + CSEB (Clearfil SE Bond) + CRR; B2: CSEB + CRR + R; C1: PBNT+ CRR; C2: CSEB+ CRR. Specimens were mounted in a universal testing machine and shear load was applied at a crosshead speed of 1 mm/min until failure. Bond strength values were calculated as MPa and the results were evaluated statistically using repeated measures of two-way ANOVA, with significance set at p < 0.05.

RESULTS

Irradiation significantly affected adhesion of composite to dentin in groups A1 and A2 (p = 0.002). Group A1 showed statistically lower bond strength than group A2 (p < 0.05). No statistically significant differences were found among the other groups (p = 0.49).

CONCLUSION

The time point of irradiation can have an adverse effect on bond strength, depending on the type of adhesive material.

Effect of prolonged photo-irradiation time of three self-etch systems on the bonding to root canal dentine

OBJECTIVES

To evaluate the effect of photo-irradiation time to the adhesive on the regional bond strength of a dual-cure resin core material to root canal dentine using photo and dual-cure adhesives with self-etching primer.

MATERIALS AND METHODS

Post spaces were prepared in extracted premolars and then the root canal dentine was treated with one of the following bonding procedures: (1) Clearfil SE Bond Primer/Bond (SE), (2) Nano-Bond Primer/Photo-cure adhesive (PNB), (3) Nano-Bond Primer/Dual-cure adhesive (DNB). Photo-irradiation was performed for 10 or 20s from a coronal direction. The post spaces were then filled with a dual-cure composite resin (Build-It FR) and light-cured for 60s. After 24h storage, each specimen was serially sliced into 8, 0.6 x 0.6mm-thick beams for the microTBS test. The bond strength data were divided into coronal and apical regions and analysed using three-way ANOVA and Games-Howell multiple comparison (alpha=0.05).

RESULTS

The microTBS of the photo-cure adhesive resin, SE and PNB, significantly decreased (p<0.05) at the apical region when the photo-irradiation time was 10s. However, the bond strength of the SE group was significantly improved at both regions when photo-irradiation time was extended to 20s (p<0.05). There were no differences in microTBS of the photo-cure adhesive resin (PNB) cured for 20s and dual-cure adhesive resin (DNB) (p>0.05).

CONCLUSION

Photo-cure adhesive was effective for application on root canal dentine when the photo-irradiation time was sufficient. Extension of photo-irradiation time to the adhesive improved the bond strength depending on the type of adhesive resin.

The effects of cavity size and incremental technique on micro-tensile bond strength of resin composite in Class I cavities

OBJECTIVE

The purpose of this study was to investigate if incremental-filling technique and cavity size would affect the bond strength of resin composite.

METHODS

Two sizes of Class I cavities were prepared in bovine dentin (large cavities: pi x (5/2)2 x 5 mm3; small cavity: pi x (3/2)2 x 3 mm3). Light-cure resin composite (Clearfil Photocore) with a self-etching primer adhesive (Clearfil SE Bond) was placed into the cavities by bulk filling (C-factor=5) or incremental filling (two layers, C-factor=3) and light-cured. As a control, 3 or 5mm thick resin composite was bonded to the flat dentin surface. After 24h storage in 37 degrees C water, the micro-tensile bond strength was measured at a crosshead speed of 1mm/min. The results obtained were statistically analyzed using two-way ANOVA and t-test at a significance level of P=0.05.

RESULTS

The results obtained showed that there was no significant difference among the filling techniques in small cavities (P>0.05). However, in large cavities, bulk filling presented the lowest bond strength (P<0.05).

SIGNIFICANCE

Not only the filling technique affected the bonding strength to the cavity floor, but the cavity size was also an influential factor in Class I cavities.

Shear Bond Strength with Increasing Light-Guide Distance from Dentin

BACKGROUND

In Class II composite restorations, the adhesive covering the gingival floor of the deep cavity preparation is 2 to 8 mm from the light guide and may not be adequately cured with a typical 10-second curing time.

PURPOSE

The purpose of this study was to evaluate the dentin bond strengths of resin composite when the curing light guide (quartz-tungsten-halogen light) was placed at various distances and to investigate the relationships between radiant exposure, degree of conversion, and shear bond strength.

MATERIALS AND METHODS

Single Bond (3M ESPE, St. Paul, MN, USA) was placed onto the dentin following the manufacturer's directions. Four groups of 10 teeth were cured for 20 seconds through a 0, 2.3, 4.6, or 6.9 mm spacer. Two other groups of 10 teeth were cured through a 4.6 mm spacer for 40 seconds and 60 seconds, respectively. Z100 resin composite (3M ESPE) was placed over the cured adhesive and polymerized at the same distance as the adhesive. After 24 hours of storage in water, the shear bond strengths were tested. The irradiance through each spacer was measured using a digital radiometer. The degree of conversion of the adhesive was determined by near infrared spectroscopy. The data were analyzed using analysis of variance and Tukey-B post hoc tests.

RESULTS

Dentin shear bond strengths decreased significantly with increasing distance, but they increased significantly when the curing time increased from 20 to 40 or 60 seconds. There is a linear correlation between shear bond strength, degree of conversion, and logarithm (radiant exposure).

CONCLUSION

Increasing curing time can compensate for the decreased bond strength owing to a decreased irradiance associated with increased curing distance.

CLINICAL SIGNIFICANCE

Under the conditions of this study, when curing the adhesives in deep proximal boxes with a quartz-tungsten-halogen light, the curing time should be increased to 40 to 60 seconds to ensure optimal polymerization.

Effect of the composite photoactivation mode on microtensile bond strength and Knoop microhardness

OBJECTIVE

This study evaluated the effect of the composite photoactivation mode on microtensile bond strength and Knoop microhardness.

METHODS

Standard class I cavities (3 x 4 x 3mm) were restored with two adhesives systems, Single Bond (SB) and Clearfil SE Bond (CE), and the TPH composite. The photoactivation of the composite was carried out using three modes: Conventional (CO: 400 mW/cm(2) x 40s), Soft-Start (SS: 100 mW/cm(2) x 10s+600 mW/cm(2) x 30s) and Pulse-Delay (PD: 100 mW/cm(2) x 3s+3 min wait+600 mW/cm(2) x 37s). For the microtensile test, beams obtained from the buccal wall bond interface were tested under tension at 0.5mm/min crosshead speed until failure. For the microhardness test, the restorations were sectioned in the mesio-distal direction and indentations were made on the internal composite surface of each half at three different depths. Data of two tests were analyzed using two-way ANOVA and LSMeans (alpha=0.05).

RESULTS

In the microtensile test, SS presented the highest values. PD presented intermediate values without differing significantly from the other modes. For adhesives, SB presented the highest values. In the microhardness test, PD presented the highest values, differing significantly from SS. CO presented intermediate values but without any statistical difference from the others. The SS-CE interaction presented the lowest values with statistical differences from all the others.

SIGNIFICANCE

By the SS technique, the highest bond strength was obtained. However, this technique made it possible for the adhesive system to intervene with the hardness of the composite.

Contraction stress and bond strength to dentinfor compatible and incompatible combinations of bonding systems and chemical and light-cured core build-up resin composites

OBJECTIVE

Recent studies have shown that adhesives containing acidic monomers combined with composites can adversely effect the polymerization reaction producing low bond strengths. This phenomenon may also occur in making composite build-ups, jeopardizing one of the key factors for a successful core build-up restoration. The aim of this study was to investigate the contraction stress development and bond strength to dentin of core build-up resin composites combined with adhesives of various acidities. In addition the hypothesis tested was that light irradiation through chemical-cured composites during curing does not influence contraction stress or bond strength to dentin.

METHODS

The chemical-cured (Clearfil Core) and light-cured (Clearfil Photo Core) core build-up resin composites were combined with two light-cured adhesives, Clearfil SE Bond (pH=1.8) and One-Step Bond (pH=4.3) and two dual-cured adhesives, Clearfil Photo Bond (pH=2.5) and All-Bond 2 (pH=6.1). Contraction stress development (at C=3) was determined for a period of 30 min in a universal testing machine where the opposing bonding surfaces were glass and dentin. After the 30 min period, the specimens were loaded in tension to determine the bond strength to dentin. To test the hypothesis, the combinations of the chemical-cured composites with the four bonding systems were also light irradiated for 40s right at the start of curing.

RESULTS

For all composite-adhesive combinations tested, the adhesion to dentin resisted the developing polymerization contraction stresses. Both, dentin as a substrate to bond at and the use of adhesives, were showed to play an important role in keeping the contraction stresses low. The chemical-cured composite (Clearfil Core) combined with the light-cured adhesive SE Bond (pH=1.8) showed for both contraction stress and bond strength significant lower values than the other combinations. The hypothesis was accepted for combinations of the chemical-cured composite with All-Bond 2 and One-Step Bond, but was not supported by combinations with Clearfil SE Bond or Clearfil Photo Bond, as a significant increase in contraction stress was found. The higher values found for bond strength were not significant.

SIGNIFICANCE

Besides combinations of chemical-cured core build-up composites with light or dual-cured adhesives as recommended by the manufacturer, also combinations with adhesives of other manufacturers are compatible, provided that the pH is higher than approximately 4.3. Chemical-cured core build-up composites combined with light-cured adhesives with a pH as low as 1.8 lead to a significantly lower stress and bond strength compared to other combinations. Light irradiation during curing through a combination of a chemical-cured composite and a low pH adhesive reactivates polymerization.

Influence of Er:YAG laser irradiation distance on the bond strength of a restorative system to enamel

OBJECTIVES

The aim of the present study was to investigate in vitro the effect of Er:YAG laser on bonding to enamel, varying the irradiation distance.

METHOD

Tensile bond strength of an adhesive restorative system to non-irradiated and irradiated enamel surfaces was evaluated. Thirty caries-free human third molars were sectioned in mesio-distal direction and embedded in acrylic resin. Enamel was flattened, and a 3-mm-diameter bonding area was demarcated. Specimens were randomly assigned into six groups: groups I-V were treated with the Er:YAG laser (80 mJ/2 Hz), varying the irradiation distance (11, 12 mm-focused, 14, 16 and 17 mm, respectively), followed by 35% phosphoric acid etching. Control group (VI) received treatment with phosphoric acid alone. Single Bond adhesive system was applied on the conditioned enamel, and composite resin cones, bonded to enamel, were fabricated with Z250. After storage, samples were tested in tensile to failure (50 kgf and 0.5 mm/min).

RESULTS

Means in MPa were: I-9.67 (+/-3.44); II-13.29 (+/-2.65); III-13.33 (+/-2.22); IV-14.87 (+/-3.58); V-16.43 (+/-4.52); VI-22.90 (+/-3.03). ANOVA and Tukey test revealed statistically significant decrease of bond strength in group I (P < 0.05). Groups II-IV presented similar results, as did groups IV and V. Control group (VI) yielded the best overall performance (P < 0.05).

CONCLUSION

Er:YAG laser irradiation adversely affected adhesion to enamel. However, bond strength was influenced by the irradiation distance, thus being stronger with the increase of distance to the target tissue.

The effect of light-curing source and mode on microtensile bond strength to bovine dentin

PURPOSE

The purpose of this study was to evaluate the effects of different light-curing techniques on the microtensile bond strength of hybrid and packable resin composite to dentin. The null hypotheses were that different light-curing techniques do not affect the adhesion of resin composites to tooth structure and that different resin composites do not have a similar bond to dentin.

MATERIALS AND METHODS

One hundred four box-shaped buccal preparations were made and dentin/enamel adhesive was applied according to the manufacturer's instructions (Single Bond 3M ESPE). A hybrid resin composite (Filtek Z250, A2, 3M ESPE) or a packable resin composite (Solitaire 2, A2, Heraeus Kulzer) were inserted in bulk and polymerized using one of these techniques (n = 13): (a) Soft-start (SS) using a halogen lamp (QTH); (b) LED low intensity; (c) Plasma arc (PAC) curing for 6 s for packable resin composite and 3 s for the hybrid resin composite; (d) Conventional (C) QTH curing for 40 s. Afterwards, specimens were thermocycled 1,000 times between 5 degrees C and 55 degrees C in tap water, and were sectioned into beams with a rectangular cross-sectional area of approximately 1 mm2. Microtensile bond strength testing was performed using a universal testing machine at a crosshead speed of 0.5 mm/min.

RESULTS

Bond strength means +/- (SD) in MPa were: Filtek Z250: SSQTH = 17.9 (5.4); LED = 17.9 (6.4); PAC = 16.8 (6.8); CQTH = 16.1 (4.6). Solitaire 2: SSQTH = 12.4 (6.4); LED = 15.5 (4.3); PAC = 16.2 (4.4); CQTH = 13.8 (5.7). The data were structured in a split-plot design and analyzed by a two-way ANOVA and Tukey's tests (alpha = 0.05).

CONCLUSION

The light-curing method did not significantly affect bond strengths. However, the bond strengths of the packable resin composite were significantly lower than those of the hybrid resin composite for all polymerization techniques, suggesting that the restorative material itself might be a more critical factor in adhesion than the curing method.

Effect of curing regime on the cytotoxicity of resin-modified glass-ionomer lining cements applied to an odontoblast-cell line

OBJECTIVE

The aim of this in vitro study was to evaluate the cytotoxicity of resin-modified glass-ionomer lining cements submitted to different curing regimes and applied to an immortalized odontoblast-cell line (MDPC-23).

METHODS

Forty round-shaped specimens of each experimental material (Fuji Lining LC and Vitrebond) were prepared. They were light-cured for the manufacturers' recommended time (MRT = 30 s), under-cured (0.5 MRT = 15 s), over-cured (1.5 MRT = 45 s) or allowed to dark cure (0 MRT). Sterilized filter papers soaked with either 5 microL of PBS or HEMA were used as negative and positive control, respectively. After placing the specimens individually in wells of 24-well dishes, odontoblast-like cells MDPC-23 (30,000 cells/cm2) were plated in each well and incubated for 72 h in a humidified incubator at 37 degrees C with 5% CO2 and 95% air. The cytotoxicity was evaluated by the cell metabolism (MTT assay) and cell morphology (SEM).

RESULTS

Fuji Lining LC was less cytotoxic than Vitrebond (p < 0.05) in all the experimental conditions. However, the cytotoxicity of Fuji Lining LC was noticeably increased in the absence of light-curing while the same was not observed for Vitrebond. The length of light-curing (15, 30 or 45 s) did not influence the toxicity of both lining materials when they were applied on the odontoblast-cell line MDPC-23.

SIGNIFICANCE

The light-activation plays an important role in reducing the cytotoxicity of Fuji Lining LC. Following the manufacturer' recommendation regarding the light-curing regime may prevent toxic effect to the pulp cells.

Influence of light intensity on dentin bond strength of self-etch systems

The purpose of this study was to investigate the influence of light intensity on dentin bond strengths of four self-etch adhesive systems. The light intensities used to polymerize specimens were controlled at levels of 150, 300, 600, and 900 mW/cm2. The two-step self-etch adhesive systems Imperva Fluoro Bond and Mac Bond II, and the one-step self-etch systems Fluoro Bond Shake-One and One-Up Bond F Plus were used with their corresponding light-cured resins. Labial surfaces of lower bovine incisors were ground with #600 grit SiC paper to expose the dentin. The dentin surfaces were treated according to each manufacturer's instructions and bonded with resin composites. A shear bond strength test was performed and the data were analyzed by one-way ANOVA followed by Newman-Keuls multiple comparison at a level of 0.05. Statistical analysis of the data indicated that light intensity affected the dentin bond strengths of the adhesive systems tested. Significantly lower bond strengths were obtained by exposure to 150 mW/cm2, and there were no differences between the bond strengths obtained at 600 and 900 mW/cm2 for all the adhesive systems used. Further research will be required to clarify the irradiance-dependent properties of light-cured resin adhesive systems.

Influence of ceramic thickness and polymerization mode of a resin luting agent on early bond strength and durability with a lithium disilicate–based ceramic system

STATEMENT OF PROBLEM

Attenuation of polymerization light energy by translucent all-ceramic materials may result in insufficient polymerization of underlying resin luting agents and inadequate early bond strength and durability. There is little information regarding the selection of an appropriate polymerization mode for cementing translucent all-ceramic restorations.

PURPOSE

The purpose of this study was to evaluate the influence of ceramic thickness and polymerization mode on the early bond strength and bond durability of a lithium disilicate-based ceramic system.

MATERIAL AND METHODS

The occlusal surfaces of 120 extracted, intact, human third molars were sectioned to expose a flattened area of dentin. The surface was etched with 32% phosphoric acid, and a single-step adhesive (One-Step) was applied to the etched dentin surfaces. Ceramic specimens (Empress 2), 6 mm in diameter and 1 mm, 1.5 mm, or 2 mm thick (n=40 per group), were fabricated using fluoropolymer resin matrixes. Each specimen was ground flat. Following hydrofluoric acid etching and silane treatment, ceramic discs of each thickness were further divided into 2 groups (n=20 per group) and bonded to the dentin surfaces with a dual-polymerized resin luting agent (Illusion), either with a catalyst (dual polymerization) or without a catalyst (light polymerization). A shear bond test was performed after 10 minutes (n=10) or after 24 hours following 1000 thermal cycles between 5 degrees C and 55 degrees C and a dwell time of 30 seconds (n=10). Debonded dentin surfaces were examined with SEM. The data were analyzed with 3-way analysis of variance (ANOVA) (alpha=.05).

RESULTS

The shear bond strengths ranged between 13.2 +/- 4.1 MPa and 15.9 +/- 2.0 MPa. Three-way ANOVA revealed that ceramic thickness, polymerization mode, storage time, or combinations of these parameters did not influence shear bond strength. The location of failure for all specimens was adhesive, between the dentin surface and bonding agent.

CONCLUSION

Both light polymerization and dual polymerization provided similar early shear bond strengths for the lithium disilicate-based ceramic system (Empress 2). The bond strength was not dependent on the thickness of the ceramic material tested. Durability of the bond was similar for both of the polymerization modes.