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

Ability of four dental radiometers to measure the light output from nine curing lights

OBJECTIVES

To evaluate the accuracy of four dental radiometers when measuring the output from nine light curing units (LCUs).

METHODS

The light output from nine light-emitting diode LCUs was measured with a laboratory-grade power meter (PowerMax-Pro 150 HD) and four dental radiometers (Bluephase Meter II, SDI LED Radiometer, Kerr LED Radiometer, and LEDEX CM4000). Ten measurements were made of each LCU with each radiometer. Analysis of variance (ANOVA) followed by Tukey tests (α=0.05) were used to determine if there was a difference between the calculated irradiance values from the power meter and those from the radiometers. Where applicable, the LCUs were ranked according to their power and irradiance values. The emission spectra from the LCUs was measured using an integrating sphere attached to a fiber-optic spectrometer (N=10). The beam profile of the LCUs was measured with a beam profiler camera.

RESULTS

Of the dental radiometers, only the Bluephase Meter II could measure power. ANOVA showed no significant difference between power values measured with the laboratory-grade meter and the Bluephase Meter II (p=0.527). The difference between the mean irradiance reported by the various radiometers for the same LCU was up to 479mW/cm². The ranking of the power values obtained using the laboratory-grade meter was the same for the Bluephase Meter II.

CONCLUSION

When compared to the calculated irradiance values from the laboratory-grade power meter, the Bluephase Meter II provided the most accurate data.

CLINICAL SIGNIFICANCE

Considering the great variation between the irradiance values provided by radiometers and their overall inaccuracy when compared to a laboratory-grade meter, dentists should not place too much faith in the absolute irradiance value. However, hand-held radiometers can be used to monitor changes in the light output of LCUs over time.

Impact of light intensity on the polymerization kinetics and network structure of model hydrophobic and hydrophilic methacrylate based dental adhesive resin

The impact of light intensity on the degree of conversion (DC), rate of polymerization and network structure was investigated for hydrophobic and hydrophilic dental adhesive resins. Two and three component photoinitiating (PI) systems were used in this study. Low light intensities had a negative impact on the polymerization efficiency for the hydrophilic resin with 2 component PI system. Incorporation of iodonium salt in the hydrophilic resin significantly improved the polymerization efficiency of the HEMA/BisGMA system and led to a substantial DC, even at low light intensities. The results suggested that shorter polymer chains were formed in the presence of iodonium salt. It appears that there is little or no impact of light intensity on the polymer structure of the 2 component PI system. Light intensity has subtle impact on the polymer structure of the 3 component PI system. In the case of the hydrophobic resin, the polymer is so highly cross-linked that the presence of shorter chains for the 3 component PI system does not cause a decrease in the glass transition temperature (T_g ) when compared to the 2 component PI system. For the hydrophilic resin, the presence of shorter polymer chains in the 3 component PI system reduces the T_g when compared with the corresponding 2 component PI system. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1666-1678, 2016.

Nondestructive observation of teeth post core space using optical coherence tomography: a pilot study

Coronal tooth lesions, such as caries, enamel cracking, and composite resin restoration cavities, have been observed by optical coherence tomography (OCT). This pilot study was performed to verify whether OCT could reveal details of root canals filled with resin core build-up. A dual-cure, one-step, self-etch adhesive system-bonding agent (Clearfil Bond SE ONE, Kuraray Noritake Dental) and dual-cure resin composite core material (Clearfil DC Core Automix ONE, Kuraray Noritake Dental) were used according to the manufacturer's instructions in root canals. OCT was performed at three stages of the core build-up: after the post space preparation, after bonding application, and after resin core fabrication. The cementum was removed in the cementum absent group and the root was left untreated in the cementum present group. Bubbles were observed in the resin cores and gaps formed between the resin core and dentin. In the cementum absent group, the internal structure of the root could be visualized clearly compared with the cementum present group. The root internal structure could be observed by OCT and the image became clearer when cementum was removed.

Effect of emitted wavelength and light guide type on irradiance discrepancies in hand-held dental curing radiometers

The purpose of this study was to determine any discrepancies in the outputs of five commercial dental radiometers and also to evaluate the accuracy of these devices using a laboratory-grade spectroradiometer. The power densities of 12 different curing light sources were repeatedly measured for a total of five times using each radiometer in a random order. The emission spectra of all of the curing light sources were also measured using the spectroradiometer, and the integral value of each spectrum was calculated to determine the genuine power densities, which were then compared to the displayed power densities measured by the dental radiometers. The displayed values of power density were various and were dependent on the brand of radiometer, and this may be because each radiometer has a different wavelength sensitivity. These results cast doubt upon the accuracy of commercially available dental radiometers.

Shear bond strength and fracture analysis of human vs. bovine teeth

Purpose

To evaluate if bovine enamel and dentin are appropriate substitutes for the respective human hard tooth tissues to test shear bond strength (SBS) and fracture analysis.

Materials and Methods

80 sound and caries-free human erupted third molars and 80 freshly extracted bovine permanent central incisors (10 specimens for each group) were used to investigate enamel and dentine adhesion of one 2-step self-etch (SE) and one 3-step etch and rinse (E&R) product. To test SBS the buccal or labial areas were ground plane to obtain appropriate enamel or dentine areas. SE and E&R were applied and SBS was measured prior to and after 500 thermocycles between +5 and +55°C. Fracture analysis was performed for all debonded areas.

Results

ANOVA revealed significant differences of enamel and dentin SBS prior to and after thermocycling for both of the adhesives. SBS- of E&R-bonded human enamel increased after thermocycling but SE-bonded did not. Bovine enamel SE-bonded showed higher SBS after TC but E&R-bonded had lower SBS. No differences were found for human dentin SE- or E&R-bonded prior to or after thermocycling but bovine dentin SE-bonded increased whereas bovine dentine E&R-bonded decreased. Considering the totalized and adhesive failures, fracture analysis did not show significances between the adhesives or the respective tooth tissues prior to or after thermocycling.

Conclusion

Although SBS was different on human and bovine teeth, no differences were found for fracture analysis. This indicates that solely conducted SBS on bovine substrate are not sufficient to judge the perfomance of adhesives, thus bovine teeth are questionnable as a substrate for shear bond testing.

Mechanical and morphological evaluation of the bond-dentin interface in direct resin core build-up method

OBJECTIVES

The purpose of this study was to evaluate the interfacial adhesion between resin and root canal dentin in the direct resin core build-up method in terms of microtensile bond strength (μTBS) and dentin micro morphology.

METHODS

Single-rooted human teeth were decoronated at the cementoenamel junction and endodontically treated. Post spaces were prepared in the roots to a depth of 10mm. The spaces were then treated with a dual-cure bonding system, and filled with dual-cure resin composite. After 24-h storage in water at 37 °C, they were trimmed into approximately 1.0-mm(2) beams for μTBS. Bond strength was analyzed with one-way ANOVA and Tukey's test. The fractured surfaces were examined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDX). Sectioned specimens were observed by ultra-high-voltage transmission electron microscopy.

RESULTS

The bond strength of root dentin decreased gradually from the coronal to apical side, and the bond strength of the coronal section was significantly higher than that of the radicular section. Moreover, the failure modes in the coronal and apical sides of the specimens differed. The apical specimens fractured within the core material, while the coronal specimens fractured at the bonding layer. SEM and EDX analyses revealed that the core material penetrated into dentinal tubules in the apical region.

SIGNIFICANCE

In the direct resin core build-up method, the interfacial adhesion of resin to root canal dentin may be insufficient in the apical region of the root canal due to poor polymerization.

Self-etching primer systems: changes in dentin bond strength with time

The purpose of this study was to investigate the development of shear bond strength of resin composites using self-etching primer systems. Four different types of self-etching primer systems with different combinations of their recommended resin composites were used. Bovine incisors were mounted in self-curing resin and the facial surfaces were wet ground on #600-SiC paper to expose the dentin. The shear bond strengths of ten samples per test group were measured at a crosshead speed of 1.0 mm/min after storage for 5, 10, and 60 min, and 24 h in distilled water at 37 degrees C. One-way ANOVA followed by Dunnett's test (alpha = 0.05) was used to examine the significance of differences between the mean bond strength at 24 h and each of the other storage periods. The dentin bond strengths of all the materials tested increased with prolonged storage time. Such differences in the changes in bond strength might have clinical implications if a restoration is subjected to high stress immediately after it has been placed. It is important to consider the development of dentin bond strength to allow the materials sufficient maturation time prior to functional loading or application of other forms of external stress.

Effects of photocuring strategy on bonding of dual-cure one-step self-etch adhesive to root canal dentin

This study evaluated the effects of light power density and light exposure time on regional bond strength of Clearfil DC Bond to root canal dentin. Post spaces were prepared in extracted premolars. Root canal dentin was treated with a dual-cure bonding system, Clearfil DC Bond, and light-cured for 10, 20, or 30 seconds using two halogen light curing units: Optilux 501 (830 mW/cm2) and Hyperlightel (1350 mW/cm2). Following which, all post spaces were filled with a dual-cure resin composite. After 24-hour storage, microtensile bond strengths (microTBS) at the coronal and apical regions were measured. At the coronal region, microTBS values were similar among all the experimental groups. At the apical region, bond strength improved when the curing time was extended to 30 seconds with Optilux 501, and likewise with Hyperlightel when curing time was extended to 20 or 30 seconds. In addition, significant differences in microTBS between the coronal and apical regions disappeared with prolonged curing times.

Light-activation of resin cement through ceramic: relationship between irradiance intensity and bond strength to dentin

This study investigated the relationship between the irradiance transmitted through ceramic and the bond strength of a resin cement to dentin. After application of an adhesive system, elastomer molds with cylindrical orifices (1.2 mm in diameter) were placed onto bovine dentin surfaces and filled with a photoactivated luting agent (Enforce; Dentsply Caulk). Light-activation was performed through a 0.6-mm-thick ceramic disc using different intensities: 250, 400, 550, 700, or 850 mW/cm(2). Control specimens were irradiated without ceramic (1050 mW/cm(2)). The radiant exposure was kept at 30 J/cm(2). Light spectral distribution was analyzed with a spectrometer. Microshear test was conducted and modes of failure were classified under SEM. Bond strength data were analyzed with ANOVA and Student-Newman-Keuls' test (alpha < or = 0.05), and failure scores with the Kruskal-Wallis test (alpha < or = 0.05). A linear regression model assessed the relationship between irradiance and bond strength. Groups light-cured at 250 and 400 mW/cm(2) presented lower bond strengths than groups activated at 850 and 1050 mW/cm(2). The linear regression showed that a decrease in light irradiance predicts a decrease in bond strength (r(2) = 0.955; p = 0.004). A predominance of mixed failures was observed. No significant alteration in the spectral wavelengths was observed. Despite the constant energy dose, the bond strength was dependent upon the irradiance level.

Influence of pressure application before light-curing on the bond strength of adhesive systems to dentin

This study evaluated the influence of defined pressure application before light-curing on the tensile bond strength (TBS) of two adhesive systems to wet and perfused dentin. Bonding sites were analyzed by scanning electron microscopy (SEM) to assess morphological changes. Dentin discs from 120 human third molars were prepared in such a way to allow simulation of intrapulpal pressure. The specimens were randomly assigned to 6 groups (n=20) according to different experimental conditions. The adhesive systems (ScotchbondTM Multi-Purpose and Syntac®) were applied either to wet or perfused dentin. In the latter, compression was applied before adhesive light-curing . TBS was recorded using an universal testing machine. Qualitative examination of the bonding sites was performed by SEM after dissolving the dentin with 50% nitric acid. Pressure application prior to light-curing resulted in a remarkable decrease of TBS for Syntac®, while no significant change was observed for ScotchbondTM MP. SEM analysis showed no considerable lengthening of the resin tags after pressure application. These findings suggest that application of adhesive systems to dentin under pressure before light-curing had no positive effect on TBS.

Influence of moisture conditions on dentin bond strength of single-step self-etch adhesive systems

This study was conducted to clarify the influence of dentin surface moisture on bond strength of single-step self-etch adhesive systems. The adhesive systems used were Adper Prompt L-Pop (AP), Clearfil tri-S Bond (CT), Fluoro Bond Shake One (FB), G-Bond (GB), and One-Up Bond F Plus (OF). Bovine mandibular incisors were wet-ground with #600 SiC to expose the labial dentin. After rinsing with tap water, the dentin surface was dried with air for 10 sec (Dry condition) or blotted (Wet condition). Adhesives were applied according to each manufacturer's instructions, followed by resin composite polymerization. Ten samples per test group were stored in distilled water at 37 degrees C for 24 h, then shear tested at a crosshead speed of 1.0 mm/min. The data were analyzed by Student's t test and Tukey HSD test at a probability level of 0.05. The mean bond strengths for Dry condition ranged from 13.9 MPa to 18.2 MPa, and those for Wet condition ranged from 7.1 MPa to 18.4 MPa. Significantly lower bond strengths were obtained for the Wet condition for GB, FB, and OF. Failure after the test was commonly due to adhesive breakdown associated with partial cohesive failure in the dentin. These data suggest that air-drying of the dentin surface is appropriate for the adhesive systems tested.