Effects of Different Radiation Doses on the Bond Strengths of Two Different Adhesive Systems to Enamel and Dentin

PURPOSE

To evaluate the effects of three different radiation doses on the bond strengths of two different adhesive systems to enamel and dentin.

MATERIALS AND METHODS

Eighty human third molars were randomly divided into four groups (n = 20) according to the radiation dose (control/no radiation, 20 Gy, 40 Gy, and 70 Gy). The teeth were sagittally sectioned into three slices: one mesial and one distal section containing enamel and one middle section containing dentin. The sections were then placed in the enamel and dentin groups, which were further divided into two subgroups (n = 10) according to the adhesive used. Three restorations were performed in each tooth (one per section) using Adper Single Bond 2 (3M ESPE) or Universal Single Bond (3M ESPE) adhesive system and Filtek Z350 XT (3M ESPE) resin composite and subjected to the microshear bond test. Data were analyzed using a two-way ANOVA followed by Tukey's test. Failure modes were examined under a stereoscopic loupe.

RESULTS

Radiotherapy did not affect the bond strengths of the adhesives to either enamel or dentin. In dentin, the Universal Single Bond adhesive system showed higher bond strength values when compared with the Adper Single Bond adhesive system. More adhesive failures were observed in the enamel for all radiation doses and adhesives.

CONCLUSION

Radiotherapy did not influence the bond strength to enamel or dentin, irrespective of the adhesive or radiation dose used.

Can Increasing the Manufacturer's Recommended Shortest Curing Time of High-intensity Light-emitting Diodes Adequately Cure Sealants?

PURPOSE

To investigate sealant depth of cure after increasing the curing times of high-intensity light-emitting diode units (LEDs).

METHODS

Three sealants (opaque-unfilled, opaque-filled, and clear-filled) were light cured in a covered-slot mold with: (a) three LEDs (VALO, SmartLite, Fusion) for six to 15 seconds; and (b) a quartz-tungsten halogen (QTH) light for 40 seconds as a control (N=10). Twenty-four hours after light curing, microhardness was measured at the sealant surface and through the depth at 0.5 mm increments. Results were analyzed via analysis of variance followed by the Student-Newman-Keuls test (significance level 0.05).

RESULTS

The opaque-filled and clear-filled sealants cured with VALO for six or nine seconds had hardness values that were statistically equivalent to or better than the QTH to a depth of 1.5 mm. Using Fusion for 10 seconds (exposure limit) did not adequately cure the three sealants beyond one mm. SmartLite at 15 seconds (maximum exposure period without overheating) did not adequately cure the sealants beyond 0.5 mm.

CONCLUSIONS

Among the tested high-intensity LEDs, only VALO at double or triple the manufacturers' shortest curing time (six or nine seconds) provided adequate curing of opaque-filled and clear-filled sealants at 1.5 mm depth compared to the 40-second QTH light.

In vitro comparison of polymerisation kinetics and the micro-mechanical properties of low and high viscosity giomers and RBC materials

OBJECTIVES

The study aims to characterise a low and high viscosity giomer bulk fill resin restorative with established low and high viscosity resin-based composite (RBC) restoratives at simulated clinical relevant specimen depths.

METHODS

The irradiance of a light curing unit (Bluephase 20i) was measured on a laboratory-grade spectrometer at distances up to 10mm from the light tip (in 1mm increments). Polymerization kinetics (real-time decrease of CC double bond and degree of cure, DC) and micro-mechanical properties (Vickers hardness/HV; Depth of cure/DOC; Indentation modulus/E) were assessed at varying specimen depths (0.1-6mm in 100μm steps for E, DOC and HV and 0.1, 2, 4 and 6mm for DC) for a 20s irradiation.

RESULTS

One and two-way ANOVA (α=0.05) were performed. The parameter material has a significant (p<0.001) effect on DC (ηP(2)=0.839), HV (ηP(2)=0.683), and E (ηP(2)=0.536), whereas the specimen depth influenced only DC (ηP(2)=0.584) but not HV (p=0.093) or E (p=0.133). The polymerisation kinetic could be described by an exponential sum function, distinguishing between the gel and the glass phase. The hardness drop out was lower than 20%, indicated a depth of cure of 6mm for all materials.

CONCLUSIONS

The low and high viscosity giomer bulk-fill restoratives fulfil the requirements of bulk-fill placement, since under the analysed irradiation conditions an adequate depth of cure of >4mm was identified. Variation of DC with specimen depth was low, with little variation at specimen depths of <4mm. The micro-mechanical properties of the giomer materials were higher compared with the conventional RBC materials.

Influence of different photo-activation distances on cytotoxicity of a dental adhesive model resin

AIM

This study evaluated the cytotoxicity of a dental bonding model resin (DBMR) submitted to different photo-activation distances.

METHODS

A monomer mixture based on Bis-GMA and HEMA was used to assess the cytotoxicity in a mouse fibroblast-cell line. To promote different photo-activation distances glass slides were interposed between DBMR surface and halogen light curing unit (LCU) tip. Afterwards, the specimens were immersed in RPMI culture medium for 24 h to obtain extracts. The extracts were incubated in contact with the cells for 24 h. Finally, an MTT colorimetric assay was used to assess the cytotoxicity. The cell viability data (absorbance) were analyzed by one way ANOVA followed by Tukey's test (P<0.05).

RESULTS

The light output decreased according to the increase in the number of glass slides between the halogen LCU tip and DBMR surface. Yet, the distance between the tip of the curing light system and the specimens had significant influence on the cytotoxicity. All extracts produced by groups submitted to different photo-activation distances showed cytotoxic effect after 24h of incubation.

CONCLUSION

The photo-activation distance and the interposition of glass slides between LCU tip and DBMR was shown to play an important role in the cytotoxic effect.

Preheating of resin-based flowable materials in a microwave device: a promising approach to increasing hardness and softening resistance under cariogenic challenge

This study aimed to evaluate whether preheated resin-based flowable restoratives would show increased hardness and softening susceptibility after an early cariogenic challenge. Fluroshield- Yellowed, Bioseal, Wave, Master Flow, Fluroshield-White, Conseal F, Filtek Z350 Flow, and Opallis Flow were tested. Preheating was performed using a microwave device. Five specimens of each preheated or room temperature material (n = 5) were fabricated. Hardness was assessed before and after a cariogenic challenge. The analysis was done by two-way analysis of variance (ANOVA) with repeated measures (cariogenic challenge) and Tukey's test for multiple comparisons (

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 light curing methods on microleakage and microhardness of different resin sealants

PURPOSE

This study's purpose was to evaluate the effect of light curing methods on the microleakage and microhardness of sealants.

METHODS

The Elipar Free Light 2 light emitting diode (LED) with 10- and 20-second curing times, and the Elipar 2500 halogen light with a 20-second curing time were compared. Four different sealants were used: (1) Delton Clear; (2) Delton Opaque; (3) UltraSeal XT Clear; and (4) UltraSeal XT Opaque. Specimens were fabricated in a silicone mold (2-mm thick) and cured. Knoop hardness was measured at the bottom and top surfaces. For the microleakage evaluation, 120 human molars were divided into 12 groups and sealed with the sealants and curing methods, as stated previously. The teeth were thermocycled and immersed in 2% methylene blue for 24 hours. Each tooth was sectioned and examined for dye penetration.

RESULTS

There were no statistically significant differences in the microleakage of sealants polymerized by either the halogen or LED curing methods. The microhardness of sealants varied according to the type of material and curing method.

CONCLUSIONS

A 10-second polymerization time with light emitting diodes was not sufficient to cure the 2-mm-thick opaque or high filler loaded sealants. Decreasing the curing time, however, had no effect on the microleakage of the sealants.

How light sources and distance of the light tip influence water sorption, solubility, and biaxial flexural strength of a composite resin

This study evaluated the water sorption (WS), solubility (SL), and biaxial flexural strength (BFS) of a resin composite based on different polymerization units, storage permeants (distilled water and 75% ethanol), and distances between the light's tip and the composite resin. Using a stainless steel mold, 80 specimens were made and separated in two independent groups, according to the duration of storage (7 days or 60 days). The specimens were photocured using either a QTH or LED light (both used at 600 mW/cm2 for 40 seconds), with the light's tip guide either 0 mm or 2 mm from the surface of the resin. In general, the 75% ethanol produced higher WS and SL values but lower BFS values compared to water. Both distances influenced the WS and SL values, especially when 75% ethanol was used (p < 0.05), although neither distance affected BFS values (p > 0.05). For nearly all groups, the WS, SL, and BFS in different solvents and at different distances for photocuring of the tested resin were not affected by the curing light used.

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.

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.

Thermal variations in the pulp chamber associated with composite insertion techniques and light-curing methods

AIM

The aim of this study was to investigate the effect of different incremental insertion techniques, photoactivation, and restorative phases on thermal variations occurring during the polymerization of Filtek Z250 composite resin.

METHODS AND MATERIALS

The experiment was conducted using 90 bovine incisor teeth. The teeth were randomly assigned to three groups according to the technique used for photoactivation with a halogen light (continuous, soft-start, or intermittent). The groups were further separated into three subgroups according to method of increment placement (bulk, oblique, or horizontal/vertical) for a total of nine groups (n=10). Restorations were placed in a controlled environment (37 masculineC and 50+/-10% RU) and the temperature recorded using a digital thermometer coupled to a Type-K thermocouple inserted in the pulp chamber through the root canal in contact with the dentin. Data were analyzed using an analysis of variance (ANOVA) and the Tukey's test.

RESULTS

Higher temperature values were found for continuous light photoactivation in combination with the placement of horizontal/vertical composite increments and photoactivation of the adhesive using a continuous light exposure.

CONCLUSION

The light source is the most important factor producing temperature changes during photoactivation of resin composite.

CLINICAL SIGNIFICANCE

Temperature increases in the pulp chamber due to light curing should be considered to avoid harming the delicate pulp tissue when large restorations or inlays/onlays require several consecutive light curing exposures for a complete cure.

Effects of water content and initiator composition on photopolymerization of a model BisGMA/HEMA resin

AIMS

The purpose of this study was to evaluate the effects of photoinitiator type and water content on the polymerization rate (Rp) and degree of conversion (DC) of a model BisGMA/HEMA-based resin.

MATERIALS AND METHODS

The comonomer mixture consisted of BisGMA/HEMA (60/40 by weight). Different two- or three-component photoinitiator systems were incorporated. Two-component systems were 0.5% CQ (camphorquinone) and 0.5% DMAEMA (2-(dimethylamino) ethyl methacrylate) or 0.5% CQ and 0.5% 4E (ethyl 4-dimethylaminobenzoate). The three-component systems were added 1% DPIHP (diphenyliodonium hexafluorophosphate) to the above systems. Each system was tested as made, or after addition of 5, 10, 15wt% water. When cured under a conventional dental light, the Rp and DC of each formulation was determined using time-resolved attenuated total reflection (ATR)-Fourier transform infrared (FTIR) spectroscopy.

RESULTS

For mixtures containing two-component initiator systems, when the hydrophobic initiator CQ was used in combination with hydrophilic DMAEMA, Rps and DCs were dramatically decreased as a function of water content. The Rps and DCs of the hydrophobic CQ/4E system were higher than those of the CQ/DMAEMA system in the presence of water. For three-component initiator systems, incorporation of DPIHP enhanced the polymerization of all mixtures in the presence of water compared to their counterpart two-component initiators. Interestingly, the CQ/DMAEMA caused greater DC and Rp when DPIHP was used.

SIGNIFICANCE

The hydrophobicity/hydrophilicity of photoinitiator components significantly affects both the DC as well as Rp when in the presence of water. The results indicate that formulation of photoinitiator components should be based on the effectiveness of the bonding systems under both dry and wet conditions.

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).

Photopolymerization of N,N-dimethylaminobenzyl alcohol as amine co-initiator for light-cured dental resins

OBJECTIVE

The present study was carried out in order to assess the suitability of N,N-dimethylaminobenzyl alcohol (DMOH) as co-initiator of camphorquinone (CQ) and 1-phenyl-1,2-propanedione (PPD) in light-cured dental resins.

METHODS

DMOH was synthesized and used as co-initiator for the photopolymerization of a model resin based on {2,2-bis[4-(2-hydroxy-3-methacryloxyprop-1-oxy)phenyl]propane} (Bis-GMA)/triethylene glycol dimethacrylate (TEGDMA). Experimental formulations containing CQ or PPD in combination with DMOH at different concentrations were studied. The photopolymerization was carried out by means of a commercial light-emitting diode (LED) curing unit. The evolution of double bonds consumption versus irradiation time was followed by near-infrared spectroscopy (NIR). The photon absorption efficiency (PAE) of the photopolymerization process was calculated from the spectral distribution of the LED unit and the molar absorption coefficient distributions of PPD and CQ.

RESULTS

DMOH is an efficient photoreducer of CQ and PPD resulting in higher polymerization rate and higher double bond conversion compared with dimethylaminoethylmethacrylate. The PAE for PPD was higher than that for CQ. However, the polymerization initiated by PPD progressed at a lower rate and exhibited lower values of final conversion compared with the resins containing CQ. This observation indicates that the lower polymerization rate of the PPD/amine system should be explained in terms of the mechanism of generating primary radicals by PPD, which is less efficient compared with CQ.

SIGNIFICANCE

The DMOH/benzoyl peroxide redox system, has recently been proposed as a more biocompatible accelerator for the polymerization of bone cements based on poly(methyl methacrylate), because cytotoxity tests have demonstrated that DMOH possesses better biocompatibility properties compared with traditional tertiary amines. The results obtained in the present study reveal the suitability of the CQ/DMOH initiator system for the polymerization of light-cured dental composites.

Effect of different photoactivation methods on the bond strength of composite resin restorations by push-out test

OBJECTIVE

Modulated curing methods could lead to a higher probability of bond preservation. Therefore, the aim of this study was to evaluate the effect of 7 curing methods on bond strength of composite resin restorations.

METHOD AND MATERIALS

Seventy bovine incisors were selected. A conical cavity was prepared in the buccal surface. Adper Single Bond adhesive system was applied according to the manufacturer's instructions, and the cavities were filled with a single increment of Esthet X (Dentsply/Caulk). The specimens were randomly assigned into 7 groups (n = 10) according to the photoactivation method: (1) continuous light 700 (700 mW/cm2) (control); (2) continuous light 150 (150 mW/cm2); (3) continuous light 250 (250 mW/cm2); (4) soft-start 75 (75 mW/cm2) + 700 mW/cm2); (5) soft-start 150 (150 mW/cm2 + 700 mW/cm2); (6) pulse-delay (150 mW/cm2 + 3 minutes + 700 mW/cm2); and (7) intermittent light (cycles at 600 mW/cm2). The energy density for all groups was 14 J/cm2. The bond strength of the composite restorations was measured by performing the push-out test in a universal testing machine (Instron). The results were submitted to ANOVA and Tukey test (P < .05).

RESULTS

Pulse-delay, soft-start 150, and soft-start 75 methods showed a significant increase in bond strength when compared with the control continuous light 700 method. Low power density and intermittent light groups showed intermediate results.

CONCLUSION

Modulation of the energy density during light curing of composite resins using pulse-delay or soft-start methods increased the bond strength of composite restorations.

Polymerization eficiency of dual-polymerized resin cements light-irradiated through ceramics and laboratory-processed resin composite

The purpose of the study was to determine the influence of light-irradiation through two ceramic and one resin composite materials on the degree of remaining double carbon bonds in 3 dual-polymerized resin cements. After mixing, the cement was inserted into a 0.5 mm deep recess in a silicon mold, covered with one ceramic or resin composite rectangular block and exposed through the block with the light from a halogen polymerization unit for 40 s. Infrared spectroscopic analysis was used to record the degree of remaining double carbon bonds. Light irradiation through 2 mm-thick ceramic and resin composite materials increased the degree of remaining double carbon bonds relative to the direct photopolymerization analogues.

Effect of high-intensity LED units at reduced curing time on in vitro bond strength of orthodontic brackets

AIM

To compare the shear bond strength of stainless steel brackets obtained by 3 high-intensive light-emitting diode (LED) units with conventional halogen polymerization.

METHODS

A standard light-curing adhesive paste was used to bond brackets using different lamps and curing times. Eighty permanent bovine incisors were obtained and randomly divided into 4 groups. The first group was bonded using a high-output halogen lamp for 20 seconds, which served as a positive control. The other 3 groups were bonded with high-intensive LED curing devices for 10 seconds. After 30 minutes, a universal testing machine was used to apply an occlusal shear force directly to the enamel-bracket interface at a speed of 0.5 mm/minute. The groups were compared using Kruskal-Wallis test.

RESULTS

Mean results and standard deviations for the groups were: group 1 = 11.22 MPa (1.68), group 2 = 10.35 MPa (1.92), group 3 = 11.19 MPa (2.62), and group 4 = 11.82 MPa (2.09). No significant difference was observed in the bond strengths of the 4 groups evaluated (P = . 176).

CONCLUSIONS

Under the conditions of the present study, the high-intensity LED units with reduced light-curing time bonded brackets to etched tooth enamel as well as the halogen-based light-curing units.

Comparative evaluation of the microhardness of 4 dental sealants

AIM

Aim of this study was the evaluation of the microhardness of 4 dental sealants polymerised with two different curing units.

METHODS

Twenty samples (5 x 5x 2 mm) were prepared with 4 different sealants; 10 samples for each group were polymerised with a plasma curing unit (Apollo 95 E DMD) and 10 with a halogen curing light (Heliolux DLX Vivadent ETS, Schaan, Liechtenstein). For each section 6 Vickers microhardness measurements were performed (VMHT 30A, Leica Wien, Austria), 3 on the surface exposed to the light and 3 on the opposite surface. After the baseline assessment all samples were stored in artificial saliva at 37 degrees C for 30, 60, 90, 180 and 360 days, and then analysed again with the microhardness indenter and observed under steromicroscope 10X (Leica DM2500 Wien, Austria). Data were then statistically analysed.

RESULTS

The hybrid composite Tetric flow (group IV) showed the higher microhardness values compared to the other tested materials (group I, II, III); surfaces exposed to curing light showed higher microhardness values than opposite surfaces. Moreover, a significant microhardness reduction was observed after 30 days; values remained unmodified after 60, 90, 180 and 360 days.

STATISTICS

Data were then statistically analysed with Anova test for repeated measures, with a global significance level of 0.05.

CONCLUSION

Because of the good mechanical properties of dental sealants they represent the first choice materials in pits and fissures sealing.

Effects of water content and initiator composition on photopolymerization of a model BisGMA/HEMA resin

AIMS

The purpose of this study was to evaluate the effects of photoinitiator type and water content on the polymerization rate (Rp) and degree of conversion (DC) of a model BisGMA/HEMA-based resin.

MATERIALS AND METHODS

The comonomer mixture consisted of BisGMA/HEMA (60/40 by weight). Different two- or three-component photoinitiator systems were incorporated. Two-component systems were 0.5% CQ (camphorquinone) and 0.5% DMAEMA (2-(dimethylamino) ethyl methacrylate) or 0.5% CQ and 0.5% 4E (ethyl 4-dimethylaminobenzoate). The three-component systems were added 1% DPIHP (diphenyliodonium hexafluorophosphate) to the above systems. Each system was tested as made, or after addition of 5, 10, 15wt% water. When cured under a conventional dental light, the Rp and DC of each formulation was determined using time-resolved attenuated total reflection (ATR)-Fourier transform infrared (FTIR) spectroscopy.

RESULTS

For mixtures containing two-component initiator systems, when the hydrophobic initiator CQ was used in combination with hydrophilic DMAEMA, Rps and DCs were dramatically decreased as a function of water content. The Rps and DCs of the hydrophobic CQ/4E system were higher than those of the CQ/DMAEMA system in the presence of water. For three-component initiator systems, incorporation of DPIHP enhanced the polymerization of all mixtures in the presence of water compared to their counterpart two-component initiators. Interestingly, the CQ/DMAEMA caused greater DC and Rp when DPIHP was used.

SIGNIFICANCE

The hydrophobicity/hydrophilicity of photoinitiator components significantly affects both the DC as well as Rp when in the presence of water. The results indicate that formulation of photoinitiator components should be based on the effectiveness of the bonding systems under both dry and wet conditions.

Degree of conversion of adhesive systems light-cured by LED and halogen light

This study evaluated the effect of blue light emitting diode (LED) and quartz tungsten halogen (QTH) on the degree of conversion (DC) of an etch-and-rinse Single Bond adhesive system (SB) and a mixture composed of primer solution and resin bond from Clearfil SE Bond self-etching adhesive system (CB) using Fourier transform infrared analysis (FTIR). Adhesives were applied to potassium bromide pellet surfaces and FTIR analyses were performed before and after photo-activation for 10 s with either LED (Freelight 1 - 400 mw/cm(2)) or QTH (XL 3000 - 630 mw/cm(2)) light-curing units (n=8). Additional FTIR spectra were obtained from photo-activated samples stored in distilled water for 1 week. The DC was calculated by comparing the spectra obtained from adhesive resins before and after photo-activation. The results were analyzed by two-way split-plot ANOVA and Tukey's test (p<0.05). Both adhesive systems exhibited low DC (%) immediately after photo-activation (SB/QTH: 18.7 +/- 3.9; SB/LED: 13.5 +/- 3.3; CF/QTH: 13.6 +/- 1.9; CF/LED: 6.1 +/- 1.0). The DC of samples light-cured with LED was lower than DC of those light-cured with QTH, immediately after light curing and after 1 week (SB/QTH: 51.3 +/- 6.6; SB/LED: 50.3 +/- 4.8; CF/QTH: 56.5 +/- 2.9; CF/LED: 49.2 +/- 4.9). The LED curing unit used to photo-activate the adhesive resins promoted lower DC than the QTH curing unit both immediately after light curing and 1 week after storage in water.

In vitro microleakage of a fissure sealant polymerized by either a quartz tungsten halogen curing light or a plasma arc curing light

BACKGROUND

The benefits of using plasma arc curing lights with their shorter curing times in the management of children are potentially great, provided there are no adverse effects.

OBJECTIVE

The aim of this study was to investigate whether the microleakage of a resin-based sealant is influenced by polymerization with either a conventional quartz tungsten halogen or a plasma arc curing light.

DESIGN

This study took the form of an in vitro randomized control trial. Seventy extracted human first and second permanent premolars and molars were randomly allocated into two groups. Their occlusal surfaces were sealed with a light-cured fissure sealant using either a quartz tungsten halogen curing light or a plasma arc curing light. The teeth were then sectioned, resulting in four surfaces per tooth, which were examined for microleakage under x 15 magnification with a light microscope. The principal unit of analysis was the tooth (worst section score) and not the section microleakage score.

RESULTS

No statistical significant difference in microleakage scoring between the two groups was demonstrated.

CONCLUSION

This study found no difference in the degree of microleakage of fissure sealants polymerized by either light source.

Dimethacrylate based on cycloaliphatic epoxide for dental composite

OBJECTIVES

The aim of this study was to investigate the kinetics and mechanical properties of dimethacrylate monomer based on cycloaliphatic epoxide for dental restorative composite.

METHODS

Dimethacrylate based on cycloaliphatic epoxide (EPCDMA) was copolymeirzed with TEGDMA by varying the curing conditions: monomer composition and light intensity. A real-time near FTIR technique was employed to monitor the double bond conversion and the rate of polymerization. Dynamic mechanical analysis was performed on a dynamic mechanical analyzer, and volume shrinkage of the cured samples was determined by pycnometric method.

RESULTS

The results of kinetics showed that, two peaks of maximum rate of polymerization (Rpmax) occurred when the amount of TEGDMA was more than 30wt%. Increasing the amount of TEGDMA, the final double bond conversion and polymerization shrinkage both increased, while the glass transition temperature (Tg) decreased. All EPCDMA/TEGDMA mixtures had slightly higher storage modulus at body temperature (37 degrees C). When compared with Bis-GMA/TEGDMA (70/30), the EPCDMA/TEGDMA (70/30) system assumed similar reactivity and volume shrinkage but higher Tg.

SIGNIFICANCE

EPCDMA had comparable mechanical properties to those of Bis-GMA.

Comparison of two methods for measuring the polymerization characteristics of flowable resin composites

OBJECTIVES

The purpose of this study was to compare two methods for assessing the polymerization characteristics of flowable resin composites.

METHODS

Two different flowable resin composites and a hybrid resin composite control were investigated. In order to measure the volumetric shrinkage (DeltaV), each material was placed into a mould and extruded into a water-filled dilatometer. The specimens were then light irradiated for 30s using a curing unit with the power density adjusted to either 100 or 600mW/cm(2). For the speckle contrast measurement, each resin composite was condensed into a glass tube and irradiated. The laser-speckle field was recorded in a digital frame. The calculated values were obtained for each pair of adjacent patterns and the changes in speckle contrast as a function of time were obtained.

RESULTS

The average DeltaV values of the resins after 180s ranged from approximately 3.3 to 4.4% for the flowable composites and from approximately 1.8 to 2.3% for the hybrid composite control. The overall magnitude of the speckle contrasts decreased soon after the initial light exposure commenced and gradually increased thereafter. The speckle contrast measurements revealed changes in the pastes due to the polymerization of the flowable resins that were greater than those obtained with the water-filled dilatometer.

SIGNIFICANCE

These data suggest that the polymerization characteristics of flowable resins can be measured successfully using two different methods. Moreover, our findings are of clinical relevance, as the data obtained under laboratory conditions might give an indication of the suitability of flowable resin composites for specific clinical applications.

Fabrication and evaluation of Bis-GMA/TEGDMA dental resins/composites containing nano fibrillar silicate

OBJECTIVE

To investigate the reinforcement of Bis-GMA/TEGDMA dental resins (without conventional glass filler) and composites (with conventional glass filler) with various mass fractions of nano fibrillar silicate (FS).

METHODS

Three dispersion methods were studied to separate the silanized FS as nano-scaled single crystals and uniformly distribute them into dental matrices. The photo-curing behaviors of the Bis-GMA/TEGDMA/FS resins were monitored in situ by RT-NIR to study the photopolymerization rate and the vinyl double bond conversion. Mechanical properties (flexural strength, elastic modulus and work-of-fracture) of the nano FS reinforced resins/composites were tested, and analysis of variance (ANOVA) was used for the statistical analysis of the acquired data. The morphology of nano FS and the representative fracture surfaces of its reinforced resins/composites were examined by SEM/TEM.

RESULTS

Impregnation of small mass fractions (1% and 2.5%) of nano FS into Bis-GMA/TEGDMA (50/50 mass ratio) dental resins/composites improved the mechanical properties substantially. Larger mass fraction of impregnation (7.5%), however, did not further improve the mechanical properties (one way ANOVA, P>0.05) and may even reduce the mechanical properties. The high degree of separation and uniform distribution of nano FS into dental resins/composites was a challenge. Impregnation of nano FS into dental resins/composites could result in two opposite effects: a reinforcing effect due to the highly separated and uniformly distributed nano FS single crystals, or a weakening effect due to the formation of FS agglomerates/particles.

SIGNIFICANCE

Uniform distribution of highly separated nano FS single crystals into dental resins/composites could significantly improve the mechanical properties of the resins/composites.

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.

Quantum yield of conversion of the photoinitiator camphorquinone

The primary absorber in dental resins is the photoinitiator, which starts the photo polymerization process. We studied the quantum yield of conversion of camphorquinone (CQ), a blue light photoinitiator, in dental resin composites using a LED lamp (3M FreeLight) and a Quartz Tungsten Halogen (QTH) lamp (VIP) as the light curing units at five different irradiances. The molar extinction coefficient, epsilon(469), of CQ was 46+/-2 cm(-1)/(mol/L) at 469 nm. The reciprocity of irradiance and exposure time holds for changes of CQ absorption coefficient, that is, irradiance x exposure time (=radiant exposure)=constant. Both LED and QTH lamps yielded the same curing threshold (the radiant exposure when CQ absorption drops to 1/e) and the same quantum yield conversion under different irradiances. In our dental resin formulation (0.7 wt.% CQ with reducing agents 0.35 wt.% dimethylaminoethyl methacrylate (DMAEMA) and 0.05 wt.% butylated hydroxytoluene (BHT)) the quantum yield was measured as 0.07+/-0.01 CQ conversion per absorbed photon.

Effect of the activation mode of post adhesive cementation on push-out bond strength to root canal dentin

OBJECTIVE

To evaluate the effect of the activation mode of adhesive cementation on push-out bond strength of fiber-reinforced resin posts to root canal dentin.

METHOD AND MATERIALS

Forty mandibular premolars were endodontically treated and randomly divided into 4 equal groups. In groups G-1, G-2, and G-3, Single Bond (3M Espe) was applied and light polymerized for 20 seconds; in group G-4, Scotchbond Multi-Purpose Plus (3M Espe) was used as an autopolymerized adhesive. The dual-cure resin cement Rely X ARC (3M Espe) was light polymerized in G-2 and G-3 but not in G-1 and G-4. The translucent post Light-Post (Bisco) was used in G-3 and the opaque post Aestheti-Plus (Bisco) in the other groups. The roots were sectioned in 3 parts (cervical, middle, apical); each slice was submitted to the push-out test at a crosshead speed of 0.5 mm/min. Data were analyzed by analysis of variance and Tukey test (a = .05).

RESULTS

Light polymerization of both the adhesive and resin cement in G-2 led to significantly higher bond strength than in G-1, where only the adhesive was light polymerized. No difference was found between G-2 (opaque post) and G-3 (translucent post). The autopolymerized adhesive showed the highest bond strength in all root regions. The middle and apical post/root regions had similar bond strength, but it was significantly lower than that in the cervical region (P <.001).

CONCLUSION

Bond strength to root dentin varied as a function of the activation mode of post adhesive cementation and post/root regions.

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.

Microtensile bond strength of photoactivated and autopolymerized adhesive systems to root dentin using translucent and opaque fiber-reinforced composite posts

STATEMENT OF PROBLEM

The use of fiber-reinforced composite resin posts in endodontically treated teeth has increased. However, selecting an adhesive system that provides reliable and long-lasting bonding to root canal dentin remains difficult.

PURPOSE

This study evaluated the microtensile bond strength of 2 adhesive systems to root dentin and 2 different fiber-reinforced composite resin posts.

MATERIAL AND METHODS

Forty single-rooted teeth were instrumented, and root canals were prepared for translucent (Light Post [LP]) or opaque (Aestheti Post [AP]) quartz fiber-reinforced composite resin posts. Two adhesive systems were used: Scotchbond Multi-Purpose Plus (SBMP) (autopolymerized) as a control group, and Single Bond (SB) (photoactivated). Teeth were assigned to 4 groups (n=10): SBMP+LP, SBMP+AP, SB+LP, SB+AP. After post cementation, roots were perpendicularly sectioned into 1-mm-thick slices, which were trimmed to obtain dumbbell-shaped specimens. The specimens were divided into 3 regions: cervical (C), middle (M), and apical (A). To determine the bond strength, the bonding area of each specimen was calculated, and specimens were attached to a device to test microtensile strength at a crosshead speed of 1 mm/min. Data were analyzed using 3-way analysis of variance and the Tukey test (alpha=.05). Fractured specimens were examined under a x 25 stereomicroscope to determine the mode of fracture.

RESULTS

There were significant differences only among root dentin regions (P<.001). The cervical third (9.16 +/- 1.18 MPa) presented higher mean bond strength values, especially for SBMP. Middle and apical regions demonstrated lower values (7.08 +/- 0.92 and 7.31 +/- 0.60 MPa, respectively). Adhesive and post main factors did not demonstrate significance. Also, no interaction was significant. No cohesive fractures within resin cement, fiber-reinforced composite resin post, or root dentin were identified.

CONCLUSIONS

Both adhesive systems tested demonstrated reliable bonding when used with translucent and opaque fiber-reinforced composite posts.

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.

Increases in intrapulpal temperature during polymerization of composite resin

STATEMENT OF PROBLEM

The polymerization of dental composite resins can generate increases in intrapulpal temperature that may damage the pulp. The development of new polymerization devices such as the argon laser makes the assessment of these temperatures important.

PURPOSE

This study compared increases in temperature generated by argon laser and halogen light when polymerizing a bonding system and a composite resin, and also sought to determine whether both types of polymerization lights generate temperature increases below the safe limit of 5.5 degrees C.

MATERIAL AND METHODS

Thermocouples linked to a temperature reading system were positioned in the pulp chamber of 10 extracted bovine incisors. Class V cavities were prepared, etched, and filled with a 1-bottle bonding system (Single Bond) and composite resin (Z-100). The test groups were as follows (n = 5 for all groups): halogen light for bonding system (HB); halogen light for composite resin (HC); argon laser for bonding system (LB), and argon laser for composite resin (LC). The polymerization parameters were halogen light operated at 600 mW/cm2 for 40 seconds, which served as control, and argon laser operated at 200 mW for 10 seconds. Data were analyzed by a 2-way (light versus material) analysis of variance (ANOVA) (alpha = .05).

RESULTS

The average temperature increases were 2.35 degrees C (HB), 2.69 degrees C (HC), 1.25 degrees C (LB), and 1.5 degrees C (LC). Significant differences between halogen light and argon laser (P = .002), but not between composite and bonding system, were demonstrated.

CONCLUSIONS

The argon laser produced significantly lower increases in pulpal temperature than the halogen light, independent of the thickness of the polymerized material.

Effect of different photoinitiator systems on conversion profiles of a model unfilled light-cured resin

OBJECTIVE

The aim of this study was to compare the efficiency of different camphorquinone (CQ)/amine photo-initiating systems for the photopolymerization of a model dental resin based in Bis-GMA/TEGDMA.

METHODS

The monomer conversion versus exposure time was measured in resins containing different types and concentrations of photoinitiators and subjected to different irradiation procedures. The conversion profiles during photopolymerization were investigated using near-infrared spectroscopy (NIR). CQ was used in combination with dimethylaminoethylmethacrylate (DMAEMA), ethyl-4-dimethylaminobenzoate (EDMAB), 4-(N,N-dimethylamino)phenethyl alcohol (DMPOH), and N,N-3,5-tetramethylaniline (TMA) at different concentrations.

RESULTS

From the conversion profiles, the approximate order of the accelerating ability of the respective amines were EDMAB approximately DMPOH>TMA>DMAEMA. The conversion profiles of all resins were sensitive to the illumination period. For a given exposure time, samples cured by sequential illumination resulted in lower conversion than samples cured by continuous irradiation. These results were attributed to a combination of both photo and thermal effects. NIR demonstrated to be a convenient method to follow the evolution of the monomer conversion during the photopolymerization of dental resins and, consequently, it is of great utility as a method for determining the relative efficacy of different photoinitiator.

SIGNIFICANCE

The DMPOH/benzoyl peroxide redox system, has been recently proposed as a more biocompatible accelerator for the polymerization of acrylic resins. The results obtained in the present study reveal the potential usefulness of the DMPOH amine in light-cured dental composites.

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.

Effective single-charge end point of cordless light-emitting diode light-curing units

INTRODUCTION

The purpose of this study was to evaluate the battery lives of cordless light-emitting diodes (LEDs) and their effect on orthodontic bracket bond strength.

METHODS

One hundred eighty-six metal orthodontic brackets were bonded to extracted molars. Two LED light-curing units (L. E. Demetron [SDS/Kerr, Orange, Calif] and Ortholux [3M Unitek, Monrovia, Calif]) were evaluated. Each light was used to bond 93 specimens. One bracket was bonded every 5 minutes until the battery ran out. The lights were activated for 20 seconds, then automatically turned off for 40 seconds every minute (33% duty cycle) without recharging. Bonded specimens were stored in water at 37 degrees C for 24 hours and then subjected to shear force with a universal testing machine until bracket failure.

RESULTS

Repeated measures ANOVA detected significantly weaker mean shear bond strength and fewer consecutive cures with the Ortholux compared with the L. E. Demetron light-curing unit. However, when the first 5 time points were excluded, there were no differences between the 2 lights, demonstrating that the lights performed similarly after the first 20 minutes of operation Just before battery failure, both lights still provided the same power density as at the beginning.

CONCLUSIONS

Both light-curing units provided adequate power density for up to 2 hours without recharging at a 33% duty cycle. There was no significant decrease in power in cordless LED light-curing units as the battery life approached its end point.

A new kinetic model for the photopolymerization shrinkage-strain of dental composites and resin-monomers

OBJECTIVES

The aim of the study was to develop a new kinetic model for the shrinkage-strain rates of dental resin composites. The effect of filler content on the shrinkage-strain kinetics and degree of conversion of dental composites was also investigated.

METHODS

A resin matrix containing 65 wt.% Bis-GMA and 35 wt.% TEGDMA was prepared. 0.5 wt.% camphorquinone and 0.5 wt.% dimethyl aminoethyl methacrylate were dissolved in the resin as photo-initiator system. Silanized glass fillers were added in different percentages to the resin-monomers. The shrinkage-strain of the specimens photopolymerized at circa 550 mW/cm2 was measured using the bonded-disc technique at 23, 37 and 45 degrees C for the matrix monomers and 23 degrees C for the composites. Initial shrinkage-strain rates were obtained by numerical differentiation of shrinkage-strain data with respect to time. Degree-of-conversion of the composites containing different filler contents was measured using FTIR spectroscopy.

RESULTS

A new kinetic model was developed for the shrinkage-strain rate using the autocatalytic model of Kamal [Kamal MR, Sourour S. Kinetic and thermal characterization of thermoset cure. Polym Eng Sci 1973;13(1):59-64], which is used to describe the reaction kinetics of thermoset resins. The model predictions were in good agreement with the experimental data. The results also showed a linear correlation between the shrinkage-strain (and shrinkage-strain rate) and filler-volume fraction. The filler fraction did not affect the degree-of-conversion of the composites.

SIGNIFICANCE

The rate of polymerization, determined via the shrinkage, being invariant with filler-fraction, suggests that only a relatively high filler-surface area, as may be obtained with nano-fillers, will affect the network-forming kinetics of the resin matrix.

Effect of led light curing on the marginal sealing of composite resin restorations

Light-emitting diode (LED) curing units are becoming increasingly popular; however, questions remain about their ability to adequately polymerize composite resins. This study was conducted to evaluate the marginal seal of restorations placed with a tungsten halogen curing unit compared to three LED curing units through a microleakage test. The results did not indicate statistical differences between the groups tested for both enamel and dentin margins. Variation of the light-curing unit (quartz tungsten halogen or LED) did not result in discernible differences in the marginal sealing of composite restorations.

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.

Volume contraction in photocured dental resins: The shrinkage-conversion relationship revisited

Polymerization shrinkage and degree of conversion (DC) of resin composites are closely related manifestations of the same process. Ideal dental composite would show an optimal degree of conversion and minimal polymerization shrinkage. These seem to be antagonistic goals, as increased monomer conversion invariably leads to high polymerization shrinkage values.

OBJECTIVES

This paper aims at accurately determining the polymerization volume contraction of experimental neat resins and to link it to the number of actual vinyl double bonds converted in single ones instead of, as generally done, to the degree of conversion.

METHODS

Different mixtures of Bis-GMA/TEGDMA (traditionally used monomers) were analyzed. Contraction of the polymers was determined by pycnometry and the use of a density column. DC was determined by the use of Raman spectrometry.

RESULTS

An univocal relationship has been found between the volume contraction and the actual number of vinyl double bonds converted into single ones. A contraction value of 20.39 cm3/mole (of converted C=C) was deduced from 27 measurements.

SIGNIFICANCE

This relationship helps in finding solutions to the polymerization shrinkage problem. A reduction of the polymerization shrinkage due to the chemical reaction may obviously be expected from the addition of molecules allowing a decrease in the number of double bonds converted per unit volume of resin matrix, while maintaining the degree of conversion (of Bis-GMA and TEGDMA) and thus the mechanical properties. Further research will be directed at this objective.

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.

Time-based Elution of TEGDMA and BisGMA from Resin Composite Cured with LED, QTH and High-intensity QTH Lights

Under the conditions of this study, when compared to standard QTH, both standard LED and high-intensity QTH light curing resulted in lower levels of the elution of TEGDMA, which is suspected to be the prime cause of cytotoxic reactions in resin composite restorations.

Effect of shorter polymerization times when using the latest generation of light-emitting diodes

INTRODUCTION

Recent studies have suggested that a 10-second cure time with a high-energy quartz-tungsten-halogen (QTH) or a light-emitting diode (LED) light might be adequate when bonding orthodontic brackets to tooth enamel. The purpose of this study was to evaluate the ability of the latest generation of QTH and LED light-curing units (LCUs) to bond orthodontic brackets to teeth at decreased polymerization times.

METHODS

Two LED LCUs (Ortholux LED, 3M Unitek, Monrovia, Calif; UltraLume LED 5, Ultradent Products, South Jordan, Utah) and a QTH LCU (Optilux 501, Demetron, Danbury, Conn) were evaluated. One hundred eighty metal orthodontic brackets were bonded to extracted human molars. The specimens were divided into 9 groups (3 lights and 3 curing times) of 20 teeth each. Each group was cured with 1 of the 3 lights for 20, 10, or 6 seconds. Thirty minutes after polymerization, the specimens were subjected to shear force on a universal testing machine until bracket failure.

RESULTS

Two-way ANOVA detected significant differences among the main effects of light type and cure time. Tukey post-hoc tests determined that brackets bonded by all light types had lower bond strengths with the 6-second cure than the 20-second cure (P < .001). The highest bond strengths were obtained with the Optilux 501 QTH LCU and the UltraLume LED 5 LCU at the longest cure time of 20 seconds.

CONCLUSIONS

It is recommended that orthodontic brackets be photopolymerized for at least 20 seconds with the QTH or the LED LCU before the archwires are engaged.

Impact of curing protocol on conversion and shrinkage stress

Since considerable shrinkage stress develops during the curing of dental composites, various soft-start photocuring protocols, aiming to lower stress but not compromise conversion, have been proposed. We hypothesized that utilizing soft-start photocuring will result in not only reduced stress, but also decreased conversion. We evaluated the impact of 3 protocols (soft-start, pulse, and standard) on the stress development and polymerization extent of an experimental composite. A novel set-up capable of simultaneous shrinkage stress, conversion, and temperature measurements on the same specimen was utilized. Analysis of the data shows that stress rises dramatically as a function of conversion in the vitrified state, and the utilization of soft-start or pulse curing results in specimens with reduced final conversion and shrinkage stress, compared with specimens cured according to the standard full-intensity protocol. Finally, this study demonstrates that the predominant reason for the reduced shrinkage stress attained with soft-start or pulse curing is a modest decrease in final conversion.

Composite resin's adhesive resistance to dentin: influence of Er:YAG laser focal distance variation

The aim of this study was to analyze in vitro the influence of Er:YAG laser focal distance variation on tensile bond strength of a composite resin to dentin. Although there are several studies using the Er:YAG laser for dentin treatment, there is a lack of available literature related to the Er:YAG laser focal distance variation. Sixty vestibular and lingual dentin surfaces from extracted human third molars, kept in a 0.4% azide sodium solution, were ground and assigned to six groups. The control group was conditioned with 35% phosphoric acid (CA). In the lased groups, the dentin surface treatment was performed by irradiation with Er:YAG laser (80 mJ/2 Hz), varying the focal distance (11, 12, 14, 16, and 17 mm), followed by acid etching. The Single Bond/Filtek Z250 (3M) resinous system was used for the specimen manufacture. The tensile bond strength tests were performed in a Universal Testing Machine with 50 kgf load cell and 0.5 mm/min cross head speed. The averages in MPa were: CA: 18.03 (+/-2.09); 11 mm; 9.92 (+/-3.34); 12 mm: 9.49 (+/-2.29); 14 mm: 10.99 (+/-3.45); 16 mm: 10.56 (+/-1.93); and 17 mm: 17.05 (+/-2.31). It was concluded that the application of Er:YAG laser in a defocused mode (17 mm) associated with acid etching was similar to the treatment of acid solely. Er:YAG laser irradiation in a focused (12 mm) and a defocused (11, 14, and 16 mm) mode coupled with acid conditioning produced the lowest values of adhesion.

Light curing time reduction: in vitro evaluation of new intensive light-emitting diode curing units

The aim of the present in vitro study was to establish the minimum necessary curing time to bond stainless steel brackets (Mini Diamond Twin) using new, intensive, light-emitting diode (LED) curing units. Seventy-five bovine primary incisors were divided into five equal groups. A standard light curing adhesive (Transbond XT) was used to bond the stainless steel brackets using different lamps and curing times. Two groups were bonded using an intensive LED curing lamp (Ortholux LED) for 5 and 10 seconds. Two more groups were bonded using another intensive LED curing device (Ultra-Lume LED 5) also for 5 and 10 seconds. Finally, a high-output halogen lamp (Optilux 501) was used for 40 seconds to bond the final group, which served as a positive control. All teeth were fixed in hard acrylic and stored for 24 hours in water at 37 degrees C. Shear bond strength (SBS) was measured using an Instron testing machine. Weibull distribution and analysis of variance were used to test for significant differences. The SBS values obtained were significantly different between groups (P < 0.001). When used for 10 seconds, the intensive LED curing units achieved sufficient SBS, comparable with the control. In contrast, 5 seconds resulted in significantly lower SBS. The adhesive remnant index (ARI) was not significantly affected.A curing time of 10 seconds was found to be sufficient to bond metallic brackets to incisors using intensive LED curing units. These new, comparatively inexpensive, curing lamps seem to be an advantageous alternative to conventional halogen lamps for bonding orthodontic brackets.

Class II composite resin restorations with two polymerization techniques: relationship between microtensile bond strength and marginal leakage

OBJECTIVE

To determine the relationship between leakage and microtensile bond strength in the same specimen of direct Class II composite restorations performed with two polymerization techniques.

METHODS

Class II slot preparations were made in 40 non-carious human third molars and restored using Single Bond and P-60 (3M ESPE) according to the manufacturer's indications. Half of the preparations had the cervical margin in enamel and half in dentin. Teeth were incrementally restored either with direct polymerization from occlusal surface or with indirect polymerization through translucent matrices and reflective wedges. Teeth were isolated with nail varnish and immersed in fucsin for 24h. Subsequently, they were sectioned into slabs that were measured for leakage (mm), and trimmed to obtain hour-glass shaped specimens for microtensile bond test. Fractured specimens were examined under magnification (40 x) to evaluate the fracture mode. Data were analyzed with Mann-Whitney and Kruskal-Wallis (microleakage), two-way ANOVA and Student-Newman-Keuls tests (bond strength). The relationship between microleakage and microtensile bond strength were analyzed with Spearman's correlation test.

RESULTS

There were no significant effects of polymerization technique and margin location on both leakage and bond strength (p>0.05). Bond strengths were higher in preparations with enamel margins than in preparations with dentin margins, when restored with indirect polymerization technique (p<0.05). No significant correlation was found between leakage and bond strength (p>0.05).

CONCLUSIONS

Polymerization techniques had no influence on microleakage and bond strength of Class II composite restorations, and there was no relationship between these variables when evaluated in the same specimen.

Shrinkage behavior of a resin-based composite irradiated with modern curing units

OBJECTIVE

The present study determined the influence of different light curing regimes (four light-emitting diode (LED) units (Freelight 1 and 2, 3M-ESPE; e-light, GC; Bluephase (prototype), Ivoclar Vivadent), two quartz-tungsten-halogen (QTH) lights (Astralis 10, Ivoclar Vivadent; Swiss Master Light, EMS) and one plasma-light curing unit (Easy Cure, DMDS)) on the curing behavior of a resin-based composite material (InTen-S, Ivoclar Vivadent).

METHODS

Polymerization shrinkage was induced by light curing the tested material with 14 different regimes of the curing units mentioned above. The contraction stress was recorded for 300 s at room temperature with a Stress-Strain-Analyzer (c(FACTOR)=0.3). The maximum contraction stresses after 300 s, the time until gelation (t(0.5N)), and the coefficient of near linear fit of contraction force/time (gradient) were analyzed. The statistical analysis was conducted using ANOVA (alpha=0.05) and Tukey's post hoc test.

RESULTS

The five tested regimes of the LED unit e-light revealed the lowest statistically significantly maximum contraction stress followed by the low intensity LED unit Freelight 1 and the plasma curing unit Easy Cure. The high intensity LED unit Freelight 2 exhibited a significantly higher contraction stress compared to Freelight 1. No significant differences between the standard and exponential modes within these curing units were found. No significant differences were found between the LED unit Freelight 2 and the pulse program of the halogen light curing unit Astralis 10. The highest polymerization stresses were observed for the high energy curing units, either QTH (Swiss Master Light and Astralis 10) or LED (Bluephase).

SIGNIFICANCE

Fast contraction force development, high contraction stress and an early start of stress build-up cause tension in the material with possible subsequent distortion of the bond to the tooth structure. The lowest polymerization stress was observed for the low energy LED lamps, while the plasma unit and the high energy QTH and LED curing units produced two to three times higher stress.

Reduced irradiation time in slow-curing of resin composite using an intensity-changeable light source

Possibility to shorten the total irradiation time in slow-curing with an intensity-changeable light source, Curetron 7 (CT-7), was investigated for four hybrid-type resin composites. Irradiation condition with CT-7 was assigned as 10 or 20 seconds at low light intensity (230 mW/cm2) and followed by 20 or 10 seconds at high intensity (600 mW/cm2) respectively (i.e., a total of 30 seconds). For a reference, irradiation was carried out for 30 seconds using a halogen lamp (900 mW/cm2). After irradiation, mechanical properties of the cured composites--in terms of microhardness and flexural strength--were evaluated. Also, cavity adaptation was examined in standardized, cylindrical dentin cavities treated with an adhesive system. Compared to the reference irradiation, slow-curing with CT-7 produced acceptable mechanical properties and better adaptation. These results suggested that total exposure time of slow-curing with CT-7 could be shortened to 30 seconds.

Effect of Stepped Exposure on Quantitative In Vitro Marginal Microleakage

PURPOSE

The aim of this in vitro study was to evaluate the effect of a soft-start curing mode on microleakage

MATERIALS AND METHODS

Standardized Class V cavities were prepared within all the margins in the buccal enamel or dentin surface of sound, freshly extracted inferior bovine incisors. Forty preparations were filled with a restorative system (Single Bond and Filtek Z250, 3M ESPE, St. Paul, MN, USA). Ten restorations of each group were made on both types of substrates and polymerized with a conventional curing technique (600 mW/cm2/40 s) or with a soft-start technique (150 mW/cm2/10 s + 600 mW/cm2/30 s). All specimens were thermocycled 3000 times and then immersed in methylene blue 2% for 12 hours. The specimen microleakage was quantitatively determined in a spectrophotometer.

RESULTS

The soft-start technique resulted in statistically significant less microleakage for each substrate (p < .05). The conventional groups exhibited 6.1 (dentin) to 15.4% (enamel) more leakage compared with the soft-start groups. When compared with the enamel margins, the dentin margins demonstrated greater microleakage: from 15.5% greater with the conventional light-curing mode to 25.6% greater with the soft-start light-curing mode.

CONCLUSIONS

The polymerization technique using a very low initial intensity (150 mW/cm2/10 s) decreased the microleakage of composite resin restorations.

CLINICAL SIGNIFICANCE

A soft-start light-curing approach to resin composite polymerization resulted in less microleakage at enamel and dentin margins in Class V cavities compared with resin composite restorations polymerized using a conventional light-curing approach.

Microtensile Bond Strength Analysis of Different Adhesive Systems and Dentin Prepared with High-Speed and Er:YAG Laser: A Comparative Study

OBJECTIVE

The aim of this study was to evaluate the bond strength of two adhesive systems (Single Bond and Clearfil SE Bond) subjected or not to a thermocycling procedure and applied to cavities prepared either with high-speed diamond bur or Er:YAG laser.

BACKGROUND DATA

One of the possible applications of dental lasers includes increasing the quality of bond strength.

METHODS

This in vitro study was carried out using a microtensile test on 16 bovine teeth, divided into eight groups. Cavities were prepared on superficial dentin of the medium portion of the buccal surface. After application of adhesive systems, composite restorations were performed at 5-mm height. After 24 h, four groups of teeth were immersed in water, and the other four were thermocycled. Bonded specimens were sectioned into serial 1x1-mm beams, which were subjected to a microtensile test. Final values of bond strength were measured, expressed in MPa, and statistically analyzed.

RESULTS

Results were as follows: G1 (26.281 +/- 5.454 MPa); G2 (10.965 +/- 3.714 MPa); G3 (18.549 +/- 6.113 MPa); G4 (14.295 +/- 3.806 MPa); G5 (18.225 +/- 5.701 MPa); G6 (5.588 +/- 2.211 MPa); G7 (18.256 +/- 3.819 MPa); and G8 (15.423 +/- 4.714 MPa).

CONCLUSIONS

Self-etching adhesive system (SE) produced more stable bond strength results than the system that indicates total etching (SB). For dentin prepared at high speed, the total etching adhesive system was more indicated, whereas Er:YAG laser-preparation dentin was not influenced by the adhesive system. The thermocycling procedure could negatively affect microtensile bond strength of both adhesive systems, being more deleterious to SB than to SE.