Effect of a DPSS laser on the shear bond strength of ceramic brackets with different base designs

This study evaluated the shear bond strength (SBS) and adhesive remnant index (ARI) of ceramic brackets with different base designs using a 473-nm diode-pumped solid-state (DPSS) laser to test its usefulness as a light source. A total of 180 caries-free human premolars were divided into four groups according to the base designs: microcrystalline, crystalline particle (CP), dovetail, and mesh. For each base design, teeth were divided into three different subgroups for light curing using three different light-curing units (LCUs) (quartz–tungsten–halogen unit, light-emitting diode unit, and a DPSS laser of 473 nm). Applied light intensities for the DPSS laser and the other LCUs were approximately 630 and 900 mW/cm², respectively. Stainless steel brackets with a mesh design served as controls. The failure modes of debonded brackets were scored using ARI. As a result, brackets bonded using the DPSS laser had the highest SBS values (16.5–27.3 MPa) among the LCUs regardless of base design. Regarding base designs, the CP groups showed the highest SBS values (22.9–27.3 MPa) regardless of LCU. Furthermore, stainless steel brackets with a mesh design had the lowest SBS values regardless of LCU. In many cases, brackets bonded using the DPSS laser had higher ARI scores and had more adhesive on their bases than on tooth surfaces. The study shows that the 473-nm DPSS laser has considerable potential for bonding ceramic brackets at lower light intensities than the other light-curing units examined.     

Temperature analysis during bonding of brackets using LED or halogen light base units

The purpose of our investigation is to compare the intrapulpal temperature changes following blue LED system and halogen lamp irradiation at the enamel surface of permanent teeth. The fixation of brackets using composite resin is more comfortable and faster when using a photo-curable composite. Several light sources can be used: halogens, arc plasma, lasers, and recently blue LED systems. An important aspect to be observed during such a procedures is the temperature change. In this study, we have used nine human extracted permanent teeth: three central incisors, three lateral incisors, and three canines. Teeth were exposed to two light sources: blue LED system (preliminary commercial model LEC 470-II) and halogen lamp (conventional photo-cure equipment). The surface of teeth was exposed for 20, 40, and 60 sec at the buccal and lingual enamel surface with an angle of 45 degrees. Temperature values measured by a thermistor placed at pulpar chamber were read in time intervals of 1 sec. We obtained plots showing the temperature evolution as a function of time for each experiment. There is a correlation between heating quantity and exposition time of light source: with increasing exposition time, heating increases into the pulpal chamber. The halogen lamp showed higher heating than the LED system, which showed a shorter time of cooling than halogen lamp. The blue LED system seems like the indicated light source for photo-cure of composite resin during the bonding of brackets. The fixation of brackets using composite resin is more comfortable and faster when using a photo-curable composite. Blue LED equipment did not heat during its use. This could permit a shorter clinical time of operation and better performance.     

The effect of curing light and chemical catalyst on the degree of conversion of two dual cured resin luting cements

The aim of this study was to evaluate the influence of different curing lights and chemical catalysts on the degree of conversion of resin luting cements. A total of 60 disk-shaped specimens of RelyX ARC or Panavia F of diameter 5 mm and thickness 0.5 mm were prepared and the respective chemical catalyst (Scotchbond Multi-Purpose Plus or ED Primer) was added. The specimens were light-cured using different curing units (an argon ion laser, an LED or a quartz-tungsten-halogen light) through shade A2 composite disks of diameter 10 mm and thickness 2 mm. After 24 h of dry storage at 37°C, the degree of conversion of the resin luting cements was measured by Fourier-transformed infrared spectroscopy. For statistical analysis, ANOVA and the Tukey test were used, with p ≤ 0.05. Panavia F when used without catalyst and cured using the LED or the argon ion laser showed degree of conversion values significantly lower than RelyX ARC, with and without catalyst, and cured with any of the light sources. Therefore, the degree of conversion of Panavia F with ED Primer cured with the quartz-tungsten-halogen light was significantly different from that of RelyX ARC regardless of the use of the chemical catalyst and light curing source. In conclusion, RelyX ARC can be cured satisfactorily with the argon ion laser, LED or quartz-tungsten-halogen light with or without a chemical catalyst. To obtain a satisfactory degree of conversion, Panavia F luting cement should be used with ED Primer and cured with halogen light.     

Influence of the LED curing source and selective enamel etching on dentin bond strength of self-etch adhesives in class I composite restorations

The aim of this study was to evaluate the influence of the LED curing unit and selective enamel etching on dentin microtensile bond strength (μTBS) for self-etch adhesives in class I composite restorations. On 96 human molars, box-shaped class I cavities were made maintaining enamel margins. Self-etch adhesives (Clearfil SE - CSE and Clearfil S(3) - S3) were used to bond a microhybrid composite. Before adhesive application, half of the teeth were enamel acid-etched and the other half was not. Adhesives and composites were cured with the following light curing units (LCUs): one polywave (UltraLume 5 - UL) and two single-peak (FlashLite 1401 - FL and Radii Cal - RD) LEDs. The specimens were then submitted to thermomechanical aging and longitudinally sectioned to obtain bonded sticks (0.9 mm(2)) to be tested in tension at 0.5 mm/min. The failure mode was then recorded. The μTBS data were submitted to a three-way ANOVA and Tukey's (α?=?0.05). For S3, the selective enamel-etching provided lower μTBS values (20.7?±?2.7) compared to the non-etched specimens (26.7?±?2.2). UL yielded higher μTBS values (24.1?±?3.2) in comparison to the photoactivation approach with FL (18.8 ±3.9) and RD (19.9 ±1.8) for CSE. The two-step CSE was not influenced by the enamel etching (p?≥?0.05). Enamel acid etching in class I composite restorations affects the dentin μTBS of the one-step self-etch adhesive Clearfil S(3), with no alterations for Clearfil SE bond strength. The polywave LED promoted better bond strength for the two-step adhesive compared to the single-peak ones.     

光照时间对自制光固化型牙科玻璃纤维桩弯曲强度影响的实验研究

目的：研究光照时间对自制光固化型牙科玻璃纤维桩弯曲强度的影响。方法：自行合成制作光固化型牙科玻璃纤维桩三点弯曲试件20个,随机分为4组（5个／组）,分别进行20s、40s、60s、80s光照固化,测三点弯曲强度,进行单因素方差分析和LSD—t检验。结果：各组弯曲强度为525．76MPa、568．27MPa、602．93MPa和604．12MPa;统计学分析显示,60s组与80s组无显著性差异（P〉O．05）,20s组、40s组和60s组或80s组两两间有显著性差异（P〈0．05）。结论：自制光固化型牙科玻璃纤维桩的弯曲强度随光照时间的延长而提高,60s后趋于平稳,综合考虑材料固化后的弯曲强度和临床操作效率,其理想光照时间为60s。     

The applicability of DPSS laser for light curing of composite resins

The applicability of diode-pumped solid state (DPSS) laser for light curing the composite resins was tested with a quartz–tungsten–halogen lamp-based unit and a light emitting diode unit. The emission spectra of the light-curing systems used match with the absorption spectrum of camphorquinone. Among the light-curing systems, DPSS laser showed the narrowest emission bandwidth. The light intensity of DPSS laser was approximately 64% of the other two light-curing units. In most specimens, DPSS laser showed the least attenuation of the number of incident photons. On the top surface, specimens cured with DPSS laser showed similar microhardness values compared to the specimens cured with the other two light-curing units. During the light curing, DPSS laser induced the lowest temperature rise (25.5 ∼ 35.5°C) in the specimens compared to the other two light-curing units (34.2 ∼ 41.7°C). In conclusion, DPSS laser has high potential to be an alternative to the other light-curing units or a new light-curing unit.     

Laser Florence 2009

In this study, we compared the microleakage of composite fillings cured with halogen bulb, LED and argon ion laser (488 nm). Twenty-four extracted human molars were divided randomly in three groups. Six cavities were prepared on the coronal part of each tooth. Standard cavities (1.7 × 2 mm) were prepared. Cavities were acid etched, sealed with Scotch Bond 1 and filled by a hybrid composite. Cavities were exposed to one light source, thermocycled and immersed in a 2% methylene blue dye solution. Dye penetration in the leakage of cavities was recorded using a digital optical microscope. Mean values of percentage of dye penetrations in microleakages of cavities were 49.303 ± 5.178% for cavities cured with LED, 44.486 ± 6.075% with halogen bulb and 36.647 ± 5.936% for those cured by argon laser. Statistically significant difference exists between cavities cured by halogen vs LED (P < 0.01), halogen vs laser (P < 0.001) and LED vs laser (P < 0.001). The lowest microleakage was observed in the cavities and composites cured with argon ion laser.     

Effect of light polymerization time,mode, and thermal and mechanical load cycling on microleakage in resin composite restorations

This study evaluated the effect of polymerization mode and time and thermal and mechanical loading cycling (TMC) on microleakage in composite resin restorations. One hundred and eighty cavities were prepared and randomly divided according to the light curing time (20, 40, or 60 s), modes (quartz–tungsten–halogen (QTH)—420 mW/cm², LED 2 (2nd degree generation)—1,100 mW/cm², or LED 3 (3rd degree generation)—700 mW/cm²), and TMC. Following standard restorative procedures, the samples were prepared for analysis in an absorbance spectrophotometer. All results were statistically analyzed using the three-way ANOVA and Tukey test (p?≤?0.05). The results revealed that the groups QTH and LED 3 submitted to TMC showed higher microleakage than those that were not submitted to TMC. Only for LED 3, 60 s showed higher microleakage than 20 s. For LED 2 and QTH, there were no differences between the times. QTH showed lower microleakage means than LED 2, when photoactivated for 20 s, without TMC. When photoactivated for 60 s, QTH showed lower microleakage means than LED 3, for the groups with or without TMC. It was concluded that TMC, the increase in polymerization time, and the irradiance were factors that may increase the marginal microleakage of class II cavities.     

Light-curing of dental resins with GaN violet laser diode: The effect of photoinitiator on mechanical strength

The purpose of this study was to evaluate whether a Gallium Nitride (GaN) -based violet laser diode (VLM500) could be used as a light source for light-cured dental resins. Three experimental unfilled resins containing different photoinitiators (camphorquinone, CQ; phenyl propanedione, PPD; or mono acylphosphineoxide, MAPO) were evaluated. These resins were light-cured with a VLM500 laser diode, and their ultimate micro-tensile strengths (μTS) were compared to those cured with three different LED light sources (Curenos, G-Light Prima-normal mode and G-Light Prima-PL mode). The VLM500 produced high μTS values in all three resins, and we concluded that this violet laser diode can be used as a light source for light-cured dental resin materials.     

Effect of diode-pumped solid state laser on polymerization shrinkage and color change in composite resins

A diode-pumped solid state (DPSS) laser emitting at 473 nm was used to test its influence on the degree of polymerization of composite resins. Eight composite resins were chosen and light cured with three different light-curing systems [a quartz–tungsten–halogen (QTH) lamp-based unit, a light-emitting diode (LED) unit, and a DPSS laser]. Polymerization shrinkage and color change in specimens were measured. According to the statistical analysis, each light-curing system produced a significantly different value of maximum polymerization shrinkage. In most specimens, the DPSS laser induced the least polymerization shrinkage. After being immersed in distilled water for 10 days, specimens light-cured by the DPSS laser had undergone less color change than those cured by the other units. In conclusion, the DPSS laser induced better or similar polymerization in terms of polymerization shrinkage and color change in composite resins compared with those of the QTH lamp-based and LED units.     

Argon ion laser curing depth effect on a composite resin

The aim of this study was to define optimal power settings as well as curing time associated with evaluating the curing depth of a composite resin as a function of Vickers hardness. The tests were performed with a hybrid composite resin cured with a halogen lamp and argon ion laser, with different exposure times and power settings. The composite resin bulk technique was used using a black polypropylene matrix with thicknesses ranging from 1 to 4 mm and Vickers microhardness was measured on the opposite surface of the light activation. ANOVA and Tukey statistical tests were used. The results showed that the groups activated by the laser for 20 s, at 200 and 250 mW, did not present statistically significant differences regarding the halogen lamp with 1 mm thickness, but the halogen lamp showed better results with thickness values more than 2 mm (p < 0.05).     

Micro-hardness evaluation of a micro-hybrid composite resin light cured with halogen light, light-emitting diode and argon ion laser

This in vitro study aimed to determine whether the micro-hardness of a composite resin is modified by the light units or by the thickness of the increment. Composite resin disks were divided into 15 groups (n = 5), according to the factors under study: composite resin thickness (0 mm, 1 mm, 2 mm , 3 mm and 4 mm) and light units. The light activation was performed with halogen light (HL) (40 s, 500 mW/cm²), argon ion laser (AL) (30 s, 600 mW/cm²) or light-emitting diode (LED) (30 s, 400 mW/cm²). Vickers micro-hardness tests were performed after 1 week and were carried out on the top surface (0 mm—control) and at different depths of the samples. Analysis of variance (ANOVA) and Tukey tests (P ≤ 0.05) revealed no statistically significant difference among the light units for the groups of 0 mm and 1 mm thickness. At 2 mm depth, the AL was not statistically different from the HL, but the latter showed higher micro-hardness values than the LED. In groups with 3 mm and 4 mm thickness, the HL also showed higher micro-hardness values than the groups activated by the AL and the LED. Only the HL presented satisfactory polymerization with 3 mm of thickness. With a 4 mm increment no light unit was able to promote satisfactory polymerization.     

Effect of aging and curing mode on the compressive and indirect tensile strength of resin composite cements

Background

Resin composite cements are used in dentistry to bond ceramic restorations to the tooth structure. In the oral cavity these cements are subjected to aging induced by masticatory and thermal stresses. Thermal cycling between 5 and 55 °C simulates the effect of varying temperatures in vitro. Purpose of this study was to compare indirect tensile to compressive strength of different cements before and after thermal cycling. The effect of the curing mode was additionally assessed.

Methods

Indirect tensile strength and compressive strength of 7 dual-curing resin composite cements (Multilink Automix, Multilink SpeedCem, RelyX Ultimate, RelyX Unicem 2 Automix, Panavia V5, Panavia SA Plus, Harvard Implant semi-permanent) was measured. The specimens were either autopolymerized or light-cured (n =?10). The mechanical properties were assessed after 24 h water storage at 37 °C and after aging (20,000 thermo cycles) with previous 24 h water storage at 37 °C.

Results

Indirect tensile strength ranged from 5.2?±?0.8 to 55.3?±?4.2 MPa, compressive strength from 35.8?±?1.8 MPa to 343.8?±?19.6 MPa.

Conclusions

Thermocyclic aging of 20,000 cycles can be considered a suitable method to simulate the degradation of indirect tensile strength but not compressive strength of resin composite cements. The effect of thermocycling and the curing mode on the resin composite cements is material dependent and cannot be generalized.

     

The “Z‐effect” phenomenon defined: A laboratory study

The Z‐effect phenomenon is a potential complication of two lag screw intramedullary nail designs used for fixation of intertrochanteric hip fractures, in which the inferior lag screw migrates laterally and the superior lag screw migrates medially during physiologic loading. The current investigation was undertaken in an attempt to reproduce the Z‐effect phenomenon in a laboratory setting. Sixteen different simulated femoral head and neck constructs having varying compressive strengths were created using four densities of solid polyurethane foam and instrumented with a two‐screw cephalomedullary intramedullary nail. Each specimen was then cyclically loaded with 250 N vertical loads applied for 10, 100, 1000, and 10,000 cycles. Measurement of screw displacement with respect to the lateral aspect of the intramedullary nail was made after each cyclic increment. The inferior lag screw migration component of the Z‐effect phenomenon was reproduced in specimens with head compressive strengths that were higher than the compressive strengths of the neck. Specimens with the greatest difference in head–neck compressive strength demonstrated the most significant displacement of the inferior lag screw without any displacement of the superior lag screw. Specimens with a femoral neck compressive strength of 0.91 MPa of and a head compressive strength of 8.8 MPa resulted in more than one centimeter of inferior lag screw lateral migration after 10,000 cycles of vertical loading. Models where the femoral head had a higher compressive strength than that of the femoral neck may simulate fracture patterns with significant medial cortex comminution that are prone to varus collapse. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 25:1568–1573, 2007     

Additional mechanical tests of bone cements.

A revision of the ISO-standard for bone cement testing has been proposed to include compressive strength after 24 hours in air and 4-point bending testing after 50 hours in a 37 degrees water bath. Nine commercially available bone cements were tested in accordance with the new program. Compressive strength varied from 78 to 100 MPa, bending strength from 48 to 74 MPa and bending modulus from 2.2 to 2.8 GPa. The highest strengths, but also the highest stiffness, were encountered with Simplex brands and low-viscosity cements.     

Influence of a Blue DPSS Laser on Specimen Thickness of Composite Resins

Abstract Objective: The purpose of the present study was to investigate the effect of 473?nm diode-pumped solid state (DPSS) laser on the curing depth of composite resins. Background data: Within the turbid media, light attenuates significantly because of the absorption and scattering. Materials and methods: For the study, three different composite resins and light-curing units (LCUs) (a quartz-tungsten-halogen [QTH], light-emitting-diode [LED], and DPSS laser) were used. The number of photons transmitted through the specimens, degree of conversion (DC), microhardness, and refractive index of the specimens on different thicknesses were evaluated. Results: The incident light exponentially decreased within the specimens. Among the LCUs, QTH showed the least photon loss. The DC obtained using the DPSS laser and QTH was significantly greater (p<0.001) than that obtained using LED. The specimens light cured using the DPSS laser showed slightly lower microhardness than that cured by the other LCUs. On each depth, the mean refractive index was not significantly different for the LCUs used. DC, microhardness, and refractive index had inverse linear correlation with specimen thickness despite exponential decrease of photons number. On the other hand, DC, microhardness, and refractive index were linearly correlated to each other regardless of LCUs. Conclusions: The DPSS laser of 473?nm achieved a similar level of polymerization within the specimens as those of the other LCUs even with much lower light intensity. This laser can be applied as a light source for light curing of composite resins.     

The influence of the energy density and other clinical parameters on bond strength of Er:YAG-conditioned dentin compared to conventional dentin adhesion

The aim of this in vitro study was to optimise clinical parameters and the energy density of Er:YAG laser-conditioned dentin for class V fillings. Shear tests in three test series were conducted with 24 freshly extracted human third molars as samples for each series. For every sample, two orofacial and two approximal dentin surfaces were prepared. The study design included different laser energies, a thin vs a thick bond layer, the influence of adhesives as well as one-time- vs two-time treatment. The best results with Er:YAG-conditioned dentin were obtained with fluences just above the ablation threshold (5.3 J/cm²) in combination with a self-etch adhesive, a thin bond layer and when bond and composite were two-time cured. Dentin conditioned this way reached an averaged bond strength of 23.32 MPa (SD 5.3) and 24.37 MPa (SD 6.06) for two independent test surfaces while showing no statistical significance to conventional dentin adhesion and two-time treatment with averaged bond strength of 24.93 MPa (SD 11.51). Significant reduction of bond strength with Er:YAG-conditioned dentin was obtained when using either a thick bond layer, twice the laser energy (fluence 10.6 J/cm²) or with no dentin adhesive. The discussion showed clearly that in altered (sclerotic) dentin, e.g. for class V fillings of elderly patients, bond strengths in conventional dentin adhesion are constantly reduced due to the change of the responsibles, bond giving dentin structures, whereas for Er:YAG-conditioned dentin, the only way to get an optimal microretentive bond pattern is a laser fluence just above the ablation threshold of sclerotic dentin.     

Safe pleural contraction employing a new tip for electrosurgical units

Background: Certain pulmonary lesions are treated by lung tissue contraction induced by heat administered by laser or electrosurgical unit (ES). ESs are comparatively less expensive, less complicated and more ubiquitous than a lasers but with their conventional tip carries the a risk of damaging the pleura. We developed a large ball tip (M-tip) for ES and evaluated its effect on the pleura in comparison with that of Nd: YAG laser in ex vivo lung.Method: We employed lobes obtained through surgical resection. Using the Nd:YAG laser, the lung was irradiated for 2 seconds at levels of 5, 10 and 20 watts (10,20 and 40 Joules). Using the M-tip ES, the pleura received treatment at levels of 10, 20 and 40 watts for 2 seconds (20, 40 and 80 Joules) in spray coagulation mode. Upon completion of these procedures, 144 tissue specimens obtained from 24 lobes were examined under light microscopy.Results: Upon the application of Nd:YAG at 20 Joules, 22 (92%) of 24 visceral pleura demonstrated amorphous degeneration. With the application of ES at 40 Joules watts, 24 (100%) samples examined demonstrated amorphous degeneration (P=0.47). Of the samples where pleural destruction was evident (Nd: YAG; 40 Joules, ES; 80 Joules), an accompanying air leak pattern (pleural destruction associated with slight parenchymal contraction) was observed in 5 (21%) of the samples treated with Nd:YAG and in 10 (42%) of those treated with the M-tip ES (p=0.12).Conclusion: The M-tip ES induced proper contraction of the pleura with relatively little destructive damage to the pleura at 40 Joules. Accordingly, it may be possible to induce pleural contraction using this new device with the same degree of safely that the Nd:YAG laser provides.     

Safe pleural contraction employing a new tip for electrosurgical units. An ex vivo experiment.

BACKGROUND: Certain pulmonary lesions are treated by lung tissue contraction induced by heat administered by laser or electrosurgical unit (ES). ESs are comparatively less expensive, less complicated and more ubiquitous than a lasers but with their conventional tip carries the a risk of damaging the pleura. We developed a large ball tip (M-tip) for ES and evaluated its effect on the pleura in comparison with that of Nd:YAG laser in ex vivo lung. METHOD: We employed lobes obtained through surgical resection. Using the Nd:YAG laser, the lung was irradiated for 2 seconds at levels of 5, 10 and 20 watts (10, 20 and 40 Joules). Using the M-tip ES, the pleura received treatment at levels of 10, 20 and 40 watts for 2 seconds (20, 40 and 80 Joules) in spray coagulation mode. Upon completion of these procedures, 144 tissue specimens obtained from 24 lobes were examined under light microscopy. RESULTS: Upon the application of Nd:YAG at 20 Joules, 22 (92%) of 24 visceral pleura demonstrated amorphous degeneration. With the application of ES at 40 Joules watts, 24 (100%) samples examined demonstrated amorphous degeneration (P = 0.47). Of the samples where pleural destruction was evident (Nd:YAG; 40 Joules, ES; 80 Joules), an accompanying air leak pattern (pleural destruction associated with slight parenchymal contraction) was observed in 5 (21%) of the samples treated with Nd:YAG and in 10 (42%) of those treated with the M-tip ES (p = 0.12). CONCLUSION: The M-tip ES induced proper contraction of the pleura with relatively little destructive damage to the pleura at 40 Joules. Accordingly, it may be possible to induce pleural contraction using this new device with the same degree of safely that the Nd:YAG laser provides.     

Compressive behavior of human bone-cement composites

Current surgical practice in the implantation of cemented total joint arthroplasties generally creates a zone of variable thickness in which polymethylmethacrylate (PMMA) is intermixed with trabecular bone. The authors' objectives in these experiments were to characterize the compressive mechanical properties of this bone-cement composite material. They found that the mechanical properties of bone-cement composite specimens, fabricated under in vitro conditions that would promote nearly complete cement filling, are closer to the properties of trabecular bone than to those of cement. For both low-viscosity cement (LVC) and PMMA specimens, with the cement introduced by either hand-packing or pressurized injection at periods of 2 and 7 minutes, the compressive strengths ranged from 29 MPa to 50 MPa and the compressive moduli from 539 MPa to 1,210 MPa. Cement volume fractions achieved using different filling methods ranged from 76% to 87%. In contrast to previous studies of bone-cement composites using high-density bovine bone, neither mechanical properties nor filling parameters correlated significantly with bone porosity measured prior to filling. The authors expect that the mechanical properties of bone-cement regions created at surgery under less than these ideal in vitro filling conditions will only approach their values as an upper limit. Thus, bone-cement composites created in situ at surgery will also exhibit mechanical properties well below previously assumed values.