Enhancement of physical properties of resin restorative materials by laser polymerization

Blue Laser for Polymerization of Bulk Fill Composites: Influence on dentin bond strength and temperature rise during curing and co-curing method

Blue diode lasers are alternative curing devices for dental composites. The aim of this study was to investigate the influence of blue diode laser polymerization on shear bond strength of bulk fill composites to human dentin and temperature rise during two types of polymerization. Composite cylinders of SDR Plus(SDR) and Ever X Flow(EX) were bonded to dentin slabs using Adhese Universal and curing devices blue diode laser (449 nm, 1.6 W) and Power Cure LED. For each material and curing device there were two polymerization approaches: 1)conventional: separate curing of adhesive; 2)co-curing: simultaneous adhesive and composite curing. Polymerization modes for each material in conventional and co-curing(c) approach were: blue laser 2000 mW/cm2 for 5 s (L5 and L5c); blue laser 1000 mW/cm2 for 10 s (L10 and L10c); Power Cure 2000 mW/cm2 for 5 s (LED5 and LED5c); Power Cure 1000 mW/cm2 for 10 s (LED10 and LED10c). Temeperature was measured using thermal vision camera. For SDR, the highest bond strength was 24.3 MPa in L10c, and the lowest 9.2 MPa in LED5c. EX exhibited the highest bond strength(21.3 MPa) in LED5, and the lowest in L5(7.7 MPa). The highest temperature rise for SDR was in L10 and L5 (7.3 and 7.2 °C), and the lowest in LED5(0.8 °C). For EX, the highest temperature rise was in L5 (13.0 °C), and the lowest in LED5 (0.7 °C). Temperature rise was higher during blue laser polymerization, especially at high intensity and with conventional curing. Preferable blue laser curing mode is co-curing at 1000mW/cm2 for 10 s.

Use of Blue and Blue-Violet Lasers in Dentistry: A Narrative Review

Introduction: Blue and blue-violet diode lasers (450 and 405 nm) seem to represent an interesting approach for several clinical treatments today. The aim of this narrative review is to describe and comment on the literature regarding the utilization of blue and blue-violet lasers in dentistry. Methods: A search for "blue laser AND dentistry" was conducted using the PubMed database, and all the papers referring to this topic, ranging from 1990 to April 2020, were analyzed in the review. All the original in vivo and in vitro studies using 450 nm or 405 nm lasers were included in this study. All the articles on the LED light, laser wavelengths other than 405 and 450 nm and using lasers in specialties other than dentistry, as well as case reports, guideline papers and reviews were excluded. Results: From a total of 519 results, 47 articles met the inclusion criteria and were divided into 8 groups based on their fields of application: disinfection (10), photobiomodulation (PBM) (4), bleaching (1), resin curing (20), surgery (7), periodontics (1), endodontics (1) and orthodontics (3). Conclusion: Blue and blue-violet diode lasers may represent new and effective devices to be used in a large number of applications in dentistry, even if further studies will be necessary to fully clarify the potentialities of these laser wavelengths.

Effectiveness of photopolymerization in composite resins using a novel 445-nm diode laser in comparison to LED and halogen bulb technology

Challenges especially in the minimal invasive restorative treatment of teeth require further developments of composite polymerization techniques. These include, among others, the securing of a complete polymerization with moderate thermal stress for the pulp. The aim of this study is to compare current light curing sources with a blue diode laser regarding curing depth and heat generation during the polymerization process. A diode laser (445 nm), a LED, and a halogen lamp were used for polymerizing composite resins. The curing depth was determined according to the norm ISO 4049. Laser output powers of 0.1, 0.5, 1, and 2 W were chosen. The laser beam diameter was adapted to the glass rod of the LED and the halogen lamp (8 mm). The irradiation time was fixed at 40 s. To ascertain ΔT values, the surface and ground area temperatures of the cavities were simultaneously determined during the curing via a thermography camera and a thermocouple. The curing depths for the LED (3.3 mm), halogen lamp (3.1 mm) and laser_{(0.5/1 W)} (3/3.3 mm) showed no significant differences (p < 0.05). The values of ΔT_surface as well as ΔT_ground also showed no significant differences among LED, halogen lamp, and laser_{(1 W)}. The ΔT_surface values were 4.1_LED, 4.3_{halogen lamp}, and 4.5 °C for the laser while the ΔT_ground values were 2.7_LED, 2.6_{halogen lamp}, and 2.9 °C for the laser. The results indicate that the blue diode laser (445 nm) is a feasible alternative for photopolymerization of complex composite resin restorations in dentistry by the use of selected laser parameters.

Mechanical and Thermal Properties of Dental Composites Cured with CAD/CAM Assisted Solid-State Laser

Over the last three decades, it has been frequently reported that the properties of dental restorative composites cured with argon laser are similar or superior to those achieved with conventional halogen and light emitting diode (LED) curing units. Whereas laser curing is not dependent on the distance between the curing unit and the material, such distance represents a drawback for conventional curing units. However, a widespread clinical application of this kind of laser remains difficult due to cost, heavy weight, and bulky size. Recently, with regard to the radiation in the blue region of the spectrum, powerful solid-state lasers have been commercialized. In the current research, CAD (computer-aided design)/CAM (computer-aided manufacturing) assisted solid-state lasers were employed for curing of different dental restorative composites consisting of micro- and nanoparticle-reinforced materials based on acrylic resins. Commercial LED curing units were used as a control. Temperature rise during the photopolymerisation process and bending properties were measured. By providing similar light energy dose, no significant difference in temperature rise was observed when the two light sources provided similar intensity. In addition, after 7 days since curing, bending properties of composites cured with laser and LED were similar. The results suggested that this kind of laser would be suitable for curing dental composites, and the curing process does not suffer from the tip-to-tooth distance.

Wear Resistance of Bulk-fill Composite Resin Restorative Materials Polymerized under different Curing Intensities

INTRODUCTION

The aim of this study was to assess the wear resistance of four bulk-fill composite resin restorative materials cured using high- and low-intensity lights.

MATERIALS AND METHODS

Twenty-four samples were prepared from each composite resin material (Tetric N-Ceram, SonicFill, Smart Dentin Replacement, Filtek Bulk-Fill) resulting in a total of 96 samples; they were placed into a mold in a single increment. All of the 96 samples were cured using the Bluephase N light curing unit for 20 seconds. Half of the total specimens (n = 48) were light cured using high-intensity output (1,200 mW/cm²), while the remaining half (n = 48) were light cured using low-intensity output (650 mW/cm²). Wear was analyzed by a three-dimensional (3D) noncontact optical profilometer (Contour GT-I, Bruker, Germany). Mean and standard deviation (SD) of surface loss (depth) after 120,000 cycles for each test material was calculated and analyzed using one-way analysis of variance (ANOVA) with a significance level at p < 0.05.

RESULTS

The least mean surface loss was observed for SonicFill (186.52 urn) cured using low-intensity light. No significant difference in the mean surface loss was observed when comparing the four tested materials with each other without taking the curing light intensity into consideration (p = 0.352). A significant difference in the mean surface loss was observed between SonicFill cured using high-intensity light compared with that cured using low-intensity light (p < 0.001).

CONCLUSION

A higher curing light intensity (1,200 mW/cm²) had no positive influence on the wear resistance of the four bulk-fill composite resin restorative materials tested compared with lower curing light intensity (650 mW/cm²). Furthermore, SonicFill cured using low-intensity light was the most wear-resistant material tested, whereas Tetric N-Ceram cured using high-intensity light was the least wear resistant.

CLINICAL SIGNIFICANCE

The wear resistance was better with the newly introduced bulk-fill composite resins under low-intensity light curing.

State-of-the-art: dental photocuring--a review

Light curing in dentistry has truly revolutionized the practice of this art and science. With the exception bonding to tooth structure, there is perhaps no single advancement that has promoted the ease, efficiency, productivity, and success of performing dentistry. Like most every major advancements in this profession, the technology underlying the successful application of light curing in dentistry did not arise from within the profession, but instead was the result of innovative adaptations in applying new advances to clinical treatment. One cannot appreciate the current status of dental photocuring without first appreciating the history and innovations of the science and industry underlying the advances from which it developed. This review will place the current status of the art within the context of its historical progression, enabling a better appreciation for the benefits and remaining issues that photocuring has brought us. Lastly, the manuscript will present thoughts for future considerations in the field, offering suggestions as to how current advances in light-generating science might yet be adapted for dental use.

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.

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).

Photopolymerization of a dental nanocomposite as restorative material using the argon laser

The aim of this study was to investigate the effect of power density and irradiation time of an argon laser on the physico-mechanical properties of light-cured dental nanocomposites. The composites were cured with 260 mW/cm(2) and 340 mW/cm(2) power densities at different irradiation times. The degree of conversion (DC), flexural strength, flexural modulus, water sorption, solubility and reaction temperature were measured. The maximum DC (50%), which was achieved after approximately 20 s irradiation, and the reaction temperature rise (20°C) were demonstrated by composite containing 20% filler cured at 340 mW/cm(2). The composite with 25% filler cured at 340 mW/cm(2) showed the highest flexural strength and modulus, which were 32.2 MPa and 1.89 GPa, respectively. The minimum water sorption (3.8%) and solubility (1.2%) were achieved with the composite containing 25% filler cured at 340 mW/cm(2). Finally, the composite with 25% filler cured at 340 mW/cm(2) showed higher physico-mechanical properties.

Photopolymerization of dental resin as restorative material using an argon laser

The effect of the 488-nm wavelength of argon laser at different power densities and irradiation times on the degree of conversion (DC), temperature rise, water sorption, solubility, flexural strength, flexural modulus, and microhardness of bisphenole A glycol dimethacrylate and triethylen glycol dimethacrylate with a mass ratio of 75:25 was studied. Camphorquinone and N,N'-dimethyl aminoethyl methacrylate were added to the monomer as a photo initiator system. The DC% of the resin was measured using Fourier transform infrared spectroscopy. The maximum DC% (50%), which was reached in 20 s, and temperature rise because of the reaction (13.5 degrees C) were both higher at 1075 than 700 mW/cm(2). Water sorption and solubility were measured according to ISO4049, which in our case were 23.7 and 2.20 microg/mm(3) at 1075 mW/cm(2), respectively. A flexural modulus of 1.1 GPa and microhardness of 19.6 kg/mm(2) were achieved above the power density. No significant difference was observed (i.e., p>0.05) for water sorption and flexural strength at 700 and 1075 mW/cm(2).

Argon laser vs conventional visible light-cured orthodontic bracket bonding: an in-vivo and in-vitro study

INTRODUCTION

Many advantages of argon lasers have been reported, including high-speed orthodontic adhesive curing and less enamel demineralization. The purpose of this study was to compare bond strengths after curing with the argon laser (10 seconds) and the conventional curing light (40 seconds) in vivo and in vitro.

METHODS

Four premolars from each of 23 volunteers were randomly assigned to either the argon laser group or the conventional light group for the in-vivo study. Shear bond strengths were measured after 14 days with custom-designed debonding pliers. In-vitro bond strengths were measured by using 4 premolars from each of 25 volunteers. Shear bond strength was measured after 14 days of thermocycling with the same protocol as the in-vivo study. Adhesive remnant index scores (ARI) were determined.

RESULTS

No significant differences were found in bond strengths according to curing method, dental arch, or sex. In-vivo results were significantly lower (P < .05) than in-vitro results. A significant (P < .05) difference in ARI scores between the curing methods was determined; no significant correlation between mean bond strengths and ARI scores was determined.

CONCLUSIONS

Bond strength for argon laser curing is comparable to conventional light curing and is sufficient for clinical applications. Although the argon laser left more adhesive on the tooth surfaces on debonding, there was no increase in enamel surface fractures.

Bond strength of a dentin bonding system using two techniques of polymerization: visible-light and argon laser

OBJECTIVE

The aim of this work was to study one dentin-bonding system associated with posterior teeth restorative composite resin by means of tensile bond strength tests varying the technique of polymerization: visible light and argon laser.

BACKGROUND DATA

Previous studies have demonstrated the ability of the argon laser to polymerize light-activated materials.

METHODS

Sixty specimens were prepared by grinding the labial surface of bovine teeth embedded in acrylic resin. The dentin bonding system used was Single Bond (3M), which has a poliacenoic acid copolimer, associated with a posterior teeth restorative composite resin (Filtek P60, 3M). The bonding sites were treated according to the instruction of the manufacturers. The 60 teeth, duly embedded and ground, were assigned to four groups with 15 teeth each: group 1, the adhesive was light cured during 10 sec with visible light (Curing Light, 3M) with power density of 410 mW/cm2 and the composite resin was light cured during 20 sec with visible light; group 2, the adhesive and the composite resin were cured during 10 seconds with argon laser with 150 mW of power; group 3, the adhesive and the composite resin were cured during 10 sec with argon laser with 200 mW of power; and group 4, the adhesive and the composite resin were cured during 10 sec with argon laser with 250 mW of power. The composite resin was light cured in layers of 1 mm of thickness until the model of teflon with 3 mm in height was completely filled.

RESULTS

The tensile bond strength test was performed in a Mini-Instron (model 4442) and the results for group 1 were 19.75 MPa (+/-4.65), group 2 were 16.09 MPa (+/-7.27), group 3 were 11.56 MPa (+/-4.50), and group 4 were 11.90 MPa (+/-5.78).

CONCLUSIONS

One can conclude that the tensile bond strength promoted by the polymerization with visible light presented greater tensile bond strength than the polymerization with argon laser with 200 mW and 250 mW, but there was no significant difference between visible light and argon laser with 150 mW. There was no significant difference between argon laser with 150 mW and argon laser with 200 mW or 250 mW.

Dentine bond strength of a composite resin polymerized with conventional light and argon laser

The use of argon laser (488 nm) has been suggested as a new alternative for polymerizing adhesive materials. This study aimed to evaluate the tensile bond strength of a microfilled composite (A110, 3M) inserted by incremental technique (3 increments of 1 mm) and by single increment (3 mm) polymerized by argon laser for 10, 20 and 30 seconds and halogen light for 40 seconds. Eighty (8 groups of 10 teeth) freshly extracted bovine teeth were stored in a freezer in distilled water for one week. The crowns were cross-sectioned from the roots. Pulpectomy was performed and the pulp chambers were sealed with wax. The buccal surfaces of the teeth were ground with wet sandpaper (grains: 120, 400, and 600) to expose the surface dentin, and the teeth were then included in acrylic resin. A metal device was used to fix each sample and a black propylene matrix25 (3 mm high with an internal millimetric delimitation) was used to insert the material according to the groups studied. The polymerization intervals were of 10, 20 and 30 seconds for the laser polymerization and 40 seconds for the conventional polymerization. Tensile tests were performed by a Universal Testing Machine 4442 (Instron) at a speed of 0.5 mm/min and 500 N load. According to the methodology used, the incremental technique increased bond strength values. There was no difference between the studied polymerization techniques when resin was filled in 3 increments.

Argon laser oral safety parameters for teeth

Argon lasers have been reported to prevent or reduce demineralization of enamel in extracted teeth and to polymerize dental composites (using 25-100 J/cm2). Prior to clinical trials on caries prevention and curing composites, safety parameters for intraoral use of the argon laser need to be established. This study was conducted to determine the enamel damage, pulp temperature changes, and associated pulpal tissue damage following irradiation at various argon laser energy levels using 1.6-6.0 watts, approximately 1 and 2 mm diameter beam for 0.2-5.0 seconds. To evaluate pulpal damage, selected dogs' teeth were irradiated in vivo, extracted 7 days postlasing, fixed, decalcified, sectioned, stained, and read for pulpal damage. Pulp temperature and enamel damage tests utilized extracted dog and human teeth. Temperature probes were inserted in the pulp chambers and temperature changes recorded as enamel surface was lased. Enamel surface damage was evaluated by visual and microscope examination. Results showed that histologic pulpal damage occurred at > 600 J/cm2. Temperature changes were < 6 degrees F in human teeth with approximately 900 J/cm2. No enamel damage was observed at these energy densities. At energy densities needed for proposed uses, no apparent damage would be expected to pulp or enamel.

Irradiance effects on the mechanical properties of universal hybrid and flowable hybrid resin composites

OBJECTIVES

A potential problem with high-intensity lights might be failure of polymer chains to grow and cross-link in a desired fashion, thereby affecting the structure and properties of the polymers formed. The purpose of this study was to evaluate mechanical properties of resin composites polymerized using four different light-curing units.

METHODS

A conventional quartz-tungsten-halogen (QTH) light, a soft-start light, an argon-ion laser, and a plasma-arc curing light were used to polymerize disk-shaped (9.0mm diameter x 1.0 mm high) and cylinder-shaped (4mm diameter x 8 mm high) specimens of a universal hybrid and a flowable hybrid composite. Biaxial flexure strength, fracture toughness, hardness, compressive strength, and diametral tensile strength were determined for each composite.

RESULTS

The use of the plasma-arc curing light, a high-intensity light, resulted in significantly lower hardness for the universal hybrid composite compared with the hardness obtained using the conventional QTH and the soft-start units. Hardness was the only mechanical property that was adversely affected by the use of a high-intensity light.

SIGNIFICANCE

High-intensity lights might affect some resin composite mechanical properties, but this effect cannot be generalized to all resin composites and all properties.

The effect of irradiation wavelength bandwidth and spot size on the scraping depth and temperature rise in composite exposed to an argon laser or a conventional quartz-tungsten-halogen source

OBJECTIVES

The purpose of this study was to investigate the effect of the spectral distribution of the curing irradiation near the maximum excitation wavelength of the photo-initiator and the effect of the irradiation spot size on the scraping depth-of-cure and temperature rise in a resin composite for both an argon laser and a quartz-tungsten-halogen lamp.

METHODS

Using bandpass filters, the spectral outputs of an argon laser and a quartz-tungsten-halogen lamp were restricted to pass selected wavelengths on to a commercial camphorquinone-based resin composite and the depth-of-cure, using scraping methods, was measured. The temperature rise in composite was measured for some of the above-mentioned sources. The spot sizes for both sources were varied and the scraping depth was measured. Lateral curing or the extent of curing away from the focused spot was also measured.

RESULTS

For constant power density and exposure time, an irradiation spectral distribution closer to the photo-initiator excitation peak yielded a higher scraping depth than a broadband spectral distribution for both sources. Under similar conditions, the argon laser resulted in a lower temperature rise in the composite than the lamp. For the same total energy imparted to the resin composite, the scraping depth increased with reducing spot size of the curing irradiation. Furthermore lateral curing of the composite well beyond the irradiation spot size was observed.

SIGNIFICANCE

The spectral and spatial characteristics of the curing irradiation need to be carefully considered as these affect the scraping depth-of-cure and temperature rise in a resin composite.

Nd:YAG laser influence on sound dentin bond strength

OBJECTIVE

In the present study, the authors evaluated tensile bond strength of composite resin to dentin treated with Nd:YAG laser before and after bonding procedures.

SUMMARY BACKGROUND DATA

Lasers have been widely used in dentistry and have contributed to the development of new technologies. Adhesive systems have been indicated for most dental procedures and have produced good results. Studies concerned with the combined use of this adhesive system was the subject of this study.

METHODS

Thirty noncarious human anterior teeth, freshly extracted, for periodontal reasons, were used. After grinding the buccal dentinal surface until its exposition, specimens were separated into three groups and received the following treatments: (group 1) control--acid etching plus primer plus bond; (group 2) laser plus acid etching plus primer plus bond; (group 3) acid etching plus primer plus bond plus laser. Specimens of composite resin (Z100, 3M, Saint Paul, MN) were constructed on an inverted truncated 3-mm diameter cone mold. Tensile bond strength was performed using Inströn Universal machine, at 0.5 mm/min speed.

RESULTS

Analysis of variance (ANOVA) (p < 0.05) determined that the type of dentinal treatments used had an influence on tensile bond strength. Tukey's test, however, showed that group 1 (15.46) and 3 (15.67) had similar results both of which were higher than group 2 (4.57).

CONCLUSIONS

Based on the results obtained, one can conclude that group 1 (without laser) and group 3 (laser after bonding) had similar results, both higher than those observed for group 2 (laser before bonding). These results indicate that more research is needed about how a hybrid layer is formed when laser radiation is used.

Effect of argon laser irradiation on shear bond strength of orthodontic brackets: an in vitro study

Argon lasers, due to their significant time savings over conventional curing lights, are being investigated for use in bonding orthodontic brackets. They are also being investigated for their ability to confer demineralization resistance on enamel. The purpose of this study was to evaluate the effects of argon laser irradiation on bond strength at 3 different laser energies (200, 230, and 300 mW) and at 3 unique time points of laser application (before, during, or after bracket placement). One hundred-fifty human posterior teeth were divided into 9 study groups and 1 control group. After debonding, the adhesive remnant index was scored for each tooth. There was no evidence of an effect of energy level on bond strength, P =.903, or of an interaction between timing of bracket placement and energy level, P =.858. When combining data across energy levels, the mean bond strength was significantly different between all 3 bracket placement groups, P <.001. In addition, the mean bond strength of teeth lased after bonding was significantly higher than the control group, P <.05. There were no statistically significant differences between adhesive remnant index scores among the 10 groups. Lasing the enamel before or after bonding does not adversely affect bond strength. Use of the argon laser to bond orthodontic brackets can yield excellent bond strengths in significantly less time than conventional curing lights, while possibly making the enamel more resistant to demineralization.

Response of associated oral soft tissues when exposed to Argon laser during polymerization of dental resins

BACKGROUND AND OBJECTIVE

Polymerization of dental resins with Argon laser produces restorations with improved physical properties when compared to conventional visible-light polymerization techniques. However, the possibility of damaging adjacent soft tissues has not been addressed.

STUDY DESIGN/MATERIALS AND METHODS

In this study, Argon laser (488/514 nm) was used for the polymerization of composite resins to determine effects on the parakeratinized gingiva adjacent to both restored and unrestored teeth in six dogs, using 10-, 20-, and 30-second polymerization exposures.

RESULTS

Gingival tissues removed at 24 hours, 72 hours, or 5 days revealed desiccated, disrupted, hyalinized connective tissue. Tissues exposed for 10 seconds showed minimal change. This minimal degree of change was most evident at 72 hours and returned to normal limits at 5 days. The 20-second exposure produced alterations evident through all time periods. Tissues exposed for 30 seconds exhibited necrosis, severe disruption, and vessiculation, which was still unresolved at 5 days.

CONCLUSION

This study demonstrates that clinically relevant Argon laser exposure (10 seconds) of parakeratinized gingiva adjacent to teeth undergoing restoration does not cause lasting damage.

In vitro temperature change at the dentin/pulpal interface by using conventional visible light versus argon laser

BACKGROUND AND OBJECTIVE

The argon laser has been promoted as a competing technology to multi-wavelength visible light as a curing source for dental restorative resins. However, the comparative thermal risk to the pulp between these two sources of light energy requires determination. The objective of this study is to compare the temperature induced at the dentin-pulpal interface between the argon laser and visible light curing unit at a variety of exposure regimens and conditions.

STUDY DESIGN/MATERIALS AND METHODS

In vitro temperatures were measured and recorded at the dentin-pulpal interface upon external light exposure. Independent variables included the dentin thickness, duration and waveform of exposure, and presence of composite resin.

RESULTS

In most instances, the argon laser resulted in less temperature rise on the pulpal-dentin interface.

CONCLUSION

The argon laser should not pose a serious thermal risk to the pulp if used at recommended energies.

Human teeth exposed to argon laser irradiation: determination of power-time-temperature working conditions

OBJECTIVE

This study was conducted to establish the operating parameters of the argon laser without thermal damage to the pulp tissue for clinical applications.

SUMMARY BACKGROUND DATA

Previous studies have mainly compared the temperature modifications of the pulp chamber in a very limited situation, where a complete view of the thermal history cannot be obtained nor even extrapolated to new applications.

METHODS

We used samples of molar and premolar tooth where a class V cavity was prepared and illuminated with an argon laser at different power levels, fixing the exposition area for all cases. Situations including open cavity and teeth restoration were analyzed. High-precision thermistors were placed in four different positions, one of which was inside the pulp chamber. The temperature evolution was monitored continuously by an interfaced computer during all laser exposure. Special attention was paid to the intrapulpal temperature variation because it is considered the most vulnerable thermal region. The temperature time evolution allowed the determination of the operating conditions (power-time-temperature variation) in which the use of the argon laser causes no pulpal damage. As a function of temperature variation, we divided the whole parameter space (power-time-temperature) into zones and the optimum zone of operation was determined.

CONCLUSIONS

We created a diagram called power-time-temperature (PTT) where zones of temperature increased under laser irradiation allow the verification of which condition is safe for clinical laser application. The results have a broad use when this type of analysis is applicable.

Laser and curing light induced in vitro pulpal temperature changes

OBJECTIVE

This study was conducted to compare in vitro pulp chamber temperature changes induced by conventional curing light and argon laser under common conditions.

SUMMARY BACKGROUND DATA

Previous in vitro studies have shown that impacting the surface of teeth with either an argon laser or conventional curing light causes pulp temperature increases of various degrees.

METHODS

The sample tooth had a class V composite restoration placed with 2.48-mm distance from the surface of the composite to a Thermister Thermometer. The thermometer was inserted into the cutaway pulp chamber to measure the temperature increase from stabilized room temperature, which was caused by exposure to argon laser or conventional curing light.

RESULTS

Temperature increases for the argon laser for the recommended curing time were 3 degrees F or less. The longer the exposure times for either method of curing, the higher the temperature increased.

CONCLUSION

At recommended curing times, in vitro pulp chamber temperature increases from laser units were significantly lower than those of the conventional curing lights.

Polymerization shrinkage of restorative resins using laser and visible light curing

OBJECTIVE

This in vitro investigation compared the amount of linear shrinkage that occurs when a light-cured composite resin is cured with a visible light source, and also with an argon laser.

SUMMARY BACKGROUND DATA

When composite resins are light-cured, they undergo a certain degree of polymerization shrinkage, which can be clinically significant and affect the efficacy of the restoration. A new protocol utilizes laser curing instead of conventional visible light.

METHODS

Two hybrid composite resins were used, Z100 and TPH-Spectrum. Dimensional change was measured in a linear direction, using a calibrated light-microscope. A total of 40 samples of composite resin was tested using two curing lights, and two hybrid composite resins, resulting in four groups of 10 samples (n = 10) each. According to manufacturer instructions, curing time for the laser was 10 sec, and for visible light was 40 sec.

RESULTS

With TPH-Spectrum, the mean shrinkage with visible light was 0.583% compared to that with laser light which was 0.591%. With Z100, the mean shrinkage with visible light was 0.565%, compared to that with laser light which was 0.551%.

CONCLUSIONS

There was no significant difference in amount of shrinkage of hybrid composite resins between using visible light or laser light. There was also no significant difference in shrinkage between the two hybrid composites for either light source.

Case report. Use of an argon laser to treat drug-induced gingival overgrowth

This article explores the use of an argon laser to treat severe drug-induced gingival overgrowth. The patient was being treated with phenytoin (Dilantin, Parke-Davis), cyclosporine and a calcium channel blocker. He had undergone a kidney transplantation and had insulin-dependent diabetes mellitus. He had severe gingival overgrowth, which prevented him from wearing his removable prostheses, and a superimposed Candida albicans infection. An argon laser was used to excise the gingival overgrowth so new maxillary and mandibular prostheses could be fabricated.

Dentistry for the 21st century? Erbium:YAG laser for teeth

The first dental laser for use in cutting human teeth in vivo was cleared by the Food and Drug Administration for marketing in the United States. The authors explored, in summary form, the data provided to the FDA for the clinical use of the erbium:yttrium-aluminum-garnet, or Er:YAG, laser. The authors concluded that using the Er:YAG laser to treat dental hard tissue is both safe and effective for caries removal, cavity preparation and enamel etching.

Effects of argon laser curing on dentin shear bond strengths

Previous studies have demonstrated the ability of the argon laser to polymerize light-activated materials and improve enamel shear bond strengths. This study was conducted to evaluate the effects of the argon laser on dentin shear bond strengths of current dentin bonding systems. Argon laser (HGM Model 8) at 231 and 280 mW, 5 sec bonding agent, 10 sec composite, and a conventional curing light (Translux EC/Kulzer) at 10 sec bonding agent, 20 sec composite were used to polymerize samples of dentin bonding systems [Scotchbond Multi-Purpose Plus (3M) and Prime Bond (Dentsply/Caulk), both with TPH (Dentsply/Caulk) composite]. A flat dentin bonding site (600 grit) was prepared on the buccal surface of extracted human teeth. Twelve samples were made for each set of parameters for both laser and conventional light totaling 48 samples. Samples were stored in distilled water in light-proof containers for 24 h at 37 degrees C. Shear bond strengths (MPa) were determined for each sample on the Instron testing machine. Mean values were calculated for each set of data and ANOVA with Fisher PLSD were used for statistical analysis. The argon laser provided bond strengths that were 21-24% greater than those of the conventional curing light system.

In vitro pulp chamber temperature rises associated with the argon laser polymerization of composite resin

STUDY DESIGN/MATERIALS AND METHODS

This in vitro study was performed upon 50 extracted human molars that provided the occlusal surfaces for standard class I preparations. The cavity floor of the 20 specimens was covered with zinc phosphate cement and the teeth were sectioned transversally at or below the cementoenamel junction. In some specimens pulp tissue was removed from the pulp chamber. The cavities of all specimens were filled with composite resin, and the resin was cured with an argon laser.

RESULTS

A statistically significant difference in the rise in temperature was obtained only in the temperature of dentin roof of the pulp chamber between the specimens with (2.2 degrees C) and without (3.1 degrees C) cement base (P < .05). There was no significant difference in the temperature of the pulp tissue between specimens with (2.7 degrees C) and without (2.2 degrees C) base cement. The peak temperature of the composite surface was 13.8 degrees C.

CONCLUSION

These data indicate that argon laser curing may be a method of choice for polymerization of the composite resin.

Lasers in dentistry

Since the development of the ruby laser by Maiman in 1960, there has been great interest among dental practitioners, scientists, and patients to use this tool to make dental treatment more pleasant. Oral soft tissue uses are becoming more common in dental offices. The possible multiple uses of lasers in dentistry, beyond soft tissue surgery and dental composite curing, unfortunately, have not yet been realized clinically. These include replacement of the dental drill with a laser, laser dental decay prevention, and laser decay detection. The essential question is whether a laser can provide equal or improved treatment over conventional care. Safe use of lasers also must be the underlying goal of proposed or future laser therapy. With the availability and future development of different laser wavelengths and methods of pulsing, much interest is developing in this growing field. This article reviews the role of lasers in dentistry since the early 1960s, summarizes some research reports from the last few years, and proposes what the authors feel the future may hold for lasers in dentistry.

Argon laser irradiation in root surface caries: in vitro study examines laser's effects

Recent research shows that laser irradiation can improve enamel's resistance to caries. This in vitro study examines the effects of argon laser irradiation on root surface caries. Treated surfaces seemed more resistant to an artificial caries medium than control surfaces.

Power density and external temperature of laser-treated root canals

The purpose of this study was to determine the power and time parameters for an argon laser that would result in the removal of pulpal tissue without excessively elevating the external temperature of the root. External temperatures were measured by attaching thermistors to the surfaces of the teeth at the cemento-enamel junction (CEJ) areas and at the root apices. Results indicate that a 1-W power setting with a pulse duration of 0.1 sec and a 1 sec interval between pulses produced a mean temperature rise of 0.89 +/- 0.27 degrees C at the cemento-enamel junction area and a mean temperature increase of 2.04 +/- 0.47 degrees C at the apex. A 2-W power setting with a 0.1 sec pulse duration and a 1 sec interval between pulses resulted in a mean temperature increase of 1.58 +/- 0.45 degrees C at the CEJ and a mean temperature rise of 2.59 +/- 0.20 degrees C at the apex. Based upon the results of this study, it was concluded that an argon laser operating at 1 or 2 W of power with a 0.1 sec pulse duration could be used to remove pulpal tissue without creating an excessive increase in the external temperature of the tooth.

Using lasers in clinical dental practice

Lasers are an impressive potential treatment modality for a variety of clinical conditions. This article profiles several clinical applications in dentistry.

Lasers in dentistry: an overview

Developments in laser dentistry have led to an increasing acceptance of this technology by both practitioners and the general public. This article provides an overview of laser systems and their dental applications.

The effect of lasers on dental hard tissues

There is a quest to find a method to remove diseased and healthy dental hard tissues without the negative stimuli associated with dental handpieces. Today, lasers are being considered as a potential replacement. This report evaluates effects of three lasers on dentin and pulpal tissues. The Er:YAG laser appears to have a lesser thermal effect.

Power and time requirements for use of the argon laser to polymerize composite resins

A carefully controlled laboratory study was conducted to determine the optimum power setting and polymerization cycle time to cure four commercially available composite resins with an argon laser. Most effective resin polymerization was achieved when Prisma APH was polymerized at 310 mW for 7 seconds, when Herculite was polymerized at 160 mW for 12 seconds, when P-50 was polymerized at 525 mW for 13 seconds and when Silux Plus was polymerized at 270 mW for 13 seconds. The exact parameters of laser power and exposure time seem to be material specific, with greater variation being noted in power setting than in exposure time.

Lasers in the limelight: what will the future bring?

Early lasers produced too much heat and melted tooth enamel. But lasers improved enough to use in dentin bonding and composite curing and to detect carious enamel.

Application of the argon laser to dentistry

A review was conducted to determine specific areas of application of the argon laser to dentistry. When appropriate, comparisons between the argon laser and other treatment methods were made. It was concluded that the argon laser has applicability in composite resin placement, in enamel and dentin bonding procedures, in preventive dental therapies, and in endodontic procedures.

Post polymerization strength values of an argon laser cured resin

A hybrid composite resin, Prisma APH, and a microfilled composite resin, Silux Plus, were compared regarding diametral tensile strength values following conventional visible light polymerization and argon lasing. The time interval between resin polymerization and physical property testing ranged from 1 hour to 20 days. Results demonstrated considerable mean tensile strength value variation in the earlier phases of the study with a lessening of the differences between the tensile strengths achieved by each method of polymerization as the 20 day interval was approached. It was concluded that composite resin testing protocols should be lengthened to be able to fully assess the effects of the widely variant, time dependent mean test results.

Argon laser initiated resin photopolymerization for the filling of root canals in human teeth

This work was undertaken to determine if 488 nm light is transmitted through dentin in quantities adequate to polmerize resin located several milimeters from the light source (an optical fiber). The spread of polymerization in a camphorquinone activated resin due to 488 nm light emanating from an opaque plastic canal was compared with light emanating from a canal of the same diameter in tooth dentin. Results indicated that irradiation of a resin-filled chamber via an opaque canal generated a series of ellipsoidal forms, while irradiation via a root canal generated bullet-shaped forms of much larger volume and weight. The base of these bullet-shaped forms was flat against the dentin-resin interface and surrounded the canal. These results indicated that 488 nm argon laser light was transmitted through dentin and could act to polymerize resin at a distance of several millimeters from the canal. Further experiments verified that resin in lateral canals of tooth roots was readily polymerized by 488 nm light applied at low power levels (50 mW). These experiments demonstrate the effectiveness of the argon laser in polymerizing light activated dental resins located within or adjacent to tooth dentin at distances up to several milimeters from the fiberoptic terminus. The flexibility and control that these procedures make possible in the obturation of root canals may lead to substantial improvements in endodontic therapy.