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 the argon laser on primary tooth pulpotomies in swine.

This study evaluated the clinical, radiographic, and histologic effects of the HGM PC Oralase argon laser on vital pulps of swine teeth. Pulpotomies were performed in vivo on 42 primary teeth from three young pigs and observed for 7 or 60 days. For each time period nine experimental teeth received an argon laser dose of 1 W, 2 sec (24.88 J/cm2), and nine experimental teeth received a dose of 2 W, 2 sec (49.74 J/cm2). Controls consisted of three teeth for each time period and did not receive exposure from the argon laser. There were no significant differences noted between the two energy densities with respect to clinical, radiographic, or histological parameters for either time period. All soft tissues remained normal and all teeth exhibited normal mobility at weekly assessments. Other than physiologic root resorption, there were no differences in pre- and postoperative radiographs in the 7 day sample; calcifications coinciding to dentinal bridges were visible radiographically in 8 of the 60-day samples. Reparative dentin formation was noted histologically in a total of 9 roots in the 7-day group and in 13 roots in the 60-day group. With the exception of teeth which had early restoration loss with resultant bacterial contamination, all other pulps appeared to retain their vitality and capability of normal pulpal healing. Use of the argon laser at the parameters described in this study did not appear to be detrimental to pulpal tissues.

Jet-assisted laser tools for tooth preparation.

Previous oral calcified-tissue laser ablations have yielded inadequate results because of the difficulty in producing a desired effect on a surface without concomitant pulp or osseous damage. The purpose of this study was to characterize a new modality of ablating teeth using argon and diode lasers (488.5 nm, 805 nm) in combination with the repetitive placement of specific photoabsorptive dyes. In this design, energy from laser light, that would otherwise be reflected, is coupled to the tooth-dye interface. Thirty-two specimens of recently extracted human enamel were sectioned and prepared into 3 x 2 x 2 rectangular blocks and smoothed with a polishing point. Two-microliter droplets of dye were placed on the external enamel surface and subsequently air-dried. Specimens were then ablated with the laser-dye combinations, producing craters approximately 100-200 mum in depth and devoid of visual carbonization. Similar irradiations were performed on enamel specimens without dye application, and displayed no cavitation or surface carbonization. SEM studies showed evidence of crater formation within the enamel surface. Optimization of laser parameters integrated with specific dispensing of dye is necessary before this technique can be studied further.

Pulpal effects of a high rep rate Nd:YAG laser.

Molar teeth in male rats were used in this study to assess the effects of enamel surface treatments of pulp survivability. The occlusal surfaces of the first and third molars in each quadrant were treated with an Nd:YAG laser (Pulsemaster, Incisive Technologies, Inc.) using a 300-mum contact tip fiber, in a figure-8 motion, for a 30 sec ablation time. The second molars were not treated. Energy parameters/animal were as follows: (1) 0.6 W, 30 mJ energy, and 20 Hz, (2) 1.2 W, 30 mJ energy, and 40 Hz, (3) 1.8 W, 30 mJ energy, and 60 Hz, (4) 2.4 W, 30 mJ energy, and 80 Hz, (5) 0.6 W, 60 mJ energy, and 10 Hz, (6) 1.2 W, 60 mJ energy, and 20 Hz, (7) 1.8 W, 60 mJ energy, and 30 Hz, (8) 1.0 W, 100 mJ energy, and 10 Hz, and (9) 2.0 W, 100 mJ energy, and 20 Hz. Animals were sacrificed at two time periods (1 and 6 weeks, postoperatively). SEM analysis of enamel was performed at 2000x magnification to observe the parameter difference in surface quality. Microscopic examination of the histological samples was accomplished at 250x magnification. Surface analyses of tooth structure revealed a wide dispersion of enamel roughness, ranging from slightly etched to moderately cavitated. Power levels above 2.4 W exhibited significantly more roughness than lower energy parameters. Efforts were made to correlate the pulp biology effect with enamel surface condition to determine a safe threshold for survivability of the pulp tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Enamel surface roughness analysis after laser ablation and acid-etching.

Laser-roughened enamel surfaces have been shown to provide for greater acid-resistance and enhanced restorative material/enamel bond strength. Extracted tooth enamel was irradiated with several lasers: CO2/Nd:YAG (CW), CO2 (RSP), Nd:YAG (CW), Nd:YAG (Q-switched), Argon (CW), and Ar:F excimer. Additional teeth were acid-etched. Energy densities were standardized at 25.47 J/cm2 for all mediums. Surface profile analyses were conducted with a profilometer to determine the amount of enamel surface roughness. The acid-etched samples exhibited both a greater amount of surface roughness and a qualitatively different type of enamel surface morphology than the laser-treated specimens. Independent use of the CO2 and Nd:YAG beams exhibited a moderate amount of roughness, while the coaxial CO2/Nd:YAG beam displayed surface roughness approaching that of the acid-etch samples. Different laser mediums produce enamel surface morphologies that are characteristic of a variety of inherent lasing parameters.

Bending strength of Fuji and Ketac glass ionomers after sonication.

Glass ionomer cements mixed by conventional methods contain voids that can decrease their overall strength. This study evaluated the effect of sonication on the reduction of air entrapment by measuring the bending strength in glass ionomer cements (Fujj-II and Ketac-fil). Glass ionomer cement was placed in identical-test vials and sonicated for 45s, 10s, or 0s. The bending strengths were measured (0.005 in min-1) after setting times of 1 or 2 weeks. Mean bending strengths (MPa +/- SD) for the 12 treatment both cements (P < 0.001) and sonication times (P < 0.001). The effect of setting time produced minimal increases in bending strength (P < 0.218). The sonication of freshly mixed glass ionomer cements is a possible solution for reducing voids to increase bending strength.

The effects of low-level energy density Nd:YAG irradiation on calculus removal.

This study assessed the effects of using an Nd:YAG laser to remove dental calculus from root surfaces. Human extracted molar teeth, with extensive calculus attachment to root surfaces, were irradiated with an Nd:YAG beam [power densities (PD) = 1.09 W/cm 2 and 2.19 W/cm 2; energy densities (ED) = 49.2 J/cm 2 and 98.4 J/cm 2]. An additional group of teeth was instrumented with a Gracey 11/12 curette. A separate group of untreated specimens served as controls. Specimens were examined under scanning electron microscopy and rated as to the degree of calculus detachment from root surfaces. Nd:YAG irradiation at low ED did not appreciably affect the integrity of the calculus root surface attachment. The higher-ED Nd:YAG irradiation appeared to mimic the type of calculus removal depicted with conventional hand instrumentation. Root surface damage from both laser ablations was negligible.

Pulpal effects of argon: fluoride excimer laser irradiation and acid-etching of rat molar enamel.

The reaction of enamel, dentine and pulpal tissues to exposure from a laser beam has been shown to depend on the type of laser medium used. The objective of this study was to examine the pulpal response in rat molars after external enamel surface treatment with either an Ar:F excimer laser or acid-gel application. Maxillary right molar occlusal surfaces in 22 animals were irradiated (energy density = 45.0 J/cm2). Maxillary left molar occlusal surfaces were treated with 37 per cent phosphoric acid for 30 s. Untreated mandibular right molars served as controls. At two postoperative time periods (1 and 6 weeks), molars were removed, sectioned, stained (H&E) and scored. Data analysis indicated no significant difference between Ar:F irradiation and controls at 1 week. Treatment with laser or acid-etching left a similar degree of pathosis at 1 and 6 weeks. Although the Ar:F excimer laser produced a more exaggerated pulp response than controls at 6 weeks, tissue vitality was maintained. The Ar:F excimer laser may be useful for ablating vital tooth structure since pulpal tissue in rat molars exhibited no damage in response to low-power irradiation.

Evaluation of the interactions between amalgam, cement and gold castings.

The purpose of this study was to determine the interactive effects between a dental amalgam, cements and a gold alloy and therefore evaluate cements as barriers to corrosion. There were 48 castings cemented to either simulated amalgam cores or teeth using zinc phosphate (ZnPO4) or glass polyalkenoate (ionomer) cement. An additional 12 castings were placed in direct contact with the amalgam restoration. Half of the specimens were thermocycled between 5 degrees and 50 degrees C for 12 weeks. The other half were stored at 37 degrees C for the same period of time. The specimens were then encased in epoxy resin and sectioned. The sectioned specimens were examined for cement loss, as well as evidence and extent of corrosion. Significantly more cement loss occurred with the ZnPO4 compared with the glass polyalkenoate (ionomer) cement when the castings were cemented to amalgam cores. Evidence of corrosion was apparent in all specimens; thermocycling produced significantly more corrosion than the 37 degrees C environment. The direct-contact group produced significantly more corrosion compared with the specimens where castings were cemented with ZnPO4.

Effect of laser-etch on bond strengths of glass ionomers.

This study evaluated the bond strength between glass ionomer cements and laser-etched dentin. Extracted human molars were sectioned sagittally, creating a flat surface. Samples were shear tested on an Instron testing machine, and mean bond strengths were recorded; statistical analyses indicated no significant differences between the Ketac cements. The bond strengths of both Ketac cements were significantly decreased when applied to laser-etched dentin, but bond strengths of Fuji-II were substantially elevated compared with the control values.

Effects of coaxial CO2/Nd:YAG irradiation on periodontal wound healing.

This study evaluated a coaxial CO2/Nd:YAG laser used during periodontal surgery in mongrel dogs for the purpose of ablating the osseous portions of root surfaces to increase reattachment of soft tissue. Periodontal defects were produced with ligatures of orthodontic wire and elastics. The left mandibular osseous root surfaces were irradiated with a defocused, CW laser beam [power density (PD) = 42.46 W/cm2, energy density (ED) = 424.63 J/cm2]. The left maxillary osseous root surfaces were treated with a beam at twice the energy density [PD = 84.93 W/cm2, ED = 849.3 J/cm2]. The mandibular right quadrant received conventional surgery and the maxillary right quadrant served as the untreated control. Fourteen days after treatment, facial/lingual attached gingivae were scored for soft tissue adherence to bone. Laser irradiation at low ED did not improve soft tissue attachment when compared to conventional treatment. Higher ED irradiation produced significantly less attachment and increased tissue necrosis.

Effects of ultrasonic instrumentation on microleakage in composite restorations with glass ionomer liners.

The aim of this study was to determine the effect of ultrasonic instrumentation on composite resin restorations lined with glass ionomer cement by measuring the extent of dye penetration at the restoration/tooth interface. Preparations, 2.0 mm in diameter and 2.5 mm in depth, were made with a 331 bur in 96 human molar teeth without a bevel. The teeth were restored with glass ionomer cement liners (Shofu) and one of two types of composite resin (Silux and P-30). Half of the samples were ultrasonically instrumented for 10 s. The teeth were immersed in 0.5% methylene blue dye solution and vertically sectioned. Microleakage was scored visually using a scale of 0 to 4. Statistical comparisons were made with chi 2 analysis and the Mann-Whitney U-test at the P less than 0.05 level. Microleakage was significantly different between both resin types (P less than 0.001), and between the lined and unlined resins (P less than 0.001) that were instrumented, particularly in the P-30 restorations. Although P-30 restorations exhibited much less microleakage than Silux, the use of a glass ionomer liner did not reliably reduce microleakage in either type of material after instrumentation with an ultrasonic device.

Enamel surface roughness and dental pulp response to coaxial carbon dioxide-neodymium: YAG laser irradiation.

The purpose of this study was to evaluate the effect of a coaxial carbon dioxide/neodymium:yttrium aluminium garnet laser beam on enamel surface roughness and the dental pulps of mongrel dogs. In four dogs, four maxillary left posterior teeth were irradiated at 16 cm source-tooth distances. Two teeth were irradiated with 16 W CO2/16 W Nd:YAG and the remaining two with 16 W CO2/40 W Nd:YAG. Two maxillary right teeth were untreated controls. In addition, mandibular premolars were irradiated at the same distance and power levels, extracted, and analysed for surface roughness. Significant differences in surface roughness were found between control samples and either power level, but not between enamel surfaces at the two power levels. Maxillary teeth were removed at 10 days postoperatively, sectioned and stained (H & E). The reaction of pulpal cells to irradiation was scored. Data analysis revealed statistically significant differences between the control and lower power Nd:YAG groups and between the control and higher power Nd:YAG groups. The difference in pulpal response between both laser groups approached significance.

Microleakage in alloy-glass ionomer lined amalgam restorations after thermocycling.

Marginal microleakage was measured around amalgam restorations lined with alloy-glass ionomer cement and coated with a glass ionomer varnish. Preparations were made in 48 human extracted mandibular molar teeth. Alloy-glass ionomer liners and varnishes were placed into selected preparations. Tytin amalgam was inserted into all of the teeth and left unburnished and unpolished. Half of the total samples were thermocycled for 5 days and the remainder were left in deionized water. The teeth were immersed in a 0.5% methylene blue dye and sectioned vertically with a diamond saw. Microleakage was scored visually at x100 magnification, and the data were analysed using the Mann-Whitney U-test (P less than or equal to 0.05). Thermocycling did not have a significant effect on microleakage, except when both an alloy-glass ionomer liner and varnish were used. Overall, the use of an alloy-glass ionomer liner made the most significant difference in reducing microleakage.

Effect of undercut placement on crown retention after thermocycling.

The aim of this study was to examine the effect of undercuts in castings and/or tooth structure on the retention of crowns luted with glass ionomer cement. After routine full-crown preparations had been made in 48 human premolars, wax patterns were fabricated for each tooth. Retentive coves were then produced with a round bur in either the tooth structure or the wax patterns, or in both. One group of teeth and patterns did not receive any undercuts; this was the control group. Castings were made in non-precious metal. All crowns were luted with glass ionomer cement. Half of the samples were thermocycled, and the remainder were kept at 37 degrees C. Crowns were removed using tension (0.012 cm min-1) and the mean bond strengths calculated. The differences in retentive strengths were tested for statistical significance using ANOVA and Scheffe's test. The presence of coves in castings and/or tooth structure significantly increased the retentive strength of castings cemented with glass ionomer, as compared with conventional crown preparations without retentive undercuts. The effect of thermocycling on the retentive strength of castings cemented with glass ionomer was not statistically significant.

Microleakage in restorations with glass ionomer liners after thermocycling.

The purpose of this study was to compare microleakage around two types of restorations lined with polyalkenoate (glass ionomer) cements after thermocycling. Preparations were made in 48 molars to a diameter and depth of 2.0 mm. Half of the preparations were lined with glass ionomer, and the remainder were not lined. Dental amalgam or glass ionomer restorative material was placed and the amalgams were left unburnished and unpolished. Selected restorations were thermocycled 625 times between 4 degrees C and 50 degrees C. Teeth were immersed in 0.5 per cent methylene blue solution, sectioned and visually scored for microleakage at X 100 magnification. Data analysis indicated significant differences in microleakage because of: thermocycling (chi 2 = 103.38, d.f. = 19,2P less than 0.0004); presence of glass ionomer liners (chi 2 = 53.28, d.f. = 19,2P less than 0.0001); and type of restorative material (chi 2 = 103.44,d.f. = 19,2P less than 0.0004). The use of a glass ionomer liner significantly reduced microleakage in both amalgam and glass ionomer restorations when subjected to thermocycling.

Evaluation of glass-cermet cores under cast crowns.

The goal of this study was to compare two core materials--glass-cermet and amalgam--in terms of crown retention when significant tooth structure is missing. The glass-cermet's ability to bond to teeth with and without the aid of retentive pins and/or grooves was examined. The effects of two storage solutions, formalin and sodium azide, on the bond of the glass-cermet were also evaluated. Sixty human molars were obtained and stored in either formalin or sodium azide. Thirty molars were prepared with one wall of tooth structure remaining, and the other 30 were prepared with two walls. Before being restored with glass-cermet, the preparations received either no retention, retentive grooves and pins, or retentive grooves only. Each preparation restored with amalgam received pins and grooves. Type III gold crowns were cemented in vitro with glass-ionomer luting agent, thermocycled 2500 times (5-50 degrees C), and then removed under a tensile force. The to amalgam and has adequate adhesion to the tooth, without additional retention, when at least two walls of the tooth remain. However, when only one wall of the tooth remains, the amalgam core is superior under tensile forces. There was a significant difference between the sodium azide and formalin storage solutions with regard to bond strength in one group (two walls, no pins, no grooves). In general, the cores placed on teeth stored in sodium azide exhibited tensile bond strengths lower than those stored in formalin.