Intra-pulpal temperature rise of different tooth types during dental bleaching supported by an Er,Cr:YSGG laser. A pilot study.

The purpose of this pilot in vitro study was to evaluate the temperature increase in the pulp chamber of the teeth, during Er,Cr:YSGG bleaching, as well as to show which teeth are the most susceptible in terms of pulp temperature increase during laser-activated bleaching treatment. Although Er:YAG studies have been published on this subject, it is the first time Er,Cr:YSGG wavelength is tested. Fifteen teeth were tested--3 each of the following--(maxillary central incisors, lateral incisors, canines, premolars and mandibular incisors). The bleaching procedure comprised an Er,Cr:YSGG laser (2780 nm, Waterlase MD, Biolase, USA) and a yellow-coloured bleaching agent with a concentration of 38 % H2O2 (Power whitening, WHITEsmile GmbH, Germany). The tip used was a 6-mm long Z-type glass tip (MZ8) of a 800 µm diameter. Average output power was set to 1.25 W, pulse duration 700 µs (S-mode), whilst the pulse repetition rate was 10 Hz. The results showed that the most susceptible teeth in terms of pulp temperature increase were the lateral maxillary incisors and the mandibular incisors. The mean temperature increase on these teeth was 1.06 and 1.00 °C, respectively, on 60 s Er,Cr:YSGG-supported bleaching.

Laser supported reduction of specific microorganisms in the periodontal pocket with the aid of an Er,Cr:YSGG laser: a pilot study.

OBJECTIVE: The aim of this study was to evaluate the effectiveness of a radial firing tip of an Er,Cr:YSGG laser as an adjunct to a nonsurgical periodontal treatment. METHODS: Twelve patients with chronic or aggressive periodontitis were treated by conventional periodontal treatment using ultrasonic devices and hand instruments and, additionally, in two quadrants with an Er,Cr:YSGG laser. A new radial firing tip (RFPT 14-5, Biolase) was used with 1.5 W, 30 Hz, 11% air, 20% water, and pulse duration 140 µs. Microbiological smears were taken before treatment, one day after lasing, and three and six months after lasing. Pocket depths of all periodontal sites were measured before and six months after treatment. RESULTS: The total bacterial load of Prevotella intermedia, Tannerella forsythia, Treponema denticola, Fusobacterium nucleatum, Porphyromonas gingivalis, and Aggregatibacter actinomycetemcomitans inside the pocket was reduced significantly throughout the whole examination time. Greater pocket depth reductions were observed in all groups. There was a slight higher reduction of pocket depth in the lased group after six months. CONCLUSIONS: These results support the thesis that Er,Cr:YSGG laser supported periodontal treatment leads to a significant reduction of periopathogenes and thereby helps the maintenance of periodontal health.

Efficacy of Er,Cr:YSGG laser with endodontical radial firing tips on the outcome of endodontic treatment: blind randomized controlled clinical trial with six-month evaluation.

Clinical reports stating the efficacy of novel root canal disinfection protocols are an important focus in endodontic research. This blind randomized clinical trial assessed the clinical efficacy of the erbium, chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser radial firing tips (RFT) versus the concomitant use of 3 % sodium hypochlorite and interim calcium hydroxide paste in necrotic teeth with chronic apical periodontitis. We hypothesized to find similar or improved bone healing in the laser-assisted endodontic treatment. Thirty-six anterior and premolar teeth were randomly assigned. In group 1, teeth were prepared with 3 % sodium hypochlorite for irrigation and calcium hydroxide as inter-appointment dressing; in group 2, teeth were prepared with saline solution and irradiated with Er,Cr:YSGG laser using RFT2 (140 µs, 37.5 mJ, 20 Hz) and RFT3 (140 µs, 62.5 mJ, 20 Hz) in the first and second appointment, respectively, four times each, moving at 2 mm s(-1) from apical to coronal. The primary outcome measure was changed in apical bone density at 6 months, using the periapical index (PAI) for blind radiographic evaluation. Twenty-nine patients were examined and subjected to statistical analysis, 12 in group 1 and 17 in group 2. There was one treatment failure in group 1. Both groups gave similar outcomes exhibiting statistically significant decreases in PAI scores.

A comparative study of temperature elevation on human teeth root surfaces during Nd:YAG laser irradiation in root canals.

The purpose of this study was to evaluate the temperatures on the root surfaces during Nd:YAG laser irradiation in root canals using pulse durations of 180 and 320 µs. Thirty extracted human teeth were used in this study. The teeth were enlarged up to ISO 40 (multi-rooted) or up to ISO 60 (single-rooted) by conventional technique using K-files. Then the teeth were placed into a water bath with a constant temperature of 37 °C and then irradiated with an Nd:YAG laser having an output power of 1.5 W, a frequency of 15 Hz, using an optic fiber of 200 µm diameter. The temperature on the root surface was measured by means of attaching thermocouples in three areas (coronal, mesial, and apical regions) of the root canals. The thermographic study showed that the average temperature elevation for both pulse durations on the root surfaces was less than 9 °C. There was no significant difference in the observed temperatures in coronal and mesial areas. Though a higher increase of temperature was observed in the apical region when the pulse length of the Nd:YAG laser was 320 µs. The results of the study showed that the temperature rises during Nd:YAG laser irradiation with parameters used in this study minimal to cause damage on bone and periodontal tissues. Moreover, it was suggested that in order to have lower temperature in the apical region, an Nd:YAG laser with a pulse length of 180 µs is preferred than one with a pulse length of 320 µs.

Effects of erbium:yttrium-aluminum-garnet and neodymium:yttrium-aluminum-garnet laser hypersensitivity treatment parameters on the bond strength of self-etch adhesives.

This in vitro study evaluated the shear bond strength (SBS) of two self-etch adhesives to coronal and root dentin treated with erbium:yttrium-aluminum-garnet (Er:YAG) or neodymium:yttrium-aluminum-garnet (Nd:YAG) lasers for dentin hypersensitivity. The coronal and root dentin surfaces of 60 extracted human cuspids were divided into three groups (n = 20): (1) control (without treatment); (2) treated with Er:YAG; (3) treated with Nd:YAG laser and a one-step (S3) or two-step self-etch adhesive (SE). A nano-composite was applied and SBS tests were performed. The mean SBS values were calculated, failure modes were determined, and data were subjected to statistical analysis (P = 0.05). Control/SE exhibited higher values than did control/S3 and Nd:YAG/S3 on coronal dentin (P < 0.05). No significant differences were observed between the SE and S3 groups in root dentin (P > 0.05). Comparisons of two dentin substrates did not show any difference except control/SE (P < 0.05). The failure modes were mainly adhesive. The SBSs of self-etch adhesives to Er:YAG or Nd:YAG laser-treated surfaces were comparable with control for both coronal and root dentin.

A comparative SEM study between hand instrument and Er:YAG laser scaling and root planing.

Scaling and root planing are one of the most commonly used procedures for the treatment of periodontal diseases. Removal of calculus using conventional hand instruments is incomplete and rather time-consuming. In search for more efficient and less difficult instrumentation, investigators have proposed lasers as alternatives or adjuncts for scaling and root planing. The aim of the present study was to compare the effectiveness of subgingival scaling and root planing with erbium: yttrium, aluminium, garnet (Er:YAG) laser and hand instrumentation in vitro. The mesial and distal surfaces of 15 periodontal loosed extracted teeth were treated randomly either by hand instrumentation or by Er:YAG laser irradiation. After choosing the "very long pulse mode" (pulse duration of about 700 micros), the output energy of 160 mJ with 920-microm beam diameter (RO7 Perio tip, Fidelis, Fotona, Slovenia) and frequency of 12 Hz were selected, both according to the best results of past studies. In addition, air water spray was used during the procedures. The morphology of the root surface was evaluated by three observers with a scanning electron microscopy in magnifications of 50x and 400x. The result of this setting showed that the rate of remained roughness on treated root surfaces in two groups of hand instruments and Er:YAG laser had a meaningful difference: The surface roughness in Er:YAG laser group was more than in hand instruments group. The present study could demonstrate the in vitro capability of the Er:YAG laser for scaling and root planing in periodontitis, although the effectiveness of this setting did not reach that achieved by hand instrumentation. It could be concluded that lower frequency and long pulse duration maybe more suitable for the micro-morphology of root surface after treatment. This theory is going to be tested with the same laser instrument in the next study.

Structural changes in human dental enamel after subablative erbium laser irradiation and its potential use for caries prevention.

Numerous studies have confirmed the potential of erbium laser irradiation for increasing the acid resistance of dental enamel. The objective of the present paper was to investigate the effect of subablative erbium laser irradiation on the structure and acid resistance of dental enamel by means of confocal laser scanning microscopy (CLSM). To this end, 12 samples of human dental enamel were irradiated with subablative energy densities (Phi) of an Er:YAG (lambda = 2.94 microm, Phi = 6 J/cm(2)) and an Er:YSGG laser (lambda = 2.79 microm, Phi = 8 J/cm(2)). The enamel surfaces of 6 samples were polished prior to irradiation. The remaining 6 samples were left intact (without polishing procedures) and, in the further course of the study, they were subjected to 1-week in situ demineralisation. All irradiated test surfaces were assigned a control surface on the same sample. The changes following laser irradiation and the in situ wearing time were assessed qualitatively using a confocal laser scanning microscope. The irradiation of dental enamel with subablative erbium laser irradiation produces fine cracks in the enamel surface. These cracks act as starting points for acid attack and favour deep demineralisation. These changes reduce or eliminate the positive effect of subablative erbium laser irradiation observed in connection with caries-preventive use. The clinical use of subablative erbium laser irradiation to prevent caries would appear not to make sense under the conditions studied.

The caries-preventive potential of subablative Er:YAG and Er:YSGG laser radiation in an intraoral model: a pilot study.

OBJECTIVE: The aim of the present study was to investigate the effect of sub-ablative Er:YAG and Er:YSGG laser radiation on the demineralization of human dental enamel in situ. METHODS: Eighteen enamel specimens were prepared to this end, nine of which were irradiated at 8 J/cm(2) with the Er:YSGG laser and nine at 6 J/cm(2) with the Er:YAG laser (125 pulses per surface). Each test surface was assigned a control surface on the same specimen. Three healthy volunteers from each group subsequently wore three enamel specimens in situ for a period of 1 week. The demineralization was assessed by determining the surface microhardness according to Knoop (KH) before and after wearing. RESULTS: Before wearing, the mean surface hardness measured on the control surfaces was 233 (SD 99) KH (CYSGG) and 162 (SD 59) KH (CYAG). After sub-ablative laser irradiation, the surface hardness values measured were already found to be lower compared to the untreated control surfaces (YSGG: 195 [SD 110] KH/YAG: 112 [SD 72] KH). Marked demineralization was observed on the control surfaces after 1 week of wearing in situ (CYSGG*: 60 [SD 57] KH; CYAG*: 53 [SD 9] KH). After wearing, the hardness on the irradiated test surfaces was ErYSGG*: 133 [SD 58] KH and ErYAG*: 89 [SD 28] KH, and was thus higher than on the control surfaces. CONCLUSIONS: The results indicate a tendency towards increased caries resistance following sub-ablative erbium laser irradiation. However, in an analysis of variance model with repeated measures, the tendency in this study failed to reach statistical significance (alpha = 0.05).

Bactericidal effect of a 980-nm diode laser in the root canal wall dentin of bovine teeth.

OBJECTIVE: The aim of this in vitro study was to investigate the antibacterial depth effect of continuous wave laser irradiation with a wavelength of 980 nm in the root canal wall dentin of bovine teeth. BACKGROUND DATA: The long-term success of an endodontic therapy often fails due to remaining bacteria in the root canal or dentin tubules, which cannot be sufficiently eliminated through the classical root canal preparation technique nor through rinsing solutions. MATERIALS AND METHODS: A total of 102 slices of bovine root dentin of different thicknesses (100, 300 and 500 micro m) were prepared. The samples were inoculated from one side with 5 micro L of an enterococcus faecalis suspension of defined concentration. Four slices per slice thickness served as a control group; the rest of the 30 slices per thickness were subjected to laser irradiation - 10 each of these slices were irradiated with distal outputs of 1.75, 2.3, and 2.8 Watts (W). After drying them for 30 sec, the back of the inoculated dentin slice was irradiated for 32 seconds with a 200- micro m fiber optical waveguide under constant movement of the fibers. The remaining bacteria were then detached in NaCl under vibration. The eluate produced by this was - taking account of the degree of dilution - plated out on sheep blood agar plates. After 24 h of incubation, the grown bacterial colonies were able to be counted out and evaluated. By doing so, they were compared with the non-irradiated, but otherwise identically treated control group. RESULTS: With a slice thickness of 100 micro m, the 980-nm diode laser achieved a maximum bacterial reduction of 95% at 1.75 W, 96% at 2.3 W, and 97% at 2.8 W. With a slice thickness of 300 micro m, a maximum of 77% of the bacteria was destroyed at 1.75 W, 87% at 2.3 W, and 89% at 2.8 W. The maximum bacterial reduction with a slice thickness of 500 micro m was 57% at 1.75 W, 66% at 2.3 W, and 86% at 2.8 W. CONCLUSION: The results of this research show that the 980-nm diode laser can eliminate bacteria that have immigrated deep into the dentin, thus being able to increase the success rate in endodontic therapy.

Influence of the spatial beam profile on hard tissue ablation. Part I: Multimode emitting Er:YAG lasers.

Uniform dosimetry is a prerequisite for reproducible laser applications in research and practice. The light-tissue interaction is dependent on the absorbed energy (J) per unit of time (tau) in the case of pulsed lasers, and on the absorbed power (W) per unit of volume (e.g. mm3) in the case of continuous-wave (cw) lasers, and thus directly dependent on the energy distribution within the laser beam. Consequently, precise knowledge of the spatial beam profile, and of the pulse duration and treatment time, is indispensable. The objective of this paper was a theoretical study of the impact of different mode profiles on energy distribution in the beam. Also examined was the question of the influence of changes in the laser parameters on the mode structure. Three erbium:YAG lasers (lambda=2.94 microm) were used for this purpose. The transversal mode structure of the lasers was observed by irradiating thermal paper and verified by means of calculations. The effect induced in the mode profile by changing the pulse energy and pulse repetition rate was investigated. The results of the tests show that changes in the laser parameters result in jumps in the transversal modes and associated energy distributions in the beam. The experiments confirm that simply changing the transversal modes has a substantial effect on the threshold energy required for the ablation of dental enamel (50 mJ with TEM00, 22.6 mJ with TEM31). In practice, inhomogeneity makes it impossible to determine the irradiated area in order to calculate the energy or power density. In addition, the energy distribution in the beam changes as a result of variation of the laser output energy and the pulse repetition rate. Consequently, simply measuring the beam diameter yields a totally incorrect result for the applied flux density when using a beam profile with a relatively high mode.

Demineralization of Er:YAG and Er,Cr:YSGG laser-prepared enamel cavities in vitro.

The aim of the present study was to establish whether cavity preparation by means of an erbium laser with efficient water cooling is capable of reducing the susceptibility of the prepared dental enamel to demineralization and thus of achieving a potential caries-protective effect in the region of cavity margins. To this end, cavities limited to the enamel were prepared in the crowns of 10 teeth each using an Er:YAG (lambda = 2,940 nm) and an Er,Cr:YSGG laser (lambda = 2,780 nm). A control cavity prepared conventionally with a diamond drill in the same occlusal zone was assigned to each of these cavities. The specimens were then subjected to a pH-cycling caries model. Analysis was performed by quantitatively measuring the demineralization front under a polarized-light microscope. The results of the study showed that enamel cavities prepared with the erbium lasers used display a statistically significant acceleration of demineralization compared to conventionally prepared cavities (p < 0.01). The Er:YAG laser cavities revealed demineralization to a depth of 133.9 (SD 25.7) microm, while the value observed with the Er,Cr:YSGG laser was 133.8 (SD 25.8) microm. The depth of demineralization in the control groups was only 77.4 (SD 13.8) microm and 79.3 (SD 37.6) microm. No difference could be found between the two lasers (p = 0.98). Based on these in vitro tests, it cannot be assumed that use of the erbium laser for cavity preparation offers any advantages in terms of resistance to secondary caries in clinical practice.

The ablation threshold of Er:YAG and Er:YSGG laser radiation in dental enamel.

The scientific investigation of fundamental problems plays a decisive role in understanding the mode of action and the consequences of the use of lasers on biological material. One of these fundamental aspects is the investigation of the ablation threshold of various laser wavelengths in dental enamel. Knowledge of the relationships and influencing factors in the laser ablation of hard tooth tissue constitutes the basis for use in patients and the introduction of new indications. The present paper examines the ablation threshold of an Er:YAG laser (lambda=2.94 micro m) and an Er:YSGG laser (lambda=2.79 micro m) in human dental enamel. To this end, 130 enamel samples were taken from wisdom teeth and treated with increasing energy densities of 2-40 J/cm(2). The sample material was mounted and irradiated on an automated linear micropositioner. Treatment was performed with a pulse duration of tau(P(FWHM)) approximately 150 micro s and a pulse repetition rate of 5 Hz for both wavelengths. The repetition rate of the laser and the feed rate of the micropositioner resulted in overlapping of the single pulses. The surface changes were assessed by means of reflected light and scanning electron microscopy. On the basis of the results, it was possible to identify an energy density range as the ablation threshold for both the Er:YAG and the Er:YSGG laser. With the Er:YAG laser, the transition was found in an energy density range of 9-11 J/cm(2). The range for the Er:YSGG laser was slightly higher at 10-14 J/cm(2).

Influence of the pulse duration of an Er:YAG laser system on the ablation threshold of dental enamel.

The present study examines the dependence of the ablation threshold on the duration of the applied laser pulses in the dental enamel of human wisdom teeth. To this end, 600 treatments with the Er:YAG laser (lambda=2940 nm) were carried out on a total of 50 extracted teeth. The laser light was coupled into a fluoride glass light guide for this purpose, in order to ensure almost gaussian distribution of the light in a radially symmetrical beam. The beam diameter on the specimen was 610 micro m. The radiant exposure on the tooth surface was varied between 2 and 20 J/cm(2), while the duration of the pulses applied was changed in four steps from 100 micro s to 700 micro s. The irradiated tooth surfaces were examined for visible signs of ablation under a reflected-light microscope. The experiments revealed that, when pulses of shorter duration are used, the limit at which ablation sets in is reduced by up to approx. 3 J/cm(2). This expands the ablation threshold range of Er:YAG laser radiation to between 6 and 10 J/cm(2). In this context, both the pulse duration and the radiant exposure have a statistically significant influence on the ablation threshold (logistic regression, p<0.0001). Although the ablation threshold of the dental enamel can be changed by varying the pulse duration of the Er:YAG laser, no clinical consequences can be expected, as the shift is only slight.

Calcium solubility of dental enamel following sub-ablative Er:YAG and Er:YSGG laser irradiation in vitro.

BACKGROUND AND OBJECTIVE: The objective of the present study was to investigate the effect of sub-ablative Er:YAG (lambda = 2.94 microm) and Er:YSGG (lambda = 2.79 microm) laser radiation on the acid solubility of dental enamel. The influence of fluoride application prior to laser irradiation was additionally evaluated. STUDY DESIGN/MATERIALS AND METHODS: To this end, 294 enamel specimens were prepared from bovine teeth and divided into 14 groups of 21 specimens each. The enamel samples were irradiated in their groups with the Er:YAG and the Er:YSGG laser, using energy densities of 4, 6, and 8 J/cm(2) in each case. Irradiation was additionally repeated in the same way on specimens, which had previously been immersed in 1% sodium fluoride solution for 15 minutes. One group was left untreated and served as a control group. A further group was not irradiated, but only immersed in the 1% fluoride solution for 15 minutes. The enamel specimens were demineralised for 24 hours in an acetate buffer solution. The calcium content in the demineralisation solution was subsequently determined with the aid of atomic absorption spectrometry. RESULTS: The results indicate a decline in calcium solubility after laser irradiation. Compared to the control group, a 20% lower calcium content was detected in the demineralisation solution after irradiation with the Er:YSGG laser at 8 J/cm(2). The difference between the laser-irradiated groups and the untreated control group was, however, not statistically significant. A significantly lower calcium content was found in the demineralisation solution after fluoridation of the specimens. Additional laser radiation had no further effect on this result. CONCLUSIONS: In summary, it can be stated that, although the erbium laser wavelengths apparently have the potential to increase acid resistance, their application solely for caries prevention would not appear to be sensible under the prevailing conditions.

Conditioning of enamel with Nd:YAG and CO2 dental laser systems and with phosphoric acid. An in-vitro comparison of the tensile bond strength and the morphology of the enamel surface.

UNLABELLED: MATERIAL AND METHOD 1: The first stage of a three-stage in-vitro investigation used 146 maxillary incisors to identify optimum setting parameters for two CO2 and Nd:YAG standard laser systems applied in enamel conditioning for bracket bonding. RESULTS: 31 of the 75 parameter combinations investigated for the Nd:YAG laser and nine of the 71 investigated for the CO2 laser proved appropriate for further investigation of tensile strength. MATERIAL AND METHOD 2: In a second stage, tensile bond strength for the selected laser settings was determined in comparison to the conventional acid-etch technique for a further 210 teeth as the control group. RESULTS: The highest average tensile strength for the Nd:YAG laser was 4.1 MPa, with comparable values of 3.3 MPa for the CO2 Laser and 4.9 MPa for the acid-etch technique. MATERIAL AND METHOD 3: The third stage of the investigation involved comparative scanning electron microscopy of enamel surface morphology following laser application and acid-etching. RESULTS: The CO2 laser was found to produce craters of various dimensions, while the Nd:YAG laser produced honeycomb structures regionally similar to enamel samples from the acid-etch technique. CONCLUSION: The CO2 and Nd:YAG dental lasers tested produce enamel conditioning and tensile bond strength sufficient to meet the requirements of bracket bonding.

Microleakage of composite fillings in Er,Cr:YSGG laser-prepared class II cavities.

BACKGROUND AND OBJECTIVE: If there is insufficient bonding to the enamel, the shrinkage of composites that occurs during polymerization can result in a gap between the filling material and the cavity wall. This gap permits the passage of bacteria or their metabolic products and also of various molecules and ions. This leads to hypersensitivity or secondary caries and is thus one of the causes of the failures encountered in composite restorations. The aim of this study was to examine the quality of the margins of composite fillings in Er,Cr:YSGG laser-prepared cavities by means of dye penetration. The results were compared with those of restoration in conventionally prepared and conditioned cavities. STUDY DESIGN/MATERIALS AND METHODS: To this end, 45 class II cavities in extracted molars were prepared. The teeth were divided into three groups. The first group served as a control group. The cavities were prepared in the classical manner by using a diamond, beveled and subsequently conditioned by the etching method. In group 2, the cavities were prepared and conditioned exclusively with the Er,Cr:YSGG laser. In group 3, laser preparation was supplemented by conditioning of the cavity with phosphoric acid. RESULTS: No significant difference could be found between the classical preparation technique in combination with etching and the laser preparation method with supplementary etching (group 3). The degree of dye penetration was highest in the group undergoing laser-prepared restoration without additional etching (group 2) (Wilcoxon test, P < 0.017). CONCLUSIONS: Although it was found in previous studies that there is no significant difference between bond strength of acid etched enamel and Er,Cr:YSGG laser etched enamel, the dye penetration rate differs. On the basis of the results of our study, the additional use of etching after Er,Cr:YSGG laser preparation is recommended as it is used in the classical cavity preparation technique.

Diode laser radiation and its bactericidal effect in root canal wall dentin.

OBJECTIVES: The aim of this study was to investigate the antibacterial effect of a diode laser in deep root canal dentin. BACKGROUND DATA: The microbial colonization of root canal dentin can lead to failures in conventional endodontic treatment if an inadequate bacterial reduction only is achieved through canal treatment and chemical disinfection. METHODS: 100 microm, 300 microm and 500 microm bovine dentin slices obtained by longitudinal sections were sterilized and inoculated on one side with an Enterococcus faecalis suspension. Laser radiation was performed on the opposite side with the diode laser (810 nm) at a setting of 3 W in continuous mode (CW). Radiation was performed using a 400-microm tapered fiber tip at an angle of approximately 5 degrees to the surface over a period of 30 seconds. The output power at the distal end of the tip was 0.6 W. The bacteria were then eluted through vibration and cultured on blood agar plates. The colony count reflected the antibacterial effect of laser radiation as a function of the layer thickness. RESULTS: A mean bacterial reduction of 74% was achieved even with a 500-microm thick slice. CONCLUSION: This investigation indicates that the diode laser radiation reduces the number of bacteria in deep layers of infected root canal wall dentin.

The bactericidal effect of Ho:YAG laser irradiation within contaminated root dentinal samples.

OBJECTIVE: This in vitro study investigates the bactericidal effect of pulsed Ho:YAG laser irradiation in the depth of contaminated dentin specimens. BACKGROUND DATA: Previous studies have shown the effectiveness of laser irradiation in bacterial reduction of infected root canal. METHODS: Root dentin of bovine teeth were sliced longitudinally in 180 samples of 100 microm, 300 microm, and 500 microm thickness, sterilized, dried, and inoculated on one side, with 1 microL of Enterococcus faecalis suspension. The opposite side's were irradiated four times for 5 seconds each with Ho:YAG laser irradiation, a wavelength of 2.10 microm, using four different energy settings: 1 W/5 Hz; 1 W/10 Hz; 1.5 W/5 Hz, and 2.0 W/5 Hz through a 320-microm quartz fiber at an angle of approximately 5 degrees. In addition, two control groups were investigated, the first was inoculated and not submitted to any treatment, the second was inoculated and treated with NaOCl and H2O2. The remaining bacteria from each dentin sample in a transport media were removed by vibration, serially diluted, and plated out on culture dishes selective for Enterococcus faecalis. RESULTS: When compared with the untreated control group or even with the group treated with NaOCl plus H2O2, counting of colonies forming units (CFU) from the laser-treated samples revealed a high significant bacterial elimination with a maximum of 98.46% and a minimum of 83.65%. CONCLUSIONS: Our findings demonstrate a significant decrease of the bacterial population in depth, suggesting that the Ho:YAG laser irradiation could be effective to eliminate the microorganisms harbored within dentin or contaminated canals.

Procedures for enamel and dentin conditioning: a comparison of conventional and innovative methods.

Composite materials have become an integral part of the wide range of filling materials currently available. Conditioning is necessary to achieve adequate bonding of the composite material to enamel and dentin. Normally, this is done by applying acid preparations to the dental surfaces. These acids have an etching effect that causes surface roughening. The increasing application of lasers in dentistry has introduced another possibility. Laser irradiation can cause roughening of enamel and dentin surfaces. Another interesting alternative is the so-called kinetic cavity preparation technique. This method also results in distinct surface roughening. The purpose of the present study, was to compare the described methods. Tensile bond strength tests and shear bond tests were carried out to examine the adhesion of a composite material to surfaces treated with these methods. Laser irradiation with certain devices and the air-abrasive technique yielded results similar to those with acid etching.

Effects of Nd:YAG-laser irradiation on monolayer cell cultures.

BACKGROUND AND OBJECTIVE: The clinical applications of Nd:YAG lasers on oral soft tissues include a wide field of surgical and periodontal procedures. This in vitro study focuses on the histological effects of Nd:YAG-laser irradiation on a fibroblast monolayer cell culture especially with regard to thermal damage and cell necrosis. The results of this basic research study provide us with clear power settings for a safe soft tissue laser treatment. STUDY DESIGN/MATERIALS AND METHODS: Two hundred forty multiwell cell cultures and 24 micro-slide Leighton tubes were laser treated. Laser irradiation was performed with a commercial free-running pulse Nd:YAG laser and a quartz fiber with a diameter of 200 microns on L-929 fibroblast cell cultures. The variable parameters were pulse energy (30-120 mJ), pulse rate (20-100 Hz), power output (1.5-3.0 W), and time of irradiation (10-60 s). The cultures were analyzed with help of vital staining, autoradiography, and cytomorphology examination. RESULTS: Depending on the different settings the laser irradiation caused inhibitions of the DNA metabolism rate and the cell division rate, a degeneratively changed cytomorphology up to cell pyknosis. An increasing pulse energy, pulse rate, or an increased time of irradiation created an extended diameter of the pyknotic cell zone. CONCLUSIONS: The laser beam creates an exactly bordered damage between cells. The cells had a very good inherent mobility, but the border between eliminated and unloaded cell zone was sharp, even after an incubation of 24 h. These stable results prove that the laser can be applied up to a micrometer distance. With the help of cell clusters it was proved that the laser beam is also able to eliminate exactly one monolayer. Cells which had been covered by another cell layer (in a cluster) were not eliminated.