A comparative study on compositional changes and Knoop hardness measurement of the cavity floor prepared by Er:YAG laser irradiation and mechanical bur cavity

OBJECTIVE: This present study was performed to compare the compositional changes of human dentin and, Knoop hardness of the cavity floor prepared by Er:YAG laser irradiation with that of the conventional bur cavity. BACKGROUND DATA: There are still no reports on the compositional changes of dental hard tissues and microhardness of the cavity floor prepared by Er:YAG laser irradiation. MATERIALS AND METHODS: Fifteen laser and 15 bur cavities were cross-sectioned, and subjected to atomic analysis by SEM-EDX and Knoop hardness testing. Statistical analyses were performed using the Mann-Whitney U test; a value of p < 0.01 was considered significant. Cross sections of the remaining five laser and five bur cavities were examined by light microscopy and then by SEM. RESULTS: The results showed that the quantities of Ca (Ca weight %) and P (P weight %) were increased significantly in the laser cavities, but no significant differences were found between the Ca/P ratio and Knoop hardness number of laser and bur cavities. The results of SEM observation revealed that the lased cavity surface was irregular, and there was also the absence of a smear layer; the orifice of dentinal tubules was exposed. CONCLUSION: Er:YAG laser device produces minimal thermal induced changes of dental hard tissue compositions; Ca/P ratio and Knoop hardness of the lased cavity floor was almost similar to the bur cavities.     

Morphological and microleakage studies of the cavities prepared by Er:YAG laser irradiation in primary teeth

OBJECTIVE: The purposes of this study were to investigate cavity surfaces morphologically, and compare microleakage at cavities prepared by Er:YAG laser after composite resin restoration versus conventional mechanical treatment in human primary teeth in vitro. BACKGROUND DATA: There have been few reports on microleakage at cavities prepared by Er:YAG laser irradiation. MATERIALS AND METHODS: A total of 30 cavities (class V) in human primary teeth were used. Half of the cavities were prepared by an Er:YAG laser system at 300 mJ pulse energy and 4 Hz, and the other half were prepared with a high-speed diamond bur. Five cavities from each group were investigated by scanning electron microscopy (SEM) and histopathological examination. Remaining cavities were filled with a composite resin without an acid-etching technique and then subjected to microleakage test in 0.6% rhodamine B solution under thermocycling. RESULTS: Microleakage (score: 2.45 +/- 1.07) at cavities prepared by laser was significantly less than that by bur (score: 1.30 +/- 0.95; p < 0.05). SEM observation showed that, compared with the relatively flat appearance of cavities prepared by bur, cavity margins prepared by laser were irregular but there was almost no smear layer at the cavity walls. CONCLUSION: It can be concluded that cavity surfaces prepared by Er:YAG laser are irregular, but microleakage at cavities prepared by the laser after filling with composite resin is better than that by mechanical bur using the dye penetration method.     

Microleakage and nanoleakage: influence of laser in cavity preparation and dentin pretreatment.

OBJECTIVE: The purpose of this study was to verify if the application of the Nd:YAG laser following pretreatment of dentin with adhesive systems that were not light cured in class V cavities and were prepared with Er:YAG laser would promote better sealing of the gingival margins when compared to cavities prepared the conventional way. BACKGROUND DATA: Previous studies had shown that the pretreatment of dentin with laser irradiation after the application of an adhesive system is efficient in achieving higher shear bond and tensile bond strength. MATERIALS AND METHODS: Er:YAG laser (Kavo-Key, Germany) with 350 mJ, 4 Hz, and 116.7 J/cm2 was used for cavity preparation. The conventional preparation was made with diamond bur mounted in high-speed turbine. Dentin treatment was accomplished using an Nd:YAG laser (Pulse Master 1000, ADT. USA) at 60 mJ, 10 Hz, and 74.65/cm2 following application of the adhesive system. The cavities were stored with Single Bond/Z100 and Prime & Bond NT/TPH. Eighty bovine incisors were used, and class V preparations were done at buccal and lingual surfaces divided into eight groups: (1) Er:YAG preparation + Prime & Bond NT + TPH; (2) Er:YAG preparation + Single Bond + Z100; (3) Er:YAG preparation + Single Bond + Nd:YAG + Z100; (4) Er:YAG preparation + Prime & Bond NT + Nd:YAG + TPH; (5) conventional preparation + Prime & Bond NT + TPH; (6) conventional preparation + Single Bond + Z100; (7) conventional preparation + Single Bond + Nd:YAG + Z100; (8) conventional preparation + Prime & Bond NT + Nd:YAG + TPH. All specimens were thermocycled for 300 full cycles between 5 degrees C+/-2 degrees C and 55 degrees C+/-2 degrees C (dwell time of 30 sec), and stored in 50% silver nitrate solution for 24 h soaked in photodeveloping solution and exposed to fluorescent light for 6 h. After this procedure, the specimens were sectioned longitudinally in 3 portions and the extension of microleakage at the gingival wall was determined following a criteria ranging from 0 to 4 using scanning electron microscopy (SEM). The medium portion sectioned of each specimen was polished and prepared for nanoleakage avaliation by SEM. RESULTS: Kruskall-Wallis and Miller statistical tests determined that group 3 presented less microleakage and nanoleakage. CONCLUSION: Application of the Nd:YAG laser following pretreatment of dentin with adhesive Single Bond non-photocured Single Bond adhesive in cavities prepared with Er:YAG promote better sealing of the gingival margins.     

Assessing microleakage on class V composite resin restorations after Er:YAG laser preparation varying the adhesive systems

OBJECTIVE: The aim of this study was to assess the performance of three bonding agents in preventing microleakage of class V cavities prepared and treated by Er:YAG laser associating with acid etching. BACKGROUND DATA: There has been very little research comparing the efficiency of single-component and self-etching adhesive systems in preventing microleakage of cavities prepared and conditioned with Er:YAG laser. MATERIALS AND METHODS: Thirty cavities - with occlusal margin in enamel and cervical in dentin/cementum - were prepared in sound human third molars using a short pulsed Er:YAG laser (500 mJ/5 Hz) The enamel and dentin surfaces were conditioned for 30 sec using lower dosimetries (120 mJ/4 Hz), and the samples were randomly assigned into three groups, according to the adhesive system: (I) Bond-1; (II) Prime & Bond NT; and (III) Etch & Prime 3.0. Groups I and II were acid-etched for 15 sec, and group III did not receive any acid treatment once a self-etching system was employed. Cavities were restored with a light-cured composite resin (JEK-Z250 Filtek-250), and after finishing, the samples were thermocycled, isolated with epoxy resin and nail varnish, immersed in a 0.2% Rhodamine B solution for 24 h, and sectioned longitudinally. The sections obtained were analyzed for leakage using an optical microscope connected to a computer and a video camera. We digitized the images using a special software program that allowed a quantitative evaluation of microleakage in millimeters. RESULTS: Statistical analysis using the Kruskal-Wallis test showed statistically significant difference between both margins, and the occlusal region presented better marginal sealing. Comparing the three resin bonding systems, Prime & Bond NT entirely sealed both margins, while Etch & Prime 3.0 provided the poorest overall results, showing a statistically significant difference (p < 0.01). CONCLUSION: It may be concluded that, for all the tested materials, microleakage values were higher in cervical (dentin/cementum) margins. Additionally, Prime & Bond NT provided a complete elimination of marginal infiltration at both margins, after treating the dental surface with laser irradiation associated with a sequent acid-etching.     

Comparison between the removal effect of mechanical, Nd:YAG, and Er:YAG laser systems in carious dentin.

OBJECTIVE: The purpose of this study was to compare the effectiveness of carious dentin removal by using an Er:YAG laser irradiation and Nd:YAG laser under a continuous water spray with that of the conventional mechanical treatment in vitro. BACKGROUND DATA: Lasers are being considered as a potential replacement of conventional mechanical systems to remove diseased and healthy dental hard tissues. METHODS: First, one half of the 10 carious lesions were treated with the round steel bur and then removed. The other half were treated with the Er:YAG laser at 200-mJ pulse energy at 2 Hz. After that, one half of another set of 10 teeth was subjected to the round steel bur in which the other half was removed using the Nd:YAG laser at 6-W output power, 20 pps, and under a continuous water spray (120 mL/min). Thermal change during each treatment and the time required for carious dentin removal was determined, and the surface characteristic was observed using the scanning electron microscopic (SEM). RESULTS: The Er:YAG or Nd:YAG laser irradiation time was almost two or three times longer than the bur treatment, respectively. From the SEM study, it was found that the lased cavity surface revealed various patterns of microirregularity, and there was also no smear layer. CONCLUSIONS: It can be suggested that under adequate water spray and with a careful irradiation technique, cavities without sign of thermal damage to the surrounding tissues as well as dental pulp could be produced with the Er:YAG and Nd:YAG laser.     

Study of microleakage at class V cavities prepared by Er:YAG laser using rewetting surface treatment

OBJECTIVE: This study was conducted to analyze microleakage in Class V cavity preparation, using rewetting (or not) just after burr or Er:YAG laser preparation of enamel and dentin walls in permanent teeth. Background Data: Several studies reported microleakage around composite restorations when cavity preparation was done or treated by Er:YAG laser. As the hybridized laser is removed when this laser is used to cut dental hard tissue, there is a need for new materials or techniques to minimize gaps and microleakage. RESULTS: Primer solution showed significant effect in enamel and dentin, at the level of 5%, when Er:YAG laser was used as a cutting tool. Using primer solution after phosphoric acid in preparations with the laser, microleakage was similar in degree to when cavities were prepared with the burr. CONCLUSION: Re-wetting surface just after Er:YAG irradiation and chemical treatment with phosphoric acid using HEMA aqueous solution seems to improve the quality of bioattachment between the adhesive system and enamel/dentin, showing similarities between restoration behaviors independently of the cutting tool, whether burr or laser.     

Histological and scanning electron microscope examination of root canal after preparation with Er:YAG laser microprobe: a preliminary in vitro study

OBJECTIVE: Until now, there has been no study that demonstrates the effectiveness of Er:YAG laser microprobes to clean and shape the root canal without using any mechanical instrumentation. MATERIALS AND METHODS: The study was conducted on 28 single-rooted extracted central incisors teeth with straight roots. Fourteen were mechanically prepared and served as the control group, and 14 were treated by Er:YAG laser only. From every group, half of the teeth were examined histiolgically and half by SEM. The instrument tested was an Er:YAG laser with microprobes 200-400 micro in diameter and 20 mm in length, coupled onto special handpieces, attached to the delivery fiber of an OPUS 20 Er:YAG laser. The Er:YAG laser was applied with the following parameters: wavelength 2.94 microm; pulse duration 400 msec; repetition rate 10 Hz; energy per pulse 140 mJ for the 400 micro microprobe and 90 mJ for the 200-micro microprobe. RESULTS: For the control group, histologically, large amounts of residual pulp tissue were found in the root canal cavity, and open tubules were seen in all the specimens; SEM examination showed very uniform root canal, from apical to cervical portion, high number of open tubules, and different levels of canal debridment. For the study group, histologically, no residual pulp tissue was found in the root canal cavity and open tubules were seen in all the specimens; SEM examination showed the root canal free of debris, removed smear layer, open dentinal tubules, and different levels of enlargement. CONCLUSION: Our results show that the Er:YAG laser special microprobes are effective in shaping, cleaning, and enlarging straight root canals faster and more efficiently then traditional methods.     

In vitro study of the effects of Nd:YAG laser irradiation on the apical sealing of endodontic fillings performed with and without dentin plugs

OBJECTIVE: The aim of this study was to evaluate the effects of Nd:YAG laser irradiation on the apical sealing of root canal fillings with or without a dentin plug. BACKGROUND DATA: Previous studies have shown that Nd:YAG laser irradiation of root canal wall dentin promotes its melting, recrystallization, and therefore a less permeable surface. MATERIALS AND METHODS: Thirty extracted and endodontically treated teeth were divided into three groups. Eight specimens of each group were evaluated by means of quantitative analysis, measuring the marginal apical dye leakage. The remaining two specimens were evaluated by means of qualitative analysis, using the scanning electron microscopy (SEM). For the quantitative analysis, the samples of group I were obturated. In group II, the apical third of the samples were irradiated by the Nd:YAG laser at four exposures of 100 mJ/pulse, 1 W, 10 Hz, 3 sec, and obturated. In group III, an apical dentin plug was condensed and lased using the same parameters of group II, and the root canals were obturated. The samples evaluated by SEM were prepared as those analyzed quantitatively; however, their root canals were not filled. RESULTS: There were statistically significant differences among the groups regarding dye leakage. Group II showed the minor leakage average, followed, in order, by groups I and III. SEM analysis revealed open dentinal tubules in group I; melting and recrystallizing of the apical root dentin in group II; and melting and recrystallizing of a portion of the dentin plug in group III. CONCLUSION: The Nd:YAG laser irradiation of the root canal apical third without the presence of dentin plug significantly improved the quality of the apical sealing under the experimental conditions tested.     

Ablation depths and morphological changes in human enamel and dentin after Er:YAG laser irradiation with or without water mist

OBJECTIVE: This investigation was performed quantitatively to determine the ranges of ablation and to evaluate the morphological changes in human enamel and dentin irradiated by Er:YAG laser with or without water mist. SUMMARY BACKGROUND DATA: Recently, several infrared lasers have been introduced in the dental clinic to remove carious dental hard tissues in anticipation of replacing the high-speed dental drill. Among them, the Er:YAG laser has shown the most promise for hard tissue ablation. METHODS: An Er:YAG laser was used to ablate human dental hard tissues using a pulse energy that ranged from 100 to 400 mJ at a frequency of 2 Hz for 5 seconds. Ablation rates with or without water mist at different pulse energies were measured, and the morphological changes on enamel and dentin were also investigated by stereomicroscopy and scanning electron microscopy (SEM). RESULTS: The relationship between ablation depths and energies was almost linear at both enamel and dentin samples. The irradiation with water mist reduced the ablation depths, but only minimally, when compared to those irradiated without water mist. Morphological findings by SEM indicated that Er:YAG laser irradiation with water mist could produce the cavities without signs of thermal damage to the surrounding enamel and dentin. CONCLUSIONS: The results of this study suggest that addition of a fine water mist directed at the ablation sites does not greatly decrease the ablation, and does not cause any carbonization and melting in the surrounding dental hard tissues.     

Effects of water flow on dental hard tissue ablation using Er:YAG laser

OBJECTIVE: The aim of this study was to investigate the effect of water on dental hard tissue ablation using Er:YAG laser as it relates to energy and pulse repetition rate, and determine the water flow rate that produces the most effective ablation at a given irradiation condition. BACKGROUND DATA: Er:YAG laser application leads to volumetric expansion and micro-explosions that result in hard tissue ablation. Ablation efficiency is improved when combined with fine water spray. MATERIALS AND METHODS: Extracted, healthy human molars were sectioned into two pieces and categorized into small groups related to water flow rate (1.69, 6.75, and 13.5 mL/min), pulse energy (250 and 400 mJ), and pulse repetition rate (5, 10, and 20 Hz). Within the combination of irradiation parameters, a laser beam was applied over enamel and dentin surfaces of the specimens, and the ablation amount was determined by differences in weight before and after irradiation. RESULTS: At a pulse energy of 250 mJ, the most effective ablation resulted from a water flow rate of 1.69 mL/min in both enamel and dentin. With 400 mJ/pulse, dentin removal was most effective at the water flow rate of 1.69 mL/min, whereas the efficiency of enamel ablation was the highest at 6.75 mL/min. Dental hard tissue ablated better as energy and pulse repetition rate increased. CONCLUSION: Effective ablation of dental hard tissue using Er:YAG laser requires that the appropriate water flow rate correspond properly to irradiation conditions. The results of this study suggest the following parameters; a water flow rate of 1.69 mL/min for enamel and dentin ablation at a pulse energy of 250 mJ and for dentin ablation at 400 mJ/pulse, and a water flow rate of 6.75 mL/min for enamel ablation at a pulse energy of 400 mJ, regardless of pulse repetition rate of 5, 10, and 20 Hz.     

Comparative study of dentine permeability after apicectomy and surface treatment with 9.6 microm TEA CO2 and Er:YAG laser irradiation

Failure of apicectomies is generally attributed to dentine surface permeability as well as to the lack of an adequate marginal sealing of the retrofilling material, which allows the percolation of microorganisms and their products from the root canal system to the periodontal region, thus compromising periapical healing. The purpose of this study was to evaluate dentine and the marginal permeability after apicectomy and surface treatment with 9.6 micro m TEA CO(2) or Er:YAG 2.94 micro m laser irradiation. Sixty-five single rooted human endodontically treated teeth were divided into five experimental groups: group I (control), apicectomy with high speed bur; group II, similar procedure to that of group I, followed by dentinal surface treatment with 9.6 micro m CO(2) laser; group III, similar procedure to group I followed by dentinal surface treatment with Er:YAG laser 2.94 micro m; group IV, apicectomy and surface treatment with CO(2) 9.6 micro m laser; and group V, apicectomy and surface treatment with Er:YAG laser 2.94 micro m. The analysis of methylene blue dye infiltration through the dentinal surface and the retrofilling material demonstrated that the samples from the groups that were irradiated with the lasers showed significantly lower infiltration indexes than the ones from the control group. These results were compatible with the structural morphological changes evidenced through SEM analysis. Samples from groups II and IV (9.6 micro m CO(2)) showed clean smooth surfaces, fusion, and recrystallized dentine distributed homogeneously throughout the irradiated area sealing the dentinal tubules. Samples from groups III and V (Er:YAG 2.94 micro m) also presented clean surfaces, without smear layer, but roughly compatible to the ablationed dentine and without evidence of dentinal tubules. Through the conditions of this study, the Er:YAG 2.94 micro m and the 9.6 micro m CO(2) laser used for root canal resection and dentine surface treatment showed a reduction of permeability to methylene blue dye.     

SEM analysis of dentin treated with the Er:YAG laser: a pilot study of the consequences resulting from laser use on adhesion mechanisms

OBJECTIVES: The purpose of this study was to compare the morphological characteristics of lased dentinal surfaces obtained by chemical etching, which was applied either before or after laser treatment. The adhesive interface after the application of an adhesive-composite system on the above mentioned dentinal surfaces was also evaluated. MATERIALS AND METHODS: Eighteen caries-free permanent molars were transversally cut to obtain the dentinal surfaces. Ten of these surfaces were divided into three main groups according to their preparation modality: laser only, laser followed by chemical etching, and chemical etching before laser. The Er:YAG laser was used with two different energy outputs: 200 and 400 mJ at 1 Hz. The eight remaining surfaces were divided into two groups and followed the same preparation as the first three groups. The only difference was a change in frequency: 4 Hz was used for treating these surfaces. An adhesive system (Scotchbond 1, 3M), a thin layer of flowable composite (Tetric Flow, Vivadent), and a regular composite (Z250, 3M) were applied to each dentinal surface and then separately light cured. In order to evaluate the dentine-restoration interface, the samples were cut longitudinally and prepared for SEM observation. RESULTS: The dentinal surfaces that were etched by the laser treatment did not demonstrate the characteristics necessary for guaranteeing a good bond with the adhesive materials. A closer observation of the dentine-restoration interface revealed some micro-fractures located just below the lased dentinal surface. CONCLUSION: The decision to use the Er:YAG laser as an alternative to conventional techniques of acid etching is currently arguable. Given that the available adhesive systems require acid conditioning, it would not be advisable to skip this operative step.     

Caries-preventive effect of Er:YAG laser irradiation with or without water mist.

OBJECTIVE: This investigation was performed to evaluate the effect of Er:YAG laser irradiation on the acquired acid resistance of sound dental hard tissues to artificial caries formation by spectrophotometry, and the ultrastructure of lased areas was investigated by scanning electron microscopy (SEM) in vitro. BACKGROUND DATA: Although an Er:YAG laser has shown the most promise for hard tissue ablation, there have not been any dissolution studies to determine if this laser is suitable for caries preventive treatments. METHODS: An Er:YAG laser was used to irradiate the enamel and dentin samples from 20 extracted human molars at 400 mJ pulse energy with or without water mist. Samples were subjected to 2 microL of 0.1 M lactic acid solution (pH 4.8) for 24 hours at 36 degrees C. The parts per million (ppm) of calcium ion (Ca2+) dissolved in each solution was determined by atomic absorption spectrophotometry and the morphological changes were investigated by SEM. RESULTS: The lowest mean Ca2+ ppm was recorded in the samples irradiated without water mist, in those by irradiated with water mist, and in the unlased samples. SEM observation showed that the lased areas had melted and seemed to be thermally degenerated when irradiated without water mist. After acid demineralization, the thermally degenerated enamel or dentin surfaces were almost unchanged. CONCLUSIONS: The results of this study suggest that Er:YAG laser irradition with and without water mist appears to be more effective for caries prevention.     

Er:YAG laser effects on enamel occlusal fissures: an in vitro study

This study evaluated by scanning electron microscopy (SEM) the morphological changes in occlusal fissure enamel, of permanent models, irradiated by Er:YAG laser using contact and noncontact fiberoptics in vitro. Previous studies have demonstrated the efficacy of Er:YAG laser for dental hard tissue removal and cavity preparation. The treatment of occlusal fissures in noncarious permanent human molars (n = 9) was carried out with Er:YAG laser (KEY Laser II) using handpiece no. 2051, noncontact, focused (12 mm), water spray-cooled, pulse energy 200 mJ, and frequency 2 Hz (group 1), and handpiece no. 2055 with a quartz fiberoptic 50/10, in contact, air cooled, pulse energy setting of 350 mJ and frequency 2 Hz (group 2) and 400 mJ/2 Hz (group 3). The specimens were sectioned, dehydrated in a graded series of aqueous ethanol, dried, and sputtering with gold. Morphological change analysis on occlusal fissures was performed by SEM. Group 1 showed removal of fissure debris and predominantly enamel etching-like patterns, and groups 2 and 3 showed irregular edges, melting, and recrystallization of fissure enamel, with a lava-like structure and bubble-like voids. The results of this in vitro study suggest that the irradiation of fissures by Er:YAG laser using a fiberoptics (contact and air cooled) produced melting and recrystallization of fissures enamel. Further studies are required with different energy parameters and water cooling to evaluate the thermal effects on teeth.     

扫描电镜观察不同方法去腐后牙本质玷污层的形态变化

背景：目前去除牙本质玷污层的方法主要有机械去腐法、化学机械去腐法、激光去腐法、空气喷砂去腐法、臭氧去腐法等,但对各去腐方法去腐后效果的研究有限,目前还没有对Er：YAG激光、Carisolv化学机械、传统高速涡轮牙法3种方法去腐后玷污层的效果比较的研究。 目的：应用电子扫描电镜观察 Er：YAG激光、Carisolv化学机械、传统高速涡轮牙钻3种方法去腐后,观察人牙本质玷污层的形态变化。 方法：选择新近拔除的中度龋坏的30颗人前磨牙或磨牙,分为3组,每组10颗,分别用Er：YAG激光、Carisolv化学机械、传统高速涡轮牙钻去腐后,用肉眼观察洞底表面,然后用电子扫描电镜放大1000,2000倍进行观察。 结果与结论：3组去腐后用探针检查窝洞,质地均坚硬,Er：YAG 激光组牙本质表面凸凹不平,似山峰状;Carisolv 化学机械组牙本质表面光泽较暗,底面较平;传统高速涡轮牙钻组牙本质表面平整,光亮,并有明显的切割痕迹。Er：YAG激光组表面无玷污层,牙本质小管清晰可见;Carisolv化学机械组可见大部分牙本质小管,表面覆盖较少的玷污层;传统高速涡轮牙钻组表面覆盖厚厚的一层玷污层,未见牙本质小管,3组间牙本质玷污层清洁度比较差异均有显著性意义（P〈0.05）。表明Er：YAG激光能有效去除玷污层,且较Carisolv化学机械、传统高速涡轮牙钻法效果好,传统高速涡轮牙钻法效果最差。     

Er:YAG and alexandrite laser radiation propagation in root canal and its effect on bacteria

OBJECTIVE: The objective of this study was to compare the bactericidal effect of the Er:YAG (wavelength 2.94 microm) and the Alexandrite (wavelength 0.75 microm) laser radiation. The spreading laser energy in the surrounding hard dental tissues round the root canal was evaluated and the bactericidal effect of both these different laser wavelengths was analyzed. SUMMARY BACKGROUND DATA: The use of a laser to clean and shape the root canal space is the latest method used for cleaning of root canals. The interest in laser endodontics was concentrated on the possibility to extirpate the contents of the root canal, to sterilize and to "melt" the walls of the root canals. The previous reports were performed with CO2, excimer, argon, Nd:YAG, Ho:YAG, and Er:YAG lasers. METHODS: Er:YAG laser system (2.94 microm, energy 100 mJ or 300 mJ, repetition rate 1 Hz, 30 pulses) and alexandrite laser system (0.75 microm, energy 250 mJ, repetition rate 1 Hz, 30 pulses) were prepared and three experimental arrangements were used during the measurements. First the energy transport through the tooth tissue was observed (frontal and side experimental setups) and then, the bactericidal effect was evaluated. RESULTS: It was demonstrated that due to the absorption in the hydroxyapatite and water content in the dentin, the Er:YAG laser radiation is fully absorbed in the root canal wall. This direct influence of the radiation could be expected only close to the sapphire tip. It was found that the tissue, which was not directly affected by the laser radiation, cannot be disinfected by the subablative effect of Er:YAG laser radiation. In the second part of the experiment the real bactericidal effect of Er:YAG ablative energy (300 mJ) could be observed. It was also shown that the alexandrite laser radiation with a wavelength of 0.75 microm spreads through the canal system space and leaks into the surrounding tooth tissues. Both lasers have bactericidal effect. CONCLUSIONS: The pulsed Er:YAG and alexandrite lasers can be efficiently used for killing dental bacteria but the spreading of their radiation in the tooth tissues are different.     

Stimulatory Effects of CO(2) Laser, Er:YAG Laser and Ga-Al-As Laser on Exposed Dentinal Tubule Orifices

We investigated the effects of lasers irradiation on the exposed dentinal tubule. Human tooth specimens with exposed dentinal tubule orifices were used. Three types of lasers (CO(2) laser, Er:YAG laser and Ga-Al-As laser) were employed. The parameters were 1.0 W in continuous-wave mode with an irradiation time of 30 s for the CO(2) laser, 30 mJ in continuous-wave mode with an irradiation time of 60 s for the Er:YAG laser, and 1.0 W in continuous-wave mode with an irradiation time of 60 s for the Ga-Al-As laser. A non-irradiated group was used as a control. After laser irradiation, the dentinal surface of each sample was observed using SEM. Afterwards, all samples were immersed in methylene blue dye solution in order to evaluate the penetration of the dye solution and observe the change in dentinal permeability after laser irradiation. SEM observation showed that the control group had numerous exposed dentinal tubule orifices, whereas these orifices were closed in the laser-irradiated groups. There was consistent dye penetration into the pulp chamber in the control group, whereas no dye penetration was evident in the laser-irradiated groups. Therefore, laser appears to be a promising treatment for reducing permeation through exposed dentinal tubules.     

Endodontic treatment with application of Er:YAG laser waveguide radiation disinfection

OBJECTIVE: The objective of this study is to examine the ability of Er:YAG laser radiation. Using a movable waveguide helps to obtain an antibacterial effect, not only in root canal walls but also in the surrounding tissues. BACKGROUND DATA: Conventional endodontic treatment is not fully effective due to microbial colonization of root canal walls dentin in premolars and molars. Various laser systems seem to be effective to kill the remaining microbial content in the root canal. The problem is in the flexibility of laser system tips. MATERIALS AND METHODS: The Er:YAG laser system was designed with a fluorocarbon polymer-coated silver hollow glass waveguide. Root canal systems of 44 premolars and molars were treated endodontically, using a step-back technique; 10 teeth were then treated with calcium hydroxide paste, and 22 teeth were irradiated by a movable waveguide. Before and after treatment, the colony-forming units were counted to determine 21 various microorganisms. RESULTS: Classical enlargement and shaping of the root canal is effective in 60%. Application of calcium hydroxide prepares sterile root canal in 80%. Er:YAG laser irradiation via movable waveguide (energy of 100 mJ, 30 pulses, repetition rate 4 Hz) can ensure residual disinfection of the root canal. CONCLUSION: Application of Er:YAG laser radiation through a flexible waveguide helps to attain antibacterial effect, not only in the root canal walls, but also in the surrounding tissues. Therapeutic doses of laser radiation guarantee one-step disinfection, including of anaerobic microorganisms.     

Morphological and atomic analytical studies on enamel and dentin irradiated by an erbium, chromium:YSGG laser.

OBJECTIVE: The purposes of this study were to investigate the morphological and atomic analytical changes and to evaluate the cutting effect on dental hard tissues of this laser in vitro. BACKGROUND DATA: There have been few reports on morphological and atomic analytical study of dental hard tissues after erbium,chromium:yttrium,scandium,gallium,garnet (Er,Cr:YSGG) laser irradiation. METHODS: Eighteen extracted human molars were sectioned into 3-mm-thick slices, which were irradiated with water-air spray by an Er,Cr:YSGG laser at 6.0 W and 20 Hz for 5 sec for enamel and 5.0 W and 20 Hz for 5 sec for dentin. The samples were then morphologically observed and examined atomic-analytically. RESULTS: Regular holes having sharp edges and smooth walls, but no melting or carbonization, were observed in both samples. An atomic analytical examination showed that the calcium ratio to phosphorus showed no significant changes between the lased areas and unlased areas (p > 0.01). CONCLUSION: These results showed that the Er,Cr:YSGG laser has a good cutting effect on dental hard tissues and offers advantages of no burning or melting after laser irradiation.     

A study on acquired acid resistance of enamel and dentin irradiated by Er,Cr:YSGG laser

OBJECTIVE: This investigation was performed to evaluate the acid resistance of lased enamel and dentin by Er,Cr:YSGG laser to artificial caries-like lesions by spectrophotometry, and the ultrastructure of lased areas was investigated by scanning electron microscopy (SEM) in vitro. BACKGROUND DATA: In recent years, many studies have been performed to evaluate the effects of Er,Cr:YSGG laser on dental hard tissues. However, there have been only a few studies to determine if this laser is suitable for caries preventive treatments. METHODS: An Er,Cr:YSGG laser was used to irradiate the enamel or dentin samples from 30 extracted human molars at 6 W (67.9 J/cm2) or 5 W (56.6 J/cm2) pulse energy, respectively, with or without water mist. Samples were subjected to 2 microl of 0.1 M lactic acid solution (pH 4.8) for 24 h at 36 degrees C. The parts per million (ppm) of calcium ion (Ca2+) dissolved in each solution was determined by atomic absorption spectrophotometery, and the morphological changes were investigated by SEM. RESULTS: The lowest mean Ca2+ ppm was recorded in the lased samples. SEM observation showed that the lased areas were melted and seemed to be thermally degenerated. After acid demineralization, the thermally degenerated enamel or dentin surfaces were almost unchanged. CONCLUSIONS: The results of this study suggested that Er,Cr:YSGG laser irradiation with and without water mist appears to be effective for increasing acid resistance.