Influence of dentin thickness on intrapulpal temperature under simulated pulpal pressure during Nd:YAG laser irradiation

The aim of this study was to evaluate the effects of dentin thickness and pulpal pressure simulation (PPS) on the variation of intrapulpal temperature (?T) when submitted to an adhesive technique using laser irradiation. Sixty sound human molars were sectioned and randomly divided into two groups (n?=?30): group 1—1 mm of dentin thickness; group 2—2 mm of dentin thickness. Each group was divided into two subgroups (n?=?15): subgroup A—absence of PPS; subgroup P—presence of PPS (15 cm H₂O), sequentially treated with the following: 37 % phosphoric acid, adhesive system (Adper Single Bond), irradiation with Nd:YAG laser (1064 nm, 10 Hz, 60 s) using 60, 80, and 100 mJ/pulse energy parameters and light-curing (10 s). The ?T was evaluated during the laser irradiation with a digital thermometer. Data were analyzed by three-way ANOVA and Tukey tests (p?<?0.05). Three-way ANOVA revealed no significant differences for dentin thickness (p?=?0.6512) on ?T. PPS significantly reduced ?T (p?=?0.0001). The laser energy parameters (p?=?0.0027) indicated that 100 mJ presented with significantly greater ?T when compared to the groups irradiated with 80 and 60 mJ. Dentin thickness did not affect ?T. The presence of PPS reduced the mean temperature values. The Nd:YAG laser energy parameters had a negative influence on the variation of temperature in the absence of PPS. In the presence of PPS, there was no risk to the pulp, since this study obtained temperature increases below 5.5 °C for all energy parameters, showing the technical viability for in vivo conditions.     

Effects of laser and acid etching and air abrasion on mineral content of dentin

The aim of this study was to evaluate the mineral content of dentin prepared using an Er,Cr:YSGG laser at four different power settings, acid etching, and air abrasion. The study teeth comprised 35 molars which were randomly divided into seven equal groups. The occlusal third of the crowns were cut with a slow-speed diamond saw. The groups were as follows: group A, control group; group B, dentin etched with 35% buffered phosphoric acid for 30 s; group C, dentin abraded at 60 psi with 50-μm aluminium oxide for 1 s; groups D–G, dentin irradiated with the Er,Cr:YSGG laser at 1.50 W (group D), 2.25 W (group E), 3.00 W (group F), and 3.50 W (group G). The levels of Mg, P, Ca, K and Na in each dentin slab were measured by inductively coupled plasma-atomic emission spectrometry (ICP-AES). Data were analysed by one way analysis of variance and Tukey HSD tests. There were no significant differences between the groups in the levels of Ca, P and Na, and the Ca/P ratio (p>0.05); however, there were significant differences in the levels of K (p<0.001) and Mg (p=0.13). In addition, the levels of Mg in the air abrasion group were higher than in the other groups (p<0.01). Etching with the Er,Cr:YSGG laser system, air abrasion and acid etching did not affect the levels of Ca, P and Na, or the Ca/P ratio, in the dentin surface.     

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.     

Influence of external cooling on the femtosecond laser ablation of dentin

In the present work, the influence of external cooling on the temperature rise in the tooth pulpal chamber during femtosecond laser ablation was investigated. The influence of the cooling method on the morphology and constitution of the laser-treated surfaces was studied as well. The ablation experiments were performed on dentin specimens using an Yb:KYW chirped-pulse-regenerative amplification laser system (560 fs, 1030 nm). Cavities were created by scanning the specimens at a velocity of 5 mm/s while pulsing the stationary laser beam at 1 kHz and with fluences in the range of 2–14 J/cm². The experiments were performed in air and with surface cooling by a lateral air jet and by a combination of an air jet and water irrigation. The temperature in the pulpal chamber of the tooth was measured during the laser experiments. The ablation surfaces were characterized by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The temperature rise reached 17.5 °C for the treatments performed with 14 J/cm² and without cooling, which was reduced to 10.8 ± 1.0 and 6.6 ± 2.3 °C with forced air cooling and water cooling, respectively, without significant reduction of the ablation rate. The ablation surfaces were covered by ablation debris and resolidified droplets containing mainly amorphous calcium phosphate, but the amount of redeposited debris was much lower for the water-cooled specimens. The redeposited debris could be removed by ultrasonication, revealing that the structure and constitution of the tissue remained essentially unaltered. The present results show that water cooling is mandatory for the femtosecond laser treatment of dentin, in particular, when high fluences and high pulse repetition rates are used to achieve high material removal rates.     

Effects of different application durations of ER:YAG laser on intrapulpal temperature change during debonding

This study was done to determine the amount of lasing time required to remove ceramic brackets safely without causing intrapulpal damage by using Er:YAG laser with the scanning method. Part 1: 80 bovine mandibular incisors with ceramic brackets were randomly assigned into four groups of 20 as one control and three study groups. In the study groups, brackets were debonded after lasing for 3, 6, and 9 s, whereas debonding was performed without lasing in the control group. Shear bond strengths and ARI scores were also measured. Part 2: 30 human premolars with ceramic brackets were randomly divided into three groups of ten, as 3, 6, and 9 s of lasing durations. Intrapulpal temperature was measured at the same lasing times by a thermocouple. Statistically significant lower shear bond strengths were found in study groups compared to the control. A negative correlation was seen between the bond strengths and ARI scores in such a way that, as the shear bond strengths decreased, the ARI scores increased. Temperature increases for all the study groups were measured below the 5.5°C benchmark. All lasing times were effective for debonding without causing enamel tear outs or bracket failures. The temperature proportionally increased with the extension of the lasing duration. Six-second lasing by the scanning method using Er:YAG laser was found to be the most effective and safest way of removing the ceramic brackets without causing damage to the enamel and pulpal tissues.     

Evaluation of different temperatures in cold air cooling with pulsed-dye laser treatment of facial telangiectasia

BACKGROUND AND OBJECTIVES: Cold air cooling is widely used in dermatological laser therapy. We investigated the influence of cold air cooling at different skin temperatures on therapeutic outcome and side effects of pulsed dye laser treatment of facial telangiectasia. STUDY DESIGN/MATERIALS AND METHODS: From September 2002 to February 2003, 17 patients with previously untreated facial telangiectasia underwent a single treatment session with flash-lamp pulsed dye laser (3.5 J/cm(2), 585 nm, 0.45 milliseconds pulse length, 10 mm beam diameter, Cynosure V). The treatment area was divided into three sub-areas: no cooling, cold air cooling to 20 degrees C and to 17 degrees C skin temperature. The skin temperature was monitored by a prototype infrared sensor system which controlled the temperature of the cold air stream (Cryo5). In a prospective study, we collected data on purpura, pain, clearance, and patient satisfaction on numerical analog scales (NAS) from 0 (meaning "no") to 3 (meaning "high"). RESULTS: Without cooling, purpura (2.53), pain (2.41), and clearance (2.35) were rated medium to high. Cooling to 20 degrees C reduced purpura (1.12) and pain (1.06), whereas the clearance (2.12) was only slightly affected. Cooling to 17 degrees C reduced purpura (0.88) and pain (0.76) even more, the clearance (2.06) was lowered marginally. Most patients preferred cooling to 20 degrees C skin temperature. CONCLUSION: In dermatological laser therapy of facial telangiectasia, the use of cold air cooling can significantly reduce side effects and increase patient satisfaction while only slightly affecting clearance. Cooling to 20 degrees C skin temperature proved to be a well-balanced middle course. For the practical use of cold air cooling, we thus recommend cooling to a level which the patient can tolerate without problems and to try to increase the energy densities.     

Effects of ArF: Excimer laser irradiation on human enamel and dentin

Round enamel and dentin surfaces of sound and carious extracted human teeth were irradiated by an ArF:excimer laser for up to 180 sec. Thermographic measurements indicated that the temperature rise due to heat accumulation caused by laser irradiation on these enamel and dentin surfaces was up to 19°C (10 HZ with 540 J/cm²), and the temperature returned to the preirradiation value within 10 sec after the irradiation was stopped. Under light microscopy, no carbonization was evident on these surfaces, and a simple recess was formed by abrasion or vaporization in the irradiated regions. In the secondary SEM, uniformly distributed fine pores and prism structures appeared slightly on the enamel surfaces. Between the peritubular and the intertubular dentin, there appeared a distinct difference in the dissolved area. The laser almost completely removed carious regions of the enamel and the dentin, and penetration extended beyond the carious regions. In the backscattered electron SEM, highly mineralized layers were observed on the enamel and dentin surfaces dissolved by the laser. © 1993 Wiley-Liss, Inc.     

Effects of different treatments on chemical and morphological features of eroded dentin

To evaluate the treatment of eroded dentin (Sensodyne Repair & Protect?, Er:YAG laser and combinations). The occlusal surfaces of 25 third molars were sectioned 1.5 mm in thickness. After an erosion cycle (5 min in demineralizing solution + 3 h in remineralizing solution; six cycles a day for 8 days), the samples were divided into five groups (n?=?5): (E) erosion ? control; (ES) erosion + Sensodyne Repair & Protect (NovaMin); (EL) erosion + Er:YAG laser (40 mJ, 10 Hz, 0.4 W, 50 μs, 3.1 J/cm², 63 W/cm²); (ELS) erosion + Er:YAG laser + Sensodyne; and (ESL) erosion + Sensodyne + Er:YAG laser. Following storage in ultrapure water (37 °C/14 days), the Ca/P ratio was evaluated by EDXRF and the morphology surfaces examined in SEM. The percentage of exposed dentin tubules was calculated. One-way analysis of variance and Tukey’s test at 5% were used to treat the data. The Ca/P ratio was higher in E and ES groups. More exposed dentin tubules were found in E group and less exposed tubules were found in the ES group (p?<?0.0001). When the toothpaste and laser were combined, the number of occluded dentin tubules was higher when laser was performed first (ELS). A positive effect was found when the laser and toothpaste were combined.     

Influence of pulse repetition rate on temperature rise and working time during composite filling removal with the Er:YAG laser

OBJECTIVE: The purpose of this study was to assess the efficacy of Er:YAG laser energy for composite resin removal and the influence of pulse repetition rate on the thermal alterations occurring during laser ablation. MATERIALS AND METHODS: Composite resin filling was placed in cavities (1.0 mm deep) prepared in bovine teeth and the specimens were randomly assigned to five groups according to the technique used for composite filling removal. In group I (controls), the restorations were removed using a high-speed diamond bur. In the other groups, the composite fillings were removed using an Er:YAG laser with different pulse repetition rates: group 2-2 Hz; group 3-4 Hz; group 4-6 Hz; and group 5-10 Hz. The time required for complete removal of the restorative material and the temperature changes were recorded. RESULTS: Temperature rise during composite resin removal with the Er:YAG laser occurred in the substrate underneath the restoration and was directly proportional to the increase in pulse repetition rate. None of the groups had a temperature increase during composite filling removal of more than 5.6 degrees C, which is considered the critical point above which irreversible thermal damage to the pulp may result. Regarding the time for composite filling removal, all the laser-ablated groups (except for group 5 [10 Hz]) required more time than the control group for complete elimination of the material from the cavity walls. CONCLUSION: Under the tested conditions, Er:YAG laser irradiation was efficient for composite resin ablation and did not cause a temperature increase above the limit considered safe for the pulp. Among the tested pulse repetition rates, 6 Hz produced minimal temperature change compared to the control group (high-speed bur), and allowed composite filling removal within a time period that is acceptable for clinical conditions.     

不同水温行物理降温的效果比较

目的 寻找较理想的物理降温方法.方法 将1 000例高热患儿随机分为A、B、C三组.A组(335例)采用比测试体温高1℃的水泡浴;B组(334例)采用传统温水擦浴;C组(331例)采用比测试体温高1°C的水擦浴.结果 三组降温速度比较,差异无统计学意义(P＞0.05);三组降温持续时间、降温效果、患儿反应程度比较,差异有统计学意义(均P＜0.01),A组效果最好,C组次之,B组最差.结论 高热患儿物理降温宜选用高于体温的水行温水泡浴,患儿不良反应小,降温效果明显且持续时间长.     

Bactericidal effect of different laser systems in the deep layers of dentin

BACKGROUND AND OBJECTIVES: In recent years, various laser systems have gained importance in the field of laser-assisted endodontics, namely the Nd:YAG, the diode, the Er:YAG, and the Er,Cr:YSGG laser. Individual studies have been carried out so far, focusing on the respective wavelength, its specific bactericidal capabilities, and potential usefulness is root-canal disinfection. The present in vitro investigation however, was performed to compare the microbicidal effect of these laser systems under standardized conditions and to draw a conclusion upon their relative effectiveness in the deep layers of dentin. STUDY DESIGN/MATERIALS AND METHODS: In total, 360 slices of root dentin with a thickness of 1 mm were obtained by longitudinal cuts of freshly extracted human premolars. The samples were steam sterilized and subsequently inoculated with a suspension of either Escherichia coli or Enterococcus faecalis. After the incubation, the samples were randomly assigned to the four different laser systems tested. Each laser group consisted of two different operational settings and a control. The dentinal samples underwent "indirect" laser irradiation through the dentin from the bacteria-free side and were then subjected to a classical quantitative microbiologic evaluation. To assess the temperature increase during the irradiation procedure, additional measurements were carried out using a thermocouple. RESULTS: Microbiology indicated that all laser systems were capable of significant reductions in both test strains. At an effective output power of 1 W, E. coli was reduced by at least three log steps in most of the samples by the tested wavelengths, with the best results for the Er:YAG laser showing complete eradication of E. coli in 75% of the samples. E. faecalis, a stubborn invader of the root canal, showed minor changes in bacterial count at 1 W. Using the higher setting of 1.5 W, significant reductions of E. coli were again observed with all laser systems, where only the diode and the Er:YAG laser were capable of complete eradication of E. faecalis to a significant extent. There was no significant relation between the temperature increase and the bactericidal effect. CONCLUSIONS: The present study demonstrates that all the wavelengths investigated are suitable for the disinfection of even the deeper layers of dentin and may prove to constitute valuable tools in state-of-the-art endodontics.     

Effects of different lasers on organic/inorganic ratio of radicular dentin

The aim of this study was to evaluate the chemical stability of endodontic-treated root dentin after different laser irradiations through Raman spectroscopy. Fifty maxillary canines were selected and prepared with K3 system. Roots were randomly distributed into five groups (n?=?10) according to the surface treatment: GI (water), GII (NaOCl?+?EDTA), GIII (NaOCl?+?EDTA?+?980 nm Diode laser), GIV (NaOCl?+?EDTA+ 1064 nm Nd: YAG laser) and GV (NaOCl?+?EDTA+ 2780 nm Er,Cr: YSGG laser). Lasers were applied for 20 s. Samples were bisected, and the organic and inorganic content of dentin was analyzed by Raman spectroscopy. Data were submitted to ANOVA and Tukey tests (p?<?0.05). None of the surface treatments alter the inorganic content (cts) (p?=?0.183). Roots irradiated with Er,Cr: YSGG laser had a reduced collagen content (GV-290.7?±?41.7) compared with the water-treated roots (GI-328.3?±?63.5) and those treated with NaOCl?+?EDTA (GII-333.9?±?55.8). Roots irradiated with Er,Cr: YSGG laser also showed a higher inorganic/organic ratio (GV-9.5?±?1.1) than roots treated with water (GI-7.7?±?1.5), NaOCl?+?EDTA (GII-8.0?±?1.4) and diode laser (GIII-8.2?±?1.6). Both organic and inorganic contents increased from cervical to apical thirds in all groups. None of the surface treatments were able to promote changes in the inorganic content of the root dentin; treatment with NaOCl?+?EDTA combined with Er,Cr: YSGG altered collagen.     

脂肪抽吸术中肿胀麻醉液留置时间和温度对出血量的影响

目的 观察脂肪抽吸术中肿胀麻醉液在皮下留置时间及温度对出血量的影响.方法 对20例美容就医患者进行脂肪抽吸术,其中10例行双上臂脂肪抽吸,另10例行双大腿脂肪抽吸,分别计算肿胀麻醉液于皮下留置不同时间和不同温度时的手术出血量.结果 20例术后出血量在21.42～77.26 ml,平均为(50.27±18.56) ml.其中肿胀麻醉液在右上臂皮下留置0.5h后进行脂肪抽吸,平均出血量为(19.89±7.52) ml,肿胀麻醉液注射完毕左上臂即行脂肪抽吸,平均出血量为(26.25±12.07) ml;右下肢使用加热至37℃的肿胀麻醉液,平均出血量为(28.60±6.07) ml,左下肢使用未加热的肿胀麻醉液(23℃),平均出血量为(29.93±9.06) ml.结论 肿胀麻醉液注射完成后留置0.5h可有效降低手术出血量.使用加热至37℃的肿胀麻醉液不增加术中出血量.     

The effect of selective brain cooling on intracerebral temperature during craniotomy

In this study we investigated the effect of topical application of cool irrigation fluid on brain tissue temperature during craniotomy. Eight patients were given a standard general anaesthetic for craniotomy. Distal oesophageal and nasopharyngeal temperatures were measured continuously and systemic normothermia was maintained. A sterile needle temperature probe was inserted 18 mm into the cerebrum to measure brain temperature. Brain temperatures were recorded for five minutes while the brain was irrigated with 1000 ml of normal saline at a temperature of 30 degrees C. Measurement continued until the brain temperature returned to baseline. The mean maximum decrease in cerebralparenchymal temperaturefollowing irrigation was 1.6 +/- 0.5 degrees C (P<0.01). The average time to return to baseline temperature after cessation of irrigation was 5.3 +/- 1.5 minutes. Cooling the brain has a marked protective effect after brain injury, but systemic hypothermia can produce significant harmful effects. This study demonstrates that the use of cool irrigation fluid during neurosurgery is a simple and effective method of cooling the brain whilst minimizing the use of systemic hypothermia.     

Bactericidal effects of diode laser on Streptococcus mutans after irradiation through different thickness of dentin

BACKGROUND AND OBJECTIVES: A reliable method to eradicate the bacteria of residual carious dentin has not yet been developed. The aim of this study was to evaluate the antibacterial effect of a diode laser on Streptococcus mutans through different thickness (500, 1,000, and 2,000 microm) of human dentin. The thermal effect of laser irradiation was also investigated. STUDY DESIGN/MATERIALS AND METHODS: Dentin specimens were inoculated with 2 microl of S. mutans on one side and irradiated by a diode laser on the other side with a power output ranging from 0.5 to 7 W. The laser tip was swept with the whole irradiation area of 7 mm x 3 mm at a speed of about 10 mm/second with a total irradiation time of 30 seconds. Cooling with distilled water (30 ml/minute) was applied simultaneously during laser irradiation. After laser irradiation, the bacteria was removed from the dentin surfaces and cultured for 48 hours at 37 degrees C anaerobically to assess the colony forming units (CFU) per ml. The morphology of the lased bacteria and the temperature rise during laser irradiation were observed by scanning electron microscope (SEM) and measured by thermocouple, respectively. RESULTS: The results revealed that 7 W of laser power could kill 97.7% of CFU through 500 microm thickness of dentin. However, the bactericidal efficiency was significantly reduced as the dentin thickness was increased. The morphological changes of lased bacteria ranged from less affected such as loss of their wall bands and existence of minicells to more severely degenerated, such as disintegration and fusion of cells with pores on the cell wall. Only the dentin specimens with a thickness of 500 microm exhibited a temperature rise greater than 5.5 degrees C after receiving 5 or 7 W of laser irradiation. CONCLUSIONS: A diode laser can eliminate the Streptococcus mutans of the residual carious dentin without inducing high pulpal temperature rise when the remaining dentin thickness is greater than 1 mm.