Precise ablation of dental hard tissues with ultra-short pulsed lasers. Preliminary exploratory investigation on adequate laser parameters.

This study aimed to evaluate the possibility of introducing ultra-short pulsed lasers (USPL) in restorative dentistry by maintaining the well-known benefits of lasers for caries removal, but also overcoming disadvantages, such as thermal damage of irradiated substrate. USPL ablation of dental hard tissues was investigated in two phases. Phase 1--different wavelengths (355, 532, 1,045, and 1,064 nm), pulse durations (picoseconds and femtoseconds) and irradiation parameters (scanning speed, output power, and pulse repetition rate) were assessed for enamel and dentin. Ablation rate was determined, and the temperature increase measured in real time. Phase 2--the most favorable laser parameters were evaluated to correlate temperature increase to ablation rate and ablation efficiency. The influence of cooling methods (air, air-water spray) on ablation process was further analyzed. All parameters tested provided precise and selective tissue ablation. For all lasers, faster scanning speeds resulted in better interaction and reduced temperature increase. The most adequate results were observed for the 1064-nm ps-laser and the 1045-nm fs-laser. Forced cooling caused moderate changes in temperature increase, but reduced ablation, being considered unnecessary during irradiation with USPL. For dentin, the correlation between temperature increase and ablation efficiency was satisfactory for both pulse durations, while for enamel, the best correlation was observed for fs-laser, independently of the power used. USPL may be suitable for cavity preparation in dentin and enamel, since effective ablation and low temperature increase were observed. If adequate laser parameters are selected, this technique seems to be promising for promoting the laser-assisted, minimally invasive approach.

Protective effect of CO2 laser (10.6 µm) and fluoride on enamel erosion in vitro.

The aim of this study was to analyze the effect of CO(2) laser (10.6 µm) irradiation with 5-µs pulse width in prevention of enamel erosion due to citric acid exposure in vitro. One hundred forty-four bovine enamel samples were cut into 5 × 5 × 2-mm-size slabs and polished to obtain plane surfaces. Enamel surfaces were covered with acid-resistant varnish, except for a central area of 2.5 mm in diameter. The samples were divided into four groups (n = 12/group/day): C-control, no treatment; L-CO(2) laser irradiation (0.3 J/cm(2), 5 µs, 226 Hz); F-topical fluoride treatment, 1.25%F(-) (AmF/NaF) for 3 min; and FL-fluoride treatment + CO(2) laser. For erosive demineralization, samples were immersed in 40 ml of citric acid (0.05 M, pH 2.3) for 20 min two times per day during 5 days. After 1, 3, and 5 days, surface loss was measured by digital profilometer. According to the repeated measure ANOVA and post hoc comparisons, all the treatments showed statistically significant reduction of enamel loss as compared to control group, in all investigated times (p < 0.0001): L (52%,31%,37%); F (28%,24%,29%); FL (73%,55%,57%). Both CO(2) laser irradiation alone (L) and the combined laser-fluoride treatment (FL) caused less enamel loss than the fluoride group (F) in all days (p < 0.0001 for L in all times; and p < 0.0001, p = 0.0220 and p = 0.0051 for F, respectively, at days 1, 3, and 5). Under the conditions of this study, CO(2) laser irradiation (0.3 J/cm(2), 5 µs, 226 Hz) could effectively reduce enamel surface loss due to citric acid exposure, in vitro. This effect was still observed after 5 days of repeated acid exposures.

Verification of nerve integrity after surgical intervention using quantitative sensory testing.

PURPOSE: The aim of this study was to apply a standardized Quantitative Sensory Testing (QST) approach in patients to investigate whether oral surgery can lead to sensory changes, even if the patients do not report any sensory disturbances. Furthermore, this study determines the degree and duration of possible neuronal hyperexcitability due to local inflammatory trauma after oral surgery. PATIENTS AND METHODS: Orofacial sensory functions were investigated by psychophysical means in 60 patients (30 male, 30 female) in innervation areas of infraorbital nerves, mental nerves and lingual nerves after different interventions in oral surgery. The patients were tested 1 week, 4 weeks, 7 weeks, and 10 weeks postoperatively. As controls for bilateral sensory changes after unilateral surgery, tests were additionally performed in 20 volunteers who did not have any dental restorations. RESULTS: No differences were found between the control group and the control side of the patients. Although not 1 of the patients reported paresthesia or other sensory changes postoperatively, QST detected significant differences between the control and the test side in the mental and lingual regions. Test sides were significantly less sensitive for thermal parameters (cold, warm, and heat). No differences were found in the infraorbital region. Patients showed significantly decreased pain pressure thresholds on the operated side. QST monitored recovery over time in all patients. CONCLUSIONS: The results show that oral surgery can lead to sensory deficits in the mental and lingual region, even if the patients do not notice any sensory disturbances. The applied QST battery is a useful tool to investigate trigeminal nerve function in the early postoperative period. In light of the increasing forensic implication, this tool can serve to objectify clinical findings.

Impaired somatosensation in tongue mucosa of smokers.

Smoking has been indicated as a risk factor for oral diseases and can lead to altered sense of taste. So far, the effects of sensory changes on the tongue are not investigated. In this study, quantitative sensory testing was used to evaluate somatosensory function in the lingual region. Eighty healthy volunteers were investigated (20 smokers, 20 non-smokers). Subjects were bilaterally tested in innervation areas of lingual nerves. Thresholds of cold and warm detection, cold and heat pain, and mechanical detection were determined. As control for systemic, extraoral effects of smoking, tests were additionally performed in 40 volunteers (20 smokers, 20 non-smokers) on the skin of the chin innervated by the mental branch of the trigeminal nerve. Cold (p < 0.001), warm detection thresholds (p < 0.001), and thermal sensory limen (p < 0.001) showed higher sensitivity in non-smokers as compared to smokers. Heat pain and mechanical detection, as well as all tests in the skin of the chin, showed no significant differences. The impaired temperature perception in smokers indicates a reduction of somatosensory functions in the tongue, possibly caused by nerve degeneration associated with smoking. Possible systemic effects of smoking do not seem to affect extraoral trigeminal branches.

In vitro investigation of intra-canal dentine-laser beam interaction aspects: II. Evaluation of ablation zone extent and morphology.

Laser endodontic tips appear to provide a promising alternative to available treatment modalities in the field of endodontology. With the shortcomings in published results regarding the intra-canal behavioural aspects of those tips, it was the aim of this study to investigate the extent of the intra-canal ablation zone and the pattern associated with those tips. Ninety intact extracted bovine teeth were used to prepare mid-root testing cylinders. The samples were divided into three groups (A, B, C), corresponding to the tip diameters. Each group was further subdivided to be irradiated at three different power settings (1500 mW, 1750 mW, 2000 mW) with an erbium, chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser with a 65% water to 35% air ratio. Collected data were subjected to analysis of variance (ANOVA) and the Tukey test. At a chosen significance level of alpha = 1%, no statistical difference was found among the groups (P > 0.01). The results suggest that shortening of the estimated working length is mandatory for the use of those tips within the canal, and that, provided that certain measurements are used for intra-canal laser ablation, this is a secure mode of treatment. Further investigation and system improvement will be required for more satisfactory results.

In vitro investigation of intra-canal dentine-laser beam interaction aspects: I. Evaluation of ablation capability (ablation rate and efficiency).

The aim of this study was to determine the amount of intra-canal dentine removed with an erbium, chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser using different endodontic tips and different power settings. Ninety intact extracted bovine teeth were selected as samples. After sectioning the roots and preparing the testing cylinders, we divided the samples into three main groups (A, B, C), with further subdivision of each group to be irradiated with three different powers (1500 mW, 1750 mW and 2000 mW). An Er,Cr:YSGG laser system (2.78 microm, 140 micros, 20 Hz and 65% water to 35% air ratio) was used for irradiation, and the loss of intra-canal dentine mass was calculated by the difference between the initial and final sample masses. Data were analysed with Kolmogorov-Smirnov, analysis of variance (ANOVA) and Tukey tests. At a significance level of alpha = 1%, the results showed statistically significant differences (P < 0.0001) between different tip groups, regarding both the ablation rate and the ablation efficiency criteria. With regard to the three irradiation power settings, statistically significant difference were recorded only between groups C and A, for the ablation rate criteria. The intra-canal ablation ability of the Er,Cr:YSGG laser improved with increasing power and/or tip diameter. The latter exhibited a stronger influence on ablation rate and efficiency. Laser intra-canal ablation is an important addition to the field of endodontics; nevertheless, further investigations and system improvements are required.

Laser-assisted in-office bleaching using a neodymium:yttrium-aluminum-garnet laser: an in vivo study.

The desire for perfect and white teeth can be accomplished in aesthetical dentistry by modern tooth bleaching methods. Within the scope of a clinical study, laser assisted in-office bleaching was applied to the teeth of 20 individual patients with a neodymium:yttrium-aluminum-garnet (Nd:YAG) laser (lambda = 1.064 microm, average power 4 W, pulse repetition rate 10 Hz, pulse duration 320 micros). The treatment was carried out in a split-mouth design, each patient having two appointments with 1 week in between. Laser activation of the bleaching agent was performed on teeth 14-11 and 34-31 per session, with a total irradiation time of 30 s per tooth. The initial and the final color of the teeth were ascertained by VITA Colorsticks and the dental chromatometer ShadeEye NCC. Whitening was detected in the laser-activated and in the non-activated quadrants. Statistical evaluation showed that the additional activation of the bleaching agent by the Nd:YAG laser had produced no significant influence on the whitening (P > 0.05). The results achieved in this study should be scrutinized critically. They give cause for one to reconsider the treatment conditions or the laser parameters used, or even to query the application of the Nd:YAG laser in general during in-office bleaching.

Visualising the procedures in the influence of water on the ablation of dental hard tissue with erbium:yttrium-aluminium-garnet and erbium, chromium:yttrium-scandium-gallium-garnet laser pulses.

The exact mechanism of the ablation of tooth hard tissue with most common wavelengths, which are 2,940 nm and 2,780 nm, is not yet clear. There are several different theories, but none of them has yet been established. Concepts and methods of looking at these mechanisms have been based on heat formation and transformation, and mathematical calculations evaluating the outcome of ablation, such as looking at the shape of cuts. This study provides a new concept, which is the monitoring of the direct interactions between laser light, water and enamel, with a high-speed camera. For this purpose, both the above-mentioned wavelengths were examined. Bovine anterior teeth were prepared as thin slices. Each imaged slice had a thickness close to that of the beam diameter so that the ablation effect could be shown in two dimensional pictures. The single images were extracted from the video-clips and then were animated. The following steps, explaining the ablation procedures during each pulse, were seen and reported: (1) low-output energy intensity in the first pulses that did not lead to an ablative effect; (2) bubble formation with higher output energy density; (3) the tooth surface during the pulse was covered with the plume of vapour (comparable with a cloud), and the margins of ablation on the tooth were not clear; (4) when the vapour bubble (cloud) was collapsing, an additional ablative process at the surface could be seen.

Human leukocyte antigen polymorphism in chronic and aggressive periodontitis among Caucasians: a meta-analysis.

AIM: Multiple studies have reported associations between periodontitis and particular human leukocyte antigens (HLA). Because associations are inconsistent, we conducted a systematic literature review and a meta-analysis focusing on Caucasian case-control studies. MATERIAL AND METHODS: A literature search reporting on the distribution of HLA class I and II phenotypes in Caucasian patients with chronic periodontitis (CP) and aggressive periodontitis (AP) was performed. Data sources included electronic databases and bibliographies of published articles. Screening and data abstraction were conducted independently by different reviewers. RESULTS: Out of 174 publications, 12 studies were considered to be suitable for meta-analysis. In patients with CP, no significant HLA associations were found. Patients with AP showed a positive association with HLA-A9 [odds ratio=2.59 (95% confidence interval 1.36-4.83), p=0.004] and HLA-B15 [1.90 (1.15-3.16), p=0.01] as well as a negative association with HLA-A2 [0.72 (0.56-0.94), p=0.01] and -B5 [0.49 (0.30-0.79), p=0.004]. On grouping all patients into one periodontitis group (AP+CP), the same deviations were confirmed with higher statistical significance. For HLA-A9 and -B15, significant heterogeneity was found between the studies. No significant associations were found with HLA class II antigens. CONCLUSIONS: HLA-A9 and -B15 seem to represent susceptibility factors for AP whereas HLA-A2 and -B5 are potential protective factors against periodontitis among Caucasians.

Influence of the water content in dental enamel and dentin on ablation with erbium YAG and erbium YSGG lasers.

The theory of the ablation of dental hard tissue with erbium lasers is based on a process of thermomechanical interaction, which is explained by the absorption of the radiation in the water component of the tissue. The abrupt evaporation of the water is the cause of tissue fragments being blasted out of the tooth structure. The aim of this study is to examine the effect of the water contained in dental hard tissues on the efficiency of ablation. 192 specimens of both bovine dental enamel and bovine dentin are irradiated with an Er:YAG and an Er,Cr:YSGG laser. Half of the specimens are dehydrated beforehand. Irradiation is carried out in subgroups: without water spray and with water spray at flow rates of 0.8 and 3 mls. The ablated volume is determined following histological preparation. Only in dentin, and then only with irradiation with the Er:YAG laser, is the water contained in the tissue found to have a significant influence (p < 0.0001) on the ablated volume. The water content has no effect on the efficiency of laser ablation in any of the other test groups. In contrast, the externally supplied water always has a significant influence on the effectiveness of the ablation process.

Dental problems and emergencies of trekkers--epidemiology and prevention. Results of the ADEMED Expedition 2008.

OBJECTIVE: Dental problems are rarely mentioned in the training of medical students or physicians in travel medicine, and there are little data on dental problems of travellers in the literature. We studied the epidemiology of dental problems amongst trekkers in Nepal to develop strategies for preventive care during/before travelling and propose a curriculum for dental First Aid training. MATERIAL AND METHODS: We undertook a prospective, cross-sectional questionnaire and clinical dental survey of Trekkers at Manang (3550 m, Annapurna Circuit, Nepal). The questionnaire was developed based on published literature and clinical experience (exploring: availability of dental kits, dental history, current dental problems, and nutritional behavior). Dental examination included: dental status, papillary bleeding index (PBI), and plaque index (Quigley and Hein; QH). Questionnaire and clinical findings were compared to data of the Annapurna Conservancy Authority about the number of days of trekkers in the region to estimate the incidence of dental problems of trekkers. RESULTS: None of the 309 participants carried a dental first aid kit. Dental problems, potentially treatable with a dental first aid kit, were reported by 50/309 (16.5%). Oral hygiene en route was significantly worse than home hygiene practice; overall increased plaque indices were found (Median QH: 2.25 in women; 2.36 in men). Participants who visited a dentist ≤6 months before departure had significantly fewer problems, and had lower PBI [males 0.07 (IQR 0.0 to 0.29), females 0.0 (IQR 0.0 to 0.11)]. Combining our findings with data of the park authorities on person days in the region (2007), we found a risk of dental problems as follows: any dental problem 1:23.7 trekking days; gingival bleeding 1:37.7 trekking days; dental pain 1:145.2 trekking days; lost fillings 1:339 trekking days; fractured teeth 1:509 trekking days. CONCLUSIONS: Dental problems can pose significant discomfort for anybody travelling in regions with low/missing infrastructure. Improved awareness regarding dental first aid is essential and physicians counseling travellers in preventive strategies should advise a dental checkup pre-departure. Dental first aid and emergency treatment in the field should be included in the training curricula in travel medicine for both undergraduate and postgraduate students.

Evaluation of new injection and cavity preparation model in local anesthesia teaching.

The aim of this study was to evaluate a recently developed preclinical injection and cavity preparation model in local anesthesia. Thirty-three dental students administered an inferior alveolar nerve block injection in the model, followed by preparation on a tooth. The injection was evaluated by three observers, and the feedback from the model was registered. After completion of the practical session, the opinion of the dental students was explored with a ten-item questionnaire. Thirty dental students (91 percent) performed the injection correctly according to the feedback of the model, and twenty-eight students (85 percent) did so according to the expert opinion. The agreement between feedback from the training model and the expert opinion was high. The students were very satisfied with the opportunity to practice with the training model, as indicated by the high scores on each item of the questionnaire. These results suggest that use of this preclinical training model in anesthesia teaching may have beneficial effects on the administration of local anesthetics by dental students.

The effect of steam sterilization on the accuracy of spring-style mechanical torque devices for dental implants.

BACKGROUND: Mechanical torque devices (MTDs) are one of the most commonly recommended devices used to deliver optimal torque to the screw of dental implants. Recently, high variability has been reported about the accuracy of spring-style mechanical torque devices (S-S MTDs). Joint stability and survival rate of fixed implant supported prosthesis depends on the accuracy of these devices. Currently, there is limited information on the steam sterilization influence on the accuracy of MTDs. The purpose of this study was to assess the effect of steam sterilization on the accuracy (±10% of the target torque) of spring-style mechanical torque devices for dental implants. MATERIALS AND METHODS: Fifteen new S-S MTDs and their appropriate drivers from three different manufacturers (Nobel Biocare, Straumann [ITI], and Biomet 3i [3i]) were selected. Peak torque of devices (5 in each subgroup) was measured before and after autoclaving using a Tohnichi torque gauge. Descriptive statistical analysis was used and a repeated-measures ANOVA with type of device as a between-subject comparison was performed to assess the difference in accuracy among the three groups of spring-style mechanical torque devices after sterilization. A Bonferroni post hoc test was used to assess pairwise comparisons. RESULTS: Before steam sterilization, all the tested devices stayed within 10% of their target values. After 100 sterilization cycles, results didn't show any significant difference between raw and absolute error values in the Nobel Biocare and ITI devices; however the results demonstrated an increase of error values in the 3i group (P < 0.05). Raw error values increased with a predictable pattern in 3i devices and showed more than a 10% difference from target torque values (maximum difference of 14% from target torque was seen in 17% of peak torque measurements). CONCLUSION: Within the limitation of this study, steam sterilization did not affect the accuracy (±10% of the target torque) of the Nobel Biocare and ITI MTDs. Raw error values increased with a predictable pattern in 3i devices and showed more than 10% difference from target torque values. Before expanding upon the clinical implications, the controlled and combined effect of aging (frequency of use) and steam sterilization needs more investigation.

Screening of CO(2) laser (10.6 µm) parameters for prevention of enamel erosion.

OBJECTIVE: The aim of this study was to screen CO(2) laser (10.6 µm) parameters to increase enamel resistance to a continuous-flow erosive challenge. BACKGROUND DATA: A new clinical CO(2) laser providing pulses of hundreds of microseconds, a range known to increase tooth acid-resistance, has been introduced in the market. METHODS: Different laser parameters were tested in 12 groups (n=20) with varying fluences from 0.1 to 0.9 J/cm(2), pulse durations from 80 to 400 µs and repetition rates from 180 to 700 Hz. Non-lased samples (n=30) served as controls. All samples were eroded by exposure to hydrochloric acid (pH 2.6) under continuous acid flow (60 µL/min). Calcium and phosphate release into acid was monitored colorimetrically at 30 sec intervals up to 5 min and at 1 min intervals up to a total erosion time of 15 min. Scanning electron microscopic (SEM) analysis was performed in lased samples (n=3). Data were statistically analysed by one-way ANOVA (p<0.05) and Dunnett's post-hoc tests. RESULTS: Calcium and phosphate release were significantly reduced by a maximum of 20% over time in samples irradiated with 0.4 J/cm(2) (200µs) at 450 Hz. Short-time reduction of calcium loss (≤1.5 min) could be also achieved by irradiation with 0.7 J/cm(2) (300µs) at 200 and 300 Hz. Both parameters revealed surface modification. CONCLUSIONS: A set of CO(2) laser parameters was found that could significantly reduce enamel mineral loss (20%) under in vitro erosive conditions. However, as all parameters also caused surface cracking, they are not recommended for clinical use.

Analysis of trigeminal nerve disorders after oral and maxillofacial intervention.

BACKGROUND: Quantitative sensory testing (QST) is applied to evaluate somatosensory nerve fiber function in the spinal system. This study uses QST in patients with sensory dysfunctions after oral and maxillofacial surgery. METHODS: Orofacial sensory functions were investigated by psychophysical means in 60 volunteers (30 patients with sensory disturbances and 30 control subjects) in innervation areas of the infraorbital, mental and lingual nerves. The patients were tested 1 week, 4 weeks, 7 weeks and 10 weeks following oral and maxillofacial surgery. RESULTS: QST monitored somatosensory deficits and recovery of trigeminal nerve functions in all patients. Significant differences (p < 0.05) between control group and patients were shown for cold, warm and mechanical detection thresholds and for cold, heat and mechanical pain thresholds. Additionally, QST monitored recovery of nerve functions in all patients. CONCLUSION: QST can be applied for non-invasive assessment of sensory nerve function (Aß-, Aδ- and C-fiber) in the orofacial region and is useful in the diagnosis of trigeminal nerve disorders in patients.

Decontamination of deep dentin by means of erbium, chromium:yttrium-scandium-gallium-garnet laser irradiation.

The aim of this in vitro study was to evaluate the depth of effectiveness of erbium, chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser irradiation on microorganism reduction. From human roots, dentin slices of 100 microm to 1,000 microm thickness were prepared. These specimens were sterilized and then inoculated with 1 microl of Enterococcus faecalis suspension. The backs of the specimens were then irradiated with Er,Cr:YSGG radiation at a pulse energy of 3.13 mJ, delivered at an incidence angle of 5 degrees to the dentin slice surface. A control group was left without irradiation. The remaining bacteria were collected in 1 ml sterilized NaCl solution, serially diluted and seeded in Columbia-Agar plates. Despite the low pulse energy of 3.13 mJ, the Er,Cr:YSGG laser irradiation resulted in significant bacterial reduction up to a dentin thickness of 500 microm (P < 0.05). Scanning electron microscopy (SEM) micrographs of the contaminated and irradiated surfaces showed the absence of a smear layer and opened dentinal tubules.

In vitro preliminary study to evaluate the capability of Er,Cr:YSGG laser in posterior teeth root-canal preparation with step-back technique.

This preliminary study was to investigate in vitro the Er,Cr:YSGG laser ablation capability, both range (enlargement aspects of laser tips corresponded to conventional endodontic files) and quality (removing of smear layer and opening of dentinal tubules) to clean and shape the root canal for final obturation step. The crowns of 15 extracted multi-rooted posterior human teeth were resected, and then 15 canals were prepared by an Er,Cr:YSGG laser up to 1.5 W (actual power output) using the step-back technique, while the other 15 canals (control) were enlarged conventionally by K-flex file. The results revealed that posterior root-canal preparation could be achieved by laser beam transmitted to the canal using endodontic tips. At a chosen significance level of alpha = 1%, the results showed no significant statistical difference between the two groups (P > 0.01). Considering the results of this current study, laser-based root-canal preparation still shows certain limitations, and further improvements are mandatory for higher achievement and better preparation outcomes.

Quantitative analysis of dental enamel removal during a microabrasion technique

Objetivo: Quantificar, por meio de perfi lometria, a profundidade de esmalte dental removido durante o emprego de uma técnica de microabrasão utilizando-se ácido clorídrico e abrasão manual com espátula plástica. Método: Trinta e seis espécimes obtidos de terceiros molares humanos foram polidos, para obtenção de superfícies planas, e divididos em 3 grupos (n = 12) de acordo com os diferentes tratamentos recebidos: tratamento placebo com água deionizada, como controle negativo (CG); microabrasão com ácido clorídrico a 6.6, OpalustreTM (G1); e ácido clorídrico a 6, Whiteness RMTM (G2). A microabrasão foi realizada, de forma padronizada, submetendo os espécimes a 4 ciclos de 10 segundos cada e abrasão manual utilizando-se uma espátula plástica com carga de 200 g. A perda da superfície de esmalte foi medida após cada um dos ciclos de tratamento por meio de perfi lômetro de contato. Resultados: Após os primeiros 10 segundos de abrasão, já foi encontrada perda de esmalte em ambos os grupos tratados (G1 e G2). Nos grupos G1 e G2, a cada ciclo de 10 segundos, foi observado um aumento signifi cativo na perda de esmalte (p ≤0.05). Após 4 abrasões de 10 segundos cada, as médias de perda de esmalte nos grupos tratados foram 46.04 μm (G1) e 54.65 μm (G2). Foi encontrada uma diferença signifi cativa entre G1 e G2 com relação à perda de esmalte de microabrasão em esmalte dental com segurança, utilizando-se ácido clorídrico e abrasão manual com espátula plástica.

Objective: To quantify, by means of profi lometry, the removal of dental enamel during the use of a microabrasion technique involving the use of hydrochloric acid and manual abrasion with a plastic spatula. Method: Thirty six specimens obtained from human third molars were polished to obtain fl at surfaces and divided into 3 groups (n = 12) according to the different treatments received: A placebo treatment with deionized water as a negative control (CG); microabrasion with 6.6% hydrochloric acid, OpalustreTM (G1); and microabrasion with 6% hydrochloric acid, Whiteness RMTM (G2). The microabrasion was performed in a standardized manner by submitting the specimens to 4 cycles of 10 seconds each and manual abrasion using a plastic spatula (200 g load). The loss of enamel surface was measured after each cycle of treatment by contact profi lometry. Results: Enamel loss was already observed after the fi rst 10 seconds of abrasion with hydrochloric acid in both treated groups (G1 and G2). After 4 abrasions of 10 seconds each, the average fi nal enamel losses in the treated groups were 46.04 μm (G1) and 54.65 μm (G2). In the G1 and G2 groups, a signifi cant increase in enamel wear was detected in each cycle in comparison to the control group (p ≤ 0.05). A signifi cant difference in enamel loss between G1 and G2 was found after 30 and 40 seconds of microabrasion. Relevance: The results of this study provide objective data for safely performing the microabrasion technique on dental enamel using hydrochloric acid and manual abrasion using a plastic spatula.

The effect of low-level laser therapy during orthodontic movement: a preliminary study.

It has been emphasized that one of the most valuable treatment objectives in dental practice is to afford the patient a pain-free treatment. By the evolution of the laser applications, the dental committee aimed to achieve this goal without analgesic drugs and painful methods. Orthodontic treatment is one of these concerns, that one of the major components of patient to reject this treatment is the pain accompanied during the different treatment phases. Another great concern of the patient is not to get through prolonged periods of treatment. The aim of this study is to evaluate the effect of the low-level (GaAlAs) diode laser (809 nm, 100 mW) on the canine retraction during an orthodontic movement and to assess pain level during this treatment. A group of 15 adult patients with age ranging from 14 to 23 years attended the orthodontic department at Dental School, Damascus University. The treatment plan for these patients included extraction of the upper and lower first premolars because there was not enough space for a complete alignment or presence of biprotrusion. For each patient, this diagnosis was based on a standard orthodontic documentation with photographs, model casts, cephalometric, panorama, and superior premolar periapical radiographies. The orthodontic treatment was initiated 14 days after the premolar extraction with a standard 18 slot edgewise brackets [Rocky Mountain Company (RMO)]. The canine retraction was accomplished by using prefabricated Ricketts springs (RMO), in both upper and lower jaws. The right side of the upper and lower jaw was chosen to be irradiated with the laser, whereas the left side was considered the control without laser irradiation. The laser was applied with 0-, 3-, 7-, and 14-day intervals. The retraction spring was reactivated on day 21 for all sides. The amount of canine retraction was measured at this stage with a digital electronic caliper (Myoto, Japan) and compared each side of the relative jaw (i.e., upper left canine with upper right canine and lower left canine with lower right canine). The pain level was prompted by a patient questionnaire. The velocity of canine movement was significantly greater in the lased group than in the control group. The pain intensity was also at lower level in the lased group than in the control group throughout the retraction period. Our findings suggest that low-level laser therapy can highly accelerate tooth movement during orthodontic treatment and can also effectively reduce pain level.

Influence of water-layer thickness on Er:YAG laser ablation of enamel of bovine anterior teeth.

Different ideas have been presented to describe the mechanism of augmented laser ablation of dental enamel with different shapes by adding water to the working environment. In this study, the influence of water-laser interaction on the surface of enamel during ablation was investigated at a wavelength of 2.94 microm with different distances between the laser tip and the enamel surface. A motion-control system was used to produce linear incisions uniformly on flat enamel surfaces of bovine anterior teeth, with free-running Er:YAG laser very short pulses (pulse length = 90-120 micros, repetition rate = 10 pulses per second). Four different output energies (100, 200, 300 and 400 mJ) were radiated on samples under distilled water from different distances (0.5, 0.75, 1, 1.25, 1.75 and 2.00 mm). The tooth slices were prepared with a cutting machine, and the surfaces of the ablated areas were measured with software under a light microscope. The average and standard deviation of all cut areas in different groups were reported. There was no significant difference when using a different pulse ablation speed (cm(3)/J) and a water-layer thickness between the tip and enamel surface of 0.5-1.25 mm with energy densities of 30-60 J/cm(2) (200-400 mJ). However, using an output energy of 15 J/cm(2) (100 mJ) and a thicker water layer than 1 mm, a linear ablation did not take place. This information led to a clearer view of the efficiency of Er:YAG laser in the conditions of this study. There are several hypotheses which describe a hydrokinetic effect of Er,Cr:YSGG. These basic studies could guide us to have a correct attitude regarding hydro-mechanical effects of water, although the wavelength of 2.78 microm has a better absorption in hydroxyl branch of water molecules. Therefore, our results do not directly interrupt with the series of investigations done with Er,Cr:YSGG. Water propagation and channel formation under water are investigated during the ablation of tooth enamel with the Er:YAG laser from different distances. Comparing the results of this study with the same research done with water/air spray concludes that the bubble formation and channel propagation in water with this wavelength leads to a more symmetric (linear) ablation process with cavity-preparation-recommended parameters.