Alessandra M. Correa-Afonso

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.

In vitro assessment of laser efficiency for caries prevention in pits and fissures

This study aimed to assess the in vitro efficacy of the lasers Er:YAG, Nd:YAG, and CO2 operating in the low energy mode for caries prevention in pits and fissures. Forty‐five caries‐free enamel occlusal sections were randomly divided into three groups: G1 − Er:YAG (80 mJ/2Hz); G2 − Nd:YAG Laser (1W and 10 Hz); and G3 − CO2 Laser (0.4 W and 20 Hz). After surface treatment, the samples were submitted to challenge with acid consisting of a 10‐day immersion in demineralizing (6 h) and remineralizing solution (18 h). Next, enamel demineralization was quantitatively evaluated by subsurface microhardness test and polarized‐light microscopy (PLM, mm2) and qualitatively assessed by scanning electron microscopy. The Wilcoxon test was used for comparison of each group with its own control. ANOVA (α = 5%) was employed for comparison among groups, and Fishers LSD multiple comparison test was applied, to check the difference in means. Concerning the microhardness analyses, statistical difference between control, and experimental areas was only detected for the CO2 group. Experimental values were higher than the controls. As for PLM analyses, smaller demineralized areas were measured for G2 (Nd:YAG) and G3 (CO2) compared with the control areas. In conclusion, the present findings suggest that the CO2 laser should be selected in order to increase the enamel resistance to acid in pits and fissures. Microsc. Res. Tech. 2011.

Deposition of lead and cadmium released by cigarette smoke in dental structures and resin composite

Cigarette smoke is a significant source of cadmium, lead, and toxic elements, which are absorbed into the human organism. In this context, the aim of this study was to investigate in vitro the presence of toxic elements, cadmium, and lead deriving from cigarette smoke in the resin composite, dentine, and dental enamel. Eight cylindrical specimens were fabricated from resin composite, bovine enamel, and root dentin fragments that were wet ground and polished with abrasive paper to obtain sections with 6‐mm diameter and 2‐mm thickness. All specimens were exposed to the smoke of 10 cigarettes/day during 8 days. After the simulation of the cigarette smoke, the specimens were examined with scanning electron microscopy (SEM) and the energy‐dispersive X‐ray analysis. In the photomicrographic analysis in SEM, no morphological alterations were found; however, the microanalysis identified the presence of cadmium, arsenic, and lead in the different specimens. These findings suggest that the deposition of these elements derived from cigarette smoke could be favored by dental structures and resin composite. Microsc. Res. Tech., 2010.

FTIR and SEM analysis of CO2 laser irradiated human enamel

OBJECTIVES Considering the enamel chemical structure, especially carbonate band, which has a major role in the caries prevention, the objective of the present study was to assess the chemical alterations on the enamel irradiated with CO(2) laser by means of FTIR spectroscopy and SEM analysis. DESIGN The enamel surfaces were analysed on a spectrometer for acquisition of the absorption spectrum relative to the chemical composition of the control sample. The irradiation was conducted with a 10.6-μm CO(2) laser (0.55W, 660W/cm(2)). The carbonate absorption band at 1600-1291cm(-1) as well as the water absorption band at 3793-2652cm(-1) was measured in each sample after the irradiation. The water band was measured again 24-h after the irradiation. The band area of each chemical compound was delimited, the background was subtracted, and the area under each band was integrated. Each area was normalized by the phosphate band (1190-702cm(-1)). RESULTS There was a statistically significant decrease (p<0.05) in the water content after irradiation (control: 0.184±0.04; irradiated: 0.078±0.026), which increased again after rehydration (0.145±0.038). The carbonate/phosphate ratio was measured initially (0.112±0.029) and its reduction after irradiation indicated the carbonate loss (0.088±0.014) (p<0.05). CONCLUSION The 10.6-μm CO(2) laser irradiation diminishes the carbonate and water contents in the enamel after irradiation.

Influence of the irradiation distance and the use of cooling to increase enamel-acid resistance with Er:YAG laser

OBJECTIVES The aim of this study was to assess the influence of irradiation distance and the use of cooling in the Er:YAG laser efficacy in preventing enamel demineralization. METHODS 84 enamel blocks were randomly assigned to seven groups (n=12): G1: control group - no treatment, G2-G7: experimental groups treated with Er:YAG laser (80mJ/2Hz) at different irradiation distances with or without cooling: G2: 4mm/2mL; G3: 4mm/no cooling; G4: 8mm/2mL; G5: 8mm/no cooling; G6: 16mm/2mL; G7: 16mm/no cooling. The samples were submitted to an in vitro pH cycles for 14 days. Next, the specimens were sectioned in sections of 80-100microm in thickness and the demineralization patterns of prepared slices were assessed using a polarized light microscope. Three samples from each group were analyzed with scanning electronic microscopy. Analysis of variance and the Fisher test were performed for the statistical analysis of the data obtained from the caries-lesion-depth measurements (CLDM) (alpha=5%). RESULTS The control group (CLDM=0.67mm) was statistically different from group 2 (CLDM=0.42mm), which presented a smaller lesion depth, and group 6 (0.91mm), which presented a greater lesion depth. The results of groups 3 (CLDM=0.74mm), 4 (CLDM=0.70mm), 5 (CLDM=0.67mm) and 7 (CLDM=0.89mm) presented statistical similarity. The scanning electronic microscopy analysis showed ablation areas in the samples from groups 4, 5, 6 and 7, and a slightly demineralized area in group 2. CONCLUSIONS It was possible to conclude that Er:YAG laser was efficient in preventing enamel demineralization at a 4-mm irradiation distance using cooling.

Thermal alteration and morphological changes of sound and demineralized primary dentin after Er:YAG laser ablation

The purpose of this study was to assess the influence of Er:YAG laser pulse repetition rate on the thermal alterations occurring during laser ablation of sound and demineralized primary dentin. The morphological changes at the lased areas were examined by scanning electronic microscopy (SEM). To this end, 60 fragments of 30 sound primary molars were selected and randomly assigned to two groups (n = 30); namely A sound dentin (control) and B demineralized dentin. Each group was divided into three subgroups (n = 10) according to the employed laser frequencies: I–4 Hz; II–6 Hz, and III–10 Hz. Specimens in group B were submitted to a pH‐cycling regimen for 21 consecutive days. The irradiation was performed with a 250 mJ pulse energy in the noncontact and focused mode, in the presence of a fine water mist at 1.5 mL/min, for 15 s. The measured temperature was recorded by type K thermocouples adapted to the dentin wall relative to the pulp chamber. Three samples of each group were analyzed by SEM. The data were submitted to the nonparametric Kruskal‐Wallis test and to qualitative SEM analysis. The results revealed that the temperature increase did not promote any damage to the dental structure. Data analysis demonstrated that in group A, there was a statistically significant difference among all the subgroups and the temperature rise was directly proportional to the increase in frequency. In group B, there was no difference between subgroup I and II in terms of temperature. The superficial dentin observed by SEM displayed irregularities that augmented with rising frequency, both in sound and demineralized tissues. In conclusion, temperature rise and morphological alterations are directly related to frequency increment in both demineralized and sound dentin. Microsc. Res. Tech., 2011.

CO2-lased enamel microhardness after brushing and cariogenic challenge

Abstract. This study aimed to assess how the wear that brushing promotes affects CO2 laser-irradiated enamel microhardness after cariogenic challenge in vitro. Forty fragments measuring 4×4  mm were randomly assigned to four groups according to the enamel surface treatment: G1—control, G2—CO2-laser irradiation, G3—brushing, and G4—CO2 laser irradiation + brushing. A laser device emitting at 10.6 μm was used (power=0.5  W, energy per pulse=0.05  mJ, and frequency=10  kHz). Specimens belonging to groups G3 and G4 were brushed (80,000 strokes) with a brushing simulator using toothpaste. Next, the samples were challenged with acid: the specimens were immersed in demineralizing and remineralizing solutions for 8 days. The acid resistance of enamel was evaluated by cross-sectional microhardness tests. The area under the curve (KHN×μm) was calculated. Analysis of variance (ANOVA) one-away and Fisher’s test were performed for the statistical analysis (p<0.05). Group G2 specimens (31,185±4706) were statistically different from specimens belonging to groups G1 (26,723±2446), G3 (28,194±1376), and G4 (28,207±2234), which were statistically similar. The brushing time used in the present study probably wore the CO2-lased enamel, so demineralization could not be prevented in the brushed group.