Effect of nanosecond- and microsecond-pulse Er,Cr:YSGG laser ablation on dentin shear bond strength of universal adhesives.

OBJECTIVE: The study aimed to evaluate the bond strength of universal adhesives to dentin after Er,Cr:YSGG laser irradiation with nanosecond-domain and microsecond-domain pulses. METHODS: Eighty extracted caries-free, sound human molars were divided into eight groups. The enamel was removed until the dentin occlusal flat dentin surface was exposed. Etch-and-rinse followed by adhesive was applied to group 1, and a self-etch adhesive was applied to group 2. Er,Cr:YSGG laser (3 mJ, 100 Hz, 100 ns), (3 mJ, 100 Hz, 150 µs), and (20 mJ, 100 Hz, 150 µs) were applied to groups 3-4, 5-6, and 7-8, respectively. The laser preparation was followed by self-etch adhesives or adhesives treatment. When the composite resin had been built up on the samples, the shear bond strength was tested, and the data were statistically analyzed using analysis of variance (ANOVA). RESULTS: Groups prepared with nanosecond-pulse laser showed significantly higher bond strength values than the microsecond-pulse laser groups and self-etch mode group, and the SEM photographs also showed more dentinal tubules and no damage in the ablation area. The shear bond strength of long pulse laser ablated was comparable to that of self-etching system when it was combined with a self-etch adhesive at low energy, but higher energy laser degraded shear bond strength. CONCLUSIONS: The pulse width of Er,Cr:YSGG laser affects the bond strength, nanosecond pulses of laser irradiation without water cooling can enhance bond strength, but microsecond pulses of laser cannot enhance bond strength.

Technical note: Estimating original crown height in worn mandibular canines using aspects of dentin morphology.

We present a novel method to estimate original crown height (OCH) for worn human mandibular canines using a cubic regression equation based on ratios of worn crown height and exposed dentin. This method may help alleviate issues frequently presented by worn teeth in dental analyses, including those in bioarchaeology. Mandibular canines (n = 28) from modern day New Zealand and English populations were selected. Crown height and dentin thickness were measured on dental thin sections (n = 19) and the resulting (log10) ratios were fitted to a cubic regression curve allowing OCH in worn crowns to be predicted. Variation in the dentin apex position was recorded and effects of angled wear slopes investigated allowing adjusted values to be generated. Our method is trialed for use on intact and sectioned teeth (n = 17). A cubic regression curve best describes the relationship between (log10) ratios and crown height deciles (R2  = 0.996, df1  = 3, df2  = 336, p < 0.001). No significant differences were detected between OCH estimates using our method and digitally recreated cusp outlines of the same crowns (t = 1.024, df = 16, p > 0.05), with a mean absolute error of 0.171 mm and an adjusted coefficient of determination of 0.923. Our approach offers a quantitative method to estimate the percentage of OCH remaining on worn mandibular canines, and by extension, the OCH. Our estimates are comparable to digitally recreated cusps but less subjective and not limited to crowns with minimal wear.

Effects of Dentin Ablation by a Q-Switching Er:YSGG Laser with a High Pulse Repetition Rate.

Objective: The aim of the study was to evaluate the characteristics of dentin ablation with a high pulse repetition rate Q-switching 2.79 µm laser. Materials and methods: Dentin was ablated using a homemade Q-switching Er:YSGG laser with a high pulse repetition rate. Er:YSGG radiation was applied with a pulse energy of 1 or 10 mJ for 100 or 3 Hz pulse repetition rate, respectively. A scanning electron microscope (SEM) was used to observe the microstructures of dentin samples after ablation. Teeth were irradiated in vitro with a 100 Hz pulse repetition rate under two different modes: free running and Q-switching. A thermocouple was applied to measure the temperature in the pulp cavity during ablation. Results: A 100 or 3 Hz Q-switching laser was used to irradiate dentin for 30 and 100 sec, respectively. There was no significant difference in ablation mass loss between the two conditions. The SEM photographs showed more dentinal tubules and no damage in the ablation area when using the 100 Hz Q-switching laser. The temperature of the pulp cavity was maintained below 41°C when using a Q-switching laser. Conclusions: The Q-switching Er:YSGG laser with a high pulse repetition rate exhibited greater ablation efficiency and better morphology than the low pulse repetition rate Q-switching laser. The experimental results also demonstrate the significant advantage of the Q-switching laser over free-running lasers for protecting dental pulp tissue. The Q-switching Er:YSGG laser with a high pulse repetition rate is expected to become an efficient new dental tool.

[Characteristics of dental hard tissues in chronic kidney disease: morphology, chemical composition, possibilities of remineralizing therapy]. / Kharakteristika tverdykh tkanei zubov pri khronicheskoi bolezni pochek: morfologiia, khimicheskii sostav, vozmozhnosti remineralizuiushchei terapii.

The aim of the work was an assessment of the morphological structure and chemical composition of dental hard tissues in persons suffering from chronic kidney disease and the effectiveness of remineralizing therapy in them. The study of the morphological structure and chemical composition of dental hard tissues in individuals suffering from chronic kidney disease and the effectiveness of 6 weeks of remineralizing therapy in the course of individual oral hygiene in combination with the intake of vitamin-mineral complex was conducted by means of ABT-55 electron microscope (Japan) combined with a LinkAN-10 000/S85 microprobe (United Kingdom) in comparison with persons without somatic pathology. It has been established that in people suffering from chronic kidney disease dental hard tissues morphological features were determined by their pathological changes due to carious process or non-carious lesions. In chronic kidney disease a significant decrease in the level of mineralization in both enamel and dentin was found, which was most pronounced in patients with chronic renal failure and did not depend on whether they received hemodialysis. The use of remineralizing therapy in people with chronic kidney disease within the framework of individual oral hygiene combined with a vitamin-mineral complex intake for 6 weeks significantly contributed to an increase in the Ca/P ratio in tooth enamel and may be seen as a useful tool for prevention of dental hard tissues pathology in the patient's group.

Effects of in-office bleaching on human enamel and dentin. Morphological and mineral changes.

BACKGROUND: The effects of HP-based products upon dental enamel and dentin are inconclusive. AIM: To evaluate changes in micromorphology and composition of calcium (Ca) and phosphate (P) in enamel and dentin after the application of 37.5% hydrogen peroxide (HP) and 35% carbamide peroxide (CP) METHODS: Crowns of 20 human teeth were divided in two halves. One half was used as control specimen and the other as experimental specimen. The control specimens were kept in artificial saliva, and the experimental specimens were divided into four groups (n=5 each): group 1 (enamel HP for 45min); group 2 (dentin HP for 45min); group 3 (enamel CP for 90min); and group 4 (dentin CP for 90min). The morphological changes were evaluated using confocal laser scanning microscopy (CLSM), while the changes in the composition of Ca and P were assessed using environmental scanning electron microscopy combined with a microanalysis system (ESEM+EDX). The results within each group and between groups were compared using the Wilcoxon test and Mann-Whitney U-test, respectively (p<0.05). RESULTS: Similar morphological changes in the enamel and no changes in dentin were assessed with both products. Ca and P decreased in enamel and dentin, without significant differences between them or with respect to their control specimens (p>0.05). CONCLUSIONS: When bleaching products with a neutral pH are used in clinical practice, both, the concentration and the application time should be taken into account in order to avoid possible structural and mineral changes in enamel and dentin.