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Susceptibility of enamel to initial erosion in relation to tooth type, tooth surface and enamel depth
This study assessed the susceptibility of different tooth types, surfaces, and enamel depths to initial erosion measured by surface microhardness loss (ΔSMH) and calcium (Ca) release. Twenty molars and 20 premolars were divided into experimental and control groups, cut into lingual/buccal halves, and ground/polished, removing 100 µm of enamel. Initial surface microhardness (SMH0) was measured on all halves. The experimental group was subjected to three consecutive erosive challenges (30 ml/tooth of 1% citric acid, pH 3.6, 25°C, 1 min). After each challenge, ΔSMH and Ca release were measured. The same teeth were consecutively ground to 200, 400, and 600 µm depths, and the experimental group underwent three erosive challenges at each depth. No difference was found in SMH0 between experimental and control groups. Multivariate nonparametric ANOVA showed no significant differences between lingual and buccal surfaces in ΔSMH or Ca release. ΔSMH was significantly greater in premolars than in molars, but not different with respect to enamel depth. Ca release decreased significantly with increasing depth. In conclusion, different teeth and enamel depths have different susceptibility to erosion, so when Ca release is used to measure erosion, the depth of the test facet in enamel should be standardized, whereas this is less important if ΔSMH is used.
The use of sub-ablative Er:YAG laser irradiation in prevention of dental caries during orthodontic treatment
This in-vitro study had two specific aims: to test using a universal testing machine whether sub-ablative Er:YAG laser irradiation prior to acid etching is effective in orthodontic bracket bonding, and, secondly, to use microhardness measurements and scanning electron microscopy (SEM) observations to investigate the effectiveness of demineralization reduction in enamel treated with sub-ablative Er:YAG laser irradiation followed by fluoride varnish application. There were 180 bovine permanent maxillary incisors selected for shear bond strength testing and microhardness measurements. Sub-ablative Er:YAG laser irradiation was set at a power density of 2.5 J/cm(2), a frequency of 7 Hz, and air/water spray. Brackets were bonded with an auto-curing resin paste. Shear bond strength was measured comparing laser irradiated and non-irradiated enamel surface, followed by SEM observation of the bracket-resin-enamel interface. Various microhardness measurements were made on enamel samples. The authors concluded that sub-ablative Er:YAG laser irradiation before acid etching does not reduce the shear bond whereas when associated with fluoride application it may play a role in caries prevention.
Biofilm layers affect the treatment outcomes of NaF and nano-hydroxyapatite
Zhang M, He LB, Exterkate RA, et al. J Dent Res. 2015 Jan 9. pii: 0022034514565644. [Epub ahead of print]
This study investigated the influence of biofilms as a stagnant layer on the efficacy of NaF and nano-hydroxyapatite (nHA). Biofilms of Streptococcus mutans C180-2 were formed on the surfaces of artificially demineralized enamel in an active attachment biofilm model. After 2 days of biofilm formation, the model was subjected to a pH-cycling schedule, together with a control group without biofilms. Specimens were treated for 5 min twice daily with water, a 10% nHA slurry, or 18.4 mM NaF. At the end of the pH-cycling period, the biofilms were removed for the determination of the viable counts, the lactic acid production, and the calcium content. The mineral changes in the demineralized enamel blocks were analyzed by transversal microradiography. No differences in the biofilm viable counts and lactic acid production were found in the different treatment groups. The mean calcium content of the biofilms in the nHA group was approximately 8-fold higher than in the other two groups. The application of NaF resulted in net remineralization, but in the presence of a biofilm, net demineralization was observed. In contrast, nHA treatment reduced further demineralization compared with the water treatment, but the presence of a biofilm enhanced this effect.