Intraoral pH measurement of carious lesions with qPCR of cariogenic bacteria to differentiate caries activity.

OBJECTIVES: A low pH environment is created by cariogenic bacteria. This study was aimed to measure pH of carious lesions intraorally using a micro-pH sensor, and assess predominant acid-producing cariogens by qPCR to differentiate caries activities. METHODS: 103 dentine lesions classified as active or arrested caries based on the clinical and radiological examinations were collected from patients after intraoral measurement of the lesion surface pH using a micro-pH sensor. Quantitative detection of genomic DNA copies of target cariogenic bacteria (mutans streptococci and Lactobacillus spp.) in each lesion was performed using real-time PCR. Correlation between the pH ranges and the number of bacterial species was examined by Spearman test. RESULTS: 50 samples were diagnosed as active and 53 as arrested lesions. Statistically significant difference was observed on average surface pH value between active and arrested lesions (p<0.05). Prevalence of Lactobacillus spp. was higher in active lesions than in arrested lesions (76% vs. 58% of samples, respectively). When the carious lesions were categorised into four different pH ranges (up to 5.5, from 5.6 to 5.8, from 5.9 to 6.1 and 6.2 or above), increased prevalence of Lactobacillus spp. was observed with decrease of pH levels. A significant negative relationship was found between pH value and number of Lactobacillus spp. (r=-0.209, p<0.05) but no such correlation was found for mutans streptococci. CONCLUSIONS: Intraoral pH measurement might be clinically useful to determine acidity of the local environment of carious lesions as one aspect of the caries activity assessment. CLINICAL SIGNIFICANCE: The population of certain bacteria may indicate activity of carious lesions. Intraoral pH measurement of the carious lesions using a micro-pH sensor may be a clinically feasible method for assessment of lesion acidity.

The clinical application of surface pH measurements to longitudinally assess white spot enamel lesions.

OBJECTIVES: Means of objectively assessing white spot enamel lesions (WSEL) are critical for determining their potential activity and monitoring the success of preventive treatments. The aim of this study was to determine whether surface pH measurements of WSEL changed during a preventive course of care designed to remineralize the lesions. METHODS: Eight healthy subjects (1 male and 7 females) with at least one WSEL were recruited (19-64 years). Each subject was placed on a preventive treatment program including the daily application of a CPP-ACP paste (MI paste, GC Corp., Japan) with custom fitted trays for more than 6 months. The surface pH values of sound enamel and WSEL were monitored for up to 2 years using a micro-pH sensor. The visual appearance of the WSEL was monitored via digital photography, and images were analyzed qualitatively on a 5-point scale to assess the success of the remineralization preventive program. The relationship between the qualitative assessment of WSEL appearance and the WSEL pH was investigated using a Spearman's rho non-parametric correlation. RESULTS: The surface pH of the WSEL was different to that of the sound enamel surrounding it in all patients at all times. All lesions showed visual improvement as the treatment period progressed. The pH of the WSEL increased towards that of sound enamel over the course of treatment significantly correlating with the visual improvement of the lesion (rho=0.63, p<0.0001). CONCLUSIONS: The clinical assessment of WSEL surface pH changes with time may have utility as an additional objective measure for the assessment of WSEL activity.

Effect of dentin pretreatment with mild acidic HOCl solution on microtensile bond strength and surface pH.

OBJECTIVES: To evaluate the pretreatment effect of mild acidic HOCl solution on the microtensile bond strength (muTBS) of a two-step self-etch adhesive to dentin and the alteration of dentin surface pH. METHODS: Thirty-nine flat ground coronal dentin specimens were divided into one control group and 12 experimental groups, which were treated with 6% NaOCl or 50, 100 and 200ppm HOCl (Comfosy) solutions for 5, 15 and 30s. After rinsing with running water for 30s, all the dentin surfaces were bonded with Clearfil SE Bond according to the manufacturer's instructions. After 24h water storage, the bonded specimens were sectioned and trimmed to an hourglass shape with a cross-sectional area of approximately 1.0mm(2) and then subjected to the muTBS test. Thirty-six mid-coronal dentin discs were used for surface pH measurement. Dentin surface pH with or without pretreatment was examined using a pH-imaging microscope (SCHEM-100). The muTBS data were analyzed by one-way ANOVA (Dunnett's T3) and the surface pH data were analyzed by non-parametric statistics (Mann-Whitney U-test). RESULTS: Pretreatment with Comfosy at concentrations of 50, 100 and 200 ppm did not significantly affect muTBS regardless of the application time compared with the control group, however the 100 and 200ppm Comfosy groups showed significantly lower surface pH values. For the NaOCl pretreatment groups, a longer application time significantly decreased the muTBS and increased the surface pH values compared to the control group. CONCLUSIONS: The 50ppm Comfosy pretreatments for 5, 15 and 30s did not affect the muTBS of the two-step self-etch adhesive to dentin and dentin surface pH.

Micro-shear bond strengths and etching efficacy of a two-step self-etching adhesive system to fluorosed and non-fluorosed enamel.

The purpose of this study was to evaluate the micro-shear bond strengths and the etching efficacy of a two-step self-etching adhesive system to fluorosed and non-fluorosed enamel. The extracted teeth, obtained from Australian and Japanese patients, were classified according to the severity of fluorosis, using the Thylstrup & Fejerskov index (TFI). Australian teeth were classified as mildly fluorosed (TFI = 1-3), whereas Japanese teeth were classified as non-fluorosed (TFI = 0). Resin composite was bonded to 20 enamel samples using Clearfil SE bond. The bonded samples were stressed at a crosshead speed of 1 mm min(-1) to determine the micro-shear bond strength. To examine the etching efficacy of primer on fluorosed and non-fluorosed enamel, the enamel-surface pH values were directly measured using a micro pH sensor. The non-fluorosed enamel showed significantly higher bond strengths compared with the fluorosed enamel. There was a statistical difference between fluorosed and non-fluorosed enamel regarding the surface pH change before and after application of the Clearfil SE bond primer. The results from this study suggest that water fluoridation has an effect on the acid resistance of enamel surfaces when treated with a two-step self-etching adhesive system and that this effect leads to reduced bond strengths.