Nigel M. King

Adverse surface interactions between one-bottle light-cured adhesives and chemical-cured composites

OBJECTIVES This study examined the effect of one-bottle adhesives with different acidities on bonding to chemical-cured and light-cured resin composites. METHODS Twenty-four non-carious human third molars were divided into eight groups. A flat dentin surface was created for each tooth. Acid-conditioned dentin surfaces were bonded with Prime&Bond NT (Dentsply), OptiBond SOLO (Kerr), Single Bond (3M) or One-Step (Bisco). Each adhesive group was covered with composite buildups, using either a light-cured (Z100, 3M) or a chemical-cured composite (BisFil 2, Bisco). Specimens were vertically sectioned into 0.9x0.9 mm beams. Microtensile bond strengths were recorded and failure modes were classified using a stereoscopical microscope. Four representative beams from each group were further prepared for SEM examination. RESULTS Two-way ANOVA showed that the effect of adhesive types, composite curing modes and their interaction were statistically significant (P<0.001). Multiple comparison tests revealed no statistically significant difference in the bond strength of the four adhesives with the light-cured composite (P>0.05). However, they were significantly lower when used with the chemical-cured composite (P<0.01). A positive correlation was observed between the acidity of adhesives and the bond strengths of the chemical-cured composite. Failure occurred predominantly along the composite-adhesive interface, with microporosities on the adhesive surface and voids within the chemical-cured composite. SIGNIFICANCE Air incorporated during mixing of chemical-cured composites only contributed partially to the decreased bond strength observed in simplified-step adhesives. Ultrastructural observations suggested the presence of a surface interaction between the uncured, acidic resin monomers from the oxygen inhibition layer of the adhesive and the initiator components in the chemical-cured composite.

The effect of casein phosphopeptide-amorphous calcium phosphate on remineralization of artificial caries-like lesions: an in vitro study.

BACKGROUND The aims of this study were to investigate the efficacy of CPP-ACP containing Tooth Mousse on the remineralization of enamel lesions and to compare its efficacy to that of a fluoride-containing toothpaste. METHODS Permanent teeth were placed in demineralizing solution for 96 hours to produce artificial caries-like lesions 120-200 microm in depth. They were sectioned into 100-150 microm thick samples and randomly assigned to five groups: for Group A, a fluoridated toothpaste (1100 ppm) was used as a positive control and in Group B, a non-fluoridated toothpaste was used as a negative control. Tooth Mousse containing CPP-ACP was tested by three different means: as a toothpaste (Group C); as a topical coating (Group D); and (Group E) as a topical coating after treating the sections with the same fluoridated toothpaste as in Group A. RESULTS The lesion depth decreased significantly by 7 per cent in Group A, 10.1 per cent in Groups C and D, and 13.1 per cent in Group E (Paired t- test, p < 0.05), while in Group B the lesion depth increased significantly by 23 per cent. CONCLUSIONS Based on the data obtained, CPP-ACP containing Tooth Mousse remineralized initial enamel lesions and it showed a higher remineralizing potential when applied as a topical coating after the use of a fluoridated toothpaste.

Translation and evaluation of a Chinese version of the child oral health-related quality of life measure

OBJECTIVE This study aims to translate and evaluate the performance of a Chinese version of the Child Oral Health-related Quality of Life (COHQoL) measure composed of the Child Perception Questionnaire (CPQ), Parental Perception Questionnaire (PPQ), and Family Impact Scale (FIS). BASIC RESEARCH DESIGN Chinese versions of the measures were derived through a forward-backward translation. A consecutive sample of 168 children attending paediatric dental and orthodontic clinics in Hong Kong were recruited along with their attending primary caregiver. Children self-completed the 37-item CPQ and their attending primary caregiver self-completed the 31-item PPQ and 14-item FIS consecutively and independently. Reassessments were conducted prior to their next appointment. RESULTS CPQ, PPQ, and FIS scores were associated with childrens global rating of oral health (P < 0.05) and oral well-being (P < 0.05) supporting their construct validity. In addition, variations in CPQ, PPQ, and FIS were apparent with respect to patient group (P < 0.05) supporting their ability to distinguish between patient groups. Cronbach alpha values (internal reliability) and intraclass correlation coefficient values (test-retest reliability) for the three measures were > 0.80. CONCLUSION A Chinese version of the three components of the COHQoL measure was developed with minor modifications. In psychometric testing, the validity of the three components was supported and they demonstrated acceptable reliability.

Water Concentration in Self-etching Primers Affects their Aggressiveness and Bonding Efficacy to Dentin

Water is required to ionize acid resin monomers for demineralization of tooth substrates. We tested the null hypothesis that altering the water concentration in two-step self-etching primers has no effect on their aggressiveness and bonding efficacy to dentin. Five experimental self-etching primers were prepared with resin-water-ethanol volume ratios of 9-0-1, 8-1-1, 7-2-1, 5-4-1, and 3-6-1. They were applied to smear-layer-covered dentin, followed by a bonding resin and composite build-ups for microtensile bond testing and TEM examination of tracer penetration. Increasing water concentration from 0–60 vol% improved acidic monomer ionization that was manifested as increasing hybrid layer thickness. However, significantly higher bond strength was observed in the 7-2-1 group, with minimal nanoleakage in the corresponding hybrid layer. When self-etching primers are formulated, a balance must be achieved to provide sufficient water for adequate ionization of the acidic monomers, without lowering the resin concentration too much, to optimize their bonding efficacy to dentin.

Effect of 2% chlorhexidine on dentin microtensile bond strengths and nanoleakage of luting cements.

OBJECTIVES The aim of this study was to investigate the effect of pre-treatment by chlorhexidine on the microtensile bond strength (mTBS) of resin cements and nanoleakage at the resin-dentine interfaces. METHODS Cylindrical composite blocks were luted to human dentine using resin cements (RelyX ARC, 3M ESPE: ARC; Panavia F, Kuraray Medical Inc.: PF; RelyX Unicem, 3M ESPE: UN) with/without pre-treatment by 2% chlorhexidine digluconate (CAVITY CLEANSER, Bisco, Inc., Schaumburg, IL, USA). CAVITY CLEANSER was applied on the acid etched dentine for 60s in the ARC group, and on smear layer-covered dentine in the PF and UN groups. After storage in water for 24h, the bonded teeth were sectioned into 1mm thick slabs and further into 0.9mm x 0.9mm beams. After immersion in water or ammoniacal silver nitrate for 24h, the beams were stressed to failure in tension. The fractured surfaces were examined by field-emission scanning electron microscopy (FE-SEM) using backscattered electron mode. The silver-stained slabs were used to examine nanoleakage within the bonded interface by FE-SEM. RESULTS The resin cement and chlorhexidine treatment had significant effects (p<0.0001) on mTBS; while the storage media had no significant effect (p=0.435). The mTBS of ARC was significantly higher than the other cements. Chlorhexidine reduced mTBS and produced pronounced nanoleakage when PF and UC were luted to dentine. CONCLUSIONS Pre-treatment with chlorhexidine affected the integrity of dentine bonding with PF and UC, while there was no adverse effect on coupling of ARC.

A Nanoleakage Perspective on Bonding to Oxidized Dentin

The mechanism responsible for sodium-hypochlorite-induced reduction in dentin bond strength and its reversal with reducing agents is unknown. This study examined the relationship between nanoleakage and reversal of compromised bonding to oxidized dentin. Acid-etched dentin was completely depleted of demineralized collagen matrix when sodium hypochlorite was used. Specimens were bonded with two single-bottle dentin adhesives. They were immersed in ammoniacal silver nitrate for 24 hrs before being processed for transmission electron microscopy. For both adhesives, tensile bond strengths of acid-etched dentin were significantly reduced after sodium hypochlorite treatment, but were reversed when sodium ascorbate was used. After sodium hypochlorite application, reticular nanoleakge patterns in hybrid layers were replaced by vertical, shag-carpet-like patterns along the demineralization front. This type of nanoleakage was completely eliminated after sodium ascorbate treatment with the materials tested. Residual sodium hypochlorite within the porosities of mineralized dentin may result in incomplete resin polymerization, and hence compromised bond strength.

Chlorhexidine release and water sorption characteristics of chlorhexidine-incorporated hydrophobic/hydrophilic resins.

OBJECTIVES The aim of this study was to evaluate chlorhexidine release from unfilled non-solvated methacrylate-based resins of increasing hydrophilicity and to examine relationships among Hoys solubility parameters, water sorption, solubility and the rate of chlorhexidine release. METHODS Resin discs were prepared from light-cured, experimental resin blends (R1, R2, R3, R4 and R5) containing 0.0, 0.2, 1.0 and 2.0 wt.% chlorhexidine diacetate (CDA). Discs were immersed in distilled water at 37 degrees C, and mass changes were recorded at different periods. Spectral measurements were made to follow change in optical densities of storage solution to examine chlorhexidine release kinetics. After a 28-day period, water sorption, solubility, and the cumulative chlorhexidine release were obtained. Additionally, antibacterial study was performed by observing the presence of inhibition zone against Streptococcus mutans. RESULTS The most hydrophilic resin (R5) exhibited the highest chlorhexidine release rate. The most hydrophobic resin (R1) exhibited the lowest rate. However, no inhibition zone was produced by any specimens stored in water for 2 weeks. The addition of CDA increased solubility significantly but had no effect on water sorption. Significant positive correlations were seen between water sorption and the cumulative chlorhexidine release. SIGNIFICANCE Chlorhexidine release from resins may be related to water-induced swelling, which in turn is enhanced by the hydrophilicity of cured polymer matrix.

Oral Health-Related Quality of Life in Hong Kong Preschool Children

Objectives: To assess the impact of early childhood caries (ECC) on the quality of life in a population of preschool children and their families in Hong Kong. Methods: A random sample of 1,296 Chinese preschool children participated in the survey and were subjected to an oral examination for their ECC status by 2 trained examiners. The parents were asked to respond to the Early Childhood Oral Health Impact Scale (ECOHIS) and an extra set of questions concerning their sociodemographic background. Results:The final data analysis included 1,261 children with a mean (±SD) age of 3.9 ± 0.66 years. The prevalence figures for ECC and severe ECC were 19.9 and 15.2%, respectively. Decayed teeth were found in 34.3% of the children while only 5.2% had filled teeth. The mean (±SD) dmft in this group of children was 1.5 ± 2.98. Higher ECOHIS scores were found in parents with lower education or income level, or with children who were born in mainland China (p < 0.05), or with children who had decayed, missing, or filled teeth (p < 0.001). In multiple regression analyses, decayed teeth and filled teeth in primary dentition were the better predictors (p < 0.001) of the ECOHIS score among the various parent and child characteristics collected in this survey. Conclusions: The findings of this study showed that parents of young children with dental caries experience perceived that both the children and other family members had poorer quality of life.

Tubular Occlusion Prevents Water-treeing and Through-and-Through Fluid Movement in a Single-bottle, One-step Self-etch Adhesive Model

Water entrapment occurs at resin-dentin interfaces of one-step self-etch adhesives. We hypothesized that by preventing water fluxes from dentin, any water entrapment would be attributed to incomplete removal of adhesive solvents. We tested this hypothesis by bonding to transparent carious dentin containing occluded dentinal tubules. An experimental single-bottle, one-step self-etch adhesive was applied to flat surfaces of caries-affected dentin surrounded by sound dentin, with or without pulpal pressure. Resin-dentin interfaces were examined with TEM after silver-impregnation. Although caries-affected dentin was highly porous, adhesive layers were devoid of silver deposits when tubules were occluded. Conversely, variable extents of water-treeing and water-droplets were identified from adhesive layers in bonded sound dentin. Water-treeing and water-droplet formation, being manifestations of evaporative and convective water fluxes, can be eliminated during bonding to occluded transparent carious dentin. However, the highly porous nature of this clinically relevant substrate after bonding may lead to potentially undesirable consequences.

Effect of chlorhexidine incorporation into a self-etching primer on dentine bond strength of a luting cement.

OBJECTIVES This study investigated the effect of incorporating chlorhexidine in a self-etching primer on the bond strength of an adhesive resin cement to dentine and on antibacterial activity. METHODS Experimental self-etching primers were prepared by adding chlorhexidine (CHX) diacetate to ED primer 2.0 (Kuraray Medical Inc.) to obtain chlorhexidine concentrations of 1.0 wt% and 2.0 wt%. Human occlusal dentine surfaces were conditioned for 30 s using the experimental primers or pure ED primer. Composite blocks were luted using Panavia F 2.0 (Kuraray Medical Inc.). After storage in water for 24 h, the bonded teeth were sectioned into 0.9 mm x 0.9 mm beams and stressed to failure in tension to examine microtensile bond strength (microTBS). Fractured surfaces were examined with a field-emission scanning electron microscopy (FE-SEM). The morphology of dentine surfaces that were conditioned with each primer was also observed under FE-SEM. An agar diffusion test was performed to examine the antibacterial effect of each primer against Streptococcus mutans and Enterococcus faecalis. RESULTS Addition of chlorhexidine to the primer had significant effects (p<0.001) on microTBS and antibacterial effect. No significant difference in microTBS was found between the groups that contained 0% and 1% chlorhexidine in the primer (p=0.095). Conversely, the group that contained 2% chlorhexidine showed significantly lower microTBS and pronounced cohesive failures within the thin layer of the primer. CONCLUSIONS Incorporation of chlorhexidine into ED primer 2.0 showed significant antibacterial activities. Conditioning with the 1% chlorhexidine-containing primer had no adverse effect on microTBS.