Cynthia K.Y. Yiu

Aging Affects Two Modes of Nanoleakage Expression in Bonded Dentin

Water sorption into resin-dentin interfaces precedes hydrolytic degradation. We hypothesized that these processes are morphologically manifested by the uptake of ammoniacal silver nitrate, which is thought to trace hydrophilic domains and water-filled channels within matrices. Water sorption is thought to be nonuniform and can be traced by the use of silver nitrate. Human teeth bonded with an experimental filled-adhesive were aged in artificial saliva (experimental) or non-aqueous mineral oil (control). Specimens retrieved for up to a 12-month period were immersed in 50 wt% ammoniacal silver nitrate and examined by transmission electron microscopy for identification of the changes in their silver uptake. Reticular silver deposits initially identified within the bulk of hybrid layers in the experimental group were gradually reduced over time, but were subsequently replaced by similar deposits that were located along the hybrid layer-adhesive interface. Silver uptake in water-binding domains of the adhesive layers increased with aging, resulting in water tree formation. These water-filled channels may act as potential sites for hydrolytic degradation of resin-dentin bonds.

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.

Differences between top-down and bottom-up approaches in mineralizing thick, partially demineralized collagen scaffolds

Biominerals exhibit complex hierarchical structures derived from bottom-up self-assembly mechanisms. Type I collagen serves as the building block for mineralized tissues such as bone and dentin. In the present study, 250-300 μm thick, partially demineralized collagen scaffolds exhibiting a gradient of demineralization from the base to surface were mineralized using a classical top-down approach and a non-classical bottom-up approach. The top-down approach involved epitaxial growth over seed crystallites. The bottom-up approach utilized biomimetic analogs of matrix proteins to stabilize amorphous calcium phosphate nanoprecursors and template apatite nucleation and growth within the collagen matrix. Micro-computed tomography and transmission electron microscopy were employed to examine mineral uptake and apatite arrangement within the mineralized collagen matrix. The top-down approach could mineralize only the base of the partially demineralized scaffold, where remnant seed crystallites were abundant. Minimal mineralization was observed along the surface of the scaffold; extrafibrillar mineralization was predominantly observed. Conversely, the entire partially demineralized scaffold, including apatite-depleted collagen fibrils, was mineralized by the bottom-up approach, with evidence of both intrafibrillar and extrafibrillar mineralization. Understanding the different mechanisms involved in these two mineralization approaches is pivotal in adopting the optimum strategy for fabricating novel nanostructured materials in bioengineering research.

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.

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.

Interaction of Glass-ionomer Cements with Moist Dentin

Glass-ionomer cements (GICs) are regarded as aqueous gels made up of polyalkenoic acid salts containing ion-leachable glass fillers. The consequence of water permeation across the GIC-dentin interface is unknown. This study used SEM, field-emission/environmental SEM (FE-ESEM), and TEM to examine the ultrastructure of GIC-bonded moist dentin. Dentin surfaces bonded with 6 auto-cured GICs were examined along the fractured GIC-dentin interfaces. Additional specimens fractured 3 mm away from the interfaces were used as controls. SEM revealed spherical bodies along GIC-dentin interfaces that resembled hollow eggshells. FE-SEM depicted similar bodies with additional solid cores. Energy-dispersive x-ray analysis and TEM showed that the spherical bodies consisted of a silicon-rich GIC phase that was absent from the air-voids in the controls. The GIC inclusions near dentin surfaces result from a continuation of the GI reaction, within air-voids of the original polyalkenoate matrix, that occurred upon water diffusion from moist dentin.

A comparison of a generic and oral health–specific measure in assessing the impact of early childhood caries on quality of life

OBJECTIVES The aim of this study was to compare the performance of a generic health-related quality-of-life measure, the Pediatric Quality of Life Inventory Version 4.0 (PedsQL 4.0) and an oral health-specific quality-of-life measure, the Early Childhood Oral Health Impact Scale (ECOHIS) in assessing the impact of severe early childhood caries (S-ECC) on the childrens quality of life. METHODS A trained and calibrated examiner conducted a clinical oral assessment of 111 children (mean age: 49 +/- 12 months): 64 of whom were categorized as having S-ECC and 47 as being caries-free. Primary caregivers completed a Chinese version of the PedsQL 4.0 and the ECOHIS. Clinical examinations were conducted blind of the parental assessments. RESULTS The ECOHIS scores were significantly higher for the S-ECC group than for the caries-free group (P < or = 0.001). No significant difference was found between the PedsQL 4.0 scores in relation to caries status, except for the subscale of physical functioning (P = 0.04). Correlation of caries status with the ECOHIS scores was strong (r = 0.66; P < 0.01). No significant correlation was found between PedsQL 4.0 scores and caries status (r = 0.02; P > 0.05). CONCLUSIONS The oral health-specific measure, ECOHIS, shows better discriminant property between children with S-ECC and caries-free children than the generic measure, PedsQL 4.0. The ECOHIS appears more sensitive than PedsQL 4.0 in assessing the impact of dental caries on the life quality of preschool children.

Translation and validation of a Chinese language version of the Early Childhood Oral Health Impact Scale (ECOHIS)

OBJECTIVE This study aimed to adapt the Early Childhood Oral Health Impact Scale (ECOHIS) for pre-school children in a Chinese speaking community and to investigate its psychometric properties (validity and reliability). METHODS A Chinese language version of the ECOHIS was derived through a forward-backward translation and tested for face and content validity among a focus group. A convenient sample of pre-school children (n = 111) was recruited (including a sub-sample with early childhood caries and caries-free children). Parents of the children self-completed the derived Chinese-ECOHIS measure. Validity of the measure was assessed by investigating the relationship between dental caries status and Chinese-ECOHIS scores (construct and criterion validity). A sub-sample of the parents repeated the ratings of the measure to enable reliability assessments. Both internal and test-retest reliability were determined. RESULTS A Chinese version of ECOHIS was derived with minor modification to the original version. Chinese-ECOHIS scores were associated with childrens caries experience (dmft) (r = 0.66, P < 0.05) supporting convergent validity. In addition, variations in ECOHIS scores were apparent with respect to caries and caries-free groups (P < 0.001), supporting the ability to distinguish between patient groups. Cronbachs alpha values (internal reliability) for total ECOHIS score were 0.91 and intraclass correlation coefficient value (test-retest reliability) was 0.64. CONCLUSIONS A Chinese version of the ECOHIS was developed and demonstrated acceptable validity and reliability. These findings can enable assessments of pre-school child oral health-related quality of life in Chinese speaking communities.

Quaternary ammonium silane-functionalized, methacrylate resin composition with antimicrobial activities and self-repair potential.

The design of antimicrobial polymers to address healthcare issues and minimize environmental problems is an important endeavor with both fundamental and practical implications. Quaternary ammonium silane-functionalized methacrylate (QAMS) represents an example of antimicrobial macromonomers synthesized by a sol-gel chemical route; these compounds possess flexible Si-O-Si bonds. In present work, a partially hydrolyzed QAMS co-polymerized with 2,2-[4(2-hydroxy 3-methacryloxypropoxy)-phenyl]propane is introduced. This methacrylate resin was shown to possess desirable mechanical properties with both a high degree of conversion and minimal polymerization shrinkage. The kill-on-contact microbiocidal activities of this resin were demonstrated using single-species biofilms of Streptococcus mutans (ATCC 36558), Actinomyces naeslundii (ATCC 12104) and Candida albicans (ATCC 90028). Improved mechanical properties after hydration provided the proof-of-concept that QAMS-incorporated resin exhibits self-repair potential via water-induced condensation of organic modified silicate (ormosil) phases within the polymerized resin matrix.