Biomedical subjects

N M King

Publications and source records attributed to N M King.

At least 19 recordsLinked to original sources

PubMed2006

Technique sensitivity associated with air-drying of HEMA-free, single-bottle, one-step self-etch adhesives.

OBJECTIVES: This study examined the effect of air-drying on bond strength to dentin and nanoleakage in resin-dentin interfaces using HEMA-free one-step self-etch adhesives. METHODS: Twelve teeth had their occlusal dentin exposed and split in half. In the group of G-BOND (GB), the adhesive was dried gently or vigorously on each slit half tooth, and then light-cured. In the group of the experimental adhesive (EX), three coats of adhesive were dried using a single air-drying process prior to light-curing or dried after each of three coats of adhesive before light-curing. The split specimens were built-up with resin composite and then subjected to microtensile bond strength testing and TEM examination. RESULTS: GB showed significantly higher bond strength after vigorous drying than after gentle drying. Three teeth of from EX group showed higher bond strength after triple drying than after single drying, while two teeth showed no significant difference. Droplets were revealed in the adhesive layer after gentle drying with GB, and silver deposits existed along the interfaces in all groups. SIGNIFICANCE: The bonding quality to dentin may be improved by using an accelerated air-drying technique; although it is impossible to remove intrinsic dentin moisture that is drawn upwards from dentin tubules.

Acid Etching, Dental↗

PubMed2006

Association between developmental defects of enamel and different concentrations of fluoride in the public water supply.

OBJECTIVES: To compare the prevalence and severity of developmental defects of enamel (DDE) among subjects whose maxillary incisors developed during periods with different concentrations of fluoride in the public water supply. METHODS: Standardized intra-oral photographs of random samples of 12-year-old children were collected in 1983, 1991 and 2001 (n = 1,990) in Hong Kong and assessed for DDE by a trained masked examiner. The fluoride concentrations in the public water supply at the times when the enamel on their maxillary incisors developed were 1.0, 0.7 and 0.5 ppm, respectively. RESULTS: The mouth prevalence of DDE for these children (based on the maxillary incisors) were 92.1, 55.8 and 35.2% in the years 1983, 1991 and 2001, respectively (p < 0.001). Most of these children were affected by diffuse opacities (89.3% in 1983, 48.5% in 1991 and 32.4% in 2001, p < 0.001). Marked differences in the mean number of teeth affected by DDE (p < 0.001) and in the maximum extent of DDE (p <or= 0.002) between 1983, 1991 and 2001 were also observed. CONCLUSIONS: A decrease in the prevalence and severity of DDE among the maxillary incisor teeth of the children corresponded to the reductions in the concentration of fluoride in the water during the time of enamel development.

Cariostatic Agents↗

PubMed2006

Hydrolysis of functional monomers in a single-bottle self-etching primer--correlation of 13C NMR and TEM findings.

Self-etching primers/adhesives that combine acidic methacrylate monomers with water in a single bottle are hydrolytically unstable and require refrigeration to extend their shelf-lives. This study tested the null hypothesis that one year of intermittent refrigeration of a 4-MET-containing simplified self-etching primer does not result in hydrolytic changes that are identifiable by transmission electron microscopy and (13)C NMR spectroscopy. Human dentin was bonded with UniFil Bond immediately after being unpacked, or after one year of intermittent refrigeration at 4 degrees C. Fresh and aged primers were analyzed by NMR for chemical changes. Ultrastructural observations indicated that there was an augmentation in etching capacity of the aged adhesive that was not accompanied by resin infiltration or effective polymerization. New NMR peaks detected from the aged ethanol-based primer confirmed that degradation occurred initially via esterification with ethanol, followed by hydrolysis of both ester groups in the 4-MET. Hydrolysis of functional methacrylate monomers occurs despite intermittent refrigeration.

Acid Etching, Dental↗

PubMed2005

The effects of child formula toothpastes on enamel caries using two in vitro pH-cycling models.

AIMS/OBJECTIVES: To compare, using two pH-cycling models, the de/remineralisation effects of children's toothpastes on primary teeth. DESIGN: In vitro single-section and pH-cycling models. METHODS: Primary teeth were placed in demineralising solution for 96 hours to produce artificial carious lesions 60-100 microm deep. They were cut into 100 microm thick sections and assigned to 6 groups. Sections in Groups A and D were exposed to a non-fluoridated toothpaste, those in Groups B and E to half-pea-sized (0.16g) and those in Groups C and F to pea-sized portions (0.32g) of a 500ppm F toothpaste. pH-cycling Model I (Groups A, B, C), without added fluoride, ran for 7 days, while Model II (Groups D, E, F), with 0.25ppm F, ran for 10 days. OUTCOME MEASUREMENTS: Lesions were evaluated using polarised light microscopy and microradiography. RESULTS: Lesions in Groups B and E progressed by 64% and 61%, respectively, while those in Groups C and F progressed by only 19% and 23% respectively. CONCLUSIONS: Both 10-day and 7-day pH-cycling models were suitable for studying carious lesion progression in primary teeth (the demineralising and remineralising solutions of the 10-day cycling model contained 0.25ppm F). A pea-sized portion (0.32g) of 500ppm F toothpaste slowed down the demineralisation progression better than a half-pea-sized portion.

Cariostatic Agents↗

PubMed2005

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.

Acid Etching, Dental↗

PubMed2005

Incompatibility of oxalate desensitizers with acidic, fluoride-containing total-etch adhesives.

The use of oxalate desensitizers on acid-etched dentin prior to adhesive application can result in subsurface tubular occlusion by calcium oxalate crystals. However, the solubility of calcium oxalate increases in acidic solution. We hypothesized that total-etch adhesives can, depending upon their pH, interact with oxalate-desensitizer-treated dentin in an adverse manner. Acid-etched human dentin treated with 2 oxalate desensitizers (BisBlock and Super Seal) was bonded with 4 simplified total-etch adhesives: One-Step (OS), Single Bond (SB), OptiBond Solo Plus (OB), and Prime&Bond NT (PB). Composite-dentin beams were examined by SEM and TEM, both of which revealed numerous spherical globules on OB- and PB-bonded, desensitizer-treated dentin, but not in OS or SB samples. Bond strengths produced by OB and PB were significantly lower in oxalate-treated specimens than those produced by OS or SB. These surface globules may have interfered with hybridization of demineralized dentin with OB and PB resins and caused compromised bond strengths.

Analysis of Variance↗

PubMed2005

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.

Acid Etching, Dental↗

PubMed2004

Effect of resin hydrophilicity and water storage on resin strength.

This study evaluated the change in the ultimate tensile strength (UTS) of five polymerised resin blends of increasing hydrophilicity, after ageing in distilled water or silicon oil. Resin blocks were prepared from each resin blend by dispensing the uncured resin into a flexible, embedding mould, containing multiple cavities. The resins were polymerised in the moulds under nitrogen at 551.6 kPa and light-activated at 125 degrees C for 10 min. After dry ageing for 24 h at 37 degrees C, the middle third of each resin specimen was trimmed into an 'I' shape. Fifteen control specimens were randomly selected from each resin blend for baseline UTS evaluation. The UTS of the experimental specimens were determined after 1, 3, 6 and 12 months of ageing in water or oil. The UTS of each group of resins at different storage periods in water or oil were analysed using the Friedman multiple ANOVA on ranks and Dunn's multiple comparison tests at 95% confidence level. Significant reduction (p < 0.01) in UTS was observed in Groups II-V resins after 12-month storage in water, while the most hydrophobic Group I resin showed no significant change (p > 0.05) in the same period. The percentage reduction in UTS increased with the hydrophilicity of the resin blends. Long-term water storage of hydrophilic resin blends such as those employed in dentine adhesives, resulted in a marked reduction in their mechanical strength that may compromise the durability of resin-dentine bonds.

Absorption↗

PubMed2004

Interaction of resin-modified glass-ionomer cements with moist dentine.

OBJECTIVES: The objective of this study was to report on a novel phenomenon that occurs when resin-modified glass-ionomer cements (RMGICs) are bonded to moist human dentine. METHODS: Dentine surfaces from extracted third molars were abraded with 180-grit SiC paper. Ten teeth were prepared for each of the two RMGICs tested (Fuji II LC, GC Corp. and Photac-Fil Quick, 3M ESPE). RMGIC buildups were made according to the manufacturers' instructions. After storage at 37 degrees C, 100% humidity for 24 h, the bonded specimens were cut occlusogingivally into 0.9 x 0.9 mm beams. Dentine surfaces bonded with the two RMGICs were examined along the fractured RMGIC/dentine interfaces. Additional beams fractured within the RMGICS and at 3 mm away from the interfaces were used as controls. The fractured beams were examined using scanning electron microscopy (SEM), field emission-environmental SEM (FE-ESEM) and transmission electron microscopy (TEM). RESULTS: SEM and FE-ESEM revealed numerous solid spherical bodies along the RMGIC/dentine interfaces. By contrast, no spherical bodies could be identified within the RMGIC fractured 3 mm distant from the bonded interface. TEM and energy dispersive X-ray analyses performed on carbon-coated ultrathin sections showed that these solid spherical bodies consisted of a thin aluminum and silicon-rich periphery and an amorphous hydrocarbon core within the air voids of the original resin matrix. CONCLUSION: The spherical bodies probably represent a continuation of GI reaction and poly(HEMA) hydrogel formation that results from water diffusion from the underlying moist dentine. Their existence provides evidence for the permeation of water through RMGIC/dentine interfaces.

Aluminum↗

PubMed2004

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.

Adhesiveness↗

PubMed2004

Osmotic blistering in enamel bonded with one-step self-etch adhesives.

One-step self-etch adhesives behave as permeable membranes after polymerization, permitting water to move through the cured adhesives. We hypothesize that osmotic blistering occurs in bonded enamel when these adhesives are used without composite coupling. Tooth surfaces from extracted human premolars were bonded with 5 one-step self-etch adhesives. They were immersed in distilled water or 4.8 M CaCl(2), and examined by stereomicroscopy, field-emission/environmental SEM, and TEM. Water blisters were observed in bonded enamel but not in bonded dentin when specimens were immersed in water. They collapsed when water was subsequently replaced with CaCl(2). Blisters were absent from enamel in specimens that were immersed in CaCl(2) only. Water trees were identified from adhesive-enamel interfaces. Osmotic blistering in enamel is probably caused by the low water permeability of enamel. This creates an osmotic gradient between the bonded enamel and the external environment, causing water sorption into the interface.

Acid Etching, Dental↗

PubMed2004

A simplified technique for the restoration of severely mutilated primary anterior teeth.

The restoration of severely carious primary anterior teeth is a challenge to the pediatric dentist. The introduction of new materials and technologies makes re-evaluation of existing treatment philosophies necessary. A technique involving the placement of an omega shaped stainless steel wire extension into the entrance of the root canal prior to restoring the crown with a compomer material is described. 96 restorations were placed in 25 children. After 18 months 81.2% of the 96 restorations, which were available for evaluation, 60 (79.9%) were intact. The technique for restoring primary anterior teeth was simple, quick and effective.

Child, Preschool↗

PubMed2004

Van der Woude syndrome: a report of two cases.

Van der Woude syndrome is a rare autosomal dominant condition with high penetrance and variable expression. It consists of a cleft lip and/or palate pits on the vermilion of the lower lip, and hypodontia. Two cases of congenital lip pits with cleft lip and alveolus and an isolated cleft palate are described to illustrate the variable presentation of the clinical features and the importance of early recognition of Van der Woude syndrome because of the genetic implications.

Anodontia↗

PubMed2003

Clinical considerations in the provision of restorative dental treatment for children under general anaesthesia: a review.

AIM: Dental treatment under general anaesthesia is one of the options for young or uncooperative children, and disabled patients. However, special considerations are necessary before proceeding with this form of anaesthesia. This article reviews the indications, complications and safety factors, the anatomic and physiological considerations, drug interactions, current treatment outcomes and the reasons for repeated anaesthesia for the provision of dental treatment under general anaesthesia for children.

Anesthesia, Dental↗

PubMed2002

Feeding and oral hygiene habits of preschool children in Hong Kong and their caregivers' dental knowledge and attitudes.

OBJECTIVES: This study was designed to gather data on infant feeding habits and oral hygiene practices of Hong Kong preschool children, on the dental knowledge and attitudes of their caregivers and on the oral health status of the same group of children. DESIGN: Cross-sectional study. SAMPLE AND METHODS: Data was gathered for a total of 369 boys and 297 girls (207 1-year-olds, 269 2-year-olds and 190 3-year-olds) with a mean age of 20.19 (+/- 0.38) months. Information related to children attending six randomly selected Maternity and Child Health Centres. It was obtained by examining the children and by interviewing the attending caregivers and completing a questionnaire. Each child was given an oral examination using a torch, disposable mirror and wooden tongue spatula. RESULTS: Only 7% of the children were exclusively breast-fed. More than 98% (656/666) of infants used a nursing bottle for at least some drinks. Over 62% (411/656) had used a nursing bottle to take fluids other than water and infant formula. At bedtime, 56% (361/656) were given a nursing bottle prior to sleep and 96% (340/361) of these bottles contained formula milk. Of these children, only 37% (131/361) finished the contents of the bottle before falling asleep. Over 73% (139/190) of the children continued to use a feeding bottle after 2 years of age. Non-nutritive sucking habits were practised by 35.6% (237/666) of the children. Visible plaque, on the labial surface of at least two maxillary incisors, was found in 19.5% (120/615) of the children. Oral cleansing habits were practised for 66.2% (441/666) of the children. Toothbrushing habits were reported for 42.3% (260/615) of the dentate children, of whom 19% (49/260) had their teeth brushed twice daily. Toothpaste was used by 49.23% (128/260) of the children and 57.3% (149/260) brushed their own teeth. Caries was seen in 7.6% of the infants (47/615). Of the caregivers, 67.7% said they did not think carious primary teeth needed to be restored. Among the mothers, 12.6% (43/342) did not know the oral condition of their child. Reportedly, 82% (417/510) and 87.5% (446/510) of the mothers had not received any oral health care information during the ante- or postnatal periods. Nearly all, 97%, of the respondents said that they would like to receive more information on oral health care.

Age Factors↗

PubMed2002

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.

Acid Etching, Dental↗

PubMed2002

Oral-facial-digital syndrome, Type I: a case report.

Oral-facial-digital syndrome is a group of congenital anomalies, which affects the face, oral structures and digits. There are nine subtypes. OFDS type I, is x-linked dominant trait mostly affecting females. Reports of OFDS type 1 in Asians are extremely rare. This paper shows a case of OFDS type 1, in a southern Chinese girl, who in addition to most of the classic features, had fusion of the mandibular canine and lateral incisor teeth.

Anodontia↗

PubMed2001

A comparison of the supra-alveolar pulp size of impeded and unimpeded mandibular rat incisors using micro-computed tomography.

The pulp space is almost totally obliterated in the incisal end of a mandibular rat incisor. Repeated shortening of the incisor has been shown to increase the pulp space below the alveolar bone level; however, little is known about that above the alveolar bone level. This study investigated the changes in the pulp space superior to the bone level after rendering the incisor unimpeded for a period of three weeks. A desktop micro-computed tomography scanning unit, which is non-invasive, non-destructive, accurate, less technique sensitive and less time consuming than conventional methods, was used to calculate the volume of the pulp space. The results showed that the pulp size increased 140% at a level 3 mm below the alveolar bone margin and more than 700% at a level 2.5 mm above the alveolar bone. Moreover, the bone level of the unimpeded incisor was found to move incisally 0.4-0.5 mm; while deposition of dentine on the mesial and distal aspects of the pulp space were affected differently to that on the buccal and lingual sides.

Animals↗