Biomedical subjects

Hak-Kong Yip

Publications and source records attributed to Hak-Kong Yip.

8 recordsLinked to original sources

PubMed2004

Direct detection of cell surface interactive forces of sessile, fimbriated and non-fimbriated Actinomyces spp. using atomic force microscopy.

Actinomyces species are predominant early colonizers of the oral cavity and prime mediators of inter-bacterial adhesion and coaggregation. Previous workers have evaluated the adhesion of Actinomyces spp. by quantitative assessment of sessile, as opposed to planktonic cells attached to substrates, but did not quantify the cell surface interactive forces. Therefore we used atomic force microscopy to directly detect the interactive force between an approaching silicon tip and sessile Actinomyces spp. adhering to a substrate, at nanonewton (nN) range force levels. A total of eight strains each belonging to fimbriated and non-fimbriated Actinomyces species were employed, namely A. bovis, A. gerencseriae, A. israelii, A. meyeri, A. naeslundii genospecies 1 and 2, A. odontolyticus and A. viscosus. The sterile mica discs, used as the adhesion substrate, were immersed in mono-species bacterial suspensions for five days to obtain a thin bacterial biofilm. Interactive forces were measured using a silicon nitride cantilever attached to a Nanoscope IIIA atomic force microscope. The interactive forces between the approaching silicon nitride tip and bacterial biofilm surfaces were randomly quantified at three different locations on each cell; namely, the cell surface proper, the periphery of the cell and the substrate and, the interface between two cells. When the interactive forces at these locations of the same species were compared, significantly higher force levels at the cell-cell interface than the other two locations were noted with A. gerencseriae (P < 0.001), A. viscosus (P < 0.01) and A. israelii (P < 0.05). When the interactive forces of different Actinomyces spp. at an identical location were compared, fimbriated A. naeslundii genospecies 2 showed the greatest interactive force at the cell surface proper (-32.6 +/- 8.7 nN, P < 0.01). A. naeslundii genospecies 1, 2 and A. viscosus demonstrated greater interactive force at the cell-mica periphery than the other five species (P < 0.05); A. viscosus (-34.6 +/- 10.5 nN) displayed greater interactive force at the cell-cell interface than the others (P < 0.01), except for A. gerencseriae (P > 0.05). These data indicate that fimbriated Actinomyces spp., including A. naeslundii genospecies 1, 2 and A. viscosus exert higher cell surface interactive forces than those devoid of fimbriae and, such variable force levels may modulate their adhesion and coaggregation during biofilm formation.

Actinomyces↗

PubMed2004

In vitro growth, acidogenicity and cariogenicity of predominant human root caries flora.

Streptococcus mutans (Sm), Lactobacillus acidophilus (La) and Actinomyces israelii (Ai) have been associated with root surface caries, which is an increasing problem in elderly Chinese. The aim of this study therefore, was to evaluate in vitro, the growth, acidogenicity and cariogenicity of these organisms, both in mono- and co-cultures using an in vitro model. Forty-eight root specimens were prepared using intact extracted human molars. Fresh, wild-type bacteria obtained from root caries lesions were assembled into seven experimental groups as either mono- or co-cultures and incubated with the root specimens. Appropriate controls were included. Growth curve of each experimental group was monitored for 24h, aerobically, at 37 degrees C using a microplate reader. The pH of the medium was recorded after 24-h incubation using a pH meter. Mean depths of artificial root lesions produced in each cultural group were measured using polarized light microscopy in specimens cut into thin sections (100+/-20 microm). Compared with mono-cultures, synergistic growth was observed in co-cultures of 'La+Sm', 'Ai+La' and 'Ai+La+Sm'. Mean lesion depth produced in La group was significantly shallower than other mono- or co-culture groups (p<0.01). The pH values of all culture media were similar after 24-h incubation. The current data elucidate the complex interactions of three predominant bacterial species considered prime agents of human root surface caries.

Acids↗

PubMed2003

Artificial mouth model systems and their contribution to caries research: a review.

The complexity of the oral environment, and ethical problems associated with studies of oral diseases in humans inevitably directed the attention to development of laboratory models, that simulate the human oral microcosm. These developments and in particular the in vitro 'artificial mouth' systems have progressed from simple and basic apparatus devised by Magitot and Miller at the end of 19th century to the currently available, highly sophisticated, computer-controlled, multi-station artificial mouth systems. These advances have metamorphosed from the early studies devised primarily to investigate factors affecting the carious process to the present designs that evaluate growth, pathogenicity, metabolism and mineralization of dental plaque under highly controlled conditions. The modern 'artificial mouth systems' can evaluate microbial interactions in simulated dental plaque and similar biofilms and monitor their physical, chemical, biological and molecular features to a very high degree of accuracy. We review and trace here the historical aspects and developments leading to the currently available artificial mouth systems and discuss their contribution to the study of oral flora, especially related to many variants of dental caries.

Biofilms↗

PubMed2003

Direct detection of Actinomyces spp. from infected root canals in a Chinese population: a study using PCR-based, oligonucleotide-DNA hybridization technique.

OBJECTIVES: The poor sensitivity of phenotypic identification techniques has hampered the taxonomic differentiation of Actinomyces. Hence we developed a sensitive and specific, PCR-based oligonucleotide-DNA hybridization technique to detect Actinomyces spp. and, used this method to detect these organisms in samples directly obtained from infected root canals. METHODS: A total of 32 samples from 28 Chinese patients, with primary root canal infections, aseptically exposed at the first patient visit, were studied. Whole bacterial genomic DNA was isolated directly from paper point samples. The variable regions of 16S ribosomal DNA of bacteria were amplified and labeled with digoxigenin for further hybridization and detection. A total of seven oligonucleotide probes specific for A. bovis, A. gerencseriae, A. israelii, A. meyeri, catalase-negative A. naeslundii (genospecies 1 and 2), catalase-positive A. naeslundii genospecies 2 and A. odontolyticus were used. RESULTS: 16 of the 32 teeth were infected with one or more Actinomyces species. The prevalence rates of the examined species were: A. odontolyticus 31.3%, A. meyeri 9.4%, A. naeslundii 9.4%, A. israelii 6.3% and A. gerencseriae 3.1%; no A. bovis was detected in any of the canals. Furthermore, A. odontolyticus was isolated more frequently from root canals with caries or a history of caries (Fisher's exact test: P=0.0496; Odds ratio=9.00, 95% confidence interval: 0.97-83.63), and A. naeslundii was significantly associated with traumatized teeth (Fisher's exact test: P=0.0121; Odds ratio=57.00, 95% confidence interval: 2.10-1546.90). However, no significant correlation was found between Actinomyces spp. and clinical symptoms and signs, such as pain, swelling, percussion to tenderness, sinus and periapical radiolucency. CONCLUSION: Actinomyces spp. may be important pathogens of root canal infections. A. naeslundii in particular may be related with traumatized teeth. A. odontolyticus appears to be involved in infections related to caries, exposure of dentinal tubules during cavity preparation and/or leaking restoration, but further clarification with large samples is necessary.

Actinomyces↗

PubMed2002

Supragingival calculus: formation and control.

Dental calculus is composed of inorganic components and organic matrix. Brushite, dicalcium phosphate dihydrate, octacalcium phosphate, hydroxyapatite, and whitlockite form the mineral part of dental calculus. Salivary proteins selectively adsorb on the tooth surface to form an acquired pellicle. It is followed by the adherence of various oral micro-organisms. Fimbriae, flagella, and some other surface proteins are essential for microbial adherence. Microbial co-aggregation and co-adhesion enable some micro-organisms, which are incapable of adhering, to adhere to the pellicle-coated tooth surface. Once organisms attach to the tooth surface, new genes could be expressed so that mature dental plaque can form and biofilm bacteria assume increased resistance to antimicrobial agents. Supersaturation of saliva and plaque fluid with respect to calcium phosphates is the driving force for plaque mineralization. Both salivary flow rate and plaque pH appear to influence the saturation degree of calcium phosphates. Acidic phospholipids and specific proteolipids present in cell membranes play a key role in microbial mineralization. The roles of crystal growth inhibitors, promoters, and organic acids in calculus formation are discussed. Application of biofilm culture systems in plaque mineralization is concisely reviewed. Anti-calculus agents used--centering on triclosan plus polyvinyl methyl ether/maleic acid copolymer, pyrophosphate plus polyvinyl methyl ether/maleic acid copolymer, and zinc ion-in commercial dentifrices are also discussed in this paper.

Bacterial Adhesion↗

PubMed2002

Comparison of atraumatic restorative treatment and conventional cavity preparations for glass-ionomer restorations in primary molars: one-year results.

OBJECTIVE: The purpose of this study was to compare the success rates of glass-ionomer cement restorations placed with the atraumatic restorative treatment approach and conventional cavity preparation methods. METHOD AND MATERIALS: Two encapsulated, high-strength, esthetic conventional glass-ionomer cements were placed in 82 Class I and 53 Class II atraumatic restorative treatment and conventional cavity preparations, and an encapsulated amalgam alloy was placed in 32 Class I conventional preparations, in vital primary molars of 60 Chinese children aged 7 to 9 years. RESULTS: The atraumatic restorative treatment preparations, made with hand instruments only, took approximately 50% longer to complete than did the preparations completed with conventional rotary instrumentation. After 1 year, there were no amalgam failures. For the glass-ionomer cement restorations, when the atraumatic restorative treatment method was used, significantly better survival rates were found for Class I (92.9%) than for Class II (64.7%) cavity preparations. There was also a strong trend for relatively better survival rates for the conventional cavity preparation method (86.7%) than for the atraumatic restorative treatment (64.7%) method for Class II cavity preparations. However, both the atraumatic restorative treatment and conventional methods appeared equally effective for Class I preparations. CONCLUSION: In a clinic setting, the use of atraumatic restorative treatment hand instruments for cavity preparation is more time consuming, and the method may also provide less mechanical retention and/or bulk of glass-ionomer cement for some Class II preparations in primary molars than does the use of conventional rotary instruments.

Child↗

PubMed2002

The atraumatic restorative treatment (ART) approach for the management of dental caries.

There is worldwide interest in and increasing usage of the conservative atraumatic restorative treatment technique or approach for the restoration of primary and permanent teeth. However, most published data on the clinical performance of the newer, high-strength esthetic conventional glass-ionomer restorative cements marketed for the procedure have been derived from short-term studies. There have been very few reports comparing different types of restorative materials and methods of cavity preparation. In primary teeth, after 1 year, success rates have been approximately 80% to 95% for Class I and Class V single-surface restorations, 55% to 75% for Class II multisurface restorations, and 35% to 55% for Class III and Class IV restorations. In permanent teeth, after 2 to 3 years, success rates have been approximately 90% for Class I and Class V single-surface restorations, but little data have been reported for other restoration classes. Failures usually result from restoration losses, fractures, and wear. Further improvements in the design of hand instruments and in the mechanical properties of the newer glass-ionomer cements are required. Currently, use of the atraumatic restorative treatment approach should be restricted to restoration of single-surface caries lesions, especially in permanent teeth, and to sealing of occlusal fissures in selected teeth.

Dental Bonding↗

PubMedDate not supplied

Management of tooth tissue loss from erosion.

Erosive tooth wear appears to be no less frequent in the United States than in the United Kingdom and Europe and is of increasing concern as a significant cause of tooth destruction in younger persons. Consumption of numerous dietary sources of acids is increasing in modern societies. In addition, involuntary regurgitation may be a significant cause of tooth erosion. These primary causes can be exacerbated by xerostomia, which is induced by many drugs. Initial preventive treatments are directed at neutralizing the effects of the acids, and initial restorative treatments should be conservative, using adhesive materials. Treatment of advanced tooth tissue loss is difficult and expensive, and preventive management is emphasized.

Acids↗