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Biomedical subjects

W H Lan

Publications and source records attributed to W H Lan.

54 records · Page 3Linked to original sources
PubMed1992

Collagen gene expression in human dental pulp cell cultures.

Pulp cells from human permanent molars were isolated and established in culture; 40% showed positive alkaline phosphatase staining. When incubated with 50 micrograms/ml of ascorbic acid and 10 mM of beta-glycerophosphate, the cells formed a mineralized extracellular matrix; they could thus have the potential to differentiate into odontoblast-like cells in vitro. Collagen synthesis was analysed by SDS interrupted gel electrophoresis, Northern blot and slot blot: the cells produced predominantly (approximately 99%) type I collagen and only trace amount of type III collagen. The ratio of alpha 1 (I) to alpha 2(I) procollagen chains was about 68:32, indicating that no significant amount of collagen type I trimer was synthesized in this system. The ratios of alpha 1(I), alpha 2(I) and alpha 1(III) procollagen mRNAs were about 61:25:1; these were compatible with the ratios of corresponding procollagen alpha chains. In addition, a novel 5.8 kb pro alpha 1(III) mRNA was detected. These observations indicate that collagen synthesis in these cultured pulp cells was regulated at the transcriptional level.

Adolescent↗
PubMed1991

Histopathologic effects of electric dosage in iontophoresis on dental pulp.

It is well recognized that dental pulp is very sensitive to electricity. However, the extent of damage and the repair capacity of pulp tissue after the electrical excitation of iontophoresis remains to be determined. Electrical current was applied to the simian teeth via cavities on the buccal or occlusal surfaces. The current strength was set at 0.1 mA-0.4 mA. The application duration was either 1 minute or 3 minutes. The total dose of electricity received by the iontophoresed teeth varied from 0.1 mA-minute to 1.2 mA-minutes. The pulps were microscopically examined at 4, 8, and 12 weeks after electrical excitation. All of the teeth were collected and processed using routine histologic methods. The following results were obtained: (1) in the group with 1-minute iontophoresis, the histologic pictures showed no apparent differences among the specimens regardless of the strength of the current applied; (2) in the group with 3-minute iontophoresis, the pulpal response correlated positively with current strength; and (3) with an electrical current of no greater than 0.4 mA and an application period of less than 3 minutes, the pulpal changes were reversible. We conclude that iontophoresis may accelerate the repair process, if the application duration is less than 3 minutes.

Animals↗
PubMed1990

[A evaluation of chlorhexidine as an endosonic irrigan].

Chlorhexidine has been utilized as a root canal irrigant since 1971. It is a broad-spectrum antimicrobial agent with minimal toxicity and residual long-term antibacterial capability. Although a sodium hypochlorite solution has been shown to have a better antimicrobial effect than chlorhexidine, its corrosive effect has prevented its further use especially since the in vitro antimicrobial effect of chlorhexidine has been shown to not be much less. However, the efficacy of chlorhexidine as an endodontic irrigant and intracanal medicament, requires further research in vivo. Therefore, in this study, the clinical effects of chlorhexidine were evaluated by comparing its antimicrobial properties with other endodontic irrigants. One hundred and fifty teeth were selected and evenly divided into 6 groups according to their pathological status. The root cancals were prepared with conventional hand filing or ultrasonic filing, respectively, and were rinsed singly with either chlorhexidine, EDTA or distilled water. The contents of each root canal before or after debridement were cultured in an incubator. The results showed that chlorhexidine with hand filing in one week and with endosonics in 48 hours had a better antimicrobial effect than did EDTA. As compared with the control group (distilled water), chlorhexidine showed marked antimicrobial effect in both hand and endosonic filing. It is concluded that chlorhexidine has an antibacterial effect as an endodontic irrigant in clinical applications.

Bacteria↗
PubMed1989

[Solvent action of sodium hypochlorite on fresh and formalin fixed tissue: a biochemical approach].

Debridement of the root canal system has long been recognized as the critical phase of success in endodontic therapy. Because of the morphological complexity of most root canals, complete removal of the pulp tissue during the mechanical preparation of these root canals is often impracticable. Sodium hypochlorite is thus currently favored by most endodontists as the routine irrigant on account of its antimicrobial action and its capacity to dissolve fresh tissue together with necrotic tissues. Formocresol is another common medicament for endodontic treatment and is usually used for pulpotomy, pulpectomy and intracanal medication. Nevertheless, it was empirically believed that formocresol may interrupt the action of sodium hypochlorite in the dissolution of residual tissue. Therefore, the present study was undertaken to testify whether formocresol can substantially retard the solvent action of sodium hypochlorite by comparing the effectiveness of 5% sodium hypochlorite on fresh and formalin-fixed tissues. Connective tissue from the abdominal wall of Sprague-Dawley rats was cut into pieces weighing 0.05 g and measuring about 2 x 10 x 10 mm. A total of 20 pieces of tissue were collected and divided into two groups: 10 pieces were used immediately as the fresh-tissue group; the other 10 pieces were fixed in 10% formalin for 7 days as the fixed-tissue group. Each group was then immersed in 5 ml of 5% sodium hypochlorite for 60 seconds, and 1 ml was aspirated from each for assay. Dialysis was performed using 2 liters of double distilled water for a period of 4 hours with the water changed hourly.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Histopathologic effects of various electric dosage on the dental pulp of the monkey with iontophoresis.

Iontophoresis may enhance the efficacy of some medicaments and help them to reach inaccessible parts of the treated area. However, the extent of tissue damage and its recovery after electric excitation remain to be determined. An animal experiment was performed to find out the proper combination of electric current and applied duration in iontophoresis that did no irreversible harm to the pulp tissue. Cavities of 2mm in diameter and 1-2mm in depth were prepared on the buccal or occlusal surfaces of the teeth of monkeys. The strength of electric current was regulated to 0.1 mA, 0.2 mA, 0.3mA and 0.4 mA, respectively. The applied duration was 1 or 3 minutes. The total amount of electricity received by the iontophoresed teeth varied from 0.1 mA-min to 1.2 mA-min in dosage. Observation was made at 4 weeks, 8 weeks and 10 weeks after experiments. The teeth, including the surrounding jaw bone, were resected and prepared for histopathologic study. The following results were obtained: (1) In the group with one-minute iontophoresis, the histologic pictures showed no apparent difference among the specimens regardless of the strength of the electric current applied and were similar to that of the control group. (2) In the group with 3-minute iontophoresis, pulp response correlated with an increase in the electric current applied. (3) Obvious histopathologic changes were shown in the 4-week specimens, mostly odontoblast disruption, vascular dilatation, hemorrhage and round cell infiltration. (4) Subsequent investigation of the 8-week specimens as well as the 10-week specimens revealed that the reparative process in the damaged pulp took a lot of time to heal.

Animals↗
PubMed1988

[A clinical evaluation of antimicrobial effectiveness of EDTA as an endosonic irrigant].

Recently the chelating agent EDTA has gained increasing attention by dentists, in view of the facts that it does not produce deleterious or corrosive effect when used as an irrigant for root canal debridement. However, the efficacy of EDTA as an irrigant in clinical practice is still not clear. Therefore, in this study EDTA was adopted as an irrigant alone to evaluate its antimicrobial effect as a reference for subsequent clinical application. One hundred single-root teeth were selected and evenly divided into 4 groups. The root canals were prepared with conventional hand filing or ultrasonic filing respectively and the canals were rinsed singly with either EDTA or distilled water for contrast. The contents of each root canal before and after debridement were cultured in an incubator. The results showed that EDTA with hand filing in 48 hours and with endosonics in both 48 hours and one week had better antimicrobial effect than did distilled water. The results also indicated that EDTA combined with endosonics manifested the best antimicrobial effect among the four groups in this experiment. The above-mentioned differences were statistically significant at the level of p less than 0.05 by Fisher's exact test.

Bacteria↗
PubMed1986

Slicing technique for tooth specimens in histological preparation.

A slicing technique for the preparation of a tooth specimen is described. A low speed saw (ISOMET) was used for this modified technique. It is a slicing machine fitted with a diamond-impregnated cutting disc of 0.5 mm in thickness. The formalin was used for lubrication to serve as both a coolant and a fixative simultaneously. It is thought that the preparation will not damage or disturb the surface of the tooth specimen by careful management under 200 rpm with a loading of 50 grams. The cutting of slices can be controlled by adjusting the specimen arm with a micrometer to the desired thickness. A high quality histological preparation can be obtained when the specimen is sliced as mentioned above soon after it is removed from the living body before decalcification. By the observation of specimens such as the resected jaw bone or other large hard tissue specimens, it is suggested that the sliced specimens of 2 mm in thickness can be obtained routinely for histological study by using this method.

Animals↗
PubMed1978

Neutralization effect of some agents on the antimicrobial activity of ammoniacal silver nitrate.

The effect of some agents on the antimicrobial activity of ammoniacal silver nitrate, an endodontic medicament, was tested with Streptococcus faecalis by the serial tube dilution method. Its results indicated that sodium hypochlorite, hydrogen peroxide, and blood had a marked inhibitory effect. However, the presence of dentin, necrotic tissue, saliva, and hydrogen sulfide gas liberated from protein decomposition showed no or little effect on the antibacterial properties of the chemical. Since antiseptics or antibiotics generally may be decomposed by necrotic tissues, these findings suggested that the use of ammoniacal silver nitrate not only may resolve the problem of recalcitrant cases in endodontic treatment but also may simplify the disinfecting procedure for root canals.

Animals↗
PubMed1977

Efficacy of ammoniacal silver nitrate in root canal therapy.

In order to find a simple and effective method for endodontic treatment of recalcitrant cases, the efficacy of ammoniacal silver nitrate was re-evaluated. The modified serial tube dilution method was conducted to determine the effective antimicrobial concentration of ammoniacal silver nitrate on selected test microorganisms and clinical isolates. The effective antimicrobial concentration for the most resistant microorganism, Streptococcus faecalis, was 5.0 X 10(-10) g/ml and the effectiveness persisted for several days. The diffusion ability of 4% ammoniacal silver nitrate into the dentinal tubules from root canal wall was also tested with freshly extracted teeth treated as in routine procedure for root canal therapy. The diffusibility was evident and the extent of infiltration was various, with more infiltration at cervical dentin than at apical one.

Ammonia↗