Protective properties of salivary pellicles from two different intraoral sites on enamel erosion.

The purpose of this study was to investigate the protective effect and ultrastructure of salivary pellicles formed in vivo near the orifices of the ducts of parotid and submandibular/sublingual salivary glands. Pellicles were formed by exposing bovine enamel slabs to the oral environment at the buccal aspect of the upper first molars and at the lingual aspect of the lower incisors in 3 subjects over periods of 24 h. Enamel specimens with and without 24-hour pellicles were immersed in citric acid (0.1 and 1%) for periods ranging from 30 s to 5 min, and processed for measurement of surface microhardness (SMH) and transmission electron microscopy (TEM). In comparison to uncovered enamel specimen significantly less decrease in SMH due to acid exposure was observed in pellicle-coated enamel specimens. Pellicles formed at the buccal aspect of the upper molars were less effective in protecting the enamel against acid-induced softening as compared to pellicles formed at the lingual aspect of the lower incisors only after 5 min exposure in 1% citric acid. TEM analysis showed that pellicle layers were dissolved continuously due to acid exposure. However, even after 5 min exposure to 1% citric acid, a residual pellicle layer could be detected on the enamel surface. In conclusion, site-dependent differences of buccally and lingually in vivo formed 24-hour pellicles have minor importance concerning the pellicle-induced protection of the enamel surface against erosive changes.

Influence of in vivo formed salivary pellicle on enamel erosion.

This study assessed the protective effect of the salivary pellicle formed in vivo during 24 h or 7 days against demineralization of bovine enamel caused by citric acid. In addition, the influence of acid treatment on the behavior of the pellicle was investigated. Enamel specimens with and without in vivo pellicles were immersed in citric acid (0.1, 1.0%) over 30, 60, and 300 s, and processed for scanning (SEM) and transmission electron microscopy (TEM), as well as for measurement of surface microhardness (SMH). Specimens coated with the in vivo formed pellicles revealed less extensive erosive demineralization of the enamel surface compared to uncovered enamel specimens. SEM analysis and SMH results did not indicate distinct differences between erosive surface alterations on enamel slabs covered with 24-hour pellicles and on those covered with 7-day pellicles. TEM analysis showed that the pellicle layer was dissolved in part from the enamel surface due to acid exposure. However, pellicle residues could be detected by TEM in all specimens, even after 5-min exposure to 1.0% citric acid. It is concluded that the in vivo salivary pellicle can resist the acidic action to some extent and provides protection to the underlying enamel surface against erosive destruction caused by short-term action of citric acid.

Molecular characteristics of Haemophilus influenzae causing invasive disease during the period of vaccination in Switzerland: analysis of strains isolated between 1986 and 1993.

The broad use of conjugated vaccines against Haemophilus influenzae type b may select for strains to which the polysaccharide vaccine does not provide immunity. We analyzed 392 consecutive H. influenzae isolates from Swiss children 0 to 16 years of age with invasive disease during the years 1986 to 1993. Bacterial strains were characterized by serotyping, capsular genotyping, outer membrane protein (OMP) subtyping, and ribotyping. Of 392 strains, 372 were serotype b, 1 was serotype a, 3 were serotype f, and 16 were nontypeable H. influenzae. After the introduction of Haemophilus conjugate vaccines in 1990, there was a relative increase of nontypeable strains from 3 to 6.6% (P = 0.27). Of the type b strains, 281 (75.5%) had the same OMP subtype and ribotype pattern. This clone predominated in the pre- and postvaccine periods. After the year 1990, the proportions of OMP subtype 1c and OMP subtype 3 tended to increase. Isolates from previously vaccinated (n = 10) and nonvaccinated patients did not differ in their subtype distributions. We conclude that the administration of conjugated vaccines decreased invasive disease caused by the most prevalent H. influenzae type b clone. However, further surveillance of circulating H. influenzae strains during the period of vaccination is indicated.

A new parameter for checking the suitability of alpha-tocopherol standards.

The quality of an alpha-tocopherol standard can be checked easily by measuring the UV absorbance at minimum (255 nm, Amin) and maximum (292 nm, Amax) wavelengths in n-hexane. If the quotient Amin/Amax exceeds 0.18, the standard contains less than 90% alpha-tocopherol and the determination at 292 nm will yield inaccurate results.

Rapid identification of mycobacteria to the species level by polymerase chain reaction and restriction enzyme analysis.

A method for the rapid identification of mycobacteria to the species level was developed on the basis of evaluation by the polymerase chain reaction (PCR) of the gene encoding for the 65-kDa protein. The method involves restriction enzyme analysis of PCR products obtained with primers common to all mycobacteria. Using two restriction enzymes, BstEII and HaeIII, medically relevant and other frequent laboratory isolates were differentiated to the species or subspecies level by PCR-restriction enzyme pattern analysis. PCR-restriction enzyme pattern analysis was performed on isolates (n = 330) from solid and fluid culture media, including BACTEC, or from frozen and lyophilized stocks. The procedure does not involve hybridization steps or the use of radioactivity and can be completed within 1 working day.