Pyrosequencing analysis of the oral microflora of healthy adults

A good definition of commensal microflora and an understanding of its relation to health are essential in preventing and combating disease. We hypothesized that the species richness of human oral microflora is underestimated. Saliva and supragingival plaque were sampled from 71 and 98 healthy adults, respectively. Amplicons from the V6 hypervariable region of the small-subunit ribosomal RNA gene were generated by PCR, pooled into saliva and plaque pools, and sequenced by means of the Genome Sequencer 20 system at 454 Life Sciences. Data were evaluated by taxonomic and rarefaction analyses. The 197,600 sequences generated yielded about 29,000 unique sequences, representing 22 taxonomic phyla. Grouping the sequences in operational taxonomic units (6%) yielded 3621 and 6888 species-level phylotypes in saliva and plaque, respectively. This work gives a radically new insight into the diversity of human oral microflora, which, with an estimated number of 19,000 phylotypes, is considerably higher than previously reported.     

Root dentin morphology after different modes of citric acid and tetracycline hydrochloride conditioning.

The purpose of this study was to assess the effect of citric acid and tetracycline HCl application to dentin surfaces by a "passive dripping" or an "active burnishing" technique. Twenty dentin blocks were prepared from freshly extracted non-diseased human impacted third molars. The blocks were root planed and randomly assigned to two groups for treatment with either citric acid or tetracycline HCl. The duration of treatment was 30, 60, 120, or 240 seconds. Control blocks were treated with distilled water. After treatment the blocks were processed for observation and measurements in the scanning electron microscope (SEM). Application of either of the acid solutions resulted in removal of the smear layer. Measurements indicated a time dependent increase in the mean dentinal tubule orifice diameter ranging from 1.05 microns in control specimens to 3.18 microns after 4 minutes treatment (citric acid group). The increase in tubule diameter was significantly greater (P less than or equal to 0.01) for both citric acid treatment modalities than tetracycline HCl treatment. There was also a time dependent increase in the depth of penetration as measured by a trumpeting of the tubule profiles, and this penetration was significantly greater (P less than or equal to 0.01) after citric acid treatments. Passive or active application of the acids did not seem to have any major impact on the measurements or on the surface morphology. It was concluded that citric acid causes more extensive changes than tetracycline HCl and that the mode of application of the agent is probably not critical.     

A magnetic resonance spin label study of human dental enamel.

The rotational mobility of nitroxide spin labels in human dental enamel indicates that the regions accessible to the largest label used were of the order of 15 Å (1.5nm). The nitroxide coupling constants were used to determine the degree of label-solvent replacement. Calibration of the microwave cavity Q with liquid water samples indicate that about 2.3 per cent by weight of the enamel samples was liquid water. 55, 50 and 23 per cent of this liquid water appeared to be removed by vacuum-drying or equilibration with ethanol or benzene, respectively. Decay of the radical species was observed; the mechanism of reduction of the labels is unknown but use of a model of diffusion with simple first order decay allowed the calculation of an apparent diffusion constant D of 6 × 10^?9cm²/s (6 × 10⁵nm²/s) at 22 °C.     

Observation of orthopedic force distribution produced by maxillary orthodontic appliances

A three-dimensional anatomic model was duplicated from a human skull, using different birefringent materials to simulate the various craniofacial structures. Individual bones of the midface were fabricated separately and then articulated in their correct sutural relation. One removable and four fixed maxillary appliances were used. The fixed appliances included the Haas, Minne-expander, Hyrax, and quad helix devices. The removable appliance incorporated an expansion screw in a full acrylic palate with appropriate retentive clasps. After the insertion of each appliance, intraoral forces were produced by incremental activation. The model was examined and photographed in the field of a transmission polariscope. Each appliance used produced a different range of load-activation characteristics. This was reflected by the differences in the stresses transmitted through the bones of the craniofacial complex and the effect on the various sutures. Stresses produced by the fixed appliances were concentrated in the anterior region of the palate, progressing posteriorly toward the palatine bone. The Haas, Minne-expander, and Hyrax appliances produced stresses that radiated superiorly along the perpendicular plates of the palatine bone to deeper anatomic structures, such as the lacrimal, nasal, and malar bones, as well as the pterygoid plates of the sphenoid. Similar stress characteristics were seen with the removable appliance. However, increased activation decreased retention of the appliance, thereby lessening the stress. The quad helix appliance proved to be the least effective orthopedic device. Although the effects of palate separation were seen with increased activation, this appliance primarily affected the posterior teeth.     

An improved split-denture technique

A technique for the construction of split dentures with a cast framework to hold the denture segments together has been described. The advantages of this technique to the patient were noted. Patients are carefully instructed first on how to insert the sections and then on how to insert the casting after the individual segments of each arch are in place.     

Growth and acid tolerance of human dental plaque bacteria

Pure cultures of representative strains of cariogenic and non-cariogenic plaque bacteria were assessed for their ability to initiate and maintain growth in broths, adjusted to initial pH levels of 7.0, 5.5 or 5.0, and to produce lactic acid from sucrose or glucose in resting-cell suspensions at pH 6.5, 5.0, 4.5 and 4.0. Streptococcus mutans, Lactobacillus casei and Streptococcus faecalis showed greater acid tolerance than strains of Streptococcus sanguis, Streptococcus salivarius, Streptococcus mitis and Actinomyces viscosus. For all species, growth initiation in broth was more acid sensitive than lactic-acid production in resting-cell suspensions. These data confirm and extend previous observations that the species of plaque bacteria most closely associated with the initiation or progression of dental caries are more aciduric than non-cariogenic species.