No abstract

In this in vitro study we investigated the influence of ionizing gamma rays on the stability in the region of the dentinoenamel junction. We removed the enamel on the labial surface of 30 incisors of bovines up to the dentinoenamel junction, so that a circular area of enamel with a diameter of 2.0 +/- 0.1 mm was left and an enamel cylinder was created. 15 teeth were irradiated by a cobalt-60-source (energy dose 70 Gy). The other 15 teeth were used as controls. Using a material testing apparatus the shear bond strengths were measured by breaking off the enamel cylinders. Furthermore, the breaking modes were investigated in SEM. Comparing the results of the shear bond strength experiments, it was obvious that the stability in the region of the dentinoenamel junction was significantly less among the irradiated teeth than among the non-irradiated teeth. The median value of the gamma ray treated teeth was x = 19.1 MPa and that of the non-ray-treated teeth was x = 37.4 MPa. The non-irradiated teeth showed fractured surfaces only in dentin in 10 cases and in 5 cases in both dentin and enamel. In contrast to that, the irradiated teeth had fractured surfaces in 12 cases exclusively in dentin and only in 3 cases the enamel was also fractured. These results lead us to conclude that changes of biophysical property of teeth can be caused by the influence of ionizing rays.

No abstract

The aim of this study was to systematically measure proximal contact strength in complete natural dentitions of 30 adults (25.3 +/- 3.0 years of age), and to analyze its relationship to tooth type, tooth location, chewing effort and time of day variation. The contact strengths were measured dynamically during removal of a calibrated 0.05-mm-thick metal strip between the proximal contacts of adjacent teeth. Proximal contact strengths were lower in the maxilla (2.51 +/- 1.36 N) compared to the mandible (4.26 +/- 1.88 N). Within the jaws, the lowest proximal contact strength was measured between canine and first premolar (2.91 +/- 1.79 N) and the highest between second premolar and first molar (3.73 +/- 1.95 N). Chewing increased the proximal contact strength within the maxilla (before: 2.51 +/- 1.36 N, after: 3.02 +/- 1.45 N) but it remained unchanged in the mandible (before: 4.26 +/- 1.88 N, after: 4.22 +/- 1.85 N). The proximal contact strength increased significantly from morning (3.39 +/- 1.86 N) to noon (3.61 +/- 1.77 N), and then decreased in the afternoon (3.43 +/- 1.60 N). It was concluded that proximal contact strength can be significantly influenced by location, tooth type, chewing and time of day variation. Based on the differences in distribution due to the effect of chewing and time of day, it is speculated that proximal contact strength is a physiological entity of multifactorial origin.

Improvement achieved by guided tissue regeneration in infrabony defects can be maintained up to 24 months after surgery. Narrow and deep infrabony defects respond radiographically and to some extent clinically more favorably to GTR therapy than wide and shallow defects. However, depth of the infrabony component was a stronger prognostic parameter than defect angle. Actual smoking impairs the results of GTR therapy in infrabony defects.