Data in the literature suggest that site-specific differences exist in the skeleton with respect to digestion of bone by osteoclasts. Therefore, we investigated whether bone resorption by calvarial osteoclasts (intramembranous bone) differs from resorption by long bone osteoclasts (endochondral bone). The involvement of two major classes of proteolytic enzymes, the cysteine proteinases (CPs) and matrix metalloproteinases (MMPs), was studied by analyzing the effects of selective low molecular weight inhibitors of these enzymes on bone resorption. Mouse tissue explants (calvariae and long bones) as well as rabbit osteoclasts, which had been isolated from both skeletal sites and subsequently seeded on bone slices, were cultured in the presence of inhibitors and resorption was analyzed. The activity of the CP cathepsins B and K and of MMPs was determined biochemically (CPs and MMPs) and enzyme histochemically (CPs) in explants and isolated osteoclasts. We show that osteoclastic resorption of calvarial bone depends on activity of both CPs and MMPs, whereas long bone resorption depends on CPs, but not on the activity of MMPs. Furthermore, significantly higher levels of cathepsin B and cathepsin K activities were expressed by long bone osteoclasts than by calvarial osteoclasts. Resorption of slices of bovine skull or cortical bone by osteoclasts isolated from long bones was not affected by MMP inhibitors, whereas resorption by calvarial osteoclasts was inhibited. Inhibition of CP activity affected the resorption by the two populations of osteoclasts in a similar way. We conclude that this is the first report to show that significant differences exist between osteoclasts of calvariae and long bones with respect to their bone resorbing activities. Resorption by calvarial osteoclasts depends on the activity of CPs and MMPs, whereas resorption by long bone osteoclasts depends primarily on the activity of CPs. We hypothesize that functionally different subpopulations of osteoclasts, such as those described here, originate from different sets of progenitors.

Within the restrictions of this study, only limited atmospheric microbial contamination is produced when using a piezoelectric ultrasonic scaler.

In a blind, randomised, 4-cell, cross-over study, the effect of rinsing with a perborate solution (1.9 g sodium perborate-monohydrate dissolved in 30 ml water/Bocasan, Oral-B) on the in vivo plaque-inhibiting effect of 0.12% chlorhexidine (Oral-B) was examined. After a thorough professional prophylaxis including interdental cleaning, 12 subjects started to rinse according to 4 different regimens: regimen (C-P-C): chlorhexidine in the morning, perborate at noon and chlorhexidine in the evening; regimen (CP-CP): chlorhexidine immediately followed by perborate in the morning and in the evening; regimen (PC-PC): perborate immediately followed by chlorhexidine in the morning and in the evening; regimen (C-C): chlorhexidine in the morning and in the evening. No further oral hygiene measures were allowed for the next 72 h. After 72 h, the subjects were scored for plaque, and a washout period of 4 days followed; cross-over was randomly assigned according to a Latin square design. Following this procedure, all subjects went through all 4 regimens. The regimens C-P-C and PC-PC resulted in significantly lower plaque-scores, 0.27 and 0.28 respectively, than regimen C-C (0.40). For the regimen CP-CP, the plaque-score was 0.28, which was not significantly different from the C-C regimen. The results suggest a positive interaction between chlorhexidine and hydrogen peroxide. Rinsing with a combination of 0.12% chlorhexidine (Oral-B) and a perborate solution (Bocasan Oral-B) can result in more effective short-term plaque growth inhibition than rinsing with chlorhexidine alone.

Previous studies have shown that rat incisor dentin contains a considerable amount of magnesium that is distributed heterogeneously. The cementum-related dentin, especially its incisal portion, is richest in magnesium. It was the purpose of the present study to investigate the changes that occur in the magnesium content during dentin maturation.Cross-sections were prepared from rat incisors at the apical, middle, and incisal levels. By means of an electron microprobe, tracings were made of the Ca-, Mg-, and P-signal frequencies. Comparison of corresponding dentin layers within and between the cross-sections showed that the Mg/P molar ratio was always higher in the cementum-related dentin (CRD) than in the enamel-related dentin (ERD) and increased from the apex toward the incisal edge. Especially in the incisal crosssection, an increase in Mg/P was found from the older (peripheral) toward the younger (central) dentin layers. As the Mg/P ratio varied from 0.07 to 0.33, the Ca/P ratio was found to fluctuate from 1.48 to 1.15. The two ratios appeared to be highly correlated (r = -0.97; p<0.001), suggesting that Mg replaces Ca and is bound to phosphate. overdose of Nembutal injected intracardially. Their lower right jaws were dissected out and stored frozen. Cross-sectional slices (1 mm in thickness) of the incisors, together with the surrounding tissues, were prepared at an apical, middle, and incisal level (Fig. 1) by use of a Microslice 2 MR (Metals Research Ltd., Cambridge, England) with a diamond saw blade under constant water cooling. After removal of the surrounding bone, the cross-sections of the incisors were dehydrated through a graded series of ethanol and propyleneoxide and embedded in epoxy resin (Epon LX112, Ladd), which was polymerized at 60°C. All specimens were embedded simultaneously in the same piece of epoxy resin, in such a way that the slices obtained from one tooth were next to each other. The incisal aspect of each slice was then serially polished with silicon carbide abrasive paper (nos. 240 to 600), followed by a 0.03-,um aluminum oxide micropolisher.Electron microprobe analysis. -After the slices were coated with a carbon layer in a Balzer BEA 250 evaporator, the specimens were subjected to electron microprobe analysis in a JEOL Superprobe 733 (10 kV, 10 WxA, beam area 1 1Lm2, ten s per J Dent Res 70(3): 187-191, March, 1991

Recently, we have shown that, in rodent incisors, the crown- and root-analogue dentin (enamel- and cementum-related dentin) show differences in mineralization rates (Beertsen and Niehof, 1986) and composition of the organic matrices (Steinfort et al., 1989). It was the aim of the present study to determine whether these differences were accompanied by differences in the inorganic components. Rat incisors were analyzed by means of hardness measurements, microradiography, and the determination of Ca, Mg, and PO4 content. The outer circumpulpal dentin layer of the enamel-related dentin (ERD) was considerably harder and denser than the comparable layer of the cementum-related dentin (CRD). Concomitantly, a higher Ca and PO4 content was found for the ERD than for the CRD, while the reverse occurred with respect to Mg. From the apical end of the incisor toward the incisal edge, the Ca/PO4 ratio tended to decrease for both ERD and CRD, while the Mg/PO4 ratio increased. All differences appeared to be statistically significant. It is concluded that differences in the non-collagenous organic matrix were accompanied by differences in the inorganic components. More specifically, a relatively high content of highly phosphorylated phosphoproteins (ERD) was associated with a higher Ca and a lower Mg content.