Minocycline impairment of both osteoid tissue removal and osteoclastic resorption in a synchronized model of remodeling in the rat.

In addition to their antibacterial effects, tetracyclines may inhibit interstitial collagenase activity and bone resorption. These properties were assessed morphometrically using minocycline (25 and 50 mg/kg/day given by the IM route) in a rat model of synchronized remodeling in which osteoclastic resorption peaks 4 days after the activating event (the extractions of the upper molars) along the antagonist mandibular cortex, a zone undergoing physiologically active formation. During the first 2 days of activation, minocycline at the two doses impaired very significantly the disorganization of both the osteoid seam and the layer of osteoblasts, a prerequisite to give osteoclasts access to the mineralized bone surface. The number of readily identifiable osteoblasts decreased slightly during this period, suggesting that minocycline prevented their transformation into lining cells. Their synthetic activity, as estimated by the size of the cells and their nucleus, appeared relatively preserved too, mostly with the higher dose. AT the peak of osteoclasia, the bone surfaces undergoing remodeling were significantly decreased in the minocycline-treated groups. The resorption surface was reduced (P < 0.0003) as well as the number of osteoclasts (P < 0.0007), which were also significantly smaller. Their resorbing activity was dramatically affected as well: they excavated lacunae whose area was significantly reduced by over 70%. In addition, formation was still a prominent activity in the treated animals. These data are compatible with the inhibition at the early stages of activation of an osteoblast-secreted collagenase whose action may be the elimination of the osteoid seam. The inhibition of an osteoclast collagenase and/or of a bone matrix bound-collagenase may be responsible for the reduction in lacunar size. A direct effect of minocycline on osteoclast resorptive activity may also participate in the low resorption profile, as tetracyclines are known to interfere with the intracellular [Ca2+].

[Emergency treatment: coronal restoration with pulpal-dentinal protection. Splints]. / Les traitement s d'urgence: reconstitutions coronaires avec protections pulpo-dentinaires. Les contentions.

The authors, explain the need of a pulpo-dentinal protection, and present the way to adopt in case of dental traumas, as well for hard tissues (coronal and radicular) and for non calcified tissues (luxations). This protection allows a cicatrisation of dento-periodontal tissues.

Changes in mast cell number during the activation phase of an induced synchronized remodeling sequence in the rat.

Increase in mast cell (MC) number has been reported in some pathological conditions with increased remodeling. However, it is not known whether MCs are involved in the physiological remodeling of bone. In the present study the possible variations in MCs were investigated during the activation phase in a rat model of synchronized remodeling. Seven groups of 10 rats were used. As early as the first day of induction, MCs increased by 50% and then decreased on day 2. The same pattern of changes recurred on days 3 and 4. Intact non-degranulating MCs increased mainly at some distance from the bone surface. Degranulating MCs conversely decreased near the cambium layer of the periosteum. Prostaglandins were not involved in these changes. These results suggest an association between the events leading to the onset of bone resorption and MCs. Degranulation might induce the release of agents active on these events.

[Sequence of experimental remodeling of the mandibular periosteum in the rat]. / Etude d'une séquence de remaniement expérimental induite sur le périoste mandibulaire du rat.

The evolution of a synchronous bone remodeling sequence has been followed with time. This sequence was induced in the buccal mandibular cortex of the rat which undergoes modeling apposition after maxillary molar extractions. The sequence has been studied in the rat on day 0, 2, 4, 6, 8 and 12 after induction. Disappearance of the layer of osteoid tissue produced on day 0 was initially observed (day 2). The resorption phase reached a peak on day 4 and then decreased until day 12. The greatest inversion was observed on day 8 and then regressed. Apposition, completely absent on day 4, was again important on day 12. The variations with time of the 2 different osteoclast profiles, those in contact with bone (considered as active) and those at a distance from the bone surface (considered as inactive) allowed to study the kinetics of these cells. Whereas their total number was unchanged on day 4 and 6, on day 4 the active osteoclasts were more numerous: this situation was completely reversed on day 6. These facts suggest that the osteoclasts present were active for 1 to 2 days, then became inactive without change in number before their disappearance. This very reproducible model seems useful for understanding certain mechanisms occurring during bone remodeling and for testing the role of some mediators or pharmacological agents on the process.