Early osteocyte response to bone resorption stimuli

Over the last decade, increasing attention has been focused on the role of the osteocyte in bone remodeling, in view of its demonstrated ability to respond to mechanical and electric stimuli applied to bone. A previous [quot ]in vivo[quot ] study performed at our laboratory demonstrated that the application of orthodontic forces results in osteocytic lacunae enlargement. To our knowledge there are no data on cell and lacunae response to an inflammatory stimulus in the literature. The aim of this work was to determine whether osteocyte response to an inflammatory stimulus is comparable to that observed under mechanical stress and whether the ensuing cellular changes involve changes in the shape of the osteocyte and/or its lacunae. Three groups of ten male Wistar rats each, 200 to 250 g body weight, were used. Group I served as control. A cotton thread cervical ligature was placed around the first upper molars of animals in Group II, and those in Group III were fitted with an orthodontic appliance designed to exert a force toward palatine. All the animals were killed 24 hours after applying the stimuli. The histomorphometric determinations were measured on the interradicular crest between the two distal roots of the first upper molars. Osteocyte and lacunar volumes were measured and lacunar shape was analyzed. Group II exhibited a dense inflammatory infiltrate and slight resorption of the crest. Group III showed slight resorption of the vestibular wall. The lacunar volume increased in both experimental groups as compared to controls. The cell volume to lacunar volume decreased. These results suggest that osteocytes respond to inflammatory as well as to mechanical stimuli of bone resorption, enlarging lacunae without changes in cell volume.

Root resorption in elderly patients

Root resorption in permanent teeth is a frequently observed pathology that may originate in various causes. Life expectancy is progressively rising, odontological preventive care is becoming more widespread and professionals are educating their patients in the importance of preventive practices. Because senior citizens are thus losing fewer teeth prematurely they will be conversely more at risk for dental problems later in life. The knowledge of the alterations that may appear in the roots of geriatric patients is particularly relevant to devising therapy and establishing prognosis. The aim of the present study was to evaluate the nature and magnitude of the histologic and histomorphometric features of root resorption and the eventual possibility of repair in elderly people. Seventy-seven uniradicular teeth of patients aged between 65 and 90 years and 18 premolars of patients aged between 14 and 20 years, were removed, fixed in 90

formalin, decalcified in EDTA and embedded in paraffin. Vestibulo-lingual sections were stained with hematoxylin-eosin and employed to perform histological and histomorphometric studies. The results showed that 30

of the teeth of younger patients and 94

of the teeth of elderly patients exhibited areas of root resorption. From the 416 resorptive areas found in elderly patients, 173 exhibited signs of repair being the volume/surface ratio of these areas 0.69 +/- 0.06. These data show that root resorption is a frequent finding in the older population under study. Resorptions are characterized by scarce depth, large areas and a high incidence of repair despite the old age of the patients.

Enlargement of periosteocytic lacunae associated to mechanical forces

Demineralization of bone has been linked to the action of osteocytes via the process of osteocytic osteolysis. The aim of this study was to assess the influence of mechanical forces produced during orthodontic movements on the osteocytic lacunae. Orthodontic movements were achieved employing a device constructed [quot ]ad hoc[quot ] for rats that exerts a force of approximately 70 gr. The experimental animals and the corresponding controls were killed 48 and 96 hours after the onset of the experiment. Histologic sections oriented along the bucco-palatine axis were employed to measure the area of osteocytic lacunae to infer information on volume in keeping with standard stereological concepts. Regions alongside resorption areas of cortical bone and resting areas of palatine bone were evaluated. Osteocytic lacunae associated to erosive surfaces were rounded and rose markedly in area after the application of the orthodontic force (58.4 +/- 6 mm2). Elongated lacunae were present in relation to resting areas (24.8 +/- 2 mm2). The present study shows an association between the increase in size of osteocytic lacunae and the resorption fronts induced by the application of orthodontic forces. This finding would suggest that the osteocyte would participate in the resorption process of bone submitted to pressure.

Iron overloading inhibits dentine mineralization

The present study reveals the inhibitory effect of iron intoxication on the process of dentine mineralization. Wistar rats were injected intraperitoneally with iron dextran at 0.88 g/kg body weight per day for 10 days during the period of odontogenesis. An age-matched group was injected intraperitoneally with bisodium etidronate (EHBP) at 20 mg/kg body weight per day for 10 days. Another age-matched group was treated with similar amounts of saline intraperitoneally and considered as control. At the end of the experimental period the animals intoxicated with iron exhibited non-mineralized dentine and mineralized bone. The animals treated with EHBP showed non-mineralized dentine and bone. These findings would suggest the existence of different mineralization mechanisms for bone and dentine.

Bone growth is impaired by uranium intoxication

Acute and chronic uranium intoxication leads to the inhibition of bone formation and impaired bone modeling and remodeling. As these are processes directly involved in bone growth the aim of this paper is to present a biometric study of bone growth--tibiae and mandibles of rats intoxicated with uranium. Wistar ratios weighing 60-80 g were used as follows, a) one intraperitoneal injection (IPI, 2 mg/Kg of body weight)) of uranyl nitrate; b) 30 daily applications on the dorsal skin of aliquots of a mixture of U308, concentrated at 2

and at 4

--percutaneous absorption(PA)-. Tibia and mandible length were smaller in both experimental groups than in their respective controls. Some of the mandibular parameters were lower in intoxicated animals than their controls which in turn results in the alteration of the mandibular shape. We conclude that impairment in bone growth can be achieved by uranium intoxication.