Angela Favia

Morphometric analysis of the deposition and mineralization of enamel and dentine from rat incisor during the recovery phase following a low-calcium regimen

The administration of a low-calcium diet to pups nursed by a mother on the same diet has been shown to induce a slowing of growth. A reduction of the apposition rate of dentine, which was normally mineralized, and a dramatic reduction of the extent of mineralization of enamel, whose organic matrix was otherwise produced in an almost normal amount, was observed in the incisors of these animals. Modifications of the mineral apposition rate of dentine, measured after administration of tetracycline (10 mg/kg), and the thickness and the microhardness of the two tissues, the latter being an expression of the degree of mineralization, were now investigated when hypocalcic pups were restored to a normal-calcium diet for 10 or 60 days. Enamel microhardness was increased by more than 60% after only 10 days of restored diet and had become the same as in the control tissue after 60 days, without any significant increase in thickness. Dentine thickness and mineral apposition rate increased significantly, to become similar to those of the controls after 60 days of restored diet. In dentine there was no significant variation of microhardness between experimental pups and controls, either during the low-calcium diet or the restorative period. These results indicate that the deposition of the organic matrix of enamel is a process independent from that of its mineralization, and that the mineralization of the organic matrix happens by its replacement even a long time after its deposition. In contrast, the deposition and mineralization of dentine are strictly interdependent processes, at least in these experimental conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of a low calcium maternal and weaning diet on the thickness and microhardness of rat incisor enamel and dentine

The deposition and mineralization of incisor hard tissues have been studied in rat pups nursed by mothers on a low calcium diet or weaned with the maternal diet. Animals were killed at 30 days (control and low calcium diets; maternally fed) or 60 days (after 30 days weaning on maternal diet). The degree of mineralization of enamel and dentine was evaluated by a microhardness method on thick transverse sections. The enamel and dentine thickness, and the diameters of the incisor sections and pulp cavity were measured on microradiographs from the sections. Microhardness values of enamel were similar in groups killed after 30 days maternal feeding, but the microhardness of root enamel was 73-74% less in the low calcium-diet weaned group. Peripulpar dentine had mean microhardness values lower than controls in the group fed maternally for 30 days, whereas the whole root dentine appeared significantly less hard in the low calcium-diet weaned group than in the controls. A significant reduction of the incisor bucco-lingual diameter was observed only in this last experimental group. Enamel thickness was significantly lower in the roots of both experimental groups and in the necks of the low calcium weaned group. The reduction in dentine thickness was greater (from -30 to -56%); in the root it was more evident on the lingual aspect. Thus calcium deficiency in the mothers diet did not influence either the deposition or the mineralization of the pups incisor enamel and dentine. However, when the offspring were weaned with the maternal calcium-deficient diet, mineralization of the tooth hard tissue was retarded.

Dens invaginatus: a qualitative-quantitative analysis. Case report of an upper second molar.

Dens invaginatus (D.I.) is a developmental anomaly caused by the infolding of the surface of a tooth crown before calcification has occurred. Its aetiology is controversial and remains unclear. It occurs in all dentitions with a prevalence that ranges from 0.25% to 7.74% and is mostly seen in the maxillary permanent incisors, particularly in the lateral incisors. Posterior teeth are infrequently involved. The purpose of this study was to investigate the morpho‐structure of a second upper molar dens invaginatus compared with a control tooth. Ground and decalcified sections were prepared and histo‐morphological evaluation of dental tissues was performed by using light microscopy, microradiography, and confocal laser scanning microscopy analysis (CLSM). The mechanical behaviour was tested by means of microhardness (HV) test. The results of our investigation showed structural anomalies of hard tissues, such as a difference in enamel prism diameter, in number and diameter of peripulpal dentinal tubules and in surface and diameter of cementocyte lacunae between D.I. and control tooth.

Variation of trabecular architecture in proximal femur of postmenopausal women.

This investigation of microstructure in the human proximal femur probes the relationship between the parameters of the FRAX index of fracture risk and the parameters of bone microstructure. The specificity of fracture sites at the proximal femur raises the question of whether trabecular parameters are site-specific during post-menopause, before occurrence of fragility fracture. The donated proximal femurs of sixteen post-menopausal women in the sixth and seventh decades of life, free of metabolic pathologies and therapeutic interventions that could have altered the bone tissue, constituted the material of the study. We assessed bone mineral density of the proximal femurs by dual energy X-ray absorptiometry and then sectioned the femurs through the center of the femoral head and along the femoral neck axis. For each proximal femur, morphometry of trabeculae was conducted on the plane of the section divided into conventional regions and sub-regions consistent with the previously identified trabecular families that provide regions of relatively homogeneous microstructure. Mean trabecular width and percent bone area were calculated at such sites. Our findings indicate that each of mean trabecular width and percent bone area vary within each proximal femur independently from each other, with dependence on site. Both trabecular parameters show significant differences between pairs of sites. We speculate that a high FRAX index at the hip corresponds to a reduced percent bone area among sites that gives a more homogeneous and less site-specific quality to the proximal femur. This phenomenon may render the local tissue less able to carry out the expected mechanical function.

Quantitative Analysis of Defects at the Dentin-Post Space in Endodontically Treated Teeth

The objective of this study was to assess frequency and extension of the defects affecting the dentin-post interface after using different combinations of irrigants and sealers. The experimental work was conducted on single-rooted teeth extracted for orthodontic reasons. The specimens were divided into different groups, according to irrigant and endodontic cement utilized, and endodontically instrumented. After fiberglass posts cementation, cross sections were obtained at apical, middle and coronal level of the root and submitted to quantitative analyses. Different types of defects were found: bubbles, bonding defects, polymerization defect, and cement residues. The percent extension of each defect and its frequency were related to the specific irrigant/sealer combination and to the root level. Detachments of the material from dentin were found only at apical and middle levels. Chlorhexidine digluconate seems to have more beneficial effects if compared to sodium hypochlorite: samples prepared with chlorhexidine digluconate showed a higher performance, with roots including null to few defects. In detail, samples treated with chlorhexidine digluconate and Pulp Canal Sealer showed the lowest frequency and the smallest dimension of defects.

Non invasive moderate loading in vivo and osteoarthritis development

Mechanical loading is known to modify joint structure through a mechano-adaptative response and to increase proinflammatory cytokines, as IL-1β, modulating VEGF secretion by condrocytes1. VEGF is a potent angiogenic factor, also detectable in later stages of OA, able to increase matrix MMPs playing an important role in the development of OA2. The aim of this study is to evaluate “in vivo” changes of bone and cartilage leading to OA by means of nonsurgical intermittent moderate loading. Forty day-old mice was randomly divided into two groups of six animals each: sedentary and exercised. The exercised group was subjected to a treadmill running at 12m/min, two times a week for four weeks. The sedentary group did not undergo any physical training and was left free to walk inside the cages. After the sacrifice the femur heads were removed and processed for paraffin embedding. On 5μm coronal sections, safranine-O staining and immunostaining for IL-1 β, MMP-13 and VEGF was performed to evaluate: articular cartilage and subchondral bone trabeculae thickness; chondrocytes number/mm2; chondrocytes volume; % cell number expressing VEGF, IL-1β and MMP-13 in articular cartilage and bone. Significant increase of chondrocytes volume, VEGF and MMP-13 expression in cartilage was detected. These data seem indicate that our non-invasive experimental model could induce early alterations in articular cartilage only, confirming chondrocytes to play a central role in the pathogenesis of OA. Other alterations, such as articular cartilage cracking and thickening and sub-chondral bone sclerosis, would appear later.

The response of healthy femoral head to a moderate mechanical loading. Preliminary results

It is well-known that most of the degenerative processes of the skeletal system are induced by an altered mechanical load. Osteoarthritis, a chronic degenerative disease affecting the synovial joints, is a typical example of pathology influenced by mechanical stimuli that occurs with the degradation of articular cartilage, osteophytes formation, sub-chondral bone and calcified cartilage thickening and leukocyte infiltration in the synovial membrane. It is still not clear whether degenerative processes of joint tissues occur simultaneously or follow a well-defined sequence of events. To better evaluate the involvement of the articular cartilage, bone and calcified cartilage, we have analysed early stage changes in the femur proximal end of mice subjected to moderate mechanical loading. Twelve mice (C57BL) 4-5 weeks old were casually subdivided into two groups: “exercised” and “sedentary”. The first group was underwent 30 min of running on an horizontal treadmill (Columbus Instruments,USA) at 12 m/min, twice a week, for 4 weeks, whereas the second one was left free to move in the cage without additional muscle work. After sacrifice, femurs were fixed in 4% paraformaldehyde in 0,1 M PBS and embedded in paraffin wax. Five micrometers frontal sections, were deparaffinized and rehydrated in a xylene-graded alcohol scale. On Safranin-O stained sections, morphometrical analysis was carried out by means of Nikon NIS-elements Br software to evaluate a) the number and the volume of the condrocytes. b) the sub-chondral bone volume, c) the thickness of trabecular bone and d) the thickness of calcified cartilage zone. The exercised mice do not show any variation at level of the bone and calcified cartilage. On the contrary, it seems that the articular cartilage, despite not showing any signs of degeneration, as altered staining or obvious injuries, reacts by increasing the volume of its chondrocytes (p<0,05). These preliminary data seem to confirm the existence of a sequence of events where articular cartilage responds to increased mechanical loading more promptly than bone and calcified cartilage.

Microdurimetric study of the mineralization rate of spongy bone in the dog

SummaryThe microhardness-testing technique was applied to the study of the mineralization rate in the spongiosa of shaft bones of four dogs of various age. When bone tissue of the same “age” is tested the results indicate a higher mineralization degree of the metaphyseal than of the epiphyseal trabeculae; the degree of the mineralization of the latter is nearly equal to that of the osteons of the diaphyseal and metaphyseal cortex. The mineralization rate appears to decrease with the age of the animal both in spongy and in compact bone.