J.T. Irving

Histological changes in experimental periodontal disease in rats mono-infected with a gram-negative organism

Abstract Gnotobiotic rats of the Sprague-Dawley strain were mono-infected at weaning with a Gram-negative, anaerobic rod isolated from a case of human periodontosis. Marked periodontal disease was evident by 42 days in the area between the first and second maxillary molars, with migration of the epithelial attachment, destruction of the alveolar bone and great impaction of debris. No plaque was formed. The bone was removed by osteoclasts. By 84 days, the periodontium was virtually all destroyed. These findings contrast with those previously reported of periodontal disease caused by Gram-positive organisms, when bone destruction was accompanied by few or no osteoclasts.

A comparison of the changes in the mandibular condyle with those in the upper tibial epiphysis during the onset and healing of scurvy

Abstract The changes in the tibial epiphysis and the mandibular condyle have been compared in scorbutic guinea-pigs. The classical changes were seen in the tibia, with the development of a large gerustmark by the 22nd day on the scorbutigenic diet. The sequence of events in the mandible was entirely different. No gerustmark formed and the cartilage became gradually wider as osteoclastic erosion slowed and stopped. On giving ascorbic acid, calcification began almost immediately in the gerustmark, but little change was seen in the tibial epiphyseal cartilage up to 72 hr after dosage. Within 24 hr, osteoclasts reappeared on the face of the wide condylar cartilage, and by 72 hr the cartilage had become of virtually normal width. Parallel studies with Sudan black showed that, as in other conditions, sudanophilia accompanied calcification. It is considered that the changes in the condyle during scurvy and healing are more consistent with its role as a remodelling than as a growth centre. It is suggested that ascorbic acid has an action on the differentiation of the osteoprogenitor cell.

A comparison of the circulatory and calcification patterns in the mandibular condyle in the guinea pig with those found in the tibial epiphyseal and articular cartilages

Abstract The capillary and calcification patterns of the tibial epiphysis, tibial articular cartilage and mandibular condyle have been compared in normal guinea pigs. The capillary pattern in the tibial epiphysis was the same as has been previously described—parallel capillaries, penetrating lacunae previously occupied by chondrocytes. The vascular patterns within the articular head of the tibia were more irregular than in the tibial epiphysis, and presented a “fork-like” arrangement of the terminal branches which penetrated the eroding capsules with looped type endings. In contrast to the tibial epiphyseal plate, but similar to the articular cartilage, a “fan-like” arrangement of capillaries was observed in the condyle, fed by one or two small arterioles. Calcification in the epiphyseal cartilage was prominant along the vertical cartilaginous partitions between the columns of chondrocytes. This pattern of mineralization was not seen in either the articular or condylar cartilage. In both of these sites the cartilage showed calcification completely circumscribing the capsules. It is considered that the tibial epiphyseal cartilage is eroded by capillary penetration, while in the condylar cartilage the process of erosion is closely related to, and dependent on, chondroclastic activity, with capillary penetration secondarily involved. The capillary and calcification patterns in the condyle more closely resemble those of the articular cartilage.

Comparison and changes in the articular, mandibular condylar and growth-plate cartilages during the onset and healing of rickets in rats

Abstract A comparison of the changes in the articular, mandibular condylar and growth-plate cartilages was made in rachitic rats. In the rachitic rat articular and condylar cartilages, the changes were similar. Both showed an increase in the width of cartilage, but only in the zone of hypertrophic cartilage. The rachitic tibial growth plate demonstrated the changes previously described by other authors, including resumed cartilage removal. Resumed cartilage removal was never seen in the articular or condylar cartilages. After vitamin D administration, the hypertrophic type of cartilage in the tibial articular cartilage was rapidly reduced in width and transformed into the non-hypertrophic form. The rachitic cartilage in the condyle was rapidly narrowed and was usually restored to normal by the tenth day, the development of calcification being similar to that seen in the early post-embryonic period of the condyle. During healing, the calcification of the growth plate resembled for a short time the pattern seen in the tibial anlage, and the condylar and articular cartilages. The rachitic disorder brings about a retrograde effect on the cellular characteristics of the tibial growth plate, while making more prominent the inherent embryonic nature of the articular and condylar cartilages.

An autoradiographic investigation of bone remodelling in the rat calvarium grown in organ culture

Abstract Organ culture studies of a portion of the rat calvarium revealed a remodelling pattern similar to that found in the intact animal. Rats aged 7, 9, 11, 13, and 15 days were injected with 1 μCi 3 H-proline per gram body weight 6 hr prior to explantation. The resultant band of label on bone surfaces served as a baseline for osteoid added in vitro . A synthetic medium, BGJb, was used with the addition of ascorbic acid, foetal calf serum, and hydrocortisone. The expiants were incubated on a metal screen in a plastic dish exposed to 95 per cent oxygen and 5 per cent carbon dioxide for 2 days and then examined histologically. A growth pattern similar to that of bone grown in vivo was observed. The osseous skeleton, like the cartilaginous anlage, has an inherent morphogenetic potential in the almost complete absence of functional demands and is not completely subject to the environment.

A comparison of circulatory and calcification changes induced in the mandibular condyle, tibial epiphyseal and articular cartilages of the guinea pig by the onset and healing of scurvy

Abstract The changes in the capillary and calcification patterns of the mandibular condyle, tibial epiphyseal plate and articular cartilage have been compared in scorbutic guinea pigs. In the scorbutic tibial epiphyseal cartilage the vascular picture was one of progressive disorganization and disruption with an overall reduction in both the metaphyseal and epiphyseal blood supply of the cartilaginous plate. In the articular and condylar cartilages the onset of scurvy brought on a similar but less drastic disruption of the organized capillary patterns. The mineralization of the scorbutic epiphyseal and articular cartilages included the entire hypertrophic zone while this did not appear to be the case in the scorbutic condylar cartilage. In the tibias of the ascorbic acid-treated animals there was a gradual recovery of the normal capillary and calcification patterns, and the reconstruction process was completed by 72-hr post-injection. The articular and condylar cartilages showed a similar but faster repair of the capillary patterns and coincident with these changes was the return of the normal calcification picture. It is considered that the absence of the gerustmark and trummerfeld zones beneath the condylar and articular cartilages is responsible for the less drastic changes as well as the faster repair in these areas. It is suggested the capillary endothelium gives rise to the chondroclasts responsible for the erosion of the condylar cartilage and that ascorbic acid has an action on the differentiation of these cells.

A histological study of regeneration of the completely disrupted periodontal ligament in the rat.

Summary The periodontal ligament of the maxillary first molar of rats was completely disrupted and studied at various time intervals during regeneration. Serial sections for collagen, elastic, reticular and oxytalan fibres, inflammation, root resorption and bacteria showed that initial healing of collagen fibres was rapid at the trans-septal and cervical areas of the tooth, while that in the apical portion, although initially slower, surpassed that of the cervical area by 10 days post-operatively. By 15 days, the regeneration of the periodontal ligament had returned it to the state of the controls but this state failed to maintain itself and organization of the periodontal ligament gradually decreased at a time when root resorption began. An increase and subsequent decrease in the number of oxytalan fibres observed suggests that these fibres play a role in regeneration of the periodontal ligament but have no apparent part in tooth support.

Deciduous central incisor tooth development and coronal cementogenesis in cattle

Abstract This study documents chronologically, growth and development of the bovine deciduous central incisor tooth from the earliest available stages of odontogenesis to exfoliation. Gross morphologic and histologic studies were carried out on 48 bovine mandibles. Three specimens were obtained at each monthly interval for 8 months of prenatal life and two specimens were obtained at several representative periods of postnatal life until 2 years of age. The following periods of deciduous central incisor tooth formation were defined: histoand morphodifferentiation, 3 months in utero; beginning of apposition and calcification, 4 months in utero; intra-oral eruption, 9 months in utero-birth; root formation complete, 6 months of age; and exfoliation, 2 years of age. Coronal cementum was found on the lingual surface of the deciduous incisor just prior to oral emergence while the tooth was still covered by a layer of tissue called the gingival sheath. Cementum was also first identified on the permanent incisor tooth crown at about 13 months of age. Coronal cementum was never observed overlying the reduced enamel epithelium, but was only seen in areas where the enamel surface of the crowns were exposed to the connective tissue of the surrounding dental sac. Continuity of root and coronal cementum was observed on the lingual surface of the developing permanent incisor tooth, thus suggesting similar cellular precursors for both structures.