Reactive dyes as vital indicators of bone growth

Molecular variations related to the regional differences in periosteal growth at the mandibular ramus

Periosteal growth at human mandibular ramus is characterized by bone apposition at the posterior border and resorption at the anterior border. Molecular control of this regional variation is unclear. This study examined the expression of several molecules involved in bone apposition/resorption at these regions in vivo and in vitro. By using growing pigs as a model, the periosteal growth was assessed at the mandibular ramus by vital staining and histological observations. In parallel, periosteal tissues were harvested and pulverized for RNA and protein extraction. Periosteal cells were also isolated, expanded in osteogenic media, and subjected to a single dose of dynamic tensile strain (0, 5, or 10% magnitude at 0.5 Hz) to examine their responses to mechanical loading. Real-time RT-PCR and Western blot analyses were used to examine mRNA and protein expression from periosteal tissues and cultured cells. Histological observation confirmed an anterior-resorption/posterior-apposition pattern in the pig mandibular ramus. Both in vivo tissue and in vitro cells demonstrated greater mRNA expression of receptor activator of NF-κB ligand (RANKL)/osteoprotegerin (OPG) ratio and bone morphogenetic protein 2 (BMP2) at the anterior region, while OPG expression at the anterior region was lower than the posterior region. In response to the application of a single dose of dynamic tensile strain, cultured periosteal cells appeared to change the expression profile of osteogenic markers but not that of RANKL/OPG and BMP2. These findings suggest that the unique regional variation of periosteal activity at the mandibular ramus is regulated by a differential expression of RANKL/OPG ratio (likely through differential induction of OPG) and BMP2.

The classic: Bone morphogenetic protein

This Classic Article is a reprint of the original work by Marshall R. Urist and Basil S. Strates, Bone Morphogenetic Protein. An accompanying biographical sketch of Marshall R. Urist, MD is available at DOI 10.1007/s11999-009-1067-4; a second Classic Article is available at DOI 10.1007/s11999-009-1069-2; and a third Classic Article is available at DOI 10.1007/s11999-009-1070-9. The Classic Article is copyright 1971 by Sage Publications Inc. Journals and is reprinted with permission from Urist MR, Strates BS. Bone morphogenetic protein. J Dent Res. 1971;50:1392-1406.

Growing the mandible: role of the periosteum and its cells

Mandibular periosteum moves in the direction of new apposition. This displacement, usually termed "migration," is thought to involve the fibrous layer of periosteum, with the deeper osteogenic layer remaining at its original location except for its blood vessels. To assess whether periosteal displacement includes cells as well as matrix and whether the osteogenic layer has a role, a longitudinal study was undertaken. Young pigs (n = 10) were injected with a replication marker and killed 3 hr, 2 weeks, or 4 weeks later. Sections of the mandibular ramus were scored for labeled cell density. Some sections were double-labeled with lectin to identify blood vessels. Statistical differences were seen between but not within age groups. Three hours after labeling, the fibroblastic layer had sparse, evenly distributed replicating cells, whereas the osteogenic layer had numerous replicating cells, especially at the caudal border. At 2 and 4 weeks later, a decrease in labeled osteogenic layer cells was accompanied by an increase in labeled osteocytes. Zones of labeled osteocytes in these late-sacrifice groups were used to approximate the position of the ramal borders at the time of injection. Beyond these zones, in active growing sites, labeled cells were found not only in the fibrous layer but also in the osteogenic layer and in bone. Therefore, periosteal displacement does involve cells and is not restricted to the fibrous layer.

Vienna-Chicago: the cultural transformation of the model system of the un-opposed molar

The discussion over the roles of genes and environment on the phenotypical specification of organisms has held a central role in science philosophy since the late 19(th) century and has re-emerged in today's debate over genetic determinism and developmental plasticity. In fin-de-siecle Vienna, this debate coincided with a philosophical debate over empiricism/materialism versus idealism/vitalism. Turn-of-the-century Vienna's highly interdisciplinary environment was also the birthplace for the model system of the un-opposed molar. The un-opposed molar system features new tissue formation at the roots of teeth and tooth drift once opposing teeth are lost. The un-opposed molar model system was revived by a group of Viennese scientists who left Vienna during the Nazi period to address Vienna's questions about evolution and heredity and about genes and environment in Chicago's post-WWII scientific exile community. Here we are using the colorful history of the un-opposed molar to investigate the role of culture and method in the scientific evolution of a model system.

Repair process of external root resorption subsequent to palatal expansion treatment

The repair process of external root resorption (ERR) and the role of retention mechanics in enhancing ERR repair were studied on eight Macaca fascicularis monkeys that were divided equally into short- and long-term groups. Six monkeys received palatal expansion appliances, and two received sham appliances. The short-term group received active treatment. The long-term group received additional retention (4 months) and relapse (2 months) treatment periods with biweekly injections of individual vital dye per phase, i.e., procion red H-8B and violet H-3R (80 mg/kg B.W.), respectively. Histomorphologic examinations included scanning electron microscopy, light, and ultraviolet microscopy. The short-term group demonstrated penetrated resorption with pulp exposure at sites with initial deficiency of the protecting odontoblastic layer (apical zone, nutrition canal). The long-term group showed two forms of ERR repair: (1) Nonfunctional retarded repair cementum, comprised of overlapped incremental lines and deprived of extrinsic fibers, was delineated in severe pulp exposure. The pulp/dentin complex showed intense incorporation of procion dye in the dentinal tubuli, conceivably related to a defense response in the form of sclerotic dentin. (2) Functional rapid repair cementum, comprised of discriminated incremental lines mainly of mixed cellular cementum, with a consistent pattern of five sequential phases: the lag phase (14 to 28 days), the incipient phase (14 days), the peak phase (14 to 28 days), the steady phase (42 to 56 days) and the retreating phase (70 days). Sharpey's fibers at functional ERR sites were scarce, never emerging from the dentinocemental junction, and not developing into principal fibers. The pulp/dentin complex showed an increase in pulp stones but no formation of tertiary dentin. The apical area responded by hypercementosis in the form of apical occlusion and a displaced pulp canal. The application of a fixed retention device is recommended in light of accelerated apposition of repair cementum during the retention period. However, increased formation of Sharpey's fibers during the relapse period might suggest a restricted duration in splinting therapy.

Dentin and osteodentin matrix formation in apicoectomized replanted incisors in cats

The reestablishment and rate of osteodentin and dentin matrix formation in 27 apicoectomized replanted and 20 control incisors in cats were studied after Procion H8-BS vital staining. In control teeth the pattern of matrix formation differed in the various pulpal zones, with a higher rate of matrix formed toward apical areas, most dominantly in maxillary incisors. Osteodentin formation could be traced after a lag period of more than 10 days after replantation. Thirty and 60 days postoperatively osteodentin matrix was found in the total pulpal length in 83% and 73% of the teeth, respectively. A common finding was a tubular osteodentin matrix in the pulpal apical third in the replanted teeth. Tubular osteodentin matrix was, however, present most incisally in some teeth 60 days postoperatively. Internal resorption corresponding to outer cervical lesions dominated the pulpal reactions in the maxillary replanted teeth after 60 days. It is concluded that under the present experimental conditions the pulp tissue possesses a high healing potential and that the osteodentin formation reflects the pulpal healing pattern after replantation traumas. The results also indicate that successful pulpal healing depends on unexposed dentinal tubules.

Growth pattern of the mandible: some reflections

The dynamics of the growth of bones is a complex process. The growth pattern of the mandible has been assessed by the application of various methods described for the study of the growth of bones. Some of these lend themselves primarily to basic experimental rather than clinical work. The use of any one of these methods will reveal certain information. With the use of two or more of them in combination, however, considerably more accurate information can be obtained. Since John Hunter's classical descriptions more than 200 years ago, advances in the understanding of the growth pattern of the mandible have been possible with the refinement of older methods and the development of newer ones. To date, serial cephalometric roentgenography in concert with radiopaque implants, which serve as fixed reliable markers, is the most accurate method to determine the growth pattern of the mandible. To this armamentarium, digital subtraction radiography, computerized tomography, and magnetic resonance imaging may be methods that will offer more detailed and accurate information.

Effects on pulp and dentin of iontophoresis of sodium fluoride on exposed roots in dogs

Experiments were performed on young permanent teeth in which there was demonstrable active dentin formation. Following surgical exposure of roots and removal of cementum with scalers, 1 percent sodium fluoride in aqueous solution was applied either topically or with direct-current iontophoresis. Two levels of current, therapeutic or five times therapeutic, were used. Observation periods were 7 and 80 days. There were no demonstrable histologic or ultrastructural alterations of the underlying pulp; nor was there a resultant change in the rate of dentin formation. While exposure of root surface dentin alone (negative control) produced no alterations, grinding the surface (positive control) caused noticeable changes in dentin, odontoblasts, and pulp.