Continuous monitoring of the movements of erupting and newly erupted teeth of limited growth (ferret mandibular canines) and their responses to hexamethonium

Activin A Promotes Osteoblastic Differentiation of Human Preosteoblasts through the ALK1-Smad1/5/9 Pathway

Activin A, a member of transforming growth factor-β superfamily, is involved in the regulation of cellular differentiation and promotes tissue healing. Previously, we reported that expression of activin A was upregulated around the damaged periodontal tissue including periodontal ligament (PDL) tissue and alveolar bone, and activin A promoted PDL-related gene expression of human PDL cells (HPDLCs). However, little is known about the biological function of activin A in alveolar bone. Thus, this study analyzed activin A-induced biological functions in preosteoblasts (Saos2 cells). Activin A promoted osteoblastic differentiation of Saos2 cells. Activin receptor-like kinase (ALK) 1, an activin type I receptor, was more strongly expressed in Saos2 cells than in HPDLCs, and knockdown of ALK1 inhibited activin A-induced osteoblastic differentiation of Saos2 cells. Expression of ALK1 was upregulated in alveolar bone around damaged periodontal tissue when compared with a nondamaged site. Furthermore, activin A promoted phosphorylation of Smad1/5/9 during osteoblastic differentiation of Saos2 cells and knockdown of ALK1 inhibited activin A-induced phosphorylation of Smad1/5/9 in Saos2 cells. Collectively, these findings suggest that activin A promotes osteoblastic differentiation of preosteoblasts through the ALK1-Smad1/5/9 pathway and could be used as a therapeutic product for the healing of alveolar bone as well as PDL tissue.

Effects of Activin A on the phenotypic properties of human periodontal ligament cells

Periodontal ligament (PDL) tissue plays an important role in tooth preservation by structurally maintaining the connection between the tooth root and the bone. The mechanisms involved in the healing and regeneration of damaged PDL tissue, caused by bacterial infection, caries and trauma, have been explored. Accumulating evidence suggests that Activin A, a member of the transforming growth factor-β (TGF-β) superfamily and a dimer of inhibinβa, contributes to tissue healing through cell proliferation, migration, and differentiation of various target cells. In bone, Activin A has been shown to exert an inhibitory effect on osteoblast maturation and mineralization. However, there have been no reports examining the expression and function of Activin A in human PDL cells (HPDLCs). Thus, we aimed to investigate the biological effects of Activin A on HPDLCs. Activin A was observed to be localized in HPDLCs and rat PDL tissue. When PDL tissue was surgically damaged, Activin A and IL-1β expression increased and the two proteins were shown to be co-localized around the lesion. HPDLCs treated with IL-1β or TNF-α also up-regulated the expression of the gene encoding inhibinβa. Activin A promoted chemotaxis, migration and proliferation of HPDLCs, and caused an increase in fibroblastic differentiation of these cells while down-regulating their osteoblastic differentiation. These osteoblastic inhibitory effects of Activin A, however, were only noted during the early phase of HPDLC osteoblastic differentiation, with later exposures having no effect on differentiation. Collectively, our results suggest that Activin A could be used as a therapeutic agent for healing and regenerating PDL tissue in response to disease, trauma or surgical reconstruction.

Mechanism and control of tooth eruption: overview and clinical implications

OBJECTIVES

To review pre- and post-emergent eruption, with particular emphasis on distinguishing isolated molar ankylosis from primary failure of eruption (PFE) and genetic considerations in eruption problems.

MATERIAL AND METHODS

Radiographic review of eruption failure patients; animal and human experiments; high precision observations of movements of erupting teeth.

RESULTS

In pre-emergent tooth eruption, the controlling element is the rate of resorption of overlying structures. A path is cleared, and then the erupting tooth moves along it. This has clinical importance in recognizing the cause of eruption problems, particularly PFE, in which all teeth distal to the most mesial involved tooth do not erupt or respond to orthodontics. In our study of by far the largest sample of PFE cases yet reported, familial cases of PFE accounted for approximately (1/4) of all cases examined. Candidate genes now are being evaluated. In post-emergent eruption, control seems to be light forces of long duration that oppose eruption, rather than heavy forces of short duration such as those during mastication. Studies of human premolars in their passage from gingival emergence to the occlusal plane show that in this phase eruption occurs only during a few hours in the early evening. The critical hours for eruption parallel the time that growth hormone levels are highest in a growing child. In this stage intermittent force does not affect the rate of eruption, but changes in periodontal blood flow do affect it.

Trigeminal nuclear complex of the ferret: anatomical and immunohistochemical studies

In order to establish the ferret as an animal model for studies of trigeminal pain, we describe the cytoarchitecture and neurochemistry of the trigeminal nuclear complex in the ferret and compare them to those of the cat and rat. The complex was divided as previously described, but the ferret differed in the extent of the nuclear boundaries. The neuroanatomical istribution of substance P-, calcitonin gene-related peptide-, galanin-, enkephalin-, serotonin-, somatostatin-, neuropeptide Y-, and neurotensin-immunoreactivity was determined throughout the rostrocaudal extent of the complex. In subnucleus caudalis, substance P-, calcitonin gene-related peptide-, enkephalin-, serotonin-, somatostatin-, neuropeptide Y-, and galanin-immunoreactivity was densest in laminae I and II. In subnucleus interpolaris, immunoreactivity for all the above neurochemicals was most dense along the lateral border and the ventral third of the caudal part of the subnucleus. Enkephalin-immunoreactive cell bodies were present in subnucleus caudalis and interpolaris. In subnucleus oralis, labelling for substance P, calcitonin gene-related peptide, galanin, enkephalin, and serotonin was most prominent in the dorsomedial part of the subnucleus. Somatostatin-immunoreactive cell bodies were distributed throughout the spinal nucleus. Labelling of serotonin, substance P, calcitonin gene-related peptide, galanin, enkephalin, and somatostatin was present in the main sensory nucleus. The motor nucleus contained fibers immunoreactive for substance P, enkephalin, serotonin and neuropeptide Y, and cell bodies immunoreactive for calcitonin gene-related peptide. The majority of neurotensin-immunoreactivity was found at the level of subnucleus caudalis, where it was densest in the trigeminal extension of the lateral cervical nucleus. The distribution of peptides in this species throughout the spinal nucleus is consistent with the notion that all the subnuclei may be involved in the processing of nociceptive inputs.

A comparison of the biomechanical properties of the periodontal ligaments of erupting and erupted teeth of non-continuous growth (ferret mandibular canines)

Extrusive loads of 0.01-0.2 N were applied to the permanent mandibular canine teeth of two groups of ferrets. In one group, aged approx. 7 weeks, the tooth had only recently emerged into the mouth. In the second group, comprising adult animals, the tooth had fully erupted and had been in function for a considerable time. Biphasic, viscoelastic-like responses followed both the application and removal of the load in both groups. However, there was significantly more mobility for all phases of the loading and recovery cycles in the erupting teeth. The data were compared with previous findings for continuously growing teeth. They highlight the marked periodontal changes which take place when tooth erupts into the mouth, provide some evidence against the generation of a tractional eruptive force, and show some differences in response between teeth of limited or continuous growth.