Neurotransmitters, cytokines, and the control of alveolar bone remodeling in orthodontics.

This article described research aimed at testing the hypothesis that tissue remodeling during orthodontic tooth movement is modulated, at least in part, by factors derived from the nervous and vascular (immune) systems. Specifically, the neurotransmitters SP and VIP and the cytokines IL-1 alpha and IL-1 beta were localized immunohistochemically in paradental tissues of cat canines that had been treated by the application of an 80 g tipping force for 1 hour to 14 days. Increased staining (concentrations) of these agents were found in areas of PDL tension and compression at different time periods. Moreover, administration of SP and IL-1 beta to human PDL fibroblasts in vitro for 1 to 60 minutes resulted in significant increases in the levels of the intracellular "second messenger" cAMP, as well as of PGE2, a plasma membrane-associated fatty acid believed to serve as a local regulator of bone cell activity. Taken together, these results tend to support the hypothesis that neurotransmitters and cytokines play a regulatory role in orthodontic force-induced alveolar bone remodeling. Consequently, determination of the cytokine synthetic activity by leukocytes of orthodontic patients may inform about their alveolar bone remodeling potential.

Pseudoelasticity and thermoelasticity of nickel-titanium alloys: a clinically oriented review. Part I: Temperature transitional ranges.

The purpose of this review was to organize a systematic reference to help orthodontists evaluate commonly used orthodontic nickel-titanium alloys. Part I of the article reviews the data available in the literature regarding the temperature transitional ranges of the alloys. The thermomechanical behavior of these compounds is, in fact, strictly dependent on the correlation between the temperature transitional range and the oral temperature range. Part II of the article will focus on the mechanical characteristics of the alloys, such as the magnitude of the forces delivered and its correlations with temperature transitional range and oral temperature.

Pseudoelasticity and thermoelasticity of nickel-titanium alloys: a clinically oriented review. Part II: Deactivation forces.

The purpose of this review was to organize a systematic reference to help orthodontists evaluate commonly used orthodontic nickel-titanium alloys. Part I of the article reviewed the data available in the literature regarding the temperature transitional ranges of the alloys. The thermomechanical behavior of these compounds is, in fact, strictly dependent upon the correlation between the temperature transitional range and the oral temperature range. Part II focuses on the mechanical characteristics of the alloys, such as the magnitude of the forces delivered and correlations with the temperature transitional range and oral temperature.

Autoradiographic localization of technetium-99 methylene diphosphonate in growth sites of young mice.

Conflicting reports about the localization of 99mTc-MDP in bone and cartilage are found in the literature. Possible binding sites include hydroxyapatite and non-osteoid matrix such as immature collagen. The present study used autoradiographs of demineralized and non-demineralized growth sites in young mice to demonstrate localization of 99Tc-MDP, and consequently 99mTc-MDP, in mineralizing cartilage and bone. Uptake of the isotope was seen in mineralizing bone and cartilage, associated with the mineral in contrast to the organic phase. The results indicate that bone seeking radiopharmaceutical uptake (BSRU) may detect alterations in the rate of mineralized phase in growth sites and thus has the potential to disclose skeletal growth disorders.

The quantitative and qualitative analysis of the craniofacial skeleton of mice lacking the IGF-I gene.

Insulin-like growth factors are mediators of growth hormone and are believed to also stimulate growth independently. Insulin-like growth factor I (IGF-I) null mutant mice exhibit a lower rate of skeletal growth compared with their wild-type (control) littermates. Although their general body dimensions seem proportionate, their heads appear shortened with a blunt nose compared with the controls. The aim of this project was threefold: 1) to investigate whether differences in shape/form exist between the craniofacial skeleton of the IGF-I null mutant mice and their control littermates by using three techniques; 2) to determine whether the three techniques yield similar, different, or complementary information regarding the size and shape of specimens; and 3) to investigate whether the histological sections obtained from the craniofacial skeleton exhibit any differences between the two groups. Thirty adult male mice, 12 mutant and 18 wild type, obtained from 11 litters were examined. Lateral and superio-inferior radiographs of their head were analyzed by the procrustes, the macroelement, and the traditional cephalometric techniques. Later, the animals were processed for routine histological examination. The IGF null mutant mice demonstrated a generalized decrease of craniofacial size (43-64% of the normal adult size) and a non-allometric change of shape when compared with their wild-type littermates. While the mandible did not exhibit any shape changes, the facial and cranial areas demonstrated prominent changes. Examination of histological sections did not reveal any structural difference between the two groups at the adult stage. Furthermore, procrustes and macroelement techniques offer a more complete, detailed, and comprehensive description of the specimens compared.

99mTc-medronate uptake in the temporomandibular joints of young rats treated with a mandibular hyperpropulsor.

To correct maxillomandibular sagittal discrepancies in growing children, most functional appliances position the mandible more anteriorly than its habitual relation with the maxilla. The aim of this study was to evaluate the effects of such a procedure on the mineralization of the temporomandibular joints in young growing rats. Temporomandibular joint uptake of a radioactive bone marker, technetium 99m methylene diphosphonate (99mTc-MDP), was measured over time as a hyperpropulsor appliance was being worn intermittently 12 hours/day. As the uptake of 99mTc-MDP decreased in control animals, it increased significantly in the joints of treated rats before returning to the baseline level after 5 weeks of treatment. These results suggest that intermittent anterior positioning of the mandible induces a high rate of bone and cartilage remodeling in the joints of growing rats and that bone-seeking radiopharmaceutical uptake, with 99mTc-MDP, may be a useful technique to monitor joint adaptation to an experimental functional change.

Substance P immunoreactivity in periodontal tissues during orthodontic tooth movement.

Neurotransmitters, such as substance P (SP), may mediate the biological response to mechanical stress applied to teeth during orthodontic treatment. This hypothesis was investigated immunohistochemically on maxillae of cats which had one maxillary canine tipped distally for a period of time ranging from 1 h to 14 days. Horizontal histological sections 5 microns thick, collected on adhesive tape while still frozen, then freeze-dried, were stained by an immunoglobulin-enzyme bridge method using rabbit anti-SP polyclonal antibodies. The specificity of the staining was evaluated either by using the serum of non-immunized rabbits in lieu of anti-SP serum, or by pre-incubating the anti-SP serum with the antigen. Only sparse SP-like immunoreactivity was detected in the dental pulp, near or in the walls of blood vessels, or in the periodontal ligament (PDL) of unstressed canines. However, the density of neuronal elements exhibiting positive staining for SP appeared to increase markedly after application of an orthodontic force. This phenomenon occurred rapidly (3 h) in the dental pulp, but later in the PDL (24 h to 14 days), mainly at compression sites. These results demonstrate that the stimulation of periodontal nerve terminals by means of orthodontic forces may induce the peripheral release of the neurotransmitter SP, suggesting that it may be an initial trigger for a biochemical cascade which comprises the activation of various types of PDL cells.