Correlations between response properties of periodontal mechanosensitive neurones in the primary somatosensory cortex of the rabbit and cortically induced rhythmical jaw movements

Neural mechanisms of nociception during orthodontic treatment

Orthodontic tooth movement is accompanied by inflammatory responses in the periodontal ligament. Chemical mediators such as interleukin-1β have key roles in nociception around teeth. Such nociceptive inputs to the periodontal ligament continue for several days and potentially induce plastic changes in higher brain regions, including the cerebral cortex. This review summarizes research on orthodontic treatment-induced modulation of neural activities in the central nervous system. Furthermore, we describe our recent findings on the spatiotemporal effects of orthodontic treatment in the somatosensory and insular cortices.

From periodontal mechanoreceptors to chewing motor control: A systematic review

PURPOSE

This critical review summarizes the current knowledge of the structural and functional characteristics of periodontal mechanoreceptors, and understands their role in the signal pathways and functional motor control.

METHOD

A systematic review of the literature was conducted. Original articles were searched through Pubmed, Cochrane Central database and Embase until january 2016.

RESULT

1466 articles were identified through database searching and screened by reviewing the abstracts. 160 full-text were assessed for eligibility, and after 109 exclusion, 51 articles were included in the review process. Studies selected by the review process were mainly divided in studies on animal and studies on humans. Morphological, histological, molecular and electrophysiological studies investigating the periodontal mechanoreceptors in animals and in humans were included, evaluated and described.

CONCLUSION

Our knowledge of the periodontal mechanoreceptors, let us conclude that they are very refined neural receptors, deeply involved in the activation and coordination of the masticatory muscles during function. Strictly linked to the rigid structure of the teeth, they determine all the functional physiological and pathological processes of the stomatognathic system. The knowledge of their complex features is fundamental for all dental professionists. Further investigations are of utmost importance for guiding the technological advances in the respect of the neural control in the dental field.

Impaired mastication reduced newly generated neurons at the accessory olfactory bulb and pheromonal responses in mice

OBJECTIVES

A large number of neurons are generated at the subventricular zone (SVZ) even during adulthood. In a previous study, we have shown that a reduced mastication impairs both neurogenesis in the SVZ and olfactory functions. Pheromonal signals, which are received by the vomeronasal organ, provide information about reproductive and social states. Vomeronasal sensory neurons project to the accessory olfactory bulb (AOB) located on the dorso-caudal surface of the main olfactory bulb. Newly generated neurons at the SVZ migrate to the AOB and differentiate into granule cells and periglomerular cells. This study aimed to explore the effects of changes in mastication on newly generated neurons and pheromonal responses.

DESIGN

Bromodeoxyuridine-immunoreactive (BrdU-ir; a marker of DNA synthesis) and Fos-ir (a marker of neurons excited) structures in sagittal sections of the AOB after exposure to urinary odours were compared between the mice fed soft and hard diets.

RESULTS

The density of BrdU-ir cells in the AOB in the soft-diet-fed mice after 1 month was essentially similar to that of the hard-diet-fed mice, while that was lower in the soft-diet-fed mice for 3 or 6 months than in the hard-diet-fed mice. The density of Fos-ir cells in the soft-diet-fed mice after 2 months was essentially similar to that in the hard-diet-fed mice, while that was lower in the soft-diet-fed mice for 4 months than in the hard-diet-fed mice.

CONCLUSIONS

The present results suggest that impaired mastication reduces newly generated neurons at the AOB, which in turn impairs olfactory function at the AOB.

Thalamic input to representations of the teeth, tongue, and face in somatosensory area 3b of macaque monkeys

Representations of the parts of the oral cavity and face in somatosensory area 3b of macaque monkeys were identified with microelectrode recordings and injected with different neuroanatomical tracers to reveal patterns of thalamic projections to tongue, teeth, and other representations in primary somatosensory cortex. The locations of injection sites and resulting labeled neurons were further determined by relating sections processed to reveal tracers to those processed for myeloarchitecture in the cortex and multiple architectural stains in the thalamus. The ventroposterior medial subnucleus (VPM) for touch was identified as separate from the ventroposterior medial parvicellular nucleus (VPMpc) for taste by differential expression of several types of proteins. Our results revealed somatotopically matched projections from VPM to the part of 3b representing intra-oral structures and the face. Retrogradely labeled cells resulting from injections in area 3b were also found in other thalamic nuclei including: anterior pulvinar (Pa), ventroposterior inferior (VPI), ventroposterior superior (VPS), ventroposterior lateral (VPL), ventral lateral (VL), center median (CM), central lateral (CL), and medial dorsal (MD). None of our injections, including those into the representation of the tongue, labeled neurons in VPMpc, the thalamic taste nucleus. Thus, area 3b does not appear to be involved in processing taste information from the thalamus. This result stands in contrast to those reported for New World monkeys.

Physiological properties of molar-mechanosensitive periodontal neurons in the trigeminal ganglion of the rat

Spike discharges from periodontal mechanosensitive neurones responding to the mechanical stimulation of molar teeth were recorded from the trigeminal ganglion of rats anaesthetized with pentobarbital sodium. Maxillary molar-sensitive units were close together in a narrow, lateral area of the maxillary division of the ganglion, whereas those of mandibular molar-sensitive units were scattered throughout the mandibular division. The majority of maxillary molar-sensitive units responded only to stimulation of the first molar. They were slowly adapting and responded most strongly to pressure applied to the lingual surface and buccal cusp of the tooth or to the buccal surface and lingual cusp. By contrast, approximately one-half of the mandibular molar-sensitive units were rapidly adapting, multitooth units that responded to tooth stimulation almost equally in all directions. The other half were slowly adapting and activated most effectively by pressure applied to the lingual surface and buccal cusp of the molar tooth. These slowly adapting units consisted of first molar-sensitive, single- and multitooth units. Differences in the response characteristics of the maxillary and mandibular molar-sensitive periodontal units may reflect differences in the sensory role of individual molars.

Oral biology and disorders of lagomorphs

Rabbit medicine, and dentistry in particular, is still at an early stage of development. With an understanding of the underlying oral physiology it is possible to devise an appropriate treatment regime for most dental problems after the nature and extent of disease has been assessed. Although many of the dental problems that are seen in practice cannot be cured, most can be controlled or managed to allow the affected rabbit to maintain a good quality of life. The continuously growing nature of the teeth makes recurrence and progression of problems the norm, so owner education and ongoing monitoring of animals is essential. By assessing the effects, beneficial or otherwise, of out treatments and communicating this to others, we will develop our knowledge and skills. Several treatments that are suggested in this article must be considered as "experimental" because they have not been assessed in large numbers of animals. If they work for you, or more importantly, if you find unexpected complications with a treatment method (as has happened with the use of calcium hydroxide paste treatment of abscess cavities) then please publicize the fact so that others can avoid the problem. Until the message on prevention can be reliably transmitted to owners, we will continue to have oral and dental problems to manage. After confidence and experience has been gained in anesthetizing rabbits it is possible to refine one's dental skills to be able to rapidly perform a thorough examination and basic treatments. Major and complex treatments require careful consideration because they may add to the animal's problems, rather than improving the situation. The best method for learning rabbit dentistry is to routinely perform postmortem examinations following euthanasia of affected animals, and spend an hour or two practicing handling the instruments and performing procedures on a cadaver. If you are not confident in your ability or do not have the best equipment for the job, the client should be informed and offered the opportunity to be referral to a "specialist."