Biomimetic Remineralization of Demineralized Dentine Using Scaffold of CMC/ACP Nanocomplexes in an In Vitro Tooth Model of Deep Caries

Currently, it is still a tough task for dentists to remineralize dentine in deep caries. The aim of this study was to remineralize demineralized dentine in a tooth model of deep caries using nanocomplexes of carboxymethyl chitosan/amorphous calcium phosphate (CMC/ACP) based on mimicking the stabilizing effect of dentine matrix protein 1 (DMP1) on ACP in the biomineralization of dentine. The experimental results indicate that CMC can stabilize ACP to form nanocomplexes of CMC/ACP, which is able to be processed into scaffolds by lyophilization. In the single-layer collagen model, ACP nanoparticles are released from scaffolds of CMC/ACP nanocomplexes dissolved and then infiltrate into collagen fibrils via the gap zones (40 nm) to accomplish intrafibrillar mineralization of collagen. With this method, the completely demineralized dentine was partially remineralized in the tooth mode. This is a bottom-up remineralizing strategy based on non-classical crystallization theory. Since nanocomplexes of CMC/ACP show a promising effect of remineralization on demineralized dentine via biomimetic strategy, thereby preserving dentinal tissue to the maximum extent possible, it would be a potential indirect pulp capping (IPC) material for the management of deep caries during vital pulp therapy based on the concept of minimally invasive dentistry (MID).     

Effect of electro-acupuncture on the response of the trigeminal nucleus evoked by electric stimulation of dental pulp in the cat]

The potential in the spinal trigeminal nucleus evoked by electrical tooth pulp stimulation is depressed by electro-acupuncture given to the acupuncture point in the course of the nerve innervating the stimulated tooth.     

Tissue contributions to sex and race: differences in tooth crown size of deciduous molars.

This study describes size of constituent deciduous tooth crown components (enamel, dentine, and pulp) to address the manner in which males characteristically have larger teeth than females, and the observation that teeth of American blacks are larger than those of American whites. Measurements were collected (n = 333 individuals) from bitewing radiographs using computer-aided image analysis. Tissue thicknesses (enamel, dentine, pulp) were measured at the crown's mesial and distal heights of contour. Deciduous mesiodistal molar crown length is composed of about 1/7 enamel, 1/3 dentine, and 1/2 pulp. Details differ by tooth type, but males typically have significantly larger dentine and pulp dimensions than females; there is no sexual dimorphism in marginal enamel thickness. Males scale isometrically with females for all variables tested here. Blacks significantly exceed whites in size of all tissues, but tissue types scale isometrically with blacks and whites with one exception: enamel thickness is disproportionately thick in blacks. While the absolute difference is small (5.56 mm of enamel in blacks summed over all four deciduous molar tooth types vs. 5.04 mm in whites), the statistical difference is considerable (P < 0.001). Aside from enamel, crown size in blacks is increased proportionately vis-à-vis whites. Principal components analysis confirmed these univariate relationships and emphasizes the statistical independence of crown component thicknesses, which is in keeping with the sequential growth and separate embryonic origins of the tissues contributing to a tooth crown. Results direct attention to the rates of enamel and dentine deposition (of which little is known), since the literature suggests that blacks (with larger crowns and thicker enamel) spend less time in tooth formation than whites.     

Material properties of coyote dentine under bending: gradients in flexibility and strength by position

We investigate the nonlinear properties of dentine from the upper canines of coyotes Canis latrans with bending tests. With the results we predict the behavior of whole canines under load. Coyote dentine is not homogeneous but is stronger and more ductile farther away from the pulp cavity. The modulus of rupture (MOR) first increases and then declines with distance from the pulp cavity. Our analysis of the composite nature of dentine produced by these gradients indicates that there may be an adaptive explanation with the composite having nearly the strength of the strongest dentine and a work of fracture greater than even the most ductile dentine. Coyote dentine is considerably stronger than human dentine. In coyotes, the peak MOR, a measure of bending strength, is 480 MPa, compared with a maximum of 225 MPa for human dentine. This value is about the same as the weakest coyote dentine that we found near the pulp cavity. Finally, enamel plays, at most, a small role in the bending strength of the whole tooth. Our results indicate that enamel under tension adds little to strength, but we cannot dismiss a small role for enamel in compression.     

Inhibition, by electro-acupuncture, of the scalp evoked potential induced by painful stimulation of the tooth in man]

Scalp potentials evoked by electrical stimulation of the tooth pulp can be diminished in amplitude by electroacupuncture. This diminution goes generally in inverse with the increase in subjective pain threshold.     

Effect of cerebral ventricles perfusion with naloxone on trigemino-hypoglossal reflex in rats

The goal of this study was to determine whether opioid receptor antagonist naloxone abolishes the influence of periaqueductal central gray (PAG) on nociceptive evoked tongue jerks (ETJ) -- a trigemino-hypoglossal reflex induced by tooth pulp stimulation. In rats under chloralose anesthesia three series of experiments were performed. In the first two groups perfusions of lateral ventricles-cerebellomedullary cistern with McIlwain-Rodnight's solution and naloxone were carried out. In group 3 naloxone was infused through a catheter through the jugular vein. The amplitudes of tongue jerks induced by tooth pulp stimulation were recorded during subsequent 10 min perfusions. Mean amplitude of tongue movements induced by tooth pulp stimulation was regarded as the indicator of the magnitude of trigemino-hypoglossal reflex. We observed that perfusion of the cerebral ventricles with naloxone (100 nmol/ml) increased the trigemino-hypoglossal reflex up to 143%. The amplitude of ETJ was significantly reduced during PAG stimulation with a train of electrical impulses. After obtaining a significant -- 93% -- inhibition of ETJ (7% of the control), naloxone (100 nmol/ml) was added to the perfusion fluid. This led to a significant increase of the reflex up to 68%. Infusion of naloxone through the jugular vein did not affect the reflex. The above results suggest that the inhibition of ETJ due to PAG stimulation is partially reversed by naloxone and mediated via interactions with endogenous opioid systems involved in modulation of nociception.     

An investigation of dentinal fluid flow in dental pulp during food mastication: simulation of fluid–structure interaction

This study uses fluid–structure interaction (FSI) simulation to investigate the relationship between the dentinal fluid flow in the dental pulp of a tooth and the elastic modulus of masticated food particles and to investigate the effects of chewing rate on fluid flow in the dental pulp. Three-dimensional simulation models of a premolar tooth (enamel, dentine, pulp, periodontal ligament, cortical bone, and cancellous bone) and food particle were created. Food particles with elastic modulus of 2,000 and 10,000 MPa were used, respectively. The external displacement loading $(5\,\upmu \hbox {m})$ was gradually directed to the food particle surface for 1 and 0.1 s, respectively, to simulate the chewing of food particles. The displacement and stress on tooth structure and fluid flow in the dental pulp were selected as evaluation indices. The results show that masticating food with a high elastic modulus results in high stress and deformation in the tooth structure, causing faster dentinal fluid flow in the pulp in comparison with that obtained with soft food. In addition, fast chewing of hard food particles can induce faster fluid flow in the pulp, which may result in dental pain. FSI analysis is shown to be a useful tool for investigating dental biomechanics during food mastication. FSI simulation can be used to predict intrapulpal fluid flow in dental pulp; this information may provide the clinician with important concept in dental biomechanics during food mastication.     

Fluoride-induced changes to proteoglycan structure synthesised within the dentine-pulp complex in vitro

Fluoride is known to influence mineralisation patterns within dentine, where alterations in the post-translational modification of proteoglycans (PG) have been proposed as an implicating factor. In light of recent studies elucidating changing PG profiles in the transition of predentine to mineralised dentine, this study investigates the influence of fluoride on the major PG populations (decorin, biglycan and versican) within the pulp, predentine and dentine. Tooth sections from rat incisors were cultured for 14 days in the presence 0, 1 and 6 mM sodium fluoride and the PG extracted from the pulp, predentine and dentine matrices. PG species and corresponding metabolites were identified by their immuno-reactivity to antibodies against decorin, biglycan and versican. Component glycosaminoglycan chains were characterised with respect to their nature, chain length and disaccharide composition. Levels of PG extracted from pulp and predentine were reduced, particularly for biglycan. Fluoride did not influence levels of decorin or versican within predentine or dentine, although the processing of these macromolecules within pulp and predentine was affected, particularly at higher fluoride concentrations. Levels of dermatan sulfate were reduced within pulp and predentine, although the effect was less pronounced for predentine. Fluoride reduced sulfation of glycosaminoglycan chains within pulp and predentine tissues, with a notable reduction in Deltadi6S evident. In all three tissues, glycosaminoglycan chain length was reduced. Considering the various roles for PG in the dentine-pulp complex, either directly or indirectly in the mineralisation process, changes in the synthesis, structure and processing of the different PG species within the pulp, predentine and dentine matrices provides a further molecular explanation for the altered mineralisation patterns witnessed during fluorosis.     

The effect of naloxone on trigemino-hypoglossal reflex inhibited by periaqueductal central gray stimulation in rats.

The aim of the study was to determine whether opioid receptor antagonist naloxone abolishes the influence of periaqueductal central gray (PAG) on nociceptive evoked tongue jerks (ETJ) - a trigemino-hypoglossal reflex induced by tooth pulp stimulation. In rats under chloralose anesthesia three subsequent series of perfusions of lateral ventricles - cerebellomedullary cistern with Mc Ilwain-Rodnight's solution, Met-enkaphalin (Enk-Met) and naloxone were carried out. The amplitudes of tongue jerks induced by tooth pulp stimulation were recorded during subsequent 10 min perfusions. Mean amplitude of tongue movements induced by tooth pulp stimulation was regarded as the indicator of the magnitude of trigemino-hypoglossal reflex. We observed that perfusion of the cerebral ventricles with Enk-Met (100 nmol/mL) inhibited the trigemino-hypoglossal reflex by 46%, whereas naloxone (100 nmol/mL), added to the solution perfusing the cerebral ventricles system, increased the reflex by 42%. The amplitude of ETJ was significantly reduced during PAG stimulation with a train of electrical impulses. After obtaining a significant 93% - inhibition of ETJ, naloxone (100 nmol/mL) was added to the perfusion fluid. This led to a significant increase of the reflex by 68%. The above results suggest that the inhibition of ETJ due to PAG stimulation is partially reversed by naloxone and mediated via interactions with endogenous opioid systems involved in modulation of nociception.     

Structure and Development of the Odontodes in an Armoured Catfish,Corydoras aeneus (Siluriformes,Callichthyidae)

Abstract In some living osteichthyans (e.g. the armoured catfishes) the postcranial dermal skeleton exhibits tooth-like structures (odontodes) similar to those present in the dermal skeleton of the ancient craniates. We have undertaken this work to compare odontode with tooth development, structure, attachment to a bony support and replacement. We studied the odontodes fixed on the scutes (i.e. postcranial dermal plates) in a growth series of Corydoras aeneus using light, scanning and transmission electron microscopy. Odontodes are constituted of a pulp cavity surrounded by a cone of dentine itself capped with hypermineralized substance. The pulp cavity is devoid of nerves and blood vessels and there are no odontoblastic processes in the dentine. The dentine cone is firmly attached to a circular bony protuberance of the scute surface, the pedicel or attachment bone, by means of a ligament. An odontode anlage develops as a small invagination of a dermal papilla projecting into the epidermis, the basal cell layer of which constitutes a dental epithelium. First, dentine is deposited, next the hypermineralized substance, then the ligament and attachment bone. Odontodes develop in two positions with regard to the scute surface: a primary position when new odontodes form at the posterior border of the enlarging scute; a secondary position when new odontodes replace old odontodes that have been shed during thickening of the scute. In this case, the ligament and part of the base of the dentine cone are resorbed but not the pedicel of attachment bone, which is covered by deposition of scute matrix after the odontode has been shed. Within the scute matrix, the embedded pedicels of successive generations of odontodes are preserved, forming piles in the scutes of adult specimens.     

Effects of stimulating midbrain central gray matter on neuronal response in the caudal trigeminal nucleus to peripheral nerve stimulation

Stimulating the midbrain central gray matter (CGM) with trains of 10–20 stimuli was found to inhibit response to electrical stimulation of infraorbital nerve and tooth pulp A-alpha and A-delta afferents at 100 msec intervals in 65% of the caudal trigeminal nucleus in neurons tested during experiments on cats under chloralose-Nembutal anesthesia. Response was inhibited most effectively in convergent neurons (activated by stimulating infraorbital nerve and tooth pulp A-alpha and A-delta afferents) to stimulating tooth pulp (0.76) and, to a somewhat lesser degree, to stimulation of A-alpha afferents (0.6). For high-threshold neurons (activated by stimulating infraorbital nerve and tooth pulp A-delta afferents), success rate of inhibiting response under the effects of CGM stimulating measured 0.71 and 0.48 for low-threshold cells (activated by stimulating infraorbital nerve A-alpha afferents). Stimulating CGM produced an excitatory response in 10 caudal trigeminal nucleus neurons within 7.5–20 msec; after this neurons showed no reaction to peripheral nerve stimulation for a 200–450 msec period. The possible involvement of these neurons in pressing the mouth-opening reflex produced by CGM stimulation is discussed in this article.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 6, pp. 729–736, November-December, 1988.     

Nano- and micromechanical properties of dentine: Investigation of differences with tooth side

The soft zone in dentine beneath the dentino-enamel junction is thought to play an important role in tooth function, strain distribution and fracture resistance during mastication. Recently reported asymmetry in mechanical properties with tooth side may point at a basic property of tooth function. The aim of our study was to test if this asymmetry was reflected in the nano- and micromechanical properties of dentine. We investigated the mechanical properties of dentine on the buccal and lingual side of nine extracted human teeth using nano- and microindentation. Properties were analysed on the natural log scale, using maximum likelihood to estimate the parameters. Two-sided 0.05-level likelihood ratio tests were used to assess the influences of surface (buccal versus lingual) and dentine depth, measured from the DEJ in crown dentine and from the CDJ in root dentine. Results showed the well known gradual increase in mechanical properties with increasing distance from the DEJ. Coronal dentine showed higher elastic modulus and hardness on the lingual side of teeth for all measurements, while root dentine was harder on the buccal side. Due to the subtlety of these effects and the small number of teeth studied, results failed to reach statistical significance. Results suggest that dentine nano- and micromechanical properties vary with tooth side in agreement with recent literature using macroscopic methods. They also reveal that buccal-lingual ratios of hardness are in opposite directions in crown and root dentine, suggesting compensatory functions.     

How the microstructure of dentine can contribute to reconstructing developing dentitions and the lives of hominoids and hominins

Accounts of dentine microstructure are less well established in the primate life history literature than those of enamel microstructure. The aim of this paper is to draw some basic comparisons between enamel and dentine, but at the same time to show how dentine microstructure can make a major but different contribution to reconstructing past lives than enamel can. Dentine has both an organic and an inorganic component. The organic component contains growth factors, stable isotopes and DNA that survive long after death. The mineral component contains trace elements and preserves an incremental record of tooth growth. These can be used to put a time scale to many past events when the chemistry or microstructure of dentine has become altered during tooth growth. Dentine microstructure allows us to reconstruct tooth root growth in the past and has contributed to a fuller understanding of the modular nature of developing dentitions among hominoids and hominins.     

The histology of tooth formation in the Australian lungfish, Neoceratodus forsteri Krefft

The histology of developing toothplates of Neoceratodusforsteri from the time of first appearance of the tooth primordia to the adult condition has been investigated. The dentition develops by the formation of a shell of primary epithelial and mesenchymal matrices. Within the shell, secondary mesenchymal matrix and central material, both containing columns of tertiary matrix, are laid down. Primary epidielial matrix appears to contain collagen and is closely associated with the epithelium of the mouth. All other tooth tissues as well as the supporting bone develop in association with mesenchyme. Primary, secondary and tertiary mesenchymal matrices appear to contain collagen. Central dentine contains some fibres, possibly of reticulin or collagen, within a matrix of unknown composition.
The tooth is attached to the underlying bone by a pedestal of bone and this grows with the tooth material.
New tooth tissues are formed in the pulp cavity in layers below the older material, causing the toothplate to grow in every dimension as the animal grows.
An evolutionary pathway is suggested for lungfish with a dentition of cusps arranged in radiating ridges.     

A longitudinal study of tooth resorption in newly metamorphosed Xenopus laevis, with comments on tooth resorption in amphibians

Late larvae and newly metamorphosed specimens of Xenopus laevis (Daudin) were reared in such a way that their growth rates were assessed as similar. After the larvae had reached Nieuwkoop and Faber Stage 65,12 were killed each day for eight days, so that the events in resorption of the first teeth to develop could be studied histologically, and an absolute time scale applied. Resorption extended over several days and occurred in two phases, (a) erosion and (b) absorption. Erosion was a process lasting several days, and involved the destruction of a small quantity of dentine and adjacent bone at the base of a standing tooth. Osteoclasts were not seen inside the pulp, but were confined to the outer aspect of the dentine and bone, and were removing the hard tissues from without. Absorption was a rapid process lasting about 48 hours, during which the majority of the dental tissue was destroyed. Osteoclasts resorbed the dentine piecemeal from within along its full length from base to tip. As a result, the vast majority (probably all) of the calcified tissues would seem to have been available for reabsorption and recycling. It seemed that erosion occurred as a result of local mechanical factors (the growing successional tooth), but that absorption was controlled by a specific timing mechanism. It is suggested that gross internal resorption of teeth may be common in Amphibia, and that even in species where crowns are shed, extensive thinning of the dentine from its pulpal aspect is likely to have occurred beforehand.     

Effect of vasopressin on neuronal responses of theNucl. Caudalis of the spinal trigeminal tract in rats

Effect of vasopressin on responses of individual neurons of thenucl. caudalis of the spinal trigeminal tract was studied on rats under urethan anesthesia; the responses were evoked by nociceptive (stimulation of the tooth pulp) or non-nociceptive (stimulation of Aa fibers of the infraorbital nerve) afferent activation. After injection of 10 nM vasopressin into the recording zone, responses evoked by stimulation of the tooth pulp were suppressed in all studied neurons of the high-threshold group; the same was true as to responses induced by stimulation of the tooth pulp and infraorbital nerve in most neurons of the convergent group. At the same time, vasopressin did not change the responses evoked by stimulation of Aa fibers of the infraorbital nerve in neurons of the low-threshold group. Possible involvement of vasopressin in the process of pain suppression is discussed.     

Influence of orotic acid upon post-excitatory facilitation released by stimulation of the tooth pulp]

The influence of orotic acid on post-excitatory facilitation of evoked potentials released by electric stimulation of the tooth pulp in the sensomotor cortex was studied. 15-360 min following application of 100 mg/kg orotic acid, increase in amplitude of potentials released by stimulation of the tooth pulp, reinforcement of the post-excitatory facilitation observable 5 msec after stimulation occurred.     

Notch signalling pathway in tooth development and adult dental cells

Notch signalling is a highly conserved intercellular signal transfer mechanism that includes canonical and non-canonical pathways. It regulates differentiation and proliferation of stem/progenitor cells by means of para-inducing effects. Expression and activation of Notch signalling factors (receptors and ligands) are critical not only for development of the dental germ but also for regeneration of injured tissue associated with mature teeth. Notch signalling plays key roles in differentiation of odontoblasts and osteoblasts, calcification of tooth hard tissue, formation of cusp patterns and generation of tooth roots. After tooth eruption, Notch signalling can also be triggered in dental stem cells of the pulp, where it induces them to differentiate into odontoblasts, thus generating fresh dentine tissue. Other signalling pathways, such as TGFβ, NF-κB, Wnt, Fgf and Shh also interact with Notch signalling during tooth development.     

Microscopic and histochemical study of odontoclasts in physiologic resorption of teeth of the polyphyodont lizard, Liolaemus gravenhorsti

Using tartrate-resistant acid phosphatase (TRAP), we examined the cytodifferentiation of odontoclast cells in resorbing areas of dental tissues during the replacement of teeth in a polyphyodont lizard, Liolaemus gravenhorsti. We also report, by means of Lectin-HRP histochemistry, the distribution pattern of some specific sugar residues of TRAPase-positive cells. For detection of TRAPase activity, the azo dye-coupling technique was used. Lectin binding sites were demonstrated by means of specific HRP-lectins. The process of tooth resorption was divided into four stages: 1) preresorption-the wall of the dental pulp is covered with an odontoblast layer, and no TRAP-positive cells are in the dental pulp; 2) early resorption-TRAP-positive multinucleate odontoclasts are present on the dental wall, but the rest of the pulp surface is still covered with an odontoblast layer; 3) later resorption-the entire surface of the pulp chamber is lined with multinucleate odontoclasts; and 4) final resorption-the tooth has been totally resorbed. Odontoclasts are usually detached from the resorbed surface, and show signs of degeneration. Of the six lectins used, PNA, ECA, and UEA-1 bind to multinucleated but not mononuclear cells. All the remaining lectins, BS-1, RCA(120), and LTA showed no binding to any cells of the teeth. The significance of saccharidic moieties such as acetyl-galactosamine, acetyl-glucosamine, and fucose sugar residues is difficult to ascertain. Perhaps these oligosaccharides might be borne on molecules associated with odontoclastic resorption or associated with multinucleation of odontoclasts after attachment to the dentine surface.