Effects of ammonia and organic acids on the intradental sensory nerve activity

Identification of Putative Bacterial Pathogens for Orofacial Granulomatosis Based on 16S rRNA Metagenomic Analysis

Orofacial granulomatosis (OFG) is a chronic inflammatory disease characterized by nontender swelling of the orofacial tissues, the underlying cause of which remains unknown. Our previous study demonstrated that tooth apical periodontitis (AP) is involved in the development of OFG. To characterize the AP bacterial signatures of OFG patients and identify possible pathogenic bacteria that cause OFG, the compositions of the AP microbiotas in OFG patients and controls were compared using 16S rRNA gene sequencing. Pure cultures of putative bacterial pathogens were established by growing bacteria as colonies followed by purification, identification, and enrichment and then were injected into animal models to determine the causative bacteria contributing to OFG. A specific AP microbiota signature in the OFG patients was shown, characterized by the predominance of phyla Firmicutes and Proteobacteria, notably members of the genera Streptococcus, Lactobacillus, and Neisseria, were found. Streptococcus spp., Lactobacillus casei, Neisseria subflava, Veillonella parvula, and Actinomyces spp. from OFG patients were isolated and successfully cultured in vitro and then injected into mice. Ultimately, footpad injection with N. subflava elicited granulomatous inflammation. IMPORTANCE Infectious agents have long been considered to play a role in the initiation of OFG; however, a direct causal relationship between microbes and OFG has not yet been established. In this study, a unique AP microbiota signature was identified in OFG patients. Moreover, we successfully isolated candidate bacteria from AP lesions of OFG patients and assessed their pathogenicity in laboratory mice. Findings from this study may help provide in-depth insights into the role of microbes in OFG development, providing the basis for targeted therapeutic approaches for OFG.

Localization and changes in NADPH-diaphorase reactivity and nitric oxide synthase immunoreactivity in rat pulp following tooth preparation

Inflammatory changes in the dental pulp are accompanied by release of a wide variety of chemical mediators. Nitric oxide, an oxidative free radical produced by the enzyme nitric oxide synthase (NOS), has been implicated in multiple inflammatory processes, which makes it a suitable marker for changes which likely occur following tooth pulp insult. Since limited information on nitric oxide in the pulp is available, it is necessary first to examine relative distributions of NOS in uninflamed and inflamed rat pulp. We accomplished this by characterizing regions of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) activity and the distribution of both macrophage NOS (macNOS) and neuronal NOS (nNOS) immunoreactivity in normal and inflamed rat molar pulp at multiple time points. The results showed that: (1) deep cavity preparation on the mesial surface of the molar produced a time-dependent inflammation, with acute inflammation early progressing to chronic, granulomatous inflammation with necrosis later that spread preferentially down the mesial root; (2) control (non-prepared) teeth showed a relatively faint and homogeneous distribution of NADPH-d and macNOS reactivity but no discernible nNOS reactivity; (3) inflamed teeth displayed localized increased intensity of NADPH-d and macNOS reactivity surrounding the inflamed area of pulp, but no increased nNOS activity; (4) pulp vessels supplying the inflamed area showed increased NADPH-d reactivity, but no increased macNOS or nNOS reactivity; and (5) neither NADPH-d, macNOS, nor nNOS reactivity was observed in pulpal nerves. Therefore, nitric oxide may mediate the pulpal inflammatory response through its effects on the paralesional pulp tissue and surrounding endothelial/vascular structures.

Teeth and tooth nerves

(1) Although our knowledge on teeth and tooth nerves has increased substantially during the past 25 years, several important issues remain to be fully elucidated. As a result of the work now going on at many laboratories over the world, we can expect exciting new findings and major break-throughs in these and other areas in a near future. (2) Dentin-like and enamel-like hard tissues evolved as components of the exoskeletal bony armor of early vertebrates, 500 million years ago, long before the first appearance of teeth. It is possible that teeth developed from tubercles (odontodes) in the bony armor. The presence of a canal system in the bony plates, of tubular dentin, of external pores in the enamel layer and of a link to the lateral line system promoted hypotheses that the bony plates and tooth precursors may have had a sensory function. The evolution of an efficient brain, of a head with paired sense organs and of toothed jaws concurred with a shift from a sessile filter-feeding life to active prey hunting. (3) The wide spectrum of feeding behaviors exhibited by modern vertebrates is reflected by a variety of dentition types. While the teeth are continuously renewed in toothed non-mammalian vertebrates, tooth turnover is highly restricted in mammals. As a rule, one set of primary teeth is replaced by one set of permanent teeth. Since teeth are richly innervated, the turnover necessitates a local neural plasticity. Another factor calling for a local plasticity is the relatively frequent occurrence of age-related and pathological dental changes. (4) Tooth development is initiated through interactions between the oral epithelium and underlying neural crest-derived mesenchymal cells. The interactions are mediated by cell surface molecules, extracellular matrix molecules and soluble molecules. The possibility that the initiating events might involve a neural component has been much discussed. With respect to mammals, the experimental evidence available does not support this hypothesis. In the teleost Tilapia mariae, on the other hand, tooth germ formation is interrupted, and tooth turnover ceases after local denervation. (5) Prospective dental nerves enter the jaws well before onset of tooth development. When a dental lamina has formed, a plexus of nerve branches is seen in the subepithelial mesenchyme. Shortly thereafter, specific branches to individual tooth primordia can be distinguished. In bud stage tooth germs, axon terminals surround the condensed mesenchyme and in cap stage primordia axons grow into the dental follicle.(ABSTRACT TRUNCATED AT 400 WORDS)

Microbiologic factors in endodontology

The role of microorganisms in the cause of endodontic lesions has been intensively investigated. Bacterial components such as endotoxin and other cell wall components are implicated in the development of pulpal and periapical inflammation. Newer anaerobic microbiologic techniques have facilitated accurate and reproducible identification of endodontic pathogens, some of which have been reclassified. This article reviews and correlates newer microbiologic findings with clinical symptoms.

Inflammation and dental pain in man

In the present article special interest has been focused on indicators of latent and manifest pulpal inflammation studied by psychophysical and electrophysiological techniques. Intradental A-delta nerve activity was recorded from two electrodes placed in the dentin on the labial tooth surface. The psychophysical measures were obtained by means of direct scaling methods in combination with sensory verbal descriptors. For stimulation cooling (ethyl chloride) and heating (hot guttapercha) of the tooth surface were employed. In addition, potentially algogenic substances, bradykinin and histamine, were administered on partly exposed pulps. Hot guttapercha induced a more complex neural response pattern than ethyl chloride. In all the recordings the responses evoked by heat showed a characteristic pattern consisting of three phases: an initial phase of short duration (i) followed by a depression in activity relative to the baseline (ii) and a slow spontaneously emerging activity in the absence of a physical stimulus (iii). The latter neutral event (iii) passed unnoticed by all the subjects. In the light of earlier experiments on feline pulp it was hypothesized that this third phase of the neural response was an indication of hyperexcitability in dental pulps and thus inflammation. Those subjects who experienced pulsating, dull, lingering pain (clinically diagnosed as pulpitis) showed a poor correlation between magnitude estimates of their mixed pain percepts and the total flux of A-delta nerve activity. Bradykinin and histamine evoked dull pain in the majority of cases probably caused by excitation of pulpal C fibers. In one experiment A-delta neural discharge of short duration could also be triggered by histamine.(ABSTRACT TRUNCATED AT 250 WORDS)

The neurophysiological basis and the role of inflammatory reactions in dentine hypersensitivity

Recent studies indicate that intradental A-type nerve fibres are responsible for the sensitivity of dentine and are activated by fluid movements in dentinal tubules (hydrodynamic mechanism). The patency of the tubules affects dentine sensitivity to a great extent. Both A delta- and A beta-type nerve fibres respond to dentinal (hydrodynamic) stimulation in a similar way. Only a few studies have been made on the regional sensitivity of dentine or the receptive areas of intradental nerve fibres. The results indicate that the fibres innervating different parts of coronal dentine are equally sensitive to dentinal stimulation but those in the cervical area may be less responsive. Inflammation in the pulp can considerably alter dentine sensitivity. In dog teeth with chronically exposed dentine, nerve responses to hydrodynamic stimulation were reduced although other functional changes indicated nerve sensitization. This may be due to spontaneously occurring changes in the exposed dentine that block the tubules. In acute experiments on cat and dog teeth with open dentinal tubules, certain inflammatory mediators increase the sensitivity of the responding nerve fibres. It seems that intradental C-fibres do not respond to hydrodynamic stimulation of dentine. They are polymodal and activated when external stimuli reach the pulp proper. They could perhaps mediate the dull pain connected with pulpitis. However, they might also have an important modifying effect on dentine sensitivity because they can release neuropeptides, which function in the inflammatory reactions.

Dentine permeability and its role in the pathobiology of dentine sensitivity

The classical hydrodynamic theory implicated fluid movement as a transducing mechanism in the production of dental sensitivity. This theory assumes that sensitive dentine must be permeable. Various measurements of dentine permeability are discussed, including: (1) factors that influence diffusive permeation across dentine; (2) factors that influence convective fluid movement across dentine; (3) osmotic activities of solutions; (4) comparison of evaporative and convective fluid movement; (5) the interaction between outward convective fluid flux on the inward diffusive flux of molecules; and (6) the importance of pulpal blood flow in the clearance of noxious substances from dentine and pulp, a balance concept. The variables involved in achieving good penetration of desensitizing agents in the presence of outward movement of dentinal fluid are also discussed, along with the presentation of a new hypothesis which emphasizes the importance of dentine as a dynamic physiological barrier that works in harmony with neurovascular elements in the pulp in an attempt to maintain the health of the pulp-dentine complex.

Correlation between thermal sensitivity and microorganisms isolated from deep carious dentin

The correlation between thermal sensitivity and the microorganisms present in 29 deep carious lesions was studied. The numbers of lactobacilli and total Gram-positive rods in the carious lesions were found to be negatively related to the length of pain triggered by cold and heat stimulants. The presence of Gram-positive cocci and non-black-pigmented Bacteroides were positively associated with both cold and heat sensitivities. Black-pigmented Bacteroides, Streptococcus mutans, and total anaerobic colony counts were positively related to the heat sensitivity. Recovery of Fusobacterium nucleatum, Actinomyces viscosus, and enterics on the selective plates was associated with cold sensitivity. Total counts of Gram-positive cocci and Gram-negative rods on the anaerobic nonselective medium were positively related to the cold sensitivity. It appeared that teeth with low numbers of lactobacilli in the carious lesions usually responded to thermal tests with longer duration of pain. Conversely, teeth with high numbers of lactobacilli in the carious lesions usually responded with shorter duration of pain.

Decreasing intradental nerve activity in the cat with potassium and divalent cations

Nerve activity was recorded from deep dentinal cavities in the canine teeth to assess the possible influence of potassium and divalent cations in decreasing this activity in hypersensitive teeth. The decreased activity after the topical application of 0.756 mol/l KCl to the cavity was primarily due to the cation. KCl elicited a biphasic response from intradental nerves, an initial transient excitatory response followed by a prolonged inhibitory period. During the inhibitory period 3 mol/l NaCl, an effective excitatory stimulus, failed to evoke intradental nerve activity. However, with time the response to 3 mol/l NaCl eventually recovered to its previous control level. Close, intra-arterial injection of KCl showed the same biphasic response and time-course of intradental nerve activity as with topical application. Therefore, whether KCl was applied topically or injected its effectiveness in altering the nerve activity was similar. Pretreatment of the dentinal cavity with CaCl2, MgCl2 or SrCl2 greatly reduced the response of intradental nerves to KCl. Therefore these divalent cations seem to have a depressant action on pulpal nerve fibres. The mechanism of action of KCl seems to be an alteration of K+ concentration immediately surrounding the intradental nerves which presumably depolarizes the nerve fibre membrane and elicits an initial firing of action potentials. Because of the persisting high levels of extracellular potassium a sustained depolarized state occurs that results in an inactivation of the action potential. Divalent cations appear to depress the excitability of the nerve cell membrane without altering membrane potential. Such ionic agents could be used in conjunction with KCl as a possible treatment for hypersensitive teeth.

Cellular reactions in pulpal and periodontal tissues after periodontal wound debridement

Periodontal wounds in monkeys were prepared with a bur followed by the application of microbially contaminated cotton pellets. 3 weeks later, the wounds were debrided by scaling followed by etching with citric acid or by treatment with carbonate/peroxidate. The cellular reactions in the periodontal tissues and in the pulp 4, 11, 25, 39 and 53 days after treatment were followed with light microscopy. The marginal periodontium showed heavy inflammatory reactions immediately after treatment, regardless of the debridement procedure. 25 days after debridement, a long epithelial junction had been formed. The apical part of the epithelium deviated from the root surface into the connective tissue, delineating a heavily inflamed part of the connective tissue. After 39 to 53 days, most of the experimental wounds were covered by an epithelial lining. The pulpal reactions were generally limited to a production of irregular dentin on the pulpal wall facing the periodontal wound. It was concluded that the marginal healing pattern following various chemical treatments to the root surface followed, in all essential aspects, conventional treatment with scaling and root planing.

The response of dog intradental nerves to hypertonic solutions of CaCl2 and NaCl, and other stimuli, applied to exposed dentine

Responses of single nerve units from the canine and incisor pulps of anaesthetized beagles to CaCl2 (3.5 M, 4.9 M and saturated) and NaCl (2.5 M and 4.0 M) were recorded. The sensitivity of these nerve units to drilling and probing of dentine, and to drying with air blasts, was also studied. Twenty-one out of 22 units responded immediately, either with a few spikes or, sometimes, with a 2-5 s train of impulses, to hypertonic CaCl2 when applied to superficial dentine. Deep in dentine, CaCl2 induced immediately responses in 15 out of 21 units. There were responses to hypertonic NaCl in 15 out of 19 units, but only when applied deep in dentine. This firing had a latency of 15-300 s (mean 94 s) and continued until the solution was washed away. Units sensitive to CaCl2 also responded to drilling, probing and drying. When applied to the exposed pulp, CaCl2 never induced nerve activity, but hypertonic NaCl induced responses in all units tested (n = 19); the latencies were 0-300 s (mean 34 s). The mechanism of nerve activation in response to hypertonic CaCl2 is probably hydrodynamic, and common to several other stimuli as in drilling, probing and air drying. Responses to hypertonic NaCl may have been induced by a direct excitatory effect of Na+-ions on the nerve endings or axons in the pulp-dentine border.

Perception of pulpal pain as a function of intradental nerve activity

The purpose of the present investigation was to find neurophysiological correlates of pain perception. The magnitude and time course of perceived pain was successfully related to the neural discharge evoked by rapid cooling of the tooth surface in 6 dental patients whose lower incisors were to be extracted for prosthodontic reasons. Two cavities were prepared on the facial surface of human lower incisors. The cavities were deepened using hand driven instruments until the pulp was visible through a thin layer of dentin. A metal tube was placed in contact with amalgam on each cavity bottom and fixed in place by composite filling material. The tubes were connected to standard equipment for electrophysiological recordings by a flexible circuit. The magnitude of perceived pain was assessed by a cross-modality matching to finger span in combination with sensory verbal pain descriptors and magnitude estimation. The striking agreement between the integrated nerve activity, probably of the A delta type and pain perception, is of great importance from the methodological point of view since it strongly argues in favor of the appropriateness of the techniques applied here to elucidate the neural substrate of some types of nociception and also to evaluate various means of relieving such pain.

Responses of feline intradental sensory nerves to hyperosmotic stimulation of dentin

The responses of intradental sensory nerves to hyperosmotic solutions of sucrose (4M) and calcium chloride (6M) applied in dentinal cavities were studied in anesthetized cats. Nerve impulse activity was recorded from canine teeth after application of the test solutions in shallow and deep cavities. In shallow cavities (thickness of remaining dentin, about 500 micron) sucrose and calcium chloride caused an immediate and transient excitation of the nerves in 3 out of 15 teeth and in 8 of 12 teeth, respectively. Treatment of such cavities with lactic acid (1M) increased the frequency of nerve responses to 100%. When applied in deep cavities (thickness of remaining dentin, 0-50 micron), sucrose induced a burst of impulses followed by continuous nerve activity, whereas calcium chloride decreased the nerve excitability. Our results support the hypothesis that solutions exerting an effective osmotic pressure excite the intradental nerves by an indirect mechanism when applied on the dentin and that they exert a direct effect on nerves when in contact with the pulp. In addition, it is suggested that acids produced in carious dentin may facilitate the induction of pain by hyperosmotic stimuli.