Leif Olgart

Localization of substance P-like immunoreactivity in nerves in the tooth pulp

&NA; The occurrence of substance P (SP)‐like immunoreactivity was studied in dental pulps of the cat. In untreated animals SP‐positive fibres were found in all areas of the pulp. Most fibres were seen in central parts of the pulp but they were also observed in relation to the odontoblasts. Single, possibly unmyelinated, or fine caliber fibres or small bundles of them were seen running close to large non‐fluorescent myelinated nerves, to blood vessels or without any obvious association with either of these structures. Fourteen days after transection of the inferior alveolar nerve no SP‐positive fibres were observed in pulps on the denervated side. Transection of the cervical sympathetic ganglion did not change the occurrence of SP‐positive fibres. The results indicate the existence of at least two types of afferent fibres in the dental pulp of the cat. Since the tooth pulp has been demonstrated to give rise only to pain sensation when stimulated, the results give morphological support for a role of SP neurones in pain transmission.

Invasion of bacteria into dentinal tubules Experiments in vivo and in vitro

Penetration of bacteria into the tubules of intact dentin exposed by fracture was compared in vitro in pairs of teeth, one of which in each pair was mounted with an intrapulpal hydrostatic pressure equivalent to 30 mm Hg. The teeth were incubated at 37°C for 21 days. Intra-pair comparisons in vivo were made of bacterial invasion into dentinal tubules beneath ground dentin surfaces and beneath fractured or acid-treated surfaces, which were exposed for 1 week. It was found that an outward fluid flow in the dentinal tubules due to intrapulpal pressure may mechanically hinder bacterial growth into the tubules. Of greater importance as an obstruction to bacterial invasion was the blocking of the outer apertures of the dentinal tubules by grinding debris. This barrier, however, seemed to be removed after some days and this would allow bacterial ingrowth into intact vital dentin. It is concluded that dentinal surfaces that have been left unprotected and are covered with plaque for some days should be treated as ...

Ultrastructure of nerves in the dentinal-pulp border zone after sensory and autonomic nerve transection in the cat

In order to investigate the origin of intradentinal nerve-like structures, unilateral transection of the sensory (inferior alveolar nerve) and/or the autonomic (cranial cervical sympathetic ganglion) supply was performed in 6 cats. After 2—4 weeks, when degenerative change was expected in the cut nerves, electrophysiological recordings from the dentin showed total absence of impulse activity in teeth subjected to sensory denervation regardless of whether or not the autonomic innervation was intact. Control teeth, on the other hand, responded to different local pain stimuli. Electron microscopic study of predentin and inner dentin in control teeth showed intratubular nerve-like structures similar to «associate cells» earlier described in human teeth. In teeth subjected to sensory nerve resection, however, the intradentinal «associate cells» showed advanced degenerative change or were absent. Resection of the sympathetic nerve supply did not influence the appearance of these intratubular structures.The pres...

Involvement of afferent nerves in pulpal blood-flow reactions in response to clinical and experimental procedures in the cat

A unilateral resection of the mandibular nerve (n = 20) was made 10-14 days before investigation of the contribution of afferent nerves in vasodilator reactions in the dental pulp. Lower canine teeth were subjected to various stimuli and pulp blood-flow responses monitored by laser Doppler flowmetry. An absence of response to bipolar electrical (5 impulses, 50 microA, 5 ms, 2 Hz) stimulation on the tooth surface was used to demonstrate a successful chronic nerve lesion. Local application of capsaicin (10(-4) M) in a deep dentinal cavity induced a long-lasting increase in pulpal blood flow in control teeth only. Bradykinin (10(-3) M) induced significantly larger responses in control than in denervated teeth (58.3 +/- 9.8% and 24.5 +/- 4.9%, respectively, p less than 0.005, n = 8); in addition, the onset was slower and the duration of the response significantly (60%) shorter than in control teeth. Intermittent grinding of surface dentine instantly increased flow in control teeth by 53.0 +/- 12.5% (n = 12) whereas in denervated teeth the response was delayed and significantly (70%) smaller. Deeper preparation produced responses of similar magnitude in control and denervated teeth (69 and 50%, respectively) but the onset was delayed in denervated teeth. Low-intensity ultrasonic stimulation caused vasodilation in intact teeth (38% increase) but had no effect in denervated teeth. This effect was abolished after local anaesthetic (mepivacaine) injection. Sympathectomy (n = 3) did not influence stimulation-induced blood-flow responses in the dental pulp.(ABSTRACT TRUNCATED AT 250 WORDS)

A new technique for recording of intradental sensory nerve activity in man

&NA; A technique was developed to record intradental sensory nerve activity in man. The method involves permanent fixation of electrodes in dentin thus enabling continuous recordings to be made. Acute as well as long term influences on excitability of sensory nerve endings in the tooth can thus be studied. A coincidence between recorded spike activity and pain sensation was observed.

Effects of adrenaline and felypressin (octapressin) on blood flow and sensory nerve activity in the tooth.

The present investigations in cats were designed to study the effects of local anaesthetics containing adrenaline and felypressin (octapressin) on dental pulp function. Intradental sensory nerve excitability was measured using electrodes placed in dentinal cavities in canine teeth. Changes in pulp blood flow were measured using the disappearance rate of a radioactive tracer placed in the same cavities. Injections (0.5 ml) of lidocaine (20 mg/ml) - adrenaline (12.5 microng/ml) or prilocaine (30 mg/ml) - octapressin (0.54 microng/ml) were given supraperiosteally in the apical area of the tooth. Adrenaline either alone or with lidocaine caused almost complete inhibition of pulp blood flow within a few minutes. This effect was followed by a total inhibition of the sensory nerve activity. In most cases there was a recovery of both functions after 3 hours. Octapressin, on the other hand, had no inhibitory effects on pulp blood flow or sensory nerve activity. Lidocaine and prilocaine were also without effect. These findings indicate a different mode of action of the two vasoconstrictors and suggest that octapressin may be preferred in infiltration anaesthesia during treatment of the vital tooth.

Outward fluid flow in dentin under a physiologic pressure gradient: Experiments in vitro

Abstract In fractured dentin in fifteen teeth, the mean flow produced by a hydrostatic pulpal pressure of 30 mm. Hg exceeded 0.6 μl/mm. 2 d; this implies that a patent tubule can be emptied about ten times a day. The histologic examination of twelve teeth suggests that the reduction in the odontoblast layer by aspiration of the cells into the dentinal tubules under exposed dentin, caries, or leaky fillings is a result of the outward flow in the tubules produced by a physiologic pressure gradient.

Spinal substance P release in vivo during the induction of long-term potentiation in dorsal horn neurons

&NA; Long‐term potentiation (LTP) in wide dynamic range (WDR) neurons in the dorsal horn has been suggested to contribute to central sensitization and the development of chronic pain. Indirect experimental evidence indicates an involvement of substance P (SP), in this respect. The aim of the present study was to monitor the extracellular level of substance P‐like immunoreactivity (SP‐LI) in the dorsal horn of the rat during and after induction of LTP in WDR neurons in vivo. Electrophysiological recordings of single (WDR) neurons were performed in parallel with microdialysis in the dorsal horn under urethane‐anaesthesia. The amount of SP‐LI in the microdialysate was determined by radioimmunoassay. As previously shown, high frequency conditioning stimulation of the sciatic nerve induced an increased firing response of WDR neurons. An increased response to C‐fibre stimulation, but not A‐fibre stimulation, could be determined. A significant increase of the extracellular level of SP‐LI in the dorsal horn was detected during, but not after, induction of LTP. These data suggest that SP may be involved in the induction of LTP by high frequency stimulation. However, the maintenance of spinal LTP following high frequency peripheral nerve stimulation does not seem to depend on an increased release of SP.

Differential effects of nitric oxide synthesis inhibition on basal blood flow and antidromic vasodilation in rat oral tissues.

The role of nitric oxide in the mediation of (a) antidromic and (b) substance P-induced vasodilation in the pulp, lip, oral mucosa and submandibular gland was investigated in anaesthetized rats by means of laser Doppler flowmetry. Bolus or continuous infusion of N omega-nitro-L-arginine methyl ester (L-NAME) increased mean arterial blood pressure and reduced basal blood flow in the pulp but not in the lip. Electrical stimulation of the inferior alveolar nerve, in the presence of phenoxybenzamine, resulted in a long lasting vasodilation in lower lip and incisor pulp. Infusion of L-NAME enhanced the antidromic vasodilation in both lip and pulp. Pretreatment with L-arginine prevented these effects. Administration of the enantiomer (D-NAME) did not exert any effect on basal blood flow and on antidromic vasodilation. Infusion of substance P resulted in a transient vasodilation in all of the oral tissues studied. L-NAME reduced this vasodilation in the submandibular gland (only the lower doses) but it potentiated the responses in the pulp and oral mucosa. Pretreatment with L-arginine prevented the potentiated responses in the pulp and those induced by the lower doses of substance P in the oral mucosa. Thus, nitric oxide appears to differentially regulate the basal blood flow and the antidromic or substance P-induced vasodilation in the microvasculature of the lip and dental pulp.

Nerve-pulp interactions

Pulpal haemodynamics are naturally intermeshed with inflammatory responses. Cellular and humoral factors may be the vehicles that aid in physiological regulation, but when these systems are overly activated, they may lead to pathological changes. Sensory nerves may initiate inflammatory reactions when activated, and interestingly, recent findings show that vasoconstrictor nerves in the pulp can inhibit the release of neurally stored vasoactive and inflammatory mediators. Thus, there are options for endogenous control of inflammation. Perhaps a variation in the effectiveness of such control can explain why symptoms of hypersensitivity and pain are so unpredictable and individual. What naturally occurring agents are involved in early tissue changes and how do they act? Some agents exert their effects both on vessels and nerves. Thus, there is an intriguing mutual interplay between nerves and tissue reactions. A prolonged, painful stimulation may generate increased blood flow and inflammation, and vice versa, inflammation may lead to pain. This complexity of mechanisms generates many questions that need answers.