Contribution of capsaicin-sensitive innervation to the continuous eruption of the rat mandibular incisors

A major component of tooth innervation is made of capsaicin-sensitive primary afferents (CSPA). These fibers play a key role in tooth pain and inflammation; little is known, however, about the role of CSPA in tooth eruption. The aim of this study was to examine the role of the capsaicin-sensitive afferents in the process of eruption of intact rat incisors. CSPA fibers in several rat groups, were subjected to one of the following experimental procedures: systemic chemical ablation, systemic ablation followed by chemical sympathectomy and localized activation. The observed effects on incisor eruption were compared to those made on controls. The total amount of eruption in control/naïve rats, measured over a total period of 144 h, was 3.18 ± 0.07 mm and decreased to 2.43 ± 0.08 mm (n = 7; p < 0.001) following systemic ablation of CSPA. Further decrease to 2.24 ± 0.08 mm (n = 7; p < 0.001) was noticed when chemical sympathectomy was added to CSPA ablation. The average rate of eruption was 1.7 ± 0.25 mm following CSPA activation, compared to an average of 0.8 ± 0.07 mm for controls (n = 7; p < 0.001). Capsaicin sensitive fibers play an important role in tooth homeostasis, and intact neural supply is required for tooth growth under normal conditions.

Reduced Depth Technique with the Posterior Superior Alveolar Block

Purpose: The posterior superior alveolar (PSA) block is one of many techniques used to provide profound anesthesia for invasive dental procedures. This technique has a long history, with a high success rate, but is not without complication risks. The purpose of this study was to determine if pulpal anesthesia of the maxillary second molar could be achieved using a posterior superior alveolar block with a reduced depth of penetration of 10 mm compared to the current suggested depth of 16 mm.Methods: Using a cold refrigerant, a thermal test was conducted using the buccal surface of a maxillary second molar of 43 participants. Positive neural responses were obtained from 100% of the participants (n=43) during the pretest. Each participant received a posterior superior alveolar block using a short (20mm), 27-gauge needle with the penetration depth reduced to 10mm. Post-test neural responses of these molars were evaluated using same cold thermal test technique.Results: Study results demonstrated that the reduced depth technique for the PSA block was successful in 88% (n=38) of the participants; pulpal anesthesia of the maxillary second molar had been achieved. Furthermore, there were zero positive aspirations and zero hematomas observed in the participants.Conclusion: The reduced needle depth technique showed promise in achieving desired results of pulpal anesthesia coupled with decreasing risk and complications associated with the PSA block. Additional blinded, randomized clinical studies are recommended to achieve evidence-based support for this reduced depth PSA block technique.

Mandibular bone block harvesting from the retromolar region: a 10-year prospective clinical study

PURPOSE

The aim of this prospective study was to evaluate the outcome of bone block harvesting from the external oblique ridge with the MicroSaw, assess the volume of the harvested block, and identify possible morbidity and complications related to the procedure.

MATERIALS AND METHODS

Bone blocks were harvested from the external oblique line of the mandible according to the MicroSaw protocol. The bone blocks were split into two thinner blocks with a diamond disk according to the split bone block (SBB) technique for biologic grafting procedures.

RESULTS

In all, 3,874 bone blocks were harvested from the external oblique line of the mandible in 3,328 patients. Four hundred nineteen patients (12.59%) underwent bilateral bone block harvesting, and 127 patients (3.82%) had more than one block harvested from the same area during the study period. In 431 cases (11.12%), only one block was required, so the second was repositioned to reconstruct its donor site. The average harvesting time was 6.5 ± 2.5 minutes, and a mean volume of 1.9 ± 0.9 cm³ was obtained (maximum 4.4 cm³). In 168 (4.33%) cases, the alveolar nerve was exposed, leading to sensory problems lasting up to 6 months. In 20 cases (0.5%), minor nerve injury resulted in hypesthesia or paresthesia that lasted for up to 1 year in most patients. No major nerve lesions with permanent anesthesia were observed. Sixty-one (1.58%) donor sites showed primary healing complications, most in smokers (80.4%). Reentry of 16 reimplanted harvested areas was performed between 6 and 40 months later, showing a well-regenerated and healed external oblique ridge.

CONCLUSION

This study demonstrated that relatively large volumes of bone block graft can be retrieved in the mandible with a low complication rate. Reimplantation of half of the bone block offers the possibility for complete regeneration of the donor site.

Clinical anatomy of the lingual nerve and identification with ultrasonography

Our objective was to investigate the pathway of the lingual nerve and find out whether it can be identified using ultrasonography (US) intraorally. It is a dominant sensory nerve that branches from the posterior division of the mandibular aspect of the trigeminal nerve, and is one of the two most injured nerves during oral surgery. Its anatomy in the region of the third molar has been associated with lingual nerves of variable morphology. If surgeons can identify its precise location using US, morbidity should decrease. We searched published anatomical and specialty texts, journals, and websites for reference to its site and US. Cadavers (28 nerves) were dissected to analyse its orientation at the superior lingual alveolar crest (or lingual shelf). Volunteers (140 nerves) had US scans to identify the nerve intraorally. Our search of published books and journals found that descriptions of the nerve along the superior lingual alveolar crest were inadequate. We found no US studies of the nerve in humans. Dissections showed that the nerve was above (n=6, 21%) and below (n=22, 79%) the crest of the lingual plate. US scans showed 140 lingual nerves intraorally in 70 volunteers. The nerve lay either above or below the superior lingual alveolar crest, which led us to develop a high/low classification system. US can identify the lingual nerve and help to classify it preoperatively to avoid injury. Our results suggest that clinical anatomy of the lingual nerve includes the superior lingual alveolar crest at the third and second molars because of its surgical importance. US scans can successfully identify the nerve intraorally preoperatively.

[Pilot clinical study of the dental cone beam CT examination before the impacted mandibular third molar extraction]

OBJECTIVE

To evaluate the diagnostic accuracy of the cone beam computed tomography (CBCT) in judging the relationship between the impacted mandibular third molar (IMTM) and the inferior alveolar canal (IAC).

METHODS

Sixty IMTM superimposing on the canal partially or touching the canal in line on panoramic radiograms were examined by CBCT. All CBCT images of these cases were observed by two dentists respectively. Then, all these IMTM were extracted by minimally invasive surgery, and the conditions of the IMTM sockets were observed. Two dentists observed the CBCT images independently and reached a consensus. Diagnosis test was performed in this study.

RESULTS

Eight IMTM sockets were bleeding during the extracted operation, and whether the IAC wall was broken could not be judged. The other 52 IMTM sockets were clear and the walls of IAC were broken in 29 IMTM extractions. The sensitivity, specificity, Youden index, positive predictive value and negative predictive value of CBCT were 82.8%, 87.0%, 88.9% and 80.0% respectively. The diagnostic accuracy judged by the two dentists and Kappa coefficient were calculated as 84.6% and 0.800.

CONCLUSIONS

The CBCT examination had good authenticity and reliability, and it was very helpful in predicting the actual relationship between the IMTM and IAC.

Anatomy of the lingual nerve in relation to possible damage during clinical procedures

Damage to the lingual nerve, resulting in transient or permanent paraesthesia or anaesthesia, is a common undesirable complication of surgical interventions to the lower third molar region. The anatomy of the nerve, as it travels from its origin high in the infra-temporal fossa, to the floor of the mouth is quite variable. The most critical part of its course is where it enters the sublingual region just alongside the lingual alveolar plate of the lower third molar. A significant number of lingual nerves are located above the alveolar bone in the gingival tissues, or very close to the bone. Retraction of the lingual mucosa can lead to lingual nerve trauma. There is no doubt that the lingual nerve is extremely vulnerable in this region and clinicians must assume that it is closely adjacent to the lingual region of the lower third molar, in all cases, in order to minimize possible damage.

Topical review: modulation of trigeminal sensory input in humans: mechanisms and clinical implications

In this review, the modulatory effects of tooth and implant loading, orofacial pain, and psychological factors on somatosensory and jaw-motor function in humans are assessed. Experimental studies on the control of jaw actions have revealed that patients with prostheses supported by osseointegrated implants show an impairment of fine motor control of the mandible. One possibility is that this may be related to the loss of afferent information from periodontal ligament mechanoreceptors, which results in considerably higher and more variable forces to hold and manipulate food between the teeth. However, psychophysical investigations have shown that patients still perceive mechanical stimuli exerted on osseointegrated implants in the jawbone. The use of somatosensory evoked potentials may revealed what specific receptor groups are responsible for this so-called osseoperception phenomenon. Orofacial pain is another modulator of trigeminal system functioning. Experimental jaw muscle pain has several effects on the somatosensory and motor function of the masticatory system, all of them serving to warn the individual about the ongoing damaging of tissues. Finally, the influence of mental state on the sensory and motor functions of the trigeminal system will be addressed. While some animal studies suggest that psychological stress can reduce acute pain, less speculative are the findings in human subjects that the anticipation of receiving a painful stimulus or undertaking difficult mental tasks can modulate jaw reflexes, including those evoked by mechanical stimuli applied to the teeth. Since such stimuli occur regularly during normal oral activities, the study of the resulting motor effects may yield clinically meaningful results in the context of other variables that modulate mandibular function.

[Evaluation of inferior alveolar nerve function with trigeminal somatosensory evoked potential during mandibular distraction osteogenesis in monkeys]

OBJECTIVE

To assess sensory function of inferior alveolar nerve in monkeys with mandibular distraction osteogenesis by use of trigeminal somatosensory evoked potential (TSEP).

METHOD

Seven young monkeys, 4 approximately 6 kg, were undergone a 13.5 mm bilateral or right-side mandibular lengthening with mandibular angle osteotomy and intraoral bone-born appliance. The inferior alveolar nerve function was assessed with TSEP before surgery, at the completion of distraction, and after four weeks of fixation.

RESULTS

No significant differences in latencies and amplitudes of TSEP between the left and right inferior alveolar nerves before surgery. At the completion of distraction, latencies of TSEP showed significant elongation (P < 0.01, P < 0.001) and amplitudes also significantly decreased (P < 0.001). After four weeks of fixation, various degrees of TSEP recovery were identified. The latencies and the amplitude were slightly improved.

CONCLUSIONS

Mandibular distraction osteogenesis affects sensory function of inferior alveolar nerves in studied monkeys evaluated with SEP, but recovery is observed four weeks after surgery.

Somatosensory-evoked potential to evaluate the trigeminal nerve after sagittal split osteotomy

OBJECTIVE

The purpose of this study was to assess the onset period of trigeminal nerve hypoesthesia during bilateral sagittal split osteotomy, with the use of the trigeminal somatosensory-evoked potential (TSEP).

STUDY DESIGN

Subjects were 10 patients with mandibular prognathism who underwent setback surgery. Intraoperative TSEP was measured 4 times: just before the commencement of the surgery, immediately after the induction of general anesthesia; after the medial periosteal dissection of the alveolar neurovascular bundle; after the sagittal split of bone; and after semirigid fixation with a titanium miniplate with the use of a monocortical screw. Postoperative TSEP was measured after the start of postoperative weeks 2, 4, 12, and 24. Normal records of the TSEP wave comprised peak (13 ms), trough (16 ms), peak (22.7 ms), and trough (36 ms) (N1, P1, N2, P2, respectively). Trigeminal hypoesthesia was assessed by the latency of P1 and N2, because they indicated the most reproducible waveforms.

RESULTS

The change in shape of the spectra indicated that prolonged latency was initiated on medial periosteal dissection and was extended further after the sagittal bone split and fixation. However, latency recovery was observed relatively quickly after the start of postoperative weeks 2 and 4.

CONCLUSIONS

Trigeminal hypoesthesia appeared to be induced by direct injury to the alveolar nerve during the bone split or by compression injury after fixation. Accordingly, the occurrence of a long-lasting postoperative trigeminal sensory hypoesthesia seemed to depend on nervous involvement of the split surface, the manner of fixation, or the intraoperative care.

Sensations and trigeminal somatosensory-evoked potentials elicited by electrical stimulation of endosseous oral implants in humans

The perception of bipolar electrical stimuli through implants was studied. The stimuli were delivered to permucosal oral endosseous implants in 15 individuals, who then reported tapping to beating sensations. In 10 out of the 15, these stimuli evoked clearly distinguishable potentials in the averaged electroencephalograms. The most prominent scalp potential was a positive wave with a latency between 18 and 25 ms, often preceded by a negative wave with a latency around 12-17 ms. In contrast, when a motor response was elicited by stimulation of the lip, a shorter latency wave around 8-11 ms was found additionally, indicating that the former-mentioned waves represent a true sensory response and not an artefact of myogenous origin. Furthermore, topical anaesthesia of the gingiva surrounding the implants in six individuals had little effect on the sensory responses. This evidence excluded peri-implant mucosal innervation as the origin of the perception and of the somatosensory-evoked waves elicited by the electrical stimulation of the oral implants. To the best of our knowledge, for the first time a sensation (osseoperception) has been elicited by electrical stimulation of endosseous oral implants and correlated with simultaneously recorded trigeminal somatosensory-evoked potentials (TSEPs).

From osseointegration to osseoperception

Periodontology has broadened its scope by the research and clinical use of osseointegrated implants. Since tactile and reflex functions have been associated with periodontal ligament neural receptors, osseoperception could be associated with endosseous and/or periosteal innervation.

Canalis sinuosus mimicking a periapical inflammatory lesion

A case is presented in which an anatomical feature, canalis sinuosus, manifested as a periapical radiolucency on an upper canine. This may have been interpreted as an inflammatory lesion and led to the patient receiving inappropriate treatment had a further radiograph not been taken. The incisive foramen and mental foramen are well known anatomical features which may mimic periapical inflammatory lesions but it is less common for a neurovascular canal to manifest as a periapical radiolucency on an upper canine.

Nerve fibers immunoreactive to calcitonin gene-related peptide, substance P, neuropeptide Y, and dopamine beta-hydroxylase in innervated and denervated oral tissues in ferrets

The effect of sensory and sympathetic denervation on the localization and distribution of nerve fibers immunoreactive (IR) to calcitonin gene-related peptide (CGRP), substance P (SP), neuropeptide Y (NPY), and dopamine beta-hydroxylase (DBH) was studied in the dental pulp, periodontal ligament (PDL), and gingiva in ferrets. Unilateral axotomy was performed by resection of the inferior alveolar nerve (IAN) 10 days before the experiment (Group 1); sympathectomy, by unilateral removal of the cervical ganglion 5 days before the experiments (Group 2). Immunohistochemistry was performed on free-floating sections by the avidin-biotin-peroxidase technique. A considerably higher density of sensory fibers IR to CGRP and SP was found in the dental pulp than in PDL and gingiva. The majority of pulpal fibers were located in the walls of blood vessels. A subodontoblastic network of fibers IR to CGRP and SP was lacking in incisors and canines and was found only in the coronal pulp in premolars and molars. Sympathetic fibers were sparsely distributed in the pulp, and they were mainly confined to large vessels running centrally in the root pulp as well as the larger vessels in apical PDL and alveolar bone. Gingiva was well supplied with CGRP- and SP-IR nerves, and some NPY and DBH fibers were located in association with larger vessels. Round cell-like structures within the basal part of the epithelium were CGRP-IR. Axotomy induced a complete loss of CGRP- and SP-IR fibers in the anterior part of the jaws, whereas sympathectomy caused a reduction, but not a total loss, of NPY- and DBH-IR nerves. It is concluded that, except for some distributional differences, the oral tissues in the ferret have an abundant sensory innervation similar to that found in other species.

Immunocytochemical demonstration of beta 1-subunit of Na+/K(+)-ATPase in the mechanoreceptive Ruffini-like endings of the rat incisor ligament

The localization of one of the isoforms of Na+/K(+)-ATPase, the beta 1-subunit, was investigated in the periodontal Ruffini endings of rat incisors by light- and electron-microscopic immunocytochemistry. Immunoreactivity for the rat beta 1-subunit followed the pattern of dendritic terminal arborization in the alveolar half of the lingual periodontal ligament. Ultrastructurally, the reaction products were localized in dilatations of axons, possibly the terminals of Ruffini-like endings in the periodontal ligament. No immunoreactivity was seen in Schwann cells. The immunostaining results support the view that the beta 1-subunit of Na+/K(+)-ATPase is the predominant isoform in sensory neurones, and that this protein is a useful marker for periodontal Ruffini-like endings.

Effect of experimental tooth movement on nerve fibres immunoreactive to calcitonin gene-related peptide, protein gene product 9.5, and blood vessel density and distribution in rats

The effect of experimental tooth movement on nerve fibers immunoreactive to calcitonin gene-related peptide (CGRP) and to protein gene product (PGP) 9.5 were studied, as well as the coincidence of these responses with changes in blood vessel density and distribution in the periodontal ligament (PDL) and pulp of young Wistar rats. The first right maxillary molar was moved mesially by an orthodontic appliance for 3, 7, 14 and 21 days. Sagittal and horizontal serial sections were incubated alternately with antibodies to CGRP, PGP 9.5 and laminin. Nerve and blood vessel density and distribution between the experimental and control sides were compared in the apical and cervical PDL, and in root and coronal pulp. The most pronounced changes occurred in the 7 day group. CGRP and PGP 9.5 immunoreactive nerves in the apical PDL showed increased density, being distributed towards the alveolar bone and frequently found in bone resorption lacunae. Numerous nerve fibres were often present adjacent to hyalinized tissue, but were never found near or within root resorption lacunae. Nerve sprouting was also present both in the root and coronal pulp. Increased nerve and blood vessel density generally coincided with each other. At day 14, periodontal nerves and blood vessels were still disorganized compared with the controls. Tissues near cellular cementum and root resorption lacunae were consistently devoid of nerve fibres. After 21 days, PDL nerve and blood vessel density and distribution were nearly at control level. However, nerve fibres were regularly found inside root resorption areas. In conclusion, experimental tooth movement induces dynamic changes in density and distribution of periodontal and pulpal nerve fibres, indicating their involvement in both early stages of periodontal remodelling and later in the regenerative processes of the PDL, generally occurring in concerted action with modulation of blood vessels.

Mandibular fractures following third molar extraction. A retrospective clinical and radiological study

Twelve patients with 13 mandibular fractures following third molar extraction were treated in our Department between 1980 and 1995. Clinical and radiographic data relating to these patients were analysed retrospectively to determine complication characteristics. Only one fracture occurred during surgery. The first week after the operation was found to be most critical for fracture occurrence. A "cracking" sound from the jaw while eating frequently indicated that a fracture had occurred, but repeated radiographic examination may be necessary for definitive diagnosis. Most teeth removed belonged to Groups II/III according to PELL & GREGORY's classification, indicating partial or total impaction of the tooth and a narrow space in the retromolar triangle. In all cases, tooth roots were superimposed on or adjacent to the inferior alveolar canal. Clinically, the age of the patient seemed to be a common predisposing factor, and patients older than 30 to 40 years were considered to be a risk group. Regardless of the degree of impaction and tooth position, the fracture type seen was uniform, i.e. preangular location and a typical course of the fracture line. After adequate fracture treatment, no further complications were noted.

Can the location of tooth agenesis and the location of initial bone loss seen in juvenile periodontitis be explained by neural developmental fields in the jaws?

Recent studies on prenatal innervation of the jaws have shown that three separate main innervation paths, constituting three bilateral neural developmental fields (incisor field, canine/premolar field, molar field) exist in each jaw. In this communication the sequences in which the fields are innervated are indicated. These correspond to the sequences of formation of teeth and jawbone. The normal pattern of tooth agenesis is closely related to the neural fields, as the region within a single field were innervation occurs last is always the area most often affected by tooth agenesis. The initial manifestations of juvenile periodontitis also appear at the sites within the different fields where innervation occurs last. It is suggested that the pubertal growth of the alveolar process does not occur in these regions due to deficient innervation, and that the infection in juvenile periodontitis might be secondary to this regional lack of bone apposition.

Parvalbumin-immunoreactive nerve endings in the periodontal ligaments of rat teeth

Parvalbumin-immunoreactive nerve fibres were most abundant in the lingual periodontal ligaments of incisor teeth. In the part of the ligament adjacent to the alveolar bone, thick and smooth parvalbumin-immunoreactive nerve fibres left main nerve bundles and passed towards the part of the ligament adjacent to the tooth. In the ligament, halfway between the bone and tooth surfaces, these nerve fibres repeatedly branched and extended one to four twigs to produce bush-like endings. Parvalbumin-immunoreactive fibres and terminals were infrequent in the periodontal ligaments of the molar teeth. It is possible that parvalbumin-immunoreactive endings are periodontal mechanoreceptors, but at present it is difficult to account for the different representations around rat molar and incisor teeth.

Electrophysiologic evidence showing the existence of sensory receptors within the alveolar bone in anesthetized cats

Single-nerve activities were recorded in the gasserian ganglia of anesthetized cats by glass extracellular micro-electrodes to determine whether sensory endings exist within the alveolar bone. Trigeminal cells responded to mechanical and/or thermal stimulation applied to the maxillary bone. Some were activated by specific kinds of fairly precise mechanical stimuli (moderate forces applied in a preferential direction); others exhibited a coarse mechanical sensitivity. In addition, electrical stimulation was applied to the maxillary bone to determine the conduction velocities of the relevant fibers. These mainly ranged between 1 and 6 m/s, which indicates that the fibers belonged to the small-diameter category (thinnest myelinated and unmyelinated fibers). Similar results were obtained from animals with osseointegrated implants. It was concluded that the alveolar bone is endowed with sensory endings capable of detecting mechanical and thermal changes, and that these receptors may provide compensatory sensitivity in edentulous subjects whose main (periodontal) sensitivity has been eliminated.

Identification of axons in the peri-implant region by immunohistochemistry

In the edentulous patient with a completely implant-supported prosthesis, periodontal ligament receptors are absent. However, the implant patient's mandibular function during mastication and clenching is significantly improved and can be similar to that of dentulous subjects. The underlying mechanisms that govern this proprioceptive control are not well understood. One possibility that has been explored only partially is that residual axonal elements in the peri-implant region may have a proprioceptive function. To survey the peri-implant region for axonal elements, this study utilized immunohistochemistry with neurofilament as the marker. Histologic sections of the peri-implant area from 12 implants placed in the mandibles of three dogs were examined for the presence of neurofilament. Two to three labeled sites per section in the peri-implant region were commonly found. However, the functional significance of these axons must be further evaluated before any conclusions regarding their role in proprioception can be made.

Response characteristics of periodontal mechanoreceptors to mechanical stimulation of canine and incisor teeth in the cat

The alveolar bone that overlies the labial aspect of the root of the right lower canine tooth was pared down until paper thin. Thirty-five periodontal mechanosensitive (PM) units sensitive to stimulation of the canine and incisor and to punctate stimulation through the thinned bone of the periodontal ligament of the canine were recorded from the inferior alveolar nerve rostral to the masseter muscle. The units showed a sustained and directionally selective response to pressure applied to the teeth. The optimal directions of stimulation for each tooth in the receptive field were parallel and oriented linguolabially. When the canine was stimulated mechanically in the optimal stimulus direction, the interspike intervals of the responses were relatively regular in most PM units (91%). The conditioning and test stimuli were applied to the adjacent canine and third incisor. The conditioning stimulus (0.10 N) was given to one of these teeth in the optimal stimulus direction. The test stimulus (0.02 N or 0.05 N) was applied to the adjacent tooth in the opposite direction in order to examine the effect of mechanical spreading of the conditioning stimulus on the adjacent tooth. In most PM units, the spike discharges evoked by the conditioning stimulus given to the incisor were stopped by the test stimulus given to the canine. When the given stimuli were reversed, the firings evoked by the conditioning stimulus were slightly depressed by the test stimulus. After removing the spot-like PM receptor site(s) in the paper-thin area of bone, all units but one did not respond to stimulation. These results provide evidence that neurones with multiple-tooth receptive fields and regular spike-interval responses recorded from the inferior alveolar nerve come from the mechanical spreading effect of the stimulation of one tooth on an adjacent tooth through the trans-septal fibre system and that neurones with irregular-interval responses are due to the ramification of PM fibres peripherally.

Threshold of tactile sensitivity perceived with dental endosseous implants and natural teeth

The aim of this study was to determine the threshold of tactile perception of endosseous dental implants and to assess the relative difference of that threshold between implants and teeth. Twenty-two subjects with implants of the ITI Dental Implant System were included in the study. All implants served as abutments for single tooth crowns and had been in function for a minimum of 1 year. A strain gauge glued to the shaft of an amalgam plugger served as a force sensor. It transformed the elastic deformation exerted onto the shaft into an electronic signal for recording. By use of the amalgam plugger, a continuously increasing force was exercised on the implants or teeth until the first sensation of touch was indicated by the patient. Statistical analysis revealed threshold values for the implants ranging from 13.2 to 189.4 g (1 g = 0.01 N) (mean 100.6; SD 47.7), while a range of 1.2 to 26.2 g (mean 11.5; SD 11.5) was found for control teeth. Thus, the mean threshold values for implants were 8.75 times higher than for teeth. This difference was highly statistically significant. A general linear models procedure was applied to determine the influence of patient age, jaw, implant position and the threshold values of teeth on the measurements obtained for implants. Only gender and the threshold values for contralateral teeth had a significant influence. These 2 parameters together explained 27% of the variability in threshold measurements. It is concluded that a more than 8-fold higher threshold value for tactile perception exists for implants compared with teeth.

Nerve fibres and cells immunoreactive to neurochemical markers in developing rat molars and supporting tissues

The distribution of nerve fibres immunoreactive to calcitonin gene-related peptide (CGRP), substance P (SP) and neuropeptide Y (NPY) was compared to the general neurochemical markers for nerves and neuroendocrine cells protein gene product 9.5 (PGP 9.5) and neurone-specific enolase (NSE), by use of the avidin-biotin peroxidase complex method in developing dental structures in rats aged 13 to 27 days. A substantially greater part of the nerve fibres was immunoreactive to CGRP and SP than to NPY. In the bell stage, nerve fibres immunoreactive to PGP 9.5, CGRP and SP were found in the dental follicle but not in the dental papilla and stellate reticulum. In the advanced bell stage, after initiation of dentine and enamel formation, PGP 9.5, CGRP- and SP-immunoreactive fibres were found in the dental papilla, while the first NPY-immunoreactive fibres were observed in the papilla when root formation started. Concomitant with the beginning of root development, a subodontoblastic nerve plexus was gradually formed and PGP 9.5-, CGRP- and SP-immunoreactive fibres were found within the dentinal tubules. From the start of root formation, CGRP-, SP- and NPY-immunoreactive nerves were shown in the developing periodontal ligament, although a mature distribution pattern was not observed until root formation was nearly completed. Ameloblasts, odontoblasts and cell-like structures in the outer enamel epithelium and within the dental lamina were PGP 9.5-immunoreactive at the bell stage. As the tooth matured, the immunolabelling gradually decreased, but was still present in some odontoblasts after tooth eruption. NSE-immunoreactive, cell-like structures were found in the periphery of the dental follicle, and persisted close to alveolar bone in the periodontal ligament when the tooth reached occlusion. Hence, it may be concluded that sensory nerves containing SP and CGRP are present in the pulp in advance of sympathetic nerves immunoreactive to NPY.

Nerve transposition and implant placement in the atrophic posterior mandibular alveolar ridge

The results obtained with a modified surgical technique for transposition of the inferior alveolar nerve followed by immediate placement of endosseous implants in mandibles with moderate to severe atrophy are presented. Ten transpositions of the inferior alveolar nerve together with the installation of 21 implants were performed in six patients. The mean postoperative follow-up time was 23 months, with a range of 12 to 46 months. All implants with functioning pontics remained stable, with no mobility nor signs or symptoms of pain and infection during the follow-up period. Postoperative radiographic evaluation disclosed no pathologic bone loss around the implants. Neurosensory evaluation was performed using the two-point discrimination test. One patient with unilateral transposition had objective neurosensory dysfunction at 12 months postoperative, although all the nerve function were reported as normal by the patients. Strict patient selection criteria are necessary, with full awareness by the patient of the possibility of long-term or even permanent nerve paresthesia, when this procedure is contemplated.

The reinnervation of healing extraction sockets in the ferret

The objective of this study was to describe the pattern of healing of pulpal and periodontal nerve fibers following tooth extraction. The mandibular canine teeth were, under general anesthesia, removed from one side of nine young ferrets. One week (two animals), one month (four animals), and three months (three animals) later, again under general anesthesia, the animals were perfused with fixative. The mandibles were decalcified, paraffin-embedded, and serially sectioned. Sample sections were stained with hematoxylin and eosin, the remainder with a silver stain for nerves. Serial reconstructions were made of the innervation in control teeth and in the extraction sockets. A grid sampling technique was used for the estimation of the innervation density in different regions at various levels in the healing socket. One week after extraction, although osteoid material was beginning to fill the socket, the pattern of innervation remained similar to that of controls in being restricted to the former location of the periodontal ligament and being densest in the apical third of the socket. One month after extraction, the innervation consisted of many fine axons or small bundles distributed throughout the healing osteoid tissue though still most dense in the periphery of the socket. The overall innervation density increased between one week and one month post-extraction. At three months, as the margins of the socket were becoming obscured, the innervation consisted largely of one or two organized nerve trunks running from the apical to the coronal aspect in either the central or lateral aspects of the socket. At no time was there evidence of neuroma formation.

The inferior alveolar artery in its bony course

Based on the dissection of 30 hemi-mandibles, the authors report a study of the inferior alveolar artery in its intraosseous course. On morphologic considerations they propose a classification of the collaterals into two groups: the principal collaterals destined for the teeth and the bony alveolar tissue and the secondary collaterals destined for the sheath and the nerve as well as the bony tissue around the canal. Loss of the teeth and absorption of the alveolar bone modify the caliber of the inferior alveolar arterial axis, the distribution of its collaterals and possibly its mode of termination. These facts suggest a consideration of the vascularization of the mandible in terms of four sectors. They arrive at practical conclusions that may be drawn from this study in stomatology.

Topographic representation of lower and upper teeth within the trigeminal sensory nuclei of adult cat as demonstrated by the transganglionic transport of horseradish peroxidase

Transganglionic transport of horseradish peroxidase-wheat germ agglutinin conjugate (HRP-WGA) entrapped in hypoallergenic polyacrylamide gel was used to study the patterns of termination of primary afferents that innervate the lower and upper tooth pulps within the trigeminal sensory nuclear complex (TSNC). HRP injections were made into the inferior and superior alveolar nerves in order to compare the central projections of the whole nerve with those from tooth pulps. In addition, the relationship between the distribution of the trigeminothalamic tract cells and the projection sites of the tooth pulp afferents was investigated by injecting HRP into the posterior ventral thalamus. HRP-labeled tooth pulp afferent fibers innervating the lower and upper teeth projected to the subnucleus dorsalis (Vpd) of pars principalis, the rostrodorsomedial part (Vo.r) and nucleus dorsomedialis (Vo.dm) of pars oralis, the medial regions of pars interpolaris, and laminae I, II, and V of pars caudalis. Terminal fields of the lower tooth pulp afferents formed a rostrocaudally running, uninterrupted column from the midlevel of Vpd to the caudal tip of caudalis. In contrast, the column of termination of upper tooth pulp afferents was discontinuous at the Vpd/Vo.r transition, and ended at the more rostral level of the caudalis than that of the lower tooth pulp afferents. The representation of the lower and upper teeth in the TSNC was organized in a somatotopic fashion which varied from one subdivision to the next, although terminal zones of the inferior and superior alveolar nerves overlapped within the Vo.r, Vo.dm, and dorsomedial part of rostral pars interpolaris. The lower and upper teeth were represented in the Vpd, Vo.r, Vo.dm, medial region of pars interpolaris, and laminae I, II, and V, in a ventrodorsal or caudorostral, dorsoventral, lateromedial, dorsoventral, and mediolateral or dorsomedial-ventrolateral sequence, respectively. The smaller, more focal terminal areas of the teeth contrasted sharply with more extensive terminal fields of the alveolar nerves. The HRP injections within the thalamus indicated that neurons in Vpd, the caudal pars interpolaris, and laminae I/V of caudalis, which are subdivisions of TSNC that receive pulpal projections, sent their axons to the ipsilateral and contralateral posterior ventral thalamus.(ABSTRACT TRUNCATED AT 400 WORDS)

Sensory nerve morbidity following Le Fort I osteotomy

The Le Fort I osteotomy has been used increasingly frequently in the management of dentofacial deformity since the wide acceptance of the down-fracture technique. The improved access provided by this technique allows movement of the Le Fort I segment in three planes. This paper reviews briefly the neuroanatomy of the area and considers how the surgical technique of Le Fort I osteotomy interferes with the sensory nerve supply. The sensory nerve function in ten patients who underwent Le Fort I osteotomy is reviewed.

Modulation of transmission in rostral trigeminal sensory nuclei during chewing

Eighty-one sensory neurons in the rostral trigeminal sensory nuclei (main sensory nucleus, nucleus oralis, and the lateral border zone of the motor nucleus) were recorded in urethan-anesthetized rabbits before and during mastication. Receptive-field characteristics were described, and responses evoked by electrical stimulation of the inferior alveolar and infraorbital nerves, sensorimotor cortex, and thalamus were recorded. Forty-four percent of neurons were stimulated by the movements of mastication; nevertheless, evidence is presented that the excitability of the 49 neurons that receive low-threshold mechanoreceptor inputs is depressed during mastication for the following reasons: The spontaneous activity of seven cells was inhibited during movement. The probability of firing in response to stimulation of the peripheral nerve on sensorimotor cortex was decreased during mastication. There was usually a corresponding increase in the latency of the action potentials. Injections of local anesthetic (prilocaine hydrochloride, 4%) into the receptive field of the neuron did not prevent the decrease in excitability during mastication. Fourteen neurons that received inputs from periodontal pressoreceptors were recorded medial to most of the low-threshold group. The excitability of six of these was reduced during jaw closure and during the occlusal phase of movement, that is, within the period in which they would be activated by pressure on the teeth. The rest were tonically suppressed. Eighteen neurons recorded in the lateral border zone of the motor nucleus had receptive fields that were of high threshold or were undefined. They responded to stimulation of the peripheral nerve at high threshold. The excitability of most of these neurons was strongly phase modulated during mastication. They were most excitable during jaw closure or during the occlusal phase of movement and inexcitable during opening. The excitability of the others was tonically depressed. In most cases, the changes in excitability described did not seem to be due to the patterns of activity of the neurons that were generated by the movements. We conclude that the pattern elaborated by the central pattern generator includes selective modifications of sensory transmission. One reason for this is to suppress reflex responses to low-threshold inputs while maintaining the protective response to tissue damage.

Clinical anatomy of the superior alveolar nerves

Unilateral dissections were carried out on 19 human cadaver heads to demonstrate the superior alveolar nerves and vessels. The positions of foramina on the infratemporal surface of the maxilla were noted and, after decalcification of the bone, a transillumination technique was used to display the nerves and vessels in situ. Considerable variation was found in the origin, path and branches of anterior superior alveolar nerves. A middle superior alveolar nerve was found in seven dissections. The clinical importance of these findings is discussed in relation to local analgesia and surgery of the maxillary antrum.

Accessory innervation of mandibular anterior teeth in cats: a horseradish peroxidase study

In 10 cats, an ipsilateral section of the inferior alveolar nerve was performed following which horseradish peroxidase was deposited in cavity preparations of either ipsicentral incisors (8) or canines (2). The animals were sacrificed in 24 h, and the ipsilateral nerve to mylohyoid and both semilunar ganglia were prepared histochemically for observation. Labeled axons were found in 6 of 8 cats, whose incisors were prepared, and 4 of the 6 had labeled ganglion cells. In the two remaining cats with incisor preparations, no labeled ganglion cells were found; however, labeled axons were found in the mylohyoid nerve. Neither labeled axons or cells were found in those cats whose canines were prepared. One case of cross-innervation was noted. These results suggest that in addition to the inferior alveolar nerve, the nerve to mylohyoid and possibly other accessory neural pathways are involved in incisor innervation in cats.

Dental nerve regeneration in rats. I. Electrophysiological studies of molar sensory deficit and recovery

Return of sensory nerve function in rat molars following cut or crush injury to the inferior alveolar nerve (IAN) was measured by observing the jaw opening reflex (JOR) response of the digastric muscle to electrical stimulation of individual molars or the gingiva. The IAN was injured from a lateral approach to the mandibular ramus at a site approximately 2 mm proximal to the incisor apex. Following nerve injury, the JOR threshold to stimulation of the first molars increased 6-fold: preoperative threshold mean = 47.4 +/- 21.3 microA (n = 27), postoperative threshold mean = 248.5 +/- 127.1 microA (n = 25). A 4-fold postoperative increase in JOR threshold was found for the second molars, and the thresholds were not significantly affected for third molars or gingiva. These postoperative results indicated that the major pathway of sensory innervation to the first and second molars was affected by the IAN injury, whereas the third molars and gingiva had alternate sources of innervation which remained unaffected by the IAN injury. At 1 week following injury, there was partial return of sensitivity, by 3 weeks there was approximately 50% recovery, and by 6 weeks complete return to normal JOR thresholds was found. The degree of sensory deficit, as reflected in JOR inhibition, and the rate of recovery were not significantly different after cut or crush injury in these experiments; however, there was a tendency for greater sensory loss and for more rapid recovery after crush injury. This study forms the basis for a subsequent autoradiographic analysis of nerve location in rat molars of known sensory deficit, partial recovery, or full sensory recovery.

Reorganization of trigeminal primary afferents following neonatal infraorbital nerve section in hamster

The infraorbital nerve was sectioned and the ipsilateral whisker follicles were cauterized in hamsters within 12 h of birth. Sixty to ninety days later application of HRP to the proximal stumps of the ipsilateral lingual, inferior alveolar, mylohyoid and auriculotemporal nerves resulted in increased numbers of labeled somata in trigeminal ganglion regions which contain primarily infraorbital cell bodies in normal animals. The labeled central processes of mandibular nerves also occupied portions of the brainstem trigeminal complex normally innervated by infraorbital axons. These findings represent the first anatomical demonstration of trigeminal primary afferent plasticity.

Dental nerve regeneration in rats. II. Autoradiographic studies of nerve regeneration to molar pulp and dentin

The autoradiographic technique was used to analyze the degeneration and regeneration of sensory nerves to rat molars and gingiva following cut or crush injury to the right inferior alveolar nerve. At 2 days after nerve injury there was almost complete denervation of the first molar, partial denervation of the second molar, and minimal effect on the innervation to the third molar and gingiva. The degree of sensory deficit and recovery for these same rats had been previously determined. Reinnervation of the first molar was analyzed in terms of axon number and location, intensity of axon labeling, and type of nerve injury. At 6 days, neither the cut injury nor crush injury rats had any reinnervation of their first molars. By 7 days, 3 of 4 rats had axons reinnervating first molars; in those teeth there was approximately one-fourth of the normal number of axons in the pulp, and very few axons in the dentin. These rats still had as large a molar sensory deficit as the 7 day rat and 6 day rats that had no reinnervation. By 3 weeks there were one-half to three-fourths of the normal axon numbers in the pulp, one-fourth to one-half of the normal axon numbers in dentin; and sensitivity was at least half-recovered. By 6 weeks, numbers of axons in the pulp and dentin were either normal or slightly less than normal; axons had grown back into dentin to the same depth as in normal teeth; and complete recovery of sensitivity had occurred. The regenerating axons had greater than normal labeling intensity at 1 week and 3 weeks in all rats. Those with the crush nerve injury had somewhat greater numbers of reinnervating axons at 1 week and 3 weeks than the cut injury rats. A structure-function comparison for the molars showed that return of sensitivity correlated with reinnervation of both pulp and dentin.

Thresholds to electrical stimulation of nerves in cat canine tooth-pulp with A beta-, A delta- and C-fibre conduction velocities

The thresholds to electrical stimulation and the conduction velocities of nerve fibres supplying the pulp of cat canine teeth have been determined. Compound action potentials and the responses of 80 single units were recorded from the inferior alveolar nerve. The properties of 4 types of coronal stimulating electrode were compared. In the single unit studies separate estimates of intradental and extradental conduction velocity of the fibres were obtained by stimulating the pulp in the crown and in the root of the tooth. The units had extradental conduction velocities ranging from 57.7 to 0.9 m . s-1 and therefore included A beta-, A delta- and C-fibres. The thresholds of the units to coronal stimulation ranged from 7 microA, 0.1 ms to 805 microA, 1.0 ms.

Trigeminal orosensation and ingestive behavior in the rat

A deafferentation procedure was used to examine the contributions of trigeminal orosensation to the control of ingestive behavior in the rat. The procedure removed somatosensory input from the mouth, sparing olfaction, lingual taste, and vibrissae inputs as well as proprioceptive afferents from and efferents to the jaw muscles. Rats with sections of tongue or jaw muscle efferents served as oromotor controls. Bilateral trigeminal orosensory deafferentation was followed by an array of effects on ingestive behavior whose magnitudes were proportional to the extent of the deafferentation. The "trigeminal syndrome" includes a disruption of food and water intake (aphagia, adipsia), impairments in the sensorimotor control of eating and drinking, decreased responsiveness to food and water, and a reduction in the level of body weight regulation. Trigeminal deafferentation spared elementary ingestive movement patterns (biting, licking, chewing) but disrupted their control by the perioral stimuli, which normally elicit them, so that eating and drinking sequences were either aborted or inefficient. Deficits in food intake varied with the sensory properties of the diet. Recovery of intake took place along a palatability gradient, and recovery of water intake paralleled that of dry food. The chronically reduced body weight was caused by a persistent hypophagia and reflects reduced responsiveness to food. These findings suggest a considerable degree of overlap in the neural mechanisms mediating the sensorimotor and motivational control of intake in the rat.

Qualitative structural development of the feline inferior alveolar nerve

The qualitative structural development of the inferior alveolar nerve was studied by electron microscopy in 56 pre- and postnatal kittens and 21 young and old adult cats. At 25 days post conception the nerve was composed of a bundle of small axons enclosed by primitive sheath cells. Three weeks later myelination had been initiated. Axons measuring 2-3 micrometers underwent local demyelination from 2 weeks before to 3 weeks after birth. This was accompanied and followed by nodalization of larger axons. A typical perineurium was first apparent in the newborn kitten. Six to eight weeks postnatally, the nerve appeared qualitatively mature, although axonal growth was far from completed. This coincides with achievement of a fully mature primary dentition shortly after the weanling period. Apart from a continued size growth, no changes were observed in the nerve during the transition from the primary to the permanent dentition. In the inferior alveolar nerve of old cats, axonal and perineurial changes co-existed with signs of dental attrition and pathology.

Axon number and size distribution in the developing feline inferior alveolar nerve

The number and size distribution of axons in the developing feline inferior alveolar nerve (IAN) were examined by electron microscopy. Seven cat fetuses and thirty kittens and cats aged from 25 days post conception (dpc) to 11 years were used. The total number of IAN axons increased from 4,400 to 16-17,000 between 25 and 40 dpc, and then decreased to about 13,000 before birth. This level was maintained up to at least 11 years. Myelinated axons first appeared by 45 dpc and constituted 28% at birth. The young adult proportion of about 45% myelinated axons was established at 2 months. In the old adult (11 years) 55% of the IAN axons were myelinated. Size measurements showed that unmyelinated axons had diameters of 0.1-0.5 micrometer at 25 dpc. From 55 dpc and on the size range extended from 0.1 micrometer to 1 micrometer. The size range of myelinated axons was 1-4.5 micrometers at birth and 1-8 micrometers 2 months postnatally. A bimodal size distribution first appeared by 2 months, and the range was 1-13 micrometers from 6 months and on. The findings were compared with age-related changes in the primary and permanent dentitions.

Evidence that substance P is a mediator of antidromic vasodilatation using somatostatin as a release inhibitor

The effect of somatostatin on nerve-induced vasodilatation and the release of substance P (SP) was studied in the dental pulp of anesthetized cats. Changes in pulpal blood flow were determined by measuring the rate of disappearance of a local depot of radioactive tracer. The release of SP was studied indirectly by determining the residual amounts of substance P-like immunoreactivity (SPLI) in the pulps by radioimmunoassay. Electrical stimulation (3 min at 10 V, 15 Hz and 5 ms) of the distal end of the cut inferior alveolar nerve (IAN) increased pulpal blood flow. After pretreatment (10 min) with somatostatin (30 pmol/min) similar nerve stimulation was without effect on pulpal blood flow. Intra-arterial infusion of somatostatin (30 pmol/min) had no effect on pulpal blood flow and did not influence the vasodilator response to SP. Following IAN stimulation (3--45 min) and subsequent incubation (30 min, 37 degrees C) of the lower canine teeth, the SPLI levels in ipsilateral pulps were significantly lower (47.5% reduction) than those in contralateral, unstimulated controls. In cats pretreated with somatostatin (30 pmol/min for 10 min, i.a.) similar nerve stimulation (3 min) did not reduce the pulpal SPLI levels as compared to controls. The results show that nerve-induced vasodilatation and release of SPLI are inhibited by somatostatin. They are consistent with the hypothesis that vasodilatation in the cat dental pulp produced by stimulation of the IAN is mediated by substance P.

Tissue concentration and release of substance P-like immunoreactivity in the dental pulp

The concentration of substance P-like immunoreactivity (SPLI) was determined in dental pulps from cat, dog and man by radioimmunoassay. Pulps from mature cats showed the highest SPLI-levels (mean 32 pmol/g); these are comparable to or higher than those found in any other organ outside the central nervous system. The SPLI concentrations were lower in pulp from immature teeth. The immunological and chromatographic behaviour of the pulpal SPLI from cat and man resembled that of synthetic substance P (SP), indicating that the assayed substance is closely related to or identical with SP. Release of pulpal SPLI in canine teeth was evoked by stimulation of the inferior alveolar nerve in anaesthetized cats. In 9 of 16 experiments the amounts of SPLI found in pulp suprafusates following stimulation (4-31 fmol) were larger than those in unstimulated controls (0-7 fmol). Stimulation also reduced the pulpal tissue concentration of SPLI to 60% of that in homologous control pulps. The high concentration of SPLI found in the dental pulp and the demonstration of nerve-induced release strengthen the hypothesis that SP serves some function in the dental pulp.