Clinically Available Assessment Measures for Lingual and Labial Somatosensation in Healthy Adults: Normative Data and Test Reliability.

PURPOSE: High-quality orofacial somatosensory inputs are essential for achieving rapid and accurate motor outputs. Little somatosensory testing is currently being completed in clinical settings. The purpose of this study is to assess the feasibility and test-retest reliability of clinical assessment tools for orofacial somatosensory testing in healthy young adults. METHOD: A total of 45 healthy young adults (ages 20-41 years) was recruited. Participants reported basic health information, completed pure-tone hearing thresholds, and were assessed using two-point discrimination discs and Von Frey hair detection and discrimination thresholds for bilateral lip and tongue. A subsample of participants (n = 18; 40%) returned to complete reliability testing. RESULTS: Descriptive results are presented for the normative group as well as the reliability group. Difference scores between Tests 1 and 2 for each testing measure and location show high agreement. CONCLUSION: Two-point discrimination and Von Frey hair monofilament assessment for both detection- and discrimination-threshold estimates have high test-retest reliability in a healthy young population. These testing measures could be a way to easily complete objective somatosensory testing of the orofacial region in a clinical context.

The effect of speech distortion on the excitability of articulatory motor cortex.

It has become increasingly evident that human motor circuits are active during speech perception. However, the conditions under which the motor system modulates speech perception are not clear. Two prominent accounts make distinct predictions for how listening to speech engages speech motor representations. The first account suggests that the motor system is most strongly activated when observing familiar actions (Pickering and Garrod, 2013). Conversely, Wilson and Knoblich's account asserts that motor excitability is greatest when observing less familiar, ambiguous actions (Wilson and Knoblich, 2005). We investigated these predictions using transcranial magnetic stimulation (TMS). Stimulation of the lip and hand representations in the left primary motor cortex elicited motor evoked potentials (MEPs) indexing the excitability of the underlying motor representation. MEPs for lip, but not for hand, were larger during perception of distorted speech produced using a tongue depressor, relative to naturally produced speech. Additional somatotopic facilitation yielded significantly larger MEPs during perception of lip-articulated distorted speech sounds relative to distorted tongue-articulated sounds. Critically, there was a positive correlation between MEP size and the perception of distorted speech sounds. These findings were consistent with predictions made by Wilson & Knoblich (Wilson and Knoblich, 2005), and provide direct evidence of increased motor excitability when speech perception is difficult.

Identification of autonomic neuronal chains innervating gingiva and lip.

The major goals of this present study were 1) to further clarify which parasympathetic ganglion sends postganglionic fibers to the lower gingiva and lip that may be involved in the inflammatory processes besides the local factors; 2) to separately examine the central pathways regulating sympathetic and parasympathetic innervation; and 3) to examine the distribution of central premotor neurons on both sides. A retrogradely transported green fluorescent protein conjugated pseudorabies virus was injected into the lower gingiva and lip of intact and sympathectomized adult female rats. Some animals received virus in the adrenal medulla which receive only preganglionic sympathetic fibers to separately clarify the sympathetic nature of premotor neurons. After 72-120h of survival and perfusion, the corresponding thoracic part of the spinal cord, brainstem, hypothalamus, cervical, otic, submandibular and trigeminal ganglia were harvested. Frozen sections were investigated under a confocal microscope. Green fluorescence indicated the presence of the virus. The postganglionic sympathetic neurons related to both organs are located in the three cervical ganglia, the preganglionic neurons in the lateral horn of the spinal cord on ipsilateral side; premotor neurons were found in the ventrolateral medulla, locus ceruleus, gigantocellular and paraventricular nucleus and perifornical region in nearly the same number on both sides. The parasympathetic postganglionic neurons related to the gingiva are present in the otic and related to the lip are present in the otic and submandibular ganglia and the preganglionic neurons are in the salivatory nuclei. Third order neurons were found in the gigantocellular reticular and hypothalamic paraventricular nuclei and perifornical area.

Effect of sodium bicarbonate-buffered lidocaine on the success of inferior alveolar nerve block for teeth with symptomatic irreversible pulpitis: a prospective, randomized double-blind study.

INTRODUCTION: The purpose of this prospective, randomized, double-blind study was to compare the anesthetic efficacy of buffered with nonbuffered 2% lidocaine with 1:80,000 epinephrine solution for inferior alveolar nerve (IAN) block in patients with mandibular posterior teeth experiencing symptomatic irreversible pulpitis. METHODS: Eighty adult patients diagnosed with symptomatic irreversible pulpitis of a mandibular posterior tooth were selected. The patients received 2 cartridges of either 2% lidocaine with 1:80,000 epinephrine buffered with 0.18 mL 8.4% sodium bicarbonate or 2% lidocaine with 1:80,000 epinephrine with 0.18 mL sterile distilled water using conventional IAN block injections. Endodontic access preparation was initiated 15 minutes after injection. Lip numbness was required for all the patients. Success was determined as no or mild pain on the basis of Heft-Parker visual analog scale recordings upon access cavity preparation or initial instrumentation. Data were analyzed by the t, Mann-Whitney, and chi-square tests. RESULTS: The success rates were 62.5% and 47.5% for buffered and nonbuffered groups, respectively, with no significant differences between the two groups (P = .381). CONCLUSIONS: Buffering the 2% lidocaine with 1:80,000 epinephrine with 8.4% sodium bicarbonate did not improve the success of the IAN block in mandibular molars in patients with symptomatic irreversible pulpitis.

Infiltration anesthesia for extraction of the mandibular molars.

PURPOSE: Profound anesthesia for mandibular molars by buccal infiltration has been tried in recent years, with promising results. This prospective, randomized, single-blinded, crossover study investigated the clinical anesthetic efficacy obtained with 1:100,000 epinephrine plus 4% articaine (A100) 1.8 versus 3.6 mL as mandibular first molar buccal infiltration during removal of impacted lower third molars. MATERIALS AND METHODS: Thirty adult patients underwent removal of symmetrically positioned impacted lower third molars in 2 separate appointments. The patients randomly received mandibular buccal first molar infiltration of A100 1.8 or 3.6 mL during surgery. For assessment of anesthetic efficacy, any pain during surgery was rated using the visual analog scale. Also, the onset, duration, and total amount of anesthetic used were recorded. RESULTS: Compared with the 1.8-mL volume of A100, the 3.6-mL volume showed a statistically higher success rate (93% vs 56%). CONCLUSIONS: Infiltration in the buccal vestibule opposite the mandibular first molar by A100 3.6 mL may be a good option for extraction of mandibular third molars, with supplemental lingual anesthesia.

Effect of local anesthesia on trigeminal somatosensory-evoked magnetic fields.

For objective neurophysiological evaluation of the function of the trigeminal system, magnetoencephalography- based TSEF (trigeminal somatosensory-evoked field) assessment would be valuable in providing spatial and temporal profiles of cortical responses. However, this necessitates knowledge of how TSEF varies with trigeminal nerve dysfunctions. We introduced a conduction block of the trigeminal nerve using local anesthesia (lidocaine) to temporally mimic nerve dysfunctions, and monitored TSEF changes. Following an electrical stimulation of the lower lip, a magnetic response with peak latency of approximately 20 ms was identified in all participants. Dipole for the peak was estimated on the post-central gyrus in the participant's own magnetic resonance image. After normalization to Montreal Neurological Institute (MNI) space and inter-participant data integration, the summary equivalent current dipole localization among participants remained in the post-central gyrus, suggesting validity of the use of MNI space. Partial anesthesia of the lower lip led to a loss of the waveform characteristics of TSEF for electrical stimulation to the trigeminal nerve. We verified that the 20-ms latency cortical response of TSEF components localized at the primary sensory cortex can serve as a robust neurofunctional marker of experimental trigeminal nerve dysfunction.

Trigeminal nerve injuries in relation to the local anaesthesia in mandibular injections.

OBJECTIVE: This study reports the signs and symptoms that are the features of trigeminal nerve injuries caused by local anaesthesia (LA). METHODS: Thirty-three patients with nerve injury following LA were assessed. All data were analysed using the SPSS statistical programme and Microsoft Excel. RESULTS: Lingual nerve injury (LNI; n = 16) and inferior alveolar nerve injury (IANI; n = 17) patients were studied. LNI were more likely to be permanent. Neuropathy was demonstrable in all patients with varying degrees of paraesthesia, dysaesthesia (in the form of burning pain) allodynia and hyperalgesia. All injuries were unilateral. A significantly greater proportion of LNI patients (75%) had received multiple injections, in comparison to IANI patients (41%) (p <0.05). Fifty percent of patients with LNI reported pain on injection. The presenting signs and symptoms of both LNI and IANI included pain. These symptoms of neuropathy were constant in 88% of the IANI group and in 44% of LNI patients. Functional difficulties were different between the LNI and IANI groups, a key difference being the presence of severely altered taste perception in nine patients with LA-induced LNI. CONCLUSIONS: Chronic pain is often a symptom after local anaesthetic-induced nerve injury. Patients in the study population with lingual nerve injury were significantly more likely to have received multiple injections compared to those with IANI.

Phentolamine mesylate for accelerating recovery from lip and tongue anesthesia.

Phentolamine mesylate, at dosages from 0.4 to 0.8 mg in adults and adolescents and at dosages from 0.2 to 0.4 mg in children aged 4 to 11 years, has been proven to be safe and effective for the reversal of soft tissue anesthesia (lip and tongue numbness) and the associated functional deficits resulting from a local dental anesthetic injection containing a vasoconstrictor. Its ability to block a-adrenergic receptors on blood vessels induces vasodilation and enhances the redistribution of the local anesthetic away from the injection site. The low dosages administered for dental local anesthetic reversal in all likelihood accounts for the lack of significant cardiovascular effects that are associated with the medical use of the drug for hypertensive conditions associated with catecholamine excess.

Functional results of electrical cortical stimulation of the lower sensory strip.

The aim of this paper is to provide functional results obtained from electrical cortical stimulation of the lower postcentral gyrus in patients who underwent either lesional or non-lesional epilepsy surgery. Group I (n=393) included those patients with gliosis or normal tissue and Group II (n=107) included patients with space-occupying lesions. For cortical stimulation, a unipolar voltage-controlled electrode was used. The tongue, lip, and hand/finger sequences over the lower postcentral gyrus lateromedially in both groups were in agreement with classic teaching. The presence of structural lesions, such as tumors and dysplasia, did not affect the vertical representation of the body parts on the lower sensory strip. Individual variations, which included mosaicism over the sensory strip, were frequent. Whether the functional variability and mosaicism within the sensory cortex result from a pathological condition or not remains to be elucidated in healthy humans using advanced non-invasive brain mapping techniques.

Anaesthetic efficacy of a labial infiltration method on the nasopalatine nerve.

BACKGROUND AND AIM: The conventional nasopalatine nerve block is commonly used to obtain anaesthesia in the anterior portion of the palate. The painful nature of this approach, however, has led investigators to seek alternative methods to obtain anaesthesia. Labial infiltration of the maxillary central incisors can be considered an effective anaesthetic approach for the anterior palate. Our study aimed to assess the anaesthetic effect of a modified labial infiltration method on the nasopalatine nerve. MATERIALS AND METHOD: A case-control clinical trial was done on 60 patients referring for extraction of maxillary incisors (mean age 44 years). The patients were divided into two groups of 30 people. For the first group, a primary conventional infiltration was given to each patient from a point between the maxillary canine and the lateral to obtain preliminary anaesthesia for the maxillary anterior labial area. The second or the control group was anaesthetised by conventional injection into incisive papilla. Two to three minutes afterwards, a labial infiltration approach was done and the amount of pain determined by OPS (objective pain score) was assessed. After five to six minutes the level of anaesthesia in the anterior palate was assessed in both groups by an explorer and recorded as pain-free, mild pain or severe pain. The sign test was used to statistically analyse the data (p <0.001). RESULTS: Total, moderate and no anaesthesia were observed in 76.7%, 13.3%, and 10% of the patients receiving anesthetic injection at the labial side. For the control group, these results were 83%, 17% and 0% respectively. CONCLUSION: This method of labial infiltration may be an effective alternative to the painful conventional palatine nerve block to obtain efficient anaesthesia of the anterior palate (p <0.001).

Hoxa2- and rhombomere-dependent development of the mouse facial somatosensory map.

In the mouse trigeminal pathway, sensory inputs from distinct facial structures, such as whiskers or lower jaw and lip, are topographically mapped onto the somatosensory cortex through relay stations in the thalamus and hindbrain. In the developing hindbrain, the mechanisms generating such maps remain elusive. We found that in the principal sensory nucleus, the whisker-related map is contributed by rhombomere 3-derived neurons, whereas the rhombomere 2-derived progeny supply the lower jaw and lip representation. Moreover, early Hoxa2 expression in neuroepithelium prevents the trigeminal nerve from ectopically projecting to the cerebellum, whereas late expression in the principal sensory nucleus promotes selective arborization of whisker-related afferents and topographic connectivity to the thalamus. Hoxa2 inactivation further results in the absence of whisker-related maps in the postnatal brain. Thus, Hoxa2- and rhombomere 3-dependent cues determine the whisker area map and are required for the assembly of the whisker-to-barrel somatosensory circuit.

Chemical and thermal stimuli have short-lived effects on the retzius cell in the medicinal leech.

During the appetitive phase of feeding, hungry leeches detect a prey by the integration of signals perceived by different sensory systems. Earlier reports suggested that chemical or thermal sensory stimulation of the lip was associated with increased afferent activity in cephalic nerves connecting the lip to the central nervous system. These authors further suggested that this activity was relayed to Retzius cells in segmental ganglia, which then released serotonin to initiate and control all aspects of feeding behavior. In this study, we show that chemosensory or thermal activation of the lip lasting for at least 5 min produces a distinct signal in the cephalic nerves consisting of action potentials of low amplitude. These small amplitude signals are clearly distinguishable from the large action potentials evoked by mechanosensory stimuli applied to the same area of the lip. Both types of sensory stimuli also evoke an increase in the firing frequency of the Retzius cells in segmental ganglia. However, the response recorded in the nerves and the Retzius cells during a maintained stimulus is not constant but decreases with an exponential time course. These results agree with our earlier observations on a semi-intact feeding preparation in which we showed that the firing frequency of the Retzius cell decreased as soon as the leech began to ingest its meal. Therefore, our data provide further evidence suggesting that it is unlikely that heat or chemical cues maintain the Retzius cell in an active state throughout the consummatory phase of feeding.

Glutamate as a transmitter in the sensory pathway from prostomial lip to serotonergic Retzius neurons in the medicinal leech Hirudo.

The involvement of glutamate in putative ingestive sensory pathways affecting the excitability of serotonergic Retzius neurons (RZ) in the leech CNS was investigated with a pharmacological approach. Exposure of the prostomial lip to 150 mM NaCl and 1 mM arginine produced excitatory as well as inhibitory responses in RZ found in the reproductive segments, while only excitatory responses were elicted in standard midbody RZ. Antagonists of glutamatergic receptors of the kainate/quisqualate type effectively inhibited chemosensory dependent excitation of RZ. Antagonists of glutamatergic receptors of the N-methyl D-aspartate type were ineffective in this regard. Cephalic nerve stimulation, like chemical stimulation of the lip, produced segment-specific responses in midbody RZ. Both the polysynaptic and monosynaptic components of the excitatory response of standard midbody RZ following cephalic nerve stimulation were inhibited in the presence of the kainate/quisqualate antagonist DNQX. These data suggest a role for glutamate as a transmitter in the neural circuitry from receptors of the leech prostomial lip to serotonergic RZ.

Some effects of auditory stimulation on perioral motor unit discharge and their implications for speech production.

The objective of this investigation was to describe the electrophysiological properties of short-latency reflexive pathways existing between the auditory system and the motoneurons involved in the control of lower lip movements for speech. The general procedure involved binaural presentation of auditory clicks (60--75 dB SL) at constant rates while subjects maintained a steady firing rate in a perioral motor unit. Post-stimulus time histograms were used to assess the effects of stimulation on the probability of firing of individual motor units. Data collected on 33 motor units in four subjects revealed a significant short-latency change in the probability of firing of 16 of these units. The mean latency of this effect was 20.4 ms. There was some indication that the direction and latency of the initial response to stimulation was dependent on the location and function of individual motor units. The likely neural pathways mediating these effects and their potential role in speech production are discussed.

Effects of amygdaloid stimulation upon trigeminal sensory fields of the lip that are established during hypothalamically-elicited quiet biting attack in the cat.

An experiment was performed in order to determine the role of the amygdala and surrounding cortex in quiet biting attack elicited from electrical stimulation of the hypothalamus. Stimulation of basal, cortical, and anterior amygdala as well as pyriform cortex and parahippocampal gyrus resulted in a suppression of the attack response and in a constriction of trigeminal sensory fields that are established during hypothalamic stimulation. Stimulation of lateral and central amygdala resulted in a facilitation of the quiet biting attack response and an expansion of the trigeminal sensory fields, and a decreased latency for the occurrence of jaw opening when the sensory field was held constant. These studies suggest that the amygdala modulated quiet biting attack behavior generated by hypothalamic stimulation at least, in part, by virtue of its control over sensory fields.

Effects of stimulation of the substantia innominata upon attack behavior elicited from the hypothalamus in the cat.

Experiments were undertaken in order to determine the role of the substantia innominata and surrounding regions in quiet biting attack elicited from electrical stimulation of the hypothalamus in the cat. Stimulation from sites in the lateral aspect of the substantia innominata resulted in a suppression of quiet biting attack and in a constriction of the 'effective trigeminal sensory fields' established during hypothalamic attack site stimulation. Stimulation from sites situated more medially in the substantia innominata resulted in a facilitation of quiet biting attack and in an expansion of the 'effective trigeminal sensory fields'. The motor component of the jaw opening response was altered in only 50% of the cases in contrast to the consistent effects observed upon the 'effective sensory fields'. Electrical stimulation of the substantia innominata had little effect upon affective display elicited from the ventromedial hypothalamus. Stimulation from sites located in the nucleus accumbens had no effect upon hypothalamically-elicited quiet biting attack and inhibited the occurrence of affective display in 2 to 5 animals tested. These studied suggest that the substantia innominata differentially modulates quiet biting attack and accomplishes this, at least in part, through its effects upon sensory mechanisms associated with the jaw opening reflex.