Relation between electrical stimulus intensity,masseteric exteroceptive reflex and sensory perception

PurposeThe purpose of this study was to characterize the relation between stimulus intensity, masseteric exteroceptive suppression (ES), and sensory perception as a possible quantitative or qualitative tool in the diagnosis of the masticatory system for prosthodontic treatment.MethodsFrom 12 males and 12 females (22–41 years), surface EMG was recorded from the left masseter muscle. Visual feedback allowed the subjects to maintain a constant clenching level of 30% maximal voluntary contraction. Thirteen fixed stimulus intensities from 5 to 35 mA in 2.5 mA increments were applied at random. A computer program calculated the duration of ES, based on the 50% level of the mean pre-stimulus EMG. The stimulation intensity at which early (ES1) or late (ES2) exteroceptive suppressions appeared first and at which subjects answered as being painful were defined as the reflex threshold (RT1 or RT2) and pain threshold (PT), respectively. The relation between sensory perception and ES was evaluated using stimulus–response (S–R) curve analysis.ResultsSignificant differences were found between PT and RT1, and between RT1 and RT2 (P < 0.001). After S–R curve analysis, the maximum duration of ES1 and ES2 was estimated at 9.6 ms and 33.5 ms, and appearance was rated as 6.2 and 4.0 on numeric rating scale (NRS), saturation was 7.6 and 6.9, and slope was 7.0 and 11.2, respectively.ConclusionsAll parameters for changes in ES following increasing incremental stimulus intensity could be analyzed. The construction of S–R curves in relation to sensory perception and ES parameters characterized the difference between ES1 and ES2.     

Reproducibility of the masseteric exteroceptive suppression period using stimulus-response curves

The present study evaluated the reproducibility of the late exteroceptive suppression period (ES2) and of pain perception. The surface electro-myogram (EMG) was recorded from the left masseter muscle in 12 males and 12 females (22-31 year). Thirteen fixed stimulus intensities from 5 to 25 mA with 2.5 mA intervals were applied at random to the left mental area, and stimulus-response (S-R) curves were built for each subject. The first stimulation intensity at which the ES2 appeared was defined the reflex threshold, while the lowest stimulus intensity the subjects scored as painful, was called the pain threshold. Using the S-R curves, the other reflex parameters (appearance level, saturation level, slope from appearance to saturation, maximum duration of ES2, and maximum suppression degree) were also determined. Two measurement sessions were scheduled. Both the reflex and the pain sensation appeared at significantly lower stimulus intensity in females than males (P < 0.05). The reflex threshold, the reflex appearance and saturation level showed a significant decrease from the first to second session (P < 0.05), while the pain threshold was significantly higher during the second session (P < 0.01). By contrast, a good reproducibility was found for the maximum duration and suppression degree of ES2. Consequently, if S-R curves would be used to study the relation between the ES2 parameters and stimulus intensity in normal subjects for their applicability in clinical conditions, maximum duration and maximum suppression degree should be focused upon, in order to avoid session and gender effects as confounding factors.     

The masseteric reflex evoked by tooth and denture tapping

The characteristics of the masseter reflex evoked by tapping a maxillary incisor were compared with the reflex pattern evoked by tapping a corresponding denture tooth after insertion of an immediate denture. Up to three inhibitory phases (I-1, I-2 and I-3), followed by excitation, were found on an averaged EMG. The tapping force threshold for the early inhibitory phase was lower than for the late phases. The pattern of the reflex was generally the same before and after insertion of the denture, but the threshold values increased. After insertion of the denture, the threshold for I-1 increased from 1 +/- 0.3N to 2.2 +/- 0.4N, the threshold for I-2 increased from 2.4 +/- 0.8N to 3.8 +/- 0.9N, and the threshold for I-3 increased from 5.1 +/- 0.6N to 8.3 +/- 0.9N. The latency period for I-1 also increased from 12.3 +/- 0.5 ms to 13.1 +/- 0.3 ms after insertion of the denture. After relining, the threshold for evoking I-1 decreased from 2.7 +/- 1.2N to 1.2 +/- 0.6N. It was assumed that the mechanoreceptors situated in the mucosa under the denture base could take over the functional role of the periodontal mechanoreceptors for evoking the masseter reflex during tapping, and that these afferents probably had connections to the same interneurones.     

The effect of sectioning the trigeminal sensory root on the periodontally-induced jaw-opening reflex

The experiment was designed to determine the pathway taken to the brain stem by periodontal afferents responsible for the digastric jaw-opening reflex induced by tooth-tapping. Cutting the trigeminal sensory roots of anesthetized decerebrate cats eliminated the ipsilateral periodontally-induced reflex, although the stretch reflexes of the jaw-closing muscles were undiminished. These results suggest that periodontal afferents causing the jaw-opening reflex reach the brainstem through the Vth sensory root, and confirm that muscle spindle afferents travel through the Vth motor root.     

Influence of age and gender on peri-implant osteogenesis. Age and gender on peri-implant osteogenesis

Among the local and systemic factors affecting bone repair, great interest is focused on age and gender. The aim of this work was to perform a histomorphometric evaluation of peri-implant bone healing response in male and female rats aged 1 and 3 months. Forty Wistar rats were i.p. anesthetized with xylazine and ketamine. A c.p. Ti implant (Implant Vel, Buenos Aires-Argentina) was placed in the right tibia following the method described by Cabrini et al. (Implant Dent 1993; 2:264-267). Group I: (GI, n = 10) female rats aged 1 month; Group II: (GII, n = 10) female rats aged 3 months; Group III: (GIII, n = 10) male rats aged 1 month; Group IV: (GIV, n = 10) male rats aged 3 months. All the animals were killed by ether overdose 30 days post-implantation. The tibiae were resected, radiographed and embedded in methyl-methacrylate. Ground sections perpendicular to the longer axis of the tibia were obtained and stained with toluidine blue. Percentage of osseointegration and peri-implant bone tissue volume were evaluated. No differences in peri-implant bone tissue histology were observed among groups. No statistically significant differences in peri-implant bone volume and percentage of osseointegration were observed between GII (adult females) and GIV (adult males). Peri-implant bone volume and percentage of osseointegration were markedly greater in GIV (adult males) than in GIII (young males) (14 +/- 1 mm2 and 8 +/- 2 mm2) p < 0.01 and (49 +/- 6% and 24 +/- 9%) p < 0.01 respectively. Using this experimental model, differences in peri-implant osteogenesis (bone volume and percentage of osseointegration) associated to gender were only observed in the young rats, and differences associated to age were found between the groups of males.     

Trigeminocardiac reflex: a unique case of recurrent asystole during bilateral trigeminal sensory root rhizotomy.

BACKGROUND: The trigeminocardiac reflex is the sudden-onset of dysrhythmia and hypotension during manipulation of any of the branches of the trigeminal nerve. The trigeminal nerve and cardioinhibitory vagus nerve constitute the afferent and efferent pathways in the reflex arc. The trigeminocardiac reflex has been reported to occur during craniofacial surgery, balloon-compression rhizolysis of the trigeminal ganglion, and tumour resection in the cerebellopontine angle. PATIENT & METHOD: A 2-year-old male patient with haemangioma near the sella turcica underwent rhizotomies of both sides of the dorsal sensory roots, of the trigeminal nerves for palliation of intractable trigeminal pain. RESULTS: In this report, we experienced two unexpected episodes of asystole after transection of the sensory roots of the trigeminal nerves. CONCLUSION: Sectioning of the intracranial dorsal sensory root of the trigeminal nerve provides clear evidence of the central role of the trigeminal nerve as the afferent pathway of the trigeminocardiac reflex arc.     

腭裂类型、年龄、性别对患者代偿性构音影响的初步研究

目的:观察研究不同类型的腭裂患者代偿性构音的发生概率.方法:将276 例完全性腭裂和不完全性腭裂患者,分别按照≤5 岁、≥6 岁分组观察代偿性构音发生率;再将各年龄段的患者按照性别分组观察.结果:完全性腭裂组比不完全性腭裂组患者发生代偿性构音的概率更大.≤5 岁组的完全性腭裂与不完全性腭裂患者的代偿性构音发生率无显著性差异,而≥6 岁组的完全性腭裂与不完全性腭裂的代偿性构音发生率存在显著性差异.代偿性构音的发生与性别无关.结论:腭裂类型、年龄与代偿性构音的形成有一定的相关性.     

Influence of auriculotemporal nerve anaesthesia on the masseteric silent period

Silent periods were evoked from the masseter muscles bilaterally in response to chin taps during a clench. Injection of 0.75 ml of 3% Mepivicaine posteromedial to each condyle led to a distribution of skin anaesthesia consistent with the distribution of the auriculotemporal nerve. Silent periods were evoked prior to and during anaesthesia in ten subjects. The silent period latencies (mean +/- standard deviation) prior to anaesthesia were 12.5 +/- 1.8 ms and 11.9 +/- 2.5 ms in the right and left masseters. During anaesthesia the latency decreased by 0.3 +/- 1.3 ms in the right masseter and by 0.3 +/- 2.1 ms on the left masseter. Neither change was statistically significant (P greater than 0.05). The silent period durations prior to anaesthesia were 20.3 +/- 4.0 ms and +/- 22.8 +/- 7.1 ms in the right and left masseters. During anaesthesia, these decreased by 2.74 +/- 5.8 ms on the right and 2.15 +/- 4.4 ms on the left. These decreases were not statistically significant (P greater than 0.05). These results failed to demonstrate an influence of the predominant nerve supply of the TMJ on either the latency or the duration of the masseteric silent period.     

Bilateral variation of the masseteric myotatic reflex and the silent period in young humans

Increased bilateral differences in jaw reflexes have been considered as pathological findings. The aim of this study was to investigate the normal variation between sides in the jaw jerk and the silent period and determine the range of its boundaries, using the present experimental set-up. Electromyographic data were simultaneously recorded from the right and left masseter muscles by surface electrodes, using a computerized recording and analysis system. The reflexes were elicited by chin taps during mandibular rest and at moderate intercuspal clenching in 20 healthy dentate adults (10 males and 10 females) with a mean age of 26 years. The reflexes were always elicited bilaterally and no overall significant differences were observed between sides for occurrence, latency, duration and amplitude of the jaw jerk and for the latency and duration of the silent period (P > 0.05). However, in the individual analysis significant bilateral variation was occasionally recorded, particularly for the jaw jerk at rest and mainly in the amplitude measurements. On the other hand, in the silent period duration measurements individual variation was very limited. Bilateral individual latency differences for the jaw jerk did not exceed 1 ms at rest (x = 0.3 +/- 0.3 ms) and 0.7 ms at clench (x = 0.3 +/- 0.2 ms), while latency differences for the silent period did not exceed 0.8 ms for the early type (x = 0.4 +/- 0.2 ms) and 4.8 ms for the late phase of depression (x= 1.9 +/- 1.7 ms). Bilateral differences for the silent period duration did not exceed 7.1 ms (x = 2.2 +/- 2.3 ms) in the early type (simple + early phase of combined types) and 3.3 ms (x = 1.5 +/- 0.9 ms) in the total duration of the combined types.     

Distribution of hemokinin-1 in the rat trigeminal ganglion and trigeminal sensory nuclear complex

ObjectiveA new mammalian tachykinin peptide encoded in a TAC4 gene was identified and designated as hemokinin-1 (HK-1). A representative of the tachykinin peptide family is substance P (SP), and the function of SP has been well characterized as a pain transmitter or modulator, while it is possible that HK-1 is involved in pruriceptive processing, but, as yet, the distribution of HK-1 peptide in the trigeminal sensory system is still unknown. Thus, the aim of the present study was to elucidate the distribution of HK-1, while comparing the expression of SP, in the trigeminal ganglion and trigeminal sensory nuclear complex.DesignThe trigeminal ganglion and the brain stem of male SD rats were used in the immunohistochemical study. Since the amino acid sequence in the carboxyl-terminal regions of HK-1 and SP is common, polyclonal antibodies of HK-1 and SP derived from 6 amino acids consisting of amino-terminal regions of these peptides were produced in guinea pig and rabbit, respectively. The immunohistochemical staining of HK-1 and SP was conducted using frozen sections of the trigeminal ganglion and brain stem in rats.ResultsImmunohistochemical studies revealed the expression of HK-1 in small- and medium-sized trigeminal ganglion neurons, in the paratrigeminal nucleus, and in lamina I of the trigeminal nucleus caudalis, while there was no immunoreactivity of HK-1 in the trigeminal nucleus principalis, trigeminal nucleus oralis, and trigeminal nucleus interpolaris.ConclusionThese findings indicate that HK-1 is a target molecule for treatment of itch in the orofaicial regions.     

Influence of age and gender on oral health and related behaviour in an independent elderly population

Abstract – Previous studies have been unable to determine the influence of advanced age on oral health because they included relatively few subjects, particularly men, over 75 yr of age. In this study a disproportionate and stratified random sample of subjects over 70 yr and living independently was selected from a list of voters in Vancouver, B.C. The sample of 521 elders was structured to provide similar numbers of men and women in three 5-yr age-groups. All of the subjects were interviewed, and 255 of them, representing a similar distribution of age and gender, were examined to investigate the influence of aging on oral health and related behaviour. In bivariate analyses neither age nor gender was associated significantly with oral health or complaints. The use of dental services during the preceding year was associated with female and younger subjects, while men and older subjects usually went to dentists only to relieve pain. Logistic regression in a multivariate model confirmed the importance of natural teeth in predicting the use of dental services (by improving the prediction from 60% to 73%). Other models offered less useful improvements in predicting complaints (64% to 70%) or oral health (56% to 60%). Overall the study demonstrates that the age and gender of independent elders have very little direct influence on the oral health or related behaviour established early in life.     

下颌骨牵引延长后下齿槽神经功能的评价

目的 采用三叉神经体感诱发电位（trigeminal somatosensory evoked potential,TSEP)检查恒河猴下颌骨牵引延长术对下齿槽神经功能的影响。方法 健康青年恒河猴7只，行下颌角部完全骨截开术，右侧或双侧安放牵引器。截骨间隙平均牵引距离为13．5mm。于术前、牵引完成时、牵引完成后4周分别进行下齿槽神经SEP检查。结果 术前下齿槽神经SEP各波的潜伏期测量值，两侧对比检验差异无显著性。牵引术完成时SEP各波的潜伏期较术前均有不同程度延长（P＜0．01，P＜0．001），波幅显著下降（P＜0．001）。术后4周各波潜伏期及波幅均有恢复，但多数差别仍有显著性。结论 TSEP检查提示下颌骨牵引延长术对下齿槽神经功能有一定影响，术后4周其功能有部分恢复。     

Influence of the muscle tension on the masseteric silent period in children and adults

summary Three subject groups who have shown different biting forces were examined in order to investigate whether the physiological phenomenon that the duration of the silent period (SPD) of the masseter muscle would be influenced by background activities of the muscles. They were classified into child (CN, n = 10) and adult groups; the adult group was then further subdivided according to the strength of maximum biting force into a normal group (AN, n = 10) and a low biting force group with some symptoms (AS, n = 5). SPD was observed in maximum) and biting on a transducer (50N, 100N and maximum). With increase of muscle activities, SPD was significantly decreased in the AN and CN groups, whereas no significant changes were found in the AS group. When comparing SPDs among the three groups at the same voluntary effort, the AN group exhibited the shortest SPD followed by the CN and AS groups. The results suggest that SPD was positively influenced by the strength of the background activities of the muscles and that immaturity of the masseters in terms of muscle activity could affect the SPD.     

健康人群的颌面部定量感觉研究

目的 探讨中国人群三叉神经和躯干神经的定量感觉在部位、年龄及性别之间的差异。方法 选择青年组和中年组健康志愿者各20例,在手背、舌尖、下唇及左右颏部分别测量冷/热感觉阈值（CDT/WDT）、冷/热疼痛阈值(CPT/HPT)、机械感觉阈值(MDT)和机械疼痛阈值(MPT),采用重复设计的方差分析进行数据分析。结果 三叉神经分布区域的温度和机械敏感性比手背皮肤高,颏部皮肤的温度敏感性比口内黏膜高;青年组比中年组对温度感觉刺激和机械刺激更为敏感,差异有统计学意义;女性对温度疼痛刺激更为敏感,差异有统计学意义。结论 温度和机械定量感觉测试的应用可以更好的理解不同感觉表型背后的机制,并且为对中国人群三叉神经区域感觉异常方面的研究提供一些基本信息。     

The role of sensory fiber demography in trigeminal and postherpetic neuralgias

In this study, we systematically investigated fiber demography, based on function and distribution, from the periphery to their destinations in the various central (sub) nuclei in the trigeminal brainstem nuclear sensory complex. Conventional and novel compelling information is provided, demonstrating that the ratio and somatotopy of types A and C sensory fibers at the site of a lesion can elucidate important puzzles in TNP disorders. For instance, we explain how of a major shift in the fibers' direction and ratio at the level of the trigeminal root entry zone (REZ) influences the pathophysiology of pre- and typical trigeminal neuralgia. As a result, there is a high A/C ratio of oral and peri-oral fibers in the supero-medial region of the REZ, which is mostly susceptible to vascular compression. However, this A/C ratio varies considerably at lower proportions in other areas along the peripheral trigeminal pathway, where an injury (viral, vessel compression, or trauma) can lead to a broader spectrum of fiber involvement and, consequently, pain outcome. In summary, we explain how fiber demography can influence pain quality, location, temporal features, progress, and treatment prognosis of TNP in those patients who develop it.     

Quantitative sensory testing (QST) in the orofacial region of healthy Chinese: influence of site,gender and age

Objective: To establish a preliminary thermal and mechanical somatosensory profile using a standardized quantitative sensory testing (QST) to investigate site, gender and age differences in healthy Chinese.

Materials and methods: Twenty younger (age: 20–40 years, 10 men, 10 women) and twenty older (age: 41–61 years, 10 men, 10 women) healthy participants completed the study. Cold detection threshold (CDT), warm detection threshold (WDT), cold pain threshold (CPT), heat pain threshold (HPT), mechanical detection threshold (MDT) and mechanical pain threshold (MPT) were measured at five sites: Left hand, bilaterally at the mental area, tip of tongue and the lower lip mucosa. Mixed model ANOVAs with repeated measures were used to analyze the data.

Results: MDT(p?p?p?=?.006) was significantly higher and WDT (p?p?p?p?p?p?=?.004) were found in the older group compared to the younger group. Significant gender differences were found with less sensitivity for WDT (p?=?.024) and MDT (p?=?.003) in men compared to women.

Conclusions: Application of standardized QST can provide valuable information of orofacial somatosensory phenotypes in a Chinese population. Age, gender and site are mandatory to control for.     

Development of sensory and reflex responses to tooth-pulp stimulation in children

Electric stimulation was applied to the tooth-pulp and tongue in 12 children divided into 3 groups according to the development of the roots of the upper first incisors, i.e. 1/2, 3/4 and fully formed. The masseter inhibitory periods (MIP) could be evoked by electric stimulation of the tongue at sensory threshold current levels in all children, but only for incisors with fully-formed roots. Stimulation of incisors with 3/4 formed roots at detection-threshold currents produced sensation 56 per cent of the time and detectable MIP on 65 per cent of stimuli. No sensation was obtained with stimuli up to 100 microA in incisors with 1/2-formed roots, but MIP was recorded with 31 per cent of stimuli. The findings indicate that reflex activity precedes sensation in the normal development of teeth, and that segmental, reflex, connections appear to be established before the cortical, sensory, projections are fully functional.