Somatosensory and trigeminal pathway abnormalities in Chinese patients with trigeminal neuralgia.

This study aimed to evaluate somatosensory function in Chinese patients with trigeminal neuralgia (TN) using a standard quantitative sensory testing (QST) battery and electrophysiological tests consisting of contact heat-evoked potentials (CHEPs) and blink reflex (BR). Twenty patients with TN and 20 sex- and age-matched healthy controls were recruited for this study. A standard QST protocol recommended by the German Research Network on Neuropathic Pain was carried out on the patients' painful and contralateral faces, the controls' right faces, and all participants' right hands. The CHEPs and BR were recorded at the Cz electrode and bilateral lower bellies of the orbicularis oculi, respectively, with thermal stimuli applied to both sides of the patient's face and the control's right face. The cold detection threshold, heat pain threshold, and mechanical pain threshold on the painful face were lower than those of healthy controls (P < 0.05), whereas the cold pain threshold and mechanical detection threshold were higher (P < 0.05) on the painful faces than those of the contralateral faces from patients or healthy controls. Mechanical pain sensitivity was higher in both test sites than in healthy controls (P < 0.05). Significantly longer N latencies (P < 0.05) and lower N-P amplitudes (P < 0.01) were detected in the patients' painful sites than in the contralateral sites and those of healthy controls. Comprehensive somatosensory abnormalities were found in painful facial sites in patients with TN, suggesting disturbances in the processing of somatosensory stimuli. Deficiencies in electrophysiological tests further revealed unilaterally impaired function of the trigeminal pathway in TN patients.

Descending serotonergic modulation from rostral ventromedial medulla to spinal trigeminal nucleus is involved in experimental occlusal interference-induced chronic orofacial hyperalgesia.

BACKGROUND: Dental treatment associated with unadaptable occlusal alteration can cause chronic primary myofascial orofacial pain. The serotonin (5-HT) pathway from the rostral ventromedial medulla (RVM) exerts descending modulation on nociceptive transmission in the spinal trigeminal nucleus (Sp5) and facilitates chronic pain. The aim of this study was to investigate whether descending 5-HT modulation from the RVM to the Sp5 is involved in the maintenance of primary myofascial orofacial hyperalgesia after persistent experimental occlusal interference (PEOI) or after delayed removal of experimental occlusal interference (REOI). METHODS: Expressions of 5-HT3A and 5-HT3B receptor subtypes in the Sp5 were assessed by immunofluorescence staining and Western blotting. The release and metabolism of 5-HT in the Sp5 were measured by high-performance liquid chromatography. Changes in the pain behavior of these rats were examined after specific pharmacologic antagonism of the 5-HT3 receptor, chemogenetic manipulation of the RVM 5-HT neurons, or selective down-regulation of 5-HT synthesis in the RVM. RESULTS: Upregulation of the 5-HT3B receptor subtype in the Sp5 was found in REOI and PEOI rats. The concentration of 5-HT in Sp5 increased significantly only in REOI rats. Intrathecal administration of Y-25130 (a selective 5-HT3 receptor antagonist) dose-dependently reversed the hyperalgesia in REOI rats but only transiently reversed the hyperalgesia in PEOI rats. Chemogenetic inhibition of the RVM 5-HT neurons reversed the hyperalgesia in REOI rats; selective down-regulation of 5-HT in advance also prevented the development of hyperalgesia in REOI rats; the above two manipulations did not affect the hyperalgesia in PEOI rats. However, chemogenetic activation of the RVM 5-HT neurons exacerbated the hyperalgesia both in REOI and PEOI rats. CONCLUSIONS: These results provide several lines of evidence that the descending pathway from 5-HT neurons in the RVM to 5-HT3 receptors in the Sp5, plays an important role in facilitating the maintained orofacial hyperalgesia after delayed EOI removal, but has a limited role in that after persistent EOI.

Genistein reverses the effect of 17ß-estradiol on exacerbating experimental occlusal interference-induced chronic masseter hyperalgesia in ovariectomised rats.

BACKGROUND: Oro-facial pain is more prevalent in women than in men, and oestrogen may underlie this sex difference. Genistein reversed the potentiation of 17ß-estradiol (E2) on glutamate-induced acute masseter nociceptive behaviour, but its role in dental experimental occlusal interference (EOI)-induced chronic masseter hyperalgesia remains unclear. OBJECTIVE: This study aimed to investigate sex differences, and to explore the role and underlying mechanisms of genistein in E2-potentiated EOI-induced chronic masseter hyperalgesia in rats. METHODS: Female and male rats were prepared to compare the sex differences of masseter hyperalgesia induced by EOI using a 0.4-mm-thick metal crown. Female rats were ovariectomised (OVX) and treated with E2 and genistein, followed by EOI. The head withdrawal threshold (HWT) was examined to assess masseter sensitivity. The protein expression of transient receptor potential vanilloid-1 (TRPV1) in the trigeminal ganglion (TG) was detected using western blotting. Immunofluorescence staining was used to reveal the colocalisation of oestrogen receptors (ERs) with TRPV1 and the percentage of TRPV1-positive neurons in the TG. RESULTS: To some extent, female rats displayed enhanced sensitivity to EOI-induced chronic masseter hyperalgesia compared with males. Female rats showed the lowest HWT in the pro-oestrus phase. Pre-treatment with genistein antagonised E2 potentiation in EOI-induced masseter hyperalgesia and blocked the effect of E2 by downregulating TRPV1 protein expression and the percentage of TRPV1-positive neurons in the TG. CONCLUSION: Female rats showed greater masseter hyperalgesia than males under EOI. Genistein antagonised the facilitation of EOI-induced chronic masseter hyperalgesia by E2 probably through inhibiting TRPV1 in the TG.

Astrocytes in the rostral ventromedial medulla contribute to the maintenance of oro-facial hyperalgesia induced by late removal of dental occlusal interference.

BACKGROUND: Astrocytes in the rostral ventromedial medulla (RVM) contribute to descending pain modulation, but their role in oro-facial pain induced by persistent experimental dental occlusal interference (PEOI) or following EOI removal (REOI) is unknown. OBJECTIVE: To explore the involvement of RVM astrocytes in PEOI-induced oro-facial hyperalgesia or its maintenance following REOI. METHODS: Male rats were randomly assigned into five groups: sham-EOI, postoperative day 6 and 14 of PEOI (PEOI 6 d and PEOI 14 d), postoperative day 6 following REOI on day 3 (REOI 3 d) and postoperative day 14 following REOI on day 8 (REOI 8 d). The nociceptive head withdrawal threshold (HWT) and activities of RVM ON- or OFF-cells were recorded before and after intra-RVM astrocyte gap junction blocker carbenoxolone (CBX) microinjection. RVM astrocytes were labelled immunohistochemically with glial fibrillary acidic protein (GFAP) and analysed semi-quantitatively. RESULTS: Persistent experimental dental occlusal interference-induced oro-facial hyperalgesia, as reflected in decreased HWTs, was partially inhibited by REOI at day 3 but not at day 8 after EOI placement. Increased GFAP-staining area occurred only in REOI 8 d group in which CBX could inhibit the maintained hyperalgesia; CBX was ineffective in inhibiting hyperalgesia in PEOI 14 d group. OFF-cell activities showed no change, but the spontaneous activity and responses of ON-cells were significantly enhanced that could be suppressed by CBX in REOI 8 d group. CONCLUSION: Rostral ventromedial medulla astrocytes may not participate in PEOI-induced oro-facial hyperalgesia or hyperalgesia inhibition by early REOI but are involved in the maintenance of oro-facial hyperalgesia by late REOI.

17ß-Estradiol Exacerbated Experimental Occlusal Interference-Induced Chronic Masseter Hyperalgesia by Increasing the Neuronal Excitability and TRPV1 Function of Trigeminal Ganglion in Ovariectomized Rats.

Pain symptoms in temporomandibular disorders (TMD) predominantly affect reproductive women, suggesting that estrogen regulates pain perception. However, how estrogen contributes to chronic TMD pain remains largely unclear. In the present study, we performed behavioral tests, electrophysiology, Western blot and immunofluorescence to investigate the role and underlying mechanisms of estrogen in dental experimental occlusal interference (EOI)-induced chronic masseter mechanical hyperalgesia in rats. We found that long-term 17ß-estradiol (E2) replacement exacerbated EOI-induced masseter hyperalgesia in a dose-dependent manner in ovariectomized (OVX) rats. Whole-cell patch-clamp recordings demonstrated that E2 (100 nM) treatment enhanced the excitability of isolated trigeminal ganglion (TG) neurons in OVX and OVX EOI rats, and EOI increased the functional expression of transient receptor potential vanilloid-1 (TRPV1). In addition, E2 replacement upregulated the protein expression of TRPV1 in EOI-treated OVX rats. Importantly, intraganglionic administration of the TRPV1 antagonist AMG-9810 strongly attenuated the facilitatory effect of E2 on EOI-induced masseter mechanical sensitivity. These results demonstrate that E2 exacerbated EOI-induced chronic masseter mechanical hyperalgesia by increasing TG neuronal excitability and TRPV1 function. Our study helps to elucidate the E2 actions in chronic myogenic TMD pain and may provide new therapeutic targets for relieving estrogen-sensitive pain.

Somatosensory changes in Chinese patients after coronectomy vs. total extraction of mandibular third molar: a prospective study.

OBJECTIVES: This study aimed to quantitatively compare the somatosensory function changes of inferior alveolar nerve (IAN) after mandibular third molar extraction with a surgery protocol of coronectomy, as opposed to the conventional method. MATERIALS AND METHODS: Patients with a lower third molar directly contacting IAN were recruited and assigned either to a test group (coronectomy group) or a control group (conventional extraction). A standardized quantitative sensory testing (QST) battery was performed for four times: one week before surgery and the second, seventh, and 28th days after surgery. Z-scores and the loss/gain coding system were applied for each participant. RESULTS: A total of 140 molars (test group: n = 91, control group: n = 49) were enrolled. The sensitivity of the mechanical detection threshold (MDT) and pressure pain threshold (PPT) significantly increased after surgery more than before surgery in both groups (P ≤ 0.001). After the surgery, the sensitivities of the cold detection threshold (CDT), cold pain threshold (CPT), and heat pain threshold (HPT) were significantly higher in the test group than in the control group (P ≤ 0.027). The risk of IANI was significantly larger (P = 0.041) in the test group than in the control group. CONCLUSIONS: QST was a sensitive way to detect somatosensory abnormalities even with no subjective complaint caused by surgery. Coronectomy had less influence on IAN function than conventional total extraction. CLINICAL RELEVANCE: The somatosensory function changes after mandibular third molar extraction were quantitatively studied, and coronectomy was proved a reliable alternation to reduce IAN injury rate.

Somatosensory abnormalities in Chinese patients with painful temporomandibular disorders.

BACKGROUND: The somatosensory phenotype of Chinese temporomandibular disorders (TMD) patients is not sufficiently studied with the use of contemporary techniques and guidelines. METHODS: A standardized quantitative sensory testing (QST) battery consisting of 13 parameters with a stringent statistical protocol developed by the German Research Network on Neuropathic Pain was performed over the most painful and corresponding contralateral sites as well as the right hand of 40 Chinese patients with TMD and pain classified according to the Diagnostic Criteria for TMD (DC/TMD). The same QST protocol was performed bilaterally over the infraorbital, mental, and hand regions of 70 age- and gender-stratified healthy Chinese controls. Z-scores and loss/gain scores were computed for each TMD patient. RESULTS: For patients, 82.5 % had somatosensory abnormalities in the painful facial region, while 60.0 % had abnormalities confined to the right hand. The most frequent abnormalities were somatosensory gain to pinprick (35.0 %) and pressure (35.0 %) stimuli, somatosensory loss to pinprick (25.0 %), cold (22.5 %), and heat (15.0 %) nociceptive stimuli. The most frequent loss/gain score was L0G2 (no somatosensory loss combined with a gain of mechanical somatosensory function) for both the facial (40.0 %) and hand (27.5 %) regions. Involving side-to-side differences in the evaluation increased the diagnostic sensitivity by 2.5-25.0 % across different parameters. CONCLUSIONS: Somatosensory abnormalities were commonly detected in Chinese TMD pain patients both within and outside the primary painful region, strongly indicating disturbances in the central processing of somatosensory stimuli. The individual variations in somatosensory abnormalities indicate a possible need for development of individualized TMD pain management.

[Influence of the occlusal interference time on masticatory muscle mechanical hyperalgesia in rats].

OBJECTIVE: To investigate the relationship between the removal time of 0.2 mm occlusal interference and the recovery of masticatory muscle mechanical hyperalgesia in rats. METHODS: Forty male Sprague-Dawley rats (200-220 g) were randomly assigned to eight groups, with five rats in each group: (1) naive group: these rats were anesthetized and their mouths were forced open for about 5 min (the same duration as the other groups), but restorations were not applied; (2) sham-occlusal interference control group: bands were bonded to the right maxillary first molars which did not interfere with occlusion; (3)occlusal interference group: 0.2 mm thick crowns were bonded to the right maxillary first molars; (4) 2, 3, 4, 5, and 6 d removal of occlusal interference groups: 0.2 mm thick crowns were bonded to the right maxillary first molars and removed on days 2, 3, 4, 5, and 6. The naive group and sham-occlusal interference control group were control groups. The other groups were experimental groups. Bilateral masticatory muscle mechanical withdrawal thresholds were tested on pre-application days 1, 2, and 3, and on post-application days 1, 3, 5, 7, 10, 14, 21 and 28. The rats were weighed on pre-application day 1 and on post-application days 1, 2, 3, 4, 5, 6, and 7. RESULTS: Between the naive group and the sham-occlusal interference control group, there was no significant difference in the masticatory muscle mechanical withdrawal threshold of bilateral temporalis and masseters at each time point. No significant difference was detected between the contralateral side and ipsilateral side in experimental groups (P>0.05). In the 2, 3, 4, and 5 d removal of occlusal interference groups, the masticatory muscle mechanical withdrawal thresholds decreased after occlusal interference and increased after removal of the crowns and recovered to the baseline on days 7, 10, 14, and 14, respectively [the masticatory muscle mechanical withdrawal thresholds of right masseter muscle were (137.46 ± 2.08) g, (139.02 ± 2.11) g, (140.40 ± 0.98) g, (138.95 ± 0.98) g, respectively]. In the 6 d removal of occlusal interference group, the masticatory muscle mechanical withdrawal threshold increased after removal of the crowns and became stable since day 14. There was a significant difference between the 6 d removal of occlusal interference group and the sham-occlusal interference group on day 28 (P<0.05), the masticatory muscle mechanical withdrawal thresholds of right masseter muscle were (131.24 ± 0.76) g and (141.34 ± 1.43) g, respectively. CONCLUSION: After removal of the 0.2 mm thick crown within 5 days, the mechanical hyperalgesia of the rats could reverse completely. The mechanical hyperalgesia of the rats could only be relieved, but not reverse completely after removal of the 0.2 mm thick crown on day 6. As the time went on, even minor occlusal interference could cause irreversible mechanical hyperalgesia of masticatory muscles. This study suggested that occlusal interference caused by dental treatment should be eliminated as soon as possible, to avoid irreversible orofacial pain.

[Three-dimensional finite element analysis of influence of occlusal surface height on stress distribution around posterior implant-supported single crown].

OBJECTIVE: To evaluate the effect of the occlusal surface height of a mandibular posterior implant-supported single crown on stress in bone tissues. METHODS: Three-dimensional finite element models of the implant-supported single crown replacing the missing right lower second premolar, mesial and distal natural teeth, periodontal membrane, alveolar bone, loaded rigid body and analog food of almond were established. Using the Federation Dentaire International (FDI) system, the first premolar, the second premolar and the first molar were represented with 44, 45, 46. Three occlusal surface heights of the crown were studied: (1) normal height; (2) 15 µm reduction in height; (3) 30 µm reduction in height. The models were loaded by independent loading with maximal occlusal force(44 by 280 N, 45 by 360 N, and 46 by 480 N) and average occlusal force(44 by 140 N, 45 by 180 N, and 46 by 240 N)on the single crown; combined loading (maximal occlusal force transformed into uniform load of 3.7 MPa on top of rigid body, in contact with points on the occlusal surface), and analog almond-like food loading (average occlusal force transformed into uniform load of 1.67 MPa in simulated food chewing, in contact with points on the occlusal surface). RESULTS: For maximal biting force under independent loading, Von Mises stress peak values in bone tissues around 44, 45, and 46 were 82.57 MPa, 45.26 MPa and 27.79 MPa; For average biting force, peak values were 41.28 MPa, 22.63 MPa and 13.89 MPa. Under combined loading, compared with the normal occlusal surface height group, Von Mises stress peak values decreased 4.6 MPa, by 0.84%; increased 7.52 MPa, by 20.04%, and decreased 1.8 MPa, by 5.84%, for 45, 46, and 44 in the 30 µm infra-occlusion group, respectively. Under food loading, Von Mises stress peak values decreased 0.34 MPa, by 1.62%; increased 1.11 MPa, by 2.66%; and increased 0.06 MPa, by 0.54%, and for 45, 46, and 44 in the 30 µm infra-occlusion group, respectively. CONCLUSION: Within the limitation of this study, within 30 µm reduction of the occlusal surface height of implant-supported single crown, no significant difference of the peak values was observed.

[Data of the quantitative orofacial somatosensory functions of healthy subjects and its influence factors analysis].

OBJECTIVE: To establish the preliminary somatosensory data stratified by gender, age group, and sites in the trigeminal region through standardized quantitative sensory testing on healthy individuals, and to evaluate the effects of gender, age, and sites on somatosensory functions. METHODS: The standardised QST battery developed by the German Research Network on Neuropathic Pain consists totally of 13 different parameters. A total of 70 healthy individuals participated. The subjects were stratified into two groups according to age: younger group (16 female, 16 male, age 24-40 years old) and elder group (20 female, 18 male, age 41-69 years old). The test was performed bilaterally over the infraorbital, mental, and hand regions. RESULTS: The preliminary orofacial somatosensory data stratified by gender, age group, and sites were presented. Female were more sensitive than male for most of the parameters (P<0.05). Age had a significant effect on most of the parameters (P<0.05), the younger group was more sensitive compared with the elder group (P<0.01) for heat pain threshold (HPT): younger group (38.07±2.94) °C, elder group (39.85±3.52) °C; warmth detection threshold (WDT): younger group (1.40±0.74) °C, elder group (1.89±1.14) °C; mechanical detection threshold (MDT): younger group (0.73±1.66) mN, elder group (1.41±2.82) mN; pressure pain threshold (PPT): younger group (171.71±92.51) kPa, elder group (196.36±73.73) kPa; cold pain threshold (CPT): younger group (25.90±5.38) °C, elder group (21.64±6.78) °C; cold detection threshold (CDT): younger group (-0.97±0.55) °C, elder group (-1.36±0.90) °C, and wind-up ratio (WUR): younger group (3.33± 2.20), elder group (2.67±1.68). The inverse results were demonstrated for mechanical pain threshold (MPT): younger group (111.50±88.93) mN, elder group (104.49±94.94) mN; mechanical pain sensitivity (MPS): younger group (6.96±5.61), elder group (8.93±6.53), and vibration detection threshold (VDT): younger group (7.44±0.52) scale, elder group (7.55±0.48) scale (P<0.05). Somatosensory function was site dependent (P<0.001), the two trigeminal sites (infraorbital and mental) were more sensitive than the hand for CDT, HPT, WDT, thermal sensory limen (TSL), MDT, MPT, MPS, and PPT (P<0.001), but the inverse result was observed for VDT (P<0.001). CONCLUSION: The preliminary orofacial somatosensory data of Han Ethnicity stratified by gender, age group, and sites were established. The study evaluated the effects of gender, age and sites on orofacial somatosensory functions by employment standardized quantitative sensory testing.

A study on variability of quantitative sensory testing in healthy participants and painful temporomandibular disorder patients.

OBJECTIVES: Quantitative sensory testing has mainly used thresholds to evaluate somatosensory sensitivity so far. The variability of different measures from session to session has also been investigated, but the variability of the single individual measures of a threshold or subject-based reports has not been considered. This study aimed to investigate the potential value of threshold variability in one session as a measure of internal consistency in somatosensory function. METHODS: The standardized quantitative sensory testing battery developed by the German Research Network on Neuropathic Pain was performed bilaterally over the infraorbital, mental, and hand regions in 70 healthy and 22 temporomandibular disorder pain participants. Somatosensory variability was investigated by calculating the Coefficient of Variation of three to five repeated measures in one threshold determination. The influences of side, gender, site, age, and presence of pain on the somatosensory variability were evaluated. RESULTS: In the healthy participants, somatosensory variability was region dependent: hand > mental and/or infraorbital for CDT, WDT, HPT, MDT-N, MPT-Y, MPT-N, WUR, and MPS (p ≤ 0.043), infraorbital > hand for VDT (p = 0.001), mental > infraorbital for HPT and WUR (p ≤ 0.001); and age dependent for WDT, TSL, CPT, HPT, MDT-Y, MDT-N, MPT-N, and WUR (p ≤ 0.017). Gender and side had no main effect on variability (p ≥ 0.136). The pain patients presented higher variability compared with healthy participants for TSL, MDT-N, MPT-Y, WUR, and PPT (p ≤ 0.033). DISCUSSION: The somatosensory variability along with the threshold would be a more complete method to investigate the somatosensory disorders and underlying pain mechanisms. The correlation between pain duration and somatosensory variability should be studied further with different pain conditions.

Effect of negative emotions evoked by light, noise and taste on trigeminal thermal sensitivity.

BACKGROUND: Patients with migraine often have impaired somatosensory function and experience headache attacks triggered by exogenous stimulus, such as light, sound or taste. This study aimed to assess the influence of three controlled conditioning stimuli (visual, auditory and gustatory stimuli and combined stimuli) on affective state and thermal sensitivity in healthy human participants. METHODS: All participants attended four experimental sessions with visual, auditory and gustatory conditioning stimuli and combination of all stimuli, in a randomized sequence. In each session, the somatosensory sensitivity was tested in the perioral region with use of thermal stimuli with and without the conditioning stimuli. Positive and Negative Affect States (PANAS) were assessed before and after the tests. Subject based ratings of the conditioning and test stimuli in addition to skin temperature and heart rate as indicators of arousal responses were collected in real time during the tests. RESULTS: The three conditioning stimuli all induced significant increases in negative PANAS scores (paired t-test, P ≤0.016). Compared with baseline, the increases were in a near dose-dependent manner during visual and auditory conditioning stimulation. No significant effects of any single conditioning stimuli were observed on trigeminal thermal sensitivity (P ≥0.051) or arousal parameters (P ≥0.057). The effects of combined conditioning stimuli on subjective ratings (P ≤0.038) and negative affect (P = 0.011) were stronger than those of single stimuli. CONCLUSIONS: All three conditioning stimuli provided a simple way to evoke a negative affective state without physical arousal or influence on trigeminal thermal sensitivity. Multisensory conditioning had stronger effects but also failed to modulate thermal sensitivity, suggesting that so-called exogenous trigger stimuli e.g. bright light, noise, unpleasant taste in patients with migraine may require a predisposed or sensitized nervous system.

[Comparison of self-controlled retruded approach and bimanual manipulation method on the relationship of incisal point displacement in the mandibular retruded contact position].

OBJECTIVE: To evaluate the relationship of incisal point displacements in the mandibular retruded contact position (RCP) between the self-controlled retruded approach and bimanual manipulation method. METHODS: Twelve healthy young volunteers were selected. The RCP was guided through the self-controlled retruded approach and bimanual manipulation method. The track of the incisal point was recorded, using the mandibular movement trace recording system. The movement direction of the incisal point in horizontal plane was observed. The distance between the incisal point of the RCP and intercuspal contact position (ICP) was measured. RESULTS: Except one volunteer's incisal point movement direction of the RCP was oblique, others were straight toward posterior. The displacements of the incisal point from the ICP to RCP guided through self-controlled approach and bimanual manipulation method were (1.15 ± 0.64) mm, (0.98 ± 0.29) mm respectively. There was no statistical significance between the two methods (P > 0.05). CONCLUSION: The displacements of the incisal point from the ICP to RCP guided through self-controlled approach and bimanual manipulation method are approximately the same.

[Pilot evaluation of masticatory efficiency and patients' satisfaction in long-centric occlusal pattern complete denture wearers].

OBJECTIVE: To assess the masticatory efficiency and patient' satisfaction in long-centric occlusal pattern complete denture wearers. METHODS: The anatomic occlusal pattern and long-centric occlusal pattern complete dentures were made for each of 10 edentulous patients with severe alveolar rigde absorption simultaneously using the technique of interchangeable artificial teeth. The order of delivery of different occlusal pattern complete denture was determined according to randomized principle. For each kind of occlusal pattern complete denture, the masticatory efficiency was measured with spectrophotometer after the dentures were worn 2, 4, 6, 8, 10 and 12 weeks. A psychometric questionnaire was completed by the patients after wearing the dentures for more than three months and analyzing the patients' rating of the denture satisfaction. RESULTS: No significant differences in masticatory efficiency was found between the long-centric occlusal pattern complete denture wearers and the anatomic occlusal complete denture wearers. The patients' grade of denture satisfaction in long-centric occlusal pattern complete dentures wearers was significantly better than that in anatomic occlusal denture wearers (P<0.05). CONCLUSION: Complete denture with long-centric occlusion can be used to improve the clinical effect of edentulous patients with severe absorption of residual alveolar rigde.

[Protective role of calcium alginate hydrogel beads in cells during calcium phosphate cement setting reaction and its influencing factors].

OBJECTIVE: To evaluate the protection of calcium alginate hydrogel beads for mouse preosteoblastic cell line (MC3T3-E1) during the setting reaction of calcium phosphate cement (CPC) pastes and to analyze related influencing factors. METHODS: The MC3T3-E1 cells encapsulated in alginate hydrogel beads were cultured in vitro with ß-tricalcium phosphate/calcium phosphate cement (ß-TCP/CPC) pastes and discs until 2 d. The cell viability and number of live/dead cells were tested using the CCK-8, Calcein-AM and PI, respectively. The effects of CPC paste and CPC disc, different treatment and time to renewal medium on cell viability were compared. RESULTS: There were no significant differences in optical density and number of live cells between ß-TCP/CPC pastes and discs (1 d: P=0.827; 2 d: P=0.965). There were different influences on cell viability between different treatment and time to renewal medium. CONCLUSION: The results indicated that the calcium alginate hydrogel beads had a good protection to MC3T3-E1 cells during the setting reaction of CPC pastes. CPC paste might affect the cell proliferation even when solidification. After setting reaction, it may be favorable for cell viability to renew the medium every 6 h in 1 d.

[Cytological study on osteoblasts and in-situ setting calcium phosphate cements].

OBJECTIVE: To evaluate biocompatibility of three kinds of self-developed injectable calcium phosphate cements (CPCs): chitosan microspheres/CPC, ß-tricalcium phosphate (ß-TCP)/CPC, and K(+)/CPC and the viability of the osteogenic cells cultured with CPC pastes and discs for 10 days. METHODS: The rabbit marrow stromal cells (rMSCs), isolated from rabbit bone marrow with density gradient centrifugation and flow cytometer, were cultured, expended and induced into osteoblasts. Alizarin red staining was used to determine the function of ossification. Then, rMSCs were incubated randomly on both the pastes and solidified discs of the 3 kinds of CPCs. The cells cultured on a 24-well plate were as blank control. Each group had 4 samples. The proliferation and differentiation of each group were observed using acid phosphatase assay (APA) and by testing the activity of alkaline phosphatase (ALP) at day 1, 4, 7, and 10. After stained by acridine orange(AO), the cells were observed, counted and analyzed with an epifluorescence microscopy. The morphology of the cells on CPCs was observed with scanning electron microscope(SEM).The data was subjected to two-way ANOVA followed by LSD test to compare between groups. RESULTS: The process of solidification of the three kinds of CPC pastes has the toxic effect on cells, which is irreversible. The proliferation( the average absortion of pastes are 0.049,0.050,0.049; the discs are 0.898,0.867,0.909;P<0.001), function(the average ALP activity of pastes after ten days are 0.775,0.782,0.798 U/g protein; the discs are 49.288,49.631, 49.744 U/g protein;P<0.001) and number of cells(the average number of cells of pastes after ten days are 3.7,3.7,3.7; the discs are 91.1,89.7,93.7;P<0.001) directly exposed to CPC paste significantly decreased compared with those contacting with the discs. By contrast, cells on the three kinds of discs showed better viability, proliferation, and ossification and cell numbers increased obviously with culture days. CONCLUSION: The process of solidification of the three kinds of CPC pastes has toxic effect on cells. Further study needs to explore a method to protect osteoblasts when seeded into the CPC paste.

[Experimental occlusal interference induces the expression of protein gene products and substance P in masseter muscles of rats].

OBJECTIVE: To investigate the peripheral mechanism by studying the histological changes of masseter muscles using HE stains and substance P (SP) and protein gene product 9.5 (PGP9.5) immunohistochemical stains. METHODS: Fifteen male Sprague-Dawley were randomly assigned into occlusal interference group (n=12) and control group (n=3). In occlusal interference group, 0.4 mm thick crowns were bonded to the rats' first molar of the maxillary. In the control group, rats were anesthetized and mouths were forced open for about 5 min but restorations were not applied. 1, 5, 10, and 21 d after 0.4 mm occlusal alteration treatment, mechanical pain thresholds of bilateral masseter muscles were quantitatively measured by modified electronic anesthesiometer in control group and occlusal interference group. The rats were euthanized by transcardiac perfusion after deep anesthetization at different time points. The paraffin sections of masseter muscles were made and processed for HE, SP, and PGP9.5 immunohistochemical staining. RESULTS: Decreased head withdrawal threshold to mechanical pressure was detected in masseter muscles on both sides following occlusal interference. Histological stains of masseter muscles presented intact following occlusal interference, and no inflammatory cells were observed in both sides. Intensely stained PGP9.5 was observed at 1 d in occlusal interference groups and maintained until the end of the experiment. SP expression was the most obviously increased at 5 d in both sides and gradually decreased to the level of control. CONCLUSION: Experimental occlusal interference-induced masticatory muscle pain is associated with peripheral sensitization of nociceptive neurons rather than muscle damage and inflammation.

Accuracy of Intraoral Scanning of Edentulous Jaws with and without Resin Markers.

Objective: To evaluate the accuracy of digital models obtained from intraoral scanning of edentulous maxilla and mandible models with and without resin markers. Methods: A pair of standard edentulous models were scanned using a laboratory scanner and saved as reference models. The edentulous models were fixed onto a phantom head and scanned with an intraoral scanner (IOS) five times each. Six resin markers were attached on the maxilla model and two on the mandible model, and another five intraoral scans were taken of each model. The scanning time and number of images were recorded. The digital models obtained using the IOS were superimposed on the reference models using image processing software. The trueness and precision of the models made using the IOS were evaluated, and the scanning time and number of images were also compared. Results: The average trueness and precision of the IOS in the maxilla model with resin markers were 135.50 ± 36.28 µm and 254.55 ± 40.62 µm, respectively, while those in the mandible were 161.40 ± 55.45 µm and 368.75 ± 91.03 µm, respectively. Placing resin markers on the edentulous maxilla and mandible did not improve the trueness of the IOS, but placing resin markers on the edentulous maxilla improved the precision and scanning efficiency. However, placing resin markers on the buccal shelf of the edentulous mandible decreased the precision and increased the scanning time. Conclusion: Resin markers placed on the hard palate of edentulous maxillae could improve the precision of the IOS and improve scanning efficiency. However, they did not affect the trueness of the IOS for edentulous maxillae or mandibles.

[Animal implantation with a new type of chitosan microspheres/calcium phosphate cement].

OBJECTIVE: To investigate bioactivity, biodegradation, bone conductive properties, and clinical maneuverability of a novel injectable chitosan microspheres/calcium phosphate cement (CPC). METHODS: The bone defect of pi x 4 mmx4 mmx6 mm was made at both thigh bones of 12 rabbits, and experimental material (chitosan microspheres/CPC) or control material (alpha-tricalcium phosphate cement, alpha-TCP) was injected into the defect respectively. The filling situation was evaluated by X-ray 3 days after operation. The rabbits were divided into three groups, four for each group. The samples with chitosan microspheres and the control with alpha-TCP were collected at 8, 16, 24 weeks after operation. Histological examination and scanning electron microscope (SEM) evaluation were performed. RESULTS: The absorption of implants with chitosan microspheres was observed at 8 weeks, and became more apparent at 16 weeks. Different size of cavities were observed in CPC after the degradation of chitosan microspheres. The chitosan microspheres/CPC was dramatically degraded after 24 weeks with a few chitosan microspheres, and new bone replaced the degraded materials. The implants with alpha-TCP were absorbed slowly compared with the chitosan microspheres/CPC. The cavities in alpha-TCP were small. CONCLUSION: The chitosan microspheres/calcium phosphate cement has the characters of good biocompatible and osteocombinative ability. Compared with the control material, adding chitosan microspheres into CPC could enhance its degradability and facilitate the new bone formation.

Somatosensory Profiling of Patients with Burning Mouth Syndrome and Correlations with Psychologic Factors.

AIMS: To compare somatosensory function profiles and psychologic factors in patients with primary burning mouth syndrome (BMS) and healthy controls and to evaluate correlations of subjective pain ratings with somatosensory and psychologic parameters. METHODS: A quantitative sensory testing (QST) protocol-including cold detection threshold (CDT), warmth detection threshold (WDT), thermal sensory limen (TSL), paradoxical heat sensation (PHS), cold pain threshold (CPT), heat pain threshold (HPT), mechanical pain threshold (MPT), wind-up ratio (WUR), and pressure pain threshold (PPT)-was performed at the oral mucosa of the tongue, buccal, and palatal sites in 30 Chinese patients (25 women and 5 men, mean age 50.9 ± 9.2 years) with primary BMS and in 18 age- and gender-matched healthy controls (15 women and 3 men, mean age 53.2 ± 7.0 years). For each BMS patient, z scores and loss/gain scores were computed. Psychologic status was evaluated in both groups using the Self-Rating Anxiety Scale and Self-Rating Depression Scale. Correlations of BMS patients' subjective pain ratings with somatosensory and psychologic profiles were assessed with the use of Pearson or Spearman correlations and multiple linear regression. RESULTS: In BMS patients, 53.3% had somatosensory abnormalities according to z scores vs 22.2% of healthy controls (P = .033). The abnormalities in BMS patients were somatosensory loss to thermal nonnoxious stimuli (TSL = 20.0%, CDT = 13.3%, WDT = 13.3%), mechanical pressure stimuli (PPT = 16.7%), pinprick stimuli (MPT = 6.7%), and thermal pain stimuli (CPT = 3.3%), and somatosensory gain to repetitive pinprick stimuli (WUR = 6.7%), pressure stimuli (PPT = 6.7%), and thermal pain stimuli (HPT = 3.3%). The most frequent loss/gain score was 13.3% for loss of thermal somatosensory function with no somatosensory gain; 13.3% for loss of thermal and mechanical somatosensory function with no somatosensory gain; and 13.3% for gain of mechanical somatosensory function with no somatosensory loss. Mild elevations in anxiety scores were seen in 30% of the BMS patients, and 50% and 36.7% had mild and moderate elevations, respectively, in depression scores. No anxiety or depression was detected in the control group. QST results, but not psychologic scores, were significantly correlated with patients' subjective pain ratings (PHS, Spearman coefficient -0.384, P = .029; CPT, Pearson coefficient -0.370, P = .034; MPT, Pearson coefficient -0.376, P = .032; PPT, Pearson coefficient 0.363, P = .037). CONCLUSION: The present findings documented distinct differences in somatosensory function in patients with primary BMS compared to controls, indicating a complex pathophysiology and interaction between impairments in nociceptive processing and psychologic functioning.