Persistent Orofacial Pain Research Articles

DEEP Study: Indirect and Out-of-pocket Costs of Persistent Orofacial Pain

Persistent orofacial pain (POFP) is common and caused by a group of conditions affecting the face, head, or mouth. Recent research highlighted a problematic care pathway with high costs to the health care provider, but the financial impact on patients and employers is not understood. This study aimed to describe patient (out-of-pocket) and employer (indirect) costs of POFP and to identify whether the dichotomized Graded Chronic Pain Scale (GCPS) was predictive of costs. A cohort of 198 patients was recruited from primary and secondary care settings in North East England and followed over a 24-mo period. Patients completed the GCPS and Use of Services and Productivity Questionnaire every 6 mo and a Time and Travel Questionnaire at 14 mo. Questionnaires examined the implications of health care utilization on patients’ everyday lives and personal finances. Time and travel costs were calculated and applied to use-of-services data to estimate out-of-pocket costs, while the human capital method and QQ method (quantity and quality of work completed) were used to estimate absenteeism and presenteeism costs, respectively. Per person per 6-mo period (in 2017 pounds sterling), mean out-of-pocket costs were £333 (95% CI, £289 to £377), and indirect costs were £1,242 (95% CI, £1,014 to £1,470). Regression analyses indicated that over 6 mo, the GCPS was predictive of the following: out-of-pocket costs—a difference of £311 between low and high GCPS per person per 6-mo period (95% CI, £280 to £342; P < 0.01, n = 705 observations over 24 mo); indirect costs—a difference of £2,312 between low and high GCPS per person per 6-mo period (95% CI, £1,886 to £2,737; P < 0.01; n = 352 observations over 24 mo). This analysis highlights “hidden” costs of POFP and supports the use of the dichotomized GCPS to identify patients at risk of higher impact and associated costs and thereby stratify care pathways and occupational health support appropriately.

Psychological Interventions for Persistent Orofacial Pain

Persistent pain has been defined as pain lasting beyond the normal time of healing (up to six months), often in the absence of observable tissue pathology. it includes a range of conditions which are likely to present in the dental setting including temporomandibular disorders, burning mouth syndrome, persistent dentoalveolar pain, trigeminal nerve injury, trigeminal neuralgia and atypical facial pain.<br/> This article reviews psychological interventions for pain. this includes interventions that have been researched in a range of persistent pain settings, including but not limited to those that have been directly applied to persistent orofacial pain (POFP).<br/> All current psychological interventions for persistent pain are underpinned by a biopsychosocial understanding of the complex and multifactorial nature of pain. the main currently applied interventions are described, along with their rationale and selected relevant research. To date, psychological treatments which have been shown to persistent pain demonstrate small but consistent improvements in pain, disability and quality of life compared to standard care.<br/> A stepped care approach to service provision is outlined, with practical ideas for administering routine psychological measures to help stratify patients towards the appropriate care pathway.

The therapeutic potential of cystathionine gamma-lyase in temporomandibular inflammation-induced orofacial hypernociception

Hydrogen sulfide (H2S) is an endogenous neuromodulator produced mainly by the enzyme cystathionine gamma-lyase (CSE) in peripheral tissues. A pronociceptive role of endogenously produced H2S has been previously reported by our group in a model of orofacial inflammatory pain. Using the established persistent orofacial pain rat model induced by complete Freund's adjuvant (CFA) injection into temporomandibular joint (TMJ), we have now investigated the putative role of endogenous H2S modulating hypernociceptive responses. Additionally, plasmatic extravasation on TMJ was measured following different treatments by Evans blue dye quantification. Thus, rats were submitted to Von Frey and Formalin tests in orofacial region before and after pharmacological inhibition of the CSE-H2S system combined or not with CFA-induced TMJ inflammation. Pretreatment with CSE inhibitor, propargylglycine (PAG; 88.4 μmol/kg) reduced temporomandibular inflammatory pain when injected locally as well as systemically. In particular, local PAG injection seems to be more effective for hypernociceptive responses in orofacial persistent inflammation since its action is evidenced in the majority analyzed periods of the inflammatory process compared to its systemic use. Moreover, local injection seems to act on temporomandibular vascular permeability, evidenced by decreased plasmatic extravasation induced by local PAG administration. Our data are consistent with the notion that the endogenous synthetized gas H2S modulates persistent orofacial pain responses revealing the pharmacological importance of the CSE inhibitor as a possible therapeutic target for their control.

Neuron-glia interaction is a key mechanism underlying persistent orofacial pain.

Excitability of neurons in the trigeminal ganglion (TG), trigeminal spinal subnucleus caudalis (Vc), and upper cervical spinal cord (C1-C2) is greatly enhanced after orofacial inflammation and trigeminal nerve injury, and TG, Vc, and C1-C2 neurons remain sensitized long after such episodes. Sensitized neurons generate various molecules, which are released from nociceptive neurons in these areas and are involved in modulating the excitability of TG, Vc, and C1-C2 nociceptive neurons. Hyperexcitable nociceptive neurons also activate satellite glial cells in the TG and microglial cells and astrocytes in the Vc and C1-C2. Glial cell activation spreads throughout the TG, Vc, and C1-C2 and triggers the release of various molecules involved in modulating nociceptive neurons in TG, Vc, and C1-C2 neurons. These findings suggest that functional interaction between neurons and glial cells is critical in persistent orofacial pain associated with orofacial inflammation and trigeminal nerve injury.

Care Pathways in Persistent Orofacial Pain: Qualitative Evidence from the DEEP Study.

Persistent orofacial pain is relatively common and known to have an adverse effect on quality of life. Previous studies suggest that the current care pathway may be problematic, but it is not well understood which health services patients access and what their experience is. The aim of this study was to explore care pathways and their impact from the perspective of patients. Qualitative interviews were conducted with a maximum variation sample of patients recruited from primary (community based) and secondary (specialist hospital based) care in the United Kingdom. Questions focused on the stages in their pathway and the impact of the care that they had received. Interviews were digitally recorded and transcribed verbatim, and analysis followed principles of the constant comparative method. NVivo 10 was used to help organize and analyze data. Twenty-two patients were interviewed at baseline, and 18 took part in a second interview at 12 mo. Three main themes emerged from the data: the "fluidity of the care pathway," in which patients described moving among health care providers in attempts to have their pain diagnosed and managed, occurring alongside a "failure to progress," where despite multiple appointments, patients described frustration at delays in obtaining a diagnosis and effective treatment for their pain. Throughout their care pathways, patients described the "effects of unmanaged pain," where the longer the pain went unmanaged, the greater its potential to negatively affect their lives. Findings of this study suggest that the current care pathway is inefficient and fails to meet patient needs. Future work needs to focus on working with stakeholder groups to redesign patient-centered care pathways. Knowledge Transfer Statement: Data from qualitative interviews conducted with patients with persistent orofacial pain suggest significant problems with the existing care pathway, consisting of delays to diagnosis, treatment, and referral. Patients describing their struggle to progress through the current care pathway highlighted the difficulties occurring while living with orofacial pain. This study suggests a need for a revised care pathway, which better meets the needs of people with persistent orofacial pain.

Persistent orofacial muscle pain: Its synonymous terminology and presentation

Objective: The purpose of the present paper is to describe the presentation of persistent orofacial muscle pain, also commonly referred to as myofascial temporomandibular disorder.Methods: In this practice survey, the authors reviewed the demographic and clinical features of 34 patients who were evaluated and diagnosed personally.Results: The majority of the 34 patients were women (82.4%), and their age at consultation averaged 44.6 ± 12.6 (SD) years. The median pain duration was 4.0 years (range: 0.2–34 years). In 97.1% of patients, the pain occurred daily and continuously, and in 51.9% it was unilateral. Chewing or eating made the pain worse in 50% of the patients, and talking in 29.4%. On examination, tightness of the masseter muscle(s) was present in 58.8%, and tenderness in 58.8%.Conclusions: Persistent orofacial muscle pain mostly affects women, generally occurs daily and continuously, and is equally often unilateral and bilateral. Chewing, eating, and talking are the most common aggravating factors, and tightness or tenderness of the masseter muscle(s) is often found on examination.

Healthcare Cost and Impact of Persistent Orofacial Pain

Few data are available on the healthcare costs of those suffering from persistent orofacial pain (POFP). This cohort and cost analysis study examined the direct costs of POFP from the perspective of the healthcare provider (specifically, the UK National Health Service) in 2012 pounds sterling and sought to identify whether dichotomized (high, IIb to IV; low, 0 to IIa) graded chronic pain scale (GCPS) status is predictive of the total cost of healthcare over the last 6 mo. The healthcare utilization data of 198 patients with POFP were collected using a structured interview and a validated “use of services and productivity” questionnaire. Unit costs were used with these utilization data to calculate direct healthcare costs in 3 categories: consultation, medication, and appliances and interventions. Consultation costs were a significant proportion of cumulative healthcare cost (P < 0.001). Dichotomized GCPS status was predictive of increased healthcare cost over the last 6 mo, accounting for an average increase of £366 (95% confidence interval, 135 to 598; P < 0.01) when moving from a low GCPS status to a high GCPS status. Given the predictive capability of dichotomized GCPS status and the success of stratified models of care for other persistent pain conditions, dichotomized GCPS status may offer an opportunity to help determine stratification of care for patients with POFP.

Treatment needs and therapy experiences in patients with temporomandibular disorders: a retrospective survey

Objectives: This study investigated a patient population suffering from temporomandibular disorders (TMD) with respect to their need for treatment, satisfaction with the information received, and the treatment provided.Methods: A survey was sent by post to 1011 patients.Results: Almost one-third of the patients had used analgesics prior to the start of any treatment. Having pain and functional jaw complaints was a risk factor for patients experiencing social restrictions. Subjects with severe complaints needed a range of conservative treatment modalities in combination with more follow-up appointments in agreement with the practitioners. Persons with remaining functional limitations were often unsatisfied with information and care they had received. The rate of compliance with prescribed treatment modalities and advice corresponded significantly higher with patient contentment with final outcome.Discussion: Patient satisfaction is often determined by a qualitative doctor–patient relationship. The influence of complaints and pain on daily functioning was illustrated. Pain medication use at baseline seems to be predictive for persistent orofacial pain (OFP).

Neurophysiological tests for facial-trigeminal pain

Comprehensive neurophysiological and psychophysical examination provides unique, sensitive and specific information about possible underlying neuropathy in patients with orofacial pain. Special ENMG techniques, brainstem reflex examinations, sensory and motor evoked potential recordings as well as quantitative sensory tests provide diagnostic biomarkers for large and small nerve fiber systems, and confirm definite diagnosis of neuropathic pain within the trigeminal distribution with up to 95–100% accuracy. They enable precise differential diagnosis between neuropathic and musculoskeletal pain within the orofacial area. Neurophysiological tests also allow accurate topographic level diagnosis from peripheral nerves to the cortex, helping to guide further imaging studies to the most likely region of underlying neuropathology, significantly increasing the overall diagnostic yield. Systematic application of neurophysiological testing has elucidated neural mechanisms of various orofacial pain conditions including trigeminal neuropathic pain, trigeminal neuralgia, persistent idiopathic orofacial pain, and burning mouth syndrome. Neurophysiological and psychophysical testing can also provide invaluable prognostic information regarding risk of persistent pain and recovery after nerve injury. Furthermore, clinical neurophysiology can measure and confirm phenomena associated with neuropathic pain, caused by deficient endogenous inhibitory systems or neuroplastic alterations. Neurophysiological tools enable more efficient treatment based on accurate diagnosis and individual profiling of the underlying pathophysiology.

Development of a Rat Model of Mechanically Induced Tunable Pain and Associated Temporomandibular Joint Responses

Although mechanical overloading of the temporomandibular joint (TMJ) is implicated in TMJ osteoarthritis (OA) and orofacial pain, most experimental models of TMJ-OA induce only acute and resolving pain, which do not meaningfully simulate the pathomechanisms of TMJ-OA in patients with chronic pain. The aim of this study was to adapt an existing rat model of mechanically induced TMJ-OA, to induce persistent orofacial pain by altering only the jaw-opening force, and to measure the expression of common proxies of TMJ-OA, including degradation and inflammatory proteins, in the joint. TMJ-OA was mechanically induced in a randomized, prospective study using 2 magnitudes of opening loads in separate groups (ie.,. 2-N, 3.5-N and sham control [no load]). Steady mouth opening was imposed daily (60 minutes/day for 7 days) in female Holtzman rats, followed by 7 days of rest, and orofacial sensitivity was measured throughout the loading and rest periods. Joint structure and extent of degeneration were assessed at day 14 and expression of matrix metalloproteinase-13 (MMP-13), hypoxia-inducible factor-1α (HIF-1α), and tumor necrosis factor-α (TNF-α) in articular cartilage was evaluated by immunohistochemistry and quantitative densitometry methods at day 7 between the 2 loading and control groups. Statistical differences of orofacial sensitivity and chondrocyte expression between loading groups were computed and significance was set at a P value less than .05. Head-withdrawal thresholds for the 2 loading groups were significantly decreased during loading (P < .0001), but that decrease remained through day 14 only for the 3.5-N group (P < .00001). At day 14, TMJs from the 2-N and 3.5-N groups exhibited truncation of the condylar cartilage, typical of TMJ-OA. In addition, a 3.5-N loading force significantly upregulated MMP-13 (P < .0074), with nearly a 2-fold increase in HIF-1α (P < .001) and TNF-α (P < .0001) at day 7, in 3.5-N loaded joints over those loaded by 2 N. Unlike a 2-N loading force, mechanical overloading of the TMJ using a 3.5-N loading force induced constant and nonresolving pain and the upregulation of inflammatory markers only in the 3.5-N group, suggesting that these markers could predict the maintenance of persistent orofacial pain. As such, the development of a tunable experimental TMJ-OA model that can separately induce acute or persistent orofacial pain using similar approaches provides a platform to better understand the pathomechanisms involved and possibly to evaluate potential treatment strategies for patients with painful TMJ-OA.

What is the impact of acute and chronic orofacial pain on quality of life?

ObjectivesOrofacial pain (OFP) is thought to substantially reduce oral health-related quality of life (OHRQoL). Little has been reported about the impact of acute dental pain and persistent (chronic) orofacial pain conditions, other than temporomandibular disorders (TMD), on OHRQoL. The aim of this study was to examine and compare OHRQoL impairment among four OFP conditions: TMD, acute dental pain (ADP), trigeminal neuralgia (TN) and persistent dentoalveolar pain disorder (PDAP). MethodsOHRQoL was measured using the OHIP-49 in a convenience sample of subjects with four OFP conditions (TMD (n=41), ADP (n=41), TN (n=21), PDAP (n=22) and a pain-free control group (n=21)). The mean OHIP-49 summary score described the level of impact and inferential and descriptive statistics were used to examine any differences inter-condition. The mean of the OHIP-14 and 5 were also measured by extracting the corresponding items from the OHIP-49. ResultsAll pain conditions presented with statistically significant (P<0.001) and clinically relevant (measured by effect sizes and the OHIP's minimal important difference) impairment when compared to the control group (P<0.001). The OHRQoL for the four OFP conditions had similar levels of impairment (TMD=62.3, ADP=55.5, TN=58.1 and PDAP=69.8). ConclusionTMD, ADP, TN and PDAP have substantial impact on OHRQoL as measured by the OHIP-49 and the extracted items for the OHIP-14 and 5. Differences among the four groups of orofacial pain conditions are likely not to be substantial.

Experimental orofacial pain and sensory deprivation lead to perceptual distortion of the face in healthy volunteers.

Patients suffering from persistent orofacial pain may sporadically report that the painful area feels "swollen" or "differently," a phenomenon that may be conceptualized as a perceptual distortion because there are no clinical signs of swelling present. Our aim was to investigate whether standardized experimental pain and sensory deprivation of specific orofacial test sites would lead to changes in the size perception of these face areas. Twenty-four healthy participants received either 0.2 mL hypertonic saline (HS) or local anesthetics (LA) into six regions (buccal, mental, lingual, masseter muscle, infraorbital and auriculotemporal nerve regions). Participants estimated the perceived size changes in percentage (0 % = no change, -100 % = half the size or +100 % = double the size), and somatosensory function was checked with tactile stimuli. The pain intensity was rated on a 0-10 Verbal Numerical Rating Scale (VNRS), and sets of psychological questionnaires were completed. HS and LA were associated with significant self-reported perceptual distortions as indicated by consistent increases in perceived size of the adjacent face areas (P ≤ 0.050). Perceptual distortion was most pronounced in the buccal region, and the smallest increase was observed in the auriculotemporal region. HS was associated with moderate levels of pain VNRS = 7.3 ± 0.6. Weak correlations were found between HS-evoked perceptual distortion and level of dissociation in two regions (P < 0.050). Experimental pain and transient sensory deprivation evoked perceptual distortions in all face regions and overall demonstrated the importance of afferent inputs for the perception of the face. We propose that perceptual distortion may be an important phenomenon to consider in persistent orofacial pain conditions.

DEEP Study: does EQ‐5D‐5L measure the impacts of persistent oro‐facial pain?

The EQ-5D-5L is a generic quality of life (QOL) measure widely used throughout the world, which has the advantage that it allows health-state preferences to be elicited. The aim of this study was to examine whether: a) variation in the standardised reference period for EQ-5D-5L from 'today' to 'the last month' had a minimal clinically meaningful difference; (b) EQ-5D-5L had convergent validity with a multidimensional pain measure in quantifying the impacts of pain. As part of a larger study into the effectiveness and efficiency of care pathways for persistent orofacial pain (POFP) (http://research.ncl.ac.uk/deepstudy), participants with POFP (n = 100) completed two versions of the EQ-5D-5L at the same time with different reference periods ('today' vs. 'last month'). Participants also completed the first section of the West Haven-Yale Multidimensional Pain Inventory (v3) to assess convergent validity. Two-tailed nonparametric inferential statistics, intra-class correlation coefficients (ICC), and within-subject change scores were used to compare the two EQ-5D-5L versions. Convergent validity was assessed using Spearman's rho correlation coefficients. Health-state valuations were significantly different (P < 0.01), and there was good similarity between the two versions' ICC 0.86 (95% CI 0.79-0.91). The within-subject mean change was 0.03 (95% CI 0.01-0.06). For convergent validity, all relationships were significant (P < 0.05) and in the expected directions. EQ-5D-5L demonstrates sufficient convergent validity to be used with POFP, and a change in the standard reference period may be unnecessary if a multidimensional pain measure is also used.

Painful Stimulation and Transient Blocking of Nerve Transduction Due to Local Anesthesia Evoke Perceptual Distortions of the Face in Healthy Volunteers

Anecdotally, orofacial pain patients sometimes report that the painful face area feels “swollen.” Because there are no clinical signs of swelling, such illusions may represent perceptual distortions. In this study, we examine whether nociceptive stimulation can lead to perceptual distortion of the face in a way similar to that of local anesthesia. Sixteen healthy participants received injections of .4 mL hypertonic saline to induce short-term nociceptive stimulation, .4 mL mepivacaine (local anesthetic) to transiently block nerve transduction, and .4 mL isotonic saline as a control condition. Injections were administered in both the infraorbital and the mental nerve regions. Perceptual distortions were conceptualized as perceived changes in magnitude of the injected areas and the lips, and they were measured using 1) a verbal subjective rating scale and 2) a warping procedure. Prior to the study, participants filled in several psychological questionnaires. This study shows that both nociceptive stimulation (P < .05) and transient blocking of nerve transduction (P < .05) can lead to perceptual distortion of the face. A test-retest experiment including 9 new healthy subjects supported the results. Perceptual distortions were positively correlated with the psychological variable of dissociation in several conditions (P < .05). Perceptual distortions may therefore be influenced by somatosensory changes and psychological mechanisms. PerspectiveKnowledge of the factors that influence the perception of the face is important to understand the possible implications of perceptual distortions in orofacial pain disorders (and possibly other chronic pain states). Such information may ultimately open up new avenues of treatment for persistent orofacial pain.

OI0357 Cognitive-behavioral pain management programs for persistent orofacial pain

Persistent orofacial pain can have significant physical and psychologic effects. Outcomes for cognitive-behavioral pain management programs (CB PMPs) for people with widespread (nonfacial) pain show improvements in physical functioning and pain-related distress. The aim of this clinical study was to evaluate the effectiveness of a CB PMP for people with persistent orofacial pain. It was hypothesized that a CB PMP tailored to meet the needs of this population would significantly reduce the detrimental physical and psychologic effects of persistent orofacial pain.

Fatigue Mediates the Relationship Between Pain Interference and Distress in Patients with Persistent Orofacial Pain

To test the role of fatigue and its subtypes (general, physical, emotional, mental, and vigor) in mediating the relationship between psychological distress and pain interference. Retrospective, de-identified records were examined for 431 patients seeking treatment for persistent orofacial pain. Primary diagnoses of participants were muscle pain (29.8%), joint pain (26.0%), neuropathic pain (19.5%), and other (ie, fibromyalgia, centrally mediated myalgia, tendonitis, dental pain, cervical spine displacement, and no diagnosis; 24.7%). Mediation models were tested with distress as the independent variable, interference as the dependent variable, and fatigue or its subtypes as the mediators. After controlling for pain duration and average levels of pain, total fatigue mediated the relationship between distress and interference. Fatigue subtypes partially mediated the relationship between distress and interference, but mediation was strongest with the composite fatigue variable. The results, however, should be interpreted cautiously, as data were collected at a single time point and do not imply causality. These results suggest that interventions targeted specifically at fatigue symptoms may be helpful for reducing interference and improving quality of life in patients with persistent orofacial pain.

Chronic orofacial pain in dental patients: retrospective investigation over 12 years.

Orofacial pain is often difficult to diagnose and treat. However, there have been few reports on the clinical observation of dental patients with orofacial pain. We retrospectively investigated the characteristics of 221 dental patients who had suffered from persistent orofacial pain. Data were collected from the outpatient medical records in our clinic over the past 12 years. More than half of the patients (53.8%) had suffered with pain for more than 6 months from pain onset until the first visit to our clinic. The main diagnoses were neuropathic pain (30.3%), myofascial pain (23.5%), psychogenic pain (20.4%), odontogenic toothache (17.2%), and others (7.7%) such as temporomandibular disorders and glossitis. The treatments included pharmacotherapy, splint therapy, and others such as nerve block, dental treatment, physiotherapy, and/or psychotherapy. Excluding the patients (52 of 221 initially enrolled patients) with unknown responses to treatment, 65.7% showed remission or a significant improvement in pain in response to treatment. Although only a small group of patients had odontogenic toothache, the rate of improvement was highest for this disorder. In conclusion, early consultation with a dentist is useful to prevent chronicity of odontogenic pain and to make a differential diagnosis in patients with orofacial pain.

Transition to Persistent Orofacial Pain after Nerve Injury Involves Supraspinal Serotonin Mechanisms

The orofacial region is a major focus of chronic neuropathic pain conditions characterized by primary hyperalgesia at the site of injury and secondary hyperalgesia outside the injured zone. We have used a rat model of injury to the maxillary branch (V2) of the trigeminal nerve to produce constant and long-lasting primary hyperalgesia in the V2 territory and secondary hyperalgesia in territories innervated by the mandibular branch (V3). Our findings indicate that the induction of primary and secondary hyperalgesia depended on peripheral input from the injured nerve. In contrast, the maintenance of secondary hyperalgesia depended on central mechanisms. The centralization of the secondary hyperalgesia involved descending 5-HT drive from the rostral ventromedial medulla and the contribution of 5-HT3 receptors in the trigeminal nucleus caudalis (Vc), the homolog of the spinal dorsal horn. Electrophysiological studies further indicate that after nerve injury spontaneous responses and enhanced poststimulus discharges in Vc nociresponsive neurons were time-dependent on descending 5-HT drive and peripheral input. The induction phase of secondary hyperalgesia involved central sensitization mechanisms in Vc neurons that were dependent on peripheral input, whereas the maintenance phase of secondary hyperalgesia involved central sensitization in Vc neurons conducted by a delayed descending 5-HT drive and a persistence of peripheral inputs. Our results are the first to show that the maintenance of secondary hyperalgesia and underlying central sensitization associated with persistent pain depend on a transition to supraspinal mechanisms involving the serotonin system in rostral ventromedial medulla-dorsal horn circuits.

An Animal Model for Trigeminal Neuralgia by Compression of the Trigeminal Nerve Root

Background: Microvascular compression of the trigeminal nerve root is a major cause of most trigeminal neuralgia (TN) in patients; however, no reliable animal model to further study the pathogenesis of TN currently exists. Objective: Our objective was to establish a novel and practical animal model for TN by chronic compression of the trigeminal (CCT) nerve root in rats, which would provide a better animal model to mimic the clinical feature of TN on the research of the pathogenesis of TN. Study Design: A randomized, double blind, controlled animal trial. Methods: Sixteen adult male Sprague-Dawley rats (200-220 g) were randomly divided into 2 groups: one group that received chronic compression of the trigeminal nerve root (the CCT group, n=8) and another group that received sham operation without compression (the sham operation group, n=8). A small plastic filament was retrogressively inserted into the intracalvarium from the inferior orbital fissure until it reached the trigeminal nerve root for compression in CCT group. Animal behaviors were observed for 4 weeks after operation. Immunohistochemistry of glial fibrillary acidic protein (GFAP), isolectin B4 (IB4), substance P (SP) and calcitonin gene-related peptide (CGRP) were performed in the trigeminal root entry zone (TREZ) and medullary dorsal horn (MDH). Results: The orofacial mechanical allodynia and heat hyperalgesia in the CCT rats were obviously increased after the operation and lasted for 28 days. Increased facegrooming behavior was also observed in the CCT rats and continued for over 21 days, returning to baseline by day 28. Immunohistochemistry for GFAP in the TREZ revealed a progressive extension of astrocytic processes in the ipsilateral TREZ of rats in the CCT group. Furthermore, the IB4 positive immunoreactive nonpeptidergic C-fiber terminals in the MDH were reduced for 4 weeks after the operation. Both SP and CGRP, expressed in the peptidergic C-fiber terminals, were found to be decreased in the ipsilateral MDH of CCT animals after the trigeminal nerve root injury. Limitations: CCT animal model with a plastic filament only imitated the mechanical compression of the trigeminal root but not to display the complex vascular physiological feature as the microvascular in the TN patient. Conclusions: The chronic compression of the trigeminal nerve root in rats effectively induced persistent orofacial neuropathic pain behaviors, and it would provide a novel and practical animal model for future research on the pathogenesis of TN. Key words: trigeminal neuralgia, nerve root compression, animal model, mechanical allodynia, heat hyperalgesia, substance P, calcitonin gene-related peptide, isolectin B4

Dentists’ preferences for diagnosis, management and referral of chronic oro-facial pain: Results from a national survey

Aim: To explore the diagnosis, treatment and referral patterns of chronic oro-facial pain patients by generalist primary care dentists (GDPs) in the UK. Methods: A cross-sectional survey was conducted using a non-stratified random sample of 500 GDPs who were selected from the General Dental Council register. A self-complete postal questionnaire with four hypothetical clinical case scenarios describing sub-types of chronic oro-facial pain (COFP) was used to investigate diagnosis, treatment and referral options of GDPs. Results: Two hundred and twenty (44%) GDPs responded. The majority correctly diagnosed temporomandibular disorder (TMD; 88%) and burning mouth syndrome (BMS; 92%). There was more variation in the diagnosis of the other cases related to persistent oro-facial pain. For TMD there was a clear preference for treatment with occlusal splint therapy, and referral to a temporomandibular joint (TMJ) specialist. The BMS scenario showed drug therapy and referral to an oral medicine specialist to be most popular. The chronic oro-facial pain cases had greater variation in management and choice of psychotherapy was related to duration of pain symptoms. Conclusions: The greater variation in responses to scenarios based on patients with chronic oro-facial pain may reflect the difficulty clinicians face in diagnosing and treating this condition. Management appears to follow a biomedical model and most clinicians chose to refer patients for treatment. There are few specialist services to cater for such referrals, indicating a need to train primary care practitioners in management of chronic COFP, along with the establishment of evidence-based guidelines.