Is phantom tooth pain a deafferentation (neuropathic) syndrome? Part I: Evidence derived from pathophysiology and treatment

rs12411980 single-nucleotide polymorphism related to PRTFDC1 expression is significantly associated with phantom tooth pain

Phantom tooth pain (PTP) is one type of non-odontogenic neuropathic toothache, which rarely occurs after appropriate pulpectomy or tooth extraction. The cause of PTP is unknown. We investigated pain-related genetic factors that are associated with PTP. Four pain-associated genes, including G protein-coupled receptor 158 (GPR158) and phosphoribosyl transferase domain containing 1 (PRTFDC1), are adjacent to each other on the human genome. Some of these four genes or their genomic region may be related to PTP. We statistically analyzed associations between single-nucleotide polymorphisms (SNPs) in the genomic region and PTP in patients with PTP (PTP group), other orofacial pain (OFP group), and healthy control subjects. We then performed a database search of expression quantitative trait loci (eQTLs). For the seven SNPs that were significantly associated with PTP even after Bonferroni correction, we focused on the rs12411980 tag SNP (p = 9.42 × 10-4). Statistical analyses of the PTP group and healthy subject groups (group labels: NOC and TD) revealed that the rate of the GG genotype of the rs12411980 SNP was significantly higher in the PTP group than in the healthy subject groups (PTP group vs. NOC group: p = 2.92 × 10-4, PTP group vs. TD group: p = 5.46 × 10-4; percentage of GG: 30% in PTP group, 12% in NOC group, 11% in TD group). These results suggest that the GG genotype of the rs12411980 SNP is more susceptible to PTP. The rs2765697 SNP that is in strong linkage disequilibrium with the rs12411980 SNP is an eQTL that is associated with higher PRTFDC1 expression in the minor allele homozygotes in the healthy subject groups of the rs2765697 SNP. Thus, PRTFDC1 expression similarly increases in the minor allele homozygotes (GG genotype) in the healthy subject groups of the rs12411980 SNP, which would lead to greater susceptibility to PTP.

Single-nucleotide polymorphisms of the SLC17A9 and P2RY12 genes are significantly associated with phantom tooth pain

Phantom tooth pain (PTP) is a rare and specific neuropathic pain that occurs after pulpectomy and tooth extraction, but its cause is not understood. We hypothesized that there is a genetic contribution to PTP. We focused on solute carrier family 17 member 9 (SLC17A9)/vesicular nucleotide transporter (VNUT) and purinergic receptor P2Y12 (P2RY12), both of which have been associated with neuropathic pain and pain transduction signaling in the trigeminal ganglion in rodents. We sought to corroborate these associations in humans. We investigated gene polymorphisms that contribute to PTP. We statistically examined the association between genetic polymorphisms and PTP vulnerability in 150 patients with orofacial pain, including PTP, and 500 healthy subjects. We found that the rs735055 polymorphism of the SLC17A9 gene and rs3732759 polymorphism of the P2RY12 gene were associated with the development of PTP. Carriers of the minor allele of rs735055 and individuals who were homozygous for the major allele of rs3732759 had a higher rate of PTP. Carriers of the minor allele of rs735055 reportedly had high SLC17A9 mRNA expression in the spinal cord, which may increase the storage and release of adenosine triphosphate. Individuals who were homozygous for the major allele of rs3732759 may have higher P2RY12 expression that is more active in microglia. Therefore, these carriers may be more susceptible to PTP. These results suggest that specific genetic polymorphisms of the SLC17A9 and P2RY12 genes are involved in PTP. This is the first report on genes that are associated with PTP in humans.

Management of chronic idiopathic pain in patients with dental implant without a clear pathological lesion: A retrospective study

Non-nociceptive, persistent idiopathic facial pain (PIFP) is a poorly localized, continuous dull pain that occurs even in the absence of apparent pathological lesions or clinical neurologic deficiency. This study aimed to investigate the disease characteristics of PIFP that developed after dental implant treatments. The clinical characteristics of pain as well as treatment method and outcomes were retrospectively analyzed in 20 patients diagnosed with PIFP. The patients developed pain either after implant fixation or prosthetic treatment. In most of the patients, the pain persisted not only around the implant region but also at a distant site from the related implant (13/20, 65%). Many patients desired removal of the implants to manage the pain although the pain was not considered to be related to the implant treatment itself. In 12 patients, the related implants were removed but 67% (n = 8/12) of the patients still experienced chronic pain after implant removal. Medication helped decrease the pain in most patients (n = 17). Pregabalin and clonazepam showed relatively higher efficiency than other medications for controlling the pain. The results showed that although the onset of PIFP was related to dental implant treatment, implant removal could not be considered a reliable option for the management of PIFP. Although medication controls the pain at least partially, complete pain control with medication should not be expected. These results demonstrate that an accurate diagnosis of PIFP is important for the selection of appropriate treatment.

Trigeminal neuropathy causes hypomyelination in the anterior cingulate cortex, disrupts the synchrony of neural circuitry, and impairs decision-making in male rats

Infraorbital nerve‐chronic constriction injury (ION‐CCI) has become the most popular chronic trigeminal neuropathic pain (TNP) injury animal model which causes prolonged mechanical allodynia. Accumulative evidence suggests that TNP interferes with cognitive functions, however the underlying mechanisms are not known. The aim of this study was to investigate decision‐making performance as well as synaptic and large‐scale neural synchronized alterations in the spinal trigeminal nucleus (SpV) circuitry and anterior cingulate cortex (ACC) neural circuitry in male rats with TNP. Rat gambling task showed that ION‐CCI led to decrease the proportion of good decision makers and increase the proportion of poor decision makers. Electrophysiological recordings showed long‐lasting synaptic potentiation of local field potential in the trigeminal ganglia‐SpV caudalis (SpVc) synapses in TNP rats. In this study, TNP led to disruption of ACC spike timing and basolateral amygdala (BLA) theta oscillation associated with suppressed synchronization of theta oscillation between the BLA and ACC, indicating reduced neuronal communications. Myelination is critical for information flow between brain regions, and myelin plasticity is an important feature for learning. Neural activity in the cortical regions impacts myelination by regulating oligodendrocyte (OL) proliferation, differentiation, and myelin formation. We characterized newly formed oligodendrocyte progenitor cells, and mature OLs are reduced in TNP and are associated with reduced myelin strength in the ACC region. The functional disturbances in the BLA‐ACC neural circuitry is pathologically associated with the myelin defects in the ACC region which may be relevant causes for the deficits in decision‐making in chronic TNP state.

Suppression of Pain in the Late Phase of Chronic Trigeminal Neuropathic Pain Failed to Rescue the Decision-Making Deficits in Rats

Trigeminal neuropathic pain (TNP) led to vital cognitive functional deficits such as impaired decision-making abilities in a rat gambling task. Chronic TNP caused hypomyelination in the anterior cingulate cortex (ACC) associated with decreased synchronization between ACC spikes and basal lateral amygdala (BLA) theta oscillations. The aim of this study was to investigate the effect of pain suppression on cognitive impairment in the early or late phases of TNP. Blocking afferent signals with a tetrodotoxin (TTX)-ELVAX implanted immediately following nerve lesion suppressed the allodynia and rescued decision-making deficits. In contrast, the TTX used at a later phase could not suppress the allodynia nor rescue decision-making deficits. Intra-ACC administration of riluzole reduced the ACC neural sensitization but failed to restore ACC-BLA spike-field phase synchrony during the late stages of chronic neuropathic pain. Riluzole suppressed allodynia but failed to rescue the decision-making deficits during the late phase of TNP, suggesting that early pain relief is important for recovering from pain-related cognitive impairments. The functional disturbances in ACC neural circuitry may be relevant causes for the deficits in decision making in the chronic TNP state.

3-year Outcome of Patients with Persistent Pain after Root Canal Treatment: The National Dental Practice-Based Research Network

INTRODUCTION

We measured the long-term outcomes of patients reporting persistent pain 6 months after root canal treatment (RCT) and assessed the characteristics differing patients with pain chronification from those with pain resolution.

METHODS

Forty-five patients previously found to have persistent pain 6 months post-RCT from the National Dental Practice-Based Research Network were approached for a 3-year follow-up, and 27 participated in the survey. The frequency of self-reported pain, its impact on the ability to perform daily activities, and health care use were measured. The differences between patients whose persistent pain continued and those whose pain resolved were assessed.

RESULTS

Five patients met criteria for pain at 3.4 years (range, 3.1-3.9 years) post-RCT, which was moderate in intensity, occurred for about 3 days in the preceding month, and kept 1 patient from usual activities. Additional health care was received by 4 of 5 patients whose pain continued compared with 7 of 22 patients whose pain resolved. A longer duration of preoperative pain and higher pain intensity and interference at 6 months were found among patients with pain chronification. Of 13 patients with specific diagnoses for the persistent pain derived at 65 ± 41 days (∼8 months) post-RCT, 10 improved regardless of the diagnosis or treatment, and 11 had a temporomandibular disorder and/or headache as comorbid diagnoses (6) or causes (6) of the persistent "tooth" pain.

CONCLUSIONS

Progression of persistent post-RCT pain occurred in 19% of patients. The majority (56%) of patients improved without additional interventions. Both the group that improved and the group that continued to experience pain had a mixture of odontogenic and nonodontogenic etiologies.

Pharmacotherapeutic outcomes in atypical odontalgia: determinants of pain relief

OBJECTIVES

There has been considerable research which has focused on clarifying the origin of pain in patients with atypical odontalgia (AO), also known as "idiopathic toothache", and on identifying effective treatment, but there has been limited success so far. In this study, we assessed the outcomes of treatment and attempted to identify factors that could account for pain remission in patients with AO.

PATIENTS AND METHODS

Data for 165 patients diagnosed with AO from June 2015 to August 2017 were retrospectively reviewed. The patients' sex, age, duration of pain, and psychiatric history were collected, along with information on pain intensity, depressive status, and catastrophizing scores. Responses at 4 and 16 weeks from the start of treatment were observed. The associations between potentially associated factors and outcome were investigated using Bayesian model averaging.

RESULTS

A 30% reduction in pain was reported by 38 patients (46.3%) at 4 weeks and by 54 patients (65.9%) at 16 weeks. The pain intensity decreased as the depression and catastrophizing score improved; all of the changes were statistically significant (P<0.001). Four elements, that is, patient sex, depression score at baseline, pain score at 4 weeks, and change in the catastrophizing score, explained 52.5% of the variation in final outcome between individual patients.

CONCLUSION

Our findings confirm the efficacy of tricyclic antidepressants (TCAs) as a treatment for AO and indicate that other medications, especially aripiprazole used in combination with a TCA, may be useful. A considerable number of patients, especially women, those with lower levels of depression at baseline, and those who responded to 4 weeks of treatment, achieved pain relief.

Development and preliminary evaluation of a new screening instrument for atypical odontalgia and persistent dentoalveolar pain disorder

AIM

To develop and preliminarily evaluate a new screening instrument for atypical odontalgia (AO) or persistent dentoalveolar pain disorder (PDAP). To evaluate the instrument's performance in detecting AO/PDAP amongst a heterogeneous group of orofacial pain conditions and pain-free controls and empirically compare its performance with an established neuropathic screening instrument (S-LANSS), which is the best available standard.

METHODS

The study design was cross-sectional; subjects recruited included a convenience sample of pain-free controls (n = 21) and four groups of orofacial pain conditions: AO/PDAP (n = 22); trigeminal neuralgia (n = 21); temporomandibular disorder (n = 41); and acute dental pain (n = 41). The instrument's internal reliability and factor structure were examined alongside its sensitivity and specificity and ROC-determined threshold score.

RESULTS

The 9 AO/PDAP-specific items were found to moderately correlate with the S-LANSS (r = 0.58; P < 0.01). The 14-items of the full instrument were examined using exploratory factor analysis and reduced to ten items in a two-factor structure that explained 96% of the variance. This 10-item final instrument had a ROC area of 0.77 (95% CI: 0.67; 0.88), sensitivity of 77% (95% CI: 55; 92%), and specificity of 69% (95% CI: 60; 77%) with an intentionally higher false-positive rate than false-negative rate. In contrast, the S-LANSS exhibited sensitivity of 32% (95% CI: 14;55%) and specificity of 78% (95% CI: 70;85%) with less optimal false-positive versus false-negative rates.

CONCLUSION

This preliminary study confirms the new screening instrument for AO/PDAP merits progression to field testing.

Neuropathic Pain Due to Iatrogenic Lingual Nerve Lesion: Nerve Grafting to Reduce Otherwise Untreatable Pain

Iatrogenic lingual nerve lesion is a well-known and unfortunate complication after mandibular third molar removal. Occasionally, the nerve injury can cause severe neuropathic pain.Here, the authors present the history of 2 patients with lingual nerve injury due to mandibular third molar removal, and with severe neuropathic pain in the craniomandibular region. Pharmacotherapy and physiotherapy did not reduce the pain, and ultimately, the lingual nerve was surgically explored. Scar tissue and a lingual nerve neuroma were observed and resected in both patients.In the first patient, the gap between the nerve stumps was bridged with an autologous sural nerve graft. In the second patient, some continuity of the lingual nerve was preserved and the resected part was substituted with an autologous sural nerve graft. Significant pain reduction was achieved in both patients and no further medical treatment was necessary at the end of follow-up.These reports show that lingual nerve reconstruction can be a successful therapy in patients experiencing severe neuropathic pain after iatrogenic lingual nerve injury. Different treatment options for neuropathic pain due to lingual nerve injury are discussed.

Evaluating Burning Mouth Syndrome as a Comorbidity of Atypical Odontalgia: The Impact on Pain Experiences

OBJECTIVE

This study aimed (1) to investigate the differences in clinical characteristics of patients between 2 groups, those who have atypical odontalgia (AO) only and those who have AO with burning mouth syndrome (BMS), and (2) to assess the influence of psychiatric comorbidity factors on patients' experiences.

METHOD

Medical records and psychiatric referral forms of patients visiting the Psychosomatic Dentistry Clinic of Tokyo Medical and Dental University between 2013 and 2016 were reviewed. The final sample included 2 groups of 355 patients: those who have AO only (n = 272) and those who have AO with BMS (AO-BMS; n = 83). Clinicodemographic variables (gender, age, comorbid psychiatric disorders, and history of headache or sleep disturbances) and pain variables (duration of illness, pain intensity, and severity of accompanying depression) were collected. Initial pain assessment was done using the Short-Form McGill Pain Questionnaire, and depressive state was determined using the Zung Self-Rating Depression Scale.

RESULTS

The average age, female ratio, and sleep disturbance prevalence in the AO-only group were significantly lower than those in AO-BMS group. AO-BMS patients rated overall pain score and present pain intensity significantly higher than did the AO-only patients (P = 0.033 and P = 0.034, respectively), emphasizing sharp (P = 0.049), hot-burning (P = 0.000), and splitting (P = 0.003) characteristics of pain. Patients having comorbid psychiatric disorders had a higher proportion of sleep disturbance in both groups and a higher proportion of depressive state in the AO-only group.

CONCLUSIONS

AO-BMS patients have different epidemiological characteristics, sleep quality, and pain experiences compared to AO-only patients. The presence of psychiatric comorbidities in both groups may exacerbate sleep quality. We suggest that BMS as a comorbid oral disorder in AO patients contributes to a more intensively painful experience.

Neuropathic orofacial pain: Facts and fiction

Definition and taxonomy This review deals with neuropathic pain of traumatic origin affecting the trigeminal nerve, i.e. painful post-traumatic trigeminal neuropathy (PTTN). Symptomatology The clinical characteristics of PTTN vary considerably, partly due to the type and extent of injury. Symptoms involve combinations of spontaneous and evoked pain and of positive and negative somatosensory signs. These patients are at risk of going through unnecessary dental/surgical procedures in the attempt to eradicate the cause of the pain, due to the fact that most dentists only rarely encounter PTTN. Epidemiology Overall, approximately 3% of patients with trigeminal nerve injuries develop PTTN. Patients are most often female above the age of 45 years, and both physical and psychological comorbidities are common. Pathophysiology PTTN shares many pathophysiological mechanisms with other peripheral neuropathic pain conditions. Diagnostic considerations PTTN may be confused with one of the regional neuralgias or other orofacial pain conditions. For intraoral PTTN, early stages are often misdiagnosed as odontogenic pain. Pain management Management of PTTN generally follows recommendations for peripheral neuropathic pain. Expert opinion International consensus on classification and taxonomy is urgently needed in order to advance the field related to this condition.

Oral sensory nerve damage: Causes and consequences

Oral sensations (i.e., taste, oral somatosensation, retronasal olfaction) are integrated into a composite sense of flavor, which guides dietary choices with long-term health impact. The nerves carrying this input are vulnerable to peripheral damage from multiple sources (e.g., otitis media, tonsillectomy, head injury), and this regional damage can boost sensations elsewhere in the mouth because of central interactions among nerve targets. Mutual inhibition governs this compensatory process, but individual differences lead to variation in whole-mouth outcomes: some individuals are unaffected, others experience severe loss, and some encounter sensory increases that may (if experienced early in life) elevate sweet-fat palatability and body mass. Phantom taste, touch, or pain sensations (e.g., burning mouth syndrome) may also occur, particularly in those expressing the most taste buds. To identify and treat these conditions effectively, emerging clinical tests measure regional vs. whole-mouth sensation, stimulated vs. phantom cues, and oral anatomy. Scaling methods allowing valid group comparisons have strongly aided these efforts. Overall, advances in measuring oral sensory function in health and disease show promise for understanding the varied clinical consequences of nerve damage.

Biopsychosocial aspects of atypical odontalgia

Background. A few studies have found somatosensory abnormalities in atypical odontalgia (AO) patients. The aim of the study is to explore the presence of specific abnormalities in facial pain patients that can be considered as psychophysical factors predisposing to AO. Materials and Methods. The AO subjects (n = 18) have been compared to pain-free (n = 14), trigeminal neuralgia (n = 16), migraine (n = 17), and temporomandibular disorder (n = 14). The neurometer current perception threshold (CPT) was used to investigate somatosensory perception. Structured clinical interviews based on the DSM-IV axis I and DSM III-R axis II criteria for psychiatric disorders and self-assessment questionnaires were used to evaluate psychopathology and aggressive behavior among subjects. Results. Subjects with AO showed a lower Aβ, Aδ, and C trigeminal fiber pain perception threshold when compared to a pain-free control group. Resentment was determined to be inversely related to Aβ (rho: 0.62, P < 0.05), Aδ (rho: 0.53, P < 0.05) and C fibers (rho: 0.54, P < 0.05), and depression was inversely related with C fiber (rho: 0.52, P < 0.05) perception threshold only in AO subjects. Conclusion. High levels of depression and resentment can be considered predictive psychophysical factors for the development of AO after dental extraction.

Current evidence on atypical odontalgia: diagnosis and clinical management

Patients with atypical odontalgia (AO) complain of medically unexplained toothache. No evidence-based diagnostic criteria or treatment guidelines are yet available. The present paper addresses seven clinical questions about AO based on current knowledge in the literature and discusses diagnostic criteria and guidelines for treatment and management. The questions are (i) What is the prevalence of AO in the community? (ii) What psychological problems are experienced by patients with AO? (iii) Are there any comorbidities of AO? (iv) Is local anesthesia effective for the relief of pain in AO? (v) Are there any characteristic symptoms of AO other than spontaneous pain? (vi) Are antidepressants effective for treatment of AO? (vii) Are anticonvulsants effective for treatment of AO? Our literature search provided answers for these questions; however, there is insufficient evidence-based data to establish guidelines for the diagnosis and treatment of AO. Overall, some diagnostic criteria for neuropathic pain and persistent dentoalveolar pain disorder may be applied to AO patients. The patient's psychogenic background should always be considered in the treatment and/or management of AO. The clinicians may need to treat AO patients using Patient-Oriented Evidence that Matters approach.

Central mechanisms in phantom limb perception: The past, present and future

Phantom limbs provide valuable insight into the mechanisms underlying bodily awareness and ownership. This paper reviews the complexity of phantom limb phenomena (proprioception, form, position, posture and telescoping), and the various contributions of internal constructs of the body, or body schema, and neuromatrix theory in explaining these phenomena. Specific systems and processes that have received little attention in phantom limb research are also reviewed and highlighted as important future directions, These include prosthesis embodiment and extended physiological proprioception (i.e., the extension of the body's "area of influence" that thereby extends one's innate sense of proprioception, mirror neurons and cross-referencing of the phantom limb with the intact limb (and the related phenomena of perceiving referred sensations and mirrored movements in the phantom form the intact limb). The likely involvements of the body schema and the body-self neuromatrix, mirror neurons, and cross-callosal and ipsilateral mechanisms in phantom limb phenomena all suggest that the perception of a "normal" phantom limb (that is, a non-painful phantom that has the sensory qualities of an intact limb) is more than likely an epiphenomenon of normal functioning, action understanding and empathy, and potentially may even be evolutionarily adaptive and perhaps necessary. Phantom pain, however, may be a maladaptive failure of the neuromatrix to maintain global bodily constructs.

Central mechanisms of orofacial pain

The orofacial pain clinician must understand the difference between peripheral and central mechanisms of pain. Particularly, one has to understand the process of central sensitization as it relates to the various orofacial pain conditions to understand orofacial pain. Understanding leads to more effective treatment.

Trigeminal neuropathic pain alters responses in CNS circuits to mechanical (brush) and thermal (cold and heat) stimuli

Functional magnetic resonance imaging was used to study patients with chronic neuropathic pain involving the maxillary region (V2) of the trigeminal nerve in patients with spontaneous pain and evoked pain to brush (allodynia). Patients underwent two functional scans (2-3 months apart) with mechanical and thermal stimuli applied to the affected region of V2 and to the mirror site in the unaffected contralateral V2 region, as well as bilaterally to the mandibular (V3) division. Patients were stimulated with brush, noxious cold, and noxious heat. Significant changes were observed in regions within and outside the primary trigeminal sensory pathway. Stimulation to the affected (neuropathic) side resulted in predominantly frontal region and basal ganglia activation compared with the control side. The differences were consistent with the allodynia to brush and cold. A region of interest-based analysis of the trigeminal sensory pathway revealed patterns of activation that differentiated between the affected and unaffected sides and that were particular to each stimulus. Activation in the spinal trigeminal nucleus was constant in location for all pain stimuli. Activation in other brainstem nuclei also showed differences in the blood oxygenation level-dependent signal for the affected versus the unaffected side. Thus, sensory processing in patients with trigeminal neuropathic pain is associated with distinct activation patterns consistent with sensitization within and outside of the primary sensory pathway.

Touching on somatosensory specializations in mammals

Specialized species often reveal general principles of brain organization and provide systems for analysis of sensory function. Subterranean species dependent on touch have particularly large somatosensory areas with modular cortical representations of sensory surfaces. Some species have added cortical areas to processing networks, have developed tactile foveas and have superior colliculi primarily devoted to somatosensation rather than vision. Recent studies reveal surprisingly large cortical representations of oral structures in primates and mole-rats. Cortical modules represent a range of different sensory surfaces in rodents, star-nosed moles and primates, indicating that similar developmental mechanisms operate in diverse species. Finally, manipulation of patterning genes in mice suggests evolutionary mechanisms for producing the specialized corticies of subterranean species.

Persistent idiopathic facial pain exists independent of somatosensory input from the painful region: findings from quantitative sensory functions and somatotopy of the primary somatosensory cortex

In 14 patients with unilateral persistent idiopathic facial pain (PIFP), classified according to the criteria of the International Headache Society, and 16 age-matched control subjects sensory functions were examined on the face by quantitative sensory testing (QST). Additionally, the somatotopy of the primary somatosensory cortex (SI) to tactile input from the pain area was evaluated by means of magnetoencephalography. Previously reported abnormalities in PIFP as a dishabituation of the R2 component of the blink reflex and psychiatric disturbances were co-evaluated. Psychiatric evaluation included a Structured Clinical Interview for axis-I DSM IV disorders (SCID-I) and employment of the SCL-90-R and a depression scale (ADS). Thresholds to touch, pin prick, warm, cold, heat and pressure pain as well as the pain ratings to single and repetitive (perceptual wind up) painful pin prick stimuli did not indicate a significant sensory deficit or hyperactivity in the pain area when compared with the asymptomatic side nor when compared with the values of healthy control subjects. QST results were not significantly altered in patients (n=4) that showed an abnormal dishabituation of the R2 component of the blink reflex. The interhemispheric difference in distance between the cortical representation of the lip and the index finger did not differ between patients and control subjects. Psychiatric evaluation did not disclose significant abnormalities at a group level. It is concluded that PIFP is maintained by mechanisms which do not involve somatosensory processing of stimuli from the pain area.

Algies faciales typiques et atypiques : du diagnostic au traitement

PURPOSE

Facial pain is a frequently encountered symptom in general medical practice and encompass a wide group of facial problems. As correct diagnosis can usually be reached by history and physical examination for well defined typical clinical entities (trigeminal neuralgia, cluster headache) atypical facial pain may have many other potential causes (sinuses infection, temporomandibular joint syndrome, dental disorders...) so that diagnosis not appear an easy task.

CURRENT KNOWLEDGE AND KEYPOINTS

Anatomical and physiological organization of facial nociceptive system, particularly trigeminal system, may explain the variability of facial pain. Although symptoms have been clearly identified mechanism of pain production remains controversial. Several factors (psychological, neurological, endocrine...) and mechanisms (neuropathic, vascular, myoarticular) may coexist and explain trouble in diagnosing and treating facial pain.

FUTURE PROSPECTS AND PROJECTS

Better knowledge in identifying the cause of facial pain may lead to improve patient care and avoid patient frustration, medical nomadism, repetitive dental and otolaryngologic procedures, and finally non-compliance with treatment.

Orofacial pain and sensory disorders in the elderly

Many orofacial pain conditions occur in the elderly. Specifically,this article reviews the prevalence of general and orofacial-related pain in the elderly. The authors also describe and discuss the likely disorders and diseases that produce facial pain and burning pain in the mouth. They do not cover jaw joint pain, oral sores, or ulceration-induced pain, as these conditions are better discussed in the context of arthritis and oral pathologies of the mouth. The authors discuss oral motor disorders, myogenous pain, vascular pain, headaches, trigeminal neuralgia, trigeminal neuropathic dis-ease, postherpetic neuralgia, burning mouth syndrome, and occlusal dysesthesia.

Prevalence of persistent pain after endodontic treatment and factors affecting its occurrence in cases with complete radiographic healing

AIMS

To (i) determine the prevalence of persistent dento-alveolar pain following nonsurgical and/or surgical endodontic treatment conducted in a teaching dental hospital and (ii) identify the risk factors associated with persistent pain after apparently successful root canal treatment.

STUDY DESIGN

A total of 175 patients/teeth were reviewed 12-59 months following treatment. The patients were examined clinically and radiographically and a detailed pain history obtained. Multiple logistic regression analysis was used to investigate the association between potential risk factors and persistent pain after successful endodontic treatment.

RESULTS

The prevalence of persistent pain after successful root canal treatment was 12% (21/175). Treatment success was determined by the absence of clinical and radiographic signs of dental disease. The factors that were significantly (P < 0.05) associated with persistent pain following endodontic treatment were: 'duration of preoperative pain' [odds ratio (OR) = 8.6], 'preoperative pain from the tooth' (OR = 7.8), 'preoperative tenderness to percussion' (OR = 7.8), 'previous chronic pain problems' (OR = 4.5), 'gender' (OR = 4.5) and 'history of painful treatment in the orofacial region' (OR = 3.8). 'Type of treatment received (surgical or nonsurgical treatment)' showed borderline significance at the 10% level.

CONCLUSIONS

The presence and duration of preoperative pain from the tooth site, lasting at least 3 months, a positive history of previous chronic pain experience or painful treatment in the orofacial region, and female gender were important risk factors associated with persistent pain after successful endodontic treatment.

Plasticity of the cortical dentition representation after tooth extraction in naked mole-rats

Naked mole-rats (Heterocephalus glaber) have a large cortical representation of their behaviorally important front teeth, accounting for 30% of primary somatosensory cortex (SI). Here we investigated the plasticity of this dental representation after the extraction of a single lower tooth. The representation of the contralateral lower incisor normally accounts for approximately 15% of somatosensory cortex in mole-rats. In five mole-rats the lower right incisor was extracted on either postnatal day 7 or 21. After 5-8 months the deprived tooth zone in S1 was investigated with multiunit microelectrode recordings. The results revealed a dramatic reorganization of the orofacial representation in SI. Neurons in the cortical lower tooth representation were responsive to tactile inputs from surrounding orofacial structures, including the contralateral upper incisor, ipsilateral lower incisor, tongue, chin, gums, and buccal pad. Neurons in the former lower tooth zone had complex receptive fields that often encompassed multiple sensory surfaces surrounding the extracted tooth in the periphery. These results suggest that the representation of the dentition in mammals is capable of significant reorganization after the loss of sensory inputs from the teeth. These data parallel findings in the somatosensory hand area of primates after deafferentation where cortex can become activated by a mixture of widely spaced surrounding sensory surfaces (e.g., chin and upper arm).

Functional imaging of the human trigeminal system: Opportunities for new insights into pain processing in health and disease

Peripheral inflammation or nerve damage result in changes in nervous system function, and may be a source of chronic pain. A number of animal studies have indicated that central neural plasticity, including sensitization of neurons within the spinal cord and brain, is part of the response to nervous system insult, and can result in the appearance of altered sensation, including pain. It cannot be assumed, however, that data obtained from animal models unambiguously reflects CNS changes that occur in humans. Currently, the only noninvasive approach to determining objective changes in neural processing and responsiveness within the CNS in humans is the use of functional imaging techniques. It is now possible to use functional magnetic resonance imaging (fMRI) to measure CNS activation in the trigeminal ganglion, spinal trigeminal nucleus, the thalamus, and the somatosensory cortex in healthy volunteers, in a surrogate model of hyperalgesia, and in patients with trigeminal pain. By offering a window into the temporal and functional changes that occur in the damaged nervous system in humans, fMRI can provide both insight into the mechanisms of normal and pathological pain and, potentially, an objective method for measuring altered sensation. These advances are likely to contribute greatly to the diagnosis and treatment of clinical pain conditions affecting the trigeminal system (e.g., neuropathic pain, migraine).

Atypical Odontalgia: A Review of the Literature

OBJECTIVE

To review previous reports of cases of atypical odontalgia to examine its epidemiological and clinical characteristics and to explore the etiology and pathophysiology of the disease.

BACKGROUND

Atypical odontalgia is one of many painful conditions that affect the oral cavity and is often overlooked in the differential diagnosis.

METHODS

A search of the literature was performed for all cases of atypical odontalgia reported from 1966 to the present.

RESULTS

The typical clinical presentation of atypical odontalgia that has been reported involves pain in a tooth in the absence of any sign of pathology; the pain may spread to areas of the face, neck, and shoulder. The existing literature suggests that this condition occurs in 3% to 6% of the patients who undergo endodontic treatment, with high female preponderance and a concentration of cases in the fourth decade of life. Deafferentation seems to be the most likely mechanism to initiate the pain, but psychological factors, alteration of neural mechanisms, and even an idiopathic mechanism have been implicated. Not all reported cases were preceded by trauma to the teeth or gums. The treatment of choice is a tricyclic antidepressant, alone or in combination with a phenothiazine. The outcome is usually fair, with many patients obtaining complete relief from pain. Especially in the absence of overt pathology, particular attention should be paid to avoiding any unnecessary and potentially dangerous dental intervention on the teeth.

CONCLUSION

Atypical odontalgia is surprisingly common, of uncertain origin, and potentially treatable.

Oral and maxillofacial surgery in patients with chronic orofacial pain

PURPOSE

In this investigation, we evaluated a population of patients with chronic orofacial pain who sought treatment at a pain center in an academic institution. These patients were evaluated with respect to 1) the frequency and types of previous oral and maxillofacial surgery procedures, 2) the frequency of previous significant misdiagnoses, and 3) the number of patients who subsequently required surgical treatment as recommended by an interdisciplinary orofacial pain team. The major goal of this investigation was to determine the role of oral and maxillofacial surgery in patients with chronic orofacial pain.

PATIENTS AND METHODS

The study population included patients seen at the Center for Oral, Facial and Head Pain at New York Presbyterian Hospital from January 1999 through April 2001. (120 patients; female-to-male ratio, 3:1; mean age, 49 years; average pain duration, 81 months; average number of previous specialists, 6). The patient population was evaluated by an interdisciplinary orofacial pain team and the following characteristics of this population were profiled: 1) the frequency and types of previous surgical procedures, 2) diagnoses, 3) the frequency of previous misdiagnoses, and 4) treatment recommendations made by the center team.

RESULTS

There was a history of previous oral and maxillofacial surgical procedures in 38 of 120 patients (32%). Procedures performed before our evaluation included endodontics (30%), extractions (27%), apicoectomies (12%), temporomandibular joint (TMJ) surgery (6%), neurolysis (5%), orthognathic surgery (3%), and debridement of bone cavities (2%). Surgical intervention clearly exacerbated pain in 21 of 38 patients (55%) who had undergone surgery. Diagnoses included myofascial pain (50%), atypical facial neuralgia (40%), depression (30%), TMJ synovitis (14%), TMJ osteoarthritis (12%), trigeminal neuralgia (10%), and TMJ fibrosis (2%). Treatment recommendations included medications (91%), physical therapy (36%), psychiatric management (30%), trigger injections (15%), oral appliances (13%), biofeedback (13%), acupuncture (8%), surgery (4%), and Botox injections (1%) (Allergan Inc, Irvine, CA). Gross misdiagnosis leading to serious sequelae, with delay of necessary treatment, occurred in 6 of 120 patients (5%).

CONCLUSIONS

Misdiagnosis and multiple failed treatments were common in these patients with chronic orofacial pain. These patients often have multiple diagnoses, requiring management by multiple disciplines. Surgery, when indicated, must be based on a specific diagnosis that is amenable to surgical therapy. However, surgical treatment was rarely indicated as a treatment for pain relief in these patients with chronic orofacial pain, and it exacerbated and perpetuated pain symptoms in some of them.

Orofacial pain: basic mechanisms and implication for successful management

Orofacial Pain is the field of dentistry devoted to the diagnosis and management of chronic, complex, facial pain and oromotor disorders. This specialty in dentistry has developed over a number of years out of the need for better understanding of a group of patients who somehow were not clearly suffering from dental pain disorders, but still did not seem to have a clearly defined medical problem. After a long period of treating patients based on the mechanicist aspect of the disease, our profession has realized the importance of basic knowledge and differencial diagnosis in order to proper manage these patients. This modification in the approach has caused severe changes in education as well as in clinical activities. Historically considered as a problem of occlusion, Orofacial Pain, including Temporomandibular Disorders (TMD) has recently reached the status of "Specialty" in Brazil. Therefore, this paper aims to discuss the main differences between musculoskeletal and neuropathic pain and the importance of basic knowledge to perform successful management.

Facial and glossal distribution of anaesthesia after inferior alveolar nerve block

The aim of this study was to subjectively determine the distribution of anaesthesia by mapping areas of sensory loss following inferior alveolar nerve block. Fifty healthy dental students were the subjects of this study (men 32, women 18). They were asked to draw the anaesthetized area on a diagram of the face and tongue 20 min after inferior alveolar nerve block. They evaluated the degree of anaesthesia by touching their faces and moving their tongues. All of the 50 subjects reported anaesthesia in the facial area. Of these, 21 (42%) reported the cutaneous distribution of anaesthesia on mental nerve territory only. Seventeen subjects (34%) reported anaesthesia on mental and buccal nerve territory. Nine subjects (18%) reported anaesthesia on mental, buccal, and auriculotemporal nerve territory. Two subjects (4%) reported anaesthesia on mental and auriculotemporal nerve territory and one subject (2%) on mental, buccal and infra-orbital nerve territory. Forty-seven of the 50 subjects (94%) reported anaesthesia of the tongue with the various degree of anaesthesia according to the area. Of these, 17 subjects (34%) reported strong anaesthesia on the anterior area and weak anaesthesia on the middle part of the tongue. Nineteen subjects (38%) reported strong anaesthesia of the lateral area and weak anaesthesia on the medial area, and 11 subjects (22%) reported anaesthesia on only the lateral side of the tongue. Three subjects (6%) reported no anaesthesia of the tongue. The distribution of anaesthesia of the facial and glossal regions determined subjectively after inferior alveolar nerve block, varies significantly between individuals.

Phantom pain and risk factors: a multivariate analysis

Phantom pain has been given considerable attention in literature. Phantom pain reduces quality of life, and patients suffering from phantom pain make heavy use of the medical system. Many risk factors have been identified for phantom pain in univariate analyses, including phantom sensations, stump pain, pain prior to the amputation, cause of amputation, prosthesis use, and years elapsed since amputation. Multivariate analyses are lacking in the literature and, therefore, no estimation of an overall risk for phantom pain can be made. The aim of this study was to analyze risk factors in a multivariate analysis in 536 subjects (19% upper limb amputees and 81% lower limb amputees). These subjects filled out a questionnaire in which the following items were assessed; side, date, level, and reason of amputation, pre-amputation pain, presence or absence of phantom pain, phantom sensations and or stump pain, and prosthesis use. The prevalence of phantom pain was 72% (95% CI: 68 to 76%) for the total group, 41% (95% CI: 31 to 51%) in upper limb amputees and 80% (95% CI: 76 to 83%) in lower limb amputees. The most important risk factors for phantom pain were "bilateral amputation" and "lower limb amputation." The risk for phantom pain ranged from 0.33 for a 10-year-old patient with a distal upper limb amputation to 0.99 for a subject of 80 years with a bilateral lower limb amputation of which one side is an above knee amputation.

Sympathetic activity-mediated neuropathic facial pain following simple tooth extraction: a case report

This is a report of a case of sympathetic activity-mediated neuropathic facial pain induced by a traumatic trigeminal nerve injury and by varicella zoster virus infection, following a simple tooth extraction. The patient had undergone extraction of the right lower third molar at a local dental clinic, and soon after the tooth extraction, she became aware of spontaneous pain in the right ear, right temporal region, and in the tooth socket. At our initial examination 30 days after the tooth extraction, the healing of the tooth socket was normal; however, the patient had a tingling and burning sensation (dysesthesia) and spontaneous pain of the right lower lip and the right temporal region, both of which were exacerbated by non-noxious stimuli (allodynia). The patient also showed paralysis of the marginal mandibular branch of the facial nerve, taste dysfunction, and increased varicella zoster serum titers. A diagnostic stellate ganglion block (SGB) 45 days after the tooth extraction using one percent lidocaine markedly alleviated the dysesthesia and allodynia. These symptoms are characteristic of neuropathic pain with sympathetic interaction. The patient was successfully treated with SGB and a tricyclic antidepressant.

Incidence of chronic neuropathic pain subsequent to surgical removal of impacted third molars

To determine the incidence of atypical odontalgia/chronic neuropathic pain subsequent to surgical removal of impacted third molars, a telephone survey and a clinical investigation were carried out. Patients operated on for impacted mandibular third molars during 1994 96 in the Oral Surgery Clinic. School of Dentistry, University of Bergen, Bergen, Norway, were contacted by telephone. Answers were obtained from 1035 (71%) out of a total of 1458 operated patients. Median observation time was 5 years 9 months, ranging from 4 years 5 months to 6 years 9 months. All except 23 (2.2%) patients stated that they had no long-term symptoms or problems from the surgical site, jaw, or face after the third molar removal. These 23 patients were all examined clinically and radiologically, and symptoms and findings were evaluated. Seventeen patients had TMJ dysfunction: primarily pain of muscular and joint origin. Three patients had a periodontal problem associated with the adjacent second molar, with deep bony pockets and recurrent periodontal infection while two had chronic pulpitis of a second molar. One patient reported a temporary maxillary pain after removal of an ipsilateral mandibular third molar. None of the patients met the criteria for a diagnosis of atypical odontalgia/neuropathic pain. A 95% confidence interval of 0-0.38% of incidence rate of postoperative neuropathic pain was calculated. It is concluded that atypical odontalgia/ chronic neuropathic pain subsequent to surgical third molar removal is rare.

Chronic facial pain: a multidisciplinary problem

Atypical facial pain is an unrecognised and unhelpful diagnosis but one which describes chronic pains that do not fit the present classification system. Due to the site of the pain, patients may seek and, indeed, receive treatment from dental practitioners and specialists, but the pain is often unresponsive and may have more in common with unexplained medical symptoms affecting other areas of the body, than with other dental symptoms. This review suggests a need for a diagnostic category of "chronic facial pain", which demands a multidisciplinary approach to diagnosis and management.