Atypical Odontalgia: A Review of the Literature

Evaluation of a magnetic resonance-compatible dentoalveolar tactile stimulus device

Abstract

Background

The organization of the trigeminal system is unique as it provides somatosensory innervation to the face, masticatory and oral structures, the majority of the intracranial contents [1] and to specialized structures (tongue, nasal mucosa, auricle, tympanic membrane, cornea and part of the conjunctiva) [2]. Somatic sensory information transmitted by the trigeminal nerve is crucial for normal orofacial function; however, the mechanisms of many chronic pain conditions affecting areas innervated by this sensory system are not well understood [3-5]. The clinical presentation of chronic intraoral pain in the area of a tooth or in a site formally occupied by a tooth with no clinical or radiological signs of pathology, referred to as atypical odontalgia (AO) [6,7], is one such chronic pain condition of particular interest to dentists that is difficult to diagnose and manage. Recent research suggests both peripheral and central nervous system mechanisms being involved in AO pathophysiology [8-10], but the majority of mechanism-based research of patients with AO has focused on the "peripheral aspect" [7].

Functional magnetic resonance imaging (fMRI) is an established research technique to study the central aspects of pain [11]. Of existing neuroimaging techniques, fMRI provides good spatial resolution of cortical and subcortical structures critical in the processing of nociception, acceptable temporal resolution, does not involve ionizing radiation, and can be performed using most MRI systems that already exist in research centers and the community. For these reasons, we sought to develop a protocol that allows us to use this tool to investigate the central mechanisms involved in the processes of intraoral pain arising from the dentoalveolar region. Using this device, our long-term objective is to improve our understanding of the underlying mechanisms of persistent dentoalveolar pain.

In the past few years several studies used fMRI to investigate the human trigeminal system [12,13], with a limited subset focusing on intraoral stimulation - specifically on the dentoalveolar processes, such as lip, tongue and teeth stimulation [14] or only teeth [15-17]. Some reasons for scarce literature on this topic may be the technical challenges involved in delivering facial/intraoral stimulation inside a MR scanner [17,18]: possibility of magnetic interference, detriment of image quality, subject discomfort and reduced working space between the subject's head and the radiofrequency coil. As a consequence a MR-compatible device would need to not only overcome these challenges but also be capable of delivering a controlled and reproducible stimuli [19], as reliability/reproducibility is a necessary feature of sensory testing [20].

Existing MR-compatible methods of dentoalveolar stimulation are limited and do not adequately deliver stimuli across a range of non-painful to painful intensities and/or cannot be adjusted to reach posterior aspects of the dentoalveolar region. Therefore our goal was to develop and test the feasibility of a device able to: 1) provide reliable and valid dentoalveolar stimuli, 2) deliver such stimulation within the restricted space of an MR head coil, 3) be compatible for use within an MR environment, and 4) produce brain activation in painfree controls consistent to those observed by others using fMRI.

Psychiatric diagnoses in patients with burning mouth syndrome and atypical odontalgia referred from psychiatric to dental facilities

BACKGROUND

Burning mouth syndrome (BMS) and atypical odontalgia (AO) are two conditions involving chronic oral pain in the absence of any organic cause. Psychiatrically they can both be considered as "somatoform disorder". From the dental point of view, however, the two disorders are quite distinct. BMS is a burning or stinging sensation in the mouth in association with a normal mucosa whereas AO is most frequently associated with a continuous pain in the teeth or in a tooth socket after extraction in the absence of any identifiable cause. Because of the absence of organic causes, BMS and AO are often regarded as psychogenic conditions, although the relationship between oral pain and psychologic factors is still unclear. Some studies have analyzed the psychiatric diagnoses of patients with chronic oral pain who have been referred from dental facilities to psychiatric facilities. No study to date has investigated patients referred from psychiatric facilities to dental facilities.

OBJECTIVE

To analyze the psychiatric diagnoses of chronic oral pain patients, diagnosed with BMS and AO, and referred from psychiatric facilities to dental facilities.

STUDY DESIGN

Psychiatric diagnoses and disease conditions of BMS or AO were investigated in 162 patients by reviewing patients' medical records and referral forms. Psychiatric diagnoses were categorized according to the International Statistical Classification of Disease and Related Health Problems, Tenth Revision.

RESULTS

The proportion of F4 classification (neurotic, stress-related, and somatoform disorders) in AO patients was significantly higher than in BMS patients. BMS patients were more frequently given a F3 classification (mood/affective disorders). However, 50.8% of BMS patients and 33.3% of AO patients had no specific psychiatric diagnoses.

CONCLUSION

Although BMS and AO are both chronic pain disorders occurring in the absence of any organic cause, the psychiatric diagnoses of patients with BMS and AO differ substantially.

Effectiveness of milnacipran for the treatment of chronic pain in the orofacial region

OBJECTIVES

The effect of milnacipran for the treatment of chronic pain in the orofacial region, including burning mouth syndrome (BMS) and atypical odontalgia (AO), was assessed while accounting for the influence of concurrent depressive symptoms on the pain-relieving effect.

METHODS

Milnacipran was administered for 12 weeks to 36 patients with chronic pain in the orofacial region (3 men and 29 women, aged between 22 and 76 years with a mean age of 59 years). Of those patients, 22 and 10 patients had BMS and AO, respectively. The initial dose of milnacipran was 15 mg a day, and the dose was raised up to 100 mg a day. Pain was assessed using the visual analog scale, and symptoms of depression were evaluated using the Hamilton Depression Rating Scale at baseline and at weeks 1, 2, 4, 6, 8, 10, and 12 of the study treatment.

RESULTS

Data from 32 patients who completed the study were included in the analysis. The visual analog scale score significantly decreased after the 12-week treatment, and it showed a similar time course of decline irrespective of concurrent depressive symptoms during the 12 weeks.

CONCLUSIONS

Treatment with milnacipran resulted in a significant improvement of chronic pain in the orofacial region irrespective of concurrent symptoms of depression. The present results suggested that milnacipran may be an effective agent for treatment of such disorders.

Idiopathic ophthalmodynia and idiopathic rhinalgia: two topographic facial pain syndromes

OBJECTIVE

To describe 2 topographic facial pain conditions with the pain clearly localized in the eye (idiopathic ophthalmodynia) or in the nose (idiopathic rhinalgia), and to propose their distinction from persistent idiopathic facial pain.

BACKGROUND

Persistent idiopathic facial pain, burning mouth syndrome, atypical odontalgia, and facial arthromyalgia are idiopathic facial pain syndromes that have been separated according to topographical criteria. Still, some other facial pain syndromes might have been veiled under the broad term of persistent idiopathic facial pain.

METHODS

Through a 10-year period we have studied all patients referred to our neurological clinic because of facial pain of unknown etiology that might deviate from all well-characterized facial pain syndromes.

RESULTS

In a group of patients we have identified 2 consistent clinical pictures with pain precisely located either in the eye (n=11) or in the nose (n=7). Clinical features resembled those of other localized idiopathic facial syndromes, the key differences relying on the topographic distribution of the pain.

CONCLUSIONS

Both idiopathic ophthalmodynia and idiopathic rhinalgia seem specific pain syndromes with a distinctive location, and may deserve a nosologic status just as other focal pain syndromes of the face. Whether all such focal syndromes are topographic variants of persistent idiopathic facial pain or independent disorders remains a controversial issue.

Reliability of intraoral quantitative sensory testing (QST)

The German Research Network on Neuropathic Pain (DFNS) has recommended a protocol with 13 quantitative sensory testing (QST) measures for detecting somatosensory abnormalities. Reliability is an important scientific property and has been adequately tested for cutaneous QST. This study evaluates intraoral sites for which no reliability trials have yet been published. Inter- and intra-examiner reliability of 13 QST measures at intra- and extraoral trigeminal sites were investigated. Twenty-one healthy volunteers from Malmö University, Malmö, Sweden (13 women and 8 men, mean age 40.4 years, range 24-71) participated. Two independent examiners previously trained in the DFNS QST protocol examined the participants using the entire protocol. Each participant was examined twice on the same day, once by each examiner (inter-examiner reliability). After 1-3 weeks, one examiner re-examined all participants (intra-examiner reliability). The measurements were made on the skin of the right cheek, the tip of the tongue, and bilaterally on the gingival mucosa of the upper premolar region. The intraclass correlation coefficient (ICC) or kappa was used to calculate variations. Most tests had acceptable to excellent inter-examiner (ICC 0.41-0.89) and intra-examiner (ICC 0.43-0.87) reliability. For each test, inter- and intra-examiner reliabilities at intra- and extraoral sites were similar. No significant differences between right and left sides were found intraorally. We conclude that inter- and intra-examiner reliabilities of most QST measures are acceptable for assessing somatosensory function in the orofacial region.

Clinical investigation of patients who develop neuropathic tooth pain after endodontic procedures

INTRODUCTION

This study aimed to determine the characteristics of patients with neuropathic tooth pain (NTP) who were selected from a group of patients who developed persistent pain after undergoing endodontic procedures.

METHODS

Of 271 patients who had chronic persistent pain that did not respond to previous endodontic procedures and were referred to the Endodontic Team of the Nippon Dental University Hospital, 16 patients (5.9%; mean age, 46.8 years; 13 women) who fulfilled the diagnostic criteria for NTP were recruited. The inclusion criteria for the patients were the presence of chronic persistent pain and other pain-related symptoms, despite the absence of major pathology.

RESULTS

Pain predominantly occurred in the maxilla (14 patients). In 10 patients (62.5%), NTP developed after retreatment. Daily application of tricyclic antidepressants produced pain relief in 11 patients (68.8%).

CONCLUSIONS

These results indicated that NTP is a rare type of chronic intractable endodontic pain and that careful diagnosis of NTP is important.

Is there hope for chronic pain and headache?

Currently the clinical needs for pain and headache management are not met. Despite the numerous and exciting recent advances in understanding the molecular and cellular mechanisms that originate pain, we cannot yet fully explain the mechanism underlying the biology of chronic pain. Pain is a natural mechanism preserving our species survival; however, when the protective quality is lost, physiologic changes to the peripheral and central nervous systems result in the formation of chronic pain states. Once we understand how this chronic pain state is created, either through genetic, environmental, therapeutic, or other triggers we may be able to enhance our species existence, limiting maladaptive pain and suffering. The future therapeutic targets will need to address the genetics, neurophysiologic changes of the neurons and brain as well as help control immune systems including the glia. The key to successful headache and pain therapy is research aimed at prevention and minimizing the plastic changes triggering chronic pain.

Effect of local anesthesia on atypical odontalgia – A randomized controlled trial

The aim of the study was to evaluate the analgesic effect of lidocaine in a double-blind, controlled multi-center study on patients with atypical odontalgia (AO)--a possible orofacial neuropathic pain condition. Thirty-five consecutive AO patients (range 31-81 years) with a mean pain duration of 7.2 years (range 1-30 years) were recruited from four different orofacial pain clinics in Sweden. In a randomized cross-over design, 1.5 ml local anesthesia (20mg/ml lidocaine and 12.5 microg/ml adrenaline) or 1.5 ml saline (9 mg/ml NaCl solution) (placebo) was injected to block the painful area. The VAS pain scores showed an overall effect of time (ANOVA: P<0.001) and treatment (ANOVA: P=0.018) with a significant interaction between the factors (ANOVA: P<0.001). Overall, VAS pain relief was significantly greater at 15-120 min following the lidocaine injections compared to the placebo injections (Tukey: P<0.05). All patients demonstrated significant disturbances in somatosensory function on the painful side compared to the non-painful side as revealed by quantitative sensory tests, however, only one significant inverse correlation was found between percentage pain relief and the magnitude of brush-evoked allodynia (Spearman: P<0.01). In conclusion, AO patients experienced significant, but not complete, pain relief from administration of local anesthetics compared with placebo. The findings indicate that the spontaneous pain in AO patients only to some extent is dependent on peripheral afferent inputs and that sensitization of higher order neurons may be involved in the pathophysiology of AO.

Blink reflexes in patients with atypical odontalgia and matched healthy controls

Atypical odontalgia (AO) is an orofacial pain condition which has been suggested to involve neuropathic pain mechanisms. The aim of this study was to use a brain stem reflex to investigate craniofacial nociceptive mechanisms in AO. In 38 AO patients and 27 matched healthy controls, the R2 component of the blink reflex (BR) was elicited using a "nociceptive-specific" electrode and recorded with surface electromyography electrodes on both orbicularis oculi muscles. The BR was tested by stimulation of both sides of the face of the participants before, during, and after an intraoral pain provocation test with capsaicin. The data were analyzed with three- and four-way mixed-model analyses of variance. The root mean square value of the ipsilateral R2 (R2i) was significantly reduced in patients compared with controls (P=0.046). No differences in R2 between stimulation sides were detected in either group (P>0.757). In all participants, R2 responses and the intensity of the pain evoked by the electrical stimulus were decreased during and after application of capsaicin compared with baseline (P<0.001). In patients, R2i onset latencies were significantly prolonged compared with controls (P=0.031). The present data show disturbances in the central processing of craniofacial information and that endogenous pain inhibitory systems in AO patients and healthy controls were activated to a similar degree by an acute intraoral nociceptive input. Additional clinical research with AO patients will be needed to determine to what extent neuropathic pain mechanisms are involved in this pain condition.

Drugs for pain management in dentistry

Pain is one of the most common reasons patients seek dental treatment. It may be due to many different diseases/conditions or it may occur after treatment. Dentists must be able to diagnose the source of pain and have strategies for its management. The '3-D's' principle--diagnosis, dental treatment and drugs--should be used to manage pain. The first, and most important, step is to diagnose the condition causing the pain and identify what caused that condition. Appropriate dental treatment should then be undertaken to remove the cause of the condition as this usually provides rapid resolution of the symptoms. Drugs should only be used as an adjunct to the dental treatment. Most painful problems that require analgesics will be due to inflammation. Pain management drugs include non-narcotic analgesics (e.g., non-steroidal anti-inflammatory drugs, paracetamol, etc) or opioids (i.e., narcotics). Non-steroidal anti-inflammatory drugs (NSAIDs) provide excellent pain relief due to their anti-inflammatory and analgesic action. The most common NSAIDs are aspirin and ibuprofen. Paracetamol gives very effective analgesia but has little anti-inflammatory action. The opioids are powerful analgesics but have significant side effects and therefore they should be reserved for severe pain only. The most commonly-used opioid is codeine, usually in combination with paracetamol. Corticosteroids can also be used for managing inflammation but their use in dentistry is limited to a few very specific situations.

Orofacial Pain--Part II: Assessment and management of vascular, neurovascular, idiopathic, secondary, and psychogenic causes

Chronic orofacial pain is a common health complaint faced by health practitioners today and constitutes a challenging diagnostic problem that often requires a multidisciplinary approach to diagnosis and treatment. The previous article by the same authors in this issue discussed the major clinical characteristics and the treatment of various musculoskeletal and neuropathic orofacial pain conditions. This second article presents aspects of vascular, neurovascular, and idiopathic orofacial pain, as well as orofacial pain due to various local, distant, or systemic diseases and psychogenic orofacial pain. The emphasis in this article is on the general differential diagnosis and various therapeutic regimens of each of these conditions. An accurate diagnosis is the key to successful treatment of chronic orofacial pain. Given that for many of the entities discussed in this article no curative treatment is available, current standards of management are emphasized. A comprehensive reference section has been included for those who wish to gain further information on a particular entity.