Classification of Orofacial Pain · 2020. 7. 3. · Classification of Orofacial Pain Gary D....

Classification of Orofacial Pain

Gary D. Klasser, Jean-Paul Goulet, Antoon De Laat, andDaniele Manfredini

AbstractDesigning a classification system for any dis-ease entity, let alone orofacial pain and morespecifically for temporomandibular disorders,is quite the task. Unfortunately, this is madeeven more difficult due to the many conditions,both physical and psychosocial, that must beaccounted for when undertaking this challengefor these aforementioned entities. In order toappreciate the utility of classification systems,it is first necessary to gain an understandingand comprehension as to their importance andhow it may be optimally operationalized forboth clinical and research activities. Other con-siderations that must be taken into account are

past and present classification systems thathave been espoused by various organizations.Each of these needs to be carefully evaluatedwithin a framework of their inherent advan-tages while exposing their limitations. Thesepreviously established classification systemsmust then be integrated with newly proposedexpanded upon or modified systems as a resultof recent findings from contemporaryevidenced-based scientific literature. Hope-fully, this will lead to an “ideal classificationsystem”whereby other factors such as geneticsand neurobiological process can be reviewedfor inclusion in this expanded schema. Addi-tionally, adopting newer approaches, such asfollowing ontological principles, will result ina more thorough and comprehensive classifi-cation system which ultimately will assist theclinician in providing improved diagnosis, theresearcher in studying more homogenousgroups, and the patient in receiving moredirected and individualized interventions.

KeywordsOrofacial pain • Temporomandibular disor-ders • Classification systems • Taxonomy •Ontology

G.D. Klasser (*)Department of Diagnostic Sciences, School of Dentistry,Louisiana State University Health Sciences Center, NewOrleans, LA, USAe-mail: [email protected]

J.-P. GouletFaculté de Médecine dentaire, Université Laval, Québec,QC, Canadae-mail: [email protected]

A. De LaatDepartment of Oral Health Sciences, K.U. Leuven,Leuven, Belgium

Department of Dentistry, University Hospitals Leuven,Leuven, Belgiume-mail: [email protected]

D. ManfrediniSchool of Dentistry, University of Padova, Padova, Italye-mail: [email protected]

# Springer International Publishing AG 2016C.S. Farah et al. (eds.), Contemporary Oral Medicine,DOI 10.1007/978-3-319-28100-1_29-1

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ContentsIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Development Strategies Towards a ClassificationSystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Current Orofacial Pain Classification Systems(General) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

International Association for the Study of Pain . . . . . . 4International Headache Society . . . . . . . . . . . . . . . . . . . . . . . 5American Academy of Craniofacial Pain . . . . . . . . . . . . . 8

Current TMD Classification Systems . . . . . . . . . . . . . . 9RDC-TMD to DC-TMD and the Expanded TMD

Taxonomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Proposed Classification Systems . . . . . . . . . . . . . . . . . . . . 12Classification of Chronic Idiopathic Orofacial Pain:

Woda et al. (2005) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Classification of TMJ Disorders: Stegenga (2010) . . . 12Classification Profile of TMD Patients:

Machada et al. (2012) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Classification of Orofacial Pains: Okeson (2014) . . . . 13Psychosocial Subtyping of TMD Patients:

Suvinen et al. (2005) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Advantages and Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Futures Classification Systems . . . . . . . . . . . . . . . . . . . . . . 15Axis III: Genetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Axis IV: Neurobiological . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Taxonomy and Ontology: A New Approachfor Classification Systems . . . . . . . . . . . . . . . . . . . . . . . 18

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Introduction

A classification is defined as a “systematicarrangement in groups or categories according toestablished criteria” (Merriam-Webster 2015).A classification allows the definition of specificentities according to specific characteristics. Ingeneral medicine and thus for orofacial pain(OFP), the characteristics of such an ideal diag-nostic system could be derived from the etiology,pathophysiology, diagnosis, and/or managementof a specific disease or disorder. For the clinician,a correct definition and classification is importantto name and classify the specific disease entitysince it will assist in planning the managementand in discussing the prognosis with the patient.

For the patient, receiving a clear and definitivediagnosis allows for a better understanding andacceptance of aspects related to etiology and path-ophysiology, promotes inclusion to a specificgroup instead of feeling “in the dark,” and facili-tates acceptance of the different steps of manage-ment. For researchers, it is imperative to havehomogenous groups when designing clinicalstudies, and for communication among each other.

An ideal classification system would need tosatisfy several requirements (Fillingim et al.2014): it should be exhaustive (comprising allclinical diseases or disorders belonging to thefield of interest), biologically plausible (the symp-toms and signs should match with known biolog-ical processes), mutually exclusive (there shouldbe no overlap between disease entities because ofcommon symptoms), clinically useful (so that itcan be used to help in treatment and prognosis),reliable (consistently applicable in a reproducibleway between clinicians and over time), and simplefor practical use. Most of the current classificationsystems regarding OFP suffer from deficits in atleast one of these qualities. In addition, sinceseveral independent groups of clinicians (originat-ing from different disciplines) try to build a clas-sification, several disease entities have beendefined differently, and this is further complicatedwhen attempts are made to implement newinsights resulting from ongoing research (Wodaand De Laat 2014).

As pointed out further in this chapter, there isno consensus (yet) regarding a universal andunique classification of OFP. Such a classificationrequests the support of a majority of clinicians andresearchers and would ideally also implementnewer insights regarding the individual differ-ences at a patient level to an otherwise identicaldiagnosis. The most recent attempt to start thisprocess is made by the ACTTION-AAPTapproach (Fillingim et al. 2014) where – in linewith the biopsychosocial model for pain – theimportance of a multiaxial evaluation and charac-terization is advocated.

2 G.D. Klasser et al.

Development Strategies Towardsa Classification System

Over time, several strategies have been developedin order to build a classification system for OFP,all with their advantages and limitations (Wodaand De Laat 2014). This section will attempt toprovide an overview of these ongoing efforts.

Traditionally, the oldest attempts to classifydiseases or disorders were based upon expertopinion, and an authority-based consensus,mostly focused on particular organ-systems orpathophysiological processes. Several societiesand medical subdisciplines created task forces ofexperts to share their knowledge and experienceand develop a restricted set of criteria to denom-inate a set of particular diagnoses. These clinicalentities were, to the extent possible, organized in ahierarchical way so as to create the classification.Examples of this approach are the classificationsystems of the International Headache Society(IHS) (Headache Classification Committee of theInternational Headache Society 2013), the Inter-national Association for the Study of Pain (IASP)(Merskey and Bogduk 1994), and the ResearchDiagnostic Criteria for Temporomandibular Dis-orders (RDC-TMD) (Dworkin and LeResche1992). Using diagnostic criteria can facilitate thesearch for homogeneous groups that would bebeneficial for both clinicians and researchers.However, certain inherent problems arisewhereby a selected set of signs and symptoms isused to characterize an already selected group asthis does not prevent the overlapping of diseaseentities. In addition, if a group of patients isselected on the basis of the criteria, it is notknown whether they all belong to a single diseaseor that it is a sample of (partially) overlappingdisease entities. The specific criteria in such adiagnostic system, however, can be evaluatedand tested for their reliability, specificity, and sen-sitivity, and this has been done (e.g., RDC-TMD)resulting in refinement and adjustment of some ofthe criteria (Schiffman et al. 2010a). Unfortu-nately, this method has also the limitation that“circular reasoning” is possible since the

validation is done on the basis of an “a priori”set of inclusion criteria.

In contrast to the method of diagnostic criteria,the methodology of cluster analysis does notdepart from an already existing disease entity,organ system, or pathophysiological process, butallows for statistical grouping within a dataset ofsigns and symptoms (Woda et al. 2005). Thistechnique to classify groups of patients surpassesthe organ system/specific tissue involved in thepain and might better approach a mechanism-based classification. In a next step, diagnosticcriteria for each cluster are necessary, which inturn need to be tested for validity, specificity, andsensitivity.

Recently, a more theoretical reflection on thebasis of ontological principles has been advocated(further discussion presented in section “Taxonomyand Ontology: A New Approach for ClassificationSystems) (Nixdorf et al. 2012). Applying this the-oretical approach helps in the development of cleartaxonomy, irrespective of new developments inetiological or pathophysiological issues. Ideally,this methodology would be applied to the diseaseentities emerging from previous cluster analysis.

In order to address the existing confusion cre-ated by the many pain classifications, to imple-ment also the new developments regarding theparadigm used to explain the genesis and experi-ence of pain (the biopsychosocial model) as wellas the call for a mechanism-based approach todiagnosis, a large-scale multidisciplinary public-private partnership was established (Fillingimet al. 2014). The ultimate goal of the ACTTION-AAPT project is to satisfy the urgent need todevelop a systematic, standardized, andevidence-based pain classification system appli-cable to all common chronic pain syndromes thatalso takes into account the biopsychosocial mech-anisms. Such classification, integrating neurobio-logical and biopsychosocial mechanisms, wouldimprove management selection and patient out-come, would facilitate communication betweenclinicians and researchers, and would be of benefitin research design and in education.

Classification of Orofacial Pain 3

Current Orofacial Pain ClassificationSystems (General)

International Association for the Studyof Pain

Thirty years ago the IASP became the first inter-national organization to introduce a provisionalcompilation of chronic pain syndromes that canaffect any part of the body. The Subcommittee onTaxonomy recognized this as the beginning of acontinuous review process that would addressgaps, inaccuracies, and inconsistencies raised byanyone with expertise in the field of pain for futuremodifications and improvements. While this firstedition provided an overall acceptable classifica-tion of relevant chronic pain syndromes to many, anumber of changes were introduced in the seconditeration published in 1994 and this was followedby more recent updates in 2011 and 2012(Merskey and Bogduk 1994). New conditionswere added, names were changed, and terms notdescribing specific syndromes were rejected. Inspite of significant advances in classifying manyconditions, very few changes were introduced tothe head and face pain syndromes.

This IASP classification system adopted anarrangement of pain syndromes in nine majorcategories regrouped either under generalizedconditions that can affect various parts of thebody or more localized conditions found at spe-cific body sites. More than 400 pain syndromesare listed in 33 subcategories. The taxonomyincludes a systematic description of pain syn-dromes with specific emphasis placed on thecase definition andmain pain features. In addition,the IASP developed a scheme enabling the codi-fication of each diagnosis in a more detailed man-ner on the basis of five axes that include: (1) bodyregion, (2) systems involved, (3) temporal char-acteristic of pain in terms of pattern of occurrence,(4) patient’s statement of intensity coupled withtime since onset of the pain, and (5) etiology.

Clinical phenotypes of OFP-related disordersare found under the major category “Relativelylocalized syndromes of the head and neck” that is

further divided in seven subcategories. Almosttwo-third of the 66 pain-related syndromes listedrepresent an OFP condition and depending on thesource and structure involved these are classifiedinto one of the five subcategories presented inTable 1. While the purpose of the IASP is tooffer a compilation of chronic pain syndromes, afew acute conditions are interwoven into the clas-sification scheme with the purpose of pointing outcontrast with other chronic pain entities. This isparticularly true for Group IV “Lesions of the ear,nose, and oral cavity” that includes conditions likemaxillary sinusitis, odontalgia “toothache 1, 2,and 3,” respectively, due to dentino-enameldefects, pulpitis, periapical periodontitis orabscess, and dry socket for which the usual coursewill rarely exceed a week or so.

More recently, the IASP interacting with theWorld Organization (WHO) established a TaskForce to develop a new pragmatic classificationof chronic pain after noticing the discrepanciesbetween the actual epidemiology of chronic painand the diagnostic codes included in the currentversion of the International Classification of Dis-eases (ICD) of the WHO. The aim is to simplifyand better standardize the categorization ofchronic pain conditions so it could be used inprimary care as well in clinical settings for spe-cialized pain management, while also fitting intothe general framework of the upcoming 11th revi-sion of the ICD. The new ICD scheme categorizeschronic pain into seven (7) groups of disorderswith priority given first to pain etiology, then tounderlying pathophysiological mechanisms, andlastly to body sites. Moreover, the principle ofmultiple parenting that allows the same diagnosisto be assigned to more than one category isapplied when needed. The seven groups ofchronic pain disorders serving as an umbrellaare: (1) chronic primary pain, (2) chronic cancerpain, (3) chronic posttraumatic and postsurgicalpain, (4) chronic neuropathic pain, (5) chronicheadache and orofacial pain, (6) chronic visceralpain, and (7) chronic musculoskeletal pain(Treede et al. 2015).


Advantages and limitations: The classifica-tion of chronic pain in the ICD is in the process ofbeing overseen by peer review. As for the currentIASP classification, with its five axes, it offers themost exhaustive and elaborate system for codingchronic pain cases. As many as ten differententries are possible per diagnosis within eachaxis, however, the coding is not necessarily auser friendly task. The IASP places emphasis onthe description of pain syndromes and diagnosticcriteria are provided only when possible and in

various formats. While they may have face andcontent validity there are no data yet on theiraccuracy. Within the context of OFP-related dis-orders, the IASP classification has very limitedvalue for the diagnosis of temporomandibular dis-orders (TMDs). Beside the arthritides, all the otherconditions are collapsed under the old denomina-tion “Temporomandibular Pain and DysfunctionSyndrome.” The reluctance of the IASP to adoptand integrate the classification criteria of otherorganizations with special interest for pain diag-nosis in specific body parts has significant draw-backs. For categories like primary headaches andneuralgias of the head and neck, similar condi-tions can have different names and diagnosticcriteria. In addition, there are conditions forwhich no counterpart exists in the IASP scheme.Even though the IASP provides a crosswalk to theIHS coding system for headaches, it neverthelesscreates some confusion. It is hard to dismiss anyof the current five axes of the IASP classification,but the addition of one giving due consideration tothe biopsychosocial and behavioral factors of thepatient’s pain experience would certainly be use-ful (Turk and Rudy 1987; Turk 1990; Fillingimet al. 2014). We know that regardless of the bio-medical diagnosis these may influence treatmentoutcomes in subgroups of chronic pain patients(Turk 1990).

International Headache Society

Not long after the IASP created their classificationsystem, the IHS published the International Clas-sification of Headache Disorders (ICHD) in 1988.It was first updated in 2004 and more recently in2013 (ICHD-3) based on changes supported byquality published evidence (Headache Classifica-tion Committee of the International HeadacheSociety 2013). The IHS offers a compilation ofall headache-related disorders and painful cranio-facial neuropathies along with other facial pains ina three part classification system. Part I and Part IIare, respectively, devoted to primary and second-ary headaches and composed of 12 major catego-ries. Part III is a repertory of painful cranialneuropathies, other facial pains, and headaches

Table 1 IASP subcategories of “Relatively localized syn-dromes of the head and neck” that include orofacial pain-related disorders with the list of conditions for Group IIIand IV (Merskey and Bogduk 1994)

Relatively localized syndromes of the head and neck

Group II: Neuralgia of the head and faceGroup III: Craniofacial pain of musculoskeletal origin1. Acute tension headache2. Tension headache: Chronic form (Scalp musclecontraction headache)3. Temporomandibular pain and dysfunction syndrome(also called Temporomandibular disorder)4. Osteoarthritis of the temporomandibular joint5. Rheumatoid arthritis of the temporomandibular joint6. Dystonic disorders, facial dyskinesia7. Crushing injury of head and faceGroup IV: Lesions of the ear, nose, and oral cavity1. Maxillary sinusitis2. Odontalgia: Toothache 1. Due to dentino-enameldefects3. Odontalgia: Toothache 2. Pulpitis4. Odontalgia: Toothache 3. Periapical periodontitis andabscess5. Odontalgia: Toothache 4. Tooth pain not associatedwith lesion (Atypical odontalgia)6. Glossodynia and sore mouth (aka Burning tongue orOral dysesthesia)7. Cracked tooth syndrome8. Dry socket9. Gingival disease, Inflammatory10. Toothache, cause unknown11. Diseases of the jaw, inflammatory conditions12. Other and unspecified pain in the jaw13. Frostbite of faceGroup V: Primary headache syndromes, vasculardisorders, and cerebrospinal fluid syndromesGroup VI: Pain of psychological origin in the head, face,and neck


arranged in two distinctive categories, one for theprimary painful craniofacial neuralgias andrelated facial pain and the other for headachesnot elsewhere classified or unspecified (Table 2).

The ICHD is primarily a hierarchical classifi-cation system for headaches with well-operationalized diagnostic criteria. Interestingly,it allows the clinician to decide how detailed thediagnosis should be within each of the 12 majorheadache categories when looking through thesubtypes of headache disorders. Thus, the codingcan range from one digit up to five dependingupon the detail of the criteria employed in thediagnosis. Clinical features and diagnostic criteriaare provided for more than 200 subforms ofheadache-related disorders with the goal of hav-ing the coding system eventually synchronizedwith the World Health Organization’s ICD-11.

Of particular interest for oral medicine special-ists are Category 11 within Part II and more spe-cifically Category 13 within Part III. Category11 focuses on secondary headache as a

comorbidity of pain disorders arising fromorofacial and neck structures while subcategories11.6 and 11.7 includes, respectively, diagnosticcriteria for headache attributed to disorder of theteeth or jaw, and headache attributed to TMDs. Asfor Category 13, it provides a list and a detaileddescription along with diagnostic criteria for cod-ing the painful craniofacial neuropathies andrelated facial pain conditions. Upon viewingTable 3 one can better appraise similarities anddifferences between the ICHD-3 and the IASP forthe classification scheme and denomination ofcraniofacial neuralgias.

Advantages and limitations: The IHS classi-fication is easy to use and depending on howspecific one needs to rule-in a diagnosis it offersa flexible hierarchical coding system and diagnos-tic criteria for all the conditions in a standardizedformat. The diagnostic criteria are clearly pre-sented and easy to follow. These are empiricallyderived and have good face and content validity,but their accuracy has yet to be tested in fieldstudies. The ICHD-3 is mostly useful for patientswith headache, facial neuralgia, or painful trigem-inal neuropathy. All the other clinical phenotypesof OFP-related disorders are not described in thisclassification system, thus limiting its general usein clinical situations involving a spectrum of OFPpatients (Zebenholzer et al. 2005; Benoliel et al.2008, 2010). One can overcome this limitation byreferring to other classification systems. As men-tioned previously for the IASP axes, no due con-sideration is given to the biopsychosocial andbehavioral factors in any part of the ICHD-3.

American Academy of Orofacial PainThe American Academy of Orofacial Pain(AAOP) and its worldwide sister organizationsregroup dentists and allied professional practi-tioners with interest in TMDs and face pain. In1990, the AAOP published its first handbook andguidelines that focused solely on the diagnosisand management of TMDs. From the second tothe present fifth edition (2013) however, theAAOP have broadened its guidelines for assess-ment, diagnosis, and management to include allclinical phenotypes of OFP-related disorderswhether it is acute or chronic (De Leeuw and

Table 2 Classification system of the International Head-ache Society for headaches and facial pains (ICHD-3)(Headache Classification Committee of the InternationalHeadache Society 2013)

Part one: Primary headaches1. Migraine2. Tension-type headache3. Trigeminal autonomic cephalalgias4. Other primary headache disordersPart two: Secondary headaches5. Headache attributed to trauma or injury to the headand/or neck6. Headache attributed to cranial or cervical vasculardisorder7. Headache attributed to nonvascular intracranialdisorder8. Headache attributed to a substance or its withdrawal9. Headache attributed to infection10. Headache attributed to disorder of homeostasis11. Headache or facial pain attributed to disorder of thecranium, neck, eyes, ears, nose, sinuses, teeth, mouth, orother facial or cervical structure12. Headache attributed to psychiatric disorderPart three: Painful cranial neuropathies, other painsand other headaches13. Painful cranial neuropathies and other facial pains14. Other headache disorders


Klasser 2013). Except for TMDs, no detailedclassification and listing are provided by theAAOP for other subtypes of OFP disorders.Nevertheless, how the AAOP handbook is orga-nized enables one to capture the scope and breadthof OFP conditions while also providing an infor-mal classification scheme mainly based on a topo-graphical approach and various tissue, structures,or organ systems that can give rise to oral andcraniofacial pain. The chapter headings listed inTable 4 presents the different categories of cranio-facial pain phenotypes that exemplifies what isconsidered as the AAOP classification scheme.Of particular interest is the designation providedby the AAOP when referring to neuropathic painand primary headache disorders. The

endorsement of the ICHD-3 scheme and denom-inations developed by the IHS avoid confusionand lack of concordance. As for TMDs, theAAOP uses the expanded taxonomy developedjointly with the International RDC-TMD Consor-tium Network that is presented in Table 5 (Pecket al. 2014). The expanded taxonomy is however acompilation of all types of TMD and hence itincludes painful and non-pain conditions.

Advantages and limitations: Although theAAOP guidelines do not offer a comprehensiveclassification scheme and specific listing ofOFP-related conditions but for TMDs, it never-theless provides a taxonomic structure that coversthe entire spectrum of OFP conditions (Peck et al.2014). Choosing to refer to the ICHD-3 for

Table 3 ICHD-3 Category 13 listing for painful cranial neuropathies and other facial pains and IASP Group II listing forNeuralgia of the Head and Neck (Merskey and Bogduk 1994; Headache Classification Committee of the InternationalHeadache Society 2013)

ICHD-3 IASP

13.1 Trigeminal neuralgia13.1.1 Classical trigeminal neuralgia

13.1.1.1 Classical trigeminal neuralgia, purely paroxysmal13.1.1.2 Classical trigeminal neuralgia with concomitant

persistent facial pain13.1.2 Painful trigeminal neuropathy

13.1.2.1 Painful trigeminal neuropathy attributed to acuteHerpes zoster

13.1.2.2 Postherpetic trigeminal neuropathy13.1.2.3 Painful posttraumatic trigeminal neuropathy13.1.2.4 Painful trigeminal neuropathy attributed to multiple

sclerosis (MS) plaque13.1.2.5 Painful trigeminal neuropathy attributed to a space-

occupying lesion13.1.2.6 Painful trigeminal neuropathy attributed to other

disorders13.2 Glossopharyngeal neuralgia13.3 Nervus intermedius (facial nerve) neuralgia13.3.1 Classical nervus intermedius neuralgia13.3.2 Nervus intermedius neuropathy attributed to Herpes

zoster13.4 Occipital neuralgia13.5 Optic neuritis13.6 Headache attributed to ischemic ocular motor nerve palsy13.7 Tolosa-Hunt syndrome13.8 Paratrigeminal oculosympathetic (Raeder’s) syndrome13.9 Recurrent painful ophthalmoplegic neuropathy13.10 Burning mouth syndrome (BMS)13.11 Persistent idiopathic facial pain (PIFP)13.12 Central neuropathic pain13.12.1 Central neuropathic pain attributed to multiple sclerosis

(MS)13.12.2 Central post-stroke pain (CPSP)

1. Trigeminal neuralgia2. Secondary trigeminal neuralgia from thecentral nervous system3. Secondary trigeminal neuralgia from facialtrauma4. Acute herpes zoster5. Postherpetic neuralgia6. Geniculate neuralgia (Ramsey-HuntSyndrome)7. Neuralgia of the nervous intermedius8. Glossopharyngeal neuralgia9. Neuralgia of the Superior laryngeal nerve10. Occipital neuralgia11. Hypoglossal neuralgia12. Glossopharyngeal pain from trauma13. Hypoglossal pain from trauma14. Tolosa-hunt Syndrome15. SUNCT Syndrome16. Reader’s (paratrigeminal) Syndrome


headaches and craniofacial neuralgia, the AAOPensures better communication through alreadyrecognized denominations of entities thus reduc-ing confusion and misunderstandings. Clearoperationalized and validated diagnostic criteriaare only available for the most common pain-related TMDs through the Diagnostic Criteria forTemporomandibular Disorders (DC/TMD) classi-fication system embedded in the expanded TMDtaxonomy. While there is an enormous task aheadregarding the validation of existing empiricallyderived diagnostic criteria for other OFP

conditions, the fact that pain-related TMDs repre-sent the most common type of nondental OFPmakes the validated DC/TMD highly useful forpatient triage and clinical decision making. As forthe psychological and behavioral factors that mayimpact on the patient’s pain experience andresponse to treatment, the AAOP fully recognizesthe importance of implementing a dual-axis diag-nostic framework but does not recommend anyspecific classification system for that matter.

American Academy of Craniofacial Pain

The American Academy of Craniofacial Pain(AACP) is another professional organizationwith interest in the assessment, diagnosis, andmanagement of craniofacial pain disorders thatpublished its own guidelines in 2009 (AmericanAcademy of Craniofacial Pain 2009). The AACPhas not developed its own classification systembut uses existing taxonomies. Hence, for neural-gias of the head and neck and for headache disor-ders, the AACP follows the classification by theIASP for the former, and the IHS classificationschemes for the latter. As for TMDs it uses theclassification proposed by Pertes and Gross formasticatory muscle and joint disorders (Pertesand Gross 1995). Craniofacial pain disordersstemming from other structures or anatomicalparts are specifically addressed throughout theAACP handbook in dedicated chapters (Table 6).When comparing Tables 4 and 6, one can seesome similarities on how the AACP and theAAOP categorize oral and craniofacial pain dis-orders, but discrepancies are unveiled upon closerinspection at the list of clinical entities included ineach pain sub-category.

Advantages and limitations: There is no realadvantages for use of the AACP classification struc-tures considering it refers to existing taxonomywhenever possible and for TMDs, the expandedtaxonomy developed jointly by the RDC-TMDInternational Consortium integrates all musculo-skeletal disorders and provides unambiguousoperationalized diagnostic criteria with knownvalidity for the most common disorders. For exam-ple, there are two different listings of masticatory

Table 4 Classification structure of orofacial pain condi-tions from the 5th edition of the American Academy ofOrofacial Pain guidelines (De Leeuw and Klasser 2013)

Vascular and nonvascular intracranial cause oforofacial painHeadache associated with vascular intracranial

disorders (IHS/ICHD-3 code 6.1 to 6.6)Headache associated with nonvascular intracranial

disorders (IHS/ICHD-3 code 7.1 to 7.8)Primary headache disordersMigraine (IHS/ICHD-3 code 1.1 to 1.6)Tension-type headache (IHS/ICHD-3 code 2.1 to 2.4)Cluster headache and other trigeminal autonomic

cephalalgias (IHS/ICHD-3 code 3.1 to 3.5)Neuropathic painEpisodic neuropathic pain (IHS/ICHD-3 code 13.1.1,

13.2, 13.3, 13.9)Continuous neuropathic pain (IHS/ICHD-3 code

13.1.2, 13.10, 13.11, 13.12.2)Dysesthesia

Intraoral pain disordersOdontogenic painNon odontogenic painOral mucosal pain

Temporomandibular disorders (see Table 5)Temporomandibular joint disordersMasticatory muscle disorders

Extracranial causes of orofacial pain and headachesPain stemming from tissues or organs in the head and

neck (IHS/ICHD-3 code 11.1, 11.3 to 11.5)Pain stemming from systemic disease (IHS/ICHD-3

code 13.12.1)Cervicogenic mechanisms of orofacial pain andheadachesCommon cervical spine disorders (IHS/ICHD-3 code

11.2, 11.8, 13.2, 13.4)

IHS International Headache Society, ICHD-3 InternationalClassification of Headache Disorders


muscle conditions in the AACP guidelines, oneunder the heading of “Extracapsular Temporoman-dibular Disorders” and the other under “Temporo-mandibular Disorders” as classified by Pertes andGross (1995; American Academy of CraniofacialPain 2009). Moreover, diagnostic criteria are pro-vided in various formats that go from a precise list ofclinical features (muscle disorders) to a more narra-tive description of the condition (joint disorders).

Current TMD Classification Systems

RDC-TMD to DC-TMDand the Expanded TMD Taxonomy

In 1992 Dworkin and LeResche published the“Research Diagnostic Criteria for Temporoman-dibular Disorders” (RDC-TMD), a dual-axisassessment protocol with operationalized diag-nostic algorithms for the most common TMDs(Dworkin and LeResche 1992). The RDC-TMDis an empirically derived classification system

Table 5 Expanded taxonomy for temporomandibular disorders (Peck et al. 2014)

I. Temporomandibular joint disorders1. Joint pain

A. Arthralgiaa

B. Arthritisa

2. Joint disordersA. Disk disorders1. Disk displacement with reduction2. Disk displacement with reduction with

intermittent locking3. Disk displacement without reduction with

limited opening4. Disk displacement without reduction without

limited openingB. Hypomobility disorders other than disk disorders1. Adhesions/adherence2. Ankylosis

a. Fibrousb. Osseous

C. Hypermobility disorders1. Dislocations

a. Subluxationb. Luxation

3. Joint diseasesA. Degenerative joint disease1. Osteoarthrosis2. Osteoarthritisa

B. Systemic arthritidesa

C. Condylysis/Idiopathic condylar resorptionD. Osteochondritis dissecansE. OsteonecrosisF. NeoplasmG. Synovial chondromatosis

4. Fracturea

5. Congenital/developmental disordersA. AplasiaB. HypoplasiaC. Hyperplasia

II. Masticatory muscle disorders1. Muscle pain

A. Myalgiaa

1. Local myalgiaa

2. Myofascial paina

3. Myofascial pain with referrala

B. Tendonitisa

C. Myositisa

D. Spasma

2. Contracture3. Hypertrophy4. Neoplasm5. Movement disorders

A. Orofacial dyskinesiaB. Oromandibular dystonia

6. Masticatory muscle pain attributed to systemic/centralpain disorders

A. Fibromyalgia/widespread paina

III.Headache1. Headache attributed to TMDa

IV.Associated structures1. Coronoid hyperplasia

aPain-related TMD


based on the biopsychosocial model of pain thatwas primarily intended for research purposes.Axis I allows the rendering of a physical diagnosisfor the most common pain and nonpain-relatedTMDs using a standardized and reliable examina-tion protocol. On the other hand, Axis II toolsenable one to identify the relevant psychosocialcharacteristics of the patients through the assess-ment of the psychological status and the gradingof TMD pain-related disability. The growingappreciation for the RDC-TMD has made it areference protocol for TMD research and that ledto their translation into more than 20 languages(http://www.rdc-tmdinternational.org/). Withtime, the RDC-TMD gained acceptance amongclinicians who began to implement their use in a

clinical setting (Manfredini et al. 2006). A numberof authors started questioning the validity of thediagnostic criteria for an Axis I physical diagnosisand showed the need to improve the originalRDC-TMD (Ohlmann et al. 2006; De Boeveret al. 2008; Schmitter et al. 2008; Steenks and deWijer 2009). This led to the funding of a carefullyplanned multisite Validation Project to assess thecriterion validity of the RDC-TMD Axis I physi-cal diagnosis for the most common TMDs andreviewed all Axis II screening tools for the eval-uation of psychosocial and behavioral factors(Schiffman et al. 2010a). The results of this land-mark study initiated the transition towards thenew evidence-based diagnostic criteria for themost common pain and nonpain-related TMDs(DC-TMD) that were recently implemented forutilization in research and clinical settings(Schiffman et al. 2014; Schiffman and Ohrbach2016). Table 7 presents the list of Axis I physicaldiagnoses that were part of the originalRDC-TMD and compares that to the newDC-TMD along with the sensitivity and specific-ity establishing the level of accuracy for the newdiagnostic criteria.

While the DC-TMD for the most commonTMDs were finalized, a joint effort by theRDC-TMD International Consortium Networkand the AAOP led to the development of anexpanded taxonomy (see Table 5) with the inclu-sion of empirically derived expert-based diagnos-tic criteria for the less common TMDs (Peck et al.2014). As mentioned previously, the expandedtaxonomy is inclusive for all subtypes of TMDwhether it causes pain or not. It is important toknow that within this framework, multiple diag-noses are also allowed except for conditionsbelonging to the same subgroup of disorders. Forexample, arthralgia and arthritis are mutuallyexclusive diagnoses within the joint pain categoryand so are the four muscle pain entities and themyalgia subtypes. Hence, that means for jointconditions where pain is not part of the diagnosticalgorithm such as degenerative joint disorder anddisk displacement with or without reduction, adiagnosis of arthralgia or arthritis can also accom-pany the primary diagnosis if joint pain is present.

Table 6 Classification structure of orofacial painaccording to the American Academy of Craniofacial Painguidelines (American Academy of Craniofacial Pain 2009)

Extracapsular temporomandibular disordersMuscle disordersLigament/tendon disorders

Headache painPrimary (IHS/ICHD-3 Part one)Secondary (IHS/ICHD-3 Part two)Other headache (IHS/ICHD-3 Part three code 14)

Neuralgias, nerve trunk and deafferentation painNeuralgia of the head and face (IASP Group II)Viral neuralgiaMiscellaneous facial painCentral cause of craniofacial painSympathetically maintained pain/Complex regional

pain syndromesTemporomandibular disorders (Adapted from Pertesand Gross 1995)Temporomandibular joint disordersMasticatory muscle disordersCongenital and developmental disorders

Myofascial painAdditional structures that can cause craniofacial painEye, ear, hamulus process, hyoid bone, salivary

glands, lymph nodes, occipital nerve, temporal, andcarotid artery.Non odontogenic intraoral pain disordersMucogingival painGlossal pain

IHS International Headache Society, ICHD-3 InternationalClassification of Headache Disorders, IASP InternationalAssociation for the Study of Pain


What mostly distinguishes the DC-TMD fromother classification systems is Axis II aimed toassess the psychosocial and behavioral factorsthat impact on the patients’ pain and can influencetreatment outcome and chronicity (Dworkin et al.2002). One of the Axis II tools is the GradedChronic Pain Scale (available for download at:http://www.rdc-tmdinternational.org/), a simpleseven items questionnaire that measures pain-related disability and intensity (Von Korff et al.1992). This is a simple and easy to use question-naire that can assist the clinician in identifyingpatients with high pain-related disability profileand decreased functioning which then usuallyrequires additional expertise for the implementa-tion of more comprehensive management strate-gies (Kotiranta et al. 2015).

Advantages and limitations: The DC-TMDis the only system that uses standardized andreliable self-report questionnaires, clinical exami-nation procedures, scoring systems, and decisiontrees while also providing estimates regarding thediagnostic accuracy of the history and examina-tion criteria for the most common pain-related andintra-articular TMDs. No other system integratesbiophysical diagnosis to a disability index thatmeasures the impact the pain has on the patient’sbehavior. In addition, the assessment tools forimplementing this dual-axis framework and a

short TMD pain screener questionnaire with verygood sensitivity and specificity are made availablefor download on the International RDC-TMDConsortium Network website (available fordownload at: http://www.rdc-tmdinternational.org/) (Gonzalez et al. 2011).

Except for two subtypes of myalgia (localmyalgia and myofascial pain) what can beexpected in terms of true- and false-positive diag-nosis when using the DC-TMD assessment pro-tocol for pain-related TMD is somewhatpredictable. Sensitivity and specificity that reach80% and 95%, respectively, make the DC-TMDscheme highly recommended to render a defini-tive clinical diagnosis for myalgia, myofascialpain with referral, arthralgia, disk displacementwithout reduction with limited opening, and sub-luxation. On the other hand, because theDC-TMD relies solely on clinical examinationprocedures, the utility is limited regarding theother disk displacement disorders and degenera-tive joint disease that are best assessed with ConeBeam CT and MRI imaging of the joint. With adiagnostic accuracy that is below 70% for truepositive diagnosis (sensitivity), the respectiveDC-TMD for the above mentioned disorders canbe used only to render a preliminary clinical diag-nosis. Finally, it is premature to recommend usingthe operationalized diagnostic criteria that were

Table 7 Original Axis I RDC/TMD and validated Axis I DC/TMDwith sensitivity (Sens.) and specificity (Spec.) values(Dworkin and LeResche 1992; Schiffman et al. 2014)

RDC/TMD (1992) DC/TMD (2014)

I. Muscle disordersA. Myofascial painB. Myofascial pain with limitation

II. Disk displacement disordersA. Disk displacement with reductionB. Disk displacement without reduction with

limited openingC. Disk displacement without reduction

without limited openingIII. Arthralgia and other joint disordersA. ArthralgiaB. OsteoarthritisC. Osteoarthrosis

I. Pain-related temporomandibular disordersA. Myalgia (Sens. 0.90/Spec. 0.99)1. Local myalgia2. Myofascial pain3. Myofascial pain with referral (Sens. 0.86/Spec. 0.98)

B. Arthralgia (Sens. 0.89/Spec. 0.98)C. Headache attributed to TMD (Sens. 0.89/Spec. 0.87)

II.Intra-articular temporomandibular disordersA. Disk displacement with reduction (Sens. 0.34/Spec. 0.92)B. Disk displacement with reduction with intermittent locking

(Sens. 0.38 Spec. 0.98)C. Disk displacement without reduction with limited opening

(Sens. 0.80/Spec. 0.97)D. Disk displacement without reduction without limited opening

(Sens. 0.54/Spec. 0.79)E. Degenerative joint disease (Sens. 0.55/Spec. 0.61)F. Subluxation (Sens. 0.98/Spec. 1.00)


developed for the less common disorders listed inthe expanded TMD taxonomy other than for apreliminary diagnosis. This is because none havebeen tested yet against an acceptable referencestandard. Nevertheless, the expanded TMD tax-onomy still represents the most validated refer-ence classification system for TMDs.

Proposed Classification Systems

Over the years, several classification systems havebeen proposed as alternative options or integra-tions to currently adopted schemes. Some of themfocused on chronic idiopathic OFP (Woda et al.2005), some other addressed specifically the fieldof TMDs (Stegenga 2010; Machado et al. 2012),and others more embedded an all-inclusive pro-posal for OFP (Okeson 2014). They will bereviewed briefly below.

Classification of Chronic IdiopathicOrofacial Pain: Woda et al. (2005)

Based on purported shortcomings of the literatureon the taxonomy of the different forms of chronicidiopathic OFP, a prospective multicenter studywas performed to provide a better framework forintroducing entities such as stomatodynia, atypi-cal odontalgia, atypical facial pain, and facialarthromyalgia within the broader context of OFP(Woda et al. 2005). The authors pointed out thatthose forms of idiopathic OFP are sometimesgrouped together and sometimes considered sep-arate conditions, and so, developed a new taxon-omy based on the results of cluster analysis.

The underlying premise of this proposal wasrather intriguing, since the authors hypothesizedthat the main subgroups of OFP syndromes (i.e.,atypical facial pain, atypical odontalgia,stomatodynia, temporomandibular disorders),which display some common clinical features,may correspond to a single disease expressed indifferent tissues: teeth, bone, oral mucosa, muscle,and joint. Based on that, they assessed the possi-bility of proposing a classification that takes intoaccount the presence of similar signs/symptoms

and thus reflects similar pathophysiological mech-anisms and treatment approaches, rather thantopography, organs, or tissues. In short, the clas-sification system results from a 111-item self-reported questionnaire including questions onpain evaluation, impact of pain on health-relatedquality of life, and psychological self-evaluation.Furthermore, an experienced examiner completedan 8-item record that exited in a tentative diagno-sis. A multivariate analysis trying to identify clus-ters of self-reported and clinically recorded signsand symptoms led to the identification of verysimilar and common mechanisms between condi-tions affecting the different stomatognathic struc-tures. Three subgroups of idiopathic disorderswere thus identified: stomatodynia,arthromyalgia, and atypical facial pain, whosedifferences are essentially based on topographiccriteria.

A notable feature of this proposal is that theterm arthromyalgia is introduced to discriminatethose idiopathic conditions, viz., joint and/or mus-cle pain of uncertain or unknown origin, fromTMD symptoms of certain origin, such as condi-tions linked to general diseases.

Classification of TMJ Disorders:Stegenga (2010)

An interesting proposal for the classification ofTMJ disorders was proposed by Stegenga(2010), who suggested that instead of positionalclassification relating the presence of joint pathol-ogy to the position of the disk, a classificationsystem based on the actual intra-articular struc-tural changes could be more suitable for clinicalpurposes. The point of this classification systemwas that, even if many clinical signs, and mostnotably joint sounds, are explainable with thepresence of disk displacement, the increasingamount of knowledge on the actual pathologicchanges occurring within the joint should haveled to more structurally oriented classificationsystems.

Based on that, two major categories of struc-tural disorders have been identified by the author,viz., the arthritic disorders (i.e., inflammatory


disorders affecting the joint, which are mainlycharacterized by pain and function impairment)and the growth disorders (which are mainly char-acterized by facial asymmetry). In short, theauthor proposed that mechanical derangementsare only one of the possible consequences ofpathological changes occurring in temporoman-dibular joints with a maladaptive load response.Thus, the author suggested classifying TMJ dis-orders into three main categories: arthritic disor-ders, growth disorders, and nonarthritic disorders.The latter are noninflammatory in nature, contraryto the arthritic disorders, which may have amechanical component (i.e., disk displacement),but are related to a joint disease due to tissuechanges at the molecular level and present withpain as the main symptom.

This classification has merits, and years afterits proposal some evidence is developing in sup-port of this concept, but it should be considered ahypothesis-driven, opinion-based, taxonomy thatwas not supported with any specific investigation.

Classification Profile of TMD Patients:Machada et al. (2012)

Also in the TMD field, Machado and colleagues(Machado et al. 2012) performed a large-sampleinvestigation attempting to profile the clinical pre-sentation of diagnostic characteristics of TMDpatients. The authors aimed to simultaneouslyclassify symptomatic patients diagnosed with avariety of TMD subtypes into homogeneousgroups based on their clinical presentation andoccurrence of comorbidities. The study designinvolved a retrospective assessment of more than300 clinical records based on the AAOP guide-lines published in 2008 (De Leeuw 2008), and theresulting diagnoses were clustered into groupsbased on symptoms occurrence.

Based on this analysis, four main symptomaticprofiles were identified: acute muscle pain(35.0%), nonpainful articular impairment(33.9%), acute articular pain (21.0%), and chronicfacial pain (10.1%). Those groups are homoge-neous as for their clinical presentation, and theirnames were suggested by the authors as being

intuitively linked to the time of onset, the location,the presence of pain, and extent of the symptoms.According to the authors, this proposal may shedlight on the most suitable strategy that should beadopted to manage TMD patients seekingtreatment.

Classification of Orofacial Pains:Okeson (2014)

A broadly diffused, opinion-based, comprehen-sive classification scheme for OFP came fromthe work(s) of Okeson (2014). The conceptbehind the proposal is that a reliable pain classifi-cation needs to be based on symptomatology.Based on that, pain conditions may be groupedinto somatic and neurogenous. Somatic painsoccur in response to the stimulation of normalneural receptors, while neurogenous pains origi-nate due to dysfunctional neurologic structures.

According to the proposed classification,somatic pain may be superficial or deep. Theformer may originate from cutaneous ormucogingival sources, which share the followingclinical features: (a) the pain has a bright, stimu-lating quality; (b) subjective localization of thepain is excellent and anatomically accurate;(c) the site of pain identifies the correct locationof its source; (d) response to provocation at thesite of pain is faithful in incidence, intensity, andlocation; (e) the application of a topical anestheticat the site temporarily arrests the pain. Alterna-tively, deep somatic pain may be visceral or mus-culoskeletal in origin, is less accuratelylocalizable by the patient than superficial pain,and may not be proportionally related to the nox-ious stimulus. As a general remark, deep somaticpains share the following features: (a) the pain hasa dull, depressing quality; (b) subjective localiza-tion of the pain is variable and somewhat diffuse;(c) the site of pain may or may not identify thecorrect location of its true source; (d) response toprovocation at the source of pain is fairly faithfulin incidence and intensity; and (e) secondary cen-tral excitatory effects frequently accompany thedeep pain.


Sometimes, the pain felt in somatic structuresmay be actually originating in neurogenous tis-sues. Such conditions have been grouped togetherby the author as neuropathic pains. Those painsusually feature a burning sensation and can pre-sent as either episodic or continuous pain. In hisproposal, the author posited that at least twogroups of episodic neuropathic pains can be iden-tified (i.e., neurovascular pain such as headaches;paroxysmal neuralgic pain such as neuralgias) aswell as three groups of continuous neuropathicpains (i.e., metabolic polyneuropathies; peripheralmediated pain such as deafferentation pain; cen-tral mediated pain such as atypical odontalgia,burning mouth syndrome, and complex regionalpain syndromes).

This classification also encompasses a group ofso-called Axis II psychological conditions, com-prising mood, anxiety, somatoform, and otherdisorders of the psychosocial spectrum that maycomplicate the history taking and clinical exami-nation and should most certainly be taken intoaccount for a definitive diagnosis especially withthe chronification of pain.

Psychosocial Subtyping of TMDPatients: Suvinen et al. (2005)

The importance of Axis II profiling of painpatients has been highlighted in several seminalpapers on TMD, which have been summarized inthe classification proposal of Suvinen and col-leagues (Suvinen et al. 2005). They emphasizedand highlighted that despite variability in termi-nology provided by authors as well as methodol-ogies employed as to how the patients arecategorized, there appears to be at least threemain groups or subtypes of TMD patients basedon the importance of physical versus psychosocialimpairment: (i) a biologically/somatically definedTMD patient group; (ii) an intermediate group,with patients who report fluctuating or recurrentsymptoms of TMD, but are generally viewed as

adaptive copers; and (iii) a complex/psycho-socially dysfunctional TMD patient group.

This identification of patients according to atri-axial schematic may allow more “keys” as towhat is the appropriate method of treatment foreach patient group, but it should be noted that themethod is not directly applicable in a clinicalsetting, since it involves the use of multiple psy-chometric evaluations and needs further valida-tion to be more globally accepted. Interestingly,according to the therapeutic model associatedwith this classification proposal, it is suggestedthat the assessment and subtyping of patients canindicate the most appropriate form of treatment. Inshort, the “simple TMD subtype” appears to bemore biomedically defined and therefore is mostlikely to benefit from relatively simple forms ofconservative management, such as counseling,physical therapies, oral appliances, and medica-tions for the acute phase. The “intermediate TMDsubtype” appears biobehaviorally functional andis likely to benefit from combined biomedical andbiobehavioral approaches of management, basedon the appropriate assessment of possible contrib-uting, aggravating, and maintaining factors. The“complex TMD subtype” appears similar to theminority of patients who may report psychologi-cal distress and psychosocial dysfunction that ispoorly correlated with biomedical and physicalfindings. This group of patients also appears tobe unable to cope and present with higher rates fordepression, somatization, maladaptive copingstrategies, sick-leave, and health care utilization.These patients may be most appropriately man-aged in multidisciplinary pain managementclinics, with appropriate skills to assess also indi-cators for hypochondriasis, somatoform disor-ders, and severe life stress, as well as generalvulnerability to possible idiopathic pain disordersin general. Based on estimates in epidemiologicaland clinical studies, the distribution of these sub-types within the community differs from those inthe tertiary referral clinics, with a preponderancein the simple/intermediate groups and a smallminority in the complex group.


Advantages and Limitations

The above proposals for classification schemesintegrate well the currently available standard ofreference, and all of them feature some strengthsas well as interesting underlying concepts. Not-withstanding, some general remarks are worthy todiscuss.

In the light of currently increasing evidence onthe diminished role of mechanical/occlusal con-cepts for the onset of TMJ disorders (Klasser andGreene 2009; Manfredini et al. 2016) as well asthe poor correlation between disk position andclinical pain symptoms (Manfredini et al. 2009),the suggestion of prolonging the assumption ofthe disk position as a central factor for classifyingpainful (may not be true for purely dysfunctionalconditions) TMJ disorders is not correct seems tobe logical. In addition, improvement in diagnosisand classification as well as knowledge on thepathophysiology of muscle disorders leading topersistent OFP presents another compelling needfor a better understanding of patients’ symptoms(Benoliel et al. 2011). On the other hand, there aresome other relevant factors that are likely moreimportant in the clinical setting. In particular, theimportance of Axis II psychosocial assessment atthe treatment outcome level cripples all “AxisI-alone” classification schemes and limits theirusefulness for clinical use. In addition, the simi-larities of chronic TMD patients’ symptoms pro-file with those of patients receiving other OFPdiagnoses support the view that subtyping TMDsbased only on the location of symptoms (i.e., jointversus muscles) does not take into account for thepossible underlying pathophysiology, which maybe much more similar than believed in the past.

Thus, it is remarkable to point out that thesearch for a suitable classification scheme forTMD and OFP is leading outside the boundariesof the dental profession. Dental occlusion can nolonger viewed as a main factor for the onset of anyof the above pain conditions. The amount of liter-ature suggesting that the association of dentalocclusion features with TMDs is, at best, veryweak, is so important to auspice that classic,mechanical views of TMDs as occlusion-relateddisorders will be definitively abandoned (Turp

et al. 2008). The ethical concerns related withthis issue have been recently debated (Manfrediniet al. 2011; Reid and Greene 2013).

Futures Classification Systems

In 2009, a momentous two and a half day work-shop was held in Miami, Florida, involving36 invited participants from 12 countriesrepresenting 11 international organizations. Theworkshop was organized by the InternationalRDC ⁄TMD Consortium Network of the Interna-tional Association for Dental Research (IADR)and the Orofacial Pain Special Interest Group(SIG) of the IASP. One of the many objectivesof this workshop is to provide a broad foundationfor the further development of suitable diagnosticsystems for TMD and, at the same time, to alsoinclude discussion regarding the creation andimplementation for a dedicated OFP diagnosticsystem. Currently, the DC-TMD is a dual axissystem based upon the biopsychosocial model ofpain (Engel 1977) with Axis I representing phys-ical assessment and Axis II assessing psychoso-cial status and pain disability (Schiffman et al.2014). The main purpose for constructing andemploying a diagnostic and classification systemwith two axes for TMD was to provide a morecomprehensive picture of how pain affected theindividual on multiple levels encompassing vari-ous physical and psychosocial domains. Thethought was this approach would be able to pro-vide a more comprehensive representation thanwhat could be obtained by limiting diagnosticassessment based only on organ system pathosis.This dual-axis system would permit early-onidentification of TMD subtypes which reflectsthe already well-established fact that emotional,cognitive, behavioral, and psychosocial dimen-sions of personal functioning is as much a factorin progression of chronicity and disablement dueto TMD-related pain as were physical findings,perhaps even more so. Specifically, a dual axisDC-TMD would allow clinicians/researchers tolocate each patient in a space coordinated bydeterminants from each axis, with each axis cap-turing clinically meaningful levels of functioning


along their respective dimensions. The intent tolocate a person and the pain disorder within a2-dimensional space reflects the principle thatthe physical aspects (disease) and psychosocialand behavioral aspects (illness) of the person are,in principle, integrated despite the limitations inthe methods used for assessing these two verydifferent levels of biological organization (Inter-national RDC/TMD Consortium Network 2009).However, to achieve true integration of physicaland behavioral data associated with the disorder, itwas ultimately identified that this would requiremore than a two-dimensional plot. Due to thisdeficiency in the current schema, many recom-mendations were proposed to enhance this mind-body dualism thereby acknowledging a legitimateunderlying unitary process. Some of the recom-mendations from this international consensusworkshop to address this issue and to be includedin subsequent revisions to the existing DC-TMDand future OFP diagnostic systems were to createan Axis III specifically devoted to genetics and toincorporate diagnostic aids (e.g., quantitative sen-sory testing and biomarkers) based on clinicalneurobiology for comprehensive assessment ofthe individual with pain on an Axis IV (Ohrbachet al. 2010).

Axis III: Genetics

Individuals are not equally susceptible to OFPincluding TMD. Genetic and epigenetic factorsinvolving susceptibility and/or vulnerability to aparticular clinical course of the disease and/ortreatment response including the development ofcomplications (e.g. unfavorable response to envi-ronmental challenge, material) contribute to thepatient’s symptoms. Therefore, the resulting paincondition should be understood as the individual’scomplex response trait with specific complaintsbeing either amplified or attenuated by theirunique genetic makeup and/or prior life experi-ences (Stohler 2004). An example of the influenceof genetic makeup occurs in relation to the func-tion of the endogenous mu-opioid system(Zubieta et al. 2001). The effects of this systemare significantly influenced by the enzyme,

catechol-O-transferase (COMT). Variability ofthis enzyme’s genotype can result in differencesin the synaptic availability of various neurotrans-mitters (catecholamines such as dopamine,epinephrine, and norepinephrine) which are sub-sequently linked to distinct traits of pain percep-tion and brain activation (Zubieta et al. 2003). Thedownstream signaling consequences can influ-ence pain sensitivity, thereby increasing suscepti-bility or providing greater resistance to chronicpainful conditions (Diatchenko et al. 2005).Prior life experiences may alter an individual’sadaptive response, thereby modifying the state ofactivation of pain-stress response systems such asthose involving the autonomic nervous andimmune systems, the hypothalamic-pituitary-adrenal axis, and the antinociceptive systemsincluding the endogenous opioid system (Guptaet al. 2007; Slavich et al. 2014). Furthermore, it isunderstood that genetic factors play a role in theetiology of persistent pain conditions, putativelyby modulating underlying processes such as noci-ceptive sensitivity, psychological well-being,inflammation, and autonomic response (Smithet al. 2011). However, to properly apply thisknowledge, we ideally need to identifygenotype-phenotype linkages relevant to the indi-vidual. A phenotype is an individual’s observabletraits, such as height, eye color, and blood type.The genotype is the genetic contribution to thephenotype. Some traits are largely determined bythe genotype, while other traits are largely deter-mined by environmental factors.

Conceptually, in order to integrate Axis II self-report experiences of the subjective state withAxis I assessment of the physical state, a modifi-cation and/or expansion in Axis I dimensions toinclude planes devoted to assessment of relevantgenetic or epigenetic components of the humangenome, thereby creating an Axis III, is required.This process of thinking is further supported byincreasing evidence that the search for genotypesin the absence of clear and operationally func-tional phenotypes may not be productive. Thus,phenotyping of the patient according to Axis IIassessment of self-reported depression, anxiety,etc., requires a complete understanding of howthe person is functioning with the simultaneous


assessment of the relevant active geneticcomponents.

As previously stated, it is currently acknowl-edged that genetic factors play a clear role in theexpression of chronic pain states. However, lessevident is how genetic components (e.g., genevariants of different genes) suspected of influenc-ing pain expression also play a role in psycholog-ical and emotional distress manifesting asdepression, anxiety, and the presence of wide-spread unexplained medical symptoms, includingwidespread chronic pains. Even more enigmatic ishow the genetic components play a role in theexpression of the physical symptoms and findingsassociated with a clinical examination. Whilegenotyping has progressed substantially, linkinggenotype to phenotype representation for paindisorders has not kept pace because of the diffi-culty in identifying a pain disorder phenotype.Phenotyping of disorders in general has laggedlargely because the traditional methods of aggre-gating characteristics based on the clinicopatho-logical method of medicine have not beenparticularly successful for these complex disor-ders associated with pain as a dominant symptom.Furthermore, available clinical findings are usu-ally not in accord with the number and extent ofreported symptoms and associated suffering. Col-lectively, the aggregate of some or all behavioralfactors with the physical characteristics associatedwith a given disorder represent our best under-standing of the clinical phenotype, yet a preciseidentification of what is included in a phenotypehas not yet been achieved. Improved phenotypingof the clinical characteristics and biobehavioralcharacteristics associated with OFP disordersand TMD is needed in order to further the researchregarding etiological mechanisms, mechanismsunderlying the progression of pain from acute tochronic, the role that genetics plays in pain per-ception, environmental contributions, and thecomplex interactions among these different levels.

Axis IV: Neurobiological

Neurobiology, as it applies to classification ofOFP, involves central neural information

processing (e.g., learning, memory). It isenvisioned that the implementation of Axis IVwill assist clinicians in capturing the dynamicand longitudinal changes that characterize theOFP patient including TMD over time. Themajority of these conditions are chronic in natureyet longitudinal (i.e., temporal) dimensions havebeen largely neglected in the diagnosis of chronicpain. It is rather paradoxical that a condition that isso strongly associated with being extended over along period of time, hence assignment of the termchronic, that the impact of the chronicity is notadequately reflected on the clinical presentation.Chronic pain patients, and more specifically TMDpatients, change in their descriptive characteristicsover time. Some changes may occur along theAxis I or physical assessment planes while it iswidely accepted that with chronicity comes themuch greater risk for profound and debilitatingchanges best captured by assessment within theAxis II planes or dimensions. There is growingscientific evidence that the dynamic and longitu-dinal parameters of change over time are majorfactors in how chronic pain patients change(Diatchenko et al. 2006; Apkarian et al. 2013;Bourne et al. 2014). From a biological perspec-tive, these changes have been ascribed to plastic-ity within the nervous system, especially higherbrain centers. The influence of central neuralinformation processing involving learning andmemory is now invoked to better explain anddescribe chronic pain’s capability for endurance(Price and Inyang 2015), and growing evidence isdemonstrating how these dimensions exerttop-down influences on the rest of physiology(Reichling and Levine 2009). Therefore, it onlyseems reasonable to require a diagnostic classifi-cation scheme to be able to capture dynamic andlongitudinal changes during diagnosticre-evaluations and to use this dynamic data toevolve longitudinally derived evidence-basedchanges in treatment decision criteria.

Another dimension regarding neurobiologicalprocesses to be considered in Axis IV is the use ofdiagnostic aids including biomarkers. Over theyears, research has enriched medical practicewith the use of specific diagnostic aids whichassist in diagnosis and enable assessment of


disease control or as a measure of intensity andseverity (Ceusters et al. 2015a). In particular, bio-markers, which are any measurable characteristicsof an organism that reflect a particular physiolog-ical state, may be useful as indicators of the pres-ence or severity of a particular disease state.Biomarkers can also be used to assess the effec-tiveness of particular therapies in ameliorating theeffects of a disease. By using easily obtained andassayed biomarkers to monitor a patient’s reactionto a particular drug, it is possible to determinewhether treatment is effective for that individualby measuring drug response rate or toxic effectsassociated with the drug. This information couldeventually lead to earlier detection of adverse drugresponse, thereby decreasing cost to the medicalsystem. Overall, biomarkers hold great promisefor personalized medicine as information gainedfrom diagnostic or progression markers can beused to tailor treatment to the individual for highlyefficient intervention in the disease process. Can-didate biomarkers and potential applicable teststhat should be considered within Axis IV can becategorized by the method used to measure them:(i) physiological (e.g., reflex responses, pressurepain thresholds, quantitative sensory testing);(ii) psychological or behavioral characteristics(e.g., dynamic pain psychophysical testing); (iii)radiological [computed tomography (CT), mag-netic resonance imaging (MRI), functional MRI(fMRI), positron emission tomography (PET)];and (iv) molecular [small molecules (aminoacids, prostaglandins, leukotrienes) and proteins(e.g., cytokines, COX)] (Ceusters et al. 2015b).Each one of these modalities has supporting evi-dence as being used either clinically and/or exper-imentally for the diagnosis, measurement ofburden of disease, or determination of the prog-nosis or efficacy of treatment for OFP conditionsincluding TMD (Ceusters et al. 2015b). Currently,the predictive value of available biomarkers indiagnosing OFP is rather low (Ceusters et al.2015b) despite ongoing research which is contin-ually attempting to change this situation(Fillingim et al. 2011; Maixner et al. 2011a).Additionally, it is unfortunate that other

diagnostic aids, be it laboratory and/or imagingstudies, are also largely only research based in thefield of OFP (Maixner et al. 2011b; Slade et al.2011; Smith et al. 2011). Therefore, due to thelimitations in our current knowledge of neurobio-logical processes, the diagnosis of OFP continuesto be mainly based upon the clinician’s ability torecognize particular combinations of signs andsymptoms in the patient. Diagnosis thereforeremains heavily reliant on patient self-report asthe proxy for the full symptom profile of thephenotype, the way in which it is related and thehow the clinician interprets this information. Thismakes diagnosis of OFP much as an art formrather than a pure science (Ceusters et al. 2015a).With the development of multiaxial systems(beyond Axes I and II), there will be a majorimprovement in disease conceptualization leadingto advancement in enhanced patient care.

Taxonomy and Ontology: A NewApproach for Classification Systems

In 1676, Thomas Syndenham, considered thefather of English medicine or also known as theEnglish Hippocrates, introduced the concept ofclassification using nosological methodology tothe field of medicine. The objective at that timewas to identify the disease in order to predict theprognosis. As time and scientific discovery pro-gressed, the framework for classification alsochanged; however, the main purpose remainedstagnant. Hence, in order for the science of med-icine to evolve an alternative method of thoughtwas needed requiring a shift from existing para-digms. This ultimately developed into the use of ataxonomic approach. The word taxonomy isderived originally from Greek from the combina-tion of the words “taxis” (order or arrangement)and “nomos” (law or science). Taxonomy isessentially a simple hierarchical arrangement ofentities listing of all of the elements in the hierar-chy with the purpose of providing a classificationof knowledge or simplistically, arrangement ofscience. From a clinical perspective, taxonomy


implies the “systemic classification of subjects,”sorted into groups to reflect similarity, with gen-erally broader groups residing over those that aremore restricted (Raj 2007). Accordingly, taxon-omy is defined as the theory and practice of clas-sification (Merskey 2007). It has been furthercommented that “For an ideal classification eachitem to be considered should be independent of allother items so that it stands in its own place in theclassification.” (Merskey 2007). Ideally, classifi-cation using taxonomic principles should bemutually exclusive and simultaneously exhaus-tive. Therefore, a question arises as to the purposeand utility of taxonomy. The necessity for its useis that health practitioners and more specificallythose involved with OFP face issues related to thecomplexities of chronic pain on a daily basis.Therefore, this requires a clear understanding ofpain syndromes thus enabling practitioners in theprovision of effective and reliable managementapproaches. Unfortunately, when confrontingpain, there are many obstacles to this approachand they include: a lack of a clear and definitivedefinition of pain, difficulties, and unreliablemethods to quantify or measure pain and observerbias when assessing patient’s pain behavior whichquantifies pain intensity (Raj 2007). Originally,taxonomy utilized a single axis classification sys-tem that was only able to classify acute fromchronic pain. This simplistic approach becomesrather inadequate when descriptors and qualifiersare required beyond the elementary, primary des-ignation for the purpose of facilitating exchangeof ideas and thoughts among clinicians andresearchers. Bonica, in 1979, echoed similar con-cerns by stating “The development and wide-spread adoption of universally accepteddefinitions of terms and a classification of painsyndromes are among the most important objec-tives and responsibilities of the IASP. It is possibleto define terms and develop a classification of painsyndromes which are acceptable to many, albeitnot all, readers and workers in the field; even if theadopted definitions and classifications are not per-fect, they are better than the Tower of Babel con-ditions that currently exist” (Bonica 1979;Merskey and Bogduk 1994). This inspired theIASP to establish a subcommittee on taxonomy

and led to the creation of the first multiaxial sys-tem. This system was based upon the followingparameters: region of the body involved inchronic pain, the organ system affected, the tem-poral characteristics and pattern of the pain, theduration and intensity, and the etiology. Despitebeing an improvement over previously usedmethods, it was not without its shortcomings andits applicability in the clinical environment. (Turkand Rudy 1990; Procacci and Maresca 1991;Ventafridda and Caraceni 1991). Similar issuesexist within classification systems related toTMD as evidenced by the older RDC-TMD andthe more contemporary DC-TMD. Despite thebenefits of these systems and attempts to addresstheir inadequacies, each system has its shortcom-ings (Schiffman et al. 2010b). The reasons whythis may be occurring are because of the excessivedetail needed in the diagnostic process to arrive ata diagnosis within a clinical environment, lack ofconsensus within and between different cliniciangroups, a lack of a coherent overarching taxon-omy based on ontological principles, and the dif-ficulty to prognosticate treatment outcomes(Nixdorf et al. 2012).

A possible alternative, and perhaps a solution,may be to consider the use of an ontologicalapproach. In general, ontology is the study orconcern about what kinds of things exist, whatentities there are in the universe, and how theyrelate to each other. Ontology essentially is a morecomplex variation of taxonomy. Besides havingthe hierarchical arrangement of the classes thatrepresent entities, each class affords severalrestrictions on its relationships to other classes oron the properties a particular class is allowed topossess. The purpose of this approach is toenhance knowledge representation. The wordontology derives from the Greek “onto” (being)and “logia” (written or spoken discourse). Histor-ically, it is a branch of metaphysics, the study offirst principles or the essence of things. Ontologyas a methodology in the classification of painprovides methods of distinguishing among cate-gories and describing data in uniform and formalways. The goal for its application is to enhance thedefinitions as it relates to pain in general and morespecifically to chronic pain conditions. Ontologies


tend to be more about the relationships betweenthings (in addition to their properties) than taxon-omies that are generally limited to classificationonly. An easy to understand difference amongthese concepts is as follows: taxonomy assigns alabel to the pain condition, while ontology pro-vides information regarding the pain and how itrelates.

Issues related to difficulties in providing diag-nostic criteria for various OFP disorders due to anoverall lack of structure have been identified. Fur-thermore, differential diagnosis of OFP condi-tions is challenging for practitioners becausepatients often present with overlapping signs andsymptoms in addition to having comorbidities.This has prompted the International RDC-TMDConsortium to initiate the development of a tax-onomy for OFP disorders based on ontology. Thegoal of the Consortium was to initially focus onclarifying terminology and their relationships, sothat standardized multisite data collection canoccur and future research, such as cluster analysismethods, can be applied to refine these criteria(Nixdorf et al. 2012). In order to promote theutility of following ontological principles and toshowcase its improvement in developing diagnos-tic criteria, the methodology was applied to thedisorders that manifest themselves through thesymptom of persistent OFP. Presently, diagnosingchronic OFP disorders is based mainly on clinicalsigns and symptoms, since the mechanismsunderlying the pathophysiological processes arelargely unknown. This results in diagnosis byexclusion which creates difficulty in achievingstandardization and often exposes the patient toinappropriate treatments or misdiagnosis(Durham et al. 2013). Unfortunately, with theexception of TMD, there is a lack of researchassessing the validity of such diagnoses andexisting classification systems. It is thereforeunclear how various disorders relate to eachother, since there is no over-arching taxonomy,and this is likely to perpetuate discipline-baseddiagnostic thinking (Nixdorf and Moana-Filho2011). Therefore, the advantages of employingontological methodology to the diagnostic criteriainclude being (i) anatomically defined, (ii) inaccordance with other classification systems for

the provision of clinical care, (iii) descriptive andsuccinct, (iv) easy to adapt for applications invarying settings, (v) scalable, and(vi) transferable for the description of pain disor-ders in other orofacial regions of interest (Nixdorfet al. 2012).

An example of how ontology may be appliedin a clinical setting is the reclassification of “atyp-ical odontalgia” which often presents as a persis-tent pain disorder. Using ontology methodologyaffords the ability for criteria to be concisely andoperationally defined and provides the potentialfor the development for subtypes of a disordersuch as has been employed with the term persis-tent dento-alveolar pain disorder (PDAPD). Per-sistent dento-alveolar pain disorder is anontologically adequate description because itremoves ambiguity thereby preventing misinter-pretation as to what each term used in that descrip-tion corresponds to in reality. For example, thepain that patients with PDAPD suffer from ispersistent, is constant over time, occurs in thedento-alveolar tissues, and surely, is a pain. Theuse of the word disorder at the end of PDAPD isimportant because it expresses that when the termis used as a diagnosis relative to some patient, itdoes not refer to that patient’s pain, but to thedisorder which forms the physical basis for thatpain (Ceusters et al. 2015a). However, noted lim-itations associated with this approach are that thecriteria introduce new terminology which do nothave widespread acceptance, are expert-derivedand not evidence-based, and are yet to be tested(Nixdorf et al. 2012). Hopefully, by followingtaxonomy using ontological metrics is an initialfirst step towards a paradigm shift in the develop-ment of a harmonized taxonomy for OFP disor-ders, which is a necessary for the improvement ofclinical research and patient care.

Conclusions

This chapter has provided an insight into the clas-sification of OFP including the topic of TMD byreviewing the available diagnostic/classificationschemes and commenting on the constructs onwhich they are based. From a quick overview, it


is apparent that none of the available classificationsystems has emerged as clearly superior to othersin terms of potentially relevant impact on theclinical practice. In particular, there is still a strongneed to improve knowledge on the pathophysiol-ogy of many OFP conditions and to weigh therelative importance of the different evaluationaxes as far as the treatment outcome is concerned.This means that even if there is no doubt thattopographically or Axis I (i.e., “physical”diagnosis)-based diagnoses are not enough toexplain the severity of the symptoms and thepredictability of their decrease with treatment,other constructs based on a more thorough evalu-ation are difficult to introduce in the clinical prac-tice due to the complexity of the derivedassessment in the clinical setting. This clinicaluncertainty mirrors in the available classificationschemes and may be best exemplified by thinkingabout an imaginary patient with TMD seeking foradvice for his/her symptoms.

A 35-years-old female complains of pain in theright TMJ area and has positive palpation of theipsilateral masseter, temporalis and lateral ptery-goid muscles as well as the TMJ. Pain onset datedback to a couple of years ago and the patient hasmoderate depression and somatization levels.Leaving apart all other possible information, thediscussion of which is beyond the scope of thischapter, the key question from a classificationviewpoint is: which are the evaluation axis thatprevails in determining the clinical picture?Should this patient be classified as having amyofascial pain plus right TMJ arthralgia (AxisI) or a moderate depression and somatization(Axis II)? And what about the possibility of hersymptoms undergoing modulation due to theexpression of her specific genome (Axis III) aswell as her particular neurobiology makeup of herpain (Axis IV)?

Over the years, improvement in pain medicineknowledge has progressively shifted the focus oftargeted treatment from the topographic or organspecific “diagnosis” to a more globally orientedapproach towards personality and psychosocialissues. The literature has shown that, for instance,Axis II findings are more predictive of treatmentoutcomes than Axis I diagnoses (Manfredini et al.

2013; Suvinen et al. 2013). This information hasto be integrated with progressive increases inknowledge on pain genetics and neurobiology,and the resulting comprehensive picture shouldbe the basis for an ideal classification.

In summary, the ultimate goal of a classifica-tion is to provide clinically useful schemes for aneasier management of patients in the clinical set-ting. Until now, despite all efforts by the severalinternational experts and organizations, none ofthe proposed classifications of OFP is free of anyshortcomings. However, the recently proposedontology-based approach could represent a prom-ising step toward an archetypal treatment-orientedclassification.

Cross-References

▶Arthritic Diseases Affecting the TMJ▶Biopsychosocial Considerations for OrofacialPain

▶ Internal Derangements of the Temporomandib-ular Joint

▶Masticatory Muscle Pain▶Neuropathic Orofacial Pain

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