Consensus development process
A type of orofacial pain encountered in clinical practice with considerable taxonomical confusion is persistent pain present in the dento-alveolar areas of the mouth, often referred to as ‘atypical odontalgia’ (6
). This condition served as an example for the application of ontological principles to develop diagnostic criteria. Descriptive aspects reported about this sort of pain and the various contexts in which instances thereof appear were delineated and discussed in terms of the L1 /L2 /L3 distinction, thereby disambiguating descriptions in the literature based on whether they denote phenomena that can be observed in individual patients or patient populations (). For example, a description such as ‘the pain is mainly unilateral’ can mean (i) that when a specific patient has pain, there is usually only pain on one side, (ii) that when a population of pain patients is observed, most of these patients exhibit pain on one side or (iii) both situations occur.
The expert in ontological realism further explained the basics of the Ontology of General Medical Science (OGMS) (14
), which are summarised in . From this perspective, multiple signs and symptoms including their nature and position under OGMS’ framework were discussed and key descriptive clinical features were identified (), while other candidate features were discarded (). Consensus on the observations that predominate in patients became the diagnostic criteria that exist in the observable domain ().
Fig. 1 Conceptual framework for Ontology of General Medical Science (OGMS). The OGMS pursues a view of disease as resting in every case on some (perhaps as yet unknown) physical basis (Williams, 2007) (33). When, for example, there is a persistent pain in some (more ...)
Features separating individuals with PDAP from those without it
Clinical features discussed and the reasons why they were not included
The most challenging tasks were to assess (i) which terms used in the domain correspond with real entities, (ii) what real entities need to exist for certain signs and symptoms to manifest themselves, (iii) to what degree do distinct pain disorders lead to similar types of signs and symptoms, and (iv) to what extent can individual patients be suffering from distinct pain disorders at the same time, yet exhibiting manifestations that can be explained by the presence of only one particular pain disorder. Clinical experts need an adequate terminology to describe, with sufficient discriminative power, the various observable phenomena, thereby making sure to name each distinct entity differently to avoid confusion (i.e. word ‘pain’ being simultaneously used as an observation, an entity, and a term to label multiple entities; see ). This approach does not require the aetiology of the phenomena to be known but nevertheless guarantees that when the underlying pathophysiology becomes clearer in the future, the terminology used to describe the entities will still remain valid.
The discussion therefore centred on the ideal terminology. Because the pain in case of what is currently believed to be denoted by the term ‘atypical odontalgia’ is long lasting and not acute, the term ‘chronic’, defined as 3 months or more (IASP definition), was initially agreed upon to be adequate. The ontologist then pointed out that under this definition of ‘chronic’, the criterion of having lasted longer than 3 months is a criterion about when the term ‘chronic’ may be used to describe a particular pain to have consistent descriptions cross-patients. At the level of the pain entity in reality itself, there is indeed no magical line, which when crossed suddenly transforms the existing non-chronic pain into a chronic pain a par with a caterpillar transforming in a butterfly. If one is allowed to name a particular pain instance chronic in line with the definition for chronic used, then that particular pain was already chronic from its very start, although it could not be known yet. The pain is in most patients continuous, present more than 90 days of 180 (15
); the anatomical location is usually in and around teeth, or in the alveolar bone where teeth once were located (dento-alveolar) – following the precedent of regionally defining pain disorders (16
). The term ‘persistent’ was considered in the place of chronic
for two reasons: (i) chronic
is thought to also capture the negative emotional experience, which for the disorder may or may not be present and (ii) continuous
suggests that the symptom of pain is uninterrupted, which is untrue in some instances. The term ‘persistent’ is not ideal because it presumes that the outcome of treatment is a failure to relieve the symptom of pain, which is contrary to long-term goal of these collaborative efforts. Looking at this from another perspective, the term ‘persistent’ relates to the clinical observation that local surgical treatments to the dento-alveolar tissues is ineffective at relieving the pain symptom of this disorder, which is useful perception to promulgate at the present time given the failure of contemporary approaches to treatment. Furthermore, the term ‘persistent’ is the term recently proposed to describe a similar pain-related phenomenon presenting within the muscles of mastication (18
) and is therefore a consistent terminology that can be used to expand this taxonomy. Finally, because pain in ontological terms is a symptom, this entity would better be described as a pain disorder
, a specific disease entity.2
Thus, all together, this results in the term ‘persistent dento-alveolar pain’ disorder, which may be shortened for everyday use to PDAP.
Changing the operationalised criteria used to define this entity, PDAP, does not affect whether this entity exists or not. Individuals with this pain disorder may express the signs and symptoms differently, but this does not affect the reality of whether they have the pain disorder or not. Therefore, conceptually, the criteria to define this pain disorder can and do vary based on the setting in which it is being used. This allows researchers investigating the underlying mechanisms of this pain disorder, those most interested in studying individuals who are known to have this pain disorder (true positive cases), to maximise the specificity of the diagnostic criteria. This will come at the expense of sensitivity, meaning that some individuals with the actual pain disorder may be excluded because the diagnostic criteria used were too stringent (false negative cases). Conversely, epidemiological researchers will need to strike a balance between diagnostic sensitivity and specificity, but will want to use diagnostic criteria that may not necessarily involve extensive examination procedures or difficult to access testing, such as imaging techniques. These situations highlight the fact that for research and clinical purposes, the criteria used to define the pain disorder may differ, but this does not change the underlying reality or the terminology used to refer to it. For this key reason, following ontological principles lead to the development of the diagnostic criteria for PDAP defined by the four components included within the name and developed recommendations for operationalisable diagnostic criteria ().
Diagnostic Criteria for PDAP
During the development of the inclusion and exclusion criteria, one potentially vexing question remained: how to best exclude pain disorders that are caused by a local aetiology, such as inflammatory disorders that may linger 3 months or more? Currently, the only methods are to perform a clinical examination along with appropriate diagnostic imaging to exclude known dental and other orofacial pain disorders that may have the overlapping symptom of continuous or near continuous pain.
Subgroups and a taxonomic structure were also mapped out. As these pain disorders can either be precipitated by known traumatic events or arise in the absence thereof (19
), a primary and secondary form was suggested, in line with the existing pain taxonomy (20
). This subdivision delineates potentially causal factors, so that future research can explore his relationship more fully. Subjects with sensory changes detectable by neurological examination, or more precise quantitative sensory testing, can be separated from those who do not demonstrate these changes; which is consistent with a more specific classification of pain disorders having neuropathic underpinnings (21