Sheldon Friel Memorial Lecture 2025—Orthodontics and Temporomandibular Disorders: evolving views on risk factors, diagnosis, and management

Abstract

Background and objectives

The role of occlusion and orthodontic treatment as potential risk factors for temporomandibular disorders (TMD) continues to be a subject of considerable debate within the scientific community. Nonetheless, current evidence suggests that the association between occlusion and TMD is generally weak and inconsistent and therefore should not be overemphasized.

Materials and Methods

This article represents the Ernest Sheldon Friel Memorial Lecture presented in 2025 at the 100th Congress of the European Orthodontic Society. It is focused on the critical and updated evaluation of the relationship among occlusion, orthodontics and TMD. Starting from the historical perspective it analyses the role of condylar position, occlusal disharmonies and occlusal interferences as risk factors of TMD and highlights the need to move beyond a narrow mechanical interpretation of occlusion towards a more integrative approach that considers the central nervous system’s processing of peripheral stimuli. In this broader context, individual differences in neuromuscular adaptability must be considered to reduce the likelihood of maladaptive outcomes following dental procedures.

Conclusions and Implications

Orthodontists should be well-informed about the multifactorial aetiology of TMD, should know the validated diagnostic criteria for TMD and be prepared with evidence-based strategies for patient management at all stages of treatment.

Historical perspectives: malocclusion and orthodontic treatment as suspects of TMD

The relationship between occlusion, orthodontics and temporomandibular disorder (TMD) has long been a topic of intense debate in dental and orthodontic communities. Clinicians and researchers have considered for many years occlusion as one of the major direct and/or indirect aetiological factors causing TMD [1]. The starting point of this hypothesis came from a paper published in 1934 by James Costen [2], an otolaryngologist, who associated the absence of molar support and/or an increased overbite to a upward and backward condylar displacement and, as a consequence, to the onset of temporomandibular joint (TMJ) pain and noises, headache, limited mandibular opening, myofascial tenderness, and symptoms related to the ears (summarized in the so-called ‘Costen’s Syndrome’). Afterwords [3, 4], it has been assumed that malocclusion might cause displacement of the condyle, suggesting the need of treating TMD through the achievement of the optimal occlusion and jaw function. The gnathological principles included, among the other, a canine protected occlusion, a coincidence between maximum intercuspation and central relation, the search of an ideal mandibular joint position, the repositioning on the mandible to recapture the disc with an occlusal splint, and changes of occlusion when there was some alteration in the skeletal relationship [5]. In the 1970s, Roth [6] introduced the orthodontic gnathology which included establishing coincidence of maximum intercuspation (or centric occlusion) with centric relation (CR) in an anterosuperior seated condylar position, to attain canine (mutually) protected occlusion and anterior guidance, and to mount pretreatment diagnostic casts on a fully adjustable articulator. Following these principles orthodontists could prevent or cure TMD by addressing an existing malocclusion associated with functional disharmony and improper CR position [7, 8]. In the 1980s [7], it has been suggested that some orthodontic techniques, including elastics, headgears, extractions, chin cups, would be the cause of TMD. A case that drew significant attention and concern within the dental and orthodontic communities was the 1987U.S. court case Brimm v. Malloy. Susan Brimm, 16 years old, presenting a Class II Division I malocclusion was treated with the removal of upper first premolars and the use of headgear. She complained of click, pain, limited opening and headache following the removal of the appliances. It has been claimed that the cause of these TMD symptoms were the consequence of the orthodontic treatment resulting in the over-retraction of the upper incisors and distal displacement of the mandible. The jury awarded the plaintiff 850 000 dollars against the Michigan orthodontist [9]. Following this landmark TMD court case the American Journal of Orthodontists published on January 1992 an entire issue dedicated to papers investigating subjects of occlusion, orthodontic treatment as they related to TMD. The conclusions were that there is no association between dental and skeletal structure and TMD; TMD cannot be predicted nor prevented; the prevalence of TMD was increasing with age; orthodontic treatment cannot be the cause and may sometimes orthodontics assist in lessening symptoms of patients with TMD; TMD cures cannot be assumed or assured through the orthodontic treatment. However, 30 years later [10], we are still debating the same topic and contradictory information are delivered by internet sites, social media and artificial intelligence that are used by patients to get information about their condition and to seek a practitioner for treatment. Indeed, when assessing the accuracy of information provided on websites of dental practices about TMD diagnosis and management it has been found that TMD were attributed to occlusal problems or malocclusion on 66.7% of the websites and recommendations to treat occlusal problems or malocclusion to alleviate TMD were made by 54.5% of the providers [11]. Also, the results of an Internet survey of non-dental professional and allied health care professionals (i.e. ENT, orthopaedic, neurologist, rheumatologist, osteopathic, chiropractic, homeopathic) showed that most of the official websites had little or no information about TMD or stated that ‘dental occlusion is an important etiologic factor for TMDs and also that most TMJ pain is caused by disk displacement’ [12]. Additionally, the information provided by chatbots should be reviewed by qualified experts, as it may be inaccurate, misleading, or even based on fabricated content (i.e. hallucination) [13]. Similarly, content shared on social media platforms is often unreliable. One study analysing TikTok videos related to TMD and bruxism found that the educational quality of these videos was generally poor, incomplete, and inaccurate [14].

Myths and dogmas versus scientific evidence

In public health, confusing myths and dogmas with science can lead to misinformation and harmful interventions. Myths and dogmas are in contrast with the concept of science that is continuously changing and improving the knowledge based on systematic observation, experimentation, and analysis that supports or refutes a hypothesis. Understanding the difference empowers people to make informed decisions based on facts, not unchallenged beliefs. Among others there are some frequent asked questions relating the occlusion and TMD that are discussed with contrasting beliefs and evidence.

Condylar position and centric relation

How the condyle and the disc should be positioned in relation to the TMJ fossa is a topic of great debate in the orthodontic and dental literature. Indeed, it has been suggested that the trapped mandibles, the reduced vertical dimension, the occlusal interferences, occlusal disharmonies can lead to a condylar malposition and consequently to TMD [4]. Also, among orthodontists, there is the suggestion of searching the anterior CR position of the TMJ to obtain the optimum functional occlusion [6]. This topic has critical implications in the clinical practice, since for many years dentists adopted numerous procedures involving repositioning of the mandible as part of dental treatments. The aim of mandibular repositioning was to obtain an optimal and repeatable condyle-to-skull relationship, to prevent from TMD development or to manage TMD signs and symptoms [13]. According to the early definition, the ideal condyle-fossa relationship (defined ‘centric relation’) was considered as a jaw position, achieved when the mouth is fully closed, that should be identified independently from tooth contact. The definition of CR underwent several changes and adjustments during time, until being integrated with some concepts related to dental occlusion. When the mandible is in its centric-relation, a good static intercuspation of upper and lower teeth (in the so-called ‘centric occlusion’) should occur. According to these premises, whenever centric occlusion corresponds to the maximum intercuspation of the teeth, the patient maintains a status of health; when discrepancies between maximum intercuspation and centric occlusion exist, an orthodontic treatment should be suggested to correct this discrepancy [14]. However, these theories have been widely questioned due to several reasons. Firstly, the clinical relevance of CR is highly questionable. A recently published paper analysed the position of the condyle after the orthodontic treatment with extraction of the four premolars showing extremely small differences (i.e. posterior shift of 0.41 mm, a posterior joint space narrowing of 0.34/0.32 mm, and the medial tilt of 0.62) that cannot be considered clinically relevant [15]. When comparing the condylar position, assessed with magnetic resonance imaging, related to different dental positions in a symptom-free population, minor a non-statistically significant differences were observed [16]. Also, when considering the anatomical point of view there is evidence that the condylar position, the joint space, the joint fossa morphology and the condylar morphology, are significantly different among individuals and in the same individual [17, 18]. Finally, it has been observed that the condyle-fossa relationship may change depending upon several factors, such as fatigue of masticatory muscles, oral behaviours, posture, tongue pressure, hydration of the disc, wear of the dental surfaces [19]. Secondly, there is no evidence that the position of the condyle within the fossa might be associated with ongoing TMD, or with increased or reduced risk to develop TMD. Studies performed on magnetic resonance imaging pointed out that condylar position is characterized by great variability, with only 50% of subjects presenting a condyle that is located centrally. Both anterior, concentric and posterior condylar positions can be found in volunteer-normal joints, and no differences in condylar position can be found between symptomatic and asymptomatic individuals. Therefore, the position of the mandibular condyle should be considered a variation of the normalcy [20]. Every individual has a unique TMJ relationship that in healthy dentate patients, should be considered as biologically acceptable [21]. On the top of that, current concepts of joint functional anatomy underlined that most of joint movements occur physiologically along the articular eminence, limiting the importance of its position within the fossa when the mouth is closed [22]. Finally, most patients can grow and adapt continuously throughout the life even with an abnormal TMJ anatomical structure. A healthy, well-adapted jaw position does not need to be analysed or changed. Therefore, there is currently no evidence to support unnecessary bite-changing and jaw-repositioning interventions as a therapeutic or preventative procedure for TMD. The differences in TMJ anatomical structure, have a greater importance in explaining the variance. Indeed, a wider fossa can predispose to disc displacement with reduction, or a steeper articular eminence can predispose to this displacement without reduction [23]. So, we can conclude that the mandibular position cannot explain the TMD aetiology. And that mandibular repositioning is not appropriate for the management of TMD patients.

Occlusal disharmonies

The relationship between malocclusion and TMD has been widely investigated in the literature, often yielding inconsistent findings. TMD can manifest as muscular or joint pain, disc displacement (with or without joint sounds), or conditions leading to TMJ osseous remodelling [24, 25]. There is a widespread belief among both orthodontists that certain occlusal characteristics (severe open bite, severe deep bite, increased overjet, posterior cross bite) may be associated with TMD leading to a change in the condylar position. However, a systematic review assessing the current evidence on dental occlusion and TMD showed scarce, sporadic, weak, and inconsistent associations with sagittal, vertical and transversal malocclusions [26]. A study performed in New Zealand 30 years later in a birth cohort investigated the association between posterior crossbite, overjet, and overbite present during adolescence and TMJ clicking sounds. The authors found that posterior crossbite and abnormal overjet/overbite values during adolescence were not associated with greater risk for TMJ clicking later in life. Also, that there were no association between the history of the orthodontic treatment and TMJ clicking [27]. A case control studies showed that orthognathic surgery is not associated with a negative impact on TMD [28] and orthodontic treatment is not associated with TMD diagnosis and disease characteristics [29]. Finally, a Cochrane review including 57 randomized clinical trials with 2846 participants concluded that there is insufficient evidence to reach conclusions regarding the effectiveness of occlusal interventions for managing symptoms of TMD [30]. TMD is a complex disorder, resulting from an interplay of different causes and recognize a multifactorial aetiology. These include bruxism, clenching, and excessive gum chewing, which can place additional strain on the masticatory system, pain sensitivity, psychological distress, injury, and the presence of other health and pain disorders. While occlusal characteristics have been proposed as a primary aetiology for TMD, the evidence remains weak and unconvincing. TMD management has transitioned from an occlusal and mechanical-based model to a medical and biopsychosocial model of care [31].

Occlusal interferences

Occlusal interferences have long been a topic of investigation in the context of TMD since 1961, when Ramfjord [32] reported a reduction in TMD signs and symptoms of following occlusal adjustment. This early observation contributed to the adoption of occlusal adjustment as a therapeutic option for TMD. More recently, a survey of 400 general practitioners revealed that 46% routinely perform occlusal adjustments [33], with a similar finding reported in Italy, where 42% of surveyed practitioners reported using this intervention [34]. Two decades ago, we conducted experimental studies examining the role of artificially induced occlusal interferences on clenching behaviour. Using the same protocol, we evaluated both TMD-free [35] and TMD-pain subjects [36] by bonding occlusal interferences that either disrupted or did not disrupt maximum intercuspation. Electromyographic activity of the masseter muscle was recorded over eight hours per day for eight consecutive days. In TMD-free subjects, real occlusal interferences were associated with a reduction in clenching episodes [35]. In contrast, TMD-pain subjects exhibited no such reduction when the interference disrupted maximal intercuspation, suggesting persistence of parafunctional clenching [36]. Further studies comparing individuals with high and low levels of parafunctional activity confirmed a reduction in clenching across both groups; however, highly parafunctional individuals reported greater discomfort, including headache and muscle pain [37]. These findings were corroborated more recently [38], showing that subjects with high parafunction experienced increased discomfort when using passive aligners. These findings suggest that individual variability—particularly in parafunctional behaviours—significantly influences the response to occlusal interferences.

Final remark

The existing literature does not support the notion that establishing an ‘ideal’ condylar position prevents TMD. Furthermore, there is no conclusive evidence that malocclusion is directly associated with TMD, nor that orthodontic treatment can prevent, cause, or cure TMD.

On average, our teeth are in contact only for very short intervals over a 24-h period. This occurs when swallowing, chewing while eating (19% of mealtime), and during occasional teeth contact or clenching [39]. One study using the experience sampling method have shown that individuals without TMD pain report only ∼9% of their waking time spent in nonfunctional tooth contact. However, when measured in individuals with myofascial pain, this percentage increases to as much as 35% of waking time [40]. In this context, it should be emphasized that maintaining a jaw posture with a few millimetres of interocclusal distance (‘rest position’) greatly reduces masticatory muscle activity and supports the clinical recommendation to keep the teeth apart [41]. Therefore, as a general remarks, it seems to be much more important for how long the teeth are in contact and with which amount of force, compared with how do the contact during intercuspation.

From teeth to brain: expanding the temporomandibular disorder framework

Occlusion is a clinically relevant factor in the dental field. Guidelines for achieving an ‘ideal occlusion’ are required when occlusal changes are necessary for orthodontic or prosthetic rehabilitation. However, it is important to emphasize that ‘ideal’ does not necessarily mean ‘healthy’, given the wide variability of occlusal characteristics among TMD-free individuals. Traditionally, occlusion has been analysed from a peripheral perspective, focusing on mechanical and anatomical factors. However, emerging evidence highlights the importance of central mechanisms in modulating occlusal perception and related discomfort. Individual variability in pain and occlusal perception plays a critical role, as patients respond differently to changes in occlusion and exhibit varying degrees of occlusal sensitivity and discomfort. It is therefore essential to shift the paradigm towards a central nervous system-based interpretation, incorporating concepts such as perception, neuroplasticity, and occlusal hypervigilance. Perception, defined as the central interpretation of peripheral stimuli, significantly influences both pain and occlusal awareness. Considering pain perception, in a study evaluating the insertion of dental separators in subjects with different anxiety levels, those with higher anxiety reported greater discomfort and pain [42]. While occlusal perception has often been studied in terms of peripheral receptors such as periodontal mechanoreceptors, muscle spindles, and TMJ afferents [43], our research has shown that central factors must also be considered. In individuals with chronic TMD pain [44] or burning mouth syndrome [45]—both centrally mediated orofacial pain conditions—occlusal perception was more acute, likely due to increased attentional focus on the occlusion. These findings support the role of top-down modulation, whereby attention and emotional valence alter sensory sensitivity [46]. Neuroplasticity, the brain’s capacity to adapt to changes, is another crucial factor enabling adaptation to occlusal modifications such as those introduced during orthodontic treatment, mandibular advancement, or orthognathic surgery [47]. In one study, neuroplastic changes were observed as early as 30 days after the initiation of orthodontic treatment [48], while adaptation following orthognathic surgery typically occurred over a longer period, ranging from 6 to 12 months [49]. However, it is important to note that in individuals experiencing pain, it has been shown a reduced brain’s capacity for neuroplastic adaptation [50]. A further consideration is occlusal hypervigilance, wherein somatosensory stimuli are exaggerated by cognitive-emotional factors like stress, anxiety, or depression [51]. This heightened vigilance may contribute to occlusal dysesthesia—a maladaptive condition characterized by persistent discomfort despite the absence of objective occlusal discrepancies [52]. Often triggered or exacerbated by repeated dental interventions, occlusal dysesthesia is increasingly understood as a disorder of central signal processing and altered psychosocial dynamics [53]. In such cases, over-treatment can perpetuate the problem, emphasizing the need for restraint and careful diagnosis [54]. Thus, while occlusion may appear inconsequential from a purely peripheral standpoint, it becomes highly relevant when viewed through the lens of central processing. This underscores the importance of respecting biological variability, acknowledging the limits of neuroadaptation, avoiding irreversible interventions in the absence of a clear diagnosis, and adopting a patient-centred, individualized approach to treatment planning. Ultimately, successful management of TMD requires integration of both peripheral and central considerations, guided by accurate diagnosis (Fig. 1).

Figure 1.

Schematic representation of patient response to occlusal change. An occlusal alteration is perceived differently depending on coping mechanisms. When avoidance mechanisms are absent, patients may develop occlusal hypervigilance, characterized by increased tactile sensitivity, negative coping strategies, negative affectivity, and a heightened sense of threat, resulting in distress. Conversely, when avoidance mechanisms are present, adaptation occurs, leading to no distress.

Future directions

Future research in the field of orthodontics and TMDs should place greater emphasis on understanding the complex interplay between peripheral and central mechanisms. Exploring the role of the central nervous system in pain modulation, neuroplasticity, and stress-related pathways could provide valuable insights into why certain individuals develop chronic TMD while others with similar risk factors do not. Furthermore, there is a pressing need for the development of innovative diagnostic tools that move beyond traditional occlusal and structural assessments to incorporate biological, psychological, and behavioural markers. Such advancements would facilitate the identification of the multifactorial causes of TMD, allowing for more personalized diagnostic profiles and tailored management strategies. Integrating neuroimaging, biomarker research, and digital technologies into clinical practice may ultimately transform the way TMD is diagnosed and managed, shifting the paradigm towards precision medicine.

Diagnostic criteria for temporomandibular disorders

TMD includes musculoskeletal conditions affecting the stomatognathic system, involving functional alterations of TMJs, masticatory muscles, and associated structures [55]. These disorders are primarily characterized by dysfunction—defined as the impaired ability to perform normal orofacial functions—and by pain, which may be acute or progress to a persistent state. The transition from acute to chronic pain is more likely in individuals with comorbid conditions and is often accompanied by significant psychosocial implications, including reduced daily functioning and diminished quality of life. According to the diagnostic criteria that have been validated in terms of sensitivity and specificity, TMD can be classified into two main categories: TMD-related pain and functional dysfunction [24]. Painful TMD (i.e. myalgia, myofascial pain with referral, arthralgia, headache attributed to TMD) is distinguished by pain located at muscle and joint areas, influenced by mandibular function, reproduced during clinical examination (i.e. familiar pain) and can provoke pain at a site beyond the boundary of the muscle being palpated (i.e. referred pain). The dysfunction subtype is characterized by joint sounds (such as clicking, crepitus or eminence click), mechanical interferences with mandibular movement (e.g. intermittent, persistent closed locking or open locking), including conditions such as disc displacement with or without reduction, degenerative joint disease, and subluxation [24]. TMDs are highly prevalent in the general population, with approximately one-third of individuals affected [56] and are particularly more common among women [57]. In the context of orthodontics, this prevalence is even higher. A recent systematic review published in 2025 reported that up to 40% of patients with malocclusions also exhibit signs and symptoms of TMD [58]. Given this high comorbidity, it is imperative that orthodontists are well-versed in the identification and management of TMD (Table 1).

Table 1.

Diagnostic criteria for TMDs (modified by Schiffman et al., 2014) [24].

TMD pain
Diagnoses	Clinical criteria
Myalgia	Pain location at temporalis and masseter muscles; modified by jaw function; familiar pain during palpation and/or jaw movements
Myofascial pain with referral	As myalgia plus referred pain beyond muscle boundary
Arthralgia	Pain location at TMJ; modified by jaw function; familiar pain during TMJ palpation and/or jaw movements
Headache attributed to TMD	Headache in temple; modified by jaw function; familiar headache during temporalis palpation or by jaw movements

TMD dysfunction
Diagnoses	Clinical criteria	Imaging
Disc displacement with reduction (DDwR)	History of TMJ clicking/popping in last 30 days or noise detected during exam	Magnetic resonsnce imaging (MRI) to confirm when needed
DDwR with intermittent locking	Criteria for DDwR plus history of intermittent limited opening/locking that unlocks with a special manoeuvre	MRI if confirmation needed
Disc displacement without reduction, limited opening	History of mouth ‘would not open all the way’ and current limited opening; maximum assisted opening < 40 mm	MRI to confirm when needed
Disc displacement without reduction, no limited opening	Past history of ‘would not open all the way’, now no limitation; maximum assisted opening ≥ 40 mm	MRI to confirm when needed
Degenerative joint disease	History of TMJ crepitus in last 30 days or during exam	Computed tomography (CT) to confirm when needed
Subluxation	History in last 30 days, jaw locks/catches in a wide-open position and cannot close without a self-manoeuver	Not necessary. CT to confirm if needed

Management of orthodontic treatment and temporomandibular disorder

The classification and evidence-based guidelines for clinical practice published in 2014 [24] and 2024 [55] are essential for ensuring appropriate diagnosis and management strategies to be integrated into orthodontic care when treating patients presenting with or at risk for TMD. The initial step in the management of patients seeking orthodontic treatment should always involve a screening for TMD. Early identification of TMD is essential, and validated screening tools are available that rely on three simple, evidence-based questions. These include: (i) ‘Do you have pain in your temple, face, jaw, or jaw joint once a week or more?’—assessing general orofacial pain; (ii) ‘Do you experience pain once a week or more when opening your mouth or chewing?’—evaluating pain provoked by mandibular movement; and (iii) ‘Does your jaw lock or become stuck once a week or more?’—identifying functional impairment [59]. A positive response to any of these questions warrants further diagnostic evaluation, including a clinical examination and differential diagnosis to distinguish between TMD-related pain and functional disorders. Treatment should be initiated prior to commencing orthodontic therapy, with the resolution of pain being a prerequisite for starting or continuing orthodontic interventions. In December 2024, a consensus statement on the standard of care for TMD was published as a result of a workshop organized by the International Network for Orofacial Pain and Related Disorders Methodology (INfORM) within the International Association for Dental Research (IADR) [60]. This consensus emphasizes a conservative, evidence-based approach, beginning with self-management strategies—such as patient education, therapeutic exercises, self-massage, thermotherapy, dietary modifications, and identification and avoidance of parafunctional behaviours. Oral appliances may be used on a provisional basis, while invasive procedures such as surgery or irreversible dental treatments are not routinely recommended. Exercises specifically designed for TMD have been validated through DELPHI consensus studies and have shown efficacy in managing both pain and dysfunction [61, 62]. Once symptoms are controlled and the condition is stable, orthodontic treatment may proceed. However, it is important to recognize that, like other musculoskeletal disorders, TMD is often characterized by symptom fluctuation. Therefore, ongoing monitoring during orthodontic treatment is crucial. A clinical decision-making flowchart is recommended: if no TMD is identified during screening, orthodontic treatment can proceed; if TMD is diagnosed, conservative treatment should be initiated. If the patient responds positively, orthodontic care may resume; if not, referral to a TMD specialist is advised. Ultimately, clinicians are encouraged to move beyond outdated myths and dogmas, embracing a dynamic, evidence-driven approach that reflects the evolving nature of scientific knowledge (Fig. 2).

Figure 2.

Clinical decision-making flowchart for screening and managing TMD in orthodontic patients.

Conclusion

Current evidence indicates that the link between orthodontics and TMD should not be overstated. No existing orthodontic approach has been proven to cause, cure, or prevent TMD-related pain or functional disorders. Orthodontists are encouraged to move beyond the traditional mechanical assessment of occlusion and adopt a more comprehensive perspective that accounts for each patient’s individual adaptability and the role of central nervous system processing, to avoid triggering maladaptive, iatrogenic responses. Orofacial pain is a common complaint among patients in everyday clinical practice. Given the frequent presence of pre-existing TMD symptoms in individuals seeking orthodontic treatment, it is essential to assess the functional condition of the masticatory system before starting therapy and to maintain continuous monitoring throughout the treatment process.

Funding

None declared.

Data availability

I have read the journal’s requirements for reporting the data underlying my submission and ‘No new data were generated or analysed in support of this research’.