The modern history of TMD essentially starts in 1934. An otolaryngologist, Dr James Costen, described a syndrome (Costen’s syndrome) related to the TMJs and ears based on the analysis of 11 cases [3, 4]. The etiology was believed to be overclosure of the mandible due to loss of dental vertical dimension subsequent to tooth loss. Symptoms of Costen’s syndrome included TMJ sounds, pain in and around the jaw, limited mandibular opening, and myofascial tenderness/pain, as well as ear symptoms such as dizziness, tinnitus, pain, and impaired hearing. The close anatomical proximity of the TMJ to the external auditory meatus and related structures was believed to contribute to the ear symptoms. Almost a decade later, the famous anatomist Dr. Harry Sicher proved that Costen’s syndrome was fallacious from an anatomical viewpoint. [5, 6] Even though Costen’s etiologic proposals were disproved, they formed an initial baseline framework for a variety of dentally based theories of TMD etiology. These included trapped mandibles, reduced vertical dimension, condylar malposition, occlusal interferences or disharmonies, and malalignments of the mandible with the skull. All of these initiated great interest, awareness, and involvement of dentists to begin assessing and treating these problems. Dentists were also stimulated to look more closely at occlusion as the major causative factor in TMDs.

During this same time period, Dr. Alan Brodie, Chair of the Orthodontic Department at the University of Illinois (and student of Dr. Edward H. Angle), wrote about the differential diagnosis of TM joint conditions in orthodontics [7, 8]. In the 1940s, 1950s, and 1960s, several prominent orthodontists such as Thompson [9–11], Moyers [12], Ricketts [13], and Perry [14, 15] petitioned orthodontists to consider mandibular kinematics, occlusion, and the TMJ as important elements in their practices. It was not until the early 1970s that the “gnathologic-prosthodontic” view made its way into orthodontics, led by Dr. Ronald H. Roth [16–20]. Roth rationalized that orthodontics was analogous to prosthodontics/restorative dentistry such as full-mouth rehabilitation, with the difference being that the orthodontists did not “cut away” at teeth. Consistent with the traditional gnathologic-prosthodontic view, Roth believed that disharmonies of the occlusion and improper condyle position would cause temporomandibular joint (TMJ) disorders [16–20]. Therefore, in addition to attaining an optimal static occlusion as outlined by Angle [21, 22] and Andrews [23], orthodontists were obliged to attain gnathologically optimal functional occlusal and condyle relationships. The gnathologic goals were (are) as follows:

When these gnathologic objectives were not achieved with orthodontic treatment, it was believed that patients would be predisposed to TMD. An extension of this thinking was that the orthodontist could mitigate or cure TMD by correcting an existing malocclusion as well as the associated functional disharmony and improper CR position [16–20]. It was also contended that orthodontic treatment would cause TMD when orthodontists ignored the functional occlusion/CR goals of the gnathologic orthodontists [16–20].

The gnathologic/orthodontic view of the past, however, was not evidence based, and the scientific evidence accumulated over the years has contradicted much, if not all, of it. Intra-oral telemetry studies [24–27], as well as a large amount of subsequent scientific data, have supported the current concepts that occlusion and/or condyle position (CR) are not the primary cause of TMD [2, 28–35]. Of importance, the modern evidence-based view does not argue that occlusion and condyle position have no relevance to the considerations of TMD, but they at most play a secondary role. The gross evaluation of a patient’s occlusion is important in the diagnosis and treatment of TMD – “…assessment of the occlusion is necessary as part of the initial oral examination to identify and eliminate gross occlusal discrepancies…” [34]. Gross occlusal interferences causing or contributing to tooth mobility, fremitus, and deviations or deflections on mandibular closure and movement, should be evaluated for possible treatment.

TMDs comprise a group of musculoskeletal and neuromuscular conditions that involve the TMJs, the masticatory muscles, and associated tissues. TMDs are essentially divided into joint/ disk disorders and masticatory muscle disorders. The masticatory muscle disorders include muscle pain, inflammation, contracture, hypertrophy, neoplasms, and movement disorders. TM joint disorders include joint pain, inflammation, degeneration, neoplasms, disc displacements, hypomobility, hypermobility, congenital or developmental disorders and fractures [2, 29, 32]. (see Chap.​ 2). Due to the limited knowledge of the etiology and natural progression of the majority of these disorders, the classification of TMDs is still a constantly evolving topic. Given the difficulties associated with defining the etiologies of TMD, contemporary TMD diagnoses and treatments are based on addressing the symptoms rather than the cause; this is an approach that requires little attention to individual etiologic factors. Similar to the treatments of other musculoskeletal disorders, management is typically palliative and symptomatic, primarily targeted at decreasing pain, decreasing loading on the muscles and joints, and facilitating the restoration of function and quality of life of patients. TMD treatments in most cases should be conservative, reversible, and based on scientific evidence [36] (see Chaps.​ 3 and 8).

Orthodontic treatment in general has not been found to cause TMD [37–43]. Orthodontics is generally described as TMD “neutral,” in that it neither causes nor cures (or mitigates) TMD [37]. Orthodontics does not prevent the development of TMD in patients who have malocclusion [32]. Therefore, it is not evidence based for orthodontists or others in the dental profession to advise patients and parents of young children that orthodontic treatment is indicated to address a child’s malocclusion to mitigate the risk of TMD developing in the future. The utilization of any specific type of orthodontic treatment, or appliance, such as headgear, elastics, chin cup, or whether extractions are performed, has not been shown to lead to any increased risk for TMD [35–53].

Dentists have vigorously debated the role of occlusion or malocclusion in causing TMD for many years. Numerous studies have investigated the relationship between both functional and morphologic aspects of occlusion and TMD; some have showed statistically significant associations (not cause-effect), while others have reported no such relationship. The differences in the findings can be explained by problems in the study designs of many of these investigations. The main problems have been: relating symptoms to disease states such as joint sounds with no pain, failing to establish a differential diagnosis, small and heterogeneous samples with lack of controls or poorly matched comparison or control groups, issues with sample selection bias, inter- and intra-examiner variation, failing to isolate contributing factors, or failing to neutralize confounding variables [42, 44].

Several functional and morphological occlusal relationships have been investigated, and a small number of them have been purported to cause people to develop TMD [42, 44]. Some of the occlusal factors are open bite, overbite, overjet greater than 7 mm, centric slides (greater than between 2 and 4 mm), unilateral posterior crossbites with and without lateral functional mandibular displacement, and missing posterior teeth. Current understanding and evidence-based literature fail to demonstrate a causal relationship between these occlusal factors and TMD signs and symptoms; thus, the relationship is only an association [42, 44, 54]. Therefore, with regard to TMDs, it is clear that occlusion today is not believed to be as important as it once was thought to be. This is largely a reflection of the significant amount of research that has taken place in the last two decades. TMD has moved from a dental and mechanical-based model to a biopsychosocial and medical model that integrates a host of biologic, behavioral, and social factors to the onset, maintenance, and progression of TMDs. These disorders are considered to have multiple associated etiologic factors, including both extrinsic and intrinsic patient factors that may contribute to the development of symptoms. Factors such as parafunction, trauma, psychosocial disorders, emotional stress, gender, genetics, and centrally mediated mechanisms are currently considered to be most important.

Centric relation (CR) has been a topic of much debate in dentistry for more than a century. The definition as well as the concept of CR has changed over the years. For more than a half century, the definition of CR within the prosthodontic community has evolved from a retruded, posterior, and for the most part, superior condyle position to an anterior-superior condyle position [55]. Dr. Ronald Roth in the early 1970s advocated a posterior-superior (retruded CR) position, and then he changed his view in the early to mid-1980s in favor of the more current anterior-superior CR position. Those arguing for an anterior-superior CR position were motivated by findings from TMJ imaging of the era, initially TMJ arthrography followed by magnetic resonance imaging (MRI), demonstrating many TMJ internal derangements with the disc often located (or displaced) anteromedially. They also realized that the pull of the elevator masticatory muscles was in an upward and forward direction, typically seating the condyles in an anterior and superior position position.

CR has been defined in so many ways that today it has lost credibility [56]. The changes in the definition of CR appear to have been quite arbitrary rather than based on evidence, spurring Dr. Lysle Johnston to sarcastically write in 1990: “It could be argued that the progressive modifications in the definition of CR have done more to eliminate centric slides than 20 years of grudging acquiescence of the precepts of gnathology.” [57] Johnston also followed with: “I know of no convincing evidence that condyles of patients with intact dentitions should be placed in CR, or that once having been placed there, the resulting improvement on nature will be stable.” [57]

There is little evidence to support the gnathologic view that centric occlusion (CO) position or maximum intercuspation (MI) should be co-incident with an arbitrary CR position. In addition, centric slides greater than 4 mm that have been found associated with TMJ arthropathies are most likely the result of TMD rather than the cause [42, 44]. It is still important, however, for orthodontists to check for centric slides and to take some note if they are greater than 2 mm in order to discern whether there is a marked slide between CO/MI and centric relation occlusion or CRO, commonly referred to as a “Dual Bite” or “Sunday Bite.” This is especially important in determining the true extent of a dental and skeletal malocclusion in three planes for orthodontic treatment planning. Kandasamy et al. [58] recently demonstrated via an MRI study that irrespective of the centric bite registration used, including the Roth Power Bite Registration, clinicians cannot accurately and predictably position condyles into specific locations in the glenoid fossae.

Further, the evidence suggests that there is a range of acceptable condylar positions and not one position that is optimal for all individuals. There is a particular optimal position for each person, with the anterior to mid-condyle positions more commonly found than retruded (posterior) CR positions. Nonetheless, there is evidence that individuals with healthy TMJs can have a retruded condylar position [31, 37, 53, 59, 60]. Further, the condyle-fossa relationship in every person may change very slightly throughout the day depending upon various factors including fatigue of the facial and masticatory muscles, parafunction, posture, tongue pressure, hydration of the disc, and so on. There is no optimal three-dimensional position/location of the TMJ condyles in the glenoid fossa [2, 32, 34]. Various orthodontic treatments such those involving extractions, headgear, inter-arch elastics, chin cups, and so forth do not necessarily cause the posterior displacement (or positioning) of the mandibular condyles nor do they necessarily predispose patients to developing TMD [35–53].

Criteria for an optimal “static occlusion” have found universal support based primarily on the work of Angle [21, 22] and Andrews [23]. It is important to be cognizant of the fact that malocclusion is not a disease and there is no persuasive evidence to demonstrate that deviations from Angle’s normal/class I relationship will predispose patients to TMD or periodontal disease [61]. Nonetheless, there is less of a consensus as to what constitutes the optimal “functional occlusion”; this refers to the contact relationship of the upper and lower teeth within the functional range of mandibular movement. This subject has been debated for over a century and views are based more so on conjecture rather than evidence. Clark and Evans stated: “The criteria that denote an ‘ideal’ functional occlusion have not been conclusively established.” [62]

There is a long-standing belief that the optimal functional occlusion for all dental patients, including orthodontic patients, is “canine-protected occlusion” (CPO or mutually protected occlusion). Canine-protected occlusion refers to contact occurring only at the canine teeth on the working side with no occlusal contact(s) on the non-working (balancing) side, during lateral or side-to-side mandibular movements. That is, the canine teeth disclude the entire dentition on laterotrusive movements out of centric occlusion. The contention by some is that failure to establish CPO during orthodontic treatment could predispose patients to TMD, as well as orthodontic relapse [16–18, 20, 63]. When discussing functional occlusion, one must qualify the difference between the terms balancing side contact and balancing side interference. A balancing side contact is a very light occlusal contact and this is considered benign. On the other hand, a balancing side interference is a gross occlusal disharmony that can cause deflection of the mandible, tooth mobility, fremitus, and so forth. Balancing side contacts are acceptable for a physiologic functional occlusion, irrespective of what tooth contact occurs on the working side. A balancing side interference is not acceptable and deviates from a healthy functional occlusion.

To regard CPO as the optimal functional occlusion for orthodontic patients is arbitrary and not supported by the evidence [64]. The routine selection and attainment of CPO as the optimal functional occlusion type for all patients ignores the importance of each person’s unique stomatognathic and neuromuscular functional status. CPO might be one of several functional occlusion schemes that are acceptable for orthodontic patients. Further, not all subjects actually function in the extreme lateral side-to-side border movements governed by the functional occlusion paradigm of CPO. Studies have also shown that the functional occlusion which exists as the mandible moves immediately laterally out of centric occlusion is not typically CPO, and individuals move in and out of one functional occlusion type to another as the mandible moves from centric occlusion to the extreme cusp to cusp lateral border movement.

No one single type of functional occlusion predominates in nature. As Woda and coworkers found back in the mid-1970s, “Pure canine protected or pure group function rarely exists and balancing contacts seem to be the general rule in the population of contemporary civilizations.” [65] Even if a particular functional occlusion is achieved, it will not necessarily be stable or retained over the patient’s life time [41, 62]. If CPO is established, one must take in to consideration that over time the functional occlusion will typically evolve into group function followed by balanced occlusion as a result of tooth attrition, changes in the oral environment, demands on the dentition with growth and aging, and occlusal settling, all affecting the vertical level and position of the canines.

CPO is difficult to achieve in an orthodontically treated population because there is less canine rise and disclusion when the canines are in an Angle’s Class I/normal relationship; the canines never come together in contact in a cusp tip to cusp tip relationship in lateral border movements like they do in a Class II relationship [66]. In a Class I canine relationship, rather than cusp tip to cusp tip laterotrusive functional relationship typical of functioning Class II canines, the canines disclude in a cusp incline plane to cusp incline plane functional relationship. This provides less canine rise and therefore more chance of having balancing side contacts/interferences. So to achieve CPO, an orthodontist would have to either establish a canine relationship that is between a Class I and a full unit Class II relationship or deliberately extrude patients’ canines past their physiologic and normal contact point/area and/or restoratively build up the canine tips to achieve CPO. This not only tends to produce a non-consonant smile arc but also produces an unesthetic “vampire look.” Achieving canine-protected occlusion routinely in orthodontics is not evidence based and is generally mutually exclusive to achieving a consonant smile arc and ideal smile esthetics [64].

In summary, none of the traditional functional occlusion schemes are inherently bad, but it does seem that group function occlusion and balanced occlusion (with no interferences and only balancing side contacts/light) appear to be the most practical for orthodontic patients over a lifetime. It is not evidence based to simply advocate one type of functional occlusal scheme over another for all patients. A patient’s static occlusion type, craniofacial morphology, parafunctional habits, chewing kinematics (vertical versus horizontal chewing patterns), and current oral health status are only some of the myriad factors that contribute to establishing the best and most practical functional occlusion scheme for each individual patient.

Articulators are mechanical devices which aim to crudely simulate mandibular movements and occlusal relationships. There are a number of different types of articulators such as arcon, nonarcon, fully adjustable, semi-adjustable, polycentric hinge, and so forth. Articulators are useful for involved prosthodontic treatments and orthognathic surgical procedures to at least maintain a certain vertical dimension, while laboratory procedures are being performed. Early on, the need to mount cases was related mostly to detecting “sagittal” discrepancies, particularly “Sunday bites.” Later on it became more about finding transverse and vertical discrepancies. Nonetheless, the utility of articulators in orthodontics to improve patient diagnoses has been the subject of much debate ever since the early 1970s, when Dr. Ronald Roth introduced the classic gnathological-prosthodontic philosophy to the orthodontic profession [16–20]. Roth believed that mounting dental study casts on articulators would aid the orthodontist in diagnosing three-dimensional condylar (CR) discrepancies. He also believed that he could position and seat condyles in a more ideal position within the glenoid fossa, and then he could base his orthodontic treatments around this condylar position (i.e., CR) with the aim of curing a pre-existing TMD or mitigating the risk of TMD developing in the future.

It is has been argued that articulator mountings with the appropriate centric bite registration will improve the orthodontic diagnostics (Angle’s classification) in 18.7–40.9 % of cases [67, 68]. Whether all cases need to be mounted is the subject of much debate. Some gnathologic orthodontists take the position that not all cases need to be mounted, so they only mount in cases needing orthognathic surgery or in TMD patients. Others have stated that they like to mount models in cases involving most adults, or those with multiple missing teeth, functional shifts and/or midline deviations, and those with deviations on opening or closing. Nonetheless, Dr. Frank Cordray, a contemporary Roth supporter, believes all cases need to be mounted because a practitioner would not be able to determine beforehand which cases will become the most challenging [63]. Ellis and Benson found that mounting of study casts in CR instead of CO did not make any difference in the eventual diagnosis and treatment planning decisions [69].

As mentioned previously, in the past, the views on the causes and treatments for TMD were centered on a mechanical dental-based model and this involved a detailed analysis of occlusion and condyle position (CR). As mentioned previously, the contemporary TMD model has moved away from focusing on these issues and has embraced a medical and biopsychosocial model. So the question is, do we need to even debate the issue of the utility of articulators in orthodontics in general, or in relation to TMDs, when there is only a minimal influence of occlusion and condyle position on the development of TMDs? In our view, the answer is a simple no. Regardless, we will still discuss the key issues in relation to articulators in orthodontics below, as there still exists a vocal and substantial proportion of the dental profession that still propagates this philosophy as the standard of care.

Let us assume that seating the condyle in the prescribed “ideal” position within the fossa and then rehabilitating the occlusion or malocclusion to this position with either orthodontics, prosthodontics and/or orthognathic surgery is critical to preventing or curing TMD. If this is the case, then in order to be able to mount a set of models properly on an articulator, one has to be able to obtain an accurate bite registration that seats the condyle in the so-called ideal CR position within the fossa. The critical issue here is whether these bite registrations are reliable and more importantly valid. Orthodontic gnathological records such as the Roth power centric bite registration and the articulator mounting instrumentation appear to be reliable (repeatability and consistency of the records/techniques) in controlled laboratory conditions [63, 70, 71]. However, are these centric bite registrations valid? That is, do any of these recording methods, including the Roth power bite registrations, actually anatomically seat the condyles in an anterior-superior position within the fossa according to imaging findings? The evidence-based data supports the view that clinicians are not able to estimate the position and location of patients’ condyles via certain bite registrations taken chairside. Kandasamy et al [58] have provided MRI data demonstrating that patient condyles are not located where gnathologists believe they would be. Based on their study, they concluded that given the small changes and the extremely unpredictable nature of condylar positioning associated with centric relation and Roth power bite registrations, advocating this modality routinely in clinical practice as a prophylactic or curative measure for TMD is an invalid and unjustified procedure [58].

There are several other problems with gnathologic bite registrations and articulators: