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Journal of Oral Rehabilitation Journal of Oral Rehabilitation 2010 37; 411–429 Review Article The role of orthodontics in temporomandibular disorders A. MICHELOTTI & G. IODICE Department of Oral Sciences, Section of Orthodontics and Temporomandibular Disor...

Journal of Oral Rehabilitation Journal of Oral Rehabilitation 2010 37; 411–429 Review Article The role of orthodontics in temporomandibular disorders A. MICHELOTTI & G. IODICE Department of Oral Sciences, Section of Orthodontics and Temporomandibular Disorders, University of Naples Federico II, Italy SUMMARY Temporomandibular Disorder (TMD) is with signs and symptoms of TMD. Because ortho- the main cause of pain of non-dental origin in the dontic treatment lasts around 2 years, orthodontic oro-facial region including head, face and related patients may complain about TMD during or after structures. The aetiology and the pathophysiology treatment and orthodontists may be blamed for of TMD is poorly understood. It is generally causing TMD by unsatisfied patients. This hypothe- accepted that the aetiology is multifactorial, involv- sis of causality has led to legal problems for dentists ing a large number of direct and indirect causal and orthodontists. For these reasons, the interest in factors. Among such factors, occlusion is frequently the relationship between occlusal factors, orthodon- cited as one of the major aetiological factors causing tic treatment and TMD has grown and many studies TMD. It is well known from epidemiologic studies have been conducted. Indeed, claims that orthodon- that TMD-related signs and symptoms, particularly tic treatment may cause or cure TMD should be temporomandibular joint (TMJ) sounds, are fre- supported by good evidence. Hence, the aim of this quently found in children and adolescents and show article is to critically review evidence for a possible increased prevalence among subjects between 15 association between malocclusion, orthodontic and 45 years old. Aesthetic awareness, the develop- treatment and TMD. ment of new aesthetic orthodontic techniques and KEYWORDS: occlusion, orthodontics, temporoman- the possibility of improving prosthetic rehabilita- dibular disorders tion has increased the number of adults seeking orthodontic treatment. The shift in patient age also Accepted for publication 26 February 2010 has increased the likelihood of patients presenting number of direct and indirect causal factors. Among Introduction these, occlusion is frequently cited as one of the major Temporomandibular disorder (TMD) is usually defined aetiological factors causing TMD (1). Numerous aetio- as a collective term that embraces a number of clinical logical and therapeutic theories are based on this problems that involve the masticatory muscles, the presumed association and have justified the use of temporomandibular joint (TMJ) and the associated several therapeutic approaches such as occlusal appli- structures and forms the most prevalent clinical entity ance therapy (2), anterior repositioning appliances (3), afflicting the masticatory apparatus. In this respect, it is occlusal adjustment (4), restorative procedures (5), considered a musculo-skeletal disorder. However, TMD orthodontic (6) and orthognathic treatment (7). Con- is also the main cause of pain of non-dental origin in versely, many types of dental interventions, including the oro-facial region including head, face and related routine orthodontic treatment, have been reported as structures (1). causes of TMD (8). The aetiology and the pathophysiology of TMD is Prior to the late 1980s, a very limited number of well- poorly understood. It is generally accepted that the designed clinical studies focusing on this subject were aetiology of TMD is multifactorial, involving a large available. Reynders (9), in a review published in 1990, ª 2010 Blackwell Publishing Ltd doi: 10.1111/j.1365-2842.2010.02087.x 412 A. MICHELOTTI & G. IODICE found that of the 91 articles published between 1966 systematic reviews have been published and most and 1988 on the relationship between orthodontic articles are case reports or case ⁄ control studies. treatment and TMD, only six were sample studies Currently, the possible relationship between ortho- involving large groups of individuals. The remaining dontic therapy and TMD signs and symptoms is still a articles were case reports (n = 30) and viewpoint matter of debate among orthodontists, dental commu- articles (n = 55), usually giving an expert’s opinion nity and dental patients. Hence, the aim of this article is with almost no data. The attention of the orthodontic to critically review evidence for a possible association community regarding TMD was heightened in the late between malocclusion, orthodontic treatment and 1980s after litigation involving orthodontic treatment TMD. as the cause of TMD in orthodontic patients (10). Evidence to suggest that orthodontics had not caused Does malocclusion cause TMD? the problem was lacking. The case went against the orthodontist, resulting in almost a million dollars being Historically, the first report of a relationship between paid out in compensation. occlusion and temporomandibular joint function was It is well known from epidemiologic studies that suggested by Costen (14), an otorhinolaryngology TMD-related signs and symptoms, particularly tempo- surgeon, who hypothesized that changes in dental romandibular joint (TMJ) sounds, are frequently condition (e.g. loss of vertical dimension and deep bite) found in children and adolescents and show increased led to anatomical changes in the temporomandibular prevalence among subjects between 15 and 25 years joint, creating ear symptoms. He stated that ‘The actual old (11). Nowadays the orthodontic patient population source of this group of complaints was confirmed by the includes both children and adults. Aesthetic aware- marked improvement which followed correction of the over- ness, the development of new aesthetic orthodontic bite, renewal of molar support to take pressure off the condyle, techniques (i.e. lingual appliances or transparent and establishment of proper articulation of the condyle within removable appliances) and the possibility of improving the fossa’. Although this hypothesis was based on the prosthetic rehabilitation have increased the number of analysis of only 11 cases, the dental profession started adults seeking orthodontic treatment. The shift in treating patients diagnosed with the so-called ‘Costen patient age also has increased the likelihood of Syndrome’ with bite-raising appliances. patients presenting with signs and symptoms of TMD Thereafter, occlusal interferences have been consid- (12). Because orthodontic treatment lasts around ered as risk factors for TMD. Ramfjord (15), through an 2 years, orthodontic patients may complain about electromyographic (EMG) study on 34 patients, stated TMD during or after treatment and orthodontists that ‘The most common occlusal factor in bruxism is a may be blamed for causing TMD by unsatisfied discrepancy between centric relation and centric occlusion; patients. This hypothesis of causality has led to legal invariably such discrepancy is accompanied by asynchronous problems for dentists and orthodontists. For this contraction or sustained strain in the temporal and masseter reason, the interest in the relationship between muscles during swallowing’. Therefore, he suggested occlusal factors, orthodontic treatment and TMD has occlusal equilibration to provide muscular balance grown and many studies have been conducted. and to eliminate the bruxism. The proposed causal Indeed, claims that orthodontic treatment may cause chain of events suggested that interference acts as a or cure TMD should be supported by good evidence. trigger for bruxism, which in turn may result in The quality of the published studies has improved overload of the masticatory muscle, tenderness, pain throughout the last decade, since 1995, when a and TMJ clicking (16, 17). Hence, the dental profession seminal article on evidence-based medicine was pub- embarked on massive occlusal equilibration looking for lished (13). According to evidence-based dentistry, an ideal occlusion (18, 19). However, EMG studies dental practitioners should use current best evidence aiming to test this hypothesis by applying experimental when making decisions about the care of each patient interferences gave inconsistent findings (20–27). Re- through a literature review, considering studies that views on this issue have pointed out that the relation- are at the highest level of scientific weight. Neverthe- ship between occlusal interferences and masticatory less, a literature search on malocclusion and TMD function is still far from being clearly understood (for a shows that nowadays metanalysis is lacking, only few review see (28, 29). Michelotti et al. (30) investigated ª 2010 Blackwell Publishing Ltd  ORTHODONTICS AND TEMPOROMANDIBULAR DISORDERS 413 the effects of an acute occlusal interference on habitual induced occlusal interference and that the N-methyl-D- muscle activity assessed in the natural environment, aspartate antagonist reduced the induced hyperalgesia and on signs and symptoms of TMDs. In the study suggesting central sensitization mechanisms. carried out in a double-blind crossover design, each It could be hypothesized that subjects who are subject served as his ⁄ her own control and was moni- occlusally hypervigilant are disturbed by the interfer- tored during 6 weeks, in four different conditions: ence and increase the activity of the masticatory interference-free condition before the application of muscles which in turn may lead to pain and dysfunc- any interference, active interference condition, dummy tion. Occlusal hypervigilance may be explained by the interference condition and interference-free condition Generalized Hypervigilance Hypothesis according to after the removal of the interferences. A strip of gold which hypervigilance is a ‘perceptual habit’ that foil was placed on the lower first molar on the occlusal involves subjective amplification of a variety of aversive contact, disturbing the intercuspal position. To create sensations, not just painful ones (34). According with the dummy interference, the strip was placed on the this hypothesis, if attention is habitually focused on vestibular surface without interfering with the intercu- sensations of a particular type, their amplification spal position. The activity of the masseter muscle increases and became autonomous (35, 36). An ipsilateral to the interference side was recorded by explanatory model for this hypothesis is shown in means of a portable EMG recorder for eight consecutive Fig. 1. hours in the natural environment. This study gave Orthodontists were introduced to the field of TMD evidence that the response of the masticatory system to following the theorising of Thompson (37) who believed active occlusal interference was a reduction in daytime that malocclusion caused the posterior and superior habitual activity of the masseter muscle. None of the displacement of the condyle. Hence, there was the need subjects reported signs and ⁄ or symptoms of TMD. The to bring downward and forward the condyle by freeing reduction may reflect an avoidance behaviour that the up the trapped mandible. Since then, various malocclu- subjects acquired during their common diurnal activi- sions have been associated with TMD signs or symp- ties. The increasing trend of the EMG activity levels toms. In 1988, Greene and Laskin (38) published a list of found after the third recording day of the active occlusal 10 myths in this field that, surprisingly after 20 years, interference condition indicates rapid adaptation to the are still a matter of debate among orthodontists: disturbed occlusal condition and is consistent with the 1 People with certain types of untreated malocclusion gradual decrease in the perception of occlusal discom- (for example, Class II Division 2, deep overbite, cross- fort. The sample investigated in this study included bite) are more likely to develop TM disorders. healthy subjects without self-report of parafunctional 2 People with excessive incisal guidance, or people activities. It is possible that the reaction to occlusal totally lacking incisal guidance (open bite), are more disturbance is different in patients with TMD. Indeed, likely to develop TM disorders. the results obtained by Le Bell et al. (31, 32) in former 3 People with gross maxillo-mandibular disharmonies patients with TMD support this view. The same study are more likely to develop TM disorders. design previously described (30) was used, thereafter, 4 Pre-treatment radiographs of both TMJs should be to investigate the effects of an acute occlusal interfer- taken before starting orthodontic treatment. The posi- ence on habitual muscle activity assessed in the natural tion of each condyle in its fossa should be assessed, and environment in a group of subjects with myofascial orthodontic treatment should be directed at producing pain. Preliminary results showed increase in daytime a good relationship at the end. (‘Good’ position usually habitual activity of the masseter muscle and increase in was defined as being a concentric placement of the masticatory muscle pain (Michelotti A, Palla S, Festa P, condyle in the fossa). Farella M, unpublished data). Consistently, a study 5 Orthodontic treatment, when properly done, reduces conducted on rats showed hyperalgesia at the mastica- the likelihood of subsequently developing TM disor- tory muscles after the application of experimental ders. occlusal interferences by directly bonding crowns of 6 Finishing orthodontic cases according to specific different heights (33). The authors also found that functional occlusion guidelines (e.g. gnathologic prin- removal of the crown after 6 days did not reduce the ciples) reduces the likelihood of subsequently develop- hyperalgesia observed for at least 1 month after the ing TM disorders. ª 2010 Blackwell Publishing Ltd 414 A. MICHELOTTI & G. IODICE Normal function Decreased parafunctional activities Avoidance behaviour Occlusal + hypovigilance Psychological tolerance Occlusal – hypervigilance Occlusal change Adaptability Physiocogical Somatosensory amplification tolerance Increased parafunctional Physiocogical tolerance activities threshold exceeded TMD symptoms Fig. 1. Different reaction to occlusal changes according to the ‘hypervigilance’ hypothesis. 7 The use of certain traditional orthodontic procedures controls are not selected according to patient referral. and ⁄ or appliances may increase the likelihood of Controls come from the same population as the cases, subsequently developing TM disorders. which reduces the possibility of selection bias and 8 Adult patients who have some type of occlusal confounding. ‘disharmony’ along with the presence of TMD symp- Population-based studies were done on 3033 subjects toms will probably require some form of occlusal to investigate the association between overbite (vertical correction to get well and stay well. occlusal discrepancy) or overjet (sagittal occlusal dis- 9 Retrusion of the mandible because of natural causes crepancy) and self-report of TMD symptoms (39), and or after treatment procedures is a major factor in the the relationship between clicking and crepitus of the aetiology of TM disorders. TMJ, overjet and overbite (40). Both studies failed to 10 When the mandible is distalized, the articular disc demonstrate a relationship between overbite or overjet may slip off the front of the condyle. and TMD signs and symptoms. None of these statements is evident according to Among different malocclusions, posterior crossbite current mainstream scientific opinion. The majority of (transversal occlusal discrepancy) is thought to have a studies carried out using an appropriate study design stronger impact on the correct functioning of the and relevant outcome measures were unable to show masticatory system. Several problems have been that orthodontic therapy has a preventive or curative ascribed to the unilateral posterior crossbite. Firstly, it effect on the occurrence of TMD. Therefore, even has been suggested that the altered morphological though various malocclusions have been associated relationship between the upper and lower dentition with TMD signs or symptoms, the studies published may result in right-to-left-side differences in the con- have not been carried out with a rigorous design and dyle–fossa relationship, and in the height of the condyle are open to criticism. Indeed, several studies investi- and the mandibular ramus resulting in an asymmetric gating the relationship between occlusal factors and mandibular growth (41–46). However, early treatment TMDs have been carried out with small sample sizes or to normalize the occlusion created appropriate condi- have used dental students ⁄ staff as controls in case– tions to obtain a normal growing pattern both in animal control design; this might lead to selection bias, partic- studies and in human studies (44–46). Secondly, jaw ularly if potential confounding variables are not taken function alteration including asymmetric pattern of jaw into account in the analysis. A population-based study muscles EMG activity (47), lower bite forces (48), of risk factors for TMD has the advantage that cases and reduced thickness of the ipsilateral masseter (49) and a ª 2010 Blackwell Publishing Ltd  ORTHODONTICS AND TEMPOROMANDIBULAR DISORDERS 415 reverse sequence chewing pattern (50, 51) have been has been conducted to date. Based on these observa- reported. Also, these functional alteration normalized tions, although there is a rationale for early correction after early correction of the crossbite (52–54). Thirdly, it of unilateral posterior crossbites in children to improve has been hypothesized that the crossbite is a compen- neuromuscular function of the stomatognathic system, satory curvature in the visceral cranium for the trans- clinicians should be cautious in recommending early mission of the asymmetry of the body to the skull. orthodontic treatment aiming only to prevent joint According to this hypothesis, dental occlusion may clicking. Consistently, Arat et al. (64) investigated con- infiuence whole body posture, and disorders of the dyle-disc positions on sagittal and coronal closed- functioning, such as chewing and swallowing, of mouth magnetic resonance imaging (MRI) in unilateral masticatory muscles can be transmitted to distal mus- and bilateral posterior crossbite patients before and culature along the so-called ‘muscle chains’ (55). 18 weeks after rapid maxillary expansion (RME). The Again, early treatment of children with unilateral authors concluded that RME is neither a risk factor nor crossbites is suggested to reduce the adaptive demands a prevention for TMD. Furthermore, it has been found on the masticatory system and to create appropriate that RME in children with unilateral posterior crossbite conditions for normal occlusal development, facial did not change articular disc position and configuration symmetry and stable head posture. Thilander et al. (65). (56) recommended the treatment of posterior crossbite The evidence for causality linking malocclusion and at a young age to prevent asymmetrical facial growth. TMD should respect several criteria as suggested by Hill Also, early treatment of posterior crossbites is advocated (66) in 1965. First of all, the causes (i.e. malocclusions) to prevent them from being passed on to the adult should precede the effects (i.e. TMDs), whereas in the dentition (57). In contrast, crossbite orthodontic cor- literature, we find studies that show the opposite [i.e. rection could hardly give benefits in adults where muscle pain causes changes in the occlusion (67)]. skeletal adaptation has already occurred (58). Finally, Then, the association must be strong and the more according to the proposed causal chain of events, severe the malocclusion, the more severe should be the posterior crossbite may result in alterations of the disease. By contrast, previous reports suggest that the disc–condyle relationship, which in turn are responsible risk of TMD may be doubled by just a few severe for disc displacement and TMJ clicking (59–62). Pullin- occlusal factors (60). Furthermore, in the case of ger et al. (60) examined five patient groups (i.e. disc evidence of causality, results from the scientific litera- displacement with reduction, disc displacement with- ture should be consistent across time. This does not out reduction, TMJ osteoarthrosis with disc displace- hold for TMD: on examining the publications from ment history, primary osteoarthritis and myalgia only) 1995 to 2009, an increasing number of studies refute or in comparison with asymptomatic controls and re- reduce the importance of the role of occlusal factors in ported that the chance of an individual with unilateral the aetiology of TMD. Finally, the major role of posterior crossbite having TMJ disc displacement with occlusion also appears unlikely when taking into reduction was 3Æ3:1. The association between TMJ disc account the higher prevalence of TMD in females displacement and unilateral posterior crossbite has been during their child-bearing years, whereas malocclusion analysed in a population-based cross-sectional study is equally distributed among genders and ages. The (63). In a sample of 1291 young adolescents recruited predominance of women seeking treatment much more from three schools, regression analysis failed to find a often than man points to a possible connection between significant association between unilateral posterior oestrogen hormones and dysfunction (68, 69). In such crossbite and disc displacement with reduction. The a case, the concept of biological plausibility is not authors concluded that posterior unilateral crossbite satisfied because the cause–effect relationship is not does not appear to be a risk factor for TMJ clicking, at consistent with our knowledge of the mechanisms of least in young adolescents and that there is an initial the disease. It can be concluded that occlusion is optimal TMJ functional adaptation to unilateral poster- currently declining in importance and is now consid- ior crossbite, at least until young adolescence. Although ered as a cofactor. Other aetiological factors, such as there appears to be some rationale for early correction trauma, parafunctional behaviour, psychosocial disor- of unilateral posterior crossbites in children, no pro- ders, gender, genetics and centrally mediated mecha- spective clinical trial of this type of treatment efficacy nisms, are considered more important. ª 2010 Blackwell Publishing Ltd 416 A. MICHELOTTI & G. IODICE medico-legal implications, has had a considerable Does orthodontic treatment cause TMD? impact on the decline of the extraction rate for Do any orthodontic procedures (i.e. orthodontic purpose (73). Indeed, condylar retro-posi- extraction, functional appliances, class tion has been found in patients with disc displacement II ⁄ III elastics, chin-cup, headgear, fixed or (74). However, correlation between disc displacement removable appliances) lead to a greater and the posterior position of the condyle is controver- incidence of TMD? sial because of the large inter-individual variation in The need to investigate on the relationship between condylar position. For instance, it has been shown that orthodontics and TMD came from the occurrence of asymptomatic subjects may have anterior, normal or legal cases in which patients blamed orthodontists for posterior position of the condyle within the fossa (75). causing TMD symptoms during or after orthodontic Actually, the ‘ideal’ position of the condyle still remains treatment (10). From the late 1980s, the orthodontic one of the controversial issues in orthodontics and in community was alerted and gave funds to investigate prosthodontics (76). Also, mounting casts on the the relationship between orthodontic treatment and articulator, using axiography to find the kinematic TMD. In 1995, a review of this topic by McNamara, centre (77) to plan the orthodontic treatment and Seligman and Okeson (70) listed eight conclusions that maintaining the condyle in the centric relation position, refute this possible association. is not supported by scientific evidence (78). Further- 1 Signs and symptoms of TMD occur in healthy more, there is no evidence in the literature to prove individuals that the positional differences are to be considered 2 Signs and symptoms of TMD increase with age, ‘pathological’. It is probable that they are merely related particularly during adolescence. Thus, TMD that orig- to the unreliable measurements obtained by using a bi- inates during orthodontic treatment may not be related dimensional diagnostic tool instead of a three-dimen- to the treatment. sional one such as individualized magnetic resonance 3 Orthodontic treatment performed during adoles- or computer tomography scan (79). Finally, even if a cence generally does not increase or decrease the retro-positioned condyle is slightly more frequently chances of developing TMD later in life. found in patients than in asymptomatic subjects, it is 4 The extraction of teeth as part of an orthodontic not possible to say whether this is the cause or treatment plan does not increase the risk of developing consequence of anterior disc displacement for remod- TMD. elling changes in the joint geometry. 5 There is no elevated risk for TMD associated with any The hypothesis that different orthodontic techniques particular type of orthodontic mechanics. (e.g. functional appliances, class II ⁄ III elastics, chin-cup, 6 Although a stable occlusion is a reasonable ortho- headgear, fixed or removable appliances) and treatment dontic treatment goal, not achieving a specific gnatho- plans can be involved as aetiological factors for TMD logically ideal occlusion does not result in TMD signs has also been tested in recent decades. Dibbets and van and symptoms. der Weele (80) compared groups of children who were 7 No method of TM disorder prevention has been treated with different orthodontic treatment proce- demonstrated. dures, functional appliances, Begg light wire, chin cups, 8 When more severe TMD signs and symptoms are four-first premolars extracted, all other types of extrac- present, simple treatments can alleviate them in most tion and no extraction. Patients were monitored for a patients. 20-year period after the start of orthodontic treatment. Although these statements were published 15 years Although signs and symptoms of TMD increased with ago, most orthodontists and dental community still age, after 20 years neither orthodontic treatment nor believe that internal derangement may be the conse- extraction showed a causal relationship with the signs quence of the retraction of the mandible during some and symptoms of TMD. Therefore, the authors con- forms of orthodontic treatment (71). In particular, it has cluded that neither orthodontic treatment nor extrac- been suggested that premolar extractions in the upper tion had a causal relationship with the signs and arch can cause a posterior displacement of the condyle symptoms of TMD. which in turn could be associated with increased risk of Henrikson and Nilner (81) compared 11–15-year-old joint dysfunction (72). This concern, as well as the treated and untreated female subjects with class II ª 2010 Blackwell Publishing Ltd  ORTHODONTICS AND TEMPOROMANDIBULAR DISORDERS 417 division 1 malocclusions with females with normal ing in a longitudinal study the effects of an orthogna- occlusions. All the patients were treated with a fixed thic procedure in a group of patients with class III appliance together with either headgear or class II malocclusion on muscular and articular signs and elastics and ⁄ or extractions. Signs and symptoms of symptoms of TMD, Farella et al. (88) reported that TMD were monitored for 2 years. They reported indi- bimaxillary osteotomy did not initiate or aggravate vidual fluctuations of TMD symptoms in all three signs and symptoms of TMD and that the occurrence of groups. In the orthodontic group, the prevalence of signs and symptoms of TMD after OS fluctuated with TMD symptoms decreased over the 2 years. The Class II an unpredictable pattern. and Normal groups showed minor changes during the According to current knowledge, the role of ortho- 2-year period. TMJ clicking increased in all three groups dontic treatment in the aetiology of TMD is not over the 2 years. Hence, orthodontic treatment did not confirmed. The conclusions listed by McNamara et al. increase the risk for or worsen pre-treatment signs of (70) are still valid. Consistently, a meta-analysis on TMD. On the contrary, subjects with Class II malocclu- orthodontics and TMD (89) reported that no study sions and signs of TMD of muscular origin seemed to indicated that traditional orthodontic treatment, benefit functionally from orthodontic treatment in a 2- including Begg appliance, Herbst appliance, Class II year perspective. elastics and extraction, bionator and headgear, facial Rey et al. (82) compared a sample of Class III patients mask and chincup, increased the prevalence of TMD. treated with orthodontics and mandibular cervical The same conclusions can be drawn from the reviews headgear, Class I patients treated orthodontically with- published by Luther (8, 90) who stated that neither out extractions and subjects who had not been previ- static nor dynamic occlusal factors (including ortho- ously treated for the presence or absence of TMD: Class dontics) can be said to ‘cause’ TMD, and from the III patients treated with mandibular cervical headgear systematic review published by Mohlin (91) who found and fixed appliances for 2–3 years had no greater that TMD could not be correlated to any specific type of prevalence of TMD signs and symptoms than Class I malocclusion, and there was no support for the belief patients treated with fixed appliances only or untreated that orthodontic treatment may cause TMD. Finally, a controls. Therefore, treatment-induced modifications in 20 year cohort longitudinal study investigating the the TMJ must be interpreted as remodelling changes. relationship between orthodontic treatment and TMD Another matter of debate among orthodontists is the concluded that orthodontic treatment neither causes influence of orthognathic surgery (OS) on TMD. Some nor prevents TMD and that participants with a history reports suggest that surgery may alleviate signs and of orthodontic treatment did not have higher risk of symptoms of TMD (83, 84); others indicate that surgery new or persistent TMD (92). might initiate or aggravate temporomandibular dys- We carried out a PubMed search using ‘Orthodontics function (85, 86). A literature review covering AND tmd’ as keywords yielded 404 studies, of which 58 the period from 1966 to 2006 aimed to answer the were indexed as review articles, two were discarded question whether orthognatic surgery does affect the because not in English, 34 were not related to the topic prevalence of signs and symptoms of TMDs. Among or were not reviews, five did not have the abstract 467 articles, three met the inclusion criteria. The available. The remaining 17 reviews are summarized in scientific evidence was insufficient to evaluate the Table 1 (line 1–17). Furthermore, a PubMed search effects that OS had on TMD (87). The lack of consistent using ‘Orthodontics AND occlusion AND tmd’ as findings across studies may be ascribed to different keywords yielded 132 studies, of which 26 were methods used to assess stomatognathic function and indexed as review articles, three were discarded dysfunction, the lack of separate evaluation of muscu- because not in English, six did not have the abstract lar and articular problems, the inclusion of different available. Among the remaining 17 reviews, five were skeletal malocclusions in the samples investigated, the not reported in the previous research and have been use of different surgical techniques and the limited added to Table 1 (line 18–22). Finally, a PubMed search follow-up time. Orthognathic surgery represents an using ‘Orthodontics AND occlusion AND tmd AND interesting model to study pain and function of the meta-analysis’ as keywords yielded three studies. masticatory system. The surgical approach provokes Among these, two were not reported in the previous tissue damage and inflammatory reactions. Investigat- research and have been added to Table 1 (line 23–24). ª 2010 Blackwell Publishing Ltd 418 A. MICHELOTTI & G. IODICE Table 1. Studies published between 1989 and November 2009 that examined the relationship between orthodontic treatment and TMD 1 Abrahamsson C et al (87) Angle Orthod 2007 TMD and orthognathic No scientific evidence surgery 2 Mohlin B et al (91) Angle Orthod 2007 TMD in relation to No correlation between TMD, malocclusion and malocclusion and orthodontics orthodontic treatment 3 Luther F (8) Br Dent J 2007 TMD and occlusion No correlation between TMD and static or dynamic occlusal factors 4 Gesch D (122) Quintessence Int 2004 Association of No morphologic or functional occlusal malocclusion and factor was found as cause of TMD functional occlusion with TMD 5 Koh H and J Oral Rehabil 2004 Occlusal adjustment There is no evidence that OA treats or Robinson PG (123) and TMD prevents TMD 6 Forssell H and J Orofac Pain 2004 Occlusal treatment for No evidence supporting the use occlusal Kalso E (124) temporomandibular adjustment disorders 7 Koh H and Robinson PG (125) Cochrane Database 2003 Occlusal adjustment Absence of evidence that occlusal and TMD adjustment treats or prevents TMD 8 Hagag G et al (126) J Med Dent Sci 2000 Occlusion, Weak correlation between occlusal prosthodontic interference and TMD. Unstable treatment and occlusion in the intercuspal position temporomandibular may cause TMD disorders 9 De Boever JA et al (127) J Oral Rehabil 2000 Occlusal therapy for Generalized prophylactic occlusal TMD adjustment is not justified. 10 Forssell H et al (128) Pain 1999 Occlusal treatments in Evidence for the use of occlusal temporomandibular adjustment is lacking disorders 11 McNamara JA Jr J Orofac Orthop 1997 Orthodontic Orthodontic treatment does not increase and Türp JC (129) treatment and or decrease the chances of developing temporomandibular TMD; The orthodontic extraction of disorders teeth does not increase the risk of TMD; no convincing evidence that orthodontic treatment cure TMD 12 McNamara JA Jr (130) Oral Surg Oral 1997 Orthodontic Not achieving a specific gnathologic treatment and ideal occlusion does not result in signs temporomandibular and symptoms of TMD; there is little disorders evidence that orthodontic treatment prevents TMD 13 Clark GT et al (131) Oral Surg Oral 1997 Occlusal therapy for No comparative studies testing the temporomandibular efficacy of occlusal adjustment in disorders preventing TMD. 14 Dibbets JM and Semin Orthod 1995 Implications of Little is known about the influence of Carlson DS (132) temporomandibular TM pathology, disc interferences or disorders for facial myofascial disorders on facial growth. growth 15 McLaughlin RP and Angle Orthod 1995 Extraction and TMD No higher incidence of TMDs in patients Bennett JC (71) treated with the extraction of premolars 16 McNamara JA Jr et al (70) J Orofac Pain 1995 Occlusion, orthodontic The relationship of TMD to occlusion treatment and and orthodontic treatment is minor. temporomandibular disorders ª 2010 Blackwell Publishing Ltd  ORTHODONTICS AND TEMPOROMANDIBULAR DISORDERS 419 Table 1. (Continued) 17 Bales JM and J Can Dent Assoc 1994 Malocclusion and Little evidence to support occlusal Epstein JB (133) orthodontics in factors in TMD. Anterior open bite may temporomandibular represent predisposing factors. disorders Orthodontic therapy may not affect the risk of developing TMD and has little role in treatment 18 Türp JC et al (134) J Oral Rehabil 2008 Dental occlusion Naturally occurring features such as centric, balancing, working or protrusive occlusal interferences, various occlusal guidance patterns, missing teeth and oral ⁄ dental parafunctions are not meaningfully associated with TMD signs and symptoms 19 Kirveskari P (135) Oral Surg Oral 1997 Occlusal adjustment in Controlled clinical trials suggest an effect the management of for occlusal adjustment on chronic temporomandibular headaches and on chronic neck and disorders shoulder pain in comparison with conventional treatments 20 Greene CS (136) Semin Orthod 1995 Aetiology of There are no special occlusal or temporomandibular orthodontic factors to be considered, disorders. and therefore occlusion-changing procedures are not generally required for successful treatment 21 Haber J (137) Curr Opin Dent 1991 Dental treatment of Current information supports the use of temporomandibular reversible treatments for these disorders disorders 22 Baker RW Sr et al (138) N Y State Dent J. 1991 Occlusion as it relates There is no research that shows that to TMJ restorative dentistry or orthodontics are aetiological factors in TMJ dysfunction 23 Kim MR et al (89) Am J Orthod 2002 Orthodontics and Because of heterogeneity, a definitive Dentofacial Orthop temporomandibular conclusion cannot be drawn. This disorder: comprehensive meta-analysis does not a meta-analysis indicate that traditional orthodontic treatment increased the prevalence of TMD 24 Tsukiyama Y et al (139) J Prosthet Dent 2001 Occlusal adjustment as The experimental evidence reviewed a treatment for was neither convincing nor powerful temporomandibular enough to support the performance of disorders occlusal therapy as a general method for treating a non-acute temporomandibular disorder, bruxism or headache Even though most of the studies consistently do not aetiology (93). The potential for the existence of gene support the correlation between orthodontic treatment environment interactions that can influence TMD risk, and temporomandibular disorders, it must be stressed using orthodontic treatment as an example of an that definitive conclusions cannot be drawn because of environmental influence, has been investigated in a the unknown cause of TMD, heterogeneity in the prospective cohort study. Interestingly, among people methodology and in the study design and lack of a with a variant of the gene encoding catechol-O-meth- widely accepted classification scheme. Recently, a yltransferase, an enzyme associated with pain respon- search has begun for a genetic influence on TMD siveness, risk of developing TMD was significantly ª 2010 Blackwell Publishing Ltd 420 A. MICHELOTTI & G. IODICE greater for subjects who reported a history of ortho- including pharmacotherapy, counselling, behavioural dontic treatment (94). This finding opens a new therapy, home exercises, physical therapy and ⁄ or scenario on the risk for developing TMD that need to occlusal appliances. As a rule, orthodontic treatment be further investigated in the future. should not be initiated as long as a patient suffers from facial pain. Indeed, experimentally induced pain in masticatory muscles has been shown to induce signif- How should orthodontic treatment be icant displacement of the gothic arch apex in the managed if the patient presents signs and anterior and transverse direction, and changes in the symptoms of TMD before or during orientation and magnitude of lateral movements. These treatment? effects were reversible and disappeared when the Before starting orthodontic treatment, it is advisable to subjects became pain-free again (67). Then comes the perform always a screening examination for the pres- third step: once the pain has been resolved and ence of TMD. For medico-legal reasons, any findings, the condition is stable over a reasonable amount of including TMJ sounds, deviation during mandibular time, initiation of orthodontic therapy may be consid- movements or pain, should be recorded and updated at ered. The treatment plan should always be tailored 6-month intervals, and informed consent should be according to the problem list of the patient, to evidence- signed by the patient (95, 96). Guidelines for the based dentistry principles and to common sense consid- examination were recently published by the American ering the characteristics of the single patient and taking Academy of Orofacial Pain (1). If the patient presents into account why the patient is seeking treatment. signs or symptoms of TMD before starting orthodontic Patients with generalized musculoskeletal pain, such as treatment, the first step is to make the diagnosis. When fibromyalgia, or patients with a systemic inflammatory the patient’s chief complaint is pain, it is important to disease, such as rheumatoid arthritis, should be man- make a differential diagnosis to determine whether the aged by an interdisciplinary team (Fig. 2). pain is because of TMD, i.e. musculoskeletal condition, TMD signs and symptoms are fluctuating and or to another disease. The second step is to resolve the unpredictable and can emerge during orthodontic pain by following a conservative treatment protocol (97) treatment. The orthodontist should inform the patient No pain Conservative treatment Myofacial pain Patient presents TMD Patient Start the signs and symptoms Differential information and orthodontic before starting an diagnosis counseling treatment orthodontic treatment TMJ Pain TMJ disease Conservative TMJ Sounds treatment Establish the No pain orthodontic treatment plan accordingly Fig. 2. TMD signs occurring before starting an orthodontic treatment. ª 2010 Blackwell Publishing Ltd  ORTHODONTICS AND TEMPOROMANDIBULAR DISORDERS 421 that because they are highly prevalent in the general Does TMD (i.e. development disorders, population and the aetiology is multifactorial, it is not arthritis, condylar resorption, osteoma) possible to establish a correlation with the orthodontic cause malocclusion? Hence, how should therapy. If the patient presents signs or symptoms of orthodontic treatment be planned? TMD during active orthodontic treatment, the first step is always to make the diagnosis. The second step is to TMDs, as classified by the American Association of stop active orthodontic treatment temporarily to avoid Orofacial Pain, embrace several TMJ disorders, includ- exacerbating factors. Activating orthodontic appliances ing developmental (i.e. hypo ⁄ hyperplasia), acquired applies forces to teeth that can cause transient (i.e. neoplasms) and inflammatory (i.e. rheumatoid discomfort or pain. Indeed, orthodontic pain induced arthritis) disorders. These disorders can cause skeletal as by means of separators resulted in a transient reduc- well as dental changes and frequently lead to marked tion in the pressure pain thresholds of the masseter facial asymmetry. Sometimes, they occur in the age and temporalis muscles (98). These reductions can group of patients generally seen by the orthodontist probably be ascribed to neuroplastic changes involving who is the first clinician that can make the diagnosis. It the brainstem second order neurons, which receive is therefore essential, when it is present, that orth- extensive convergent inputs from trigeminal afferents odontists recognize the condition before beginning (99, 100). The third step is to resolve the pain by orthodontic treatment so that patients will not consider following the same conservative treatment protocol as it a consequence of their therapy. Therefore, their suggested above (i.e. pharmacotherapy, counselling, recognition is of great importance in planning and behavioural therapy, home exercises, physical ther- managing orthodontic treatment. apy). If required, an occlusal appliance can also be used to evaluate the interference-free position of the Unilateral condylar hyperplasia mandible. Afterwards, when the patient is pain-free, orthodontic treatment can be continued as previously Condylar hyperplasia (CH) (101) is a pathological planned or, if necessary, modified according to the overgrowth condition in the condylar process, which patient’s condition (Fig. 3). leads to variable abnormal mandibular and ⁄ or facial Fig. 3. TMD signs occurring during orthodontic treatment. ª 2010 Blackwell Publishing Ltd 422 A. MICHELOTTI & G. IODICE asymmetry. This disorder of unknown origin is charac- recovers almost completely at patient follow-up. In terized by persistent or accelerated unilateral condylar experimental animals, remodelling of the excised con- growth. CH usually develops during puberty and rarely dylar head and formation of new articulating cartilage begins after the age of 20. Identification of the sex when a proper mandibular function is maintained has hormone receptors in and around the TMJ and the been noted (105).Therefore, TMJ functioning can re- pubertal onset of CH strongly suggest a hormonal cover well despite the major trauma caused by the HC to influence in the aetiology (102). the articulating surface of the condyle. Orthodontic The slowly progressive unilateral enlargement of the treatment is necessary to obtain teeth alignment. At the mandible causes facial asymmetry and shifting of the end of growth, usually additional OS is also needed to midpoint of the chin to the unaffected side, and most of correct maxillo-mandibular relationship and compen- the time a cross-bite malocclusion. Concomitant with satory tilting of the maxillary plane. the increased downward and forward growth of the mandible, which carries the teeth with it, there is Chondroma or osteochondroma compensatory eruption of the maxillary teeth and downward growth of the maxillary alveolar process, Chondroma or osteochondroma of the condyle occurs as well as upward growth of the mandibular alveolar singly or as part of an autosomal dominant syndrome process in an attempt to maintain the occlusion. A known as osteochondromatosis. As it can produce signs panoramic imaging is considered a reliable basic tool to and symptoms similar to unilateral condylar hyperpla- evaluate mandibular asymmetries (103). Radiographi- sia, a differential diagnosis has to be made. The cally, the TMJ appears normal or there may be pathogenesis of osteochondroma is still under debate. symmetrical enlargement of the condyle and elongation In the most accepted view, it is a metaplastic change in of the mandibular neck (Fig 4). New 3D imaging the periosteum and ⁄ or the osteochondral layer in the methods, such as cone beam computed tomography, mandibular condyle, leading to production of cartilage are now available. that subsequently ossifies. Single photon emission computed tomography or The mean age of discovery of osteochondromas of the bone scintigraphy with 99mTc methylene disphospho- mandibular condyle is reported to be the fourth decade nate is necessary to reveal possible asymmetric growth of life. Generally, it grows rapidly, causing quick activity in the mandibular condyles. If the difference in changes in facial symmetry. Moreover, because of the the uptake of the radiotracer between the condyles rapid growth, dental compensation may not occur and exceeds 10%, which is considered to be the cut-off value an open bite develops (86). Another distinguishing (104), there is the indication for high condylectomy characteristic is the fact that with a chondroma or (HC), or condylar shaving, on the affected side to stop osteochondroma, the condyle is asymmetrically en- excessive growth. During this procedure, 2–3 mm of the larged with unusual morphological characteristics condylar head, that is the growing condylar cartilage as (Fig. 5). well as the uppermost part of the subchondral bone, is removed. Patients with CH usually present jaw function Rheumatoid arthritis within normal limits without TMD signs or symptoms. Immediately after HC, Maximal Mouth Opening is Juvenile idiopathic arthritis (JIA) is a term that usually reduced because of surgical side effects, but indicates a childhood disease characterized primarily Fig. 4. Condylar Hyperplasia left TMJ. ª 2010 Blackwell Publishing Ltd  ORTHODONTICS AND TEMPOROMANDIBULAR DISORDERS 423 Fig. 5. Osteochondroma right TMJ. by arthritis persisting for at least 6 weeks, starting alteration in dental occlusion. In these cases, the patient before the sixteenth birthday. (106) All joints can be may develop a progressive class II malocclusion and an involved in JIA, including the TMJ. From 50% to 78% anterior open bite caused by loss of ramal height (109, of patients with rheumatoid arthritis will show some 110) (Fig. 6). involvement of the TMJ. One or both TMJs can be Panoramic imaging is a good diagnostic tool for involved in JIA, and the TMJ may even be the initial evaluating erosive alterations. Nowadays, MRI is con- joint to be involved (107, 108). Involvement of the TMJ sidered to be the gold standard to diagnose TMJ often occurs without clinically detectable signs and involvement (111, 112). The radiographic findings with symptoms, therefore delaying diagnosis. Patients with juvenile rheumatoid arthritis include erosion of the involvement of the TMJ usually complain of a deep, articular surface of the condyle, flattening and erosion dull, aching pain in the preauricular region that is of the articular eminence and loss of the joint space. exacerbated by function, swelling of the preauricular When rheumatoid arthritis is suspected on the basis of tissues during the acute phases, and progressive limi- the clinical and radiographic findings, laboratory tests tation of jaw movement. Severe damage to the periar- (rheumatoid factor, erythrocyte sedimentation, antinu- ticular and articular structures occurs in a late stage. As clear antibodies) can be used to confirm the diagnosis. the most important growth centre of the mandible is Controlling JIA with systemic drugs is always the first located on the articular surface of the mandibular step in the treatment protocol. In growing patients, condylar head, destructive changes during the growth treatment includes the application of a functional period affect mandibular development with subsequent orthopaedic orthodontic appliance to favour the regen- Fig. 6. Rheumatoid arthritis right and left TMJs. ª 2010 Blackwell Publishing Ltd 424 A. MICHELOTTI & G. IODICE erative capacity of the condyle and to improve condylar is generally suggested, with reversible treatments for alterations (113–115). Interestingly, in a 5-year follow- TMD problems. Therefore, treatments should address up study of paediatric patients with JIA, a decrease in not only the physical diagnosis, but also the psycho- the frequency of TMJ involvement was observed (109, logical distress and the psychosocial dysfunction found 113, 116). When the resultant malocclusion is severe, a in patients affected with chronic pain conditions (118). combination of orthodontics and OS is required to attain Indeed, case severity and chronicity represent critical both an acceptable occlusion and an improvement in factors in the decision-making process. When severe facial aesthetics. Distraction osteogenesis (117) can pain is present, occlusal treatments (such as orthodon- increase bone volume by gradual traction of a fracture tics and prosthodontics) have to be postponed until callus formed between osteotomized bony segments. symptoms are improved. There is a current consensus Application of this technique is recommended for the on treatment strategies being reversible. This therapeu- treatment of a severe dentofacial deformity with signif- tic approach is supported by evidence showing that no icant hard and soft tissue deficiency. treatment modality has been proven better than others. Long-term follow-up of patients with TMD shows that 75–85% of the patients with chronic pain are cured or Conclusion improve significantly irrespective of the treatment TMD is a multifactorial pathology, and it is difficult to modality used (119). demonstrate a direct correlation between one of the With regard to TMJ dysfunction, the treatment goals causes, such as occlusion, and TMD. The variables are should of course be to reduce pain and to improve so many and so mixed that, nowadays, we do not have function. The reversible therapies commonly used for adequate diagnostic instruments to establish a clear the management of TMJ dysfunction include physio- correlation or to know if how and when a malocclusion therapy (to improve movements and function), phar- can unbalance the stomatognathic system. Even macotherapy (anti-inflammatory, antidepressants etc.), though currently occlusion is considered a potential occlusal therapy (occlusal appliances) and psychological cofactor with a much lower weight when compared to therapy (cognitive behavioural therapy). These modal- the beliefs underpinning the Costen Syndrome, we ities can be offered together or as a single management have to consider that absence of evidence does not strategy (120, 121). Intraoral appliances, such as mean evidence of absence. Based on this concept, oro- occlusal stabilization splints, have been for many facial pain and TMD require a comprehensive team decades the main treatment for jaw dysfunction and approach. It is important to rule out other causes of continue to be a common treatment modality. Several facial pain before investigating the teeth as the potential hypotheses have been suggested to explain their action, aetiological factor. According to evidence-based den- but scientific validation is still lacking. Therefore, it is tistry, dental practitioners should use current best difficult to establish the efficacy of splints in the evidence when making decisions about the treatment management of TMDs. Occlusal therapy should be of each patient, integrating individual clinical expertise considered only to address TMD patient discomfort with with the best available clinical evidence. occlusion. When the treatment protocol includes a dental It must be stressed that for the vast majority of intervention, this must be done to address patient patients with TMD, the prognosis is favourable. There- discomfort and obtain an occlusion that is stable. 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