Use of Lower Michigan Splint – Case Report

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clinical case

Wojciech Drobek

1

_{, anna Paradowska}

2

_{, Beata Kawala}

3

Use of Lower Michigan Splint – Case Report

Zastosowanie dolnej szyny Michigan– opis przypadku

1_{Private Dental Office, Jastrzębie Zdrój}

² Department of Facial abnormalities, Department of Maxillofacial Orthopedics and Orthodontics, Wroclaw Medical University, Wroclaw, Poland

3_{Department of Maxillofacial Orthopedics and Orthodontics, Wroclaw Medical University, Wroclaw, Poland}

Abstract

Temporomandibular disorders (TMDs) and occlusal parafunctions form an increasing problem in the society. The etiology of the condition is very complex and obscure. TMDs may be associated with destabilization of occlusion (unbalanced bite), physical, metabolic, hormonal and psychological factors, detrimental body posture, parafunc-tional activity as gum chewing etc. The most common and serious symptoms of the TMDs are orofacial pain, lim-ited mouth opening, sounds recorded in the temporomandibular joints and acute malocclusion. The most plausible etiologic explanation of the aforementioned signs and symptoms may be an increased muscular tension in the masticatory musculature. a proper occlusion is regarded to be crucial to a successful treatment of the TMDs. in many cases additional procedures as behavioral modification, physiotherapy, manual techniques should be under-gone. as a method of choice in patients with nocturnal parafunctional activities occlusal splints are fabricated. The purpose of the latter is the reduction of the muscular tension in the masticatory system. Usually upper acrylic splints are made. The aim of this paper is to present a case of an adult patient with temporomandibular disorders, treated with lower Michigan splint as the introductory procedure to the proper orthodontic treatment (Dent. Med.

Probl. 2010, 47, 2, 251–256).

Key words: Michigan splint, temporomandibular disorders.

Streszczenie

W ostatnich latach obserwuje się coraz częstsze występowanie dysfunkcji stawów skroniowo-żuchwowych i zabu-rzeń zgryzu. etiopatogeneza jest złożona i wciąż niejasna. Zaburzenia w stawie skroniowo-żuchwowym mogą być związane z utratą stabilności okluzji (zgryz niezbalansowany), czynnikami fizycznymi, metabolicznymi, hormo-nalnymi lub psychologicznymi, lecz także nieprawidłową postawą ciała czy żuciem gumy. najczęstszymi objawami zaburzeń stawów skroniowo-żuchwowych są: ból twarzowej części czaszki, patologicznie ograniczona ruchomość żuchwy, objawy akustyczne w stawach skroniowo-żuchwowych oraz ostre zaburzenia zwarcia. najbardziej praw-dopodobnym wytłumaczeniem tych objawów wydaje się wzmożone napięcie mięśniowe. Kluczem do leczenia zaburzeń okluzyjnych jest przywrócenie prawidłowych warunków zgryzowych. W wielu przypadkach konieczne okazuje się również wprowadzenie dodatkowych metod terapeutycznych, takich jak modyfikacja behawioralna, fizykoterapia czy techniki manualne. U pacjentów, u których stwierdza się nocną aktywność parafunkcjonalną, metodą leczenia z wyboru jest wykonanie szyny zwarciowej. celem takiego postępowania jest ograniczenie napię-cia mięśniowego w układzie ruchowym narządu żunapię-cia. Zazwyczaj wykonuje się górne płyty akrylowe. Opisano przypadek pacjentki z zaburzeniami skroniowo-żuchwowymi, leczonej dolną szyną typu Michigan. Terapia szyną okluzyjną poprzedzała leczenie aparatem ortodontycznym (Dent. Med. Probl. 2010, 47, 2, 251–256).

Słowa kluczowe: szyna Michigan, zaburzenia stawów skroniowo-żuchwowych.

Dent. Med. Probl. 2010, 47, 2, 251–256

issn 1644-387X © copyright by Wroclaw Medical University and Polish Dental society

Dysfunctions of temporomandibular joint and the associated musculature, called temporo-mandibular disorders (TMDs) and occlusal para-functions are very common in the society. The most frequent parafunction mentioned in the

sci-entific literature is bruxism. The ethiopathogen-esis of TMDs is complex and most common fac-tors named by some authors are: destabilization of occlusion (unbalanced bite), physical, metabolic, hormonal and psychological factors. The

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detri-mental body posture may lead to an inappropri-ate cuspidation and result in temporomandibular disorders. On the other hand, an increased tonic-ity of the suboccipital musculature can be crucial for the initiation of parafunctional activity of the jaw musculature. The results of the recent research show that the most important etiological factor of the focused affliction is an increased tension of the orofacial musculature, especially of the mandible elevating muscles. This, in turn, may lead to non-physiological mandibular articulation and cause the nociceptive afferent input from the muscula-ture, joints or both to the central nervous system. Dysfunctions and orofacial pain may be increased by the habit of chewing gum [1–3].

centric relation is thought to be the condi-tion of relaxed occlusion and is determined as the occlusion in which the condyles are in their most anterosuperior position in the articular fossae resting against the posterior slope of the articular eminence with the discs properly inserted. anoth-er description of the lattanoth-er condition with regard to the mandible is the musculoskeletally stable position of the lower jaw. an appropriate centric occlusion is located between a centric relation and maximum intercuspidation with so called occlusal slide between them in the sagittal anterior direc-tion. an eventual disturbance between them can be a perpetuating factor for the temporomandibu-lar disorders. an inappropriate relation of upper and lower dental arches and even minor discrep-ancies between joint-determined and occlusion-determined mandibular position may cause many inconveniences, among them presence of facial or intraoral pain, joint noises, physical distress or may influence neuromuscular condition [4].

a proper centric occlusion in the course of treatment of the TMDs can be established by means of occlusal splints. One should keep in mind, however, that the main purpose of the fab-rication of the relaxation Michigan occlusal splint is, according to its name, the relaxation of the jaw muscles and decrease of the nocturnal parafunc-tional activity. The splint should be fabricated by an experienced team consisting of the dentist and the laboratory technician to avoid any discomfort to the patient. it also should be remembered that the lower to upper jaw relation may differ after the treatment is finished in comparison to the initial state. This potential risk is observed mainly after the treatment with so called anterior reposition-ing splints and is rare when relaxation splints were used. Repositioning of the jaw by use of splint may cause a reduction of signs and symptoms of temporomandibular disorders. in some cases the patient should be “fixed” in the maximal inter-cuspidation as it can be the easiest way to reduce

acoustic symptoms of temporomandibular disor-ders, and later the centric relation should be estab-lished [4]. Many clinical studies reveal that the po-sition of mandible is repopo-sitioned after the splint therapy, which in consequence causes replacement of the position of condyles, reduction of pain and establishes the proper mandible position [4–6]. in some cases the splints are not necessary, however. The selective grinding, teeth restorations, crowns, bridges and dentures help to cure temporoman-dibular joint derangements [7]. On the other hand, the main purpose of the treatment of the TMDs in patients heading for the orthodontic treatment is the alleviation of pain, reduction of the muscle fatigue, restoring of the physiological mandible mobility and, eventually, reduction of the joint sounds. all patients in whom the orthodontic treatment is to be started should be pain-free at least three months before commencement of the active orthodontic therapy.

in most cases the upper occlusal splints are fabricated. The treatment, however, should be planned in accordance with the patients needs and indications. For example, in order to avoid unwanted and disadvantageous tooth movement, the lower splint may be introduced [8].

Temporomandibular disorders are very often associated with many systemic diseases, such as rheumatoid arthritis, multiple sclerosis, myas-thenia gravis, Parkinson’s disease, drug-induced parkinsonism, ischemic stroke or inflammatory bowel diseases [9, 10]. Therefore, a thorough pa-tient history should be collected before the active functional treatment starts.

Case Report

Patient a.D., aged 32, was a patient of Depart-ment of Maxillofacial Orthopedics and Orthodon-tics, Wroclaw Medical University. The accurate patient history did not reveal any somatic or lo-cal disease. Due to dissatisfying esthetics of smile, the patient was highly determined for orthodontic treatment. intraoral examination revealed lack of teeth: 16, 17, 18, 26, 36, 37, 46, 48. The canines were in the class i bilaterally. The angle class could not be established due to lack of molars. Diastemata in upper dental arch were present (Figs. 1–3). also mesiorotation of tooth 27 was observed. in lower dental arch tooth 35 was distolocated and rotated. Teeth 37 and 47 were mesioinclinated. also tooth 47 was superposed. The median line in the upper arch was shifted 2 mm to the right due to the loss of teeth and multiple diastemas.

in order to estimate the functional status of the patient’s masticatory system the manual

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func-tional analysis was performed. an intensive cen-tric and eccencen-tric parafunctional activity (both diurnal and nocturnal) was present. examination of temporomandibular joints revealed adaptation of the bilaminar zone in the right and left tem-poromandibular joint in all potential directions. no overloading vectors in relation to compensated compression of the bilaminar zone or the distrac-tion of the joint capsule were found. antero-lat-eral hypermobility of the right articular disc and antero-medial hypermobility of the left articular disc were also observed. Myofascial pain of the suboccipital musculature was present. local mus-cle soreness of the Masseter and temporal musmus-cles on the left and right side were diagnosed.

Before the commencement of the orthodon-tic treatment, it was obligatory to reduce occlusal parafunctional activities in order to avoid exacer-bation of the symptoms. On the first appointment the procedures leading to the behavioral modifica-tion were introduced and the impressions of up-per and lower dental arches were taken. The casts were fabricated in the clinic laboratory and the in-traoral situation was thoroughly assessed. Basing on this analysis, especially due to extrusion and mesioinclination of the tooth 47, a lower Michigan acrylic splint in centric relation was fabricated. The splint enabled the restoration of the occlusal contacts in the areas of primary edentulous alveo-lar ridge. an upper splint could worsen the posi-tion of tooth 47. Due to the temporomandibular disorders, especially the local muscle soreness of the mandible elevators, the increase of the vertical bite dimension must be held as minimal as only necessary to produce the splint. in the first step the pre-trimmed wax was placed into patient’s mouth and the intermaxillar relation was deter-mined. The second step was the determination of the eccentric lateral canine and protrusive incisor protected guidance of the wax pattern (Figs. 4–7). The pattern was later transferred to the labora-tory and the wax was replaced by the translucent acrylic resin. On the subsequent appointment the lower definite occlusal relaxation Michigan splint was inserted. The patient was taught how to re-move and to insert the appliance and instructed to wear the splint at nights only to avoid daytime harmful habits (Figs. 8–9).

Fig. 1. Patient a.D., intraoral relation Ryc. 1. Pacjentka a.D., relacja wewnątrzustna

Fig. 2. Patient a.D., intraorally, right side, lower

second molar in supraocclusion

Ryc. 2. Pacjentka a.D., wewnątrzustnie, prawa strona,

supraokluzja drugiego zęba trzonowego dolnego

Fig. 3. Patient a.D., canine class i on the left side Ryc. 3. Pacjentka a.D., klasa i kłowa po stronie lewej

Fig. 4. Wax pattern on a cast, frontally

Ryc. 4. Wzornik zwarciowy na modelu gipsowym,

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Discussion

Temporomandibular joint disorders form an increasing problem in the society. The ethio-pathogenesis is multifactoral and still remains somewhat obscure and unclear. The symptoms of temporomandibular disorders depend on the type of disorder and the most important are pain, lim-ited mouth opening and joint sounds. The major-ity of the signs and symptoms are caused by an increased tension of the masticatory musculature [1–3]. General somatic predisposing factors were not found in the focused patient.

Fig. 5. Wax pattern on a cast, right side

strona prawa

Fig. 6. Wax pattern on a cast, left side

strona lewa

Fig. 7. Wax pattern intraorally

Ryc. 7. Wzornik zwarciowy zewnątrzustnie

Fig. 8. acrylic lower Michigan split intraorally Ryc. 8. Dolna szyna akrylowa typu Michigan

wewnątrzustnie

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The main therapeutic target of the commenced treatment was the reduction of the increased mus-cular activity of jaw closing musculature. accord-ing to the well documented therapeutic strategies, the first step introduced was behavioral modifica-tion. starting from the second appointment at the faculty, physical modalities as self-treatment pro-tocol were gradually prescribed [11]. Due to the persistent nocturnal activity, the intraoral occlu-sal splint was proposed by the medical team and then accepted by the patient. a full teeth coverage hard acrylic resin Michigan splint was manufac-tured, which is in line with treatment procedures recommended by many authors [12–14]. The lat-erotrusive guidance was secured by canine paths, while protrusive movement of the mandible was incisally protected with a total disclusion in pos-terior arch segments. an interesting point of view present conti et al [15] who found no differences in reduction of parafunctional activity between patients wearing typical Michigan splints (as in our study) and patients treated by flat, full cov-erage splints with group guidance in eccentric occlusion. The patients in this study had painful joint clicks as well, suggesting the highly probable nociceptive input from the bilaminar zone in the temporomandibular joint. The lack of the statisti-cally significant differences between both groups should be a subject of the further research.

in patients with no nociceptive input ema-nating from the temporomandibular joint only the nocturnal use of intraoral appliances is sug-gested. among the high variability of splints, full arch coverage hard acrylic splints with canine protected laterotrusive movements are highly rec-ommended. One should keep in mind, however, that the intraoral occlusal appliances form only an adjacent therapeutic modality to main treatment conservative strategies as jaw relaxation, warm packs, massage, manual techniques [16].

in most cases, the upper splints are performed. The exceptions are made when the upper splint could change the position of teeth inappropri-ately [8]. Due to extrusion and mesioinlinatio of tooth 47 in the patient, the lower splint was per-formed. The lower splint prevented the further det-rimental mesioinclinating movement of 47 and en-abled to preserve its present position in the dental arch. The splint worn only in the night time regime helped to reduce the muscular fatigue and played a crucial role in alleviation of patient’s morning complaints. The accurate mode of action of oc-clusal splints remains, however, still unclear and causes numerous controversies [17, 18]. Thus, the further research of the action mechanisms and indicative spectrum of occlusal splints in patients heading for orthodontic treatment or prosthetic rehabilitation is highly desirable.

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Address for correspondence:

Wojciech Drobek 1 Maja 3 44-330 Jastrzębie Zdrój Poland Tel./fax: +48 503 642 281 e-mail: w-drobek@o2.pl Received: 28.10.2009 Revised: 19.04.2010 accepted: 14.05.2010

Praca wpłynęła do Redakcji: 28.10.2009 r. Po recenzji: 19.04.2010 r.