10.14639/0392-100X-N1641
Objective. This retrospective study aimed to verify the outcomes of stabilising occlusal splint therapy prescribed to 22 patients with unilateral definite Ménière’s disease and comorbid temporomandibular joint disorder. Methods. The results of a battery of audiometric and vestibular tests were recorded before and after 6 months of treatment, as well as the scores of disease-specific questionnaires. Results. The average hearing threshold in the affected ear and the acoustic immittance were unchanged. No spontaneous and positional nystagmus were recorded. Caloric hyporesponsiveness and vestibular myogenic evoked responses did not vary. No changes of stabilometric body sway parameters in eyes opened condition and with optokinetic stimulation delivered to the unaffected labyrinth were observed. A significant reduction was recorded in eyes closed condition and with the optokinetic stimulation toward the affected ear. The Tinnitus Handicap Inventory, the Situational Vertigo Questionnaire and the Numeric Pain Rating Scale scores improved. The number of vertigo attacks was reduced. Conclusions. Occlusal splint therapy is a favourable option to reduce aural symptoms of Ménière’s disease and comorbid temporomandibular joint disorder, even if its pathophysiological mechanism remains elusive.
text/xml
1827-675X
1641
en
Luca Pani
http://creativecommons.org/licenses/by-nc-nd/4.0
ACTA Otorhinolaryngologica Italica
headache
Occlusal splint therapy in patients with Ménière’s disease and temporomandibular joint disorder
Text.Serial.Journal
https://www.actaitalica.it/
42
Vestibology
2022-02-07
2021-04-27
2022-03-07
2022-03-07
89-96
1
Luca Pani
2022/02/07
10.14639/0392-100X-N1641
89
Medical Toxicology-headache and Drug Abuse Research Center, Department of Biomedical, Metabolic and Neural Sciences, University of Modena and Reggio Emilia, Modena, Italy; Pharmacology Unit, Department of Biomedical, Metabolic and Neural Sciences, University of Modena and Reggio Emilia, Modena, Italy; Department of Psychiatry and Behavioral Sciences, University of Miami, Miami, USA; VeraSci, Durham, NC, USA 
1827-675X
headache
en
96
Occlusal splint therapy in patients with Ménière’s disease and temporomandibular joint disorder
https://www.actaitalica.it/article/download/1641/733
42
ACTA OTORHINOLARYNGOLOGICA ITALICA 2022;42:89-96; doi: 10.14639/0392-100X-N1641




Vestibology


Occlusal splint therapy in patients with Ménière’s
disease and temporomandibular joint disorder
La terapia occlusale nei pazienti con malattia di Ménière e disordini dell’articolazione
temporomandibolare
Daniele Monzani1, Carlo Baraldi2,3, Enrico Apa1, Matteo Alicandri-Ciufelli1, Carlo Bertoldi4, Elisabeth Röggla5,
Simona Guerzoni3, Daniele Marchioni6, Luca Pani3,7,8,9
1
  Otolaryngology Unit, Department of Medical, Surgical and Pediatric Sciences, University of Modena and Reggio Emilia, Modena, Italy;
2
  School in Neurosciences, Department of Biomedical, Metabolic and Neural Sciences, University of Modena and Reggio Emilia, Modena,
Italy; 3 Medical Toxicology-headache and Drug Abuse Research Center, Department of Biomedical, Metabolic and Neural Sciences, University
of Modena and Reggio Emilia, Modena, Italy; 4 Dentistry and Oro-maxillofacial Surgery Unit, Department of Surgery, Medicine, Dentistry,
Transplantation Morphology, Oncology and Regenerative Medicine, University of Modena and Reggio Emilia, Modena, Italy; 5 Poliambulatorio
Elios, Modena, Italy; 6 Otolaryngology Unit, Department of Surgical, Odontostomatologic and Pediatric Sciences, University of Verona, Verona,
Italy; 7 Pharmacology Unit, Department of Biomedical, Metabolic and Neural Sciences, University of Modena and Reggio Emilia, Modena,
Italy; 8 Department of Psychiatry and Behavioral Sciences, University of Miami, Miami, USA; 9 VeraSci, Durham, NC, USA


SUMMARY
Objective. This retrospective study aimed to verify the outcomes of stabilising occlusal
splint therapy prescribed to 22 patients with unilateral definite Ménière’s disease and co-
morbid temporomandibular joint disorder.
Methods. The results of a battery of audiometric and vestibular tests were recorded before
and after 6 months of treatment, as well as the scores of disease-specific questionnaires.
Results. The average hearing threshold in the affected ear and the acoustic immittance
were unchanged. No spontaneous and positional nystagmus were recorded. Caloric hypo-
                                                                                                      Received: April 27, 2021
responsiveness and vestibular myogenic evoked responses did not vary. No changes of sta-              Accepted: September 19, 2021
bilometric body sway parameters in eyes opened condition and with optokinetic stimulation             Published online: February 7, 2022
delivered to the unaffected labyrinth were observed. A significant reduction was recorded
in eyes closed condition and with the optokinetic stimulation toward the affected ear. The            Correspondence
Tinnitus Handicap Inventory, the Situational Vertigo Questionnaire and the Numeric Pain               Carlo Baraldi
Rating Scale scores improved. The number of vertigo attacks was reduced.                              Medical Toxicology-headache and Drug Abuse
Conclusions. Occlusal splint therapy is a favourable option to reduce aural symptoms of               Research Center, Department of Biomedical, Me-
Ménière’s disease and comorbid temporomandibular joint disorder, even if its pathophysi-              tabolic and Neural Sciences, University of Modena
ological mechanism remains elusive.                                                                   and Reggio Emilia
                                                                                                      via del Pozzo 71, 41124 Modena, Italy
KEY WORDS: temporomandibular joint disorder, Ménière’s disease, occlusal splint, vertigo,
                                                                                                      Tel.+39 0594 222104. Fax +39 0594 222454
headache                                                                                              E-mail: infocarlo.baraldi@gmail.com

RIASSUNTO
Obiettivo. Questo studio esplora gli effetti dello splint occlusale in 22 pazienti affetti da           How to cite this article: Monzani D, Baral-
malattia di Ménière monolaterale e disturbi dell’articolazione temporo-mandibolare.                     di C, Apa E, et al. Occlusal splint therapy
Metodi. I pazienti sono stati sottoposti a diversi test audiometrici e vestibolari prima e dopo sei     in patients with Ménière’s disease and tem-
                                                                                                        poromandibular joint disorder. Acta Otorhi-
mesi di trattamento con splint occlusale, oltre a questionari specifici per la malattia di Ménière.
                                                                                                        nolaryngol Ital 2022;42:89-96. https://doi.
Risultati. La soglia uditiva media nell’orecchio malato e l’impedenza acustica sono rimaste in-         org/10.14639/0392-100X-N1641
variate e non è stato registrato nessun nistagmo clinicamente significativo. I potenziali evocati
miogenici non hanno subito variazioni. Il numero di crisi di vertigine si è ridotto significativa-    © Società Italiana di Otorinolaringoiatria
mente durante il trattamento (p = 0,003). I parametri stabilometrici misurati ad occhi chiusi e       e Chirurgia Cervico-Facciale
con la stimolazione otticocinetica verso il labirinto malato (p 0,0001) sono significativamente
migliorati. I punteggi del Situational Vertigo Questionnaire (p = 0,002), del Tinnitus Handicap                      OPEN ACCESS
Inventory (p < 0,0001) e del Numeric Pain Rating Scale (p < 0,0001) sono migliorati.
                                                                                                      This is an open access article distributed in accordance with
Conclusioni. La terapia con splint occlusale è efficace nel ridurre alcuni sintomi della ma-          the CC-BY-NC-ND (Creative Commons Attribution-Non-
lattia di Ménière in comorbidità con il disordine dell’articolazione temporomandibolare,              Commercial-NoDerivatives 4.0 International) license. The
anche se il suo meccanismo fisiopatologico rimane indeterminato.                                      article can be used by giving appropriate credit and mentio-
                                                                                                      ning the license, but only for non-commercial purposes and
PAROLE CHIAVE: disordine dell’articolazione temporo-mandibolare, malattia di                          only in the original version. For further information: https://
Ménière, splint occlusale, vertigine, cefalea                                                         creativecommons.org/licenses/by-nc-nd/4.0/deed.en




                                                                                                                                                                89
D. Monzani et al.




Introduction                                                      cal reports of those patients who were also diagnosed with
                                                                  TMD-related pain, according to the rules of the Research
Temporomandibular joint disorders (TMDs) are a group of
                                                                  Diagnostic Criteria for Temporomandibular Disorders con-
common musculoskeletal dysfunctions involving the tempo-
                                                                  sortium network and orofacial pain special interest group 7
romandibular joint (TMJ) and the associated musculature.
                                                                  and who completed the prescribed occlusal splint therapy,
The aetiology of TMDs is multifactorial: dental occlusion
                                                                  were included. Medical reports of patients affected by in-
abnormalities, masticatory parafunctions, degenerative or
                                                                  tra-articular TMD, users of orthotic appliances and those
inflammatory conditions involving TMJ, traumatic injuries,
                                                                  undergoing orthodontic treatment at the time of the refer-
inappropriate orthodontic treatments, psychological distress
                                                                  ral were not considered. Finally, 22 medical reports were
and oestrogen levels that may act alone or simultaneously 1.
                                                                  selected. Among these, 10 subjects suffered from headache
Possible clinical symptoms related to TMD are pain and/or
                                                                  attributed to TMD (ICD-10, G44.89), 10 from myofas-
noise at the temporomandibular joint as well as pain and/
                                                                  cial pain (ICD-10 M79.1) and 2 from arthralgia (ICD-10
or tenderness perceived across jaw and masticatory muscles.
                                                                  M26.62). The sample population was composed of Cauca-
These symptoms may cause limitation of the mandibular
                                                                  sian patients with a mean age of 38.6 ± 6.9 years (range:
movements, thus reducing the patients’ quality of life 1. Ad-
                                                                  28-51 years). Sixteen patients were female (72.7%), 12
ditionally, many TMD sufferers may also complain of head-
                                                                  patients suffered for right MD and 10 for left MD. TMD
ache 2 and otologic symptoms such as ear-fullness, otalgia,
                                                                  was unilateral in 14 cases and bilateral in the others. All
hearing loss, tinnitus and vertigo 3, although no cause-and-
                                                                  patients experienced persistent tinnitus, dizziness, otalgia,
effect relationship between TMDs and aural symptoms has
                                                                  and subjective hearing loss in the interictal period. None
been yet definitively identified. Tinnitus, ear fullness, hear-
                                                                  underwent ablative surgery, while 6 patients had been pre-
ing loss and vertigo are also symptoms of Ménière’s disease
                                                                  viously submitted to intratympanic gentamicin injections
(MD), a disease of unknown aetiology which is frequently,
but not exclusively, featured by the endolymphatic hydrops        procedure and 18 had received pharmacological prophylax-
of the inner ear. TMDs have been more frequently docu-            is (L-channel calcium channel antagonists, beta-blockers
mented in association with MD than in the general popula-         and betahistine dihydrochloride) lasting 6 months before
tion, even if the co-occurrence rate is unknown. Moreover,        starting the occlusal therapy. Only antiemetic medication,
Bjorne and Agerberg suggested an aetiological overlap of          such as thiethylperazine maleate rectally and/or levosulpir-
the two conditions, which is further strengthened by the im-      ide injections were used, if needed, during treatment.
provement of otologic symptoms in MD sufferers after co-
ordinated treatment of both temporomandibular and cervical        Stabilizing splint therapy
spine disorders 4. A more recent study showed that the use of     Only when both the two senior dentists (C.Be, E.R) who ex-
a dental orthotic alone is effective in reducing tinnitus and     amined MD patients agreed on the diagnosis of TMD, com-
dizziness in TMD-suffering patients 5. It should be noticed       pleted by temporomandibular joint computed tomography, a
that both the above-mentioned studies reported improvement        custom-fabricated hard acrylic splint fitting over the occlusal
of aural symptoms only by patients’ subjective evaluation         and incisal surfaces of the maxillary teeth was delivered.
and no instrumental techniques. Therefore, the aim of this        This full-coverage hard acrylic occlusal appliance (stabilisa-
cohort, retrospective study was to evaluate the effective-        tion splint-SS) is currently supposed to reduce neuromuscu-
ness of a splint therapy in relieving tinnitus and dizziness      lar hypertone of the temporalis and masseter muscles, thus
in patients suffering from MD and TMD, using audiological         obtaining stable occlusal relationships with uniform tooth
and vestibular tests as appropriate. Subjective evaluation of     contacts throughout the dental arch and stabilizing temporo-
symptoms of MD, facial pain and headache were also inves-         mandibular joints. Obviously an in-depth description regard-
tigated by the mean of disease-specific questionnaires.           ing the step-by-step construction of SS is beyond the scope
                                                                  of the present article. All patients were asked to wear the
                                                                  SS at night, while sleeping, starting from the night after its
Materials and methods                                             delivery. Since SS might be adjusted as the masticatory mus-
Patients                                                          cles relax, all patients’ splints were checked monthly and
The medical reports of 2658 outpatients who attended the          adjusted to maintain a stable contact relationship with each
tertiary centre of audiology of the University Hospital of        opposing mandibular tooth in the position of relaxed closure.
Modena (Italy) between 1 January 2017 and 31 December
2018 were retrieved. Among these, 108 cases diagnosed             Otoneurological examination
with definite MD, according to the international criteria of      Data were extracted from two consecutive clinical assess-
the Barany Society 6, were selected. Finally, only the medi-      ments, scheduled 6 months apart from each other, in the



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                                                 Stabilising occlusal splint for temporo-mandibular joint disorder and comorbid Ménière’s disease




interval period of the MD. This time interval was based on          platform sensitive to vertical force. The force-plate was
a previous study that appreciated a significant reduction of        mounted on 3 strain-gauge force transducers, positioned at
otologic symptoms in TMD-affected patients undergoing               the vertices of an equilateral triangle, providing descrip-
occlusal therapy 5. The mean pure-tone audiometry thresh-           tion of body sway in terms of displacement of the center of
olds (PTA) for air and bone conduction at 0.5, 1, 2, and            pressure (statokinesiogram-SKG). Patients stood barefoot
4 kHz were calculated [PTA = (threshold at 0.5 kHz+1                on the platform with arms by their side and the displace-
kHz+2 kHz+4 kHz)/4], according to the accepted standards            ments of their center of pressure (COP) were continuously
(ISO 8253-1, 1989). Only air-conduction hearing threshold           detected over a period of 52.2 sec with a sampling frequen-
of the affected ear was reported and the stage of the dis-          cy of 50 Hz, both with eyes opened (EO) and closed (EC).
ease classified as follows: stage I, PTA < 26 dB; stage II,         In particular, the area (S-expressed in mm2) and the length
26 < PTA < 40 dB; stage III, 41 < PTA < 70 dB; and stage            (L-expressed in mm) of the SKG as well as the velocity of
IV, PTA > 70 dB. Acoustic immittance was recorded by                displacements of the COP (V- expressed in mm/s) were de-
an impedenzometer. The maximum pressure (expressed in               tected. The S was computed by continuously detecting the
daPa) and the peak compliance (expressed in mm) were re-            COP displacement over time and calculating a confidence
corded before and after occlusal therapy. Electronystagmo-          ellipse that corresponds to the 90% of the sample positions,
graphic study of spontaneous nystagmus recorded binocu-             expressed in mm2.
larly in primary gaze and in the darkness was performed:            After that, each patient was asked to face the wall in front
if the average slow phase velocity, calculated over a 20s           of him/her, where a digital projector offered a full-field
period, was below 3°/s, the nystagmus was considered not            horizontal optokinetic (OKN) stimulation represented by
significant. Also, bithermal irrigation (33°C and 44°C) of          vertical alternating dark and light stripes of 30 cm in di-
both ear canals was performed and the vestibular paresis            ameter, delivered at a speed of 30°/sec. S, L and V were
formula of Jongkees was used. Caloric hypo-responsive-              also measured during this stimulation, delivered towards
ness was defined as more than a 25% asymmetry. Dix-                 the affected ear as well as the un-affected ear. This test was
Hallpike and Semont manoeuvers were always performed                performed because OKN stimulations are known to impair
to detect positional/paroxysmal nystagmus by the mean of            visually-evoked postural responses in MD 8. S, L and V val-
videonystagmoscopy. Cervical vestibular-evoked myogen-              ues measured under OKN stimulation are indicated with
ic potentials (cVEMPs) were performed to test ipsilateral           S-OKN, L-OKN and V-OKN, respectively.
saccular function. Each subject was tested while supine, the
head raised 30° from the horizontal plane to provoke the            Questionnaires
contraction of the sternocleidomastoid muscle. The active           Before and after each clinical assessment, patients were
electrode was placed on the middle third of the sternocleid-        asked to fill in a standardised battery of self-administered
omastoid muscle and a reference electrode was placed on             questionnaires: the Numeric Pain Rating Scale (NPRS) 9,
the upper border of the sternum. The ground electrode was           the Tinnitus Handicap Inventory (THI) 10 and the Situ-
placed on the forehead. Acoustic stimuli were short-tone            ational Vertigo Questionnaire (SVQ) 11. The NPRS is a nu-
bursts with a frequency of 500 Hz, presented five times per         meric tool in which a respondent selects a whole number
second through a TDH-49 earphone, in the affected ear.              (0–10) that best reflects the intensity of pain in the last 24
The rise-plateau-fall time was 1-2-1. cVEMPs responses              hours. Numbers are located on a horizontal bar where 0
were initially obtained by an acoustic stimulus of 95 dB HL         corresponds to “no pain” and 10 to the worst pain 9. The
and only if responses were absent it was increased to 100           THI is composed of 25 items, which score ranges from 0
dB HL. The duration of the stimulus was 10 msec. Results            to 4 (0 = never, 2 = sometimes, 4 = always) and analyzes
from 200 repetitions in each ear were averaged. The mean            the functional limitation (12 questions), the emotional re-
peak latencies (expressed in msec) of the P13 and N23               actions (8 questions) and the catastrophic perception (5
waves of cVEMPs were measured. The rectified amplitude              questions) caused by tinnitus. The score ranges from 0 to
was calculated by dividing the raw peak-to-peak ampli-              100; the higher the score, the higher the severity of tinnitus
tude (dB) by the background electromyography activity               annoyance is 10. The SVQ is a 19-items questionnaire in-
recorded during the 20 msec interval prior to the stimulus          vestigating the presence of visual vertigo, a disorder char-
onset. The test was performed twice to test reproducibil-           acterized by symptoms of dizziness, disorientation, and
ity. The number of vertigo attacks in the six months before         general discomfort induced by the presence of large mov-
and throughout occlusal therapy was extracted by a self-            ing objects in the visual field that often trigger dizziness in
rate vertigo diary. Static stabilometry results were recorded       MD patients. In particular, SVQ investigate what visual en-
before and at the end of the occlusal therapy using a force         vironments, such as watching moving traffic or trains, can



                                                                                                                                             91
D. Monzani et al.




cause vertigo and how much: for every item a maximum of                                      Electronystagmography showed no significant spontane-
4 points are given according to the stimuli ability to induce                                ous nystagmus in any patient before and after treatment.
or worse vertigo, while 0 points are assigned if the stimuli                                 Jonkees’s formula applied to caloric tests responses docu-
are unable to cause it. If a patient did not experience one                                  mented a caloric hypo-responsiveness in 18 patients before
or more described situations, the answer should be “not                                      occlusal therapy and in 19 at the end. The mean canal ca-
experienced”. The overall score is given by the following                                    loric asymmetry was (29.1 ± 7.7) at the beginning of the
formula: Total score/(19- number of questions in which pa-                                   occlusal therapy and (30.2 ± 6.7) at the end (p = 0.102).
tient signed “not experienced”) 11.                                                          No paroxysmal positional nystagmus was detected at the
                                                                                             time of the two consecutive examinations. The mean peak
Statistical analysis                                                                         latency of the P13 and N23 wave of the cVEMPs at the
Continuous data were expressed as mean ± standard de-                                        baseline were (16.8 ± 1.6) msec and (25.9 ± 1.7) msec; af-
viation, while categorical ones were indicated as subject-                                   ter occlusal splint therapy, P13 latency was (15.8 ± 2) msec
counts and percentages. Continuous variables were com-                                       and N23 latency was (24.9 ± 2.1) msec, showing no sig-
pared using the one-way analysis of variance followed by                                     nificant differences (p = 0.069 and p = 0.089, respectively).
the Tuckey-Kramer post-hoc comparison test. Categorical                                      Rectified peak-to-peak amplitude was (1.72 ± 0.3) dB be-
variables were compared using Fisher’s exact test. Statisti-                                 fore occlusal therapy and (1.67 ± 0.28) dB after it, showing
cal calculations were made using STATA Ic13 software. P-                                     no significant difference (p = 0.605). cVEMPs could not
values lower than 0.005 were considered significant.                                         be elicited in 6 patients (27.3%) at the two consecutive as-
                                                                                             sessments. These results are summarised in Figure 1. The
                                                                                             number of crises significantly decreased from (2.2 ± 1.7) to
Results
                                                                                             (0.9 ± 1.3) (p = 0.003). No differences were found between
MD lasted for a mean time of 15 ± 4 years, while the mean                                    the S, L and V parameters under EO conditions at baseline
length of TMD history was (3 ± 0.7) years. At baseline,                                      and after 6 months (all p > 0.005), while all of them were
8 patients (36.5%) were classified in stage II, 13 patients                                  significantly reduced in the EC condition (all p < 0.0001)
(59 %) in stage III and only 1 patient (4.5%) in stage IV                                    (Tab. I). The horizontal OKN stimulation displayed a sig-
of the MD. The same percentages were recorded at the                                         nificant reduction of S-OKN (p < 0.0001), L-OKN and V-
end of the treatment. No correlation was found between                                       OKN (p < 0.0001) during its delivery toward the afflicted
the side of unilateral MD and unilateral TMD (p = 0.7952).                                   side after SS treatment. No differences of S-OKN, L-OKN
The configuration of the audiogram was pike’s peak in 6                                      and V-OKN were observed if the same optic stimulation
patients (27.3%), flat in 14 patients (63.6%) and rising in                                  was delivered towards the unaffected side (p > 0.005 in all
two (9.1%). PTA at the baseline was (47.23 ± 13.7) dB                                        parameters). The mean slow phase velocity and the total
and (46.9 ± 13.9) dB at the final assessment (p = 0.9354).                                   number of saccades of the optokinetic reflex (OKN-SPV)
All patients exhibited a type A tympanogram according to                                     did not vary from baseline to final assessment if the optic
the Jerger’s classification system and, in the affected ear,                                 flow was delivered in both directions (all p > 0.005) (Tab.
none showed a gap between bone and air conduction hear-                                      II). The mean value of the NPRS at baseline was (4.7 ± 1.7)
ing threshold exceeding 10 dB. Middle ear pressure was                                       and after 6 months of occlusal splint therapy was signifi-
(0.91 ± 0.32) daPa at the baseline and (0.88 ± 0.24) daPa af-                                cantly reduced to 1.4 ± 1.1 (p < 0.0001) thus suggesting
ter the treatment, while compliance varied from (1.9 ± 29.1)                                 a relevant pain relief. The total score of the THI signifi-
to (-11.8 ± 29.8); no significant differences were found for                                 cantly decreased from the first administration (33.6 ± 9.1)
either parameter (p = 0.847 and p = 0.204, respectively).                                    to the final one (21.4 ± 5.1) (p < 0.0001), showing a general


Table I. Stabilometric parameters under EO and EC conditions.
 Variable                                           Baseline                                              6 months                                       P-value
 L-EO                                                     464.07 ± 103.61                             437.06 ± 85.43                                      0.4436
 L-EC                                                     613.68 ± 102.81                            427.76 ± 110.96                                     < 0.0001
 S-EO                                                     227.23 ± 100.63                             194.36 ± 82.57                                      0.243
 S-EC                                                     491.23 ± 241.78                            313.91 ± 122.89                                     < 0.0001
 V-EO                                                      13.51 ± 1.92                                12.12 ± 2.35                                       0.057
 V-EC                                                      15.11 ± 1.24                                11.71 ± 3.06                                      < 0.0001
L: statokinesiogram length; S: statokinesiogram surface; V: velocity of the displacements of the centre of pressure; EO: eyes opened; EC: eyes closed.




92
                                                                    Stabilising occlusal splint for temporo-mandibular joint disorder and comorbid Ménière’s disease




Table II. Stabilometric parameters and electronystagmography recordings of the optokinetic nystagmus recorded with optokinetic stimulations delivered toward
the affected ear and the intact one.
 Variable                                               Baseline                              6 months                               P-value
 OKN-L, affected side                                       733.94 ± 104.66                           460.28 ± 120.27                                < 0.0001
 OKN-L, unaffected side                                     512.48 ± 68.48                            478.92 ± 75.93                                  0.0991
 OKN-S, affected side                                       588.73 ± 323.68                           363.68 ± 190.74                                  0.002
 OKN-S, unaffected side                                     356.95 ± 145.71                           344.27 ± 140.29                                 0.7702
 OKN-V, affected side                                         15.73 ± 1.69                              11.03 ± 1.95                                 < 0.0001
 OKN-V, unaffected side                                       13.32 ± 1.6                                12.27 ± 2.1                                  0.0836
 OKNSPV-affected side                                         9.69 ± 2.15                                9.12 ± 1.39                                    0.2
 OKNSPV-unaffected side                                       13.08 ± 1.25                              12.62 ± 1.72                                  0.3127
 Sacc-affected side                                           21.55 ± 3.65                              22.73 ± 1.45                                  0.0987
 Sacc-unaffected side                                         26.55 ± 1.22                              26.27 ± 1.08                                  0.4088
OKN-L: statokinesigram length under optokinetic stimulation; OKN-S: statokinesogram surface under optokinetic stimulation; OKN-V: velocity of the displacements of the center of
pressure under optokinetic stimulation; OKNSPV: slow phase velocity of the optokinetic nystagmus; Sacc: number of saccadic movements of the optokinetic nystagmus.



improvement of tinnitus annoyance. The ‘functional’ sub-                                   of the Eustachian tube due to an abnormal contraction or
scale score showed indeed the most significant difference                                  spasm of the tensor veli palatini muscles. Caloric responses
(p < 0.0001) between baseline (19.3 ± 6.6) and final assess-                               were stable between the two assessments (Fig. 1) and the
ment (11.1 ± 5.1), the ‘emotional’ subscale score decreased                                paroxysmal positional nystagmus due to otolith dysfunc-
from (11.2 ± 5) to (8.3 ± 2.5) disclosing a less remarkable                                tion was absent, thus excluding the coexistence of other
reduction (p = 0.025) and the ‘catastrophic’ subscale score                                vestibular end-organ disorders at the time of the two exami-
resulted (3.1 ± 2.9) at first assessment and (2.1 ± 2.2) af-                               nations. The rate of occurrence of vertigo attacks was inter-
ter occlusal therapy and unchanged (p = 0.131). The SVQ                                    estingly reduced during the occlusal treatment compared to
score was (3.3 ± 0.5) before treatment and (2.6 ± 0.7) at the                              the previous period. Past experiments stated that ipsilateral
end of it and showed a significant reduction (p = 0.002).                                  dark cell region of the vestibular ampullas receives afferent
This data is summarised in Figure 2.                                                       fibers from the trigeminal ganglion and the trigeminal in-
                                                                                           nervation to the cochlear blood vessels could be involved
Discussion                                                                                 in the homeostatic disturbances of the inner ear, such
                                                                                           as hydrops, in guinea pigs 13. Unfortunately, analogous
TMDs have been associated with audiometrically docu-                                       pathophysiological data are not available in humans and a
mented hearing loss 12 but no study, to our knowledge,                                     cause-effect mechanism between an abnormal trigeminal
has reported significant, objective amelioration of hearing                                nociceptive pattern caused by TMDs in MD patients and
threshold after occlusal splint therapy or any other therapy                               a possible decrease of vertigo attacks as a consequence of
for TMDs. Additionally, our study showed no improvement                                    occlusal therapy remains elusive. Moreover, the reduction
of the PTA. It should be also observed that all patients suf-                              of acute attacks of vertigo could be also due to the natural
fered from definite MD and its mean duration was about                                     history of the disease or to amelioration of the TMD only.
fifteen years. So far, it is conceivable that hearing loss at                              Obviously, occlusal splint may ameliorate patients’ stabil-
the time of the occlusal treatment was no longer fluctuat-                                 ity, thus improving vertigo as well.
ing and reversible as in the first stages of the disease and                               In this study, an amelioration of the stabilometric param-
histopathological changes in the cochlea are presumably                                    eters such as L, S and V in EC conditions only when the
permanent. It is also conceivable that SS therapy per se                                   OKN was delivered towards the affected labyrinth denotes
is not capable of modifying cochlear damage in humans.                                     a central function of the occlusal splint itself. The study
Furthermore, middle ear pressure and compliance did                                        also showed the stationary nature of P13-N23 latency and
not differ before and after occlusal therapy and resulted                                  rectified inter-peak amplitude of cVEMPs over the selected
within normal ranges in all cases (-100 < daPa < 100 and                                   time interval (Fig. 1). This result must be interpreted with
0.3 < ml < 1.5 respectively). This result seems to exclude                                 caution because, to our knowledge, no prospective stud-
that the pathophysiology of some aural symptom associ-                                     ies have explored the behaviour of sacculo-collic reflexes
ated to TMDs such as ear-fullness, tinnitus and subjective                                 in MD over time. On the contrary, a conservative occlusal
hearing loss could be identified in a perturbed ventilation                                therapy carried on by SS may be an effective option to im-



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D. Monzani et al.




Figure 1. Caloric asymmetry, P13 and N23 peak latencies and amplitude before and after occlusal splint therapy (p > 0.005 in all cases).


prove body balance in patients suffering for TMDs and co-                          of sensory information and modulation of postural reflexes
existing MD. It should be underlined that the improvement                          and gait 16. Moreover, vestibular ascending pathways are
of body sway parameters has been observed only in the                              known to reach the insula in humans 17 and both a pos-
EC condition and when OKN stimulation was delivered to                             terior and an anterior pain-related cortical area have been
the afflicted ear. The lack of significant postural improve-                       described within the insular cortex 18,19. Finally, robust ves-
ment under EO conditions between baseline and the end of                           tibular stimulation is known to activate the anterior cingu-
treatment confirms the results of a previous experience that                       late cortex 20 that is also activated by noxious stimuli and is
documented the efficacy of static visual cues on counter-                          involved in pain processing 21.
acting vestibular and somatosensory abnormal information                           Taken together, these data suggest that the stabilising effect
in patients with peripheral vestibular dysfunctions and co-                        of splint therapy on postural control may be more probably
morbid TMD 14. In contrast, the lack of visual information                         attributed to a reduced interference of pain on the corti-
causes vestibular impairment and the abnormal propriocep-                          cal vestibular network rather than to a peripheral vestibular
tive pattern of the stomatognathic apparatus of these pa-                          mechanism. In fact, no documented and significant changes
tients to emerge, giving reason for the higher values of S,                        occurred in the inner ear while pain was rated as greatly re-
L and V both at the baseline and after 6 months of SS, if                          duced after occlusal therapy. Given this, an analogous cen-
compared to the EO conditions. In fact, stabilometric pa-                          tral mechanism could also explain the improvement of pos-
rameters were markedly improved after occlusal therapy                             tural responses to optokinetic stimulation of MD patients
in the EC condition. A possible pathophysiological expla-                          who are known to be particularly sensitive to moving visual
nation of this therapeutic effect is based on an experience                        scenes 8. Both the anterior and the posterior insula and the
that observed trigeminal terminals in contact with vestibu-                        anterior cingulate cortex are activated during optokinetic
lospinal neurons in the inferior and lateral vestibular nuclei,                    nystagmus 22. Balance amelioration in response to moving
giving evidence of a trigemino-vestibulospinal pathway in                          visual cues is also supported by the significant reduction
rats 15. In humans, such connections are not known and                             in the SVQ score after occlusal therapy in this study. The
their existence could only be suspected. On the contrary,                          significant decrease in the SVQ score indicates that a lower
recent fMRI studies in humans clearly demonstrated that                            number of visual triggers and/or their frequency are able
splint therapy triggers activation in parietal sensorimotor                        to induce vertigo/dizziness. This result suggests reduced
integration areas that are also involved in the processing                         sensitivity to moving visual environments of patients with
                                                                                   vestibular disorders as a consequence of more effective
                                                                                   central integration of conflicting sensory information from
                                                                                   visual and vestibular receptors. The improvement of tin-
                                                                                   nitus showed by this study has been already documented
                                                                                   in patients treated by a multimodal therapeutic approach
                                                                                   for TMD and comorbid MD 5, thus supporting the hypoth-
                                                                                   esis of an abnormal somatosensory component in the origin
                                                                                   and/or persistence of tinnitus in TMD sufferers 23. In fact,
                                                                                   in humans trigeminal-auditory anatomical connections are
Figure 2. Numeric Pain Rating Scale (NPRS) score, Tinnitus Handicap Inven-
                                                                                   far from being documented even if the modulation of tin-
tory (THI) and Situational Vertigo Questionnaire (SVQ) before and after occlusal   nitus by jaw manoeuvers is widely diffuse among acute
splint therapy.                                                                    and chronic tinnitus sufferers 24. At present, it is reason-



94
                                                 Stabilising occlusal splint for temporo-mandibular joint disorder and comorbid Ménière’s disease




able to suggest that improvement of tinnitus annoyance in           AbbVie, USA; BCG, Switzerland; Boehringer-Ingelheim,
this cohort is more probably due to the reduction of the            Germany; Compass Pathways, UK; EDRA-LSWR, Italy;
hypertone of masticatory muscles 25 obtained by SS rather           Inpeco SA, Switzerland; Relmada, USA; Johnson &amp;
than to a substantial change in both the middle and the in-         Johnson, USA; Takeda, USA; VeraSci, USA; Vifor, Swit-
ner ear. Some potential limitations of the current study are        zerland. DM, EA, MAC, CBe, ER and DMa have no con-
noteworthy. For example, we did not perform any kind of             flict of interests to declare.
acuphenometry to assess pitch and loudness of tinnitus in
order to objectify basic features. Nonetheless, the use of          Funding
a symptom-specific questionnaire like the THI is probably           This research did not receive any specific grant from fund-
more appropriate to assess the beneficial effects of any            ing agencies in the public, commercial, or not-for-profit
therapy in tinnitus-sufferers since tinnitus perceived handi-       sectors.
cap is largely independent from its audiometrically-derived
measures 16. The study design did not include untreated             Authors’ contributions
participants as controls or a comparison group treated with         DMo, DMa, MAC and LP conceived the study. CBa, EA,
non-occluding oral appliances (active placebo). On the              ER,CBe, MAC and SG recruited patients. CBa, SG, LP and
other hand, effective therapy for TMDs must not be delib-           DM made statistical calculations. All authors read and ap-
erately avoided in patients suffering from such symptoms            proved the last version of the manuscript.
only to appreciate a placebo effect or the result of no treat-
ment. Finally, the sample size was small and even if it was         Ethical consideration
from a hypothesis-generating study, a larger, multicentre           This retrospective study was approved by the Modena
confirmatory study is needed.                                       Ethics Committee (protocol number: 2121, study code
                                                                    NOC11) and each participant signed an informed consent
Conclusions                                                         for study participation and data publication. All procedures
                                                                    were conducted in accordance with the latest version of the
An SS appliance can be a conservative and safe treatment            declaration of Helsinki.
option for patients suffering from TMD and comorbid MD
because of an increased control of visually-evoked postural
responses and better vestibulo-spinal control of posture
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