Anatomical and functional aspects of ligaments between the malleus and the temporomandibular joint

Development of the human primary and secondary jaw joints

This study investigates the development of the primary and secondary jaw joints in humans, focusing on their concomitance and subsequent disconnection. Development begins with the primary temporomandibular joint as a connection between Meckel's cartilage and the incus, while the secondary temporomandibular joint develops anteriorly as an articulation between the mandibular condyle and the mandibular fossa. Previous research in mice has provided insights into the morphogenesis of these joints, but their specific development of the 3D morphogenesis in humans remains unclear. To address this gap, histological serial sections of embryos and fetuses ranging from 19 to 230 mm crown-rump length were analyzed. The 3D morphogenesis of the middle ear and the temporomandibular joint was examined, paying attention to the morphological characteristics, timing, and potential mechanisms of movement and disconnection. The primary jaw joint is initially formed at 25 mm (8th week), followed by the appearance of the secondary jaw joint arising at 87 mm (12th week). Both joints persist present simultaneously, until a separation occurs between 150 and 230 mm (18th-24th week). It is remarkable that both joints remain concomitant and function somehow for a period exceeding 6 weeks, with the mechanism of their separation still unclear. Understanding the precise timing and functional movements involved with these temporarily connected joints is crucial for comprehending the overall development of the temporomandibular joint. Further research is needed to explore the molecular and cellular processes underlying these developmental changes.

Development of the Primary and Secondary Jaw Joints in the Mouse

This study assesses the morphogenesis of the primary and secondary jaw joints. A collection of 11 murine heads, ranging from prenatal stage E13.5 to postnatal stage P10, were prepared as histological serial sections (thickness 8-10µm) and stained conventionally in order to examine them with light microscopy. Next, the regions of the developing temporomandibular joint and the middle ear ossicles were three dimensionally reconstructed using AnalySIS® software. This study gained new insight into the spatio-temporal development of the temporomandibular joint and the auditory ossicles. Furthermore, we newly visualized in 3D that during the developmental period from stages E16 to P4 two morphologically well-functional joints (the primary and secondary jaw joints) exist on either side and are mechanically connected via Meckel's cartilage. Potential separation mechanisms of these two joints are discussed and options for mathematical analysis are suggested.

Oral splint therapy in patients with Menière's disease and temporomandibular disorder: a long-term, controlled study

PURPOSE

To assess the effect of oral splint therapy on audio-vestibular symptoms in patients with Menière's disease (MD) and temporomandibular disorder (TMD).

METHODS

Retrospective case-control study. Treatment group: 37 patients with MD and TMD who received gnatological treatment.

CONTROL GROUP

26 patients with MD and TMD who had never received gnatological treatment. The number of vertigo spells in 6 months (primary endpoint), pure-tone audiometry average (PTA), MD stage, functional level, Dizziness handicap Index (DHI), Tinnitus handicap Index (THI) and Aural Fullness Scale (AFS) were compared at baseline and after 24 months according to groups. Analysis of Covariance was used to determine the treatment effect.

RESULTS

Groups were comparable for demographic, clinical data, baseline PTAs and the number of vertigo spells. Analysis of covariance showed a significant effect of gnathological treatment on number of vertigo spells ([Formula: see text] = 0.258, p < 0.001), PTA ([Formula: see text] = 0.201, p < 0.001), MD stage ([Formula: see text] = 0.224, p < 0.001), functional level ([Formula: see text] = 0.424, p < 0.001), DHI ([Formula: see text] = 0.421, p < 0.001), THI ([Formula: see text] = 0.183, p < 0.001), but not for AFS ([Formula: see text] = 0.005, p = 0.582). The treatment group showed vertigo control of class A in 86.5% and class B in 13.5% of patients. In the control group, vertigo control was of class A in 19.2% of patients and class B in 11.5%, class C in 30.8%, class D in 11.5%, class E in 19.2% and class F in 7.7%. Classes of vertigo control differed significantly (X² test, p < 0.001).

CONCLUSIONS

Oral splint therapy could represent a viable treatment in patients with TMD and uncontrolled MD disease. The effects are maintained at least after 2 years.

Evaluation of morphological variations of petrotympanic fissure using computed tomography imaging of the temporal bone

PURPOSE

Petrotympanic fissure (PF) is important for both dentists and otolaryngologists to know the temporal anatomy well especially for pre-surgical radiological evaluations. Computed tomography (CT) is indispensable method for temporal bone imaging. The purpose of this study was to evaluate PF morphology and position using CT.

METHODS

CT scans of 300 patients (600 PFs) were retrospectively evaluated. PF types were recorded by dividing into 3 groups (Type 1,2 and 3). Length of the mandibular fossa (MF) and PF, vertical diameter (VD) of the PF at the MF level, midpoint and tympanic cavity (TC) level were measured. PF position types were subdivided as low, midline and high.

RESULTS

Type 1, 2 and 3 was found in 18.7%, 51.5% and 29.8% of the cases, respectively. The mean length of the MF and PF was 18.33 mm and 3.77 mm, respectively. The mean VD of the PF at the MF level, midpoint and TC level was 1.71, 0.98 and 0.97 mm, respectively. The low, midline and high position of PF was observed 14.5%, 54.3% and 31.2% of the cases, respectively.

CONCLUSION

Length of the MF and PF in males was significantly higher than females. VD of the PF at the MF level in Type 1 and Type 3 was significantly higher than type 2. In type 1,VD of the PF at the midpoint was significantly higher than type 2 and type 3. VD of the PF at the TC level in Type 1 and Type 3 was significantly higher than type 2.

Petrotympanic Fissure Architecture and Malleus Location in Temporomandibular Joint Disorders

The aim of this research was to assess possible relationships between petrotympanic fissure (PTF) characteristics, malleus position, and temporomandibular joint disorders (TMD). A retrospective study was performed, including patients with TMD. Magnetic resonance imaging (MRI) and cone-beam computed tomography (CBCT) examination were used to evaluate temporomandibular joint (TMJ) disc position and condylar bone changes. Fifty-eight TMJs from twenty-nine patients (23:6 females: males) were assessed. Erosive changes (DDR-disc displacement with a reduction of 6 (24%), DDwR-disc displacement without a reduction of 8 (61.5%) vs. normal disc position 3 (15%), p = 0.012) and condyle osteophytes production (DDR 6 (24%), DDwR 9 (69.2%) vs. normal condyle 7 (35%), p = 0.012) were more frequent in subjects with disc displacement compared to normal disc position; malleus was closer to PTF in cases with erosive changes (median 2.15 interquartile range: (1.85–2.75) vs. 2.75 (2.25–3.15), p = 0.029) as well as those with condylar osteophytosis (2.25 (1.91–2.75) vs. 2.75 (2.33–3.32), p = 0.015); the PTF length was higher in cases with condylar osteophytosis compared to those without (4.45 (3.50–4.77) vs. 3.67 (3.34–4.28), p = 0.039). The disc position and disc shape were not related to PTF or malleus position. Malleus position and PTF dimensions were not associated with the PTF type. In cases with erosive changes and condylar osteophytosis, malleus was closer to PTF.

Improved visualization of the chorda tympani nerve using ultra-high-resolution computed tomography

Background

Recognition of the anatomical course of the chorda tympani nerve (CTN) is important for preventing iatrogenic injuries during middle-ear surgery.

Purpose

This study aims to compare visualization of the CTN using two computed tomography (CT) methods: conventional high-resolution CT (C-HRCT) and ultra‐high-resolution CT (U-HRCT).

Materials and methods

We performed a retrospective visual assessment of 59 CTNs in normal temporal bones of 54 consecutive patients who underwent both C-HRCT and U-HRCT. After dividing CTN into three anatomical segments (posterior canaliculus, tympanic segment, and anterior canaliculus), two neuroradiologists scored the visualizations on a four-point scale.

Results

On C-HRCT, the visual scores of the posterior canaliculus, tympanic segment, and anterior canaliculus were 3.5 ± 0.7, 1.6 ± 0.6, and 3.1 ± 0.7, respectively. The respective values were significantly higher in all segments on U-HRCT: 3.9 ± 0.2, 2.4 ± 0.6, 3.5 ± 0.6 (p < 0.01). Although the difference in scores between methods was greatest for the tympanic segment, the visual score on U-HRCT was lower for the tympanic segment than for the anterior and posterior segments (p < 0.01).

Conclusion

Ultra‐high-resolution CT provides superior visualization of the CTN, especially the tympanic segment.

Microscopic reconstruction and immunohistochemical analysis of discomalleolar ligament

Discomalleolar ligament represents the vestiges of the primitive lateral pterygoid muscle which penetrates in the caudal end of Meckel's cartilage; during the development of newborn, the petrotympanic fissure close almost completely leaving inside the discomalleolar ligament. After entering in tympanic cavity, some fibers of the discomalleolar ligament insert to walls of cavity, other fibers continue with the lateral margin of the anterior ligament and insert in the neck of malleus; in contrast, other Authors demonstrated that discomalleolar ligament is an independent structure inserted in proximity of the neck of the malleus. Although the discomalleolar ligament can be considered as a structure of clinical importance, it is not described by anatomy textbooks. Moreover, it is likely that important correlations between temporomandibular diseases and otological symptoms exist. We have studied discomalleolar ligament submitting the specimens to the 3D volume rendering technique, light microscopy, reconstructing a wide light microscopic fields to analyze the real connection between retrodiscal connective tissue and middle ear, and immunofluorescence methods in order to analyze the consistence of ligament. We have shown two types of connections between TMJ and ear: first, with external acoustic meatus and, second, with middle ear through discomalleolar ligament. The different insertion represents a strong support in order to demonstrate that the TMJ disorders can determine variations of tension that are transmitted on the tympanic membrane provoking tinnitus in according to clinical features. Then, we propose that it is necessary to mention, also in anatomy textbook, the discomalleolar ligament as ligament distance of TMJ.

The discomallear ligament: anatomical, microscopical, and radiologic analysis

BACKGROUND

Several anatomic relationships between the ear and the temporo-mandibular joint have been proposed to account for the presence of tinnitus during temporo-mandibular disorders. Among the otomandibular structures, the discomallear ligament (DML) is interposed between the malleus and the retrodiscal capsular complex. The aim of present paper was to study through dissection the frequency and morphology of DML, to characterize its type of collagen, and to evaluate the DML on routine computed tomography (CT).

METHODS AND RESULTS

The study has been conducted on five un-embalmed adult cadavers, and in all cases, the DML was present (100%). It was constituted mainly by fibers of collagen I, with abundant elastic fibers. On CT exams of 40 patients with no reported pathology of the ear, on axial images, a dense structure, going from the upper end of the petrotympanic fissure to the neck of the malleus, was present in all the cases. In 90%, it showed a triangular shape, in 5% a rectangular shape, and in 5% a curved course. The mean length of the antero-medial side was 2 ± 0.6 mm and that of the antero-lateral side was 1.63 ± 0.5, and the mean area was 1.29 ± 0.83 mm².

CONCLUSION

The DML could represent an anatomical structure that joining the temporo-mandibular joint and the malleus may play a role in the otologic symptoms during temporo-mandibular disorders.

Correlation Between Tinnitus and Petrotympanic Fissure Status Among Patients With Temporomandibular Joint Dysfunction

PURPOSE

The objective of this study was to evaluate the correlation between tinnitus and petrotympanic fissure (PTF) subtypes in patients diagnosed with temporomandibular joint dysfunction (TMD).

MATERIALS AND METHODS

One hundred patients with TMD (50 with tinnitus, 50 without tinnitus) were evaluated retrospectively using cone-beam computed tomography (CBCT). CBCT images were analyzed according to PTF subtype diagnosis (types 1 to 3). PTF structure was classified as type 1 (wide tubular formation), type 2 (double conical structure), or type 3 (single conical structure).

RESULTS

Although there was a negative correlation between tinnitus and PTF type (P < .001), there was no correlation between age and tinnitus or between age and subtype of PTF. There was no significant association between gender and tinnitus or PTF type (P > .05).

CONCLUSIONS

A short, wide PTF (type 1) might be associated with an increased incidence of tinnitus in patients with TMD.

The canine jaw-ear connection: The malleomandibular and tympanomandibular ligaments

In the human, two ligaments derived from the first embryonic pharyngeal (branchial) arch that unite the mandible and temporomandibular joint (TMJ) with the middle ear have been identified as the discomalleolar ligament (DML) and sphenomandibular ligament (SML), also known as the malleomandibular ligament (MML), anterior ligament of the malleus (AML), and tympanomandibular ligament (TML). Neither of these structures has been previously described in the dog. The homologue of the human sphenomandibular ligament (SML) exists in the dog and is represented as a fibrous remnant of Meckel's cartilage. In the newborn puppy, the ligament is a true malleomandibular ligament (MML), extending from the medial mandible to the rostral process of the malleus with no intermittent attachments. In the adult dog, the ligament is entrapped within a bony passageway, likely due to the development and ossification of the tympanic bulla, making it difficult to grossly view the complete course of the ligament. The majority of the ligamentous fibers attach near the tympanic bulla in the adult dog, thus this portion of the ligament has been named the tympanomandibular ligament (TML). Those fibers of the ligament not attaching near the tympanic bulla appear to continue through a canal, located between the tympanic annulus and the surrounding tympanic bone, to become continuous with a connective tissue sheet within the cavity of the middle ear that has attachments to the malleus and incus. Tension on the adult canine TML did not result in movement of the malleus.

Anatomical study of the human discomallear ligament using cone beam computed tomography imaging and morphological observations

In the present study, the human discomallear ligament (DML) was observed in structures at both macroscopic and cone beam computed tomography levels. Assessments were made regarding the distribution of calcitonin-gene-related peptide (CGRP), protein gene-product (PGP) 9.5, and substance P (SP) of the DML based on immunohistochemical analyses of the anatomical properties of jaw movements using 27 Japanese human cadavers (mean, 79.3 +/- 8.6 years; male, 74.9 +/- 8.0; female, 82.8 +/- 7.5). The DML of the anterior region was connected to the TMJ disc. The DML of the posterior region was attached to both the head and the anterior process of the malleus through the petrotympanic fissure, which formed a narrow channel. The structure of the petrotympanic fissure through the DML was attached to the malleus, and this structure was associated with the mobility of the malleus. In the anterior and posterior parts of the disc-associated connective tissue of the DML, CGRP-, PGP9.5- and SP-positive nerve fibers were located around numerous blood vessels, a condition which may be correlated with chronic pain syndrines disorders and the auditory system.

Histological study of the extratympanic portion of the discomallear ligament in adult humans: a functional hypothesis

This study was carried out on histological aspects of the extratympanic portion of the discomallear ligament (DL) in adult humans. The temporomandibular joint (TMJ) was dissected bilaterally in 20 cadavers; in 15 cases the articular disc (AD) and the retroarticular tissue were extirpated. The extratympanic portion of the DL had the shape of a base-down triangle, in relation to the AD, and an upper vertex, in relation to the petrotympanic fissure. In five cases, the base, measured bilaterally, had an average length of 6.4 mm, while the distance from the base to the upper vertex averaged 9.3 mm in length. The extratypanic portion of the DL is an intrinsic ligament of the TMJ, composed of collagen fibres and abundant elastic fibres. We propose that this ligament could act as a tensor of the synovial membrane in movements of the TMJ.

Clinical anatomy of the chorda tympani: a systematic review

OBJECTIVE

The chorda tympani is at risk of iatrogenic injury throughout its course. This paper reviews the clinical anatomy of the nerve in adults.

DESIGN

Systematic literature review.

METHOD

Relevant English-language articles were identified using five electronic databases and one search engine. Data from approximately 70 scientific papers were supplemented with information from selected reference texts.

RESULTS

The anatomy of the chorda tympani differs from standard descriptions, particularly regarding its exit from the middle ear and area of lingual innervation. Whilst it is known to convey taste sensation from the anterior two-thirds of the tongue and parasympathetic innervation to the submandibular and sublingual salivary glands, the chorda tympani probably has additional sensory and secretomotor functions.

CONCLUSION

A detailed understanding of the anatomy of the chorda tympani may help to reduce the risk of iatrogenic injury during head, neck and middle-ear surgery, and to explain the variable consequences of such injury.

Prevalence of the types of the petrotympanic fissure in the temporomandibular joint dysfunction

BACKGROUND

Petrotympanic fissure (PTF) is a fissure in the temporal bone that runs from the temporomandibular joint (TMJ) to the tympanic cavity (TC). In PTF, the discomallear ligament (DML) connects the malleus in the tympanic cavity and the articular disc and capsule of the temporomandibular joint. PTF with the DML is a possible cause of aural symptoms related to temporomandibular joint dysfunction (TMD).

PURPOSE

To investigate the prevalence of different types of PTF in TMD using dental volumetric tomography (DVT) and determine whether PTF type correlates with age.

MATERIAL AND METHODS

DVT scans in the sagittal planes of PTFs of 134 patients with TMD were examined for the types of PTF present. Three main PTF types were described: wide, tunnel-shaped structure (type 1); tunnel-shaped structure that is wide open in the PTF entrance to the mandibular fossa and gradually thins out in the tympanic cavity (type 2), tunnel-shaped structure that is wide open in the entrance of the mandibular fossa, with a middle region with a flat-shaped tunnel structure and a narrow exit in the tympanic cavity (type 3).

RESULTS

In DVT scans, PTF types 1, 2 and 3 were seen in 67.2%, 1.5%, and 31.3% of cases, respectively. We found no significant relationship between age or gender and PTF type.

CONCLUSION

The low percentage of type 2 PTF and high percentage of type 1 PTF must be taken into consideration during pre-surgical planning related to TMD. However, future well-designed clinical studies involving larger numbers of subjects will be necessary to confirm the findings of this study.