Occlusion and Posture

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Occlusion and Posture

This detailed summary explores the debated connection between posture, the trigeminal system, and prosthetic rehabilitation in the diagnosis of orofacial disorders, including Temporomandibular dysfunctions (TMDs). This complex relationship is examined through the lens of vestibular evoked myogenic potentials (VEMPs), which are diagnostic tools used to study the integration of sensory inputs from the vestibular system into motor responses affecting jaw muscles. The discussion also touches on broader implications in the fields of neurology and rehabilitation, offering insights into the intricate interactions within the human body's sensory and motor systems.

The chapter begins by addressing the ongoing debate regarding the correlation between dental occlusion, posture, and temporomandibular disorders. It points out the critical need for a careful evaluation of clinical symptoms without being swayed by prevailing medical doctrines that might lead to diagnostic errors.

VEMPs are discussed as a pivotal diagnostic approach to understanding the trigeminal/vestibular correlation. The narrative explains how VEMPs, specifically the click-evoked cervical vestibular myogenic potentials (cVEMPs), are influenced by visual motions that create an illusory sensation of movement, known as vection. The increase in cVEMP amplitude during vection illustrates the neurological connection between sensory perceptions and motor responses, highlighting the body's complex response mechanisms.

The text delves into the controversies surrounding the relationship between dental occlusion and postural stability. It presents both supporting and opposing views within the scientific community, backed by numerous references and studies. Proponents argue that disturbances in the craniomandibular system can influence overall postural alignment through neuromotor pathways and myofascial connections. Critics, however, question the clinical relevance of these correlations, citing studies with inconclusive or conflicting results.

A significant portion of the discussion is devoted to the methodologies used in studying the occlusion-posture relationship. The challenges of accurately measuring and interpreting the complex interactions between dental malocclusions and body posture are examined. The summary critiques the limitations of current research, including small sample sizes and the lack of comprehensive, high-quality studies that integrate dynamic and static assessments of posture and dental occlusion.

The narrative prepares to introduce a specific clinical case that exemplifies the practical implications of these theories in medical practice. It sets the stage for a detailed examination of a patient with marked temporomandibular and postural anomalies, intending to apply and possibly validate or refute the discussed theories through real-world application.

In concluding, the summary underscores the necessity of maintaining an open, evidence-based approach when diagnosing and treating conditions that may involve the integration of dental, postural, and neurological factors. It calls for more rigorous and expansive research to better define the connections between the stomatognathic system and overall body health, suggesting that future studies should aim to clarify these complex relationships using advanced diagnostic tools and more representative sample sizes.

This comprehensive overview not only sheds light on the specific topic of VEMPs and their role in understanding craniofacial and postural interrelations but also reflects on the broader implications for clinical practices in neurology, orthodontics, and physical therapy.

Keywords

Vestibular Evoked Myogenic Potentials (VEMPs) - Refers to the diagnostic tools used to study the interaction between the vestibular system and muscle responses, crucial for understanding sensory and motor integration in the context of occlusion and posture.

Temporomandibular Dysfunctions (TMDs) - Describes disorders related to the temporomandibular joint, which are central to discussions of occlusion and postural stability in the medical and dental fields.

Trigeminal System - Points to the nerve system involved in facial sensation and motor functions, which is discussed in relation to its connection with vestibular inputs and its implications for occlusion and posture.

Orofacial Disorders - Broad term covering disorders of the face and mouth, relevant here for the discussion of how these conditions intersect with posture and neurological functions.

Postural Stability - Concerns the body's ability to maintain a stable posture, a key topic in the debate over the impact of dental occlusion on overall body posture.

Dental Occlusion - Refers to the alignment of teeth and the way the upper and lower teeth come into contact, which is analyzed for its potential impact on bodily posture and neuromuscular function.

Neuromuscular Responses - Relates to the responses of the muscular system to neural stimuli, particularly in the context of how occlusion may affect these responses.

Cervical Vestibular Myogenic Potentials (cVEMPs) - A specific type of VEMP that helps illustrate the interaction between visual stimuli and vestibular responses, showing how sensory illusions like vection can influence muscular responses in the neck.

Prosthetic Rehabilitation - Refers to the use of prosthetics in the rehabilitation process, especially relevant in discussions of restoring function and alignment in patients with orofacial disorders.

Myofascial Connections - Pertains to the connective tissue that surrounds and supports muscles, discussed in the context of how these structures may link the masticatory system to broader postural dynamics.

 

Article by  Gianni Frisardi

 

Introduction

As an introduction to the section of chapters concerning 'Occlusion and Posture' we can partially report a concise introduction by Monika Nowak et al. on which we will make the first conceptual reflections reported by our pensive Linus.

Posture is understood as the position of the human body and its orientation in space which requires the analysis and integration of stimuli from three systems: vision, vestibular and proprioception. Over the years, numerous observations have been made on the factors influencing postural stability. The role of the craniomandibular system is now being increasingly analyzed in relation to it. Many theories attempt to explain the association between the masticatory organ and posture, including myofascial chains, trigeminal nerve activation or deactivation, and subsequent interaction in the brainstem. However, this is a controversial topic in the scientific community. There is both evidence to support that relationship and to refute it.

Content supporting correlation

The authors of the scientific reports, who recognize the associations between the systems in question, give two indications for the possible interactions. The first, i.e. ascending disturbances, refers to the situation in which bad posture and disturbances of the peripheral structures (e.g. lower limbs), through myofascial neuromotor activities and the dura mater, functionally condition the cranio-mandibular structures. Conversely, a chain of descending disorders is present when anomalies of the craniomandibular region affect posture and body areas located more distally, including the pelvis and lower extremities.

And on this nothing to say because no one can deny an anatomical-functional correlation between vestibular systems, cerebellum, trigeminal and peripheral neuromotor system. This is not an opinion but a proven scientific observation already reported somewhere in Masticationpedia.

Figure 1: Vestibula Evoked Myogenic Potentials (see chapter 'Complex Systems'

VEMPs, translated into Myogenic Vestibular Evoked Potentials are proof of this. Acoustic stimuli can evoke EMG reflex responses in the masseter muscle called Vestibular Evoked Myogenic Potentials (VEMPs). Although these findings have previously been attributed to activation of cochlear (high-intensity sound) receptors, these may also activate vestibular receptors. Because anatomical and physiological studies in both animals and humans have demonstrated that the masseter muscles are a target for vestibular inputs, the authors of this study reevaluated the vestibular contribution for masseter reflexes. This is a typical example of a basic level 'Complex System' as it consists of only two cranial nervous systems but, at the same time, they interact by activating monosynaptic and polysynaptic circuits (Figure 1).

Tmj disorders and posture

It has been shown that changes in the temporomandibular joint (TMJ) can have a direct impact on muscle activity in terms of posture, stability and physical performance. However, there is a lack of high-quality studies using advanced measurement tools to better understand the phenomenon under investigation. The study authors evaluated the impact of masticatory abnormalities on postural control and focuses on evaluating individuals with specific malocclusions that determine the anteroposterior position of the mandible. According to some researchers, malocclusion, like TMD, can affect the osteoarticular system of the whole body and become a source of persistent pain and favor the development and to become chronic of some postural defects. According to the cited authors, occlusal disturbances can lead to an altered stimulation of the periodontal proprioceptors, causing changes in the tension of the neck muscles and postural muscles and changes in the position of the head, followed by compensatory changes in the anatomical regions in their immediate vicinity. Over time, this can affect the posture, center of gravity position, or foot contact with the ground.

This could also be true but at the same time it should be demonstrable in order not to make diagnostic errors such as the one we will present in the section dedicated to 'Occlusion and Posture. Indeed, the patient we will present exclusively reported a masticatory disorder such as to require continuous rehabilitative reconstructions from his dentist. How can we demonstrate this occlusal disturbance at the neuromotor level such that it can also condition the vestibular system, the cerebellum and other brain centres?

Figure 2:Trigeminal electrophysiological responses.

Faced with a marked asymmetry such as the one shown in Figure 2, we certainly cannot deny a trigeminal disorder which is often related to a malocclusion. In Figure 2A we can see a slight asymmetry of the interferential EMG trace between the right and left masseter as well as the MEPs of the trigeminal root (Figure 2B) as well as the absence of the action potential on the right masseter in the mandibular reflex responses (Figure 2C ). As we will see in the chapters concerning this patient, these abnormal trigeminal electrophysiological responses have nothing to do with occlusal disturbances, much less postural disturbances.

However, there is still a gap in scientific knowledge on the relationship between craniofacial structure and spinal postural control in patients with malocclusion. Furthermore, the available documents show problems related to the small number of subjects, the small number of tested parameters or the selection of reliable measurement tools.

Malocclusion, which these studies focus on, can result from abnormalities in the structure and alignment of the bones of the jaw and mandible in relation to each other or from an abnormal arrangement of the dental arches.

Bruxism and Posture

Angle suggested a classification of occlusion and malocclusion based on the anteroposterior position of the first molar and the position of the canines.Malocclusion is often a congenital condition, resulting from hereditary or environmental factors. It is also caused by local factors, such as an abnormal pattern of breathing or postural defects, as well as oral parafunctions such as nail biting or teeth grinding (bruxism).According to Lombardo's analyses, occlusal anomalies occur on average in 56% of the general population. Their prevalence increases with age. Given their increasing prevalence in later age groups and the consequences they entail, it is reasonable to expect a large number of adult patients who will require complex and expensive multidisciplinary treatment.

Regarding bruxism we certainly cannot speak of scientific certainties or take into consideration the incidence of bruxism in the population because, as described in the specific chapter concerning our patient 'Bruxer', he had a perfect occlusion and neuromuscular responses apparently up to standard if it hadn't been for the study of the case and have highlighted a neuronal hyperexcitability with the test of the _rcMIR masseter inhibitory recovery cycle (Figure 3).

Figura 3: _rcMIR in brusiste patient

Although the patient was in a state of neuronal hyperexcitability which affected the entire left leg with stiffness of the upper limbs, he never accused postural problems. With this we want to underline that although there are correlations between different cerebral association areas such as the vestibular, the trigeminal, the midbrain and so on, this does not give the clinician the right to base the diagnosis on these certainties. As, of course, we will repeat repeatedly throughout the 'Normal Science' section to justify the next section which will focus on the aspect of the anomalies and therefore the crisis of the paradigm.

Given the high proportion of patients with malocclusions and the conflicting reports of these reports, the need for further knowledge and analysis of individual malocclusions and associated musculoskeletal abnormalities under dynamic and static conditions is reasonable. There is still a lack of research on the effect of occlusion on postural stability and plantar pressure distribution during standing and walking in the same group of adults with Angle Class I, II, and III.

Contents to refute the correlation

As far as the authors contesting the correlation between occlusion and posture are concerned, we can report the results of Giuseppe Perinetti et al. of 122 subjects, including 86 males and 36 females (age range 10.8 to 16.3 years) who tested negative for temporomandibular disorders or other conditions affecting the stomatognathic systems, with the exception of malocclusion. An assessment of dental occlusion included dentition stage, molar class, overjet, overbite, anterior and posterior crossbite, scissor bite, mandibular crowding, and dental midline deviation. Furthermore, body posture was recorded through static posturography using a vertical force platform. Recordings were performed under two conditions:

1. mandibular rest position (RP)
2. dental intercuspid position (ICP).

The conclusion was that all posturographic parameters showed great variability and were very similar between recording conditions. Furthermore, a limited number of weakly significant correlations, mainly for the overbite phase, were observed when using multivariate models.

The author's current findings were that regarding the use of posturography as a diagnostic aid for subjects affected by dental malocclusion, they do not support the existence of clinically relevant correlations between malocclusion typology and body posture.

Another interesting article in the group contesting the correlation comes from Benjamin Scharnweber et al. examined 87 male subjects with a mean age of 25.23 ± 3.5 years (18 to 35 years). The dental models of the subjects were analyzed. Postural control and plantar pressure distribution were recorded from a weight bearing platform. Possible orthodontic and orthopedic influencing factors were determined from a medical history or questionnaire. All tests performed were randomized and repeated three times each for intercuspid position (ICP) and locked occlusion (BO).

In this study, the ICP occlusal position was found to increase body sway in the frontal (p ≤ 0.01) and sagittal (p ≤ 0.03) planes compared to the BO position, whereas all other 29 correlations were independent of position of the occlusion.

For both ICP or BO cases, angle therapy, midline shift, crossbite, or orthodontic therapy was found to have no influence on postural control or plantar pressure distribution (p > 0.05).

In conclusion, the author confirms that persistent dental parameters have no effect on postural sway. Furthermore, postural control and plantar pressure distribution were found to be independent postural criteria.

«After this due introduction to the 'Occlusion and Posture' section we can move on to the specific chapter concerning a patient with evident postural problems.»

Bibliography & references