Potential Myogenous Temporomandibular Disorders Following Iatrogenic Occlusal Disturbance: A Pilot Study

INTRODUCTION

Temporomandibular disorder comprises a group of chronic pain conditions that can involve the TMJs, masticatory muscles, and associated structures and tissues.¹ Temporomandibular disorder is most commonly observed in individuals between the ages of 20 years and 40 years.^2,3 Approximately 33% of the population has at least one TMDs symptom, and 3–6% to 7% of the population has TMD with sufficient severity to cause them to seek treatment.^3,4 The subtypes of TMDs routinely seen in patients are myofascial pain and arthralgia, followed by disc displacements with reduction.⁵

The TMDs are multifactorial in etiology, as biomechanical, neuromuscular, biopsychosocial, and neurobiological factors may contribute to the disorder.⁶ To highlight their role in the pathogenesis of TMDs, these factors are classified as⁴

• Predisposing factors (structural, metabolic, and psychological conditions),
• Initiating factors (trauma from occlusion, traumatic injuries), and
• Aggravating factors (parafunctional, psychosocial, or hormonal).

Although the occlusal interferences (OI) had been considered as a significant contributor in characterizing TMD, lately this has been questioned based on epidemiological and experimental studies, and there is a current trend toward making a weak correlation between OI and TMD.⁷

Recently, the iatrogenic factors resulting from dental practice have also been claimed to be contributing factors in TMD.⁷ Dental treatments affect the shape of the dental units, thus interfering morphologically and functionally with the harmony of the masticatory system and its components, especially the occlusal condition.⁸ Therefore, the emergence of TMD signs and symptoms after restorative treatment is not rare. It seems that the acute morphological alteration of the occlusal conditions as a result of restorative or prosthodontic restoration may interfere with the established functional equilibrium, disturbing the coordinated pattern and timing of jaw muscle contraction.⁷

Most restorative procedures affect the shape of the occlusal surface; however, the iatrogenic effect of dental restoration in TMD etiology has rarely been studied. Hence, this pilot study was aimed to investigate the relationship between sudden iatrogenic occlusal disturbance and its effect on the myogenous TMD.

MATERIALS AND METHODS

RESULTS

A total of 30 female patients with a mean age of 24 ± 5.3 years were included in the present pilot study. The study participants were divided into three groups, namely:

Group I: patients receiving direct occlusal restoration (operative clinic) total of 10 patients (33.33%).

Group II: patients receiving indirect occlusal restoration (fixed prosthesis clinic) 2 patients (6.67%).

Group III: patients receiving oral prophylaxis (periodontal clinic) 18 patients (60%).

The distribution of subjects was 40% in the treatment group, and 60% in the control group.

The treatment-induced occlusal disturbances were observed in 8 (80%) of the participants in group I and all the patients in group II, whereas no occlusal disturbances were found in the control group.

Furthermore, the mean change in occlusal force on the treated teeth was found to be 5.6 ± 1.1 Newtons. This change in occlusal force was not statistically significant (p > 0.05). As expected, no change in bite force was observed in the control group. Also, none of the patients reported any symptoms related to pain or restriction in function in the TMJ. Hence, the results recorded no relation between the abrupt changes in the occlusal force due to dental treatment and the development of the myogenous TMD.

DISCUSSION

The present study was conducted to examine the relation, if any, between OI resulting from dental treatment and mygenous TMDs. It was observed that a very high percentage of dental treatments resulted in the creation of occlusal disturbances, and there was a slight change in the bite force in the restored dentition. However, this change was not statistically significant, and it did not produce any symptoms related to TMJ.

The first point to ponder is the alarmingly high percentage of occlusal disturbances introduced after the treatment. It could be because the procedures were performed in a student clinic rather than by experienced dentists. There is a significant difference in the quality of the restoration produced by a skilled practitioner and an amateur. However, in spite of the large number of OI in the restored teeth, none of the patients reported any symptoms related to the TMJ. Furthermore, the mean change in the bite force produced after the restorative treatment was also negligible. These findings further weaken the argument favoring the relationship between OI and TMDs.

The capacity of the masticatory muscles to exert sufficient bite force between the teeth is an indicator of normal function.⁹ In patients with TMD, there is a diminished capacity of the masticatory muscle activity. As a result, the maximal bite force values are generally lower in patients with TMD than in the population in general.^9,10 Hence, bite force was used as an indicator of TMD in the present.

The etiology of TMDs is multifactorial, and various authors have emphasized the importance of occlusion. However, whether occlusion plays a crucial role in the pathogenesis of TMD remains controversial. This argument is based on various epidemiological and experimental studies, and there is a current trend toward making a weak correlation between OI and TMD. It had been reported that 85 to 90 percent of the population exhibit some form of OI.^7,11 Other studies conducted in different population groups with different ages and gender have shown that various types of occlusal disturbances were significantly but often weakly correlated with the signs and symptoms of TMD.^7,12,13 Furthermore, experimental studies have also reached controversial results. Some studies have demonstrated no electromyographic response to the artificial OI,^14,15 whereas others showed that occlusal disturbances were significantly associated with consistent clinical changes in the electromyographic response as well as clinical symptoms.^16–18

The findings of the present study are contrasting to those of a 10-year controlled longitudinal clinical study that researched the probable etiological significance of restorative treatment leading to TMD among 40 participants. It showed that signs and symptoms of TMD were more evident in subjects with restored dentition than in subjects with intact dentition.¹⁹ This is generally attributed to inappropriately contoured fillings leading to occlusal instability. Furthermore, over-contoured anterior crowns without adequate lingual concavity will direct the jaw along a retruded closing path, forcing the condyle onto a more sensitive vascular innervation area. This results in the condyles to be more distally placed leading to hyperactivity and fatigue in posterior temporalis and the suprahyoid muscles and deep masseter muscles, thereby resulting in inter-articular disc displacement.⁷

Nevertheless, occlusal interference can cause TMJ dysfunction. Uncoordinated mandibular movements seem to be one of the neuromuscular responses of the masticatory system to OI. Restorative procedures aim to alleviate TMJ dysfunction by eliminating as many OI as possible. However, despite the best efforts and technical skill of the clinicians, OI can be inadvertently incorporated in the restored occlusal morphology.²⁰

CONCLUSION

Within the limitations, it can be concluded from the present study that:

• Occlusal disturbance after operative and fixed treatment among patients treated in students’ clinic was significantly high.
• A change in the occlusal force of 5.6 Newton did not produce any symptoms indicative of TMJ disorders.

CLINICAL SIGNIFICANCE

Iatrogenic OI may cause/exacerbate TMDs; hence, extreme caution should be exercised by the clinicians to avoid causing harm to the patients.

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