ORIGINAL RESEARCH


https://doi.org/10.5005/jp-journals-10019-1417
International Journal of Prosthodontics and Restorative Dentistry
Volume 13 | Issue 3 | Year 2023

Effect of Hard and Soft Occlusal Splints on Electromyographic Activity of Masseter and Anterior Temporalis in Patients with Moderate to Severe Occlusal Wear: A Randomized Controlled Trial


Ruchi Goel1, Veena Jain2, Chanchal Gupta3, Achal K Srivastava4, Gunjan Pruthi5

1–3Department of Prosthodontics, Centre for Dental Education and Research (CDER), All India Institute of Medical Sciences (AIIMS), Delhi, India

4Department of Clinical Neurophysiology, All India Institute of Medical Sciences (AIIMS), New Delhi, India

5Department of Prosthodontics, Postgraduate Institute of Medical Education and Research, Chandigarh, India

Corresponding Author: Gunjan Pruthi, Department of Prosthodontics, Postgraduate Institute of Medical Education and Research, Chandigarh, India, Phone: +91 9999968841, e-mail: gunjan_prostho@yahoo.co.in

Received on: 21 June 2023; Accepted on: 03 August 2023; Published on: 29 September 2023

ABSTRACT

Purpose: To compare the effect of hard and soft splints on muscle activity and self-reported clinical outcomes in patients with moderate to severe tooth wear at different intervals.

Materials and methods: Participants within the age range of 18–45 years having moderate to severe wear of teeth were allocated into group IHS (n = 8) receiving hard splints and group IISS receiving soft splints. Electromyography (EMG) activity of masseter and anterior temporalis were recorded during postural rest position (PRP) and maximum voluntary clenching (MVC) at baseline (T0), 24 hours (T1), 4 weeks (T2) and at 8 weeks (T3) with and without splint. EMG activity of controls with no or minimal tooth wear was recorded only at baseline. Nonparametric tests were used for within-group and intergroup comparisons, followed by post hoc analysis with Bonferroni correction.

Results: Baseline EMG activity was higher in experimental groups than that of controls, but the difference was nonsignificant (p > 0.05). At 24 hours, both the groups showed significantly lower (p < 0.05) EMG activity with the splint as compared to without the splint. Hard splints led to decreased muscle activity, while soft splints led to an increase at 4 and 8 weeks as compared to baseline EMG activity of controls, and the difference was nonsignificant except for anterior temporalis during MVC in group IHS. The intergroup comparison revealed insignificant differences at all time intervals (p > 0.05), while it was significant for anterior temporalis in MVC at 4 and 8 weeks (p < 0.05).

Conclusion: Muscle activity varied with different materials of the splint and duration of use. Both splints helped in the adaptation of muscles to new vertical dimensions of occlusion at 8 weeks with lesser variation between with and without splint position. The effect of the splint was more pronounced on the activity of the anterior temporalis than the masseter muscle.

How to cite this article: Goel R, Jain V, Gupta C, et al. Effect of Hard and Soft Occlusal Splints on Electromyographic Activity of Masseter and Anterior Temporalis in Patients with Moderate to Severe Occlusal Wear: A Randomized Controlled Trial. Int J Prosthodont Restor Dent 2023;13(3):137–144.

Source of support: Nil

Conflict of interest: None

Keywords: Enamel wear, Muscle activity, Permissive splint, Postural rest position, Vertical dimension

INTRODUCTION

Tooth wear, also known as tooth surface loss (TSL), is a complex phenomenon with multifactorial etiology and high prevalence. Physiologic tooth wear can be associated with age and may lead to various consequences like dentinal hypersensitivity, loss of vertical dimension, and, overall, a disturbed balance between different components of the stomatognathic system. As TSL progresses, compensatory mechanisms fail to maintain the original vertical dimension of the patient, leading to insufficient space to accommodate restorative materials.1,2

Permissive centric stabilization splints help in muscle deprogramming and restoring the stability of the temporomandibular joint in a reversible manner before reorganizing the patient’s occlusion at a new vertical dimension. They also provide important diagnostic and prognostic information during the stabilization or prerestorative phase.3-6 So, it is crucial to study the effects of splints on muscle activity, the optimal duration of wear to bring the desired effect, and the difference in the action of splints fabricated in different materials. One of the methods which have been vastly explored in literature is the electromyography (EMG) of masticatory muscles, as it is a good clinical indicator to assess the health of the stomatognathic system, masticatory muscle’s efficiency, and functional mechanism of splints.7

Previous studies7-10 have reported a reduction in the EMG activity of anterior temporalis and masseter muscles with the use of hard splints, while the effect of a soft splint on EMG activity was variable. Most of these studies were conducted either in healthy individuals or in patients with a history of bruxism or temporomandibular joint disease (TMD). Hard splints worn for 3 months helped in restoring the muscles to their initial resting state after increasing the vertical dimension of patients with generalized attrition.11 However, fabrication of a hard splint is time-consuming, technique sensitive, and may require additional chair side time for occlusal adjustment. It is also associated with the risk of poor compliance of the patients due to its rigidity, thus, defeating its own purpose of breaking the muscle engram of the patients. Alternatively, many clinicians have used soft splints as they are quick to fabricate and have higher patient acceptance.12 Few studies have reported that soft splint therapy led to clenching habits and occlusal changes, though other studies have proved that no occlusal changes occurred with time if occlusal adjustments were made during the insertion of the splint.13,14

Kolcakoglu et al.15 observed better pain relief in children with nocturnal bruxism, but the difference in muscle activity was nonsignificant in hard and soft splint groups as measured on a portable EMG device. The influence of hard vs soft splints on muscle pain, muscle fatigue, bite force, or brain activity has been studied earlier in healthy subjects or bruxers immediately after splint insertion or a maximum of up to 6 weeks.16-20 Nonsignificant difference was reported between hard vs soft splint therapy till 15 weeks by Pettengill et al.,21 while soft splint was reported to be more beneficial in pain relief in another study18 for a similar time period. A hard splint was found to provide earlier relief in clinical symptoms of temporomandibular joint (TMJ) disorders as compared to a soft splint in a recent clinical trial, but the scoring criterion used to assess the outcome could not be interpreted well.22 To the best of our knowledge, literature is still scanty to report the effect of hard and soft splints on EMG activity of muscles in patients with tooth wear, which is, however, relevant to study, especially when we need to alter the vertical dimension of the patients before definitive phase. Since patient compliance plays a crucial role in achieving the desired results, it is equally important to know the patient’s perception of the splints, and it has not been reported so far.

Therefore, the purpose of this randomized controlled trial was to compare the effect of hard and soft splints on muscle activity of masseter and anterior temporalis muscles in patients with moderate to severe wear measured at postural rest position (PRP) and maximum voluntary clenching (MVC), immediately and up to 8 weeks, with and without splint. The research hypothesis of the study was “significant difference would be found in EMG activity of masseter and anterior temporalis muscles in occlusal wear patients receiving either hard or soft splints after 8 weeks of splint use.”

MATERIALS AND METHODS

Trial Design

This randomized controlled trial was begun after obtaining ethical clearance from the Institution Ethics Sub Committee (IESC/T-442/2012) and followed Consolidated Standards of Reporting Trials (CONSORT) guidelines (Fig. 1).23

Fig. 1: Flowchart as per CONSORT guidelines

Sample Size Estimation and Randomization

The convenience sampling method was used to enroll a total of 16 participants. Each participant was allocated to one of the two experimental groups (n = 8): group IHS (hard splint–heat cure stabilizing splint) and group IISS (soft splint–thermo-vacuum formed soft polyvinyl splint) using computer-generated block randomization list, stratified by gender and severity of the wear. Eight age and gender-matched controls following the same inclusion and exclusion criteria except for wear score (score 0 or 1) were selected to record their baseline EMG activity, but they did not receive any splint therapy.

Inclusion and Exclusion Criteria

Patients within the age range of 18–45 years, irrespective of gender, and with signs of tooth wear were referred to Prosthodontic Department from the Oral Medicine Department for further screening and recruitment as study participants. Inclusion criteria were the presence of moderate to severe occlusal wear (score 2 or 3 according to Pergamalian et al.),24 full complement of caries-free and periodontally healthy dentition (excluding third molars), no previous history of dental treatment involving enameloplasty, onlays, crowns or alteration of occlusion. Any individual with a diagnosis of bruxism, neuromuscular disorder, TMJ disorder/TMD, systemic problems like myasthenia gravis, osteoarthritis, or rheumatoid arthritis, etc., history of analgesics to combat pain in joints or any other drug history which could affect the muscle function were excluded.

Diagnostic Evaluation and Consent

Bruxism was evaluated using a noninstrumental approach given by Lobbezzo et al.,25 which included self-reported clenching and fatigue of jaw muscles with or without pain in TMJ. Patients were explained about bruxism or clenching and were asked to monitor their habits for the next 1–2 weeks. Repeat history was taken, and family members were also enquired about any relevant observations, like a grinding sound while sleeping. Clinically, the subjects were palpated for any clicking sound or muscle hypertrophy. All the eligible participants were explained in detail about the study plan, desired compliance with wearing splints, EMG study, and follow-up visits. Written informed consent was obtained as per the Helsinki Declaration26 from those who agreed to get enrolled in the study.

Splint Fabrication

Maxillary and mandibular casts were mounted on a semi-adjustable articulator using a face-bow and centric relation (CR) record. An anterior deprogrammer (Lucia jig) was used to guide the mandible in CR and to create a separation of approximately 1 mm in the molar region and 3 mm separation in the anterior region. Hard splints were made in heat-cure acrylic resin on the maxillary cast. In centric occlusion, evenly distributed bilateral posterior contacts and light contacts of anterior teeth were developed. Anterior guidance was adjusted to develop posterior disocclusion during eccentric movements.27 Adjustments of clasps were made if required before referring participants for EMG recordings (Fig. 2). The soft occlusal splint was fabricated over the maxillary cast using a 3 mm thick, soft polyvinyl sheet (Bioplast; Scheu-dental GmbH, Iserlohn, Germany) in a pressure molding device (Biostar Scheu-dental; GmbH, Iserlohn, Germany) with a thermally controlled, infrared heater.28 Splint was adjusted to establish uniform contact of posterior teeth and light contact of anterior teeth in centric occlusion (Fig. 3). All splints were fabricated by one operator to control variation in appliance construction and were checked for seating and accuracy by an experienced supervisor. Participants were instructed to wear the splint all day and night except during eating and to report immediately if they felt any discomfort after wearing the splint. Individual compliance was checked regularly through phone calls.

Fig. 2: Hard splint in position

Fig. 3: Soft splint in position

Electromyography (EMG)

A single trained technician from the Neurology Department performed all the EMG recordings after explaining the procedure to the participants and seating them comfortably with unsupported heads. Eight-channel EMG was standardized with fixed calibration (Nicolet Biomedical, Madison, United States of America).11,29 Anterior temporalis and masseter muscles were palpated, and the bipolar silver chloride surface electrodes were placed using conduction gel and secured with an adhesive tape (Fig. 4). A section of signals recording where the activities in all channels were steady over 5 seconds was taken.11,29 Quantitative values of amplified motor unit potentials in microvolts (µV) were measured from base to peak of the recorded graph using computer-assisted programming (Medelec Synergy), and the mean value of three readings was computed and tabulated in a Microsoft Excel sheet.

Fig. 4: Electrode placement on face

Recording of EMG activity was performed on each participant at fourtime points, that is, pretreatment/baseline (T0), after 24 hours (T1), at 4 weeks (T2), and at 8 weeks (T3) after splint insertion. At each visit, EMG activity was recorded for two positions: at PRP and MVC, both with and without splint. For the volunteer group, EMG activity was recorded only at the time of their recruitment for the study at both muscle functioning positions. A dental nurse who was blinded with study objectives and type of splint helped the participants to report their experience in speech/phonetics, pain/tenderness in TMJ, muscle tiredness, check biting, and headache subjectively on a self-designed Likert scale of 0–3 (0 = none, 1 = mild, 2 = moderate, and 3 = severe) after insertion of splints at follow-up visits.

Statistical Analysis

Statistical analysis was done using Statistical Package for the Social Sciences (SPSS) software (IBM Corp. Released 2011. IBM SPSS Statistics for Windows, Version 20.0. Armonk, New York, United States of America: IBM Corp.). No data for demographic details were presented as the mean and standard deviation or percentage, and muscle activity was presented in median (minimum–maximum) in microvolts. The normality of the data was checked using the Shapiro–Wilk test. Friedman test was used to determine intragroup change, followed by Wilcoxon signed-rank test with Bonferroni corrections for carrying out multiple comparisons. Intergroup comparison was carried out by Kruskal–Wallis test and Mann–Whitney U test. The confidence interval was set at 95%, and a p-value of <0.05 was considered statistically significant.

RESULTS

All participants completed the study without any evident deviation from the experimental protocol. The mean age, distribution, and wear score of participants has been described in Table 1.

Table 1: Demographic details of the participants enrolled in the study
Parameters Matched volunteers (n = 8) Group I HS hard splint (n = 8) Group II SS soft splint (n = 8) p-value
Age (mean ± SD) 33.88 ± 5.38 34.25 ± 6.23 34.62 ± 8.62 0.454
Gender n (%) Male 5 (62.5%) 5 (62.5%) 5 (62.5%) 1.000
Female 3 (37.5%) 3 (37.5%) 3 (37.5%)
Occlusal wear score n (%) 0 6 (75%) 0 0 Group IHS vs control: 0.026
1 2 (25%) 0 0 Group IISS vs control: 0.026
2 0 2 (25%) 2 (25%)
3 0 6 (75%) 6 (75%) Group IHS vs IISS: 1.000

Patient-reported Outcome Measures after Splint Insertion

In group IHS, two participants reported mild, and five reported moderate difficulty in speech; two participants reported mild cheek biting after 24 hours (T1) of delivery of the splint. While in group II, five participants reported mild difficulty in speech; two participants complained about mild cheek biting while using the soft splint. This indicates that more participants had trouble in speech with a hard splint than with a soft splint, while an equal number reported mild cheek biting from both groups after wearing splints for 24 hours. None of the participants reported pain/tenderness in TMJ, muscle tiredness, or headache. After the required adjustments of splints and counseling of participants, no further complaint was reported at subsequent follow-up visits (Table S1 with individual values).

Evaluation of EMG Activity of Masticatory Muscles

Electromyography (EMG) recording at PRP and MVC, with and without splint, showed no statistically significant difference (p > 0.05) in masticatory muscle activities on the right and left sides. Hence, an average of muscle activities on both sides was calculated for analysis. The within-group comparison showed a significant difference in muscle activity in both groups at 24 hours with and without splint position (p = 0.01), while it was nonsignificant at other time points.

The difference in baseline (T0) EMG activity of masticatory muscles during PRP and MVC for both the experimental and controls were statistically nonsignificant, although the baseline muscle activity was higher in experimental groups than in controls (p > 0.05) (Table 2). Group IHS showed a decrease in EMG activity at 4 and 8 weeks as compared to the baseline EMG of control group, but the difference was statistically nonsignificant (p > 0.05), except for anterior temporalis during maximum voluntary clench, which showed significantly lower EMG activity (p = 0.006, with splint at 4 weeks, p = 0.007, without splint at 4 weeks, p = 0.027, with splint at 8 weeks, p = 0.03, without splint at 8 weeks). Group II SS showed an increase in muscle activity at 4 and 8 weeks as compared to the baseline EMG of the control group in both positions, but the difference was statistically nonsignificant (p > 0.05) (Table 3, Figs 5 and 6).

Table 2: Baseline (T0) EMG activity of masseter and anterior temporalis muscles at PRP and MVC
Muscle EMG activity recording position Baseline EMG activity [median (minimum-maximum)] (µV) p-value
Group I hard splint (n = 8) Group II soft splint (n = 8) Control (n = 8)
Masseter PRP 9.04 (4.54–23.48) 9.76 (5.49–26.48) 8.68 (5.43–11.06) 0.612
MVC 240.25 (72.1–542) 564.90 (98.16–621.8) 273.53 (94–532.5) 0.236
Anterior temporalis PRP 15.56 (9.26–36.51) 17.8 (10.93–40.4) 14.88 (9–20.1) 0.464
MVC 357.23 (86.1–584.3) 850.58 (249.3–954.3) 560.33 (202.06–882.41) 0.309

EMG, electromyography; PRP, postural rest position; MVC,maximum voluntary clenching

Table 3: Difference in EMG activity of masseter and anterior temporalis muscles in the experimental groups after 4 and 8 weeks of splint therapy in comparison to baseline EMG activity of the control group
Groups Muscle Function Baseline EMG activity in the control group: median (minimum-maximum) (µV) EMG activity in the experimental group after splint therapy: median (minimum-maximum) (µV)
After 4 weeks After 8 weeks
With splint Without splint With splint Without splint
Experimental group p-value Experimental group p-value Experimental group p-value Experimental group p-value
Group I (Hard Splint) vs Control Masseter Rest 8.68 (5.43–11.06) 6.47 (3.2–14.6) 0.142 6.72 (3.1–14.9) 0.190 7.71 (4–18.9) 0.600 7.71 (4–19) 0.562
Clench 273.53 (94–532) 192.04 (58–374) 0.115 194.48 (59.2–379.7) 0.429 218.41 (65–460) 0.248 218.57 (64.9–453.7) 0.190
Anterior temporalis Rest 14.88 (9–20.1) 9.46 (5.3–16.7) 0.059 10.08 (6–17.3) 0.156 13.40 (8.1–21) 0.674 12.72 (8–20.9) 0.638
Clench 560.33 (202.1–882.4) 238.35 (68.2–380.3) 0.006* 245.49 (71.9–355.7) 0.007* 318.38 (74.9–476.1) 0.027* 303.57 (74.1–468. 3) 0.032*
Group II (Soft Splint) vs Control Masseter Rest 8.68 (5.43–11.06) 9.10 (5.05–25.5) 0.834 8.84 (4.4–23.8) 0.960 10.82 (5.2–27.8) 0.462 9.75 (6–29) 0.638
Clench 273.53 (94–532) 510.08 (87–567) 0.294 480.50 (85.6–561.2) 0.128 616.68 (101–651) 0.172 619.60 (103.7–631) 0.317
Anterior temporalis Rest 14.88 (9–20.1) 15.59 (9.7–36.1) 0.462 14.23
(8.8–36.9)
0.711 18.11
(10.8–38.3)
0.294 17.20
(10.8–39.2)
0.373
Clench 560.33 (202.1–882.4) 698.75 (194.6–903.3) 0.674 667.17 (187.5–919.7) 0.795 839.75 (226.2– 935.7) 0.462 807.33 (245.3–923) 0.429

*p < 0.05 is considered significant

Figs 5A and B: EMG activity of masseter and anterior temporalis in both the experimental groups at different time points at postural rest position: (A) With splint; and (B) Without splint

Figs 6A and B: EMG activity of masseter and anterior temporalis in both the experimental groups at different time points at maximum voluntary clenching: (A) With splint; (B) Without splint

Intergroup comparison between experimental groups showed nonsignificant differences in the activity of both muscles, with and without a splint at 24 hours (p > 0.05), though lower EMG activity was observed with a splint than without a splint (Table 4). At 4 and 8 weeks in both the groups, there was nonsignificant difference in with and without splint muscle activity except for a significant difference between group IHS and group IISS for anterior temporalis in MVC, at 4 weeks (p = 0.04, with and without splint) and 8 weeks (p = 0.04, with splint, p = 0.03, without splint).

Table 4: Intergroup comparison of EMG activity of masseter and anterior temporalis muscles with a splint and without splint at three different time intervals
Groups Muscle Function EMG activity after splint therapy: median (minimum-maximum) (µV)
After 24 hours After 4 weeks After 8 weeks
Group I (hard Splint) Group II (soft splint) p-value Group I (hard splint) Group II (soft splint) p-value Group I (hard splint) Group II (soft splint) p-value
With splint Masseter Rest 7.20 (3.6–20.5) 7.91 (4.3–20.2) 0.529 6.47 (3.2–14.6) 9.10 (5.05–25.5) 0.294 7.71 (4–18.9) 10.82 (5.2–27.8) 0.294
Clench 216.38 (65.2–414.5) 462.23 (90.7–557) 0.115 192.04 (58–374) 510.08 (87–567) 0.074 218.41 (65–460) 616.68 (101–651) 0.056
Anteriortemporalis Rest 12.03 (6.4–32.8) 12.73 (8.9–30.7) 0.600 9.46 (5.3–16.7) 15.59 (9.7–36.1) 0.067 13.40 (8.1–21) 18.11 (10.8–38.3) 0.208
Clench 277.58 (74.2–428.2) 674.66 (190.5–723.3) 0.141 238.35 (68.2–380.3) 698.75 (194.6–903.3) 0.046* 318.38 (74.9–476.1) 839.75 (226.2–935.7) 0.046*
Without splint Masseter Rest 9.05 (4.5–23.4) 9.76 (5.5–26.4) 0.430 6.72 (3.1–14.9) 8.84 (4.4–23.8) 0.294 7.71 (4–19) 9.75 (6–29) 0.345
Clench 240.25 (72.1–542) 564.90 (98.1–621.8) 0.156 194.48 (59.2–379.7) 480.50 (85.6–561.2) 0.093 218.57 (64.9–453.7) 619.60 (103.7–631) 0.059
Anteriortemporalis Rest 15.57 (9.3–36) 17.80 (10.9–40.4) 0.497 10.08 (6–17.3) 14.23 (8.8–36.9) 0.115 12.72 (8–20.9) 17.20 (10.8–39.2) 0.142
Clench 357.24 (86.1–584.3) 850.58 (249.3–954.3) 0.103 245.49 (71.9–355.7) 667.17 (187.5–919.7) 0.046* 303.57 (74.1–468.3) 807.33 (245.3–923) 0.036*

*p < 0.05 is considered significant

DISCUSSION

The research hypothesis is partially accepted as intergroup comparison yielded nonsignificant differences except statistically significant differences observed in EMG activity of the anterior temporalis muscle during MVC at 4 and 8 weeks after the splint insertion. In this study, the baseline muscle activity was higher in experimental groups than in volunteers with minimal or no tooth wear and no history of splint use. This indicates that ongoing tooth wear was affecting the muscle activity of the participants, and the severity of tooth wear is relevant. But the variation was nonsignificant because of uniformity in their distribution among groups and controls. The nonsignificant difference between the muscle activities of matched volunteers and experimental groups at different time points suggests that it always remained within the physiological limits.

Few participants reported cheek biting and a perceived difficulty in speech during the initial period. But with adjustments and chair-side counseling, no discomfort was reported at subsequent visits. Splints given in the maxillary arch can lead to more difficulty in speech, but it was preferred as it leads to equal intensity contacts and is recommended when the splint must be worn for 24 hours.30 Narita et al.17 also reported increased tiredness of muscles when patients clenched over a soft splint as compared to a hard splint during one point assessment of six subjects. Psychological and muscular adaptation to a foreign body with time might change this observation.

A nonsignificant difference was observed between the right and left side muscles in this study. This is suggestive of a harmonious relationship between muscles and joints after the insertion of splints. Roark et al.8 found the decreased activity of temporalis and an increase in muscle activity of the masseter with a hard splint when right and left side muscles were compared during MVC in healthy subjects. They concluded that the effectiveness of splints might be due to different reasons than the redistribution of unfavorable loading of the joints.

Response of muscles to the splints has always been variable, as reported in previous studies.7,8,15-17 Holmgren et al.7 noticed a change in muscle activity in 71% of patients, but that change was inconsistent before and after clenching on hard splint in bruxers. Fear of tooth fracture due to biting on hard material, a sudden increase in vertical dimension due to the thickness of the material, or incomplete seating of the splint over any tooth can lead to a decrease in muscle activity, while removal of premature contacts or reduction of pain may result in higher muscle activity. The best possible mechanism which can be attributed to a change in muscle activity is the unloading of muscles from any unfavorable forces and helping the condyles to sit in the most retruded position, which decreases the inhibitory signals to the brain.7

Overall results of this study revealed higher muscle activity with the soft splint as compared to the hard splint at all-time intervals, including baseline. Increased muscle activity with the soft splint can occur due to the resiliency of the material and a greater number of occlusal contacts because of stimulated proprioceptive afferent neurons.17 On the other hand, participants might have avoided the full application of force on the hard splint for fear of breaking the splint or the tooth. The number of occlusal contacts and occlusal force increase proportionately with clenching, but as the soft splint tends to deform under occlusal force, it dissipates the force applied to it.17 This effect may be more evident than hard splints, especially under MVC.

Most studies have measured the activity of the masseter and anterior temporalis as these are easily accessible for the placement of electrodes.11,16,31 In this study, anterior temporalis showed higher activity as compared to masseter in both groups at all-time intervals, and this difference was more noticeable at 4 and 8 weeks during MVC, with or without splint. A significant difference in the baseline activity of the anterior temporalis in MVC was also noted between the hard splint and control groups. Anterior temporalis has been reported to be affected more by the change in vertical dimension.32 Al-Quran et al.16 observed an increased activity of jaw elevator muscles of healthy subjects with a soft splint while the muscle activity decreased with a hard splint, at different intensities of clenching. Although the effect was greater on anterior temporalis than masseter in their study as well, variations have been observed in other studies. It has been suggested that the overall therapeutic effect is always achieved by a balancing act between the masseter and anterior temporalis and probably among all jaw muscles, and the aim of any treatment is to achieve this harmony.

Both the experimental groups showed lower muscle activity after 24 hours of splint insertion when EMG activity was recorded with a splint in position as compared to that without a splint. This indicates that there was a change in the muscle activity with a splint in position, but still, the change was not much evident when the patient was not wearing the splint. Immediate changes after splint insertion could be subjected to the change in sensory signals from peripheral receptors located in TMJ, muscles, periodontal ligament, and soft tissues under the influence of new material in the mouth.16 This difference was unnoticed without a splint, as it might be too early to alter subconscious reflex patterns or heal the tissues being affected by gradual TSL. Savabi et al.10 observed a nonsignificant difference in muscle activity in the maximum clenching position without a splint and immediately after the insertion of a hard splint in healthy subjects. Changes in the vertical dimension, number of occlusal contacts, and amount of comfort are crucial factors to influence muscle activity, especially in the initial period.

Results of this study also indicate that the material of the splint is significant when worn by patients with tooth wear. They help the stomatognathic system to adapt to a new vertical dimension. However, the effect of splints is reversible.29 So, it is important to investigate the appropriate duration which would be required to produce a harmonious relationship between CR and centric occlusion of the patient prior to proceeding with definitive rehabilitation. Hard splint therapy for up to 3 months has been recommended in patients with TMJ joint disorders or patients with generalized attrition before definitive therapy.11 Adding 3 months of stabilization phase to a long restorative phase can be clinically challenging for a few patients. So, in this study, the effect was evaluated at 24 hours, 4 weeks, and 8 weeks.

Both splints led to an evident change in muscle activity at 4 weeks. Muscle activity increased from 24 hours to 4 weeks’ time with a soft splint in PRP and MVC, and it decreased with a hard splint. This was followed by a significant increase in muscle activity in both groups from 4 to 8 weeks. The nonsignificant difference, with or without a splint, indicates that the muscles might have started getting adapted to new verticals with the continued use of splints. Muscles were in the most stable position with and without a splint after 8 weeks of splint therapy, irrespective of the material of the splint, and the activity was approximating that of reference baseline activity. Soft splints led to higher muscle activity at different time points as compared to hard splints, and this difference can be attributed to the resiliency of the material.5,17,28

Limitations of the study include convenience sampling and condylar position was not assessed on radiographs before and after splint therapy. Participants showed full compliance with both splints but subjective preference from patients’ perspective could not be confirmed. The results of this study should be investigated further with a larger sample size and comparing the muscle activity achieved with splints and after definitive rehabilitation at the same vertical dimension of occlusion.

CONCLUSION

Based on the observations of this clinical study, it can be concluded that splints helped in achieving a harmonious effect on muscle activity of individuals with TSL and helped them in adapting to a new vertical dimension of occlusion. The effect of splint use was more pronounced on the activity of the anterior temporalis than the masseter muscle. Objective evaluation of muscle activity may be considered in patients undergoing permissive splint therapy to ensure better stability of the stomatognathic system. Preferred duration of wear of splints of up to 8 weeks can be suggested before patients undergo definitive rehabilitation.

Table 5: Number of participants in the experimental groups who reported symptoms after splint therapy at three different time points
Symptoms A problem in speech/phonetics Pain/tenderness in TMJ Tiredness in muscle Cheek biting Headache
24 hours 4 weeks 8 weeks 24 hours 4 weeks 8 weeks 24 hours 4 weeks 8 weeks 24 hours 4 weeks 8 weeks 24 hours 4 weeks 8 weeks
Group I: (hard splint) None 0 5 8 8 8 8 5 8 8 4 6 8 6 8 8
Mild 2 3 0 0 0 0 3 0 0 2 2 0 2 0 0
Mod 5 0 0 0 0 0 0 0 0 2 0 0 0 0 0
Severe 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Group II: (soft splint) None 2 8 8 8 8 8 6 8 8 6 8 8 8 8 8
Mild 5 0 0 0 0 0 2 0 0 2 0 0 0 0 0
Mod 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Severe 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

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