Relationship between masseter muscle activity during wakefulness and temporomandibular disorder-related symptoms

BACKGROUND

Masseter muscle activity during wakefulness may be associated with temporomandibular disorder (TMD)-related symptoms, psychosocial status and pain-related disability; however, this relationship is unclear.

OBJECTIVES

This study aimed to determine the relationship between masseter muscle electromyography (EMG) burst/duration during wakefulness and TMD-related symptoms, psychosocial status and pain-related disability.

METHODS

Sixty participants were assessed masseter muscle activity during wakefulness using a data-logger-type ultraminiature EMG system and TMD-related symptoms, psychosocial status and pain-related disability through Axis I and II of the diagnostic criteria for TMD (DC/TMD). EMG bursts lasting longer than 0.25 s but less than 2.0 s and those lasting longer than 2.0 s were classified as phasic and tonic bursts, respectively.

RESULTS

Participants with palpation-related pain in the temporalis and masseter muscles, as assessed through the DC/TMD examination form in Axis I, had more bursts (number/h) (p = .035 and p = .009, respectively) and longer duration (time/h) (p = .013 and p = .004, respectively) of tonic bursts of the masseter muscle during wakefulness. Participants with palpation-related pain in the masseter muscles had higher oral behaviour scores during wakefulness using Axis II (p = .001), which affected the number and duration of tonic bursts of the masseter muscle activity during wakefulness (p = .011 and p = .007, respectively).

CONCLUSION

As tonic bursts mainly reflect clenching, individuals with pain in the masseter muscles by palpation may have a high frequency and longer duration of clenching, as well as a high frequency of oral behaviours during wakefulness.

Malocclusion impairs cognitive behavior via AgRP signaling in adolescent mice

Introduction

Occlusal disharmony induced by deteriorating oral health conditions, such as tooth loss and decreased masticatory muscle due to sarcopenia, is one of the causes of cognitive impairment. Chewing is an essential oral function for maintaining cognitive function not only in the elderly but also in young people. Malocclusion is an occlusal disharmony that commonly occurs in children. The connection between a decline in cognitive function and malocclusion in children has been shown with chronic mouth breathing, obstructive sleep apnea syndrome, and thumb/digit sucking habits. However, the mechanism of malocclusion-induced cognitive decline is not fully understood. We recently reported an association between feeding-related neuropeptides and cognitive decline in adolescent mice with activity-based anorexia. The aim of the present study was to assess the effects of malocclusion on cognitive behavior and clarify the connection between cognitive decline and hypothalamic feeding-related neuropeptides in adolescent mice with malocclusion.

Methods

Four-week-old mice were randomly assigned to the sham-operated solid diet-fed (Sham/solid), sham-operated powder diet-fed (Sham/powder), or malocclusion-operated powder diet-fed (Malocclusion/powder) group. We applied composite resin to the mandibular anterior teeth to simulate malocclusion. We evaluated cognitive behavior using a novel object recognition (NOR) test, measured hypothalamic feeding-related neuropeptide mRNA expression levels, and enumerated c-Fos-positive cells in the hypothalamus 1 month after surgery. We also evaluated the effects of central antibody administration on cognitive behavior impairment in the NOR test.

Results

The NOR indices were lower and the agouti-related peptide (AgRP) mRNA levels and number of c-Fos-positive cells were higher in the malocclusion/powder group than in the other groups. The c-Fos-positive cells were also AgRP-positive. We observed that the central administration of anti-AgRP antibody significantly increased the NOR indices.

Discussion

The present study suggests that elevated cerebral AgRP signaling contributes to malocclusion-induced cognitive decline in adolescents, and the suppression of AgRP signaling can be a new therapeutic target against cognitive decline in occlusal disharmony.

A novel auxiliary device enhances miniscrew stability under immediate heavy loading simulating orthopedic treatment

OBJECTIVES

To evaluate miniscrew stability and perform a histomorphometric analysis of the bone around the miniscrew under a load corresponding to orthopedic force.

MATERIALS AND METHODS

Thirty-two miniscrews were implanted into eight rabbit tibias. Auxiliary group rabbits received auxiliary devices with miniscrews (n = 8, 28 days; n = 8, 56 days), and those in the nonauxiliary control group received miniscrews without auxiliary devices (n = 8, 28 days; n = 8, 56 days). Elastics were placed between miniscrews to apply a load of 5 N. Miniscrew stability was evaluated using a Periotest. Bone-to-implant contact (BIC) and spike implantation depth were measured histomorphologically.

RESULTS

Periotest values in the auxiliary group were significantly lower than those in the nonauxiliary group at all time periods. There was no significant difference in BIC between the auxiliary and nonauxiliary groups at 28 or 56 days postimplantation. The implantation spike depth in the auxiliary group was significantly greater at 56 days compared to that at 28 days. Newly formed bone was observed around the spike of the auxiliary device at 56 days.

CONCLUSIONS

The results suggest that the use of miniscrews in conjunction with auxiliary devices provides stable skeletal anchorage, which may be useful in orthopedic treatments.

Late reversible complete atrioventricular block and PR interval normalization after antegrade slow pathway ablation for atrioventricular nodal re-entrant tachycardia with pre-existing PR prolongation

Late complete atrioventricular block (CAVB) is a rare periprocedural complication in the treatment of atrioventricular (AV) nodal re-entrant tachycardia. However, it can necessitate permanent pacemaker implantation. We present a case of late CAVB that developed during the periprocedural period. Its pathogenesis was attributed to the indirect or functional effects on the fast pathway of the AV node due to the presence of paroxysmal supraventricular tachycardia with PR prolongation. Additionally, PR prolongation regressed to within the normal range after curing the late CAVB, and the advanced AV block with treadmill exercise stress test also improved 1:1 AV conduction with time. Periprocedural complications such as bradyarrhythmia may be reversible if late CAVB occurs within a few weeks after ablation. Thus, urgent permanent pacemaker implantation should be carefully considered.

Learning objective

Late high-grade atrioventricular (AV) blocks can develop during the periprocedural period even if antegrade slow pathway ablation does not result in a complete AV block. Late high-grade AV block is a relatively rare periprocedural complication. However, it can necessitate permanent pacemaker implantation. Additionally, if a late high-grade AV block develops within a few weeks after ablation, bradyarrhythmia—such as periprocedural complications—may be reversible and indicate that permanent pacemaker implantation should be carefully considered.

Effects of intra-oesophageal acid infusion and a stress task on masseter muscle activity and autonomic nervous activity in wakefulness

BACKGROUND

Gastroesophageal reflux disease may be an important risk factor for awake bruxism. Additionally, it has been known that a psychological stress task affects masseter muscle activity, and autonomic nervous system (ANS) activity modulation induces masseter muscle activity.

OBJECTIVES

This study aimed to investigate whether task-induced stress and experimental oesophageal acid infusion increase masseter muscle activity and alter ANS activity, compared to rest task and oesophageal saline infusion, respectively.

METHODS

Polygraphic monitoring, consisting of electromyography of the masseter muscle and electrocardiography, was performed in 12 healthy adult men during 30-min interventions with intra-oesophageal saline or acid infusion, while reading a book quietly, as rest, and while performing calculation, as a stress task.

RESULTS

At rest, masseter muscle activity and parasympathetic nervous system (PNS) activity during acid infusion were significantly higher (P = .019) and lower (P = .021) than during saline infusion, respectively. During saline infusion, both masseter muscle activity and sympathetic nervous system (SNS) activity or PNS activity while performing the calculation task were higher (P = .022 and .012, respectively) or lower (P = .007) than those during the reading task, respectively. In two-way repeated-measures ANOVA, intra-oesophageal infusion (saline or acid) significantly affected masseter muscle activity (P = .008) and PNS activity (P = .021). However, performing tasks (reading or calculation) significantly affected only PNS activity (P = .028).

CONCLUSION

Intra-oesophageal acid infusion significantly increased masseter muscle activity and decreased PNS activity. In contrast, stress task not only significantly decreased PNS activity, but only modestly increased masseter muscle activity and SNS activity.

Evaluation of miniscrew stability using an automatic embedding auxiliary skeletal anchorage device

OBJECTIVE

To clarify the in vivo effect of an automatic embedding device on miniscrew stability.

MATERIALS AND METHODS

42 miniscrews were implanted into rabbit femurs. The miniscrews with the novel auxiliary device formed the auxiliary group (n = 11 at 4 weeks; n = 11 at 8 weeks) and the miniscrews without the auxiliary device formed the nonauxiliary control group (n = 9 at 4 weeks; n = 11 at 8 weeks). Cortical bone thickness, distance from the cortical bone surface to the miniscrew head, and implantation depth of the spike were measured using micro-computed tomography. The mechanical retention force was evaluated by measuring the displacement of the miniscrew head after it was loaded perpendicular to its long axis. In the lateral displacement test, effects of the auxiliary (with vs without auxiliary), and time (4 vs 8 weeks) were assessed using the Brunner-Langer nonparametric analysis of longitudinal data in factorial experiments.

RESULTS

The mean implantation depth of the spike in the auxiliary group at 4 and 8 weeks was 0.28 mm (median: 0.33; SD: 0.12) and 0.37 mm (median: 0.33; SD: 0.19), respectively. The retention force was approximately 2.0 to 2.8 and 1.6 to 1.8 times greater in the auxiliary group than in the nonauxiliary group at 4 and 8 weeks, respectively.

CONCLUSIONS

The auxiliary device improved the mechanical retention force without the need to increase miniscrew length or diameter. This may enable the safe use of miniscrews in difficult areas.

Development of a novel spike-like auxiliary skeletal anchorage device to enhance miniscrew stability

INTRODUCTION

Miniscrews are frequently used for skeletal anchorage during edgewise treatment, and their clinical use has been verified. However, their disadvantage is an approximately 15% failure rate, which is primarily attributed to the low mechanical stability between the miniscrew and cortical bone and to the miniscrew's close proximity to the dental root. To solve these problems, we developed a novel spike-like auxiliary skeletal anchorage device for use with a miniscrew to increase its stability.

METHODS

The retention force was compared between miniscrews with and without the auxiliary skeletal anchorage device at each displacement of the miniscrew. The combined unit was also implanted into the bones of 2 rabbits in vivo, and implantation was visually assessed at 4 weeks postoperatively while the compression force was applied.

RESULTS

The retention force of the combined unit was significantly and approximately 3 to 5 times stronger on average than that of the miniscrew alone at each displacement. The spiked portion of the auxiliary anchorage device embedded into the cortical bone of the hind limb at approximately a 0.3-mm depth at 4 weeks postimplantation in both rabbits.

CONCLUSIONS

The auxiliary skeletal anchorage device may increase miniscrew stability, allow a shortened miniscrew, and enable 3-dimensional absolute anchorage. Further evaluation of its clinical application is necessary.

Localized silicon distribution in supragingival calculus from Japanese monkeys (Macaca fuscata)

Using an electron-probe microanalyser, the distribution of silicon and other elements in supragingival dental calculus in domestic Japanese monkeys (Macaca fuscata) was studied. In two out of four monkeys kept in animals centres, a localized silicon distribution was found in both fracture and oral surfaces of the calculi. The silicon-rich area consisting of silicon alone resembled opal, but the areas containing silicon and other metal ions such as magnesium, aluminium, potassium and iron resembled clay minerals. In eight domestic monkeys, including the four animals described above, abundant calculus deposits were found. However, in four captured wild monkeys and in one which had been kept for less than a year at an animal centre, no dental calculus was found. There was almost no dental plaque accumulation in captured wild monkeys. It is suggested that calculus formation in Japanese monkeys is dependent on length of exposure to a commercial diet.

Inhibitory effect of prostaglandin oligomeric derivatives on 9,10-dimethyl-1,2-benzanthracene-induced hamster lingual carcinomas

The inhibitory effects of prostaglandin oligomeric derivatives OC-3186 and OC-5186 were examined in hamster lingual carcinoma induced by 9,10-dimethyl-1,2-benzanthracene (DMBA). These compounds caused a regression of 40-90% in the size of lingual carcinomas in the hamster within several days after systemic or local administration.