Fluid pressurization and tractional forces during TMJ disc loading: A biphasic finite element analysis.

OBJECTIVES: To investigate the ploughing mechanism associated with tractional force formation on the temporomandibular joint (TMJ) disc surface. SETTING AND SAMPLE POPULATION: Ten left TMJ discs were harvested from 6- to 8-month-old male Yorkshire pigs. MATERIALS AND METHODS: Confined compression tests characterized mechanical TMJ disc properties, which were incorporated into a biphasic finite element model (FEM). The FEM was established to investigate load carriage within the extracellular matrix (ECM) and the ploughing mechanism during tractional force formation by simulating previous in vitro plough experiments. RESULTS: Biphasic mechanical properties were determined in five TMJ disc regions (average±standard deviation for aggregate modulus: 0.077±0.040 MPa; hydraulic permeability: 0.88±0.37×10-3 mm4 /Ns). FE simulation results demonstrated that interstitial fluid pressurization is a dominant loading support mechanism in the TMJ disc. Increased contact load and duration led to increased solid ECM strain and stress within, and increased ploughing force on the surface of the disc. CONCLUSION: Sustained mechanical loading may play a role in load carriage within the ECM and ploughing force formation during stress-field translation at the condyle-disc interface. This study further elucidated the mechanism of ploughing on tractional force formation and provided a baseline for future analysis of TMJ mechanics, cartilage fatigue and early TMJ degeneration.

A pilot study of nocturnal temporalis muscle activity in TMD diagnostic groups of women.

Temporomandibular disorder (TMD) incidences are believed to be related to parafunctional behaviours like teeth clenching. This pilot study aimed to (i) develop an automated clench-detection algorithm, and (ii) apply the algorithm to test for differences in nocturnal clenching in women with and without TMD. Subjects gave informed consent to participate. Adult women were categorised using Diagnostic Criteria for TMD according to presence/absence (+/-) of both TM joint disc placement (DD) and chronic pain (P) into two groups (+DD+P, -DD-P) with 12 subjects each. Surface temporalis electromyography was recorded during oral tasks performed by subjects at two laboratory sessions. The data were used to characterise muscle activity per N of bite force (µV/N) for each subject, develop the clench-detection algorithm and test its accuracy. Ambulatory surface temporalis electromyography was self-recorded by each subject over three nights and analysed using the algorithm and bite force (N) versus muscle activity µV/N calibrations. Bonferroni-adjusted homoscedastic t-tests assessed for significant between-group differences in clenching (P < 0·05). Sensitivity, specificity and accuracy of algorithm-detected laboratory clenches were all ≥96%. During self-recordings 95% of clenches had durations of <4 s and peak forces of <10 N in both groups. Mean clench durations were significantly longer (P = 0·042) in +DD+P (1·9 ± 0·8 s) than -DD-P subjects (1·4 ± 0·4 s). Mean temporalis duty factors (%clench time/total recording time) were significantly larger (P = 0·041) in +DD+P (0·47 ± 0·34%) than -DD-P (0·26 ±0·22%) subjects. Nocturnal temporalis muscle activities detected by a validated algorithm were longer per clench and recording time in +DD+P compared to -DD-P women.

Daily left prefrontal repetitive transcranial magnetic stimulation for medication-resistant burning mouth syndrome.

Burning mouth syndrome (BMS) is a persistent and chronic burning sensation in the mouth in the absence of any abnormal organic findings. The pathophysiology of BMS is unclear and its treatment is not fully established. Although antidepressant medication is commonly used for treatment, there are some medication-resistant patients, and a new treatment for medication-resistant BMS is needed. Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive brain stimulation technology approved by the US Food and Drug Administration (FDA) for the treatment of depression. Recent studies have found beneficial effects of TMS for the treatment of pain. A case of BMS treated successfully with daily left prefrontal rTMS over a 2-week period is reported here. Based on this patient's clinical course and a recent pain study, the mechanism by which TMS may act to decrease the burning pain is discussed.

Periodontal manifestations of collagen vascular disorders.

Chronic degeneration of connective tissue components can be produced by a variety of autoimmune mechanisms. The designations connective tissue disease and collagen-vascular disease are commonly used to describe such conditions when a patient exhibits chronic, immune-mediated deterioration of connective tissue structures in a systemic distribution. Recognized conditions that fit this definition include rheumatoid arthritis, lupus erythematosus, progressive systemic sclerosis, CREST syndrome, and mixed connective tissue disease. Several characteristic oral manifestations of these conditions are recognized. Xerostomia associated with any of these conditions in addition to dryness of the eyes is the definition of secondary Sjögren's syndrome. Fibrosis of facial skin and the resulting limited jaw opening are diagnostic features of progressive systemic sclerosis. Several periodontal manifestations are associated with these connective tissue disorders. Dramatic periodontal ligament space widening that is associated with some cases of progressive systemic sclerosis has been appreciated for more than five decades. However, it has been more recently reported that the majority of progressive systemic sclerosis patients exhibit at least subtle generalized periodontal ligament widening when intraoral radiographs are carefully evaluated. This finding is, however, of limited periodontal significance because the teeth are typically not mobile. Comparisons of periodontitis indices such as pocket depth between healthy subjects and patients with progressive systemic sclerosis do not reveal significant differences (21). In addition, recent evidence suggests a tendency for more severe or progressive manifestations of periodontitis as a consequence of xerostomia that may result from these diseases.

Bad news and good news: what the dentist needs to know about transmissible spongiform encephalopathies.

Since reports of the "mad cow disease" epidemic in Great Britain erupted in the international press, sensational and intimidating articles about the risk that bovine spongiform encephalopathy and related diseases may pose to humans have appeared. The bad news is that compelling scientific evidence suggests so-called prion disease can and has infected humans, although the overall risk appears to be low. Furthermore, at present, there is no reliable antemortem diagnosis, specific treatment, or vaccine to prevent the disease. The agent thought to be responsible for this unusual class of disease is a rogue protein (called a prion) that, unlike all other agents known to cause infectious disease, contains neither DNA nor RNA. According to a popular hypothesis, normal membrane-associated prion proteins undergo conformational changes that can cause disease. The "bad" prion forms cause holes or a spongy appearance in the brain in all disease variants, hence the generic designation of spongiform encephalopathy. The good news is that risk for exposure to prion disease is exceedingly remote in the dental practice and that current universal infection control procedures are probably sufficient.