Experimental comparison between tractional and compressive stress on temporomandibular joint.

OBJECTIVE: We experimentally compared the effects of compressive and tractional mechanical stress on the temporomandibular joint (TMJ) of rabbits to assess the etiology of progressive condylar resorption. MATERIALS AND METHODS: We performed a cortical osteotomy using custom-made devices that were lengthened by 0.25 mm every 12 h for 1 week after surgery. During this time, the rabbit TMJ was under compressive or tractional mechanical stress. The samples in each group were examined using micro-computed tomography and histological staining. RESULTS: Scores for the area of bone resorption were higher in the compressive group than in the tractional group. Moreover, scores for the depth of bone resorption were higher in the compressive group than those in the tractional group. We observed a significantly higher prevalence of resorption in the subcondylar bone in the compressive group than in the tractional group. There were substantially more cells that were positive for tartrate-resistant acid phosphatase in the compressive group than in the control and tractional groups. CONCLUSIONS: The outcomes here suggest that excessive mechanical stress, particularly compressive mechanical stress, may significantly affect morphological bone change findings in the TMJ.

Diagnostic performance of MR imaging of three major salivary glands for Sjögren's syndrome.

OBJECTIVE: We analyzed the diagnostic performance of the MR imaging findings of the parotid, submandibular, and sublingual glands to discriminate between patients with and without Sjögren's syndrome. METHODS: We retrospectively analyzed the correlation between the MR imaging and histopathological findings obtained from 69 patients with clinically suspected Sjögren's syndrome. We evaluated the heterogeneous signal intensity distribution on T1- and T2-weighted images, the multiple high-signal-intensity spots on MR sialograms, and the volume of the parotid, submandibular, and sublingual salivary glands. RESULTS: The multiple high-signal-intensity spots in the parotid gland showed the highest sensitivity and diagnostic accuracy (82% and 83%, respectively). In addition, the multiple high-signal-intensity spots and the heterogeneous signal intensity distribution in the submandibular gland showed high specificity (100% and 88%, respectively). The volume of the submandibular gland, but not that of the parotid or sublingual gland, was smaller in patients with Sjögren's syndrome. CONCLUSIONS: The presence of multiple high-signal-intensity spots on an MR sialogram in the parotid gland should be considered the best diagnostic indicator for Sjögren's syndrome. The presence of spots, heterogeneity, and the change to smaller volumes in the submandibular gland were also helpful because of their high specificity, particularly in advanced cases.

Diagnostic value of capsule-like rim enhancement on magnetic resonance imaging for distinguishing malignant from benign parotid tumours.

The purpose of this study was to clarify the diagnostic value of capsule-like rim enhancement (CLRE) on magnetic resonance imaging (MRI) for distinguishing malignant from benign tumours of the parotid gland. We retrospectively evaluated contrast-enhanced T1-weighted images of 100 patients with malignant and benign parotid tumours for the presence, completeness, and irregularity of CLRE and its maximum thickness. We investigated any correlation of imaging and histopathological findings for 51 cases showing CLRE with available histology. The presence and completeness of CLRE did not differ significantly between benign and malignant tumours. Malignant tumours had more irregular CLRE than benign tumours (P<0.05). The mean CLRE thickness was significantly greater for malignant (2.4 mm) than benign tumours (1.4 mm) (P<0.0001). The two types of tumour were most accurately distinguished using a cut-off value of 1.5 mm thickness. Histopathology demonstrated the general correspondence of thick CLRE on MRI in malignant tumours with thick but sparse fibrous tissue and infiltration of tumour cells and lymphocytes, whereas thin CLRE in benign tumours typically represented dense fibrous tissue without infiltration of tumour cells. CLRE was more irregular and thicker in malignant tumours than in benign tumours, which may be of help in differentiating them.

High serum levels of IGF-I contribute to promotion of endochondral ossification in mandibular condyle and cause its specific elongation in acromegaly-like rats.

Mandibular protrusion accompanies acromegaly or acrogigantism. To clarify the detailed mechanisms, we used an acromegaly-like rat model recently developed by exogenous administration of insulin-like growth factor I (IGF-I). Human recombinant IGF-I (640 microg/day) continuously was infused subcutaneously to 10-week-old male rats (n=12) for four weeks. Control, sham-operated animals (n=12) were injected with saline alone. Twelve rats (six from each group) were killed immediately after ending administration at age 14 weeks. Another 12 rats (six from each group) were housed for an additional four weeks after treatment ended. Mandibular condylar length increased significantly in the IGF-I rats compared with the control rats, but no significant intergroup difference was found in the lengths of the coronoid and angular processes. Cartilaginous layer width, bone matrix volume, and the number of osteoblasts in the mandibular condyle increased significantly in the IGF-I group. These histopathological changes in the condyle disappeared after IGF-I administration was discontinued; however, the morphological change in condylar length remained. These findings suggest that mandibular protrusion in patients with acromegaly or acrogigantism may be evoked by superfluous elongation of the mandibular condyle and that such elongation can be induced by endochondral ossification caused by high IGF-I serum levels.

A case of masticatory disturbance incidental to trigeminal schwannoma: changes in occlusal force and masticatory sensation before and after radiosurgery.

We report here a case of masticatory disturbance evoked by trigeminal schwannoma, in which we have evaluated the changes in occlusal force and masticatory sensation before and after treatment for the tumour. The patient was a 43-year-old woman and her chief complaint was a loss of masticatory sensation on her left side. MR imaging revealed an enhanced tumour in the left cavernous sinus/Meckel's cave. The left masseter muscle function and occlusal force showed remarkable decreases before treatment; however, the sensory thresholds of her facial skin and dental pulp were not significantly different from the control side, indicating that her loss of masticatory sensation was not due to sensory disturbance but to occlusal force weakness. Gamma-knife radiosurgery resulted in a significant improvement in masticatory sensation following an increase in occlusal force.

Morphological and histopathological changes in tongues of experimentally developed acromegaly-like rats.

An acromegaly-like rat model recently developed by exogenous administration of insulin-like growth factor I (IGF-I) was used to investigate morphological and histopathological tongue changes and clarify whether the changes were reversible. Human recombinant IGF-I (640 microg/day) was continuously subcutaneously infused into ten-week-old male rats for four weeks (IGF-I group; n = 6). Control sham-operated animals were injected saline alone (control group; n = 6). Rats were sacrificed immediately on ending administration at the age of fourteen weeks. Another 12 rats (6 from each group) were housed for an additional four weeks after administration ended. Total IGF-I (human + rat) increased significantly during administration, returning to control levels afterwards. Tongue weights significantly increased with histopathological changes present (increases in the muscle-bundle width, spaces between muscle-bundles and epithelium thickness) in the IGF-I group compared to control rats. Tongue size returned to control levels after discontinuation of IGF-I administration. These findings suggest that the characteristic tongue enlargement was developed experimentally in our acromegaly-like rat model, and that such morphological and histopathological tongue changes are reversible on normalization of circulating IGF-I levels.

Insulin-like growth factor-I stimulates acromegaly-like specific mandibular enlargement in rats.

To help us investigate the time course of mandibular enlargement in acromegaly or acrogiantism to determine the most suitable period for occlusal treatment in this disease, our aim was to develop a rat model of acromegaly (acrogiantism). In this study, prominent mandibular enlargement was induced by continuous subcutaneous infusion of human recombinant insulin-like growth factor-I (IGF-I) (640 microg/day) in 10-week-old male rats for 4 weeks (n = 6); the control sham-operated group was injected with saline alone (n = 6). Circulating human IGF-I was clearly detectable in the IGF-I group during the four-week administration period, while endogenous rat IGF-I levels decreased. Total IGF-I (human + rat) increased significantly during administration, returning to control levels afterwards. The length of every bone examined (mandible, maxilla, and femur) showed a significant increase compared to control rats, especially the mandible. Although the mandible did not continue to grow after discontinuation of IGF-I administration, it did not return to control size, unlike the maxilla and femur, and disharmonious jaw size (between maxilla and mandible) persisted even after circulating IGF-I levels normalized. These findings in our rat model suggest that mandibular occlusal treatment should only be considered for acromegalic (acrogiantic) patients after serum IGF-I levels have normalized and bone growth has ceased.

A simple, yet accurate method for detecting and quantifying secretions from human minor salivary glands using the iodine-starch reaction.

The lack of published information about the minor salivary glands is due in part to the difficulties experienced in collecting and quantifying their secretions. In fact, no method exists for measuring their secretions that is both simple and accurate. This investigation examined the accuracy of our newly developed method (which simply employs the iodine-starch reaction) in 10 healthy non-medicated adults. A strip painted with a solution of iodine in absolute alcohol then with a fine starch powder mixed with castor oil was placed at a designated location on the lower-lip mucosa for 2 min to collect saliva. Black-stained spots of various sizes corresponding to the individual glands could be accurately visualized. After removal of the strip, the total stained area (mm2) was calculated by digitizing the spot areas using a computer system. The correlation coefficient (r) between known volumes of saliva and stain size was 0.995, indicating a close correlation. The correlation coefficient (r) between area values obtained in the first trial in each subject (Y) and the second (X; 10 min later) was 0.963, and the simple regression equation was close to Y=X, indicating good reproducibility. The mean flow rate microl/cm2 per min) obtained by converting mean total area to volume and thence to flow rate was 0.49+/-0.26, in good agreement with published values obtained by others. These results suggest that our newly developed method allows both the distribution and secretion rate of the minor salivary glands to be observed, and that it should be of practical value due to its simplicity, accuracy, and reproducibility.

Usefulness of heavily T(2) weighted magnetic resonance images for the differential diagnosis of parotid tumours.

OBJECTIVES: To evaluate the usefulness of heavily T(2) weighted (T2W) magnetic resonance (MR) images for the differential diagnosis of parotid tumours. METHODS: Conventional T2W and heavily T2W images obtained from 43 patients with parotid tumours were reviewed retrospectively. Tumours were classified pathologically into three types: pleomorphic adenoma (25 cases), Warthin's tumour (7 cases) and malignant tumour (11 cases). During interpretation of each MR image, special attention was paid to the homogeneity and signal intensity displayed by the solid portions of the tumours. RESULTS: Heavily T2W images could distinguish pleomorphic adenoma from Warthin's tumour and malignant tumours based on the homogeneity and signal intensity of the solid portions, whereas conventional T2W images could not. On conventional T2W images, neither homogeneity nor signal intensity differed significantly among these three tumour types. On heavily T2W images, malignant and Warthin's tumours appeared more homogeneous than pleomorphic adenoma (P<0.0061); signal intensity from pleomorphic adenoma was significantly different to signal intensity from malignant tumours (P<0.05) and Warthin's tumour (P<0.005). CONCLUSIONS: Heavily T2W MR images can be useful in distinguishing pleomorphic adenoma from Warthin's tumour and malignant tumours.

Dependence of pulpal blood-flow responses on baseline blood-flow in the cat.

It has been shown earlier that electrical stimulation of the distal cut end of the inferior alveolar nerve (IAN) in the cat evokes three different patterns of pulpal blood-flow (PBF) response in the ipsilateral mandibular canine tooth (a decrease, a biphasic response, or an increase). The response to a given stimulus sometimes changed to another pattern even in one and the same experimental animal during the course of the experiment. It is known that the evoked decrease is due to activation of the sympathetics and that the increase is due to antidromic activation of sensory fibres; but, it is unknown why the response varies so much. It is hypothesised that the baseline blood-flow (BBF) modulates vasomotor responses in the dental pulp. To test this hypothesis, the effects of BBF on PBF responses elicited by the IAN stimulation mentioned above were investigated. Dynamic changes in PBF in cat mandibular canine teeth were elicited by electrical stimulation of the distal cut end of the IAN, at various BBF, with blood-flow monitored by laser Doppler flowmetry. The amplitude of the PBF vasodilator response increased as BBF was adjusted downwards (by cooling the tooth). In contrast, the amplitude of the PBF vasoconstrictor response increased as the BBF rose. Vasodilator responses could be transformed into vasoconstrictor responses, and vice versa, by alterations in the BBF. No systemic blood-pressure changes were elicited throughout the experiment. These results indicate that a consideration of baseline vascular tone is important, whenever the size of PBF responses to various stimuli is discussed or calculated.

Evaluation of pulse sequences used for magnetic resonance sialography.

OBJECTIVES: To determine the most appropriate sequences for the visualization of small parotid ducts in MR sialography. METHODS: MR images of a phantom consisting of distilled water in polyethylene tubes were obtained with turbo-spin echo (TSE), single-shot turbo-spin echo (SSTSE), half-fourier acquisition, single-shot turbo-spin echo (HASTE) and turbo gradient-spin echo (TGSE) pulse sequences and compared visually and quantitatively. MR sialograms obtained from healthy volunteers and patients with Sjögren's syndrome (SS) were obtained using the same four sequences. RESULTS: In the phantom, TSE images were best and the contrast-noise ratio (CNR) highest. In the volunteers, the main ducts were especially clearly visualized with TSE and in SSTSE; however, the majority of secondary and/or tertiary parotid ducts were not depicted by any of the sequences used. In SS patients, images of small main ducts and small pseudocysts were clearer using TSE. However, TSE could not depict the narrow main ducts or peripheral ducts or very small pseudocysts. CONCLUSIONS: TSE is considered the most suitable MR sequence for assessing small parotid gland ducts. However, further improvement is needed since it does not always visualize them sufficiently.