A morphologic study of the recovery of the rat submandibular gland after retrograde infusion. I. Water-soluble radiographic contrast medium

The recovery of the rat submandibular gland after retrograde infusion of water-soluble radiographic contrast medium was studied using an experimental model. During continuous monitoring of the developing intraglandular pressure, the glands were subjected to ductal and slight parenchymal filling or heavy parenchymal filling with the medium. The animals were killed after varying recovery periods, and the tissue was prepared for light and electron microscopic examination. Dilation of the ductal lumina, induced during ductal and slight parenchymal filling, was successively reduced and, generally, the parenchyma had a normal appearance at 30 h. In glands subjected to heavy parenchymal filling, the changes in the intralobular ducts were more pronounced and were also seen at later times after infusion. Alterations in the acini, comprising fusion of secretory granules, vacuole formation and dilation of the acinar lumina and intercellular canaliculi, were observed. At later times, atrophy of the parenchymal cells occurred together with an apparent proliferation of the connective-tissue stroma, as well as an increase in the number of small blood vessels. An inflammatory cell-infiltrate was seen in both groups of animals, but was most prominent in glands subjected to heavy parenchymal filling. The infiltrate, comprised primarily of macrophages and polymorphonuclear leukocytes, reached a peak at 20 h after infusion. At later times, mast cells and occasional eosinophils were seen. The observed alterations and the pattern of recovery are most likely due to the induced intraglandular pressure and the following inflammatory reaction. It is also possible that the changes, to some extent, are influenced by the presence of the contrast medium in the tissue.     

Eruptive changes in the axial inclination of lower incisor teeth--a longitudinal study

A longitudinal cephalometric study investigated the change in lower incisor inclination in a group of 32 subjects over a period from 5-10 years of age, with yearly cephalometric radiographs and 6 monthly study models. In a previous study, it was shown that in all of these subjects, the lower incisors became more proclined over this 5 year period. Changes in the rate of proclination of the lower incisors over this period were studied, and this was related to events such as eruption, and contact with the upper incisors or palatal mucosa where this occurred. The association between the inclination of lower incisors before and just after eruption, and their "final" inclination was investigated, and the possible explanations and implications of the findings are discussed.     

A histological study of reparative dentinogenesis in the rat incisor after colchicine administration

Reparative dentinogenesis after administration of a large dose of colchicine was studied histologically in the dental pulp. A dose of 1.0 mg/kg of colchicine was injected intravenously into 48 rats. The animals were killed at intervals of 1, 2, 3, 4, 5, 6, 8, 10 and 12 days after the injection. Considerable necrosis was noted in the pulp cells, including odontoblasts and fibroblasts, 1 day after colchicine administration. After 3–5 days, cell proliferation with active revascularization was observed in the necrotic cell layer adjacent to intact dentine which had been formed before colchicine administration. After 6–8 days, a non-mineralized collagenous matrix appeared in the cell proliferation zone and by 8–10 days, newly developed odontoblasts were observed adjacent to a newly deposited layer of dentine matrix. The formation of the non-mineralized collagenous matrix seems to trigger the development of new dentine and the cells which produced the non-mineralized collagenous matrix appear to differentiate into odontoblasts.     

A morphologic study of the recovery of the rat submandibular gland after retrograde infusion

The recovery of the rat submandibular gland after retrograde infusion of water-soluble radiographic contrast medium was studied using an experimental model. During continuous monitoring of the developing intraglandular pressure, the glands were subjected to ductal and slight parenchymal filling or heavy parenchymal filling with the medium. The animals were killed after varying recovery periods, and the tissue was prepared for light and electron microscopic examination. Dilation of the ductal lumina, induced during ductal and slight parenchymal filling, was successively reduced and, generally, the parenchyma had a normal appearance at 30 h. In glands subjected to heavy parenchymal filling, the changes in the intralobular ducts were more pronounced and were also seen at later times after infusion. Alterations in the acini, comprising fusion of secretory granules, vacuole formation and dilation of the acinar lumina and intercellular canaliculi, were observed. At later times, atrophy of the parenchymal cells occurred together with an apparent proliferation of the connective-tissue stroma, as well as an increase in the number of small blood vessels. An inflammatory cell-infiltrate was seen in both groups of animals, but was most prominent in glands subjected to heavy parenchymal filling. The infiltrate, comprised primarily of macrophages and polymorphonuclear leukocytes, reached a peak at 20 h after infusion. At later times, mast cells and occasional eosinophils were seen. The observed alterations and the pattern of recovery are most likely due to the induced intraglandular pressure and the following inflammatory reaction. It is also possible that the changes, to some extent, are influenced by the presence of the contrast medium in the tissue.     

Maturation of periodontal connective tissue in new-born rat incisor.

The organization of collagen and ground substance in the periodontium of the rat incisor was studied during the first 12 days of postnatal life. Tissues were rapidly frozen in isopentane at ?150 °C, and cut in a cryostat without decalcification. Maturation of fibres and ground substance was followed using correlated biophysical (polarization microscopy), histochemical (paS, toluidine blue and collagen immunofluorescence), and empirical (Van Gieson and silver impregnation) methods.Periodontal ligament cells contained glycoprotein granules, probably precursors of ground substance. Glycogen was prominent in young bone cells. At birth, the periodontal ligament consisted of unorganized isotropic argyrophilic fibres strongly reactive to collagen immunofluorescent staining; with further development many fibres became oriented and showed anisotropy. They were mainly disposed parallel to the tooth axis with lateral ramifications into bone. Concurrently, collagen of cementum, bone borders, and pericellular matrix of osteocytes showed intense immunofluorescence. When taken together with distinct metachromasia seen in these areas, this indicates a loose aggregation of their macromolecular constituents. Ground substance of the periodontal ligament acquired metachromasia a few days after birth.Principal fibres were subjected to heat, a variety of enzymes and one fixative. Collagenase abolished birefringence and immunofluorescence. Principal fibres were not equally stable during heating. Some fibre groups became isotropic at 62 °C (T_s), others were unaffected or partially affected. Hyaluronidase treatment lowered T_s to 57 °C, and eliminated the heat resistance of thermostable fibres. Evidently, ground substance stabilized the principal fibres. It appears that collagen-ground substance interactions affect stable-labile transformations involved in fibre remodelling, and may influence eruption.     

Soft tissue changes after maxillo-mandibular advancement in OSAS patients: A three-dimensional study

IntroductionMaxillo-mandibular advancement (MMA) is the most successful surgical treatment for OSAS. This study prospectively evaluated soft tissue changes in typical OSAS patient before and after MMA.Material and methodsTen patients with severe OSAS, who underwent MMA, were considered. Age, BMI, polysomnographic recordings and cephalometric data were examined. Facial surface data acquired using a 3D laser scanner before (T0) and 1 year (T1) after surgery were pooled by electronic surface averaging to obtain the mean T0 and T1 facial model. A virtual optimal face (V) was used as control group. Mean T0, T1 and V models were compared.ResultsThe mean AHI improved from 69.8 ± 35.2 to 17.3 ± 16.7. The mean maxillary advancement was 9.2 mm ± 1.2 and the mean mandibular advancement was 10.4 mm ± 2.2. The comparison between T0 and T1 showed an overall increase of the sagittal projection of the cheeks, lips and of the chin. The comparison between T1 and V showed a transversal increase of the cheeks at the cross section through ch (cheilon).ConclusionMMA is a highly effective treatment for OSAS. The evaluations of 3D laser scanning showed that surgery in OSAS patients didn't cause an impairment of the facial appearance.     

Histomorphometric study of the periodontal vasculature during and after experimental tipping of the rat incisor.

The periodontal vasculature encircling the entire length of the rat lower incisor was studied at the time of tipping movement and 3 months later. In 12 rats (212+/-4 g b.w.), loads (0.19+/-0.016 N) were applied to the lower left incisor in a linguointrusive direction. After 2 weeks of loading, six experimental animals were killed with the loading springs in place. The springs were removed in the six remaining rats, which were killed 12 weeks later. Six additional rats with intact teeth served as control. All incisors were fixed, demineralized, embedded in glycol methacrylate and cross-sectioned perpendicular to the long axis of the tooth. The distance of each section (2 microm) from the apex was calculated. A computerized image-analysis program was used to measure the width and area of the labial and lingual periodontal ligament to establish whether the measured segments corresponded to the compressed or expanded zones. In each cross-section, the various types of blood vessels were counted and the cross-sectional area of all venous vessels was measured. The results showed that after 2 weeks of loading (1) the general trend of vascular changes was similar under pressure and tension; (2) the large-diameter vessels were unaffected by loading; (3) the mean number of terminal arterioles had decreased significantly, while the number of capillaries and postcapillary venules had increased significantly in the apical tooth part; (4) the venous blood vessel area had decreased significantly in the apical tooth part; (5) the intensity of the vascular reaction was dependent on the degree of tissue distortion; and (6) after 12 weeks' recovery the vascular changes were still present, demonstrating a rebound effect. The findings suggest that microvascular alterations following tooth loading are not directly related to the spatial effect of loading itself and are of a much longer duration than expected.     

Evaluation of the three-dimensional soft tissue changes after anterior segmental maxillary osteotomy

The aim of this study was to assess the three-dimensional soft tissue changes following anterior segmental maxillary osteotomy, in terms of magnitude and direction in correlation to hard tissue changes, using cone beam computed tomography (CBCT). The study included 6 patients (age range 17-35 years) suffering from dental maxillary protrusion that required surgical correction by anterior segmental maxillary osteotomy. For each patient, preoperative and postoperative CBCT, photographs, and orthodontic casts were taken before and 6 months after operation to analyse soft tissue changes, in terms of magnitude and direction in correlation to hard tissue changes, using linear and angular measurements. Hard and soft tissue changes were only observed in the maxillary region, upper lip area and nasal tip. Soft tissue mean change included 53% backward displacement of the labrale superius in relation to bone displacement and 18.7% mean increase in the naso-labial angle. The highest correlation coefficient was obtained between the hard and soft tissue changes in the upper lip region. Anterior segmental maxillary osteotomy might be recommended as the treatment modality of choice in patients with maxillary or dento-alveolar protrusion, the technique is simple, safe, and postoperative complications are minimal.     

Histomorphometric study of the periodontal vasculature of the rat incisor.

This study assessed quantitatively the vascular system in the cementum-related periodontal ligament (PDL) along the rat incisor. The lower left incisors of six rats (+/- 200 g) were subjected to routine histological procedures and cross-sectioned serially (2 microns), and the distance between each section and the apex was computed. The PDL of five sections at different levels along the tooth was divided into mesial, lingual, and lateral parts. The number and area of small and terminal arterioles, capillaries (C), sinusoids (S), post-capillary venules (PCV), and connecting venules, as well as the area of the PDL, were established. Blood vessels (BV) occupied 47 +/- 2% of the PDL area in the apical half and 4 +/- 2% at the incisal end. Of the total BV area, 41%, 32%, and 27% were located on the lingual, mesial, and lateral tooth sides, respectively. The majority of BV belonged to the venous system (98.5 +/- 0.6% and 82.5 +/- 3.0% in the apical and incisal parts, respectively). The apical venous system comprised 95.4 +/- 1.6% S and 3.2 +/- 1.0% PCV, reversing to 27.2 +/- 14.2% S and 55.2 +/- 11.3% PCV in the incisal half. The number of arterial profiles increased gradually from 6.8 +/- 1.5 at the apex to 25.3 +/- 2.4 in the incisal part and that of C from 9.0 +/- 1.18 to 25.0 +/- 4.3. The extensive vascularization in the apical half of the PDL is consistent with the high metabolic demands and with the need for protective cushioning of the constantly growing dental and periodontal tissues.2+_     

A morphologic study of the recovery of the rat submandibular gland after retrograde infusion. II. Lipid-soluble radiographic contrast medium

Lipid-soluble radiographic contrast medium was infused retrogradely through the main excretory duct of the rat submandibular gland until ductal and slight parenchymal filling or heavy parenchymal filling was achieved, as determined by the developing intraglandular pressure. The glandular tissue was fixed by vascular perfusion at different times following infusion, and examined by light and electron microscopy. Dilation of the intralobular ducts and scalloping of the luminal border were pronounced after both degrees of filling. Widening of the acinar lumina and intercellular canaliculi occurred early. Masses of fused secretory granules were commonly seen in the cytoplasm of the acinar cells and formation of vacuoles occurred frequently. In some acinar cells, densely packed granules filled the major part of the cytoplasm. Large lysosomes and autophagic vacuoles, frequently present in the various parenchymal cells, often contained apparent contrast medium. In addition, widening of the intercellular spaces between parenchymal cells was seen, particularly in the acini and intercalated ducts. An inflammatory cell-infiltrate, primarily comprised of polymorphonuclear leukocytes, was particularly prominent at 20 h and 30 h after infusion. The changes were generally more pronounced and persisted for a longer time in glands subject to heavy parenchymal filling. Large cyst-like spaces surrounded by inflammatory cells were seen in the lobules and in the interlobular connective tissue of these glands. At later times, areas containing apparent contrast medium surrounded by macrophages, were frequently observed in the connective-tissue stroma. Atrophy of the parenchymal cells was seen later, after heavy parenchymal filling, and a proliferation of the connective tissue had occurred. The changes were most probably caused by the elevated intraglandular pressure induced during infusion, and the subsequent cell damage and inflammatory reaction. A foreign body reaction, induced by the retained lipid-soluble contrast medium, was probably partly responsible for the morphological alterations observed, following infusion.     

A cephalometric study of changes in point A under the influence of upper incisor inclinations.

Today the ANB angle is commonly used for defining the anteroposterior apical base relationships of the jaws. The factors that influence the ANB angle have been studied by various investigators. The axial inclination of the maxillary central teeth is one of the factors influencing the location of point A. In this study the relationship between the axial inclination of the upper central incisor and the location of point A was studied. Four criteria that define the location of the maxillary central teeth were used: I (incisal point), Ap (apical point), R (rotation point), and I-SN (angle between I and SN plane). A significant positive correlation was found between the location of points A and R. We also calculated a regression equation for this relationship.     

Effect of loading on the migration of periodontal fibroblasts in the rat incisor

The influence of occlusal loading on periodontal fibroblasts was investigated in hypoloaded (shortened out of occlusion), functionally loaded and hyperloaded (constant linguointrusive mechanical loads of 9.4 ± 0.06 g) lower left rat incisors. One hour following injection of ³H-thymidine, half of the animals in each group were killed, while the remaining rats were killed 2 weeks later. The decalcified incisors were embedded in glycolmethacrylate and sectioned (2 μm) serially, perpendicularly to the long tooth axis. Labeled and unlabeled fibroblasts in the tooth-related periodontal ligament were counted in 8 × 80μm consecutive layers. Cell density (CD) and labeling index (LI) were plotted according to their location on the apico-incisal and cementum-bone axes. Loading caused a decrease in CD and a shift of cells from the cementum towards the middle of the ligament, proportionally to load intensity and duration. The average tooth-to-bone movement of the cells was 2 μm/day in the hypoloaded and 4 μm/day in the two loaded groups. The mean daily tooth eruption rate was 975 ± 60 4 μm, 499 ± 18 μm and 103 ± 27 μm in the hypo-, functionally-and hyperloaded teeth, respectively. The respective concomitant average daily cell migration rates in the incisal direction were 786 μm, 500 μm and 500 μm, i.e. 80%, 100% and 485% of the tooth eruption rates. The gross disparity between cell velocity and tooth movement under conditions of restrained eruption indicates active motility of the fibroblasts, rather than their passive tooth-eruption dependent translation.     

Jaw-muscle activity changes after the induction of osteoarthrosis in the temporomandibular joint by mechanical loading

AIMS: To examine the effect of mechanical loading on the induction of temporomandibular joint osteoarthrosis (TMJ OA). METHODS: Mechanical stress was applied to the rat TMJ by forced jaw opening of 3 hours a day for 5 days. The electromyographic (EMG) activity of the masseter and digastric muscles was continuously monitored by radio-telemetry. It was characterized by the total time each muscle was active (duty time), the number of bursts, and the average burst length. For histologic analysis, rats were sacrificed before, immediately after, and 3 weeks after the period of forced jaw opening. RESULTS: The condylar cartilage revealed OA-like lesions with a decrease in the number of chondrocytes immediately after forced jaw opening. Three weeks later, the OA-like lesions were repaired to some extent. After the forced jaw opening, the duty time of the masseter increased, whereas the duty time of the digastric decreased significantly (P < .01) at the 5% activity level. Three weeks later, the masseter duty time had decreased and the digastric duty time had slightly increased, returning to the levels observed before forced jaw opening. CONCLUSION: These results suggest that mechanical overloading of the TMJ induced OA-like lesions with a simultaneous influence on jaw muscle activity, especially at the low activity level. This might imply that muscle activity adapted to reduce the effects of (forced) joint overloading.     

An electron microscopic study of dental plaque of the rat incisor.

Because rat incisors continuously erupt they provide an opportunity for the study of dental plaque at all stages of its development. The youngest plaque would be visible at the gingival margin of the tooth as it erupts, and the older plaque higher on the tooth. The ultrastructural features of these plaques were studied by transmission electron microscopy. Cocci and short rods colonized the cementum surface, forming a monolayer. The plaque had a maximum thickness of about 40 microns, with the inner third rich in fibrillar matrix and the organisms forming microcolonies perpendicular to the tooth surface. Cells were haphazardly distributed in a loose matrix on the surface of the plaque. In the area of plaque disorganization the cementum was covered by isolated groups of bacteria and the matrix had holes in it. The rat mandibular incisor may provide a unique model for study of how plaque on cementum is initially formed, matures and finally is degraded.