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M R Sims

Publications and source records attributed to M R Sims.

At least 37 records · Page 2Linked to original sources
PubMed1991

An ultrastructural evaluation of the relationship between epithelial rests of Malassez and orthodontic root resorption and repair in man.

Contrary to previous reports, epithelial cell clusters with ultrastructural features similar to classically defined epithelial rests of Malassez were found, for the first time, in areas of repairing orthodontic root resorption. These observations were made on the buccal root surface of premolars extracted for orthodontic purposes from adolescent patients who had required rapid maxillary expansion. Ultrastructurally, the epithelial clusters ranged in size from 2-8 cells and were characterized by the presence of true desmosomes (macula adherens) and tonofilaments. Certain ultrastructural features of the epithelial cell clusters indicate that they may be involved in mediating repair cementogenesis subsequent to migration into the resorption bay.

Adolescent↗
PubMed1990

A morphometric, electron microscopic analysis of tissue channels shown by ionic tracer in normal and tensioned rat molar apical periodontal ligament.

A 1.0 newton continuous, extrusive load was applied to the right maxillary molar for 30 min to determine the presence of channels as shown by the distribution of tracer across the interstitial compartment of normal and tensioned PDL. Sodium ferrocyanide (1% w/v), perfused via the common carotid arteries, was the tracer probe and tris(ethylenediamine) cobalt III chloride (1% w/v) the precipitating ion. Left molar control PDL had an overall mean of 0.43 +/- 0.05/microns2 tissue channels at 0.2 microns from the vascular endothelium, and 0.15 +/- 0.04/microns2 at 7-8 microns. On the experimental side, the overall mean number of tissue channels was 0.65 +/- 0.13/microns2 at 0-2 microns and 0.19 +/- 0.07/microns2 at 7-8 microns. A significant depth effect (P less than 0.01) was present in the control and experimental interstitial tissues for tissue channels adjacent to the endothelium of different categories of vessel. Extrusion increased the tissue channel density adjacent to arterial capillaries (P less than 0.01), venous capillaries (P less than 0.01) and postcapillary-sized venules (P less than 0.01). These findings implicate these three types of vessel as being functionally important in fluid exchange across endothelial boundaries in the PDL.

Animals↗
PubMed1990

Stereo-pair three-dimensional imaging of microvascular architecture in primate dental tissues.

The morphology of microvascular beds in dental tissues is poorly documented at the ultrastructural level. SEM stereo-pair imaging of microcorrosion casts reveals the markedly contrasting vascular architecture and capillary anastomoses within the nasopalatine foramen, soft palate and gingival regions of the marmoset. This primate was studied as an analogue for man to further our knowledge of periodontal anatomy and function.

Animals↗
PubMed1989

Tooth extrusion effects on microvessel volumes, endothelial areas, and fenestrae in molar apical periodontal ligament.

Extrusive tooth loads, simulating short-term orthodontic movements, have not previously been used for transmission electron microscopic quantification of their effects on the periodontal ligament vessels. In this study, a continuous extrusive load of 1.0 N, applied to the rat maxillary first molar for 30 minutes, produced statistically significant changes in the microvascular bed of the tensioned apical periodontal ligament. The mean vascular volume, as a percentage of apical periodontal ligament volume, increased (p less than 0.01) in postcapillary-sized venules, venous capillaries, arterial capillaries, and terminal arterioles from 16.6% to 22.3%, 2.0% to 2.7%, 0.4% to 1.0%, and 1.0% to 2.5%, respectively. Mean endothelial surface area per cubic millimeter of apical periodontal ligament tissue increased (p less than 0.01) in postcapillary-sized venules from 16.8 to 25.7 x 10(6) microns 2/mm3, in venous capillaries from 3.0 to 4.8 x 10(6) microns 2/mm3, and in arterial capillaries from 0.7 to 1.5 x 10(6) microns 2/mm3. The number of fenestrae per square micron of endothelium in postcapillary-sized venules, venous capillaries, and arterial capillaries showed a mean increase from 0.02 to 0.07, 0.11 to 0.31, and 0.02 to 0.21 fenestrae/microns 2, respectively (p less than 0.01). Fenestrae per cubic millimeter of periodontal ligament tissue also demonstrated a statistically significant increase with extrusion (p less than 0.01) in postcapillary-sized venules from 0.37 to 1.55 x 10(6) fenestrae/mm3, in venous capillaries from 0.27 to 1.34 x 10(6) fenestrae/mm3, and in arterial capillaries from 0.02 to 0.22 x 10(6) fenestrae/mm3. Fenestrae in control vessels had a mean diameter of 54.2 +/- 0.56 nm (SE) compared with 61.1 +/- 0.7 nm in tensioned vessels (p less than 0.01). This investigation demonstrates multiple ultrastructural changes in the periodontal ligament microvascular bed after tooth extrusion.

Animals↗
PubMed1989

Morphometry of neural structures in the mouse periodontal ligament mesial to the mandibular first molar.

The periodontal ligament mesial to the mandibular first molars of three mice was analysed stereologically between the alveolar crest and the tooth apex. Ultrathin tissue sections were collected at statistically predetermined intervals, 50 and 200 microns apart, examined in the TEM and quantified using standard point counting procedures (Gundersen et al. 1988). Findings include evidence that, in the mouse, some unmyelinated axons arise from myelinated axons and that anatomically discrete arrangements of unmyelinated axons occur in the apericytic wall sections of postcapillary-sized venules. Morphometric data indicate that unmyelinated axons constitute approximately 95 percent of all periodontal axons. The greatest relative proportion of myelinated axons is the bone third of the ligament, at depths between 600 and 800 microns, where the ratio of unmyelinated to myelinated axons is 5:1. Ultrastructurally, the ligament contains a variety of anatomically discrete neural structures in juxtaposition to periodontal blood vessels. These structures include nerve endings contiguous with K-cells, partially exposed terminal axons, preterminal and terminal axons protruding into the vessel lumina, and lamellated receptors. Mitochondria-rich terminals and fine nerve endings approximated pericytes in the walls of postcapillary-sized venules and arteriovenous anastomoses. Typically, these neural structures were characterised by the presence of an associated oxytalan fibre meshwork. This study also provides quantitative parameters for axon distribution within the ligament.

Animals↗
PubMed1989

Evidence of acute inflammation in the periodontal ligament subsequent to orthodontic tooth movement in rats.

Experimental orthodontic tooth extrusion can result in red cell diapedesis through the PDL vascular wall. Diapedesis is an early sign of acute inflammation. At the ultrastructural level, red cell migration is demonstrated occurring through the endothelial junction of a postcapillary-sized venule. This phenomenon is considered to be indicative of unphysiological tooth loading.

Animals↗
PubMed1987

Ultrastructure of the venous ampulla in the interradicular microvascular bed of the mandibular molars of Mus musculus.

The interradicular periodontal ligament of mandibular molars contains an apparently unique dilated vessel straddling the interradicular alveolar bone. This structure is designated a venous ampulla. The vessel possesses a luminal length and width of approximately 200 X 100 microns, respectively. Ultrastructurally, the endothelium has an average thickness of 0.35 micron, a continuous basement membrane, and an incomplete layer of pericytes. Open endothelial junctions are not present. The anatomy of the vessel wall differs markedly on the dental- and bone-related aspects. Calculated ratios for the luminal diameter to wall thickness vary from 1:80 to 1:150. Postcapillary-sized limbs from this vessel drain into the interradicular septum of bone and the ligament microvascular bed. Arterial supply to the ampulla is provided via arteriovenous anastomoses characterized by their association with myelinated and unmyelinated nerve groups. Oxytalan fibers are present throughout the wall of the venous ampulla, penetrating to the abluminal side of the endothelium where they are associated with unmyelinated axons and free nerve endings. Elsewhere, oxytalan fibers are related to the arteriovenous anastomoses and their accompanying myelinated and unmyelinated nerves located adjacent to the endothelium. Pericytes form membranous contacts with the endothelium of the arteriovenous anastomoses and have processes penetrating the endothelium basement membrane.

Animals↗
PubMed1987

A scanning electron-microscopic, stereo-pair study of methacrylate corrosion casts of the mouse palatal and molar periodontal microvasculature.

Microvascular beds of the palate, gingiva and periodontal ligament had interconnected but distinct, regional patterns. The palatal vasculature reflected mucosal-crest morphology: crestal capillary vessels of the rugae anastomosed with sagitally-orientated rows of 8 microns capillary loops, and, in the inter-rugal troughs, these formed a flat plexus overlying collecting veins more than 100 microns in diameter. Maxillary and mandibular molar ligaments had similar microvascular patterns. The molar gingiva had a circular, outer capillary and inner venous system linked by radial anastomoses. The outer (7 microns) capillaries enclosed the three molars in a continuous horizontal loop coursing beneath the crestal epithelium; the inner (10-15 microns) venous vessels encircled each molar just below the epithelial attachment. Glomerulus-like vascular formations, with an arterial and venous stalk, were associated with the inner circular system and extended toward the crevicular epithelium. Axially aligned, post-capillary, periodontal-ligament vessels (21 microns) anastomosed with the inner circular system, forming different patterns in the occlusal, middle and apical thirds. The apical pattern comprised an enveloping plexus of anastomosing venous vessels supplied by arterio-venous shunts; similar shunts were present throughout the ligament. The microvascular bed of the mandibular inter-radicular ligament was characterized by the presence of a large venous ampulla measuring 60 by 200 microns. Some regions of the ligament microvasculature drained via the medullary vessels into 50 microns-diameter venules located interdentally deep to the molar apices. Volumetrically, the ligament microvascular bed was predominantly of post-capillary venules, and morphologically, a paired arterial and venous system was not demonstrated.

Animals↗
PubMed1987

A transmission electron-microscope stereological study of the blood vessels, oxytalan fibres and nerves of mouse-molar periodontal ligament.

Mandibular, mesiobuccal ligament was sectioned from the alveolar crest to the apex at predetermined levels. Data collected using standard point counting procedures was analysed for main effects due to animal, side of mouth, depth and zone across the ligament. Statistically-significant variations only occurred between different lateral thirds with the middle third containing the most oxytalan fibres and the bone third the greatest vascular and neural volumes. Stereology showed that the ligament was 3-7 times more vascular than other connective tissues. Eighty-eight per cent of the periodontal blood volume was enclosed in vessels with a mean lumenal diameter of 20.9 microns and characterized by a thin endothelial lining and few perivascular cells. These vessels had a surface density of 125.1 cm2/cm3. Oxytalan fibres had a length density of 1258 X 10(3) cm/cm3 and a mean caliper diameter of 0.7 micron. Furthermore, 78 per cent of fibres were adjacent to cells, 14 per cent within principal collagen fibres and 8 per cent in the walls of blood vessels. The length density of nerves within the ligament was 255.9 X 10(3) cm/cm3. Unmyelinated axons constituting 95 per cent of periodontal nerve fibres had a mean caliper diameter of 1.4 micron.

Animals↗
PubMed1984

Ultrastructural evidence of nerve and oxytalan fibre associations in the endoneurium of human periodontal ligament.

Human periodontal ligament from premolars contained numerous fibres of the oxytalan meshwork system affiliated with unmyelinated endoneurium and myelinated nerves in the endoneurium. These fibres consisted of bundles of microfibrils and were present within 0.5 mu of Schwann cells and their unmyelinated axons. This ultrastructural association has not been previously demonstrated.

Adolescent↗
PubMed1984

Ultrastructural analysis of the microfibrillar component of mouse and human periodontal oxytalan fibers.

Microfibrillar populations were quantified for mouse and human periodontal ligament oxytalan fibers in cross-section. Ten mouse fibers (Group 1) and ten human fibers (Group 2) were randomly selected from representative levels of the ligament and digitized for the total fiber area (TFA) and the microfibrillar component area (MFA). A third group of specific mouse oxytalan fibers (RER) was also evaluated. Quantified fiber dimensions varied markedly as did the percentage microfibrillar area for each group. Staining revealed morphologically different components within each fiber. Mouse and human microfibrils were composed of varying numbers of microfilaments. Analysis of covariance showed that the structural relationship between MFA and TFA was linear for each of the three groups. Slopes for the Group 1 mouse and human microfibrillar components were the same (p greater than 0.1) but different (p less than 0.05) for the RER group. Intercepts for all three groups were significantly different at the 1% level. The relevance of these species specific findings is discussed.

Actin Cytoskeleton↗
PubMed1983

Electron-microscopic affiliations of oxytalan fibres, nerves and the microvascular bed in the mouse periodontal ligament.

Throughout the ligament, oxytalan fibres were contiguous to myelinated nerves, unmyelinated exposed axons and free nerve endings. In the cervical and apical regions, accumulations of vessel-related simple and complex mechanoreceptor units were associated with collagen fibrils and fibres of the oxytalan system. The various receptors and nerve endings penetrated to the abluminal surface of the endothelial wall in the different categories of vessels constituting the microvascular bed. Periodontal receptors with oxytalan fibres were also present in the septal wall of dividing vessels and related to endothelial protrusions into the lumen of microvessels. Similarities existed between periodontal mechanoreceptors and baroreceptors. Anatomically, the oxytalan-fibre meshwork provided coupling between the various mechanoreceptor units in the microvascular bed. This periodontal model has morphological characteristics which support the hypothesis that the oxytalan-fibre meshwork forms part of a proprioceptor system for the regulation of vascular flow.

Animals↗