Bacterial colonization associated with fixed orthodontic appliances. A scanning electron microscopy study.

This investigation was undertaken to assess bacterial plaque accumulation adjacent to orthodontic brackets. Experiments were carried out on 11 subjects who were scheduled for orthodontic treatment including extraction of two or four premolars. Metal brackets were bonded to the premolars to be extracted using macro-filled bonding composite. A conventional elastomeric ring was placed around one bracket and a steel ligature wire around the bracket on the contralateral tooth. The subjects were told to continue their normal oral hygiene regimen. Teeth were extracted at 1, 2, or 3 weeks after bracket bonding. Scanning electron microscopic (SEM) examination of brackets, excess composite, and buccal enamel revealed that mature plaque was present on excess composite at 2 and 3 weeks after bonding, whereas plaque on the gingival enamel surface was still at an early stage of development. The results demonstrate that excess composite around the bracket base is the critical site for plaque accumulation due to its rough surface and the presence of a distinct gap at the composite-enamel interface. The method of ligation does not appear to influence the bacterial morphotypes on both composite and enamel surfaces.

A radiographic comparison of apical root resorption after orthodontic treatment with a standard edgewise and a straight-wire edgewise technique.

The purpose of this study was to compare the severity of apical root resorption occurring in patients treated with a standard edgewise and a straight-wire edgewise technique, and to assess the influence of known risk factors on root resorption incident to orthodontic treatment. The sample consisted of 80 patients with Angle Class II division 1 malocclusions, treated with extraction of at least two maxillary first premolars. Variables recorded for each patient included gender, age, ANB angle, overjet, overbite, trauma, habits, invagination, agenesis, tooth shedding, treatment duration, use of Class II elastics, body-build, general factors, impacted canines, and root form deviation. Forty patients were treated with a standard edgewise and 40 with a straight-wire edgewise technique, both with 0.018-inch slot brackets. Crown and root lengths of the maxillary incisors were measured on pre- and post-treatment periapical radiographs corrected for image distortion. Percentage of root shortening and root length loss in millimetres were then calculated. There was significantly more apical root resorption (P < 0.05) of both central incisors in the standard than in the straight-wire edgewise group. No significant difference was found for the lateral incisors. Root shortening of the lateral incisors was significantly associated with age, agenesis, duration of contraction period (distalization of incisors), and invagination, while root shortening of the central incisors was related to treatment group and trauma.

Microvascular system of the rat incisor enamel organ. A scanning electron microscopic study of vascular corrosion casts.

The rat incisor is a commonly used model in studies of tooth eruption, amelogenesis and effects of mechanical loading on the dental and periodontal tissues. The purpose of this study was to assess the three-dimensional architecture of the microvascular bed of the rat incisor enamel organ, to describe the direction of blood flow, and to provide a histometric assessment of the vascular categories that can be statistically analyzed. Vascular corrosion casts were prepared and examined by scanning electron microscopy. The microvasculature of the labial periodontal space was arranged in three distinct layers. The inner layer in direct relation to the enamel organ consisted of a capillary network which was drained by short venules at the cemento-enamel junction. The intermediate layer consisted of arterioles oriented parallel to the long axis of the incisor mainly mid-labially, branching off smaller arterioles to the capillary network. The outer layer was formed by flattened sinusoid vessels of larger caliber. Blood supply was from the anterior superior alveolar artery branches through the arterioles into the capillary network. Drainage was postero-laterally along the cemento-enamel junction via short venules which emptied into the sinusoid vessels, finally to flow through Volkmann's canals into the alveolar bone via small venules. The findings demonstrate that the microvasculature of the rat incisor enamel organ has an exceptionally high level of physiologically-adapted structural organization.

Microvascular adaptation to transmucosal implants. A scanning electron microscopic study in the rat.

The profuse gingival microvasculature surrounding natural teeth has a unique architecture that contributes to the biologic seal and the anti-infective defense in the sulcular region. This study tested the hypothesis that this characteristic vascular arrangement is not replicated when gingival tissues adapt to a transmucosal implant. In 20 4-week-old Wistar rats, the upper first molar was extracted bilaterally and the gingiva at this site excised. Four weeks later, a 5-mm-long titanium screw was implanted at the extraction site on one side. After another 4 weeks, the rats were injected with liquid plastic resin through the carotid arteries and vascular casts prepared for scanning electron microscopy. The results showed that within 4 weeks after implant insertion, the microvasculature of the regenerated soft tissues immediately surrounding the implant had formed a characteristic arrangement that consisted of a dense subepithelial network as well as an orderly array of vertically oriented capillary loops. The density and diameter of the capillaries varied within a wide range, possibly related to the extent of healing and/or inflammatory conditions. On the contralateral, edentulous side, the capillaries formed a flattened meshwork showing a conspicuous absence of capillary loops. This study indicates that, when a transmucosal implant is inserted in an edentulous area, the mucosal microvasculature adapts and forms an arrangement very similar to that surrounding natural teeth.

Effect of specimen preparation method on relative volume of the microvasculature--a light microscopic study in rat tongue.

The study of corrosion casts by scanning electron microscope is an established means of investigating three-dimensional microvascular architecture. However, concern has been raised that the volume of the vasculature is affected by the perfusion procedure. Ten rats (group A) were standard perfusion fixed, while 10 rats (group B) were perfused with acrylic resin after fixation. Vascular volume was assessed by computer-aided analysis of thin sections of tongue lamina propria. The results showed that vascular volume in lamina propria of rat tongue is 13.6 +/- 4.1% (mean +/- SD). No significant differences in vascular volume were found between group A and group B specimens. It can be concluded that plastic-perfused specimens may be as reliable as histologic sections in obtaining a true image of vascular systems. Thus, corrosion casts are suitable for histometric analysis of the microvasculature.

Revascularization of an excisional wound in gingiva and oral mucosa. A scanning electron microscopic study using corrosion casts in rats.

The purpose of this study was to examine microvascular regeneration associated with gingival wound healing. A full-thickness piece of gingiva and oral mucosa was excised along the palatal aspect of the right maxillary first and second molars in 20 young Wistar rats. The contralateral side served as unoperated control. After 2, 4, 7, 10 or 20 days of healing, microvascular corrosion casts were produced and examined by scanning electron microscopy. At 2 days, vessels surrounding the wound were dilated and impressions representing sites of leukocyte margination were prominent in the walls of venules. Capillary buds were emerging from venules and capillaries. At 4 days, the vessel buds had lengthened and connected in pairs to produce capillary loops. At 7 days, new vessels extended deeply into the wound space, mainly from the medical side, in a palisade-like pattern. At 10 days, the denuded bone surface was still not completely revascularized and Volkman's canals opening to the wound area were empty. At 20 days, the bone surface was covered by large, irregular vessels which originated mainly from the palatal mucosa. The periodontal ligament was less important in the tissue repair process, while the bony vasculature contributed little or not at all to revascularization of the healing gingiva and palatal mucosa.

The vasculature of the periodontal ligament: a scanning electron microscopic study using corrosion casts in the rat.

The purpose of this study was to examine the 3-dimensional architecture of the microvascular system of the rat periodontal ligament (PDL). Vascular corrosion casts were prepared and examined by scanning electron microscopy. Cervically, arterioles and venules communicated with the profuse capillary network of the gingiva. The mid-root segment of the PDL contained arterioles and venules that mainly coursed occluso-apically near the alveolar wall, as well as capillary loops located closer to the root surface. Arterioles entered the PDL through vascular canals from the bone marrow, then coursed coronally and branched into an interconnected network of capillaries. The capillaries formed hairpin loops pointing coronally. At the tip, the capillary loops were enlarged in diameter and had an irregular luminar surface. The capillaries then coursed apically, anastomosing freely, until entering a venule. Large venules mainly followed a coronal-apical path, giving the PDL vasculature a palisade-like appearance. These vessels either left the PDL through vascular canals in the alveolar wall or connected in an apical, venous cap with venules exiting through the apical foramen. The results show that the microvasculature forms a highly organized system presumably related to the specialized functions of the periodontium. Cervically, a dense capillary system may be required for antimicrobial defense and rapid tissue turnover. The vasculature in the middle segment supports the suspensory structures, while the venous cap in the apical region may be designed to cushion masticatory forces.(ABSTRACT TRUNCATED AT 250 WORDS)

Microvasculature of the dorsum of the rat tongue: a scanning electron microscopic study using corrosion casts.

The purpose of this study was to examine the microvascular system of the dorsum of the rat tongue in relation to the subepithelial connective tissue relief. Methylmethacrylate corrosion casts of the vasculature as well as specimens in which the epithelium had been removed were prepared and examined by scanning electron microscopy (SEM). The SEM images revealed four distinct layers in the vasculature of the lamina propria. Superficially, Layer 1 comprised the irregularly shaped ends of capillary loops. Layer 2 consisted of parallel ascending and descending capillaries. These two layers were drained by the subjacent Layer 3, a fish-net-like venous plexus. More deeply, Layer 4 contained arterioles ascending from the muscular layers of the tongue. The vessels of larger papillary structures formed cylindric networks supplied by several arterioles and drained through a single venule to the venous plexus in Layer 3. At their base, the capillary loops often showed a constriction, suggestive of a sphincter. Arteriovenous anastomoses were rare. The epithelium-connective tissue interface showed short conical papillae as well as larger papillary structures which corresponded in both distribution and size to the capillary loops found in the vascular casts. The results confirm that the tongue is highly vascularized and demonstrate that the vascular supply to the papillae, taste buds, and other surface structures forms a highly organized and specific system which is adapted to the specific functions of this organ in the rat.