Image layer characteristics of the PC 1000 (mark II)

The objective of this study was to investigate empirically the image layer characteristics of the PC 1000 Mark II. Radiographs were taken of a lead resolution grid positioned at 1 mm increments along angular intervals of the projected x-ray beam. The receptor was T-Mat G film combined with Lanex Regular Screens. The path of the effective rotation center was determined using a film positioned horizontally at right angles to the slit beam. The vertical magnification factor, horizontal magnification and Distortion Index, corrected for the position of the tomographic layer, were calculated using a reference object placed at various resolution limits of the image layer. The beam projection angle was compared to the average dental arch shape and proximal contact angle. The maximum resolution observed at the central plane of the image layer was 4 lp · mm⁻¹. The image layer width at the 1.5 lp · mm⁻¹ resolution contour varied from 12 mm anteriorly to 41 mm posteriorly. The vertical magnification factor within the image layer showed a linear increase along the beam path from 1.21 to 1.36. The horizontal magnification varied from 1.07 to 1.71, and the Distortion Index from 0.85 to 1.15. The beam projection angulations to the average arch shape ranged from 90° anteriorly to 115° in the premolar segments and 105° in the molar regions. The empirically derived image layer of the PC 1000 Mark II conforms to the shape of the average dental arch and that found using MTF analysis. The spatial resolution attained using a standard receptor is within the acceptable range.     

FRCSEd (Oral and Maxillofacial Surgery): a milestone in the history of Oral and Maxillofacial Surgery in the United Kingdom

The British Association of Oral and Maxillofacial Surgeons (BAOMS) and the Royal College of Surgeons of Edinburgh (RCSEd) have had leading roles in organisation, assessment and improvement of surgical training in the United Kingdom. This was particularly well illustrated by the establishment of the fellowship examination in Oral and Maxillofacial Surgery (FRCSEd, OMFS).     

Temperatures in and around mandibular fractures

This study measured the temperature in and around mandibular fractures in 20 anaesthetized patients. A fine calibrated thermocouple attached to a digital thermometer was used to measure temperature at the bone surface margin of a mandibular fracture and 5 and 10 mm from the fracture; within the fracture against the bone at 5, 7 and 10 mm depths and at the base of 7 mm deep biopsy cavities 5 and 10 mm distant from the fracture line immediately after biopsy, then 1 and 2 min later. On the surface the temperature was approximately 1 degrees C warmer than at the 5 and 10 mm sites distant from the fracture. Temperature reduced at the 1 and 2 min readings after the biopsy cavity cutting. This study confirmed that the surface temperature is lower than internal bone temperatures.     

Effect of inactivation of gtf genes on adherence of Streptococcus downei

The activity of glucosyltransferases (GTF), a group of enzymes that synthesize water-soluble and -insoluble glucans from sucrose, significantly contributes to the cariogenicity of mutans streptococci. Streptococcus downei produces four glucosyltransferases, GTFI, which produces insoluble glucan, and GTFS, GTFT, and GTFU, which synthesize soluble glucans. We have previously reported that inactivation of gtfS results in altered adherence and have now examined its interaction with other enzymes by constructing mutants which were gtfS, gtfS/gtfT, gtfS/gtfI and gtfI. The mutants were tested for their ability to accumulate on wires and on plastic microtiter trays in the presence of sucrose. The gtfS mutant displayed a reduced ability to adhere compared to the wild type but there was no further reduction of adherence in a gtfS/gtfT mutant. In contrast, the gtfS/gtfI double mutant showed a drastic reduction in adherence and when gtfI alone was inactivated, bacteria were unable to adhere to a hard surface. The results confirmed that insoluble glucan is required for strong adherence to a smooth surface but that the amount and structure of this glucan is dependent upon the availability of soluble glucans to act as primer molecules.     

Chemoluminescence generation and MTT dye reduction by polymorphonuclear leukocytes from periodontal disease patients

Alterations of polymorphonuclear leukocytes (PMNs) functions have been reported in patients with severe forms of some periodontal disease. In this study we evaluated the chemoluminescence generation and MTT dye reduction by human PMN in patients with juvenile periodontitis (JP), rapidly progressive periodontitis (RPP) and adult periodontitis (AP) during protein kinase C (PKC) activation or during the phagocytosis of opsonized zymosan. The results demonstrated that only PMNs of JP patients showed a decreased chemoluminescence generation and MTT dye reduction during the phagocytosis of opsonized zymosan (p < 0.05). The time to reach the maximal peak during the PKC activation on the chemoluminescence reaction was evaluated and JP PMNs patients demonstrated a depressed value (7.0 ± 0.4 min) compared with healthy volunteers (13.8 ± 0.5 min). The etiology and importance of such cellular alterations in the immunopathogenesis of the periodontal disease are discussed.     

Acute irradiation effects on morphology and function of rat submandibular glands

In this study the morphologic and functional changes were compared after irradiation (single dose, 15 Gy) of rat submandibular salivary glands. Before and 1-10 days after local irradiation of the gland region, samples of submandibular saliva were collected after stimulation by pilocarpine. At the same time-points and also 3 h postirradiation submandibular glands were carefully extirpated and prepared for histocytologic examination (LM, TEM). Maximal increase of the lag phase and decrease of the flow rate were observed 3 days after irradiation, while [K+] and [Na+] increased and decreased, respectively, from days 1 and 3 after irradiation. Morphologic changes were observed from the third hour after irradiation, were maximal 3 days after irradiation and had partially recovered by day 10. Three hours and 1 day after irradiation degranulation of convoluted granulated tubes (CGT) was observed. Three days after irradiation the most striking morphologic changes in serous and mucous cells were distension of the cisternae of the RER, degeneration of mitochondria and vacuolization of the cytoplasm. Fibril-like condensations of electron dense material in the mucous granules were observed 3 h, 1 and 6 days after irradiation. Regranulation of CGT cells was observed from day 6. From this study it is concluded that changes in salivary gland function can be observed before major morphologic changes occur. Functional changes persist after the morphologic changes seem to have virtually returned to normal.     

Retrograde root filling with composite and a dentin-bonding agent. 1

Abstract A method is described, by which retrograde root filling with a composite resin can be performed. The cavity design is a slightly concave dissection of the apical part of the root, which is treated with the bonding agent Gluma followed by an application of Retroplast. Retroplast is a chemically curable composite containing silver for radiopacity and aerosil to obtain a suitable consistency. Endodontically treated teeth with a eugenol-containing root canal sealer did not affect the strength of the bond between Retroplast and apical dentin. A tight seal between the composite and the cavity surface was observed by light and SEM microscopy, and histology of tissue surrounding fillings placed in monkeys revealed absence of inflammatory cells around the filling and a close contact between filling and fibro-blasts with collagenous fibers. In some cases, cementum and Sharpey's fibers formed in contact with the filling. Fillings placed in humans performed successfully in most cases, and the main causes of failure were either inadequate hemostasis during filling, or root fracture unnoticed by the time of filling. The retrograde technique promises a new treatment principle, with a root canal effectively sealed and the periapical ligament restored after apicoectomy.     

Assessing treatment effectiveness of removable and fixed orthodontic appliances with the occlusal index

Orthodontists from different backgrounds may have different opinions about removable and fixed orthodontic appliances, but there have been few objective comparisons of their relative treatment effectiveness. It is the purpose of the present study to analyze objectively the effectiveness of these two types of appliances. Eighty cases involving patients who had been treated with removable appliances and 67 cases of patients treated with fixed appliances were studied with respect to the Occlusal Index (OI). Scores indicating severity of malocclusion were obtained from pretreatment and posttreatment study casts. The effectiveness of the fixed appliance (represented by average reduction in OI score) was much greater than that of the removable appliance. The result of treatment with the fixed appliance was also found to be much better than that of the treatment with the removable appliance (indicated by the much lower posttreatment OI score in the fixed-appliance cases). The Occlusal Index was designed to measure features of basic malocclusion and is not a very sensitive index for assessing symptoms of a developing malocclusion. The fact that both the treatment effectiveness and the treatment results of the removable appliance were found to be inferior to those of the fixed appliance may indicate that the removable appliance has been used largely to correct "symptoms" rather than basic malocclusion.