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Biomedical subjects

M A Almeida

Publications and source records attributed to M A Almeida.

29 records · Page 2Linked to original sources
PubMed1994

Effect of different time intervals between sealant application and bracket bond on adhesive strength.

The effect of variation of time between the use of the sealant and the composite itself on the bond strength of the enamel-resin-bracket system was tested in vitro for two composites. Eighty brackets were bonded to extracted human molars, half for each composite. The sealant was applied 1 minute, 2.5 minutes, 5 minutes, and 10 minutes before the use of the composite. The brackets were submitted to a shear force until debonding. Means and standard deviations were calculated. No statistically significant differences were found among the different times of sealant application and between the two composites tested, when a two-way analysis of variance was carried out.

Adhesives↗
PubMed1994

Direct bonding brackets: unfilled versus unfilled/filled resins.

The clinical and clinical/laboratorial performance of unfilled/filled and only unfilled resins for direct bonding of orthodontic brackets were evaluated. In the clinical part, brackets were bonded using both techniques in alternate quadrants of eleven patients of the Orthodontic Clinic, State University of Rio de Janeiro. A total of 118 teeth, 59 in each group, were tested and bond failure frequencies were recorded for six months. For the clinical/laboratory part, upper and lower premolars to be extracted for orthodontic reasons, were selected. Thirty-two brackets were bonded in vivo--16 using unfilled/filled and 16 using only unfilled resins--and the teeth were kept in the mouth for two months. After extraction, the teeth were secured in plastic rings and an Universal Instron Machine was used to debond the brackets. No statistically significant differences were observed for clinical failure rates, nor for laboratory debonding strength between the two techniques. Failures occurred preponderantly at the bracket/resin interface, so that most of the resin remained bonded to the enamel surface on both groups.

Adolescent↗
PubMed1994

Skeletal and dental arch asymmetries in individuals with normal dental occlusions.

The aim of this study was to determine whether skeletal and/or dental asymmetries are presented in individuals with normal dental occlusions. Frontal cephalometric radiographs and dental arch casts were obtained from 20 Brazilians from Rio de Janeiro whose mean age was 22.4 years. Normal dental occlusions were present in all individuals. Nine bilateral triangles were established on the radiographs for the craniodentofacial complex. The area for each triangle was calculated, and the frequency of asymmetries on the dental casts was investigated. When comparing right and left sides on the radiographs, Student's tests did not show statistically significant differences in triangle areas, although the areas were not symmetrical. Males and females showed similar results when the areas of the radiographic triangles were compared between sexes. Maxillary and mandibular dental midlines, palatal raphe on the casts, and median sagittal plane on the radiographs were almost coincident. Additionally, the frequency of molar asymmetries on the dental casts was not statistically different, but molar asymmetries greater than 1 mm were present in 50% of the sample.

Adolescent↗
PubMed1994

Incisor retraction and profile changes in adult patients.

The aims of this study were to evaluate the changes in the facial profile related to maxillary incisor retraction and to check for correlations between changes in the lip and changes in the positions of the teeth and alveolar bone during orthodontic treatment. Initial and final lateral cephalometric radiographs of 25 nongrowing Brazilian patients were selected for this study. All patients initially presented with Class I or II malocclusions and had their maxillary incisors retracted at least 2 mm during orthodontic treatment. Changes in lip position, length, and width, as well as changes in the positions of the alveolar bones and incisors, were calculated. Statistically significant differences from pretreatment to posttreatment were observed for all measurements except for upper lip length and point A. A high correlation was demonstrated between changes in the lower lip sulcus and point B and between changes in the lower lip sulcus and the mandibular incisor. Changes in the maxillary and mandibular incisors did not show a high correlation to the total lip changes, but high correlation coefficients were obtained when the changes in lip width were excluded from the total lip changes. In other words, changes in lip width tended to mask the changes in lip position caused by retraction of the maxillary incisors.

Adolescent↗
PubMed1994

Skeletal and dental arch asymmetries in Class II division 1 subdivision malocclusions.

The aim of this study is to determine whether or not skeletal and/or dental asymmetries were presented in patients with Class II division 1 subdivision malocclusions. Frontal cephalometric radiographs and dental arch casts were obtained from thirty Brazilians from Rio de Janeiro; the mean age of the sample was 11.6 years. Nine bilateral triangles were established on tracings of the radiographs to describe the cranio-dento-facial complex. The area of each triangle was calculated, and the frequency of AP and transverse asymmetries on the dental casts were determined. When comparing Class I and Class II sides on the radiographs, Student t-tests did not show any statistically significant differences in triangle areas. However, the frequency of asymmetries on the dental casts were statistically significant at the 1% level. These asymmetries were more evident in the anteroposterior plane than in the transverse plane and in the lower arches than in the upper arches. It was concluded that Class II division 1 subdivision malocclusions are characterized by dental deviations and not skeletal dysplasia in the frontal plane.

Adolescent↗
PubMed1993

Direct bond brackets: cotton roll versus rubber dam isolation.

Forty-four brackets were bonded "in vivo" using cotton roll and rubber dam isolation. Maxillary and mandibular premolars, to be extracted for orthodontic reasons, were used in this study. After bonding, the teeth were retained in the mouth for at least 30 days. They were extracted using surgical elevators. After extraction, the teeth were secured in plastic rings using gypsum and kept in water for 7 days until debonding. A Universal Instron Machine was used to produce a shear force at a speed of 0.1 cm/min until each bracket was removed. No statistically significant differences for debonding strength were observed between the two types of isolation, nor between the buccal and palatal surfaces of the teeth. One hundred percent of the failures occurred at the bracket/composite interface.

Acid Etching, Dental↗
PubMed1993

Polishing after debracketing: its influence upon enamel surface.

The effect of different time periods of polishing, after debonding orthodontic brackets, upon enamel surface was investigated. Nine brackets were bonded onto nine healthy human teeth, extracted for severe periodontal disease. The brackets were removed after twenty-four hours and the composite was removed from the dental surface with a tungsten carbide bur. Three of these teeth were polished with a rubber cup, pumice and water for 30 seconds. Three others had the same procedure for 10 seconds and the last group did not received any polishing. The three groups were examined at the Scanning Electron Microscope and compared with the sound enamel of the same teeth. The results showed that pumicing is necessary after debracketing, although, even after 30 seconds of polishing, composite is still found on the enamel surface. The three procedures did not provide a surface equal to the sound enamel, but better results were obtained by increasing polishing time.

Dental Debonding↗
PubMed1993

Direct bonded space maintainers.

The aim of this study was to evaluate clinically a bonded space maintainer, which would reduce chair-side time and cost. Sixty appliances were fabricated from 0.7 mm stainless steel round wire and bonded using light-cured composite to the two teeth adjacent to the site of extraction of a posterior primary tooth. Twenty males and sixteen females (age range 5-9-years-old) were selected from the Pedodontic clinic of the State University of Rio de Janeiro. The sixty space maintainers were divided into two groups according to the site in which they were placed: a) absent first primary molar and b) absent second primary molar. Impressions and study models were obtained prior to and 6 months after bonding the appliances. During this period only 8.3% of failures were observed, most of them from occlusal or facial trauma. Student t-test did not show statistically significant alterations in the sizes of the maintained spaces during the trial period.

Child↗
PubMed1988

[Intestinal absorption of glucose in anesthetized rats. I. Standardization of a method for screening of oral hypoglycemic agents].

This paper presents a method for the screening of natural hypoglycaemic drugs that interfere with the intestinal absorption of glucose. Luminal perfusion of the small intestine (whole length) was carried out on 24 h fasted adult Wistar rats, anaesthetized with sodium pentobarbital. Two rubber Nelaton cannulae were introduced into the organ, the first at the proximal end of the duodenum, just after the pylorus and a second larger one near the ileo-cecal valve. After a preliminary washing with warm physiological saline to remove any alimentary residues and secretions, warm saline containing glucose (plain or with added putative absorption inhibitors), was then introduced into the gut. Ten minutes later the contents was expelled with air and the preparation fully washed with plain warm saline. All perfusates were separately collected up to volume in graduated flasks kept in chipped ice. The glucose concentration was measured in triplicate samples by the specific glucose-oxidase method. The intestinal absorption of the sugar was calculated by difference from the glucose concentration found in the initial solution and in the final perfusate. The method is reliable and highly reproducible.

Animals↗
PubMed1981

The serum levels of unbound bilirubin that induce changes in some brain mitochondrial reactions in newborn guinea-pigs.

Bilirubin in different concentrations was injected in newborn guinea-pigs and the following parameters were determined: serum total and unbound bilirubin, whole brain bilirubin content and oxygen consumption, NADH-cytochrome c reductase and ATPase activities in brain mitochondria. The results showed a significant correlation between decreased rates of brain metabolism and the elevation of serum total and unbound bilirubin.

Adenosine Triphosphatases↗