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Biomedical subjects

N R Gjerdet

Publications and source records attributed to N R Gjerdet.

At least 55 records · Page 3Linked to original sources
PubMed1989

Strain shielding 12 weeks after femoral reaming and nailing in rats.

The purpose of this study was to investigate the in vivo strain-shielding in rat femora 12 weeks after intramedullary nailing with either flexible or rigid implants. Five days prior to death, unidirectional strain gauge units were implanted on the anterior bone surface bilaterally. Median strain values of reamed only and polyacetal-nailed femora ranged from 67 to 90 percent of the intact side. Removal of polyacetal nails and sham operations gave negligible changes in strain. Strain of the steel-nailed femora was 51 percent of the intact side. Removal of nails increased strain to 91 percent of the intact side. Testing of femora after removal of implants revealed stiffness of 116 and 103 percent of normal in reamed-only and polyacetal-nailed groups, respectively. Stiffness in the steel-nailed group was reduced to 85 percent of normal. None of these changes were statistically significant. This study indicates that rigid intramedullary nails cause strain shielding at the anterior, mid-diaphyseal surface of rat femora 12 weeks after insertion. Removal of rigid implants seems to restore the loading configuration immediately.

Animals↗
PubMed1989

Porosity of rat femora following intramedullary reaming and nailing.

The present study evaluated cortical porosity and thickness of intact rat femora 12 weeks after intramedullary reaming and nailing. The right femora were reamed and received either flexible polyacetal nails or rigid stainless steel nails. A third group was reamed but not nailed. The left femora were used as controls. The anterior cortical wall was analyzed at the mid-diaphyseal level. Neither reaming nor reaming combined with nailing influenced porosities with a diameter less than 10 microns. For larger pores, polyacetal nailing doubled the porosity, whereas steel nails increased porosity by a factor of 4.5. A slightly increased porosity was observed for the reamed group. Reduced cortical thickness was found in both nailed groups, whereas cortical thickness was increased in the reamed group compared with the control side. Implantation of rigid and flexible intramedullary nails in rat femora increased porosity along the anterior cortical wall.

Acetals↗
PubMed1988

Ranking of histologic tissue responses in the biologic evaluation of dental materials.

Implantation tests are frequently used to evaluate biological properties of dental materials. The tissue reactions have been rated as no, slight, moderate and severe responses, mainly based on a quantitative assessment of the cellular response. The distinction between categories is subject to discussion, and interexaminer calibration is necessary to obtain reproducible results. This paper presents a statistical method of evaluating tissue reaction by ranking photographic prints representing histologic sections. Polyethylene tubes, carrying the materials, were implanted subcutaneously in guinea pigs. The tissue reactions at the tube ends, where the material was exposed to the tissue, were evaluated. Photographs of 20 histologic sections were selected. Five investigators from a scientific staff and five from a group of assisting personnel with minimal instruction ranked the reactions on the prints in increasing order of severity. Assisting personnel received 1 h of instruction before the ranking. Generally, the rank ordering of the different examiners showed good agreement. Qualitative histopathologic examination of the sections indicated a marked variation in the cellular response, which limits the value of the quantitative assessment.

Animals↗
PubMed1987

Controlled bending instability in the healing of diaphyseal osteotomies in the rat femur.

Ninety-six rats underwent a midshaft transverse osteotomy followed by osteosynthesis with an intramedullary nail, so that the effect of bending instability on time to union and on the mechanical properties of experimental diaphyseal fracture could be evaluated. Rotation was reduced by cementing both nail ends to the bone. Rigid nails made of stainless steel were used on one group and flexible nails made of polyacetal resin were used on another group. Serial radiographs were evaluated at 4-6-week intervals. Twelve animals with either nail type were killed at 4, 8, 16, and 24 weeks. Both femora were mechanically tested and the callus diameters were measured. There was no significant difference in time to union between the two groups. The cross-sectional area of callus was significantly higher at 8 and 16 weeks in femora with flexible nails. The strength, toughness, and resilience of the bone increased in this group until 24 weeks. Between 16 and 24 weeks, these parameters did not improve in femora with rigid nails. Poorer mechanical properties in femora with steel nails are interpreted as an effect of stress protection of the bone. This study, therefore, indicates that flexible nails prevent stress protection effects without delaying union.

Acetals↗
PubMed1987

Limb lengthening by epiphyseal distraction. An experimental study in the caprine femur.

Epiphyseal distraction of the left distal femur was accomplished in 10 goats (aged 3-4.5 months). A modified Hoffmann external fixation device was used as a unilateral distraction frame. A distraction rate of 1.5 mm/day was applied for 5.5 weeks. Epiphysiolysis occurred after 3-7 days of distraction. After the lengthening procedure, the growth plate had reduced in height in eight animals on radiographic examination. In two animals the growth plate was fused. Three animals were killed at 4 (Group 1) and 8 (Group 2) weeks and four animals at 16 (Group 3) weeks after the end of the distraction period. The gain in leg length obtained by distraction was reduced owing to growth retardation in the distal femur of the operated limb. The average final lengthening was 24.9, 19.4, and 13.4% in Groups 1, 2, and 3, respectively. Femur and tibia from both sides were tested mechanically in torsion. Only one femur fractured in the elongation area. All but one elongated femur fractured in the area of the diaphysis subjected to distractional force. The torsional strength of the elongated femur compared with control was reduced to approximately 50% in all groups. The corresponding torsional strength of the tibia on the elongated extremity compared with control was reduced to approximately 75% in all groups. The difference in relative strength of femur compared with that of tibia was statistically significant. This finding can be explained by a stress-protective effect on the femur in the distraction area caused by the external device.

Animals↗
PubMed1987

Computerized evaluation of the effectiveness of subgingival scaling in jaw models. An introduction to the program developed at the School of Dentistry, University of Bergen.

The purpose of the present study was to improve the quality and the effectiveness of subgingival scaling managed by dental students. A training program was developed and the scaling was performed in jaw models. The teeth of these models were modified in order to ensure a quick inspection of the scaled root surfaces. Artificial "calculus", consisting of a mixture of shellac, umbra, pumice and plaster dissolved in ethanol, was painted on the root surfaces. Following the completion of the scaling test, remaining "calculus" was evaluated by adoption of a grading system. This system had scores from 0 to 3 and was defined by illustrated and described criteria. A menu-directed computer program was developed in order to ensure a rapid transformation of surface scores into clinically-related variables. The output from this program gave valuable information about the proficiency of individual students, as well as about the whole class of students as one body. Other advantages and potentials of this system are described.

Computers↗
PubMed1987

Traumatic ulcers and pain during orthodontic treatment.

In the present investigation the frequency of oral ulcers and pain in 161 orthodontic patients was recorded. Of all patients, 95% had experienced pain, but 84.5% said that the pain lasted a few days only. About 11% maintained that the treatment was constantly painful. Significantly more patients coming from private clinics complained of pain than those attending treatment at the Department of Orthodontics. About 50% said that activating or changing archwire was most annoying, whereas 28.7% said ulceration and 21% said headgear was the most annoying part of the treatment. According to 75% of the patients, sleeping habits were not influenced. Only eight patients reported truancy, and seven of these had done this only once. Of all patients, 6.2% had requested interim visits. Small wounds caused by the fixed appliance were reported by 75.8% of the patients, and 2.5% had suffered badly from ulceration caused by the fixed appliances. More girls than boys reported ulceration. There was a significant sex difference as regards recurrent aphthous ulceration (RAU). Increase in the frequency of RAU was reported by 23.1% of the girls and 9.6% of the boys while they had fixed appliances.

Activator Appliances↗
PubMed1987

Metal release from heat-treated orthodontic archwires.

Stainless steel and cobalt-chromium orthodontic archwires were subjected to an immersion corrosion test. Wires in the as-received state and wires subjected to a 1-min heat treatment at different temperatures were tested. Iron from the stainless steel and cobalt from the cobalt-chromium product were analyzed in artificial saliva after 1 week of immersion. Both products were analyzed for nickel. The results showed that the cobalt-chromium wire in the as-received state released more metals than the stainless steel. The metal release from the stainless steel wire increased rapidly when subjected to 400 degrees C or higher. For the cobalt-chromium product the increase started at about 500 degrees C. At temperatures above 500 degrees C the release of metals was 15 to 60 times higher than the lowest values. The present results should be considered in procedures involving application of heat to orthodontic wires.

Chemical Phenomena↗
PubMed1987

Tissue reactions to implanted orthodontic wires in rabbits.

Tissue response to a Fe-Cr-Ni and a Co-Cr-Ni orthodontic wire, in the as-received state and with silver soldered joints, was investigated. Specimens with polytetrafluoroethylene (PTFE) as a reference material were implanted in the subcutaneous tissue of rabbits. Six rabbits were sensitized to nickel, four animals were sham-sensitized, and two were left untreated. The results showed that the as-received wires gave no tissue response relative to the PTFE control. In soldered specimens that were moderate to extreme reactions adjacent to the soldered joint and around the wire portion as well. The soldered Co-Cr-Ni wire elicited the most severe reactions, most pronounced in the nickel-sensitized animals. The agar overlay cell culture test of some retrieved implants showed pronounced cytotoxicity of the soldered specimens. Leachable toxic components of the silver solder seemed to be of major importance in the observed cell culture and tissue response to the soldered specimens.

Animals↗
PubMed1987

Abrasivity of toothpastes. An in vitro study of toothpastes marketed in Norway.

The purpose of this study was to measure the abrasivity of 23 toothpastes available on the Norwegian market. Additionally, the pH was registered. The testing was based on The British Standards Institution's specification for toothpastes, using a profilometer technique to evaluate the abrasion. The results showed that the abrasivity ranged from 0.049 to 1.367 relative to a standard reference paste. The products were classified as having 'none/slight', 'medium', or 'high' abrasivity. The pH varied between 3.7 and 10.1. Products with low pH showed evidence of a combined erosive/abrasive effect. For some brands there were statistically significant differences between the fluoride and the nonfluoride version.

Dentifrices↗
PubMed1987

Spontaneous correction of femoral torsion. Diaphyseal osteotomies studied in kittens.

Inward or outward torsion of about 25 degrees was produced in the right femur of kittens by midshaft osteotomy and plate fixation. The left femurs served as controls. The anteversion angle of the femoral necks was measured in axial radiographs taken preoperatively and up to 58 weeks postoperatively. As the bones grew in length, the difference in the anteversion angle between matched femurs was gradually corrected.

Animals↗
PubMed1986

Wear of the Christiansen hip prosthesis.

The wear was examined in 39 Christiansen total hip prostheses, which were removed because of mechanical loosening after being used 5 (3-11) years. In the polyacetal acetabular cups, the head had made an eccentric defect, the mean volume of which was 680 (180-3310) mm3. The mean penetration of the head into the wall of the cup was 0.8 (0.1-3.2) mm. In two additional cups the head had penetrated right through the wall of the cup. In three prostheses the polyacetal sleeve of the trunnion was so worn that the head bore directly on the stem. There was a positive correlation between wear and the time the prostheses had been used before symptoms of loosening presented.

Adult↗
PubMed1985

The effect of abrasion on corrosion of dental Co-Cr alloys. An in vitro study.

The effect of abrasion on corrosion of two dental Co-Cr alloys was investigated in vitro. The metals were abraded with a toothbrush and with a piece of tooth enamel. Changes in corrosion potentials and metal release due to the abrasion were measured. Abrasion by tooth enamel caused a persistent drop in corrosion potentials. The release of both chromium and, in particular, cobalt was higher than during brushing. The two alloys tested did not significantly differ with regard to mode and rate of corrosion. It was demonstrated that the corrosion behavior of electrochemically passive dental alloys was affected by abrasion of a magnitude normally encountered during clinical service.

Chromium Alloys↗
PubMed1985

Marginal adaptation of resin veneers to gold castings.

The magnitude of the fissures between resin facing materials and gold castings was measured by light microscopy. Two different products and two different processing procedures were used. The effect of water sorption on the fissure size was also studied. Mean fissure sizes varied between 3 and 25 microns. The best adaptation between the resin material and the gold alloy was obtained by the conventional closed flasking technique compared with free processing in a pressure vessel. When processed by closed flasking the product that did not contain microfiller showed fissure widths approximately one fourth of those resulting from the open processing technique. The other product, containing microfiller, was less sensitive with regard to processing. The effect of water sorption on the fissure width was most evident in the test groups containing specimens processed in flask.

Chemical Phenomena↗
PubMed1984

Stability of femoral neck osteotomies fixed by von Bahr screws or by compression hip screw.

Subcapital cadaveric femoral neck osteotomies were internally fixed either by a compression hip screw and a lag screw or by two von Bahr screws. The specimens were then subjected to mechanical testing. Continuously increasing axial compression loads were applied on the femoral head until failure and simultaneously the displacement of the osteotomies was measured. With loads up to 2 kN (about 3 times the body weight) no differences were found between the two groups in the displacement of the osteotomies.

Aged↗
PubMed1984

Effects of instability on fracture healing in the rat.

The effect of bending and rotational instability on the healing of a femoral osteotomy was studied in rats using intramedullary fixation with nails made of either steel or flexible polyacetal. All osteotomies were made rotationally unstable by reaming the medullary cavity to a diameter wider than the nails. At 16 weeks, four osteotomies had healed, and 17 had not healed. However, bending tests gave higher values for strength and energy absorption in non-unions with flexible as compared to Stiff nails. Rotational instability thus caused a high rate of non-union in the present model, which has given safe healing when the osteotomy has been stabilized for rotation. Flexible nailing increased strength and energy absorption in bones with non-union, but did not affect the incidence of healing.

Acetals↗