Biomedical subjects

N R Gjerdet

Publications and source records attributed to N R Gjerdet.

At least 37 records · Page 2Linked to original sources

PubMed1995

Marginal ridge strength of teeth with tunnel preparations.

The aim of this study was to investigate how the cavity design of tunnel preparations influences the strength of the marginal ridge and to assess the ability of a restoration to support it. Extracted upper premolars were divided into eight experimental groups and one control group of intact teeth. The size and the position of the tunnel preparation in relation to the marginal ridge differed in four of the groups, the preparations remaining unfilled, while teeth in four corresponding groups were filled. The teeth were subjected to incremental dynamic forces until fracture of the marginal ridge occurred at which point a 'maximum energy-index' was calculated. The relationship between this index and the experimental variables was analysed by the Cox proportional hazards model. The results for both filled and unfilled teeth indicated that the distance from the preparation to the marginal ridge is more influential on weakening the ridge than is the buccopalatinal size of the opening. A conservative tunnel restoration situated 2 mm from the marginal ridge, does not significantly weaken an otherwise intact tooth.

Bicuspid↗

PubMed1994

Allergenic potential of two orthodontic bonding materials.

The sensitization potential of two orthodontic bonding materials, one conventional premix product and one nonmix product, was evaluated by a modified guinea pig maximization test. The nonmix product, consisting of a liquid to be applied to the tooth surface and a paste which was placed on the bracket base, caused reaction in 50% of the tested animals. This material should be considered to be a possible cause of allergy in patients or professionals handling it.

Adhesives↗

PubMed1994

Leaching of additives and degradation products from cold-cured orthodontic resins.

Unstimulated saliva was collected from orthodontic patients and subjected to combined gas-chromatography and gas-chromatography/mass-spectrometry analyses. Saliva was collected before insertion of removable orthodontic appliances made of cold-cured resins. Saliva was then collected 1-2 months after insertion of the appliances and 1 week after they had been removed. Phenyl benzoate (PB) and phenyl salicylate (PS) were identified in pooled saliva samples from patients wearing the appliances. Biphenyl and 2-methoxy-4-hydroxy-benzophenone in addition to PB and PS were identified in a study with in vitro specimens made of orthodontic resin. The leaching of compounds from these test specimens processed by a powdering technique and a pre-mix technique was compared.

Biphenyl Compounds↗

PubMed1993

Bone strength in infants.

The results from a study of bone strength in normal infants is presented. The fibular bones of infants dying from SIDS were tested mechanically by a three-point bending test and the behaviour of the bony structure determined by measuring several variables. Correlations between these variables and infant age, length, weight and length of fibular bones were found and base-line values for bone strength established.

Biomechanical Phenomena↗

PubMed1993

Immune response to nickel and some clinical observations after stainless steel miniplate osteosynthesis.

Fifteen patients undergoing internal fixation for mandibular fractures were examined for delayed type hypersensitivity (DTH) reaction to nickel before and after implantation of stainless steel miniplates. A lymphocyte transformation test (LTT) was used to measure the immune response before implantation and at removal of plates and screws. The clinical complications during fracture healing were also recorded. The results show that the in vitro LTT may be useful in nickel hypersensitivity testing. A significant increase in lymphocyte transformation was found as a response to nickel stimulation (0.5 microgram Ni/ml) at removal of the implants. We conclude that, despite an increase in LTT after stainless steel implantation, no adverse clinical complications related to DTH could be recorded after short-time observation.

Adolescent↗

PubMed1993

Periodontal attachment loss assessed by linear and area measurements in vitro.

The aim of the present study was to investigate the relationship between linear and area measurements of periodontal attachment loss, and to determine the root surface area on different tooth-types. Extracted permanent teeth were collected in a national survey including a systematic random sample of 500 Norwegian dentists. The response rate was 70%. Altogether 329 teeth were received, 81 of them (excluding 3rd molars) were subjected to both linear and area measurements of attachment loss. Using a dissecting microscope (10 x), 4 to 8 duplicate linear measurements were recorded per tooth. The areas of both lost and remaining periodontal attachment were measured by a method based on controlled release of Cu and Co metal ions from coatings applied to the root surface. Linear loss of attachment for single-rooted teeth (n = 63) was mean = 44.0% and the area loss mean = 49.2%. The corresponding measurements for multi-rooted teeth (n = 18) were mean = 30.3% and mean = 35.1%, respectively. The correlation between linear and area loss was r = 0.78 for single-rooted and r = 0.75 for multi-rooted teeth (p < 0.01). The lower correlation in multi-rooted teeth is probably due to the more complex root anatomy. It is concluded that there is a strong correlation between linear loss of attachment and area of periodontal support lost for teeth with early to moderate loss of attachment, and that linear measurements tend to underestimate the remaining periodontal attachment.

Alveolar Bone Loss↗

PubMed1993

Leaching of organic additives from dentures in vivo.

Samples of saliva were collected from subjects with dentures. These samples were collected both before the dentures were replaced and 1 week after the subjects had received their new dentures. Dibutylphthalate and phenyl benzoate were detected in the saliva samples with a gas-chromatography and a gas-chromatography/mass-spectrometry technique. We also quantified the dibutylphthalate in the saliva. In addition, in an in vitro study, we identified biphenyl leached from heat-cured denture base polymer plates. Our study suggests that subjects with dentures have higher contents of the above organic substances in saliva than subjects without dentures and that organic additives leach from new heat-cured dentures.

Adult↗

PubMed1992

Composition and in vitro corrosion of orthodontic appliances.

The high incidence of nickel allergy and the increasing use of nickel-containing dental biomaterials has been of growing concern. The purpose of this investigation was to analyze different types of alloys used in orthodontics, and to study whether nickel and chromium will be released from these alloys when stored in physiologic saline. Face-bows, brackets, molar bands, and arch wires were analyzed. Most of the different parts in the face-bows, brackets, and molar bands were similar to conventional 18/8 stainless steel. Except the wires, most appliances included a variable amount of silver solder, the greatest in face-bows. After 14 days in 0.9% sodium chloride (NaCl), the largest amount of nickel and chromium were leached out from the face-bows and the least amount from the arch wires. Soldered stainless steel face-bows seemed to be very susceptible to corrosion. The release of nickel seemed to be related to both the composition and the method of manufacture of the appliances, but the release was not proportional to the nickel content.

Chromium↗

PubMed1992

Fatty acids of healthy and periodontally diseased root substance in human teeth.

In this comparative study, samples of root substance from healthy and periodontally diseased human teeth were analyzed for fatty acids by means of a gas-chromatographic technique. The sample preparation procedure allowed specimens from individual teeth to be analyzed. The content of the fatty acids C16:0, C16:1, C18:0, and C18:1 in the superficial layer of the periodontally diseased teeth was significantly higher than that of healthy teeth. In the inner layer, there was no such difference. Four different 3-hydroxy fatty acids (3-OH C14:0, 3-OH C15:0, 3-OH C16:0, and 3-OH C17:0) were identified by combined gas-chromatography/mass-spectrometry in the tooth substance of periodontally diseased teeth. This indicates the presence of lipid A, which is the toxic component of bacterial lipopolysaccharides.

Chromatography, Gas↗

PubMed1992

Metal release from arch bars used in maxillofacial surgery. An in vitro study.

Surgical arch bars (splints) are used in maxillofacial surgery as an aid to intermaxillary fixation procedures. Two different types of stainless steel arch bars, a solid bar and a silver-brazed bar, were studied with regard to metal release in vitro. Arch bars were ligated to jaw models and immersed in 0.9% saline solution. The electrolyte was analyzed for Ni, Cr, Fe, Cu, Zn, and Cd by atomic absorption spectrophotometry on days 3, 10, and 28. The amounts of metal released from the brazed arch bar were 140-600 times higher than those released from the solid arch bar. Clinical implications are suggested.

Chromium↗

PubMed1991

Glass ionomer cements used as bonding materials for metal orthodontic brackets. An in vitro study.

The forces required to debond orthodontic brackets on human teeth were studied in vitro. The brackets were bonded with different glass ionomer cements (GICs), and a composite resin (Concise). The shear force required to remove the brackets was recorded at different time intervals after bonding. The bond strength was considerably lower for the GICs compared with brackets bonded with the composite resin, at all time intervals that were studied. Moreover, the bond strength increased more slowly for the GICs compared with the resin. Different GICs displayed a varying setting time. The bonding strength of GICs increased more than 50 per cent between 10 and 20 minutes setting time.

Acrylic Resins↗

PubMed1991

Nickel and iron in saliva of patients with fixed orthodontic appliances.

Saliva was obtained from patients receiving treatment with fixed orthodontic appliances. One saliva sample was taken without appliances, and another at least 3 weeks after placement. In some patients samples were also taken immediately after insertion of the appliance. Nickel and iron were quantified by electrothermal atomic absorption spectroscopy. There was a large scatter in the results. No statistically significant differences were found either in the concentrations or in absolute masses of nickel or iron in samples taken without appliances and in those obtained when the appliances had been in the mouth for at least 3 weeks. For samples taken immediately after placement of the appliance, there was a significant increase in both concentrations and masses of nickel and iron. It thus seems that there is a high initial release of metals, and the effect diminishes with time.

Adolescent↗

PubMed1991

Release of fluoride and metal ions from root surfaces after topical application of TiF4, SnF2, and NaF in vitro.

Aqueous solutions of TiF4 cause a rapid uptake and a long-lasting retention of fluoride when applied to dentin. The aim of this study was therefore to investigate the pattern of fluoride release after TiF4 application in vitro, compared with SnF2 and NaF application. TiF4, SnF2, and NaF were applied for 4 min and 1 min to standardized areas of six groups of root surface specimens immersed in distilled water. Untreated specimens were used as controls. The water was changed daily for 30 days, and F concentrations measured by an ion-selective electrode. All test groups showed a rapid decline in F concentration. In the 4-min group F concentration more than double the detection limit of the F electrode could be registered the first 28 days for TiF4, 11 days for SnF2, and 7 days for NaF. In the 1-min group periods of F registration were shorter. Analysis of Sn by atomic absorption spectrophotometry showed decreasing concentrations in the first 12-day samples in the 1-min and 4-min groups. Traces of Ti were found in the first few samples, but no pattern of release could be observed.

Administration, Topical↗

PubMed1991

Age-dependent mechanical properties of rat femur. Measured in vivo and in vitro.

Strain gauges were implanted on the anterior surface of the femoral diaphysis of rats aged 6, 12 or 52 weeks. Strain was recorded while the rats were running on a treadmill. The peak strain was of the same magnitude at different animal ages, although there was a somewhat lower value for 52-week-old animals. Stiffness calculated from in vivo strain measurements and from a 3-point bending test on excised femora was correlated: stiffness increased with age. Maximum bending stress increased from 6-12 weeks of age, but then there was no further increase. Ultimate load, on the contrary, increased steadily over the entire 52-week period. This indicates that higher load-bearing capacity with increased age in adult rats is due to increased dimensions of the bone rather than its material properties. The present study demonstrates that conventional in vitro measurements of mechanical properties of bone correspond to measurements of strain during physical activity, and that both are valid measurements of physical properties of bone.

Age Factors↗

PubMed1991

Effects of intramedullary reaming and nailing of rat femur. A mechanical and chemical study.

This study was undertaken to explore the association between mechanical and chemical effects of intramedullary reaming and nailing. The right femora of 80 rats were reamed and nailed with steel nails. Forty rats were evaluated from 3 days to 24 weeks postoperatively. The other 40 rats had the nail removed after 12 weeks, and they were then followed from 3 days to 24 weeks after nail extraction. Evaluation consisted of in vivo strain recording, geometric measurements, mechanical three-point bending test, and chemical analyses of hydroxyproline and calcium contents. Reaming and nailing caused immediate weakening of the bone as measured by in vitro mechanical tests, but within 3 weeks the mechanical properties were fully restored, whereas in vivo strain remained reduced throughout the experimental period in rats with nails. Removing the nail increased in vivo strain to a level close to that of the intact femur. Remodeling of the bone resulted in greater external anteroposterior diameter, cross-sectional area, area moment of inertia, and amount of hydroxyproline and calcium in the operated on femur as compared with the intact side. This indicates that the repair processes resulted in greater bone mass of the operated on femur than of the intact femur. Thus, there is evidence that nailing techniques effectively assist tissues by repair and remodeling.

Animals↗

PubMed1990

[Dentin adhesives].

Chemical adhesion of resin based restorative materials to dentin using adhesives presents a complex problem due to the different nature of polymeric materials and tooth substance. It is indicated that the problems arise mainly from properties of the filling material, eg polymerization shrinkage. Glass ionomer cements exhibit excellent clinical retention in spite of the low bonding forces found in laboratory tests.

Adhesives↗

PubMed1989

Traumatic ulcers and pain in adults during orthodontic treatment.

In the present investigation the frequency of oral ulcers and pain in 79 adults orthodontic patients was recorded. Only four of all patients had never had oral ulceration during treatment, but 83% of the patients characterized the trouble as minor. About 47% of the patients said that ulcers caused by the fixed appliance were the most annoying part of the treatment, and 38% said that activation of the appliance caused the most discomfort. In about 63% of the patients there was less pain when the treatment had lasted for some months, and in 24% there was no significant change in the discomfort. The pain following activation lasted for only 2-3 days (71%), but 20% had pain for more than 3 days, and five individuals felt pain constantly. The recurrence of aphthous ulceration (RAU) was not significantly affected during the orthodontic treatment, and in only one case was there an increase in the occurrence of herpes labialis.

Adult↗

PubMed1989

Immediate strain shielding after femoral reaming and nailing. An in vivo study in rat femora.

Following intramedullary reaming and nailing of rat femora, in vivo changes in dynamic strain were correlated with in vitro measurements of the bones. Reaming and nailing procedures were performed 2 days after implantation of unidirectional strain gauges at the anterior, mid-diaphyseal level of the femur. Structural stiffness of polyacetal nails were three times as stiff as intact bone. Reaming only decreased the median strain value by 26 percent, and this value was not reduced by insertion of polyacetal nails. Steel nailing reduced the strain by 74 percent. Tested by three-point bending, reaming increased stiffness by 5 percent at the anterior aspect. The presence of nails gave stiffness values that were 9 percent (polyacetal) and 56 percent (steel) higher than the reamed only condition. Our results indicate that steel nailing following reaming causes marked reduction in strain at the anterior, mid-diaphyseal surface, whereas reduction in strain caused by polyacetal nails is negligible.

Animals↗