Morten Berge

Corrosion of silver soldered orthodontic wires

The amounts of metals liberated from silver soldered stainless steel and cobalt-chromium orthodontic wires were measured. Measurements were taken after 3 days and 24 days immersion in 0.9% sodium chloride solution. High amounts of copper and zinc and some cadmium from the silver solder were found. The silver soldered stainless steel wire corroded more than the cobalt-chromium type, and liberated more nickel and chromium than did the cobalt-chromium wires.

Bending Strength of Intact and Repaired Denture Base Resins

Results of bending strength and deflection at fracture of intact and repaired denture base resin specimens were obtained. Both heat-cured and cold-cured resins of two different products were used. After storage in distilled water at 37 degrees C for 1 month, some of the intact heat-cured specimens were dried in air at 21 +/- 1 degree C for 24 h before testing. This induced a lowering of the bending strength. There was no difference in strength between the two products. However, the intact heat-cured specimens of SR 3/60 showed higher results of deflection at fracture than Vertex. Repaired specimens had a bending strength between 42.9% and 61.2% compared with the intact heat-cured specimens tested immediately after storage in water. The repair performed with the low-viscosity self-cured resin resulted in higher bending strength values than when using repair material with the higher initial viscosity. Drying the broken heat-cured specimens for 24 h at 21 +/- 1 degree C before the repair and painting with monomer liquid on the fractured surfaces of the heat-cured resin was without effect on the bending strength of the repaired specimens.

Liberation of copper, zinc, and cadmium from different amalgams

Release of copper, zinc, and cadmium from six different amalgams in 0.9% NaCl solution has been registered during a 4-week period. The products showed widely different corrosion behavior. A dispersion-type amalgam released the smallest amounts of copper but the largest amounts of zinc. A product containing indium had a high rate of copper dissolution. Cadmium was liberated to a great extent from a copper amalgam. The rate of corrosion varied greatly for the different products during the time of the experiment. The liberation of copper and zinc was inversely correlated.

Flexural strength of joined and intact amalgam

Flexural strength of joined and intact specimens of five different alloys were measured. The same alloys were also tested in compression. Joined specimens were also tested in compression. Joined specimens were made by condensing fresh amalgam against the ground surface of 1 week old amalgams. Joined specimens had a flexural strength between 11.5% and 51.4% compared to the intact specimens. The high copper alloys obtained the lowest values for fracture toughness and plastic strain when tested in compression. A positive correlation was shown between flexural strength of joined specimens and plastic strain and between flexural strength of intact specimens and fracture toughness.

Oral appliance treatment in moderate and severe obstructive sleep apnoea patients non-adherent to CPAP

Summary The aim of this retrospective study was to evaluate the effect of individually adjusted custom‐made mandibular advancement device/oral appliance (OA) in treatment of patients with moderate and severe obstructive sleep apnoea (OSA), who were non‐adherent to continuous positive airway pressure (CPAP) therapy. During 2007‐2013, 116 patients with moderate (n = 82) and severe (n = 34) OSA non‐adherent to CPAP treatment were referred for dental management with an individually adjusted OA at a specialist sleep clinic. Ten of the participants (8·6%) were lost to follow‐up, leaving the data set to consist of 106 patients (71 men/35 women, mean age 57 year, range 28‐90). Nocturnal respiratory polygraphic recordings were performed at baseline and follow‐up. Average time between baseline polygraphy and follow‐up was 12 months. A successful OA treatment outcome was based on polygraphy at the follow‐up and divided into three groups: 1 = AHI <5; 2 = 5 ≤ AHI <10 and >50% reduction in baseline AHI; and 3. >50% reduction in baseline AHI. If there was a ≤ 50% reduction in baseline AHI at the follow‐up, the treatment was considered as a failure. The overall treatment success rate was 75%. There was no significant difference in success rates between patients in the moderate and severe categories (69% and 77%, respectively). Low oxygen saturation (SpO2 nadir) had a high predictive value for OA treatment failure. OA treatment of patients non‐adherent to CPAP is efficient and especially promising for the severe OSA group who are at greatest risks for developing serious comorbidities, if left untreated.

A 2-year follow-up study of incisai tooth wear in dental students

This report was derived from cross-sectional and longitudinal analyses of prevalence, pattern, and severity of incisal wear in 64 dental students who had virtually complete dentitions at the first examination and unchanged dentitions at the re-examination. They were first examined in 1991 and re-examined after 24 months in 1993. The average age of the students in 1991 was 23 +/- 1.7 years. Assessment of incisal wear was made on stone casts based on silicone impression material in accordance with the Incisal wear Index (IwI). The results showed that the prevalence of incisal wear had not changed during the observation period. The severity of incisal wear for maxillary and mandibular central and lateral incisors had remained essentially the same, whereas the severity of wear of maxillary and mandibular canines had increased during the observation period. There was no statistically significant relationship between age and IwI. The wear pattern found for anterior teeth is discussed in relation to the cuspid protection and the group function theories of occlusion.

Re-examination of incisal tooth wear in children and adolescents.

The material presented in this report was derived from a longitudinal study of the development and progress of incisal tooth wear in children and adolescents. The study group was established in 1991-1992 (baseline examination) and consisted of participants between 8 and 15 years of age. They were re-examined in 1993 (interim examination) and in 1994 (final examination). In all, 77 school children (30 females and 47 males) participated in the three examinations. The timespan between baseline and interim was on average 15 months and the period between interim and final examination averaged 16 months. The total observation period was approximately 32 months. Assessments of incisal wear was made on stone casts using the incisal wear index which was shown to have good reproducibility. The results demonstrated that the prevalence and severity of incisal wear had increased significantly with age. In general the rate of incisal wear progression was higher between baseline and interim than between interim and final examination. In this respect certain differences between the tooth types seemed to exist. At baseline the relationship between age and incisal wear was positive and statistically significant for all tooth types. At the final examination the strength of this relationship had decreased for maxillary and mandibular central and lateral incisors. For canine teeth of both jaws the relationship between age and incisal wear was no longer statistically significant at the final examination.

Flexural strength of a high-temperature soldered cobalt-chromium alloy

The flexural strength of a high-temperature soldered cobalt-chromium alloy was compared with that of the intact alloy. In one test group the specimens were soldered by Vitallium welding rods and in the other group Bego cobalt-chromium solder was used. The cylindrical portion of all specimens was mounted equally in an Instron testing machine. No statistically significant differences were found in flexural strength between the groups.

Fixed restorations produced for recipients of dental prosthodontic treatment: A comparison between general dental practice and a dental school

Fixed prosthodontic work ordered by general dental practitioners was examined through registrations made in commercial dental laboratories. A comparison was made with similar data from student files on fixed prosthodontic treatment at the University Clinic in Bergen, Norway, which is located in the same geographic area. The results indicated that the distributional pattern of fixed restorations within the dentition was much the same in the individuals attending the general dental practitioners as in those treated at the dental school. While the practicing dentists preferred metal-ceramics in most cases, most of the restorations inserted at the dental school were based on the metal-resin technique.

Porosity of resin veneer materials

The present investigation has studied the effects of different types of resins and different processing and curing methods on the number and size of pores occurring in resin facing materials. The mean number of pores per square millimeter varied between 0.5 and 4. The highest numbers occurred in unfilled heat-polymerized acrylic resin and in light-activated resin, whereas the lowest numbers were found in heat-polymerized micro-filled resin. Specimens processed in accordance with the free technique and cured under pressure consistently obtained lower numbers of pores than the corresponding specimens processed in a flask. Most of the pores were less than 50 micron diameter in all test groups. From a clinical point of view, a dense resin with a limited content of pores may give the most favorable results in terms of mechanical, esthetic, and hygienic properties of the veneer.