Helene M Tvinnereim

Publications (5)6.39 Total impact

• Article: Lead levels in primary teeth in children from urban and rural areas in Ethiopia.

  Helene M Tvinnereim, Wondwossen Fantaye, Rolf Isrenn, Kjell Bjorvatn, Zenebe Melaku, Redda Teklehaimanot
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  ABSTRACT: Lead (Pb) is one of the most important and widely distributed pollutants in the environment. Lead concentration in human primary teeth reflects children's exposure to the metal during early life. OBJECTIVE.: In this study we wanted to get preliminary information of the level of lead exposure in Ethiopian children in rural as well as urban areas. Primary incisors, exfoliated 1998-2000, were collected from Addis Ababa, the capital, and two rural villages in the Rift Valley. The teeth were analyzed for lead concentrations by graphite furnace atomic absorption Spectrophotometry. Very high lead concentrations were not found. However, teeth from Addis Ababa had statistically significant higher lead concentrations than teeth from the Rift Valley. Teeth from both villages showed very low Pb-concentrations, but one village (Village A) had significantly higher concentrations than the other (Village K). The living conditions of the two villages were similar, the main diference being the fluoride content of the drinking water. The village with the lowest tooth-lead had the highest fluoride concentration. Our findings indicate that child lead exposure in Ethiopia is relatively low, especially in the rural populations.
  Ethiopian medical journal 01/2011; 49(1):61-6.
• Article: Qualitative and quantitative fracture analyses of high-strength ceramics.

  Marit Øilo, Helene M Tvinnereim, Nils R Gjerdet
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  ABSTRACT: The aims of this study were to assess the applicability and repeatability of qualitative and quantitative analyses of the fracture patterns of four different high-strength ceramics. Ten bar-shaped specimens of four high-strength ceramics with different material composition and fabrication methods had been fractured by three-point bending in water (n = 40). Commonly used fractographic patterns for brittle materials, such as mirror and mist, were used to characterize and quantify the fractured surfaces of these specimens. The analyses were performed twice, on separate occasions, by the same operator. Assessment of the association between fractographic patterns and fracture stress was carried out, and repeatability assessments of the measurements were performed. The fracture initiator site and the common fractographic markers surrounding this site were found in all specimens. Statistically significant correlations were found between certain fracture patterns and stress at fracture. The repeatability of the measurements of the different fractographic patterns varied among the materials. Fracture analyses seem applicable as a tool to determine the fracture initiation site and to estimate the force vectors involved in the fracture of dental high-strength ceramics.
  European Journal Of Oral Sciences 05/2009; 117(2):187-93. · 1.88 Impact Factor
• Article: The firing procedure influences properties of a zirconia core ceramic.

  Marit Oilo, Nils Roar Gjerdet, Helene M Tvinnereim
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  ABSTRACT: High-strength ceramics for dental restoration are used as an understructure (core) that subsequently is covered by veneering ceramic. The veneering process involves a firing procedure at high temperatures at least once, usually two to five times. The aim of this study was to investigate whether these firing procedures affect the mechanical properties of a zirconia ceramic. Thirty-three specimens of an industrially sintered yttria-stabilized zirconia ceramic (DC Zircon, DCS Dental AG, Allschwil, Switzerland) were cut into bars (1.2mmx4mmx20mm). One set of specimens (n=13) remained untreated (controls). Another set of specimens (n=10) was heat-treated once, corresponding to the first step of the veneering process. The third set of specimens (n=10) was heat-treated five times to mimic the full veneering process. Flexural strength, microhardness, dimensions and surface roughness were measured. The fracture patterns were assessed by light microscopy. The untreated specimens showed a statistically significant higher flexural strength (20%) and microhardness (9%) than both of the test groups (p< or =0.001). No significant differences were found for fracture patterns, dimensions or surface roughness. The heat treatment associated with the veneering procedure on a zirconia core material reduced the flexural strength of the core after the first firing. Subsequent firings were not detrimental to the properties measured.
  Dental Materials 05/2008; 24(4):471-5. · 3.13 Impact Factor
• Article: Dental technicians' experiences with all-ceramic extra-coronal restorations.

  Marit øilo, Gunhild V Strand, Helene M Tvinnereim
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  ABSTRACT: The aim of this study was to identify the dental technicians' experiences with extra-coronal all-ceramic restorations. A questionnaire was mailed to all laboratories registered in The Norwegian Association of Dental Laboratory Owners (n=186). The response was 149 (80%). All-ceramic restorations were produced by 93 (62%) of the responding laboratories. A few of these (1 7%) produced the majority (67%) of the restorations. The dental technicians reported low rates of remakes (median 2%) for all-ceramic restorations. The low production and the limited number of laboratories that perform this work show that there is room for extended training and more expertise in this field.
  The European journal of prosthodontics and restorative dentistry 01/2007; 14(4):174-8.
• Article: Alumina additions may improve the damage tolerance of soft machined zirconia-based ceramics.

  Marit Oilo, Helene M Tvinnereim, Nils Roar Gjerdet
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  ABSTRACT: The aim of this study was to evaluate the damage tolerance of different zirconia-based materials. Bars of one hard machined and one soft machined dental zirconia and an experimental 95% zirconia 5% alumina ceramic were subjected to 100,000 stress cycles (n = 10), indented to provoke cracks on the tensile stress side (n = 10), and left untreated as controls (n = 10). The experimental material demonstrated a higher relative damage tolerance, with a 40% reduction compared to 68% for the hard machined zirconia and 84% for the soft machined zirconia.
  The International journal of prosthodontics 24(2):172-4. · 1.38 Impact Factor