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Biomedical subjects

Timo Närhi

Publications and source records attributed to Timo Närhi.

9 recordsLinked to original sources
PubMed2006

Specialisation and specialist education in prosthetic dentistry in Europe.

This presentation reports on the results of a meeting of prosthodontists from selected European countries. The aim of the meeting was to analyse and promote specialisation and specialist education in Prosthetic Dentistry in Europe. Representatives for Europe were selected from the European Prosthodontic Association (EPA) board, the Education and Research Committee of International College of Prosthodontists (ICP), countries with a legally recognised speciality, countries without a recognised speciality but organised training programmes and countries with neither of these situations. Data about specialisation and specialist training in Prosthodontics in Europe was scrutinised and discussed. The programmes for countries with specialist training had relatively similar content, mostly of three years duration. There was strong agreement that a recognised speciality raises the level of care within the discipline for both specialists and non-specialists. In several of the countries where a speciality had been introduced it had been initiated by pressure from public health planning authorities. The conclusions are that from a professional viewpoint an advancement of the speciality over Europe would develop the discipline, improve oral health planning and quality of patient care. A working group for harmonisation was recommended.

Education, Dental, Graduate↗
PubMed2005

Compound changes and tooth mineralization effects of glass ionomer cements containing bioactive glass (S53P4), an in vivo study.

In this study, modifications of glass ionomer cements (GICs) were made by adding bioactive glass (BAG) to GIC to obtain bioactive restorative materials. This study used SEM, EDS and visual analysis to examine the bioactivity and the ability of the study materials to mineralize dentin. Conventional cure and resin-modified light-curing GIC were used. The materials consisted of powder and liquid. Three experimental materials were made by mixing 10-30 wt% of BAG powder with GIC powders. Commercially available GIC without BAG were used as controls. Class III restorations were made in altogether 62 intact beagle dog teeth, and the operation was performed under general anesthesia. The restorations were followed clinically for 1, 3 or 6 weeks. Resin-modified GIC containing BAG showed uniform CaP surface formation on the restorations. Mineral depositions in the close vicinity of the restoration-dentin interface and in deeper parts of dentin tubules were also noticed in resin-modified GIC containing BAG particles. It can be concluded that resin-modified GIC containing BAG have good potential in clinical applications where enhanced mineralization is expected.

Analysis of Variance↗
PubMed2005

Compressive strength and surface characterization of glass ionomer cements modified by particles of bioactive glass.

OBJECTIVES: The aim of this study was to determine compressive strength, Young's modulus of elasticity, and Vickers' surface hardness, of conventional cure and resin-modified glass ionomer cements after the addition of bioactive glass (BAG) particles into the cements. METHODS: Experimental glass ionomer cement (GIC)-BAG materials were made by mixing 10- or 30-wt% of BAG particles with conventional cure and resin-modified GIC powders. Materials were processed into cylindrical specimens and immersed in water for 1, 3, 7, 14, 30 and 180 days before mechanical tests. SEM and EDS analysis was used to characterize the changes in surface topography and the main elemental composition. RESULTS: The compressive strength of the test specimens decreased with the increasing amount of BAG. The compressive strength of resin-modified GIC increased during the immersion, but remained at a lower level than that of the other materials. The conventional cure GIC-based materials had on average 55% higher surface microhardness than the resin-modified materials. In the elemental composition, more Ca was detected in the BAG-containing materials than in the pure GICs. The amount of F was significantly higher (p < 0.001) on all resin-modified materials, being highest on resin-modified GIC with 30-wt% of BAG after 180d of immersion. SIGNIFICANCE: The addition of BAG to GIC compromises the mechanical properties of the materials to some extent. Thus, their clinical use ought to be restricted to applications where their bioactivity can be beneficial, such as root surface fillings and liners in dentistry, and where high compressive strength is not necessarily needed.

Analysis of Variance↗
PubMed2004

Use of sol-gel-derived titania coating for direct soft tissue attachment.

A firm bond between an implant and the surrounding soft tissue is important for the performance of many medical devices (e.g., stents, canyls, and dental implants). In this study, the performance of nonresorbable and reactive sol-gel-derived nano-porous titania (TiO(2)) coatings in a soft tissue environment was investigated. A direct attachment between the soft tissue and the sol-gel-derived titania coatings was found in vivo after 2 days of implantation, whereas the titanium control implants showed no evidence of soft tissue attachment. The coated implants were in immediate contact with the connective tissue, whereas the titanium controls formed a gap and a fibrous capsule on the implant-tissue interface. The good soft tissue attachment of titania coatings may result from their ability to initiate calcium phosphate nucleation and growth on their surfaces (although the formation of poorly crystalline bonelike apatite does not occur). Thus, the formation of a bonelike CaP layer is not crucial for their integration in soft tissue. The formation of bonelike apatite was hindered by the adsorption of proteins onto the initially formed amorphous calcium phosphate growth centers, thus preventing the dissolution/reprecipitation processes required for the formation of poorly crystalline bonelike apatite. These findings might open novel application areas for sol-gel-derived titania-based coatings.

Adhesiveness↗
PubMed2003

Antimicrobial effects of glass ionomer cements containing bioactive glass (S53P4) on oral micro-organisms in vitro.

The antimicrobial effects of two glass-ionomer cements (GICs), GC Fuji II and Fuji II LC, mixed with different amounts (0 wt%, 10 wt% and 30 wt% of the total powder weight) of bioactive glass (BAG), S53P4, on Streptococcus mutans and Candida albicans were studied in vitro. The growth inhibition was tested using agar diffusion. The materials were also studied in a liquid media. The effect of the material extracts on acid production was studied using cell suspensions. The antimicrobial activity of the materials was examined by incubating the cell suspensions with the material powder. In the agar diffusion test, only the GICs containing 30 wt% BAG inhibited the growth of S. mutans. When the materials were tested in culture medium, no inhibitory effects on S. mutans were detected. The only materials to inhibit acid production of S. mutans were the GIC extracts without added BAG. Furthermore, they also had antibacterial activity against S. mutans when tested as powders. We found very few effects of the tested materials on C. albicans. The only material with an antimicrobial effect on C. albicans was BAG when incubated in a suspension with C. albicans. This is the first time that this effect has been demonstrated for C. albicans. By adding BAG to GICs the structure of the material becomes more brittle than the structure of GICs without BAG. Thus, in addition to the composition of the tested materials, their structure may also have influenced the results. In summary, commercially available GICs and GIC disks containing 30 wt% of BAG exerted antibacterial effects on S. mutans. BAG exerted antimicrobial effects on both S. mutans and C. albicans.

Acids↗
PubMed2002

In vitro evaluation of poly(epsilon-caprolactone-co-DL-lactide)/ bioactive glass composites.

In vitro bioactivity of composites of poly(epsilon-caprolactone-co-DL-lactide) P(CL/DL-LA) containing different amounts (40, 60 and 70 wt%) of bioactive glass, S53P4, was evaluated. Two ranges of granule size of bioactive glass (< 45 microm and 90-315 microm) were blended with P(CL/DL-LA) copolymer in a batch mixer. The composites were characterised by dynamic mechanical thermal analysis. The molecular weight and the melting temperature of the copolymer matrix were adjusted to enable the application of the composite material by injection below 50 degrees C. Formation of Ca-P deposition on the surface of the composites after dissolution in simulated body fluid at 37 degrees C was recorded by scanning electron microscopy. Degradation of the composite material was measured by water absorption and changes in the average molecular weights as a function of the dissolution time. In vitro bioactivity was found to be dependent on the weight fraction and granule size range of the bioactive glass used. The presence of the bioactive filler also accelerated the degradation compared with the neat polymer sample.

Biocompatible Materials↗
PubMedDate not supplied

A 5-year follow-up of signs and symptoms of TMD and radiographic findings in the elderly.

PURPOSE: The aim was to clarify the associations among subjective symptoms, clinical signs of temporomandibular disorders (TMD), and radiographic findings in the mandibular condyles of elderly people during a 5-year follow-up. MATERIALS AND METHODS: As part of a comprehensive medical survey of a random sample born in 1904, 1909, and 1914 (Helsinki Aging Study), 364 subjects living in Helsinki participated in the dental part of the examination during 1990 and 1991; after 5 years, 103 of these were reexamined. Comprehensive data on TMD were available for 94 subjects, and radiographic data were available for 88. TMD were assessed by Helkimo's anamnestic and clinical indices, and radiographic status was assessed by panoramic radiographs. RESULTS: During the 5-year follow-up, reported anamnestic symptoms of TMD for men changed little (9%); among women, the change from baseline was 42%. When the unchanged indices were compared, the gender difference was obvious. At baseline, 5% of the women, but no men, had severe signs (clinical index III) of TMD. At the end of follow-up, none showed severe signs. Comparison of radiographic findings between baseline and follow-up showed no differences, nor did differences appear in associations between radiographic findings and anamnestic or clinical indices. CONCLUSION: During the 5-year follow-up, signs and symptoms of TMD in these elderly individuals became milder or vanished. The radiographic status of the condyles remained stable, and no association appeared between radiographic findings and signs and symptoms of TMD.

Aged↗
PubMedDate not supplied

A survey of the use of mandibular implant overdentures in 10 countries.

PURPOSE: This preliminary international survey compared provision of implant-retained overdentures to fixed implant-supported prostheses for edentulous mandibles. MATERIALS AND METHODS: Questionnaires based on a 2001 Swedish study were sent to prosthodontists and specialist clinics in nine additional countries. RESULTS: Response rate varied from 53% to 100% in 10 national surveys and should allow careful comparison of results. The relationship between implant overdentures and fixed implant-supported prostheses in treatment of edentulous mandibles varied much; in Sweden, the proportion of overdentures was 12%, whereas it was 93% in The Netherlands. In all countries, the most common reason for choice of the overdenture was reduced cost. In all but two countries, the majority of respondents thought that patients with implant overdentures were equally or more satisfied with overdentures as those with fixed implant-supported prostheses. CONCLUSION: There were great differences among the 10 countries in choice of implant treatment of the edentulous mandible. The relative proportion of mandibular overdentures to fixed prostheses was low in Sweden and Greece and varied from one to two thirds in the other countries, except The Netherlands.

Canada↗