The Colony-Forming Unit (CFU) method can be used for identification of microorganisms and for testing the effect of antimicrobial substances and techniques. It is a sensitive and widely accepted method within microbiology. In this method, the number of living cells (cells able to reproduce) present in a suspension is counted on a nutrient agar surface.

The deterioration in dental health that occurs when elderly people move into institutional care can be dramatic. Good, life-long habits of dental hygiene are broken, either because the move is associated with significant new health problems, or because daily routines have been upset. Regardless of the reason, rapid development of caries and other dental problems are observed in institutionalized patients.

Dental materials are subject repeatedly to masticatory forces, both directly on an occlusal surface, and indirectly through interactions with an abutment or via a connecting unit.

Glass-ionomer cements (GIC) adheres to tooth substance but the strength of the GIC is lower than other filling materials. Even though traditional GIC products have been used for Class II restorations in pediatric patients, the longevity of the restoration is often regarded as inferior to other materials.

Although questions have been raised regarding reproducibility and animal welfare, the rabbit Draize eye test has remained an accepted method to evaluate skin irritation for many years. For the last decade, in vitro 3D skin models are developed to predict and classify skin irritation potential of chemicals. Several methods have been validated by ECVAM (European Centre for the Validation of Alternative Methods) and achieved regulatory acceptance internationally for replacement of the rabbit Draize test. Among the approved skin systems is the Epiderm™ system from Matek.

Placing restorations due to dental caries is still a commonly performed treatment by dental practitioners in Norway. The aim of the thesis was to explore dentists’ treatment decisions on approximal caries and to assess the longevity of approximal restorations in posterior teeth and reasons for their failure. The research employed a questionnaire and included a practice-based study.

One of the newest additions to NIOM’s instrumentation is equipment for optical radiation measurements.

Up to 60% of the patients who underwent tooth bleaching reported one or more side effects within 14 days after treatment. For some patients the pain was persisting for a year.

The ability to prepare experimental materials is mandatory for a research and test institute of dental materials. Using experimental materials assures that all the components of the material will be carefully controlled and experiments can be set up with variations only in the desired substance(s).

NIOM is a unique independent institution for dental materials testing and research which promotes patient safety through its work, the Control Committee of the Nordic Council concluded after having inspected NIOM in 2013. The Control Committee’s main task is to exercise control over activities financed by joint Nordic funds as well as to ensure that resolutions are implemented.

NIOM scientists were invited to the national dental conventions in Sweden and Norway this autumn. You can here read the conclusions of the lectures given on bulk-fill materials, nano-materials, safety of tooth bleaching, and quality of custom-made dental restorations imported from overseas and made at national laboratories.

A possible mechanism for the toxicity of methacrylate monomers is elucidated in a recent publication from NIOM. The resin matrix of dental restorative materials consists of combinations of methacrylate monomers like bisphenol A-glycidyl dimethacrylate (BisGMA), triethylene glycol dimethacrylate (TEGDMA) and glycerol dimethacrylate (GDMA) in composite fillings, while 2-hydroxyethyl methacrylate (HEMA) is a major constituent in most dental adhesives.

Flow cytometry is a technology that simultaneously measures and then analyzes multiple characteristics of single particles, usually cells, as they flow in a fluid stream through a beam of light.

Ageing of zirconia (zirconium dioxide) based materials is associated with surface structural changes caused by humidity at elevated temperatures. Tetragonal phase is the stable structure of zirconia at the sintering temperature. Yttria, magnesia or other oxides are added to zirconia materials to maintain this favourable crystalline form also at room temperature. With variable temperatures in the mouth, catalyzed by humidity, the structure at the surface will slowly transform to a monocline phase. A tetragonal to monocline phase transformation is assumed to reduce the bond strength between zirconia cores and veneering ceramics. This transformation is also regarded as detrimental to monolithic zirconia prostheses or implants due to the volumetric expansion of the crystals at the surface.

HET-CAM test (hen’s egg-chorioallantoic membrane test) is a test used to determine the irritation potential of substances and is an alternative test to the Draize Rabbit Eye Test. In the test, incubated hen’s eggs are opened carefully on day 9 and the chorioallantoic membrane (CAM) is exposed.

A laboratory investigation indicated that the cell-damaging potential seemed to match the degree of leaching of particular polymer-based endodontic materials. The methacrylate-based polymeric root canal sealing materials were responsible for this effect: Even the cured materials leached components and caused cells of oral origin to die when kept in contact with material extracts. The severity of cell death increased with the time that the material was available in the cell culture.

Evaluation of the biocompatibility of dental materials may be a complex task. Chemical analysis using in vitro investigations may be helpful to elucidate the biocompatibility of the materials through investigation and control of eluted substances. The aim of such investigations is to increase patient safety.

Fractographic analyses of all-ceramic crowns that have failed during clinical use show different fracture features compared with those commonly observed in laboratory studies. Until now, in vitro tests which have been published usually show contact damage induced at the loading point – occlusally for molars and premolars and lingually for incisors. Clinically failed crowns, on the other hand, seem to fracture from cracks initiated in the cervical margin in the core material, usually in the approximal region.

Dental treatment may expose both the patient and the dental professionals to 2-hydroxyethyl methacrylate (HEMA). The compound is a monomer commonly used in resin-based dental materials. Incomplete polymerization of dental resin components can result in release of monomer to the oral cavity.

Adhesive dentistry is based upon a durable bond between the restoration and the dentin. However, loss of bond strength between resin and dentin with time represents a challenge to modern restorative dentistry.

Monomers from composite fillings may impair the immune response of macrophages.