Light-cured Composites Research Articles

Temperature rises produced by light sources and composites during curing.

A differential thermal analyser has been modified and a technique developed to enable the temperature rises which occur during the setting of visible light-cured composites to be measured. Two factors are responsible for this rise: the exothermic nature of the reaction in the material, and light used to initiate the cure which is transmitted through the composite. Both have been measured for a particular combination of one light source and one composite. The increase produced by the material is comparable to that in two paste autopolymerising systems as they set, however this is all but eclipsed by heat from the light source. The rise produced by the light increases with increasing exposure time and decreasing composite thickness, to reach up to 21.4°C for the selected combination of composite and light unit (though this rise may be reduced in vivo by other factors). The modified DTA and technique are suitable for the measurement of temperature rises (of which that from the light is of prime importance) together with corresponding times. However, whilst it is possible to obtain the heat of reaction for the composite the dominance of heat from the light source reduces the accuracy of this measurement and an alternative approach should be considered for heats of reaction.

Sequentially light-cured composites: Strength of bond between layers

Sequentially light-cured composites: Strength of bond between layers

The use of light-cured composites to cement acid-etched fixed partial dentures

The use of light-cured composites to cement acid-etched fixed partial dentures

Interface strength of incremental placement of visible light-cured composites

The strength of bond at the interface was determined when a visible light-cured composite resin is immediately added to a previously cured surface. In general, small particle composites (Aurafill excepted) tend to lose a small amount of strength at the interface, whereas the microfilled and hybrid composites do not.

Biocompatibility test of light-cured composites in vitro.

The in vitro cytctoxicity to HeLa S3 cells of set specimens of five commercially available light-cured composites was examined by the cell colony-forming method for 6 weeks. Both visible and ultraviolet light-cured composites showed moderate to strong cytotoxicity in the early stage of the experiment, followed by rapid disappearance of cytotoxicity. The light-cured composites showed in vitro biological behaviors similar to those of conventional composites, MFR and composites for core use.

Visible light-cured composites and activating units

In summary, visible light-activated composites offer better regulation of working time. Their composition differs from chemically activated composites only in the initiators and activators. The physical and mechanical properties of adequately polymerized photoactivated composites are similar to chemically activated composites. Depth of cure evaluations of the photoactivated composites are dependent on many factors, both experimental and inherent. There is currently no consensus on depth of cure values and evaluation methods. It is suggested that, if necessary, visible light-activated composites should be placed and polymerized in about 2-mm increments. It is prudent to use a longer exposure time. Exposure of visible light composites to dental operatory lights or strong ambient lighting (or both) during restorative procedures should be minimized to avoid premature polymerization. There are differences in design, spectral distribution, and radiation intensity of photoactivating light units. No definitive information is currently available on the effectiveness and optimal conditions for use of different light/composite combinations. Little information is currently available on the bioeffect of visible light radiation on human optical systems and oral tissue. At the present time there are reports of afterimages but no long-lasting bioeffects. It is strongly recommended that precautions should be taken in the care, use, and operation of photoactivating light units. Protective filter glasses should be used.

Build-up and repair of light-cured composites: bond strength.

Interfacial bond strengths of light-activated composites were measured as a function of age using a transverse strength test. Bond strength between layers decreased with the age of the initial layer and reflected the setting curves of the composites. The highly-filled composites exhibited the greatest bond strengths. Uncut surfaces provided a better substrate for bonding than did ground surfaces. Use of a bonding agent on both uncut and ground surfaces improved bond strengths. Mean repair strengths of light-activated composites were similar to those of self-curing composites. Composites with ground surfaces aged for one wk had mean repair strengths 27% of the cohesive strength without bonding agent and 48% with bonding agent.

A two-year visible evaluation of a visible light-cured composite : WILSON N. H. F. and SMITH G. A. J. Dent.12 (1984) 62–70

A two-year visible evaluation of a visible light-cured composite : WILSON N. H. F. and SMITH G. A. J. Dent.12 (1984) 62–70

A two-year evaluation of a visible light-cured composite

The 9-month, 1-year and 2-year results of a comparative trial demonstrate differences in the clinical performance of restorations of a visible light-cured and a two-paste composite restorative. While the functional characteristics of the restorations of both the materials investigated generally tended to deteriorate during the two-year period of the trial, significantly larger numbers of the restorations of the visible light-cured restorative deteriorated in terms of colour match and cavomarginal discolouration. The surface finish of the restorations of the visible light-cured restorative was considered to be superior to that found on the restorations of the two-paste system. Possible reasons for the differences in the performance of the restorations of the two materials investigated are discussed. It is concluded that neither of the materials investigated can be considered to be ideal restoratives for anterior teeth.

The surface finish of a visible light-cured composite

Scanning electron microscopy has been used to assess and compare the quality of the surfaces of 50 restorations of two commercially available composite restorative materials — one a visible light-cured system (Fotofil) and the other a two paste system (Adaptic). The effects of six different finishing techniques have been investigated. For the restorations of both types of composite resin the most satisfactory finish was obtained with a series of finishing discs (Soflex). The quality of the surface finish achieved on the restorations of the visible light-cured composite was superior to that found in the comparable restorations of the two paste system. The large size and hardness of the filler particles used in the two paste system and the inclusion of air during the mixing of this material are probably responsible for its relatively poor performance.

In vitro Wear of Microfilled and Visible Light-cured Composites

Wear of microfilled composites, a visible light-cured composite, and a conventional composite were characterized by two-body abrasion and single-pass sliding. There were differences in abrasion rates among the materials. Tangential forces, wear track widths, and surface failure modes were different among materials. Wear characteristics are combinations of these properties.