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Polymerization of Resin Based Composites (RBCs) initiated by a light curing unit activating photoinitiators. Different RBCs require different light energy levels for proper curing. Manufacturers are now producing RBCs with more than one initiator and not all of these will be properly polymerised with blue LED lights. An added problem is that manufacturers do not always indicate the type of photoinitiators in their materials. This review discusses the importance of matching the spectral output of LCUs to the absorption spectra of RBCs and the consequences of spectral mismatch. Resin based composites (RBCs) were first introduced in the 1960s and with development of effective and reliable dentine bonding systems2, have been used routinely as a filling material for both anterior and posterior teeth. The early RBCs were either chemically cured two component materials or photo-initiated materials that used UV initiators in the beginning and then transitioned to visible light initiators such as camphorquinine which was introduced in 1978.3 The first report of a light curing material was of an ultraviolet (UV) cured fissure sealant. However, due to the limited penetration depth of the UV light and the potential health hazards, this system was quickly abandoned. The advancement of science yielded light curing materials which contributed to a significant clinical progress over the UV and chemically cured RBCs. Additional advancements to direct RBC restoration materials included luting agents for ceramic restorations, pit and fissure sealants and resin modified glass ionomers. Polymerization in an RBC is initiated by a light curing unit (LCU); this technology is based on the use of photoreactive systems that absorb light irradiation from the LCUs at appropriate wavelength. Then the photoinitiators contained in the RBCs, absorb the incoming photons from the LCU and the monomers in the molecular structure become excited and in that active state, there is a change from monomers into a polymer network. The success of this technology hinges on matching the spectral emission of the LCU with the requirements of the photoinitiator system to convert the monomers into a polymer network. The amount of activated photo initiator depends on the concentration of photoinitiator in the material, the number of photons to which the material is exposed and the energy of the photons (wavelength), the latter depending on the curing light.The most common photoinitiator in dental materials today is camphorquinone, which has a peak activity around 470 nanometres. The factors affecting polymerization include filler type, size and loading, the thickness and shade of the restorative material, the effectiveness of light transmission (eg. light guide tips being free from debris and scratches), exposure time, distance of the light source from the restorative material and light intensity. It is important to note that the photoinitiator activation occurs at specific wavelengths, in other words, the optimum efficiency is obtained when the peak absorptivity ...

The antero-posterior position of the mental foramen was studied in 68 Chinese and 44 British skulls of known or calculated age at death. All skulls showed low pre-mortem tooth loss and had a good occlusion. The position of the foramen was related to the body of the mandible as well as to the standing mandibular teeth using two previously published methods. There was no significant difference in the size of the Chinese and British mandibles. There was a significant difference between the two groups when measurements relating the foramen to the body of the mandible (symphysis menti) were considered, the foraminal position being more distal in the Chinese group. The modal position of the foramen in the Chinese sample was along the long axis of the second premolar, whereas in the British sample it lay between the apices of the first and second premolar. The foraminal position apparently moved distally in both groups with age and this was likely to be associated with mesial tooth drift and age-related attrition.

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Comparisons of both gingival and enamel margins within each of the groups showed no significant difference owing to configuration factor (C-factor; p > .5 in all cases, calculated with Kruskal-Wallis nonparametric analysis of variance [ANOVA]) and Dunn's multiple comparison test). All groups showed microleakage at the gingival margins irrespective of C-factor or bonding agent (box-shaped cavities, p = .8862; V-shaped cavities, p = .9623; using the ANOVA). Microleakage was not observed at all enamel margins regardless of C-factor or bonding agent, and there were no significant differences between the groups (box-shaped cavities, p = .9869; V-shaped cavities, p = .9550; using the Kruskal-Wallis nonparametric ANOVA).

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Unreacted monomers in adhesive systems may cause a reduction in material properties, an increase in the long-term instability of the restoration, and pulpal irritation. The degree of dentine demineralization, adhesive penetration, and the degree of conversion (DC) across the dentine-adhesive interface of self-etch adhesives were measured using micro-Raman spectroscopy. Two-step, self-etch AdheSE, one-step self-etch AdheSE One, and etch-and-rinse Excite (control) (Ivoclar Vivadent AG, Schaan, Liechtenstein) were studied. Nine human molars were allocated to three groups and a flat dentine surface was prepared. A smear layer was produced by grinding dentine with 600-grit silicone-carbide discs under water. After application and polymerization of the adhesive, teeth were sectioned to produce four 1-mm-thick slices per tooth for micro-Raman spectroscopy. There were statistically significant differences in the depth of dentine demineralization between all adhesives. The depth and degree of demineralization decreased in the order: Excite>AdheSE>AdheSE One. The mean +/- standard deviation (SD) values for DC within the adhesive layer were 85.2 +/- 2.9% (Excite), 81.4 +/- 4.2% (AdheSE), and 54.3 +/- 10.1% (AdheSE One), and within the hybrid layer were 55.2 +/- 22.5% (Excite), 65.1 +/- 16.9% (AdheSE), and 42.0 +/- 16.2% (AdheSE One). All systems showed a discrepancy between dentine demineralization and adhesive penetration. A significant amount of unreacted monomers were associated with all systems but particularly with the etch-and-rinse system.