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SUMMARYThis study investigated the effects of an at-home bleaching gel containing 15% carbamide peroxide on the susceptibility of tooth-colored restorative materials to different staining solutions. The tooth-colored restoratives used in this study were a nano resin composite (Filtek Z350), a packable resin composite (Filtek P60), a polyacid-modified composite (Dyract AP) and a glassionomer cement (Ketac Molar Easymix). Each material was equally divided into two groups (n=34): the bleaching group and the control group. This study included two treatment segments. In the first part (days 1-14), the specimens of the bleaching group were bleached with 15% carbamide peroxide gels for eight hours daily, while the specimens in the control group were stored in deionized water. Subsequently, four specimens from each group were randomly selected for observation under an environmental scanning electron microscope. In the second part (days 15-42), the samples were not bleached. Instead, they were stored in five different kinds of solutions. Color measurements for each sample were taken at six different time periods using a spectrophotometer. The data was then analyzed using SPSS statistical software. After two- The staining susceptibility of esthetic restorative materials is significantly affected by the use of 15% carbamide peroxide. The effects of bleaching on the surface morphology and color of restorative materials are material dependent. INTRODUCTIONColor stability is considered an important factor in the success of an esthetic restoration.1-2 In the literature, color stability has been defined as the ability of a material to retain its color over a period of time and in a specified environment.2 To maintain excellent esthetic properties, tooth-colored restorative materials should have good color stability. It has been shown that both extrinsic and intrinsic factors contribute to color changes of restorative materials. Intrinsic factors influencing color changes involve chemical changes of the materials. The causes for such chemical discoloration have been identified as the oxidation of monomer or catalysts, exposure to various energy sources and immersion in water for a long period.3-6 Extrinsic factors influencing color changes include staining by adsorption or absorption of colorants, a result of contamination from exogenous sources, such as coffee, tea, other stain-producing beverages and colored solutions. [7][8][9] In recent years, many tooth-colored restorative materials have been introduced into the market. The staining susceptibility of these materials has been widely investigated.

©Operative Dentistry, 2010, 35-6, 672-681 M Hussain • Y Wang Clinical RelevanceThe bonding strength of resin composite to bleached enamel can be enhanced by increasing the light exposure time of light-emitting diode units if bonding is delayed for 24 hours. SUMMARYThis study evaluated the effect of prolonged light-curing time using a light-emitting diode unit (LED) on the shear bond strength of a resin composite to enamel immediately after bleaching. The enamel surfaces of human molars were divided into four groups: one control and three bleaching groups. One bleaching group (CP) was exposed to a 10% carbamide peroxide bleaching agent and bonded after 24 hours. The other two bleaching groups (HP) were bleached with a 38% hydrogen peroxide bleaching agent, then bonded either within one hour (HPA) or after 24 hours (HPB). All groups were subdivided into two subgroups and cured for two different times (20 or 40 seconds) with an LED unit. Shear bond strength (SBS) was tested with a universal-testing machine and the data were analyzed by ANOVA and post-hoc tests. Scanning electron micrographs of representative specimens were taken. A significant difference was seen between the control and HPA groups for both curing times (p=0.000). However, neither the CP nor HPB groups showed any significant differences compared with the control groups (p>0.05). Twoway ANOVA showed that a significant effect of the curing time factor was recorded for all groups (p=0.000). Prolonged curing time, using an LED unit with a light intensity of 500 mW/cm 2 , increased resin-enamel bonding strengths for the control and bleached groups when bonding was performed after 24 hours of immersion in deionized water. However, the SBS was still compromised when bonding was performed immediately to enamel bleached with 38% HP.

Coronectomy is a widely-accepted technique available for the treatment of impacted wisdom teeth. The fundamental principle is to prevent trauma to the inferior dental nerve (IDN). Many publications have demonstrated its positive outcomes but there is no literature available regarding coronectomy of deciduous teeth. This case report highlights the complex approach to managing a severely infraoccluded 85 in the mixed dentition of a 10-year-old female. The report demonstrates and discusses the combined orthodontic and oral surgical approach to prevent damage to the IDN and to allow space for orthodontic movement. This case demonstrates how nerve sparing techniques in the mixed dentition are achievable.Clinical relevance statement When managing severely infraoccluded and impacted deciduous second molars, clinicians must be aware that the option of a coronectomy should be considered and may be the difference between sparing the nerve or causing permanent injury.Objective The reader should understand that coronectomy is a suitable treatment option in managing impacted deciduous teeth.