The ability of thiourea to scavenge hydrogen peroxide and hydroxyl radicals during the intra-coronal bleaching of bloodstained root-filled teeth

The document attached has been archived with permission from the Australian Dental Association. An external link to the publisher’s copy is included.Background: Hydrogen peroxide, an agent used in the intra-coronal bleaching of root-filled teeth for over a century, has been shown to diffuse from the pulp chamber to the outer root surface. Furthermore, it has been demonstrated that destructive hydroxyl radicals, the by-products of the bleaching process, have been detected on the external root surface. The control of such diffusion may be of importance in minimizing the risk of invasive cervical resorption (ICR) which has been linked to intra-coronal bleaching of discoloured root-filled teeth using hydrogen peroxide. The aims of the present in vitro study are to quantify the diffusion of hydrogen peroxide and hydroxyl radicals to the outer root surface following intra-coronal bleaching, and to evaluate the ability of thiourea incorporated into the bleaching protocol to scavenge residual hydrogen peroxide and hydroxyl radicals. Methods: Thirty-five single rooted premolar teeth with intact cementum at the cemento-enamel junction were used in this project. Thirty teeth were stained with red blood cells and root-filled with gutta-percha and AH26. The five unstained teeth were root-filled and constituted a negative control (Group 1). The stained teeth were divided equally into the following experimental groups and subjected to various intra-coronal bleaching regimes: Group 2 – ‘walking bleach’ with 20μl 30 per cent w/w hydrogen peroxide; Group 3 – 20μl 30 per cent w/w hydrogen peroxide and thermocatalytically activated; Group 4 – 20μl acidified thiourea; Group 5 – 20μl acidified thiourea and 20μl 30 per cent w/w hydrogen peroxide; Group 6 – 20μl acidified thiourea and 20μl one per cent sodium hypochlorite; Group 7 – 20μl acidified thiourea, 20μl one per cent sodium hypochlorite and 20μl 30 per cent w/w hydrogen peroxide. The reaction products of the bleaching process were quantified at the outer root surface using high performance liquid chromatography and electrochemical detection (HPLC-ECD).Results: Results showed that hydrogen peroxide used alone in Groups 2 and 3 was able to be detected at the outer root surface in 100 per cent of the samples, and that the presence of the hydroxyl radical generated in both groups was detected in equal amounts (P<0.05). When thiourea was incorporated into the bleaching protocols in Groups 5–7, it was shown to scavenge both hydrogen peroxide and hydroxyl radicals to a significant degree (P<0.05). Conclusions: Acidulated thiourea is an effective scavenger of residual hydrogen peroxide and hydroxyl radicals generated during the intra-coronal bleaching of bloodstained root-filled teeth.DS Farmer, P Burcham, PD Mari

Gamma Oscillation in Schizophrenia

Dysfunctional neural circuitry has been found to be involved in abnormalities of perception and cognition in patients with schizophrenia. Gamma oscillations are essential for integrating information within neural circuits and have therefore been associated with many perceptual and cognitive processes in healthy human subjects and animals. This review presents an overview of the neural basis of gamma oscillations and the abnormalities in the GABAergic interneuronal system thought to be responsible for gamma-range deficits in schizophrenia. We also review studies of gamma activity in sensory and cognitive processes, including auditory steady state response, attention, object representation, and working memory, in animals, healthy humans and patients with schizophrenia

An examination of the language construct in NIMH's research domain criteria:Time for reconceptualization!

The National Institute of Mental Health’s Research Domain Criteria (RDoC) Initiative “calls for the development of new ways of classifying psychopathology based on dimensions of observable behavior.” As aresult of this ambitious initiative, language has been identifi d as an independent construct in the RDoC matrix. In this article, we frame language within an evolutionary and neuro- psychological context and discuss some of the limitations to the current measurements of language. Findings from genomics and the neuroimaging of performance during language tasks are dis- cussed in relation to serious mental illness and within the context of caveats regarding measuring language. Indeed, the data collec- tion and analysis methods employed to assay language have been both aided and constrained by the available technologies, methodologies, and conceptual defi Consequently, differ- ent fields of language research show inconsistent defi s of language that have become increasingly broad over time. Individ- ually, they have also shown significant improvements in conceptual resolution, aswell as inexperimental and analytic techniques. More recently, language research has embraced collaborations across disciplines, notably neuroscience, cognitive science, and computa- tional linguistics and has ultimately re-defi classical ideas of language. As we move forward, the new models of language with their remarkably multifaceted constructs force a re-examination of the NIMH RDoC conceptualization of language and thus the neuroscience and genetics underlying this concept

CAD/CAM technology and esthetic dentistry: a case report.

Advances in dental materials as well as in computer technology have made CADCAM-fabricated restorations not just possible in dentistry but plentiful. When using CADCAM systems, operators can fabricate restorations from several materials, including ceramics, metal alloys, and various composites. This case report describes the replacement of a porcelain-layered zirconia-based (coping) crown on a left lower cuspid that presented with a veneering ceramic chipping on a lithium-disilicate CADCAM-fabricated crown. It demonstrates how all-ceramic systems offer a promising alternative in the restoration of anterior teeth