Degradation effects of dietary solvents on microhardness and inorganic elements of computer-aided design/computer-aided manufacturing dental composites

Abstract Background Computer-aided design/computer-aided manufacturing (CAD/CAM) dental composites were introduced with superior mechanical properties than conventional dental composites. However, little is known on effects of dietary solvents on microhardness or inorganic elemental composition of CAD/CAM composites. Objectives The objectives of this study were to evaluate the degradation effects of each dietary solvent on the microhardness of the different CAD/CAM dental composites and to observe the degradation effects of dietary solvent on the inorganic elements of the dental composites investigated. Methods Fifty specimens with dimensions 12 mm x 14 mm x 1.5 mm were prepared for direct composite (Filtek Z350 XT [FZ]), indirect composite (Shofu Ceramage [CM]), and three CAD/CAM composites (Lava Ultimate [LU], Cerasmart [CS], and Vita Enamic [VE]). The specimens were randomly divided into 5 groups (n = 10) and conditioned for 1-week at 37°C in the following: air (control), distilled water, 0.02 N citric acid, 0.02 N lactic acid and 50% ethanol-water solution. Subsequently, the specimens were subjected to microhardness test (KHN) using Knoop hardness indenter. Air (control) and representative postconditioning specimens with the lowest mean KHN value for each material were analyzed using energy dispersive X-ray spectroscopy (EDX). Statistical analysis was done using one-way ANOVA and post hoc Bonferroni test at a significance level of p = 0.05. Results Mean KHN values ranged from 39.7 ± 2.7 kg/mm2 for FZ conditioned in 50% ethanol-water solution to 79.2 ± 3.4 kg/mm2 for VE conditioned in air (control). With exception to LU, significant differences were observed between materials and dietary solvents for other dental composites investigated. EDX showed stable peaks of the inorganic elements between air (control) and representative postconditioning specimens. Conclusions The microhardness of dental composites was significantly affected by dietary solvents, except for one CAD/CAM composite [LU]. However, no changes were observed in the inorganic elemental composition of dental composites between air (control) and 1-week postconditioning

Natural radioactivity levels in commercialized bottled drinking water and their radiological quality assessment

This work presents radiological data on most commonly sold bottled water brands in the urban areas of Bangladesh. A significant fragment of the population use bottled water as their source of daily water intake. It is known from the literature that some varieties of bottled waters contain natural radionuclides in higher concentration than the traditional municipal tap water. In this study, concentrations of naturally occurring radioactive materials, particularly 226Ra, 228Ra, and 40K, and its annual effective dose with its stochastic effects were determined in available brands of bottled mineral water manufactured in Bangladesh. The measurement was performed by gamma-ray spectroscopy using a hyper-pure germanium detector. The activity concentration of the radiologically important nuclides 226Ra and 228Ra were found within the permissible limits of 1 and 0.1 Bq l−1, respectively, recommended by World Health Organization (WHO) in almost all samples. The annual effective doses caused by natural radioactivity of 228Ra for the infants (0–1 year) and adolescent (12–17 year) groups exceeded the recommended WHO guideline level of 0.1 mSv y−1 for drinking water in most of the cases. Particularly for those age groups, the estimated doses are extremely high. In general, the carcinogenic risk due to natural radioactive doses for all bottled water samples were found below the acceptable limit of 10−3

Assessment of Natural Radioactivity Levels and Potential Radiological Risks of Common Building Materials Used in Bangladeshi Dwellings.

The concentrations of primordial radionuclides (226Ra, 232Th and 40K) in commonly used building materials (brick, cement and sand), the raw materials of cement and the by-products of coal-fired power plants (fly ash) collected from various manufacturers and suppliers in Bangladesh were determined via gamma-ray spectrometry using an HPGe detector. The results showed that the mean concentrations of 226Ra, 232Th and 40K in all studied samples slightly exceeded the typical world average values of 50 Bq kg(-1), 50 Bq kg(-1) and 500 Bq kg(-1), respectively. The activity concentrations (especially 226Ra) of fly-ash-containing cement in this study were found to be higher than those of fly-ash-free cement. To evaluate the potential radiological risk to individuals associated with these building materials, various radiological hazard indicators were calculated. The radium equivalent activity values for all samples were found to be lower than the recommended limit for building materials of 370 Bq kg(-1), with the exception of the fly ash. For most samples, the values of the alpha index and the radiological hazard (external and internal) indices were found to be within the safe limit of 1. The mean indoor absorbed dose rate was observed to be higher than the population-weighted world average of 84 nGy h(-1), and the corresponding annual effective dose for most samples fell below the recommended upper dose limit of 1 mSv y(-1). For all investigated materials, the values of the gamma index were found to be greater than 0.5 but less than 1, indicating that the gamma dose contribution from the studied building materials exceeds the exemption dose criterion of 0.3 mSv y(-1) but complies with the upper dose principle of 1 mSv y(-1)

Resuming clinical teaching in the era of COVID-19 : experiences and protocols from a dental school in Malaysia

The rapid spread of the global pandemic COVID-19 had challenged the Malaysian Healthcare and Education Systems. Teaching and learning at dental schools across the country were drastically changed to online approach as the nation enforced Movement Control Order (MCO). However, translation of psychomotor skills still require hands-on approach to produce competent dentists upon graduation, but most dental schools were not prepared for the prevention of COVID-19 transmission that require more strict cross infection protocol. The aim of this paper was to describe the response by a dental school in Malaysia to COVID-19 in modifying the clinical teaching and learning, infrastructure, facilities, and clinical services, and enhancing the infection control protocol through risk assessment of COVID-19 transmission and prevention strategies. The paper also discusses the limitations of our approach, challenges in providing clinical services and supervision as well as implications of changes to our practice. In conclusion, COVID-19 has modified the delivery and implementation of clinical teaching and learning in Malaysia. However, within the limited fund and resources, dental teaching institutions need to adapt to the new normal clinical environment in order to ensure that dentals students graduate on time with sufficient clinical training

Radiation hazard indicators for ²²⁶Ra, ²³²Th and ⁴⁰K radionuclides in the various building materials under study.

<p>AM±SD denotes arithmetic mean±standard deviation.</p><p>Radiation hazard indicators for ²²⁶Ra, ²³²Th and ⁴⁰K radionuclides in the various building materials under study.</p

Dose contribution due to the content of ²²⁶Ra, ²³²Th and ⁴⁰K in building materials to the inhabitants.

<p>Dose contribution due to the content of ²²⁶Ra, ²³²Th and ⁴⁰K in building materials to the inhabitants.</p

Comparison of the average activity concentrations of the studied building materials with other published data.

<p>Comparison of the average activity concentrations of the studied building materials with other published data.</p

Application of a new system for classifying root canal morphology in undergraduate teaching and clinical practice: a national survey in Malaysia

Aim To evaluate and compare the feedback of final year undergraduate dental students in eight Malaysian dental schools on the application of a new system for classifying root canal morphology in teaching and clinical practice. Methods One PowerPoint presentation describing two classification systems for root canal morphology (Oral Surgery Oral Medicine Oral Pathology, 1974 38, 456 and its supplemental configurations, International Endodontic Journal 2017, 50, 761) was delivered to final year undergraduate dental students in eight dental schools in Malaysia by two presenters (each presented to four schools). To examine students' feedback on the utility of each system, printed questionnaires consisting of six questions (five multiple choice questions and one open-ended question) were distributed and collected after the lecture. The questionnaire was designed to compare the classification systems in terms of accuracy, practicability, understanding of root canal morphology and recommendation for use in pre-clinical and clinical courses. The exact test was used for statistical analysis, with the level of significance set at 0.05 (P = 0.05). Results A total of 382 (out of 447) students participated giving a response rate of 86%. More than 90% of students reported that the new system was more accurate and more practical compared with the Vertucci system (P 0.05). The students' responses for all questions were almost similar for both presenters (P > 0.05). Conclusions The new system of International Endodontic Journal 2017, 50, 761 for classifying root and canal morphology was favoured by final year undergraduate dental students in Malaysia. The new system has the potential to be included in the undergraduate endodontic curriculum for teaching courses related to root and canal morphology