Assessing the suitability of fused deposition modeling to produce acrylic removable denture bases.

OBJECTIVE: To study the feasibility of using poly methyl methacrylate (PMMA) filament and fused deposition modeling (FDM) to manufacture denture bases via the development of a study that considers both conventional and additive-based manufacturing techniques. MATERIALS AND METHODS: Five sample groups were compared: heat and cold cured acrylic resins, CAD/CAM milled PMMA, 3D-printed PMMA (via FDM), and 3D-printed methacrylate resin (via stereolithography, SLA). All groups were subjected to mechanical testing (flexural strength, impact strength, and hardness), water sorption and solubility tests, a tooth bonding test, microbiological assessment, and accuracy of fit measurements. The performance of sample groups was referred to ISO 20795-1 and ISO/TS 19736. The data was analyzed using one-way ANOVA. RESULTS: Samples manufactured using FDM performed within ISO specifications for mechanical testing, water sorption, and solubility tests. However, the FDM group failed to achieve the ISO requirements for the tooth bonding test. FDM samples presented a rough surface finish which could ultimately encourage an undesirable high level of microbial adhesion. For accuracy of fit, FDM samples showed a lower degree of accuracy than existing materials. CONCLUSIONS: Although FDM samples were a cost-effective option and were able to be quickly manufactured in a reproducible manner, the results demonstrated that current recommended testing regimes for conventionally manufactured denture-based polymers are not directly applicable to additive-manufactured denture base polymers. Therefore, new standards should be developed to ensure the correct implementation of additive manufacturing techniques within denture-based fabrication workflow.

Evaluation of reproducibility of the chemical solubility of dental ceramics using ISO 6872:2015.

STATEMENT OF PROBLEM: The current chemical solubility method in the International Standards Organization (ISO) 6872 (2015) specifies only the total surface area of specimens for testing (≥30 cm2) but does not describe the morphology or geometry. This could impact the reproducibility of the test outcomes. PURPOSE: The purpose of this in vitro study was to investigate the factors influencing the reliability of the ISO 6872:2015 "Dentistry-Ceramic materials" test for chemical solubility. MATERIAL AND METHODS: Chemical solubility analysis of a range of materials and specimen geometries was performed in accordance with ISO 6872:2015. Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP), VITABLOCS Mark II, IPS e.max Press, and IPS e.max ZirPress materials were formed into a range of cubic and spherical geometries to comply with the 30-cm2 minimum surface area requirement. The surface microstructure of the specimens was analyzed using a scanning electron microscope, inductively coupled plasma optical emission spectrometry (ICP-OES) was used to analyze the solutes, and surface hardness of the specimens was measured by using a Vickers hardness tester before and after testing. An optimized solubility test was devised, which eliminated specimen handling once the specimens had been ground and polished. This modified test was performed on VITABLOCS Mark II and Y-TZP. RESULTS: The results of the original chemical solubility method of ISO 6872:2015 showed significantly variable findings for each tested material, with a predictable relationship between geometry and chemical solubility. The hardness values decreased significantly after the solubility testing. The optimized method showed significantly improved reproducibility of the chemical solubility measurement compared with the original ISO 6872:2015 test. CONCLUSIONS: The results of the current chemical solubility standard method can be manipulated while still complying with the ISO 6872:2015 standard.

A blended learning course taught to different groups of learners in a dental school: follow-up evaluation.

This article reports the results of a follow-up study conducted to investigate students' perceptions about a blended learning health informatics course that combined online and traditional classroom instruction. The course is taught to five different groups of students at the School of Clinical Dentistry of the University of Sheffield each academic year: first-, third-, and fourth-year dental students, dental hygiene and therapy students, and postgraduate dental students. The goal of the study was to determine the impact of the modifications made to the course after the first year of implementation. To accomplish this goal, students' perceptions of this blended learning course were compared after the first and second implementations. The methodology used for this study was action research. The data were collected using three processes: questionnaires were used to collect contextual data from the students taking the course; a student-led, nominal group technique was used to collect group data from the participants; and a non-participant observer technique was used to record the context in which certain group and individual behaviors occurred. Depending on group assignment, between 41.5 and 91.5 percent of students believed that the blended-learning course had added to their skills. The online learning environment was perceived as a useful resource by 75 percent of students in four of the five student groups, but only 45 percent of the fourth-year dental students indicated it was a useful resource. The perceived lack of sufficient online support material was one of the main concerns of the students at the nominal group evaluation sessions. The non-participant observer technique identified different engagement levels among the student groups. Discernible differences were identified, with improvement in some areas and a decline in others compared to a previous evaluation. The change in the delivery method influenced the students' comprehension of the material negatively and the learning environment positively, but did not influence online collaboration among students.

Evaluating a blended-learning course taught to different groups of learners in a dental school.

The purpose of this study was to present and evaluate a blended-learning course developed for undergraduate (B.D.S.), postgraduate, and diploma (hygiene and therapy) students at the University of Sheffield School of Clinical Dentistry. Blended learning is the integration of classroom face-to-face learning with online learning. The overall methodology used for this study was action research. The data were collected using three processes: questionnaires to collect contextual data from the students taking the course; a student-led, nominal group technique to collect group data from the participants; and a non-participant observer technique to record the context in which certain group and individual behaviors occurred. The online component of the course was accepted as a valuable resource by 65 percent of those responding. While online information-sharing occurred (31 percent of the students posted in forums), there was no evidence of online collaboration, with only 8 percent replying to forum postings. Accessibility of the online environment was one of the main concerns of the students at the nominal group sessions. Differences regarding overall engagement with the course between the student groups (years) were observed during the sessions. The majority of the students were satisfied with the Information and Communication Technologies (ICT) course. No statistically significant differences between males and females were found, but there were differences between different student cohorts (year groups).

Surface analysis of porcelain fused to metal systems.

OBJECTIVE: The effect of four different, commonly performed, metal-ceramic alloy, surface preparation stages, were investigated to observe surface compositional changes. METHODS: Two metal-ceramic alloys were examined (Pd/Ag alloy and a Ni/Cr alloy). Discs 12 mm diameter and 2mm thick were produced using the lost wax casting process. Prior to casting alloy ingots were examined using X-ray fluorescence spectrometry (XRF) to determine bulk composition. The four preparation stages were (1) devesting and Al2O3 blasted; (2) ground smooth and Al2O3 blasted; (3) oxidation firing; (4) firing cycle for opaque porcelain application. X-ray photoelectron spectroscopy (XPS) surface analysis was performed after each surface preparation stage to determine changes in surface composition. SEM with EDS was also used to identify surface composition. RESULTS: XRF and manufacturers compositional analysis of the alloys showed similar findings for the major elements. XPS analysis showed that at preparation stages 3 and 4 evidence of elemental migration to the surface (In with Pd/Ag alloy and Cr and Mn with Ni/Cr alloy). Alumina was also seen on the alloy surfaces, with SEM/EDS confirming Al2O3 particles embedded in the surface of the alloys. SIGNIFICANCE: Surface composition is very different from the batch composition. Surface preparation stage 3 is essential in bringing to the alloy surface elements which could be directly involved in the metal-ceramic bond. Elements and their oxides, in various forms, cover the surface of the alloys. Al2O3 particles can remain embedded in the alloy surface during porcelain application.