Effect of heat treatment on compressive fracture strength and microstructure of CNC milled zirconia dental restoration

• Main Author: Mahdzir, Mira Mazlina
• Format: Thesis
• Language: English; English
• Published: 2022
• Subjects: T Technology (General); TA Engineering (General). Civil engineering (General)
• Online Access: http://eprints.utem.edu.my/id/eprint/26689/1/Effect%20of%20heat%20treatment%20on%20compressive%20fracture%20strength%20and%20microstructure%20of%20CNC%20milled%20zirconia%20dental%20restoration.pdf; http://eprints.utem.edu.my/id/eprint/26689/2/Effect%20of%20heat%20treatment%20on%20compressive%20fracture%20strength%20and%20microstructure%20of%20CNC%20milled%20zirconia%20dental%20restoration.pdf; http://eprints.utem.edu.my/id/eprint/26689/; https://plh.utem.edu.my/cgi-bin/koha/opac-detail.pl?biblionumber=121992&query_desc=kw%2Cwrdl%3A%20cdr%2022728

Zirconia is commonly used in dental crown restoration due to its high strength, non-reactive and aesthetic properties compared to other materials. Zirconia crown fabricated using CNC milling machine can produce a final product with high accuracy and less time-consuming. However, the milling process affects the quality of the zirconia's surface, as a result of the tool and workpiece contact during the milling operation. This can lead to disruption of the microstructure and affect the fracture toughness of the zirconia crown. This deterioration becomes more apparent when the zirconia is not heat treated, but the suitable heat treatment temperature which can simultaneously improve the surface quality of the dental restoration is not known. Hence, the aims of this study are to analyse the compressive fracture strength of CNC milled zirconia dental restorations after being exposed to various heat-treatment temperatures, and to study the effectiveness of heat treatment in improving the surface quality of dental restoration. Therefore, eighteen samples from Y-TZP zirconia are grouped into two groups, which are the heat-treated and the untreated group. Three samples are set for the untreated and the remaining 15 samples are divided into 3 groups of different temperature which are 1400°C, 1500°C and 1600°C, with three samples per temperature setting. After heating, surface roughness of each sample is taken. Then, specimens are subjected to a single-load-testing to determine their compressive fracture strength. Next, the specimens are sputter coated to enhance the image before analysing the fractography under the SEM machine. This study shows that heat treatment does influence the compressive fracture toughness and surface roughness compared to untreated samples. However, there is no significant differences can be seen when the temperature increases. Nevertheless, it shows that the grain size increases when the temperature increases. Hence, optimum temperature to achieve better compressive fracture toughness and surface quality could not be determined. For future study, CNC machine must be more user-friendly and data- informative when fabricating the dental crown. Meanwhile, in order to determine the specimen's surface roughness, an optical profilometer should be employed in the future. The heating treatment furnace should have a heating and cooling rate for each temperature. Last but not least, since this experiment yielded no results about the transformation phase of the sample after being heat treated, X-Ray Diffraction (XRD) should be used in future research