M.Tech(Res) Thesis Defence: Mr. Astik Kumar (29/07/26)
Thesis title:
A study on Materials, Manufacturing, and Biological aspects of Micro Ceramic Injection Moulded Zirconia Toughened Alumina and Zirconia Ceramics
Faculty advisor(s):
Prof. Subodh Kumar and Prof. Prosenjit Das
When?
29th July, 2026 (Wednesday), 02:30 PM (India Standard Time)
Where
BPCR, Department of Materials Engineering(hybrid mode)
Abstract
The study explores the development of advanced ceramic materials i.e., zirconia toughened alumina (ZTA) and zirconia for orthodontic applications—processed through micro ceramic injection moulding (µ-CIM), a modern fabrication technique capable of producing complex-shaped, high-precision near net shape micro scale ceramic components. While both ZTA and zirconia are known for their strength, toughness, and chemical stability, their adaptation into micro-scale geometries with precise features and high repeatability, especially for orthodontic appliances, is still relatively unexplored, especially using µ-CIM. This work aims to bridge that gap by combining novel material design, statistical process optimisation, as well as processing-microstructure correlation to produce reliable, structurally sound, and biologically safe ceramic micro parts.
To achieve the above stated goal, a specially formulated polymeric binder system consisting of polyethylene glycol (PEG), cellulose acetate butyrate (CAB), stearic acid, and phenothiazine is mixed with the ZTA and zirconia ceramic for feedstock preparation. Moreover, magnesium oxide (MgO) is added to the ceramic feedstock as a grain growth inhibitor, ensuring fine grain structure, microstructural stability, and enhanced mechanical/physical properties of the sintered ceramic. Post feedstock development, injection as well as thermal debinding parameters are optimised based on thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) studies, wherein solvent debinding conditions are optimised based on trial experiments. Afterwards, a L9 Taguchi design is adopted to systematically study the effects of sintering process conditions such as temperature, heating rate, and dwell time on the microstructural, mechanical, physical, as well as biological properties of the sintered ceramic (ZTA and zirconia). Density measurements revealed that both ZTA and zirconia achieved more than 98% of their theoretical densities, indicating successful sintering and minimal structural defects. Vickers hardness testing demonstrated excellent surface resistance and integrity, especially in ZTA samples where zirconia particles provided crack-bridging effects and improved load resistance, which is further validated via indentation fracture toughness measurements. Apart from hardness tests, structural integrity of the µ-CIM ceramics is tested via debonding studies as well as tie wing strength assessment. Furthermore, soundness of the µ-CIM processed ceramics are checked via micro-computed tomography (micro-CT), which confirmed the absence of internal voids or structural defects. Additionally, field emission scanning electron microscopy (FESEM) is employed to gain deep insight into the effectiveness of presence of MgO in the formulation towards limiting the grain growth, maintaining uniform and dense microstructures with defined grain boundaries—especially beneficial for mechanical strength and wear performance. Whereas colour and thermal stability of sintered orthodontic micro parts are studied via colorimetry and thermocycling studies. Finally, biological performance of the novel µ-CIM processed ceramics are studied via in-vitro cytotoxicity as well as in-vivo animal studies, which depicted no adverse cellular responses, excellent cell viability, zero toxicity, and absence of urea, creatinine, alanine transaminase, aspartate transaminase, calcium in the blood sample. These attributes strongly establish biocompatibility of novel µ-CIM processed ceramic parts and their potential for contact with biological tissues as well as possible deployment in orthodontic appliances.