Preparation And Properties Evaluation Of Laminated Invisible Orthodontic Diaphragm

At present,there is no unified standard for the performance of the diaphragm in the field of invisible orthodontics,and the diaphragm material is basically monopolized by foreign countries.Therefore,it is of great significance to develop domestic invisible orthodontic diaphragm materials.In this dissertation,the performance of two kinds of imported orthodontic diaphragms was analyzed,and the performance reference index of the diaphragms for invisible orthodontics was established.Three kinds of materials,thermoplastic polyurethane(TPU),poly(ethylene terephthalateco-1,4-cylclohexylenedimethylene terephthalate)PETG and polycarbonate(PC),were selected to prepare the orthodontic membranes by laminating.The properties of the membranes were characterized comprehensively.The conclusions are as follows:(1)According to the performance test parameters of Biolon diaphragm and Erkodur diaphragm,the performance reference indexes of invisible orthodontic diaphragm were determined as follows.Tensile strength was 50-60 MPa.Flexural strength was 20-28 MPa.Tensile modulus was 1700-2100 MPa.Flexural modulus was 1700-2400 MPa.Light transmittance was>85%.Haze was<4%.Stress relaxation rate was<20 kPa/min.Stress relaxation percentage was<20%.Impact strength was>22 kJ/m2.Water absorption was<15 mg/cm3.(2)The PC sheet had little effect on the transparency of the TPU membrane,and the light transmittance of the composite membranes was about 90%.The PC sheet effectively enhanced the mechanical strengths of the TPU sheets.The tensile strength of the double-layer TPU/PC composite membranes was above 50 MPa,while the tensile modulus above 1800 MPa,and the bending performance was excellent.In addition,the 256-hour water absorption of the composite membrane did not exceed 10 mg/cm3.The 4-hour stress relaxation rate was less than 15 kPa/min,and the relaxation percentage was less than 20%.However,the haze of the double-layer TPU/PC composite membranes was higher than the established index,so the haze of the composite membrane needed to be further reduced to meet the orthodontic requirements.(3)The introduction of the PC sheet improved the stress relaxation performances of the PETG membranes,which hardly affected the transparency of the membrane materials while enhancing the mechanical properties of the PETG membranes.And the biocompatibility of PETG/PC composite films was good.When the thickness of the PC sheet layer was 0.2 mm,the 4-hour stress relaxation rate and relaxation percentage of the laminated PETG/PC composite film were 16.7 kPa/min and 19.3%,respectively.The tensile stress,tensile modulus,flexural stress and flexural modulus were 51 MPa,1860 MPa,26 MPa and 2140 MPa,respectively.The impact strength was 33 kJ/m2.Water absorption was 7.7 mg/cm3.Relative cell viability was 89%,and hemolysis ratio was 3.1%.The obtained membranes could be used for invisible appliances.(4)The double-layer PETG/PC2858(0.9 mm/0.2 mm)composite membranes with the best comprehensive performance were molded according to the preparation process of invisible orthodontic braces,and an invisible appliance comparable to imported appliances was prepared.