Translucent Alumina Orthodontic Bracket via HIP Densification
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Solution Overview
Problem
Conventional orthodontic ceramic brackets lack sufficient strength and translucency to achieve both high aesthetic value and functional effectiveness, particularly in complex shapes, with alumina ceramic brackets having bending strengths less than 700 MPa.
Innovation Solution
Development of an orthodontic bracket using a translucent ceramic with at least 99.5 wt% alumina, achieving a bending strength of at least 700 MPa, with an absorption/scattering coefficient of no more than 2.8 mm−1 and spectral reflectance factor of no more than 15% for visible light, through a production method involving sintering and hot isostatic pressing (HIP) treatment of highly-pure alumina fine powder.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional alumina ceramic brackets are used, then beauty and superior durability compared to plastics are achieved, but bending strength is insufficient (less than 700 MPa) for complex thin shapes
Solution Approach 1:
The patent changes the material parameters by using ultra-high purity alumina (99.99 wt%) and controlling crystal grain size (1.0-3.0 μm) to achieve bending strength of 700 MPa or more, enabling complex thin shapes while maintaining structural integrity
Solution Approach 2:
The patent creates a composite ceramic material system combining ultra-high purity alumina with specific crystal grain size control and controlled porosity to achieve both high strength and aesthetic properties simultaneously
2Illumination intensity
If conventional alumina ceramic brackets are used, then strength is improved, but translucency is insufficient for high aesthetic value
Solution Approach 1:
The patent optimizes the absorption/scattering coefficient to 3.0 mm⁻¹ or less and controls crystal grain size to 1.0-3.0 μm, achieving high translucency while maintaining bending strength of 700 MPa or more through precise parameter control
3Illumination intensity
If plastic brackets are used, then aesthetic appeal is achieved, but durability is insufficient with discoloration and inadequate rigidity
Solution Approach 1:
The patent develops a ceramic composite material with ultra-high purity alumina that combines the translucency and aesthetic appeal of plastics with the durability, rigidity, and resistance to discoloration of ceramic materials
Solution Approach 2:
The patent changes the material composition to 99.99 wt% alumina purity and controls crystal grain size to achieve both aesthetic translucency and superior durability simultaneously
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The resulting orthodontic bracket exhibits twice the bending strength of conventional brackets, enabling thin, complex shapes without breakage, enhancing aesthetic value and reducing patient discomfort, while allowing for mass production through injection molding without machining.
Implementation Method 1
a method of sintering the material at a temperature of from 1,200 to 1,300° C.
Implementation Method 2
subjecting the resultant to an HIP treatment at a temperature of from 1,200 to 1,350° C. and under a pressure of at least 50 MPa
Data Source
AI summary
A method for producing an orthodontic bracket is comprised of sintering a molded body of highly-pure alumina fine powder at a temperature of 1,200° C. to 1,300° C. to obtain a sintered body composed of crystals having a relative density of 96% to 99.5% and an average crystal grain size of at most 1 μm, and thereafter subjecting the sintered body to an HIP treatment at a temperature of 1,200° C. to 1,350° C., under a pressure of at least 50 MPa. Such an orthodontic bracket has high strength and high translucency, can be processed into a complicated shape, similar to that of a metal bracket, and maintains excellent translucency.