Machining Lithium Metasilicate Ceramic with Diamond Tools
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Solution Overview
Problem
Current dental ceramic materials face challenges in achieving a balance between easy machinability for quick production of dental restorations and maintaining high strength and chemical durability, particularly with lithium disilicate materials that exhibit high wear and long processing times during machining, and significant shrinkage during sintering.
Innovation Solution
A method involving a metastable lithium metasilicate glass ceramic that can be easily machined using diamond tools with specific grain sizes and machining strategies, followed by a heat treatment to convert it into a lithium disilicate glass ceramic with enhanced mechanical and optical properties, minimizing shrinkage and tool wear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If lithium disilicate materials are used for dental restorations, then high strength and chemical durability are achieved, but machining time increases and tool wear becomes very high
Solution Approach 1:
The patent applies preliminary action by performing a heat treatment step before machining to create a softened state of the lithium disilicate material. This preliminary heat treatment reduces the material's hardness and strength temporarily, enabling easy machining with standard tools. After machining, a final heat treatment restores the material's high strength properties, thus resolving the contradiction between ease of machining and final strength requirements.
Solution Approach 2:
The patent utilizes parameter changes by controlling temperature to alter the material properties of lithium disilicate. During machining, the material is maintained at elevated temperatures (below its transformation point) to reduce its strength and improve machinability. After machining, cooling and final heat treatment restore the material to its high-strength state, effectively changing physical parameters to resolve the contradiction between machinability and strength.
2Strength
If lithium disilicate materials are used for dental restorations, then high strength is achieved, but tool wear becomes very high
Solution Approach 1:
The patent applies preliminary action by performing a heat treatment step before machining to create a softened state of the lithium disilicate material. This preliminary heat treatment reduces the material's hardness and strength temporarily, enabling easy machining with standard tools. After machining, a final heat treatment restores the material's high strength properties, thus resolving the contradiction between ease of machining and final strength requirements.
Solution Approach 2:
The patent utilizes parameter changes by controlling temperature to alter the material properties of lithium disilicate. During machining, the material is maintained at elevated temperatures (below its transformation point) to reduce its strength and improve machinability. After machining, cooling and final heat treatment restore the material to its high-strength state, effectively changing physical parameters to resolve the contradiction between machinability and strength.
3Loss of time
If ceramic materials are machined in green state to achieve easy machinability, then machining time is reduced, but shrinkage during sintering becomes drastic
Solution Approach 1:
The patent utilizes parameter changes by controlling temperature to alter the material properties of lithium disilicate. During machining, the material is maintained at elevated temperatures (below its transformation point) to reduce its strength and improve machinability. After machining, cooling and final heat treatment restore the material to its high-strength state, effectively changing physical parameters to resolve the contradiction between machinability and strength.
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
This approach significantly reduces machining time while maintaining strength, accuracy, and dimensional integrity, achieving high-strength, chemically stable, and optically appealing dental restorations with minimal shrinkage.
Implementation Method 1
A machining strategy for machining a dental ceramic blank into a dental article is provided
Implementation Method 2
a heat treatment to convert it into a lithium disilicate glass ceramic with enhanced mechanical and optical properties
Data Source
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AI summary
The invention relates to a method of reducing the time for machining a dental ceramic blank, wherein the fracture toughness (Klc) and the flexural strength (σf) of the dental ceramic material are known, comprising calculating an estimate of the maximal surface critical flaw size and an estimate of the maximal volume critical flaw size of the dental ceramic using the following formula: c=Klc/σf2 wherein c is the maximal surface critical flaw size and 2c is the maximal volume critical flaw size; implementing a machining strategy using a series of diamond tools, wherein the diamond tools comprise embedded diamonds; wherein the machining strategy comprises rough, intermediate and fine machining steps; wherein each step comprises a tool path and machining parameters, wherein the tool path and machining parameters are carried out by at least one of the series of diamond tools; wherein the grain size of the embedded diamonds is larger than approximately the estimated maximal size of the surface critical flaw and smaller than approximately the estimated maximal size of the volume critical flaw.