Glass-Ceramic Dental Restoration Crystallization Process
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Solution Overview
Problem
Current glass-ceramic materials for dental restorations lack the ability to mimic the inhomogeneous structure and mechanical properties of natural teeth, particularly in terms of strength and aesthetics, and are laborious to manufacture, with existing methods requiring multiple steps and high tool wear during machining.
Innovation Solution
A process involving a basic glass body composition of 65-72 wt-% SiO2, 10.1-15 wt-% Li2O, and 10.1-15 wt-% Al2O3, subjected to a nucleation step followed by two distinct crystallization steps at different temperature ranges to form varying crystalline phases, allowing for a structured glass-ceramic body with adjustable mechanical and optical properties across different regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a high strength glass-ceramic material (lithium disilicate) is used for dental restorations, then mechanical strength is improved, but machining becomes difficult with very high tool wear and long processing times
Solution Approach 1:
The patent segments the crystallization process into two distinct stages: a first crystallization step forming lithium metasilicate crystals, and a second crystallization step forming lithium disilicate crystals. This segmentation allows the material to have different phases with different properties - the lithium metasilicate phase provides machinability while the lithium disilicate phase provides strength, thus resolving the contradiction between strength and ease of manufacture
Solution Approach 2:
The patent utilizes parameter changes by controlling crystallization temperature and time to transform the material properties. The first crystallization occurs at lower temperature (560-680°C) to form soft lithium metasilicate phase for easy machining. After machining, a second crystallization at higher temperature (880-980°C) transforms the material to high-strength lithium disilicate phase, thus achieving both ease of manufacture and high strength through parameter changes
2Illumination intensity
If the restoration thickness is reduced to a few hundreds of micrometers, then aesthetics is improved, but strength becomes insufficient
Solution Approach 1:
The patent creates a composite glass-ceramic material containing two types of crystalline phases: lithium metasilicate (Li2SiO3) and lithium disilicate (Li2Si2O5). The lithium metasilicate phase provides toughness and strength, while the lithium disilicate phase provides translucency and aesthetics. This composite structure allows thin restorations to maintain both aesthetic translucency and sufficient mechanical strength
3Ease of manufacture
If a homogeneous glass-ceramic structure is used, then manufacturing is simplified, but the ability to mimic natural tooth structure and appearance is reduced
Solution Approach 1:
The patent applies local quality by creating regions with different crystalline phase compositions within the glass-ceramic body. The material contains both lithium metasilicate-rich regions and lithium disilicate-rich regions, each providing different properties. This local variation in composition allows the material to mimic the inhomogeneous structure of natural teeth while still being manufacturable through controlled crystallization processes
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 process enables the creation of a glass-ceramic body with inhomogeneous crystalline phases that mimic the structure and appearance of natural teeth, providing superior mechanical properties and aesthetics, while reducing manufacturing complexity and tool wear during CAD/CAM machining.
Implementation Method 1
subjected to a nucleation step followed by two distinct crystallization steps
Implementation Method 2
followed by two distinct crystallization steps at different temperature ranges to form varying crystalline phases
Implementation Method 3
subjecting the basic glass body to a thermal treatment whereby a crystalline phase embedded in a glass matrix is formed
Data Source
Figure 1
Figure 2
AI summary
The present invention relates to a glass composition comprising 65 to 72 wt-% SiO2, at least 10.1 wt-% Li2O and at least 10.1 wt-% Al2O3 based on the total weight of the composition, the proportion of Li2O to Al2O3 being from 1:1 to 1.5:1, wherein the glass composition further comprises 0 to 2 wt-% K2O, 1 to 4 wt-% Na2O, 0 to 1.5 wt-% CaO, 0 to 1.0 wt-% MgO, 0 to 1.5 wt-% B2O3, 0 to 1.5 wt-% CeO2, 1 to 5 wt-% P2O5, 0 to 3 wt-% CaF2, 0 to 2.0 wt-% AlF3, 0 to 1.0 wt-% Ag, 0 to 5 wt-% ZrO2 and 0 to 4 wt-% TiO2 based on the total weight of the composition.