Dental Composite Shrinkage Stress Reduction via Stable Radicals

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Solution Overview

Problem

Current dental composites face challenges with polymerization shrinkage stress, which affects the interfacial bond strength between the composite and tooth, leading to issues like microleakage and recurrent caries, despite advancements in photopolymerization technology.

Innovation Solution

Incorporating a polymerizable stable radical, such as those containing a 2,2,6,6-tetramethylpiperidin-N-oxyl moiety, into the dental restorative composition to delay gelation and vitrification points during polymerization, reducing shrinkage stress while maintaining mechanical strength and modulus.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Shape

If traditional photopolymerization technology is used to achieve tooth-like appearance, then aesthetic properties are improved, but polymerization shrinkage stress increases leading to compromised interfacial bonding

Engineering Contradiction:

Improvetooth-like appearanceVSAvoidinterfacial bond strength

Core Design Contradiction:

ShapeVSStrength

Solution Approach 1:

The patent changes the chemical parameters of the polymerization system by incorporating polymerizable stable radicals (such as TEMPO derivatives) into the dental composite formulation. This modification alters the polymerization kinetics to achieve controlled radical polymerization, which reduces polymerization shrinkage stress while maintaining the aesthetic properties and mechanical strength of the restoration.

Inventive Principle:

Principle #35Parameter changes

2Stability of the object's composition

If polymerization shrinkage is restricted to improve composite integrity, then material stability is improved, but shrinkage stress transfers to tooth structure causing damage

Engineering Contradiction:

Improvecomposite integrityVSAvoidshrinkage stress

Core Design Contradiction:

Stability of the object's compositionVSStress or pressure

Solution Approach 1:

The patent introduces polymerizable stable radicals as intermediary species that mediate the polymerization process. These stable radicals (e.g., TEMPO derivatives) act as controlled radical sources that slow down the polymerization rate, allowing the composite to polymerize more gradually and reduce the transfer of shrinkage stress to the tooth structure while maintaining composite integrity.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Strength

If conventional resin systems are used to achieve adequate mechanical properties, then strength and modulus are improved, but polymerization shrinkage stress remains high

Engineering Contradiction:

Improvemechanical strengthVSAvoidpolymerization shrinkage stress

Core Design Contradiction:

StrengthVSStress or pressure

Solution Approach 1:

The patent creates a composite polymerization system that combines conventional photoinitiators with polymerizable stable radicals. This composite approach integrates the benefits of traditional photopolymerization (adequate mechanical properties) with the advantages of controlled radical polymerization (reduced shrinkage stress), achieving both strength and low stress through material composition optimization.

Inventive Principle:

Principle #40Composite materials

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 use of polymerizable stable radicals significantly reduces polymerization shrinkage stress, enhancing the mechanical properties and longevity of dental restorations without compromising flexural strength, modulus, or wear resistance, thereby improving the composite-tooth interface and overall restoration quality.

Implementation Method 1

photopolymerization technology

Methodology Applied

Scientific EffectPhotopolymerization: Photopolymerisation

Implementation Method 2

delay gelation and vitrification points during polymerization

Methodology Applied

Scientific EffectGelation: Gel

Implementation Method 3

delay gelation and vitrification points during polymerization

Methodology Applied

Scientific EffectVitrification: Vitrification

Data Source

PatentUS10780026B2Methods of forming dental composites and compositions for reduced shrinkage stress

Publication Date: 2020.09.22 DENTSPLY SIRONA INC

AI summary

A method of forming a dental composite includes photopolymerizing a dental composition. The dental composition includes a free-radically polymerizable (meth)acrylate resin, 75 percent by weight or greater of filler particles, and about 0.005 percent to about 5 percent by weight of at least one polymerizable stable radical. The photopolymerizing forms the dental composite such that the dental composite has a flexural modulus of about 9500 MPa or greater and the polymerizable stable radical reduces shrinkage stress of the dental composite caused by the photopolymerizing by 10% or greater. A method of forming a dental composite composition includes combining a free-radically polymerizable (meth)acrylate resin, 75 percent by weight or greater of filler particles, and about 0.005 percent to about 5 percent by weight of at least one polymerizable stable radical to form the dental composite composition.