Effect of Cement Layer Thickness on the Immediate and Long-Term Bond Strength and Residual Stress between Lithium Disilicate Glass-Ceramic and Human Dentin

At a Glance

Metadata	Details
Publication Date	2021-09-08
Journal	Materials
Authors	João Paulo Mendes Tribst, Alison Flávio Campos dos Santos, Giuliane da Cruz Santos, Larissa Sandy da Silva Leite, Julio Chávez Lozada
Institutions	Universidade de Taubaté, Universidad Nacional de Córdoba
Citations	24
Analysis	Full AI Review Included

Technical Analysis and Documentation: Advanced Interface Stability Studies

Executive Summary

This study, analyzing the long-term stability of adhesively luted ceramic restorations, provides critical insights into the role of material thickness and residual stress—areas where 6CCVD’s advanced diamond materials offer unparalleled solutions for validation and research extension.

Long-Term Durability is Thickness Dependent: While immediate bond strength (µTBS) was unaffected by cement layer thickness (60 µm to 180 µm), long-term aging (140 days) resulted in significant bond strength degradation in the thickest (180 µm) group.
Stress Correlation: Finite Element Analysis (FEA) confirmed that increased cement layer thickness directly correlates with a higher magnitude of residual tensile stress generated by polymerization shrinkage.
Optimal Range Identified: The research recommends thinner cement layers (60-120 µm) to ensure superior long-term bond durability and minimize stress concentration at the ceramic/dentin interface.
Methodological Rigor: The study relied on high-precision sample preparation (1 mm² cross-section beams) and sophisticated numerical modeling, requiring materials with highly stable and predictable mechanical properties.
6CCVD Value Proposition: 6CCVD specializes in providing ultra-stable Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD) substrates, ideal for validating FEA models and serving as non-degrading reference materials in complex aging and micro-mechanical testing environments.

Technical Specifications

The following data points were extracted from the study, focusing on mechanical properties and critical test results.

Parameter	Value	Unit	Context
Cement Layer Thickness (Tested Groups)	60, 120, 180	µm	Key experimental variable
Aging Simulation Duration	140	days	Long-term bond durability test
Aging Simulation Temperature	37	°C	Storage in distilled water
Immediate µTBS (60 µm)	11.2 ± 7.4	MPa	Short-term bond strength (Highest mean)
Aged µTBS (180 µm)	3.7 ± 3.6	MPa	Lowest long-term bond strength (Significant difference)
Lithium Disilicate Elastic Modulus	95.0	GPa	Input for FEA modeling
Resin Cement Elastic Modulus	7.0	GPa	Input for FEA modeling
Resin Cement Volumetric Shrinkage	1.74	%	Used for thermal analogy in FEA
Highest Stress Peak (180 µm Cement)	0.17	MPa	Calculated residual tensile stress in cement layer
Recommended Cement Thickness	60-120	µm	For improved bond durability

Key Methodologies

The experiment combined precise material handling, micro-mechanical testing, and advanced numerical simulation.

Sample Preparation: Human molars were embedded in chemically cured acrylic resin and flattened using sandpaper (#600) under constant cooling water to expose flat dentin.
Ceramic Sectioning and Crystallization: Lithium disilicate blocks (IPS e.max CAD) were sectioned (6 x 6 x 7 mm³) using a low-speed diamond saw and crystallized at 850 °C for 10 min.
Surface Treatment: Ceramic blocks were etched with 10% hydrofluoric acid (20 s) and treated with a silane coupling agent (60 s volatilization). Dentin was etched with 37% phosphoric acid (15 s).
Luting and Thickness Control: Dual cure resin cement (Variolink II) was applied, and ceramic blocks were cemented to dentin under specific loads (500 g, 1000 g, or 3000 g) to achieve the target cement layer thicknesses (60, 120, and 180 µm).
Precision Sectioning: After 24 hours of storage, the assemblies were sectioned into 1 mm² cross-section beams using a precision cutting machine (Isomet 1000) under constant cooling.
Testing and Analysis: Half of the beams were tested immediately (µTBS); the other half were aged (140 days at 37 °C). FEA was performed using ANSYS 19.2 to simulate polymerization shrinkage stress via thermal analogy.

6CCVD Solutions & Capabilities

6CCVD provides the high-performance CVD diamond materials and precision engineering services necessary to replicate, validate, and extend this critical research into long-term material stability and stress analysis.

Applicable Materials

To replicate the high-precision mechanical testing and FEA validation required by this study, 6CCVD recommends the following materials:

Optical Grade Single Crystal Diamond (SCD): Ideal for serving as a non-degrading, ultra-stiff substrate (Elastic Modulus > 1000 GPa) for validating FEA models. Its known, stable properties eliminate substrate variability, allowing researchers to isolate the effects of the adhesive layer and ceramic material.
Polycrystalline Diamond (PCD) Plates: Available in large formats (up to 125mm), PCD is suitable for high-throughput mechanical testing where large, uniform surfaces are required for bonding studies.
Heavy Boron-Doped Diamond (BDD) Films: For extending the research into real-time monitoring, BDD can be integrated as an electrochemical sensor layer to detect water sorption or degradation products at the adhesive interface during the 140-day aging simulation.

Customization Potential

The study relied on precise 1 mm² cross-section beams and specific surface treatments. 6CCVD’s capabilities directly address these requirements:

Research Requirement	6CCVD Customization Service	Technical Specification Match
Precision Sample Geometry	Custom Laser Cutting & Dicing	We provide SCD/PCD plates cut to exact dimensions (e.g., 1 mm x 1 mm beams) for microtensile or shear testing, ensuring high geometric fidelity.
Controlled Surface Finish	Ultra-Precision Polishing	SCD surfaces polished to Ra < 1nm and inch-size PCD polished to Ra < 5nm, guaranteeing reproducible bonding conditions and minimizing surface flaws that initiate failure.
Interface Integration	Custom Metalization Services	We offer in-house deposition of Au, Pt, Pd, Ti, W, and Cu. This allows researchers to test the effect of various metal bonding layers (e.g., Ti/Pt/Au) on diamond substrates, simulating complex biomedical interfaces.
Substrate Thickness	Wide Range Thickness Control	SCD and PCD films available from 0.1µm to 500µm, and substrates up to 10mm, enabling researchers to precisely control the thickness of the rigid component in multi-layer assemblies for FEA validation.

Engineering Support

The relationship between cement thickness, residual stress, and long-term degradation is complex, requiring expert material selection. 6CCVD’s in-house PhD team specializes in the mechanical and thermal properties of CVD diamond. We can assist researchers and engineers with material selection for similar Biomedical/Dental Adhesion and Stress Analysis projects, ensuring the diamond substrate meets the stringent requirements for FEA validation and micro-mechanical testing.

Call to Action: For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

This study tested whether three different cement layer thicknesses (60, 120 and 180 μm) would provide the same bonding capacity between adhesively luted lithium disilicate and human dentin. Ceramic blocks were cut to 20 blocks with a low-speed diamond saw under cooling water and were then cemented to human flat dentin with an adhesive protocol. The assembly was sectioned into 1 mm2 cross-section beams composed of ceramic/cement/dentin. Cement layer thickness was measured, and three groups were formed. Half of the samples were immediately tested to evaluate the short-term bond strength and the other half were submitted to an aging simulation. The microtensile test was performed in a universal testing machine, and the bond strength (MPa) was calculated. The fractured specimens were examined under stereomicroscopy. Applying the finite element method, the residual stress of polymerization shrinkage according to cement layer thickness was also calculated using first principal stress as analysis criteria. Kruskal-Wallis tests showed that the ‘‘cement layer thickness’’ factor significantly influenced the bond strength results for the aged samples (p = 0.028); however, no statistically significant difference was found between the immediately tested groups (p = 0.569). The higher the cement layer thickness, the higher the residual stress generated at the adhesive interface due to cement polymerization shrinkage. In conclusion, the cement layer thickness does not affect the immediate bond strength in lithium disilicate restorations; however, thinner cement layers are most stable in the short term, showing constant bond strength and lower residual stress.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma14185153

References

2017 - ADM guidance-Ceramics: All-ceramic multilayer interfaces in dentistry [Crossref]
2013 - The current state of adhesive dentistry: A guide for clinical practice
2018 - Self-etching primers vs acid conditioning: Impact on bond strength between ceramics and resin cement [Crossref]
2021 - Failure load and shear bond strength of indirect materials bonded to enamel after aging
2003 - Resin-ceramic bonding: A review of the literature [Crossref]
2018 - Influence of ceramic material, thickness of restoration and cement layer on stress distribution of occlusal veneers [Crossref]
2012 - Effects of cement thickness and bonding on the failure loads of CAD/CAM ceramic crowns: Multi-physics FEA modeling and monotonic testing [Crossref]
2021 - The influence of the resin-based cement layer on ceramic-dentin bond strength [Crossref]
2019 - Comparison of the accuracy of fit of metal, Zirconia, and lithium disilicate crowns made from different manufacturing techniques [Crossref]
2019 - Comparison of the fit of lithium disilicate crowns made from conventional, digital, or conventional/digital techniques: Fit of lithium disilicate crowns