| Metadata | Details |
|---|
| Publication Date | 2021-09-08 |
| Journal | Materials |
| Authors | JoĂŁo Paulo Mendes Tribst, Alison FlĂĄvio Campos dos Santos, Giuliane da Cruz Santos, Larissa Sandy da Silva Leite, Julio ChĂĄvez Lozada |
| Institutions | Universidad Nacional de Córdoba, Universidade de Taubaté |
| Citations | 24 |
| Analysis | Full AI Review Included |
- Core Finding: Cement layer thickness (CLT) significantly impacts the long-term durability and residual stress of adhesively luted lithium disilicate (LD) restorations, although immediate bond strength remains unaffected.
- Immediate Bond Strength (”TBS): No statistically significant difference was found between the 60 ”m, 120 ”m, and 180 ”m CLT groups immediately after cementation (p = 0.569).
- Long-Term Degradation: After 140 days of aging, the 180 ”m group showed a statistically significant reduction in bond strength (3.7 ± 3.6 MPa), performing worse than the 60 ”m and 120 ”m groups (p = 0.028).
- Residual Stress Correlation: Finite Element Analysis (FEA) demonstrated that residual tensile stress, caused by polymerization shrinkage, increased proportionally with CLT, peaking at 0.17 MPa in the 180 ”m cement layer.
- Failure Mechanism: The higher residual stress and increased exposure of polymeric material in thicker layers (180 ”m) likely contributed to greater susceptibility to aging degradation (water sorption and slow crack growth).
- Clinical Recommendation: To ensure optimal bond durability and lower residual stress, thinner cement layers (60-120 ”m) are strongly recommended for lithium disilicate restorations.
| Parameter | Value | Unit | Context |
|---|
| Cement Layer Thickness (CLT) Groups | 59.74 ± 8.41 / 119.89 ± 21.85 / 182.66 ± 98.66 | ”m | Measured average thicknesses (Nominal: 60, 120, 180 ”m) |
| Immediate ”TBS (60 ”m) | 11.2 ± 7.4 | MPa | Highest short-term bond strength |
| Aged ”TBS (180 ”m) | 3.7 ± 3.6 | MPa | Lowest long-term bond strength (Significant reduction) |
| Aging Simulation Duration | 140 | Days | Storage in distilled water |
| Aging Simulation Temperature | 37 | °C | Water storage condition |
| Lithium Disilicate Elastic Modulus | 95.0 | GPa | FEA Input (IPS e.max CAD) |
| Resin Cement Elastic Modulus | 7.0 | GPa | FEA Input (Variolink II) |
| Resin Cement Volumetric Shrinkage | 1.74 | % | FEA Input (Simulated via thermal analogy) |
| FEA Stress Peak (Cement, 180 ”m) | 0.17 | MPa | Maximum First Principal Stress in cement layer |
| FEA Stress Peak (Dentin, 180 ”m) | 0.15 | MPa | Maximum First Principal Stress at dentin interface |
| FEA Stress Peak (Dentin, 60 ”m) | 0.13 | MPa | Maximum First Principal Stress at dentin interface (Lowest) |
- Sample Preparation: Human dentin substrates were prepared by flattening occlusal surfaces under constant cooling (using #600 sandpaper) and embedded in chemically cured acrylic resin.
- Ceramic Fabrication: Lithium disilicate (LD) blocks (IPS e.max CAD) were sectioned, ground, and crystallized following manufacturer instructions (850 °C/10 min).
- Adhesive Protocol: LD surfaces were etched (10% HF acid, 20 s) and silanized (Monobond Plus, 60 s volatilization). Dentin was etched (37% phosphoric acid, 15 s) and bonded (Excite F DSC adhesive, light cured 15 s).
- Cementation and CLT Control: Dual-cure resin cement (Variolink II) was applied. Three distinct CLT groups were established by applying different seating loads (500 g, 1000 g, or 3000 g weight) during cementation.
- Specimen Sectioning and Grouping: Cemented assemblies were sectioned into 1 mm2 cross-section beams. CLT was measured via stereomicroscopy, confirming groups centered around 60 ”m, 120 ”m, and 180 ”m.
- Bond Strength Testing (”TBS): Half of the beams were tested immediately. The remaining half underwent accelerated aging (140 days in distilled water at 37 °C) before microtensile testing (0.5 mm/min crosshead speed).
- Finite Element Analysis (FEA): A 3D model was used to simulate the three CLTs. Polymerization shrinkage was modeled using thermal analogy (linear thermal expansion coefficient of 0.005766, temperature reduced by 1 °C) to calculate First Principal Stress (tensile residual stress).
- Advanced Restorative Dentistry:
- Establishing evidence-based guidelines for the clinical cementation of high-strength ceramics (e.g., lithium disilicate), prioritizing thin cement layers (60-120 ”m) to maximize long-term survival rates.
- CAD/CAM Prosthetics Design:
- Informing digital workflow parameters (e.g., die spacer settings) to ensure the manufactured restoration fit minimizes the cement gap, thereby reducing polymerization shrinkage stress and potential marginal failure.
- Dental Materials R&D:
- Guiding the development of new resin-based luting agents, focusing on materials that exhibit lower volumetric shrinkage (less than 1.74%) or enhanced resistance to hydrolytic degradation (water sorption) to maintain bond integrity, especially in thicker clinical gaps.
- Biomaterials Testing and Simulation:
- Utilizing FEA and thermal analogy as predictive tools for evaluating the mechanical stability and stress distribution in multi-layered adhesive systems before extensive in vivo or long-term in vitro testing.
View Original Abstract
This study tested whether three different cement layer thicknesses (60, 120 and 180 ÎŒm) 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 ââcement layer thicknessââ 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.
- 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