Development and application of calcium silicate particles for adhesive interface preservation

Author(s)

Marina Damasceno e Souza de Carvalho Chiari

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Faculdade de Odontologia (FO/SDO)
• Defense date: 2023-07-17

Examining board members

Roberto Ruggiero Braga; Josimeri Hebling Costa; Victor Pinheiro Feitosa; Fabio Dupart Nascimento

• Advisor: Roberto Ruggiero Braga

Abstract

Bioactive glasses, calcium silicates and calcium orthophosphates particles application on dental adhesives are an effective strategy to reduce collagen enzymatic degradation at the hybrid layer and to promote apatite precipitation at dentin-adhesive interface. Therefore, this project aims were: 1) investigate the effect of sol-gel synthesis variables over calcium silicate (CS) particles characteristics. Particles were characterized by the obtained phase (X-ray diffraction/XRD), calcium and silicon/Ca:Si ratio (X-ray fluorescence/FRX), size distribution (laser scattering), surface area (BET method), density and morphology (scanning and transmission electron microscopy SEM/TEM); 2) evaluate the effect of 5 wt% of particles incorporation to a commercial dental adhesive (Adper Scotchbond Multipurpose, 3M ESPE) on the degree of conversion (DC), cohesive strength after 24 hours and 12 months of deionized water storage and ions release over 60 days in deionized water; 3) evaluate, after 24 hours, 6 and 12 months of storage in simulated body fluid (SBF), the effect of adding CS to a commercial adhesive system or to an experimental pre-treatment containing CS in relation to hardness and elastic modulus of the composite, adhesive layer, hybrid layer and dentin; 4) evaluate, after 24 hours and 12 months of storage in SBF, the effect of adding CS to a commercial adhesive system or experimental pre-treatment in relation to microtensile bond strength (TBS), collagenolytic activity of proteases (in situ zymography, reverse zymography, hydroxyproline and fluorescence spectroscopy assays) and scanning electron microscopy/energy dispersive x-ray spectroscopy (SEM/EDX) of the adhesive interface. DC, cohesive strength, ions release, hardness/elastic modulus and TBS data were subjected to analysis of variance (ANOVA). In all cases, Tukey test was used for pair-wise comparisons. The global significance level (±) was set at 5%. Particles characterization, in situ zymography, reverse zymography, hydroxyproline and fluorescence spectroscopy assays and SEM/EDX results were descriptively presented. DRX confirmed the formation of different calcium silicate phases. Ca:Si ratio was dependent of the precursors molar ratio and ranged from 1.9 to 5.2. In most cases, particles agglomerates synthesized with higher surfactant amounts were smaller. Particles density ranged from 3.05 to 3.62 g/cm3. The materials presented as micrometric agglomerates formed by spherical or irregular nanoparticles with surface area ranging from 9 to 62 m2/g. DC was not affected by CS presence in the adhesive (p>0,05). For adhesive interface evaluation, pre-treatment containing CS presented reductions for TBS (pooled data: without pretreatment/ w/o P: 37.0±11.2A, pre-treatment without CS/P(-): 34.7±8.3AB, pre-treatment with CS/P(+): 30.7± 9.6B, p<0.05). Aged specimens presented 36.5% reduction for TBS (pooled data for 24 hours: 41.9±6.5A, 12 months: 26.6±2.5B, p<0.01). Composite hardness and elastic modulus were not affected by CS addition to the adhesive or pretreatment. For 24 hours at the adhesive layer, CS in the adhesive (Ad(+)) reduced hardness in comparison to the adhesive without particles (Ad(-)) (Ad(-): 21.3±0.9A; Ad(+): 16.2±1.8B, p<0.05). For elastic modulus, CS in the adhesive (pooled data Ad(-): 4.5±0.9A; Ad(+): 3.8±0.4B) or pre-treatment (w/o P: 4.4±0,9A, P(-):4.5±0.7A; P(+):3.6±0.4B) or storage period (pooled data for 24 hours: 4.7±1.0A, 6 months 3.9±0.5B, 12 months 3.9±0.5B) presented statistically significant reductions (p<0.01). At the hybrid layer CS added to the adhesive and/or pre-treatment lead to increases for hardness and elastic modulus over 6 or 12 months of storage (p<0.05). For dentin, CS at added to the adhesive increased hardness and elastic modulus (pooled data for hardness: Ad(-) 68.0±12.5B e Ad(+) 71.7±12.8A; pooled data for elastic modulus: Ad(-) 17.9±3.0B e Ad(+) 18.8±3.1A, p<0.05). Pre-treatment containing CS was also effective for hardness and elastic modulus maintenance after aging, whereas w/o P and P(-) groups presented reductions for mechanical properties after 6 months storage (p<0.01). After 12 months storage, SEM/EDX presented higher mineral content at the hybrid layer. In situ zymography revealed that the presence of particles in the adhesive and/or pre-treatment was able to promote enzymatic inhibition for both periods. Although reverse zymography did not indicate enzymatic inactivation and/or gelatin protection against degradation for CS containing groups, the hydroxyproline and fluorescence spectroscopy for MMP-2 activity assays demonstrated that the presence of particles in the adhesive was effective against enzymatic degradation. The results suggest that lower bond strength of the adhesive interface after storage can be related to the adhesive layer degradation. CS presence in the adhesive and/or pre-treatment may contribute to the longevity of the adhesive interface through mineral precipitation in the hybrid layer and enzymatic activity inhibition. (AU)

• FAPESP's process: 20/05986-5 - Development and application of calcium silicate nanoparticles for dental remineralization
• Grantee: Marina Damasceno e Souza de Carvalho Chiari
• Support Opportunities: Scholarships in Brazil - Doctorate