Dissertation committee:
Καμποσιώρα Φωτεινή, Επίκουρη Καθηγήτρια, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, ΕΚΠΑ
Ζηνέλης Σπυρίδων, Καθηγητής, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, ΕΚΠΑ
Παπαβασιλείου Γεώργιος, Επίκουρος Καθηγητής, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, ΕΚΠΑ
Κούρτης Στέφανος, Αναπληρωτής Καθηγητής, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, ΕΚΠΑ
Αρτοπούλου Ιόλη, Επίκουρη Καθηγήτρια, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, ΕΚΠΑ
Σαραφιανού Ασπασία, Επίκουρη Καθηγήτρια, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, ΕΚΠΑ
Σιλβέστρος Σπυρίδων, Επίκουρος Καθηγητής, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, ΕΚΠΑ
Summary:
Objectives: The purpose of this study was the microstructural, elemental and mechanical characterization of contemporary CAD/CAM resin-based composite (RBC) materials used for prosthetic restorations and the assessment of the effect of aging procedures on color, gloss and surface roughness of these materials. Materials and Methods: Six CAD/CAM RBC materials [Brilliant CRIOS (Coltene Whaledent AG), Cerasmart (GC), Lava Ultimate (3M ESPE), Tetric CAD (Ivoclar Vivadent), Shofu Block HC (Shofu), Grandio Blocs (VOCO GmbH)] and a lithium disilicate material [IPS e.max CAD, Ivoclar Vivadent] were tested. Lithium disilicate specimens were processed in the pre-crystallized (“blue”) state and then they were crystallized for 20 to 25 minutes at a temperature of 840°C in a ceramic furnace approved by the manufacturers without glazing (Programat P510, Ivoclar Vivadent AG, Schaan, Liechtenstein). Two independent experiments were performed to address the aims of the study as follows: 1. Ten high translucency (HT) A2 shade rectangular blocks (14 Х 12 Х 18 mm) for each material, after metallographic grinding and polishing under continuous water cooling up to 4000 grit SiC paper and 1 μm alumina slurry were subjected to Instrumented Indentation Testing (ΙIT) with the use of a universal hardness testing machine (ZHU0.2/Z2.5, Zwick Roell, Ulm, Germany). Martens Hardness (HM), Indentation Elastic Modulus (EIT), Elastic (ηIT) and Creep indices (CIT) were determined according to formulas provided by ISO 14577. The diagonal length of each indentation was measured and HV was determined. The results of HM, EIT, ηΙΤ, HV, and CIT were statistically analyzed by one-way ANOVA and Tukey post hoc test employing the material as a discriminating variable (α=0.05), while the possible correlations were determined by Spearman’s correlation test. One specimen from each group was examined by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX). 2. Thirty rectangular specimens (14 mm X 10 mm X 10 mm) for each material were fabricated with the use of a wet milling machine (DGSHAPE DWX-42 W, Roland DG Corporation, Shizuoka-ken, Japan). The specimens were polished and finished according to manufacturers’ recommendations for each material. All specimens were cleaned and stored in distilled water at room temperature for 24 h. Specimens of each material were randomly divided into three subgoups (n = 10) and each subgroup was subjected to one of the following aging procedures: immersion in coffee solution for 30 days at 37οC (Group 1), water thermocycling for 5000 cycles at 5-55oC according to ISO TR 11450 (Group 2) and photoaging in a light-emitting apparatus operated under the following conditions: 300–800 nm wavelength, 765 W/m2 irradiance, 64800 kJ/m2 daily radiant exposure, 37 ◦C chamber temperature and 150000 kJ/m2 total energy delivered (Group 3). Changes of color (ΔΕ*ab) and color coordinates L*, a* and b* after aging were calculated with a colorimeter according to ISO/TR 28642:2016. Changes in the values of gloss and 3D surface roughness parameters (Sa, Sz, Sq, Sc, Sv, Str, Sdr) after aging were measured. The color differences ΔE*ab of the seven materials before aging with the A2 Vita Classical Shade guide tab were also calculated. Kruskal-Wallis tests, paired t-tests, one-way ANOVA and Bonferroni post-hoc tests were used for statistical analysis (α=0.05). The 50:50% perceptibility threshold (PT) of ΔE*ab=1.2 and the 50:50% acceptability threshold (AT) of ΔE*ab=2.7 were used to interpret the results. Results: Backscattered Electron images and EDX analysis demonstrated differences in size, shape and type of fillers along with elemental composition among materials tested. Statistically significant differences were identified for all mechanical properties tested. Lithium disilicate showed significantly higher HM (4302±135 N/mm2), HV (586±12) and EIT (101±5 GPa) values and significantly lower CIT (2.1±0.2%) than all resin based composite materials. Among composite materials, Grandio Blocs had the significantly higher HM (953±7 N/mm2), HV (136±1) and EIT (23±1 GPa) followed by Lava Ultimate (НM=674±25 N/mm2, HV=105±2, EIT=15±1 GPa). The elastic index ranged from 41% to 52%, with Shofu Block demonstrating the significantly highest ηIT (52 ± 1%) values. Cerasmart had a significantly higher CIT value (8.4 ± 0.1%) than all other materials tested, while lithium disilicate had the lower one (CIT =2,1±0,2). Spearman’s correlation revealed that all mechanical properties tested exhibited correlations with each other, apart from ηІΤ. Color changes ranged from 3.03 to 4.41 after coffee immersion, from 1.33 to 2.55 after thermocycling and from 1.02 to 2.75 after photoaging. No statistically significant differences for ΔE*ab were found among materials after coffee immersion and thermocycling (p>0.05). Unacceptable color differences (ΔE*ab>2.7) were found between all materials before aging and Vita Classical shade guide A2 tab. Gloss changes ranged from -9.48 to -1.6 GU after coffee immersion, from -7.9 to 0.1 GU after thermocycling and from -6.78 to 0.5 after photoaging. Lithium disilicate had significantly higher gloss changes than all composite materials after aging. No significant differences in gloss changes were found among composite materials after aging (p>0.05). Tetric CAD demonstrated the significantly lower gloss and the higher surface roughness after polishing. Surface roughness alterations of the materials tested presented the following range of values: [ΔSa (nm)]; Gr1:-23 to 41, Gr2:-23 έω to 16, Gr3:-22 to 96, [ΔSq (nm)]; Gr1:-31 to 55, Gr2:-34 to 65, Gr3:-28 to 172, [ΔSz (nm)]; Gr1:-757 to 1819, Gr2:-87 to 1088, Gr3: -540 to 1479, [ΔSc (μm3/μm2)]; Gr1:-0.04 to -0.06, Gr2:-0.04 to 0.04, Gr3:-0.05 to 0.13, [ΔSv (nm3/nm2)]; Gr1:-2.4 to 6.4, Gr2:-2.3 to 0.9, Gr3:-0.6 to 25.5, [ΔStr (μm)]; Gr1: -0.046 to 0.121, Gr2:-0.148 to 0.050, Gr3:-0.15 to 0.12, [ΔSdr (%)]; Gr1:-0.79 to 0.59, Gr2:-0.34 to 0.67, Gr3:-0.19 to 1.15. Apart from gloss after thermocycling, aging procedures caused significant alteration of gloss and surface roughness parameters from baseline levels. Conclusions: SEM-EDX analysis demonstrated differences in microstructure and elemental composition of CAD/CAM materials tested. All materials tested demonstrated significant differences in their mechanical properties and thus differences in their clinical performance may be anticipated. Lithium disilicate had a better combination of hardness, elastic modulus and creep than all resin-based composites tested. Among RBCs tested, materials with increased filler loading, such as GB and LU had the most favorable combination of hardness, elastic modulus and creep index indicating that these materials may have better clinical performance under intraoral loading conditions. All mechanical properties tested exhibited significant correlations with each other, apart from ηΙΤ. Aging procedures caused perceptible but acceptable color changes, while no significant differences in color stability were found among materials after coffee immersion and thermocycling. CAD/CAM materials demonstrated small but visible gloss changes, with no significant differences among composite materials after aging procedures. Surface roughness parameters of the tested CAD/CAM materials were significantly affected by aging, but aging procedures influenced materials differently. Aging procedures affected the CAD/CAM materials tested indicating that these materials may be prone to color and surface alterations in the oral environment that could compromise the esthetics and the longevity of the restorations. Clinical studies are needed to investigate the long-term behavior of these newly introduced materials.
