حمد علي حمد الجميعة

البحوث المنشورة

Methods. 36 specimens (n = 3), based on two resin composites incorporating PowerCure rapid-olymerization technology in two consistencies (PFill; PFlow) and two

comparators with matching consistencies (Eceram;  Flow), were investigated from the same manufacturer (Ivoclar AG, Liechtenstein). Specimens were prepared within 4mm diameter cylindrical molds, of either 1 mm or 4 mm depths respectively, to simulate near-surface and deep loca- tions in a bulk-fill restoration. The independent variables in this study were: materials, thickness and time. Two high irradiance polymerization protocols were utilized for Power- Cure materials: 2000 and 3050 mW/cm2 for 5 and 3 s, respectively. A standard (1200 mW/cm2 ) polymerization protocol was used with control materials. FTIR was utilized to measure DC in real-time for 24 h post-irradiation. The data were analyzed using Welch’s-ANOVA, Games- Howell post-hoc test, kinetic dual-exponential sum function and independent sample t-tests (p = 0.05).

Results. The DC of the materials ranged between 44.7–59.0 % after 5 min, which increased after 24 h reaching 55.7–71.0 % (p < 0.05). Specimen thickness did not influence the overall DC. At 5 min, the highest DC was shown in EFlow. But PFlow, irradiated for 3 s and 5 s exhib- ited comparable results (p > 0.05). PFill composite irradiated with the 3 s and 5 s protocols did not differ from ECeram (p > 0.05). Specimen thickness and material viscosity affected polymerization kinetics and rate of polymerization (RPmax).

Faster polymerization occurred in 1 mm specimens (except PFill-5 s and ECeram). PFill and PFlow exhibited faster conver- sion than the controls. RPmax varied across the specimen groups between 4.3–8.8 %/s with corresponding DC RPmax between 22.2–45.3 %.

Significance. Polymerization kinetics and RPmax were influenced by specimen thickness and material viscosity. PFill and PFlow materials produced an overall comparable conversion at 5min and 24h post-irradiation, despite the ultra-short irradiation times, throughout the 4 mm specimen thickness.

Methods. Two bulk-fill composites (Ivoclar AG) were studied: Tetric PowerFill (PFill) and Pow-erFlow (PFlow). Split molds were used to fabricate cylindrical {4 mm (dia) × 4 mm} paste. specimens, irradiated at 23 ◦C at 0 mm from the top surface with a BluephasePowerCure LED-LCU, with 3 s or 5 s modes, emitting 3 and 2 W/cm2,  espectively. Postirradiation specimens were immediately transferred to an apparatus equipped with a flat-ended indentor of 1.5 mm diameter. 14 MPa compressive stress at the indentor tip was applied centrally in < 2 min and maintained constant for 2 h. Indentation (I) magnitudes were recorded in real-time (t), with I(t) data re-expressed as % indentation relative to the 4 mm specimen height. After 2 h, the indentor was unloaded and indentation recovery was monitored for a further 2 h. Parallel sets of measurements were made where indentation was delayed for 24 h. Further measurements were made with more conventional composites: EvoCeram Bulk Fill  ECeram) and Tetric EvoFlow Bulk Fill (EFlow).

These were irradiated for 20 s at 1.2 2W/cm . Kinetic data were curve-fitted to exponential growth functions and key parameters analyzed by ANOVA and post-hoc tests ( =

0.05).

Results. I(t) plots looked initially similar to bulk creep/recovery: rapid deformation plus viscoelastic response; then, upon unloading: rapid (elastic) recovery followed by partial vis- coelastic recovery. However, unlike multiply irradiated and stored bulk-creep  pecimens, the present specimens were exposed to only 3 or 5 s “occlusal” irradiation; generating “hard” surfaces. Subsequently, during the 2 h indentation, the polymer matrix network continued to harden and consolidate. Upon initial loading, I(t) reached 2–3% indentation, depending upon the formulation. Upon unloading at 2 h, elastic recovery was only ca. 1 %. Delayed loading for 24 h, generated I(t) plots of significantly reduced magnitude. Most importantly, however, the I(t) plots for ECeram and EFlow, after 20 s irradiation, showed I(t) magnitudes quite comparable to the PFill and PFlow rapid-cure composites.

Significance. Macroscopic indentation creep has been shown to be a workable procedure that can be applied to rapid-cure materials to assess their immediate surface integrity and developing viscoelastic characteristics. The applied stress of 14 MPa was relatively severe and the indentation/recovery profiles of PowerFill materials with only 3 or 5 s irradiation demonstrated comparability with their established 20 s cure siblings, evidencing the suitability of the PowerCure system for clinical application

composites

Methods. A 25 × 5 × 2.8-mm stainless-steel mold with 2.5 mm single-edge center notch, following ASTM standards [E399-90], was used to fabricate 135 specimens (n = 15) of the composite materials and randomly distributed into groups. For the baseline group, specimens were  abricated and then tested after 24-h storage in water. For the biofilm challenge, specimens were randomly placed in a six-well tissue culture plate and kept at 37 °C with  acterial growth media (Brain Heart Infusion (BHI); Streptococcus mutans) changed daily for 15 days. For the water storage challenge, specimens were kept in 5 ml of deionized distilled autoclaved water for 30 days at 37 °C. μCT evaluation by scanning the specimens was  erformed before and after the proposed challenge. Fracture toughness (KIc) testing was carried out following the challenges.

Results. μCT surface area and volume analyses showed no significant changes regardless of the materials tested or the challenge. Filtek and Admira fracture toughness was significantly lower after the biofilm and water storage challenges. OASys mean fracture toughness values after water aging were significantly higher than that of baseline. Toughness values for OASys composites after biofilm aging were not statistically different when ompared to either water or baseline values.

Conclusion. The fracture toughness of Bis-GMA and ormocer-based dental resin composites significantly decreased under water and bacterial biofilm assault.

However, such degradation in fracture toughness was not visible in OASys-based composites.

Methods. Two ultra-rapid photo-polymerized bulk fill (URPBF) materials: PFill and PFlow were studied, along with their comparators ECeram and EFlow. PFill contains an addition fragmentation chain transfer (AFCT) agent. The URPBR materials were irradiated using two different 3 s high irradiance protocols (3000 and 3200 mW/cm2 based on Bluephase PowerCure and VALO LCUs, respectively) and one 10 s standard protocol (1200 mW/cm2 based on a Bluephase PowerCure LCU). Bonded disk and Bioman II instruments were used to measure Polymerization shrinkage % and shrinkage stress MPa, respectively, for 60 min at 23 ± 1 °C (n = 5). Maximum shrinkage-rate and maximum shrinkage stress-rate were also calculated for 15 s via numerical differentiation. The data were analyzed via multiple One-way ANOVA and Tukey post-hoc tests (α = 0.05).

Results. PFill groups, regardless of their irradiance protocol, showed significantly lower PS than the comparator, ECeram (p < 0.05). However, PFlow irradiated via different protocols, was comparable to EFlow and ECeram (p > 0.05). PFill consistently produced stress results which were significantly lower than ECeram (p < 0.05) and were comparable for both high irradiance protocols (p > 0.05). PFlow only exhibited significantly higher shrinkage stress when polymerized with the 3 sVALO protocol (p < 0.05).

The maximum shrinkage strain-rate (%/s) was significantly lower in PFill-10s and PFill-3s groups (using PowerCure LCU) compared to ECeram. However, no differences were seen between PFlow and EFlow (p > 0.05). The maximum shrinkage stress-rate of PFill and PFlow was comparable between different irradiation protocols, as well as to their

comparator ECeram (p > 0.05).

Significance. High irradiation protocols over ultra-short periods led to slightly lower shrinkage strain but slightly higher stress, possibly due to reduced network mobility. The AFCT agent incorporated in PFill composite seemed to reduce shrinkage stress development, even with high irradiance protocols

maps during intra-dental photo-irradiation within a molar cavity restored with either Ultra-Rapid Photo-Polymerized Bulk Fill (URPBF) composites or a pre-heated thermoviscous bulk-fill composite, compared to a standard bulk-fill resin-based-composite (RBC). The specific objectives included visual assessment of the temperature maps and quantitative assessment of several temperature/time plots at four different locations.

Methods. A caries-free lower first molar cavity served as a natural tooth mold. Resin composites were placed without intermediary adhesive. Two URPBF composites (PFill;

PFlow) and one pre-heated thermo-viscous bulk-fill composite (Viscalor: VC) were compared to a contemporary bulk-fill composite (One Bulk Fill: OBF). Two LED-LCU devices were used: Bluephase PowerCure (PC) and Elipar S10 (S10), with three light-irradiation protocols (PC-3s, PC-10s and S10-10s). 2D temperature maps over the entire coronal area were recorded for 120s during and after irradiation using a thermal imaging camera. Changes at four different levels were selected from the data sets: (0, 2 and 4 mm from the cavity top and at 1 mm below the dentin cavity floor). The maximum temperature attained (Tmax), the mean temperature rise (ΔT), the time (s) to reach maximum temperature and the integrated areas (°C s) under the temperature/time (T/t) plots were identified. Data were analysed via three-way ANOVA, One-way ANOVA, independent ttests and Tukey post-hoc tests (p < 0.05).

Results. All RBCs showed qualitatively similar temperature-time profiles. PFlow reached Tmax in the shortest time. PC-3s (3000 mW/cm2) generated comparable ΔT to S10-

10s, except with PFill, where ΔT was greater. Despite the same irradiance (1200 mW/cm2), Elipar S10 led to higher Tmax and ΔT compared to PC-10s. The highest Tmax and ΔT were observed at the 2 mm level, and the lowest were at 1 mm depth into the underlying dentin.

Significance. Coronal 2D temperature maps showed rises largely confined within the bulk-fill RBC materials, with maxima at 2 mm rather than 4 mm depth indicating some

extent of thermal insulation for the underlying dentin and pulp. RBCs polymerized via different irradiation protocols showed similar temperature changes. With the PC-3s

protocol – also with pre-heated VC – minimal temperature rises at 1 mm within dentin suggest their clinical safety when sufficient remaining dentin thickness is present.

Methods. Eight representative RBCs were selected based on different clinical categories: three bulkfills (OBF, Filtek One Bulk Fill; VBF, Venus Bulkfill; EBF, Estelite Bulkfill),

three conventional non-flowables (XTE, Filtek Supreme XTE; GSO, GrandioSo; HRZ, Harmonize) and conventional flowables (XTF, Filtek Supreme XTE Flow; GSF, GrandioSo Flow). Stainless steel split molds were used to fabricate cylindrical specimens (4 mm (dia) × 4 mm). These were irradiated (1.2 W/cm2) for 20 s on the top surface. Postirradiation specimens (n = 3), within their molds, were centrally loaded with a flat-ended 1.5 mm diameter indenter under 14 MPa stress: either immediately (<2 min) or after 24h delayed indentation. Stress was maintained for 2 h, then – after removal – recovery measurements continued for a further 2 h. Indentation depth (%) versus time was measured continuously to an accuracy of <0.1 μm. Data were analyzed by One-way ANOVA and Tukey post-hoc tests (α = 0.05).

Results. Time-dependent viscoelastic indentation was observed for all RBCs. For immediate indentation, the maximum indentation range was 1.43–4.92%, versus 0.70–2.22% for 24 h delayed indentation. Following 2 h recovery, the residual indentation range was 0.86–3.58% after immediate indentation, reducing to 0.22–1.27% for delayed indentation. The greatest immediate indentation was shown by VBF followed by XTF and GSF. OBF, HRZ, XTE and GSO had significantly lower indentations (greater hardness). XTE showed a significantly reduced indentation maximum compared to OBF (p < 0.05). Indentations delayed until 24 h post-irradiation were reduced (p < 0.05) for most materials.

Significance. The indentation-creep methodology effectively characterized resin-based composites within several categories. Viscoelastic properties evaluated by the indentation-creep method confirmed that highly filled RBCs were more resistant to indentation. Indentations were reduced after 24 h post-irradiation due to further matrixnetwork development.

المؤتمرات العلمية:

To determine the effect of aging methods on the fracture toughness of a conventional Bis-GMA-based resin composite (Filtek Supreme), an ormocer-based resin composite (Admira), and an experimental hydrophobic oxirane/acrylate interpenetrating network resin system (OASys)-based composite.

Methods

A 25 × 5 × 2.8-mm stainless-steel mold with 2.5 mm single-edge center notch, following ASTM standards [E399-90], was used to fabricate 135 specimens (n = 15) of the composite materials and randomly distributed into groups. For the baseline group, specimens were fabricated and then tested after 24-h storage in water. For the biofilm challenge, specimens were randomly placed in a six-well tissue culture plate and kept at 37 °C with bacterial growth media (Brain Heart Infusion (BHI); Streptococcus mutans) changed daily for 15 days. For the water storage challenge, specimens were kept in 5 ml of deionized distilled autoclaved water for 30 days at 37 °C. μCT evaluation by scanning the specimens was performed before and after the proposed challenge. Fracture toughness (KIc) testing was carried out following the challenges.

Results

μCT surface area and volume analyses showed no significant changes regardless of the materials tested or the challenge. Filtek and Admira fracture toughness was significantly lower after the biofilm and water storage challenges. OASys mean fracture toughness values after water aging were significantly higher than that of baseline. Toughness values for OASys composites after biofilm aging were not statistically different when

compared to either water or baseline values.

Conclusion

The fracture toughness of Bis-GMA and ormocer-based dental resin composites significantly decreased under water and bacterial biofilm assault.

However, such degradation in fracture toughness was not visible in OASys-based composites.