Build-up Materials Research Articles

Effect of different indirect composite onlay and core materials on fracture resistance of endodontically treated maxillary premolars.

Purpose To compare and evaluate the effects of different indirect composite onlay and/or core buildup materials on the fracture resistance and fracture mode of restored endodontically treated premolars.Methods Two conventional handmade indirect composite resins (SR Nexco (NC) and Ceramage (CM)) and two core buildup materials, dual-cure composite resin (MultiCore Flow (MC)), and short fiber-reinforced composite resin (EverX Posterior (EXP)), were selected. Sixty maxillary premolars were randomly divided into six groups (n=10). Group 1 included intact teeth (INT; positive control). Mesio-occluso-distal cavity preparation and endodontic treatment was performed on the remaining premolars. Group 2 was restored with polymer-reinforced zinc oxide eugenol intermediate restorative material (IRM; negative control), whereas the experimental groups (groups 3-6) were restored with core buildup material and indirect composite onlay (MC_NC, MC_CM, EXP_NC, and EXP_CM). The specimens received compressive loading using a universal testing machine, at 45° to the long axis with a crosshead speed of 0.5 mm/min until fracture. Fracture modes were visually analyzed. Fracture resistance was measured and statistically analyzed using two-way and one-way ANOVA (α=0.05).Results Only the type of indirect composite onlay affected the fracture resistance of the experimental groups (P=0.009). The MC_CM group showed the highest fracture resistance, which was significantly higher than that of the MC_NC group (P=0.031). No statistically significant differences were found between the INT group and other experimental groups(P>0.05). All groups had a greater incidence of restorable than unrestorable failures.Conclusions The type of indirect composite onlay affected the fracture resistance of restored endodontically treated maxillary premolars.

Comparative evaluation of shear bond strength at the interface of monolithic zirconia with two distinct core build-up materials: An in vitro study.

The study aimed to evaluate and compare the shear bond strength (SBS) at the interface of monolithic zirconia with zirconomer (Zr) core build-up, a new type of glass ionomer cement to monolithic zirconia with composite resin core build-up material. In vitro a comparative study. A total of 32 disk-shaped samples of monolithic zirconia and two distinct core build-up materials: Zr (n = 16) and composite resin (n = 16) were used. The two components, monolithic zirconia with Zr core build-up and monolithic zirconia with composite resin core build-up, were bonded using zirconia primer and self-adhesive, dual-cure cement. The samples were subsequently thermocycled, and the SBS was tested at their interfaces. The failure modes were determined using a stereomicroscope. Data were evaluated using the descriptive analysis for mean, standard deviation, confidence interval, and independent t-test for intergroup comparison. Descriptive analysis, independent t-test, Chi-square test. The mean SBS (megapascals) of monolithic zirconia to Zr core build-up (0.74) was statistically significant when compared to monolithic zirconia with composite resin core build-up material (7.25) (P ≤ 0.001). Zirconomer core build-up showed 100% adhesive failure; composite resin core build-up had 43.8% cohesive, 31.2% mixed, and 25.0% adhesive failures. When evaluating the two core build-up materials' bindings to monolithic zirconia, Zr and composite resin core build-up showed statistically significant differences. Although Zr has been demonstrated to be the optimal core build-up material; however, additional investigation is required to determine how it bonds to monolithic zirconia more effectively.

Effect of Fluorographene Addition on Mechanical and Adhesive Properties of a New Core Build-Up Composite.

This study aims to develop a restorative material having such mechanical and adhesive properties that it can be used both as a reconstruction material and as a luting cement. The experimental core build-up composite (CBC) was derived from a self-adhesive cement by the modification of its chemical formula, requiring the use of dedicated dentin and ceramic primers. The adhesive properties to zirconia and dentin were analyzed with a micro-Shear Bond Strength test (mSBS). The mechanical properties were analyzed by a flexural strength test. The results were compared with those obtained for other commercially available cements and core build-up materials, both before and after addition of 2 wt.% fluorographene. The CBC obtained average values in the mSBS of 49.7 ± 4.74 MPa for zirconia and 32.2 ± 4.9 MPa for dentin, as well as values of 110.9 ± 9.3 MPa for flexural strength and 6170.8 ± 703.2 MPa for Young's modulus. The addition of fluorographene, while increasing the Young's modulus of the core build-up composite by 10%, did not improve the adhesive capabilities of the primers and cement on either zirconia or dentin. The CBC showed adhesive and mechanical properties adequate both for a restoration material and a luting cement. The addition of 2 wt.% fluorographene was shown to interfere with the polymerization reaction of the material, suggesting the need for further studies.

Towards 2D dosimetry using monolithic active pixel sensors and a copper grating

Higher energy and intensity X-ray radiotherapy treatments are coming into wider use, having the benefit of requiring fewer treatment fractions and fewer hospital visits per patient. However, small percentage errors in multileaf collimator positioning and dose become bigger problems with higher doses per fraction. Hence, real-time treatment verification becomes essential. Where devices downstream from the patient suffer from scattering in the patient, upstream devices can disturb the therapeutic beam. Here, a method is proposed for performing dosimetry upstream using monolithic active pixel sensors, which can be made thin enough to disturb the beam by <1%. In order to calculate the dose to the tumour, a verification device needs to make a measurement of the photon field. Some photons will Compton scatter an electron in the silicon and generate a signal. However, this signal is obscured by energy deposits from contamination electrons, originating from Compton scattering in the accelerator head and air. Often extensive build-up material is added to verification devices to reduce the electron contamination and enhance the photon signal. However, this leads to degradation of the beam intensity to the patient. Instead we propose using thin strips of 50 µm thick copper in a grating pattern and measuring the difference in the signal with and without it. The contamination electrons are relatively undisturbed by the presence of the thin copper strips and the photon signal generated via Compton scattering is enhanced under the strips. Hence the difference in the two signals mostly consists of energy deposits originating from the therapeutic photons. From this the dose to the patient can be derived. The 50 μm of copper is thin enough to keep the beam attenuation below 1%, but in itself would give a total signal response which consists of 38% contamination electrons. Using the grating technique, we show that the electron contamination can be reduced to 2.6% of the total signal. This allows the photon signal only to be extracted from the data and thus the dose to patient with a very thin upstream detector can be calculated using a Monte Carlo model to extrapolate the photon flux into the tumour.

An In Vitro Study Comparing the Diametral Tensile Strength of Composite Core Build-Up Material With Three Different Prefabricated Post Systems.

Statement of problemDental restorations are subjected to tensile stresses from oblique or transverse loading of their complex geometric forms, making tensile strength a fundamental mechanical property. Since composite core build-up materials are brittle, the integrity of the post and core depends on their tensile strength and resistance to fracture when utilized with various prefabricated post systems. Therefore, it is essential to determine the tensile strength of the prefabricated metallic and nonmetallic posts used to reinforce the composite resin core.PurposeThis study compared the diametral tensile strength (DTS) of three prefabricated post systems with composite core build-up material.Material and methodologyTen composite resin cores from four different groups were formed. The control group was the composite resin core without a post (group 1). Group 2 was composed of composites with metal posts, group 3 was composed of composites with glass fiber posts, and group 4 was composed of composites with carbon fiber posts. All the samples were kept in a humid place for seven days to mimic the conditions in the mouth. DTS was determined by recording the tensile force required to fracture the core material by performing a diametral compression test for tension after a week. The observations were analyzed using a one-way analysis of variance (ANOVA), followed by a post-hoc test.ResultsThe tensile strength of the resin core material was decreased by 28.1%, 20.8%, and 10.4% by using posts made of stainless steel, carbon fiber, and glass fiber, respectively. Among the three post systems, stainless steel had the lowest mean DTS values, while glass fiber had the highest mean DTS values.ConclusionComposite core glass fiber post systems showed higher tensile strength than other post systems.

Release of monomers in dental wastewater during treatment. A comparative in vitro and in vivo study based on Fabric phase Sorptive extraction

The main objective of this research was to detect monomers that are released during dental restorative procedures related to the oral cavity and then discharged into the environment through the drainage of the dental unit. This study involves the collection of wastewater from the spray system of a high-speed dental handpiece before it winds up in the central drain after the grinding of resin composite materials. The study was executed in two phases: an in vitro experiment and an in-vivo experiment. Three representative dental materials were used; a resin composite for direct restorations, a core-build up material, and a computer-aided designand computer-aided manufacturing (CAD/CAM) material. On both occasions, the water from the spray-system of the handpiece during the milling of the specimens was extracted using water suction and analysed by high-pressure liquid chromatography (HPLC) and verified with HPLC-PDA after Fabric Phase Sorptive Extracttion. In the first phase, triethylene glycol dimethacrylate (TEGDMA) was detected in the wastewater samples of all the materials tested whereas bisphenol-A (BPA) was not detected. Urethane dimethacrylate was released only from the CAD/CAM material (0.66 ± 0.14 ng/μL) while BisGMA was not detected. In the second phase the core build-up material released an amount of BPA (0.42 ± 0.14 ng/μL) while after 7 days, the amount of BPA increased (0.97 ± 0.07 ng/μL). The resin composite indicated for direct restoration material released the highest amount of TEGDMA (p < 0.001).The contamination of the environment by dental procedures is possible because monomers are released from different dental restorative materials and are detected in the wastewater of dental units.

Effect of Different Post Materials and Adaptability on Fracture Resistance and Fracture Mode in Human Endodontically Treated Teeth.

Objective To investigate the effect of different post materials and adaptability on fracture resistance and fracture mode of endodontically treated teeth. Materials and Methods Sixty extracted human mandibular premolars were selected and divided into 6 groups (n = 10) according to the restorative method after endodontic treatment: no ferrule presented and restored without fiber post (Group C), 2.0 mm ferrule presented and restored without fiber post (Group CF), restored with D.T. Light-Post (Group PDT), restored with anatomically customized D.T. Light-Post, relined with resin composite (Group ADT), restored with Hi-Rem prosthetic post (Group PHR), and restored with anatomically customized Hi-Rem prosthetic post, relined with resin composite (Group AHR). After restoring with core build-up materials, all specimens were loaded at 45° in a universal testing machine until failure. Visual inspection of all specimens for fracture modes was performed. The data were analyzed using one-way ANOVA, and the fracture mode was reviewed using the chi-square test. Results Anatomically customized groups presented statistically significant higher fracture resistance than prefabricated groups and group C (P < 0.05). Without post, group CF displayed significantly higher fracture resistance than group C (P < 0.05). Group C, CF, PDT, and PHR showed some specimens with unfavorable fractures. Conclusions Anatomically customized posts presented highest fracture resistance among all groups. There was no significant difference in fracture mode across all groups.

Comparative Evaluation of Shear Bond Strength Of Various Core Build – up Materials In Maxillary Anterior Teeth - An In-Vitro Study

Need for the study: Incisors are commonly damaged by caries or trauma. The major portion of the crown part of a damaged anterior tooth could be restored with a core build-up material which not only reinstate aesthetics but also withstand an array of forces in the oral cavity. Aim: To evaluate the Shear Bond Strength(SBS) of Zirconomer, Resin Modified Glass Ionomer cement(RMGIC), Microhybrid Composite and Nanocomposite as core build-up materials in maxillary anterior teeth. Methodology: 48 extracted intact human maxillary central incisors were collected and divided into four groups.Anatomic crown was trimmed upto fifty percent which involved the enamel and partly the dentin of each tooth. The experimental teeth were mounted in chemical cure acrylic resin and restored with Zirconomer, RMGIC, Microhybrid Composite and Nanocomposites. The samples were subjected to Shear Bond Strength(SBS) analysis using a universal testing machine (UTM). Results: Composites exhibited better mechanical properties than Glass Ionomer Cements. Nanocomposites had the highest Shear Bond Strength followed by microhybrid composites but there was no statistical significance. Conclusions: Nanocomposite possess better mechanical properties and also offers superior esthetics due to its supercilious polishability, proving to be the ideal core build-up material for maxillary anterior teeth. Key-words:Core build up- Composite-Glass Ionomer Cements-Shear Bond Strength

Effects of Sr/F-Bioactive Glass Nanoparticles and Calcium Phosphate on Monomer Conversion, Biaxial Flexural Strength, Surface Microhardness, Mass/Volume Changes, and Color Stability of Dual-Cured Dental Composites for Core Build-Up Materials.

This study prepared composites for core build-up containing Sr/F bioactive glass nanoparticles (Sr/F-BGNPs) and monocalcium phosphate monohydrate (MCPM) to prevent dental caries. The effect of the additives on the physical/mechanical properties of the materials was examined. Dual-cured resin composites were prepared using dimethacrylate monomers with added Sr/F-BGNPs (5 or 10 wt%) and MCPM (3 or 6 wt%). The additives reduced the light-activated monomer conversion by ~10%, but their effect on the conversion upon self-curing was negligible. The conversions of light-curing or self-curing polymerization of the experimental materials were greater than that of the commercial material. The additives reduced biaxial flexural strength (191 to 155 MPa), modulus (4.4 to 3.3), and surface microhardness (53 to 45 VHN). These values were comparable to that of the commercial material or within the acceptable range of the standard. The changes in the experimental composites’ mass and volume (~1%) were similar to that of the commercial comparison. The color change of the commercial material (1.0) was lower than that of the experimental composites (1.5–5.8). The addition of Sr/F-BGNPs and MCPM negatively affected the physical/mechanical properties of the composites, but the results were satisfactory except for color stability.

Modified irradiation technique for transfusable blood using a clinical linear accelerator

Whole blood irradiation prior to blood transfusion mitigates the risk of Transfusion Associated Graft versus Host Disease (TA-GvHD) to the receiver. This study aimed to improve dose homogeneity, also to benefit from a faster technique and a simplified blood irradiation workflow. An acrylic box accommodating eight units of blood has been fabricated, build-up material being used to ensure dose homogeneity. A linear accelerator dose distribution treatment plan for blood bag irradiations has been evaluated, measurement of dose using nanoDot optically stimulated luminescent dosimeters (OSLD) allowing comparison with calculated dose. By using build-up material, dose distribution was within 95%–107% of the prescribed dose. With all eight units of blood accommodated in the box, an irradiation time of 20 min per box has been needed. Compared to a previously adopted procedure, use of the acrylic box and build-up material maintains dose homogeneity, also simplifying the workflow, the technique also being easy to undertake by the operators.

Evaluation of Microleakage Using Dye-penetration Method in Three Different Composite Resin Core Build-up Materials: An In Vitro Study

Aim of the current research is to establish and assess the microleakage in bulk-fill composite, nanohybrid ormocer-based resins, and nanofilled composite resin core build-up materials employing the dye-penetration technique. Sixty human mandibular first premolar teeth with a solitary root canal without dental caries were chosen for this research. Each specimen was subjected to decoronation of 2 mm from the cementoenamel junction (CEJ), following which the root canal treatment procedure was rendered complete. A space for the post was made for all the 60 samples. Following positioning of the post, specimens were allocated into one of the following three investigational groups (20 specimens in every group) on the basis of the core build-up materials used as group I: bulk-fill composites, group II: nanohybrid ormocer-based resins, and group III: nanofilled resin composites. Direct composite was used for core build-up and subjected to light-curing. Following this, the specimens were immersed in 1% methylene blue solution for 24 hours interval. Each section was evaluated for dye diffusion employing a stereomicroscope with software at a magnifying power of 40× and surface contact between dentin and base of the material was evaluated under scanning electron microscope. Nanohybrid ormocer-based composites exhibited the least microleakage at 1.12 ± 0.14, in pursuit by nanofilled composite resins at 1.79 ± 0.09, and finally the bulk-fill composites at 2.85 ± 0.11, amid the investigational groups studied. A statistically significant difference amid the three dissimilar cores buildup substances was found upon analysis of variance. Despite the study limitations, this research came to a conclusion that each of the three investigated core build-up substances exhibited microleakage. However, amid the three, nanohybrid ormocer-based composites depicted the lowest amount of microleakage in pursuit by the nanofilled resins and the bulk-fill composites. Core build-up is an important requirement as the remaining tooth substance following root canal treatment reduces and needs reinforcement with core build-up to sustain the tooth structure and provide resistance. A vital mandate for enduring efficiency of the restoration in the mouth is high-quality adhesive bond of these agents to cavity walls with diminished microleakage.

Development and dosimetric verification of 3D customized bolus in head and neck radiotherapy

The commercial flat bolus cannot form perfect contact with the irregular surface of the patient’s skin, resulting in an air gap. The purpose of this study was to evaluate the feasibility of using a 3D customized bolus from silicone rubber. The silicone rubber boluses were studied in basic characteristics. The 3D customized bolus was fabricated at the nose, cheek and neck regions. The point dose and planar dose differences were evaluated by comparing with virtual bolus. The hardness, thickness, density, Hounsfield unit (HU) and dose attenuation of the customized bolus were quite similar to a commercial bolus. When a 3D customized bolus was placed on the RANDO phantom, it can significantly increase buildup region doses and perfectly fit against the irregular surface shape. The average point dose differences of 3D customized bolus were −1.1%, while the commercial bolus plans showed −1.7%. The average gamma results for planar dose differences comparison of 3D customized bolus were 93.9%, while the commercial bolus plans were reduced to 91.9%. Overall, A silicone rubber bolus produced the feasible dosimetric properties and could save cost compared to a commercial bolus. The 3D printed customized bolus is a good buildup material and could potentially replace and improve treatment efficiency.

Chemical and mechanical properties of dual-polymerizing core build-up materials

ObjectivesTo investigate the chemical (degree of conversion (DC)) and mechanical properties (Martens hardness (HM), elastic indentation modulus (EIT), and biaxial flexural strength (BFS)) of four dual-polymerizing resin composite core build-up materials after light- and self-polymerization.Materials and methodsRound specimens with a diameter of 12 mm and a thickness of 1.5 mm were manufactured from CLEARFIL DC CORE PLUS (CLE; Kuraray), core·X flow (COR; Dentsply Sirona), MultiCore Flow (MUL; Ivoclar Vivadent), and Rebilda DC (REB; VOCO) (N = 96, n = 24/material). Half of the specimens were light-polymerized (Elipar DeepCure-S, 3 M), while the other half cured by self-polymerization (n = 12/group). Immediately after fabrication, the DC, HM, EIT, and BFS were determined. Data was analyzed using Kolmogorov–Smirnov, Mann–Whitney U, and Kruskal–Wallis tests, Spearman’s correlation, and Weibull statistics (p < 0.05).ResultsLight-polymerization either led to similar EIT (MUL; p = 0.119) and BFS (MUL and REB; p = 0.094–0.326) values or higher DC, HM, EIT, and BFS results (all other groups; p < 0.001–0.009). When compared with the other materials, COR showed a high DC (p < 0.001) and HM (p < 0.001) after self-polymerization and the highest BFS (p = 0.020) and Weibull modulus after light-polymerization. Positive correlations between all four tested parameters (R = 0.527–0.963, p < 0.001) were found.ConclusionsFor the tested resin composite core build-up materials, light-polymerization led to similar or superior values for the degree of conversion, Martens hardness, elastic indentation modulus, and biaxial flexural strength than observed after self-polymerization. Among the tested materials, COR should represent the resin composite core build-up material of choice due to its high chemical (degree of conversion) and mechanical (Martens hardness, elastic indentation modulus, and biaxial flexural strength) properties and its high reliability after light-polymerization. The examined chemical and mechanical properties showed a positive correlation.Clinical relevanceThe chemical and mechanical performance of dual-polymerizing resin composite core build-up materials is significantly affected by the chosen polymerization mode.

59 - Characterization of Experimental Short Fiber Reinforced Dual-Cure Core Build-Up Composites

As a core build-up material, dual-cured (DC) resin-based composites are getting popular. This study aimed to evaluate certain physical properties of a new experimental short fiber-reinforced DC resin composites (SFRCs) in comparison with different commercial conventional DC materials (Gradia Core, Rebilda DC, Luxa Core and Visalys CemCore). Degree of monomer conversion (DC%) was determined by FTIR-spectrometry using either self or light-curing mode. The flexural strength (FS), modulus (FM), and fracture toughness (FT) were measured using a three-point bending setup. The surface microstructure of each resin composite was investigated with scanning electron microscopy (SEM). Data were statistically analyzed with analysis of variance ANOVA (p = 0.05). The light-curing mode showed significant (p<0.05) effect on the DC% and flexural properties of tested DC resin composites and differences were material-dependent. SFRC exhibited the highest fracture toughness (2.3 MPa m1/2) values and Luxa showed the lowest values (1 MPa m1/2) among the tested materials (p<0.05). Gradia and SFRCs showed the highest flexural modulus (p<0.05), while the other resin composites had comparable values. The new DC short fiber-reinforced core build-up resin composite differed significantly in its fracture toughness compared to the tested conventional DC composites.

Evaluation of effect of core build-up materials on fracture resistance of endodontically treated teeth

Background: Restoration of teeth after endodontic treatment is becoming an integral part of reconstructive dentistry. Aim: The aim of this study was to evaluate the effect of different core build-up materials on fracture resistance of endodontic ally treated teeth. Materials and methods:Freshly extracted forty permanent mandibular first molars were selected. Standardized access cavities were prepared, following which mesial canals were prepared up to F2 (8%25) and distal canals up to F3 (9%30)and obturated. The coronal portion of the specimen was altered by removing the mesial wall and retaining buccal, lingual and mesial walls of 2mm and distal 5mm girth.Ten specimens each were rehabilitated with high copper amalgam, type IX GIC, posterior composite and Alkasite as core build-ups. All the specimens were finally rehabilitated with a metal crown. The specimens were tested for fracture resistance using a universal testing machine under oblique (135oto the long axis of teeth) cyclic loading. The number of cycles taken to fracture,and the fracture site was recorded.The results of mechanical cyclic loading to evaluate fracture resistance showed that compositecore endured the maximum number of cycles to fracture followed by amalgam, Alkasite and type IX GIC.To test the statistical significance inthe difference of mean value KICamong four groups, Kruskal-Wallis one-way analysis of variance was applied. Bonferroni’s multiple comparison test was performed to determine which group significantly differed from the others. Results:From the results of this study, the composite was considered to be the best core build-up material. The newer material, Alkasite can bear stress almost to that of amalgam restoration. Conclusion:This studysuggeststhat Alkasite could be used as a core material for restoring the endodontically treated teeth.

Comparative evaluation of fracture resistance of various core buildup materials on endodontically treated teeth: An in vitro study

Aim: The present study aimed to evaluate and compare the fracture resistance of four different core build-up materials on endodontically treated teeth. Materials and Methods: In this in vitro study, sample size estimation was done using G*power software (version 3.1.9.2), an effect size of 0.66 was obtained at 95% confidence interval. 48 Teeth samples were decoronated 2 mm above the Cementoenamel junction. Root canal treatment done, followed by preparation of post space and fiberglass posts of 10 mm length was cemented with resin cement into the root canal and 4 mm above the prepared tooth. All the samples were randomly divided into 4 groups of 12 samples for four different core build up materials. All teeth were restored with a Nickel chromium crown of standard dimensions and cemented with glass ionomer cement. Fracture resistance measured by applying the load at an angle of 135° to the long axis of the tooth at a crosshead speed of 0.05 mm/min until failure. Analysis was performed using KRUSKAL-WALLIS to compare mean values and standard deviation of fracture resistance, followed by post – hoc MANN WHITNEY test for assessing the significant difference of fracture resistance between the four groups. Results: Resistance to fracture was greater in Luxacore Z group followed by Vitremer, Denfil and Filtek. However, no statistically significant differences in the fracture resistance were observed among the groups. Conclusion: The results indicate that Luxacore Z core build-up material exhibits superior fracture resistance. Resin modified glass ionomer cement had fracture resistance comparable to Luxacore.

Flexural Property of a Composite Biomaterial in Three Applications

Resin composite is widely used in the dental field in clinics as a biomaterial. For example, it has been used as a composite material, a type of biomaterial, to repair caries and restore masticatory function, and as a luting agent to adhere the restoration to the tooth substrate. In order to demonstrate its function, we have measured the mechanical strength. From such basic research, we explain the potential of a dental material through the measurement of flexural strength and modulus of elasticity. In this research, we introduce commercial products that are actually used as composite materials suitable for tooth substrate and provide readers with their properties based on flexural strength and modulus of elasticity. In clinical performance, it might be advisable to delay polishing when a composite material is used for a luting material, a filling material and a core build-up material, as the flexural strength and the flexural modulus of elasticity were improved after 1 day of storage, and flexural strength and characteristics are considered as important mechanical properties of oral biomaterials.

Investigation of mechanical performances and polymerization shrinkage of dual-cured resin composites as core build-up material

This study systematically compared the mechanical performances and polymerization shrinkage of two novel dual-cured resin composites (DCRC) with one conventional packable light-cured resin composite (LCRC) for their application as core build-up material by micro-hardness test, flexural strength test, push-out test, and digital image correlation analysis. The LCRC had a significantly higher micro-hardness (p<0.05) whereas the bond strength demonstrated no difference. The mean values of three materials ranged from 35.16 and 64.82 for the Vickers hardness and from 4.66 MPa to 11.53 MPa for the bond strength. The flexure strength of the three materials was not statistically different from each other. LCRC demonstrated 1.88% of volumetric shrinkage while the two DCRC showed 5.06% and 4.91%, respectively. In general, the DCRC demonstrated a comparable flexural strength and bond strength as the LCRC, however, the significant polymerization shrinkage of DCRC should be emphasized.

Handling of beam spectra in training and application of proton RBE models

Published data from cell survival experiments are frequently used as training data for models of proton relative biological effectiveness (RBE). The publications rarely provide full information about the primary particle spectrum of the used beam, or its content of heavy secondary particles. The purpose of this paper is to assess to what extent heavy secondary particles may have been present in published cell survival experiments, and to investigate the impact of non-primary protons for RBE calculations in treatment planning. We used the Monte Carlo code Geant4 to calculate the occurrence of non-primary protons and heavier secondary particles for clinical protons beams in water for four incident energies in the [100, 250] MeV interval. We used the resulting spectra together with a conservative RBE parameterization and an RBE model to map both the rise of RBE at the beam entry surface due to heavy secondary particle buildup, and the difference in estimated RBE if non-primary protons are included or not in the beam quality metric. If included, non-primary protons cause a difference of 2% of the RBE in the plateau region of an spread out Bragg peak and 1% in the Bragg peak. Including non-primary protons specifically for RBE calculations will consequently have a negligible impact and can be ignored. A buildup distance in water of one millimeter was sufficient to reach an equilibrium state of RBE for the four incident energies selected. For the investigated experimental data, 83 out of the 86 data points were found to have been determined with at least that amount of buildup material. Hence, RBE model training data should be interpreted to include the contribution of heavy secondaries.

Early failures when using three different adhesively retained core build-up materials\u2014a randomized controlled trial

ObjectivesTo compare the failure rates for three different adhesively retained core build-up composites up to the incorporation of a permanent fixed dental prosthesis (FDP), and to identify potential failure risk factors.Material and methodsA randomized controlled trial of 300 participants in need of a core build-up to restore a vital abutment tooth before prosthetic treatment was conducted. Participants were assigned by stratified block randomization to one of three study groups: Rebilda DC (RDC), Clearfil DC Core (CDC), or Multicore Flow (MF). Test teeth were prepared by use of the respective manufacturer’s adhesive system. The total-etch technique was used for RDC and MF, and the self-etch technique for CDC. Participants were treated by dentists (n = 150) or dental students (n = 150). Failure rates of core build-ups before incorporation of FDPs were investigated using univariate and multiple logistic regression.ResultsThe overall failure rate was 8% (n = 23). Rate differences between the three investigated groups did not reach statistical significance (p > 0.05). The mean time between placement of core build-ups and placement of fixed dental prostheses was 12.2 (SD: 14.2) weeks. Conversely, larger cavities (> 3 surfaces) and treatment by dental students were independently associated with an increased failure risk (p < 0.05).ConclusionsThe main risk factors for early failure seem to be the size of the core build-up and clinical experience of the operator, whereas failure rates of core build-up materials combined with a self-etch approach seem to be similar to the rates of materials combined with the total-etch technique.Clinical significanceThis research article should give clinicians an impression of the short-term performance of different adhesively retained core build-ups using different adhesive techniques/materials. Moreover, predominant influencing factors for the success or failure should be pictured.