Effects of nanofillers on mechanical properties of fiber-reinforced composites polymerized with light-curing and additional postcuring

Changes in color and contrast ratio of resin composites after curing and storage in water

Purpose

To verify the color change and contrast ratio of resin composites after curing and after 30 days of storage in water.

Methods

Dentin A2 shades of different light-cured dental resin composites (Vittra APS, FGM, Brazil; Z350 XT, 3M ESPE, EUA; Tetric N-Ceram, Ivoclar Vivadent, Liechtenstein, and Charisma Diamond, Heraeus Kulzer, Germany) were tested. Ten rounded specimens (8 mm × 2 mm) were prepared for each material. Reflectance for all samples was obtained using a spectrophotometer (Minolta CM 3700d, Konica Minolta, Japan) before curing, immediately after curing, and after 30 days of storage in water. The color change (ΔE*lab) and contrast ratio (CR) data were analyzed using a one-way analysis of variance with Tukey's and paired t-tests (α = 1%).

Results

For all materials tested, significant color changes were noticeable after curing and after 30 days in water (p < 0.01). Significant changes in the CR values before curing, after curing, and 30 days of storage in water were observed in the resin composites investigated (p < 0.01) except for Z350 (p > 0.01).

Conclusion

The CR values and color changes after curing and 30 days of storage in water varied depending on the material tested. This study corroborates the clinical practice of curing a small amount of unpolymerized resin composite on the tooth surface to select the desired shade before undertaking esthetic restorative procedures.

Effect of Composite Core Materials on Fracture Resistance of Endodontically Treated Teeth: A Systematic Review and Meta-Analysis of In Vitro Studies

Various material properties are involved in the success of endodontically treated restorations. At present, restorative composites are commonly employed as core build-up materials. This study aimed to systematically review the literature to assess the effect of using composite core materials on the in vitro fracture of endodontically treated teeth. Two different reviewers screened the literature, up to June 2021, in five distinct electronic databases: PubMed (MedLine), Scopus, Scielo, ISI Web of Science, and EMBASE. Only in vitro studies reporting the effect of the use of composite core materials on the fracture resistance of endodontically treated teeth were included. A meta-analysis was carried out using a software program (Review Manager v5.4.1; The Cochrane Collaboration, Copenhagen, Denmark). The risk of bias in each study was assessed following the parameters of another systematic review. A total of 5016 relevant papers were retrieved from all databases. After assessing the title and abstract, five publications remained for qualitative analysis. From these, only three studies remained for meta-analysis. The fracture strength of endodontically treated teeth where a core build-up composite was used was statistically significantly higher than the control (p = 0.04). Most of the analyses showed a high heterogenicity. The in vitro evidence suggests that the composite core build-up with higher filler content tended to improve the fracture resistance of the endodontically treated teeth, in comparison with conventional composite resins. This research received no external funding. Considering that this systematic review was only carried out on in vitro papers, registration was not performed. Furthermore, there were no identified clinical studies assessing core build-up materials; therefore, more well-designed research on these materials is needed.

Universal Adhesive for Fixed Retainer Bonding: In Vitro Evaluation and Randomized Clinical Trial

This study aims to assess the efficacy of a universal adhesive (Scotchbond Universal, 3M ESPE) (SB) in total-etch mode, compared to a traditional orthodontic primer (Transbond XT Primer, 3M ESPE) (XT Primer), to perform bonding of orthodontic fixed retainers along with the Transbond XT Light Cure Adhesive Paste (3M ESPE). For the in vitro study, a round section wire (Ortosmail Krugg) was bonded using XT Primer for 20 bovine incisors (Group 1) and SB for other 20 (Group 2). Samples were debonded in a universal testing machine applying a tangential force to specimens (crosshead speed of 1 millimeter per minute). Shear bond strength (SBS) and adhesive remnant index (ARI) scores were calculated. For the in vivo study, 100 patients needing upper and lower canine-to-canine fixed retainers after orthodontic treatment were randomly assigned to two groups of 50 participants each, i.e., group 1 (retainer bonding with XT Primer) and group 2 (retainer bonding with SB). Over two years, examinations were carried out monthly, and detachments were registered by considering the teeth and arches affected. In vitro, no statistically significant differences in SBS and ARI scores were demonstrated between the two groups, both showing a mean bond strength of about 12 MPa and major frequency of ARI "2" (>50% remnant adhesive on the enamel). Conversely, a significantly lower failure rate over 2 years was assessed clinically for group 2 in both arches. Independently of the adhesive and arch, incisors reported a significantly higher failure rate than canines. Scotchbond Universal used in total-etch mode could be a valid alternative to the traditional orthodontic Transbond XT Primer.

Microwave-Assisted Fabrication of Mesoporous Silica-Calcium Phosphate Composites for Dental Application

Herein, the microwave-assisted wet precipitation method was used to obtain materials consisting of mesoporous silica (SBA-15) and calcium orthophosphates (CaP). Composites were prepared through immersion of mesoporous silica in different calcification coating solutions and then exposed to microwave radiation. The composites were characterized in terms of molecular structure, crystallinity, morphology, chemical composition, and mineralization potential by Fourier-transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), and scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy (SEM-EDX). The application of microwave irradiation resulted in the formation of different types of calcium orthophosphates such as calcium deficient hydroxyapatite (CDHA), octacalcium phosphate (OCP), and amorphous calcium phosphate (ACP) on the SBA-15 surface, depending on the type of coating solution. The composites for which the progressive formation of hydroxyapatite during incubation in simulated body fluid was observed were further used in the production of final pharmaceutical forms: membranes, granules, and pellets. All of the obtained pharmaceutical forms preserved mineralization properties.

Exposure of Biomimetic Composite Materials to Acidic Challenges: Influence on Flexural Resistance and Elastic Modulus

Acidic conditions of the oral cavity, including soft drinks and cariogenic bacteria, represent a damage for restorative biomimetic composite materials. The aim of this study is to assess the influence of two different acidic challenges on the flexural strength and elastic modulus of five composites: x-tra fil (Group 1, XTF), GrandioSO x-tra (Group 2, GXT), Admira Fusion x-tra (Group 3, AFX), VisCalor bulk (Group 4, VCB), and Enamel Plus HRi (Group 5, EPH). Thirty samples for each group were randomly divided and assigned to three different treatments: storage in distilled water as the controls (subgroups 1a-5a), 3 weeks distilled water + 1 week Coca-Cola (subgroups 1b-5b), and 4 weeks Coca-Cola (subgroups 1c-5c). For each subgroup, the flexural strength and elastic modulus were measured using an Instron universal testing machine, and data were submitted to statistical analysis. Considering subgroups B, no material showed a significant difference in the flexural strength with the controls (p > 0.05), whereas for subgroups C, only GXT and VCB showed significantly lower values (p < 0.05). AFX reported the lowest flexural strength among the materials tested. As regards the elastic modulus, no material showed a significant variation after acidic storages when compared with the respective control (p > 0.05). AFX and EPH reported the lowest elastic modulus compared to the other materials. All composites tested showed adequate flexural properties according to the standards, except for AFX. This biomimetic material, along with EPH, might be indicated for V class (cervical) restorations considering the lowest values of elasticity reported.

Fracture Resistance of Three Post Types in the Restoration of Anterior Primary Teeth

Background:

Extensive restorative treatments of anterior primary teeth are challenging in pediatric dentistry.

Objective:

This study aimed to compare the fracture resistance of three post types for restoring the anterior primary teeth.

Methods:

This in-vitro study was carried out on 90 extracted maxillary anterior primary teeth with intact roots. They were randomly allocated into six groups to be restored with conventional composite resin post, X-tra fill composite resin post, Tetric N Ceram composite resin post, prefabricated glass fiber post with conventional composite build-up, prefabricated glass fiber post with X-tra fill composite build-up, and prefabricated glass fiber post with Tetric N Ceram composite build up. The samples were polished and placed in acrylic resin blocks with 1 mm of part of cervical root being out, thermocycled (×5000) and tested for fracture resistance. Intra-class correlation test, Kruskal-Wallis test and one-way ANOVA were used for statistical analyses (α=0.05).

Results:

The mean fracture resistance was significantly different among the six groups. It was the highest in prefabricated glass fiber post with conventional composite build-up (418.64 N), prefabricated glass fiber post with X-tra fill composite build-up (403.63 N) and prefabricated glass fiber post with Tetric N Ceram composite build up (361.63 N); and the lowest in Tetric N Ceram group (280.65 N). The groups were significantly different concerning the fracture strength and fracture state.

Conclusion:

Since the anterior teeth restored with prefabricated glass fiber posts were far more fracture resistant, and prefabricated glass fiber posts can be promisingly used for the restoration of anterior primary teeth.

Egyptian Propolis-Loaded Nanoparticles as a Root Canal Nanosealer: Sealing Ability and in vivo Biocompatibility

Background

Successful endodontic therapy is mainly governed by the satisfactory sealing ability of the applied root canal sealer. Also, tolerability of root canal structure to accommodate the presence of a sealer participates in the efficiency of the treatment. Hence, this study was aimed to extrapolate our previous one that was concerned with the preparation and evaluation of novel nature-based root canal sealers. Our current work is focused on the evaluation of sealing ability and in vivo biocompatibility.

Materials and Methods

Egyptian propolis was extracted (ProE) and encapsulated in polymeric nanoparticles (ProE-loaded NPs). Two root sealers, PE sealer and PE nanosealer, were fabricated by incorporating ProE and ProE-loaded NPs, respectively. The sealing ability of the developed sealers was tested by a dye extraction method. An in vivo biocompatibility study was conducted using a subcutaneous implantation method for two and four weeks. At the same time, a model sealer (AH Plus®) was subjected to the same procedures to enable accurate and equitable results.

Results

The teeth treated with PE sealer exhibited weak sealing ability which did not differ from that of unfilled teeth. PE nanosealer enhanced the sealing ability similarly to the model sealer with minimal apical microleakage. Studying in vivo biocompatibility indicated the capability of the three tested sealers to induce cell proliferation and tissue healing. However, PE nanosealer had superior biocompatibility, with higher potential for cell regeneration and tissue proliferation.

Conclusion

PE nanosealer can be presented as an innovative root canal sealer, with enhanced sealing ability as well as in vivo biocompatibility. It can be applied as a substitute for the currently available sealers that demonstrate hazardous effects.

The Effect of Finishing and Polishing Sequences on The Surface Roughness of Three Different Nanocomposites and Composite/Enamel and Composite/Cementum Interfaces

The purpose of this study was to investigate the effect of final surface treatment and dental composite type on the roughness of the composite surface, composite/enamel interface, and composite/cementum interface, as well as on the polishing time. Class V cavities prepared in extracted teeth (n = 126) were restored using one of the three nanohybrid composites with different filler sizes. The specimens were randomly assigned to three different finishing and polishing sequences. The roughness (Ra) of the investigated surfaces was measured using the contact profilometer. The time required to achieve visible gloss was documented. The data were analyzed using ANOVA with Tukey's post hoc test (p < 0.05). There was no significant influence of the composite type on the restoration surface roughness (p = 0.088), while the polishing method had a significant impact (p < 0.001). The Ra of the composites ranged between 0.08 µm and 0.29 µm, with the lowest values (0.09 µm ± 0.05 µm) found in the aluminum oxide disc group (p < 0.001). The time to achieve a visible composite gloss was influenced by the polishing method, composite type, and interactions between these factors (p < 0.001). The interface roughness was significantly greater than that of the composite surface (p < 0.001), and depended on the composite type and polishing system employed.

Glass Fiber Reinforced Composite Orthodontic Retainer: In Vitro Effect of Tooth Brushing on the Surface Wear and Mechanical Properties

Fiber reinforced composites (FRCs) are metal free materials that have many applications in dentistry. In clinical orthodontics, they are used as retainers after active treatment in order to avoid relapse. However, although the modulus of the elasticity of FRCs is low, the rigidity of the material in the form of a relatively thick retainer with a surface cover of a flowable resin composite is known to have higher structural rigidity than stainless steel splints. The aim of the present study is to measure load and bending stress of stainless steel wires, as well as flowable resin composite covered and spot‑bonded FRC retainer materials after tooth brushing. These materials were tested with a three point bending test for three different conditions: no brushing, 26 min of brushing, and 60 min of brushing. SEM images were taken before and after different times of tooth brushing. Results showed that stainless steel was not significantly affected by tooth brushing. On the other hand, a significant reduction of values at maximum load at fracture was reported for both FRC groups, and uncovered FRCs were most affected. Concerning maximum bending stress, no significant reduction by pretreatment conditions was reported for the materials tested. SEM images showed no evident wear for stainless steel. Flowable resin composite covered FRCs showed some signs of composite wear, whereas spot‑bonded FRCs, i.e., without the surface cover of a flowable resin composite, showed signs of wear on the FRC and exposed glass fibers from the FRC's polymer matrix. Because of the significant changes of the reduction of maximum load values and the wear for spot‑bonded FRCs, this technique needs further in vitro and in vivo tests before it can be performed routinely in clinical practice.

Effect of Long-Term Brushing on Deflection, Maximum Load, and Wear of Stainless Steel Wires and Conventional and Spot Bonded Fiber-Reinforced Composites

Fiber-reinforced composite (FRC) retainers are an aesthetic alternative to conventional Stainless Steel splints. They are generally used with a full bonded technique, but some studies demonstrated that they could be managed with a spot bonding technique to significantly decrease their rigidity. In order to propose this FRC spot bonding technique for clinical use, the aim of this study was to evaluate mechanical properties and surface wear of fibers left uncovered. Tests were made by simulating tooth brushing, comparing FRC spot bonding technique splints with stainless steel and FRC traditional technique splints. Specimens were tested both at 0.1 mm of deflection and at maximum load, showing higher values of rigidity for the FRC full bonded technique. After tooth brushing, no significant reduction in values at 0.1 mm deflection was reported, while we found a similar reduction in these values for the Stainless Steel and FRC spot bonding technique at maximum load, and no significant variation for the FRC full bonded technique. SEM images after tooth brushing showed wear for FRC fibers left uncovered, while no relevant wear signs in metal and conventional FRC fibers were noticed. Results showed that FRC spot bonding technique has advantages in mechanical properties when compared to the FRC traditional full bonding technique, also after tooth brushing. However, the surface wear after tooth brushing in the FRC spot bonding technique is considerable and other tests must be performed before promoting this technique for routine clinical use.

Sealability of Different Root Canal Nanosealers: Nano Calcium Hydroxide and Nano Bioactive Glass

Background:

The success of the endodontic treatment is largely dependent on the sealing achieved by root canal obturation. The application of sealer fills imperfections and increases adaptation of the root filling to the canal walls.

Aim:

To evaluate the sealability of experimental nanosealers (nano calcium hydroxide and nano bioactive glass) and to compare it with the commercial zinc oxide eugenol sealer using a dye penetration method.

Materials and Methods:

Sixty single-rooted mandibular premolars were selected. The tooth crowns were removed so as to obtain standardized 15-mm-long root specimens. The root canal was instrumented with Protaper Ni-Ti rotary file and the final file size was up to # F4/.06 (in vitro study). They were then randomly allocated into 3 groups of 20 specimens each (n=20) according to the sealer used for obturation, and all samples were filled with single cone gutta-percha (#40/06) and one of the tested sealers. All teeth were coated with nail polish and then suspended in 2% methylene blue dye for 7 days. Stereo-microscope (x10) was used to evaluate the sealability of newly introduced nanosealers. The data were statistically analyzed by ANOVA test followed by post hoc analysis (P < 0.05).

Results:

Significant improvement shown by the presented study suggests that nano calcium hydroxide sealer showed significantly less dye leakage than nano bioactive glass sealer and zinc oxide eugenol sealer.

Conclusion:

The results of this study showed that the synthesized nano-powder sealers are suitable for use in root canal therapy to prevent leakage.

The root canal can be sealed better by using smaller nano-powder particle sizes. In addition, the two groups exhibited significant differences in leakage in comparison with commonly used ZOE sealer.

The Influence of Non-Uniformities on the Mechanical Behavior of Hemp-Reinforced Composite Materials with a Dammar Matrix

As a result of manufacture, composite materials can appear to have variations to their properties due to the existence of structural changes. In this paper, we studied the influence of material irregularity on the mechanical behavior of two categories of bars for which we have used hemp fabric as a reinforcing material. The common matrix is a hybrid resin based on Dammar and epoxy resin. We molded two types of bars within each of the previously mentioned categories. The first type, also called "ideal bar", was made of layers in which the volume proportion and the orientation of the reinforcing material was the same in each section. The ideal bar does not show variations of mechanical properties along it. The second type of bar was molded to have one or two layers where, between certain sections, the reinforcing material was interrupted in several segments. We have determined some mechanical properties, the characteristic curves (strain-stress), the tensile strength, and elongation at break for all the sample sets on trial. Moreover, we have studied the influence of the non-uniformities on the mechanical behavior of the composites by entering certain quality factors that have been calculated after experimental determinations.

Experimental synthesis of size-controlled TiO2 nanofillers and their possible use as composites in restorative dentistry

The aim of this work was to obtain an efficient protocol with a green, fast and facile way to synthesize TiO2 NPs and its application as fillers for enhancement of desired dental properties of light curing dental composites. A comparative study comprised the fabrication of light curing restorative composite materials with incorporating different fillers with varying wt%, varying resin material composition, to determine optimal dental restoration by focusing on the physical properties of dental materials. It was observed that the as-prepared green synthesized TiO2 nanohybrid particles contributed to the improvement in physical properties, thus promoting the green and rapid synthesis of nanohybrid fillers. In addition, mechanical values for experimental cured resin materials with bare and surface modified fillers were obtained. The experimental light curing nanocomposites with 5 wt% (wt%) nanohybrid surface modified filler particles with BisGMA (60 wt%), TEGDMA (20 wt%) and UDMA (20 wt%) resin composition provided increased physical strength and durability with higher compressive stress 195.56 MPa and flexural stress 83.30 MPa. Furthermore, the dental property, such as polymerization shrinkage (PS) obtained from volumetric method was decreased up to 3.4% by the addition of nano-hybrid fillers. In addition to this, the biocompatible and antimicrobial nature of TiO2 and its aesthetics properties such as tooth-like color makes TiO2 favorable to use as fillers. This study presents a green and facile method for the synthesis of TiO2 nanohybrid particles that can be successfully used as fillers in an experimental light curing resin matrix for enhancing its dental properties. This describes the potential of the green synthesized TiO2 nanohybrid particles to use as fillers in restorative dentistry.

Flexural Properties and Elastic Modulus of Different Esthetic Restorative Materials: Evaluation after Exposure to Acidic Drink

BACKGROUND

Acidic beverages, such as soft drinks, can produce erosion of resin composites. The purpose of the present study was to investigate mechanical properties of different esthetic restorative materials after exposure to acidic drink.

METHODS

Nine different composites were tested: nanofilled (Filtek Supreme XTE, 3M ESPE), microfilled hybrid (G-ænial, GC Corporation), nanohybrid Ormocer (Admira Fusion, Voco), microfilled (Gradia Direct, GC Corporation), microfilled hybrid (Essentia, GC Corporation), nanoceramic (Ceram.X Universal, Dentsply De Trey), supranano spherical hybrid (Estelite Asteria, Tokuyama Dental Corporation), flowable microfilled hybrid (Gradia Direct Flo, GC Corporation), and bulk fill flowable (SureFil SDR flow, Dentsply De Trey). Thirty specimens of each esthetic restorative material were divided into 3 subgroups (n=10): specimens of subgroup 1 were used as control, specimens of subgroup 2 were immersed in 50 ml of Coca Cola for 1 week, and specimens of subgroup 3 were immersed in 50 ml of Coca Cola for 1 month. Flexural strength and elastic modulus were measured for each material with an Instron Universal Testing Machine. Data were submitted to statistical analysis.

RESULTS

After distilled water immersion, nanofilled composite showed the highest value of both flexural strength and elastic modulus, but its flexural values decreased after acidic drink immersion. No significant differences were reported between distilled water and acidic drink immersion for all other materials tested both for flexural and for elastic modulus values.

CONCLUSIONS

Even if nanofilled composite showed highest results, acidic drink immersion significantly reduced flexural values.

Structure and Properties of ZrO₂⁻20%Al₂O₃ Ceramic Composites Obtained Using Additive Technologies

This investigation focused on obtaining samples from ceramic composite materials, based on the ZrO₂⁻20%Al₂O₃ system, using the additive layer-by-layer fusion technology for thermoplastic systems. The structure and phase composition of the initial powders were studied, experimental samples were produced, and the structure and properties of the experimental samples that were obtained using additive technologies were analysed. The measured static bending strength of the samples was 450 ± 70 MPa, microhardness was 14 GPa, and the elasticity modulus was 280 ± 25 GPa. The strength of these samples are slightly inferior to that of similar materials, obtained using Ceramic Injection Molding technology because our samples were characterised by the residual porosity of about 15%.

Travel beyond Clinical Uses of Fiber Reinforced Composites (FRCs) in Dentistry: A Review of Past Employments, Present Applications, and Future Perspectives

The reinforcement of resins with short or long fibers has multiple applications in various engineering and biomedical fields. The use of fiber reinforced composites (FRCs) in dentistry has been described in the literature from more than 40 years. In vitro studies evaluated mechanical properties such as flexural strength, fatigue resistance, fracture strength, layer thickness, bacterial adhesion, bonding characteristics with long fibers, woven fibers, and FRC posts. Also, multiple clinical applications such as replacement of missing teeth by resin-bonded adhesive fixed dental prostheses of various kinds, reinforcement elements of dentures or pontics, and direct construction of posts and cores have been investigated. In orthodontics, FRCs have been used also for active and passive orthodontic applications, such as anchorage units, en-masse movement units, and postorthodontic tooth retention. FRCs have been extensively tested in the literature, but today the advances in new technologies involving the introduction of nanofillers or new fibers along with understanding the design principles of FRC devices open new fields of research for these materials both in vitro and in vivo. The present review describes past and present applications of FRCs and introduces some future perspectives on the use of these materials.

Gingival-derived mesenchymal stem cells: An endless resource for regenerative dentistry

The gingiva, the masticatory portion of the oral mucosa, is excised and discarded frequently during routine dental treatments and following tooth extraction, dental crown lengthening, gingivectomy and periodontal surgeries. Subsequent to excision, healing eventually happens in a short time period after gingival surgery. Clinically, the gingival tissue can be collected very easily and, in the laboratory, it is also very easy to isolate gingival-derived mesenchymal stem cells (GMSCs) from this discarded gingival tissue. GMSCs, a stem cell population within the lamina propria of the gingival tissue, can be isolated from attached and free gingiva, inflamed gingival tissues, and from hyperplastic gingiva. Comparatively, they constitute more attractive alternatives to other dental-derived mesenchymal stem cells due to the availability and accessibility of gingival tissues. They have unique immunomodulatory functions and well-documented self-renewal and multipotent differentiation properties. They display positive signals for Stro-1, Oct-4 and SSEA-4 pluripotency-associated markers, with some co-expressing Oct4/Stro-1 or Oct-4/SSEA-4. They should be considered as the best stem cell source for cell-based therapies and regenerative dentistry. The clinical use of GMSCs for regenerative dentistry represents an attractive therapeutic modality. However, numerous biological and technical challenges need to be addressed prior to considering transplantation approaches of GMSCs as clinically realistic therapies for humans.

Reliability of Orthodontic Miniscrews: Bending and Maximum Load of Different Ti-6Al-4V Titanium and Stainless Steel Temporary Anchorage Devices (TADs)

Temporary anchorage devices (TADs) have been introduced into orthodontic clinical practice in order to allow tooth movements while avoiding strain on adjacent teeth. Miniscrews are available in the market with different diameters and materials. Accordingly, the purpose of the present report was to measure and compare the forces to bend and fracture different mini implants. Ti-6Al-4V titanium and stainless steel TADs of different manufacturers (Spider ScrewHDC; Mini Implants⁻Leone; Benefit⁻Orteam; Storm⁻Kristal) were evaluated. Two different diameters (1.5 mm and 2.0 mm) were tested. The sample included 10 unused specimens for each group, blocked in an Instron Universal Testing Machine, and a shear load was applied at the neck of the miniscrew. The force to bend the miniscrew was measured at 0.1 mm and 0.2 mm deflections. Also, the maximum force before screw fracture was recorded. Data were submitted for statistical analysis. Results showed significantly higher forces for 2.0 mm than 1.5 mm screws, both at 0.1 mm and 0.2 mm deflections and at maximum load. Moreover, no significant differences were reported between titanium and stainless steel miniscrews of equal diameters.

Reliability of Orthodontic Miniscrews: Bending and Maximum Load of Different Ti-6Al-4V Titanium and Stainless Steel Temporary Anchorage Devices (TADs)

Temporary anchorage devices (TADs) have been introduced into orthodontic clinical practice in order to allow tooth movements while avoiding strain on adjacent teeth. Miniscrews are available in the market with different diameters and materials. Accordingly, the purpose of the present report was to measure and compare the forces to bend and fracture different mini implants. Ti-6Al-4V titanium and stainless steel TADs of different manufacturers (Spider ScrewHDC; Mini Implants⁻Leone; Benefit⁻Orteam; Storm⁻Kristal) were evaluated. Two different diameters (1.5 mm and 2.0 mm) were tested. The sample included 10 unused specimens for each group, blocked in an Instron Universal Testing Machine, and a shear load was applied at the neck of the miniscrew. The force to bend the miniscrew was measured at 0.1 mm and 0.2 mm deflections. Also, the maximum force before screw fracture was recorded. Data were submitted for statistical analysis. Results showed significantly higher forces for 2.0 mm than 1.5 mm screws, both at 0.1 mm and 0.2 mm deflections and at maximum load. Moreover, no significant differences were reported between titanium and stainless steel miniscrews of equal diameters.

Bending Properties of Fiber-Reinforced Composites Retainers Bonded with Spot-Composite Coverage

Orthodontic and periodontal splints are prepared with round or flat metallic wires. As these devices cannot be used in patients with allergy to metals or with aesthetic demands, fiber-reinforced composite (FRC) retainers have been introduced. Stiffness of FRC materials could reduce physiologic tooth movement. In order to lower rigidity of conventional FRC retainers, a modified construction technique that provided a partial (spot) composite coverage of the fiber has been tested and compared with metallic splints and full-bonded FRCs. Flat (Bond-a-Braid, Reliance Orthodontic Products) and round (Penta-one 0155, Masel Orthodontics) stainless steel splints, conventional FRC splints, and experimental spot-bonded FRC retainers (Everstick Ortho, StickTech) were investigated. The strength to bend the retainers at 0.1 mm deflection and at maximum load was measured with a modified Frasaco model. No significant differences were reported among load values of stainless steel wires and experimental spot-bonded FRC retainers at 0.1 mm deflection. Higher strength values were recoded for conventional full-bonded FRCs. At maximum load no significant differences were reported between metallic splints (flat and round) and experimental spot-bonded FRCs, and no significant differences were reported between spot- and full-bonded FRC splints. These results encourage further tests in order to evaluate clinical applications of experimental spot-bonded FRC retainers.

Spot-Bonding and Full-Bonding Techniques for Fiber Reinforced Composite (FRC) and Metallic Retainers

Fiber reinforced Composite (FRC) retainers have been introduced as an aesthetic alternative to conventional metallic splints, but present high rigidity. The purpose of the present investigation was to evaluate bending and fracture loads of FRC splints bonded with conventional full-coverage of the FRC with a composite compared with an experimental bonding technique with a partial (spot-) resin composite cover. Stainless steel rectangular flat, stainless steel round, and FRC retainers were tested at 0.2 and 0.3 mm deflections and at a maximum load. Both at 0.2 and 0.3 mm deflections, the lowest load required to bend the retainer was recorded for spot-bonded stainless steel flat and round wires and for spot-bonded FRCs, and no significant differences were identified among them. Higher force levels were reported for full-bonded metallic flat and round splints and the highest loads were recorded for full-bonded FRCs. At the maximum load, no significant differences were reported among spot- and full-bonded metallic splints and spot-bonded FRCs. The highest loads were reported for full bonded FRCs. The significant decrease in the rigidity of spot-bonded FRC splints if compared with full-bonded retainers suggests further tests in order to propose this technique for clinical use, as they allow physiologic tooth movement, thus presumably reducing the risk of ankylosis.

Compressive strength and the effect of duration after photo-activation among dual-cure bulk fill composite core materials

Objectives:

To assess compressive strength and effect of duration after photoactivation on the compressive strength of different dual cure bulk fill composites.

Methods:

Seventy-two disc shaped (4x10mm) specimens were prepared from three dual cure bulk fill materials, ZirconCore (ZC) (n=24), MulticCore Flow (MC) (n=24) and Luxacore Dual (LC) (n=24). Half of the specimens in each material were tested for failure loads after one hour [MC1 (n=12), LC1 (n=12) & ZC1 (n=12)] and the other half in 7 days [MC7 (n=12), LC7 (n=12), ZC7 (n=12)] from photo-polymerization using the universal testing machine at a cross-head speed of 0.5 cm/minutes. Compressive strength was calculated using the formula UCS=4f/πd². Compressive strengths among different groups were compared using analysis of variance (ANOVA) and Tukey’s multiple comparisons test.

Results:

Maximum and minimum compressive strengths were observed in ZC7 (344.14±19.22) and LC1 (202.80±15.52) groups. Specimens in LC1 [202.80 (15.52)] showed significantly lower compressive strength as compared to MC1 [287.06 (15.03)] (p<0.01) and ZC1 [276.82 (11.51)] (p<0.01). ZC7 [344.14 (19.22)] specimens showed significantly higher (p<0.01) compressive strengths compared to LC7 [324.56 (19.47)] and MC7 [315.26 (12.36)]. Compressive strengths among all three materials were significantly higher (p<0.01) at 7 days as compared to one hour.

Conclusions:

Bulk fill material with Zr nano-hybrid filler (ZC) showed high compressive strength compared to MC and LC. Increasing the post photo-activation duration (from one hour to 7 days) significantly improves the compressive strengths of dual cure bulk fill material.