Fabrication and characterization of biomimetic ceramic/polymer composite materials for dental restoration

In Vitro Assessment of a New Block Design for Implant Crowns with Functional Gradient Fabricated with Resin Composite and Zirconia Insert

This study aims to evaluate and compare the mechanical resistance, fatigue behavior and fracture behavior of different CAD/CAM materials for implant crowns. Eighty-eight implant crowns cemented-screwed with four sample groups: two monolithic G1 Zirconia (control) and G3 composite and two bi-layered G2 customized zirconia/composite and G4 prefabricated zirconia/composite. All static and dynamic mechanical tests were conducted at 37 °C under wet conditions. The fractographic evaluation of deformed and/or fractured samples was evaluated via electron microscopy. Statistical analysis was conducted using Wallis tests, which were performed depending on the variables, with a confidence interval of 95%, (p < 0.05). The Maximum Fracture Strength values displayed by the four groups of samples showed no statistically significant differences. The crown-abutment material combination influenced the failure mode of the restoration, transitioning from a fatigue fracture type located at the abutment-analog connection for monolithic materials (G1 and G3) to a brittle fracture located in the crown for bi-layered materials (G2 and G4). The use of layered crown materials with functional gradients appears to protect the crown/abutment connection area by partially absorbing the applied mechanical loads. This prevents catastrophic mechanical failures, avoiding long chairside time to solve these kinds of complications.

Fatigue behavior of multilayer ceramic structures in traditional and reverse layering designs

PURPOSE

This study evaluated the fatigue failure load (FFL) and the number of cycles for fatigue failure (CFF) of traditional (porcelain layer up) and reversed (zirconia layer up) designs of porcelain-veneered zirconia samples prepared with heat-pressing or file-splitting techniques.

MATERIALS AND METHODS

Zirconia discs were prepared and veneered with heat-pressed or machined feldspathic ceramic. The bilayer discs were bonded onto a dentin-analog according to the bilayer technique and sample design: traditional heat-pressing (T-HP), reversed heat-pressing (R-HP), traditional file-splitting with fusion ceramic (T-FC), reversed file-splitting with fusion ceramic R-FC), traditional file-splitting with resin cement (T-RC), and reversed file-splitting with resin cement (R-RC). The fatigue tests were performed using the stepwise approach at 20 Hz, 10,000 cycles/step, step-size of 200 N starting at 600 N, and proceeding until failure detection or up to 2600 N if enduring. The failure modes (from radial and/or cone cracks) were analyzed in a stereomicroscope.

RESULTS

The reversed design decreased the FFL and CFF of bilayers prepared with heat-pressing and file-splitting with fusion ceramic. The T-HP and T-FC reached the highest results, which were statistically similar between them. The bilayers prepared by the file-splitting with resin cement (T-RC and R-RC) were similar to the R-FC and R-HP groups regarding FFL and CFF. Almost all reverse layering samples failed by radial cracks.

CONCLUSIONS

The reverse layering design did not improve the fatigue behavior of porcelain veneered zirconia samples. The three bilayer techniques behaved similarly when used in the reversed design.

Biomimetic Nacre-like Hydroxyapatite/Polymer Composites for Bone Implants

One of the most ambitious goals for bone implants is to improve bioactivity, incapability, and mechanical properties; to reduce the need for further surgery; and increase efficiency. Hydroxyapatite (HA), the main inorganic component of bones and teeth, has high biocompatibility but is weak and brittle material. Cortical bone is composed of 70% calcium phosphate (CaP) and 30% collagen and forms a complex hierarchical structure with anisotropic and lamellar microstructure (osteons) which makes bone a light, strong, tough, and durable material that can support large loads. However, imitation of concentric lamellar structure of osteons is difficult to achieve in fabrication. Nacre from mollusk shells with layered structures has now become the archetype of the natural "model" for bio-inspired materials. Incorporating a nacre-like layered structure into bone implants can enhance their mechanical strength, toughness, and durability, reducing the risk of implant catastrophic failure or fracture. The layered structure of nacre-like HA/polymer composites possess high strength, toughness, and tunable stiffness which matches that of bone. The nacre-like HA/polymer composites should also possess excellent biocompatibility and bioactivity which facilitate the bonding of the implant with the surrounding bone, leading to improved implant stability and long-term success. To achieve this, a bi-directional freeze-casting technique was used to produce elongated lamellar HA were further densified and infiltrated with polymer to produce nacre-like HA/polymer composites with high strength and fracture toughness. Mechanical characterization shows that increasing the ceramic fractions in the composite increases the density of the mineral bridges, resulting in higher flexural and compressive strength. The nacre-like HA/(methyl methacrylate (MMA) + 5 wt.% acrylic acid (AA)) composites with a ceramic fraction of 80 vol.% showed a flexural strength of 158 ± 7.02 MPa and a Young's modulus of 24 ± 4.34 GPa, compared with 130 ± 5.82 MPa and 19.75 ± 2.38 GPa, in the composite of HA/PMMA, due to the higher strength of the polymer and the interface of the composite. The fracture toughness in the composition of 5 wt.% PAA to PMMA improves from 3.023 ± 0.98 MPa·m1/2 to 5.27 ± 1.033 MPa·m1/2 by increasing the ceramic fraction from 70 vol.% to 80 vol.%, respectively.

Micromechanical interlocking structure at the filler/resin interface for dental composites: a review

Dental resin composites (DRCs) are popular materials for repairing caries or dental defect, requiring excellent properties to cope with the complex oral environment. Filler/resin interface interaction has a significant impact on the physicochemical/biological properties and service life of DRCs. Various chemical and physical modification methods on filler/resin interface have been introduced and studied, and the physical micromechanical interlocking caused by the modification of fillers morphology and structure is a promising method. This paper firstly introduces the composition and development of DRCs, then reviews the chemical and physical modification methods of the filler/resin interface, mainly discusses the interface micromechanical interlocking structures and their enhancement mechanism for DRCs, finally give a summary on the existing problems and development potential.

Mechanical Properties and In Vitro Biocompatibility of Hybrid Polymer-HA/BAG Ceramic Dental Materials

The aim of this study is to prepare hybrid polymer-ceramic dental materials for chairside computer-aided design/computer-aided manufacturing (CAD/CAM) applications. The hybrid polymer-ceramic materials were fabricated via infiltrating polymerizable monomer mixtures into sintered hydroxyapatite/bioactive glass (HA/BAG) ceramic blocks and thermo-curing. The microstructure was observed by scanning electron microscopy and an energy-dispersive spectrometer. The phase structure was analyzed by X-ray diffraction. The composition ratio was analyzed by a thermogravimetric analyzer. The hardness was measured by a Vickers hardness tester. The flexural strength, flexural modulus, and compressive strength were measured and calculated by a universal testing machine. The growth of human gingival fibroblasts was evaluated by a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) colorimetric assay and immunofluorescence staining. The results showed that the sintering temperature and BAG content affected the mechanical properties of the hybrid polymer-ceramic materials. The X-ray diffraction analysis showed that high-temperature sintering promoted the partial conversion of HA to β-tricalcium phosphate. The values of the hardness, flexural strength, flexural modulus, and compressive strength of all the hybrid polymer-ceramic materials were 0.89-3.51 GPa, 57.61-118.05 MPa, 20.26-39.77 GPa, and 60.36-390.46 MPa, respectively. The mechanical properties of the hybrid polymer-ceramic materials were similar to natural teeth. As a trade-off between flexural strength and hardness, hybrid polymer-ceramic material with 20 wt.% BAG sintered at 1000 °C was the best material. In vitro experiments confirmed the biocompatibility of the hybrid polymer-ceramic material. Therefore, the hybrid polymer-ceramic material is expected to become a new type of dental restoration material.

Efficacy of contemporary agents on disinfection and surface roughness of polyetheretherketone implant abutments

AIM

The present study was designed to estimate the disinfection and surface roughness (Ra) of colonized (E. coli, C. albicans, S.aureus, and S. mutans) PEEK implant abutment disinfected with PDT, chemical, and herbal agents.

MATERIAL AND METHODS

The American Type Culture Collection (ATCC) inoculated E.coli, C.albicans, S.mutans, and S.aureus in an in-vitro scenario using 60 PEEK implant abutment samples provided by the manufacturer. Following that, the samples were distributed in four disinfection methods categories - group 1: 5mM Rose Bengal PS (RB), group 2: ultrasonic disinfection (UD), group 3: 2% glutaraldehyde (GaH), and group 4: tea tree oil (TTO). To scrutinize the data and compare the means and standard deviations of CFU/mL (log10) for exposed E. coli, Candida albicans, S.aureus, and S.mutans, a two-way ANOVA and Tukey's multiple comparison test were performed.

RESULTS

Specimens treated with 2% GaH, UD, and TTO validated a significant reduction in E. coli, C. albicans, S aureus, and S. mutans CFU/mL (log10) colonies. Intragroup assessment designated that there is no reduction in CFU/mL (log10) of E.coli and C.albicans when PEEK implant abutment specimens are irradiated with 5Mm RB. A decline is seen in values of S. aureus, and S. mutans microbial strains on treatment with all four cleansers while the computation of C.albicans and E.coli colonies unveiled significant reduction with GaH, UD, and TTO except RB (p<0.05). The results of Ra showed that PEEK fabricated implant abutment specimens, when treated with UD (3.472±0.561μm), displayed a significantly higher Ra value as compared to other analyzed cleansing methods.

CONCLUSION

. Disinfection with 2% glutaraldehyde and Tea tree oil showed maximum antimicrobial efficacy and lower Ra values for PEEK implant abutments colonized with bacterial strains of E.coli, C.albicans, S.aureus, and S.mutans.

Additively Manufactured Dental Crown with Color Gradient and Graded Structure: A Technique Report

To assess the feasibility of manufacturing a dental crown with internal color gradient and graded structure design using additive manufacturing technology, a mandibular first molar was prepared and a monolayer dental crown with 1.5 mm uniform thickness was designed in a dental software (STL_C1 ). The monolayer crown design was sliced into multiple layers of 0.1 mm thickness and a design for a multilayer crown was obtained (STL_C2 ). A multilayer crown was manufactured with gradient color and graded structure using a material jetting printer. Different materials with different colors and properties were used and mixed in different ratios during manufacturing to achieve the prospected design. The feasibility of manufacturing such a crown was reported. This report confirms that multilayer dental crowns with internal gradient color and graded structure are possible when using a multimaterial jetting printer.

Two-layer additively manufactured crown: Proof of concept

OBJECTIVES

To assess the feasibility of additively manufacturing a crown with a 2-layer design.

METHODS

A mandibular first molar tooth preparation titanium die for a full coverage restoration was obtained. The die was used to design a monolayer (ML group) and 2-layer (2L group) anatomically contoured crown. In the ML group, the specimen was manufactured with a hard polymer (Rigur RGD450; Stratasys). In the 2L group, the crown was splinted into 2 parts: the intaglio that represented 25% of the total crown volume that was manufactured with a resilient polymer (Vero; Stratasys) and the exterior that represented the remaining crown volume that was manufactured with a hard polymer (Rigur RGD450; Stratasys). Specimens were manufactured using a material jetting printer (Connex3 Object260; Stratasys). The marginal and internal discrepancies of ML and 2L specimens were visually assessed.

RESULTS

The ML and 2L specimens were manufactured using a material jetting printer that obtained a visually acceptable marginal and internal discrepancy.

CONCLUSIONS

The 2-layer dental crown can be manufactured using a material jetting printer.

CLINICAL SIGNIFICANCE

Material jetting technology has the capability to fabricate a 2-layer dental crown design which can be fabricated using materials with different properties.

PICN Nanocomposite as Dental CAD/CAM Block Comparable to Human Tooth in Terms of Hardness and Flexural Modulus

Polymer infiltrated ceramic network (PICN) composites are an increasingly popular dental restorative material that offer mechanical biocompatibility with human enamel. This study aimed to develop a novel PICN composite as a computer-aided design and computer-aided manufacturing (CAD/CAM) block for dental applications. Several PICN composites were prepared under varying conditions via the sintering of a green body prepared from a silica-containing precursor solution, followed by resin infiltration. The flexural strength of the PICN composite block (107.8–153.7 MPa) was similar to a commercial resin-based composite, while the Vickers hardness (204.8–299.2) and flexural modulus (13.0–22.2 GPa) were similar to human enamel and dentin, respectively. The shear bond strength and surface free energy of the composite were higher than those of the commercial resin composites. Scanning electron microscopy and energy dispersive X-ray spectroscopic analysis revealed that the microstructure of the composite consisted of a nanosized silica skeleton and infiltrated resin. The PICN nanocomposite block was successfully used to fabricate a dental crown and core via the CAD/CAM milling process.

Characterisation of mechanical and surface properties of novel biomimetic interpenetrating alumina-polycarbonate composite materials

OBJECTIVE

To determine the mechanical and surface characteristics of two novel biomimetic interpenetrating phase alumina-polycarbonate (Al₂O₃-PC) composite materials, comprising aligned honeycomb-like porous ceramic preforms infiltrated with polycarbonate polymer.

METHOD

Two composite materials were produced and characterised. Each comprised a porous structure with a ceramic-rich (polymer-poor) top layer, graduated through to a more porous ceramic-poor (polymer-rich) bottom layer. In addition, pure polycarbonate and dense alumina specimens were subjected to the same characterisation namely: density, compression, three-point bend, hardness, surface loss and surface roughness testing. Scanning electron microscopy and micro computerised tomography were employed for structural examination.

RESULTS

Three-dimensional aligned honeycomb-like ceramic structures were produced and full interpenetration of the polymer phase was observed using MicroCT. Depending on the ceramic volume in the initial aqueous ceramic suspension, the density of the final interpenetrating composites ranged from 2.64 to 3.01g/cm³, compressive strength ranged from 192.43 to 274.91MPa, flexural strength from 105.54 to 148.47MPa, fracture toughness from 2.17 to 3.11MPa.m^½, hardness from 0.82 to 1.52GPa, surface loss from 0.71 to 1.40μm and surface roughness, following tooth brushing, from 0.70 to 0.99μm. Composite specimens showed characteristic properties part way between enamel and polycarbonate.

SIGNIFICANCE

There was a correlation between the initial solid ceramic loading in the aqueous suspension, used to produce the porous ceramic scaffolds, and the subsequent characteristic properties of the composite materials. These novel composites show potential as aesthetic orthodontic bracket materials, as their properties fit part way between those of ceramic, enamel and polycarbonate.

The Bacterial Anti-Adhesive Activity of Double-Etched Titanium (DAE) as a Dental Implant Surface

This work aimed to compare the capability of Streptococcus oralis to adhere to a novel surface, double-etched titanium (DAE), in respect to machined and single-etched titanium. The secondary outcome was to establish which topographical features could affect the interaction between the implant surface and bacteria. The samples’ superficial features were characterized using scanning electron microscopy (SEM) and energy dispersive x-ray spectrometry (EDS), and the wetting properties were tested through sessile methods. The novel surface, the double-etched titanium (DAE), was also analyzed with atomic force microscopy (AFM). S. oralis was inoculated on discs previously incubated in saliva, and then the colony-forming units (CFUs), biomass, and cellular viability were measured at 24 and 48h. SEM observation showed that DAE was characterized by higher porosity and Oxygen (%) in the superficial layer and the measurement of the wetting properties showed higher hydrophilicity. AFM confirmed the presence of a higher superficial nano-roughness. Microbiological analysis showed that DAE discs, coated by pellicle’s proteins, were characterized by significantly lower CFUs at 24 and 48 h with respect to the other two groups. In particular, a significant inverse relationship was shown between the CFUs at 48 h and the values of the wetted area and a direct correlation with the water contact angle. The biomass at 24 h was slightly lower on DAE, but results were not significant concerning the other groups, both at 24 and 48 h. The DAE treatment not only modifies the superficial topography and increased hydrophilicity, but it also increases the Oxygen percentage in the superficial layer, which could contribute to the inhibition of S. oralis adhesion. DAE can be considered a promising treatment for titanium implants to counteract a colonization pioneer microorganism, such as S. oralis.

Material characterization and Streptococcus oralis adhesion on Polyetheretherketone (PEEK) and titanium surfaces used in implantology

The aim of this study was to evaluate the interaction between Streptococcus oralis and Polyetheretherketone (PEEK), a novel material recently introduced in implantology. The topographical characterization and the Streptococcus oralis adhesion on this material were compared with other titanium surfaces, currently used for the production of dental implants: machined and double etched (DAE). The superficial micro-roughness of the PEEK discs was analyzed by scanning electron microscopy (SEM) and, the Energy Dispersive Spectrometer (EDS) analyzed their chemical composition. Atomic Force Microscopy (AFM) was used to characterize the micro-topography and the sessile method to evaluate the wettability of the samples. Microbiological analysis measured the colony forming units (CFUs), the biomass (OD₅₇₀ detection) and the cell viability after 24 and 48 h after Streptococcus oralis cultivation on the different discs, that were previously incubated with saliva. Results showed that PEEK was characterized by a micro-roughness that was similar to machined titanium but at nano-level the nano-roughness was significantly higher in respect to the other samples. The EDS showed that PEEK superficial composition was characterized mainly by Carbonium and Oxygen. The hydrophilicity and wetting properties of PEEK were similar to machined titanium; on the contrary, double etched discs (DAE) samples were characterized by significantly higher levels (p < 0.05). PEEK was characterized by significant lower CFUs, biomass and viable cells in respect to the titanium surfaces. No differences were found between machined and DAE. The anti-adhesive and antibacterial properties showed by PEEK at 24 and 48 h against a pioneer such as S. oralis, could have an important role in the prevention of all pathologies connected with biofilm formation, like peri-implantitis in dentistry or prosthetic failures in orthopedics.

Wear mechanism of human tooth enamel: The role of interfacial protein bonding between HA crystals

Human tooth enamel, the most mineralized tissue in body, contains less than 2 wt% protein. Consequently, the importance of the protein to enamel mechanical response has always been overlooked. In this study, the role of minor protein in providing enamel microstructure and mechanical performance, especially tribological properties, were studied using deproteinization treatment and nano-indentation/scratch technique. Via the change from the original to the deproteinated conditions, a nanostructure degeneration from the assembly of hydroxyapatite (HA) crystals into nano-fibers to crystal aggregation has been found between the high-wear-resistance and low-wear-resistance on the enamel surface. Correspondingly, an energy dissipation to cause a unit volume of wear on enamel surface decreases by 50%, and wear volume increases by 80%. With the presence of protein, the occurrence of enamel wear requires to break the interfacial protein bonding between the HA crystals in nano-fibers and the break dissipates considerable energy, which benefits the enamel to resist wear. Thus, the protein in enamel, although of a very low content, is essential to resisting wear by mediating the assembly of rigid HA crystals via interfacial protein bonding. Replicating functions of the protein component will be critical to the successful development of bio-inspired materials that are designed for wear-resistance.

Fracture resistance of endodontically treated teeth restored with various esthetic posts

BACKGROUND

Dental esthetic materials are constantly introduced to meet the increasing esthetic demand in contemporary dental practice.

OBJECTIVE

To test the fracture resistance of endodontically treated teeth (ETT) restored with different esthetic post materials like fiber-reinforced composite post (FRC), polyether ether ketone (PEEK), and polymer infiltrated ceramic (PIC).

METHODS

Thirty-six human root canal treated single-rooted premolar teeth were decoronated 3 mm above the cemento-enamel junction and prepared to receive the post. They were randomly divided into three groups (n= 12) to be restored with FRC, PEEK, and PIC. After appropriate surface treatment, they were cemented with self-adhesive luting cement and restored with full veneer crowns. The samples were thermocycled, subjected to a compressive static load at 45∘ angulation until fracture. Obtained data were analyzed by one-way ANOVA and Tukey's HSD post hoc comparison test.

RESULTS

The results indicate that the ETT restored with PEEK post had the maximum fracture load (1929.94 N), followed by PIC endodontic post group (1810.65N), and FRC post (1715.68N). Meanwhile, ETT restored with FRC showed a predominantly favorable fracture, whereas PEEK restored teeth had a more unfavorable fracture.

CONCLUSION

Of all the esthetic post materials, the group for which PEEK endodontic post was used displayed higher fracture resistance.

3D Digital Image Correlation Analysis of the Shrinkage Strain in Four Dual Cure Composite Cements

The introduction of resin-based cements and an adhesive-bonding system in daily dental practice has given the opportunity to increase the retention of previously conventional cemented restorations and the optimal results in esthetic. This experimental study employed the 3D Digital Image Correlation Method (3D-DIC) for detecting shrinkage strain in four dual cured composite cements. The aim was to visualize measure, analyze, and compare strain fields in four resin-based cements using the 3D-DIC method. A total of 72 samples were divided into 4 groups considering variations in sample types, diameter, and thickness. Four types of composite cements: RelyX U200 (3 M ESPE, St. Paul, MN, USA), MaxCem Elite (Kerr, Orange, CA, USA), Multilink Automix (Ivoclar Vivadent, Schaan, Liechtenstein), and SeT PP (SDI, Australia) were used. Each type had diameters of 3 mm, 4 mm, and 5 mm, respectively, combined with two different values of thickness: 1 mm and 2 mm. Thickness had an important role on strain detected in all tested materials showing higher strain in samples with 2 mm thickness compared to 1 mm samples. Shrinkage strain values were the highest in Set PP samples indicated the possibility of undesirable de-bonding.

In Vitro Evaluation of the Effect of Different Surface Treatments of a Hybrid Ceramic on the Microtensile Bond Strength to a Luting Resin Cement

Introduction: The aim of the present study was to investigate the effect of different surface treatments of a hybrid ceramic, Vita Enamic, on the micro-tensile bond strength (µ-TBS) to resin cement. Methods: Ten blocks (3×10×8 mm) were retrieved from the original blocks and divided into 5 groups according to the different surface treatments performed: Groups 1: 35% acid phosphoric for 60 seconds (PA); group 2: Sandblasting with 50 µm Al₂ O₃ particles for 10 seconds (SB); groups 3: 9.5% hydrofluoric acid for 60 seconds (HF), group 4: The Er:YAG laser (2 W, 10 Hz) (ER1), group 5: The Er:YAG laser (3 W, 10 Hz) (ER2). All treated surfaces were salinized and the blocks with similar surface treatments were bonded together using a dual-cured resin cement and light-cured. After 24-hour storage in water, the blocks were cut into beams (1 mm²). Half of the specimens in each group (n=16) were tested immediately and the rest were subjected to thermocycling between 5°C and 55°C for 6000 cycles before the µ-TBS test at a crosshead speed of 0.5 mm/min. The data were analyzed using two-way analysis of variance (ANOVA) and Tukey HSD tests and the significance level was set at 0.05. The failure mode was evaluated by using a stereomicroscope. Results: The µ-TBS was clearly influenced by surface treatment methods (P < 0.001) and thermocycling significantly decreased the bond strength values in all groups (P = 0.007). The highest value (66.07 MPa ± 11.3) was obtained for the HF groups with no thermocycling and the lowest values were observed in the laser groups with no significant difference among different irradiation parameters. Adhesive failure was mainly observed in the PA and SB groups while mixed failure was predominantly shown in the laser and HF groups. Conclusion: This study demonstrated that surface treatment of VE with HF and salinization could improve the bond strength to a dual-cured resin cement, and Er:YAG laser irradiation with the evaluated parameters did not promote the adhesion of the resin cement to VE.

Reinforcement of dental resin composite via zirconium hydroxide coating and phosphate ester monomer conditioning of nano-zirconia fillers

OBJECTIVES

The present study aimed to evaluate effects of conditioning with the phosphate ester monomer 10-methacryloyloxydecyl dihydrogen phosphate (MDP), with and without precoating with zirconium hydroxide for nano-size zirconia fillers, on mechanical properties of dental resin composites.

MATERIALS AND METHODS

Nano-zirconia fillers coated with or without zirconium hydroxide [Zr(OH)₄] were prepared. Transmission electron microscopy (TEM), Fourier infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) were used to observe the coating and to characterize Zr(OH)₄ coating on the zirconia filler surface. Zirconia fillers with or without Zr(OH)₄ coating were conditioned with MDP and were subsequently used to prepare experimental resin composites. XPS was used to analyze the Zr-O-P bonds on the filler surface after MDP conditioning. Moreover, three-point bending strength and elastic modulus of prepared resin composites were measured, and Weibull analysis was performed. Resin composites without addition of zirconia fillers and the ones with addition of untreated or silane conditioned-zirconia fillers were set as controls. Cell counting kit (CCK)-8 was used to test cell cytotoxicity of these zirconia fillers-containing experimental resin composites.

RESULTS

Nano-zirconia fillers were coated with Zr(OH)₄ through chemical deposition. FTIR and XPS analysis confirmed the increase of hydroxyl groups after Zr(OH)₄ coating. XPS detected the highest contents of Zr-O-P bonds on MDP-conditioned zirconia fillers with pre-Zr(OH)₄ coating, followed by MDP-conditioned zirconia fillers. Resin composite with added MDP-conditioned zirconia fillers with and without Zr(OH)₄ coating exhibited greater three-point bending strength, elastic modulus values, and Weibull moduli. According to the cytotoxicity classification, resin composites containing experimental zirconia fillers were considered to have no significant cell cytotoxicity.

CONCLUSION

Nano-zirconia fillers conditioned with MDP, with or without precoating with Zr(OH)₄, improve the mechanical properties of resin composites, and are potentially safe for clinical use.

Mechanical behavior of restorative dental composites under various loading conditions

Mechanical engineering and its scientific principles constitute an essential core in medical science. Currently, different composite resins are widely used as restorative dental materials. However, their lack of adequate strength and toughness has led to research that is aimed at improving the mechanical properties of dental composites. In the present study, the behavior of three different dental materials is investigated under static and dynamic loading conditions. In the experimental tests, a split Hopkinson pressure bar is utilized which corresponds to the most commonly used experimental setup for examining material behavior under a high rate of loading. The examined dental composites experience impacts during their service life and also during car accidents or sport injuries. Hence, in the study, impact loading is modeled in an experiment. A series of compression tests is conducted from low to high strain rates up to 40s^-1, and the dynamic elastic moduli of three different dental composites are measured. Furthermore, studies on the compressed surface of the dental composite specimens are performed to improve the analysis with respect to the hardness of the materials. The responses of the examined composites to dynamic loadings verify the impact resistance of the materials. The results indicate the load-carrying capabilities of the dental composites. These results can be used for materials development and existing computational models.

Bond strength between composite repair and polymer-infiltrated ceramic-network material: Effect of different surface treatments

OBJECTIVE

To evaluate the bond strength of a polymer-infiltrated ceramic-network (PICN) material and to composite repair after different surface treatments.

MATERIALS AND METHODS

Eighteen blocks of the PICN material were obtained from CAD/CAM blocks, aged and randomly divided into 2 groups: 5% hydrofluoric acid (HF) or sandblasting with aluminum oxide particles (SAND). For each condition, three treatments were tested: silane (Sil), silane-containing adhesive (Ad), or silane + silane-containing adhesive (SilAd). The treated PICN surfaces were restored with composite resin. The microtensile bond strength test was performed in a universal testing machine, and data (MPa) were compared with two-way Analysis of variance (anova) and Tukey (α = 0.05). Roughness (Ra) and contact angle (CA) were obtained after HF and SAND conditions.

RESULTS

The greatest bond strength values were obtained for the groups Sil and SilAd, for both HF and SAND pretreatments. The Ra values of SAND were statistically greater than HF. The CA generated by the adhesive on SAND surface was lower than HF surface.

CONCLUSIONS

The use of silane improves the bond strength of the composite repair to PICN substrate compared to the single use of silane-containing adhesive. The HF pretreatment is most indicated when the silane-containing adhesive is applied alone.

CLINICAL SIGNIFICANCE

Fractured PICN restorations can be repaired with composite resin, because the surface is treated with hydrofluoric acid or sandblasting followed by the individual use of silane.

Effect of the Composition of CAD/CAM Composite Blocks on Mechanical Properties

The aim of this study was to evaluate the effect of the composition of CAD/CAM blocks on their mechanical properties. Nine different CAD/CAM blocks, enamel and dentine, were tested. Sixteen samples of each material were separated for Vickers microhardness test (n=6, 5 readings per specimen), nanohardness test (n=6, 5 readings per specimen), filler weight (n=3), and SEM imaging (n=1). Data were statistically analysed using one-way ANOVA. Vita Mark II ceramic showed significantly higher values of hardness (in both nano- and microscale) and elastic modulus (6.83 GPa, 502 kg/mm², and 47.7 GPa), respectively, than other materials. CAD/CAM composite blocks showed comparable values of hardness and elastic modulus to those of dentine but lower than those of enamel and ceramics. SEM images highlighted different filler-matrix microstructure of CAD/CAM composite blocks. It was concluded that (1) hardness and elastic moduli are positively correlated with ceramic filler percentage and microstructure and (2) CAD/CAM composite materials have comparable hardness and elastic moduli to tooth structure.

A Comparative Study on the Mechanical Properties of a Polymer-Infiltrated Ceramic-Network Material Used for the Fabrication of Hybrid Abutment

Polymer-infiltrated ceramic-network (PICN) material is a new type of material used for the hybrid abutments of dental implants. This study aimed to compare flexural strength, bond strengths, and fracture-resistance values of PICN with lithium disilicate ceramic (LDS) and to evaluate the effect of thermocycling on the tested parameters. Twenty specimens were fabricated using computer-aided design and manufacturing (CAD-CAM) technology for each material according to three-point bending (n = 10), microshear bond strength (µSBS), and a fracture-resistance test (hybrid abutment, n = 10). All specimens of each test group were divided into two subgroups, thermocycled or nonthermocycled. Hybrid abutments were cemented on titanium insert bases and then fixed on implants to compare fracture resistance. Failure loads were recorded for each test and data were statistically analyzed. Thermocycling decreased bond strength to the resin luting agent and the fracture-resistance values of both materials (p < 0.001), whereas flexural-strength values were not affected. LDS ceramic showed significantly higher flexural strength, bond strength, and fracture-resistance values than PICN material (p < 0.001). Within the limitations of this study, LDS may be a preferable hybrid-abutment material to PICN in terms of mechanical and bonding properties.

Majeed M. Comparative Evaluation of the Fracture Strength of Monolithic Crowns Fabricated from Different all-ceramic CAD/CAM Materials (an in vitro study)

The objective of this in vitro study was to evaluate and compare the fracture strength of monolithic crowns fabricated from five different all-ceramic CAD/CAM materials (lithium disilicate, zirconia, reinforced composite, hybrid dental ceramic, and zirconia-reinforced lithium silicate) using single load to failure test. Forty sound human maxillary first premolar teeth extracted for orthodontic purposes were selected for use in this study. Teeth were prepared according to a standard protocol with 1 mm deep chamfer finishing line, 4 mm axial height with planer occlusal reduction and 6º total convergence angle. Teeth were then divided into five groups of eight teeth each according to the material used for the fabrication of the monolithic crowns as follow: Group A: Crowns fabricated from lithium disilicate (IPS e.max CAD, Ivoclar Vivadent), Group B: Crowns fabricated from zirconia (CEREC Zirconia, Dentsply Sirona), Group C: Crowns fabricated from reinforced composite (BRILLIANT Crios, COLTENE), Group D: Crowns fabricated from hybrid dental ceramic (VITA ENAMIC, VITA Zahnfabric), Group E: Crowns fabricated from zirconia-reinforced lithium silicate (CELTRA DUO, Dentsply Sirona). Teeth of all groups were then scanned with CEREC Omnicam digital intraoral scanner and the crowns were then designed using CEREC Premium software (version 4.4.4) and milled using CEREC MC XL milling unit. Post-milling, crowns of each group were subjected to either a firing procedure or to a polishing only according to the manufacturer's instructions of each material. The internal surfaces of the crowns of each group were then subjected to surface treatment according to the manufacturer's instructions of each material and the crowns were then cemented on their respective teeth using a universal dual-cured adhesive resin cement (Duo-Link Universal, Bisco Inc.). All teeth with the cemented crowns were then stored in deionized distilled water at room temperature for 24 hours before testing. All samples were then subjected to compressive axial loading until fracture in computer-controlled universal testing machine (Zwick Z010, Ulm, Germany) at a crosshead speed of 0.5 mm/min. The data were statistically analyzed using one-way ANOVA test and LSD test at a level of significance of 0.05. The results of this study showed that the highest mean value of fracture strength was recorded by Group B (2337.37), followed by Group C (1880.59), Group E (1404.49), Group A (1085.39) and Group D (767.06), respectively with statistically highly significant differences among the different groups (p<0.01). From the results of this study, it seems that the differences in the chemical composition and microstructure of the tested all-ceramic CAD/CAM materials may be responsible for the differences in the fracture strength of the fabricated crowns.

Effects of Ceramic Density and Sintering Temperature on the Mechanical Properties of a Novel Polymer-Infiltrated Ceramic-Network Zirconia Dental Restorative (Filling) Material

BACKGROUND Polymer-infiltrated ceramic-network (PICN) dental material is a new and practical development in orthodontics. Sintering is the process of forming a stable solid mass from a powder by heating without melting. The aim of this study was to evaluate the effects of sintering temperature on the mechanical properties of a PICN zirconia dental material. MATERIAL AND METHODS A dense zirconia ceramic and four PICN zirconia dental materials, with varying porosities, were sintered at three different temperatures; 12 PICN zirconia dental materials based on these porous ceramics were prepared, as well as a pure polymer. After the specimen preparation, flexural strength and elastic modulus values were measured using the three-point bending test, and fracture toughness were determined by the single-edge notched beam (SENB) method. The Vickers hardness test method was used with an indentation strength (IS) test. Scanning electron microscopy (SEM) was used to examine the microstructure of the ceramic surface and the fracture surface. RESULTS Mechanical properties of the PICN dental materials, including flexural strength, elastic modulus, fracture toughness, and hardness, were more similar to the properties of natural teeth when compared with traditional dental ceramic materials, and were affected by the density and sintering temperature. SEM showed that the porous ceramic network became cohesive and that the length of cracks in the PICN dental material was reduced. CONCLUSIONS PICN zirconia dental materials were characterized by similar mechanical properties to natural dental tissues, but further studies are required continue to improve the similarities with natural human enamel and dentin.

Edge chipping resistance and flexural strength of polymer infiltrated ceramic network and resin nanoceramic restorative materials

STATEMENT OF PROBLEM

Two novel restorative materials, a polymer infiltrated ceramic network (PICN) and a resin nanoceramic (RNC), for computer-assisted design and computer-assisted manufacturing (CAD-CAM) applications have recently become commercially available. Little independent evidence regarding their mechanical properties exists to facilitate material selection.

PURPOSE

The purpose of this in vitro study was to measure the edge chipping resistance and flexural strength of the PICN and RNC materials and compare them with 2 commonly used feldspathic ceramic (FC) and leucite reinforced glass-ceramic (LRGC) CAD-CAM materials that share the same clinical indications.

MATERIAL AND METHODS

PICN, RNC, FC, and LRGC material specimens were obtained by sectioning commercially available CAD-CAM blocks. Edge chipping test specimens (n=20/material) were adhesively attached to a resin substrate before testing. Edge chips were produced using a 120-degree, sharp, conical diamond indenter mounted on a universal testing machine and positioned 0.1 to 0.7 mm horizontally from the specimen's edge. The chipping force was plotted against distance to the edge, and the data were fitted to linear and quadratic equations. One-way ANOVA determined intergroup differences (α=.05) in edge chipping toughness. Beam specimens (n=22/material) were tested for determining flexural strength using a 3-point bend test. Weibull statistics determined intergroup differences (α=.05). Flexural modulus and work of fracture were also calculated, and 1-way ANOVA determined intergroup differences (α=.05) RESULTS: Significant (P<.05) differences were found among the 4 CAD-CAM materials for the 4 mechanical properties. Specifically, the material rankings were edge chipping toughness: RNC>LRGC=FC>PICN; flexural strength: RNC=LRGC>PICN>FC; flexural modulus: RNC<PICN<LRGC<FC; and work of fracture: RNC>LRGC=PICN>FC.

CONCLUSIONS

The RNC material demonstrated superior performance for the mechanical properties tested compared with the other 3 materials.

From Artisanal to CAD-CAM Blocks

Indirect composites have been undergoing an impressive evolution over the last few years. Specifically, recent developments in computer-aided design–computer-aided manufacturing (CAD-CAM) blocks have been associated with new polymerization modes, innovative microstructures, and different compositions. All these recent breakthroughs have introduced important gaps among the properties of the different materials. This critical state-of-the-art review analyzes the strengths and weaknesses of the different varieties of CAD-CAM composite materials, especially as compared with direct and artisanal indirect composites. Indeed, new polymerization modes used for CAD-CAM blocks—especially high temperature (HT) and, most of all, high temperature–high pressure (HT-HP)—are shown to significantly increase the degree of conversion in comparison with light-cured composites. Industrial processes also allow for the augmentation of the filler content and for the realization of more homogeneous structures with fewer flaws. In addition, due to their increased degree of conversion and their different monomer composition, some CAD-CAM blocks are more advantageous in terms of toxicity and monomer release. Finally, materials with a polymer-infiltrated ceramic network (PICN) microstructure exhibit higher flexural strength and a more favorable elasticity modulus than materials with a dispersed filler microstructure. Consequently, some high-performance composite CAD-CAM blocks—particularly experimental PICNs—can now rival glass-ceramics, such as lithium-disilicate glass-ceramics, for use as bonded partial restorations and crowns on natural teeth and implants. Being able to be manufactured in very low thicknesses, they offer the possibility of developing innovative minimally invasive treatment strategies, such as “no prep” treatment of worn dentition. Current issues are related to the study of bonding and wear properties of the different varieties of CAD-CAM composites. There is also a crucial need to conduct clinical studies. Last, manufacturers should provide more complete information regarding their product polymerization process, microstructure, and composition, which significantly influence CAD-CAM material properties.

Comparative characterization of a novel cad-cam polymer-infiltrated-ceramic-network

BACKGROUND

The field of dental ceramics for CAD-CAM is enriched with a new innovative material composition having a porous three-dimensional structure of feldspathic ceramic infiltrated with acrylic resins.The aim of this study is to determine the mechanical properties of Polymer-Infiltrated-Ceramic-Network (PICN) and compare its performance with other ceramics and a nano-ceramic resin available for CAD-CAM systems.

MATERIAL AND METHODS

In this study a total of five different materials for CAD-CAM were investigated. A polymer-infiltrated ceramic (Vita Enamic), a nano-ceramic resin (Lava Ultimate), a feldspathic ceramic (Mark II), a lithium disilicate ceramic (IPS-e max CAD) and finally a Leucite based ceramic (Empress - CAD). From CAD-CAM blocks, 120 bars (30 for each material cited above) were cut to measure the flexural strength with a three-point-bending test. Strain at failure, fracture stress and Weibull modulus was calculated. Vickers hardness of each material was also measured.

RESULTS

IPS-EMAX presents mechanical properties significantly better from the other materials studied. Its strain at failure, flexural strength and hardness exhibited significantly higher values in comparison with the others. VITA ENAMIC and LAVA ULTIMATE stand out as the next most resistant materials.

CONCLUSIONS

The flexural strength, elastic modulus similar to a tooth as well as having less hardness than ceramics make PICN materials an option to consider as a restorative material.

KEY WORDS

Ceramic infiltrated with resin, CAD-CAM, Weibull modulus, flexural strength, micro hardness.

Preparation of antibacterial and radio-opaque dental resin with new polymerizable quaternary ammonium monomer

OBJECTIVE

A new polymerizable quaternary ammonium monomer (IPhene) with iodine anion was synthesized and incorporated into Bis-GMA/TEGDMA (50/50, wt/wt) to prepare antibacterial and radio-opaque dental resin.

METHODS

IPhene was synthesized through a 2-steps reaction route, and its structure was confirmed by FT-IR and (1)H-NMR spectra. IPhene was incorporated into Bis-GMA/TEGDMA (50/50, wt/wt) with a series of mass fraction (from 10 wt.% to 40 wt.%). Degree of monomer conversion (DC) was determined by FT-IR analysis. Polymerization shrinkage was determined according to the variation of density before and after polymerization. The flexural strength, modulus of elasticity, and fracture energy were measured using a three-point bending set up. Radiograph was taken to evaluate the radio-opacity of the polymer. A single-species biofilm model with Streptococcus mutans (S. mutans) as the tests organism was used to evaluate the antibacterial activity of the polymer. Bis-GMA/TEGDMA resin system without IPhene was used as a control group.

RESULTS

FT-IR and (1)H-NMR spectra of IPhene revealed that IPhene was the same as the designed structure. ANOVA analysis showed that when mass fraction of IPhene was more than 10 wt.%, the obtained resin formulation had lower DC, polymerization shrinkage, FS, and FM than control resin (p<0.05). Polymers with 20 wt.% and 30 wt.% IPhene had higher fracture energies than control polymer (p<0.05). IPhene containing samples had higher radio-opacity than control group (p<0.05), and radio-opacity of IPhene containing sample increased with the increasing of IPhene mass fraction (p<0.05). Only polymers with 30 wt.% and 40 wt.% of IPhene showed antibacterial activity (p<0.05).

SIGNIFICANCE

IPhene could endow dental resin with both antibacterial and radio-opaque activity when IPhene reached 30 wt.% or more. Though sample with 30 wt.% of IPhene had lower FS and FM than control group, its lower volumetric shrinkage, higher fracture energy, higher radio-opacity, and antibacterial activity still made it having potential to be used in dentistry.

Characterization of a polymer-infiltrated ceramic-network material

OBJECTIVES

To characterize the microstructure and determine some mechanical properties of a polymer-infiltrated ceramic-network (PICN) material (Vita Enamic, Vita Zahnfabrik) available for CAD-CAM systems.

METHODS

Specimens were fabricated to perform quantitative and qualitative analyses of the material's microstructure and to determine the fracture toughness (KIc), density (ρ), Poisson's ratio (ν) and Young's modulus (E). KIc was determined using V-notched specimens and the short beam toughness method, where bar-shaped specimens were notched and 3-point loaded to fracture. ρ was calculated using Archimedes principle, and ν and E were measured using an ultrasonic thickness gauge with a combination of a pulse generator and an oscilloscope.

RESULTS

Microstructural analyses showed a ceramic- and a polymer-based interpenetrating network. Mean and standard deviation values for the properties evaluated were: KIc=1.09±0.05MPam(1/2), ρ=2.09±0.01g/cm(3), ν=0.23±0.002 and E=37.95±0.34GPa.

SIGNIFICANCE

The PICN material showed mechanical properties between porcelains and resin-based composites, reflecting its microstructural components.