Metal Organic Framework-Incorporated Three-Dimensional (3D) Bio-Printable Hydrogels to Facilitate Bone Repair: Preparation and In Vitro Bioactivity Analysis.

Hydrogels are three-dimensional (3D) water-swellable polymeric matrices that are used extensively in tissue engineering and drug delivery. Hydrogels can be conformed into any desirable shape using 3D bio-printing, making them suitable for personalized treatment. Among the different 3D bio-printing techniques, digital light processing (DLP)-based printing offers the advantage of quickly fabricating high resolution structures, reducing the chances of cell damage during the printing process. Here, we have used DLP to 3D bio-print biocompatible gelatin methacrylate (GelMA) scaffolds intended for bone repair. GelMA is biocompatible, biodegradable, has integrin binding motifs that promote cell adhesion, and can be crosslinked easily to form hydrogels. However, GelMA on its own is incapable of promoting bone repair and must be supplemented with pharmaceutical molecules or growth factors, which can be toxic or expensive. To overcome this limitation, we introduced zinc-based metal-organic framework (MOF) nanoparticles into GelMA that can promote osteogenic differentiation, providing safer and more affordable alternatives to traditional methods. Incorporation of this nanoparticle into GelMA hydrogel has demonstrated significant improvement across multiple aspects, including bio-printability, and favorable mechanical properties (showing a significant increase in the compressive modulus from 52.14 ± 19.42 kPa to 128.13 ± 19.46 kPa with the addition of ZIF-8 nanoparticles). The designed nanocomposite hydrogels can also sustain drug (vancomycin) release (maximum 87.52 ± 1.6% cumulative amount) and exhibit a remarkable ability to differentiate human adipose-derived mesenchymal stem cells toward the osteogenic lineage. Furthermore, the formulated MOF-integrated nanocomposite hydrogel offers the unique capability to coat metallic implants intended for bone healing. Overall, the remarkable printability and coating ability displayed by the nanocomposite hydrogel presents itself as a promising candidate for drug delivery, cell delivery and bone tissue engineering applications.

Post-fatigue fracture load, stress concentration and mechanical properties of feldspathic, leucite- and lithium disilicate-reinforced glass ceramics.

Objective: To evaluate the mechanical properties of different CAD/CAM ceramic systems and the post-fatigue fracture and stress distribution when used as cemented crowns. Materials and methods: Sixty (60) CAD/CAM monolithic crowns were milled using three different ceramic materials (FD - Feldspathic [Vita Mark II]), LE - Leucite-based ceramic [IPS Empress CAD] and LD - Lithium Disilicate [IPS e.max CAD]) and adhesively cemented on resin composite dyes. Specimens were stored in distillated water (37 °C) for 7 days. After, half of the crowns were submitted to immediate fracture load test while the other half was submitted to fatigue cycling. The average cement layer of approximately 80 µm was assessed using scanning electron microscopy (SEM). The average thickness was used in the three-dimensional (3D) Finite Element Analysis (FEA). For each ceramic material, the density, Poisson ratio, shear modulus, Young modulus, fracture toughness, and true hardness were assessed (n = 3). The data was used to assess the Maximum Principal Stress throughout 3D-FEA according to each material during load to fail and post-fatigue. Data were submitted to two-way ANOVA and Tukey test (α = 0.05). Results: LD showed the highest compression load, density, shear modulus, Young modulus, fracture toughness and true hardness values. While LE presented the lowest mechanical properties values. There is no difference in the Poisson ratio between the evaluated ceramics. Conclusion: LD was susceptible to aging process but presented stronger physicomechanical properties, showing the highest post-fatigue fracture load and highest stress magnitude.

Stress Distribution of Monolithic and Veneered 3-unit Zirconia FDPs - Finite Element Analysis.

PURPOSE: To evaluate the effect of restoration design on fracture resistance and stress distribution of veneered and monolithic 3-unit zirconia fixed partial dentures (FDPs) using finite element analysis (FEA). MATERIALS AND METHODS: Identical epoxy resin replicas of mandibular second premolar and second molar (to serve as abutment for the 3-unit bridge) were divided into four groups (n = 10): monolithic zirconia (MZ) restorations; conventional layering veneering technique (ZL), heat-pressed technique (ZP), or CAD/CAM lithium disilicate glass ceramic (CAD-on). Specimens were subjected to compressive cyclic loading on the mesio-buccal cusp of the pontic (load range 50 to 600 N; aqueous environment; 500,000 cycles) in a universal testing machine. Data were statistically analyzed at 5% significance level with Fisher exact test and Kaplan-Meier survival analysis. 3D models were constructed in accordance with experimental groups. The stress distribution in each model was analyzed and evaluated according to the location and magnitude of the maximum principal stresses (MPS) using ANSYS software. RESULTS: Specimens from ZL and ZP groups failed at different stages of the 500,000 cycles fatigue, while CAD-on and MZ restorations survived fatigue test. Statistically, there was a significant difference between the groups (P < .001). The MPS were located under the mesial connector in both monolithic and bilayered 3-unit zirconia FDPs. These stresses were found to be higher in monolithic geometries compared to bilayered zirconia FDPs. CONCLUSION: Monolithic 3-unit zirconia and CAD-on zirconia frameworks resulted in superior fracture resistance. Restoration design significantly affected the stress distribution of 3-unit zirconia FDPs.

Friction and archwire engagement in contemporary self-ligating appliance systems : An in vitro comparison.

PURPOSE: The aim of this study was to compare classical friction (FR) in passive self-ligating brackets (P-SLBs), active self-ligating brackets (A-SLBs) and a traditional twin bracket, in vitro, and to identify the point of initiation of bracket-archwire engagement. METHODS: Nine bracket systems of 0.022 in slot size were FR tested: 5 P­SLB systems; 4 A­SLB systems; and a control group of twin brackets with elastomeric ligatures. Single upper right central incisor brackets were mounted on a custom metal fixture for testing. Straight sections of various round and rectangular nickel-titanium (NiTi) archwires (0.016, 0.018, 0.018â€¯× 0.018, 0.020â€¯× 0.020, 0.016â€¯× 0.022, 0.017â€¯× 0.025, 0.019â€¯× 0.025, and 0.021â€¯× 0.025 in) were ligated to the bracket and peak static FR (cN) was measured with an Instron Universal Testing Machine. Ten unique tests each utilizing a new bracket and new archwire were conducted for each group in the dry state. RESULTS: FR was significantly different between control, P­SLB and A­SLB systems (P < 0.001). P­SLB groups displayed no significant differences in FR between each other, regardless of archwire size. A­SLB groups did exhibit significant differences in FR between each other depending on both the bracket system and archwire size. Each A­SLB system tested possessed a distinctly different pattern of initiation of bracket-archwire engagement. CONCLUSIONS: FR between the archwire and bracket slot differs between P­SLB and A­SLB systems, with a distinct pattern of FR and bracket-archwire engagement for each A­SLB system. Understanding the different bracket-wire interactions of SLB systems should help orthodontic clinicians to plan effective and efficient biomechanics with the bracket system of their choice.

Titanium Alloy Implants with Lattice Structures for Mandibular Reconstruction.

In recent years, the field of mandibular reconstruction has made great strides in terms of hardware innovations and their clinical applications. There has been considerable interest in using computer-aided design, finite element modelling, and additive manufacturing techniques to build patient-specific surgical implants. Moreover, lattice implants can mimic mandibular bone's mechanical and structural properties. This article reviews current approaches for mandibular reconstruction, their applications, and their drawbacks. Then, we discuss the potential of mandibular devices with lattice structures, their development and applications, and the challenges for their use in clinical settings.

Sol-Gel Derived Tertiary Bioactive Glass-Ceramic Nanorods Prepared via Hydrothermal Process and Their Composites with Poly(Vinylpyrrolidone-Co-Vinylsilane).

Bioactive glass (BG) nanoparticles have wide applications in bone repair due to their bone-bonding and biodegradable nature. In this work, nanometric rod-shaped ternary SiO2-CaO-P2O5 bioactive glass particles were prepared through sol-gel chemistry followed by a base-induced hydrothermal process at 130 °C and 170 °C for various times up to 36 h. This facile, low-temperature and surfactant-free hydrothermal process has shown to be capable of producing uniform nanorods and nanowires. One-dimensional growth of nanorods and the characteristics of siloxane bridging networks were dependent on the hydrothermal temperature and time. Hardened bioactive composites were prepared from BG nanorods and cryo-milled poly(vinylpyrrolidone-co-triethoxyvinylsilane) in the presence of ammonium phosphate as potential bone graft biomaterials. Covalent crosslinking has been observed between the organic and inorganic components within these composites. The ultimate compressive strength and modulus values increased with increasing co-polymer content, reaching 27 MPa and 500 MPa respectively with 30% co-polymer incorporation. The materials degraded in a controlled non-linear manner when incubated in phosphate-buffered saline from 6 h to 14 days. Fibroblast cell attachment and spreading on the composite were not as good as the positive control surfaces and suggested that they may require protein coating in order to promote favorable cell interactions.

Bone Repair and Regenerative Biomaterials: Towards Recapitulating the Microenvironment.

Biomaterials and tissue engineering scaffolds play a central role to repair bone defects. Although ceramic derivatives have been historically used to repair bone, hybrid materials have emerged as viable alternatives. The rationale for hybrid bone biomaterials is to recapitulate the native bone composition to which these materials are intended to replace. In addition to the mechanical and dimensional stability, bone repair scaffolds are needed to provide suitable microenvironments for cells. Therefore, scaffolds serve more than a mere structural template suggesting a need for better and interactive biomaterials. In this review article, we aim to provide a summary of the current materials used in bone tissue engineering. Due to the ever-increasing scientific publications on this topic, this review cannot be exhaustive; however, we attempted to provide readers with the latest advance without being redundant. Furthermore, every attempt is made to ensure that seminal works and significant research findings are included, with minimal bias. After a concise review of crystalline calcium phosphates and non-crystalline bioactive glasses, the remaining sections of the manuscript are focused on organic-inorganic hybrid materials.

Porous and biodegradable polycaprolactone-borophosphosilicate hybrid scaffolds for osteoblast infiltration and stem cell differentiation.

The composition and microstructure of bone tissue engineering scaffolds play a significant role in regulating cell infiltration, proliferation, differentiation, and extracellular matrix production. While boron is an essential trace element for bone formation, growth, and health, boron-containing biomaterials are poorly studied. Specifically, the effect of boron in hybrid scaffolds on stem cell differentiation is unknown. We have previously reported the synthesis and characterization of class II hybrid biomaterials from polycaprolactone and borophosphosilicate glass (PCL/BPSG). In this study, PCL/BPSG hybrid porous scaffolds were fabricated by a solvent-free casting and particulate leaching method having consistent pore-size distribution, controlled porosity, and pore interconnectivity. The mechanical properties with respect to porogen loading and degradation time demonstrated that these scaffolds were competent for bone tissue engineering applications. In cell culture experiments, significant number of cells infiltrated and adhered into the scaffolds interior. Induced pluripotent stem cells (iPSCs) differentiation to osteogenic lineage was dependent on the amount of boron incorporated into the hybrid scaffolds. Consistent with this, scaffolds containing 2-mol% boron (calculated as % of the inorganic component) had an optimum effect on lineage expressions for alkaline phosphatase (ALP), osteopontin (OPN) and osteocalcin (OCN). These results suggest that PCL/BPSG hybrid scaffolds with optimum-level boron may enhance bone formation.

A novel technique for measurement of orthodontic mini-implant stability using the Osstell ISQ device.

OBJECTIVES: To develop and validate a method for application of the Osstell ISQ device in the assessment of mini-implant stability. MATERIALS AND METHODS: An adaptor was developed for attachment of Osstell's SmartPeg onto a variety of orthodontic mini-implants. For validation of the adaptor, Benefit mini-implants were inserted into bone blocks that mimicked different stability conditions. The Osstell device was used to assess mini-implant stability with the adaptor (test measurement) and conventional SmartPeg attachment (gold-standard measurement). Implant stability quotient (ISQ) values were assessed for agreement, repeatability, and reproducibility. RESULTS: Strong positive correlations were found between ISQ values obtained using the novel adaptor and the conventional attachment. Repeatability and reproducibility of ISQ values with the adaptor were similar to those obtained with the conventional attachment. CONCLUSIONS: A method was developed and validated to assess the stability of orthodontic mini-implants using the Osstell system. The novel mini-implant adaptor provided repeatable and reproducible measurements of mini-implant stability, which agreed with those obtained using a conventional SmartPeg attachment. This adaptor permits noninvasive stability assessment of various designs of mini-implants, most of which are incompatible with the conventional SmartPeg attachment.

Influence of crown design and material on chipping-resistance of all-ceramic molar crowns: An in vitro study.

BACKGROUND: All-ceramic restorations have become popular and the trend is ongoing. However, the incidence of chipping within the veneering layer has been a commonly reported failure in clinical practice. OBJECTIVES: The aim of this in vitro study was to evaluate the effect of ceramic crown design (monolithic vs bi-layered) and material on the chipping resistance of molar crowns submitted to compressive cyclic loading. MATERIAL AND METHODS: Fifty identical epoxy resin replicas of a mandibular first molar with crown preparation were divided into 5 groups (n = 10) as follows: the MLD group - monolithic CAD/CAM lithium-disilicate glass-ceramic (LDGC) crowns; 30 zirconia cores were veneered with either feldspathic porcelain by hand-layering technique (ZHL) or by heat-pressing technique (ZVP), or with milled LDGC veneers and subsequently fused to the cores (ZLD); 10 porcelain-fused-to-metal (PFM) crowns acted as a control group. All crowns were cemented using Panavia® F2.0 resin cement (Kuraray Dental, Tokyo, Japan). After storage in water at 37°C for 1 week, the specimens were subjected to compressive cyclic loading at the mesiobuccal cusp which was tilted at 30°. A load cycle of 50-450 N was used and specimens were maintained in an aqueous environment throughout 500,000 cycles in a universal testing machine (Instron, Norwood, USA). The data was statistically analyzed at 5% significant level with Fisher's exact test and Kaplan-Meier survival analysis. RESULTS: Significant differences in survival rates of the specimens used in the groups (p < 0.001) were found. Specimens of the PFM, ZHL and ZVP groups underwent failures at different stages of the 500,000 fatigue cycles, while specimens of the MLD and ZLD groups survived the entire fatigue test. ZHL and ZVP crowns had the worst chipping-resistance, while PFM crowns performed slightly better. The Kaplan-Meier test revealed significantly higher survival rates for the MLD and ZLD specimens compared to the other 3 groups. CONCLUSIONS: The use of LDGC as a monolithic molar crown and as a veneer over a zirconia core resulted in superior resistance to cuspal chipping.

Bioactivity, Degradation, and Mechanical Properties of Poly(vinylpyrrolidone-co-triethoxyvinylsilane)/Tertiary Bioactive Glass Hybrids.

Currently, composite and class I hybrid biomaterials are used for tissue regeneration applications. To improve and better control biomaterial properties, we synthesized class II organic/inorganic (O/I) hybrids, in which organic polymers and inorganic tertiary bioactive glass (TBG) were covalently cross-linked. To tailor their microstructure, bioactivity, degradation, and mechanical properties, we altered the degree of cross-linking by varying the amount of functional groups in the polymer that mediate covalent bonding to the TBG. We synthesized class II hybrids in a two-step process: first, vinylpyrrolidone (VP) and triethoxyvinylsilane (TEVS) were copolymerized at various molar ratios to obtain different amounts of silane functional groups in the copolymer; second, TBG and the copolymer were mixed and allowed to undergo hydrolysis and polycondensation forming Si-O-Si- and Si-O-P-bridging networks between the organic and inorganic phases. Higher amounts of functional groups increased copolymer-TBG covalent bonding and decreased  degradation and the release of TBG dissolution products. Incubation in simulated body fluid led to biomimetic apatite deposition on the hybrid biomaterial surfaces, which was primarily dependent on O/I weight ratios. A higher TBG content improved apatite deposition and biocompatibility. Porous and interconnected three-dimensional scaffolds, fabricated by indirect 3D printing using polycaprolactone as a sacrificial template, had intriguing yield and compressive strengths, compressive moduli, and toughness. These studies demonstrate, for the first time, that the functionality of our synthesized copolymers greatly affects the nature of O/I matrix formation and degradation behavior of the class II hybrid biomaterials, creating possibilities for tailoring the physical, biochemical, and mechanical properties of scaffold biomaterials for tissue regeneration and related applications.

Sustainable Bio-Based Phenol-Formaldehyde Resoles Using Hydrolytically Depolymerized Kraft Lignin.

In this study bio-based bio-phenol-formaldehyde (BPF) resoles were prepared using hydrolytically depolymerized Kraft lignin (DKL) as bio-phenol to partially substitute phenol. The effects of phenol substitution ratio, weight-average molecular weight (Mw) of DKL and formaldehyde-to-phenol (F/P) ratio were also investigated to find the optimum curing temperature for BPF resoles. The results indicated that DKL with Mw ~ 1200 g/mol provides a curing temperature of less than 180 °C for any substitution level, provided that F/P ratios are controlled. Incorporation of lignin reduced the curing temperature of the resin, however, higher Mw DKL negatively affected the curing process. For any level of lignin Mw, the curing temperature was found to increase with lower F/P ratios at lower phenol substitution levels. At 25% and 50% phenol substitution, increasing the F/P ratio allows for synthesis of resoles with lower curing temperatures. Increasing the phenol substitution from 50% to 75% allows for a broader range of lignin Mw to attain low curing temperatures.

Surface Roughness of Methacrylate- and Silorane-Based Composites After Finishing and Polishing Procedures.

OBJECTIVE: To compare the effect of surface finishing and polishing protocols on the surface roughness (Ra) of methacrylate-based and silorane-based resin composites. METHODS AND MATERIALS: Fifty specimens (5 mm x 2 mm) of each composite material were prepared using a split mold: Filtek™ Supreme Ultra (3M ESPE), Tetric EvoCeram® (Ivoclar Vivadent), Tetric Ceram™ HB (Ivoclar Vivadent), and Filtek™ LS Low Shrink (3M ESPE). Specimens were divided into five groups (n = 10) according to the following procedures: G1 - 15-µm fine diamond bur (FDB); G2 - 15-µm FDB followed by a 20-fluted tungsten carbide bur; G3 - 15-µm FDB followed by diamond-impregnated micropolishing points (D-FINE Double Diamond Polishing System, Clinician's Choice); G4 - 15-µm FDB followed by diamond-impregnated micropolishing points (Flame Point Pre-polisher and Shine, Brassseler USA); and G5 - 15-µm FDB followed by the application of a surface sealer (PermaSeal®, Ultradent Products, Inc.). Ra was measured in three different regions using a surface profilometer (Mitutoyo Surfest SJ-210, Mitutoyo America). RESULTS: Multiple comparisons were obtained using a one-way ANOVA with Tukey's B rank order test ( = 0.05). No significant differences in Ra were observed among the resin composites tested in the same condition. The use of a FDB generated the highest roughness values, while the use of a surface sealer resulted in the lowest roughness values for all resin composites tested (P < .05). No significant difference in Ra was observed between the use of a multi-fluted carbide bur and the rubber point D-FINE Double Diamond Polishing System for all resin composites tested.

Mechanically-competent and cytocompatible polycaprolactone-borophosphosilicate hybrid biomaterials.

Organic-inorganic class II hybrid materials have domain sizes at the molecular level and chemical bonding between the organic and inorganic phases. We have previously reported the synthesis of class II hybrid biomaterials from alkoxysilane-functionalized polycaprolactone (PCL) and borophosphosilicate (B2O3-P2O5-SiO2) glass (BPSG) through a non-aqueous sol-gel process. In the present study, the mechanical properties and degradability of these PCL/BPSG hybrid biomaterials were studied and compared to those of their conventional composite counterparts. The compressive strength, modulus and toughness of the hybrid biomaterials were significantly greater compared to the conventional composites, likely due to the covalent bonding between the organic and inorganic phases. A hybrid biomaterial (50wt% PCL and 50wt% BPSG) exhibited compressive strength, modulus and toughness values of 32.2 ± 3.5MPa, 573 ± 85MPa and 1.54 ± 0.03MPa, respectively; whereas the values for composite of similar composition were 18.8 ± 1.6MPa, 275 ± 28MPa and 0.76 ± 0.03MPa, respectively. Degradation in phosphate-buffered saline was slower for hybrid biomaterials compared to their composite counterparts. Thus, these hybrid materials possess superior mechanical properties and more controlled degradation characteristics compared to their corresponding conventional composites. To assess in vitro cytocompatibility, MC3T3-E1 pre-osteoblastic cells were seeded onto the surfaces of hybrid biomaterials and polycaprolactone (control). Compared to polycaprolactone, cells on the hybrid material displayed enhanced spreading, focal adhesion formation, and cell number, consistent with excellent cytocompatibility. Thus, based on their mechanical properties, degradability and cytocompatibility, these novel biomaterials have potential for use as scaffolds in bone tissue engineering and related applications.

Effect of Finishing Procedures on the Surface Roughness of Resin-modified Glass-Ionomer Materials.

This study examined the influence of finishing procedures on the surface roughness of different formulations of resin-modified glass ionomers (RMGIs) available in capsules compared with standard resin composites (RCs). Disc samples of three RMGIs and two RCs were fabricated using a metal mold (5 mm x 1.5 mm). Samples were randomly divided into seven groups (N = 10) and subjected to finishing and polishing procedures using a combination of carbide or diamond burs, followed by either rubber points or aluminum-oxide discs. Three different regions of each sample were analyzed using a contact profilometer to determine the average roughness (Ra). The main surface roughness was calculated using a two-way analysis of variance (ANOVA) and the Bonferroni correction for multiple comparisons. A dual-stage combination of a fine carbide bur followed by the use of the finest two grits of aluminum-oxide discs was found to produce the smoothest finished and polished surface. the smoothest surfaces were found to be on the two RCs and one of the RMGIs.

Interaction of primary human trabecular meshwork cells with metal alloy candidates for microinvasive glaucoma surgery.

BACKGROUND: Microinvasive glaucoma surgery (MIGS) is a relatively new addition to the glaucoma treatment paradigm. Small metallic stents are inserted into the trabecular meshwork in order to increase aqueous humour drainage. MIGS procedures are rapidly being adopted owing to a more favourable side effect profile when compared with traditional surgery. Remarkably, this rapid rate of utilization has occurred without any published studies on the effect of metal alloys used in these stents on human trabecular meshwork cells (HTMCs). Therefore, this study aimed to determine the effect of candidate metal alloys for MIGS on HTMC morphology, viability and function. METHODS: Human trabecular meshwork cells were cultured on the surfaces of titanium (polished and sandblasted), a titanium-nickel (nitinol) alloy and glass (as control substratum). Fluorescence imaging was used to assess cell morphology and spreading. A lactate dehydrogenase cytotoxicity assay, cell death detection ELISA, MTT cell viability assay, BrdU cell proliferation assay and fibronectin ELISA were also conducted. RESULTS: Cells cultured on sandblasted titanium exhibited significantly greater spreading than cells cultured on other substrata. In comparison, HTMCs cultured on nitinol displayed poor spreading. Significantly more cell death, by both necrosis and apoptosis, occurred on nitinol than on titanium and glass. Also, cell viability and proliferation were suppressed on nitinol compared with titanium or glass. Finally, HTMCs on both titanium and nitinol produced greater amounts of fibronectin than cells grown on glass. CONCLUSIONS: Substratum topography and metal alloy composition were found to impact morphology, viability and function of primary HTMC cultures.

A Comparison of the Mechanical Measures Used for Assessing Orthodontic Mini-Implant Stability.

PURPOSE: Mechanical loosening remains a common complication associated with mini-implant failure. The purpose of this study was to compare common mechanical measures of mini-implant stability to determine their association and reliability. MATERIALS AND METHODS: Ninety self-drilling orthodontic mini-implants from 6 manufacturers were inserted into artificial bone blocks. Insertion torques (ITs) and Periotest values (PVs) were measured. Subsequently, mini-implants underwent pull-out testing for measures of pull-out load (POL) and screw displacement (ScrD). Stability measurements were compared using one-way ANOVA, associations among them were assessed using correlation analyses, and reliability was evaluated using coefficients of variation (COVs). RESULTS: Variations in stability of mini-implants were found, specific to the mechanical measure used for assessment (P < 0.05). The strongest correlations were found between IT and PV (r = -0.68) and between IT and POL (r = 0.66). Overall, PV showed the greatest variability (COV: 11%-100%) compared with IT (≤11%), POL (≤4%), and ScrD (≤19%). CONCLUSIONS: IT, PV, and POLs only agreed moderately in their assessment of mini-implant stability, and Periotest showed the least reliability in predicting mini-implant stability. As such, independent and interchangeable use of these stability measures should be avoided.

Reinforcement of flowable dental composites with titanium dioxide nanotubes.

OBJECTIVES: Flowable dental composites are used as restorative materials due to their excellent esthetics and rheology. However, they suffer from inferior mechanical properties compared to conventional composites. The aim of this study was to reinforce a flowable dental composite with TiO2 nanotubes (n-TiO2) and to assess the effect of n-TiO2 surface modifications on the mechanical properties of the reinforced composite. METHODS: n-TiO2 were synthesized using an alkaline hydrothermal process and then functionalized with silane or methacrylic acid (MA). Nanotubes were characterized by scanning and transmission electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy. Commercially available flowable composite (Filtek™ Supreme Ultra Flowable Restorative, 3M ESPE) was reinforced with varying amounts of nanotubes (0-5wt%). Flowability of the resulting composites was evaluated using a Gillmore needle method. Dynamic Young's modulus (E) was measured using an ultrasonic technique. Fracture toughness (KIc) was assessed using a notchless triangular prism and radiopacity was quantified. Viability of NIH/3T3 fibroblasts was evaluated following incubation on composite specimens for 24h. RESULTS: Electron microscopy revealed a tubular morphology of n-TiO2. All reinforced composites exhibited significantly greater values of E than unreinforced composite. Composites reinforced with 3wt% n-TiO2 functionalized with MA exhibited the greatest values of E and KIc. Cytotoxicity assays revealed that reinforced composites were biocompatible. Taken together, flowable composites reinforced with n-TiO2 exhibited mechanical properties superior to those of unreinforced composite, with minimal effects on flowability and radiopacity. SIGNIFICANCE: n-TiO2-reinforced flowable composites are promising materials for use in dental restorations.

Effects of artificial aging conditions on yttria-stabilized zirconia implant abutments.

STATEMENT OF PROBLEM: Most ceramic abutments are fabricated from yttria-stabilized tetragonal zirconia (Y-TZP). However, Y-TZP undergoes hydrothermal degradation, a process that is not well understood. PURPOSE: The purpose of this in vitro study was to assess the effects of artificial aging conditions on the fracture load, phase stability, and surface microstructure of a Y-TZP abutment. MATERIAL AND METHODS: Thirty-two prefabricated Y-TZP abutments were screwed and tightened down to external hexagon implants and divided into 4 groups (n = 8): C, control; MC, mechanical cycling (1×10(6) cycles; 10 Hz); AUT, autoclaving (134°C; 5 hours; 0.2 MPa); and TC, thermal cycling (10(4) cycles; 5°/55°C). A single-load-to-fracture test was performed at a crosshead speed of 0.5 mm/min to assess the assembly's resistance to fracture (ISO Norm 14801). X-ray diffraction (XRD) analysis was applied to observe and quantify the tetragonal-monoclinic (t-m) phase transformation. Representative abutments were examined with high-resolution scanning electron microscopy (SEM) to observe the surface characteristics of the abutments. Load-to-fracture test results (N) were compared by ANOVA and Tukey test (α=.05). RESULTS: XRD measurements revealed the monoclinic phase in some abutments after each aging condition. All the aging conditions reduced the fracture load significantly (P<.001). Mechanical cycling reduced the fracture load more than autoclaving (P=.034). No differences were found in the process of surface degradation among the groups; however, the SEM detected grinding-induced surface flaws and microcracks. CONCLUSIONS: The resistance to fracture and the phase stability of Y-TZP implant abutments were susceptible to hydrothermal and mechanical conditions. The surface microstructure of Y-TZP abutments did not change after aging conditions.

The role of bone sialoprotein in the tendon-bone insertion.

Tendons/ligaments insert into bone via a transitional structure, the enthesis, which is susceptible to injury and difficult to repair. Fibrocartilaginous entheses contain fibrocartilage in their transitional zone, part of which is mineralized. Mineral-associated proteins within this zone have not been adequately characterized. Members of the Small Integrin Binding Ligand N-linked Glycoprotein (SIBLING) family are acidic phosphoproteins expressed in mineralized tissues. Here we show that two SIBLING proteins, bone sialoprotein (BSP) and osteopontin (OPN), are present in the mouse enthesis. Histological analyses indicate that the calcified zone of the quadriceps tendon enthesis is longer in Bsp(-/-) mice, however no difference is apparent in the supraspinatus tendon enthesis. In an analysis of mineral content within the calcified zone, micro-CT and Raman spectroscopy reveal that the mineral content in the calcified fibrocartilage of the quadriceps tendon enthesis are similar between wild type and Bsp(-/-) mice. Mechanical testing of the patellar tendon shows that while the tendons fail under similar loads, the Bsp(-/-) patellar tendon is 7.5% larger in cross sectional area than wild type tendons, resulting in a 16.5% reduction in failure stress. However, Picrosirius Red staining shows no difference in collagen organization. Data collected here indicate that BSP is present in the calcified fibrocartilage of murine entheses and suggest that BSP plays a regulatory role in this structure, influencing the growth of the calcified fibrocartilage in addition to the weakening of the tendon mechanical properties. Based on the phenotype of the Bsp(-/-) mouse enthesis, and the known in vitro functional properties of the protein, BSP may be a useful therapeutic molecule in the reattachment of tendons and ligaments to bone.