The influence of hygroscopic expansion of resin supporting dies on the fracture resistance of ceramic restorations during thermal cycling.

OBJECTIVES: To evaluate the hygroscopic expansion characterization of resin composite dies during thermal cycling, and their influence on the fracture resistance of dental ceramic materials as well as the effect of pre-immersion on these measurements. METHODS: Disc-shaped specimens (φ = 15.0 mm, h = 1.2 mm) and anatomical crown dies of four resin composites (epoxy, Z350, P60, G10) were fabricated. Disc-shaped samples were continuously soaked in distilled water and the volume expansion was measured at different time point by Archimedes method. Disc-shaped samples were pre-immersed for 0, 7, or 30 days, elastic modulus and hardness were measured using Nanoindentation test; thermal cycling (TC) test was performed (5 °C-55 °C, 104 cycles), and volume expansion during TC was measured. Four kinds of resin die with pre-immersion for 0, 7, or 30 days were cemented to 5Y-Z crown, or epoxy dies without pre-immersion were cemented to 5Y-Z, 3Y-Z and lithium disilicate glass (LDG) crowns, and load-to-failure testing was performed before and after TC. Finite element analysis (FEA) and fractography analysis were also conducted. RESULTS: The hygroscopic expansion was in the order: epoxy > Z350 > P60 > G10. Except for G10, the other three resin composites exhibited different degrees of hygroscopic expansion during TC. Only the elastic modulus and hardness of epoxy decreased after water storage. However, only the fracture loads of 5Y-Z and LDG crowns supported by epoxy dies were significantly decreased after TC. FEA showed a stress concentration at the cervical region of the crown after volume expansion of the die, leading to the increase of the peak stress at the crown during loading. SIGNIFICANCE: Only the hygroscopic expansion of epoxy dies caused by TC led to the decrease in the fracture resistance of the 5Y-Z and LDG crown, which may be related to the decrease in the elastic modulus of the epoxy die and the tensile stress caused by it.

Stepwise degradable PGA-SF core-shell electrospinning scaffold with superior tenacity in wetting regime for promoting bone regeneration.

Regenerating bone in the oral and maxillofacial region is clinically challenging due to the complicated osteogenic environment and the limitation of existing bone graft materials. Constructing bone graft materials with controlled degradation and stable mechanical properties in a physiological environment is of utmost importance. In this study, we used silk fibroin (SF) and polyglycolic acid (PGA) to fabricate a coaxial PGA-SF fibrous scaffold (PGA-SF-FS) to meet demands for bone grafts. The SF shell exerted excellent osteogenic activity while protecting PGA from rapid degradation and the PGA core equipped scaffold with excellent tenacity. The experiments related to biocompatibility and osteogenesis (e.g., cell attachment, proliferation, differentiation, and mineralization) demonstrated the superior ability of PGA-SF-FS to improve cell growth and osteogenic differentiation. Furthermore, in vivo testing using Sprague-Dawley rat cranial defect model showed that PGA-SF-FS accelerates bone regeneration as the implantation time increases, and its stepwise degradation helps to match the remodeling kinetics of the host bone tissue. Besides, immunohistochemical staining of CD31 and Col-1 confirmed the ability of PGA-SF-FS to enhance revascularization and osteogenesis response. Our results suggest that PGA-SF-FS fully utilizing the advantages of both components, exhibites stepwise degradation and superior tenacity in wetting regime, making it a promising candidate in the treatment of bone defects.

Effect of low-temperature degradation on the fatigue performance of dental strength-gradient multilayered zirconia restorations.

OBJECTIVES: Fatigue and low-temperature degradation (LTD) are the main factors contributing to zirconia restoration failure. This study evaluated the effect of LTD on the fatigue performance of the novel "strength & shade-gradient" multilayered zirconia restorations. METHODS: Discs (15 mm × 1.2 mm) of each yttria content layer from a newly developed strength-gradient multilayered zirconia were fabricated and under accelerated aging in an autoclave at 134℃ for 0 h, 32 h, and 64 h. Then, the phase transformation, microstructure, and mechanical properties after LTD were assessed. In addition, the crown samples, including the multi-Zir, 3Y-Zir, and 5Y-Zir were fabricated, and their monotonic and fatigue load before and after LTD, percentage of fatigue degradation (Sd) and the fracture morphology were investigated. Statistical analyses were performed using paired samples t-test (α' = α/3 = 0.017), one-way ANOVA and Weibull analysis. RESULTS: After LTD, the phase transformation, surface roughness, depth of transformed zone, and residual stress were increased and inversely associated with the yttria content. The indentation elastic modulus and hardness after LTD decreased; however, there was no significant difference between the different yttria content layers. The monotonic and fatigue load of multi-Zir restorations decreased, but their Weibull modulus increased, and Sd decreased, similar to 3Y-Zir. The crack origin was associated with the cervical region. CONCLUSION: These results show that although LTD reduces the absolute fatigue strength of strength-gradient multilayered zirconia restorations, it also reduces the effect of cyclic fatigue itself on the strength of zirconia (relative to monotonic strength), which might be due to the increase of residual stress. CLINICAL SIGNIFICANCE: The novel "strength & shade-gradient" multilayered zirconia restorations show a promising performance during in vitro LTD and fatigue test and their reliability to some extent is comparable to 3Y-Zir. Yet, further in vivo longitudinal studies are warranted to confirm their precise performance.

Methodology improvement of bulk compressive creep test: Deformation measurement and loading rate.

OBJECTIVES: (1) To identify improvements when bulk compressive creep testing of dental resin composite materials to reduce the sensitivity to the surface morphology and parallelism of specimens, to generate more accurate strain (displacement) measurement values. (2) To investigate the effect of loading rate on the creep and recovery behavior under bulk compressive creep test. METHODS: Cylindrical composite resin specimens were subjected to bulk compressive creep test with conventional and modified methodology (with/without introduction of stainless steel hemisphere and preload process). Furthermore, specimens undertook different loading rates ranging from 1 N/s to 50 N/s. Maximum deformation, creep deformation, permanent set as well as percentage of recovery during the creep and recovery procedure were compared, and surface topography changes before and after preload process was evaluated by laser scanning confocal. Burgers model was used to investigate the effect of improvements to each part of viscoelastic deformation of resin specimens. RESULTS: (1) The influence of surface evenness of resin specimens could be reduced by addition of preload process before the bulk compressive creep test resulting in significantly decreased permanent set (p = 0.002), and increased recovery to 91.7 % (p < 0.001). While the standard deviation of maximum deformation, permanent set and percentage of recovery had the smallest values when hemisphere was introduced to loading chain. (2) With increasing loading rate of bulk compressive creep tests, creep deformation increased and this trend became statistically significant when the loading rate reached 50 N/s. SIGNIFICANCE: The accuracy of deformation measurement during bulk compressive creep test could be improved by means of introducing stainless steel hemisphere to the loading chain, and adding preload process to loading protocol.

The polycaprolactone/silk fibroin/carbonate hydroxyapatite electrospun scaffold promotes bone reconstruction by regulating the polarization of macrophages.

Macrophages are known to modulate the osteogenic environment of bone regeneration elicited by biological bone grafts. Alteration in certain chemical components tends to affect macrophages polarization. Comparatively to hydroxyapatite (HAp), carbonate hydroxyapatite (CHA) consists of 7.4 (wt%) carbonate ions and more closely resembles the mineral content of bone. It remains unknown whether CHA scaffolds or HA scaffolds have better osteogenic properties. In this study, we fabricated PCL/SF scaffold, PCL/SF/HAp scaffold and PCL/SF/CHA scaffold using the electrospinning technique. Despite comparable mechanical properties, the PCL/SF/CHA scaffold exhibited better osteogenic properties than the PCL/SF/HAp scaffold. Although no significant differences were observed between the two scaffolds for promoting osteoblast differentiation in vitro, the PCL/SF/CHA group appeared to be more effective at promoting bone regeneration in cranial defects in vivo. The PCL/SF/CHA scaffold was found to promote macrophage polarization toward M2 via activating the JAK/STAT5 pathway which caused a pro-osteogenic microenvironment to facilitate osteoblast differentiation. The results of this study indicated a higher potential of CHA to substitute HAp in the production of bone scaffolds for better bone regeneration.

Effect of acid-alkali treatment on serum protein adsorption and bacterial adhesion to porous titanium.

Modification of the titanium (Ti) surface is widely known to influence biological reactions such as protein adsorption and bacterial adhesion in vivo, ultimately controlling osseointegration. In this study, we sought to investigate the correlation of protein adsorption and bacterial adhesion with the nanoporous structure of acid-alkali-treated Ti implants, shedding light on the modification of Ti implants to promote osseointegration. We fabricated nontreated porous Ti (NTPT) by powder metallurgy and immersed it in mixed acids and NaOH to obtain acid-alkali-treated porous Ti (AAPT). Nontreated dense sample (NTDT) served as control. Our results showed that nanopores were formed after acid-alkali treatment. AAPT showed a higher specific surface area and became much more hydrophilic than NTPT and NTDT (p < 0.001). Compared to dense samples, porous samples exhibited a lower zeta potential and higher adsorbed protein level at each time point within 120 min (p < 0.001). AAPT formed a thicker protein layer by serum precoating than NTPT and NTDT (p < 0.001). The main adsorbed proteins on AAPT and NTPT were albumin, α1 antitrypsin, transferrin, apolipoprotein A1, complement C3 and haptoglobin α1 chain. The amounts of bacteria adhering to the serum-precoated samples were lower than those adhering to the nonprecoated samples (p < 0.05). Lower-molecular-weight proteins showed higher affinity to porous Ti. In conclusion, acid-alkali treatment facilitated protein adsorption by porous Ti, and the protein coating tended to prevent bacteria from adhering. These findings may be utilized for Ti implant modification aimed at reducing bacterial adhesion and enhancing osseointegration. Graphical abstract.

Effect of supporting dies' mechanical properties on fracture behavior of monolithic zirconia molar crowns.

The aim of this study was to investigate the effects of supporting dies with different mechanical properties on the fracture strengths and failure modes of monolithic zirconia crowns, and identify a suitable die material for testing high-strength ceramic restorations. Thirty six dies from teeth, porous titanium and composite-resin with 36 zirconia crowns were fabricated based on 3D model. Crowns were cemented, then underwent load-to-fracture testing. Fractographic analysis was performed with scanning electron microscopy, and finite element analysis was made. During loading, a high stress concentration zone formed near the loading point and on surface of die. Cracks generated on failure penetrated the crown and extended to die in 9 teeth group specimens, while composite-resin samples exhibited fracture of both crowns and dies. All dies remained intact in porous titanium group. Fracture mode was undistinguishable in all groups. It was concluded that porous titanium appears suitable as die material for dental restorations with high fracture strength.

Establishment of optimal variable elastic modulus distribution in the design of full-crown restorations by finite element analysis.

To establish optimal elastic modulus distribution throughout the entire all-ceramic crown, aiming at improvement of the mechanical properties of the restoration as well as the adhesive interface, seven 3D models of mandibular first premolars of zirconia monolithic and bilayer crowns and lithium disilicate monolithic and bilayer crowns were constructed. The elastic modulus distribution of 8-layer crown A referred to human enamel, B was calculated by a genetic algorithm (GA) to minimize the principle stresses on the crown, and C minimized the shear stresses at the cementing lines. After applying a static load of 600 N, the maximum principle stresses were calculated and analyzed by finite element analysis (FEA). Group C were found to have the lowest peak shear stress at the cementing line and moderate peak tensile stress in the crown. Introduction of the modified elastic modulus distribution from human enamel into the entire all-ceramic crown reinforces the mechanical properties of the whole restoration as well as the adhesive interface against chipping and debonding.

Effects of pore size and porosity on cytocompatibility and osteogenic differentiation of porous titanium.

To find out the optimal porosity and pore size of porous titanium (Ti) regarding the cytocompatibility and osteogenic differentiation. Six groups of porous Ti samples with different porosities and pore sizes were fabricated by the powder metallurgy process. The microstructure and compressive mechanical properties were characterized. The cytocompatibility was examined by a series of biological tests as protein absorption with BCA assay kit, cell attachment with laser scanning confocal microscopy and vinculin expression, cell proliferation with CCK-8 assay. Cell differentiation and calcification were detected by qPCR and Alizarin Red S dying respectively. Pores distributed homogeneously throughout the porous Ti samples. The compressive test results showed that Young's modulus ranged from 2.80 ± 0.03 GPa to 5.43 ± 0.34 GPa and the compressive strength increased from 112.4 ± 3.6 MPa to 231.1 ± 9.4 MPa. Porous Ti with high porosity (53.3 ± 1.2%) and small pore size (191.6 ± 3.7 µm) adsorbed more proteins. More MC3T3-E1 cells adhered onto dense Ti samples than onto any other porous ones already after culture and no difference was identified within the porous groups. The porous structure of porous Ti with a porosity of 53.3 ± 1.2% and an average pore size of 191.6 ± 3.7 µm facilitated cell differentiation and calcification. Small pores were not beneficial to the osteo-initiation at the very beginning. Porous Ti with a porosity of 53.3 ± 1.2% and an average pore size of 191.6 ± 3.7 µm fabricated by powder metallurgy process showed the expected mechanical property and improved osseointegration as implants in dental treatment.

The bulk compressive creep and recovery behavior of human dentine and resin-based dental materials.

OBJECTIVE: To evaluate and compare the viscoelastic properties of dentine and resin-based dental materials by bulk compressive test and the Burgers model. MATERIALS AND METHODS: Sound dentine, three resin composites as well as a resin-based cement were prepared into cylindrical specimens (n = 8). A bulk compressive creep test was applied with a constant load of 300 N (23.9 MPa) for 2 h, followed by another 2 h recovery. The maximum strain, creep stain, percentage of recovery and permanent set was measured using a linear variable displacement transducer. The viscoelastic properties were characterized via the Burgers model, and the instantaneous elastic, viscous as well as elastic delayed deformation were separated from the total strain. Data were analysed via ANOVA (or Welch's Test) and Tukey (or Games-Howell Test) with a significance level of 0.05. RESULTS: Sound dentine presented the lowest maximum strain, creep strain, permanent set and the highest percentage of recovery, followed by 3 resin composites with comparable parameters, while the cement showed a significantly higher maximum strain, permanent set and lower percentage of recovery (p < 0.001). The Burgers model presented acceptable fits for characterization viscoelastic processes of both dentine and resin-based dental materials. Viscous and elastic delayed strain of dentine was significantly lower than those for tested materials (p < 0.001) with the highest instantaneous elastic strain percentage. Similar viscous and delayed strain was found among the 4 resin-based materials (p > 0.05). SIGNIFICANCE: Sound dentine exhibited superior creep stability compared to resin-based dental materials. The viscous deformation in sound dentine could be ignored when loading parallel to dentine tubules.

Influence of veneer pore defects on fracture behavior of bilayered lithium disilicate glass-ceramic crowns.

OBJECTIVE: To identify the conditions under which fabrication pore defects within veneering porcelain in bilayered lithium disilicate glass-ceramic (LDG) crowns will influence and jeopardize the mechanical integrity of the structure. METHODS: Thirty standardized molar crowns (IPS e.max Press) were fabricated and microCT scanned to 3D-analyze the size, morphology and distribution of pores in veneering porcelain, followed by in vitro fracture test and SEM fractographic observation. Finite element analysis (FEA) of the microCT reconstructed models was used to evaluate the stress state. RESULTS: The volumes of pores in samples ranged from 3241µm3 to 1.29×109µm3 with the equivalent radius between 10µm to 680µm. Deviation of sphericity of pores ranged from 0.10 to 0.81 and the average of 99.97% pores was near 0.63. For the smaller pores their distribution tended to be uniform, while the larger pores were irregular with elongated ellipsoidal form and located at or near the veneer-core interface. During wedge loading blunt contact fracture testing 21 crowns failed from the fissure on the occlusal surface, of which 16 failed from surface or near surface pores, 2 from the midpoint of the oblique ridge, and 7 from larger interfacial pores. FEA analysis indicated that defects were detrimental to veneer integrity only in regions of tensile stress and where the pore radius associated with crack initiation ranged from 30 to 50µm. Pore morphology appeared to have only a minor effect on fracture. SIGNIFICANCE: Within the limitation of the microCT resolution and FEA, it suggests that pores radius large than 30-50µm and located in the tensile stress area like grooves and fissures on the occlusal surface or near surface as well as cervical margins of veneering porcelain will jeopardize the bilayered structure and mechanical integrity of LDG.

Evaluation of fiber posts vs metal posts for restoring severely damaged endodontically treated teeth: a systematic review and meta-analysis.

OBJECTIVES: This review was undertaken to answer a controversial clinical question with high-quality evidence: When severely damaged teeth are restored, which type of post (metal or fiber) demonstrates superior clinical performance? DATA SOURCES: The meta-analysis was conducted according to the guidelines in the Cochrane handbook. Electronic databases (MEDLINE, EMBASE, CENTRAL) and gray literatures were screened up to January 2018. Only randomized controlled trials (RCTs) with follow-up of at least 3 years were included. The quality of included studies was assessed by the Cochrane Collaboration's tool. Meta-analysis compared survival, success, post debonding, and root fracture incidence of teeth restored with fiber and metal posts. The GRADE system (Grading of Recommendations, Assessment, Development and Evaluations) was used to assess the strength of the evidence. Of 1,511 records, 14 full texts were obtained. Only four RCTs with follow-up times of 3 to 7 years met the selection criteria. The methodologic quality of included RCTs was low risk of bias. Fiber posts presented significantly higher survival rates than did metal posts (RR 0.57, 95% CI: 0.33 to 0.97, P = .04), while no difference was observed in success rates, post debonding rates, or root fracture rates. The GRADE assessment indicated a high quality of evidence for survival rates and a moderate quality for success rates. CONCLUSION: It was concluded that fiber posts displayed higher medium-term (3 to 7 years) overall survival rates than did metal posts when used in the restoration of endodontically treated teeth with no more than two coronal walls remaining.

Effects of polyethylene glycol content on the properties of a silk fibroin/nano-hydroxyapatite/polyethylene glycol electrospun scaffold.

To study the effects of polyethylene glycol (PEG) content on the mechanical properties and degradation of silk fibroin, nano-hydroxyapatite, and PEG (SF/nHAP/PEG) electrospun scaffolds, and according to the PEG ratio in the scaffold (SF : nHAP : PEG), test groups were divided as follows: PEG-0 (10 : 2), PEG-0.5 (10 : 2 : 0.5), PEG-1 (10 : 2 : 1), and PEG-2 (10 : 2 : 2). A series of tests to determine the mechanical properties, degradation rates, and osteogenic characteristics was undertaken. PEG facilitated SF degradation (PEG-1 > PEG-0.5 > PEG-0 > PEG-2), and the mass loss of the scaffolds in PEG-1 was more than 30%, while in PEG-2 it was less than 20% after 8 days (P < 0.05). The addition of PEG strengthened the mechanical properties of the scaffold (PEG-1 > PEG-2 > PEG-0.5 > PEG-0), as the Young's modulus increased from 41.72 ± 3.40 MPa for PEG-0 to 76.12 ± 3.73 MPa for PEG-1 (P < 0.05). PEG was favorable for the osteogenic differentiation of BMSCs (PEG-0.5 > PEG-1 > PEG-2 > PEG-0). The enhancements were attributable to the increased hydrophilicity and nHAP dispersion, as well as to the secondary structure transformation of SF. The PEG content was deemed to be optimal when the SF/nHAP/PEG ratio was equal to 10 : 2 : 1.

Effects of acid-alkali treatment on bioactivity and osteoinduction of porous titanium: An in vitro study.

BACKGROUND: To elucidate the bioactivity and bone regeneration of porous titanium surfaces treated using acid-alkali combination, and to define the optimal alkali reaction time. METHODS: Ten groups of porous Ti with at least 3 per group undergoing different acid-alkali treated time were prepared. The surface was characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), bicinchoninic acid method (BCA), optical contact angle measurement and Raman spectrometry. Compression testing was performed with a universal testing machine. The bioactivity and osteoinduction were evaluated by a series of biological tests using a simulated body fluid (SBF) test, cell proliferation test, vinculin, ALP and OCN expression, and cell mineralization. RESULTS: The acid-alkali treatment formed micro- and nano-scale structures on the sample surfaces. The alkali treatment for 12 h achieved the sharpest nano-scale surface relief and the most protein absorption. The treated porous surface was coated with a NaHTiO3 layer. The acid-alkali etching did not compromise the elastic modulus and compressive strength of the porous Ti samples. In addition to hydroxyapatite, a perovskite phase was also formed on the treated porous samples in SBF. Non-treated dense Ti showed more cell adhesion and proliferation (P < 0.05), while osteoinduction and mineralization were more pronounced on the treated porous sample (P < 0.05). CONCLUSION: Acid-alkali treatment is an effective means of generating nano-scale relief on porous Ti surface, and is beneficial for bioactivity and bone regeneration. The 15 min acid and 12 h alkali etching is the optimal combination. The osteoinductive efficacy may be attributable to the surface physical chemistry and the formation of hydroxyapatite and perovskite layers, rather than direct cell adhesion and proliferation.

Three-dimensional characterization and distribution of fabrication defects in bilayered lithium disilicate glass-ceramic molar crowns.

OBJECTIVE: To investigate and characterize the distribution of fabrication defects in bilayered lithium disilicate glass-ceramic (LDG) crowns using micro-CT and 3D reconstruction. METHODS: Ten standardized molar crowns (IPS e.max Press; Ivoclar Vivadent) were fabricated by heat-pressing on a core and subsequent manual veneering. All crowns were scanned by micro-CT and 3D reconstructed. Volume, position and sphericity of each defect was measured in every crown. Each crown was divided into four regions-central fossa (CF), occlusal fossa (OF), cusp (C) and axial wall (AW). Porosity and number density of each region were calculated. Statistical analyses were performed using Welch two sample t-test, Friedman one-way rank sum test and Nemenyi post-hoc test. The defect volume distribution type was determined based on Akaike information criterion (AIC). RESULTS: The core ceramic contained fewer defects (p<0.001) than the veneer layer. The size of smaller defects, which were 95% of the total, obeyed a logarithmic normal distribution. Region CF showed higher porosity (p<0.001) than the other regions. Defect number density of region CF was higher than region C (p<0.001) and region AW (p=0.029), but no difference was found between region CF and OF (p>0.05). Four of ten specimens contained the largest pores in region CF, while for the remaining six specimens the largest pore was in region OF. SIGNIFICANCE: LDG core ceramic contained fewer defects than the veneer ceramic. LDG strength estimated from pore size was comparable to literature values. Large defects were more likely to appear at the core-veneer interface of occlusal fossa, while small defects also distributed in every region of the crowns but tended to aggregate in the central fossa region. Size distribution of small defects in veneer obeyed a logarithmic normal distribution.

All-Trans Retinoic Acid-Induced Craniofacial Malformation Model: A Prenatal and Postnatal Morphological Analysis.

OBJECTIVE: To characterize the prenatal and postnatal craniofacial bone development in mouse model of all-trans retinoic acid (ATRA) exposure at different ages by a quantitative and morphological analysis of skull morphology. METHODS: Pregnant mice were exposed to ATRA at embryonic day 10 (E10) and 13 (E13) by oral gavage. Skulls of mice embryos at E19.5 and adult mice at postnatal day 35 (P35) were collected for high-resolution microcomputed tomography (microCT) imaging scanning and section HE staining. Reconstruction and measurement of mouse skulls were performed for prenatal and postnatal analysis of the control and ATRA-exposed mice. RESULTS: Craniofacial malformations in mouse models caused by ATRA exposure were age dependent. ATRA exposure at E10 induced cleft palate in 81.8% of the fetuses, whereas the palatine bone of E13-exposed mice was intact. Inhibitions of maxilla and mandible development with craniofacial asymmetry induced were observed at E19.5 and P35. Compared with control and E13-exposed mice, the palatine bones of E10-exposed mice were not elevated and were smaller in dimension. Some E10-exposed mice exhibited other craniofacial abnormalities, including premature fusion of mandibular symphysis with a missing mandibular incisor and a smaller mandible. Severe deviated snouts and amorphous craniofacial suture were detected in E13-exposed mice at P35. CONCLUSION: These morphological variations in E10- and E13-exposed mice suggested that ATRA was teratogenic in craniofacial bone development in mice and the effect was age dependent.

Effect of core ceramic grinding on fracture behaviour of bilayered zirconia veneering ceramic systems under two loading schemes.

OBJECTIVE: The aim of this in vitro study was to evaluate the effect of core ceramic grinding on the fracture behaviour of bilayered zirconia under two loading schemes. METHODS: Interfacial surfaces of sandblasted zirconia disks (A) were ground with 80 (B), 120 (C) and 220 (D) grit diamond discs, respectively. Surface roughness and topographic analysis were performed using a confocal scanning laser microscope (CSLM) and a scanning electron microscopy (SEM). Relative monoclinic content was evaluated using X-ray diffraction analysis (XRD) then reevaluated after simulated veneer firing. Biaxial fracture strength (σ) and Weibull modulus (m) were calculated either with core in compression (subgroup Ac-Dc) or in tension (subgroup At-Dt). Facture surfaces were examined by SEM and energy dispersive X-ray spectroscopy (EDS). Maximum tensile stress at fracture was estimated by finite element analysis. Statistical data analysis was performed using Kruskal-Wallis and one-way ANOVA at a significance level of 0.05. RESULTS: As grit size of the diamond disc increased, zirconia surface roughness decreased (p<0.001). Thermal veneering treatment reversed the transformation of monoclinic phase observed after initial grinding. No difference in initial (p=0.519 for subgroups Ac-Dc) and final fracture strength (p=0.699 for subgroups Ac-Dc; p=0.328 for subgroups At-Dt) was found among the four groups for both loading schemes. While coarse grinding slightly increased final fracture strength reliability (m) for subgroups Ac-Dc. Two different modes of fracture were observed according to which material was on the bottom surface. Components of the liner porcelain remained on the zirconia surface after fracture for all groups. SIGNIFICANCE: Technician grinding changed surface topography of zirconia ceramic material, but was not detrimental to the bilayered system strength after veneer application. Coarse grinding slightly improved the fracture strength reliability of the bilayered system tested with core in compression. It is recommended that veneering porcelain be applied directly after routine lab grinding of zirconia ceramic, and its application on rough zirconia cores may be preferred to enhance bond strength.

Three-dimensional Reconstruction of the Microstructure of Human Acellular Nerve Allograft.

The exact inner 3D microstructure of the human peripheral nerve has been a mystery for decades. Therefore, it has been difficult to solve several problems regarding peripheral nerve injury and repair. We used high-resolution X-ray computed microtomography (microCT) to scan a freeze-dried human acellular nerve allograft (hANA). The microCT images were then used to reconstruct a 3D digital model, which was used to print a 3D resin model of the nerve graft. The 3D digital model of the hANA allowed visualization of all planes. The magnified 3D resin model clearly showed the nerve bundles and basement membrane tubes of the hANA. Scanning electron microscopy (SEM) was used to analyse the microstructure of the hANA. Compared to the SEM images, the microCT image clearly demonstrated the microstructure of the hANA cross section at a resolution of up to 1.2 µm. The 3D digital model of the hANA facilitates a clear and easy understanding of peripheral nerve microstructure. Furthermore, the enlarged 3D resin model duplicates the unique inner structure of each individual hANA. This is a crucial step towards achieving 3D printing of a hANA or nerve that can be used as a nerve graft.