Znic (Zn) alloys with good cytocompatibility and suitable degradation rate have been a kind of biodegradable metal with great potential for clinical applications. This paper summarizes the biological role of degradable Zn alloy as bone implant materials, discusses the mechanical properties of different Zn alloys and their advantages and disadvantages as bone implant materials, and analyzes the influence of different processing strategies (such as alloying and additive manufacturing) on the mechanical properties of Zn alloys. This paper provides systematic design approaches for biodegradable Zn alloys as bone implant materials in terms of the material selection, product processing, structural topology optimization, and assesses their application prospects with a view to better serve the clinic.
Orthopedics ; Zinc ; Alloys ; Dental Materials ; Prostheses and Implants

OBJECTIVE: To compare the retentions of different designs of cobalt-chromium (Co-Cr), pure titanium (CP Ti), and titanium alloy (Ti-6Al-4V) removable partial denture (RPD) circumferential clasps manufactured by selective laser melting (SLM) and to analyze the stress distribution of these clasps during the removal from abutment teeth. METHODS: Clasps with clasp arm size A (1.9 mm width/1.1 mm thickness at the body and 0.8-taper) or B (1.2 times A) and 0.25 mm or 0.50 mm undercut engagement were modeled on a prepared first premolar die, named as designs A1, A2, A3, and A4, respectively. The density and elastic modulus of SLM-built Co-Cr, CP Ti, and Ti-6Al-4V were measured and given to different groups of clasps. The density, elastic modulus, and Poisson ' s ratio of enamel were given to the die. The control group was the cast Co-Cr clasp with design A1, to which the density and elastic modulus of cast Co-Cr alloy were given. The Poisson's ratio of all metals was 0.33. The initial 5 N dislodging force was applied, and the maximum displacement of the clasp along the insertion path was computed. The load was reapplied with an increment of 5 N than in the last simulation until the clasp was completely dislodged. The retentive force range of different groups of clasps was obtained. The retentive forces of the SLM-built Co-Cr, CP Ti, and Ti-6Al-4V clasps with equivalent computed retentive force range to the control group were validated through the insertion/removal experiment. The von Mises stress distributions of these three groups of SLM-built clasps under 15 N loads were analyzed. RESULTS: SLM-built Co-Cr, CP Ti, and Ti-6Al-4V clasps with designs B1 or B2, and Co-Cr clasps with design A2 had higher retentive forces than those of the control group. SLM-built CP Ti and Ti-6Al-4V clasps with design A1 had lower retentive forces than those of the control group. SLM-built Co-Cr clasp with design A1 and SLM-built CP Ti and Ti-6Al-4V clasps with design A2 had equivalent retentive forces to those of the control group. The insertion/removal experiment showed that the measured retentive forces of these three groups of SLM-built clasps were (21.57±5.41) N, (19.75±4.47) N, and (19.32±2.04) N, respectively. No statistically significant measured retentive force difference was found among these three groups of SLM-built clasps (P>0.05). The maximum von Mises stress of these three groups of SLM-built clasps exceeded their responding yield strength except for the Ti-6Al-4V one. CONCLUSION SLM-built Co-Cr circumferential clasps had higher retention than CP Ti and Ti-6Al-4V ones with the same clasp arm size and undercut engagement. The retention of SLM-built circumferential clasps could be adjusted by changing the undercut engagement and clasp arm size. If SLM-built circumferential clasps are used in clinical practice, the Ti-6Al-4V clasp with clasp arm size A and 0.50 mm undercut engagement is recommended considering the long-term use of RPD in the patient's mouth.
Chromium Alloys ; Dental Clasps ; Denture Retention ; Denture, Partial, Removable ; Finite Element Analysis ; Humans ; Lasers ; Titanium

Various engine-driven NiTi endodontic files have been indispensable and efficient tools in cleaning and shaping of root canals for practitioners. In this review, we introduce the relative terms and conceptions of NiTi file, including crystal phase composition, the design of the cutting part, types of separation. This review also analysis the main improvement and evolution of different generations of engine-driven nickel-titanium instruments in the past 20 years in the geometric design, manufacturing surface treatment such as electropolishing, thermal treatment, metallurgy. And the variety of motion modes of NiTi files to improve resistance to torsional failure were also discussed. Continuous advancements by the designers, provide better balance between shaping efficiency and resistance to of NiTi systems. In clinical practice an appropriate system should be selected based on the anatomy of the root canal, instrument characteristics, and operators' experience.
Dental Alloys/chemistry* ; Dental Instruments ; Equipment Design ; Nickel/chemistry* ; Root Canal Preparation ; Titanium/chemistry*

PURPOSE: The aim of this study is to evaluate the effectiveness of MnO₂-diatom microbubbler (DM) on the surface of prosthetic materials as a mouthwash by comparing the biofilm removal effect with those previously used as a mouthwash in dental clinic.MATERIALS AND METHODS: DM was fabricated by doping manganese dioxide nanosheets to the diatom cylinder surface. Scanning electron microscopy (SEM) was used to observe the morphology of DM and to analyze the composition of doped MnO₂. Stereomicroscope was used to observe the reaction of DM in 3% hydrogen peroxide. Non-precious metal alloys, zirconia and resin specimens were prepared to evaluate the effect of biofilm removal on the surface of prosthetic materials. And then Streptococcus mutans and Porphyromonas gingivalis biofilms were formed on the specimens. When 3% hydrogen peroxide solution and DM were treated on the biofilms, the decontamination effect was compared with chlorhexidine gluconate and 3% hydrogen peroxide solution by crystal violet staining.RESULTS: Manganese dioxide was found on the surface of the diatom cylinder, and it was found to produce bubble of oxygen gas when added to 3% hydrogen peroxide. For all materials used in the experiments, biofilms of the DM-treated groups got effectively removed compared to the groups used with chlorhexidine gluconate or 3% hydrogen peroxide alone.CONCLUSION: MnO₂-diatom microbubbler can remove bacterial membranes on the surface of prosthetic materials more effectively than conventional mouthwashes.
Alloys ; Biofilms ; Chlorhexidine ; Decontamination ; Dental Clinics ; Dental Plaque ; Diatoms ; Gentian Violet ; Hydrogen Peroxide ; In Vitro Techniques ; Manganese ; Membranes ; Microscopy, Electron, Scanning ; Mouthwashes ; Oral Hygiene ; Oxygen ; Porphyromonas gingivalis ; Streptococcus mutans

OBJECTIVE: To assess the effects of two surface treatments (sandblasting, SB; microarc-oxidation, MAO) and resin luting on shear bond strength and durability of titanium alloy and composite-resin. METHODS: Eighty cylindrical titanium alloy specimens with a diameter of 10 mm and a height of 8 mm were fabricated by CAD/CAM technique. It was divided into two groups according to the surface treatment methods: sandblasting with Al2O3 particles on the surface of SB specimens; porous ceramic film structure could be formed on the surface of MAO specimens after surface treatment. Each group was classified into SB-resin luting-N group (not used), SB-resin luting-Y group (used), MAO-resin luting-N group (not used), MAO-resin luting-Y group (used) depending on whether or not resin luting was applied. Each specimen was bonded and cured with the Cemerage resin, and the shear bond strength after 0 and 5 000 thermocycling was tested. The results were statistically analyzed. The surface morphology of titanium alloy specimens before and after the shear bond strength test was observed by scanning electron microscopy (SEM). RESULTS: The shear bond strength between titanium alloy and composite-resin was the highest in the SB combined with resin luting group after 0 thermocycling (16.2±1.8) MPa; was the lowest in MAO group after 5 000 thermocycling (8.9±1.5) MPa. The shear bond strength of SB and MAO surface treatment methods combined without resin luting group after 5 000 thermocycling were (10.7±2.2) MPa and (8.9±1.5) MPa, which were statistically lower than those in the thermocycling 0 (P=0.000 and P=0.001). The shear bond strength of SB and MAO surface treatment methods combined with resin luting group after 5 000 thermocycling were (15.5±2.1) MPa and (11.7±1.3) MPa, respectively, which were lower than those in the thermocycling 0 group, but there was no statistical significance (P=0.087 and P=0.234). CONCLUSION Both the surface treatment methods of SB and MAO combined with resin luting can improve the shear bond strength and durability of titanium alloy and composite-resin. The SB combined with resin luting is more significant. At present, the effect of SB is better than that of MAO due to the limitation of technical parameters of micro-arc oxidation.
Alloys ; Composite Resins ; Dental Bonding ; Materials Testing ; Resin Cements ; Shear Strength ; Surface Properties ; Titanium

OBJECTIVE: To construct a model for a controlled memory (CM) nickel-titanium (NiTi) file and another M-wire NiTi file with the same geometry by using finite element analysis. To evaluate the flexibility of a CM NiTi file by using three dimensional finite element method and to compare its mechanical responses with that M-wire NiTi. METHODS: Based on the reverse engineering, the 21 mm long, 25#/08 taper Hyflex NT NiTi file and Hyflex CM NiTi file were fixed by the cantilever bending model at a distance of 9.5 mm from the tip of the file. The mechanical tester's indenter was loaded/unloaded at a distance of 3 mm from the tip of the file. The maximum displacement was 3 mm, the load displacement curve was obtained. Subsequently, by using a micro-CT to scan (layer spacing of 8 μm) NiTi files, and ABAQUS (6.10) was introduced to construct a geometric model. Hyflex NT was considered as a shapememory alloy constitutive model, Hyflex CM was considered as a power-hardening plastic constitutive model, respectively. Comparing the load-displacement curve of cantilever bending in the three-dimensional finite element model with the load-displacement curve in the experiment. RESULTS: Two tetrahedral element models were constructed, the total number of nodes was 99 353 and the total number of cells was 63 744. When the loading displacement was 1 mm, the stress distribution of the cross section at 6.1 mm from the tip of the file was observed. The upper and lower surfaces were subjected to the maximum bending stress and entered the phase transformation yield stage. The finite element simulation could clearly show the deformation of the file. Various information such as deformation characteristics and stress distribution in the process were well fitted to the actual experimental curve. CONCLUSION The constitutive behavior of the material has a significant effect on the mechanical behavior of NiTi file. The finite element model established for the NiTi file of the CM wire can accurately capture the characteristics of various deformation processes of the NiTi root canal file, and it has a good fit with the actual experimental curve. The finite element model can be used for study on bending properties of CM wire.
Dental Alloys ; Equipment Design ; Finite Element Analysis ; Materials Testing ; Nickel ; Root Canal Preparation ; Stress, Mechanical ; Titanium

PURPOSE: The present study was designed to examine the clinical fit of fixed dental prosthesis fabricated by the milling-sintering method using a presintered cobalt-chromium alloy. MATERIALS AND METHODS: Two single metal-ceramic crowns were fabricated via milling-sintering method and casting method in each of the twelve consecutive patients who required an implant-supported fixed prosthesis. In the milling-sintering method, the prosthetic coping was designed in computer software, and the design was converted to a non-precious alloy coping using milling and post-sintering process. In the casting method, the conventional manual fabrication process was applied. The absolute marginal discrepancy of the prostheses was evaluated intraorally using the triple-scan technique. Statistical analysis was conducted using Mann-Whitney U test (α=.05). RESULTS: Eight patients (66.7%) showed a lower marginal discrepancy of the prostheses made using the milling-sintering method than that of the prosthesis made by the casting method. Statistically, the misfit of the prosthesis fabricated using the milling-sintering method was not significantly different from that fabricated using the casting method (P=.782). There was no tendency between the amount of marginal discrepancy and the measurement point. CONCLUSION: The overall marginal fit of prosthesis fabricated by milling-sintering using a presintered alloy was comparable to that of the prosthesis fabricated by the conventional casting method in clinical use.
Alloys ; Clinical Study ; Crowns ; Dental Prosthesis ; Humans ; Methods ; Prostheses and Implants

OBJECTIVE: To evaluate the accuracy of optical coherence tomography (OCT) in detecting root cracks after root canal instrumentation using histological gold standard. METHODS: Twenty complete extracted human mandibular incisors that were free of caries, calculus, and root treatment were chosen and accessed coronally with a diamond bur, then mounted in resin blocks with alginate impression material using simulated periodontal ligaments, and the apex was exposed 3 mm. The teeth were stored in water at room temperature. Then the teeth were then instrumented to the major apical foramen (AF) at #30/0.09 using ProTaper Universal rotary nickel titanium system (Dentsply Maillefer, Ballaigues, Switzerland), irrigation with 1% sodium hypochlorite (NaOCl) by using a 26-gauge needle followed after each instrument. The apical root was scanned with 360° of rotation by Swept-Source Optical Coherence Tomography (SS-OCT) (wavelength: 1 310 nm, scan rate: 20 kHz, axial resolution: 16 μm) with driving device (stepper motor and lifting platform). The reconstruction images of axial planes 1, 2 and 3 mm from the apex were examined and the root cracks were blindly diagnosed by two observers. The horizontal section was performed at 1, 2 and 3 mm from the apex using low speed disc saw (Leica SP1600, Wetzlar, Germany). The presence of cracks was noted under an optical stereomicroscope (ZOOM-630E) with a cold light source using as gold standard to evaluate the accuracy of OCT in detecting root cracks after root canal instrumentation. RESULTS: After canals instrumentation with ProTaper Universal rotary nickel titanium system to #30/0.09, root cracks were detected in 9 of 20 teeth by histological examination. Crack lines were observed on 13 of 60 horizontal sections and cracks on 12 of the 13 sections were detected by OCT. No cracks were observed in the other 47 of the 60 horizontal sections,none of which was misdiagnosed by OCT. The overall accuracy rate for detection of root cracks with OCT was 0.983, the sensitivity was 0.923, the specificity was 1.000, the positive predictive value (PPV) was 1.000 and the negative predictive value (NPV) was 0.979. CONCLUSION OCT may be a promising nondestructive imaging method for diagnosing root canal cracks after canal instrumentation.
Bicuspid ; Dental Alloys ; Dental Pulp Cavity ; Dentin ; Humans ; Incisor ; Nickel ; Root Canal Preparation ; Root Canal Therapy ; Titanium ; Tomography, Optical Coherence ; Tooth Apex ; Tooth Root

OBJECTIVE: To compare the surface microstructures and cyclic fatigue resistance of HyFlex EDM with HyFlex CM and HyFlex NT. METHODS: Twelve 25 mm-long 25#/- HyFlex EDM and twelve 25 mm-long 25#/0.06 taper HyFlex CM or HyFlex NT were selected. The surface microstructure of the 2 instruments which were randomly selected from each group was observed by using scanning electron microscope (SEM). The remaining 10 instruments from each group were submitted to the cyclic fatigue test by using a simulated stainless steel root canal with 60° angle of curvature and curvature radius of 3.5 mm. The time till fracture was recorded, the number of cyclic fatigue (NCF) was calculated, the length of fracture fragment was evaluated, and the topographic features were analyzed by using SEM. The data were analyzed by using one-way analysis via SPSS 23.0 software. The statistical significance level was set at 0.05. RESULTS: SEM observation of the surface and microstructural characterization revealed peculiar melting appearance and evenly distributed micropores on the surface of HyFlex EDM while observations of the surface of both HyFlex CM and HyFlex NT demonstrated machining grooves and irregularities. The NCF of HyFlex EDM was 838±223, which was significantly higher than not only that of HyFlex CM (582±99), but also that of HyFlex NT (81±20) (P<0.05), and the difference between the latter two groups was significant, as well (P<0.05). The length of fractured fragments of HyFlex EDM was (7.27±0.28) mm, which was significantly longer than the HyFlex CM and HyFlex NT, with values of (6.72±0.26) mm and (6.62±0.37) mm, respectively (P<0.05). Topographic features demonstrated typical cyclic fatigue for all the three groups while the region of crack origins was more for HyFlex EDM and HyFlex CM than that of HyFlex NT. As far as the dimple area was concerned, that of HyFlex EDM was deeper and larger than that of HyFlex CM and HyFlex NT. CONCLUSION Within the limitations of this study, electro-discharge machining leads to peculiar melting appearance with micropores instead of machining grooves and irregularities on the surface of HyFlex EDM, which may be the reason why HyFlex EDM exhibits significantly better cyclicfatigue resistance than HyFlex CM and HyFlex NT.
Dental Alloys ; Dental Instruments ; Equipment Failure ; Humans ; Materials Testing ; Nickel ; Root Canal Preparation ; Titanium

OBJECTIVE: To compare the effects of autoclave on surface microstructure and cyclic fatigue resistance of K3XF and K3. METHODS: Forty-eight size 25, 0.06 taper 25 mm-long K3XF or K3 were randomly divided into 4 groups (n=12). The instruments from group 1 were not autoclaved, and the groups 2 to 4 underwent autoclave for 10 cycles, 20 cycles, and 30 cycles, respectively. The surface microstructure of two instruments randomly selected from each group was observed using scanning electron microscope (SEM). The remaining 10 instruments were submitted to the cyclic fatigue test by using a simulated metal root canal with curvature of 60° and radius 3.5 mm. The time till fracture was recorded, the number of cyclic fatigue (NCF) calculated, the fragment length evaluated, and the topographic features were analyzed using SEM. The data were analyzed using the two-way ANOVA analysis by SAS 9.3 software at a significance level of P<0.05. RESULTS: SEM observation identified rough features on the surface of K3XF with micropores existing evenly. K3 was characterized by machining grooves, which located specifically in the flute, leaving a smooth cutting edge. After autoclave, SEM observation indicated that the micropores in the surface of K3XF became larger and more, whereas the machining grooves in the surface of K3 were squeezed, out of shape and flaking. As far as the NCF was concerned, new K3XF was 210±59, and no significant difference was found after 10, 20, and 30 cycles of autoclave for K3XF, values being 178±37, 208±48, and 227±43, respectively (P>0.05). For K3, the new one was 145±38, and no significant difference in NCF was demonstrated after 10 and 20 cycles of autoclave, with the values of 128±43 and 124±46, respectively (P>0.05). However, after 30 cycles of autoclave of K3, significant increase to 216±38 was identified (P<0.05). Topographic features demonstrated typical cyclic fatigue for all the groups. CONCLUSION The surface roughness of K3XF was increased after autoclave, while the cyclic resistance remained stable after up to 30 cycles.
Dental Alloys ; Dental Instruments ; Disinfection ; Equipment Failure ; Hot Temperature ; Materials Testing ; Nickel ; Root Canal Preparation/instrumentation* ; Titanium