Optimization of surface roughness, phase transformation and shear bond strength in sandblasting process of YTZP using statistical machine learning.

Sandblasting process is often applied to roughen the intaglio of yttria tetragonal zirconia polycrystals (YTZP) surfaces for easy and quality adhesion and micro-shear retention with dentine/resin cements. Sandblasting process parameters have shown to influence, at different scales, surface roughness, phase transformation and shear bond strength, all of which are referred, herein, as performance characteristics. This study aimed to find the parametric settings of sandblasting parameters that could simultaneously optimize these performance characteristics, hypothetically testing the probability. YTZP surfaces were sandblasted at different levels of incidence angle (IA), abrasive particle size (AP), pressure(P) and sandblasting time (ST) following the Taguchi method based on the two-level parametric process settings (L8(27)). Surface morphologies, roughness (SR), monoclinic content (MC), and shear bond strength (SS) were characterized by the SEM, average surface roughness, XRD, and shear bond strength tests, respectively. Rough surfaces containing scratches, plastic deformation streaks, micro cracks and pitting were observed. According to the Taguchi method, the same optimum sandblasting parametric setting maximized SR and MC but failed to maximize SS. Subsequently, the principal component analysis embedded in statistical machine learning was applied to find the optimum sandblasting parametric setting that maximized all the performance characteristics. The optimum sandblasting setting of IA = 45°, AP = 110 µm, ST = 20 s and P = 400 kPa predicted the maximum values of SR = 0.773 µm, MC = 36% and SS = 16.6 MPa. Analysis of variance confirmed AP and P as the most influencing parameters affecting all performance characteristics. Finally, these results provide a systematic and comprehensive route for optimizing sandblasting roughening of YTZP surfaces which can be adopted in adhesive dental and orthodontic industry.

Association of Dopamine Transporter Gene (DAT1) 40 bp 3' UTR VNTR Polymorphism (rs28363170) and Cannabis Use Disorder.

Introduction: Cannabis remains the most widely used illicit drug among Nigerians, often associated with psychiatric disorders. Since genetic predisposition has been implicated in substance use disorders, we, therefore, aimed at finding out the relationship between dopamine transporter gene (DAT1) polymorphism and cannabis use disorder. Methods: We recruited 104 patients from a tertiary psychiatric facility in Lagos, Nigeria, who were diagnosed with cannabis use disorder according to ICD-10 and 96 non-smokers as a comparative group. The smokers were screened with Cannabis Use Disorder Identification Test (CUDIT), and cannabis dependence was assessed with the Severity of Dependence Scale (SDS). Genotyping was carried out for the 40 bp 3' UTR VNTR of the DAT1 (rs28363170). Results: The frequencies of 9R/9R, 9R/10R, 10R/10R among non-smokers and smokers were 14 (14.3%), 25 (26.2%), 57 (59.5%) and 17 (16.3%), 54 (51.9%), 33 (31.7%) respectively. The genotype distribution was in Hardy Weinberg equilibrium (HWE) only in the smokers' population (χ² = 1.896, P = .166). Individuals with the 10R allele were almost twice as likely as the 9R carriers to smoke cannabis (OR = 1.915, 95% CI: 1.225-2.995). However, this polymorphism was not associated with the quantity of cannabis smoked, age at onset of smoking, CUDIT, and SDS scores. Conclusion: The DAT VNTR polymorphism was associated with cannabis smoking but not cannabis use disorder.

Investigation of indentation size effect and R-curve behaviour of Li2O-SiO2 and Li2O-2SiO2 glass ceramics.

Indentation size effect (ISE) and R-curve behaviour of Li2O-SiO2 and Li2O-2SiO2 glass ceramics are investigated using micro-indentation and indentation-strength (IS) techniques, respectively. Vickers micro-indentations were applied on both materials at the load of 0.10-19.6 N to determine the load influence on the measured hardness. For the IS-measured fracture toughness, the load ranged from 1.96 to 19.6 N. The hardness decreased with increasing load by 20% and 18% on Li2O-SiO2 and Li2O-2SiO2 glass ceramics, respectively, indicating the ISE behaviour on both materials. The fracture toughness increased with the load by 27% and 59% on Li2O-SiO2 and Li2O-2SiO2 glass ceramics, respectively, signifying the R-curve behaviour. The ISE behaviour of both materials was analysed using the Meyer's, Hays-Kendall (HK), proportional specimen resistance (PSR), Nix-Gao (NG), modified PSR (MPSR) and elastic plastic deformation (EPD) models while the R-curve behaviour was analysed by the fractional power law. The Meyer's index of both materials was less than 2, strongly confirming the ISE existence. The HK, PSR and NG models were only suitable to determine intrinsic Vickers hardness for Li2O-2SiO2 glass ceramic while the MPSR and EPD models were successful for both materials. The fractional power law gave higher R-curve steepness for Li2O-2SiO2 than Li2O-SiO2 glass ceramics. Also, material and brittleness indices predicted, respectively, higher quasi-plasticity and better machinability for Li2O-2SiO2 than Li2O-SiO2 glass ceramics indicating superior performance in the former to the latter. Finally, this study presents a new significant insight into the micro-mechanisms of fracture tolerance behaviour of these glass ceramics which is critical to their functional performance as structural ceramics.

Influence of CAD/CAM milling, sintering and surface treatments on the fatigue behavior of lithium disilicate glass ceramic.

This paper reports on the process-fatigue relation of lithium disilicate glass ceramic (LDGC) using low-cycle, high-load Hertzian indentations with a rigid indenter to simulate teeth grinding/clenching of LDGC restorations with different surface asperities obtained in CAD/CAM milling, sintering, polishing and glazing. The maximum contact stresses were evaluated as functions of the number of load cycles and surface treatments using the Hertzian model. Indentation-induced surface damage was viewed using scanning electron microscopy (SEM) to understand the relationships among microstructures, surface asperities, crack morphology and propagation. Different processes and surface treatments significantly affected the maximum contact stresses of indented LDGC surfaces (ANOVA, p < 0.05), which were all significantly reduced with the number of cycles (ANOVA, p < 0.05). Quasi-plastic deformation was dominant in single-cycle indentation of all processed and treated surfaces. In higher cycle indentations, inner cone cracks were formed on all surfaces; median and transverse cracks were formed on the roughest surfaces processed by CAD/CAM milling and sintering. Ring cracks, fretting, pulverization, micro-bridges, surface smearing and wedging, and edge chippings were also propagated on all surfaces. The process-fatigue relation provides an understanding of the mechanical functions of surface asperities produced in different processes and treatments. It indicates that the mechanically assisted growth of surface asperities with different roughness strongly affected the indentation-induced surface damage. Finally, the smoothest surfaces produced by CAD/CAM milling, polishing and sintering sustained the highest contact stresses and the least fatigue damage at higher cycles, ensuring their superior fatigue performance compared to other processed LDGC surfaces.

Elasticity, plasticity and analytical machinability prediction of lithium metasilicate/disilicate glass ceramics.

This paper applied non-linear theory of elasticity (NLTE) to partition indentation-induced deformations into elasticity and plasticity for lithium metasilicate glass ceramic (LMGC), sintered and pressed lithium disilicate glass ceramics (SLDGC and PLDGC). It also used elastic plastic fracture mechanics (EPFM) approach to analytically predict machinability for these materials. Using the Sakai's series elastic and plastic deformation model that applied NLTE, the resistances to plasticity for LMGC, SLDGC and PLDGC were extracted from their respective indentation-extracted plane strain moduli and contact hardness values. Plane strain moduli and resistances to plasticity were used to calculate elasticity and plasticity for these materials. Furthermore, the EPFM approach in the Sakai-Nowak model was applied to deconvolute resistances to machining-induced cracking for these materials. All properties were extracted at 10 mN peak load and 0.1-2 mN/s loading rates to determine the loading-rate influence on these properties. The resistances to plasticity of LMGC and SLDGC were loading rate dependent (ANOVA, p < 0.05) and the resistance to plasticity of PLDGC was loading rate independent (ANOVA, p > 0.05). The strain rate sensitivity model was used to find the intrinsic resistances to plasticity for LMGC and SLDGC. The elastic displacement/deformation components were dominant for LMGC at all loading rates. For SLDGC and PLDGC, the deformation mechanisms were dynamic with the plastic and elastic deformation components dominating at low loading and high loading rates respectively, a phenomenon attributed to indentation energies. The decrease in plastic displacements for all materials with increase in loading rate was due to the strain hardening behaviour. Also, PLDGC revealed the highest absorbed energy followed by SLDGC and LMGC. Finally, PLDGC had the highest resistance to machining-induced cracking followed by SLDGC and LMGC. This study provides a quantitative basis to rank materials in terms of brittleness, ductility and resistance to mechanically-induced cracking.

A review of engineered zirconia surfaces in biomedical applications.

Zirconia is widely used for load-bearing functional structures in medicine and dentistry. The quality of engineered zirconia surfaces determines not only the fracture and fatigue behaviour but also the low temperature degradation (ageing sensitivity), bacterial colonization and bonding strength of zirconia devices. This paper reviews the current manufacturing techniques for fabrication of zirconia surfaces in biomedical applications, particularly, in tooth and joint replacements, and influences of the zirconia surface quality on their functional behaviours. It discusses emerging manufacturing techniques and challenges for fabrication of zirconia surfaces in biomedical applications.

Fracture, roughness and phase transformation in CAD/CAM milling and subsequent surface treatments of lithium metasilicate/disilicate glass-ceramics.

This paper studied surface fracture, roughness and morphology, phase transformations, and material removal mechanisms of lithium metasilicate/disilicate glass ceramics (LMGC/LDGC) in CAD/CAM-milling and subsequent surface treatments. LMGC (IPS e.max CAD) blocks were milled using a chairside dental CAD/CAM milling unit and then treated in sintering, polishing and glazing processes. X-ray diffraction was performed on all processed surfaces. Scanning electron microscopy (SEM) was applied to analyse surface fracture and morphology. Surface roughness was quantitatively characterized by the arithmetic average surface roughness Ra and the maximum roughness Rz using desktop SEM-assisted morphology analytical software. The CAD/CAM milling induced extensive brittle cracks and crystal pulverization on LMGC surfaces, which indicate that the dominant removal mechanism was the fracture mode. Polishing and sintering of the milled LMGC lowered the surface roughness (ANOVA, p < 0.05), respectively, while sintering also fully transformed the weak LMGC to the strong LDGC. However, polishing and glazing of LDGC did not significantly improve the roughness (ANOVA, p > 0.05). In comparison of all applied fabrication process routes, it is found that CAD/CAM milling followed by polishing and sintering produced the smoothest surface with Ra = 0.12 ± 0.08µm and Rz = 0.89 ± 0.26µm. Thus, it is proposed as the optimized process route for LMGC/LDGC in dental restorations. This route enables to manufacture LMGC/LDGC restorations with cost effectiveness, time efficiency, and improved surface quality for better occlusal functions and reduced bacterial plaque accumulation.

Surface quality of yttria-stabilized tetragonal zirconia polycrystal in CAD/CAM milling, sintering, polishing and sandblasting processes.

This paper studied the surface quality (damage, morphology, and phase transformation) of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) in CAD/CAM milling, and subsequent polishing, sintering and sandblasting processes applied in dental restorations. X-ray diffraction and scanning electron microscopy (SEM) were used to scan all processed surfaces to determine phase transformations and analyse surface damage morphology, respectively. The average surface roughness (Ra) and maximum roughness (Rz) for all processed surfaces were measured using desk-top SEM-assisted morphology analytical software. X-ray diffraction patterns prove the sintering-induced monoclinic-tetragonal phase transformation while the sandblasting-induced phase transformation was not detected. The CAD/CAM milling of pre-sintered Y-TZP produced very rough surfaces with extensive fractures and cracks. Simply polishing or sintering of milled pre-sintered surfaces did not significantly improve their surface roughness (ANOVA, p>0.05). Neither sintering-polishing of the milled surfaces could effectively improve the surface roughness (ANOVA, p>0.05). The best surface morphology was produced in the milling-polishing-sintering process, achieving Ra=0.21±0.03µm and Rz=1.73±0.04µm, which meets the threshold for bacterial retention. Sandblasting of intaglios with smaller abrasives was recommended as larger abrasive produced visible surface defects. This study provides technical insights into process selection for Y-TZP to achieve the improved restorative quality.

Development of fixed dose combination tablets of aripiprazole plus divalproex sodium and their simultaneous determination using HPLC-UV.

A vast majority of psychiatric patients are effectively treated with combination of drugs to improve efficacy and adherence, but due to limited research and development in fixed dose combination (FDC) in psychiatry, these products are not commonly available. The aim of this study is to prepare cost effective FDC tablets containing aripiprazole and divalproex sodium. Two batches of fixed dose combination tablets, FDC1 and FDC2, were successfully prepared using wet granulation technique. Furthermore, aripiprazole tablets A1 and A2 and divalproex tablets D1 were also formulated as reference to compare the in vitro availability profile. An accurate and simple isocratic HPLC method was established and validated for the simultaneous quantification of aripiprazole and valproic acid in the FDC tablets. A reversed-phase C18 (250 × 4.6 mm) column in isocratic mode was used. The mobile phase consisted of acetonitrile and 0.32% KH2PO4 (60:40, v/v), flow rate was set at 1.0 mL/min and the detection was performed at 210 nm. Average percent recoveries of aripiprazole and valproic acid were 96.0 and 95.5%, respectively, meeting the official requirements. The newly developed FDC product may be used for the better therapeutic outcomes of combined use of aripiprazole and valproic acid, which may improve patient adherence.

Nano-mechanical behaviour of lithium metasilicate glass-ceramic.

This paper reports the first study on the mechanical behavior of lithium metasilicate glass-ceramic using nanoindentation and in situ scanning probe imaging techniques. Indentation contact hardness, Hc, and Young's modulus, E, were measured at 10 mN peak load and 0.1-2 mN/s loading rates to understand the loading rate effect on its properties. Indentation imprints were analysed with the in situ scanning probe imaging to understand indentation mechanisms. The average contact hardness increased by 112% with the loading rate (ANOVA, p<0.05) while the Young's modulus showed the loading rate independence (ANOVA, p>0.05). A strain rate sensitivity model was applied to determine the intrinsic contact hardness. Extensive discontinuities and largest maximum, contact and final depths were also observed at the lowest loading rate. These phenomena corresponded to inhomogeneous shear-band flow and densification leading to the material strain softening. The in situ scanning probe images of indentation imprints showed plastic deformation at all loading rates and shear band-induced pileups at the lowest loading rate. With the increase in loading rate, the induced pile-ups decreased. The continuum model predicted the largest densified shear zone at the lowest loading rate. Finally, these results provide scientific insights into the abrasive machining responses of lithium metasilicate glass-ceramic during dental CAD/CAM processes using sharp diamond abrasives.

Comparative effectiveness of chewing stick and toothbrush: a randomized clinical trial.

BACKGROUND: With the increasing rate of oral diseases, the global necessity of effective and economical products for its prevention and treatment has intensified. AIM: THIS STUDY WAS TO COMPARE THE EFFECTIVENESS OF TWO ORAL HYGIENE AIDS: Chewing stick and manual toothbrush, for plaque removal and gingival health after one month of a randomized clinical trial. MATERIALS AND METHODS: Dental students (age 18-22 years) of a public sector dental hospital were recruited. Sample size was determined using the American Dental Association guidelines. Participants were randomized into two interventional groups and provided with either chewing sticks or toothbrushes. Pre- and post-intervention examinations were executed by two blind and calibrated examiners using plaque and gingival dental indices. Statistical analysis included descriptive statistics, paired t-test, and two sample independent t-tests. RESULTS: Fifty subjects were recruited with mean age 20 ± 0.66 years (80% were females and 20% were males). Except for the mean plaque scores of toothbrush users (which increased at post-intervention examination), all other scores showed reduction. In contrast to the final mean gingival scores, a significant difference (P = < 0.0001) in the final mean plaque score was observed for the two respective interventional groups. CONCLUSION: Chewing stick has revealed parallel and at times greater mechanical and chemical cleansing of oral tissues as compared to a toothbrush.

Nano-scale mechanical properties and behavior of pre-sintered zirconia.

This paper reports on the mechanical properties and material behavior of pre-sintered zirconia using nanoindentation with in situ scanning probe microscopy. Indentation contact hardness, Hc, and Young׳s modulus, E, were measured at loading rates of 0.1-2mN/s and 10mN peak load to understand the loading rate effect on its properties. Indentation imprints were analyzed using in situ scanning probe imaging to understand the indentation mechanisms. The average measured contact hardness was 0.92-1.28GPa, independent of the loading rate (ANOVA, p>0.05). Young׳s moduli showed a loading rate dependence, with average 61.25GPa and a great deviation at a low loading rate of 0.1mN/s, which was twice the average moduli at the loading rates of 0.5-2mN/s. Extensive discontinuities and the largest maximum penetration, final and contact depths were also observed on the load-displacement curves at the lowest loading rate. These phenomena corresponded to microstructural compaction (pore closure and opening) and kink band formation, indicating the loading rate dependence for microstructural changes during nanoindentation. The in situ scanning probe images of indentation imprints show plastic deformation without fracture at all loading rates, compaction at the low loading rate and pore filling at the high loading rate. The mechanical behavior studied provides physical insight into the abrasive machining responses of pre-sintered zirconia using sharp diamond abrasives.

Outcome of macular hole surgery.

OBJECTIVE: To document the outcome of macular hole surgery in terms of improvement of visual acuity and the duration of closure of macular hole. DESIGN: Interventional quasi experimental study. PLACE AND DURATION OF STUDY: Ophthalmology Department, Civil Hospital, Karachi. SUBJECTS AND METHODS: Twenty-four eyes of 22 patients with macular hole underwent surgical repair. Vitrectomy with maculorrhexis (internal limiting membrane peeling) and fluid-gas exchange followed by prone positioning for one to two weeks was carried out. Postoperative follow-up was done for one year. Main outcome measures were visual acuity, closure of macular hole and ocular complications. Data was analyzed by using SPSS Version 10. Non-parametric sign test with chi-square statistic was used to compare the pre-operative and postoperative outcome. RESULTS: The macular hole was successfully closed in 17 eyes that revealed high statistical significance regarding improvement in visual acuity. Earlier, significant improvement figured in 17/24 cases was observed at three-month post-operative examination (p<0.0001). An insignificant success figured in 8/24 due to postoperative complications at six-month follow-up. Visual acuity improved upto two or more lines in 17 eyes at one-year follow-up. Twelve cases developed cataract, 7 developed increased intra-ocular pressure (transient), one had glaucoma and one retinal detachment. CONCLUSION: Vitrectomy with maculorrhexis (internal limiting membrane peeling) and fluid-gas exchange can successfully close macular holes and improve vision.

Management of macular pucker.

OBJECTIVE: To document the outcome of macular pucker surgery in terms of improvement of visual acuity. DESIGN: Interventional quasi experimental study. SETTING: Ophthalmology Department, Civil Hospital, Karachi. PATIENTS AND METHODS: Twenty-two patients with macular pucker underwent surgical repair. Pars plana posterior vitrectomy with epiretinal membrane peeling and internal limiting membrane peeling (maculorrhexis) was carried out. Postoperative follow-up was done for one year. Main outcome measure were visual acuity, causes and ocular complications. Data was analyzed using SPSS Version-10. Non-parametric sign test with chi-square statistic was used to compare the pre-operative and postoperative outcome. RESULTS: The macular pucker was successfully removed in 18 patients that revealed high statistical significance regarding improvement in visual acuity. Earlier, significant improvement (18 / 22 cases) was observed at three-month postoperative examination (p < 0.0001). Insignificant (9/22) postoperative complications were noted at six-month post-operative follow-up. Metamorphopsia was relieved in 18 patients. Ten patients developed cataract, 4 patients developed increased intra-ocular pressure (transient) and two patients developed retinal detachment. CONCLUSION: Pars plana posterior vitrectomy with epiretinal membrane peeling and internal limiting membrane peeling (maculorrhexis) can successfully remove macular pucker, improve vision and relieve metamorphopsia.