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Finite element analysis of zygomatic implants in intrasinus and extramaxillary approaches for prosthetic rehabilitation in severely atrophic maxillae

Ishak MI, Kadir MR, Sulaiman E, Kasim NH

Int J Oral Maxillofac Implants, 2013 May-Jun;28(3):e151-60.
PMID: 23748334 DOI: 10.11607/jomi.2304

To compare the extramaxillary approach with the widely used intrasinus approach via finite element method.
Finite element analysis of different surgical approaches in various occlusal loading locations for zygomatic implant placement for the treatment of atrophic maxillae

Ishak MI, Abdul Kadir MR, Sulaiman E, Abu Kasim NH

Int J Oral Maxillofac Surg, 2012 Sep;41(9):1077-89.
PMID: 22575179 DOI: 10.1016/j.ijom.2012.04.010

The aim of this study was to compare two different types of surgical approaches, intrasinus and extramaxillary, for the placement of zygomatic implants to treat atrophic maxillae. A computational finite element simulation was used to analyze the strength of implant anchorage for both approaches in various occlusal loading locations. Three-dimensional models of the craniofacial structures surrounding a region of interest, soft tissue and framework were developed using computed tomography image datasets. The implants were modelled using computer-aided design software. The bone was assumed to be linear isotropic with a stiffness of 13.4 GPa, and the implants were assumed to be made of titanium with a stiffness of 110 GPa. Masseter forces of 300 N were applied at the zygomatic arch, and occlusal loads of 150 N were applied vertically onto the framework surface at different locations. The intrasinus approach demonstrated more satisfactory results and could be a viable treatment option. The extramaxillary approach could also be recommended as a reasonable treatment option, provided some improvements are made to address the cantilever effects seen with that approach.
Friction at nanopillared polymer surfaces beyond Amontons' laws: Stick-slip amplitude coefficient (SSAC) and multiparametric nanotribological properties

Ishak MI, Dobryden I, Martin Claesson P, Briscoe WH, Su B

J Colloid Interface Sci, 2021 Feb 01;583:414-424.
PMID: 33011410 DOI: 10.1016/j.jcis.2020.09.038

Frictional and nanomechanical properties of nanostructured polymer surfaces are important to their technological and biomedical applications. In this work, poly(ethylene terephthalate) (PET) surfaces with a periodic distribution of well-defined nanopillars were fabricated through an anodization/embossing process. The apparent surface energy of the nanopillared surfaces was evaluated using the Fowkes acid-base approach, and the surface morphology was characterized using scanning electron microscope (SEM) and atomic force microscope (AFM). The normal and lateral forces between a silica microparticle and these surfaces were quantified using colloidal probe atomic force microscopy (CP-AFM). The friction-load relationship followed Amonton's first law, and the friction coefficient appeared to scale linearly with the nanopillar height. Furthermore, all the nanopillared surfaces showed pronounced frictional instabilities compared to the smooth sliding friction loop on the flat control. Performing the stick-slip amplitude coefficient (SSAC) analysis, we found a correlation between the frictional instabilities and the nanopillars density, pull-off force and work of adhesion. We have summarised the dependence of the nanotribological properties on such nanopillared surfaces on five relevant parameters, i.e. pull-off force fp, Amontons' friction coefficient μ, RMS roughness Rq, stick-slip amplitude friction coefficient SSAC, and work of adhesion between the substrate and water Wadh in a radar chart. Whilst demonstrating the complexity of the frictional behaviour of nanopillared polymer surfaces, our results show that analyses of multiparametric nanotribological properties of nanostructured surfaces should go beyond classic Amontons' laws, with the SSAC more representative of the frictional properties compared to the friction coefficient.
Insights into complex nanopillar-bacteria interactions: Roles of nanotopography and bacterial surface proteins

Ishak MI, Jenkins J, Kulkarni S, Keller TF, Briscoe WH, Nobbs AH, et al.

J Colloid Interface Sci, 2021 Dec 15;604:91-103.
PMID: 34265695 DOI: 10.1016/j.jcis.2021.06.173

Nanopillared surfaces have emerged as a promising strategy to combat bacterial infections on medical devices. However, the mechanisms that underpin nanopillar-induced rupture of the bacterial cell membrane remain speculative. In this study, we have tested three medically relevant poly(ethylene terephthalate) (PET) nanopillared-surfaces with well-defined nanotopographies against both Gram-negative and Gram-positive bacteria. Focused ion beam scanning electron microscopy (FIB-SEM) and contact mechanics analysis were utilised to understand the nanobiophysical response of the bacterial cell envelope to a single nanopillar. Given their importance to bacterial adhesion, the contribution of bacterial surface proteins to nanotopography-mediated cell envelope damage was also investigated. We found that, whilst cell envelope deformation was affected by the nanopillar tip diameter, the nanopillar density affected bacterial metabolic activities. Moreover, three different types of bacterial cell envelope deformation were observed upon contact of bacteria with the nanopillared surfaces. These were attributed to bacterial responses to cell wall stresses resulting from the high intrinsic pressure caused by the engagement of nanopillars by bacterial surface proteins. Such influences of bacterial surface proteins on the antibacterial action of nanopillars have not been previously reported. Our findings will be valuable to the improved design and fabrication of effective antibacterial surfaces.
Giant Cell Tumor of the Ribs and Aneurysmal Bone Cyst Presenting With Hemothorax in a Child

Alias H, Doris Lau SC, Loh CK, Ishak MI, Mohammed F, Jamal R, et al.

J Pediatr Hematol Oncol, 2017 11;39(8):e463-e465.
PMID: 28859035 DOI: 10.1097/MPH.0000000000000960

Giant cell tumor (GCT) is one of the most common tumors of bone and is the most common precursor of aneurysmal bone cysts (ABC). The clinical behavior of concurrent GCT and ABC can be very aggressive in children. GCT of the ribs, with or without ABC, is rarely seen in children. We report a case of an 8-year-old girl with GCT and associated ABC of the ribs who presented with sudden onset of chest pain and breathlessness due to a hemothorax. The patient was successfully treated by surgical resections and arterial embolization. She has remained well for 4 years after the initial surgery.
Assessment of stress shielding around a dental implant for variation of implant stiffness and parafunctional loading using finite element analysis

Ishak MI, Daud R, Noor SNFM, Khor CY, Roslan H

Acta Bioeng Biomech, 2022;24(3):147-159.
PMID: 38314490

PURPOSE: The aim of this study was to evaluate the mechanical stimuli transfer at the bone-implant interface via stress and strain energy density transfer parameters. This study also aimed to investigate the effect of different implant stiffness and parafunctional loading values on the defined mechanical stimuli transfer from the implant to the surrounding bone.
METHODS: A three-dimensional finite element model of two-piece threaded dental implant with internal hexagonal connection and mandibular bone block was constructed. Response surface method through face-centred central composite design was applied to examine the influence of two independent factors variables using three levels. The analysis model was fitted to a second-order polynomial equation to determine the response values.
RESULTS: The results showed that the implant stiffness was more effective than the horizontal load value in increasing the stress and strain energy density transfers. The interaction between both factors was significant in decreasing the likelihood of bone resorption. Decreasing the implant stiffness and horizontal load value led to the increased stress transfer and unexpected decrease in the strain energy density, except at the minimum level of the horizontal load. The increase in the implant stiffness and horizontal load value (up to medium level) have increased the strain energy transfer to the bone.
CONCLUSIONS: The stress and strain energy density were transferred distinctively at the bone-implant interface. The role of both implant stiffness and parafunctional loading is important and should be highlighted in the preoperative treatment planning and design of dental implant.
Resolving physical interactions between bacteria and nanotopographies with focused ion beam scanning electron microscopy

Jenkins J, Ishak MI, Eales M, Gholinia A, Kulkarni S, Keller TF, et al.

iScience, 2021 Jul 23;24(7):102818.
PMID: 34355148 DOI: 10.1016/j.isci.2021.102818

To robustly assess the antibacterial mechanisms of nanotopographies, it is critical to analyze the bacteria-nanotopography adhesion interface. Here, we utilize focused ion beam milling combined with scanning electron microscopy to generate three-dimensional reconstructions of Staphylococcus aureus or Escherichia coli interacting with nanotopographies. For the first time, 3D morphometric analysis has been exploited to quantify the intrinsic contact area between each nanostructure and the bacterial envelope, providing an objective framework from which to derive the possible antibacterial mechanisms of synthetic nanotopographies. Surfaces with nanostructure densities between 36 and 58 per μm2 and tip diameters between 27 and 50 nm mediated envelope deformation and penetration, while surfaces with higher nanostructure densities (137 per μm2) induced envelope penetration and mechanical rupture, leading to marked reductions in cell volume due to cytosolic leakage. On nanotopographies with densities of 8 per μm2 and tip diameters greater than 100 nm, bacteria predominantly adhered between nanostructures, resulting in cell impedance.