Numerical investigation of the optimal porosity of titanium foam for dental implants.

Background: This paper aims to indicate numerically the accurate porosity used for dental implants, following the emphasis on the preference for titanium foam on pure titanium implants. A 3D-optimized numerical model is created to demonstrate the detailed differences between models. Method: A 3D finite element model was generated using Abaqus for titanium and titanium foam implants with different porosities (50,60,62.5,70, and 80%) fixed in cortical and cancellous bone. The mechanical data for titanium foam is extracted from published literature. We evaluate an artificial intelligent equation for the stress-strain response of titanium foam with various porosities to describe their variations. Results: To evaluate the stress-strain variations for different porosities, exponential artificial intelligence provides high accuracy (>0.99). The numerical results show that titanium foam implants appear to transfer more loads to the bordering bones due to their lower stiffness and higher energy absorption, which can help reduce stress shielding problems. In surrounding bones, the maximum VM stress occurs at the neck region from 5.42 MPa for pure titanium to 21.53 MPa for titanium foam with 80% porosity. Additionally, a porosity of 62.5% appears to be the most suitable since Young's modulus for this porosity (13.82 GPa) is close to the cortical bone's modulus (14.5 GPa). This suitability is shown in FEA by the similarity in stress level between pure titanium and the corresponding porosity. Overall, titanium foam implants appear to be a promising option for improving the effectiveness and longevity of bone implants in surgical dentistry. Conclusion: Systematic numerical studies on titanium foam dental implants with different porosities. Analysis of the FE results shows that titanium foam with a porosity of 62.5% is more beneficial for use in dental implants.

Effect of power arm length combined with additional anterior torque on the axial orientation of the maxillary incisors during en-masse retraction: A finite element analysis.

INTRODUCTION: This study aimed to clarify the effect of power arm length combined with additional torque incorporated into the archwire on the controlled movement of the anterior teeth using the finite element method. METHODS: An adult patient requiring medium anchorage after extraction of the maxillary first premolars was selected for this study. The power arms were placed between the lateral incisor and the canine at 3 levels: 3 mm, 6 mm, and 9 mm. A 150 g of retraction force was applied from each height of the anterior hook to the first molar tube, with 0°, 5°, and 10° of applied lingual root torque on the incisors. RESULTS: A 3-mm hook with 10° of applied torque, a 6-mm hook with 5° of applied torque, or a 9-mm hook with no extra torque constituted the best combinations targeted at controlling the inclination of incisors during retraction. Extrusion and distal tipping of the canine were observed. Moreover, mesial tipping and mesiopalatal rotation of the molar were unavoidable. Finally, intercanine and intermolar widths were decreased. CONCLUSIONS: Adding extra torque on the incisors or using high torque brackets is recommended for patients with maxillary first premolar extraction.

Three-dimensional comparison of continuous and segmented arch techniques in the traction of palatally impacted canines using a non-linear finite element analysis.

OBJECTIVE: To compare the three-dimensional (3D) effects of canine traction on the maxillary teeth when using two different traction methods, the continuous and the segmented arch wire techniques; then to test whether adding a transpalatal arch (TPA) would affect their response to traction. DESIGN: Finite element analysis. METHODS: A cone-beam computed tomography (CBCT) scan of a patient with bilateral palatally impacted canines was chosen, from which a 3D model was derived and imported into ABAQUS. Two arch wires were modelled, a continuous round one and a segmented rectangular one. Four models were obtained by adding a TPA to both techniques. A 100° imposed rotation was then applied at the intersection between the vertical loop and the horizontal segment of each wire. Initial displacement of the maxillary tooth in the labio-lingual and in the vertical directions was measured. The absolute maximum principal stress of the periodontal ligament (PDL) was also assessed. RESULTS: Traction using a continuous arch wire led to different movement patterns of all teeth, some of them were tipped in a labial direction while others were lingually tipped. Traction using a segmented arch wire resulted in a retroclination of the posterior teeth and a proclination of the anterior teeth with a high level of stress on the premolars' PDL. Adding the TPA only affected the displacement of the first molars. The right side showed a maximum displacement of the first premolar, while the left side showed it on the lateral. The total displacement on the right side was higher than the left side. CONCLUSION: The segmented technique caused a uniform displacement of all teeth while the continuous one showed a non-uniform displacement. The angulation and position of the vertical loop affected the displacement of the maxillary teeth. The addition of a TPA acted only on the first molars.

Three-dimensional comparison of the effects of sliding mechanics in labial and lingual orthodontics using the finite element method.

INTRODUCTION: The extraction of maxillary first premolars is usually the treatment of choice to resolve crowding, alveolar protrusion, or Class II malocclusion. The demand for a lingual orthodontic treatment is increasing because of its esthetic value; therefore, understanding lingual biomechanics is essential to every clinician. This study compared the 3-dimensional (3D) effects of sliding mechanics in labial and lingual orthodontics using the finite element method. METHODS: Twelve 3D finite element models were created with different power arm heights and miniscrew positions. A 150 g of retraction force was applied from the head of the miniscrew to the power arm. The 3D displacement of the original nodes was measured, and the stress distribution on defined element zones of the periodontal ligament. RESULTS: Different force directions led to different movement patterns and stress distribution. The lingual models showed a more important lingual crown tipping, extrusion, and higher stress values than the labial models. Results were not affected by the vertical position of the miniscrew. CONCLUSIONS: Bodily en-masse retraction was not achieved in all models. Adding extra torque to the archwires is essential to prevent excessive lingual crown tipping. The lingual appliance induced more lingual tipping and extrusion of the anterior teeth. Expanding the archwire is important to minimize the risk of intercanine width reduction. The vertical position of the miniscrew does not affect the results of en-masse retraction.

Pentacyclic triterpenes modulate liposome membrane fluidity and permeability depending on membrane cholesterol content.

Since the membrane-related processes represent an integral part of the biological activities of drugs, their effect on the membrane dynamics is actually considered. In this study, we investigated the effect of pentacyclic triterpenes (TTPs), oleanolic acid (OA) and erythrodiol (ER), on the fluidity and permeability of liposomes membranes differing by their cholesterol content. All liposomes were prepared by reverse phase evaporation technique (REV). Spin-labeled liposomes exposed or not to TTPs were used for fluidity studies by using 5- and 16-doxyl stearic acids (DSA). TTPs-loaded liposomes (phospholipid:cholesterol of 1:1), and preformed vesicles exposed to TTPs were used for permeability studies by monitoring the release of sulforhodamine B (SRB) at 37 °C. The apparent release constants of SRB were determined by Higuchi model based on a biphasic curve shape (0-10 h; 10-48 h). TTPs-loaded liposomes were characterized for their size and homogeneity. Results showed that ER increased the membrane fluidity at the upper region of the membrane while the both TTPs produced a condensing effect at the deeper region of the membrane. The membrane composition was a critical parameter modulating the effect of TTPs on the membrane permeability. Also, this study consolidated the fact that a fluidizing membrane agent is not necessarily a permeabilizing-membrane compound.

Corticoids modulate liposome membrane fluidity and permeability depending on membrane composition and experimental protocol design.

Given that literature data may give inconsistent results on the effect of a drug on lipid membrane properties, this work aims to investigate the impact of the liposome composition and experimental protocol design on glucocorticoids (GRs: cortisol, cortisone, fludrocortisone acetate, methylprednisolone, prednisolone and prednisone)-modulating membrane fluidity and permeability. GRs-loaded liposomes consisting of dipalmitoylphosphatidylcholine (DPPC) and cholesterol (CHOL) were prepared by reverse phase evaporation technique (REV) at DPPC:CHOL:GR molar ratios of 100:100:2.5, and 100:100:10. The formulations were characterized for their size and homogeneity, encapsulation efficiency and loading rates of GRs, incorporation rates and loading rates of DPPC and CHOL. Changes in DPPC membrane fluidity (CHOL% 0, 10, 20, 30 and 100) after exposure to methylprednisolone were monitored by using 5- and 16-doxyl stearic acids (DSA) as spin probes. For permeability studies, the above-mentioned GRs-loaded liposomes and the preformed liposomes exposed to GRs (2.5 mol%) were compared for the leakage of an encapsulated fluorescent dye, sulforhodamine B (SRB), at 37 °C in buffer (pH 7.5) containing NaCl. The SRB release kinetics were analyzed by the Higuchi model for two release phases (from 0 to 10 h, and from 10 to 48 h). All formulations exhibited a monodispersed size distribution of liposomes with a mean particle value close to 0.4 µm, also the DPPC and CHOL were highly incorporated (>95%). High loading rate values of DPPC and CHOL were also obtained. Except for fludrocortisone acetate (51%) and prednisolone (77%), high loading rate values of GRs were obtained (>81%). Fluidity and permeability studies showed that the GR concentration, CHOL content, experimental protocol design including the period of incubation represent critical parameters to be considered in analyzing the effect of drugs on the membrane properties.

Cholesterol modulates the liposome membrane fluidity and permeability for a hydrophilic molecule.

The effect of cholesterol (CHOL) content on the permeability and fluidity of dipalmitoylphosphatidylcholine (DPPC) liposome membrane was investigated. Liposomes encapsulating sulforhodamine B (SRB), a fluorescent dye, were prepared by reverse phase evaporation technique (REV) at various DPPC:CHOL molar ratios (from 100:0 to 100:100). The release kinetics of SRB was studied during 48 h in buffer (pH 7.4) containing NaCl at 37 °C. The DPPC:CHOL formulations were also characterized for their size, polydispersity index and morphology. Increasing CHOL concentration induced an increase in the mean liposomes size accompanying with a shape transition from irregular to nanosized, regular and spherical vesicles. The release kinetics of SRB showed a biphasic pattern; the release data was then analyzed using different mathematical models. On the overall, the SRB release was governed by a non-Fickian diffusion during the first period (0-10 h) while it followed a Fickian diffusion between 10 and 48 h. Changes in DPPC liposome membrane fluidity of various batches (CHOL% 0, 10, 20, 30 and 100) were monitored by using 5- and 16 doxyl stearic acids (DSA) as spin labels. CHOL induced a decrease in the bilayer fluidity. Concisely, CHOL represents a critical component in modulating the release of hydrophilic molecules from lipid vesicles.