Eshamsul Sulaiman

Effects of different implant–abutment connections on micromotion and stress distribution: Prediction of microgap formation

OBJECTIVES The aim of this study was to analyse micromotion and stress distribution at the connections of implants and four types of abutments: internal hexagonal, internal octagonal, internal conical and trilobe. METHODS A three dimensional (3D) model of the left posterior mandible was reconstructed from medical datasets. Four dental implant systems were designed and analysed independently in a virtual simulation of a first molar replacement. Material properties, contact properties, physiological loading and boundary conditions were assigned to the 3D model. Statistical analysis was performed using one-way analysis of variance (ANOVA) with a 95% confidence interval and Tukeys Honestly Significant Difference (HSD) multiple comparison test. RESULTS The internal hexagonal and octagonal abutments produced similar patterns of micromotion and stress distribution due to their regular polygonal design. The internal conical abutment produced the highest magnitude of micromotion, whereas the trilobe connection showed the lowest magnitude of micromotion due to its polygonal profile. CONCLUSIONS Non-cylindrical abutments provided a stable locking mechanism that reduced micromotion, and therefore reduced the occurrence of microgaps. However, stress tends to concentrate at the vertices of abutments, which could lead to microfractures and subsequent microgap formation.

Nanomechanical properties, wear resistance and in-vitro characterization of Ta2O5 nanotubes coating on biomedical grade Ti–6Al–4V

Tantalum pentoxide nanotubes (Ta2O5 NTs) can dramatically raise the biological functions of different kinds of cells, thus have promising applications in biomedical fields. In this study, Ta2O5 NTs were prepared on biomedical grade Ti-6Al-4V alloy (Ti64) via physical vapor deposition (PVD) and a successive two-step anodization in H2SO4: HF (99:1)+5% EG electrolyte at a constant potential of 15V. To improve the adhesion of nanotubular array coating on Ti64, heat treatment was carried out at 450°C for 1h under atmospheric pressure with a heating/cooling rate of 1°Cmin-1. The surface topography and composition of the nanostructured coatings were examined by atomic force microscopy (AFM) and X-ray electron spectroscopy (XPS), to gather information about the corrosion behavior, wear resistance and bioactivity in simulated body fluids (SBF). From the nanoindentation experiments, the Youngs modulus and hardness of the 5min anodized sample were ~ 135 and 6GPa, but increased to ~ 160 and 7.5GPa, respectively, after annealing at 450°C. It was shown that the corrosion resistance of Ti64 plates with nanotubular surface modification was higher than that of the bare substrate, where the 450°C annealed specimen revealed the highest corrosion protection efficiency (99%). Results from the SBF tests showed that a bone-like apatite layer was formed on nanotubular array coating, as early as the first day of immersion in simulated body fluid (SBF), indicating the importance of nanotubular configuration on the in-vitro bioactivity.

Finite element analysis of different surgical approaches in various occlusal loading locations for zygomatic implant placement for the treatment of atrophic maxillae.

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.

Finite Element Analysis of Zygomatic Implants in Intrasinus and Extramaxillary Approaches for Prosthetic Rehabilitation in Severely Atrophic Maxillae

PURPOSE To compare the extramaxillary approach with the widely used intrasinus approach via finite element method. MATERIALS AND METHODS A unilateral three-dimensional model of the craniofacial area surrounding the region of interest was developed using computed tomography image datasets. The zygomatic implants were modeled using three-dimensional computer-aided design software and virtually placed according to the described techniques together with one conventional implant and a prosthesis. The bone was assumed to be linear isotropic with a stiffness of 13.4 GPa, while the implants were of titanium alloy with a stiffness of 110 GPa. Masseter forces were applied at the zygomatic arch, and occlusal loads were applied to the surface of the prosthesis. The stresses and displacements generated on the surrounding bone and within the implant due to the simulated loading configuration were analyzed. RESULTS The bone-implant interface and zygomatic implant body for the intrasinus approach produced 1.41- and 4.27-fold higher stress, respectively, compared with the extramaxillary approach under vertical loading. However, under lateral loading, the extramaxillary approach generated 2.48-fold higher stress than the intrasinus at the bone-implant interface. The zygomatic implant in the extramaxillary approach had twofold higher micromotion than those with intrasinus approach under lateral loading. CONCLUSIONS No one technique was found to be superior; however, if lateral loading is used, the intrasinus approach is the most favorable for the rehabilitation of severely atrophic maxillae.

Stress distributions in maxillary central incisors restored with various types of post materials and designs

Different dental post designs and materials affect the stability of restoration of a tooth. This study aimed to analyse and compare the stability of two shapes of dental posts (parallel-sided and tapered) made of five different materials (titanium, zirconia, carbon fibre and glass fibre) by investigating their stress transfer through the finite element (FE) method. Ten three-dimensional (3D) FE models of a maxillary central incisor restored with two different designs and five different materials were constructed. An oblique loading of 100 N was applied to each 3D model. Analyses along the centre of the post, the crown-cement/core and the post-cement/dentine interfaces were computed, and the means were calculated. One-way ANOVAs followed by post hoc tests were used to evaluate the effectiveness of the post materials and designs (p=0.05). For post designs, the tapered posts introduced significantly higher stress compared with the parallel-sided post (p<0.05), especially along the centre of the post. Of the materials, the highest level of stress was found for stainless steel, followed by zirconia, titanium, glass fibre and carbon fibre posts (p<0.05). The carbon and glass fibre posts reduced the stress distribution at the middle and apical part of the posts compared with the stainless steel, zirconia and titanium posts. The opposite results were observed at the crown-cement/core interface.

Effect of ferrule height and glass fibre post length on fracture resistance and failure mode of endodontically treated teeth

The purpose of this study was to evaluate the combined effect of ferrule height and post length on fracture resistance and failure mode of endodontically treated teeth restored with glass fibre posts, composite resin cores and crowns. Ninety human maxillary central incisors were endodontically treated and divided into three groups (n = 30) according to the ferrule heights: 4, 2 and 0 mm, respectively. Post spaces in each group were prepared at 2/3, 1/2 and 1/3 of the root length (n = 10). The specimens were received fibre posts, composite resin core build up and cast metal crowns. After thermocycling, compressive static load was applied at an angle of 135° to the crowns. Two-way analysis of variance showed significant differences in the failure load in the ferrule height groups, no significant differences in post length groups and no significant interaction between ferrule heights and post lengths. More restorable failure modes were observed.

Effects of different zygomatic implant body surface roughness and implant length on stress distribution

Among factors to contribute for the primary implant stability are implant design parameters as well as implant body surface condition. Through this study, the stress distribution within bone around implant will be investigated under variation of implant lengths and surface conditions by using three dimensional finite element analysis. Six finite element models involving three different zygomatic implant lengths - 46.5 mm, 41.5 mm and 36.5 mm with a smooth surface and rough surface of implant body have been analyzed. Three dimensional models of craniofacial including soft tissue and prosthesis were constructed from computed tomography (CT) images datasets. The implant models were developed using computer-aided design (CAD) software and all models were analyzed via finite element analysis software. A 230N of vertical force was applied on top surface of prosthesis in second premolar region and a masseter load of 300N applied at zygomatic arch. The result showed that the increase of zygomatic implant length shows an ability to reduce both cortical and cancellous bone stress. Besides, the use of rough implant surface has resulted in reduction of stress value at bone-implant interface as well as at surrounding bone. The alveolar bone seems to play a lesser significant role in the zygomatic implant anchorage compared to the zygomatic bone.

Effects of Different Angulation Placement of Mini-Implant in Orthodontic

Orthodontic is one of the treatments in dentistry field which concerned on malocclusion treatments such as improper bites, tooth irregularity and disproportionate jaw relationships. The mini-implant (OMI) is one of the components used in the orthodontic treatment, besides braces and spring. The application of OMI has been well accepted in orthodontic treatment. However, one of the main factors of OMI failures is the implant insertion procedure in which the clinician find it difficult to obtain the best angle to insert the OMI. Therefore, this study aims to evaluate stress in an OMI and bones using the finite element analysis (FEA) with variations of insertion angles and to identify their optimal angle for the implant placement. The three dimensional (3D) model of a left maxillary posterior bone section was constructed based on CT image dataset. That 3D model consists of cortical bone, cancellous bone, second premolar, first molar and second molar teeth. The 3D model of OMI was placed between root of second premolar and first molar teeth. The OMI was simulated with seven different angles of insertions: 30˚, 40˚, 50˚, 60˚, 70˚, 80˚ and 90˚. Within the seven different insertion angles, the results showed that the increase of insertion angle reduced the maximum equivalent von Mises stress in cortical bone, cancellous bone and OMI. Based on this FEA study, the optimal angle placement of OMI is when the implant positioned at vertical angle (90˚) to the bone surface.

Simulation on the effects of dental implant threads to the osseointegration potential

In this paper, effect of the implant thread profile on the stability and osseointegration at the peri-implant bone were evaluated by finite element analysis. These study include five different common threads profile of implant body - buttress, reverse buttress, V-shape, sinusoidal and square - that were evaluated via finite element analysis. Three dimensional model of a mandible was reconstructed from CT dataset and a region of interest was selected at the left side around the first molar. The mandible was separated into two types - compact cortical and porous cancellous. This will allow for proper load transfer to the mandible during simulation of the mastication process. A generic abutment model was virtually connected to the implant body, and a crown representing the first molar was placed onto the abutment. The motion of the implant body relative to the bone was calculated under occlusal load ranging from 10N to 200N applied to the crown. Result showed that the reverse buttress and V-shape thread offer high stability by provide less micromotion at the dental implant body.

Finite element analysis on internal hexagonal and internal conical abutment

Implant-abutment connection plays an important role in the long-term success of dental implant. It should be able to resist bacterial leakage. Colonization of bacterial in microgaps along implant-abutment interfaces will lead to inflammatory reaction. One of the factor which have been identified to produce microgaps is micromotion. This study was conducted to analyse micromotion and stress distribution on mating surface of internal conical and internal hexagonal implant-abutment connections. Three dimensional (3D) model of mandible around the first molar was reconstructed from two dimensional (2D) CT data scan. The reconstructed 3D model includes a layer of cortical bone, cancellous bone, mucosa, prosthesis of first molar and adjacent teeth. Dental implant body and two-piece abutment with different implant-abutment connection were designed and inserted separately to simulate the replacement of the first molar. Axial load were applied on the top centre of the prosthesis and on the adjacent teeth to simulate occlusal force. Micromotion was observed to be lower around internal hexagonal abutments compared to internal conical. However, internal hexagonal connection produce stress concentration at its vertices, thus increase the possibility to be fractured.