Istabrak Hasan

Experimental and histological investigations of the bone using two different Oscillating Osteotomy techniques compared with conventional rotary osteotomy

Over the past decade, coinciding with the appearance of a number of new ultrasonic surgical devices, there has been a marked increase in interest in the use of ultrasound in oral surgery and implantology as alternative osteotomy method. The aim of this study was the comparison of the effect of osteotomies performed using ultrasonic surgery (Piezosurgery(®)), sonic surgery SONICflex(®) and the conventional bur method on the heat generation within the bone underneath the osteotomy and light-microscopy observations of the bone at different cutting positions in porcine mandibular segments. It was found that the average heat generated by SONICflex(®) sonic device was close to that by conventional rotary bur (1.54-2.29°C), whereas Piezosurgery(®) showed a high generated heat up to 18.17°C. Histological investigations of the bone matrix adjacent to the defect radius showed intact osteocytes with all three instruments and similar wide damage diameter at the bottom region. SONICflex(®) showed smooth cutting surfaces with minimal damage in the upper defect zone. Finally, presented results showed that sonic surgery performed with SONICflex(®) is an alternative osteotomy method and can be used as an alternative to the conventional bur method.

Biomechanical finite element analysis of small diameter and short dental implant.

Abstract Short and mini dental implants have been widely used as treatment alternatives in certain selected clinical situations. However, a profound scientific analysis of the mechanical and biomechanical impact of the reduced length and diameter of these implant geometries has not been published until now. Using finite element analysis, a series of different experimentally designed short and mini implants have been analysed with regard to their load transfer to the alveolar bone and have been compared to respective standard commercial implants. Mini implants have been inserted in an idealised bone bed representing the anterior mandibular jaw region and loaded with a force of 150 N. An immediate loading condition was assumed and analysed using the contact analysis option of the FE package MSC.Marc/Mentat. Short implants were inserted in an idealised posterior bone segment and loaded in osseointegrated state with forces of 300 N. Clearly increased bone loading was observed for the short and mini dental implants compared with standard implants, clearly exceeding the physiological limit of 100 MPa. The determined biomechanical characteristics could explain the slightly increased failure rate of short and mini dental implants.

Biomechanical finite element analysis of small diameter and short dental implants: extensive study of commercial implants.

Abstract In recent years, mini and short dental implants have become increasingly popular as treatment alternatives for patients in whom the bone is unsuitable for a standard implant. As yet, no detailed scientific analysis of the mechanical and biomechanical impact of the reduced diameter and length of these implants has been published. We analysed 21 commercially available implants (13 mini, eight short) with respect to material behaviour and load transfer to the alveolar bone, using finite element (FE) analysis. Following μCT scanning and geometry reconstruction, FE models of mini implants and short implants were inserted into idealised bone segments. Mini implants were analysed in the anterior mandibular jaw region at a force of 150 N under immediate loading, using a contact analysis in the FE software package Marc Mentat 2007. Short implants were inserted in posterior bone segments and analysed in the osseointegrated state at an occlusal force of 300 N. Von Mises stresses (up to 1150 MPa) in mini implants partly exceeded the ultimate strength. Implant diameter and geometry had a pronounced effect on stresses in the cortical plate (up to 266 MPa). Strains in spongy bone and stresses in cortical bone around short implants were markedly increased compared to those in standard implants. An increased risk of bone damage or implant failure may be assumed in critical clinical situations.

Development of a novel intraoral measurement device to determine the biomechanical characteristics of the human periodontal ligament

Periodontal diseases like gingivitis and periodontitis have damaging effects on the periodontium and commonly affect the mechanical properties of the periodontal ligament (PDL), which in the end might lead to loss of teeth. Monitoring tooth mobility and changes of the material properties of the PDL might help in early diagnosis of periodontal diseases and improve their prognosis. It was the aim of this study to develop a novel intraoral device to determine the biomechanical characteristics of the periodontal ligament. This includes the measurement of applied forces and resulting tooth displacement in order to investigate the biomechanical behaviour of the periodontium with varying loading protocols with respect to velocity and tooth displacement. The developed device uses a piezoelectric actuator to apply a displacement to a tooths crown, and the resulting force is measured by an integrated force sensor. To measure the tooth displacement independently and non-invasively, two magnets are fixed on the teeth. The change in the magnetic field caused by the movement of the magnets is measured by a total of 16 Hall sensors. The displacement of the tooth is calculated from the movement of the magnets. The device was tested in vitro on premolars of four porcine mandibular segments and in vivo on two volunteers. The teeth were loaded with varying activation curves. Comparing the force progression of different activation velocities, the forces decreased with decreasing velocity. Intensive testing demonstrated that the device fulfils all requirements. After acceptance of the ethical committee, further testing in clinical measurements is planned.

Bone stability around dental implants: Treatment related factors.

The bone bed around dental implants is influenced by implant and augmentation materials, as well as the insertion technique used. The primary influencing factors include the dental implant design, augmentation technique, treatment protocol, and surgical procedure. In addition to these treatment-related factors, in the literature, local and systemic factors have been found to be related to the bone stability around implants. Bone is a dynamic organ that optimises itself depending on the loading condition above it. Bone achieves this optimisation through the remodelling process. Several studies have confirmed the importance of the implant design and direction of the applied force on the implant system. Equally dispersed strains and stresses in the physiological range should be achieved to ensure the success of an implant treatment. If a patient wishes to accelerate the treatment time, different protocols can be chosen. However, each one must consider the amount and quality of the available local bone. Immediate implantation is only successful if the primary stability of the implant can be provided from residual bone in the socket after tooth extraction. Immediate loading demands high primary stability and, sometimes, the distribution of mastication forces by splinting or even by inserting additional implants to ensure their success. Augmentation materials with various properties have been developed in recent years. In particular, resorption time and stableness affect the usefulness in different situations. Hence, treatment protocols can optimise the time for simultaneous implant placements or optimise the follow-up time for implant placement.

Computational simulation of internal bone remodelling around dental implants: a sensitivity analysis

This study aimed to predict the distribution of bone trabeculae, as a density change per unit time, around a dental implant based on applying a selected mathematical remodelling model. The apparent bone density change as a function of the mechanical stimulus was the base of the applied remodelling model that describes disuse and overload bone resorption. The simulation was tested in a finite element model of a screw-shaped dental implant in an idealised bone segment. The sensitivity of the simulation to different mechanical parameters was investigated; these included element edge length, boundary conditions, as well as direction and magnitude of the implant loads. The alteration in the mechanical parameters had a significant influence on density distribution and model stability, in particular at the cortical bone region. The remodelling model could succeed to achieve trabeculae-like structure around osseointegrated dental implants. The validation of this model to a real clinical case is required.

Radiographic evaluation of bone density around immediately loaded implants.

Understanding the changes in bone density after insertion of dental implants and their relation to immediate loading is essential to achieving improvements in their survival rate. Histological investigations of the bone bed in humans are limited, which in turn hampers opportunities to deepen knowledge about the remodelling process around dental implants. The aim of the present study was to follow the change in bone density by measuring the grey values of cone beam computed tomography (CBCT) at different periods subsequent to implant insertion. The CBCTs of 20 individual immediately loaded implants were evaluated at three time points: prior to surgery, one month following, and six months after the operation. The grey values were measured at different regions around the implants. Reduction in the grey values was observed with respect to the reference values after one month and six months from implant insertion in the apical, middle, and cervical regions. No correlation was detected either between the change in grey values and drilling method or with the measured primary and secondary stabilities by Osstell ISQ instrument. Cone beam computed tomography can be used as a qualitative method to support clinical follow up and monitor the changes in bone density around implants in critical cases.

In vivo measurements and numerical analysis of the biomechanical characteristics of the human periodontal ligament

The periodontal ligament is a complex tissue with respect to its biomechanical behaviour. It is important to understand the mechanical behaviour of the periodontal ligament during physiological loading in healthy patients as well as during the movement of the tooth in orthodontic treatment or in patients with periodontal disease, as these might affect the mechanical properties of the periodontal ligament (PDL). Up to now, only a limited amount of in vivo data is available concerning this issue. The aim of this study has been to determine the time dependent material properties of the PDL in an experimental in vivo study, using a novel device that is able to measure tooth displacement intraorally. Using the intraoral loading device, tooth deflections at various velocities were realised in vivo on human teeth. The in vivo investigations were performed on the upper left central incisors of five volunteers aged 21-33 years with healthy periodontal tissue. A deflection, applied at the centre of the crown, was linearly increased from 0 to 0.15mm in a loading period of between 0.1 and 5.0s. Individual numerical models were developed based on the experimental results to simulate the relationship between the applied force and tooth displacement. The numerical force/displacement curves were fitted to the experimental ones to obtain the material properties of the human PDL. For the shortest loading time of 0.1s, the experimentally determined forces were between 7.0 and 16.2N. The numerically calculated Youngs modulus varied between 0.9MPa (5.0s) and 1.2MPa (0.1s). By considering the experimentally and numerically obtained force curves, forces decreased with increasing loading time. The experimental data gained in this study can be used for the further development and verification of a multiphasic constitutive law of the PDL.

Biomechanical time dependency of the periodontal ligament: a combined experimental and numerical approach

The analysis of the non-linear and time-dependent viscoelasticity of the periodontal ligament (PDL) enables a better understanding of the biomechanical features of the key regulator tissue for tooth movement. This is of great significance in the field of orthodontics as targeted tooth movement remains still one of the main goals to accomplish. The investigation of biomechanical aspects of the PDL function, a difficult area of research, helps towards this direction. After analysing the time-dependent biomechanical properties of pig PDL specimens in an in vitro experimental study, it was possible to confirm that PDL has a viscoelastic anisotropic behaviour. Three-dimensional finite element models of mini-pig mandibular premolars with surrounding tissues were developed, based on micro-computed tomography (μCT) data of the experimental specimens. Tooth mobility was numerically analysed under the same force systems as used in the experiment. A bilinear material parameter set was assumed to simulate tooth displacements. The numerical force/displacement curves were fitted to the experimental curves by repeatedly calculating tooth displacements of 0.2mm varying the loading velocities and the parameters, which describe the nonlinearity. The experimental results showed a good agreement with the numerical calculations. Mean values of Youngs moduli E1, E2 and ultimate strain ε12 were derived for the elastic behaviour of the PDL for all loading velocities. E1 and E2 values increased with increasing the velocity, while ε12 remained relatively stable. A bilinear approximation of material properties of the PDL is a suitable description of measured force/displacement diagrams. The numerical results can be used to describe mechanical processes, especially stress-strain distributions in the PDL, accurately. Further development of suitable modelling assumptions for the response of PDL under load would be instrumental to orthodontists and engineers for designing more predictable orthodontic force systems and appliances.

Biomechanics and load resistance of small-diameter and mini dental implants: a review of literature

Abstract In recent years, the application of small-diameter and mini dental implants to support removable and fixed prosthesis has dramatically increased. However, the success of these implants under functional biting forces and the reaction of the bone around them need to be analyzed. This review was aimed to present studies that deal with the fatigue life of small-diameter and mini dental implants under normal biting force, and their survival rate. The numerical and experimental studies concluded that an increase in the risk of bone damage or implant failure may be assumed in critical clinical situations and implants with <3 mm diameter have a risk of fracture in clinical practice. The survival rate of the small-diameter and mini dental implants over 5 years was 98.3–99.4%.