Ionut Ichim

Mechanical responses to orthodontic loading: A 3-dimensional finite element multi-tooth model

INTRODUCTION The initial mechanical response to orthodontic loading comprises biologic reactions that remain unclear, despite their clinical significance. We used a 3-dimensional finite element analysis to investigate the stress-strain responses of teeth to orthodontic loading. METHODS The model was derived from computed tomography data, with adequate boundary conditions and tissue characterization, with orthodontic hardware to provide a more accurate reflection of events during orthodontic therapy. This study also incorporated the adjacent dentition. Two cases were analyzed: a single-tooth system with a mandibular canine, and a multi-tooth system consisting of the mandibular incisor, the canine, and the first premolar, subjected to orthodontic tipping forces. RESULTS AND CONCLUSIONS The systems experienced elevated distortion strain energies in the alveolar crest, whereas the tensile and compressive stresses coincided with the apical sites clinically associated with root resorption. Stress levels were considerably greater in the multi-tooth system than in the single-tooth system. The results for the single-tooth model agree with those previously reported. The numeric studies show how orthodontic tooth movement develops different stress fields and how root resorption might occur as a result of hydrostatic compressive stress-induced tissue necrosis.

Mandibular Biomechanics and Development of the Human Chin

The development of the chin, a feature unique to humans, suggests a close functional linkage between jaw biomechanics and symphyseal architecture. The present study tests the hypothesis that the presence of a chin changes strain patterns in the loaded mandible. Using an anatomically correct 3-D model of a dentate mandible derived from a CT scan image, we analyzed strain patterns during incisal and molar biting. We then constructed a second mandible, without a chin, by ‘defeaturing’ the first model. Strain patterns of the second model were then compared and contrasted to the first. Our main finding was that chinned and non-chinned mandibles follow closely concordant patterns of strain distribution. The results suggest that the development of the human chin is unrelated to the demands placed on the mandible during function.

Measuring Intraoral Pressure: Adaptation of a Dental Appliance Allows Measurement During Function

This article introduces a new way of recording intraoral pressures from a range of locations within the oral cavity. To measure pressure flow dynamics during swallowing, we fitted eight miniature pressure transducers capable of measuring absolute pressures to a chrome-cobalt palatal appliance with a labial bow. Unlike previous devices, our design provides a rigid, custom-fitted platform for the simultaneous recording of pressures at eight locations within the oral cavity during function. We placed an anterior pair of gauges to measure lingual and labial contact against the left central incisor tooth, and two pairs of gauges to measure pressure contributions of the lateral tongue margin and cheeks on the canine and first molar teeth. Finally, lingual pressure on the midline of the palate was measured by two gauges, one at the position of the premolars and one on the posterior boundary of the hard palate. We then recorded intraoral pressures in five adult volunteers seated in an upright position and asked to swallow 10 ml of water. Labial pressures on the canine rose rapidly from a resting level of 10 kPa to 33 kPa, while pressure profiles from the labial aspects of the incisor and first molar teeth followed a negative pattern, peaking at −12 kPa for the incisor and −15 kPa for the molar sensor. Pressure profiles recorded from the palatal aspects of the first molar and the canine appeared to be similar, but the former fell to −13 kPa before rising to 9 kPa, and the canine pressure rapidly increased to 22 kPa before returning to its resting level of 4 kPa. The pressure profile of the palatal aspect of the central incisor was strikingly different; at the start of the swallow, pressure dropped precipitously to −20 kPa, before slowly rising to 10 kPa. It then followed the general pattern of the other two sensors, before peaking again at 10 kPa and then returning to a resting level of 4 kPa. We also showed that there were significant negative pressures in the mouth during function, and that pressure profiles varied markedly between individuals.

Numerical Simulation of Crack Formation in All Ceramic Dental Bridge

Ceramics have rapidly emerged as one of the major dental biomaterials in prosthodontics due to exceptional aesthetics and outstanding biocompatibility. However, a challenging aspect remaining is its higher failure rate due to brittleness, which has to a certain extent prevented the ceramics from fully replacing metals in such major dental restorations as multi-unit bridges. This paper aims at simulating the crack initiation and propagation in dental bridge. Unlike the existing studies with prescriptions of initial cracks, the numerical model presented herein will predict the progressive damage in the bridge structure which precedes crack initiation. This will then be followed by automatic crack insertion and subsequent crack growth within a continuum to discrete framework. It is found that the numerical simulation correlates well to the clinical and laboratory observations.

Experimental simulation of non-ballistic wounding by sharp and blunt punches

Despite a long history of gross and microscopic descriptions of blunt and sharp force injury to the dermal tissues, few have addressed the mechanisms underlying such trauma. The need to develop an understanding of how non-ballistic injury occurs calls for an ability to biomechanically model the process. We recently introduced a basic skin and subcutaneous model, which we used to investigate wounding from a spherical object. Here we employ the same model to examine wounding caused by a sharp wedge shaped object and a blunt rectangular object. Macroscopic examination and SEM views of the surface and cross sections of blunt and sharp force tears show that while in the former there is a clean cut through the skin into the underlying sponge, in the latter there is a tissue plug confined to the skin that is smaller than the impacting rectangle. Fracture initiation in the subdermal tissue occurs at the angles of the impacting object. In sharp force trauma, there is localized breaching of the skin layer coupled with the wedging action of the impacting object. Because the subdermal tissue, in this case the underlying hydrated foam, is attached to the base of the skin, it will contribute to further tearing of the foam beneath the line of contact.

Understanding Craniofacial Blunt Force Injury: A Biomechanical Perspective

One of the most important tasks in forensic investigation of blunt force trauma is to determine accurately the nature and magnitude of the forces applied to the skin. The primary emphasis of research into blunt force trauma has focused on analysing the demographics rather than the mechanobiology of such injuries. Nevertheless, a large body of literature has accumulated on the biomechanics of skin. Here we review this evidence, together with the complex role of intrinsic factors such as age, sex and ethnicity on the wounding susceptibility of skin. We also review how the skin responds to blunt trauma, and try to relate this to the estimation of the force of impact. Finally, we review the current biomechanical models of blunt force trauma, and introduce our own model and its preliminary findings. Contrary to the impression gained from the literature, wounding can be modelled in a basic simulation of the contact events during blunt force impact, and the results be evaluated quantitatively. We conclude that subject-specific parameters could be calculated from a more sophisticated model in order to provide a more robust set of values that can be used to predict forces used in generating skin wounds.

FEA Evaluation of the Resistance Form of a Premolar Crown

PURPOSE The purpose of this study was to evaluate the influence of buccal and lingual wall convergence angles on the ability of the preparation to resist rotational displacement. MATERIALS AND METHODS An intact premolar digitized by micro-CT yielded a 3D reproduction of a human tooth. Simulated crown preparations with known buccolingual axial wall convergence angles (4°, 8°, 12°, 16°, 20°, 24°, 28° 32°), sloped-shoulder marginal area, and occlusal reduction were created and restored with a ceramic crown. The tooth restoration was loaded with a 200 N force at 45° to the incline of the buccal cusp. The responses of the restored tooth with luting agents were analyzed using the 3D finite element method. RESULTS This study demonstrated that a convergence angle of the preparation above 12° produced a decrease of the resistance of the crown to rotational effects. The study also showed that the use of luting agents that provide bonding between the restoration and dentine improved the rotational resistance of the crown on preparations with large convergence angles. CONCLUSIONS Use of buccolingual convergence angles greater than 12° reduced the resistance form of the preparation. Luting agents capable of delivering strong bonding between the crown and the preparation improved the resistance in highly tapered preparations.

Computational Fracture Modelling in Bioceramic Structures

Bioceramics have rapidly emerged as one of major biomaterials in modern biomedical applications because of its outstanding biocompatibility. However, one drawback is its low tensile strength and fracture toughness due to brittleness and inherent microstructural defects, which to a certain extent prevents the ceramics from fully replacing metals used as load-bearing prostheses. This paper aims to model the crack initiation and propagation in ceramic fixed partial denture, namely dental bridge, by using two recently developed methods namely continuum-to-discrete element method (CDEM) in ELFEN and extended finite element methods (XFEM) in ABAQUS. Unlike most existing studies that typically required prescriptions of initial cracks, these two new approaches will model crack initiation and propagation automatically. They are applied to a typical prosthodontic example, thereby demonstrating their applicability and effectiveness in biomedical applications.

Damage Evaluation of Bone Tissues with Dental Implants

Dental implants have been extensively used in prosthetic dentistry over the last two decades. Clinical experience shows that the healing and osseointegration process can heavily influence the success of the implantation. It is critical to understand the damage extent in different time frames. This paper aims at exploring the mechanical damage of dental implantation over the healing process. The 3D finite element analysis (FEA) models were developed based on computerised tomography (CT) scan technology to investigate the load-induced damage of interfacial osseointegration, as well as cortical and cancellous bone tissues. Unlike the existing linear finite element (FE) stress analysis, this study takes into account the damage accumulation and micro-crack nucleation under a framework of bone/interface remodelling. This study reveals the damage in the surrounding bone tissues and bone-implant interfaces at different stages of the healing process, and consequently premature load tolerances are suggested.

Contact-Driven Crack Formation in Dental Ceramic Materials

Natural human tooth consists of multiple layered quasi-brittle biomaterials, which make dental restorations experience a complex stress state under masticatory contact loading. As such, many restorations are prone to failure and a constant effort is made to improve the mechanical characteristics of the restorative materials. Clinical observations have shown that improved strengths and fracture toughness in ceramic materials do not necessarily lead to an anticipated higher functional longevity of the restoration. While substantial experimental investigations have been carried out to identify the contact induced fracture in such multi-layer material systems, numerical modelling of this event was largely unexplored. This paper presents a new numerical method to account for micro-damage driven fracture in various multi-layered biomaterial structures. In this study, a Rankine constitutive model is adopted and the crack initiation and propagation are automatically implemented in an explicit finite element (FE) framework. The effects of indenter radius, surface curvature and thickness of layered biomaterials on the cracking patterns are investigated. The results show good agreement with the experimental studies in literature.