Academic Unit of Restorative Dentistry

Sheffield, United Kingdom

Academic Unit of Restorative Dentistry

Sheffield, United Kingdom
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Hajizadeh M.,Sahand University of Technology | Ghalichi F.,Sahand University of Technology | Mirzakouchaki B.,Tabriz University of Medical Sciences | Shahrbaf S.,Academic Unit of Restorative Dentistry
Orthodontic Waves | Year: 2014

Purpose: Orthodontic bracket debonding during treatment period is an unbecoming occurrence for both orthodontists and patients. Various clinical and numerical studies have been done to specify different parameters which affect the bond strength of bracket-adhesive-tooth system. Pattern of stress distribution seems to be an appropriate factor to estimate bond strength of different systems. Since it is not possible to experimentally define stress distribution in bracket-adhesive-tooth systems, three dimensional finite element method is used. The purpose of this study is to obtain and compare stress distribution of five bracket-adhesive-tooth systems with various enamel surface morphologies as an indicator parameter of these systems' bond strength. Materials and methods: In order to specify and compare stress in five different teeth, including maxillary central incisor, mandibular central incisor, maxillary canine, and maxillary and mandibular premolar, 3D STL files of teeth and brackets were reconstructed in MIMICS10 and were imported to HYPERMESH for each tooth, separately. Space between enamel and bracket was filled with orthodontic adhesive, mechanical property of each layer was assigned and appropriate boundary conditions were applied. Results: It was observed that stress distribution in bracket, adhesive and tooth due to shear load application had irregular pattern. For all of systems stress concentration was observed either on the borders or incisal and gingival regions of enamel-adhesive bonding region and adhesive layer. Conclusion: Despite the overall similarity in stress distribution pattern of different bracket-adhesive-tooth systems, some differences on pattern of stress distribution and magnitude of stress were also observed. This may bring about more susceptibility of curved enamel surface teeth to lower bond strength, damage and fracture than flat enamel surface teeth. © 2013 Elsevier Ltd and the Japanese Orthodontic Society.


Shahrbaf S.,Academic Unit of Restorative Dentistry | Vannoort R.,Academic Unit of Restorative Dentistry | Mirzakouchaki B.,Tabriz University of Medical Sciences | Ghassemieh E.,Sir Frederick Mappin Building | Martin N.,Academic Unit of Restorative Dentistry
Dental Materials | Year: 2013

The effect of preparation design and the physical properties of the interface lute on the restored machined ceramic crown-tooth complex are poorly understood. The aim of this work was to determine, by means of three-dimensional finite element analysis (3D FEA) the effect of the tooth preparation design and the elastic modulus of the cement on the stress state of the cemented machined ceramic crown-tooth complex. The three-dimensional structure of human premolar teeth, restored with adhesively cemented machined ceramic crowns, was digitized with a micro-CT scanner. An accurate, high resolution, digital replica model of a restored tooth was created. Two preparation designs, with different occlusal morphologies, were modeled with cements of 3 different elastic moduli. Interactive medical image processing software (mimics and professional CAD modeling software) was used to create sophisticated digital models that included the supporting structures; periodontal ligament and alveolar bone. The generated models were imported into an FEA software program (hypermesh version 10.0, Altair Engineering Inc.) with all degrees of freedom constrained at the outer surface of the supporting cortical bone of the crown-tooth complex. Five different elastic moduli values were given to the adhesive cement interface 1.8 GPa, 4 GPa, 8 GPa, 18.3 GPa and 40 GPa; the four lower values are representative of currently used cementing lutes and 40 GPa is set as an extreme high value. The stress distribution under simulated applied loads was determined. The preparation design demonstrated an effect on the stress state of the restored tooth system. The cement elastic modulus affected the stress state in the cement and dentin structures but not in the crown, the pulp, the periodontal ligament or the cancellous and cortical bone. The results of this study suggest that both the choice of the preparation design and the cement elastic modulus can affect the stress state within the restored crown-tooth complex. © 2013 Academy of Dental Materials.


Chai W.L.,University of Malaya | Brook I.M.,University of Sheffield | Palmquist A.,Gothenburg University | Van Noort R.,Academic Unit of Restorative Dentistry | Moharamzadeh K.,Academic Unit of Restorative Dentistry
Journal of the Royal Society Interface | Year: 2012

For dental implants, it is vital that an initial soft tissue seal is achieved as this helps to stabilize and preserve the peri-implant tissues during the restorative stages following placement. The study of the implant-soft tissue interface is usually undertaken in animal models. We have developed an in vitro three-dimensional tissue-engineered oral mucosal model (3D OMM), which lends itself to the study of the implant-soft tissue interface as it has been shown that cells from the three-dimensional OMM attach onto titanium (Ti) surfaces forming a biological seal (BS). This study compares the quality of the BS achieved using the threedimensional OMM for four types of Ti surfaces: polished, machined, sandblasted and anodized (TiUnite). The BS was evaluated quantitatively by permeability and cell attachment tests. Tritiated water (HTO) was used as the tracing agent for the permeability test. At the end of the permeability test, the Ti discs were removed from the three-dimensional OMM and an Alamar Blue assay was used for the measurement of residual cells attached to the Ti discs. The penetration of the HTO through the BS for the four types of Ti surfaces was not significantly different, and there was no significant difference in the viability of residual cells that attached to the Ti surfaces. The BS of the tissue-engineered oral mucosa around the four types of Ti surface topographies was not significantly different. © 2012 The Royal Society.


Hajizadeh M.,Sahand University of Technology | Ghalichi F.,Sahand University of Technology | Mirzakouchaki B.,Sahand University of Technology | Shahrbaf S.,Academic Unit of Restorative Dentistry
ASME 2012 11th Biennial Conference on Engineering Systems Design and Analysis, ESDA 2012 | Year: 2012

Fixed orthodontic treatment is based on effective bonding of bracket to enamel surface. During orthodontic therapy, load is applied on bracket slot by orthodontic wire, and then it is transferred to adhesive layer and enamel surface (state I). After the completion of treatment period, orthodontic brackets are debonded by load application on the incisal region of bracket-adhesive interface (state II). In order to compare the diversity in stress distribution pattern of these two states, micro CT images of maxillary premolar tooth and bracket were transformed to STL files and imported to Hypermesh software to create high quality 3D finite element models. Space between enamel and bracket was filled with orthodontic adhesive material which sets to 0.2 mm at thickest region. Mechanical property was assigned to each layer and appropriate boundary conditions were applied. By using a load distributing element RBE3, firstly 150 N shear load was applied on the bracket slot to simulate bracket-adhesive-tooth system of state I and secondly the same load was applied on the incisal area of bracket and bracket-adhesive bonding to simulate bracket-adhesive-tooth system of state II. Generated stresses on the bracket, the adhesive and the tooth in both systems were obtained and compared to each other. The Findings of this study, reveal that the effect of bonding loads was directly transform to the adhesive layer and the enamel surface; hence, treatment period would decrease. Alternatively, debonding loads would bring about higher stresses on the bracket and facilitate debonding action. Copyright © 2012 by ASME.


Van Noort R.,Academic Unit of Restorative Dentistry
Dental Materials | Year: 2012

Objectives: Major changes are taking place in dental laboratories as a result of new digital technologies. Our aim is to provide an overview of these changes. In this article the reader will be introduced to the range of layered fabrication technologies and suggestions are made how these might be used in dentistry. Methods: Key publications in English from the past two decades are surveyed. Results: The first digital revolution took place many years ago now with the production of dental restorations such as veneers, inlays, crowns and bridges using dental CAD-CAM systems and new improved systems appear on the market with great rapidity. The reducing cost of processing power will ensure that these developments will continue as exemplified by the recent introduction of a new range of digital intra-oral scanners. With regard to the manufacture of prostheses this is currently dominated by subtractive machining technology but it is inevitable that the additive processing routes of layered fabrication, such as FDM, SLA, SLM and inkjet printing, will start to have an impact. In principle there is no reason why the technology cannot be extended to all aspects of production of dental prostheses and include customized implants, full denture construction and orthodontic appliances. In fact anything that you might expect a dental laboratory to produce can be done digitally and potentially more consistently, quicker and at a reduced cost. Significance: Dental device manufacturing will experience a second revolution when layered fabrication techniques reach the point of being able to produce high quality dental prostheses. The challenge for the dental materials research community is to marry the technology with materials that are suitable for use in dentistry. This can potentially take dental materials research in a totally different direction. © 2011 Academy of Dental Materials.


PubMed | Academic Unit of Restorative Dentistry
Type: Journal Article | Journal: The journal of contemporary dental practice | Year: 2011

There are many different ceramic systems available on the market for dental restorations. Glass-ceramics are a popular choice due to their excellent esthetics and ability to bond to tooth structure allowing a more conservative approach. However, at present, these materials have insufficient strength to be used reliably in posterior regions of the mouth.The aim of this review article is to discuss the types of novel glass-ceramic currently be investigated including composition, microstructure and properties.Current research in glass-ceramics focuses on the quest for a highly esthetic material along with sufficient strength to enable crowns and bridgework to be reliably placed in these areas.There is a gap in the market for a machinable resin bonded glass-ceramic with sufficient strength as well as excellent esthetics.


PubMed | Academic Unit of Restorative Dentistry
Type: Journal Article | Journal: Dental materials : official publication of the Academy of Dental Materials | Year: 2011

Major changes are taking place in dental laboratories as a result of new digital technologies. Our aim is to provide an overview of these changes. In this article the reader will be introduced to the range of layered fabrication technologies and suggestions are made how these might be used in dentistry.Key publications in English from the past two decades are surveyed.The first digital revolution took place many years ago now with the production of dental restorations such as veneers, inlays, crowns and bridges using dental CAD-CAM systems and new improved systems appear on the market with great rapidity. The reducing cost of processing power will ensure that these developments will continue as exemplified by the recent introduction of a new range of digital intra-oral scanners. With regard to the manufacture of prostheses this is currently dominated by subtractive machining technology but it is inevitable that the additive processing routes of layered fabrication, such as FDM, SLA, SLM and inkjet printing, will start to have an impact. In principle there is no reason why the technology cannot be extended to all aspects of production of dental prostheses and include customized implants, full denture construction and orthodontic appliances. In fact anything that you might expect a dental laboratory to produce can be done digitally and potentially more consistently, quicker and at a reduced cost.Dental device manufacturing will experience a second revolution when layered fabrication techniques reach the point of being able to produce high quality dental prostheses. The challenge for the dental materials research community is to marry the technology with materials that are suitable for use in dentistry. This can potentially take dental materials research in a totally different direction.

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