RESEARCH GRANTS AWARDED IN ACADEMIC YEAR 2000-2001

There are currently 15 university-funded and 4 externally-funded projects. In addition, 9 projects with no funding were undertaken by Faculty staff this year.

New Research Projects funded by ARF in Year 2000

Use of Salivary Biomarkers in Risk Assessment for Periodontal Diseases
A/P Lim Lum Peng

The objective of the current project is to evaluate the use of salivary biomarkers in risk assessment for Periodontitis. 3 groups of individuals will be involved: smokers with periodontitis, non-smokers with periodontitis, healthy controls. All subjects will be assessed clinically for gingival inflammation, plaque and loss of attachment using standard periodontal parameters. Unstimulated saliva will be collected for each patient and the saliva samples will be analysed for: Salivary flow rate, IgA, Iysozyme secretion rate and cortisol levels.The results will be analysed to compare the differences in the various salivary biomarkers between groups.
To date there have been very few studies reported in the use of salivary biomarkers in assessing periodontal disease risk. The laboratory methodology of analyzing salivary IgA, cortisol and Iysozyme have already been established by Koh and co-workers in the Department of Community Medicine, NUS. The results may have significant implications in future in identifying at risk individuals using non-invasive methods and instituting suitable treatment strategies to control periodontal disease at an early stage.

Critical Bending Moment of Implant Component Screw Joint Interfaces
A/P Keson Tan

The screw-joint preload between osseointegrated dental implant components at the fixture-abutment interface has recently been measured directly in a previous study by the PI (Screw-Joint Preload of Osseointegrated Implant Components NUS RP 950320). Also, other previous work had focused on measuring the screw-joint preload at the transmucosal abutment-gold cylinder interface. The definition of the level of these preloads have added to current understanding of functional stress distribution in the implant prosthesis screw joint and is of great importance in the prediction of clinical longevity and selection of an implant system by clinicians. Optimal preload confers screw joint stability and previous analyses had primarily focused on vertical loads, i.e. tension or compression. A third type of load on these screw joints that needs to be resisted by optimal preload is bending moment. Clinical overload situations which lead to excessive bending moment have been reported by various authors as being the cause of prosthetic and osseointegration failure. This study defines a new bioengineering concept termed critical bending moment, which is the bending moment at which the non-axial load applied overcomes the screw joint preload and causes the loss of contact between the mating surfaces of the screw joint components. When the screw joint opens up, all the external load will instantaneously be taken up by the screw shank and rapidly lead to screw failure. The level of bending moment at which this critical overload occurs for particular abutment systems would be of great significance in designing and specifying biomechanical situations that minimise risk for prostheses in function.

Multi-dimensional imaging, visualization, and modeling for craniofacial anomalies and orthodontics applications
A/P Kelvin Foong Weng Chiong
A/P Ong Sim Heng

Advancement in three-dimensional surface laser imaging technologies has spawned new applications in dentistry. Surface contours of the craniofacial region are easily registered with a laser beam, and facial morphology can be studied and analysed in three-dimensions. Dental impressions have also been scanned with a laser beam to construct a three-dimensional model of the patientís teeth for restorative purposes. Recently, developmental work has been performed at NUS to acquire surface features on three-dimensional images of dental arches for automatic identification of landmarks, arch form analysis and simulation of orthodontic treatment. Specifically, the Vision and Image Processing (VIP) Laboratory is now able to automatically define three-dimensional palatal segments and arch forms of infants with the cleft lip and palate deformity. In addition, current work focuses on the development of a versatile orthodontic treatment simulator that is capable of comprehensive 3-D space analysis, simulation and modeling of treatment outcome, as well as modeling of growth effects on the cleft palate.

Three-dimensional imaging and its application are fast becoming the standard tools for diagnosis and treatment planning and simulation in dentistry. Building on our current expertise in surface image analysis and visualisation of dental models, the VIP lab will further be embarking to jointly develop an orthognathic surgical simulator with CNRS of France. The VIP lab of NUS will be developing three-dimensional models for the skeletal and dental bases to complement the developmental work on facial soft tissue simulation by CNRS.

Load Fatigue Performance of Implant-Abutment Combinations
A/P Keson Tan Beng Choon

The aim of this study is to investigate the load fatigue performance of various implant-abutment combinations newly introduced into the clinical arena. The external hex implant-abutment interface has been called upon to provide anti-rotational resistance, prosthetic indexing functions and screw joint interface stability beyond what it was originally designed for. Newer implant-abutment combinations now have varying diameters as well as proprietary interfaces. These interfaces now may be classified as external or internal connection and the geometry of the interface now incorporate features for rotational resistance, indexing and lateral stabilisation and may be described as hexagonal, octagonal, cone screw, cone hex, cylinder hex, spline, cam, cam tube and pin/slot. Most studies characterise the "strength" of the implant-abutment connection by using monotonic tensile or bending load-to-failure testing methodology and comparisons of relative superiority are made on this basis. Load fatigue from functional chewing loads is now considered to be a more physiologically relevant biomechanical failure mode. Rotational fatigue testing of implant-abutment connections is a new approach to the elucidation of the relative performance of these new implant-abutment combinations and will provide a more realistic selection basis for prediction of clinical longevity.

Tissue Engineering of an Autogenous Periodontal Transplant for the Regeneration of the Periodontium
Dr Varawan Sae-Lim

Regeneration by autogenous cell transplantation is one of the most promising tissue engineering technics as it has the potential to provide the ideal autogenic construct. This project aims to develop a cell culture system which allows the tissue engineering of a 3-D scaffold/ periodontal fibroblast/osteoblast construct based on the PCL scaffolds developed earlier for tissue engineering bone and cartilage (Hutmacher et al 2000a,b). Human periodontal ligament fibroblast and osteoblasts are to be obtained and seeded onto a three-dimensional scaffold. The bioresorbable template provides the necessary support for cellular proliferation, differentiation and production of extracellular matrix, facilitating the assimilation in-vivo, eventually defining the overall configuration of the new periodontium with new attachment on the previously denuded root surfaces.

To Observe and Compare the Expressions of bone Matrix Proteins and Growth Factors using Immunohistochemical methods, in Membraneous Bone Healing in Rat Calvarial Defects
Dr Winston Tan Kwong Shen

Osteoadherin belongs to the family of leucine-rich repeat proteins and is an attachment protein specific for osteoblasts. It was recently isolated by Dr Mikael Wendel, my collaborator (Wendel et al 1998) and sequenced. The expression of osteoadherin during bone healing is uncertain.

Bone sialoprotein is found in the skeleton and dentine and its role in bone healing is also uncertain. Studies have shown that it can bind to osteoblasts, is a potent nucleator in the mineralisation front of bone (Hunter& Goldberg 1993) and is also expressed during bone mineralisation in embryogenesis (Chen et al 1992).

VEGF, FGF, TGF-B and BMP are factors closely related to osteogenesis and TGF-B has also been linked to the regulation of osteoblast migration, differentiation and proliferation during mandibular fracture repair in rats (Steinbrech et al 2000).

The expression of these factors and proteins (especially for Osteoadherin) at different stages of membranous bone healing has not been well characterized. The scope of the proposal would be to study the spatial expression of these factors at various time intervals. It would have implications in the construct of factor release mechanisms in tissue engineering, as well as add to the current body of knowledge on bone regeneration.

The Influence of the Colour of Different Post and Core Systems on the All-Ceramic Crown Restorations
Dr Loh Poey Ling

The demand in esthetic dentistry has increased in the past few years. A number of "esthetic" materials for crown restorations have been released in the market. All ceramic crown is one of those that have been recognized to be more esthetic since there is no metal substructure and is more translucent. Meanwhile, an endodontically treated tooth often need post and core. The metal post and core may compromise the esthetics of the restorations. The questions have been raised if the prefabricated "black color" post with composite buildup will also cause the black appearance when restored with the all ceramic crown, and whether the different crown systems will give the same result. Very few studies have explored in this area.

The purpose of the proposed investigation is to evaluate the influence of color of different post and core systems on all ceramic crown restorations. Different posts and cores systems will be built up on clear plastic blocks. Then the crowns will be fabricated and cemented. The color will be measured with the spectrophotometer. Comparison in the color change of the various crowns supported by different post and cores will be made. Comparison will also be made for the various crowns supported by natural teeth preparations.

Comparison of Shear-peal bond strength of orthodontic brackets to various ceramic systems
Dr Chay Siew Han

This study aims to gain more information on the shear-peel bond strength of the brackets to the all-ceramic systems, namely the Finesse and Empress II and compare them to the VMK 68 (feldsphatic porcelain).

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