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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
81

Novel diagnostic systems for the assessment of tooth colour and stain in clinical trials

Mohan, Naveen January 2008 (has links)
Tooth whitening is becoming popular in the world today due to peoples' increased awareness of their cosmetic appearance. Tooth whitening is usually achieved either by the physical removal of stain using abrasives or by chemically reducing it with the help of bleaching agents. Product evaluations have been carried out by different investigators and manufacturers to assess the whitening efficacy of different products. Techniques employed in product testing should be standard, reliable, precise and accurate so that meaningful comparisons may be carried out. Tooth whitening and stain has been conventionally assessed by means of visual techniques with the help of shade guides and stain indices. Emergence of instrumental techniques has reduced the subjectivity of conventional techniques and has also provided more standardised methods and parameters for product evaluation. The present clinical studies investigate two novel digital techniques for their suitability to assess and quantify tooth colour and stain. A White Light Digital Imaging system was tested for its capability to assess tooth colour and stain. A novel . Fluorescence Imaging system (Quantitative Light Induced Fluorescence system) was investigated for its suitability to quantify stain. Clinical implementation of a novel whiteness index was also tested for its ability to measure tooth colour and stain. The digital techniques and the parameters were investigated for their ability to assess tooth colour and stain with the help of clinical trials through product evaluation and comparison. The proposed Whiteness Index was concluded as a more appropriate index, amongst the colour parameters, to measure differences in tooth whiteness. The White Light Digital Imaging system was efficient in measuring tooth colour and diffused stain. QLF was concluded as more suitable in detecting and quantifying well defined stain areas on the tooth surface.
82

Replacement of plastic restorations in clinical dental practice and the effect that a simple training programme can have on the decision making process

McAndrew, Robert January 2008 (has links)
AIM: To investigate how a simple training programme affected restoration replacement decision making by a group of sixteen dentists. METHOD: This project had two distinct phases, one involving a simulated clinical examination of 111 restorations and the other a clinical examination of 66 restorations. On both occasions, two experienced clinicians using the United States Public Health Service (USPHS) criteria determined the restorative status of the restorations these evaluations determined the gold standard status with respect to restoration integrity for the restorations. All evaluations were completed under strictly controlled clinical conditions with standard equipment and lighting provided. After completing the simulated clinical phase half of the sixteen dentists were randomly assigned to undertake restoration evaluation training (test group). The results of the simulated clinical and clinical examinations between the test and the non-trained group (control group) were compared by the non-parametric statistical analysis of a number of parameters i.e. the number of restorations scheduled for replacement, the time taken to complete examinations, sensitivity, specificity, positive predictive value, negative predictive value, Dice's coincidence index and Cohen's Kappa statistic. RESULTS: There were no statistical differences between the groups at baseline with test and control groups scheduling a similar number of restorations for replacement (36.25 7.78 and 34.75 7.93). After training the test group took longer to complete a repeat simulated clinical examination 59.2515.06 minutes, when this was compared with that of the initial examination, 39.1318.54 minutes. However, there were no other statistically significant differences when baseline measurements were compared. The clinical phase highlighted a number of statistically significant results when the test and the control group were compared the number of restorations scheduled for replacement (6.00 3.01 and 9.7113.15), examination time (27.8613.45 and 36.7113.74) and agreement with the gold standard for restoration replacement (0.8510.27 and 0.79 0.06). CONCLUSION: Within the limits of this study, it was concluded that examiner training can have a significant effect on plastic restoration replacement decision making by dentists.
83

Development and characterisation of an ex vivo model system for bone repair

Smith, Emma Louise January 2009 (has links)
Limitations in current model systems for researching bone repair have hampered the development of alternative clinical therapies. This thesis aimed to develop and validate an ex vivo rat mandible model, to investigate specific molecular and cellular processes involved in bone repair. Maintenance of cell and tissue architecture and viability was shown within mandible slices cultured for up to 21 days, both intact and fractured. Autoradiographic studies showed that resident cells were actively synthesising and secreting proteins, and cells of the osteoblast lineage were shown to survive throughout the culture period. The model was responsive to exogenously added growth factors TGF-p1 and BMP-2, with increased cellular migration / proliferation and expression of bone matrix proteins observed. A second model system, an in vitro bone slab cell culture system, demonstrated that endogenous growth factors could be released from the matrix of bone by chemicals such as EDTA, calcium hydroxide, and sodium hydroxide. Different growth factor release kinetics were observed with each treatment, and released growth factors were capable of actively influencing the behaviour of osteogenic cells. Pre-treatment of mandible slices with these chemical treatments yielded similar results, with an observed increase in cell number, proliferation, and bone matrix protein expression. The ex vivo mandible model developed within this study may represent an ideal system for investigating specific processes of bone repair, as well as a promising alternative to in vivo testing of novel clinical therapeutics.
84

Development of a novel system to measure and calculate tooth movements for studying the properties of the periodontal ligament

Liu, He January 2006 (has links)
Motion analysis techniques have been widely used in biomechanics for measuring large-scale motions such as gait, posture etc, but have not yet been significantly explored for measuring smaller movements such as tooth movement under load. In principle, very accurate measurements could be possible and this could provide a valuable tool in many engineering applications. The aim of this study was to develop a novel system to measure and calculate tooth movements with 6DOF in 3D space for studying the properties of the periodontal ligament. The Qualisys ProReflex-MCU120 motion capture system has been developed to measure micro-movements. The calibration frame was designed and made for the system calibration. The system accuracy was 1.17%, 1.67% and 1.31% for diamond markers 1.81%, 2.37% and 1.39% for spherical markers in x, y and z directions in the range of 20 - 200pm. These results demonstrated that the system is accurate enough to measure small-scale movements. To measure tooth movement, two retroreflective marker clusters, two pointers and one plane for the pointer calibration were created. The two marker clusters were fixed on the measured tooth and the reference tooth for measurements. The pointer was used to identify the three landmarks for identifying anatomical coordinate system of tooth. Data analysis software was developed and evaluated for calculating tooth movement in 6DOF. In the data analysis software, the three coordinate systems method was used with transformation matrices to give 6DOF results. The evaluation results of a complete system were 3.2%, 2.8% and 2.4% for rotations 5.3%, 7.7% and 4.7% for translations in x, y and z directions in the term of accuracy. For producing tooth measurements, loading devices and loading control system were designed and tested. The experiments were carried out on human volunteers in clinical setting. Loads of 0.196N, 0.294N and 0.49N were separately applied to the measured tooth in the buccal direction and the intrusive direction for 10s and 30s, respectively. The experimental results demonstrated that, with the buccal loading, the tooth translations were 32pm for load of 0.294N, and 41pm for load of 0.49N in the y direction of the anatomical coordinate system, tooth rotations were 0.09 and 0.07 for load of 0.294N, and 0.1 and 0.06 for load of 0.49N in the x and z directions with the intrusive loading, tooth movements were 37pm, 15pm and 54pm for load of 0.196N, and 140pm, 51pm and 25pm for load of 0.49N in the x, y and z directions, tooth rotations were 0.04 , 0.07 and 0.2 for load of 0.196N, and 0.26 , 0.195 and 0.35 for load of 0.49N about the x, y and z directions. Overall, a novel system of measuring and calculating tooth movement has been developed. It could be useful in applications in many other engineering fields.
85

Blind source separation via independent and sparse component analysis with application to temporomandibular disorder

Cheong Took, Clive January 2007 (has links)
Blind source separation (BSS) addresses the problem of separating multi channel signals observed by generally spatially separated sensors into their constituent underlying sources. The passage of these sources through an unknown mixing medium results in these observed multichannel signals. This study focuses on BSS, with special emphasis on its application to the temporomandibular joint disorder (TMD). TMD refers to all medical problems related to the temporomandibular joint (TMJ), which holds the lower jaw (mandible) and the temporal bone (skull). The overall objective of the work is to extract the two TMJ sound sources generated by the two TMJs, from the bilateral recordings obtained from the auditory canals, so as to aid the clinician in diagnosis and planning treatment policies. Firstly, the concept of 'variable tap length' is adopted in convolutive blind source separation. This relatively new concept has attracted attention in the field of adaptive signal processing, notably the least mean square (LMS) algorithm, but has not yet been introduced in the context of blind signal separation. The flexibility of the tap length of the proposed approach allows for the optimum tap length to be found, thereby mitigating computational complexity or catering for fractional delays arising in source separation. Secondly, a novel fixed point BSS algorithm based on Ferrante's affine transformation is proposed. Ferrante's affine transformation provides the freedom to select the eigenvalues of the Jacobian matrix of the fixed point function and thereby improves the convergence properties of the fixed point iteration. Simulation studies demonstrate the improved convergence of the proposed approach compared to the well-known fixed point FastICA algorithm. Thirdly, the underdetermined blind source separation problem using a filtering approach is addressed. An extension of the FastICA algorithm is devised which exploits the disparity in the kurtoses of the underlying sources to estimate the mixing matrix and thereafter achieves source recovery by employing the i-norm algorithm. Additionally, it will be shown that FastICA can also be utilised to extract the sources. Furthermore, it is illustrated how this scenario is particularly suitable for the separation of TMJ sounds. Finally, estimation of fractional delays between the mixtures of the TMJ sources is proposed as a means for TMJ separation. The estimation of fractional delays is shown to simplify the source separation to a case of in stantaneous BSS. Then, the estimated delay allows for an alignment of the TMJ mixtures, thereby overcoming a spacing constraint imposed by a well- known BSS technique, notably the DUET algorithm. The delay found from the TMJ bilateral recordings corroborates with the range reported in the literature. Furthermore, TMJ source localisation is also addressed as an aid to the dental specialist.
86

Three-dimensional study of facial changes in children aged 11-14 years

Kau, Chung How January 2007 (has links)
Conclusions: The following conclusions could be drawn from this study of facial morphology: 1. The three-dimensional laser capture technique described is both valid and reliable. 2. The study has shown that the use of three-dimensional imaging is a feasible method in the analyzing and perceiving of changes to the face over time. 3. Males and females show differing facial morphology. 4. The magnitudes of surface changes are larger in males than in females. 5. There is a significant difference in the timing of the surface changes in males than in females, with males exhibiting later changes. 6. There is forward growth particularly occurring in the nose, brows, lios and vertical dimensions of the face. 7. There seems to be a deepening of the eyes and flattening of the cheeks. 8. Clinicians should be aware of three-dimensional surface changes that result from growth and treatment. 9. Growth has been shown to be variable in this age group of 11-14 year olds. Some children have illustrated significant growth changes whilst others very little, and this may depend on the period of capture related to their growing period. 10. There was a difference between the facial morphology of females who received and did not receive orthodontic treatment. These differences were seen particularly in the upper and lower lip regions. 11. However, there was very little difference in individuals who received and did not receive orthodontic treatment. 12. Asymmetric growth patterns were seen occurring in 35% of the cohort studied with right sided differences being more than left sided differences.
87

Development of an ex-vivo co-culture system to model pulpal infection by Streptococcus anginosus group bacteria

Roberts, Jessica L. January 2010 (has links)
A reproducible model of infection of dental tissues by SAG bacteria has been produced which shows attachment patterns of bacteria and the effect on host tissues. This model can be used to further investigate processes involved in endodontic infections, including expression of virulence factors by bacteria and host response from the dental tissues. It may also be used in the future for testing novel antimicrobials for use in treating pulpal disease.
88

The effects of surface modification on the osseointegration of titanium dental implants

Colombo, John Samuel Lawrence January 2010 (has links)
In vitro , BMSCs cultured on M appeared more rounded, while they were more elongated on GB or TCP. BMSCs attached preferentially to M. The matrix formed appeared as a thin layer covering M, while matrix was thicker on the GB and TCP surfaces, infilling topographical features. Surface modification appeared to have little effect on the osteogenic activity of BMSCs. However, titanium was found to suppress differentiation down the adipogenic pathway and expression of inflammatory cytokines compared to plastic. Surface modification appeared to have little effect on osteoblasts activity or osseointegration, although roughened surfaces may provide better mechanical interlocking with bone. In vivo, no differences in the progression of osseointegration around any of the modified surfaces were observed. In DM, osteoblasts activity was altered and bone healing was delayed. There is therefore clearly scope to investigate surface modifications such as biomimetic coatings for use in compromised clinical situations.
89

Fatigue studies on dental composites and bonding systems

Padipatvuthikul, Pavinee January 2007 (has links)
Introduction: Adhesion has become an important concept in modern restorative dentistry. It offers the ability to bond materials to the tooth without invasive tooth preparation. Numerous in-vitro strength tests have been used to determine the bond strength of adhesive systems. However, because the occlusal forces applied to. a restoration are complex, and made up of a combination of forces, no one test can satisfactorily predict the in-vivo behavior of an adhesive system. The majority of bond strength studies have used monotonic tests to assess the bond strength of materials and between the materials and the tooth. These tests are expedient, but do not simulate the cyclic forces that operate in the mouth. Tests that characterize this type of . stress are called fatigue tests. Fatigue can result in wear and fracture of materials or bonds. .Objectives: To investigate fatigue behavior of modern resin composites and resinbonded joints of both metal to enamel and ceramic to enamel. The main approaches to fatigue assessment, 'Fatigue Limit' and 'Fatigue Life'were compared Materials and Methods: Surface effects of fatigue One hundred and eighty samples of two historical composites1-2 and seven modern composites3 - 9 were subjected to 2000 stress cycles between 0 and 120N or 0 and 400N. Surface damage was measured as the diameter of the fatigue scar and subsurface damage was determined by silver nitrate staining. The hardness of both the surface and subsurface was also determined. Fracture Composite to composite Two hundred and twenty composite disks were fabricated using three materials.7 • 9 After one day, one week, four weeks, and twelve weeks, fifty-five specimens of each material were removed from' water and divided into three groups of fifteen and one group of ten. Each group of samples was treated with one of three bonding systems10- 12 before adding a sec~nd increment. For each material, ten samples were subjected to Shear test in a Universal Testing Machine13 (CHS= 50 mmlmin). The fatigue limit test using fifteen samples per group were used to determine the fatigue limit using the staircase method (Draughn 1979). Metal or Ceramic to Enamel (via resin) Three hundred and forty-two discs of Ni/Cr-alloy14 were cast and treated by either sandblasting with aluminium oxide, or by sandblasting followed by electrolytic-etching in HCI. The disks were bonded to etched enamel with one of three dental bonding systems.1S - 17 One hundred and seventy-one ceramic disks were fabricated by sintering ceramic powder.18 One surface of each disk was etched with porcelain etching-gel19 for fifteen minutes and sandblasted with 50 J.Im A120 3. The prepared disks were then divided into three groups and were bonded to etched enamel using one of three dental bonding systems.1S - 17 Ten specimens of each group were sUbjected to a shear bond test (CHS 50 mm/min) and seventeen specimens of each group to a staircase fatigue test to determine the fatigue limit of the bonds. The remaining specimens from each group were placed in the custom made fatigue testing machine and allowed to cycle to failure between 0-20 kg, 0-10 kg or 0-5 kg (n=10 per load). The number of cycles at failure was analysed by Weibull statistics to determine the fatigue life Results: The surface studies in composites indicated that both surface and subsurface damage increased with increasing load. In general, small-particle composites experienced less damage than the large particle materials. At 12 kg, the surface damage was inversely proportional to the surface hardness, whereas at 40 kg, it was proportional to the subsurface hardness. At both loads, subsurface damage was directly proportion to subsurface hardness. For the composite to composite bonds, the fatigue limit values were approximately 30% of the shear bond strength values and the values were significantly different (p<0.01) for all nine groups. For metal to enamel bonds, the fatigue limit (after 5000 cycles) varied between 10.7 and 16.8 MPa compared to 21.3 and 48 MPa for the shear strength. The values for all groups was significantly different (p<0.001). There was no significant correlation between the shear bond strength and the fatigue limit values (Pearson Correlation P<0.01). For all groups, the threshold stress at which the samples equid withstand over one million cycles (fatigue Life) was 2.5 MPa. For ceramic to enamel bonds, the fatigue limit (after 5000 cycles) varied between 11.41 and 13.74 MPa compared to 21.3 and 48 MPa for the shear strength. The values for all groups were significantly differ~nt (p<0.001). There was no significa~t correlation between the shear bond strength and the fatigue limit values (Pearson Correlation P<0.001). For all groups, the threshold stress at which the samples could withstand over one million cycles (fatigue Life) was 2.5 MPa. Conclusion: Fatigue damage to the surface and subsurface of composite was related to the hardness of the material. The values of the fatigue limit were significantly lower than the shear bond strength values. There was no correlation between fatigue limit and shear bond strength. The long term safety limit for resin bonded joints to enamel is 2.5 MPa. Neither the shear test, nor the fatigue limit test was an accurate predictor of the long-term fatigue behaviour of resin-bonded restorations. A fatigue limit test using 100,000 cycles may be a useful predictor of the fatigue life which, in these studies, was half of the fatigue limit at 100, 000 cycles but the only reliable test is to test to failure. The data presented in this thesis indicated that the shear bond strength is not pred!ctor of long term failure. lClearfil Posterior, Cavex. Holland. 20cclusin. ICI. UK. 3Concise, 3M. USA. 4Admira, VOCO, Germany. 5Grandio. VOCO. Germany. 6Grandio Flow, VOCO, Germany. 7Spectrum, Dentsply, Germany. 8Durafill VS, Heraeus Kulzer, Germany. 9Herculite XRV, Kerr, USA. 10Prime&Bond. Dentsply, Germany. 110ptibond solo plus, Kerr, USA. 12BisGMAffEGDMA. 3M ESPE. USA. 13Nene Instruments Ltd.• UK. 14yerabond II, Aalba Dent Inc., USA. 15Calibra with Prime & Bond Resin, Dentsply, Germany. 16Panavia with ED-Primers. Kuraray, Japan. 17Nexus with Optibond Solo Plus Resin, Kerr, USA. 18Vitadur Alpha, VITA Zahnfabrik. Germany. 19Porcelain Etch-it gels, American Dental Supply. USA.
90

Redefining professional roles in healthcare : the business of dentistry

Dancer, Joanna M. January 2010 (has links)
No description available.

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