Noor Hayaty Abu Kasim | University of Malaya, Malaysia (original) (raw)

Papers by Noor Hayaty Abu Kasim

OBJECTIVES: The aim of this study was to analyse micromotion and stress distribution at the conne... more OBJECTIVES: The aim of this study was to analyse micromotion and stress distribution at the connections of implants and four types of abutments: internal hexagonal, internal octagonal, internal conical and trilobe. METHODS: A three dimensional (3D) model of the left posterior mandible was reconstructed from medical datasets. Four dental implant systems were designed and analysed independently in a virtual simulation of a first molar replacement.

Induced pluripotent stem cell-based therapy for treating genetic disorders has become an interest... more Induced pluripotent stem cell-based therapy for treating genetic disorders has become an interesting field of research in recent years. However, there is a paucity of information regarding the applicability of induced pluripotent stem cells in dental research. Recent advances in the use of induced pluripotent stem cells have the potential for developing disease-specific iPSC lines in vitro from patients.

ABSTRACT The aim of this study was to assess the wear of tungsten carbide burs and round rotary d... more ABSTRACT The aim of this study was to assess the wear of tungsten carbide burs and round rotary diamond instruments through measurements of rake angle and visual observations respectively under a field emission scanning electron microscope. Sixty short and long head pear-shaped tungsten carbide burs and 18 round rotary diamond instruments that had been used to complete< 5,> 5 and> 10 cavity preparations (n= 10/group) were selected from the 3rd and 4th year dental students, Faculty of Dentistry, University of Malaya.

ABSTRACT The main objective of this study was to assess knowledge on tooth bleaching among patien... more ABSTRACT The main objective of this study was to assess knowledge on tooth bleaching among patients visiting dental health care centres in Klang Valley. A total of 200 patients were conveniently selected and interviewed using structured questionnaires. Among the 200 respondents, 75.5% knew about bleaching.

Abstract: Eleven compounds: goniomicin A (1), goniomicin B (2), goniomicin C (3), goniomicin D (4... more Abstract: Eleven compounds: goniomicin A (1), goniomicin B (2), goniomicin C (3), goniomicin D (4), tapisoidin (5), goniothalamin (6), 9-deoxygoniopypyrone (7), pterodondiol (8), liriodenine (9), benzamide (10) and cinnamic acid (11), were isolated from the stem bark of Goniothalamus tapisoides. All compounds were identified by spectroscopic analysis and, for known compounds, by comparison with published data.

The purpose of this study was to validate the use of digital dental study casts obtained from Con... more The purpose of this study was to validate the use of digital dental study casts obtained from Cone beam CT Scan (CBCT) against gold standard; that is traditional dental study cast measured with digital caliper.

Thirty-four study casts of Malaysian Aborigines were selected from Centre of Malaysian Pribumi Studies Databank. Palatal depth of each study casts were measured using Mitutoyo digital caliper. Subsequently, all the study models were scanned using i-CAT CBCT and the palatal depth were measured using i-CAT software. Data were analysed using SPSS version 12.0 where Intraclass correlation and paired T-test were employed.

There was no significant difference in palatal depth between CBCT and Mitutoyo digital caliper (p>0.05). Average measures for Intraclass Correlation is 0.753 indicate that it is consistently good.

Within the limitation of this study palatal depth measurement produced by CBCT was as accurate as the digital caliper. However, more samples and parameters should be added to further substantiate the result of this study.

The purpose of this study was to investigate the light intensity of selected light curing unit wi... more The purpose of this study was to investigate the light intensity of selected light curing unit with varying distance and angulation of the light curing tip and lightmeter.

Four types of light units; Spectrum 800 (Dentsply), Coltulux 3 (Coltene), Elipar FreeLight 2 (3M Espe) and Starlight Pro (Mectron) were evaluated for light intensity at various distance between the light curing tip and the lightometer Cure Rite Denstply (0, 1, 3, 5, 10 and 15 mm). The light curing units were angulated at 45 degrees, 60 degrees and 90 degrees at a standardized 5 mm distance.

The intensity of light curing is affected by the distance between the light curing tip and the lightmeter. However, the decrease in light intensity of the light curing unit was found not to obey the inverse square law for the distances 0 to 15 Mm.

The study found that there was no significant difference between 45 degrees and 600 angulation between the light curing tip and the lightmeter. However, the decrease in light intensity is significant when compared to the light tip is placed perpendicular (90 degrees) to the aperture of the light meter.

This paper focuses on the usage of a novel binder system base on palm oil product to produce sint... more This paper focuses on the usage of a novel binder system base on palm oil product to produce sintered parts of stainless steel 316L produced by vertical injection molding technique for biomedical application. The stainless steel 316L powder was mixed using z-blade mixer with the thermoplastic binder system comprising of polyethylene, paraffin wax, stearic acid and palm stearin which was derived from palm oil at different volume percent (%). The feedstock then was studied in term of viscosity and shear rate using capillary rheometer. The feedstock was molded using vertical injection molding machine. After molding, the green molded part was immersed into the solvent to extract part of the binder system followed by sintering under vacuum atmosphere at the temperature of 1360 degrees C. The physical and mechanical properties of the sintered part such as density, hardness, shrinkage, ultimate tensile strength and elongation were measured. Biocompatibility study of in vitro test using cell osteosarcoma MG-63 was observed and discussed.

Objective: The main purpose of this paper is to present a new method of predicting clinical perfo... more Objective: The main purpose of this paper is to present a new method of predicting clinical performance using mechanical loading in a ball mill.

Methods: A series of four experiments (two involving a hybrid composite and one each on orthodontic brackets and bands) is described in which the ball mill was used to subject specimens to mechanical fatigue.

Results: A reproducibility study using composite beam specimens showed no significant difference between the Mean Survival Time (MST) in all the three experimental runs (P = 0.42). When subjected to thermal cycling, the MST of the cycled group was 155.0 min compared to 247.0 min fur the control group (P < 0.01). The MST of untreated and sandblasted brackets was 7.9 h and 14 h respectively (P < 0.01). There is also a significant difference (P < 0.001) in the MST of sandblasted bands when compared to the untreated bands.

Conclusions: The ball mill proved to be a convenient and reproducible means of producing mechanical fatigue and may be useful in predicting the clinical performance of dental materials.

Objective: To analyse thermo-mechanical stress in endodontically treated teeth restored with Mult... more Objective: To analyse thermo-mechanical stress in endodontically treated teeth restored with Multilayered Structured Dental Posts (MSDPs) under cold and hot conditions using Finite Element Analysis (FEM). Methods: Three MSDPs of multilayer design of xTi-yHA composition added to a zirconia layer (model A), an alumina layer (model B) and a titanium layer (model C) were compared with zirconia (model D) and titanium (model E) posts. The fractions of Ti and HA was varied gradually. Changes in temperature of an endodontically restored tooth model were calculated as a result of hot and cold response. The resulting thermo-mechanical stresses were analysed and compared using FEM in models A, B, C, D and E. Results: It was noted that Models A, B and C returned to near body temperature better than that Models of D and E. There was no evident difference in all MSDPs models. The smallest Von Mises thermal stresses were observed in MSDPs (models A, B and C) compared to models D and E. There were no also differences in Von Mises thermal stresses for all MSDPs. The magnitude of interface of stresses in models D and E with the surrounding tooth structures were greater than those in MSDPs especially in area close to middle third of the dental posts. The peak stress by thermal irritant for models D and E are approximately three times higher than models A, B and C. Conclusion: The findings of this study showed that pure zirconia and titanium posts produced greater thermal stresses than MSDPs.

Objectives: This study aim to evaluate the cutting efficiency of tungsten carbide burs (TC) and r... more Objectives: This study aim to evaluate the cutting efficiency of tungsten carbide burs (TC) and rotary diamond instruments by measuring their rake angle and visual examination of their cutting surfaces respectively, using scanning electron microscopy (SEM).

Materials and Method: 60 short and long head pear-shaped TC and 18 round rotary diamond instruments that had been used to prepare < than 5, > than 5 and > than 10 cavities were selected from the 3rd & 4th year dental students, Dental Faculty, University of Malaya. 12 cylindrical and flame rotary diamond instruments were also selected from the 5th year students. The rake angle of TC was measured and surfaces of diamond instruments were evaluated using Field Emission Scanning Electron Microscope (FESEM). Each test group comprised of 10 samples and new burs constituted the control group. The data were analysed descriptively and statistically using Two-way ANOVA, SPSS version 12.

Results: The rake angles of control, < than 5 and > than 5 groups were significantly higher compared to > than 10 groups, p< .05. Rotary diamond instruments used to prepare < than 5 cavities showed intact diamond particles with distinct cutting facets comparable to control group. Instruments used to prepare > than 10 teeth showed blunt and dislodged diamond particles.

Conclusions: The rake angle of TC is significantly lower and diamond instruments showed blunt diamond particles after cutting > than 10 preparations.

Objective: This study evaluated the effect of an active oxygen based disinfectant, 2% Perform® (S... more Objective: This study evaluated the effect of an active oxygen based disinfectant, 2% Perform® (Schulke & Mayr, Germany) on the dimensional accuracy of four alginates, Alginoplast (Heraeus Kulzer, Holland), Kromopan (LASCOD, Italy), Alginmax (MAJOR, Italy) and Duplast (Dentsply, China). Method: A cobalt chromium master model with four cylindrical studs representing 2 canines and 2 molars was constructed. A total of 40 impressions for each alginates were taken and treated in 4 different conditions, Immediate pour (control); 10 minutes immersion in distilled water; 10 minutes immersion in 2% Perform® and 30 minutes in 2% Perform®. The impressions were then poured in Type III stone. Dimensional changes between the master model and the resultant casts were measured using traveling microscope. The % change at an antero-posterior dimension (C) and 3 different interarch dimensions (A,B and D) were noted. Results: Two way ANOVA showed significant interaction between alginates and treatment conditions except for dimension B and D. One-way ANOVA test and Student-Newman-Keuls indicated no significant difference (P> 0.05) in dimensional accuracy of impressions treated with Perform® for 10 minutes compared to the control group except for Alginoplast (dimension A) and Duplast (dimension C and D). The maximum deviation in the dimension after 10 minutes Perform® immersion was 0.552% for Duplast and 0.147% to 0.213% for other alginates. Immersion in Perform® for 30 minutes produced maximum deviation of 0.591% for Duplast in dimension C whilst 0.223% to 0.235% for other alginates. Conclusion: Active oxygen based disinfectant has an effect on the dimensional accuracy of the resultant cast for the 4 alginates. Although some results indicated significant change, the magnitude of deviation was clinically negligible. Apart from Duplast, all the alginates indicated good stability in 2% Perform® even up to 30 minutes of immersion time. (This study was supported by University of Malaya ; R&D FO200/2003D)

This article focuses on the physical characterization of Silverfil (R) amalgam. Analysis of the a... more This article focuses on the physical characterization of Silverfil (R) amalgam. Analysis of the amalgamated material semi-quantitatively showed that Silverfil (R) comprised of approximately two thirds mercury and one third silver. No other elements were detected. Examination of the amalgamated material by x ray mapping and metallographically showed no evidence of free mercury present. Silverfil (R) has strong affinity towards the mercury ion. X-ray Diffraction analysis showed that the amalgamated Silverfil (R) is similar to a mineral in nature called "Moschellandsbergite". The advantages of Silverfil (R) over conventional amalgam were highlighted.

Introduction: Owing to the variety of materials and methods employed, comparison of the results a... more Introduction: Owing to the variety of materials and methods employed, comparison of the results and findings from bonding studies is difficult. Until recently, several types of teeth have been used in published research papers as a substrate in orthodontic bonding research including bovine incisors, fresh and rebonded human premolars.

Objectives: The purpose of this study was to compare the shear bond strength of an adhesive bonded to different tooth surfaces (human premolar, bovine incisor and rebonded human premolar).

Methods: Two groups of thirty premolar teeth and one group of bovine incisors had brackets attached in a standardized manner using Transbond XT (3M Unitek). The adhesive was cured using conventional halogen light and a specially designed tool to standardize the distance between the light curing tip and the adhesive. The debonding force was measured using Instron universal testing machine. ANOVA and Post Hoc Dunnett C test were performed to determine any significant difference among groups (p<0.05).

Results: The results of Post Hoc Dunnett C test indicated no statistical differences between the human premolar group and rebonded group. However, the differences existed in bond strength
between bovine group versus human premolar group and bovine group versus human rebonded premolar group. Bovine group had the highest bond strength with mean values of 8.5 (S.D ± 4.2) MPa. Human premolar and rebonded groups had mean bond strengths of 6.1(S.D ± 4.5) and 4.9 (S.D ± 2.7) MPa, respectively.

Conclusions: This study revealed that bovine teeth produced higher bond strength compared to b o t h f r e s h a n d re b o n d e d h u m a n p r e m o l a r. Therefore, findings in any bond strength studies u s i n g b ovi n e t e e t h s h o u l d b e i n t e r p re t e d wi t h caution.

Objectives: To identify the nature of multiple intelligences among dental students and investigat... more Objectives: To identify the nature of multiple intelligences among dental students and investigate the relationship between these intelligences and performance in the various skill areas of dentistry. Methods: Sixty-one final year dental students at the Faculty of Dentistry, University of Malaya in Malaysia were administered a Multiple Intelligence Inventory [(MII), David Larear, 1991)] after their final written examinations. MII comprised 80 4-point likert items assessing eight types of multiple intelligences: Verbal/Linguistic, Visual Spatial, Logical Mathematical, Musical Rhythmic, Intra Personal, Body Kinesthetic, Inter Personal and Naturalist. These intelligences were correlated with six academic performance scores: Amalgam Class II, Composite, Crown & Bridge, Endodontic, Problem Based Learning and the Final Written Exam. The data were analysed by Pearson Product Moment Correlation and t-test. Results: Significant correlations were found between Intrapersonal intelligence and Composite (r = .32; p < .05) and between Body Kinesthetic and Composite scores (r = .26; p < .05). High Amalgam Class II scorers obtained significantly higher scores on Intrapersonal Intelligence than low scorers (t = 2.49; p < .05). High Composite scorers have significantly higher Body Kinesthetic intelligence than low scorers (t = .29; p < .05). Low endodontic scorers obtained significantly higher scores on Visual Spatial intelligence than high scorers (t = 2.06; p < .05). High PBL scorers obtained significantly higher Interpersonal (t = 2.06; p < .05) and Naturalist Intelligence (t = 3.57; p < .05) than low scorers. Conclusions: There appears to be no significant correlations between the various types of multiple intelligences and achievement in dentistry except for the correlations between Composite scores and Intrapersonal and Body Kinesthetic Intelligence. Generally, there were no significant multiple intelligence differences among high and low performers.

In the implementation of criterion-based assessment some disparities in the interpretation of the... more In the implementation of criterion-based assessment some disparities in the interpretation of the assessment criteria have been observed.Therefore it is essential that a standardization exercise be carried out to ensure equitable and fair assessment. Objectives: The purpose of the study was to evaluate inter-examiner variability and examiners' internal consistency in applying a criterion-based assessment. Method: The subjects consisted of 9 full-time staff of the Department of Conservative Dentistry, University of Malaya, 4 part-time staff and 2 postgraduate students. One buccally-approached and one palatally-approached Class III cavity preparation were assessed according to a set of criteria developed by the department. Both preparations were cut by undergraduates in their preclinical year of study. Examiners rated each cavity on a 5-point scale (1=Redo, 2=Modification required, 3=Pass with minor mistakes, 4=Pass, and 5=Good). Ratings were analyzed based on the Many-facet Rasch model using its computer application, Facets, version 3.48.0. Results: Varying levels of examiner severity were found ranging from -1.99 logits to 0.18 logit. However, the majority of the examiners fall between -1.04 logits and -0.31 logit. The percentage of exact agreement was 45.5%. Several examiners were found to be inconsistent in their ratings as indicated by the Infit and Outfit mean-square statistics. Results also revealed range restrictions amongst some examiners. With respect to the assessment criteria, some were misfitting; these include (1) shape of cavity outline, (2) bevel width, (3) bevel thickness, (4) preservation of contact point and (5) placement of labial wall. On the other hand, several criteria demonstrated high agreement amongst examiners. These were (1) 90o cavo-surface angle, (2) rounded internal line angle, and (3) contour of axial wall. Conclusions: This study has highlighted the need for standardization of assessment criteria intepretation and better staff training in the assessment of preclinical students' operative skills.

Objective: To compare the surface microhardness of composites(Spectrum®TPH, Filtek™Z350, Ceram•X ... more Objective: To compare the surface microhardness of composites(Spectrum®TPH, Filtek™Z350, Ceram•X mono and Ceram•X duo-enamel shade) before and after immersion in alcohol containing mouthrinses (Listerine), alcohol-free mouthrinses (Oral-B) and experimental herbal mouthrinses based on plant extract (mouthrinses X, Y and Z). Methods: 60 disc-shaped specimens of approximately 10mm x 2mm were perpared from various composites using perspex split mould and was cured for 40 seconds. The irradiated surface was polished using Sof-Lex pop-on polishing discs. The specimens were randomly divided to 6 groups. Microhardness was recorded before immersion (control group) using a load of 200g for 15 seconds using Vickers microhardness tester, (Shimadzu Corp, Kyoto, Japan). All specimens were then immersed in 20ml of Listerine,Oral B- Tooth and gum care alcohol-free mouth rinses, Experimental Mouth rinses X, Y and Z and distilled water for 24 hours at 37º C, after which micro hardness value was measured again. Data collected was analyzed using one-way ANOVA / Games-Howell post-hoc test for multiple comparisons between groups. Specimens were also subjected to surface analysis using AFM (Ambios Technology Universal Scanning Probe Microscopy™).Results: Filtek Z350 exhibited the highest Vickers microhardness number (VHN) and Ceram X Duo had the lowest VHN before immersion. All tested composite showed significant decreased in surface microhardness (VHN) compared to before immersion. Filtek Z350 showed the highest VHN and TPH Spectrum showed the lowest VHN after immersion. Ceram X Duo showed the roughest surface before immersion. The surface roughness of Ceram X Mono was high when immersed in experimental mouthrinses. Conclusions: Filtek Z350 exhibited significantly higher VHN compared to other composites tested. All composites showed significant decreased in VHN compared to before immersion. There was no significant different of VHN between mouthrinses, however it was material dependent. This study was supported by the Vot F:Grant no F0350/2005C, University of Malaya.

Objectives: This study is an attempt to enhance the properties of conventional PMMA denture mater... more Objectives: This study is an attempt to enhance the properties of conventional PMMA denture material by incorporation of a polyfunctional polyol derived from palm oil by copolymerization with methyl methacrylate monomer to overcome the low fatigue resistance property of PMMA.

Methods: A series of copolymerizations of palm oil polyol with MMA was performed in solution. The polyol was added from 40-20 %, MMA from 20-40% , benzoyl peroxide as initiator was at 0.04% and toluene used as solvent was at 60 % of the total weight. The copolymerization was carried out in a 500ml-round-bottom reaction flask, equipped with a magnetic stirrer, for 7.5 hour at 80ºC, in a water bath. The yield of each copolymerization obtained was recorded and the conversion was estimated gravimetrically. Later, the polymers acquired were analyzed by FTIR.

Results: The copolymerizations have achieved conversions that ranged from 24% to 95%, where the higher conversion was obtained when the reactant mixture contain higher amount of MMA. The reaction produced a clear color, light-weighted copolymer that has the potential to be developed as denture material. The evidence of incorporation of the polyol into PMMA was given by the FTIR measurements, by comparing the spectrum of the copolymer to the spectrum of PMMA and polyol. Evaluations of the mechanical properties were currently being carried out.

Conclusion: The new copolymers have potential of being developed into new dental materials. The branching structure of the copolymer was expected to improve the impact strength of PMMA. In addition, the palm oil based polyol was made from natural sustainable material.

This study was supported by E-Science fund, Grant No.: 03-0103-SF0190 and University of Malaya, Postgraduate Research Vote Grant No. : PS 079C/ 2007C and National Science Fellowship (NSF 2007/2008).

Objective: The aim of this study was to investigate the degree of conversion and cross-linking of... more Objective: The aim of this study was to investigate the degree of conversion and cross-linking of polyurethane dimethacrylate (PUDMA), derived from palm oil polyol, for dental resin application.

Methods: Polyurethane dimethacrylate was synthesized by reacting excess amount of Methylene diphenyl diisocyanate (MDI) with palm oil polyol. The resulting isocyanate polyurethane prepolymer was then acrylated using hydroxymethacrylate (HEMA). Fourier transform infrared spectroscopy was used to ascertain the formation of PUDMA, and to determine the degree of conversion (DC) of: I) PUDMA, II) Bis-GMA, III)Bis-EMA,IV) Bis-GMA/TEGDMA (3:1), V) Bis-GMA/TEGDMA(3:1)/Bis-EMA (3:1), VI) PUDMA/Bis-EMA (3:1), VII) Bis-GMA/TEGDMA(3:1)/PUDMA (1:1), and VIII) Bis-GMA/TEGDMA(3:1)/PUDMA/Bis-EMA (1-1-1). The photo initiator system Camphorquinone (CQ) and Ethyl-4-N,N-dimethylaminobenzoate (EDMAB) was used with ratio 0.25% and 0.75% by weight, respectively, for all monomers. The results were analyzed using one way ANOVA and Post Hoc Dunnett T3 for multiple comparisons.

Results: The FTIR spectrum of PUDMA showed that the isocyanate peaks was absent and appearance of urethane peak. The results of degree of conversion showed that, the unreacted C=C in Bis-GMA is more than 50 %, however, the DC of PUDMA is 63% with cross linking 0.4. The resin systems which contain PUDMA showed higher DC and cross-linking than that of other resin system.

Conclusions: The degree of conversion of PUDMA monomer is highly significant than Bis-GMA, with more cross-linking. The PUDMA could improve the DC and cross-linking of resin system. Therefore, PUDMA may have promising mechanical properties and biocompatibility.

Objectives:Biocompatibility is an important desirable property for a dental polymer and it can be... more Objectives:Biocompatibility is an important desirable property for a dental polymer and it can be achieved by utilizing more materials from natural sources. The flexural strength of an experimental polymer prepared from MMA monomer modified with palm-oil polyol was compared to two commercial resins,namely the Lucitone 199® (Dentsply Trubyte, USA) and Impact (Ivoclar Vivadent, Liechtenstein). Methods: The experimental polymer was prepared by copolymerizing MMA monomer and palm oil polyol. The resulting polymer was cast into a plate form and sectioned using a precision diamond saw (Buhler, Germany) to form 10 specimens of dimension, 65mm x 11mm x 5mm. These specimens were then polished to achieve a nominal dimension of 64mm x 10mm x 3.3mm. Another 10 specimens were prepared using Lucitone 199® and Impact according to the manufacturers' instructions and were polished by the same procedure. Their flexural strengths were determined using a three point bend test on an Instron Universal Testing Machine (Anytown, Australia)according to the procedure of test method ISO 1567. Data obtained was analysed using Oneway ANOVA (SPSS 12.0) at 95% confidence interval. Results: The mean flexural strength of Lucitone 199® was 127.39MPa (±16.54), Impact was 177.57MPa (±11.44) and experimental polymer was 51.62MPa (±4.21). Although the experimental polymer has exhibited higher flexural strength than PMMA homopolymer, it has lower flexural strength when compared to Lucitone 199® and Impact denture base resins, both of which were filler-reinforced materials. Conclusions:In this preliminary study, the experimental polymer contained a significant proportion of non-petroleum based materials derived from palm oil. Its lower flexural strength is expected to be enhanced and improved through the incorporation of reinforcing fillers or fibers in future work.

There was no significant difference in palatal depth between CBCT and Mitutoyo digital caliper (p>0.05). Average measures for Intraclass Correlation is 0.753 indicate that it is consistently good.

Conclusions: The ball mill proved to be a convenient and reproducible means of producing mechanical fatigue and may be useful in predicting the clinical performance of dental materials.

Conclusions: The rake angle of TC is significantly lower and diamond instruments showed blunt diamond particles after cutting > than 10 preparations.

Objectives: The purpose of this study was to compare the shear bond strength of an adhesive bonded to different tooth surfaces (human premolar, bovine incisor and rebonded human premolar).

This study was supported by E-Science fund, Grant No.: 03-0103-SF0190 and University of Malaya, Postgraduate Research Vote Grant No. : PS 079C/ 2007C and National Science Fellowship (NSF 2007/2008).