Biomedical subjects

A U Yap

Publications and source records attributed to A U Yap.

At least 19 recordsLinked to original sources

PubMed2001

On-line computerized diagnosis of pain-related disability and psychological status of TMD patients: a pilot study.

Temporomandibular disorders (TMD) is a collective term embracing a number of clinical problems, which involve the masticatory musculature, the temporomandibular joint or both. Virtually all theories dealing with the aetiology and treatment of TMD have recognized the importance of psychological factors. This paper reports the development of a computerized on-line program (NUS TMD v1.1) for the diagnosis of pain-related disability and psychological status of TMD patients based on Axis II of the research diagnostic criteria (RDC)/TMD (Dworkin, S.F. & LeResche, L. 1992. Journal of Craniomandibular Disorders: Facial Oral Pain, 6, 301), which was developed to redress the lack of diagnostic criteria in TMD research. Methods adopted by RDC/TMD for use in assessing Axis II status include a seven-item questionnaire for grading chronic pain severity, the Symptom Checklist 90 Revised (SCL-90-R) and a jaw disability checklist. A pilot study, based on 37 new TMD patient records, was conducted to study the pain-related disability and psychological status of TMD patients using this newly developed program. The mean age of the predominantly Chinese population (86.5%) was 32.19 years (range 20-72 years) with a sex distribution of 24 females and 13 males. Most patients (78%) had low disability, with 12 patients having low intensity and 17 patients having high intensity pain. Approximately 73% of the sample population were moderately or severely depressed. Patients that were moderately and severely depressed had significantly higher scores for limitation related to mandibular functioning than normal patients. The three most frequent jaw disabilities were: eating hard foods (84%), yawning (78%) and chewing (65%).

Activities of Daily Living↗

PubMed2001

Chemical degradation of composite restoratives.

The chemical environment is one aspect of the oral environment, which could have an appreciable influence on the in vivo degradation of composite restoratives. The effects of chemical media on surface hardness of four composite restoratives (Silux [SX], Z100 [ZO], Ariston [AR] and Surefil [SF]) were investigated. The relationship between hardness and the thickness of the degradation layer was also studied. Thirty six specimens (3 x 4 x 2 mm) were made for each material. Following polymerization, the specimens were stored in artificial saliva at 37 degrees C for 24 h. The specimens were then randomly divided into six groups of six, subjected to microhardness testing (load = 500 gf, dwell time = 15 s) and stored in the following chemicals for 1 week at 37 degrees C: artificial saliva (S), distilled water (W), 0.02 N citric acid (C), 0.02 N lactic acid (L), heptane (H) and 75-25% ethanol-water solution (E). After conditioning, the specimens were again subjected to hardness testing and sectioned. Change in hardness (DH) was computed and the thickness of the degradation layer (DL) was measured using a computerized image analysis system at 600x magnification. Results of statistical analysis (ANOVA/Scheffe's [P < 0.05]) of DH based on materials were as follows: SX - E > all other mediums; ZO - W > C; and AR - S, W, E > H (> indicates significantly greater hardness change). No significant difference in DH was observed between the different chemicals for SF. The effects of chemical media on DH were found to be material dependent. A significant but weak positive correlation (Pearson's correlation [P < 0.05]) exists between change in hardness and thickness of the degradation layer.

Analysis of Variance↗

PubMed2000

Influence of water exposure on three-body wear of composite restoratives.

The objective of this investigation was to study the influence of water exposure on the three-body wear of composite restoratives. A three-body wear instrumentation was used to investigate the wear resistance of five composite restoratives [Silux Plus (SX), Z100 (ZO), Ariston pHc (AR), Surefil (SF) and Tetric Ceram (TC)] with and without exposure to water. An amalgam alloy [Dispersalloy (DA)] was used as control. Ten specimens were made for each material. The specimens were conditioned in artificial saliva at 37 degrees C for 24 h and randomly divided into two groups of 5. The first group was subjected to wear testing immediately after the 24 h conditioning period, while the second group was conditioned in distilled water at 37 degrees C for 7 days prior to wear testing. All materials were wear tested at 15 N contact force against SS304 counter-bodies for 20,000 cycles with millet seed slurry as third-body. Wear depth (microm) was measured using profilometry, and results were analyzed by ANOVA/Scheffe's and independent sample t-tests at significance level 0.05. Ranking of wear resistance was as follows: without water exposure: DA > ZO > SF > AR > SX > TC; with water exposure: DA > ZO > SX > SF > AR > TC. Wear factor ranged from 2.20 for ZO to 7.13 for TC without water exposure and from 46.00 for ZO to 143.00 for TC with exposure to water. Exposure to water significantly increased three-body wear for all composite restoratives, but did not affect wear of the amalgam alloy. The effects of water exposure must be considered for the evaluation of wear in all polymeric composite restoratives.

Composite Resins↗

PubMed2000

Field amplified stacking injection--capillary electrophoresis for quantitative analysis of released methacrylic acid from dental composites.

Field-amplified stacking injection-capillary electrophoresis (FASI-CE) applied for the first time to the study of dental materials is demonstrated in this report. CE was used to separate methacrylic acid from the other degraded components. Due to the background electrolyte being weakly basic and methacrylic acid being negatively charged, in-capillary enrichment of the analyte was achieved by FASI. A detection limit of less than 50 ppb was obtained with good reproducibility (relative standard deviation < 3%). The method was applied to the analysis of four commercially available dental composites. Results showed that FASI-CE was effective in monitoring the fabrication process and product quality of restorative materials fabricated from methacrylate-based composites by analyzing the amount of methacrylic acid released from the residual methacrylate monomers.

Composite Resins↗

PubMed2000

Release of methacrylic acid from dental composites.

OBJECTIVE: The aim of this study was to investigate the release of methacrylic acid from four commercial dental composite restoratives (Silux Plus (3M), Z100 (3M), Ariston pHc (Vivadent) and Surefil (Dentsply)). METHODS: Three specimen disks (10(0.2) mm in diameter and 2(0.2) mm thick), were prepared for each material using custom-made molds. Each disk was placed in artificial saliva for 24 h at 37 degrees C, rinsed and subsequently immersed in 1.5 ml of deionised water in an airtight glass container. The container was continuously shaken at a speed of 80 rpm for 24 h at 37 degrees C in an orbital incubator. After 24 h (Day 1), the water was removed and analyzed. The specimen disk was then re-immersed into another 1.5 ml of fresh deionised water. The procedure of removing and refilling of the water was repeated for a total of 7 days. The sample solutions were filtered and injected into the capillary electrophoresis system for analysis immediately after collection. Statistical analysis was performed by ANOVA and Scheffe's test. RESULTS: For Days 1-7, methacrylic acid released in water at 37 degrees C by Ariston was significantly greater than that of the other composites. Ranking from least to greatest total (cumulative over 7 days) methacrylic acid release was as follows: Z100 (5.66 ppm) < Silux (8.81 ppm) < Surefil (20.21 ppm) < Ariston (519.04 ppm). Methacrylic acid release was greatest at Day 1 for all materials and generally decreased with time. SIGNIFICANCE: Some composites may release high levels of methacrylic acid. The biological effects of such high levels of methacrylic acid is not known and warrant further in vivo and in vitro investigations.

Analysis of Variance↗

PubMed2000

Comparative wear ranking of dental restoratives with the BIOMAT wear simulator. Part II. An SEM evaluation.

The qualitative wear of amalgam alloys and composite resins opposing cast chromium alloys after impact-sliding wear simulation with the BIOMAT wear simulator was assessed. An impact stress of 28 MPa was adopted to allow for stresses generated during parafunctional activities. The worn specimens were examined using SEM at both impact sites and region of sliding wear. For amalgam alloys, ranking from the smoothest to the roughest surface under SEM observation was as follows: unicompositional alloy>admixed alloy>gallium alloy. For composite resins the ranking was: microfilled composite>small particle composite>hybrid composite. The qualitative SEM assessment results were consistent with our earlier volumetric wear results and supports the hypothesis that surface microstructure affects wear. Composite selection for teeth opposing cast chrome prostheses should be done with caution and knowledge of the composition of the material as three-body wear may occur.

Composite Resins↗

PubMed2000

The effect of polishing systems on microleakage of tooth coloured restoratives: Part 1. Conventional and resin-modified glass-ionomer cements.

The purpose of this in vitro study was to investigate the effect of polishing systems on the microleakage of conventional and resin-modified glass-ionomer cements. Class V cavities were prepared at the cemento-enamel junction of 80 freshly extracted posterior teeth. The prepared teeth were randomly divided into two groups and restored with conventional or resin-modified glass-ionomer cements. The restored teeth were stored in distilled water at 37 degrees C for 1 week after removal of excess restorative with diamond finishing burs. The restored teeth were then divided into four groups of 10 and finished and polished using the following systems: Two Striper MFS; Sof-Lex XT; Enhance Composite Finishing and Polishing System; Shofu Composite Finishing Kit. The finished restorations were subjected to dye penetration testing. Results showed that the microleakage at dentin margins of conventional glass-ionomer cements and enamel margins of resin-modified glass-ionomer cements are significantly affected by the different polishing systems.

Analysis of Variance↗

PubMed2000

The effect of polishing systems on microleakage of tooth-coloured restoratives. Part 2: composite and polyacid-modified composite resins.

The purpose of this in vitro study was to investigate the effect of polishing systems on the microleakage of composite and polyacid-modified composite resins. Class V cavities were prepared at the cemento-enamel junction of 80 freshly extracted posterior teeth. The prepared teeth were randomly divided into two groups and restored with conventional or polyacid-modified composite resins. The restored teeth were stored in distilled water at 37 degrees C for 1 week after removal of excess restorative with diamond finishing burs. The restored teeth were then divided into four groups of ten and finished/polished using the following systems: Two Striper micron finishing system (MFS), Sof-Lex XT (Sof-Lex), Enhance composite finishing and polishing system (Enhance), and Shofu composite finishing kit (Shofu). The finished restorations were subjected to dye penetration testing. Results showed that the microleakage resistance at both enamel and dentin margins of composite and polyacid-modified composite resins are not significantly affected by the different polishing systems.

Adhesives↗

PubMed2000

Effects of aging on repair of resin-modified glass-ionomer cements.

The effects of aging on the repair bond strengths of resin-modified glass-ionomer cements after different methods of surface conditioning were studied. Surface conditioning methods included the following: maleic acid; maleic acid with resin application; polyacrylic acid; polyacrylic acid with resin application. Shear bond testing between the aged and new material was carried out with an Instron Universal testing machine. Surface conditioning with maleic acid and resin application gave the highest repair bond strengths at 3 and 6 months. There was, however, no statistically significant difference in bond strengths between the different treatment groups after both 3 and 6 months storage. Intergroup comparisons revealed no significant difference in failure modes after both storage periods. For all treatment groups, no significant difference in repair bond strengths was noted between storage after 1 week, 3 and 6 months. There appears to be a general decrease in repair bond strengths for all treatment groups after 3 months storage. The clinical repair of resin-modified glass-ionomer cements after this period of time is therefore not recommended.

Acid Etching, Dental↗

PubMed1999

Acid-base complex reactions in resin-modified and conventional glass ionomer cements.

Resin-modified glass ionomer cements are a recent development in which the desirable properties of glass ionomer cements and resin-composites are combined. The presence of resin may, however, retard the acid-base reaction of the ionomer component. This has led to a debate regarding the classification of resin modified materials as true glass ionomer cements, and the actual duration of the acid-base reaction after initial setting via light polymerization has taken place. To investigate this issue, a novel method employing FT-IR spectrophotometry was used to monitor the acid-base complexation reaction in a resin-modified glass ionomer cement (Fuji II LC) and a conventional, chemically cured cement (Fuji II Cap). This method involved subtraction of the background "resin" spectrum from the Fuji II LC spectra and subsequent application of a baseline to obtain the plot of absorbance area ratio in the range of 1685 to 1510 cm(-1) (complexed carboxyls) to that in the range of 1750 to 1685 cm(-1) (free carboxyls). This study demonstrates evidence of a delayed acid-base reaction for the resin-modified cement, which levels off after 168 hours of cement mixing. In contrast, the complexation reaction of the conventional glass ionomer cement was essentially complete after 24 hours.

Glass↗

PubMed1999

Comparative wear ranking of dental restoratives with the BIOMAT wear simulator.

Fundamental in vitro wear tests are important for the study of wear mechanisms, provision of data during material development and screening of materials prior to clinical trials. The aim of this project was to compare the wear of six dental restoratives using the BIOMAT wear simulator which was developed to simulate jaw movements and stresses generated in the occlusal contact areas during the chewing process. The correlation of wear to hardness of the restoratives was also assessed. Wear ranking from the least to the most volumetric wear was as follows: high copper unicompositional alloy, Tytin (T) < high copper admixed alloy, Valiant PhD (V) < microfilled composite resin, Silux Plus (S) < gallium alloy, Galloy (G) < heavily filled composite resin, Z100 (Z) < hybrid composite resin, P50 (P). The high copper amalgam alloys had significantly greater wear resistance when compared with all the composite resins. The gallium alloy, microfilled and heavily filled composite resins also exhibited significantly less wear than the hybrid resin. Wear ranking with the BIOMAT simulator was similar to that obtained in vivo. Ranking from the hardest to softest material: high copper unicompositional alloy, T < gallium alloy, G < high copper admixed alloy, V < hybrid composite resin, P < heavily filled composite resin, Z < microfilled composite resin, S. The amalgam alloys were significantly harder than the heavily filled and microfilled composite resins. There was no apparent correlation between wear performance and material hardness.

Bisphenol A-Glycidyl Methacrylate↗

PubMed1999

Temporomandibular disorders--an overview.

Temporomandibular disorders (TMD) have been an area of increased clinical and scientific inquiry in dentistry. This is due to increased patient awareness and desire for treatment as well as scientific advances in the fields of epidemiology, neurobiology and diagnostic imaging. This article sets out to introduce this disorder and describes its aetiology and management.

Humans↗

PubMed1999

Temporomandibular disorders in rheumatoid arthritis.

OBJECTIVE: To determine the frequency and character of temporomandibular disorders (TMD) in Oriental patients with rheumatoid arthritis (RA) and to investigate the relationship between TMD and RA in a tertiary referral center. METHODS: Symptoms and signs related to TMD were investigated in 80 patients (67 female, 13 male) who fulfilled the American College of Rheumatology 1987 revised criteria for RA. Diagnoses of TMD including muscle, disk displacement, or temporomandibular joint (TMJ) disorders were made based on clinical assessment. TMJ disorder was then correlated with the clinical, laboratory, and radiological features of RA. RESULTS: The mean age of the study population was 49.7 years and the mean duration of RA was 86.9 months. Eleven patients (13.8%) had active RA at the time of TMD assessment. About 76% of the study population had seropositive disease and 62% had peripheral joint erosions. Osteoarthrosis of the TMJ was the most common TMD in this Oriental population. Joint sounds on opening (35%), joint sounds on moving sideways or forward (27.5%), and pain in jaw joints (23.7%) were common TMD symptoms. Deviated mouth opening (45%) and coarse crepitus (15-21.3%) were most prevalent on examination. CONCLUSION: Patients with RA who had prolonged disease duration of RA and active peripheral joints tended to have osteoarthrosis of the TMJ. Presence of rheumatoid factor or peripheral joint erosions was not associated with TMJ osteoarthrosis.

Adult↗

PubMed1998

Bruxing-type dental wear simulator for ranking of dental restorative materials.

An instrumented dental wear test simulator was developed to simulate jaw movement in the chewing process between two molar teeth. It simulated the natural impact with sliding masticatory action, known as bruxing (defined as the gnashing, grinding, or clenching of teeth) type of wear, in order to simulate a worst-case dental wear scenario. In vitro wear testing of dental restorative materials was performed. Impact and sliding wear were simulated on the machine, with water as the lubricant, on three metal alloys (Tytin, Valiant Ph.D., Galloy) and three composite resins (Silux Plus, Z100, P50). The impact force for each machine cycle was brought closer to the maximum natural masticatory forces by the use of a shock absorbing layer. To replicate the natural masticatory action, the specimens had a surface profile with the shape of a conical depression. Ranking of the materials' performance on the wear test simulator was seen to be consistent with published clinical ranking. Metal alloys showed greater wear resistance than composite resins. Among the different metal alloys, those with lower hardness and compressive strengths exhibited greater wear. Composite resins with large filler particles wore worse than those with small filler particles. Results were compared with previous work on impact with sliding on a flat surface without a cushioning layer. It was concluded that the magnitude of the impact force and the angle of approach during impact with sliding wear are important parameters in the in vitro wear ranking of dental restorative materials.

Bruxism↗

PubMed1998

Effects of storage, thermal and load cycling on a new reinforced glass-ionomer cement.

The objective of this in-vitro study was to determine the influences of storage, thermal and load cycling as well as combinations of these treatment procedures on the microleakage patterns of a new 'condensable' silver reinforced restorative glass-ionomer cement (Shofu Hi-Dense). Class II preparations with gingival margins in dentine were made on 50 freshly extracted, non-carious molar teeth and restored with Shofu Hi-Dense according to the manufacturer's instructions. The restorations were subsequently stored for 1 week, finished and randomly assigned into five groups of 10 and treated as follows: Group 1 - control (uncycled); Group 2 - thermocycled; Group 3 - mechanically load cycled; Group 4 - three months storage, uncycled; Group 5 - three months storage, thermal and load cycled. The storage medium throughout the experiment was artificial saliva at 37 degrees C. All treatment procedures had no significant influence on microleakage at the enamel-cement interface. These treatment modalities, however, resulted in a significant increase in leakage at the dentine-cement interface. With the exception of the 1 week storage, uncycled group, the dentine-cement interface had significantly greater leakage than the enamel-cement interface.

Cermet Cements↗

PubMed1998

Effects of stabilization appliances on nocturnal parafunctional activities in patients with and without signs of temporomandibular disorders.

This study was designed to investigate the short-term effects of stabilization appliances on parafunctional oral motor behaviour (bruxing and clenching) during sleep in patients with and without signs of temporomandibular disorders (TMD). Results revealed that stabilization appliances do not stop nocturnal parafunctional activities in both groups of patients. Active wear facets on the guide ramps of appliances were created by bilateral mandibular excursions. The extension of these facets indicate that the mandible moves laterally far beyond the edge-to-edge contact relationship of the canines during eccentric bruxism. Results also indicate that, with the exception of temporomandibular joint (TMJ) clicks, stabilization appliance therapy is effective in eliminating the signs of TMD evaluated.

Adult↗

PubMed1998

Effects of finishing/polishing time on surface characteristics of tooth-coloured restoratives.

This study compared the effects of immediate and delayed finishing/polishing procedures on the surface characteristics (surface roughness and hardness) of tooth-coloured restoratives including a microfilled, a heavily filled and a polyacid-modified composite resin and a resin-modified glass-ionomer cement. Eighty-four specimen discs were made for each material; the first 12 were used as controls and the remaining 72 specimens were randomly divided into two equal groups. The first group was finished/polished immediately after light polymerization and stored for 1 week in distilled water at 37 degrees C while the second group was finished/polished after 1 week storage in distilled water at 37 degrees C. Finishing and polishing was carried out using the following systems: Enhance system, white stones with Vaseline and Super-snap disks system. The finished/polished surfaces were subjected to profilometric evaluation and microhardness testing. The effects of delayed finishing/polishing procedures on surface roughness and hardness appear to be both material and technique dependent. Delayed finishing/polishing of polyacid-modified composite resins and resin-modified glass-ionomer cements generally resulted in a smoother surface. The surface roughness of composite resins after finishing/polishing procedures were generally not influenced by the finishing/polishing time. For all materials, delayed finishing/polishing with the various techniques generally resulted in a surface of similar hardness to or harder than that obtained with immediate finishing/polishing and the control group.

Bisphenol A-Glycidyl Methacrylate↗

PubMed1998

Comparison of marginal sealing ability of new generation bonding systems.

The purpose of this in vitro study was to evaluate the enamel and dentine marginal sealing ability of four new generation composite bonding systems. Two Class V preparations, which were solely in enamel and dentine/cementum, were made on the buccal surfaces of 96 freshly extracted molar teeth. The teeth were randomly divided into four groups of 24 and restored with composite resin (Silux Plus) utilizing the following bonding systems: Scotchbond Multi-purpose (SB), Fuji Bond LC (FB), Prime & Bond 2.0 (PB) and Bisco One-step (BC). The restorations were finished immediately after photo-polymerization and stored in saline at 37 degrees C for 1 week. Half of the specimens in each group were then thermally stressed for 500 cycles. All restorations were then subjected to dye penetration testing, sectioned and scored. Results revealed no statistically significant difference (P < 0.05) in dye penetration scores for the different bonding systems with the exception of leakage at the dentine margins of thermally stressed specimens where FB exhibited significantly better sealing ability compared with the other bonding systems and BC exhibited significantly less leakage than PB. The marginal seal of 'one-step' (PB and BC) and resin-modified glass-ionomer (FB) bonding systems appear to be as effective as 'two step' systems like SB. Thermal stresses had some influence on marginal seal but this was both product and tissue specific.

Bisphenol A-Glycidyl Methacrylate↗