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Biomedical subjects

K C Chan

Publications and source records attributed to K C Chan.

At least 19 recordsLinked to original sources
PubMed1992

Microleakage between different types of base materials.

This study investigated the sealing properties of various combinations of base materials. Three chemically cured and three light-activated base materials were combinationally used to make 15 sample groups. The samples were thermocycled and immersed in 0.05% crystal violet solution for 1 hour. They were then embedded in clear casting resin, sectioned, and photographed. The interfaces of the samples were digitized. The ratio of the total interface length to the penetration of leakage was calculated and compared. The results indicated that the combination of Cavalite and VLC Dycal materials had the least microleakage and was significantly different from the other 14 groups.

Acrylic Resins↗
PubMed1992

Effects of 'resin-compatible' cavity varnishes on composite resin microhardness.

Although the use of cavity varnishes with composite resins has traditionally been discouraged, several "resin-compatible" varnishes are currently available. This in vitro study evaluated the effects of resin-compatible cavity varnishes on a hybrid composite resin. The results of the study indicate that these varnishes soften the composite resin in contact with varnished dentin.

Composite Resins↗
PubMed1992

Continuous wave Doppler echocardiography after surgical repair of coarctation of the aorta.

OBJECTIVE: To find how closely pressure gradients across the aortic arch derived from Doppler echocardiography reflect gradients measured by catheter after surgical repair of coarctation of the aorta. DESIGN: Pressure drop across the aortic arch was measured simultaneously by continuous wave Doppler and double lumen catheter in 20 patients with repaired coarctation of the aorta. RESULTS: The peak pressure drop estimated by Doppler was almost invariably higher than the peak to peak gradient measured by catheter, as might be expected. Wide variation was seen between the Doppler measured pressure drop and instantaneous peak gradient measured by catheter, ranging from +22 to -17 mm Hg. The reasons for these differences are unclear but are probably related to a combination of complex flow dynamics in the aortic arch, difficulty in closely aligning the Doppler beam with flow, and inability to measure flow velocity immediately proximal to the site of the surgical repair with continuous wave Doppler. CONCLUSIONS: Continuous wave Doppler echocardiography may significantly overestimate or underestimate the pressure drop after repair of coarctation and it should be interpreted with caution in individual patients. Catheterisation with angiography remains the reference standard for assessment of surgical repair of the aortic arch.

Adolescent↗
PubMed1991

Leakage of a light-activated base: effect of dentin bonding agents.

This study investigated the sealing properties of Cavalite light-activated base material in conjunction with various dentin bonding agents. Thirty extracted molars were selected and cleaned. Slot preparations with standard dimensions were made. The prepared cavities were filled with Cavalite material after application of the dentin bonding agents Gluma, Prisma Universal Bond, Scotchbond 2, and Tenure. Samples were thermocycled for 180 cycles between 3 degrees C and 60 degrees C, then immersed in 0.05% crystal violet solution for 2 hours. The samples were embedded in clear casting resin, sectioned, and examined with a light microscope. Results indicated that Cavalite material used alone, without a dentin bonding agent, allowed the greatest degree of dye penetration. Cavalite material with Tenure bonding agent had the lowest degree of leakage. Cavalite material used with Scotchbond 2, Gluma, or Prisma Universal Bond bonding agents allowed an intermediate degree of dye penetration. According to an analysis of variance, however, there was no statistical difference in the effects of Tenure, Scotchbond 2, and Gluma bonding agents.

Acrylic Resins↗
PubMed1990

Sequential forearm intravenous regional and infiltration anaesthesia: value for haemostasis.

Intravenous regional anaesthesia using 0.5% lignocaine with a forearm tourniquet is a satisfactory technique for operations on the distal forearm, wrist and hand. Since recovery of pain sensation is rapid, haemostasis after release of tourniquet becomes difficult and sometimes impossible. Local wound infiltration or metacarpal block with 1% lignocaine just before release of the tourniquet can allow subsequent haemostasis and wound closure to be carried out without causing pain. 55 patients received this sequential forearm intravenous regional and infiltrative anaesthesia. Subsequent haemostasis and wound closure could be carried out without pain in 51 patients (92.7%); three patients (5.5%) noticed mild discomfort but the operations could be finished without any additional anaesthetic agent. No complications were encountered with this modified technique.

Adolescent↗
PubMed1990

Cardiovascular malformations in Malaysian neonates with Down's syndrome.

A prospective study was done to determine the incidence of cardiovascular malformations in neonates with Down's syndrome. 17/34 (50%) of the babies with Down's syndrome born at the Maternity Hospital, Kuala Lumpur, Malaysia had congenital heart defects. These included 7 cases of ventricular septal defect (VSD), 3 cases of patent ductus arteriosus (PDA), 2 cases of atrio-ventricular canal defect, 2 cases of ventricular septal defect with patent ductus arteriosus, 1 case of hypertrophic cardiomyopathy, 1 case of hypertrophic obstructive cardiomyopathy and 1 case of complex cyanotic heart. Only 8/17 (47%) of these babies had any clinical signs suggesting underlying cardiac defects. In view of the common occurrence of cardiac anomalies, it is recommended that echocardiographic screening should be carried out on all neonates with Down's syndrome.

Down Syndrome↗
PubMed1989

Leakage of chemical and light-cured basing materials.

This study investigated the sealing properties of chemical and light-cured basing materials in dentin. Fifty extracted molars were selected and cleaned. Slot preparations with standard dimensions were made. The prepared cavities were filled with Cavitec, Life, Ketac-Bond, VLC Dycal, and Cavalite materials. Samples were immersed in 0.05% crystal violet solution for 2 hours. The samples were then embedded in clear casting resin, sectioned, and examined with a microscope. Results indicated that Cavalite and Ketac-Bond materials allow a greater degree of dye penetration that the three other materials. Cavitec, VLC Dycal, and Life materials were similar to each other in degree of dye penetration.

Acrylic Resins↗
PubMed1989

Spontaneous resolution of pulmonary stenosis.

Pulmonary stenosis diagnosed in infancy usually increases in severity with age or, if it is mild, may remain so for many years. We report the case of a child in whom moderately severe pulmonary stenosis in infancy appeared to completely resolve by the age of 8 years.

Female↗
PubMed1989

Functional aortic atresia in congenitally corrected transposition.

An infant with congenitally corrected transposition and severe regurgitation through the left atrioventricular valve presented with clinical and Doppler echocardiographic features of aortic atresia. This eventually proved to be functional. This clinical situation had not, to the best of our knowledge been previously reported before.

Aortic Valve Stenosis↗
PubMed1989

A prospective study on 284 digital fractures of the hand.

We report a prospective study on 284 digital fractures of the hand in 235 patients. Management followed clear guidelines set out in a protocol. Important factors in the selection of the treatment method were, acceptable alignment, functional stability, and associated "significant" soft tissue injuries. "Functionally" stable fractures treated by free mobilization had satisfactory results. Unstable fractures treated by splints or Kirschner wire fixation produced unsatisfactory results. "Open fracture," "comminuted fracture," and "associated significant soft tissue injuries" were identified as unfavorable prognostic factors. The anatomic site of the fractures was not important in determining the final outcome. About 15% of the displaced fractures became functionally stable after closed reduction and their results were comparable with the undisplaced fractures. About 30% of the patients had various degrees of difficulty after they returned to work. About 14% of the patients eventually changed their jobs because of their residual disability.

Adolescent↗
PubMed1989

Psychosocial factors influencing outcome in patients with low-back pain.

A psychosocial analysis of 58 patients with low-back pain was conducted. Three groups of patients with different outcomes were delineated with distinctly different psychosocial profiles. Patients who recovered uneventfully had a better income, reported more satisfaction with hospitalization or medical personnel, and had prolonged pain-free periods. Patients with the worst outcomes in terms of poor work role adjustment and severe pain complaints were more likely to be immigrants from mainland China, to be engaged in heavy manual labor, to be involved in compensation claims for work-related injuries, manifested a high degree of anxiety and depressive symptoms, and were hostile toward medical personnel. An intermediate group of patients with adequate work role adjustment but severe to moderate levels of pain were characterized by being females with varying combinations of anxiety and depressive symptoms. A preliminary clinical interview guide for screening potential problematic patients was developed.

Adult↗
PubMed1989

Propranolol induced bradycardia in tetralogy of Fallot.

When an 18 month old girl who had tetralogy of Fallot and episodes of severe cyanosis with loss of consciousness was treated with propranolol there was some improvement. But when the dose was increased she had further episodes of near syncope. Holter monitoring showed extreme intermittent bradycardia with pauses of up to 2.6 seconds. The episodes of near syncope and the bradycardia resolved after propranolol was stopped. Apparent failure of propranolol treatment may on rare occasions be related to drug induced bradycardia rather than to continued episodes of severe cyanosis.

Bradycardia↗
PubMed1989

Curing light-activated composite cement through porcelain.

The purpose of the study was to determine the exposure times needed to harden a light-activated composite cement through various thicknesses of porcelain. A negative exponential model was developed with which the relative hardness of a composite could be predicted from the product of the exposure time and the square root of the light intensity at 470 nm. Hardness data obtained by varying the exposure time and porcelain thickness were found to fit this model. A relationship was derived to predict the required exposure time, t, of a composite under porcelain with a transmission coefficient, Tc, and a thickness, l:t = toTc-1/2, where to is the exposure time of the composite alone.

Composite Resins↗