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Biomedical subjects

S M Chung

Publications and source records attributed to S M Chung.

97 records · Page 6Linked to original sources
PubMedDate not supplied

Fracture resistance of compomer and composite restoratives.

This study evaluated and compared the fracture toughness of compomers and composites. Three compomer (Compoglass F [CG], Vivadent; F2000 [FT], 3M-ESPE; Dyract Posterior [DP], Dentsply) and three composite (Tetric Ceram [TC], Vivadent; Z250 [ZT], 3M-ESPE; Esthet X [EX], Dentsply) restoratives were selected for the study. Single-edged notched specimens (25 x 2 x 2 mm) were fabricated according to manufacturers' instructions and conditioned in distilled water at 37 degrees C for one week prior to testing. Seven specimens were made for each material. The specimens were loaded to failure using an Instron microtester with a crosshead speed of 0.5 mm/minute. Data were subjected to ANOVA/Scheffe's test and Independent Samples T-test at significance level 0.05. The mean fracture toughness (K(IC)) ranged from 0.97 to 1.23 MPam 1/2 for compomers and 1.75 to 1.92 MPam 1/2 for composites. The fracture toughness of compomers was significantly lower than their composite counterparts. No significant difference in K(IC) values was observed among the different composites. When the compomers were compared, FT had significantly higher fracture toughness than DP and CG. In view of their poorer resistance to crack propagation, compomers are not recommended for use in stress-bearing areas.

Analysis of Variance↗
PubMedDate not supplied

Wear behavior of new composite restoratives.

This study investigated the wear resistance of recently introduced nanofill (Filtek Supreme [FS], 3M-ESPE) and ormocer (Admira [AM], Voco) composites and compared their wear characteristics to microfill (Filtek A110 [AO], 3M-ESPE]), minifill (Esthet X [EX], Dentsply; Filtek Z250 [ZT], 3M-ESPE) and polyacid-modified (Dyract AP [DY], Dentsply) composites. Six specimens were made for each material. The specimens were conditioned for one week in distilled water at 37 degrees C and subjected to wear testing at 20 MPa contact stress against SS304 counter-bodies using reciprocal compression-sliding wear instrumentation. Distilled water was used as lubricant. Wear depth (microm) was measured using profilometry every 5,000 cycles up to 20,000 cycles. The results were analyzed using ANOVA/Scheffe's test (p<0.05). Wear of the materials was cycle and fatigue dependent. Although no significance in wear was observed between materials after 5,000 cycles of wear testing, significant differences were observed at 10,000 cycles and greater. After 20,000 cycles of wear testing, ranking was as follows: ZT > DY >AM > AO > FS > EX. Wear ranged from 39.90 microm for EX to 113.32 microm for ZT. The wear resistance of ZT and DY was significantly lower than AO, FS and EX In addition, ZT experienced significantly more wear than AM. Under the conditions of this in-vitro study, the wear resistance of nanofill and ormocer composites was comparable or superior to polyacid-modified, microfill and minifill composites.

Analysis of Variance↗
PubMedDate not supplied

Effects of aging on mechanical properties of composite restoratives: a depth-sensing microindentation approach.

This study investigated the effects of aging on the hardness and modulus of two composites (Tetric Ceram [TC], Vivadent; Esthet X [EX], Dentsply), a conventional (Compoglass [CG], Vivadent) and a posterior compomer (Dyract Posterior [DP], Dentsply) using a depth-sensing microindentation approach. Seven specimens (3-mm wide x 3-mm long x 2-mm deep) of each material were made and conditioned in distilled water at 37 degrees C. Hardness and modulus of the materials were determined at seven and 30 days using depth-sensing microindentation testing with the Instron MicroTester. Hardness was determined by dividing the peak load over the maximum projected contact area while effective modulus was calculated by analysis of the loading/unloading P-h curves and the analytical model according to Oliver and Pharr (1992). Results were analyzed using one-way ANOVA/Scheffe's post-hoc test and Independent Samples t-test at significance level 0.05. Mean Vickers Hardness (HV) ranged from 46.60 to 58.67 and 44.44 to 59.41 at seven and 30 days, respectively. Mean indentation modulus ranged from 9.57 to 9.95 and 9.19 to 10.03 for the same time periods. At both time periods, EX was significantly harder than all the other materials and HV values for TC were significantly greater than CG. No significant difference in hardness and modulus was observed between seven and 30 days for all materials with the exception of CG. For the latter, a significant decrease in mechanical properties was detected over time.

Analysis of Variance↗
PubMedDate not supplied

Influence of dietary solvents on strength of nanofill and ormocer composites.

The objective of this study was to determine the influence of dietary solvents on the shear punch strength of nanofill (Filtek Supreme [FS], 3M-ESPE) and ormocer (Admira [AM], Voco) composites. The strength of these materials was also compared to a minifill composite (Z250 [ZT], 3M-ESPE), a compomer (F2000 [FT], 3M-ESPE) and a highly viscous glass ionomer cement (Ketac Molar Quick [KM], 3M-ESPE). Thirty-two specimens (8.7 mm diameter and 1-mm thick) of each material were made, randomly divided into four groups of eight and conditioned for one week as follows-Group 1 (control): distilled water at 37 degrees C; Group 2: 0.02M citric acid at 37 degrees C; Group 3: 50% ethanol-water solution at 37 degrees C and Group 4: heptane at 37 degrees C. After conditioning, the specimens were restrained with a torque of 2.5 Nm and subjected to shear punch strength testing using a 2-mm diameter punch at a crosshead speed of 0.5 mm/minute. The shear punch strength of the specimens was computed and data subjected to ANOVA/Scheffe's tests at significance level 0.05. With the exception of AM, the strength of all materials was not significantly influenced by dietary solvents. For AM, conditioning in heptane resulted in significantly higher shear strength values. The strength of the nanofill and ormocer composites was lower than the minifill composite but higher than the compomer and highly viscous glass ionomer cement investigated.

Analysis of Variance↗
PubMedDate not supplied

Management of osteonecrosis in sickle-cell anemia and its genetic variants.

Osteonecrosis secondary to sickling disorders differs from most other forms of osteonecrosis, because vaso-occlusive episodes generally involve many other organs. For this reason optimum management and care of these patients requires a team approach. The spectrum of clinical symptoms and bone involvement varies widely from one patient to another, even among patients with the same abnormal hemoglobin patterns. Although the efficacy of conservative therapeutic measures has not been definitely established, these may be all that can be offered because of the patient's other problems. Before contemplating surgery, the surgical and anesthetic risks should be evaluated and measures taken to prevent complications. The varus osteotomy, Chiari pelvic osteotomy, prosthetic or total hip replacement, and the Neer shoulder prosthesis may benefit a limited number of carefully selected patients.

Adolescent↗
PubMedDate not supplied

Supracondylar fractures of the humerus in children treated by closed reduction and percutaneous pinning.

During the period from 1973 to 1978, 38 children with displaced supracondylar fractures of the humerus were treated at The Children's Hospital of Philadelphia by closed reduction and percutaneous pin fixation. The technical details of the procedure include (1) reduction under general anesthesia with adequate relaxation; (2) insertion of crossed pins from the medial and lateral side with the elbow in acute flexion; (3) and intraoperative clinical and roentgenographic examination of the pinned fracture with the elbow in extension to determine the adequacy of the reduction, with particular attention to the carrying angle. By Flynn's criteria acceptable results were obtained in 19 of the 25 patients studied. Three results were unacceptable due to cubitus varus of 2 degrees, 5 degrees, and 10 degrees, respectively, and three to loss of flexion. Although rotational malalignment occurred in 19 patients, as manifested by a change in shoulder rotation, in no patient was it clinically significant, either cosmetically or functionally. There were no neurologic or vascular complications from the treatment. This is a safe and reliable technique for obtaining and maintaining an excellent reduction in this difficult fracture while preserving vascular function.

Bone Nails↗