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Biomedical subjects

D C Chan

Publications and source records attributed to D C Chan.

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

A scanning electron microscopic study of enamel surfaces treated with topical fluoride agents in vivo.

The morphological appearance of human enamel treated with topical fluoride (F) agents was studied. Maxillary acrylic appliances carrying the enamel sections were worn for 24 h following 5-min application of neutral NaF gel-drops, APF gel and Duraphat varnish. All F treatment induced surface coatings composed of globules, suggestive of CaF2. The sizes of the globules varied according to the F agents and, in general, were less than 1 micron in diameter. The globules formed following neutral NaF gel-drops and APF were spherical; while those produced by Duraphat were flattened, forming a sheet-like deposit. Irregular masses of organic-like material were seen on F- untreated enamel, which were exposed to the oral environment for 24 h (controls). The prolonged retention of a F-rich surface coating may act as a reservoir of F supplement to the enamel microenvironment, which thus contributes to remineralization.

Acidulated Phosphate Fluoride↗
PubMedDate not supplied

Caries protection after orthodontic band cementation with glass ionomer.

This study evaluated the resistance of the enamel to an artificial caries challenge after removing orthodontic bands cemented with a glass ionomer cement (GIC). Ten extracted caries-free molars were cleaned with a slurry of pumice and randomly divided into 2 groups of 5 teeth each: Group 1: Cementation with GIC (Fuji) and Group 2: Cementation with a zinc phosphate cement (Mizzy). Both cements were handled according to manufacturer's instructions. Before cementing the bands, an area of S x S mm was masked with adhesive tape on the lingual surfaces of all teeth. The orthodontic bands were cemented over this adhesive tape. After band cementation, the occlusal and gingival margins of the band were delineated with a bur on the tooth surface. The teeth were thermocycled (200 cycles, 5-55 degrees C, 30-second dwell time) and stored in distilled water for 24 hours. Then, the bands and adhesive tape were removed and the teeth again stored in distilled water for a week, changing the water daily. The teeth were then varnished with the exception of a 5 x 5 mm window (including previously exposed and covered areas) on the buccal and lingual surfaces. All teeth were then placed in an acidified gel (pH 4.5) for 5 weeks to produce artificial caries. At least three sections from the exposed and covered areas were made from the buccal and lingual challenged areas. Sections were ground to approximately 100 microns. Polarized microscopy and image analysis were used to analyze the results.(ABSTRACT TRUNCATED AT 250 WORDS)

Dental Caries↗
PubMedDate not supplied

Effect of rinse time on microleakage between composite and etched enamel.

This study compared microleakage of composite bonded to etched flattened enamel in seven groups of five extracted maxillary molars. The facial enamel of the molars was ground flat and etched for 20 seconds with 37% phosphoric acid gel. In one group, etching gel was not rinsed but dried only. In four groups, gel was rinsed with an air/water spray for varying amounts of time. In the other two groups, gel was rinsed with water only for two different amounts of time. Etched surfaces were dried, and a liquid resin was applied and polymerized; a button of composite resin was polymerized to the flattened surface. Specimens were thermocycled, stained, then sectioned longitudinally. Microleakage was measured at the occlusal and gingival enamel margins and expressed as a percentage of the total length of interface. A mean (SD) percentage microleakage was determined at the occlusal and at the gingival margins for each group as follows: no rinse--89.60 (14.34); one second--water 0 (0), air/water 0 (0); three seconds--water 0.98 (1.34), air/water 0 (0); five seconds--air/water 0 (0); 20 seconds--air/water 0 (0). Because of abnormal distribution, data were analyzed using Wilcoxon two-sample tests. The no-rinse group had significantly more microleakage than any of the other groups (P = 0.0067), which were not significantly different from each other (P = 0.18). A one-second rinse with either water or air/water spray was as effective as a 20-second rinse with air/water spray in preventing microleakage at the resin-enamel interface.

Acid Etching, Dental↗
PubMedDate not supplied

Retention of Class 3 composite restorations: retention grooves versus enamel bonding.

This study compared the tensile loads required to dislodge class 3 composite restorations with and without retention grooves. Thirty extracted human maxillary central incisors were divided into two groups of 15 teeth each. A C-shaped class 3 preparation with lingual access was cut into one approximal surface of each incisor to standardized dimensions using a #329 bur. A 0.5-1.0 mm 45 degrees bevel was prepared on the lingual and gingival enamel margins. In one group, an incisal retention point and a gingival retention groove were prepared with a #1/4 round bur to a depth of 0.25-0.5 mm; the other group had no retention grooves/points. A nonretentive 2 mm round "well" with diverging walls was cut 0.5-1.0 mm into the axial dentin to accommodate the head of a pin that was inserted prior to composite restoration. Each pin shaft extended approximally from its incisor. A bonding agent (Universal Bond 3 Primer and Adhesive, L D Caulk) was applied to each preparation, and composite resin (Prisma APH, L D Caulk) was inserted incrementally. Each increment was exposed to 40 seconds of polymerization light. Restoration surfaces were finished and polished with Sof-Lex disks (3M Dental Products). Specimens were thermocycled 6 to 60 degrees C, for 500 cycles, with a 30-second dwell time. They were then positioned in an aligning device, and pins were loaded in tension in an Instron Testing Machine at a head speed of 2 mm/minute to restoration failure. Mean (SD) failure loads in Newtons were: no grooves 83.6 (19.8); grooves 69.6 (18.1).(ABSTRACT TRUNCATED AT 250 WORDS)

Composite Resins↗
PubMedDate not supplied

The effect of microabrasion on restorative materials and tooth surface.

The effect of microabrasion on human enamel has been well documented; however, no information is available on its effect on dentin or restorative materials. The purpose of this study was to evaluate the effect of the microabrasion technique on the surface roughness of restorative materials and enamel and dentin surfaces. Flat disks of amalgam, composite resin, porcelain, and glass ionomer were evaluated. Labial enamel of three maxillary incisors and three molars that were flattened buccally to expose dentin were also tested. The Prema microabrasion compound was applied to each sample with a 10:1 gear-reduction, slow-speed handpiece for 5 seconds, then rinsed for 10 seconds. Roughness was determined with a profilometer. This procedure was repeated 20 times for each sample. A polyvinylsiloxane impression of the surface was taken after 0, 5, 10, 15, and 20 applications and examined under a scanning electron microscope. Enamel surface roughness did not improve as previously reported, suggesting that changes in optical characteristics may not be as important as removal of enamel in obtaining esthetic results. Dentin and glass ionomer exhibited an increase in roughness, such that their presence contraindicates the technique. Amalgam was essentially polished. Porcelain was most resistant to the effects of microabrasion. Judicious use of the technique, especially when restorative materials are present, is advised.

Analysis of Variance↗