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Biomedical subjects

C L Chew

Publications and source records attributed to C L Chew.

36 records · Page 2Linked to original sources
PubMed1989

Flange design in removable partial dentures.

Flange design is an important component in the success of removable partial dentures. There are a number of factors such as undercuts, state of residual ridge, aesthetics, etc. that would influence the design. All these factors are interrelated and must be considered together. Only then will the denture serve its function for aesthetics without compromising the health of the remaining supporting tissues. The importance of each factor and its relationship to others are discussed.

Denture Bases↗
PubMed1986

Food breakdown patterns produced by human subjects possessing artificial and natural teeth.

The abilities of thirty-two complete denture wearers and thirty-two dentate subjects to break down raw carrot particles were compared. The particle size distributions produced were broader in those subjects that broke down food rapidly per chew and, conversely, narrower in those that were slower. This did not appear to depend on dental status. An analysis of mastication as composed of two separable processes, one describing the means by which particles come to be broken (selection) and the other, the size distributions of a particle upon fracturing (breakage), indicated that both processes were variable. It is concluded that no qualitative differences in the manner by which the two groups reduce food is apparent. To support this, a small study on dentate subjects suggests the covering of the palatal mucosa with an acrylic plate does not affect masticatory performance.

Adult↗
PubMed1986

Relationship between jaw movement and food breakdown in human mastication.

Different quantities and sizes of peanuts were offered to six human subjects for mastication at two or three experimental sessions during which jaw movements and chewing cycle duration were measured. The amplitude of vertical movement and cycle duration depended on the position of a chew in a sequence of chews (masticatory sequence). Cycle duration also depended on the position of a given masticatory sequence during the first experimental session, the earlier sequences tending to be longer. Lateral jaw movements fluctuated about a reasonably constant value during a sequence and were unaffected by different food inputs. The amplitude of vertical movements increased markedly with an increase in food weight but was unaffected by change in the initial food particle size. These results were analyzed in the light of previous reports on the comminution of peanuts. It is hypothesized that observed jaw movements were unrelated to food particle size but that the amplitude of each vertical movement depended on the volume of food that was broken by the teeth during the next closing stroke. This food volume was provided and selected by bulk movements of the tongue during the preceding jaw opening.

Adult↗
PubMed1986

Dimensional stability of two impression materials.

Elastomeric impression materials are widely used in dentistry to obtain accurate impressions. The most recent group of these materials is the additional polymerised silicones which have been shown to produce great accuracy. An auto-mixing system has been developed to provide ease of manupilation. The material is mixed as it is syringed through a mixing tip. The dimensional accuracy of the material mix by this system is compared to that of a hand mixed material. Results show that the dimensional accuracy of this new material is good and the system easy to use. The limitations of the material are also discussed.

Chemical Phenomena↗
PubMed1985

The acid-etched fixed partial denture: a two-year report.

A 2-year report on 10 acid-etched fixed partial dentures was presented. Similar to other studies, it indicates that the acid-etched fixed partial denture is a clinically acceptable restoration for properly selected patients.

Acid Etching, Dental↗
PubMedDate not supplied

Clinical performance and physical properties of twelve amalgam alloys.

An assessment of the marginal failure rate of 1,041 restorations of twelve alloys was made at one year. In addition, physical property tests were conducted. A correlation was found between the clinical performance and creep (.79), flow (.62) and 24-hour compressive strength (.60).

Chemical Phenomena↗
PubMedDate not supplied

Bond strengths of glass ionomer restoratives to primary vs permanent dentin.

An in vitro experiment was conducted to evaluate the shear bond strength of a conventional GIC (glass ionomer cement) and a RMGIC (resin modified glass ionomer cement) when applied to dentin of primary and permanent teeth. Results show that the bond strength of the RMGIC was more than thrice that of the conventional GIC. Fracture analysis showed that the bond failures were cohesive in the cement.

Acrylic Resins↗
PubMedDate not supplied

Mechanical properties of an improved visible light-cured resin-modified glass ionomer cement.

This study investigates the mechanical properties (hardness, flexural strength and compressive strength) of a new light-cured resin-modified glass ionomer cement (Fuji II LC Improved). Effects of the increased powder:liquid ratio on mechanical properties and the correlation between different mechanical properties were also studied. Mechanical properties of the cement at manufacturer's recommended powder:liquid ratio (F), 2% (F2) and 4% (F4) increased powder weight were measured after one day, one week and one month storage in distilled water at 37 degrees C. Hardness testing (KHN; n = 5) was done with a digital microhardness tester (load = 500 g, dwell time = 15 seconds). Flexural and compressive strength testing (MPa; n = 5) were conducted based on ISO 4049 and BS6039, respectively. Results were analyzed using ANOVA/Scheffe's test (p < 0.05) and Pearson's correlation (p < 0.01). The maximum mechanical properties of Fuji II LC Improved were achieved at one week. The hardness, flexural and compressive strength at one week was significantly higher than at one day. A decrease in all mechanical properties was observed at one month. Mechanical properties were significantly affected by increased powder:liquid ratio. After one month storage, significance was as follows: Hardness--F, F2 > F4; Flexural strength--F4 > F, F2 and F > F2; Compressive strength--F, F2 > F4 and F2 > F. A significant very strong and negative correlation was observed between flexural and compressive strengths (r = 0.97).

Compressive Strength↗
PubMedDate not supplied

Influence of thermal cycling on OCA wear of composite restoratives.

This study investigated the effects of thermal cycling on wear of four commercial composite resins (Silux, Z100, Ariston and Surefil). Specimens of each material were divided into three treatment groups comprising a control and two different thermal cycling regimes. Control specimens were stored in distilled water at 35 degrees C for 178 hours. Thermal cycled specimens were stored in distilled water at 35 degrees C for 173 hours and subjected to five hours (300 cycles) of a thermal cycling regime consisting of the cycle ABAC, where A and B represent the fixed temperatures of 35 degrees C (28 seconds) and 15 degrees C (two seconds) and C, depending on the treatment group, was either 45 degrees C or 60 degrees C (two seconds). All specimens were subsequently subjected to wear testing at 20 MPa contact stress against SS304 counterbodies with distilled water as the lubricant. Wear depth (microm; n=6) was measured using profilometry every 2,000 cycles up to 10,000 cycles. Results were analyzed using ANOVA/Scheffe's test (p<0.05). The effect of thermal cycling on wear was material-dependent. The wear of Silux and Z100 were not significantly affected by thermal cycling. Thermal cycling of Ariston at an upper temperature of 60 degrees C significantly decreased wear resistance. Thermal cycling affected only the early wear resistance of Surefil.

Analysis of Variance↗
PubMedDate not supplied

Long-term dissolution of mercury from a non-mercury-releasing amalgam.

The hazards of mercury from dental amalgams have long been recognized. This study examined the mercury release from a "non-mercury-releasing" dental amalgam, Composil, over a 104-week period. Four cylindrical specimens were incubated in 10 ml of purified water at 37 degrees C. The incubate was changed at the end of each 24-hour period and assayed for its mercury content at biweekly intervals. Mercury estimation was carried out using cold-vapor, atomic absorption spectrophotometry over a 104-week period. Results showed that the overall mean release of mercury was 43.5 +/- 3.2 micrograms/cm2/24 hr, and the amount of mercury released remained fairly constant during the duration of the experiment. This study showed that Composil releases mercury in quantities that far exceed those detected in other amalgam systems.

Analysis of Variance↗
PubMedDate not supplied

The influence of temperature on the dimensional stability of poly (vinyl siloxane) impression materials.

It may be desirable to extend the working time of poly(vinyl siloxane) impression materials when making a multiple-unit impression. Alteration of the base-catalyst ratio is not possible with automix systems, but chilling the impression material provides an alternative. This study evaluated the dimensional accuracy of chilled impression material and the effect on accuracy of reheating the impression to mouth temperature prior to pouring. Two brands of poly(vinyl siloxane) impression material were evaluated both after refrigeration and at room temperature. Impressions were poured at room temperature and reheated to mouth temperature prior to pouring. Gypsum dies were recovered and measured. Refrigeration had no statistically significant effect on dimensional accuracy. Reheating the impression had no clinically significant effect on accuracy.

Dental Impression Materials↗