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Biomedical subjects

G Oilo

Publications and source records attributed to G Oilo.

At least 73 records · Page 4Linked to original sources
PubMed1979

Oxidation of noble metal alloys for porcelain veneer crowns.

It has been found that oxide-forming elements in the alloy are important for the blood strength between the metal and the procelain. The purpose of the present investigation was to study the formation of oxides during pretreatment and firing of porcelain. Four commerically available Ceramo-Metal alloys were studied. The specimens were heated at 980 degrees C for five hours in air, and the weight was continuously recorded. In addition porcelain was fired on to the alloys. Metallographic examinations were conducted on both oxidized and fired speciments. The weight gain data also indicated an increased oxygen uptake with a larger amount of oxidizable elements in the alloy. Most of the oxygen gain and time indicated that the oxygen uptake was diffusion controlled. The weight gain data also indicated an increased oxygen uptake with larger amount of oxidizable elements in the alloy. Most of the oxygen in the oxidize alloys was located as oxide along grain boundaries in the metal.

Crowns↗
PubMed1979

[Microleakage].

Explore the source record for details and available documents.

Adhesiveness↗
PubMed1978

The influence of surface roughness on the retentive ability of two dental luting cements.

Two series of brass cones and two series of dentine posts with varying surface roughness were produced. Maximum roughness value and arithmetical mean roughness were recorded for each cone. Brass crowns were cemented either with zinc phosphate cement (De Trey's zinc Cenment Improved) or with polycarboxylate cement (Durelon). A tensile stress was applied until the crown and the cone separated. The retentive force in relation to retention area was measured. The results showed that the retentive ability of both cements increased with increasing surface roughness. The increase in retention was greater for brass than for dentine. Differences were also found between the two cements; on smooth surfaces the zinc phosphate cement had a lower retentive ability than the polycarboxylate cement, but on rough surfaces the opposite relationship was observed.

Acrylic Resins↗
PubMed1978

Adaption of luting cement to enamel, dentin and restorative material.

Thirty-two teeth with artificial crowns cemented with four different cements were sectioned and the cementing interfaces were studied by means of a replica technique. Scanning electronic microscopic examination of the replicas demonstrated that slits occurred in all specimens either at the cement/tooth interface, the cement/alloy interface or both. Differences between the various cements in width and length of the slits could not be assessed by this method, but marked variations in the localization of the slits were noted. A composite resin cement showed slits only at the cement/tooth interface. A zinc phosphate and an EBA cement showed slits at both interfaces whereas a polycarboxylate cement was the only cement which exhibited good adaption to enamel and dentin, leaving gaps at the cement/alloy interface.

Adhesiveness↗
PubMed1978

Stress/strain behavior of some dental luting cements.

The compressive strength, modulus of elasticity and the plastic strain at fracture have been studied for several dental luting cements. Stress/strain diagrams of cylindrical specimens using two different crosshead speeds (2 mm/min and 0.1 mm/min) at 23 degrees and 37 degrees C showed that large differences existed between various luting cements. A zinc phosphate cement exihibited high strength, high modulus of elasticity and a small plastic strain at fracture. A resin cement also had high strength, but elastic and plastic strains were high. A polycarboxylate and an EBA-cement both showed low values of strength and modulus of elasticity combined with a high degree of plastic deformation at fracture. Testing with low strain rate at 37 degrees C accentuated the differences between these two materials and the zinc phosphate cement.

Composite Resins↗
PubMed1978

The extent of slits at the interfaces between luting cements and enamel, dentin and alloy.

Four different cements were used to assess the presence of slits at the cement/tooth or the cement/alloy interfaces using a tooth-crown model. The model consisted of ground sections of teeth and plane plates of silver/palladium alloy. The plates were fixed with bolts between two brass plates and with three different dimensions of the cement film between tooth and alloy, i.e. 50 micrometer, 100 micrometer and 200 micrometer. The tooth-alloy specimens were sectioned and the adaption of cements was studied with an indirect technique (replica) in a scanning electron microscope. The extent of slits was expressed as the length of all slits relative to the total length of the interface in each specimen. The results showed that the zinc phosphate cement and polycarboxylate cement exhibited a slight to moderate tendency to formation of slits at the interfaces. The EBA cement had a small extent of slits adjacent to thin cement films, but more slits were observed with increasing film thickness. The composite resin cement had a marked tendency to slit formation independent of the cement film thickness.

Adhesiveness↗
PubMed1978

[Compressive strength and deformation of dental cements].

Several dental cements have been tested for compressive strength, modulus of elasticity and plastic strain at fracture. Sylindrical specimens (4 x 6 mm) were compressed to fracture with two different crosshead speeds (2 mm/min, 0.1 mm/min) at two temperatures (23 +/- 1 degrees C and 37 +/- 1 degrees C). The results showed that the zinc phosphate cement had relatively high strength and a very small elastic and plastic strain during compression. The luting type of glass-ionomer cements showed properties near to that of the zinc phosphate cement. The other cements had either lower strength or higher elastic and plastic deformation than the zinc phosphate cement. Several cements showed a marked reduction of the mechanical properties when tested at a low crosshead speed or at 37 degrees C.

Composite Resins↗
PubMed1978

Adhesive bonding of dental luting cements; influence of surface treatment.

Tensile bond strength of four different luting cements to smooth dentin surfaces was measured. A chisel edged, stainless steel ring was cemented to the butt end of a dentin cylinder. The dentin was polished to a plane and smooth surface before cementation. The cements were also applied to dentin surfaces that were treated with a pumice slurry, etched with different acid solutions, or covered with different liners. The results showed that the polycarboxylate cement had a tensile bond strength to smooth, untreated dentin of approximately 4 MN/m2. The zinc phosphate and EBA cements had a bond strength of 0,6 MN/m2 and the composite resin cement had no measurable bond to untreated dentin. All dentin treatments showed in general a decreasing effect on the bond strength of zinc phosphate, polycarboxylate and EBA cements, whereas that of composite resin cement showed a slight increase.

Adhesiveness↗
PubMed1977

Effect of bevelling on the occurrence of fractures in the enamel surrounding composite resin fillings.

Three different types of cavities: (1) with a 90 degree cavo-surface angle, (2) with a bevel at the cavity margin 0-25-0-50 mm wide, and (3) with a bevel at the cavity margin 0-5-1-0 mm wide, were prepared in extracted human teeth. Fifteen cavities of all three types were filled with Adaptic. Fifteen cavities of Type 2 and of Type 3 were filled with cosmic and the same number and types of cavities with prestige. The fillings were polished 10 min after starting the mix of the composite resins. Fractures in the enamel at the cavity margins were visualized by discoloration with methylene blue. Fractures were observed around all types of cavities, but, for all types of materials, an increased bevel at the margin gave an increased number of fillings without fractures in the enamel. However, great variations in the frequency of fractures were also observed; i.e. Adaptic showing a small frequency, Cosmic a medium and Prestige a great frequency of fillings connected with fractures at the enamel margin.

Composite Resins↗
PubMed1976

Linear dimensional changes during setting of two polycarboxylate cements.

The linear dimensional changes of two polycarboxylate cements have been studied. The measurements were performed on specimens placed on a mercury bath, and were started 3 min after commencing the mix. The specimens were allowed to set at 37 degrees C under various environmental humidity. Specimens from one of the polycarboxylate cements (Durelon), were made using both the universal liquid and the thin liquid meant for cementation. The powder/liquid ratios (P/L) were either 2-5 or 1-5.. Specimens from the second cement (Poly-C), were made using the liquid meant for cementation only with a P/L of 1-5. The dimensional changes of Durelon were dependent on the powder/liquid ratio and the environmental humidity during setting. Under dry conditions this cement showed a maximum contraction of 4-60% after 14 days when a high P/L was used and 6-10% when a low P/L was used. After 1 day under wet conditions no significant differences between cements with high and low P/L were registered, and the mean contraction was 1-10%. The dimensional changes of Poly-C were dependent on the environmental humidity, and after 14 days under dry conditions a maximum contraction of 5-50% was registered and after 1 day under wet conditions a contraction of 0-60%. The contraction of the polycarboxylate cements tested in this study started earlier and were in general more pronounced than that observed for a zinc phosphate cement (Oilo, 1975).

Acrylates↗
PubMed1976

Adaptation of amalgams to cavity walls.

The adaptation of amalgam fillings to the cavity walls has been studied. Cavities were made in human teeth and filled with four different amalgams: (1) amalgam with an expansion of approx. 10 mum/cm after 48 h; (2) amalgam with no dimensional change after 48 h (balanced); (3) amalgam with a contraction of approx. 10 mum/cm after 48 h; and (4) amalgam with a contraction of approx. 20 mum/cm after 48 h. The filling surface and parts of the surrounding enamel were planed, polished and studied under the microscope. The degree of contact between the amalgam and the cavity wall and the number and dimensions of the marginal defects were observed. Fillings made from expanding or balanced amalgams mostly had good contact with the cavity wall, and the marginal defects were small and scattered. Around fillings made from contracting material, a slit formation was observed, and in these areas fractures of both the amalgam and the enamel margins had regularly changed the slit to a V-shaped gap 10-20 mum wide. Greater defects exceeding 50 mum were also frequently observed. The results showed a gradual decrease in the quality of adaptation from fillings made of expanding material to those made of contracting material. It was further shown that the polishing procedure caused fracturing of both the unsupported enamel and amalgam margins thus widening the defects considerably.

Dental Amalgam↗
PubMed1975

Linear dimensional change during setting of a zinc phosphate cement. A methodological study.

A method for studying the linear dimensional changes of dental cements during setting has been described. The measurements started 3 min after commencing the mix with specimens placed on a mercury bath. Measurements were performed at 37 degrees C and under various environmental humidity. The specimens were made of a fine grain zinc phosphate cement with high powder/liquid ratio (3/1:g/ml) and low powder/liquid ratio (2/1:g/ml), and the measurements showed that the cement contracted during setting under both wet and dry conditions. Under wet conditions cements with both high and low powder/liquid ratio showed the same contraction, with 0-43% after 30 min reaching a maximum of 0-66% after 1 day. Under dry conditions the contraction was more pronounced, and somewhat dependent on the powder/liquid ratio. The cement with the high powder/liquid ratio showed 1-33% contraction after 30 min with a maximum of 3-83% after 7 days, whereas the corresponding values for cement with low powder/liquid ratio were 0-79% and 4-76%.

Chemical Phenomena↗