Gudbrand Øilo

A novel miniature bite force recorder and its clinical application

Solid state components were used to construct a miniature bite force recorder suitable for registrations in large study groups. A semiconductor was chosen as the sensory unit. The complete recording system included a power supply, the bite force recorder, a chart recorder and a millivoltmeter. Laboratory calibration tests were performed to screen the limitations of the recorder. Series of loads were applied in the range from 10 to 1000 N. Eight females and eight males, 20 to 25 years old, were asked to produce a succession of maximum bites at three second intervals for as long as possible. The bite force recorder was positioned between the first molars on the left side. The laboratory tests showed that loads in the range from 10 to 1000 N were recorded with an error less than four percent. In the clinical tests, the mean maximal bite force was 500 N ranging from 330 to 680 N. The number of maximum bites varied from 5 to 27. No statistically significant differences were observed between the sexes as regards the maximal bite force and the number of bites.

An index for evaluating wear of teeth

An index for evaluation of dental wear based on Ryges system comprising three satisfactory and two not acceptable categories was tested in two different age groups of individuals with brain damage. Group 1 consisted of 12 individuals, 3 women and 9 men, with a mean age of 34.5 years. Group 2 consisted of 13 individuals, 4 women and 9 men, with a mean age of 45.1 years. The wear was evaluated by three examiners, two dentists and one dental hygienist. The examiners worked independently, having available at all times the written criteria and a photographic guide illustrating the lowest limit of each category. Each tooth was given a rating in accordance with the index, and the interexaminer agreement of 612 such evaluations was approximately 85%. Each person was given an individual wear rating corresponding to the most severe category comprising 90% of the tooth ratings. The difference in the distribution of individual ratings between the two groups was tested for significance by the ridit method. Significantly greater wear was observed in group 2 than in group 1, indicating a good sensitivity of the index.

Occlusal contact wear of prosthodontic materials An in vivo study

The wear of gold, porcelain, and heat- and light-cured resins in occlusal contact with resin and porcelain teeth has been studied in vivo. Both weighing of removable segments of fixed partial prostheses and a replica technique allowing scanning electron microscope observations of the worn surfaces were used. The results showed that all materials had the greatest loss of substance when the opposing teeth were of porcelain. The heat-cured, unfilled resin was the least wear-resistant material, followed by light-cured resin, porcelain, and gold. The heat-cured resin showed a combined tribochemical and fatigue type of wear. The light-cured resin and porcelain showed mainly a fatigue type of wear, whereas gold showed a combined abrasive and fatigue type of wear.

In vitro quality testing of dentin adhesives

A tensile and a shear bond strength test are compared, using two well-known and two more recently marketed dentin adhesive systems: Gluma (Bayer), Scotchbond 2 (3M), Scotchbond Multi-Purpose (3M), and Syntac (Vivadent). The adhesives were used to bond composite resins to the buccal surface of human third molars. Specimens stored for 24 h before testing did not show significant differences between bond strength values obtained by either the tensile or the shear test method for any of the materials. The bond strength of thermocycled specimens did not differ for Gluma, was significantly lower for Scotchbond 2, and significantly higher for Scotchbond Multi-Purpose and Syntac. SEM observations showed increasing amounts of cohesive failure in resin with increasing bond strength values. Cohesive fractures in dentin were also observed. It is concluded that either the tensile or the shear test method can be used for quality testing of dentin adhesives. Thermocycling may provide interesting information about the quality of a bond.

The suitability of a new index for the evaluation of dental wear

The suitability of a new index for rating dental wear by different observers was tested. Four dentists, who were first calibrated using the scoring system and then subjected to an inter-examiner agreement test before and after a field study, rated 167 individuals in total in their private dental practices. The incisal/occlusal state of the teeth with regard to restorations and dental wear was recorded. The inter-examiner agreement test proved satisfactory when rating main groups of wear but not so good when rating subcategories. However, a marked improvement in agreement developed between the first and the second test. The individuals composing the field study group are probably not representative of Scandinavian populations in general. Relatively few teeth were missing, and the teeth were well restored. Only the highest age group (80-89 years) displayed the most severe degree of wear to any extent. However, wear into the dentin was observed in 20% of the teeth already in the youngest age group (20-29 years). These teeth were solely incisors and canines of both jaws. In conclusion, we found that the index should be well suited for the evaluation of dental wear in large groups of people by different investigators after adequate training in use of the system has been provided and that tooth wear may be a relatively small problem in urban Scandinavian populations with regular dental care.

Dental Casting Alloys with a Low Content of Noble Metals: Physical Properties

Several physical properties such as strength (UTS and fracture and proof stress), modulus of elasticity, strain (elastic and plastic elongation), hardness, and hardening ability were determined for five low-gold alloys and two conventional gold casting alloys (types III and IV). The composition and the structure (pores and defects) of the cast tensile test specimens were also studied. The results showed that alloys with a low content of noble metals could have properties comparable to those of the traditional types III and IV dental gold casting alloys. A marked difference was seen in the plastic elongation (ductility). A great number of defects (pores and oxide inclusions) were also observed, especially in the specimens with a high content of both palladium and silver.

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.

Wear mechanisms of resin and porcelain denture teeth

The aim of this investigation was to describe the wear mechanism in occlusal contact areas of porcelain and acrylic resin denture teeth opposing different dental materials. A 55-year-old man with earlier extensive wear was given two complete dentures, as identical as possible, in the upper jaw. One of the dentures had diatoric teeth in cross-linked resin and the other denture had diatoric teeth in porcelain. The dentures were antagonizing a new gold-acrylic fixed bridge from 46 to 36. Two contralateral segments of the bridge were made as removable double crowns. The removable segments were made in different materials: gold, porcelain, light-cured resin, and heat-cured resin. Wear of the denture teeth was studied by scanning electron microscopy on replica models made after 1 and 2 months of antagonizing contact with the various materials. Wear of both porcelain and modern cross-linked resin teeth was mainly a fatigue type of wear. Abrasion was observed when hard particles were assumed to be part of the wear debris.

Adhesive bonding of dental luting cements; influence of surface treatment

Oilo, G. 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/m3. 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.

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

Oilo, G. 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 μm, 100 μm and 200 μm. 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 poly carboxylate 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 mor...