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Biomedical subjects

G Oilo

Publications and source records attributed to G Oilo.

At least 19 recordsLinked to original sources
PubMed1992

Biodegradation of dental composites/glass-ionomer cements.

Studies of the degradation processes, types of tests, and measurements and analyses of substances leaching out from resin-based composite materials and glass-ionomer cements are reviewed. For both types of materials, the initial release rate rapidly decreases to a low, but nearly constant, level. For composites, various types of degradation processes have been demonstrated. Elements from filler particles and degradation products from the resin (e.g., formaldehyde) leak out. Many substances are not properly identified. It is, however, difficult for in vitro and in vivo degradation to be compared. For glass ionomers, a total disintegration of a surface layer is observed, together with a slow release of elements from the bulk. Of the elements released, fluoride is the most interesting. Marked differences have been shown between in vitro and in vivo solubility tests.

Biodegradation, Environmental↗
PubMed1992

Bond strength of glass-ionomer cement and composite resin combinations.

The tensile bond strength to dentin was measured for three glass-ionomer cement and composite resin combinations: two light-curing glass-ionomer cements (Vitrebond and XR-Ionomer) and one traditional glass-ionomer cement (Ketac-Bond), two adhesive systems (Scotchbond, and XR-Bonding System), and a corresponding composite resin. The bond strength of this "sandwich" was also compared with that of the same cements used in bulk. Vitrebond showed a significantly higher bond strength in bulk than did the other two cements. Of the sandwiches, the XR-Ionomer and XR-Bond combination showed a bond strength significantly higher than that of the Vitrebond and Scotchbond or Ketac-Bond and Scotchbond combination. The fracture of the bond was mainly adhesive for Vitrebond, cohesive for XR-Ionomer when used in bulk and adhesive-cohesive when used in a sandwich, and cohesive for Ketac-Bond.

Acrylic Resins↗
PubMed1992

The effect of early water contact on glass-ionomer cements.

The purpose of this study was to observe the effect of immersion in water at 3, 5, 7, and 10 minutes after mixing on the surface of three regular and one light-curing glass-ionomer cements by measuring penetration of a methylene blue solution. Early solubility of these cements was also measured and compared with that of a zinc phosphate and a polycarboxylate cement. A blue-stained zone was observed in all glass-ionomer cements, but an inner, opaque zone was observed in only two of the regular glass-ionomer cements. Extending the time between start of mixing and immersion in water decreased the width of both zones in all cements and markedly lowered the loss of substance from the surface of regular glass-ionomer cements. However, time after mixing had no or only a limited effect on the loss of substance from the light-curing glass-ionomer cement, the zinc phosphate cement, or the polycarboxylate cement.

Glass Ionomer Cements↗
PubMed1991

Fracture toughness measurements of some dental core ceramics: a methodologic study.

Fracture toughness is regarded as an important property of dental ceramics. The most widely used methods for fracture toughness (KIc) determination are based on assessment of cracks created by hardness indentations. Different formulas have been developed for KIc calculations and all these methods and formulas include empirical factors based on pure ceramics, i.e. non-composite ceramics. These factors may, however, vary for a specified method for materials with different and complex structure. An important question is whether the various proposed methods and formulas lead to approximately the same numerical KIc values or at least to the same ranking of materials. The aim of this work was to compare two indentation methods and various formulas for calculation of KIc values when used on four commercial composite dental ceramics. The two applied methods and the different formulas showed substantial differences in the obtained values for one and the same material and a different ranking of various materials. It is unknown which method gives the most correct KIc values for these ceramic materials.

Aluminum Oxide↗
PubMed1991

Luting cements: a review and comparison.

The paper discusses strength, retention, film thickness, working time, solubility, early sensitivity to water, biocompatibility and handling properties of zinc phosphate, polycarboxylate and glass ionomer cements. Zinc phosphate cement has acceptable strength, working time and biological properties. It is easy to handle, even when mixing large quantities. Polycarboxylate cement has less strength, different flow properties and a shorter working time, but excellent biocompatibility. The polycarboxylate cement is an alternative where pulp reactions are expected to occur and the load on the restoration during mastication is limited. Glass ionomer cement has the highest strength and retentive properties and a low solubility. It is difficult to spatulate, the working time is short, and contact with water during setting is critical for the quality of the surface layer of the material. The biological properties of glass ionomer cements are similar to those of zinc phosphate cements. It is an alternative to zinc phosphate cement where normal retention is impossible to obtain.

Glass Ionomer Cements↗
PubMed1990

Tensile bond strength of dentin adhesives: a comparison of materials and methods.

The influence of two different storage conditions on the bond strengths of four dentin adhesives [Gluma, Scotchbond (dual), Scotchbond 2, and Tenure] was studied. 5000 cycles from 7 degrees C to 60 degrees C reduced the bond strength significantly for all materials except Gluma, as compared with that found after 24 h of storage in water at 37 degrees C. The influence of two different tensile test methods and two different locations, i.e., occlusal and buccal, of the dentin substrate on the bond strength of Gluma and Scotchbond 2 was also studied. The type of dentin as well as the choice of tensile test method changed the bond strength values significantly. One method gave as much as 3x higher bond strength values for one material when used on the same type of dentin. Bond strength values obtained on the dentin from the buccal side of the tooth were from 20% to 50% higher than those obtained on occlusally located dentin with the same method.

Benzoates↗
PubMed1990

Wear of prosthodontic materials--an in vivo study.

The aim of this investigation was to study quantitative and qualitative aspects of the wear process of some prosthodontic materials in three different persons in vivo. The in vivo models combined two methods: removable double crowns and a replica technique. The wear resistance of gold (types III and IV), porcelain and a microfilled resin was studied opposing metal ceramic crowns and in one person when opposing all four materials. All three persons had earlier histories of occlusal wear of teeth and/or restorations. The wear rate of gold and porcelain showed equal values antagonizing metal ceramic crowns in all three persons. The microfilled resin had a wear rate three or four times higher in the same situations. No significant difference in wear resistance could be found between type III and type IV gold alloys. The wear mechanism seemed to be a fatigue type in porcelain, and in gold a combined fatigue and abrasive type of wear. The microfilled resin showed mainly a fatigue type of wear but some observations indicating a tribochemical reaction were also made.

Composite Resins↗
PubMed1990

Wear of teeth in a mentally retarded population.

The study includes an evaluation of dental wear in 69 individuals, 44 men and 25 women, of mean age 35 years and range 18-59 years, living in a home for mentally retarded persons. Wear was evaluated with a newly developed index based on Ryges' system, where the need for treatment is the key issue. The index consisted of three categories representing clinical situations from no wear to moderate, age dependent wear without problems for the patient, and two categories in which treatment was found to be necessary either to prevent future problems or to improve the present situation. A relatively large number of teeth showed considerable wear in the 20-29 year age group. Wear was observed predominantly in incisors and canines. Only 1% of cases were considered to require treatment. Wear increased with age, and more than 5% of teeth were diagnosed as needing treatment in the 30-39 year and 40-49 year age groups. Wear in the studied population was found to be more severe than that observed in an urban population from the same area in a parallel study.

Adolescent↗
PubMed1989

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.

Dental Porcelain↗
PubMed1989

Retentive strength of dental composite to metal surfaces.

Retentive strength of the metal-composite interface was studied with tensile tests for 10-mm and 4-mm diameter specimens. In both series nonperforated and perforated metal surfaces with various numbers of holes were used. The specimens were tested after 1 day of storage in air and after thermocycling in water at 7 degrees C and 60 degrees C, respectively. The nonperforated specimens had the highest retentive strength values for both small and large specimens. The retentive strength decreased with increasing number of perforations and for nonperforated specimens with large retentive area. Thermocycling reduced the tensile force required to break the specimens by 4% to 50%. The fracture surface was mostly located close to the metal surface, indicating that this is the zone of stress concentration. With increasing length of the bond edge a reduction of the retentive strength was observed.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1989

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.

Adult↗
PubMed1989

Abrasives in snuff?

The purpose of this study was to determine and calculate the inorganic contents of four brands of snuff. Visual inspection of wet snuff showed fairly large, yellow crystal-like particles. Scanning electron microscopy and X-ray dispersive (EDX) analyses were used to study both wet snuff and ashes of snuff, whereas light emission spectrography was used to determine elements in the ashes. The crystal-like particles did not dissolve in distilled water or in ethanol heated to 60 degrees C. EDX analyses showed that most elements remained in the particles after washing. The total weight percentage of inorganic material in snuff was calculated after burning dried snuff until constant weight was obtained. The ashes of snuff did not contain any crystal-like particles but consisted of a small-grained amorphous mass. The following elements were detected: Ag, Al, Ba, Ca, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, P, Pb, Si, Sr, Ti, Va, and Zr. Other elements such as rare earths were not searched for. The weight percentage of inorganic elements ranged between 12.35 +/- 0.69 and 20.95 +/- 0.81. Provided snuff is used in the same manner as chewing tobacco, and some people admit to doing so, there is a risk that its relatively high contents of inorganic material and heavily soluble salts may be conducive to excessive abrasion of teeth and restorations.

Calcium↗
PubMed1988

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.

Bruxism↗
PubMed1988

Flexural strength and internal defects of some dental porcelains.

The flexural strength, number (n), size, and form of pores in seven different dental porcelains were examined. The flexural strength was approximately 100 MPa for the core materials for metal bonding, 116 MPa for traditional alumina porcelains (NBK 1000, Vitadur N), 150 MPa for two new high-alumina porcelains (Vita Hi Ceram, Cerestore), and 240 MPa for a castable glass (Dicor). The mean pore diameter was approximately 10 microns in all porcelains except Dicor, but with a large and varying range. Dicor showed a mean pore size of 1 micron. The pore density varied from 36.5/mm2 in one of the porcelains for metal bonding to 4367/mm2 in Cerestore. The mean cross-sectional area occupied by pores was below 10% for most porcelains except Vitadur N and Cerestore, showing 17.5% and 32.5%, respectively. No correlation was found between flexural strength and frequency or cross-sectional area of pores of the various products.

Aluminum Oxide↗
PubMed1987

An index for evaluating wear of teeth.

An index for evaluation of dental wear based on Ryge's 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.

Adult↗