In vitro shear bond strength of two resin composites to dentin with five different dentin adhesives.

OBJECTIVE: The aim of this in vitro study was to evaluate the shear bond strength to dentin of five different dentin bonding agents in combination with two resin composites (Tetric and Z-100). METHOD AND MATERIALS: Human third molars were selected for the study, and cylindrical posts of either Tetric or Z-100 were bonded vertically to a standard flat dentinal area, prepared on the buccal surface of the teeth. A chisel-shaped shearing blade, attached to the crosshead of a universal testing machine, was positioned so that its edge was immediately adjacent to the adhesive joint. The shear bond strengths to dentin of 10 resin composite-dentin adhesive combinations were measured. RESULTS: The results showed that the bond strength of dentin bonding agents may depend on the choice of restorative material. The in vitro bond strength of dentin bonding agents also differed significantly. In several cases, the bond strength exceeded the cohesive strength of dentin. CONCLUSION: It seems important for clinicians to be acquainted with the variation in bond strength values that is experienced with any bonding system.

In vivo wear ranking of some restorative materials.

An in vivo experiment to determine the wear of restorative materials (gold, ceramic, and microfilled resin) was performed in a patient with bruxism. Telescopic crowns were placed on teeth 35, 36, and 37. The opposing surfaces were all made from ceramic material. The weight loss of the materials was recorded after 30, 60, and 90 days and converted to volume loss. Replicas for scanning electron microscopic studies were obtained. Gold and ceramic material wore equally, while the wear of microfilled resin was two and a half times as much. The ceramic material and the microfilled resin chipped and fractured, but the gold did not. Mainly abrasive and fatigue types of wear were found in all materials.

Bond strength testing--what does it mean?

In this paper, bond strength and various important factors in bond strength testing are discussed as well as the limitations in the interpretation and clinical relevance of such tests. Standardisation of bond strength testing is needed, and the solutions found in the new ISO document, ISO CD TR 11405 Dental Materials--Guidance on testing of adhesion to tooth structure, are referred to. Tensile and shear test methods are discussed and the bond strength values obtained with these methods compared. The influence of dentine substrate variations, such as remaining dentine thickness and surface treatment or removal of smear layer, are discussed as well as the storage conditions of specimens for in vitro tests, that is, short term, long term and thermocycling, and their relevance to the clinical situation. The information obtained from microscopical studies of fractured surfaces indicates that some adhesives may, under optimal conditions, obtain a bond strength sufficient to fracture the dentine.

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 structure of dentin surfaces exposed for bond strength measurements.

The structure of dentin on three different levels, near enamel, central, and deep dentin, was examined. The solid area available for bonding was studied in a scanning electron microscope (JSM 840) connected to a computer-assisted image analysis instrument (IBAS 2). The number of tubule openings per unit area (frequency) and the area percentages of these tubule openings were recorded. Three dentin disks were obtained from both buccally and occlusally located dentin of a single tooth (third molars were used), and the two deeper levels were each 1.25 mm deeper than the level above. The disks showed an increasing number of tubules with an increasing diameter the deeper into the dentin they were cut. Disks from the occlusal part of the tooth showed, in general, a higher number and area percentage of tubule openings than the corresponding disks from the buccal part. The variation across each disk was also larger for disks from the occlusal part than from the buccal part of the tooth. This variation increased with increasing depth of dentin. The most solid dentin with the lowest variation was found in superficial disks of buccally located dentin.

Wear resistance of some prosthodontic materials in vivo.

The purpose of this study was to compare a gravimetric method and an impression technique in the evaluation of occlusal substance loss. The wear of gold, porcelain, and microfilled resin was studied in vivo. The gravimetric method showed lower substance loss for porcelain than for gold, whereas the microfilled resin had the highest substance loss. To obtain a higher accuracy for the measurement of occlusal substance loss of restorative materials with an impression technique, the test area has to be restricted, the antagonizing occlusal contacts carefully recorded before the test period, and the number of cuts increased. The observed structure of wear facets (SEM) corroborated with previous findings of the wear mechanism of these materials; that is, gold has mainly abrasive wear in contact with porcelain, whereas porcelain has a fatigue type and microfilled resin a tribochemical type of wear.

Tensile bond strength of maxillofacial adhesives.

A common technique for fixation of facial prostheses is the use of skin adhesives. The present study compared the tensile bond strength of five RTV-silicone elastomers used with four different skin adhesives to human skin. The elastomers were: Silskin II, MDX4-4210, Cosmesil, Cosmesil HC2, and RS 330 T-RTV. The adhesives were: Dow Corning 355 medical adhesive, PSA 1, Daro, and 9874 3M double-coated medical tape. The RTV silicones were cured as described by the manufacturer, fixed in circular metal holders, and glued to the skin (inner aspect of forearm) with the various adhesives. The specimens were pulled off 20 seconds after fixation by use of a universal testing machine with a crosshead speed of 1 mm/minute. Eight specimens of each silicone and adhesive combination were tested, and a mean bond strength was calculated for each combination and compared by Duncan's multiple range test on a personal computer. Significant differences were observed among the various combinations of silicones and adhesives. Dow Corning 355 adhesive showed the highest bond strength with all materials, and the medical tape had the lowest. Differences between the RTV silicones were also significant. The strongest bond with all adhesives was MDX4-4210 elastomer and the weakest for RS 330 T-RTV elastomer.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.