Bond strength of luting materials to ceramic crowns after different surface treatments.

The aim of present study was to evaluate the effect of different pre-treatments of alumina and zirconia copings on the bond strength of different luting materials. Pull out tests was performed on 60 alumina and 80 zirconia copings. Randomly selected, copings were divided in groups of i) un-treated alumina and zirconia copings, (n=20) ii) alumina and zirconia copings sandblasted with 50 or 110 microm alumina particles respectively (n=20), iii) zirconia copings treated with monolayer of glass pearls fused to the inner surface (n=20), iv) zirconia copings treated with silanized glass pearls (n=10). Zinc phosphate, Panavia 21 and VarioLink II were used for cementation. Pull out tests were done in an Instron universal testing machine with a speed of 0.5 mm/min and fracture loads was measured in N. Untreated zirconia copings cemented with zinc phosphate showed significantly higher bond strength values compared to those with sandblasted surfaces. No difference was seen between untreated alumina copings and those with sandblasted surfaces. Sandblasting decreased bond strength of zirconia and alumina copings. Glass pearls increased bond strength of zirconia copings, which was even better after silanization. Variolink II in combination with alumina gave significantly lower bond strength.

Thin hydroxyapatite coating produced by the ion beam dynamic mixing method.

An ion beam dynamic mixing (IBDM) method was used to produce thin hydroxyapatite coatings on titanium substrates. Structure, solubility and bond strength of coatings were evaluated. The hydroxyapatite-type structure was obtained from heat-treated coatings. As-coated coatings seemed to be almost dissolved within 1 d in Hanks' solution. The thin layer of films, however, was recognized with a firm intermediate compound (such as Ti3P4) to the substrate by X-ray photoelectron spectroscopy, indicating the high tensile bond strengths from the as-coated films. Although slight reductions of the bond strength were observed in heat-treated specimens, the strengths were not reduced by immersion in Hanks' solution for 30 d.

Fracture toughness and flexural strength of dental ceramics for titanium.

Three brands of dental ceramics for veneering to titanium: TitanBond (O'Hara), Ti-Ceram (Ducera) and Titankeramik (Vita) were tested to compare their fracture properties in wet and in dry conditions. Eight polished and precracked specimens of each material were stored in water at 37 degrees C for 28 d and then preloaded in a four-point bending jig with a constant load of 50 N for 24 h under water. Five of the specimens were fractured by a four-point bending test also under water at 37 degrees C. Crack depths were measured in three different positions in each of the remaining three specimens. Fracture load and crack depths were used to calculate the fracture toughness. Another ten polished specimens were used to measure the flexural strength with a four-point bending test after storage in water at 37 degrees C for 28 d. Equal procedures and numbers of specimens were used to measure fracture toughness and flexural strength without preloading and storage in water.

The principal stress distribution in a root with a loaded post in model experiments.

The principal stress distribution in a root with a loaded post was analyzed in model experiments, in which emphasis was directed to the cervical boundary of the root where the stresses are greatest. Maximum stresses were found in the inner proximal sides, and were stronger when the prepared root canal walls were parallel. When contact between post and root was reduced, stresses decreased. These findings point to the importance of sparing tooth substance in the proximal parts of the canal in order to reduce the risk of breaking the cement layer and loosening the post.

Marginal failure of amalgam class II restoration.

Analysis of stresses in a bicuspid with an amalgam Class II restoration was carried out with the finite element method. When stresses were known, creep in the margin of the restoration was calculated. If the buccal cusp was loaded, the maximum compressive stresses were found in the buccal part of the restoration.

A long-term evaluation of abrasion of dental composite resins.

A long-term study was performed on the abrasion of dental composites stored in different solutions for six months. No difference in wear resistancewas noticeable between the water and lactic acid group. But the composite with regular filler showed reduced wear resistance when compared with a microfiller composite.

Solubility control of thin calcium-phosphate coating with rapid heating.

The thin calcium-phosphate (Ca-P) coatings produced by the ion-beam-mixing method instead of the plasma-spraying method have been found to be amorphous, resulting in films that easily dissolved in simulated body fluid. These coatings crystalized with conventional heat treatment in an electric furnace but tended to crack easily. Therefore, the purpose of this study was to find a suitable heat treatment that controls the solubility of Ca-P coatings without weakening their adhesion to titanium (Ti) substrate. Thin coatings (approximately 1 microm) were coated onto Ti substrates, followed by heat treatment in a conventional furnace and rapid heating by infrared radiation and laser radiation. X-ray diffraction analysis revealed untreated films to be amorphous but to become crystalline after being heated in a furnace at 500 degrees C, heated rapidly with infrared radiation higher than 600 degrees C and with laser radiation at output power of 10W. We evaluated solubility by estimating the film thickness after immersion in simulated body fluid for 5 weeks: Untreated films dissolved within 1 day. Coatings treated with infrared radiation at 600 degrees C dissolved minimally. Cracks were observed in coatings subjected to infrared radiation at 800 degrees C and furnace-heated at 500 degrees C. Coatings treated with laser radiation tended to dissolve easily, with non-uniform surface degradation. X-ray photoelectron spectroscopy analysis at the interface between the coating and the Ti substrate showed that cracks were the result of decreased Ca-implanted layers and too much growth of Ti-P compounds. No difference was recognized in the Ti-oxidation state among specimens. These data indicate that rapid, homogeneous, and comparatively low-temperature heating, such as defocused infrared radiation, controls Ca-P solubility and ensures the adherence of the coatings to the substrate.

An abrasion test for composite resins.

An abrasive wear test for composite resins was proposed. A slurry of glass pearls and abrasive particles were used. The abrasive effect was examined for different particle sizes. Particle sizes were found which gave the same order of wear as found clinically for an amalgam, a composite resin, and unfilled resin.

Description and evaluation of a simplified method to achieve passive fit between cast titanium frameworks and implants.

Because osseointegrated implants have no resilience in bone, passive fit between dental implants and prosthetic superstructures has been identified, both from biologic and mechanical perspectives, as a potential discriminating prognostic factor. Distortion of the metal framework during the casting procedure has been cited as a main cause of misfit. The objectives of the present article were to describe a recently presented method (Cresco Ti Precision method) intended to correct for distortion in cast titanium frameworks, and to elucidate and evaluate the method by photoelastic and strain gauge techniques. The method appears to be an efficient and accurate procedure for correcting for distortion in cast titanium frameworks.

Stress analysis of cemented or resin-bonded loaded porcelain inlays.

Ceramic inlays have become an interesting alternative to amalgam fillings. There are two main ways to affix the inlay to the tooth: by use of either a cement or a composite adhesion system. The aim of the investigation was to examine the two methods' influence on stresses in the inlay and the shear-stress state in the gluing materials. The finite element method (FEM) was used to calculate the stresses and displacements. A two-dimensional inlay was modeled with a 200-N point load on the occlusal surface just over the isthmus. Composite and cement linings were stimulated with and without adhesion, and the stresses were calculated. The results showed a marked compression of the dentin below the proximal part of the inlay. The direct effects of the different elastic constants of the two lining materials influenced the stresses in only a minor way. Complete adhesion reduced stresses in the inlay, compared with cemented inlays, with no adhesion along the pulpal wall. Higher shear stresses were also calculated in the cement compared with the composite.

Porcelain bond to laser-welded titanium surfaces.

OBJECTIVES: The purpose of this investigation was to determine if laser-welding titanium had an effect on the bond strength of porcelain to metal. This is an important consideration since the metal copings for many multi-unit porcelain restorations are fabricated as single units and then either soldered or welded. METHODS: The bond strength of porcelain to laser-welded titanium was measured with a four-point bending test and the interface was examined using SEM/EDX analysis. RESULTS: The result showed no statistically significant differences (p<0.05) in bond strengths between laser-welded surfaces and mechanically machined surfaces and neither were there any alterations in composition identified after the welding. The use of a special bonding agent did not improve the bond strength significantly. SIGNIFICANCE: Fusing porcelain to laser-welded areas in titanium fixed restorations implies no deterioration of bond strength.

Profile of work-related health complaints among Swedish dental laboratory technicians.

The purpose of the present investigation was to assess the prevalence and nature of occupation-related health problems among Swedish dental laboratory technicians. A 4-page questionnaire listing seven groups of health complaints was completed by 489 male and 242 female technicians, representing 56% of the active members of their organization. Similar information from 163 males and 160 females with other occupations was used for comparison. The biannual prevalence of health problems among the technicians was 79%, comprising musculoskeletal (68%), dermal (34%), respiratory 31%, neurological (26%), systemic (19%) and eyesight/hearing problems (15%). Job-specific ergonomic and stress factors were responsible for musculoskeletal and neurological (finger) reactions whereas chemical insults, grinding dusts and indoor climate caused dermal, respiratory and systemic reactions. There was no age prevalence as regards health complaints, but female technicians consistently showed a large prevalence of musculoskeletal, dermal systemic and neurological complaints than their male counterparts (P < 0.05, chi2). A similar sex difference was also present in the control group. A considerable part of the reactions were perceived to be of minor importance, bringing the total biannual prevalence down to 57%. However, the prevalence of job-related health complaints was still higher among the technicians than in control groups for all indicators except systemic and eyesight/hearing problems. The profile of health complaints among dental laboratory technicians was characterized by musculoskeletal, neurological and dermal reaction, underlining the importance of job-specific ergonomic and chemical hazards. Only a few of the technicians had consulted medical personnel.

Light energy transmission through cured resin composite and human dentin.

OBJECTIVE: This study determined the amount of light energy transmitted through various densities of cured resin composite and human dentin when 2 different light intensities were used. METHOD AND MATERIALS: The maximum light energy (mW/cm2) transmitted through disks (0.46 to 5.85 mm thick) of 7 resin composites and human dentin was measured when either a Standard or a Turbo light guide was attached to a curing light. The effects of the 2 light guides, the specimen thickness, and type of specimen dentin on light energy transmission were determined. RESULTS: The mean light energy reading at the surface of the specimens was 682.1 mW/cm2 with the Standard light guide and 1,014 mW/cm2 with the Turbo light guide. For all the specimens, there was an exponential decrease in light energy transmitted as the specimen thickness increased. The analysis of covariance showed that the specimen, thickness, and light guide all had a statistically significant effect. Significantly more light energy (about 42%) was transmitted through the specimens when the Turbo light guide was used. CONCLUSION: When the Turbo light guide was used, about 42% more light energy was transmitted through the cured composite specimens. There was an exponential decrease in the light energy transmitted through 7 resin composites and dentin as the specimen thickness increased.

Mercury vapor from dental amalgams, an in vitro study.

The aim of this investigation was to examine in vitro the rate of mercury vapor from different types of dental amalgams. Amalgam surfaces of three different states were used, polished, oxidized and corroded. The influence of temperature, tooth brushing and water on the specimens was also examined. The results showed great differences between the polished amalgams stored in air and amalgams corroded in artificial saliva. Single composition types released more mercury than conventional and dispersed ones. Higher temperature raised and water lowered the vapor rates. When the surfaces of the amalgams were brushed with a tooth paste, an instant increase of mercury vapor occurred.

Marginal failure of amalgam. Effect of alloy selection and bite forces.

Four amalgam alloys were used in a two and a half year study. 163 class II restorations were made and the marginal breakdown was studied. The biting forces of the patients were estimated and divided in three groups. The result indicated that the conventional amalgam showed more breakdowns than the high copper amalgams. Among these a dispersed and a ternary amalgam had least marginal failures. The amount of defects tended to be correlated to the biting force for the conventional and the dispersed amalgam.

Cervical gap formation in class II composite resin restorations.

In vitro, class II restorations were made in three materials, one regular, one microfilled composite and one experimental condensable composite with a porous filler. The aim was to study cervical marginal gap widths appearing in composite restorations when acid etch technique was used. The gaps were about 35 micron for the two contemporary materials and about 10 micron for the experimental one.

Secondary caries related to various marginal gaps around amalgam restorations in vitro.

Secondary caries lesions were produced in vitro by immersing human tooth-blocks with amalgam restorations every third day for 4 weeks in glucose- or sucrose-containing broth inoculated with a strain of Streptococcus mutans. The lesions at the cavity walls were related to various standardized micro-spaces (0, 30, 40, 60 and 80 microns) around the restorations. When a thick, sucrose induced layer of plaque covered the margin, dentine caries was found in all cases where a gap was present (30 microns or more). In the presence of a thin, glucose induced layer of plaque, dentine caries was detected only in the specimens with 60 and 80 microns gap-widths. Caries lesions were detected on the outer free enamel surfaces in all specimens. Lesions in the enamel of the cavity walls were observed with polarized light in 46% in the presence of sucrose- and in 21% in the presence of glucose-induced plaque.

Effect of selenium on mercury vapour released from dental amalgams: an in vitro study.

Wet corroded and air oxidized surfaces from different types of dental amalgams were used in this in vitro study. The mercury vapour released before and after standardized brushing with a conventional (ACTA) and an experimental selenium-containing toothpaste was examined. The results showed differences between the wet corroded and the air oxidized surfaces. High copper, non- gamma 2- amalgams, released more mercury vapour than the conventional one throughout the experiment. When the amalgam surfaces were brushed with the conventional toothpaste, an increase of the released vapour was noted. The use of the selenium containing toothpaste resulted in all cases, in significantly lower amounts of mercury vapour.

A 5-year evaluation of ceramic inlays (CEREC).

The intention of this study was to evaluate the clinical function of porcelain inlays made with the Cerec technique after 5 years. 115 inlays were produced in 46 patients and of these were 51 inlays evaluated. Epoxy models were made from impressions and the gap width and depth was measured in a microscope. SEM pictures were also produced to illustrate the ditching. The measured marginal defects showed a mean width and depth of (SD) 373 (147) and 111 (67) microns respectively. No significant differences of the ditchings could be detected between molars and premolars. Only 3 inlays were found to be fractured of all inlays produced.

Inhibiting effect on demineralization of permanent root surfaces after different topical application of fluorides and a solution containing Fe- and Al-ions.

Fifteen roots were used in this study to compare different topical fluoride compounds on the inhibiting effect of artificial root surface carious lesions. A 2% NaF-solution, Duraphat and a test solution-containing Fe+3, Al+3 with and without fluoride were tested. The results indicated that only the test solution independent of fluoride was able to increase acid resistance. No differences could be observed between the controls and the surfaces treated with the other fluoride agents. The test solution thus seem to be applicable against root surface caries.