Bonding of light-cured glass ionomer cement to polycarbonate resin treated with experimental primers

The effect of experimental primers on the shear bond strength of polycarbonate composite resin with light-cured glass ionomer cements was investigated. Mixtures of methylmethacrylate (MMA) with the comonomers 2-hydroxyethyl methacrylate (HEMA), triethyleneglycol methacrylate (TEGDMA), and bisphenol-A-glycidymethacrylate (bisGMA) were used as primers. Polycarbonate composite resin rods of circular cross section and plates were bonded, with and without precured and nonprecured primers, using 2 light-cured glass ionomer cements (commercially available [LC] and experimental [EX]). In addition, commercial polycarbonate composite resin brackets with precured 50% TEGDMA/MMA primer were bonded to etched human enamel with both cements. Shear bond strengths were measured. Results were compared by ANOVA and Scheffe's tests at P = .05. The 30% HEMA/MMA, 50% TEGDMA/ MMA, 10% bisGMA/MMA, and 30% bisGMA/MMA primers produced the higher shear bond strengths (9.5 to 20.8 MPa) with LC and EX to polycarbonate composite resin. The 50% TEGDMA/MMA primer was most effective in improving the shear bond strengths of both LC and EX. Precured 50% TEGDMA/ MMA primer on a commercial resin bracket was effective in providing good shear bond strength to enamel.

A comparison of shear bond strengths of three visible light-cured orthodontic adhesives

The purpose of this study was to evaluate the shear bond strength and the site of bond failure for 2 visible light-cured composites (Transbond XT and Enlight) and a resin-modified glass ionomer cement (RMGIC; Fuji Ortho LC). Seventy-five extracted human premolars were collected and randomly divided into 3 test groups. Brackets were bonded to the teeth in each test group with the respective adhesive according to the manufacturers' instructions. Each specimen was debonded using an Instron Universal Testing Machine at a crosshead speed of 0.1 mm/min. The mode of bond failure was observed by using light microscopy. The results of this study demonstrated that the light-cured composites had a higher shear bond strength than the RMGIC. The adhesive-remnant scores were similar for the composites with the mean values at about 2, which indicates that more than half of the adhesive remained on the tooth. The RMGIC had a mean score of 3, which was significantly different from the composites and indicated that all of the adhesive remained on the tooth with a distinct impression of the bracket.

Torque transmission between square wire and bracket as a function of measurement, form and hardness parameters

The aim of the study was to investigate the influence of cross section, edge geometry and structural hardness on torque transmission between square wire and bracket. For this purpose, 5 different brands of stainless steel square wire in 3 dimensions (0.016" x 0.016", 0.016" x 0.022" and 0.017" x 0.025") were inserted into edgewise brackets with a slot size of 0.018" and loaded with different torques (1 and 3 Ncm). The slot and wire geometries were analyzed by computer on ground specimens before and after loading. In addition, the Vickers hardness and micro-hardness of the unstressed and stressed metal surfaces were determined. While the slot size was very accurately maintained, the wire dimensions deviated downwards by an average of 10%. Torque transmission led to notching and bending-up phenomena on the bracket slot flanks. A torque loading of 3 Ncm increased the torque play of 0.016" x 0.022" wires by 3.6 degrees, and of 0.017" x 0.025" wires by 3.7 degrees. In the case of 0.016" x 0.016" wires, an effective torque transmission was no longer possible. The average Vickers hardness of the wires was 533 kp/mm2, and that of the brackets 145 kp/mm2. The micro-hardness in the deformation area of stressed internal slot walls increased with increasing load transmission from 204 to 338 kp/mm2. As a result of excessively small wire dimensions and plastic deformation of the brackets, a relatively large torque play occurs. Deformation and notching in the area of the internal slot walls are inconsistent with demands for recycling brackets. A standardization of bracket wire systems stating the actual torque play would be desirable.

Contribution to the biological assessment of orthodontic acrylic materials. Measurement of their residual monomer output and cytotoxicity

The acrylic materials used in orthodontics for the fabrication of removable appliances are subjected in the oral cavity to processes of change which influence their physical, mechanical and biological properties. It is therefore essential that every newly developed material must be judged in terms of its clinical value. In the present study, 2 orthodontic cold-cure acrylics, Orthocryl and Forestacryl, and 4 orthodontic photocure acrylics, Triad, Wil-O-Dont, Odontolux and Lux-A-Tech, were investigated and compared with 2 prosthetic acrylic materials: the cold-cure acrylic Palapress and the hot-cure acrylic Paladon. The quantity of residual monomers from methyl methacrylate (MAA) or urethane dimethacrylate (UDMA) eluted from the sample in a given time after the processing was estimated by high pressure liquid chromatography (HPLC). The cytotoxic properties of the materials were examined by Mosmann's proliferation-inhibition test with an established culture of fibroblasts (= MTT test). The hot-cure acrylic Paladon produced by far the smallest amount of eluted residual monomer and the least growth inhibition in the MTT test. The prosthetic cold-cure acrylic Palapress achieved significantly better results than the orthodontic cold-cure materials Orthocryl and Forestacryl. The photocure acrylics released less UDMA than did the cold-cure acrylics MMA. In the cell culture test, all the orthodontic materials examined were assessed as "slightly cytotoxic"; the prosthetic acrylics were graded under ISO-standard 10993-5 as "noncytotoxic". After soaking the plastic material in water for 3 days its cytotoxic properties, as exemplified by the cold-cure acrylic Forestacryl and the photocure acrylic Triad, were reduced, and during the following investigation no more inhibition of growth was observed. It was possible to confirm with the tests used that, for Triad, it is necessary to carefully remove the oxygen-inhibition layer of the photocure acrylic in order to improve the biological properties. The influence of the plastic material on fibroblast cultures was assessed, among other methods, by the quantity of residual monomers liberated. These were significantly reduced after soaking the manufactured substance in water for 3 days. Careful laboratory treatment of the photocure acrylics is necessary in order to improve their biological properties.

Effect of 1.23 percent APF gel on fluoride-releasing restorative materials

This study evaluated the effect of a 1.23 percent APF gel on the surface morphological characteristics and surface roughness of one high-viscosity (Fuji IX GP), three polyacid-modified resin-based composites (Dyract AP, F2000 and Compoglass F) (PMRC), and two resin-modified glass-ionomer cements (Vitremer and Fuji II LC). A microfilled nonfluoridated resin-based composite (Silux Plus) was used as a control. All materials were handled according to the manufacturers' instructions. The fluoride gel used in the study was a 1.23 percent acidulated phosphate fluoride gel (APF) (Nupro APF). The specimens were repeatedly exposed to the APF gel with cotton applicators for a period that simulated the equivalent of 4 yrs (1 min/6 mo) under prophylactic fluoride treatment. Average surface roughness (Ra) of the control and treated specimens was measured. Three separate Ra measurements along the direction of rotation of the finishing and perpendicular to the finishing direction and edge of the mold were made for each specimen surface. In each group, specimens with Ra closest to the mean were removed from the molds, sputter-coated with gold and examined using a scanning electron microscope. The results showed that all tested materials, except Vitremer, displayed increased surface roughness values following APF treatment. However, this was not statistically significant for Compoglass F, Vitremer and Fuji II LC. Among PMRC materials, F2000 displayed the highest Ra average value, although the differences between F2000 and Dyract AP and of Compoglass F and Dyract AP was not statistically significant. Comparisons of the Ra values between Silux Plus and the other test materials revealed statistically significant differences except for Dyract AP and Compoglass F. No statistically significant difference was found between the Ra values of Vitremer and Fuji II LC following APF treatment. Among all groups, Fuji IX GP displayed the highest surface roughness.

Bond strength of various fluoride-releasing orthodontic bonding systems. Experimental study

The aim of the study was to compare the shear bond strength of a fluoride-releasing composite resin adhesive (Light Bond, Reliance) and a light-cured resin-reinforced glass ionomer cement (Fuji Ortho LC, GC America) bonded to extracted teeth under different enamel surface conditions. Forty human premolars were divided at random into 4 groups of 10 specimens. Stainless steel brackets were attached to the enamel surface by 1 of the 4 protocols: 1. Fuji Ortho LC, moist non-etched enamel; 2. Fuji Ortho LC, moist etched (37% H3PO4); 3. Light Bond, dry etched (37% H3PO4); 4. Light Bond, dry etched (Etch & Prime 3.0, Degussa). The teeth were stored in deionized water at 37 degrees C for 48 hours. Shear bond strengths was determined at a crosshead speed of 1 mm/min. The residual adhesive on the enamel surface was evaluated with the modified Adhesive Remnant Index (ARI). Analysis of variance (ANOVA) and Duncan's test were used to compare the 4 groups. Significance was predetermined at p = 0.05. Significant inter-group differences were found (p < 0.0001). The mean SBS (and SD), in MPa were: Group 1: 15.9 (4.7); Group 2: 20.3 (2.5); Group 3: 16.7 (2.6); Group 4: 11.7 (2.5). Glass ionomer cement without etching and composite with Etch & Prime showed adhesive failures at the enamel and good enamel integrity after debonding. The other specimens showed mixed or adhesive fractures at the bracket failure sites. Glass ionomer used on wet tooth surfaces without etching shows a clinically acceptable bond strength with clean separation from the enamel after debonding.

[The fixation of nonremovable dentures: the rational choice of the material]

Adhesion and marginal permeability of materials used for fixation of whole-cast dentures and surface micro-relief were studied in vitro and in vivo on dogs. Three groups of materials were studied: zinc-phosphate, polycarboxylate, and glass-ionomeric. Polycarboxylate cements effectively fixed dentures irrespective of the status of abutment teeth, and glass-ionomeric cements w V.M. Marker and prognostic phospholipase A2 test in inflammatory diseases of the periodontium.

The effect of pH on the corrosion of dental metal alloys

The aim of this study was to determine the effects of the oral environment's pH on the corrosion of dental metals and alloys that have different compositions, using electrochemical methods. The corrosion rates and the cathodic Tafel slopes were obtained from the current-potential curves. The effect of pH on the corrosion of dental metals and alloys was dependent on their composition. Dissolution of the ions occurred in all of the tested pH states. The dissolution was moderately low for samples containing titanium because its surface was covered with a protective layer, whereas the dissolution was maximal for the samples containing tin and copper. Addition of cobalt and molybdenum to the alloys improved their corrosion resistance; these cobalt and molybdenum alloys were not effected by changes in the pH. Dissolution of the precious metal alloys increased as the percentage of noble metals increased. The corrosion characteristics of dental metals and alloys are important because the corrosion tendencies of dental alloys in the mouth may cause health hazards, weakening and the aesthetic loss of dental restorations.

The influence of humidity on the overall mass transfer coefficient of the Wheeler-Jonas equation

The Wheeler-Jonas model is well known for its good prediction of breakthrough times for organic vapors on activated carbon beds. However, it is valid only in dry conditions: no prewetting of the filter and no humidity in the ambient air during use. One of the parameters that is likely to be influenced is the overall mass transfer coefficient kv. By measuring over 200 breakthrough times, with 7 different vapors on 4 different types of activated carbon, a simple but satisfactory model for the influence of moisture on kv was established. The only items of information needed, compared with the application of the Wheeler-Jonas equation under dry circumstances, are the water isotherm and the total pore volume of the activated carbon.

Estimating the overall mass transfer coefficient k(v) of the Wheeler-Jonas equation: a new and simple model

The modified Wheeler-Jonas model is well known for its good prediction of breakthrough times for organic vapors on activated carbon beds. To use this model adequately one must estimate the overall adsorption rate coefficient kv. In this work a new equation is proposed to calculate kv. The relevant parameters of this equation are the airstream velocity, the affinity constant beta of the organic vapor, and the mean diameter of the carbon particles. Very accurate predictions were obtained for breakthrough times on a wide range of carbons using the calculated values of kv. Compared with other models, this model shows a higher accuracy and a lower degree of uncertainty.

Interfacial strength between molded UHMWPE and PMMA-MMA monomer treated UHMWPE

To solve aseptic loosening of cemented acetabular cup and tibial plateaus of hips and knee joint prostheses in total joint replacement, adhesion between the polymeric prostheses made of ultra-high molecular weight polyethylene (UHMWPE) and bone cement made of polymethyl-methacrylate (PMMA) has been investigated. Previous studies using xylene, PMMA, and MMA monomer solution to treat bulk surfaces of UHMWPE resulted in 11.5 +/- 0.65 MPa as the maximum interfacial strength between the treated UHMWPE and bone cement. The present study eliminates the use of xylene; instead, UHMWPE powders were treated with MMA monomer and PMMA-MMA solution, dried, and then compression-molded with untreated UHMWPE powders. The interfacial tensile strengths were measured and the best molding conditions investigated by varying temperature, pressure, and time. Temperature was the predominant factor when compared to that of pressure or time. The maximum interfacial strength between the treated UHMWPE and untreated UHMWPE was 16.3 +/- 0.94 MPa with the molding conditions of 166.5 degrees C, 38.7 MPa, and 1 h. Scanning electron microscopic (SEM) pictures show the coating of the nodules and fibrils of UHMWPE powder with PMMA. Pulled out aggregated nodular space and coated PMMA after fracture could be seen easily from PMMA-MMA treated UHMWPE powder.

A new method of determining the J-integral fracture toughness of very tough polymers: application to ultra high molecular weight polyethylene

The thrust of the present work was the development of a new modification to the ASTM E813-89 method for determining the J-integral fracture toughness, JIc, of ductile polymers. The advantages and limitations of the modification, vis a vis the ASTM E813-89 and the hysteresis methods, are presented. The modification was then applied to investigate the effect of sterilization method on the JIc of ultra-high-molecular-weight polyethylene (UHMWPE) specimens that were subsequently aged (heated, in a cylindrical pressure vessel, in oxygen gas at 507 kPa and 70 degrees C for 14 d). Relative to the unsterilized material, it was found that gamma-irradiating the polymer leads to a significant drop in its JIc, while sterilization using either ethylene oxide or gas plasma produced no effect on its JIc. The clinical implications of the present results for the in vivo performance of UHMWPE counterfaces, and, hence, hip and knee arthroplasties, are fully discussed.

Retention of a core material supported by three post head designs

STATEMENT OF PROBLEM

There are few studies on the retention of core build-up materials to prefabricated post head designs, especially for a new ceramic post design.

PURPOSE

This in vitro study compared the retention of 2 types of core build-up materials (Ti-Core titanium-reinforced composite and a GC Miracle Mix silver-reinforced glass ionomer) supported by 3 post head designs (Flexi-Post, AccessPost, and Cerapost dowel). For all test groups, heads of the posts were placed into the core material at a 90-degree angle to the surface. Test specimens (unloaded) were then placed into a special jig and retention test was performed using an 810 MTS testing machine.

MATERIAL AND METHODS

This study consisted of 6 groups with 10 specimens per group. A 3 x 2 factorial design was used to test for statistical significance and results were considered significant when P <.05.

RESULTS

Results of the retention test were as follows: group 1, Flexi-Post/Ti-Core 220.0 lb (982.1 N), group 2, AccessPost/Ti-Core 212.7 lb (949.6 N), group 3, Cerapost/Ti-Core 41. 8 lb (186.6 N), group 4, Flexi-Post/Miracle Mix 43.4 lb (193.8 N), group 5, AccessPost/Miracle Mix 61.6 lb (275 N), and group 6, Cerapost/Miracle Mix 7.5 lb (33.5 N). Results of the ANOVA revealed a highly significant difference between posts and cores (P <.0001).

CONCLUSION

Post head designs of the stainless steel AccessPost and Flexi-Post dowels offers greater retention then the smooth ceramic head design of the Cerapost dowel. In addition, the composite core material (Ti-Core) offers greater retentive strength values than the glass ionomer material (Miracle Mix).

In vitro comparison of fluoride release of six direct core materials

STATEMENT OF PROBLEM

Fluoride has been shown to deter caries and has been incorporated into core build-up materials. However, there is considerable variation in the formulation and release of fluoride from core build-up materials.

PURPOSE

This in vitro study compared the fluoride released by 6 commercially available fluoride-releasing core materials over time.

METHODS AND MATERIAL

Ten specimen disks (9 for Corestore) of each of the 6 core materials were fabricated, finished, measured, and immersed in deionized water in individual polystyrene jars. The jars were stored in a humidor at 37 degrees C between test periods. At the same time each day for 7 consecutive days, then at days 14, 22, 28, 59, and 89, the fluoride release was measured from each specimen disk in parts per million by testing the storage medium. The data were analyzed using 1-way ANOVA and Tukey-Kramer multiple comparison tests (P <.05).

RESULTS

Five of the 6 core build-up materials tested showed an initial high concentration of fluoride release during the first day and gradually tapered over the study period. Fuji II LC consistently released more fluoride than any other material throughout the 89-day testing period.

CONCLUSION

Fuji II LC released the most fluoride and was significantly different from the other materials tested. The maximum amount of fluoride was released by 5 of the 6 materials during the first 24 hours and gradually tapered over the 89-day testing period.

Viscoelastic properties of denture base resins obtained by underwater test

The viscoelastic properties of denture base polymers, such as poly(methylmethacrylate) (PMMA), polycarbonate (PC), polysulfone (PSF) and polyethersulfone (PES) which have been used in current clinical dentistry were investigated. In addition, water absorption, diffusion coefficient of water into material, cubical expansion, specific volume and residual monomer were also determined. From the results of this study, the viscoelastic behaviours of the denture base polymers in water have been discussed. The relaxation modulus (Er(5)) which was calculated using a stress at 5 s from the start of measurement for the specimen which reached an equilibrium moisture content (wet specimen), decreased from 23.1 to 25.5% compared with that of PMMA stored in a desiccator (37 degrees C) for 1 week (dry specimen). In contrast, this decreasing ratio was 7.0 to 10.0% for PC, PSF and PES. It is suggested that this phenomenon is caused by the increase of specific volume (cm3/g) with water absorption in each material. The water absorption of the PMMA group was relatively large in comparison with other material and was 1.81-1.85%. This value was within the range from 0.38 to 1.74% for PC, PSF and PES. The diffusion coefficients of water for PC, PSF and PES increased by approximately 1.5-2.7 times that of PMMA. Furthermore, the coefficient of cubical expansion of the wet specimen was larger than that of the dry specimen. The increasing ratio was 1.03-1.10 times for the PMMA group and 1. 18-2.38 times for PC, PSF and PES. The variation of Er(5) of the PMMA group with temperature in water was larger than those of PC, PSF and PES.

Effect of prefabricated metal post-head design on the retention of various core materials

Retention of various post heads to core restorative materials is an important factor in the selection of prefabricated post systems and restorative materials for the restoration of endodontically treated teeth. This study examines the retention of a post-core prefabricated system in relation to core material and post-head design. A total of 60 samples were prepared using two different post systems (ParaPost Plus (PP) and ParaPost Unity (PU), with amalgam, composite or glass-ionomer as one of the core materials. The samples were tested using the Instron testing machine. The PP was superior to the PU prefabricated post with respect to the retention of various core materials. Retention values in descending order of magnitude were found to be: composite, amalgam and glass-ionomer (significantly lower). The rhomboid serrated design of PP was superior in retention to the rounded smooth UP system. Composite material proved to be superior in retention, closely followed by amalgam, with glass-ionomer significantly less retentive.

Effects of surface treatments on shear bond strengths between a resin cement and an alumina core

STATEMENT OF PROBLEM

Although bonding to all-ceramic restorations is desirable, there is little information on the use of resin cements containing a phosphate monomer, and the importance of different surface treatments on their adhesion to high-strength core materials.

PURPOSE

This study attempted to determine the shear bond strength values between Panavia 21 resin cement (Kuraray) and an alumina core material (In-Ceram) after 3 surface treatments and the application of a silane coupling agent.

MATERIAL AND METHODS

Forty-five In-Ceram cylindrical rods were fabricated and assigned to 3 groups. Group I specimens were treated with a 9.5% hydrofluoric (HF) acid, group II with a 5% HF acid, and group III were sandblasted. All specimens were coated with a silane coupling agent (Cavex Clearfil Photobond and Activator) before cementation with Panavia 21 to sandblasted nickel-chromium rods. As a control, group IV consisted of 8 porcelain (Vitadur Alpha) rods treated with a 5% HF acid and silane. All specimens were subjected to a load of 1.2 kg during cementation, then stored under water for 36 hours. A jig mounted on a Hounsfield Universal Testing machine was used at a crosshead speed of 0.5 mm/min to test the shear bond strengths.

RESULTS

The results were 14.65 +/- 4.64 MPa for group I, 18.03 +/- 6.13 MPa for group II, and 22.35 +/- 5.98 MPa for group III In-Ceram specimens; and 18.05 +/- 8.46 MPa for control (group IV).

CONCLUSION

The use of Panavia 21 resin cement and a silane coupling agent can achieve a successful bond between either sandblasted or 5% HF acid-etched In-Ceram core material.

Comparative evaluation of secondary heat treatment and a high intensity light source for the improvement of properties of prosthetic composites

This study determined the hardness and water solubility of two prosthetic composites polymerized with three curing modes for the purpose of evaluating the influence of secondary heating and a high intensity light source on resulting material properties. Two prosthetic composite materials (Artglass and Dentacolor) were cured with the following methods: (1) exposure by means of a photo-curing unit with a xenon stroboscopic light source (Dentacolor XS) for 120 s; (2) exposure with the xenon unit for 120 s, followed by heating in an oven (KL 100) at 100 degrees C for 15 min; and (3) exposure by means of a photo-curing unit with two metal halide lamps (Hyper LII) for 120 s. Knoop hardness and water solubility were determined according to standardized testing methods. Although post-cure heat treatment considerably elevated the Knoop hardness number for both materials, the greatest hardness number was generated with the use of the metal halide unit. Water solubility of the Dentacolor material was lowest when the material was cured with the metal halide unit, followed by the secondary heated group, whereas, solubility of the Artglass material was unaffected by the curing modes. This suggests that the use of a high intensity light source is more effective than the application of secondary heating for improving the post-curing properties of composites.

Effects of four mixing methods on setting expansion and compressive strength of six commercial phosphate-bonded silica investments

Six commercial phosphate-bonded silica investments were mixed with four different mixing methods such as hand, two conventional blade-driven vacuum mixers and a new planetary mixing device, and examined for their setting expansion and compressive strength. The two properties often altered, depending upon the mixing method and the investment. The setting expansion of three investments were significantly affected by the mixing method while those of the other three were not. Compressive strength of all six investments varied by changing the mixing method. It is emphasized here that a mixing method and mixing condition must be properly set for each investment to improve the fit of the final metallic castings. This study also suggests that the planetary mixing device is a useful substitute for conventional blade-driven vacuum mixers.

Corrosion resistance of a magnetic stainless steel ion-plated with titanium nitride

This in vitro study evaluated the corrosion resistance of a titanium nitride (TiN) ion-plated magnetic stainless steel (447J1) for the purpose of applying a magnetic attachment system to implant-supported prostheses made of titanium. The surface hardness of the TiN ion-plated 447J1 alloy with varying TiN thickness was determined prior to the corrosion testing, and 2 micrometers thickness was confirmed to be appropriate. Ions released from the 447J1 alloy, TiN ion-plated 447J1 alloy, and titanium into a 2% lactic acid aqueous solution and 0.1 mol/L phosphate buffered saline (PBS) were determined by means of an inductively coupled plasma atomic emission spectroscopy (ICP-AES). Long-term corrosion behaviour was evaluated using a multisweep cyclic voltammetry. The ICP-AES results revealed that the 447J1 alloy released ferric ions into both media, and that the amount of released ions increased when the alloy was coupled with titanium. Although both titanium and the TiN-plated 447J1 alloy released titanium ions into lactic acid solution, ferric and chromium ions were not released from the alloy specimen for all conditions. Cyclic voltamograms indicated that the long-term corrosion resistance of the 447J1 alloy was considerably improved by ion-plating with TiN.

Shear bond strengths of orthodontic plastic brackets

The purpose of the present study was to evaluate the shear bond strengths of plastic brackets and the influences of the bracket filler contents on the bonding. The shear bond strengths of 4 plastic brackets (Spirit; Spirit MB; Clear Bracket; Aesthetic-Line) bonded to enamel with 4 orthodontic adhesives (Orthomite Superbond; System 1+; Transbond XT; and Kurasper-F) were compared with the strength of a conventional metal bracket. The findings of this study indicated the following: (1) shear bond strength of the 4 plastic brackets was significantly lower than that of the conventional metal brackets (P <.05), with most of the values ranging from 3 MPa to 6 MPa; (2) when comparing the bond strengths of plastic brackets, Aesthetic-Line had the largest value followed by Spirit MB, Spirit, and Clear Bracket, and when the plastic brackets were bonded with Orthomite Superbond, they showed relatively stronger bond strengths than when bonded with the other adhesives. Clear Bracket showed relatively lower values especially when bonded with System 1+; (3) the application of primer did not increase the durability of the bond strengths when bonding Spirit and Clear brackets; and (4) fillers contained in each plastic bracket ranging from 9.18% to 19. 52% were fairly well distributed and showed the same morphology of a fiber type 10 microm in diameter with different lengths. The filler concentration tended to correlate with the bond strength. The exposed fillers on the bracket base surface may play a more important role in plastic bracket adhesion than the macro-morphology of the base surface.

[An enamel adhesion study of Esterfill adhesives with chemical and light hardening]

The purpose of this work is to define the dependence of adhesive bond strength on a way of cure of adhesive system, application of the primer and bond in two step or in one step in vitro. Chemically curing "Esterfill bond" (AB) and both light-curing primer and bond, and composite hybrid light-curing restorative material "Esterfill PHOTO" (EP) (DIAS LTD, Russia) were used. The shear bond strength was measured according to recommendation of ISO 11405:1994. The apparatus for these tests corresponds to ISO 10477, addition I. Shear bond strength was measured on enamel of 83 extracted human molars. Teeth were divided into 7 groups. Before using of adhesive system enamel was etched by 37% phosphoric acid during 60 sec. For measuring of shear bond strength the post composite restorative material "EP" (dentin) has been used. The received data show that the shear bond strength does nat depend on the type of cure, the composition of the bonds being similar. Using primer before application of the bond increases the shear bond strength approximately by 4-5 MPa. The inclusion of the primer in the content of the bond system increases the adhesion to enamel by 9 MPa.

Development of small diameter intramedullary nails made from ISO 5832-9 stainless steel

BACKGROUND

In order to improve strength in small diameter intramedullary nails, a system was designed in which the implants were manufactured from 30% coldworked ISO 5832-9 stainless steel.

METHODS

Nail diameters were 9 and 10 mm for the femur, and 8 and 9 mm for the tibia. The nails were solid rods and the screws were partially threaded. Pre-clinical bending yield tests established that the 8-, 9- and 10-mm diameter rods had strengths comparable, respectively, with 10-, 12- and 14-mm diameter Grosse-Kempf nails. Forty-eight femoral and 98 tibial shaft acute fractures were treated with this system. Postoperatively, patients were allowed to gently bear weight as tolerated.

RESULTS

There was one broken nail, occurring 10 months after femoral nailing. There were six broken screws, occurring between 3 and 6 months postoperatively in two patients and after more than 6 months in four patients. The broken screws had no adverse clinical effect. Five patients required late bone grafting or exchange nailing, and 15 patients required dynamization.

CONCLUSION

This design of small diameter locked intramedullary nails was strong enough to allow early weightbearing.

Monkey pulpal response and microtensile bond strength beneath a one-application resin bonding system in vivo

OBJECTIVES

The aim of this in vivo study was to investigate the biocompatibility and microtensile bond strength of a one-application resin bonding system.

METHODS

Class V cavities were prepared on the facial surfaces of 36 intact monkey teeth, and the cavities were restored with an experimental one-application resin bonding system (TOF-1; Tokuyama Corp., Tokuyama, Japan) and a hybrid resin composite (PALFIQUE ESTELITE; Tokuyama Corp., Tokuyama, Japan). Histopathological changes of the restored teeth were evaluated at 3, 30 and 90 days after operation (N = 10). Microtensile bond tests were performed at 3 and 90 days after operation (N = 10).

RESULTS

Only two of 30 pulps showed a slight inflammatory cell infiltration. There were no statistically significant differences in the incidence of slight inflammatory cell infiltration among time periods. Bacterial penetration along the cavity walls could not be detected in any specimen. The mean microtensile bond strength at 3 days after operation was 20.6 MPa, and that at 90 days was 14.9 MPa. Differences in bond strengths between the 3 day specimen and the 90 day specimen were statistically significant (p < 0.05).

CONCLUSIONS

The one-application resin bonding system exhibited acceptable biologic compatibility to the monkey pulp. Although there were statistically significant differences in bond strengths between the 3 day specimen and the 90 day specimen, this material provided a hermetic seal, eliminating bacterial microleakage.

Effect of light-cure time on the initial shear bond strength of a glass-ionomer adhesive

With the introduction of photosensitive (light-cured) restorative materials in dentistry, various methods were suggested to enhance the polymerization of these materials including layering and the use of more powerful light-curing devices. The purpose of this study was to determine the effects of increasing the light-cure time on the initial shear bond strength (in the first half hour) of a resin-modified glass-ionomer adhesive. Eighty-six teeth were divided into 4 groups according to either; (1) the adhesive system used, namely resin, reinforced glass ionomer, or composite, and (2) the light-cure time for the glass ionomer adhesive, namely 40, 45, and 50 seconds. The bonding approach followed the manufacturer's instructions unless otherwise specified. The results of the analysis of variance comparing the 4 experimental groups (F = 19.4) indicated the presence of significant differences between the groups (P =. 0001). In general, the shear bond strength was greater for the composite adhesive system (¿x(-) = 5.2 +/- 2.9 MPa), followed by the 2 groups bonded with the resin-reinforced glass-ionomer adhesive and light cured for 50 seconds (¿x(-) = 3.8 +/- 1.1 MPa) and 45 seconds (¿x(-) = 3.4 +/- 2.7 MPa). On the other hand, the shear bond strength was significantly lower for the group bonded with the glass ionomer adhesive and light cured for 40 seconds only (¿x(-) = 0.4 +/- 1.0 MPa). The present findings indicated the following: (1) the resin-reinforced glass-ionomer adhesive has a significantly lower shear bond strength in the first half hour after bonding when compared to a composite resin adhesive; (2) the initial bond strength of the glass-ionomer adhesive was significantly increased by increasing the light-cure time for an additional 5 to 10 seconds; (3) the mean increase in the shear bond strength between 5 and 10 seconds of additional light curing was not significant but the variability was less with the longer cure time.