Porosity in manually and machine mixed resin-modified glass ionomer cements.

The powder and liquid components of resin-modified glass ionomer cements are available in manual and machine mixed forms. This study quantified the effect mixing methods have on the porosity and shear strength of a resin-modified glass ionomer cement (RMGIC). A RMGIC (Fuji II LC) was manually or machined mixed according to manufacturer's instructions. Thin, disc-shaped specimens (n = 5) were made by compressing the cement between glass platens to a thickness of approximately 76 microns. The specimens were light cured for 120 seconds. Digital images of the specimens were recorded using a measuring microscope and slide film scanner. Digital imaging software was used to determine the number and volume of the cement's pores. Shear test specimens of manual and machine mixed cements (n = 10) of each group (approximately 800 microns thickness) were made as previously described. Shear punch tests were conducted using a 3.75 mm diameter punch mounted on a universal testing machine. The mean number and total volume of pores in the manually mixed specimens was considerably greater than that of the machine mixed group (p < 0.05). The shear punch test results of the machine mixed group was significantly higher than the manual mixed group, (p < 0.05).

Effects of abutment size and luting cement type on the uniaxial retention force of implant-supported crowns.

STATEMENT OF PROBLEM: The assumption that increasing the diameter of the abutment/crown components will provide greater resistance to crown loosening forces than standard-sized components has not been reported either with clinical trials or in the laboratory. PURPOSE: This study attempted to determine what effect abutment dimension and type of luting agent have on the retention of the prosthetic crown. METHODS AND MATERIAL: Test specimens consisted of standard, wide, and "experimental" CeraOne titanium abutments and matching CeraOne gold cylinders cemented with a zinc phosphate permanent or a zinc oxide eugenol provisional cement. The mean uniaxial force (Newtons) and the load (MPa) required to dislodge the cylinder from the abutment was determined. Statistical analysis of the sample data was performed using a 2-way analysis of variance test (alpha=.05). RESULTS: Mean uniaxial resistance force (Newtons) was significantly greater for zinc phosphate cement than for zinc oxide cement (P <. 001). Abutment size was a significant factor when permanent luting cement is used (P <.001). Retention strength per unit area (MPa) of the wide abutments was lower than the standard size and "experimental" abutments. CONCLUSION: Permanent luting cement produced uniaxial retention forces approximately 3 times greater than provisional cement. The increase in surface area provided by a wide abutment did not result in an improvement in retention strength over the standard abutment.

Resistance to condensation of 'condensable' resin composites as evaluated by a mechanical test.

This study compared the resistance-to-condensation forces of recently introduced condensable resin composites to that of amalgams and conventional resin composites. Using the flat platens of a servohydraulic testing machine, cylindrical specimens of each material 2.8 mm in diameter and 5.5 mm in length were compressed diametrally over two seconds to a thickness of 0.75 mm. Peak forces generated during compression were recorded. This method ranked the various classes of restorative material for resistance to condensation in the same order as most clinicians subjectively reported, with the highest forces observed with admixed dental amalgams, followed in order by spherical amalgams, condensable resin composites and conventional resin composites. Although peak forces observed with the condensable resin composites were generally higher than those observed with conventional resin composites, these were significantly lower than the peak forces observed with amalgams.

Effect of plasma arc curing on the microleakage of Class V resin-based composite restorations.

PURPOSE: To evaluate the effect of plasma arc light-curing on the microleakage of Class V resin-based composite (RBC). MATERIALS AND METHODS: Facial and lingual Class V cavities were prepared at the cemento-enamel junction of extracted third molars. Restorations of the two materials (Z250; Amelogen) were placed, using the supplied dentin adhesives (Single Bond; PQ 1, respectively), and light-cured by either a halogen light curing unit (H) or a plasma arc curing unit (P). After thermal cycling, the teeth were immersed in methylene blue dye, then sections of the restored teeth were visually assessed for leakage. RESULTS: No leakage was observed at the interface between enamel and RBC in any restoration in this study. At gingival margins, the incidence of leakage (slight/severe) was: Z250 H = 2/4, P = 6/6; Amelogen H = 3/4, P = 1/12, where n = 16. The greatest incidence of leakage was observed in restorations cured by the plasma arc method. A two-way ANOVA of leakage data rankings showed curing method to be a significant factor (P = 0.002), restorative material not to be a significant factor (P = 0.24), and no significant interaction between material and curing method (P = 0.38).

Qualitative and quantitative determination of dental amalgam restoration volume.

STATEMENT OF PROBLEM: Volume of tooth structure replaced by an existing restoration, as assessed by visual and radiographic examination, is one diagnostic measure used by dental practitioners and dental insurance agencies to determine the relative need to restore a tooth with a full-coverage cast restoration. However, use of these methods has not been validated. PURPOSE: This study compared the volume of a range of dental amalgam restorations placed in typodont teeth, as estimated by dentists, dental students and laypersons, with the actual volume of each restoration. METHODS AND MATERIAL: Sixty subjects (20 dental school faculty, 20 dental students, and 20 clerical staff [laypersons]) participated. After reviewing photographic images of typodont teeth with mesial-occlusal-distal dental amalgam restorations, subjects estimated the volume of each restoration using various restorations on different teeth as a percentage of its tooth's coronal volume. The actual volume of each dental amalgam restoration and that of the coronal portion of the prepared teeth was calculated with a volumetric displacement technique. The single sample 2-sided t test with a.05 level of significance was used to evaluate the null hypothesis (H0 ): The survey participant's estimates of each restoration's percentage volume are the same as the measured volume values versus the alternative hypothesis (H1 ): estimates differed from the measured volume values. One-way analysis of variance was used to determine the significance of any difference between the estimates of the 3 survey test groups. RESULTS: Average volumes reported by all 3 groups were significantly different than the measured volume values (P <.05). Experience and dental training did not significantly affect a participant's ability to evaluate restoration volumes with greater accuracy. Results reported by dentists, dental students, and laypersons were not significantly different (P >.05). CONCLUSIONS: The volume of a restoration is inaccurately assessed by visual and radiographic examination.

Effects of food/oral simulating fluids on microstructure and strength of dentine bonding agents.

This study evaluated the effect a food simulating solution, 75% v/v ethanol/water, and an artificial saliva, Moi-Stir, have on the microstructure and on the diametral tensile strength (DTS) of three dentine bonding agents (Tenure, Scotchbond Multi-Purpose and Optibond). The microstructure was examined by using a scanning electron microscope (SEM). The DTS data were analysed using ANOVA and the Tukey LSD test. The microstructural observations were compared with changes in DTS. The SEM observation revealed deterioration of all bonding agents due to conditioning in the solutions for 30 days. The different solutions appeared to cause different reactions in the bonding agents. However, these effects may be exaggerated due to the presence of an air-inhibited surface layer. Those conditioned in Moi-Stir showed swelling. The presence of filler particles in the Optibond bonding agent appears to decrease the deterioration resulting from soaking. Materials conditioned in ethanol exhibited both dissolution and thinning. Diametral samples of each bonding material were tested after being conditioned in the above-mentioned solutions for 1, 7, 14 and 30 days. Conditioning significantly decreased the DTS of all bonding agents, except Optibond in Moi-Stir. Filled Optibond maintained its DTS longer than did the two unfilled bonding agents. The decrease in DTS of all the ethanol-conditioned groups is a function of the square root of time (P < 0.001) and conforms to Fick's laws of diffusion. The filled Optibond showed a lower ethanol diffusivity (0.5 x 10(-5) cm2 s-1) than the other two unfilled bonding agent systems (average 1.2 x 10(-5) cm2 s-1) (P < 0.05). The high ethanol diffusivities were thought to be due to the presence of HEMA, a hydrophilic resin, in the bonding agent. These results also suggest that solution uptake occurred through the resin matrix. Filler particles may therefore play an important role in weathering resistance of these materials to oral environment solutions. The physical appearance and strength of dentine bonding agents are significantly altered by exposure to oral environment solutions.

Bond characteristics of porcelain fused to milled titanium.

OBJECTIVES: A bonding agent has recently been introduced that prepares the surface of milled titanium copings for bonding to low fusing dental porcelains. This study evaluated the effectiveness of the bonding agent by comparing the shear and three-point bending strength of specimens made with three combinations of materials: 1) milled titanium/porcelain with bonding agent, 2) the same milled titanium/porcelain without bonding agent, and 3) cast high palladium/conventional porcelain. METHODS: Shear specimens consisting of porcelain cylinders 6 mm in diameter and 8 mm in length were fired to the ends of metal cylinders 6 mm in diameter and 13 mm in length. Three-point bend specimens made of 25 x 3 x 0.5 mm metal bars were veneered with 8 x 3 x 1 mm of porcelain in the bar's center. Specimens were tested in shear and bending in a universal testing machine. The data were analyzed using one-way ANOVA and Newman-Kuels post hoc tests (p = 0.05). RESULTS: When a titanium bonding agent was used, porcelain to titanium bond strength was slightly but statistically significantly greater than the porcelain to high palladium bond strength. The result was the same when measured by both shear and three-point bending tests. Without the bonding agent, the shear strength of porcelain to titanium was significantly lower than that of the bonding agent and high palladium groups. SIGNIFICANCE: The use of a bonding agent improves the bond strength of porcelain-fused-to-milled titanium.

The effects of peroxide bleaching on composite to enamel bond strength.

OBJECTIVES: The objective of this in vitro study was to evaluate the effects of an in-office type of bleaching regimen on the composite to enamel bond. METHODS: The enamel on forty extracted human teeth was subjected to a 25% hydrogen peroxide bleaching treatment. Ten additional unbleached specimens served as controls (Group A). The 40 bleached specimens were divided into four equal groups (Groups B-E). Composite cylinders were bonded to the prepared surfaces at various time intervals following bleaching. Group B was bonded immediately, Group C at 1 d, Group D at 1 wk, and Group E at 1 mon post-bleaching. RESULTS: Mean shear bond strength values showed a significant decrease in bond strength for Group B. However, the bond strength returned to normal values after 1 d and remained normal for at least 1 mon. Scanning electron microscope examination showed an apparent decrease in the number of resin tags present in the enamel/composite interface for Group B compared with the other groups including controls. SIGNIFICANCE: Polymerization inhibition of the resin bonding agent is the likely mechanism for the effects of the bleaching on bond strength.

Mechanical properties of heat-treated composite resin restorative materials.

Clinical methods for heat treating composite resin restorations have been developed. In this investigation, the effect of heat treatments on the diametral tensile strength of composite resin was determined. The composite resin restorative materials were selected according to the manufacturers' suggested use for anterior or posterior teeth, filler particle composition, and light-cured or chemical polymerization. Samples were prepared according to American Dental Association specification No. 27, and heat treatments were accomplished with a Coltene DI 500 oven for curing at approximately 120 degrees C for 7 minutes. Heat treatment substantially increased the diametral tensile strength tested, with the exception of the anterior hybrid particle (p less than 0.05). Composite resins with fine-particle inorganic fillers were significantly stronger than hybrid and microfilled composite resins.

Shear bond strength of dental amalgam bonded to dentin.

The objective of this study was to determine the shear bond strength of dental amalgam bonded to dentin with adhesives. Four groups of 15 permanent posterior teeth were used in this study. The occlusal enamel of the teeth was removed to produce a flat dentin surface. The teeth were embedded in phenolic rings with acrylic resin. Vinyl polysiloxane ring molds 4 mm thick with 4.5 mm circular openings were attached to the exposed dentin surface. Adhesives applied to the dentin surfaces prior to amalgam placement and condensation included: Amalgambond, a 4-META/TBB-MMA, HEMA based system (A), Panavia EX, a modified phosphate ester of Bis-GMA luting system (P), and Ketac-Cem, a glass ionomer luting cement (K). A dentin bonding agent and composite resin restoration system (Scotchbond 2/Silux Plus) was included for comparison. The specimens were stored in 37 degrees C water for 7 days prior to testing. Shear bond tests were done in an Instron machine at a crosshead speed of 0.02 inches per minute. The data were analyzed by ANOVA at 5% level of significance. The differences in shear bond strengths of the four test groups were not statistically significant (P = 0.115). Fracture patterns of the bonded amalgams, examined by SEM, were adhesive in appearance for Groups A and K and cohesive for Group P.

Effect of disinfectant solutions on the wettability of elastomeric impression materials.

The wettability of impression material affects the number or volume of air bubbles generated during the pouring of gypsum casts. This study was done to determine the effect of various commercial disinfectant solutions on the wettability of elastomeric impression materials. The technique of measuring advancing contact angles of aqueous solutions of calcium sulfate was used to determine changes in the wettability of four types of impression material before and after immersion in one of five disinfectants. All disinfectant solutions that were tested increased the wettability of polysulfide. Chlorine dioxide produced the greatest increase in the wettability of polysulfide by decreasing the contact angle on polysulfide at least 48 degrees. All disinfectants decreased the wettability of hydrophilic addition silicone by increasing the contact angle up to approximately 30 degrees. The differences were significant as determined by paired Student t-tests. Addition silicone was the material most resistant to change in contact angle. Chlorine dioxide had the greatest beneficial effect on wettability.