John W. Reinhardt

The Effect of Dental Amalgams on Mercury Levels in Expired Air

The expired air of a group of 48 persons, 40 with and eight without dental amalgam restorations, was analyzed for its mercury content before and after chewing. Expired air samples were collected in polyethylene bags, and a known quantity of each was pumped into the mercury detector for measurement. The results showed that examined subjects with dental amalgams had higher pre-chewing mercury levels in their expired air than those without amalgams. After chewing, these levels were increased an average of 15.6-fold in the former and remained unchanged in the latter group. It was concluded that in situ dental amalgams can increase the level of mercury in expired air.

Bond strength and microleakage of current dentin adhesives

OBJECTIVES The purpose of this in vitro study was to evaluate shear bond strengths and microleakage of seven current-generation dentin adhesive systems. METHODS Standard box-type Class V cavity preparations were made at the cemento-enamel junction on the buccal surfaces of eighty extracted human molars. These preparations were restored using a microfill composite following application of either All-Bond 2 (Bisco), Clearfil Liner Bond (Kuraray), Gluma 2000 (Miles), Imperva Bond (Shofu), OptiBond (Kerr), Prisma Universal Bond 3 (Caulk), Scotchbond Multi-Purpose (3M), or Scotchbond Dual-Cure (3M) (control). Lingual dentin of these same teeth was exposed and polished to 600-grit. Adhesives were applied and composite was bonded to the dentin using a gelatin capsule technique. Specimens were thermocycled 500 times. Shear bond strengths were determined using a universal testing machine, and microleakage was evaluated using a standard silver nitrate staining technique. RESULTS Clearfill Liner Bond and OptiBond, adhesive systems that include low-viscosity, low-modulus intermediate resins, had the highest shear bond strengths (13.3 +/- 2.3 MPa and 12.9 +/- 1.5 MPa, respectively). Along with Prisma Universal Bond 3, they also had the least microleakage at dentin margins of Class V restorations. SIGNIFICANCE No statistically significant correlation between shear bond strength and microleakage was observed in this study. Adhesive systems that include a low-viscosity intermediate resin produced the high bond strengths and low microleakage. Similarly, two materials with bond strengths in the intermediate range had significantly increased microleakage, and one material with a bond strength in the low end of the spectrum exhibited microleakage that was statistically greater. Thus, despite the lack of statistical correlation, there were observable trends.

Build-up and Repair of Light-cured Composites: Bond Strength

Interfacial bond strengths of light-activated composites were measured as a function of age using a transverse strength test. Bond strength between layers decreased with the age of the initial layer and reflected the setting curves of the composites. The highly-filled composites exhibited the greatest bond strengths. Uncut surfaces provided a better substrate for bonding than did ground surfaces. Use of a bonding agent on both uncut and ground surfaces improved bond strengths. Mean repair strengths of light-activated composites were similar to those of selfcuring composites. Composites with ground surfaces aged for one wk had mean repair strengths 27% of the cohesive strength without bonding agent and 48% with bonding agent.

Composite Resin Compatibility and Bond Longevity of a Dentin Bonding Agent

The shear strength of a commercial dentin bonding agent was studied using human dentin in vitro. The agent was tested for compatibility with three proprietary composite resins. In addition, some samples were subjected to prolonged water immersion and thermocycling to determine effects on bond strength. There was no statistically significant difference in shear strengths when the three composite resins were used. In addition, there was no difference in shear strengths among those samples thermocycled or immersed for up to one year. The implications of this study are that the dentin bonding agent may be used with several composite resins with no significant difference in bond strengths, and that the bond seems stable when subjected to immersion or simulated intra-oral thermal stresses.

Exhaled mercury following removal and insertion of amalgam restorations

P atient exposure to mercury from dental amalgam and restorative procedures has not been studied as extensively as mercury exposure to dental personnel. One. study found that in a group of 114 adults not undergoing dental treatment, only six had measurable mercury in the urine, and one of those persons was using a mercurial diuretic.’ This was compared to a group of 24 persons currently undergoing dental treatment. Of that group five showed mercury in the urine before and after treatment. The possibility of mercury absorption from sources other than dental amalgam, such as mercurial antiseptics and germicides, was discussed. The study concluded that dental amalgams do not appear to be an important source of mercury absorption and excretion. In another study Frykholm2 used a radioisotope of mercury in placing four or five amalgam restorations in each of five patients. The urinary excretion of radioactive mercury gradually increased for each individual and reached an average peak of 2.5 pg/liter on the fifth day following treatment. In each case the level then dropped to zero by the seventh or eighth day, at which time the radioactive amalgams were removed to avoid further exposure. On the day following removal, urinary levels of mercury rose to 5 pg/liter and then dropped to zero in 2 days. Some investigators have found urinary excretion of mercury to be quite irregular and therefore an unreliable measure of quantity absorbed. Following exposure there is an early rapid phase of urinary excretion followed by a slower phase that may account for more

Shear strengths of ten commercial dentin bonding agents.

Abstract Numerous chemical agents have recently been introduced for the purpose of bonding composite resins to dentin. This in vitro study examined the shear bond strength of 10 dentin bonding agents which are commercially available. The bonding agents were used to attach a visible-light-curing microfilled composite resin (Silux) to extracted human teeth. Significant differences in bond strength were found using the different dentin bonding agents. The mean shear strengths ranged from 1 to 93 kg/cm2. Many of the products created a dentin bond which is stronger than that reported for glass ionomer restorative materials. There was no difference in the bond strengths of each product when bonded by either of two investigators.

The effect of removal of the smear layer on microleakage of Class V restorations in vitro

Abstract The effect of removal of the dentinal smear layer on microleakage of Class V restorations in vitro was evaluated using 3 restorative techniques: a composite resin with its dentin bonding agent, a composite based with glass-ionomer lining cement, and a glass-ionomer restorative cement. The agent used to remove the smear layer was a commerical 10% polyacrylic acid. Removal of the smear layer did not have any affect on microleakage of each of 3 types of restorations considered separately. The results favor removal of the smear layer only when a glass-ionomer linear is used under the composite restoration. The microleakage of the glass-ionomer restorations was greater than either the composite or composite based with glass-ionomer liner.

Determining smoothness of polished microfilled composite resins

lhe surface roughness of composite resin restorations presents a problem to the restorative dentist. Plaque accumulation, gingival irritation, and increased staining of the restoration result from the surface roughness.‘.’ Glazes of unfilled or lightly filled resin have been advocated for improving the surface smoothness of polished composite resins.4 Although a glazed composite resin restoration provides greater surface smoothness than an unglazed restoration, the glaze must be applied periodically.5 Regardless of whether one chooses to use a glazing material, the finishing and polishing procedures are important to the success of the restoration. Many studies on the best method for polishing composite resin restorations have been reported, but the results have been contradictory. Some studies found that carbide finishing burs or finishing burs followed by a white stone provide an acceptable surface.6-s One study determined that a 12-fluted carbide finishing bur followed by zirconium silicate disks was the best of four procedures tested.9 Another report, favoring fine sandpaper and aluminum oxide disks, found carbide burs to be the worst of those procedures tested. lo Although one study showed polishing pastes to be superior to conventional techniques, another found pastes to be less acceptable.“-” Polishing disks were found superior in other studies.“, I4 In an effort to eliminate the problems of surface roughness, new composite resin materials using smaller filler particles have been developed. Some of the new

Acid etch bonded cast orthodontic retainers

We have described a technique which involves the use of a cast orthodontic retaining appliance bonded by the acid etch technique and composite resin for semipermanent retention. The technique provides an alternative form of treatment which offers some unique advantages over previous retentive techniques.

Comparison of the retentive strength of two cast gold pin techniques

The retention contributed by the use of pins with gold castings can be substantially increased by the technique of placing a threaded pin in the dentin and making a casting with a threaded receptacle to fit the pin. The basis for the improvement is the greater retention of threaded pins to dentin compared to that of smooth, cemented pins that are part of the casting. The limitation on the retention achieved with the new technique is the cohesive strength of the cement. Zinc phosphate cement provided the highest retention, and EBA and polycarboxylate cements provided lower and similar retention when threaded pins were cemented to threaded receptacles.