Microleakage of three luting agents used with stainless steel crowns.

The microleakage through margins of stainless steel crowns cemented with polycarboxylate, zinc phosphate, or glass ionomer cement was evaluated by measuring the amount of 4SCa leakage through the crown margins through 56 days after cementation in an in vitro environment. There was no cement-specific difference in marginal leakage as measured by this technique. The amount of leakage for each cement stabilized three days after crown placement and remained constant throughout the experimental period. The data suggest that the newer glass ionomer cement provides comparable protection to that of the other two traditional cements used with stainless steel crowns. Glass ionomer cement is the newest introduction to cements used for placing stainless steel crowns. The adaptation of glass ionomer material to tooth structure has been shown to be better than the adaptation of other restorative materials (Chan et al. 1985; McLean et al. 1985; Norris et al. 1986; Hicks et al. 1986). The close adaptation of glass ionomer to dentin and enamel has precipitated the development of formulations of glass ionomer for cementing extracoronal restorations. Yet, it is quality of the tooth preparation for the stainless steel crown in conjunction with the cement (Rector et al. 1985; Savide et al. 1979; Noffsinger et al. 1983) which retain the cemented crown onto primary teeth. Therefore, the most important properties of using a luting agent in the placement of stainless steel crowns onto primary teeth are those relating to resistance to local environmental factors. The amount of microleakage through the stainless steel crown margin is of particular concern (Andrews et al. 1976; Grieve et al. 1981). Many studies have examined various cements in terms of microleakage by using dye penetration and radiopermeability techniques (Mondelli and Galan 1987; Myers et al. 1983; Gordon et al. 1985; Shen and Herrin 1986). Dye penetration studies examine the permeability of the margin to a dye, after which an assessment of the linear amount of penetration is made (Crim and Shay 1987; Kanca 1987; Gordon et al. 1986). Radiopermeability studies do not require direct identification of leakage by the investigator in terms of penetration, as the measurement is determined by the scintillation counting device. The scintillation counting device quantitatively measures the amount of radioactivity in a solution which has traversed a margin or junction (Herrin and Shen 1985). This latter technique thus appropriate for producing a continuous variable subject to parametric statistical interpretation. Little has been done to examine the luting agent-related permeability of the cemented stainless steel crown using any technique. The purpose of this investigation was to determine the amount of microleakage through the margins of stainless steel crowns cemented onto primary teeth with glass ionomer cement relative to the marginal microleakage of stainless steel crowns cemented with zinc phosphate and polycarboxylate cements. Materials and Methods Twenty primary molars were selected from a supply of exfoliated or extracted teeth from the Department of Pathology at The University of Texas Dental Branch. Teeth were selected that had little or no decay, and sufficient intact tooth structure so that a good crown marginal seal could be obtained on the basis of a good clinical examination. Each of the 20 teeth were hand scaled and cleaned to remove debris and stored in room temperature tap water. Teeth (specimens) were mounted in a self-curing acrylic base to allow ease in handling. Each specimen was weighed and the acrylic was trimmed so that each specimen weighed 4.5 g. Pediatric Dentistry: September, 1988 Volume 10, Number 3 195 The acrylic was coated with polyurethene to provide a sealed surface. Standard stainless steel crown preparations were made on all teeth. A #6 round bur-size hemispherical preparation was made at the center of the occlusal surface. A pretrimmed and precrimped stainless steel crown (Ion -3M Dental Products Division; St Paul, MN) was custom fitted for each tooth. Each crown was crimped and contoured to allow for the best marginal fit achievable on the basis of a thorough examination with an explorer. The specimens were randomly divided into four groups. Each specimen was labeled by group; i.e., control (no cement), zinc phosphate (Fleck’s Cement-Mizzy Inc, Clifton Forge, VA), polycarboxylate (Durelon -Premier Dental Products Co, Norristown, PA), or glass ionomer (Ketac-Cem -ESPE-Premier Sales Corp, Norristown, PA). The specimens were dried thoroughly and a damp cotton pellet (deionized water) was placed in the occlusal recess (Fig 1). Five F~G 1. Pellet containing 45Ca placed into occlusal well. microliters of a 2.0 ~tCi/~tl solution of 4sCa was pipetted onto the saturated cotton pellet of each specimen. Each custom crown was cemented or placed onto its specific specimen (Fig 2). Each specimen then was positioned in its own 8oz jar containing 70 ml of physiologic saline, and a screw-top lid was placed (Fig 3). The jars were put into a large electric water bath maintained at 37°C and then submerged about twothirds of their height. One day, 3 days, 7 days, and 8 weeks after placement of the crowns, two 50-~tl samples of fluid were pipetted from each specimen jar and placed into separate scintillation mini-vials. Six ml of scintillation fluid (Ready F~G 2. Crown placement. Solv TM -Beckman; Fullerton, CA) was added to each of the 40 vials. The vials were lidded, labeled, and placed in counting racks in which scintillations per minute were measured by a liquid scintillation counter (Beckman). Results The radioactivity in each sample was corrected for background; the counting efficiency was calculated using the external standard method and was expressed as disintegrations per minute. Disintegrations per. minute were corrected to express what would have been the original level of activity considering the 164-day half life of 4sCa using the equality: A = Aoe (-0.693t/T1/2) where: A = converted activity at time of sample A° = original activity of isotope (2.0 ~tCi/~tl) FIG 3. Specimen immersed in saline. t -number of days after isotope production T1/2 = half life of 4sCa (164 days) Analysis of variance confirmed no significant difference between the leakage of radioisotope through the margins of crowns placed without cement and those placed with any of the three cements at each of the four sampling times after crown placement (Fig 4). There was no statistical difference in the leakage of radioisotope through the margins of crowns cemented with glass ionomer cement, zinc phosphate cement, and polycarboxylate cement at any sampling time postcementation. Scintillation counts were.statistically lower one day postcrown placement that at any subsequent sampling time through 56 days (P < .05; Fig 4). Radioisotope leakage through the margins of all specimens was not detectably different at any sampling time after I day for any of the cements.