Evaluation of various forms of calcium hydroxide in the monitoring of microleakage R.L. Rehfeld1 R.B. Mazer2 K.F. Leinfelder3. C.M. RusselP

'Dental Student, School of Dentistry 2Department of Restorative Dentistry 3Director, Biomaterials Clinical Research 4Graduate Student, Department of Cariology School of Dentistry University of Alabama Box 49 SDB Birmingham, AL 35294 Received June 19,1990 Accepted May 15,1991 *To whom correspondence should be addressed Dent Mater 7:202-205, July, 1991

Abstract-Calcium hydroxide has been shown to be an effective medium for the in vivo microleakage testing of amalgams. The purpose of this study was to determine the relative effectiveness of several forms of calcium hydroxide in the measurement of this clinical problem. It was also the purpose of this study to determine whether a relationship exists between the pH of the Ca(OH)2 liner and its ability to detect microleakage. Standardized Class V preparations were generated on the buccal surfaces of extracted molars. The axial walls of the preparations were based either with Dycal, Dycal VLC, Pulpdent Liquid, or pure Ca(OH)2. A series of teeth without a calcium hydroxide base served as the negative control. All teeth were restored with a spherical amalgam and kept in de-ionized water. The surfaces of the restorations were then subjected to 20 mL of 2°C water for a period of one min. After three min, a color-indicating pH paper was positioned over the restored area for detection of the presence of hydroxyl ions atthe amalgam/tooth interface. Regardless of the form of calcium hydroxide, all indicated extensive microteakage immediately after insertion of the restoration. In all cases, the number of samples generating positive results for leakage decreased over a period of time. The rate of decrease, however, was substantially dependent upon the form of calcium hydroxide used as well as its pH. The reagent grade of Ca(OH)2 generated the greatest percentage of positive results for the longest duration.

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icroleakage testing of restorative materials has been carried out for many years. The majority of these tests evaluate the penetration of fluids along the margins of the restoration. The primary difference among the various testing methods has generally been the selection of the penetrating medium. Many studies have used thermocyclingin radioactive substances, followed by tooth sectioning and autoradiography. While radioactive 32p and 131I have been used by various investigators over the years (Wainwright et al., 1959), the most common tracer has been 45Ca (Hampel, 1959; Armstrong and Simon, 1958; Taylor et al., 1959; Kawamura et al., 1983). Various colors of dye have also been used in microleakage studies. Most commonly, these have included aniline blue, fluorescein (Alpersteinet al., 1983), and basic fuchsin (Leinfelder et al., 1986). Depending upon the investigator, these tests have been used both with and without thermocycling. The greatest disadvantage to these methods is that they require sectioning of the restored teeth. Consequently, none of them can be recommended for clinical testing. In this regard,Burrows (1969) suggested the use of a Ca(OH)2 base as a means for determining microleakage. The method consisted of monitoring pH changes at the restoration-tooth interface by means of colorindicating pH paper. Since this method required no sectioning of the restored tooth being evaluated, or immersion in dyes or radioactive tracers, it had the potential for use in in vivo testing. Recently, in fact, this method has been shown to be quite effective in monitoring microleakage in the oral cavity (Leinfelder et al., 1986). Since the composition of dental calcium hydroxide bases is quite varied, it can be expected that they would exhibit a wide range of properties. These include solubility, acid penetration, and range ofpH (de Freitas, 1982, 1984; Pereira et al., 1980; Forsten, 1984; McComb, 1983; Hwas and Sandrik, 1984; Forsten and Sbderling, 1983). It is possible, there-

202 Rehfeld et al./ Various Ca(OH)Jorms for monitoring of microleakage

fore, that some types of calcium hydroxide bases may be more effective than others in the monitoring ofmicroleakage. The purpose of this' study, then, was to determine the relative effectiveness of different forms of calcium hydroxide in the monitoring of microleakage. It was also the intent of this investigation to determine a possible relationship between the pH of the calcium hydroxide liner and its ability to detect microleakage. All testing was carried out in conjunction with an ADA-certified amalgam restorative material. M A T E R I A L S AND METHODS

Non-carious molar teeth previously stored in formalin were cleaned with pumice and then transferred to de-ionized water at 37°C. Only those teeth that were considered sound and free of cracks and caries lesions were selected for the study. A No. 56 carbide bur was used to generate standardized Class V cavity preparations on the buccal surfaces of each tooth. All cavosurface margins were located in enamel. In every case, the preparations were extended 4 mm mesiodistally, 2 mm occluso-gingivally, and 2 mm pulpally. All cavity preparat{ons were generated in the presence of an ample water spray. After the preparation was thoroughly washed and dried, one of four different forms of calcium hydroxide was applied to the surface of the axial wall. In each case, a small-ball burnisher (1.0 mm diameter) was used to apply a thin layer of the calcium hydroxide liner to the axial wall. Care was taken to avoid all other surfaces adjacent to the axial wall. A description of each type of calcium hydroxide product included in the study as well as the respective manufacturer is given in the Table. These included a reagent-grade calcium hydroxide, Pulpdent, Dycal, and Dycal VLC. All proprietary forms of calcium hydroxide were manipulated in accordance with the manufacturer's recommendations. The reagent grade of calcium hydroxide, however, was mixed with water (1:1) to form a paste. After application to the

axial wall, it was gently dried with air until it took on a frosty white appearance. A total of 45 microleakage samples was included in the study. Each form of calcium hydroxide was represented by 10 samples. Oneset of specimens was not treated with calcium hydroxide and served as the negative control. This group, however, contained only five specimens. After the calcium hydroxide liner was applied, all preparations were restored with a high-copper amalgam (Tytin, S.S. White, King of Prussia, PA). All amalgams were triturated for seven s at a medium speed (Varimix III, L.D. Caulk, Milford, DE). The alloy was then handcondensed in two increments by use of a 1.4-mm-diameter condenser for the first and a 2.3-ram- diameter condenser for the second. No horizontal condensation was used. The restoration was then carved to normal anatomic form only. No burnishing or polishing procedures were used. At this point, all the teeth were identified with a numerical code and then stored in 37°C de-ionized water in preparation for microleakage testing. Tytin was selected as the amalgam restorative material, since it consists entirely of spherical particles. Due to their shape, the alloy is more difficult to force against the wall of the preparation by use of standard condensation techniques. Consequently, as a spherical particle alloy, it tends to exhibit more marginal leakage than do those with irregularly shaped particles (Mahler and Nelson, 1984). Microleakage Procedures.--Prior to being tested, each sample was washed with de-ionized water. Next, a 20-mL quantity of de-ionized ice water (1-3°C) was dripped over the restored surface over a period of one min. Then, a dampened color-indicating pH paper (pHydrion 6-8, Micro Essential Lab., Brooklyn, NY) wasplaced over the restored surface and held in position under light pressure for one min. A color shift from yellow to blue on the pH paper in the area overlying the margins of the restoration was recorded as a positive test for microleakage. This procedure is essentially the same as that described previously by Leinfelderet al. (1986). At the end of the study, the restorations were carefully removed, and the remaining calcium hydroxide base was exposed to the dampened pH paper in an effort to determine its ability to release

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hydroxyl ions. Microleakage tests were carried out for up to 203 days. All specimens, including the control, were tested on a randomized basis. Since all of the specimens exhibited the same physical appearance, identification during testing was highly improbable. By use ofthe Two-tailed Fisher Exact test, all combinations of the various test groups at each test period were analyzed for statistically significant differences in microleakage. Significance was presumed for any p value less than 0.05.

RESULTS The results of the microleakage tests for the various forms of Ca(OH)2are shown in Figs. 1 and 2. Each data point represents the percent of samples for a given form of calcium hydroxide exhibiting a positive microleakage result. The microleakage values obtained for the first 30 days are presented in Fig. 1. Those for the entire length of the study are presented in Fig. 2. As can be seen in the second Fig., the values generally fell intothree different groups. As a rule,

Dental Materials ~July 1991 203

TABLE

VARIOUS RESTORATIVE MATERIALS AND pH INDICATING AGENTS INCLUDED IN THE STUDY Material

Type

Manufacturer

Tytin

High-Cu amalgam, Spherical

S.S. White, King of Prussia, PA

Calcium Hydroxide

Reagentgrade

Pulpdent Liquid

Ca(OH)2 base

Pulpdent Corp., Brookline, MA

Dycal

Ca(OH)2 base

L.D. Caulk/Dentsply, Milford, DE

Adv. Form III

Chemical-cured

L.D. Caulk/Dentsply, Milford, DE

Prisma VLC

Ca(OH)2 base

L.D. Caulk/Dentsply, Milford, DE

Dycal

Light-cured

L.D. Caulk/Dentsply, Milford, DE

pHydrion 6- 8

Color-indicating pH paper

Micro Essential Laboratory, Brooklyn, NY

the amalgam restorations with the pure form of calcium hydroxide (Group 1) exhibited the greatest percentage of microleakage over the longest period of time. Dycal (regular) and Pulpdent samples generally fell into the middle group. During the first month of testing (Fig. 1), however, the teeth based with the Pulpdent were not statistically distinguishable (p

Evaluation of various forms of calcium hydroxide in the monitoring of microleakage.

Calcium hydroxide has been shown to be an effective medium for the in vivo microleakage testing of amalgams. The purpose of this study was to determin...
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