The Influence of Finishing Technique on Microleakage X i n Yi Ya, M.M." Gerard Wieczkwski, D.D.S. f Elaine L. Davis, Ph.D.S Robert B. Joynt, D.D.S.9

Four different finishing techniques were used in a dentin bonding agendcomposite resin restorauon to evaluate the possible influence of finishing technique on microleakage. Results indicated that finishing technique affects the ability of the restorative system to resist microleakage. Under the conditions of this study, best results were achieved with a 30-fluted bur followed by a short wet polish. Samples finished dry with polishing disks demonstrated considerable microleakage. This study also suggests that homogeneous nonagglomerated microfilled composite resin does not require disk finishing.

T

were evaluated for microleakage at the enamel and dentin margins. Twenty freshly extracted human mandibular molar teeth were used. A Class V cavity, approximately 4 mm in length x 4 mm in width x 2 mm in depth, was prepared on both the buccal and lingual surfaces. A #56 bur rotating at high speed with air-water coolant was used to create the cavity preparations. Preparations were completed with the #56 bur in a conventional speed handpiece. The preparations were located so that the occlusal margin was placed in enamel and the gingival margin was in dentidcementum. Enamel margins were beveled with a fine diamond. Restorative materials were placed in accordance with the manufacturer's instructions. The enamel surface was etched for 15 sec prior to the placement of restorative materials. Tenure Dentin Conditioner was then applied to the dentin with a small brush and left undisturbed for 30 sec. The surface was washed with an air-water spray for 20 sec and air-dried. Two drops of Tenure Solution A and Tenure Solution B were mixed in a plastic dappen dish and applied with a brush to the conditioned dentin surface. Following a 20-sec drying period, a second application was made and dried with an air blast from a dental syringe. Visar Seal (Den-Mat) was applied to the treated dentin surface with a brush and polymerized for 20 sec with visible light. Perfection composite resin was then applied to the treated cavity surface in two increments, with each increment cured for 40 sec. Four groups of 10 restorations each were established on the basis of finishing technique:

he prevention of microleakage depends largely on the maintenance of the seal of the restorative material to tooth structure. The restorative system must produce a bond to the cavity walls of sufficient strength to resist the stresses generated during polymerization shrinkage of the restorative resin and during normal occlusal function. Most in vitro microleakage studies have concentrated on the comparison of different restorative systems. However, microleakage results are sensitive to such factors as the time and method of storage between preparation and testing, thermocycling effects, and the type of composite resin used.1.2 Composite resin finishing techniques have varied considerably among microleakage studies.3-5 While some methodologies are vaguely stated, others are not mentioned at all. The purpose of this study was to investigate the possible effect of finishing technique on microleakage of a composite resin restorative system.

METHODS AND MATERIALS Tenure dentin bonding agent (Den-Mat, Santa Maria, CA) and Perfection composite resin (Den-Mat) *Assisrant Professor, Deparnnent of Operative Dentistry and Prosthodontics Department, Dental Hospital, The Fourth Military Medical University, Xian, P.R China TAssociare Professor and Chairman, Department of Operative Dentistry;

Ussimnt Professor, Deparnnents of Operative Dentistry and Behavioral SEienCes; %AssistantProfessor.Deparnnent of Operative Dentistry; State University of New York at Buffalo.School of Dental Medicine, BuEalo, New York. Address reprint requms to Elaine L Davis, Ph.D., State University of New Yo& at %&do, school of Dental Medicine, 235 Squire Hall, Main Street Camps, Bdalo, NY 14214. 0 1990 B. C. Decker Im.

1. 30-fluted bur with water, 10-15 seconds Extra-

142

Influence of Finishing Techniques on Microleakage

Smooth Polishing Paste polish; 2. 8-fluted bur with water, 50-60 seconds ExtraSmooth Polishing Paste polish; 3. Fine diamond bur with water, Finishing Disks Coarse to Polishing Disks NMC (Vivadent USA, Tonawanda, NY); 4. White stone without water, Finishing Disks Coarse to Polishing Disks NMC. All restorations were finished to a smooth, highly polished surface. Specimen apices were then sealed with Geristore (Den-Mat) to prevent dye penetration. The entire tooth was sealed with nail polish to within 1 mm of the restoration margin. Teeth were stored in 100 percent humidity at 37°C for 24 hours, then thermocycled at 4"C, 37"C, 54"C, and 37°C for 2,000 cycles. A complete cycle lasted 1 min and consisted of 15 sec at each temperature. After thermocycling, specimens were placed in 2 percent basic fuchsin dye solution for 24 hours. Upon removal from the dye solution, specimens were completely embedded in self-cure acrylic resin. After the resin had set, they were sectioned longitudinally at the center of the restoration with a low-speed diamond saw (Buehler Ltd, Lake Bluff, IL). Microleakage was determined as presence or absence of dye along the restoration-dentin interface. The tooth sections were examined at 30 X magnification under an optical microscope using the eyepiece reticula. The extent of leakage was also recorded in mm, and the mean score for each tooth was calculated by averaging the dye penetration in the two sections. The occlusal (enamel) and gingival (dentin) cavity walls were evaluated for microleakage separately.

RESULTS No microleakage occurred at the occlusal margins. Therefore, only results pertaining to the dentinal margins are presented in Table l. Because of the skewness of the data, nonparametric statistical methods were used, with microleakage dichotomized as presence or absence of dye. Chi square analysis indicated a significant overall relationship between finishing technique and microleakage (p < 0.05). Individual chi square comparisons, using the Bonferroni correction, indicated significant differences between the 30-fluted bur and both fine diamond and white stone finishing techniques (experiment-wise P < 0.05). There was no statistically significant differTable I . Mlcloleakage at the Dentin Margln (n=10 p e r group) Flnlshlng Instrument

30-fiuted bur

8-fluted bur flnedlarnond whlte stone

Mean Penetrdon

Imm) 0

.56

-75 1.16

No. of Samples Wlfb No l e a k a g e

10

6 3

2

143

ence in microleakage between the two fluted bur groups.

DISCUSSION Previous microleakage studies have paid little or no attention to finishing technique, and a short review of the literature revealed considerable variation in finishing method. After restoration placement, excess composite resin can be removed by various burs or stones, with or without water coolant, and restorations can be finished using polishing disks with or without lubricating paste. Clinically, anterior composite resin restorations are usually finished with disks to a smooth, highly polished surface. However, the microleakage studies reviewed for this study did not provide details regarding finish of the restoration. Results of this investigation indicate that the finishing technique does make a difference in a material's microleakage resistance. Under the conditions of this study, best results were achieved with a 30-fluted bur followed by a short wet polish. Samples finished dry with polishing disks (Groups 3 and 4 ) demonstrated considerable microleakage. Because the disks are used dry and the amount of filling material was small, excessive heat may have been generated during the polishing process. The difference in thermal coefficients of expansion between tooth structure and composite resin could have resulted in stress at the interface, creating gaps that allowed microleakage to occur. No microleakage occurred at the enamevrestoration margin. This suggests that finishing technique may be a concern only when the restoration's cavosurface margin is in dentidcementum. Disk finishing techniques were developed as a means of polishing microfilled composite resin restorations. However, these techniques possess several disadvantages; they are time-consuming and difficult to use in embrasures and at gingival margins.6 One study has also shown that composite resins finished with disks are subject to surface cracking.' The results of this study indicate that at least one composite resin (Perfection) does not require disk finishing. Perfection composite resin is a newly developed nonagglomerated system. Compared with prepolymerized splintered microfilled composite resins, homogeneous nonagglomerated composite resin has more submicrofillers, which makes it more polishable. Clinically, fluted bur finishing could not only save chairside time because of the fewer steps involved, but also allow for better interproximal and gingival margin finishing. Microleakage and bond strength are two important parameters in the evaluation of dentin bonding agent (DBA) systems. Higher bond strengths result from better adhesion at the DBNtooth structure interface. Greater resistance to microleakage would be anticipated for systems with higher bond strengths. However, previous studies have found little or no correlation

JOURNAL OF ESTHETIC DENTISTRY/VOLUME 2, NUMBER 5 SeptemberlOctober I990

4. Kanca J. The effect on microleakage of four dentin-enamel bonding systems. Quintessence Int 1989;20:359-361. 5. Crim GA, Shay JS. Microleakage pattern of a resinveneered glass-ionomer cavity liner. J Prosthet Dent 1987;58:2 73-2 76. 6 . Litt F, Setcos JC, Phillips RW. New finishing instruments of composite resins. J Am Dent Assoc 1983;1070:575-580. 7. Lambrechts P, Vanherle G. Observation and comparison of polished composite surfaces with the aid of SEM and profilometer. J Oral Rehabil 1982;9:169-182. 8. Tsai YH, Swam ML, Phillips RW, Moore BK. A comparative study: bond strength and microleakage with dentin bonding systems. Oper Dent 1990;15:5 3-60. 9. Gordon GE, Falcone DJ, Johnson GH. Correlation of shear strength and microleakage in dentin bonding systems. J Dent Res 1990;69:285 (Abstract No. 1415).

between bond strength and microleakage resistance.8.9

The impact of finishing technique o n t h e restoration/ tooth structure interface provides o n e explanation for the poor correlation between bond strength and microleakage results.

References 1. Wendt S Jr, Mclnnes-Ledoux P, Dickinson G. The effect

of thermocycling in microleakage analysis. J Dent Res 1989;68:889 (Abstract No. 184). 2 . Prati C, Nucci C. Marginal gap, microleakage and shear bond strength of adhesive restorative systems. J Dent Res 1989;68:996 (Abstract No. 1036). 3. Retief DH, OBrien JA, Smith LA, Marchman JL. In vitro investigation and evaluation of dentin bonding agents. Am J Dent 1988;l (Special Issue):176-183.

144

Influence of finishing technique on microleakage.

Four different finishing techniques were used in a dentin bonding agent/composite resin restoration to evaluate the possible influence of finishing te...
250KB Sizes 0 Downloads 0 Views