Dent Mater 8:327-331, September, 1992

Effect of tooth storage and cavity cleansing on cervical gap formation in Class II glass-ionomer/composite restorations M. BriinnstrSm ~, P. Coli 2, M. Blixt I Department of Oral Pathology, School of Denttstry, Karohnska Instttute, Hudd~nge, Sweden 2Guest researcher, Genoa, Italy

Abstract. Class II cavJt,es w~th the cerv,cal margin just below the C-E junction and with two cervical retention grooves were prepared ~nintact human premolars, 31 cawtles in teeth stored frozen and 29 cavuties in teeth stored in 1% chloramine solution. The teeth from both storage conditions were assigned to two groups; ,n one group, the cavities were cleaned with a water spray, in the other group, with a cleaner containing 0.2% EDTA and 1% NaF All cavities were lined with Vitrebond and restored w,th P50. Cervical contraction gaps were disclosed by a fluorescent resin penetration technique. The length and width of each gap were analysed A contraction gap was revealed in 17 of the 31 cavities in teeth stored frozen (54.8%) and in 22 of the 29 restorations Jn the teeth stored in chloramine (75.8%). The w,dth of the gap was sign,ficantly greater in teeth stored in chloramlne (p = 0.0004). No statistical difference in gap formation was found between cavities cleaned w,th water or with the detergent containing 0.2% EDTA and sodium fluoride. Since the cavity cleansing procedure was not a significant factor in gap formation, apparently removing the superficial smear layer with the cavity cleaner does not impair the bonding of Vitrebond to the dentin. However, gap formation appeared to be significantly affected by the storage conditions of the extracted teeth. It is suggested that teeth to be used in bond strength and leakage experiments should be stored frozen rather than stored ,n 1% chloramine soluhon INTRODUCTION Inconsistent results of tn vitro investigations of bonding procedures in composite restorations may be due to the large number of variables in the test methods. Crim and GarciaGodoy (1987) found storage time of the restoration before testing to be an important factor, but other studies have not supported this finding (Retiefet al., 1989). Another variable is the way in which the teeth are stored from the time of extraction until the experiment. Few investigations have been conducted to determine the most appropriate storage technique for teeth to be used in studies of the adaptation of restorations (Retief et al., 1989). In some studies, the extracted teeth have been stored in tap water at room temperature for up to 6 wk or more, w~thout disinfection or sterilization (Crim and Garcia-Godoy, 1987; Crim and Abbott, 1988; Hansen and Asmussen, 1989; Kanca, 1992). Pulp tissue and components of the dentin may be

degraded and bacteria may alter the pulpo-dentinal complex. The same applies to teeth stored in physiological saline solution (Prati et al., 1990; Sorensen et al., 1991). In order to avoid infection and preserve the tooth structure, teeth have been stored either in buffered 10% formalin (Ben-Amar et al., 1987; 1988a; 1988b; Bullardetal., 1988; Cooley and Barkmeier, 1991) or 70c2 alcohol (Gwinnett, 1988; O'Brien, et al., 1987) for various periods. These solutions may also have some negative influence on the organic components of the dentin. This may also be true for teeth stored in a water and thymol solution (Reinhardt et al., 1987; Donly et al., 1990), or 1% chloramine (J0rgensen et al., 1985; Retiefet al., 1990; ~ilo and Olsson, 1990). Before storage in solution, the teeth are usually only scrubbed and mechanically cleaned in tap water. This procedure has been routine in the investigating department: the teeth have then been wrapped in wet gauze and frozen in a plastic bag at around -8°C. However, since many clinics lack freezing facilities, more teeth would be available for experiments if the teeth could be stored in 1% chloramine solution. Another important question is pretreatment of the dentin before insertion of a lining material such as light-cured glassionomer cement (GIC). The cavity may be cleaned with a slurry of pumice and water followed by conditioning for 10 s with polyacrylic acid (Mount, 1991). For Vitrebond (3M Dental Products, St Paul, MN, USA), the manufacturer recommends spraying with water only: i.e., most of the smear layer is undisturbed and may be partly removed under a contraction gap filled with fluid (Brannstrom, 1984). Most of the smear layer should be removed without softening of the dentin surface. The smear plugs in the tubular apertures should not be disturbed, but reinforced with fluoride. A high concentration of NaF applied to a dry dentin surface should promote the accumulation of CaF2 at the tubule apertures. A statable cleanser with 1% NaF and 0.2% EDTA, including a surface active component, was developed for this purpose: Tubulicid Red Label (Dental Therapeutics AB, Nacka, Sweden). The effectiveness has been confirmed by Br~innstrom et al. (1979) and Meryon et al. (1987). A slight increase in adhesive strength of composites after this treatment has been reported (Stangel et al., 1987;Abate and Macchl, 1988), as well as a 20% reduction of dentin permeability (Haller et al., 1992).

Dental Matenals/September 1992 327

However, GIC lining may adhere to the dentin by chemical action at the interface. Application of NaF-EDTA followed by air jet drying might produce a very thin, water soluble film and NaF crystals on the dentinal surface, which may disturb the GIC bonding. The purpose of the present study was two-fold: 1) to determine if storing experimental teeth, frozen, or in 1% chloramine solution, influenced the dentin bonding properties of Vitrebond in vitro; and 2) to compare the bonding ability of Vitrebond to dentin after cleansing the cavity with Tubulicid Red or with a water spray. Assessment of these variables was based on the number and size of cervical gaps in Class II cavities with cervical margins just below the C-E junction.

MATERIALSAND METHODS The material comprised intact young human premolar teeth extracted for orthodontic reasons, brushed and cleaned in tap water without using any antibacterial solution. The teeth were then stored in one of two ways: in a wet gauze in a plastic bag at around-8°C for 1 to 3 months. Before use, the teeth were placed in cold water for 5-10 min and then allowed to equilibrate to room temperature for 10-20 min. The other teeth were immersed in 1% chloramine solution in water for 1 to 3 months. Sixty Class II cavities were prepared, 31 in teeth stored frozen and 29 in 1% chloramine solution. The proximal box was about 4 mm wide and 1.5-2 mm deep. The cavity preparation is shown in Fig. 1. The cervical wall was located just below the cementum-enamel junction. The cavity was prepared with a fissure carbide bur (Maillefer No. 016, Ballaigues, Switzerland) at high speed, under water coolant. A small round bur (Meisinger No. 2, Dusseldorf, Germany) was used at low speed to cut retention grooves on the lateral walls. At the cervical wall, double retention grooves were made with a special notched chisel (Dental Therapeutics AB, Nacka, Sweden). The enamel on the lateral and occlusal wall was bevelled for 0.5 to 1 mm with a diamond point (D+Z, Berlin, Germany) at low speed. After lining, all cavities were etched for 15 s with an acid gel (37% H3PO4, 3M Dental Products, St Paul, MN, USA), followed by 10 s of water rinsing and then airjet drying for 10 s. The light-cured resin-bonded ceramic, P50, in combination with the adhesive, Scotchbond 2 (3M Dental Products), was used throughout this study. Group 1 consisted of 14 cavities in teeth stored frozen and 15 in teeth stored in chloramine. After spraying with water and then with air, a thin layer, 50-100 ~m, of Vitrebond lining material (Note: name change from Vitrabond; powder Batch No. 7152 and liquid Batch No. 7152). The powder and liquid were mixed for 10-15 s and applied to the cavity walls and light-cured for 30 s. The liner covered the whole dentin surface and was removed only from the bevelled enamel, which was etched; then, according to the manufacturer's instructions, Scotchprep dentin primer (3M Dental Products) was applied for 60 s, followed by a 15 s air blast. To facilitate the removal of excess composite, a polystyrene liner, Tubulitec (Dental Therapeutics AB) was applied to the surface outside the cavity. Scotchbond 2 was applied in a thin layer and lightcured for 20 s. A plastic matrix strip was used on the proximal surface. Ph0 was applied in bulk and light-cured from the cervical region for 40 s and then from the occlusal wall for

328 Brannstrom et aL/Cervlcal gap m glass

Fig. 1. Mesio-distalsectionoftheClassllcavity. Thecervicalmarginislocatedjust below the C-E junction. Retention grooves are made on the axial wall by a small round bur. Two retention grooves are made on the cervical wall by a notched chisel. The scores used to evaluate the length of the FEB penetration were: 0 = No penetration, I = penetration to the middle of the cervical wall, II = to the inner cervical corner, III = along the axial wall.

80 s. Clinically, it is possible to light-cure from the cervical wall using the light wedge technique introduced by Lutz et al. (1986). It has been noticed that bulk application in the proximal box with retention grooves gave the same results as incremental application in cavities without grooves (BenAmar et al., 1988b). In addition, with bulk application the risk for variables between the restorations was reduced. Composite excess was removed with a hand instrument only because rotating instruments produce grinding debris which would tend to plug the aperture of any contraction gap. Group 2 was comprised of 17 cavities in teeth stored frozen and 14 in teeth stored in chloramine. The treatment was the same as in Group I except that instead of water the cavities were cleaned with Tubulicid Red Label, a detergent containing 0.2% EDTA and 1% NaF. As recommended by the manufacturer, the cavity was first rubbed for a few seconds with a cotton pellet soaked with the solution, which was then left in the cavity for 30 s before air drying for 15 s. In addition to the manufacturer's instructions, a drop of cleaner was then reapplied for fluoride impregnation, immediately followed by a 15 s air blast. In order to disclose any lack of bonding and the presence and location of a contraction gap, a previously used method was followed (Br~innstrhm et al., 1984; Torstenson and Br~innstr6m, 1988). After the excess composite was removed and polymerization was almost complete (3 min after the end of light curing), one drop of Concise Enamel Bond resin (3M Dental Products) containing a fluorescent dye (FEB) was applied at the cervical margin. The resin may penetrate an air-filled gap by capillary action. The teeth were ground (not sectioned) longitudinally from lingual to buccal, perpendicular to the restorations, using a large, perforated diamond wheel (D+Z, Berlin, Germany) under water cooling. The surface was polished under water cooling. Each tooth was examined and photomicrographs were taken at two or three ground levels with reflected UV

tonomer/composlte restorations

TABLE 1: RESULTS OF THE GAP WIDTH MEASUREMENTS Group 1 (Water)

Group 2 (Tubuhcld)

Totals (Row)

Storage Cond~t,on

G/R*

Mean _+SD

Range

G/R**

Mean __.SD

Range

G/R*

Mean _+SD

Range

Frozen

8/14

274_+268

30- 67

9/17

218_+302

25- 85

16/31

**246_+2.82

30- 85

Chloramlne

13/15

#616+328

50-100

9/14

#621_+537

65-155

22/29

*'619-+426

50-155

Totals(Col)

21/29

+445_+ 328

30-100

18/31

+420_+474

25-155

* Number of Gaps/Number of Restoratives ** S,gnlficant difference between mean values (p = 0 0004)

# No significant difference between mean values (p = 0 80) + Some spec,mens exh,b,ted FEB penetrat,on but gap w,dth was imposs,ble to measure

light, at a magnification up to 210x using an E. Leitz Ortoplan microscope (GmbH, Wetzlar, Germany). For each restoration, the width and the length of FEB penetration were measured to assess the severity of gap formations. The gap width of each cavity was determined by calculating the mean of the smallest and greatest widths measured for every ground level. For statistical analysis, an analysis of variance (ANOVA) test was applied. The length of the penetration was scored from 0 to III on different areas of the margins of the restoratmns as shown in Fig. 1. For statistical analys~s, the Chi Square test was applied. RESULTS

In all cavities, except three specimens with diffuse penetration of FEB, a gap was present between Vitrebond and the dentin. The number and the width of the gaps are shown in Table 1. The depth penetration of the gaps ]s shown in Table 2. A gap was present at the cervical wall in 8 out of 14 restorations from Group 1 (frozen then cleaned with water spray). The width varied between 0 and 10 pm. In 7 cases, penetration was limited to the outer half of the cervical wall (score I) and in one case, it reached the axial wall (score III). The second half of Group 1 restorations that were cleaned with water after storage in chloramine exhibited gaps in 13 out of 15 specimens. The width of the gap varied between 0 and 14 pm. For these specimens, the FEB reached only the outer half of the cervical wall (score I) m 12 cases and the axial wall (score III) in only one case. Gaps were seen in more than half the Group 2 specimens made in teeth that had been frozen and then cleaned with Tubulicid Red. The gap width varied between 0 and 10 pro. In all 9 restorations with penetration, the FEB stain was found no deeper than the outer half of the cervical wall (score I). For the teeth stored in chloramine before cleansing with Tubulicid Red, 9 out of 14 restorations exhibited a gap that varied in width between 0 and 21 ~m. In 8 of these restorations, the FEB stain penetrated no further than the outer half ofthe cervical wall (score I) and ]n one case, it reached the inner half (score II ~. Restorations prepared ]n teeth that had been frozen exhibited smaller gaps than in those cut in teeth stored in chloramine. This difference was statistically significant (p = 0.0004). Cavities cleaned with water and cavities cleaned with Tubulicid Red did not show a statistical difference in the width of developed gaps (p = 0.80). To calculate the Chi-Square value for the gap length, it was necessary to exclude the scores II and III, because the number of specimens (11) was too small for a reliable statistical result.

TABLE 2: DISTRIBUTIONOF RESTORATIVESACCORDINGTO THE GAP LENGTH GAP LENGTH SCORES Group 1 (Water) Group 2 (Tubuhcld) StorageCond,tron

0

I

II III

0

I

II III

Frozen

6

7

1

8

9

Chloram~ne

2 12

1

5

8

1

Total#

8 19

2

13 17

1

Total* 0

I

II III

14 16

1

7 20

1 1

* No significant difference between storage condJhons (p = 011) # No significant difference between treatments (p = 0 28)

There was no statistical difference between restorations based on the cleansingprocedures (x~= 1.147, p = 0.284) nor between the two different storage systems (x2 = 2.627, p = 0.105) with respect to gap length.

DISCUSSION Whereas there was good adaptation of the restorations to the enamel margins, a gap often appeared at the dentinal cervical wall. In this region, Vitrebond had been detached, probably during polymerization shrinkage of the composite. These results support an earlier investigation with scanning electron microscopy in which contraction gaps of approximately 10 pm were found for restorations with Vitrebond (Cooley and Barkmeier, 1991). It should be noted that in the latter experiments, the teeth had been stored in 10% formalin solution; the results were quite similar to those in the present study for teeth stored in 1% chloramine solution. In this study, the teeth stored frozen exhibited gaps that were smaller than the other specimen. It is possible that a gap of 1 pm or less, t.e., no bonding, could exist where no penetration of FEB was observed in the microscope. In theory, such a small gap may be further reduced in vivo by delayed hygroscopic expansion of Vitrebond, but this has not yet been demonstrated. Bacterial growth, pulpal irritation and secondary caries may occur if the cavity has been cleaned with water only, usually leaving a smear layer of a few microns containing some microbes. The smear layer will be replaced by microbes and the fluid-filled gap may thus increase a few microns in size (Brannstrom and Nyborg, 1973). Chloramine presumably changed the organic structure of the dentin, resulting in weaker chemical and/or mechamcal bonding of Vitrebond. Compared to cavities in teeth stored frozen, the bond in teeth stored in chloramine was less resistant to contraction forces during polymerization shnnkDental Matenals/September 1992 329

age of the composite. This may also apply to various resin bonding agents. Retief et al. (1989) studied the effect of storage media on the shear bond strength of Scotchbond 2/Silux to dentin. The values for teeth stored in saline solution at 4°C were significantly higher than values obtained for teeth stored in 70% ethanol or 0.05% thymol, and were higher, (but not with statistical significance), than the ones for teeth stored in 1% chloramine and 10% formalin. In most teeth, the FEB penetrated only to the middle ofthe cervical wall. As indicated in a separate study (Coli et al., in press), it is possible that the retention grooves counteracted the development of a gap further inward. The results indicated that pretreatment with Tubulicid Red Label did not impair the bonding of Vitrebond to dentin. Removal of the superficial smear layer and reinforcement of the smear plugs at the tubular apertures before lining could be an advantage. Bacteria in the smear layer are removed and with a high concentration of NaF (1%) applied to a dry dentin surface, CaF2 precipitation may be expected. Such a treatment is not irritating to the pulp, not even when applied to nearly exposed pulps (Br~innstrom and Nyborg, 1971, 1973; Torstenson et al., 1982; Brannstrom et al., 1983). Received December 16, 1991/AcceptedAugust 10, 1992 Address correspondenceand repnnt requests to: M. Brannstrom Department of Oral Pathology School of Dentistry Karohnska Institute Box 4064 S-141 04 Hudchnge, Sweden

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ionomer/composlte restorations

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Dental Matenals/September 1992 331

composite restorations.

Class II cavities with the cervical margin just below the C-E junction and with two cervical retention grooves were prepared in intact human premolars...
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