J. Dent. 1990;

18: 203-208

203

In vitro marginal microleakage associated with five dentine bonding systems and associated composite restorations C. C. Youngson, Department

N. J. A. Grey and D. M. Martin

of Restorative

Dentistry,

University

of Leeds, Leeds Dental School, UK

ABSTRACT Fifty sound premolar teeth, extracted for orthodontic purposes and stored at room temperature in physiological saline since extraction, were prepared with a standardized minimal two-surface Class II cavity. The teeth were then ascribed randomly to five groups, each of ten teeth. Each of four groups was restored using a different dentine bonding system and the associated posterior composite resin according to the manufacturer’s instructions. The fifth group was restored with Superbond C & B dentine bonding system and Occlusin composite. After immersion in de-ionized water for at least 7 days, the teeth were sealed with nail varnish to within 1 mm of the margin of the restoration. The teeth were then immersed in 5 per cent buffered Eosin for 48 h. Following mesiodistal sectioning the sections were photographed and subjected to image analysis to establish the length of dye penetration at the tooth/restoration interface and the amount of dye penetration into the crown dentine. Tripton/Occlusin and XR Bond/Herculite XB groups showed a significantly (P < 0.05) smaller amount of leakage than Gluma/Lumifor or Scotchbond 2/P50 combinations when assessed as a percentage of the tooth/restoration interface exhibiting leakage. When the percentage of crown dentine showing dye penetration was considered, the Tripton/Occlusin group showed less leakage than the other material combinations. It is concluded that Tripton, when used with the recommended composite, will allow significantly less microleakage than Gluma/Lumifor, Scotchbond 2/P50 or Superbond C & B/ Occlusin combinations and a similar amount to XB Bond/Herculite XB in vitro.

KEY WORDS: J. Dent 1990; 1990)

Dentine bonding sqtems, 18: 203-208

Composite resins, Microleakage

(Received 20 September 1989;

reviewed 1 November 1989;

accepted 29 March

Correspondence should be addressed to: Mr C. C. Youngson, Department of Restorative Dentistry, University of Leeds, Leeds Dental School, Clarendon Way, Leeds LS2 9LU, UK.

INTRODUCTION Since the advent of specialised composite resin restoratives for posterior teeth in the early 198Os, their use has grown with increased professional and public awareness of the availability and desirability of a tooth-coloured alternative to amalgam restorations. With acceptable 5-year clinical results for at least one posterior composite system now available (Rowe, 1989) it is probable that the growth in use of aesthetic posterior restorations will continue. Posterior composites do, however, suffer from a number of limitations. It has been widely recognized that the *This study was supported by I.C.I. Dental. Macclestield, UK. D 1990 Butterworth-Heinemann 0300-5712/90/040203-06

Ltd.

placement of these restorations is technique sensitive, with one author (Anusavice, 1989) listing over 20 factors to be considered. Many workers now feel that the use of rubber dam is essential to avoid moisture contamination following acid etching and during placement of the composite restoration. One advantage of amalgam restorations is that corrosion products forming after the restoration has been in the mouth for some time have a sealing effect at the margins (Jodaikin, 1972; Jodaikin and Goldstein, 1988). This will tend to prevent ingress of bacteria or their toxins around the restoration, thereby reducing the likelihood of pulpal reactions and possible reversible or irreversible pulpitis (Brannstrom, 1984).

204

J. Dent. 1990;

18: No. 4

A number of methods of reducing microleakage associated with composite restorations have been investigated. Although developed initially as a means of gaining added retention, the acid-etch technique has been shown to reduce microleakage for composites (Glyn Jones et al., 1978). Similarly, the dentine bonding systems, which were developed mainly to gain retention via physicochemical bonding to dentine as well as enamel, have been shown to reduce microleakage associated with composites (BenAmar ef al., 1984; Glyn Jones et al., 1988). There has been a rapid expansion in the filler technology of composites but the resins used have remained essentially unchanged, being either BIS-GMA or urethane dimethacrylate. The dentine bonding systems are usually based upon either of these resins but, depending on their bonding mechanism, have modifications of their functional groups allowing bonding to hydrophilic dentine and, simultaneously, to the hydrophobic composite resin. The ‘universal bonding’ system available with a number of composite restorative materials is usually an untilled resin which penetrates the etched enamel micropores and provides mechanical retention. The bonding mechanism varies for most bonding systems but these can be divided into those which: 1. Bond to dentine collagen. 2. Bond to a mineral phase, following removal of the smear layer. 3. Bond to a mineral phase, retaining the smear layer. There is controversy as to the functions of, and desirability of retaining, the smear layer (Pashley, 1984). Brannstrom and Nyborg (1973) have argued that this operatively produced layer is contaminated with viable bacteria and so, if it is intended to retain this layer, it should be disinfected. The cleanser or primer related to each of the various bonding systems now available commercially affects the smear layer differently, cleansers remove the smear layer and are ‘washed off whilst primers tend to disrupt the smear layer but are left in situ: 1. Gluma cleanser (Bayer, Leverkusen, FRG) (0.5 M EDTA, pH 7.4) removes the smear layer. 2. Scotchbond 2 primer (3M Co., St Paul, MN, USA) (incorporating maleic acid, pH 1.5) ‘solubilizes’ the smear layer. 3. Superbond C & B primer (Sun Medical Co. Kyoto, Japan) (citric acid/ferric chloride) removes the smear layer. 4. Tripton primer (ICI Dental, Macclestield, UK) (polyhexanide, pH 4.6) retains and disinfects the smear layer. 5. Bond XR Primer (Kerr Mftg. Co., Romulus, MI. USA) (a phosphonated dimethacrylate resin derivative in an ethanol solvent) essentially removes the smear layer.

In addition to the micro-mechanical method of achieving retention from enamel, obtained with the untilled resin of bonding system, there may also be a, less chemical interaction involving enamel important, hydroxyapatite, especially with the bonding systems which are designed to bond to the mineral phase of dentine. However, this is less likely with the dentine bonding systems which bond primarily to dentine collagen. It must be noted that there is a lack of understanding of the complete mode of action of these and other bonding systems. Those involved in the clinical use of these materials, in the absence of evidence of problems related to use of bonding systems, will tend to consider less the mode of action, but rather seek the most effective system which can be used. It should also be observed that Superbond C&B is designed to be used as an acid-etch retained bridge cement, but due to its claimed ability to ‘collagen graft’ through the TBB/4-META complex to the organic phase of dentine, can be considered a dentine bonding system. The aim of the present study was to determine which bonding system/composite resin combination resulted in least microleakage in vitro.

MATERIALS AND METHODS Fifty sound premolar teeth, extracted for orthodontic purposes, were stored in normal saline at room temperature within 10 min of extraction. All teeth exhibited incomplete root formation although only those with at least two-thirds root completion were included in the present study. All teeth were examined by transillumination under X 4 magnification to exclude those teeth exhibiting enamel fractures as these may have allowed dye ingress. The 50 teeth were ascribed randomly to groups, each of 10 teeth. One operator, using X 4 magnification, prepared a minimal Class II MO or DO cavity to a standardized pattern, remaining 1 mm above the amelo-cemental junction in the box portion with a cave-surface angle of 90 degrees (70 degrees occlusally). All cavities were cut at 400000 r.p.m. under water spray using a friction grip cylindrical diamond bur, dimensions 0.5 mm X 2.0 mm. The cavities were finished with a cylindrical BakerCurson bur in the same handpiece. No cavity enamel margins were intentionally bevelled. The cavity dimensions were approximately: Box height, marginal ridge-gingival floor Occlusal depth at isthmus Width of proximal box

4mm 2.5 mm 4mm

The resultant cavity was always at least 1 mm into dentine and line angles were sharp. The cavities were restored by a second operator using one of five techniques.

Youngson

Table 1. Summary

Group T SB2 G z

er al.: Microleakage,

dentine

bonding

systems

and composites

205

of group treatments

Enamel etch 60s 60s 60s 60s 60s

Dentine treatment Prime 30 s Prime 60 s Cleanse 30 s/Prime 30 s ;;~e3~~s/Cure 10 s

One group of teeth (Group T) was restored with Tripton/Occlusin (ICI Dental, Macclesfield, UK), a second (Group SB2) was restored with Scotchbond 2/P50 (3M Co. St Paul, MN, USA), a third group (Group G) used Gluma/Lumifor (Bayer Dental, Leverkusen, FRG), the fourth group (Group x) XR Bond/Herculite XR (Kerr Mftg. Co., Romulus, MI, USA) and the final group (Group S) used Superbond C&B (Sun Medical Co., Kyoto, Japan)/Occlusin. For each group the cavities were treated and the materials manipulated according to the manufacturers’ instructions. These treatments are summarized in Table I. All composites were placed using an incremental buildup (Lutz et al., 1986) against a Mylar matrix (3M Co.). The light source for each group was a Visilux 2 light unit (3M Co.) with a new bulb fitted at commencement of the study. This was checked by curing a 3 mm deep increment of composite in a matrix which allowed examination, with a sharp probe, of the surface furthest from the curing light. The efficiency of the light unit was tested by checking output with an InterBaler Lampchecker (Clark Dental Equipment Systems Ltd, Hockley, UK). The light output was found to be constant throughout the study and was checked after every ten restorations. Each increment was cured for 60 s. Following placement, the composite was finished on the occlusal surface, according to the manufacturers’ instructions, and re-cured for a further 60 s. No finishing was carried out cervically. After restoration the teeth were re-immersed in deionized water for at least 7 days to allow hygroscopic expansion of the composite. The teeth were then sealed to within 1 mm of the cavity margins with three layers of nail varnish and the coronal portion of each tooth immersed in 5 per cent Eosin buffered to pH 7.4 for48 h at 20°C. The teeth were then sectioned longitudinally, through the midline, in a mesiodistal plane using a diamond disc with water coolant. One-half of each tooth was randomly chosen and allowed to dry, the other half being replaced in de-ionized water for future reference. The dried specimens obtained were photographed the same day using Kodak Ektachrome 50 A.S.A. film through a Zeiss Tessovar (Carl Zeiss, Oberkochen Ltd, Welwyn Garden City, UK) at a magnification of X 2.25. The exposure time was 20 s and the specimens illuminated with incident light from a Schott KL1500 (Schott Glass Ltd, Stafford, UK) fibreoptic light unit. A millimetre scale

Resin cure 30s 20s 20s 20s 8 min

Composite Occlusin P50 Lumifor Herculite Occlusin

XR

was incorporated on the transparency to allow computer calibration. The specimens were viewed by a 80 mm macro/zoom lens linked to a Magiscan 2 (Joyce Loebl, Dukesway Team Valley, Gateshead, Tyne and Wear, UK) image analysis apparatus. The resultant on-screen magnification was X 15. Software was devised ‘in-house’ to allow a number of measurements to be recorded and processed. All image analysis was carried out by one operator (to obtain a consistent analysis) after the samples had been randomized. As all the restorations were of composite resin this removed possible bias in the results. The following measurements were recorded: 1. The length of dye penetration at the tooth/ restoration interface at the gingival and occlusal margins of the specimen. 2. The length of the tooth/restoration interface. 3. The area of crown dentine, and the area of the dentine exhibiting dye penetration. From these measurements, the following results can be obtained: 4. The percentage showing dye leakage 5. The percentage dye penetration (per

of the restoration/tooth interface (per cent L). of the crown dentine which shows cent A).

RESULTS The means and standard deviations of the percentage length (per cent L) and area (per cent A) for each group are given in Table II. The sets of data were analysed using a one-way analysis of variance to test if there was any significant difference between the means. When evidence of a significant

Tab/e II. Means and standard deviations cent A for each group

T SB2 G :

Mean

Per cent L s.d.

53.9 81.1 79.5 55.0 72.8

36.4 13.5 16.3 22.5 18.3

of per cent L and per

Per cent A Mean s.d. 12.2 21.9 24.2 15.1 27.9

9.1 10.2 8.1 11.8 6.9

J. Dent. 1990;

206

18: No. 4

100 90 80 6 ‘;

70

z ii

60

$ ZL 7J L0

40

3 i

30

OQ

50

T

20

SB2 G X Group

S

Fig. 2. Mean percentage area of dye penetration (per centA).

10

shows a histogram of the mean percentage of area of dye penetration (per cent A) for each group. During analysis the tooth/restoration interface length and crown dentine areas were examined. No statistically significant differences were found between the groups for these parameters, confirming the standardization procedures. It was observed that the area of dye penetration tended to be associated with the cervical margin, emphasizing this area as the ‘weak link’ in posterior composite restorations. After statistical analysis it was found that the ‘rank order’ of the different restorative techniques differed for the parameters of percentage leakage length and percentage leakage area.

0 T

SB2 C X Group

S

Fig, 1. Mean percentage length of leakage (per cent L).

difference was found between means, they were ranked in increasing order and compared in pairs using Duncan’s multiple range test (Duncan, 1975). All comparisons presented here were done at an overall level of 5 per cent. Tables ZZZand ZV show the results of these comparisons. Plots of the observed values and residuals for both the parameters of percentage length and percentage area did not exhibit any great differences in variability between the groups. Fig. 1 shows a histogram of the mean percentage of length of leakage (per cent L) for each group. Fig. 2

Table 111.Percentage leakage length (per cent L): analysis of variance table Source

d.f.

ss

MS

F value

Group Error

4 45

6907.45 26 145.41

1726.86 581 .Ol

2.97

Total

49

33052.86

Pr < F 0.0292

Using Duncan’smultiple rangetest to controlthe type 1 comparisonwiseerror rate,the means of the groups are linked as follows: Group:

T

XR

53.94

55.03

S 72.75

G 79.50

SB2 81.08

Table IV. Percentage leakage area (per cent A): analysis of variance table Source

d.f.

Group Error

4 45

1389.91 4496.69

Total

49

5886.49

ss

MS

F value

347.45 99.93

3.48

Pr < F

0.0147

Using Duncan’smultiple rangetest to controlthe type 1 comparisonwiseerror rate, the means of the groups are linked as follows: Group:

T

XR

SB2

12.21

15.11

21.92

G 24.16

S 27.90

Youngson

et al.: Microleakage,

DISCUSSION The results indicate that Tripton/Occlusin system (Group T) resulted in the least microleakage, both in terms of linear penetration (per centl) along the restoration/cavity interface, and of area of spread into dentine. Looking at degree of linear penetration in isolation, Group T exhibited less (P < 0.05) leakage than Groups G and SB2 but not significantly less than that shown by groups X or S. Group X showed significantly less (P

In vitro marginal microleakage associated with five dentine bonding systems and associated composite restorations.

Fifty sound premolar teeth, extracted for orthodontic purposes and stored at room temperature in physiological saline since extraction, were prepared ...
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