18

J. Dent. 1992;

20: 18-26

Marginal adaptation of four tooth-coloured inlay systems in vivo B. Van Meerbeek, S. Inokoshi,* G. Willems, M. J. Noack,t M. Braem,$ P. Lambrechts, J.-F. Roulett and G. Vanherle Aspirant National Fund of Scientific Research, Department of Operative Dentistry and Dental Materials, Catholic University of Leuven, Belgium, *Department of Operative Dentistry, Tokyo Medical and Dental University, Japan, tDepartment of Operative Dentistry and Endodontics, FU, Policlinic North Berlin, Germany and #Department of Orofacial Morphology and Function, Rijksuniversitair Centrum Antwerpen, Belgium ABSTRACT This study investigates the margin quality of four different tooth-coloured inlay systems using computer-aided quantitative margin analysis under scanning electron microscopy. Three types of restorations involved chairside procedures using a commercial CAJD-CAM apparatus: one type of inlay restoration was milled from preformed glass ceramic blocks, the other two inlay types were milled from preformed porcelain blocks. The fourth system was based on an experimental indirect composite inlay system. Each inlay type was luted with its respective dual-curing luting composite, which was supplied with the system. After 6 months of clinical service, all four systems revealed a significant percentage of submargination indicating occlusal wear of the luting composite. The porcelain inlays and the composite inlays luted with their respective experimental luting composite showed the best marginal adaptation. Luted glass ceramic inlays, in particular, suffered from a significantly higher percentage of inlay margin fractures (9 per cent) and marginal openings (4 per cent) than the other systems. A possible explanation is that the glass ceramic subsurface structure at the inlay-lute interface was weakened by etching with ammonium bifluoride. KEY WORDS: Ceramics, Composites, Inlays, Margin analysis J. Dent. 1992;

20: 18-26

(Received 10 April 1991;

reviewed 11 June 1991;

accepted 14 July 1991)

Correspondence should be addressed too: Dr B. Van Meerbeek, Catholic University of Leuven, School of Dentistry, Department of Operative Dentistry and Dental Materials, U.Z. St.-Rafael, Kapucijnenvoer 7, B-3000 Leuven, Belgium.

INTRODUCTION Over the last decade, great progress has been made in the field of aesthetic dentistry. Materials and techniques devoted to functional restorative dentistry are not necessarily those of choice aesthetically (Erickson, 1985; Van Meerbeek et al., 1991). Although the use of composite resins to restore anterior teeth is generally accepted, many problems are associated with their use in the posterior region (Vanherle and Smith, 1985; Reinhardt, 1989; Roulet et al., 1991). Therefore, materials that more closely match human enamel are desirable. Ceramic materials are claimed to be more aesthetic and durable in tivo (Grossman, 1985; Craig, 1989; Klaiber and Haller, 1989). In addition, high-quality dental ceramics are among the most biocompatible materials developed for dental restorations (Bergman, 1990; Baumann and Heidemann, 1991). However, excessive wear of antagonistic enamel may pose objections in using such materials (Delong et D (1992) Butterworth-Heinemann 0300-5712/92/010018-09

Ltd.

al., 1989). Therefore, more enamel-friendly ceramics have recently been marketed (Grossman, 1991; Krejci, 1991). Computer-aided design (CAD) and computer-aided manufacturing (CAM) of dental restorations offer new perspectives for conservative restorations of posterior teeth with ceramic inlays (M&mann, 1988). Although limited to simple restoration designs, like inlays, onlays and labial veneers, the Cerec-system (Ceramic Reconstruction, Siemens, Bensheim, Germany) enables the dentist to design and fabricate a ceramic restoration at the chairside in a single appointment without auxiliary laboratory support (Heymann, 1989; Mijrmann et al., 1989). Although the milling accuracy of the ceramic inlay has yet to be optimized, excellent marginal integrity of such restorations has been reported (Brandestini et al., 1985; Mijrmann et al., 1985, 1986, 1990; Htirzeler et al., 1990; Bronwasser et al., 1991).

Van Meerbeek

et al.: Margin

analysis of tooth-coloured

inlays

19

Table 1. Grouping of the investigated inlay systems G~OUD

Manufacturer

Inlay system IX Cerec*-Dicer MGC KUL Cerec*-Vita Porcelain COL Cerec*-Vita Porcelain 3ML P-50 Indirect inlay system Dual-curing luting composite DIC Dicer MGC Luting Composite KUL Kulzer Microfill Pontic C COL exp. Cerec-Coltene Duo Cement 3ML exp. 3M luting composite Bonding DIG KUL COL 3ML

resin Prisma Universal Bond Estiseal Duo Bond Scotchbond 2

Caulk-Dentsply, Milford, DE, USA Vita Zahnfabrik, Bad Slckingen, Germany Vita Zahnfabrik 3M. St Paul, MN, USA Caulk-Dentsply Kulzer, Wehrheim, Germany Coltene, Altstatten, Switzerland 3M Caulk-Dentsply Kulzer Coltene 3M

*Cerec-apparatus:Siemens, Bensheim, Germany.

Indirect composite restorations are preferred over direct composite restorations for their enhanced mechanical properties, reduced side-effects of polymerization contraction and better control of clinical procedures (Klaiber and Haller, 1989). In the present study, the margin quality of restorations of four composite luted inlay systems was determined using computer-aided quantitative margin analysis under scanning electron microscopy (SEM). Marginal adaptation was assessed at baseline and after 6 months of clinical service.

MATERIALS

AND METHODS

The present study involved 32 Class II restorations in premolar and permanent molar teeth made from four different tooth-coloured inlay systems (Table I). Three types of restorations involved chairside procedures using the Cerec-apparatus (Siemens Version 01/09/1989, Bensheim, Germany). the fourth type of restoration was based on an experimental indirect composite inlay system using P-50 as composite resin (3M, St Paul, MN, USA). Each inlay was luted with its respective dual-curing luting composite, which was supplied with the system (Table I). The Dicer-milled inlays (DIC) were luted with Dicer MGC Luting Composite (Caulk-Dentsply, Milford, DE, USA); the Cerec-porcelain restorations were luted either with Microlill Pontic C (KUL; Kulzer, Wehrheim, Germany) or an experimental Cerec-Colt&e Duo Cement (COL; Coltene, Altstatten, Switzerland). Finally, the P-50 composite inlays were luted with an experimental 3M luting composite (3ML; 3M). The Class II cavities were restored with one of the four restorative systems selected at random and were equally distributed between the four systems. All restorations were inserted by two experienced dentists over a 3-week period, following the directions provided by the manufacturers. The patients were dental

students between the ages of 20 and 25 years, periodontally sound dentitions of normal occlusal.

Clinical

with

procedures

The teeth were carefully cleaned with a pumice-water slurry. Standard inlay cavities with at least one proximal box form and sufficient buccal and lingual enamel, which was well supported by dentine, were prepared using conventional cutting techniques. The cavity walls were slightly divergent and the enamel margins were not bevelled. Isolation of the cavity was performed with rubber dam. A calcium hydroxide liner (Life, Kerr, Torino, Italy) was placed over the deepest dentine, and a glass polyalkenoate base (Shofu GlasIonomer Base Cement, Kyoto, Japan) was used to eliminate undercuts. For the restorations using the Cerec-system, the threedimensional data of the cavity were recorded by the computer of the Cerec-apparatus using an optical topographic scanning procedure. The full three-dimensional outline of the restoration was designed by the dentist on the computer. These data were then used to control an electronic milling machine in the preparation of the inlays out of prefabricated blocks of dental ceramic with a rotating diamond-coated disc. In the DIC group, the restorations were milled from premanufactured DicorCerec blocks (Caulk-Dentsply), while in the KUL and COL groups, the inlays were milled from premanufactured porcelain Vita-Cerec blocks (Vita Mark I, Vita Zahnfabrik, Bad Sackingen, Germany). After the interproximal contact points were adjusted intraorally, the proximal surfaces were polished using flexible discs (Sof-lex Pop-on set, 3M). The finished inlays were etched according to the instructions of the manufacturer, the Dicer inlays for 30 s with Dicer Etching Gel based on 10 per cent ammonium bifluoride (Caulk-Dentsply), and the porcelain inlays for 60 s with Vita Cerec Etch based on 4.9 per cent hydrofluoric

20

J. Dent. 1992;

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acid (Vita Zahnfabrik). The inlays were thoroughly rinsed and subsequently dried with moisture-free air. Silanization of the etched inlays was performed with their respective silane coupling agents, which were supplied with each system. Two thin layers of a mixture of Silane Primer and Silane Activator (Caulk-Dentsply) were brushed on the etched Dicer inlay surface, whereas the etched porcelain inlays were soaked in Silicoup (Kulzer) for at least 60 s. Finally, the silanized restorations were gently dried. A transparant matrix band of the Hawe-Lucifix Matrix System (Hawe Neos Dental, Gentilino, Switzerland) was placed to ensure good cervical adaptation and was carefully wedged with light reflecting Luci-wedges (Hawe Neos Dental). All the enamel margins of the preparations were etched with 31 per cent phosphoric acid (Scotchflo, 3M), thoroughly rinsed and dried. The respective bonding agent was applied in a thin layer on the etched enamel and the silanized inlay (Table Z). Equal amounts of the dualcuring luting composite base and catalyst were mixed and transferred to the cavity with a Hawe Centrix syringe (Hawe Neos Dental) (Table r). Sufficient luting composite was dispensed to cover all the cavity walls. The restoration was inserted with moderate pressure and major excess cement was carefully removed using an explorer. Under slight pressure on the inlay by a ladmore, all exposed surfaces were successively light cured with a light activating unit (Luxor Lamp, ICI, Macclesfield, UK). The interproximal areas were first irradiated from the buccal and subsequently from the lingual side via the lightreflecting wedges (Hawe Neos Dental), with the occlusal restoration surface being cured finally. Following polymerization and removal of excess luting composite resin, the occlusal surface and fissures were contoured and finished using tine (30 pm) and extra-fine (15 urn) grit finishing diamonds (Esthetic Trimming Diamond set, Fig. 4091.314, Komet, Lemgo, Germany), rubber points (Shofu Ceramiste), flexible discs (Sof-lex Pop-on set, 3M) and diamond paste (1 nm DiamantPolierpaste, Orodent, Antwerp, Belgium) in rubber cups. Finally, composite finishing strips (Sof-lex Finishing Strips, 3M) were used to finish the interdental areas. In the 3ML group an impression of the inlay cavity was taken using a vinyl polysiloxane impression material (Express, 3M) and immediately cast using an experimental, fast-setting, epoxy resin (3M). The P-50 inlay was formed on this cast. After polymerization, the occlusal anatomy and marginal fit was relined extraorally using multibladed carbide burs (Composite Finishing System, Kerr, Romulus, MI, USA) for gross contouring, fine (30 pm) and extra-fine (15 pm) grit finishing diamonds (Esthetic Trimming Diamond set, Fig. 4091.314, Komet), and flexible discs (Sof-lex Pop-on set, 3M), for finishing and polishing. A post-cure treatment at 120°C for 5 min was carried out to anneal the composite inlay. The adaptation and occlusion in vivo was checked and adjusted as necessary. Thereafter, all the enamel margins of the preparation were etched with 37 per cent phosphoric

Tab/e II. Margin qualities (MQ) of the enamel-lute inlay-lute interface

MQ(l-10) MQI MQ2 MQ3 MQ4

MQ5

MQ6 MQ7 MQ8 MQ9 MQlO

and the

Enamel-lute interface (outer margin)

Inlay-lute interface (inner margin)

Continuity to enamel Small defects Submargination with smooth transition Submargination with enamel margin free (step) Marginal overhang with smooth transition

Continuity to inlay Small defects Submargination with smooth transition Submargination with inlay margin free (step) Marginal overhang with smooth transition Marginal overhang with defects Marginal opening smaller than 1 pm Marginal opening larger than 1 pm Composite margin fracture Inlay margin fracture

Marginal overhang with defects Marginal opening smaller than 1 pm Marginal opening larger than 1 pm Composite margin fracture Enamel margin fracture

acid (Scotchflo, 3M), and Scotchbond 2 (3M) was applied on the etched enamel and the inlay (Table I). Finally, the inlay was bonded into place as it has been described for the Cerec inlays (Table Z). Minimal finishing and polishing of the margins was carried out. Final finishing of the inlays was carried out before the baseline evaluation at 2-3 weeks after placement.

Margin

analysis

The margins were analysed at baseline and after 6 months of clinical service. Replicas were made for the evaluation in the scanning electron microscope (Stereoscan 100, Cambridge Instruments, Dortmund, Germany). An impression of each inlay restoration was obtained using individual acrylic impression trays and President Light Body (Colt&e). An accurate impression of the interproximal cervical margin was so difficult to achieve that this area was considered inaccessible for analysis. The impressions were cast with Araldite epoxy resin (Araldate DRL and Hardner, Ciba Geigy, Dilbeek, Belgium). All replicas were mounted on metal stubs and sputter coated with gold (Sputtering device 07 120, Balzers Union, Liechtenstein). The margin quality was determined by means of a computer-aided quantitative margin analysis at X 200, using the method described by Lutz and Roulet (Lutz, 1980; Roulet et al., 1989). The restoration margins were traced on the SEM screen with a digitizer which enabled the length of the margins to be measured by computer. Simultaneously, the margin quality was assessed and assigned to the corresponding lengths. The inlay margins were separately evaluated with regard to the enamel-lute and the inlay-lute interface using 10 well-defined criteria (Table ZZ). Margin analysis was limited to the occlusal and proximal enamel margins, which were located above the

Van Meerbeek

et al.: Margin

analysis of tooth-coloured

inlays

21

100 x 90 F 80 I70 t 60

60 t

0

MO1

MO2

MO3

MO4

MO5

MO6

MO7

MO8

MO9

MO10

L

MO1

MO2

MO3

Margin Ouallty

MO4

MO5

MO6

MO7

MO8

MO9

MO10

Margm Quality

7. Margin analysis of the inlay systems investigated in percentages per criterion at the enamel-lute interface at baseline according to the criteria of Table II. *P < 0.05. El, DIC; ?? , KUL; 0, COL; ?,3ML. ?

Fig.

2. Margin analysis of the inlay systems investigated in percentages per criterion at the enamel-lute interface after 6 months of clinical service according to the criteria of Table II. *P < 0.05.8, DIC; ?? , KUL; Ef, COL; Cl, 3ML.

Fig.

.80

60

-80

’

MO1

MO2

MO3

MO4

MO5

MO6

MO7

MO8

MO9

MO10

MO1

MO2

MO3

Margin Quality

Fig. 3. Differences in margin qualities between baseline and 6-month results in percentages per criterion at the enamellute interface according tocriteria of Table II. A positive proportional change indicates an increase of the specific margin quality and vice versa for a negative proportional change. *P < 0.05. 8, DIC; H, KUL; Et, COL; 0, 3ML.

interproximal contact-point. Taking this interproximal contact-point as a reference, the totals of margin lengths measured were approximately equal for both recall evaluations. The scores obtained for each criterion are expressed as percentages. The percentages of the margin qualities were statistically analysed using non-parametric tests of the SPSS/PC + program (SPSS/PC +, Version 3.0, Germany). Significant differences between the materials were computed using the Kruskal-Wallis one-way analysis of variance by ranks and the Wilcoxon-Mann-Whitney test, and differences between the baseline and 6-month results were analysed

MO4

MO5

MO6

MO7

MO8

MO9

MO10

Margin Quality

Fig. 4. Margin analysis of the inlay systems investigated in percentages per criterion at the inlay-lute interfaceat baseline according to the criteria of Table II. *P < 0.05. 8, DIC; W, KUL; EI, COL; ?,3ML. ?

using the Wilcoxon Castellan, 1988).

signed

ranks

test

(Siegel

and

RESULTS The results of the margin analysis are displayed in Figs l6. The charts show the margin qualities in percentages of the total length of margin investigated. The changes in the percentages scored for each criterion between the baseline and the 6-month assessments are shown in Figs 3 and 6. A positive percentage stands for an increase of that specific margin quality after 6 months, and vice versa for a negative percentage.

22

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1992;

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No. 1

40 r

80

-40

-

-60

I

MQI

MO2

MQ3

MO4

MQ5

MQ6

MQ7

MQ6

MQ9

MQlO

Margin Quality

-801

MQI

MO2

MQ3

MQ4

MQ5

MQ6

MQ7

MQ8

MQ9

MO10

Margin Quality

Fig. 5. Margin analysis of the inlay systems investigated in

Fig. 6. Differences in margin qualities between baseline and

percentages per criterion at the inlay-lute interface after 6 months of clinical service according to the criteria of Table II. *P < 0.05. RI, DIC; ?? , KUL; Ei, COL; 0, 3ML.

6-month results in percentages per criterion at the inlay-lute interface according to the criteria of Table II. A positive proportional change indicates an increase of the specific margin quality and vice versa for a negative proportional , KUL; a, COL; Cl, 3ML. change. *P < 0.05. RI, DIC; ??

For the enamel-lute interface, no statistical differences were apparent for the four inlay systems at baseline with regard to the criterion ‘continuity to enamel’ (Fig. 1, MQl). All the systems showed a perfect margin in more than 50 per cent of the restorations and an acceptable margin (‘acceptable’ when MQl and MQ2 are summed) in at least 60 per cent of the KUL group to a maximum of 76 per cent for the DIC group (Fig. 1, MQl + MQ2). A substantial part of the total length of the enamel-lute interface involved overhangs with smooth transition (MQ5) and with marginal defects (MQ6) in all systems (Fig. 1). Only a small percentage was classed as submargination (MQ3 and MQ4) and marginal composite fractures (MQ9) (Fig. I). Finally, almost no marginal openings (MQ7 and MQ8) or enamel margin fractures (MQlO) were observed (Fig. 1).

After 6 months of clinical service, the percentages of the different margin qualities were markedly different. The amount of ‘continuity to enamel’ decreased (Fig. 2, MQl): in the COL and 3ML group to approximately 50 per cent of the margin length; in the DIC group to 36 per cent; in the KUL group to 14 per cent. The latter percentage was significantly lower (KW = 19.5, d.f. = 3, 2P < 0.01; m = 8,n = 8, W,= 97-100,2P < 0.05) than thoseobtained with the other systems. A significant increase (IV = 8, I’+= 36, 2P < 0.05) in the percentage of submargination with smooth transition (MQ3) and with the enamel margin free (MQ4) is apparent for all systems in Fig. 3. When MQ3 and MQ4 are summed (Fig. 2, MQ3 + MQ4): in the COL group 13 per cent of the total length of the margin was classed as submargination; in the 3ML group 21 per cent; in the DIC group 35 per cent, and in the KUL group 46 per cent. Regarding ‘submargination with smooth transition’ (MQ3), the percentages in the DIC group and KUL group were significantly higher

(KW = 16.3,d.f. = 3,2P < O.Ol;m = 8,n = 8, W, = 94-96, 2P < 0.05) than in the other two groups (Fig. 2). Finally, the percentages of overhangs, marginal openings, composite and enamel margin fractures changed little (Fig. 3). At the inlay-lute interface no statistical differences were analysed between the four inlay systems at baseline with regard to the criterion ‘continuity to inlay’ (Fig. 4, MQl). All the systems revealed an acceptable margin (‘acceptable’ when MQl and MQ2 are summed) above 90 per cent of the total length of the margin (Fig. 4, MQI + MQ2). The remaining margin length is somewhat equally distributed among the other criteria. After 6 months, a dramatic decrease was observed in the margin quality at the inlay-lute interface (Figs 5. 6). The level of ‘continuity to inlay’ (MQl) decreased in the KUL group to 14 per cent of the margin length; in the DIC group to 26 per cent; in the COL group to 37 per cent; in the 3ML group to 65 per cent (Fig. 5). The latter percentage of perfect adaptation is significantly better (KW = 20, d.f. = 3,2P < 0.01; m = 8, n = 8, W, = 94-100,2P < 0.05) than that obtained with the other systems. A significant increase (IV = 8, T+ = 36, 2P < 0.05) of the percentage of submargination with smooth transition (MQ3) and with the enamel margin free (MQ4) was observed for all materials (Figs 5, 6, MQ3 and MQ4 are summed): in the 3ML group to 20 per cent of the total length of the margin; in the COL group to 3 1 per cent; in the DIC group to 38 per cent; in the KUL group to 56 per cent (Fig. 5). The percentage of marginal openings smaller (MQ7) and larger than 1 urn (MQ8) significantly (N = 8, T+= 36, 2P < 0.05) increased for the Dicer inlays to 6 per cent (Figs 5, 6). The DIC and KUL group show a significant

Van Meerbeek

et al.: Margin

analysis

of tooth-coloured

inlays

23

d Fig. 7. Photomicrograph of submargination (MQ3 and MQ4) indicating occlusal wear of the luting composites. The surface roughness decreases from Microfill Pontic C (a) over

Dicer MGC Luting Composite (b) and the experimental 3M luting composite (c) to Cerec-Colt&e Duo Cement (d). (I, inlay; C, luting composite; E, enamel; X 98.)

increase (iV = 8, T+ = 36, 2P < 0.05) above 7 per cent in the amount of inlay margin fractures (Figs 5, 6, MQlO).

Table 111.Maximum particle size of the luting composites investigated (Inokoshi et al., 1991 b)

Luting composite

DISCUSSION The use of quantitative margin analysis is a widely accepted method of assessment for describing the marginal behaviour of dental restorations (Luescheret al., 1977; Lutz, 1980; Brandestini et al., 1985; Mijrmann et al., 1985; Geppert and Roulet, 1986; Lui et al., 1987; Roulet, 1987a, b, 1989; Roulet et al., 1989, 1991; Kirchberg, 1990; Noack et al., 1990). The margin of a restoration shows a wide variety in morphology, therefore, the behaviour of a filling at its margins is an important parameter in predicting the longevity of the restoration (Roulet, 1987a, criteria, b, 1989; Roulet et al., 1989). Ten well-defined adapted to the typical morphology of inlay margins, were selected to characterize the margin quality (Table II; Noack et al., 1990). For all systems, the luting composites were apparently washed out of the margins (Fig 7). A significant increase

Microfill Pontic C Dicer MGC luting composite Exp. 3M Iuting composite Exp. Cerec-ColtBne Duo Cement

Particle size (Wl 38-59 1 l-20 1 I-20 3

in the amount of submargination was detected after only 6 months of clinical service, indicating severe wear of the luting composite (Figs 3,6). The amount of submargination of Microfill Pontic C was found to be particularly high (Fig. 2), and this may be explained by its high surface roughness reflecting its composition with large filler particles and interparticle spaces (Fig. 7a; Inokoshi et al., 1991b)-the name ‘Microfill’ may have been wrongly chosen. Dicer MGC luting composite degraded somewhat less during the 6 months of clinical service (Fig. 7b). The experimental Cerec-Coltene Duo Cement and the experimental 3M composite luting resin exhibited the least

24

J. Dent. 1992; 20: No. 1

Table IV. Knoop hardness (KHN) of the inlay materials investigated compared to the values for enamel and dentine

KHN (kg/mm’) Enamel* Dentinet P-50$ Vita Mark I§ Dicer MGC II

380 68 119 (&3) 493 (* 13) 319 (k8)

Batch number

88L2 707078 100289

*Caldwellerab, 1957; fCraig, 1989; $3M, St Paul,MN, USA; Wita Zahnfabrik, Bad Sackingen, Germany; II Caulk-Dentsply, Milford, DE, USA.

amounts of submargination. Morphologically, these materials are less rough and mainly contain small filler particles (Fig. 7c, d; Inokoshi et al., 1991b). The approximate maximum particle size is given in Table III for the four luting composites investigated. The observation of substantially increased submargination (MQ3 and MQ4) already after 6 months of clinical service must be confirmed with measured wear data. However, little information about the wear characteristics of luting composite is available, consequently there is a need for further research into their optimum composition. Nevertheless, support has been given to the present findings by Essig et al. (1991) who measured the in viva wear of two hybrid dual-curing luting composites, Microlill Pontic C (Kulzer) and Dicer MGC Luting Composite (CaulkDentsply), and one microtilled dual-curing luting composite, Dual Cement (Vivadent). After 1 year, the average loss of substance for Dicer MGC Luting Composite was 60 urn, for Microfill Pontic C 51 urn, and for Dual cement only 7.5 urn. It has been concluded that submicron composite resin luting agents are significantly more wear resistent than macrotilled luting composites (Essig et al., 1991). Although the clinical evaluation showed bonded inlay restorations of high aesthetic quality, the SEM observation revealed for all four systems that approximately 9 per cent of the enamel-lute margins included deficiencies (Fig. I, MQ2, mean percentage for the four systems), about 4 per cent submargination (Fig. 1, MQ3 + MQ4, mean percentage for four systems) and about 25 per cent of the margin length included luting composite excess even at the baseline assessment (Fig. I, MQ3 + MQ4, mean percentage for the four systems). These results confirm the clinical findings of Qualtrough et al. (1988, 1989). Overhangs of tooth-coloured luting composite were clinically difficult to detect visually. Consequently, the use of a coloured varnish such as GC masking varnish (GCcarp., Tokyo, Japan) to mark the cavity margins and to protect the adjacent enamel from being etched and accidently being grinded during tinishing procedures, is strongly recommended (Hachiya et al., 1985). Studies on the marginal adaptation of Class I composite restorations (Bergmann et al., 1990) and Cerec inlays (Losche and Roulet, 1991) concluded that the use of a coloured varnish to mark the restoration margins decreases marginal

overhangs and lowers the danger of inadvertantly reducing enamel during contouring and finishing. Comparing the baseline and 6-month results, we observed that the amount of marginal overhangs changed little (Figs 3, 6, MQ5 and MQ6). This is not surprising since although overhangs are subject to wear, the intensity is not sufficiently high to remove the whole luting composite excess. After 6 months of clinical service the total amount of excess remained classed as ‘marginal overhang’. On comparing the different inlay materials, the Dicer inlays presented a surface that could be polished more readily. The very fine crystal size allows the material to be brought to a smooth and highly polished condition (Grossman, 1991). However, the high surface hardness of premanufactured Vita Mark I porcelain complicated polishing it to high gloss. Consequently, its hardness and roughness undoubtedly affect the wear behaviour of the opposing tooth. A study of Delonget al. (1989) on the wear of enamel when opposed by ceramic systems revealed that a Dicer system would be clinically more favourable in protecting the natural dentition when enamel is to be opposed by a ceramic restoration. The Knoop hardness values of the three inlay materials investigated in comparison to the values for enamel and dentine are measurement by shown in Table IV (Knoop Hardness Ernst Leitz GMBH Wetzlar under 300g for 10 s). The Knoop hardness for Dicer-Cerec and Vita-Cerec approximates the hardness values reported by Apse et al. (1990). Brand newvita-Cerec porcelain blocks (Vita Mark II, Vita, Bad Sackingen, Germany) with reduced hardness have recently been marketed. The Cerec porcelain inlays luted with the experimental Cerec-Colt&e Duo Cement and the P-50 composite inlays luted with the experimental 3M luting composite showed the best marginal adaptation. For the P-50 composite inlay, the relatively high amount of ‘continuity to inlay’ at the 6-month recall indicates an apparently higher stability of the experimental 3M composite luting resin (Fig. 5). The advantages of this composite luting resin over the other cements may be attributed to the higher continuity between both materials, resulting in superior properties in dealing with temperature changes, occlusal stress and water sorption. The inlay itself and the composite luting cement apparently wear to a more identical degree so that the well-adhered margin remains categorized as ‘continuity to inlay’. Indeed, at the enamellute interface, the margin quality of the 3ML system is not significantly better than for the COL system (Fig. 2, MQl); Fig. 7c clearly shows an underfilled enamel-lute interface (MQ3 and MQ4), while the inlay-lute interface can be categorized as ‘perfect margin’ (MQl). Luted Dicer inlays show a significantly (P < 0.05) higher percentage of marginal openings (MQ7 and MQ8) and inlay margin fractures (MQlO) than porcelain and composite inlays after 6 months of clinical service (Fig. 5). The bond of a luting composite to glass ceramic with a silane coupling agent apparently deteriorates with time. Indeed. at the 6-month recall an adhesive failure was

Van Meerbeek

Kg. 8. Photomicrograph (arrows; MQIO) at an observed for the Dicer composite; E, enamel; X

of a large inlay margin fracture occlusal attrition facet, typically inlay system. (I, inlay; C, luting

29.)

observed in 6 per cent of the margin length, and margin inlay fractures in approximately 9 per cent (Figs 5, 8, 9). SEM evaluation of the Dicer-lute interface revealed that prolonged etching of Dicer by 10 per cent ammonium bifluoride weakens the subsurface structure of the glass ceramic inlay at its margin (Inokoshietal., 1991a). Wear of the luting composite exposes the inlay margin to direct of these factors occlusal forces (Fig. 8). The combination probably causes the weakened Dicer edges to crack, possibly resulting in marginal openings (Figs 8,9). Shorter etching time, less thorough etching with a gentler acid or a post-etching ultrasonic rinse to remove the weakened part could solve this problem (Inokoshi et al., 1991a). The high percentage of inlay margin fractures in the KUL group may be related to its high percentage of submargination, which results in the exposure of the inlay margins. Almost no marginal openings were observed for this system after6 months. It is concluded that degradation of marginal integrity of CAD/CAM ceramic inlays can already be noticed after 6 months of clinical service. The rather high percentage of submarginated inlays suggests that wear of the luting composites has occurred. Of the inlay systems investigated, the porcelain Cerec inlays luted with Microfill Pontic C exhibited the highest percentage of submargination, whereas porcelain Cerec inlays luted with the experimental Cerec-Colt&e Duo Cement and the P-50 indirect composite inlays luted with the experimental 3M luting composite were considered to perform in a more acceptable manner. Acknowledgements The authors wish to thank Professor Dr D. Scheuermann and Mr F. Terloo, Department of Histology and Cytology, Rijksuniversitair Centrum Antwerpen, Belgium, for their extensive instrumental support.

et al.: Margin

analysis of tooth-coloured

inlays

25

fig. 9. Photomicrograph of a hairline gap (arrows; MQ7) along the inlay-lute interface, typically observed forthe Dicer inlay system. (I, inlay; C, luting composite; E, enamel; x 98.)

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