Retention of composite inlays in enamel dentin cavities A. Peutzfeldt E, Asmussen Department of Dental Materials and Technology Royal Dental College N0rre AII¢ 20 DK-2200 Copenhagen N, Denmark Received September 8, 1989 Accepted October 8, 1990 This investigation was supported by Grant 12-8578 from the Danish Medical Research Council. Dent Mater 7:11-14, January, 1991

Abstract-The retention of composite inlays depends on acid-etching of marginal enamel of the preparation. In many cases, only little marginal enamel is available, making loss of retention a liability. The present study evaluated the retention of three brands of composite inlays under various conditions. Inlays were fabricated and cemented in standardized enamel/dentin cavities prepared in extracted human teeth. The force necessary to extract a cemented inlay was used to express the retention of the inlay. The effects of thermocycling and choice of dentin-bonding agent on inlay retention were also determined. Inlays made of Estilux posterior C VS were more retentive than inlays of either Brilliant or SR-Isosit. The latter two products were found to provide similar retentive strengths. The retention of Estilux posterior C VS and SR-Isosit inlays declined when samples were thermocycled. Treatment with Gluma increased retention of inlays, resulting in retentive strengths of the same magnitude for all three inlay systems. The choice of dentin-bonding agent was found to affect composite inlay retention to a greater extent than the choice of either composite brand, mode of inlay curing, or effect of thermocycling.

omposites have recently been introduced as inlay/onlay systems. The aims of the involved additional extra-oral cure of the inlays/onlays are: (1) to improve mechanical properties through a decrease in remaining double bonds and (2) to reduce gap formation. The reduced gap formation is supposed to be accomplished as a consequence of polymerization contraction of the composite taking place outside the mouth prior to cementation of the inlays/onlays. The only possible gaps are those caused by contraction of the relatively thin layer of resin cement. This contraction has been reported by some authors to be negligible (Lutz eta/., 1987; Schaller et a/., 1988), while others (Feilzer et al., 1989) have found increased wall-to-wall polymerization contraction in thin resin layers. If an appreciable contraction does occur, it could mean insufficient retention of the inlays/onlays. In case the monomer conversion of the additionally cured inlays/onlays is substantially increased, durable bonding of the inlays/onlays to the resin cement may be impossible to obtain. As an estimation of the bond strength between resin cement and inlay/onlay, the bond strength of composite repair might be used. Chan and Boyer (1983) found the repair strength to be approximately twothirds of the tensile strengths of the composites investigated. Bonding of the resin cement to enamel is provided by acid-etching of the enamel, and bond strengths of up to 20 MPa have been reported (Zidan et al., 1980). However, one is often faced with the fact that the largest area of an inlay/onlay preparation is composed of dentin. In such cases, the retention relies on bonding between dentin and the resin cement, and will be influenced by the use and type of dentin-bonding agent. One of the three inlay/onlay systems investigated (Brilliant) does not include a dentin-bonding agent. The other two systems (Estilux poste-


rior C VS and SR-Isosit) include dentin-bonding agents, which, however, have been found to be of relatively low efficacy. With Dentin Adhesive of the Estilux system, Asmussen et al. (1989) measured 0.5 MPa after one day in water at 37°C and 0.0 MPa after one year. For Dentin Protector of the Isosit system, the corresponding values were 6.7 MPa after one day and 3,4 MPa after one year. In the study by Asmussen et al. (1989), Gluma was included and gave rise to bond strengths of 9.8 MPa after one day and 10.7 MPa after one year. Two of the three inlay/onlay systems investigated (Brilliant and Estilux posterior C VS) are based on photo-curing composites which, after initial cure with a polymerization unit, are transferred to a light or light/ heat oven for additional curing. These systems allow for indirect as well as direct techniques to be used. The third system (SR-Isosit) involves hydro-pneumatic heat polymerization of the restorative resin, and these inlays/onlays can be fabricated only by the indirect technique. It was the purpose of the present study to compare the forces necessary to extract cemented composite inlays from enamel/dentin cavities. The effects of different dentin-bonding agents were also investigated. MATERIALS AND METHODS

The materials used in the investigation are listed in Table 1. Human incisors and molars, which had been extracted from two weeks to three months prior to the start of this study and then kept in 1% chloramine, were embedded in epoxy resin (Epofix, Struers, DK) and left for 24 h so the resin would polymerize. The teeth were ground on carborundum paper No. 1000 until a flat enamel surface appeared. On incisors the facial surface was used, and on molars the facial or mesial surface. Standard cavities extending into dentin (Fig. 1: depth = 2.15 mm, diameter at top =

Dental Materials~January 1991 11

Fig. I. Standard cavity used. Depth = 2.15 mm, diameter at top = 3.50 mm, and total taper = 10 °. E = enamel, D = dentin.

3.50 mm, taper = 10°) were prepared by use of w a t e r s p r a y and burs mounted in a Clou 10 B drilling machine (Clou, Copenhagen, DK). Inlays were then fabricated in the following manner for each of the three inlay/only systems:

Brilliant. - A t 37°C and after separation of the cavity, composite was applied into t h e cavity a r o u n d a stainless steel nail, placed head down, and polymerized for 60 s with a Translux CL polymerization unit (Kulzer & Co., Wehrheim, Germany). The inlay was removed by aid of the nail, transferred to room temperature, and then cured for seven rain in a DI-500 light-/heatcuring oven (Colt~ne AG, Altst~itten, Switzerland). Back at 37°C, the

........;:;i;i;!;!;!::~L" TOOT JIG H


L Fig. 2. Schematic drawing of testing assembly used to determine the retentive strengths of inlays.

cavity wails and inner surfaces of the inlay were smoothed with a 30-1~m diamond bur. The enamel was etched for 45 s, washed with water for 15 s, and dried with an air blast. Chemically-curing low-viscosity resin was mixed for 10 s, brushed on the etched

N 400

- [ ] DIRECT []



- []



200 -

l 100

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Fig. 3. Retentive strengths of three composites used as inlays. Height of bars represents mean value; T-shaped figure, standard deviation.


enamel, and t h i n n e d with compressed air. Duo Cement was mixed for 30 s and applied onto the inner surfaces of the inlay. The inlay was then fixed in the cavity, and the cement polymerized for 40 s. Mixing of resin and cement took place at room temperature, while application was performed in a 37°C room. In another series, inlays were produced indirectly as follows: Impressions (Deguflex, D e g u s s a AG, Frankfurt, Germany) were taken of the cavities at 37°C, poured immediately with gypsum (Vel-Mix Stone, Kerr, Romulus, MI, USA) at 23°C, and separated from the dies after one h. After another 23 h, the dies were brushed with Separator, and inlays were produced and cemented in the teeth as described above.

Estilux posterior C VS. Cavities were covered with ADS gel. XR 1 (radiopaque composite) was applied to the pulpal half of the cavity around the stainless steel nail, and polymerized for 20 s. The upper half was filled with A 20, which was polymerized for 20 s. After removal from the cavity by way of the nail fixed in the composite, the inlay was covered with ADS gel, tra~zsferred to room temperature, and'cured in a Dentacolor XS unit (Kulzer & Co., Wehrheim, Germany) for six min. At 37°C, the ADS gel was removed from the inlay and cavity with water spray, and the inner surfaces of the inlay w e r e smoothed with a 30-rLm diamond bur. The enamel was etched for 60 s, rinsed with water for 20 s, and dried with a jet of air. The cavity walls were covered with a thin layer of Dentin Adhesive. Low-viscosity resin was brushed onto the cavity walls and inner surfaces of the inlay. Microfill Pontic C was mixed for 20 s at ambient temperature, applied to the inlay, and after placement of the inlay at 37°C, polymerized for 40 s. As with the Brilliant system, a series of inlays was also produced by the indirect technique. -

SR-Isosit. - T h e composite of this system is cured by heat and pressure, allowing inlays to be made by the indirect technique only. At ambient temperature, the stone dies produced as described above

were treated with Separating Fluid and SR-Isosit-N-Fluid. SR-IsositDentin was applied into the pulpal halves of the cavities around a steel nail. The upper half of each cavity was filled with SR-Isosit-Incisal, which was then covered with a thin layer of SR-Isosit-N-Fluid. The inlays on the dies were transferred to an Ivomat IP3 polymerization apparatus (Ivoclar AG, Schaan, Liechtenstein) and cured for 10 rain at six bar and 120°C. The inlays were removed from the dies, and the inner surfaces of the inlays were sandblasted with aluminum oxide (grain size = 110 ~m) at two bar. The inlays were etched for 30 s, washed with water, and dried with a blast of air. At 37°C, the cavities were rinsed with 4% H202, washed with water, and dried. The dentin was covered with Dentin Protector and dried lightly. Dentin Protector was removed from enamel surfaces with a 30-~m diamond bur. The enamel was etched for 45 s, washed with water for 15 s, and dried with an air jet. Back at room temperature, Dual Cement was mixed for 20 s and applied to the inlay. The inlay was finally cemented at 37°C, and the cement was photocured for 40 s. For each of the three inlay/onlay systems, a series of specimens was prepared in which the dentin surfaces of the enamel/dentin cavities were treated with Gluma in the following way: After the enamel was etched, 0.5 M EDTA (pH adjusted to 7.4 by means of NaOH) was rubbed onto the dentin surfaces for 60 s by means of a cotton swab. The surfaces were rinsed with water for 15 s and dried with a jet of air. Gluma [an aqueous mixture of HEMA (2h y d r o x y e t h y l m e t h a c r y l a t e ) and glutaraldehyde] was then rubbed onto the dentin and left for 60 s, and the cavity was dried with compressed air. The dentin surfaces were covered with low-viscosity resin, and the inlays were cemented. Treatment with Gluma meant that application of both Dentin Adhesive and Dentin Protector was omitted. After cementation of the inlays, the teeth were stored in water at 37°C for one week. The retentive strength was then measured (a) at once or (b) after the specimens were thermocycled between two water baths of 15°C and

TABLE 1 MATERIALS USED Material Brilliant Separator Etchant Gel Duo Bond Duo Cement Estilux posterior C VS ADS-Gel Dentin Adhesive Esticid-Gel Estiseal LC Microfill Pontic C SR-Isosit Separating Fluid Dentin Protector SR-Isosit-N-Fluid Heliobond Dual Cement Scotchbond Etching Gel

Batch No. Dentin D3, 191088-03 160888-01 010988-02 010988-02 160881-01 XR1, 31.12.89 24 A 20, 31.12.89 25 506025 300689 029 31.12.91 041 31.12.90 039 base, 30.06.91 023 catalyst, 30.06.90 023 Incisal, 770188 Dentin 22 1C, 400287 11 6 91 B 640602 3615 CC 652102 base, 442501 catalyst, 440301 8GH

Manufacturer Colt~ne AG, AItst~tten, Switzerland

Kulzer & Co., Wehrheim, Germany

Ivoclar AG, Schaan, Liechtenstein

3M Company, Minnesota, USA


Estilux posterior C VS


Treatment Direct Indirect Thermocycled Gluma Direct Indirect Thermocycled Gluma Indirect Thermocycled Gluma

55°C, respectively, for 900 cycles at 2 rpm. The time in each bath was 15 s. The thermocycled Brilliant and Estilux inlays were made by the direct technique and the Isosit inlays by the indirect technique. The retentive strength was determined by means of a Universal Testing Machine (Instron Ltd., UK) at a cross-head speed of 1 mm/min (Fig. 2). Each of the described series consisted of five specimens. For each of the 11 testing conditions, the mean force and standard deviation were computed. After the retention testing, the empty cavities were soaked in erythrosine for 60 s, then rinsed with water. The dentin was thereby dyed red. On the periphery of each cavity, eight

Enamel Area 3.64 _+ 1.01 5.62 __ 4.24 5.22 ± 2.10 4.26 _ 1.40 6.07 ± 1.58 6.14 ± 2.95 4.58 -- 1.59 3.74 __ 1.40 5.38 __ 2.67 6.33 __ 2.45 4.24 ± 0.76

points were marked 45° apart. In a stereomicroscope, the depth of the enamel layer was measured at each point. The eight values of depth were totaled, and the enamel area was estimated for each tooth. The mean value and standard deviation were calculated for the five teeth in each group, and the 11 values of mean enamel area were compared statistically. RESULTS The results of the investigation are listed in Table 2 and Fig. 3. The 11 values of enamel area (Table 2) were subjected to analysis of variance (Hald, 1952) and were found not to differ, with statistical significance (p > 0.05). For this reason, the reten-

Dental Materials~January 1991 13




Estliux posterior C VS

Direct Indirect

Estilux posterior C VS







* *


Thermocycted Gluma Direct







NS ** ***



p > 0.05 p < 0.05. p 0.2). This may have to do with our working with enamel/ dentin cavities and not with flat enamel surfaces, and with the ensuing differences in transmission of forces between the two experiraental models. Correlations, however, were found between flexural strength (Brilliant, 155 MPa; Estilux, 165 MPa; and Isosit, 136 MPa) and retention (r = 0.78; p < 0.05) and between modulus of elasticity (Brilliant, 6.7 GPa; Estilux, 13.1 GPa; and Isosit, 3.8 GPa) and retention (r = 0.97; p < 0.001). Thus, also in cavities, the mechanical properties of a composite probably play a role in the bonding and retention of a filling or inlay/onlay. With regard to thermocycling, the temperature changes had no detrimental effect on the retention of the Brilliant inlays. Despite a decline in retention for Estilux inlays when thermocycled, the retentive strength was stillhigher than that of nonthermocycled Brilliantand I~sit inlays. An even more pronounced fall in retentive strength, in consequence of thermocycling, was observed with inlays made of Isosit. The


decrease in retention brought about by thermocycl/ng may stem from two phenomena, both of which are known to cause a reduction in bond strength: (1) The diffusion of water between enamel and the cement/inlay is accelerated, and (2) changing the temp e r a t u r e c r e a t e s s t r e s s at the interface of the two components because of different coefficients of thermal expansion. Smith (1985) reported that microfilled composites had coefficients of thermal expansion higher than those of posterior and conventional composites. Isosit is microfllled and has the largest coefficient of thermal expansion; this may account for the fact that Isosit inlays were the most affected by being thermocycled. The substantial increases in retention observed after treatment with G h m a agree with the bond strength results of Asmussen et al. (1989). Especially in cavities with a large dentin proportion, it seems advisable for Gtuma or another dentinbonding agent of similar bond-mediating capacity to be used. REFERENCES ASMUSSEN, E.; DE ARAUJO, P.A.; and PEUTZFELDT, A. (1989): In-vitro Bonding of Resins to Enamel and Dentin: an Update, Trans Aead Dent Mater 2: 36-63. BRUNING, J.L. and Kzm~z, B.L. (1977): Computational Handbook of Statistics, 2nd ed., Illinois, USA: Scott, Foresman and Company. CHAN, ILC. and BOYER,D.B. (1983): Repair of Conventional and Microfilled Composite Resins, J Prosthet Dent 50: 345-350. FEILZER, AJ.; DE GEE, A.J.; and DAVIDSON, C.L. (1989): Increased Wall-to-Wall Curing Contraction in Thin Bonded Resin Layers, J Dent Res 68: 48-50. HALD, A. (1952): Statistical Theory with Engineering Applications, New York, USA: John Wiley & Sons, Inc. Lvrz, F.; KREJCI, I.; and MOR~N, W. (1987): Die zahnfarbene Seitenzahn Restauration, Phillip J 4: 127-137. PEUTZFELDT, A. and ASMUSSEN, E. (1991):Mechanical Properties of Three Composite Resins Used in the Inlay/0nlay Technique, J Pros~het Dent (in press). SCHALLER, H.G.; GOTZE, W.; and BERTRAM, V.

(1988): Prfifung der Wandst~ndigkeit versch/edener Kompositkunststoffe im Seitenzahnbereich, Dtsch Zahn~r-ztl Z 43: 914-918. SMITH, D.C. (1985): Posterior Composite Dental Resterative Materials: Materials Development. In: Posterior Composite Resin Dental Restorative Materials, G. Vanherle and D.C. Smith, Eds., The Netherlands: Peter Szulc Publishing Co., p. 55. ZZD~, 0.; ASMUSSEN, E.; and JORGENSEN, K.D. (1980): Correlation between Tensile and Bond Strength of Composite Resins, Scand J Den~ Res 88: 348-351.

Retention of composite inlays in enamel dentin cavities.

The retention of composite inlays depends on acid-etching of marginal enamel of the preparation. In many cases, only little marginal enamel is availab...
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