LINING MATERIAL WITH SPECIAL REFERENCE TO DROPSIN A comparative study by C.G. Plant, B.D.S, F.D.S and M. J. Tyas, B.D.S

The pH of Dropsin and three other cavity lining materials was measured. The histological effects on the pulp of Dropsin and two of these materials is described and compared. There was no direct correlation between the pH of the materials during setting and the changes they caused in the pulp. Water absorption by a setting lining material as a possible cause of pulpal damage.

A survey was undertaken of 1,000 den- Dynacap (Pye) pH meter was the instru- Results tal practitioners throughout the United ment used in these measurements, with Figure 1 shows the pH during setting Kingdom. This showed that Dropsin both electrodes and material enclosed of the four materials tested in 87 % was widely used, being the fifth most in a humidity oven at 37°C. relative humidity at 37°C. The first pH popular lining material. 16.3 % of 686 Moisture or fluid from two sources may measurement for each material was dentists, who replied to the survey, sta- affect a lining material whilst it is in the made at the first full minute after ted that they used Dropsin as a cavity mouth. The first is the moisture in the air mixing. Because the mixing time for liner. Despite this wide use there are no in the oral cavity and this can be simu- each material was different this made reports in the literature about the mate- lated in vitro by using a humidity oven. the time from the start of the mix to the rial or its effect on the dental pulp. The second source of moisture, that first pH measurement vary according Dropsin cavity lining material is marke- from vital dentine, cannot be simulated to the material used. ted by Harald Nordin SA in vitro. Neither was it possible, with the (Chailly/Switzerland). The manufacturer equipment available, to measure the pH Fig. 1. Variation of pH with time for state that the material has a neutral pH of lining material in vivo on vital dentine. lining materials. 1_ minutes after mixing and is, there- As the passage of fluid from non-vital fore, harmless to the dental tissues. dentine to lining material is artificial, it Dropsin: at 1 minute after the start of The purpose of this work was twofold: was decided to provide the maximum mixing, the pH of Dropsin was 2.2. A first, to investigate the pH of Dropsin amount of moisture by surrounding the pH of 4 was reached after 9 minutes whilst it was setting; secondly, to setting material with air with as high a and after 24 hours the pH was 6.8. observe any effects it might have on the relative humidity as possible. SS White cavity lining: 2 minutes after pulp and to investigate any correlation This was achieved by placing the set- the start of mixing the pH was 4.5. it of these effects with the pH. ting material in a humidity oven at 37+- then rose sharply to pH 6.4 at 5 minu- Composition 1°C with distilled water thus providing a tes then fell to the region of pH 5. At 30 The manufacturer would not divulge the relative humidity of 87+-5 %. The pH minutes the pH began to rise and rea- exact composition of Dropsin but they was measured over a period of 24 ched pH 6.8 at 24 hours. indicated that the constituents were: hours, each material being tested three Zinc phosphate cement: a pH of 1.7 Liquid Phosphoric acid-25 % times. Before each test the electrodes was recorded at 2 minutes. The pH Aluminium hxdroxide-8% were cleaned, washed and buffered rose gradually but did not reach pH4 Distilled water-67% using standard buffer solutions; at the for 1 hour. Thereafter the pH rose stea- end of each test the validity of the pH dily to rach 6.4 at 24 hours. Powder Zinc oxide measurements were checked with a Zinc oxide/eugenol: the pH fell from Calcium hydroxide standard buffer solution. 5.8 at 5 minutes to 5.1 at 7 minutes Magnesium oxide A standardized powder/liquid ratio and and maintained this level until 1 hour. Aluminium hydroxide mixing time was used for each material From this time the pH rose gradually to to determine the standard reach 6.6 at 24 hours. (I)pH of Dropsin during Setting powder/liquid ratio and mixing time These results apply to one batch of The object of the first part of this work several trial mixes were made. Due material in each case; different bat- was to establish the pH of Dropsin attention was paid to the manufacturers ches were not evaluated. immediately after mixing and to record general instructions regarding the Discussion the changes in the pH during the consistency of each material. The pow- The pH values of the four materials ensuing 24 hours. For purposes of der/liquid ratio of the mix giving the were very similar after 24 hours, and comparison the pH changes of three consistency most suitable for the stan- were in the range of 6 to 7. in the first other lining materials were also recor- dard. These ratios and mixing times, as 10 minutes, however, two distinct pairs ded over the same period of time. The given below were used throughout all of material were seen. other lining materials used were S.S. the investigation. White cavity lining, S.S. whit zinc phos- phate cement and zinc oxide/eugenol Powder/Liquid Ratio and Mixing time for materials used (B.P.) Materials and Method Material Manufacturer P/L ratio Mixing time The pH of Dropsin and the three mate- Dropsin Nordin SA, Switzerland 2/1 0.5 rials listed above were measured by S.S. White cavity lining SS White (GB) 3/1 1.5 using a glass electrode with a calomel Zinc phosphate cement " 1.5/1 1.5 reference electrode inserted into the Zinc oxide/eugenol " 5/1 4 setting material on a glass stab. A (1)SS White cavity lining and zinc methods shown below. After was suffered by the pulp with any oxide/eugenol, having almost iden- extraction the apical third of the of the material used in this survey. tical pH in the 5 and 6 region.. root was removed by means of a Only one tooth showed evidence of (2)Dropsin and zinc phosphate hand saw and the tooth placed into inflammation-this being with the which have a much more acid reac- 10 % neutral buffered formalin. control material SS White cavity tion of between pH 1.6 and 4.4. The teeth were decalcified and lining, where a mild degree of If the hydrogen ion concentration is serial sections prepared through inflammation of the odontoblast a major factor in causing pulpal the cavity site where the minimum layer was seen. damage it would be reasonable to thickness of dentine between cavity Very small isolated areas of inflam- assume from the above results that: floor and pulp remained. Sections matory cells were seen in the body (1)SS White cavity lining and zinc were stained with haematoxylin and of the pulp in three sections. These oxide/eugenol would cause similar eosin. were well away from the zone of charges in the pulp and that these The sections were examined for the tubules cut during cavity prepara- would be relatively mild. features listed in the tables; reduc- tion and their presence is thought (2)Dropsin and zinc phosphate, tion in odontoblasts, vacuolisation to be unrelated to this procedure. because of their early acidity, would in the odontoblast layer, aspiration Similar focal collections of inflam- cause more severe changes. The of odontoblasts, hyperaemia, matory cells have been reported by changes due to Dropsin, however, vacuoles I the pulp and inflamma- Shovelton and Marsland(1960) should be less severe, particularly if tory cells in the odontoblast layer. beneath cavities prepared with an the pulp only undergoes marked An arbitrary scale for degrees of air turbine handpiece. change when the hydrogen ion change was used, 0=no change, concentration remains high for 1=mild, 2=moderate, 3=severe. All Table II shows that Dropsin caused more than a few minutes. slides carried one number only, so a small degree of change in the that there was no indication of the pulp, mainly in the form of a mild (II) Effect of Dropsin in the Pulp material used in the cavity. The reduction I odontoblasts. The The main aim of this section was to examinations were carried out by control materials, SS White cavity establish the histological response one person so that the arbitrary lining and zinc oxide/eugenol if of the pulp to Dropsin when this scale of change was applied considered as a single group (Table material is used as a cavity lining. A consistently. III), caused a more marked change further aim was to attempt to corre- than Dropsin. In 7 of the 18 teeth a late this histological response with Grouping of Teeth moderate or severe reduction in the pH of Dropsin. (1) Dropsin lining-29 teeth. odontoblasts took place whereas For purposes of comparison and to A creamy mix of Dropsin was used with Dropsin only 4 out of 29 teeth act as controls, SS White cavity to build up a lining of normal thick- suffered similar effects. lining and zinc oxide/eugenol were ness. Care was taken to cover all also used to obtain a histological exposed dentine on the cavity floor. In tables IV and V, the controls are response. As with Dropsin these The lining was allowed to set fully subdivided into a group of zinc results were compared with results until it was hard to a probe and was oxide/eugenol. From this it can be of the pH determinations. then covered with amalgam or zinc seen that SS White cavity lining oxide/eugenol. was the material mainly responsible Materials and Method The teeth were extracted fro 3 to for the changes shown in the Fifty-five sound teeth, which were 175 days after the procedure. control group as a whole. 6 out of 8 to be extracted for orthodontic pur- (2)Controls-26 teeth. teeth filled with SS White cavity poses, were used in this experi- (a)Cavities in 18 of the control teeth lining showed moderate to severe ment. Occlusal or buccal cavities were completely filled with either reduction in odontoblasts. The were cut in 51 of these teeth using SS White cavity lining material or results for zinc oxide/eugenol tungsten-carbide burs, round No 5 zinc oxide/eugenol dressing. (Table V) confirm its bland nature as and flat fissure no 558. A ball-bea- SS White cavity lining was placed in reported by Gurley and Van Huxsen ring Kavo handpiece was used, run- 8 cavities and zinc oxide/eugenol (1940) and others. ning at a speed of 30.000 rpm dressing in 10. throughout cavity preparation, The teeth were extracted from 3 to The results obtained from control which was achieved by intermittent 77 days after cavity preparation. cavities which were unfilled (Table cutting (5 to 10 seconds cutting (b)Four control teeth were extracted VI) showed a mild to moderate periods) using a light pressure. The immediately after cavity prepara- degree of vacuolisation in the aim was to cut well into dentine tion in order to study any histologi- odontoblasts in 3 out of 4 teeth with the floor of the cavity placed cal changes caused by this proce- used. This vacuolisation is also as near to the pulp as possible dure. seen in the experimental cavities without explosing. Cotton-wool (c)Four sound teeth were also col- although for some reason it is less pledges were used to dry the cavity lected during this series to form in cavities lined with Dropsin, as use of a air syringe has been unoperated controls. occurring in only 3 cases out of 29. shown to cause pulpal changes (Bränström 1960). Results When the cavities were completed Results of histological examination they were treated by one of the showed that no extensive damage Table II. Effect of Dropsin on the pulp (number of teeth showing changes) Total teeth in group 29 Reduction in Vacuolisation Aspiration Vacuoles Inflammatory cells odontoblast of odontoblast of odontoblast Hyperoemia in pulp in odontoblast layer

Number showing normal appearance 8

Degree of change 0 11 26 25 27 28 29 1141 3 1 1 0 23 1 1 1 0 0 31 1 0 0 0 0

Table III. Effect of control materials S.S. White Cavity Lining and Zinc Oxide/Eugenol on the pulp Total teeth in group 18 Reduction in Vacuolisation Aspiration Vacuoles Inflammatory cells odontoblast of odontoblast of odontoblast Hyperoemia in pulp in odontoblast layer

Number showing normal appearance 7

Degree of change 0 11 13 16 15 18 17 10 3 1 3 0 1 23 2 1 0 0 0 34 0 0 0 0 0

Table IV, Effects of S.S. White Cavity Lining on the pulp (number of teeth showing changes) Total teeth in group 8 Reduction in Vacuolisation Aspiration Vacuoles Inflammatory cells odontoblast of odontoblast of odontoblast Hyperoemia in pulp in odontoblast layer

Number showing normal appearance 1

Degree of change 0 2 5 6 6 8 7 10 1 1 2 0 1 23 2 1 0 0 0 33 0 0 0 0 0

Table V, Effects of Zinc Oxide/Eugenol on the pulp (number of teeth showing changes) Total teeth in group 10 Reduction in Vacuolisation Aspiration Vacuoles Inflammatory cells odontoblast of odontoblast of odontoblast Hyperoemia in pulp in odontoblast layer

Number showing normal appearance 6

Degree of change 0 9 8 10 9 10 10 10 2 0 1 0 1 20 0 0 0 0 0 31 0 0 0 0 0

Table VI, Effects of Cavity Preparation on the pulp (number of teeth showing changes) Total teeth in group 4 Reduction in Vacuolisation Aspiration Vacuoles Inflammatory cells odontoblast of odontoblast of odontoblast Hyperoemia in pulp in odontoblast layer

Number showing normal appearance 1

Degree of change 0 3 1 4 4 4 4 11 1 0 0 0 0 20 2 0 0 0 0 30 0 0 0 0 0 Discussion The histological results given above References There is considerable difficulty in do not have a close correlation with Bränström, M. (1960) Acta. Odont. measuring the pH of setting materials the pH measurements described in Scand, 18, 17 and for most of the time the lining the first part of this paper. SS White Nyborg, H. (1960) odont. Revy, 11, 37 materials were in the set state when cavity lining causes more damage to Harvey, W. le Brocq, L.F., and measurement was required. It is the pulp than zinc oxide/eugenol Rakowski, L (1944) Brit. Dent. J 77, 61, generally considered that measure- although the pH of these materials is 89 ments of pH should be made in solu- very similar. Kent, B. E, and Wilson, A, D (1969) J. tion, but the electrodes used in this It should be remembered however, Dent. Rest. 48, 412 experiment are also recommended that the zinc oxide/eugenol and SS Manley, E. B (1943) Proc. Roy. Soc. for semi-solids. An alternative means White cavity lining materials are not Med 36, 488 of measuring the pH of cavity lining is aqueous systems and, therefore, the Nixon, G. S. (1959) Ph. D. thesis, the indirect method in which the set recorded values may not have the University of Glasgow. material is crushed and dissolved in same significance as those of zinc Norman, R. D., Schwartz, M. L. and distilled water and the pH of the resul- phosphate cement and Dropsin. Philips, R. W. (1960) J. dent. Res. 45, ting solution determined. Hearvey et Dropsin has a similar pH to zinc phos- 136. al. (1944) utilised this method of pH phate cement in the early stages of Shoveelton, D.S., and Marsland, E.A. determination but pointed out its limi- setting but the response of the pulp (1960) Brit. Dent. J. 109, 225 tation. Whilst that method gives a true to these two materials is quite diffe- pH of the resulting solution it does not rent. Dropsin causes a mild reaction, bear a direct relationship to the set mainly in the form of reduction of material at any particular time. For odontoblasts, whereas it has been this reason it was decided to use reported that zinc phosphate causes glass electrodes inserted into the set- severe pulpal changes (Brännström ting lining material. The final pH rea- and Nyborg, 1960; Manley, 1943). dings of the semi-solid should be Conversely, SS White cavity lining, reliable because of the high water which has a higher pH than Dropsin, content, assuming that the electrodes has a more marked effect on the pulp. are not disturbed from their original These results indicate that hydrogen contact with the material. A similar ion concentration is not directly rela- method of measuring the pH of a ted to pulpal damage and that factors semi-solid has been described by other than hydrogen ion concentra- Norman et al. (1966) in which anti- tion per se must be sought to explain mony electrodes were used. The the pulp reactions that have been author were unable to obtain reprodu- observed. It may be that a material in cible results by using antimony elec- contact with dentine may have to trodes and these were abandoned. maintain a low pH for a certain mini- Norman et al. (1966) found the pH of mum time before pulpal changes are setting zinc phosphate cement to the produced. However, Nixon (1959) has higher than indicated by the present shown that a marked reaction occurs results. in the pulp of human teeth when they A further criticism of all ph measure- are subject to a zinc phosphate filling ments of cements and lining materials for as little as 40 minutes. It is possi- is the cement-tooth interface is the ble that a critical pH may exist bet- critical area and the pH of this may be ween the pH of zinc phosphate different from the pH of the internal cement and that of Dropsin and that a mass of the cement. It is possible that material with a pH above this level will fluid from the dentinal tubules could not damage the pulp. Evidence react with the cement or lining mate- against this, however, is the more rial at this interface and thereby buffer marked pulpal reaction caused by SS extremes of pH. White cavity lining when compared The measurement of pH at the lining- with Dropsin. dentine interface on a vital tooth is not however, possible with any equip- ment available at present. The method of measuring pH used in this work seems the nearest approach to this ideal. The measurement is a direct one on material with a high water content and the results were reproducible from day to day. This approach is in agreement with that used by Kent and Wilson (1969). EFFECT OF DIFFERENT CAVITY LINING MATERIALS ON THE POLYMERISATION OF COMPOSITES

ADRIAN R. LUSSI and PETER HOTZ

Department of Conservative, Preventive and Paedodontic Dentistry, University of Bern, Switzerland

Summary been the subject of investigation cavity liner for other composites (NEWMAN et al. 1983, MATSUMOTO (Herculite, Dual-Cement). A zinc oxide- The aim of this study was to investi- et al. 1986, HOTZ et al. 1989, BURKE eugenol cement (Super EBA) was used gate in vitro the effect of different et al. 1990). It was found that polyme- as a negative control (Tab. 1). cavity lining materials on the poly- risation is inadequate, at least at the merisation of a chemically curing base of the filling, if the exposure time Fabricating the specimens composite (Brilliant) and a light- is too short, if the increments polyme- Standard holes (“cavities”) with a dia- curing composite (Brilliant Lux). rised are too thick or if the unit is not meter of 4 mm and a depth of 1.9 mm Super EBA zinc oxide-eugenol functioning properly. This leads to a ± 0.1 mm were drilled in Plexiglas (Fig. cement was used as a negative reduction in the final hardness on the 1). Plexiglas was used as preliminary control for the cavity lining mate- inside of a filling, which can have clini- tests indicated a comparable depth of rials. The degree of polymerisation cal consequences, as the filling may polymerisation in the composite inser- (conversion rate) was determined fracture when loaded and the marginal ted in Plexiglas and in cavities of using the Knoop microhardness fit may be impaired. Temporary resto- extracted teeth. It was also found in a test. rations with a zinc oxide-eugenol previous test that the depth of polyme- It was found that the majority of the content can also cause significant sof- risation of composites in “cavities” in cavity liners tested (Ketac-Bond, tening of the light-curing composites brass plates and Plexiglas plates was Vitrebond, Dropsin, Dycal, Alkaliner) fitted later (HOTZ et al. 1992). Various similar. With all the materials the mar- inhibited the depth of polymerisa- cavity lining materials can also impair gin was softer than the core of the fil- tion in the adjacent composite polymerisation of chemically curing ling regardless of the cavity wall mate- layers to the same degree as Super composites. Cavity liners with a zinc rial (HOTZ et al. 1992). Any possibility EBA. Alkaliner exhibited a similar oxide-eugenol content, calcium salicy- of the Plexiglas interface affecting the result with Herculite and Dual- late cements and chemically curing microhardness of the composite Cement, the other composite mate- glass ionomer cements had a marked through the cavity liner could be ruled rials tested. The light-curing glass effect (CIVJAN et al. 1973, GRAJO- out, as the cavity liners used did not ionomer cement (Vitrebond) had the WER et al. 1974, MARSHALL et al. have a significant effect on the depth least effect on polymerisation. The 1982, LINGARD et al. 1981). Results of polymerisation of the composites light-curing composites used in this with the zinc phosphate cement were tested (LUSSI & HOTZ, unpublished). test were more affected than the slightly contradictory, as in most cases chemically curing material. polymerisation inhibition was only Swiss Monthly Dental Magazine 104: 854-858 (1994) minimal (CIVJAN et al. 1973, GRAJO- WER et al. 1974). Introduction There have only been a few studies on the effect of cavity lining materials on The increased controversy about the polymerisation of light-curing com- amalgam and other metal filling mate- posites. BERRONG et al. (1989), for rials in recent years has caused uncer- example, found that the composite tainty among patients (Lussi 1987, material was impaired by glass iono- Fig. 1 Test set-up. Plexiglas “cavity” Lussi et al. 1989). This uncertainty, mer cement. (diameter 4 mm, depth 1.9 mm) with combined with higher aesthetic cavity liner (1) and composite (2). expectations, has increased the The aim of this study was to investi- Knoop microhardness measured at demand for tooth-coloured posterior gate in vitro the effect of different 25 µm, 50 µm, 100 µm, 500 µm and fillings. cavity lining materials on the polymeri- 1000 µm from the cavity liner. The many systems currently on the sation of chemically curing and light- market (porcelain inlays/ overlays, curing composite materials. The The cavity liners were inserted into the composite inlays/ overlays, veneers) degree of polymerisation (conversion “cavities” according to the manufactu- all involve cementation using compo- rate) was determined using the Knoop rer’s instructions. Twice the recom- site materials. Adhesion of composite microhardness test. mended exposure time was used with to enamel, dentine or porcelain has light-curing cavity lining materials to been and still is the subject of many Materials and methods attain maximum polymerisation. Self- studies. To what extent the degree of curing cavity liners were cured in air polymerisation of light-curing compo- The effect of five cavity liners (Ketac- saturated with steam. After the cavity sites and light-curing glass ionomer Bond, Vitrebond, Dropsin, Dycal and liner was cured in accordance with the cements depends on the light source, Alkaliner) on the polymerisation of two clinical criteria, the composites (Tab. 1) its output and maintenance as well as composites (Brilliant Lux, Brilliant) was were inserted into the “cavities” and the length of exposure has also often tested. Only Alkaliner was tested as a polymerised. A coverglass was pres- sed onto the filling to ensure uniform Tab. 1 Cavity liners and composites used compression. The exposure time using a Translux CL lamp (Kulzer, Germany) Manufacturer Type Curing was 120 sec., with the coverglass being removed after 20 sec. Previous Ketac-Bond® Espe, Seefeld, D Glass ionomer self-curing tests had indicated that an exposure Vitrebond® 3M, St Paul, MN, USA Glass ionomer light-curing time of 60 sec. was adequate to poly- Dropsin® Nordin, Chailly, CH Zn-phosphate self-curing merise a layer of composite 2 mm Super EBA® Staident, Staines, GB ZnO-eugenol self-curing thick (HOTZ et al. 1989). The lamp was Alkaliner® Espe, Seefeld, D Ca(OH)2 self-curing tested at regular intervals with a radio- Dycal® De Trey Dentsply, Constance, D Ca(OH)2 self-curing meter (Demetron, Danbury, CT, USA) Brilliant Lux® Coltène, Altstätten, CH Composite light-curing and never fell below the displayed out- Brilliant® Coltène, Altstätten, CH Composite self-curing put of 40 mW/cm2. Ten specimens Herculite® Kerr, Basle, CH Composite light-curing were fabricated for each composite Dual-Cement® Vivadent, Schaan, FL Composite light-curing/self-curing and cavity liner. The specimens were post-cured in a hot-air cabinet (T = the cavity liner, it was assumed that polymerisation was greater with 37∞C) for a minimum of 7 days before the final hardness of each composite Herculite light-curing composite. being tested. had been attained at this depth. Calculation of the surface percentage Hardness measurements taken further enabled the total reduction in hard- away from the cavity liner, i.e. nearer ness caused by a specific cavity liner Determining the degree of poly- the light source, did not indicate any to be calculated (Fig. 3). It indicated a merisation difference in curing hardness. The significant effect on different composi- The specimens were each embedded degree of polymerisation in each seg- tes to a depth of 500 µm for the majo- in small glass tablets in cold-curing ment (Fig. 2) was determined by com- rity of cavity liners. Dycal, Ketac-Bond synthetic resin (Epofix, Struers, paring the calculated surface with the and Vitrebond, which only inhibited Denmark). After the resin had fully har- possible surface. As the final hardness Brilliant to a depth of 200 µm, were dened, the specimens were sliced of the composites tested was not the exceptions. open vertically through the centre of same, the surface of the last segment the filling using a diamond disc with was standardised to 100% to allow Knoop hardness glycerine coolant. Then they were comparison. As the measurements embedded in Paladur (Kulzer, were not distributed normally, non- Fig. 2 Determining the degree of Germany) with the ground surface parametric techniques were applied. polymerisation. The shaded surface facing up in plane-parallel steel rings Differences in polymerisation were indicates areas of reduced polymeri- and prepolished with moist silicon checked for significance using the sation. sandpaper grit size 500 (30 µm), 1000 Wilcoxon test. The significance level (18.3 µm) and 4000 (5 µm) on a Knuth was set at p ≤ 0.01. rotor (Struers, Denmark) and polished to a high-lustre with 3 µm polishing spray (Struers) on a cloth-covered poli- Results shing disc. Polymerisation of the com- posite specimens was recorded using The final hardness (distance from the the Knoop hardness test on a Leitz cavity liner 1000 µm) of the five com- Miniload-2 unit (Leitz, Switzerland), (DE posites tested varied between 43.6 LANGE et al. 1980, FERRACANE 1985, Knoop hardness (Dual-Cement) and HASEGAWA et al. 1991, KAYS et al. 88.4 Knoop hardness (Brilliant). The 1991, PIRES et al. 1993). The diamond hardness of Brilliant Lux was statisti- was pressed onto the surface with a cally significantly lower than the final force of 100 ponds for 30 sec. during hardness up to 200 µm from the cavity each measurement. The Knoop micro- liner (Tab. II). Curing of Brilliant Discussion hardness was measured twice at 25 paste/paste system was on average µm, 50 µm, 100 µm, 200 µm, 500 µm better. The hardness was only signifi- The conversion rate of composites can and 1000 µm from each cavity liner cantly lower than the final hardness up be reliably recorded using microhard- (Fig. 1). The mean was determined at to 50 µm from the interface of the ness tests (FERRACANE 1985, DE each distance for subsequent calcula- composite and cavity liner. Super EBA WALD & FERRACANE 1987). It is advi- tions. and Alkaliner were exceptions, as sable to determine the hardness after curing of the composite was signifi- storage for 7 days at 37∞C, as poly- Statistical analysis cantly impaired up to 100 µm. The merisation has been completed as far The degree of polymerisation was effect of Alkaliner cavity liner on the as possible by that time (LEUNG et al. determined using the standard proce- hardness was also tested with 1983). Dental practitioners are well dure for recording demineralisation and Herculite and Dual-Cement composi- aware that cavity liners with a zinc remineralisation phenomena (FEA- tes as a comparison. The light-curing oxide-eugenol content can impair the THERSTONE et al. 1990). As no signifi- and self-curing Dual-Cement exhibited polymerisation of composites when cant differences in hardness could be a significantly lower hardness up to 50 there is direct contact. It emerged from determined at 500 µm to 1000 µm from µm from the cavity liner; inhibition of this study, however, that all other Tab. II Knoop microhardness of different composites with different cavity liners depending on the distance from the interface (x±SEM) Composite Cavity liner Knoop microhardness at a distance from the cavity liner of

Brilliant Lux Ketac-Bond Vitrebond Dropsin Super EBA Alkaliner Dycal

Brilliant Ketac-Bond Vitrebond Dropsin Super EBA Alkaliner Dycal

Herculite Alkaliner Dual-Cement Alkaliner The hardness figures marked with an asterisk and the figures to the left are statistically significantly different from the final hardness (1000 µm). materials tested, i.e. calcium salicylate posite materials appeared to change the interface is important in this res- cements, glass ionomer cement, light- little due to this effect (POWELL & pect. There is no reason to advise curing glass ionomer cement and also HUGET 1993). An in vitro experiment against the application of the tested zinc phosphate cement, impaired poly- indicated, however, that the marginal cavity lining materials based on these merisation with chemically curing com- integrity of cemented composite inlays results. In areas adjacent to the pulp, posites and also, more markedly, with could be impaired by different cavity pulp protection should still be used light-curing composites. The differences lining materials, with the modulus of with the entire spectrum of activity of, were relatively small and the light-curing elasticity of the cavity liner playing an e.g. calcium salicylate cements. glass ionomer cement was the best. The important role (KREICI et al. 1998, Though the materials tested are similar causes of this polymerisation inhibition STAEHLE et al. 1992). It can be assu- in relation to the level of significance, are not known. Possible causes could med from this study that not only the the results indicate that light-curing be chemical influences, e.g. liquid modulus of elasticity of the cavity liner glass ionomer cement has advantages. content of the cavity liner, availability of but also the softening of composite at free radicals, pH and presence of poly- merisation inhibitors, about which little is known. The effect of the temperature should also be taken into consideration. Exposure of the composite specimens with the Translux CL also increased the temperature of the material (HANSEN & ASMUSSEN 1993). This can have a positive effect on the conversion rate. It is possible, however, that the interface may be cooled by the material under- neath and this could affect polymerisa- tion. LUNDEN & KOCH (1992) found improved polymerisation with in vivo cured fillings compared with in vitro pla- ced fillings. They also attributed this observation to the increased tempera- Surface percentage 25 – 50 ture in the oral cavity. On the other hand Surface percentage 25 – 100 µm our measurements, for which the speci- Surface percentage 25 – 200 µm mens were preheated to 37 C and the ∞ Surface percentage 25 – 500 µm composite material was inserted at Surface percentage 25 – 1000 µm 37∞C, did not indicate that the tempera- ture had any effect. It is impossible to say how critical Fig. 3 Polymerisation inhibition of different composites (x±SEM) by cavity liners polymerisation inhibition at the inter- depending on the distance from the interface (in surface percentages between 500 – 1000 µm to 100% standardised surfaces). The columns marked with an asterisk and the face of the cavity liner is clinically. columns to the left are statistically significantly different from the surface percentages Some physical properties of the com- of 25 – 1000 µm.