CLINICAL DENTISTRY AND RESEARCH 2011; 35(2): 2-9

CorrespondenceGürel Pekkan, DDS, PhD

Department of ProsthodonticsFaculty of Dentistry

Dumlupınar University Merkez Kampus, Tavşanlı Yolu 10. Km,

Kütahya, TurkeyPhone: +90 274 2652031 (2172)

Fax: +90 274 2652277E-mail: gurelp@gmail.com

Gürel Pekkan, DDS, PhD Department of Prosthodontics, Faculty of Dentistry,

Dumlupınar University,

Kütahya, Turkey

Serkan Sarıdağ, DDS, PhDKocaeli Dental Hospital,

Darıca, Kocaeli, Turkey

Nilüfer Çelebi Beriat, DDS, PhDSchool of Dental Technology,

Hacettepe University,

Ankara, Turkey

EVALUATION OF THE RADIOPACITY OF SOME LUTING, LINING AND FILLING DENTAL CEMENTS

ABSTRACT

Background and Aim: To investigate the radiopacity of

different luting, lining and filling dental cements used in

prosthetic dentistry in comparison with human and bovine

dental hard tissues.

Material and methods: Eight cylindrical samples of each

material (6 x 1 mm) were prepared from Aqualox (APC),

Durelon (DE) and Adhesor Carbofine (ACF) zinc polycarboxylate

cements, Cavex zinc oxide eugenol provisional filling cement

(CZC), Adhesor zinc phosphate cement (AZP), Ketaccem

Easymix (KCE) and Kavitan Plus A2 (KPL) glass ionomer luting

cements, Provicol (PRC), Cavex (CTL) and PreVISION CEM (PTC)

provisional luting cements, Dycal calcium hydroxide cement

(DYC), Coltosol F temporary filling material (CLF) and Ketac Molar

glass ionomer restorative material (KTM). The optical densities

of each material, along with one tooth section (human canine),

bovine dentin and enamel samples, and an aluminium step

wedge, were measured from radiographical images using a

transmission densitometer. The data were analysed by Kruskal-

Wallis and Dunnett T3 tests for post hoc comparison (α=0.05).

Results: The radiopacity values of all materials were

statistically significantly higher than human dentin except PRC

(p<0.05). KTM, KPL, KCE, DYC and CTL had statistically similar

radiopacity values to bovine enamel. The radiopacity values of

CLF, APC, ACF, DE, CZC and AZP were statistically significantly

higher than bovine enamel (p<0.05).

Conclusions: The glass ionomer materials had the lowest

radiopacity values. DYC and provisional luting cements had

moderate radiopacity values that are higher than glass

ionomer materials. The zinc phosphate cement had the highest

radiopacity values.

Key words: Dental Cements, Filling Cements, Lining Cements, Luting Cements, Radiopacity

Submitted for Publication: 11.11.2010

Accepted for Publication : 06.27.2011

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CLINICAL DENTISTRY AND RESEARCH 2011; 35(2): 2-9

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INTRODUCTION

Dental cements are used for base, core foundation, provisional restorative material, for luting restorations and fixed partial dentures to abutments.1 Dental cements must be biocompatible, prevent caries, have enough retention, resist against microleakage, have optimum optical properties and in addition must have sufficient radiopacity.2 Radiopacity is a desirable property of intra-oral materials including direct-filling restorative materials,3-12 cavity liners,8-11 core build up materials,9,13 luting agents5,6,11,14-17 and adhesive systems.18 Radiopacity of restorative materials aid in radiologically detecting the form, contour and deficiencies of restorations, as well as localise the dental pulp.3-7 Hence, the radiopacity of restorative materials facilitates the detection of secondary caries under the restoration and enables the observation of periodontal effects of the overhangs in the restoration.4,15

Some studies revealed that combinations of composite luting cements and/or glass ionomer cements may show gap-like features because of differences in radiopacity.10,11 The degree of radiopacity required for an ideal clinical performance may vary according to the class of material.19 According to some authors, the radiopacity of the material must be equal or higher than the radiopacity of dentin.12,17

Other authors consider that the restorative materials should have radiopacity values equivalent to or greater than that of enamel.5,20 The International Organization for Standardization (ISO) has published radiopacity evaluation protocol and set guidelines for radiopacity of polymer-based filling, restorative and luting materials.21 According to the protocol, the radiopacity of a dental material is expressed as optical density value or in terms of equivalent aluminium (Al) thickness (in millimeters) using a reference calibration curve under controlled radiographic conditions. These materials should have radiopacity equal to or greater than that of aluminium Al.22 Several factors may affect the radiopacity of dental cements. The material composition and thickness, exposure settings, angulation of the x-ray beam, and the methodology used for evaluation have all been documented as factors.8-13

A growing number of dental cements have been introduced and are used in some cases in combinations, especially, when restoring extensively damaged teeth. The information about the difference or the similarity of the radiopacity values of the various dental cements is needed to be investigated. Hence, there is especially no information about the radiopacity of provisional luting cements in the literature.

The purpose of this study was to investigate the radiopacity of various luting, lining and filling dental cements used in prosthetic dentistry in comparison with human and bovine dental hard tissues.

MATERIALS AND METHODS

In this study, the radiopacity levels of 13 different luting, lining and filling dental cements were tested. The materials used in this study, selected from those that have common clinical usage in prosthetic and restorative dentistry. The materials and the manufacturers for the materials used in this study are listed in Table 1. Samples of human canine dentin (HD) and bovine dentin (BD) and enamel (BE) were used as reference of radiopacity, whereas an Al step wedge was used to internal control of radiopacity. Cement specimens were prepared using teflon moulds (6.0 mm in diameter x 1.0 mm in thickness). Eight cylindrical samples of each material (6 x 1 mm) were prepared according to manufacturer instructions. In total, 104 (n=8) specimens were obtained. All specimens were wet ground through 400-grit silicon carbide paper (SiC) (Struers, Willich, Germany) to create a flat surface and measured with a digital calliper (Youfound Precision Co., Ltd, Zhejiang, China) to verify the critical tolerance of 1.0 ± 0.01 mm. All specimens were stored dry in a box at room temperature (at least 24 hours) until they tested. Eight bovine enamel and dentin disk specimens were prepared from bovine lower incisor teeth (6 x 1 mm). Bovine dentin and enamel specimens were obtained by longitudinal sectioning of the buccal side of teeth after separating the roots. Longitudinal sections of human permanent canine teeth were also prepared to the same thickness using a micro-slicing device (Accutom, Struers Co, Copenhagen, Denmark) (n=8). An Al step wedge (Alu-Keil; PEHA Med. Geräte GmbH, Sulzbach, Germany) was prepared. The step wedges maximum thickness was 14 mm; each step had a thickness of 1mm, length of 4 mm, and width of 14 mm. One specimen of each material, bovine dentin and enamel, a human canine tooth section and Al step wedge were positioned side by side on occlusal D speed radiographical film (Kodak Ultra-speed; Eastman Kodak Company, Rochester, NY) (Figure 1). A special holder was mounted to ensure a fixed focus/film distance. The films were exposed for 0.38 seconds with a dental X-ray system (Trophy; Vincennes, France) at 70 kV and 8 mA; the object-to-film distance was 30 cm. All films were processed immediately in a standard automatic processor (Velopex Extra-X; Medivance, Harlesden, UK) using fresh developer and

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CLINICAL DENTISTRY AND RESEARCH

Figure 1. A view of one specimen from each material, bovine dentin and enamel, a human canine slice and Al step wedge positioned on an occlusal radiograph.

Materials Material type Manufacturer

Provicol, (PRc) provisional luting cement Voco gmbH, cuxhaven, germany

Ketac Molar, (KTM) restorative glass ionomer cement 3M Espe ag, seefeld, germany

Kavitan Plus a2, (KPl) glass ionomer cement spofa Dental a.s., Prague, czech Republic

Ketaccem Easymix, (KcE) glass ionomer luting cement 3M Espe ag, seefeld, germany

Dycal, (DYc) calcium hydroxide cement Dentsply DeTrey gmbH, Konstanz, germany

cavex, (cTl) temporary luting cement cavex Holland BV, Haarlem, The netherlands

PreVision cEM, (PTc) temporary luting cement Heraeus Kulzer gmbH co. Kg., Hanau, germany

coltosol F, (clF) temporary filling materialcoltene Whaledent, gmbH + co. Kg, langenau,

germany

aqualox, (aPc) zinc polycarboxylate cement Voco gmbH, cuxhaven, germany

adhesor carbofine, (acF) zinc polycarboxylate cement spofa Dental a.s., Prague, czech Republic

Durelon, (DE) zinc polycarboxylate cement 3M Espe ag, seefeld, germany

cavex, (cZc) zinc oxide eugenol provisional filling cement cavex Holland BV, Haarlem, The netherlands

adhesor, (aZP) zinc phosphate cement spofa Dental a.s., Prague, czech Republic

Table 1. Materials used in the study.

fixer (Velopex Ready Mixed Developer and Fixer; Hexagon

International (GB) Ltd, UK) (Figure 2).The optical density of the radiographical images was measured with a transmission densitometer (Pehamed

Figure 2. Appearance of representative sample radiograph. Canine tooth (left), (top row) AZP, CTL, KTM, CLF, DYC; (second row) DE, PRC, KPL, PTC, BD; (bottom row) ACF, APC, KCE, CZC, BE; Al step wedge

Denso-Dent Densitometer; PEHA Med. Geräte GmbH) (mean of at least 3 readings per specimen) with an aperture size of 3 mm (DIN 6868/55) (Figure 3). Following the method of El-Mowafy and Benmergui17, the optical density data for

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the Al steps were entered into a computer, and the best possible exponential fit was used for curves of Al optical density. A graph was plotted to illustrate the relationship between step wedge thickness and optical density values (ODVs) with the following equation: [y=-0.483Ln(x) + 1.965] (Figure 4). From that graph, ODVs of the specimens were used to determine the equivalent Al thickness (eq Al) values. Kruskal-Wallis and Dunnett T3 multiple range tests were conducted to statistically analyze the ODVs of the materials. SPSS 13.0 for Windows (SPSS Inc., Chicago, IL) statistical software was used for the analyses.

RESULTS

The ODVs of the specimens, human dentin, bovine enamel and dentin are presented in Table 2. The lower values of optical density represent greater radiopacity. Results of statistical analysis of ODVs are also summarised in Table 2. Figure 5 shows the equivalent Al thickness values of the tested materials in mm Al, graphically. Higher values of eq Al thickness represent greater radiopacity. Among the materials tested, PRC had statistically significantly lower radiopacity values than human and bovine dentin (p<0.05). The radiopacity values of all other materials were statistically significantly higher than human dentin (p<0.05). There was no statistically significant difference between the radiopacity of bovine and human dentin. The radiopacity values of glass ionomer cements and also DYC, CTL and PTC were not statistically different from that of bovine enamel (p>0.05). CLF, APC, ACF, DE, CZC and AZP had statistically higher radiopacity values than bovine enamel (p<0.05). AZP had the highest radiopacity values.

Figure 3. Transmission densitometer for dental radiographs.

DISCUSSION

In present study, all materials except PRC had radiopacity values equivalent to or greater than that of bovine enamel. Bovine teeth have similar morphological and histological characteristics to human teeth.23,24 One reason for the use of bovine teeth in this study is the type of the device used for radiopacity testing. The measurement device used in this study measures the radiopacity of a space with an approximate area of 7 mm2 (the measurement point was 7 mm2). This area is equivalent to a circular space with a diameter of 3 mm. In this study, disks with a diameter of 6 mm and a thickness of 1 mm were obtained from the enamel of bovine mandibular incisors. It is not possible to prepare a specimen of human dental enamel with these dimensions. Also bovine dentin specimens were prepared in the same dimensions. As expected, the radiopacity values of human and bovine dentin did not show statistically significant difference (p>0.05). PRC is an eugenol-free provisional luting cement with calcium hydroxide. It has a small amount mixture of zinc oxide in its composition. It was the only material not more radiopaque than human and bovine dentin. Among all materials, except PRC, the glass ionomers had the lowest radiopacity values. These materials contain alumino silicate glass that makes them radiolucent.25 However, the radiopacity results of glass ionomer luting cement, KCE, is in accordance with Williams and Billington10 who reported that the radiopacity of a glass ionomer luting cement was equivalent to that of enamel. In contrast to the results in this study, Prevost et al.14 reported the radiopacity of glass ionomers was less than that amount of dentin. Hara et al.19 also stated that the conventional glass ionomer restorative cements had insufficient radiopacity. However, the glass ionomer restorative cements, KTM and KPL, tested in this study had radiopacity values similar to bovine enamel. DYC and provisional luting cements had moderate radiopacity values that are higher than glass ionomer materials. Provisional luting cements and CLF have zinc oxide in their compositions. According to the authors’ knowledge in this study, the radiopacity of provisional luting cements have not been investigated. The radiopacity values of these materials are reported for the first time in the literature. Pires de Souza et al.26 investigated the radiopacity of calcium hydroxide cement and found similar radiopacity values as DYC in this study. There is also limited information about the radiopacity of the temporary filling materials. The radiopacity values of temporary filling materials, CLF and CZC, were higher than the results of Tagger and Katz.27

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radiopaque materials, but could be detected adjacent to radiolucent porcelain inlays.7 The radiopacity of provisional luting and filling cements is also of great importance. If these materials do not have enough radiopacity as seen in PRC, the excess cement would not be detected radiographically in especially subgingival located cavity or abutment margins. Postcementation protocols do not presently include radiographic examination. Nevertheless, these cements are also used as implant restorative cements.31 Radiographic evaluation after second-stage implant surgery to verify the positions of the implants and the implant-abutment fit, as well as immediately after prosthesis connection, has been suggested.32 Inaccurate removal of cement excess would lead to periodontal problems. The radiopacity values of glass ionomer cements tested in this study were in accordance with the other studies.10,14,29 The author’s opinion is that the glass ionomer cements should be used carefully in restorations with subgingival margins because their radiopacity were not significantly higher than bovine enamel like other zinc-based cements.When the radiopacity of the materials of 1 mm in thickness as in this study is equal to or greater than that amount of enamel is accepted as the minimum requirement, the radiopacity of the materials tested in this study is sufficient enough apart from PRC. However, if the radiopacity of the dental cements has to be greater than that of enamel tissue,5,20 both zinc phosphate and polycarboxylate cements

The zinc polycarboxylate cements had higher radiopacity values than provisional luting cements. Zinc phosphate cement had the highest radiopacity values. Prevost et al.14 stated that the radiopacity of zinc phosphate cement was far greater than that of enamel. Matsumura et al.28 reported that the radiopacity of eight zinc phosphates, seven polycarboxylates, and two glass ionomers exceed that of enamel, whereas the radiopacity of a glass ionomer was less than that amount of dentin.Radiopacity depends on selection of the polymer matrix, on the type and proportion of radiopaque filler, their size, density and addition level.1,29 The filler particles that impart radiopacity to zinc phosphate, glass ionomer and resin luting agents are zinc oxide, magnesium oxide, fluoroaluminosilicate glass, barium, strontium, and zirconium. Considering that the atomic numbers of aluminium, silicon, and calcium are 13, 14 and 20, respectively, the high radiopacity value of zinc oxide-based cements is probably derived from the considerable content of elemental zinc (atomic number 30).20 The use of relatively radiolucent luting agents could lead to overhangs and undetected recurrent decay.7 Their use would be particularly contraindicated in situations where the margin is located in a difficult access area prone to recurrent decay.15 Radiolucent cements should not be used with ceramic inlay systems in particular.30 In an in vitro study, significant excess could not be detected in association with radiopaque resin composite inlays, even with the most

Figure 4. Optical density calibration curves for Al step wedge.

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are more sufficient in terms of radiopacity. It is known that thickness of the samples is determining in radiopacity studies and thin samples have less radiopacity.26 Clinically, luting cements are usually used in thicknesses between 25–100 µm. Therefore, having a much higher radiopacity of the dental cements than the equal thickness of enamel would facilitate detecting them radiographically. Although

it is thought that the glass ionomers, provisional luting cements, DYC and CLF have similar radiopacity with enamel, their radiological diagnosis would be difficult when they are used in thin film thickness forms. So, it would be appropriate to develop these dental cements having more radiopacity than the enamel tissue.

Material code Optical density mean values ± SD Min - Max. optical density values Statistical category*

PRC 1.971 ± 0.032 1.930 – 2.020 A

Human Dentin (HD) 1.820 ± 0.059 1.740 – 1.900 B

Bovine Dentin (BD) 1.801 ± 0.057 1.750 – 1.910 B, c

KTM 1.696 ± 0.035 1.660– 1.750 C, D

KPl 1.668 ± 0.027 1.640 – 1.730 D

KCE 1.660 ± 0.031 1.610 – 1.710 D

Bovine Enamel (BE) 1.660 ± 0.056 1.570 – 1.750 D, E

DYc 1.636 ± 0.059 1.570 – 1.730 D, E, F

cTl 1.591 ± 0.113 1.480 – 1.750 D, E, F

PTC 1.558 ± 0.051 1.480 – 1.660 E, F

clF 1.517 ± 0.061 1.410 – 1.610 F

APC 1.145 ± 0.032 1.090 – 1.180 g

ACF 1.065 ± 0.024 1.020 - 1.090 H

DE 1.031 ± 0.038 0.980 - 1.070 H, I

cZc 0.997 ± 0.062 0.910 – 1.070 H, I

aZP 0.972 ± 0.025 0.950 - 1.000 I

* Different letters demonstrate significant difference by Dunnett T3 multiple comparisons test (p<0.05).

Table 2. Mean, standard deviation (SD), minimum (Min.) and maximum (Max.) optical density values of materials. Higher values represent lower radiopacity. The results statistically categorized.

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3. Zinc containing AZP, CZC and DE cements had the highest radiopacity values.

4. CTL, PTC, CLF, APC, ACF, DE, CZC and AZP had statistically higher radiopacity values than bovine enamel (p<0.05).

Clinically, the most radiopaque cements are recommended. However, the degree of radiopacity of dental cements is not the only selection criteria and clinicians should be aware of the physicochemical and mechanical properties of the dental cement materials.

ACKNOWLEDGEMENTS

This study is presented as a poster in the 34th Annual Conference of the European Prosthodontic Association and 1st Conference of Association of Prosthetic Dentistry of Kosovo, 23-25 September 2010, Pristhina, Kosovo.

REFERENCES

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It was reported that the variability in radiopacity measurements of the same restorative materials among different studies depends on a number of factors, including speed of the X-ray film, exposure time, voltage used and the age of the developing and fixing solutions.17,33 In current study, the exposure time, voltage, and age of the developing and fixing solutions were standardized and conventional x-ray film technique was used. Sabbagh et al.34

stated that despite the numerous benefits offered by the digital imaging system (low irradiation dose, instant image, image manipulation), the conventional x-ray film technique seems to be more accurate for radiopacity measurements.One of the limitations of this study was that specimens were maintained in a set dry state. The radiopacity values may be affected by moisture adsorption from or loss to the oral environment. Another limitation is the thickness of the specimens. The thickness of the cement specimens does not simulate the thicknesses in the clinical applications. However, it is impossible to differentiate the radiopacities of different materials in thinner forms, especially for the materials that are less radiopaque. Further studies are required to evaluate these effects.

CONCLUSIONS

1. All materials except PRC had statistically higher radiopacity values than human and bovine dentin (p<0.05).

2. Among materials tested glass ionomer materials had the lowest radiopacity values except PRC.

Figure 5. Bar chart representation of the equivalent Al thickness values of the materials.

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31. Wadhwani C, Hess T, Faber T, Pineyro A, Chen CS. A descriptive study of the radiographic density of implant restorative cements. J Prosthet Dent 2010; 103: 295-302.

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