Retentive and compressive strengths of modified zinc oxide–eugenol cements

JJOD 398

Journal of Dentistry Journal of Dentistry 28 (2000) 69–75 www.elsevier.com/locate/jdent

Retentive and compressive strengths of modified zinc oxide–eugenol cements S.Y. Lee a,*, C.C. Wang a, D.C. Chen a, Y.L. Lai b a

b

School of Dentistry, National Yang-ming University, Taipei, Taiwan, Republic of China Dental Department, Veterans General Hospital-Taipei, Taipei, Taiwan, Republic of China Received 14 September 1998; accepted 18 April 1999

Abstract Objectives: This investigation sought to improve the handling and physical properties of a commonly used temporary zinc oxide–eugenol cement by changing the base/accelerator (B/A) ratio or combining it with a petroleum jelly or fluoride varnish. Methods: Twelve modifications of a temporary cement were evaluated in terms of retentive strength, compressive strength at 24 h, film thickness and by scanning electron microscopy. Results: Decreasing the B/A mixing ratio increased the retentive and compressive strengths, but reduced the film thickness of the cement. By increasing the percentage of incorporated petroleum jelly or fluoride varnish in the cement, there was a progressive decrease in the retentive and compressive strengths and in film thickness. Conclusions: Modifications of a zinc oxide–eugenol temporary cement to change the B/A ratio or to incorporate additives resulted in variations in physical properties. All modified forms of the cement had a film thickness less than 25 mm and a compressive strength below 35 MPa. With a wide range of retentive strength, modified forms of zinc oxide–eugenol cement may be found to have diverse clinical applications. q 1999 Elsevier Science Ltd. All rights reserved. Keywords: Temporary cement; Retention; Compressive strength; Film thickness; Progressive cementation

1. Introduction The properties required when cementing a temporary crown, which is to be removed in a few days, are not the same as those required when an extensive fixed prosthesis is to be temporarily cemented for a period of a month or more. The retentive properties of a temporary cement should be sufficient to avoid early loss of the restoration; on the other hand, it should not be too retentive, complicating removal when required. Temporary cements, must therefore, possess a range of retentive strength for various clinical applications [1–3]. In recent years, the use of implant retained restorations has increased. Implant retained restorations may be cemented or screw-retained; each method having inherent advantages and disadvantages [4,5]. Cemented implant retained restorations have the advantages of simplicity, hermetic sealing of the abutment–crown interface, favorable esthetics and crown contour, and a single interface * Corresponding author. Tel.: 1 886-2-28267235; fax: 28264053. E-mail address: [email protected] (S.Y. Lee)

1 886-2-

between abutment and implant [6]. However, several authors have demonstrated complications with this approach that lead to retreatment [4,7]. In view of the reported complications, attaching fixed restorations to implant abutments using a provisional cement is a viable alternative [8,9]. The use of a provisional cement allows retrievability, so that a restoration can be temporarily cemented to evaluate the occlusion and loading, the tissue response, and to correct any errors [1]. Instead of having a number of temporary cements of different strengths, it is common practice to modify a single temporary cement according to the requirements. Zinc oxide and eugenol is superior to other cements, notably in respect of its palliative effect on the pulp. The addition of additives, such as o-ethoxybenzoic acid (EBA) and polystyrene, may increase the strength of zinc oxide–eugenol (ZOE) cements [10–15]. However, such additives may have a deleterious effect on film thickness and solubility [16–18]. In an attempt to achieve a convenient setting time and strength of cement, changing the ratio of base to accelerator has been advocated [14,15,19]. It is generally recognized that adding petroleum jelly to a temporary cement reduces retention and cement hardness [1,6]. Olin et al. [1] added

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petroleum jelly into equal quantities of base and accelerator of a ZOE cement (TempBond, Kerr Co., Orange, CA, USA) and found that the retentive strength was significantly reduced from 8.8 to 1.6 kg. Fluoride and potassium nitrate are other possible additives [20–22]. Hodosh et al. [20] studied a sedative ZOE temporary cement containing potassium nitrate. They found it significantly reduced the incidence and the severity of sensitivity following tooth preparation. The addition of fluoride compounds to ZOE cements has been shown to increase the microhardness of cement covered dentine [23]. Lewinstein et al. [22] demonstrated that ZOE combined with a fluoride varnish (Duraphat, Inpharma GmbH, Cologne, Germany) enhanced the adhesion of the modified cement to the dentinal surface of the prepared tooth. Although various reports have provided some information on the clinical use of modified ZOE cements, there is still a lack of data relevant to clinical practice. The present study was undertaken to determine the physical properties of some modified ZOE cements to suit varying clinical requirements. The physical properties investigated were retentive strength, film thickness and compressive strength at 24 h.

2. Materials and methods The materials used in this study are listed in Table 1. TempBond, an ADA Class I Type 2a cement, was chosen as the control due to its widespread use and availability. Two modifiers, petroleum jelly and a fluoride varnish (Duraphat) were used. Besides different ratios of base to accelerator being employed, the modifiers were added in various proportions to the standard mixture (Table 2). All mixing and testing procedures of the cements were carried out at an ambient temperature of 23 ^ 28C and a relative humidity of 50 ^ 2%. 2.1. Retentive strength Ten standardized metal abutments were machined from stainless steel rods with a diameter of 10 mm. Each abutment had a cone angle of 108, a preparation height of 6 mm, and a 1 mm shoulder. Each abutment was then numbered and marked on the submarginal area. Impressions of the metal abutments with marked reference points were made Table 1 Cement and modifiers used in the study Material

Lot no.

Manufacturer

Density (g/ml)

TempBond

7-1289

Petroleum Jelly Duraphat

0395

Kerr Corp. Orange, CA, USA Benjunin, St. Louis, MO, USA Inpharma Gmbh, Cologne, Germany

3.75 (Base) 1.08 (Accelerator) 0.85

61311

1.05

with a polyvinyl-siloxane material (President, Coltene Whaledent, New York, NY, USA) and were poured with an improved stone (Die Keen, Columbus Dental, St. Louis, MO, USA). Stone dies were then painted to within 1 mm of the margins with three coats of die spacer (Yeti Dentalprodukte GmbH, Engen, Germany). The wax patterns were formed on stone dies, and marginal adaptation was refined at × 10 magnification. Each pattern was marked along with its respective die, in order that the casting could be repeatedly removed and replaced in the same position on the metal abutment. The patterns were then immediately sprued and invested in a phosphate bonded investment (GC Fujivest, GC Taiwan Corp., Taipei Hsien, Taiwan) and cast in a non-precious alloy (Wiron88, Bego, Bremen, Germany) in an induction casting machine. The castings were finished and returned to their respective abutments and adapted with the use of a silicone disclosing medium (Fit Checker, G.C. Dental Industrial Corp., Tokyo, Japan). The internal surfaces of the casting were then air abraded with 50 mm aluminum oxide at 2.8 kg/cm 2. The cements were mixed according to the predetermined proportions (Table 2) and spatulated on a dry, glass slab. Cementation was performed for 30 s after the start of mixing, using a standard seating force of 98 N applied with a loading apparatus for 10 min. After cementation, the specimens were placed in storage in a 100% relative humidity at 378C for 24 h. At the time of testing, the specimens were firmly held in a custom-made drill chuck attached to a universal testing machine (CMS5000, China Materials Technology and Science Co., Taipei, Taiwan). The peak axial force necessary to dislodge each crown was determined using a crosshead speed of 5 mm/min. The failure modes were categorized as follows: (a) adhesive failure at the metal–cement interface; (b) cohesive failure within the cement; and (c) complex adhesive and cohesive failure. After each testing cycle, remnants of the luting cement were removed using a soft brush under tap water. The metal Table 2 Mixing and proportioning of modified ZOE cements tested Code

Group

Proportioning

C (control) R1 R2 R3 R4 P1 P2 P3 P4 F1 F2 F3 F4

B/A (1:1) B/A (3:1) B/A (2:1) B/A (1:2) B/A (1:3) B/A/P (1:1:1/2) B/A/P (1:1:1) B/A/P (1:1:3/2) B/A/P (1:1:2) B/A/F (1:1:1/2) B/A/F (1:1:1) B/A/F (1:1:3/2) B/A/F (1:1:2)

Base:Accelerator ˆ 1:1 Base:Accelerator ˆ 3:1 Base:Accelerator ˆ 2:1 Base:Accelerator ˆ 1:2 Base:Accelerator ˆ 1:3 Base:Accelerator:Petroleum ˆ 1:1:1/2 Base:Accelerator:Petroleum ˆ 1:1:1 Base:Accelerator:Petroleum ˆ 1:1:3/2 Base:Accelerator:Petroleum ˆ 1:1:2 Base:Accelerator:Duraphat ˆ 1:1:1/2 Base:Accelerator:Duraphat ˆ 1:1:1 Base:Accelerator:Duraphat ˆ 1:1:3/2 Base:Accelerator:Duraphat ˆ 1:1:2

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Table 3 Mean values and standard deviations for dislodging force (n ˆ 10)

B/A ratio effect B/A (3:1) B/A (2:1) B/A (1:1) B/A (1:2) B/A (1:3) Petroleum effect B/A/P (1:1: 0) B/A/P (1:1:1/2) B/A/P (1:1:1) B/A/P (1:1:3/2) B/A/P (1:1:2) Fluoride Effect B/A/F (1:1: 0) B/A/F (1:1:1/2) B/A/F (1:1:1) B/A/F (1:1:3/2) B/A/F (1:1:2) a b

Failure mode a

Mean (N)

Standard deviation

Scheffe’s multiple comparison b

A1C A A A A

120 183 252 269 279

19 18 7 8 6

×

A A1C A1C A1C C

252 137 49 35 13

7 9 7 5 2

×

A A A1C A1C C

252 191 164 138 124

7 11 18 6 20

×

×

×

×

× ×

×

×

×

×

×

× ×

A, adhesive failure; C, cohesive failure; A 1 C, both adhesive and cohesive failure. Groups linked by vertical lines denote no significant difference (a ˆ 0.05).

dies and crowns were placed in a cement removing solution (Cement-Remover, Leaderal Co., Taipei Hsien, Taiwan) for 10 min in an ultrasonic bath, cleaned under tap water, placed in a 95% ethanol ultrasonic bath for another 10 min, and then into an ultrasonic bath of distilled water for 5 min, and then dried before the next cementation. Each metal crown and abutment pair was recemented with another modified ZOE cement under the previously described conditions, to give a total of 10 specimens for each luting agent.

2.2. Compressive strength The compressive strength was determined using a modification of the test described in ISO 3107 specification. Fifteen cylindrical specimens of each cement type were made using silicone-lubricated stainless steel split molds and fine sanded with 1200-grit siliconecarbide paper and water to produce a cylinder of 4 mm (diameter) × 6 mm. The specimens were examined and rejected if any voids were found. All

Table 4 Mean values and standard deviations for compressive strength at 24 h (n ˆ 15)

B/A ratio effect B/A (3:1) B/A (2:1) B/A (1:1) B/A (1:2) B/A (1:3) Petroleum effect B/A/P (1:1: 0) B/A/P (1:1:1/2) B/A/P (1:1:1) b B/A/P (1:1:3/2) b B/A/P (1:1:2) b Fluoride effect B/A/F (1:1: 0) B/A/F (1:1:1/2) B/A/F (1:1:1) B/A/F (1:1:3/2) b B/A/F (1:1:2) b a b

Mean (MPa)

Standard deviation

Scheffe’s multiple comparison a

3.9 6.5 11.9 14.4 16.0

0.2 0.5 0.6 1.3 1.0

×

11.9 3.8 – – –

0.6 0.4 – – –

× (t-test) a

11.9 9.0 6.5 – –

0.6 0.8 0.4 – –

×

×

×

×

×

× (t-test) a

×

×

Groups linked by vertical lines denote no significant difference (a ˆ 0.05). Optimum specimens could not be retrieved due to their weakness.

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Table 5 Mean values and standard deviations for film thickness (n ˆ 10) Scheffe’s multiple comparison a

B/A ratio effect

Mean (mm)

Standard deviation

B/A (3:1) B/A (2:1) B/A (1:1) B/A (1:2) B/A (1:3) Petroleum effect B/A/P (1:1: 0) B/A/P (1:1:1/2) B/A/P (1:1:1) B/A/P (1:1:3/2) B/A/P (1:1:2) Fluoride effect B/A/F (1:1: 0) B/A/F (1:1:1/2) B/A/F (1:1:1) B/A/F (1:1:3/2) B/A/F (1:1:2)

16.3 15.6 14.1 10.7 9.7

1.0 0.8 0.7 0.7 0.5

× ×

14.1 10.7 8.9 8.2 6.8

0.7 1.0 0.9 0.9 0.8

×

14.1 12.0 11.3 9.7 8.5

0.7 0.8 1.3 0.7 1.6

×

a

×

× ×

×

× ×

× ×

×

× ×

Groups linked by vertical lines denote no significant difference (a ˆ 0.05).

specimens were maintained in distilled water at 37 ^ 28C until the time of testing. Testing was then performed at a set time of 24 h on the universal testing machine at a cross-head speed of 1.0 mm/min. The values for the compressive strength are reported as the average of 15 specimens.

2.3. Film thickness A fresh mix of each cement type was placed between flat, square, glass plates of uniform thickness, each with an area of 2 cm 2. Two minutes after the start of mixing, a load of 15 kg was applied on the top plate. Ten minutes after the

Fig. 1. SEM micrograph of R1, C, R4, P2 and F2 cements showing the zinc eugenolate matrix distribution (upper row); back-scattering SEM of the same field of each cement in the upper row demonstrating the electron opaque zinc oxide particles (lower row).

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mixing was started, the thickness of the two plates with the cement film between them was determined with the aid of a micrometer. The difference between the thickness of the plates with and without cement between them was then considered to be the film thickness. An average of 10 tests for each cement was reported to the nearest 1 mm. Some cements were then observed under scanning electron microscopy (SEM). A one-way analysis of variance and subsequent pairwise comparisons using Scheffe’s F test (p , 0.05) were taken to indicate significance on all data except the results of petroleum effects on the compressive strength, where a Student’s t-test was performed with p , 0.05. A statistical software package (SPSS/PC 1 , SPSS Inc., Chicago, IL, USA) was used for the analysis.

3. Results The results presented in Tables 3–5 were subjected to statistical analysis. They showed that there were significant differences among the cements in terms of retentive strength, film thickness and compressive strength. By lowering the base/accelerator (B/A) ratio, there was an increase in retention and compressive strengths, but decrease in film thickness. The results also indicated that the retentive and compressive strengths of tested cements were gradually decreased as the percentage of the modifiers, both petroleum jelly and Duraphat, in the cement increased. The differences between the film thickness values that were measured between the groups were small in actual values, but were shown to be statistically significant. SEM revealed that the set cement consisted of zinc oxide particles surrounded by a matrix of zinc eugenolate. R4 group, B/A (1:3), had the most saturated matrix of the cements tested. However, few zinc oxide particles were observed in the back-scattering micrographs (Fig. 1). In the R1 group, B/A (3:1), zinc oxide particles were dominant and agglomerated (Fig. 1).

4. Discussion To confirm the efficiency of the cement removal procedures and the repeatability of the retentive testing system, two standard mixes of B/A (1:1) were tested for the dislodging force in the pilot study. No statistical difference was noted between two standard groups using a paired t-test (a ˆ 0.05). After finishing the retention tests with all modified cements, the third standard mix of B/A (1:1) was introduced in the end of the retention test to examine consistency and durability of the whole retention test system. A paired t-test revealed no significant difference between standard II and III groups (a ˆ 0.05). Theoretically, zinc eugenolate, Zn(C10H11O2)2, is a bisligand chelate [18,24]. The stochiometric ratio of the zinc

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oxide to the eugenol is 1:4. ZnO 1 2C10 H12 O2 ! Zn…C10 H11 O2 †2 1 H2 O However, according to the manufacturer’s instruction for TempBond, each tube of accelerator paste (15 g) has 4.4 g of eugenol and each tube of base paste (55 g) contains 44 g zinc oxide. The recommended mixing ratio of B/A is 1:1 by volume, which results in a mixing weight ratio as 10:1. Therefore, there was a considerable excess of zinc oxide in the “standard” preparation. However, the optimal mixing ratio for each ZOE cement depends on how much activated zinc ion can be incorporated into the reaction. For TempBond, by increasing the accelerator ratio (R4 group), more zinc eugenolate matrix was obtained (Fig. 1); this was thought to be responsible for the higher compressive strength and retention [25]. On the other hand, increasing the B/A ratio (R1 group) significantly reduced the compressive strength and retention, but the film thickness was increased. It is possible that the increase in film thickness may have resulted from agglomeration of zinc oxide particles, as shown more clearly by the back-scattering SEM (Fig. 1). By modifying the B/A ratios of the cement, it is possible to alter the physical properties of the cement to give the greatest convenience in handling, retention and strength along with complete seating of castings. It is evident that the compressive strength could be raised by further decreasing the B/A ratio. However, the desirable consistence of the cement and its value for temporarily cementing restorations might be lost. The addition of petroleum jelly was found to significantly affect the retention of the cements. This is in agreement with previous work. Olin et al. [1] added petroleum jelly to TempBond, one third the volume of the total mix. They observed an 82% decrease of value in the retention test. The present laboratory findings not only showed similar decrease of retention of B/A/P (1:1:1), but also indicated that the retention, compressive strength and film thickness decreased as the percentage of petroleum jelly in the cement increased. Ideally, a thinner cement may allow a more complete seating of the crown during cementation. The one-way analysis and Scheffe’s test for the film thickness demonstrated overall significant differences among the groups (Table 5). However, the differences in actual values were very small and also all the results satisfied the criteria (below 25 mm) described in the International Standard (ISO 3107). Hence, any possible benefit in terms of retention from the reduced film thickness was probably negated by the overriding effect of compressive strength (Table 4). Moreover, as shown in SEM, the modifier-containing groups exhibited more characteristics of a weak zinc eugenolate matrix (Fig. 1), which was prone to breakdown and cement failure. Cement interface failure is defined as the surface or area of cement failure. Adhesive failure is a cement fracture at a metal/cement interface, and cohesive

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Retentive strength (N)

350 300

2

R = 0.97

250 200 150 100 50 0 0

5

10

15

20

Compressive Strength (MPa)

Fig. 2. Retention plotted against compressive strength of the cement.

failure implies fracture within the cement. The cement/ crown interface was not investigated as the inner surface of the metal crown was sand blasted and provided a much higher retention compared to that of the smooth abutment. In the control group, B/A (1:1), the cement failure occurred primarily at the abutment/cement interface. Nearly, all the petroleum jelly-contained cements reflected some cohesive cement failure, indicating that petroleum jelly reduced the physical properties of the cement (Table 3). Furthermore, specimens for compressive testing of some petroleum jelly contained groups that could not be even retrieved from the split molds due to their weakness. Petroleum jelly, like adding Duraphat to TempBond, has similar but weaker effects on the properties of retention, compressive strength and film thickness of the cement (Table 5). Lewinstein et al. [22], after investigating the retentive strength of ZOE cements with and without fluoride, reported that incorporating fluoride varnish to the cement in one-half length of base and accelerator increased retentive strength by approximately 29%. However, this research revealed a 24% decrease in retention when the cement was mixed with the same proportion of Duraphat in group B/A/F (1:1:1/2). The disparity between the findings of these studies may be attributed to different abutments for retention test. Lewinstein et al. [22] used natural teeth as

Retentive strength (N)

300

abutments, whereas this study dislodged metal crowns from metal abutments. These results suggest that fluoride may have effects on enhancing the bonding between cement and tooth surface [23]. An investigation of the effects of different abutment systems on retentive properties might prove interesting. Compressive strength is considered a critical indicator of success, because a high compressive strength is necessary to tolerate masticatory forces, although the exact value is unknown. In common with our findings, a previous study [25] has shown that the compressive strength of a luting cement is an important factor in the retention of crowns on teeth where there is mechanical interlocking (Fig. 2). This raises the question as to why a glass-ionomer cement exhibited a relatively high retentive strength and the lowest compressive strength in an in vitro study [9]. One answer is that the failure mode of separating an adhesive cement during testing may be quite different from that of separating a non-adhesive cement. The different cement failure modes are indicative of various failure mechanisms that may have clinical relevance. In the temporary cementation of restorations, the cement usually needs to serve only as a seal, as many restorations have considerable mechanical and frictional retention. Too strong a cement may render subsequent removal of the restoration difficult, if not impossible. As noted earlier, no cement is likely to meet all requirements. The temporary cements investigated in this study showed a wide range of ability to retain castings under test conditions. While it is difficult to predict clinical performance based solely on in vitro tests, the high degree of variability in the retentive strengths of these cements provides useful information when the selection of a temporary cement is necessary (Fig. 3). This is especially true for cement-retained implant prostheses which are retrievable, the cement chosen being the determining factor in the retention attained [4,6]. With proper selection of cements, implant prostheses can be removed at various intervals. In instances where the cements fail to provide adequate retention, the principle of progressive cementation can be applied, whereby stronger cements are progressively used until adequate retention is achieved [10].

250

5. Conclusion

200 150 100 50 0 P4 P3 P2 R1 F4 P1 F3 F2 R2 F1

C

R3 R4

Fig. 3. Modified temporary cements provide a wide variety of retentive strengths by which the principles of progressive cementation can be followed.

In conclusion, a ZOE cement can be modified to gain wide range of properties simply by changing the B/A ratio, or adding modifiers such as petroleum jelly and fluoride varnish. The ease of removal of a restoration can be influenced by increasing the B/A ratio or adding modifiers. When high retentive strength is needed, a decrease in the B/ A ratio is recommended. The film thickness of all the modified cements was less than 25 mm as specified in ISO 3107 for ZOE temporary cements. The compressive and retentive strengths of the tested cements were closely related. The

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higher the compressive strength, the better the retention. Of the 12 cements tested in this study, all satisfied the ISO 3107 requirements (below 35 MPa) for a cement for temporary cementation. Further research is required on cement performance in clinical practice to develop a predictive correlation between laboratory measurements and clinical performance. As well as retention measurement, other clinical factors also need to be investigated, including pulpal sensitivity, effects on dentin hardness and secondary caries. Acknowledgements This study was supported in part by a grant from VGHTaipei to whom we extend our thanks. Special thanks are extended to Dr C.Y. Su for SEM assistance and Dr L.Y. Chi for review and comment. References [1] Olin PS, Rudney JD, Hill EM. Retentive strength of six temporary dental cements. Quintessence International 1990;21:197–200. [2] Ayad MF, Rosenstiel SF, Salama M. Influence of tooth surface roughness and type of cement on retention of complete cast crowns. Journal of Prosthetic Dentistry 1997;77:116–121. [3] Oldham DF, Swartz ML, Phillips RW. Retentive properties of dental cements. Journal of Prosthetic Dentistry 1964;14:760–768. [4] Hebel KS, Gajjar RC. Cement-retained versus screw-retained implant restorations: achieving optimal occlusion and esthetics in implant dentistry. Journal of Prosthetic Dentistry 1997;77:28–35. [5] Dixon DL, Breeding LC, Lilly KR. Use of luting agents with an implant system: Part II. Journal of Prosthetic Dentistry 1992;68:885–890. [6] Breeding LC, Dixon DL. Compression resistance of four interocclusal recording materials. Journal of Prosthetic Dentistry 1992;68:876– 878. [7] Kerby RE, McGlumphy EA, Holloway JA. Some physical properties of implant abutment luting cements. International Journal of Prosthodontics 1992;5:321–325. [8] Singer A, Serfaty V. Cement-retained implant-supported fixed partial dentures: a 6-month to 3-year follow-up. International Journal of Oral and Maxillofacial Implants 1996;11:645–649. [9] Ganor Y, Indig B, Gross M. Retrievable cemented crown options on implant-supported angled abutments: a case report. Quintessence International 1996;27:679–684.

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[10] Phillips RW, Love DR. The effect of certain additive agents on the physical properties of zinc-oxide eugenol mixtures. Journal of Dental Research 1961;40:294–303. [11] Norman RD, Phillips RW, Swartz ML, et al. The effect of particle size on the physical properties of zinc-oxide eugenol mixtures. Journal of Dental Research 1964;43:252–262. [12] Civjan S, Huget EF, Wolfhard G, et al. Characterization of zinc oxideeugenol cements reinforced with acrylic resin. Journal of Dental Research 1972;51:107–114. [13] Silvey RG, Myers GE. Clinical study of dental cements VI. A study of zinc phosphate, EBA-reinforced zinc oxide eugenol and polyacrylic acid cements as luting agents in fixed prostheses. Journal of Dental Research 1977;56:1215–1218. [14] Jendresen MD, Phillips RW, Swartz ML, et al. A comparative study of four zinc oxide and eugenol formulations as restorative materials I. Journal of Prosthetic Dentistry 1969;21:176–183. [15] Jendresen MD, Phillips RW. A comparative study of four zinc oxide and eugenol formulations as restorative materials II. Journal of Prosthetic Dentistry 1969;21:300–309. [16] Wilson AD, Batchelor RF. Zinc oxide-eugenol cements II. Study of erosion and disintegration. Journal of Dental Research 1970;49:593– 598. [17] Norman RD, Swartz ML, Phillips RW. Studies on film thickness, solubility, and marginal leakage of dental cements. Journal of Dental Research 1963;42:950–958. [18] Wilson AD, Clinton DJ, Miller RP. Zinc oxide–eugenol cements IV. Microstructure and hydrolysis. Journal of Dental Research 1973;52:253–260. [19] Anderson Jr JR, Meyers GE. Physical properties of some zinc oxide– eugenol cements. Journal of Dental Research 1966;45:379–387. [20] Hodosh AJ, Hodosh S, Hodosh M. Potassium nitrate–zinc oxide eugenol temporary cement for provisional crowns to diminish postpreparation tooth pain. Journal of Prosthetic Dentistry 1993;70:493– 495. [21] Hodosh M, Hodosh SH, Hodosh AJ. Maintenance of pulpal vitality using potassium nitrate-polycarboxylate cement cavity liner. Quintessence International 1991;22:495–502. [22] Lewinstein I, Daniel Z, Azaz B, et al. Effect of fluoride varnish on the retentive strength of provisional crowns luted with various temporary cements. Journal of Prosthetic Dentistry 1992;68:733–736. [23] Wolf O, Gedalia I, Reinsstein I, et al. Effect of addition of Cafpo3 to a zinc oxide–eugenol base liner on the michrohardeness and fluoride content of dentin. Journal of Dental Research 1973;52:467–471. [24] Wilson AD, Mesley RJ. Zinc oxide–eugenol cements III. Infrared spectroscopic studies. Journal of Dental Research 1972;51:1581– 1588. [25] Jorgensen KD, Holst K. The relationship between the retention of cemented veneer crowns and the crushing strength of the clements. Acta Odontologica Scandinavica 1967;25:355–359.

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