Dental Materials Journal 2009; 28(3): 261–266

Original Paper

Development of a new temporary luting agent consisting of PEMA and —Residue ratio and bond strength of luting cements for abutment materials

Hidetoshi OKADA, Yoshinori ISHIDA, Hiroshi NOGUCHI, Ichiro RYUKATA and Katsuya NAGAYAMA

Department of Biomaterials Science, Ohu University School of , 31-1 Misumido, Tomita-machi, Koriyama, Fukishima-ken 963-8601, Japan Corresponding author, Hidetoshi OKADA; E-mail: [email protected]

PEMA- and eugenol-based trial agents (PE 1.0, PE 1.6) possessed the requisite dental engineering properties that satisfied the requirements for temporary luting agents. To assess their clinical applicability, this study examined the following properties after the trial agents were removed: their residue ratios on the abutment surface and the bond strengths of resin- modified and resin cement for the abutment materials. The residue ratio of PE 1.0 on the abutment material after temporary restoration removal was lower than those of comparable temporary luting agents (polycarboxylate cement type, -eugenol cement type), and no residue was recognized for PE 1.6. On bond strength, those of the resin- modified glass ionomer cement and resin cement for the resin core and bovine dentin surface after the removal of trial agents tended to be the same or increase in comparison to commercial temporary luting agents. In conclusion, results of this study suggested that the trial agents were suitable for clinical use.

Keywords: Temporary luting agents, Luting cements, Bond strength

Received Jun 21, 2007: Accepted Oct 1, 2008

that the trial agent could ensure easy removability of INTRODUCTION temporary restorations when needed. In dental practice, the repair of dental prostheses — However, the trial agent contained eugenol as such as the or — typically entails a one of its main components. Eugenol is considered to temporary restoration which mimics the final be an adhesion inhibitor for resin-type materials2,3), prosthesis. The latter must then be cemented with a and current mainstream luting cements are either of temporary luting agent to provide a seal around the resin type or resin-modified glass ionomer type. In margin of the temporary restoration. However, most clinical practice, it is important that temporary commercial temporary luting agents are luting agents do not adversely affect the adhesive manufactured by improving luting cements. At property of the luting cement after the temporary present, no commercially available products meet all restoration is removed. Therefore, this study also the conditions required of temporary luting agents, examined the bond strength of luting cements on such as proper bond strength capable of fixing the abutment materials after the trial agents were temporary restoration for a certain period of time removal. while enabling easy removal from the abutment The trial agents used in this study were PEMA- when needed. and eugenol-based. For the adherends, they were In a previous study1), we showed that a trial namely 12% gold-silver-palladium alloy, resin core, agent exhibited similar performance to commercially and bovine dentin, whereby the residue ratio was temporary luting agents in terms of setting time, calculated over a specified area of these plane consistency, and water uptake. In terms of bond adherend specimens. The tensile strengths of the strength with a temporary restoration using a self- trial agents were examined, as well as the bond curing resin crown and stainless steel abutment, the strengths of the resin-modified glass ionomer cement trial agent achieved a value identical to those and resin cement for the various abutment materials obtained with commercial temporary luting agents. after removing the trial agents. Moreover, after the bond strength test, the trial agent left less residue on the stainless steel abutment MATERIALS AND METHODS than commercial temporary luting agents. In clinical practice, the lack of residue on the Materials abutment carries a vital implication. On this ground, Table 1 shows the details of the materials used in the absence of trial agent’s residue on the stainless this study: material codes, their main components steel abutment1) made it favorable for clinical use. and the manufacturers. The trial agents (hereinafter This is because the residue ratio is a good indicator known as “PE”) examined in this study contained 262 Dent Mater J 2009; 28(3): 261–266

Table 1 Materials used in this study Code Material Main compose Manufacture Temporary luting agent PE Development temporary agent Powder: PEMA (1.0,1.6) Liquid: Eugenol TES HY-BOND temporary cement Powder: Zinc oxide SHOFU Liquid: Polyacrylic acid NED Neodyne  Powder: Zinc oxide NEO SEIYAKU KOUGYO Liquid: Eugenol Luting cements RES HY-BOND RESIGLASS Powder: Alumino-Silicateglass SHOFU Liquid: Polyacrylic acid PAN PANAVIA F 2.0 Base: Methacryl-acid monomer KURAREY Filler: Silica Abutment materials ME CASTWELL. M.C 12% Gold-silver-palladium alloy G. C RE UNIFIL CORE UDMA, Silica, 4-MET G. C DE Dentin of bovine tooth

Fig. 1 A schematic diagram of the test specimen comprising the temporary restoration and abutment material.

Fig. 2 Segments on which the temporary luting agent residue were counted on a specific surface (arrow indicates the temporary luting agent residue).

PEMA and eugenol as their base components, and The adherends were polished (Phoenix 4000, that their powder/liquid ratios were respectively 1.0 Buehler Co. Ltd., Waukegan, USA) with #120 (PE 1.0) and 1.6 (PE 1.6). For comparison purpose, waterproof abrasive papers. As for the materials, commercial temporary luting agents of they were mixed and operated at a room temperature polycarboxylate cement type (TES) and zinc oxide- of 23±2°C and at a humidity of 50±5%. eugenol cement type (NED) were used. The luting cements were used with resin-modified glass ionomer Specimen preparation and thermal cycling cement (RES) and resin cement (PAN). The For the test specimens, resin block and abutment adherends were 12% gold-silver-palladium alloy materials were temporarily bonded at an adherend (ME), resin core of dual-cure type (RE), and bovine area of 5×5 mm marked using a masking tape (Fig. tooth dentin (DE). The resin block was made of a 1). Film thickness of temporary luting agents was self-curing MMA resin (Tempron, GC Co. Ltd., Tokyo, controlled at 100 μm, and resin block was bonded to Japan). adherend under a load of 10 kg. Ten specimens were Dent Mater J 2009; 28(3): 261–266 263 prepared for each test condition. was removed using a dental instrument. In addition, The temporarily bonded specimens were the same area was cleaned with absorbent cotton and subjected to a thermal cycling process of cold bath distilled water. (4°C: 30 seconds) and hot bath (60°C: 30 seconds). After removal of the temporary luting agent (i.e., After 100 cycles, the resin block was removed by the trial agents), luting cements were filled to a shear stress. The number of thermal cycles was thickness of 2 mm using a plastic tube with an inner determined to be 100 because it was established in a diameter of 6 mm. The luting cements were applied previous report4) to be equivalent to the service in accordance with the cementing operation method period of temporary restorations in an oral condition specified by the manufacturers. Bonding agent PAN for 10 days. was provided with a metal primer and a self-etching primer, hence surface treatment was done using the Temporary luting agent remaining on the abutment metal primer for ME and the self-etching primer for surface after temporary restoration removal DE. For the controls (CON), the luting cements were After the temporary restoration (i.e., resin block) was applied directly to the abutment materials without removed, the abutment surface was photographed using the temporary luting agents. using an optical microscope (Scopeman, Moritex Co. The specimens were kept at a temperature of Ltd., Tokyo, Japan). The photographed image was 37°C and at a relative humidity of about 100% for 24 then divided into 100 segments, whereby the area of hours (LaboStar LHL-112, TABEI Co. Ltd., Osaka, each segment was 0.25 mm2. Segments on which the Japan). After which, shear bond strength test was temporary luting agent remained were counted, and conducted at a crosshead speed of 0.5 mm/min using the residue ratio (%) on the specified surface thereby the universal testing machine. Bond strength data calculated (Fig. 2). obtained were subjected to statistical analysis using one-way ANOVA and Tukey’s HSD test at a Tensile strength test of trial agents significance level of p=0.05. For the tensile strength test, specimens were prepared to a size of 10 mm width × 65 mm length × RESULTS 2.5 mm thickness. The specimens were subjected to the thermal cycling process of cold bath (4°C: 30 Residue ratios of temporary luting agents on seconds) and hot bath (60°C: 30 seconds) at 100 abutment surface after temporary restoration removal cycles. After thermal cycling, the tensile strength Figure 3 shows the residue ratios of the temporary test of the specimens was conducted using a luting agents remaining on the abutment surface universal testing machine (Model 1310DW, Aikoh after the resin block was removed. For PE 1.0, the Engineering Co. Ltd., Osaka, Japan) at a crosshead residue ratios were 17% for ME, 100% for RE, and speed of 0.5 mm/min. 18% for DE. PE 1.6 stuck entirely to the resin block side with no residue on the abutment materials. For Bond strength of luting cements on abutment surface TES, the residue ratios were 100% for ME and RE, after removal of temporary luting agent and 43% for DE. For NED, the residue ratios were On the abutment surface, any remaining temporary 52% for ME, 100% for RE, and 71% for DE. luting agent which could be seen with the naked eye

Fig.3 Residue ratios of temporary luting agents on Fig.4 Tensile strengths of trial agents. abutment surface. 264 Dent Mater J 2009; 28(3): 261–266

Fig.5 Bond strengths of RES on abutment materials. Fig.6 Bond strengths of PAN on abutment materials.

Tensile strengths of trial agents recognized among all the test conditions. On bond Figure 4 shows the tensile strengths of the trial strength with RE, no significant differences in bond agents. PE 1.6 showed a significantly higher value strength were recognized among CON, PE 1.0, and than PE 1.0. PE 1.6, neither was there any difference between the values of TES and NED. However, the values of TES Bond strength of RES to the abutment surface after and NED were significantly lower than those of CON, the removal of temporary luting agent PE 1.0, and PE 1.6. On bond strength with DE, CON Figure 5 shows the bond strength results between and PE 1.6 showed significantly higher values than the abutment materials and RES after the temporary TES and NED. No significant differences were luting agent was removed. On bond strength with recognized among the other test conditions. ME, CON showed a significantly higher value than all the temporary luting agents. For NED, it showed DISCUSSION a significantly lower value than the other temporary luting agents. No significant differences in bond From our previous study, it was found that trial strength were recognized among PE 1.0, PE 1.6, and agents containing PEMA and eugenol possessed the TES. requisite characteristics and properties — in terms of On bond strength with RE, CON showed a curing time, consistency, film thickness, and bond significantly higher value than all the temporary strength — to serve as temporary luting agents1). As luting agents, whereby that of NED was significantly no residue was found on the stainless steel abutment, lower than the other temporary luting agents. For or that only a negligible remnant remained, after the PE 1.6, it showed a significantly higher value than temporary restoration was removed in the previous PE 1.0 and TES. Between PE 1.0 and TES, no study1), the trial agents were anticipated to be useful significant differences in bond strength were temporary luting agents for clinical use since they recognized. would facilitate easy removability. In prosthetic On bond strength with DE, CON showed a dentistry, another consideration to be taken into significantly higher value than all the temporary account is that the final restoration needs to be luting agents except PE 1.6. For NED, it showed a permanently cemented to the abutment after the significantly lower value than the other temporary temporary restoration is removed. Therefore, luting agents. Among PE 1.0, PE 1.6 and TES, no another important characteristic of temporary luting significant differences in bond strength were agents is that they should not adversely affect the recognized. bond strength between the abutment and the luting cement. Bond strength of PAN to the abutment surface after In light of the key requirements of temporary the removal of temporary luting agent luting agents in clinical use, this study evaluated the Figure 6 shows the bond strength results between following properties of the trial agents: (1) residue the abutment materials and PAN after the temporary ratios of the trial agents on abutment surface; and luting agent was removed. On bond strength with (2) effect of the trial agents on the bond strength of ME, no significant differences in bond strength were the luting cements with the abutment material. Dent Mater J 2009; 28(3): 261–266 265

Residue of temporary luting agent on abutment 4). Nonetheless, in light of their tensile strength surface after temporary restoration removal results, it was thought that fracture would rarely As shown in Fig. 3, no residue was recognized for PE occur within the temporary luting agent layer of PE 1.6 on the abutment surface. In this experiment, the 1.6 or PE 1.0. surfaces of both the resin block and abutment As described above, the trial agents — especially material were polished with #120 abrasive papers. PE 1.6 — exhibited properties superior to the This meant that with a small difference in surface conventional temporary luting agents in that it was roughness between the abutment material and the not necessary to remove any temporary luting resin block, the mechanical binding force between the material sticking to the abutment after the temporary luting agent and the resin block or temporary restoration was removed. abutment material should also be presumably similar. However, as shown in Fig. 5, there were Bond strength between abutment and luting cement statistically significant differences in bond strength after removal of temporary luting agent between PE 1.6 and the comparison agents. For the resin cement (PAN), there were no significant Therefore, other adhesion factors — which were also differences in bond strength between both trial related to the residue remaining on abutment surface agents and the CON condition for all the adherends — played a role for this result. (Fig. 6). In the case of PAN, a metal primer was PEMA was a base component of the trial agents, used for the surface pretreatment of ME and a self- and it is also used as a base component for the lining etching primer for DE. It has been reported that the materials of resin dentures. It has been reported effect of a material temporarily used tends to that the PEMA-eugenol mixture is chemically disappear when the adherend surface is pretreated adhesive to the MMA resin5). Therefore, this could with a surface treatment agent9). However, no be the reason why the bond strength between PE 1.6 significant differences in bond strength were and the resin block was greater than that yielded recognized between the trial agents and the CON between the trial agent and the abutment material5). condition for RE without surface treatment. In addition, it has been reported that both TES and On the other hand, although NED also contained NED were not elastic, but which was a property eugenol, the bond strength of PAN tended to become demonstrated by the trial temporary luting agents lower than the trial agents. On this basis, the view after setting6,7). In this experiment, shear stress was that the dissolution degree of eugenol in the trial used to remove the resin block. When the external agents would affect the bond strength of resin cement force was applied to the specimen with sandwich became untenable. As a result, the residue ratio of structure, it was thought that stress was temporary luting agent remaining on the abutment concentrated on the temporary luting agent layer surface became a more effective and reliable indicator with low mechanical strength8). As a result, the trial than the existence of eugenol. According to the SEM agents could have sustained a larger elastic observation of Noguchi et al.10), the residue of the deformation than NED and TES. However, although temporary sealing material — which was the same the bond strength of PE 1.6 to the abutment material as the trial agent examined in this study — after was significantly lower than that to the resin block, temporary restoration removal was less than in the it was thought that interfacial failure tended to occur case of NED. In the current study, 100% residue on the abutment material side8). This could be the remaining on the RE surface was recognized for both reason why the entire layer of PE 1.6 was adhered to PE 1.0 and NED after the resin block was removed. the resin block after shear strength test. In addition, In terms of bond strength comparison between PE the residue ratios of PE 1.0 and PE 1.6 were different 1.0 and NED after removal of the temporary luting on the abutment surface. It was thought that the agent, that of PE 1.0 was significantly greater than adhesive property of PE 1.6 for the resin block was in the case of NED. Therefore in the case of PAN, it greater than that of PE 1.0, because the PEMA value seemed that when compared to commercial of PE 1.6 was greater than that of PE 1.0 (i.e., more temporary luting agents, the trial agents were resin was present). superior on two fronts: easy removability of the PE 1.6 showed greater tensile strength than PE temporary restoration when needed and not 1.0. In the previous report1), it was shown that adversely affecting the bond strength of the luting eugenol in PE 1.0 exhibited greater dissolution in cement for the final restoration. distilled water than PE 1.6. Therefore, it was For the resin-modified glass ionomer cement speculated that there was a surplus of non-reacted (RES), the bond strengths obtained with the trial eugenol in PE 1.0. As the dissolution reaction agents, TES, and NED were significantly lower than between PEMA and eugenol was more complete in the CON condition (Fig. 5). This was most probably PE 1.6 than in PE 1.0, it thus contributed to the because RES, which was based on glass ionomer greater tensile strength of PE 1.6 than PE 1.0 (Fig. cement, caused a chelate bond to form between the 266 Dent Mater J 2009; 28(3): 261–266 adherends and carboxyl group11). However, if the ACKNOWLEDGMENTS hydroxyl and methoxy groups of eugenol were bonded in advance with the metal ions of the abutment This study was supported in part by a Grant-in-aid surface, then the forming of ionic bond between RES for Scientific Research (Grant-in-aid for Young and the abutment would be inhibited12,13) — thereby Scientists (B): Subject no. 16791201) from the adversely affecting the bond strength between RES Ministry of Education, Culture, Sports, Science and and the abutment. However, with regard to the trial Technology of Japan. agents, their bond strength values to the various abutment materials were greater than was the case REFERENCES of NED or even TES. Therefore, concerning the bond strength of luting cements on abutment materials, it 1) Okada H, Ishida Y, Noguchi H, Nagayama K. was thought that the residue ratio of temporary Development of a new temporary luting agent luting agents played a more significant role than consisting of PEMA and eugenol. 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