|Year : 2014 | Volume
| Issue : 2 | Page : 135-139
Evaluation of marginal adaptation and traction resistance of zirconium crowns made up using two different techniques and cemented on pins with three types of cements
Priscila C Chagas1, Luiz Gustavo C Bastos1, Max José P Lima2
1 Department of Dentistry, Escola Bahiana de Medicina E Saúde Pública, Salvador, Bahia, Brazil
2 Department of Dentistry, Federal University of Bahia, Salvador, Bahia, Brazil
|Date of Web Publication||16-Sep-2014|
Luiz Gustavo C Bastos
Rua Silveira Martins, 3386, Cabula. Cep: 41.150-100 Salvador - Bahia
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Objective: The aim was to assess marginal adaptation of zirconium crowns made up by manual milling (pantograph) and computerized (computer assisted designing/computer assisted machining [CAD/CAM]) before and after cementation; and the efficiency of 3 types of cements in retaining these crowns: Zinc phosphate, resin modified glass ionomer cement (RelyX Luting 2) and resin cement (RelyX U200).
Materials and Methods: Out of 30 zirconium crowns, 15 were milled by the pantograph, and 15 by CAD/CAM. Each group was divided into 3 subgroups according to the cement used. Cementation was done over the analog universal pin 4.5 mm × 4 mm and submitted to mensuration of marginal interface of its four faces with stereoscopic magnifier (×20). Then, they were directed to a machine of universal test (EMIC), and submitted to an axial traction with speed of 0.5 mm/min until its displacement.
Results: Before cementation, CAD/CAM crowns (47.60; 40.20; 43.40 μm) demonstrated a greater desadaptation comparing to pantograph crowns (28.20; 35.60; 30.40 μm). RelyX Luting 2 showed less marginal desadaptation postcementation on CAD/CAM crowns (53.80 μm ± 8.43 μm) and pantograph (39.80 μm ± 12.696 μm), when compared with zinc phosphate (62.00 μm ± 12.86; 45.20 μm ± 24.035) and to RelyX U200 (73.80 μm ± 44.49 μm; e 53.00 μm ± 10.817 μm). RelyX Luting 2 also obtained better efficiency on traction resistance (9.48 Kgf ± 2.49 Kgf; e 24.54 Kgf ± 6.73 Kgf), when compared to zinc phosphate (8.71 Kgf ± 4.00 Kgf; and 11.85 Kgf ± 3.15 Kgf) and RelyX U200 (8.08 Kgf ± 0.62 Kgf; and 14.78 Kgf ± 5.94 Kgf).
Conclusions: Lower values on marginal discrepancy were found on pantograph crowns comparing to CAD/CAM crowns. RelyX Luting 2 obtained not only a lower marginal desadaptation, but also a better efficiency on traction resistance among the three cements. However, there was no significant statistical difference that could prove the influence of desadaptation on displacement resistance.
Keywords: Cementation, dental implants, traction resistance
|How to cite this article:|
Chagas PC, Bastos LC, Lima MP. Evaluation of marginal adaptation and traction resistance of zirconium crowns made up using two different techniques and cemented on pins with three types of cements. J Dent Implant 2014;4:135-9
|How to cite this URL:|
Chagas PC, Bastos LC, Lima MP. Evaluation of marginal adaptation and traction resistance of zirconium crowns made up using two different techniques and cemented on pins with three types of cements. J Dent Implant [serial online] 2014 [cited 2019 Sep 17];4:135-9. Available from: http://www.jdionline.org/text.asp?2014/4/2/135/140873
| Introduction|| |
On implant-supported rehabilitation, better aesthetics and resistance may be obtained by using zirconium pillars.  It can be done by using manual or computerized milling. The pantograph uses a process of "key coping;" whereas computerized methods sculpt pillars on wax and scanned, and then prefabricated ceramic blocks are milled, reproducing its form through computer assisted designing/computer assisted machining (CAD/CAM) system. 
The success of these restorations depends on cements' solubility.  Dental cements may be made out of zinc phosphate, glass ionomer cement (GIC), and resins. Zinc phosphate cement has mainly mechanical adherence, not chemical. Besides, this cement has a good flow and small thickness of cementation coat. However, its high solubility favors marginal infiltration. 
Resin modified GIC (RMGICs) were developed mainly to improve conventional GICs, incorporating a resin matrix.  They have an adequate coat thickness, and low solubility. Its disadvantage is a greater viscosity, which may cause an incorrect prosthesis seating, and subsequent marginal desadaptation. 
Resin cements have colors similar to teeth colors.  Although, its contraction may cause difficulty on material seating.  Its main characteristic is insolubility, increasing its resistance to fracture. 
Cementation agents influence on retaining by type, composition, and viscosity. , And, significant marginal discrepancies, may expose the cement in oral cavity,  causing its dissolution,  retaining of biofilm, and subsequent infiltration; gaging mechanical reliability under functional load.  Clinical values considered acceptable must be under 120 μm. ,
Therefore, the aim of this study was to verify though lab tests:
- Which type of zirconium crown, manual or computerized, has better marginal adaptation
- Which cement (zinc phosphate, RelyX Luting 2 and RelyX U200) has better marginal adaptation for each crown
- The efficiency of the three types of cement on resistance of traction displacement
- If marginal crowns' desadaptation may influence on these cements' performance.
| Materials and methods|| |
After a level ruler (Tramontina - ref. 43100/012, Garibaldi, Brasil) flatten the table that was holding the models of a delineator B2 (Bio-Art, Sγo Carlos, Brasil), 15 analogs of the universal pin (Neodent - ref. 101.040, Curitiba, Brazil) with diameter of 4.5 mm and height of 4 mm were installed on PVC tubes (Tigre - ref. 22.17.020.1, Camaçari, Brazil) containing colorless acrylic resin (Jet, Clαssico, Brasil), at a temperature of 22°C ± 2°C a stable humidity, through its transferor attached to the active part of delineator assuring a free insertion of angles.
On a calcined cylinder (Neodent - ref. 108.062), was waxed a handle with blue wax (Kota, Sγo Paulo, Brasil), with circular section of 2 mm of diameter and 6 mm of internal diameter, and substituted by a red acrylic resin Duralay (Reliance Dental, Worth, EUA). With this standard-model, it was made 15 crowns using Pantograph (Zirkonzahn, South Tyrol, Italy) with a zirconium block with dimensions of 15 cm × 15 cm × 5 cm (Zirkonzahn, South Tyrol, Italy), following manufacturer's directions, and then syntherized during 12 h in a machine (Zirkonofen 600/V2, South Tyrol, Italy) under a temperature of 1280°C. Using this model, 15 CAD/CAM crowns were usinated (Ceramill, Amann Girrbach, Caltini, Brazil), according to anterior protocol.
Assessmentof marginal adaptation
A video camera charge coupled device, model MDCE-5A (Sumbow Medical Instruments, Ningbo, China), was attached to a stereoscopic microscope Opton TNE-10B (Opton microscopes, China) of the Oral Biochemical Lab at the Institute of Science and Health (ICS) - UFBa, with amplification of ×20, and connected to a computer. The crowns were placed horizontal on the base by a silicone mould. Its four faces were viewed perpendicularly to the axis of image collect with magnification of ×200.
It was made randomly with round diamond bur n° 1014, two parallel points on each side of specimen: One on the crown and another one on the pin. On precementation, with a ruler of Corel DRAW 12 program (Corel Corporation, Ottawa, Canada), a line was made touching the most external edge of each point, and then a line connecting these parallel lines, obtaining a value in millimeters (mm) of distance between points. The same way was measured marginal gap. On postcementation was measured the distance between points. The face's average of each specimen determined a single value which was divided by 200. The difference of distances between points pre- and post-cementation was added to marginal gap. At the end, the values were converted in micrometers (μm) [Figure 1].
|Figure 1: Assessment of marginal adaptation on a stereoscopic glass, before and after cementation|
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Cementation was executed in a room with temperature at 23°C ± 2°C and stable humidity. Manufacutrer's instructions of the three types of cements used (zinc phosphate cement - S.S. WHITE, Petrópolis, RJ; CIVMR - RelyX Luting 2, 3M ESPE, Germany; resin cement - RelyX U200, 3M ESPE, Germany) were carefully followed. After its manipulation, the cement was inserted in the crown with a insertion spatula n° 1, in a thin layer, covering its axial internal. After that, it was digitally pressed over the analog for 2 s and then by the active point of the delineator with load of 5 kg during 5 min. The crowns were then immersed in distilled water, kept on plastic containers and inserted in a kiln at 37°C during 10 days, until traction test.
It was used a universal test machine EMIC DL 2000 (EMIC, Equipment and Systems of Test LTDA, PR - Brazil), of Prosthesis Lab of Dentistry School - UFBa; at a speed of 0.5 mm/min. The crowns were submitted to an axial traction force by a hook (Maguro - ref. 1930, size 6/0) attached to a mechanical driver, until its displacement.
Resistance values were obtained in force of kilogram individually.
To compare the adaptation before and after cementation it was applied the Student's t-test for paired samples. To verify the resistance and adaptation according to the type of crown and the type of cement it was used ANOVA, followed by post-hoc of Tukey or the Exato of Kruskal-Wallis test followed by post-hoc of Dunn when three groups and the Student's t-test or Exato of Mann-Whitney when with two groups. To identify the relation among them it was applied Spearman Correlation. The level of significance is 5%.
| Results|| |
Descriptive values for each type of crown, according to each type of cement are shown as followed:
- Variable desadaptation, before and after cementation. It may be observed that crowns made up by pantographs showed lowered values of gap comparing to CAD/CAM [Table 1]
- Variable desadaptation, after cementation. It shows that for both types of crowns, marginal disarrangement was lower for RelyX Luting 2, and higher for RelyX U200 [Table 2]
- Variable resistance. ORelyX Luting 2obtained better retantion on both types of crown; and with pantograph crowns, the values become superior, even though they are statistically significant only when compared to zinc phosphate. Such as, RelyX U200 and RelyX Luting 2, when individually compared among crowns [Table 3]
- Variable maladaptation, according to resistance values. It proves that marginal imbalance did not influence on resistance values of these cements [Table 4].
|Table 1: Marginal adaptation: Comparison between before and after cementation|
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|Table 2: Marginal adaptation: Correlation between type of cement×type of crown|
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| Discussion|| |
The values of marginal adaptation found by RelyX Luting 2, were 30 μm (manual crown) and 43 μm (CAD/CAM crown). While RelyX U200, were 35 μm and 40 μm. This shows that adaptation precision is greater on manual milling. Although Grenade et al. compared the adaptation of single unit zirconium coping and concluded that CAD/CAM system obtained less values of marginal disarrangement showing acceptable results.
Resin modified GIC and resin cement, seem to promote marginal disadaptations due to its viscosity comparing to zinc phosphate cement as observed by Güncü et al. and Rosenstiel et al. In this study, however, RelyX Luting 2, obtained a lower marginal disadaptation postcementation, no matter the type of crown: manual (39 μm) or CAD/CAM (53 μm). This, clinically, may implicate in a less exposition of cement in oral cavity, which minimizes its possible solubility. RMGICs are composed of silica and monomers covered by silane.  Silane has affinity for silica which if found in conventional ceramics and which is deficient in zirconium. It is possible that silica works as a surface treatment, favoring the bonding. At postcementation moment, it is observed that RelyX U200 demonstrated the worst efficiency, showing values of 53 μm and 73 μm. These results are in agreement with the study of Martνnez-Rus et al.,  and are also considered clinically acceptable. However, there was no statistically significant difference between the zinc phosphate and resin cements concerning resistance. ,
The greater values of traction resistance were found on RMGIC. Although, Consani et al., Tjan and Li  and Brukl et al.,  concluded that resin cement obtained better retaining when compared to RMGIC, zinc phosphate, and conventional GIC. On Güncü et al. and Squier et al. studies, prosthesis cemented with zinc phosphate showed a greater retaining than GIC. However, other studies report the superiority of GICs when compared to zinc phosphate cements ,, orsimilarity among these cementing agents. ,
In this study, it was not found statistically significant values that indicate correlation between marginal disarrangement and resistance which shows that the values on gaps postcementations did not influence on the values of resistance on displacement. ,
| Conclusion|| |
Facing the limitations of this study, it is concluded that:
- The crowns milled by pantograph had lower values of marginal desadaptation comparing CAD/CAM crowns
- RelyX Luting 2 showed lower values of marginal disarrangement, no matter the type of crown
- RelyX Luting 2 also showed greater resistance to traction for both type so crowns
- It was not observed a correlation between marginal discrepancies postcementation and traction resistance.
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[Table 1], [Table 2], [Table 3], [Table 4]