| کلیدواژههای انگلیسی مقاله |
Zirconia, Implant-Supported, Retrieval, IntroductionDental implants are considered to be a scientifically and clinically proven treatment option for many types of edentulism [ 1,- 2,]. Due to the promising properties of zirconia such as its aesthetic aspects, biocompatibility, strength, accuracy, and translucency, its use in implant-supported restorations is increasing [ 3,- 5,].Two types of restorations may be used in implant cases screw-retained or cement-retained [ 6,]. Cemented restorations have some advantages such as better aesthetic aspects, passive fit, and lower fabrication costs. In addition, compared to screw-retained restoration, the fabrication process of cement-retained restoration is simpler and the creation of its occlusal morphology is more accurate. Meanwhile, cemented restorations exhibit more serious biological complications than screw-retained restorations (peri-implant inflammation as a consequence of possible remaining excess cement) and it is difficult to retrieve the restoration in the case of screw loosening, ceramic chipping, or evaluating the peri-implant tissue [ 7,- 10,]. The main advantage of screw-retained restorations is retrievability. In addition, they are more biocompatible because there is no excess cement in the sulcus. However, screw-retained restorations show more technical problems. The restoration screw might be fractured or loosened and the laboratory process for constructing them is more sophisticated and expensive. Due to the existence of screw access opening, creating an accurate occlusion is more difficult and the rate of porcelain fracture is higher [ 11,- 15,].The main concern with cemented restorations is retrievability [ 16,]. Several methods have been suggested to overcome this issue. Doerr [ 17,] proposed the construction of a template to recognize the location of the screw. Daher et al. [ 18,] used digital photographs to recognize the location of the screw. Another solution is using small lingual screws to attach the crown to the abutment [ 19,]. Some investigators proposed placing a small stain on the layering ceramic at the location of the screw access opening [ 20,]. All of the mentioned methods may be helpful in finding the location of the screw access hole. However, in all of this methods perforation of framework and veneering porcelain is necessary which may decrease the strength of the restoration [ 21,]. Another suggestion is to use provisional cementation [ 22,]. However, in using provisional cementation, the degree of retention is unpredictable and may require additional appointments for the patient to re-cement the restoration. In our previous study [ 23,], we designed a ledge in the framework of cement-retained implant-supported metal ceramic restorations in the location of screw access hole to support remaining porcelain after perforation of framework. This design has the advantages of cement-retained restoration as well as the convenience of retrieval [ 23,]. Due to increasing demands for all ceramic restorations in the current study, zirconia based implant supported crowns were tested. The purpose was to compare the strength of crowns which containing ledge with those without a ledge. There were two null hypotheses. First, preparing a hole in the location of abutment screw in zirconia based cement-retained restoration to provide has not any effect on the strength of it. Second, preparing a ledge in the site of the screw access hole on the coping of the zirconia-based cement-retained restoration would not prevent the weakening of the restoration due to the probable future perforation of the occlusal surface.Materials and MethodAn implant analog (DioCorp, Busan, South Korea) with the diameter of 5mm and the height of 6.5mm was connected to a straight titanium abutment (DioCorp, Busan, South Korea) with the diameter of 5mm, the height of 7mm, and the collar height of 3mm. This complex was used as a pattern to mill 33 brass dies exactly similar to model by using a lathe (CNC 350 Arix Co Tainan Hesin, Taiwan). A total of 9.5mm of each sample was embedded in an acrylic resin block vertically (Figure 1,). Subsequently, the dies were sprayed with scan spray and scanned using a 3D-laser scanner (3Shape D810 3Shape, Copenhagen K, Denmark). The data were transferred to CAD software (3Shape&apos,s CAD Design software 3Shape, Copenhagen K, Denmark). By considering a 30-&,micro m space for the cement, a mandibular molar coping with a uniform thickness of 1mm around was designed. Twenty-two zirconia copings were milled from pre-sintered Y-TZP blanks (IPS Emax Zir CAD, Ivoclar Vivadent) in a milling machine (inLab MC, Sirona) and then sintered. Eleven samples were used for the control group and the other eleven samples were used for the second group (conventional). A 2mm diameter circle was drawn in the center of the occlusal table in the second group. Eleven zirconia frameworks were designed with the same sizes and shapes as those of the first and second groups except that a ledge was existed in the location of the screw access channel (Figure 2,). The ledge was 1 mm in thickness and 1.5mm in height and it was located around a 2mm hole in the center of the occlusal surface. A silicone index was used to standardize porcelain application to all the samples. The crowns were then cemented by using zinc oxide-eugenol cement (TempBond Kerr Mfg Co., Romulus, MI) to their corresponding dies. A 20-N load was applied during cementation for 15 minutes. A hole was prepared in the location of the abutment screw access channel in group 2 by using a 2 mm zirconia bur (Komet diamond bur, Lemgo, Germany) on a high-speed handpiece. Then the holes in groups 2 and 3 (designed in the framework) were filled with a photo-polymerized composite resin (3M ESPE Dental Products, Canada) (Figure 3,). Afterward, all the crowns underwent thermal cycling for 500 cycles from 50&,deg C to 65&,deg C for 30 seconds with 12-second intervals to simulate oral conditions [ 24,]. Finally, all the specimens were subjected to vertical static compressive load by using a universal testing machine (Zwick-Roell Z020 Zwick Gmb H &,amp amp Co. KG, Ulm, Germany) until they were fractured. The force was applied perpendicular to the occlusal surface in the central part of the crown by using the rounded edges of the loading piston a rate of 2 mm/min.Figure 1. Brass die embedded in acrylic resin blockFigure 2. The ledge designed in the zirconia framework in the location of screw access channel of the third group Figure 3. The holes in groups 2 and 3 IBM SPSS statistical software (SPSS 22, IBM Corp) was used for data analysis. One-way ANOVA test was used for comparing the mean fracture resistance values of the samples. Then, pairwise comparison among the groups was done by using Tamhane post-hoc test. ResultsThe least mean fracture resistance value was seen in group 2 (conventional) (960.09&,plusmn 210.67 N). In the special design group (group 3) this value was 1357.81&,plusmn 361.68 N and in control group it was measured 1270.18&,plusmn 312.67 N (Table 1,). The one-way ANOVA results showed statistically significant difference among the groups regarding the fracture resistance value (p= 0.011 and F=5.28). Tamhane post-hoc test was used to compare the fracture resistance values among the groups. The fracture resistance value was higher in the special design group than that of the conventional design (p= 0.018). The fracture resistance value of the conventional design group was less than that of the control group (p= 0.042). The value of mean fracture resistance between the control group and the special design group was not statistically different.GroupNMeanSD*,MinMaxControl 111270.18312.679191730Conventional 11960.09210.676721370Special design111357.81361.689132000*Standard deviation |
| نویسندگان مقاله |
Mitra Farzin |
Dept. of Prosthodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
Reza Derafshi |
Dept. of Prosthodontics, Biomaterials Research Center, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
Rashin Giti |
Dept. of Prosthodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
Masumeh Taghva |
Dept. of Prosthodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
|