Seung -
نویسندگان
چکیده
Objectives: The aim of this prospective cohort study was to compute the long-term clinical survival and complication rates of alumina-toughened zirconia abutments used for implant-supported restorations and to evaluate the effects of several clinical variables on these rates. Material and methods: From May 1998 to September 2010, 213 patients aged 18 years or older were recruited. The patients received 611 external hex implants and 328 implant-supported fixed restorations using alumina-toughened zirconia abutments. During the follow-up, each restoration was coded as a dental event, which included loosening or fracture of abutment screws, and abutment fracture. From the coded data, the effects of the investigated clinical variables—restored area (anterior/posterior), number of prosthodontic units (one/two units or over), prosthesis type (single-unit/multiunit without pontic/multiunit with pontic), implant system, and patient gender— on the survival of the abutments were evaluated. Survival analysis using Kaplan–Meier method and Cox proportional hazard model was applied. The 5-year survival and complication rates of the abutments were assessed. Results: The number of prosthodontic units and the type of prosthesis had a significant association with complication rates (P < 0.05). Kaplan–Meier survival analysis estimated that the cumulative 5-year complication rate of the abutments used in single restorations was 19.7%. Multiunit-fixed dental prostheses without and with pontics had complication rates of 3.9% and 3.8%, respectively. The 5-year survival rate of the abutments was more than 95%, regardless of the type of prosthesis. Conclusions: Alumina-toughened zirconia abutments are likely to exhibit excellent long-term survival in clinical use for fixed restorations. Single tooth replacement with the abutment at the molar region may require special care and extra attention. Titanium has been established as the material of choice for implant reconstruction due to its well-documented biocompatibility and mechanical properties (Adell et al. 1981). Clinical studies have documented superior survival rates for fixed implant restorations supported by titanium abutments (Andersson 1995). However, in a recent systematic review, certain complications were associated with metal abutments supporting fixed implant restorations (Pjetursson et al. 2007). One of the major issues noted was aesthetic concern. A previous meta-analysis showed more frequent aesthetic complications at metal abutments than those at ceramic abutments (Sailer et al. 2009). The unnatural bluish appearance causing aesthetic problems stems from the thin soft tissue of the peri-implant, which is incapable of screening the reflective light from the metallic abutment surface (Yildirim et al. 2000). As an alternative to titanium, the aluminium oxide abutment was next introduced in 1994. However, the inferior mechanical properties (i.e., low ability to withstand fractures) of alumina were not sufficient to be used alone as an implant abutment. Therefore, high strength, durable ceramic zirconia was developed and used as an implant abutment later in the 1990s (Belser et al. 2004; Guazzato et al. 2004). Ceramic abutments including zirconia are well known to be superior to metal These authors contributed equally to this work. Date: Accepted 18 December 2011 To cite this article: Kim S-S, Yeo I-S, Lee S-J, Kim D-J, Jang BM, Kim SH, Han JS. Clinical use of alumina-toughened zirconia abutments for implant-supported restoration: prospective cohort study of survival analysis. Clin. Oral. Impl. Res. 24, 2013, 517–522 doi: 10.1111/j.1600-0501.2011.02413.x © 2012 John Wiley & Sons A/S 517 abutments in terms of their aesthetics, which prevent the gingival discoloration that is common with metal abutments (Jung et al. 2007). In addition, the results of a recently published study showed that significantly fewer bacterial colonies were found on zirconia surfaces compared with titanium surfaces (Rimondini et al. 2002; Scarano et al. 2004). Moreover, the favourable soft and hard tissue reaction to zirconia was comparable to the reaction to titanium (Kohal et al. 2004). Clinically, a previous 4-year prospective study indicated that the success rate of zirconia abutments in the anterior dental region was 100% (Glauser et al. 2004). However, clinical studies on zirconia abutments, especially in posterior restorations and implant-supported fixed partial dentures, are still scarce (Bae et al. 2008). The aim of this study was to compute the long-term clinical survival and complication rates of alumina-toughened zirconia abutments used for implant-supported restorations and to evaluate the effects of several clinical variables on these rates. In addition, whether the survival/complication rate would be affected by the type of prosthesis or by the location of its placement in the mouth were also discussed. Material and methods Subjects This study was performed at the Department of Prosthodontics at Seoul National University Dental Hospital in Seoul, South Korea, from May 1998 through to September 2010. Eligible participants were adults aged 18 years or older with successfully osseointegrated implant fixtures. Exclusion criteria were pregnancy and radiation therapy involving the head and neck area. A total of 213 fixed prosthodontic patients were recruited. The mean age of the patients was 57 years (range: 20– 86 years). All patients were treated with implant-supported single-unit fixed dental prostheses (FDPs), multiunit FDPs without pontics, or multiunit FDPs with pontics at Seoul National University Dental Hospital. The institutional review board for the protection of human subjects reviewed and approved the research protocol (IRB054/06-10). The number of restorations examined in this study was 328. The following clinical variables were investigated: restored area (anterior and posterior restorations), number of prosthodontic units (one unit and two units or over), type of prosthesis (single-unit FDPs, multiunit FDPs without pontics, and multiunit FDPs with pontics), external hexagon implant systems, and patient gender (Table 1). Alumina-toughened zirconia abutments The all ceramic alumina-toughened zirconia abutments (ZirAce, Acucera, Pocheon, Korea) used for this prospective clinical study were composed of alumina reinforced yttria and niobia co-doped tetragonal zirconia polycrystalline (Al2O3/Y(Nb)-TZP). This composite is known to be free of low temperature degradation during the ageing process and has 700 MPa biaxial flexural strength and 8.1 MPa·m fracture toughness (Kim et al. 2000). Such properties facilitate procedures in the mouth and the laboratory using high speed diamond burs or low speed diamond wheels for adjusting into the final shape. In addition to this, abutments are light yellow in colour, similar to the natural teeth, adding to their desirability in aesthetics. The coefficient of thermal expansion of alumina-toughened zirconia is approximately 9.92 9 10 /C and veneer porcelain for zirconia can be applied on the abutment directly (Lee et al. 2002). Clinical procedures After a certain period of healing time for external hexagon type implant fixtures, an impression was taken at the implant fixture level and master casts were fabricated. The appropriate dimensions of the prefabricated alumina-toughened zirconia abutments were selected according to the fixture diameter, soft tissue height, position and shape of adjacent teeth, and inter arch distance. Adjustment of the prefabricated abutment into the final contour with high speed diamond burs under copious water spray was performed. Next, the superstructure was fabricated with gold alloys or zirconia depending on the clinical situation for cementation type of prosthesis. The modified alumina-toughened zirconia abutments were screw-tightened to the implant fixtures with a torque of 30– 35 Ncm. The definitive prostheses were permanently cemented onto the abutments with resin-modified glass ionomer cement (Fujicem, GC, Tokyo, Japan). In some cases involving single tooth prostheses that were retained by screws, the alumina-toughened zirconia abutment was directly overlaid with veneer porcelain for zirconia and was screwtightened with a torque force of 35 Ncm onto the fixtures. Survival and complication rates This prospective cohort study investigated the applicability of alumina-toughened zirconia abutments for implant-supported restorations using survival analysis, some advantages of which were mentioned in a previous study (Lee et al. 2010). Survival time was coded by the month after placement of the prosthesis. Implant abutment failure was coded as event data. Screw loosening, screw fracture, and abutment fracture were designated as complications in this study. Survival was classified as an abutment that functioned in the mouth regardless of the complications. Only a fractured abutment was excluded from survival data. Removal of the alumina-toughened zirconia abutment because of its fracture was designated as a failure. For subjects whose followup times ended without a failure event, the end status was recorded as “censored” because the actual duration of time to the failure event was unknown. Intact aluminatoughened zirconia abutments that were functioning properly during this investigation period were, therefore, coded as censored. Statistical analysis Odds ratio statistics were evaluated for all clinical variables. Kaplan–Meier survival curves were plotted, and the log rank test was used to identify the variables associated with the alumina-toughened zirconia abutment failure. Prognostic variables were identified with the Cox proportional hazard model using stepwise variable selection method. Table 1. The clinical variables investigated in this study Variables Number of restorations Restored area Anterior 60 Posterior 268 Number of prosthetic units One unit 133 Two units or over 195 Type of prosthesis Single-unit FDPs 133 Multiunit FDPs without pontics 165 Multiunit FDPs with pontics 30 Implant system Osseotite 15 USII 42 TiUnite Mk III 179 Hexplant 39 Restore 53 Gender Female 165 Male 163 Biomet Korea Co., Ltd., Seoul, Korea Osstem, Seoul, Korea Nobel Biocare AB, Göteborg, Sweden Warantec, Seoul, Korea Lifecore Biomedical, LLC., Chaska, USA 518 | Clin. Oral. Impl. Res. 24, 2013 / 517–522 © 2012 John Wiley & Sons A/S Kim et al Alumina-toughened zirconia abutments for implant restoration
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