Clinical outcome of three-unit lithium-disilicate glass–ceramic fixed dental prostheses: Up to 8 years results
Introduction
The use of all-ceramic materials for fixed restorations in dentistry has become more and more important for patients and clinicians in the last decades. Due to the successful use of all-ceramic crowns both in the anterior and posterior segments [1], [2], [3] and with the introduction of advanced dental technology and high-strength ceramic materials, all-ceramic systems for three-unit fixed dental prostheses (FDPs) may become a viable treatment option.
To increase the mechanical strength of all-ceramic restorations different core materials were used. They were made either from glass-infiltrated alumina ceramic (In-Ceram Alumina) [4], pure alumina ceramic (Procera) [5] or lithium-disilicate based glass–ceramic (IPS Empress II, IPS e.max Press; both Ivoclar-Vivadent, Schaan, Liechtenstein). Recently, another type of ceramic, yttria stabilized zirconia polycrystals (Y-TZP) has been made available to dentistry through the CAD/CAM technology [6], [7], [8].
Such restorative all-ceramic systems have to fulfill biomechanical requirements and should provide longevity similar to metal–ceramic restorations [9] while providing enhanced esthetics [10]. However, it must be taken into consideration that aging and stress fatigue in the oral environment, as well as function and para-function, all affect the longevity of all-ceramic restorations [11]. Therefore, it is well established in the dental literature that evaluation of all-ceramic restorations over 5 years of service is the gold standard. Thus, the inclusion criteria in two meta-analyses [12], [13] included a minimum 5-year follow-up period. A shorter period was considered inadequate for assessing relevant clinical applications.
For In-Ceram Alumina successful long-term outcome of short-span FDPs was reported in a prospective [14] (observation time at least 5 years) and a retrospective [15] (observation time up to 9 years, mean 76 months) clinical study. Further in the actual literature also for zirconia ceramic 3–5 year results are available. They show, that zirconia offers sufficient stability as a framework material [16], [17], [18], [19] and that three- to four-unit FDPs made of Y-TZP with anatomically designed frameworks are promising prosthetic alternatives even in the premolar and molar regions [16], [18], [19].
In contrast, for lithium-disilicate based glass–ceramic three-unit FDPs, only results with an observation less than 5 years have been published so far [20], [21], [22], [23]. One study [20] showed a 93% success rate for posterior FDPs after 2 years observation time. For Empress II the survival rate ranged between 96% [21] after 1 year (posterior FDPs) and 50% success rate for anterior and posterior FDPs [22]. However, lithium-disilicate based glass–ceramic has been improved regarding physical properties and came to the market as IPS e.max Press. IPS e.max Press has smaller crystals than Empress II and provides a flexural strength of approximately 400 MPa and a fracture toughness of approximately 3.0 MPa m1/2 (both values approximately 10% higher than for Empress II). Preliminary results of the authors with FDPs made from IPS e.max Press [23] demonstrated no failures after a mean follow-up period of 48 months.
In summary, for In-Ceram Alumina and zirconia ceramic successful 5-year outcome data for short-span FDPs have been presented. However, it is essential to gather long-term data for other ceramic systems, before considering these type of restorations as a viable option for anterior and posterior FDPs.
Therefore, the primary aim of the present follow-up study was to assess the clinical outcome of three-unit lithium-disilicate glass–ceramic FDPs after a service period of at least 5 years when cemented either adhesively or conventionally.
Section snippets
Study design
Patients referred to the Department of Prosthodontics of the University at Kiel, Germany, with the indication for three-unit FDPs were selected for the study. All participants were healthy and had an almost complete dentition. Informed consent was obtained from all subjects on a written form approved by the Ethical Committee of the Medical Faculty of the University at Kiel.
All restorations were constructed as three-unit FDPs. No cantilever FDPs were provided. The edentulous space had to be
Patients drop-outs
From the original 29 patients two patients had passed away during the observation period. They had incorporated altogether 3 FDPs. The FDPs were successful until death. These FDPs were defined as drop-outs. All other patients took part regularly at the annually recall sessions.
Outcome of FDPs
The following results include the data of all remaining 33 FDPs. The 5-year recall was performed for all FDPs, the 6-year recall for 32 FDPs, the 7-year recall for 22 FDPs, and the 8-year recall for 3 FDPs. The mean
Discussion
In similar studies the patients were treated by four [14] or only by one [15] clinician. The small number of clinicians, each treating a high number of cases, provided similar experience levels for high quality treatment. In the present study, 13 clinicians with a vocational experience between 1 and 5 years treated the patients. No treatment sensitivity concerning the factor “clinician” was apparent in this study.
The primary aim of the present study was to assess the clinical outcome of
Conclusion
It can be summarized that anterior and posterior three-unit FDPs made out of a lithium-disilicate glass–ceramic (e.max press) had a cumulative survival rate of 93% after 8 years. The type of cementation (conventionally versus adhesively) showed no significant differences in the failure or complication rates, respectively. Our results demonstrate that the replacement of missing single teeth by three-unit FDPs with this glass–ceramic involves no increased risks over the evaluated observation
Acknowledgments
This study was supported by Ivoclar-Vivadent, Schaan, Liechtenstein.
The authors are grateful to Dipl Ing. F. Lehmann for his advices regarding the fractography analysis. They further want to thank participating dentists and patients for their kind cooperation and the dental technicians B. Schlueter and R. Gerhardt for the laboratory work.
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