Originalarbeit englisch - ZZI 02/2014

Clinical outcomes of implant-supported and rigidly double crown-retained prostheses in edentulous mandibles: An 8-year retrospective study

E. Frisch1, P. Ratka-Krüger2, K. M. Lehmann3

Introduction: Different treatment options have been proposed for implant-supported rehabilitation of patients with edentulous mandibles. In particular, long-term data on double crown-retained prostheses are scarce. Our study provides data on implant-supported MDC-retained prostheses in patients attending supportive post-implant therapy (SIT) for > 8 years.

Material and methods: Between 1992 and 2009, 32 patients with edentulous mandibles were restored with overdentures supported by 4 implants (IODs) and double crowns using the Marburg Double Crown (MDC) technique. For retrospective evaluation of implant and prosthetic survival/success and technical/biologic complications, only patients attending SIT were included.

Results and discussion: Twenty-seven patients (20 female/7 male, mean age: 73.88 ± 10.44 years) with 108 implants met the inclusion criteria. The mean follow-up period was 8.27 ± 4.75 years. Two implants (1.85 %) were lost before loading (cumulative survival rate: 98.15 %). Four implants (3.74 %) in 3 patients (11.11 %) showed peri-implantitis (cumulative success rate 94.51 %). No denture had to be remade (prosthetic survival rate 100 %) and 14 dentures (52 %) required no repairs up to the time of the study. Minor technical maintenance procedures (e.g., abutment loosening, screw loosening, acrylic fracture or relining) were required at a rate of 0.130 treatments/patient/year (T/P/Y).

Conclusions: Within the limitations of this study, we conclude that implant-supported MDC-retained prostheses represent a suitable treatment option for edentulous mandibles. No increased risks for peri-implant disease or increased technical maintenance have to be expected even for longer periods.

Keywords: implants; edentulism; double crowns; telescopic crowns; peri-implantitis; technical complications

Cite as:

Frisch E, Ratka-Krüger P, Lehmann KM: Clinical outcomes of implant-supported and rigidly double crown-retained prostheses in edentulous mandibles: an 8-year retrospective study. Z Zahnärztl Implantol 2014;30:113–127

DOI 10.3238/ZZI.2014.0113–0127


In recent decades, dental implants have greatly expanded and improved the treatment options for edentulous patients. Various treatment approaches using implant-supported fixed and removable dentures are available today. While implant-supported prostheses in the edentulous mandible are retained predominantly with resilient bars or bar attachments, ball abutments, magnetic attachments, double crowns or locator abutments, similar treatment guidelines for the edentulous maxilla are lacking [2, 37].

Double crowns were used relatively late and only in small numbers as retaining elements for implant-supported dentures, initially in the form of tapered crowns [4,17, 19, 27] and then as resilient telescopic crowns [15, 18]. Use of double crowns for bony support of removable partial dentures on implants (IRPDs) was proposed for the edentulous mandible from the mid-1990s [11, 12]. Later, tapered connections with ceramic primary crowns retained by a fine gold electroformed coping cemented into a tertiary framework were also presented [40, 41]. The single-cast secondary technique (SCST) is a useful variation for double crown-retained removable partial dentures (RPDs). In this technique, the components of the secondary construction, that is, the framework and secondary crowns, are cast in a single process and from one material (CoCrMo alloy) [9, 26]. There are therefore no technically weakened joints between the secondary crowns and the prosthetic saddles. For this reason and on account of the roughly doubled elasticity modulus of the CoCrMo alloys compared with precious metal alloys [29], comparatively more delicate constructions can be achieved with a thinner secondary crown layer. This also allows palate-free, double crown-retained partial dentures in the maxilla, usually without a transverse band. In the mandible, a sublingual bar can be omitted. The RPD is supported and retained by Marburg double crowns [45]; such constructions show good long-term results [13, 14, 44].

In two systematic reviews of the literature [21, 39],
only four clinical studies on double crown-retained IRPDs were identified. In these, implant survival rates of 95–100 % over 3 to 10 years are reported [8, 16, 24, 42]. However, prostheses designed with resilient telescopic crowns without direct implant support were investigated predominantly.

This retrospective study presents data on the survival and success rates and on biological and technical complications of purely implant-supported restorations retained by MDCs in the edentulous mandible after more than 8 years of intraoral service.

Material and Methods

The study was conducted in a private practice that specializes in implantology (Northern Hessia Implant Center, Hofgeismar, Germany). It is based on analysis of primary patient data and evaluates the clinical results of IRPDs in the edentulous maxilla supported and retained by MDCs on 4 implants. The study was examined and approved by the Ethics Committee of the Albert Ludwig University Freiburg, Germany (no. 46/10).

Patients who were treated as described above in the period from 01–01–1992 to 31–12–2010 were included in the study. They were asked to participate voluntarily after receiving written information. The basic requirement was that all patients had been treated surgically and with implant-based restoration in the study practice and had taken part in the practice’s internal supportive post-implant therapy (SIT).

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