International Poster Journal of Dentistry and Oral Medicine



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Int Poster J Dent Oral Med 13 (2011), No. 2     15. June 2011

Int Poster J Dent Oral Med 2011, Vol 13 No 2, Poster 533

Retention Characteristics of Implant-Supported Milled Bar Attachments – a comparative in vitro study

Language: English

Dr. Sonia Mansour, Daniel Voigt, Prof. Dr. Jürgen M. Setz, OA Dr. Arne F. Boeckler,
Centre for Dentistry and Oral Medicine, Department of Prosthodontics, Martin-Luther-University Halle-Wittenberg, Germany

July 14-17, 2010
88th General Session & Exhibition of the IADR


In implant dentistry different anchorage systems (locators, balls, telescopes, bars) have been proved successful [1]. Milled bars are an alternative option for the retention of implant supported overdentures [2]. They present a rigid anchorage system between the implants. The individual manufactured suprastructures adjust precisely and rigidly to the milled bars. Lateral and rotary movements are limited. In addition to standard treatment (Fig. 1,2) the prosthodontic rehabilitation of compromised situations (cleft palate, maxillary ablation) using this retention concept promises excellent results in individual cases (Fig. 3) [3]. Different materials maybe used for the fabrication of milled bars such as precious and non-precious metals or zirconium. There are different retention concepts for the suprastructure like electroplated matrices (Fig. 4,5) or spark eroded friction pins (Fig. 6,7). In literature retention forces of different attachments average 1-40N [4]. There are no data in literature describing retention forces of milled bars. Furthermore wear of the retention system components can clinically causes loss of retention.


The aim of this study was to compare initial and long-term retention characteristics and wear of milled bars from different materials and different retention concepts used to retain overdentures to dental implants.

Fig. 1 Fig. 2
Fig. 3 Fig. 4
Fig. 5 Fig. 6
Fig. 7  
bar electroplated
group material / alloy material / alloy material / alloy
GG gold gold  
EG cobald-chromium gold  
TG titanium gold  
ZG zirconium gold  
EF cobald-chromium   cobald-chromium
TF titanium   titanium
ZF zirconium   gold
Tab. 1
Fig. 8 Fig. 9
Fig. 10

Material and Methods

Seven different milled-bar (Fig. 8) suprastructure combinations with different retention concepts (Tab.1) were fabricated. The test model was made from epoxy resin (RenCast CW 2428-1, Vantico) in which 2 implants (Xive, Friadent) were polymerized. Five specimens (20x7x2mm) of each group (n=35) were produced according to manufacturer's data and screwed to the implants. Electroplated gold suprastructures with a layer thickness of 300µm (Solaris, Degudent) were luted (Panavia F, Kuraray) to the individual framework (Fig. 4,5). Spark eroded friction pins (7x0,9/0,95) were fixed using laser welding (Fig. 6,7). In an universal testing machine (Z 005, Zwick, Fig. 9) retention forces were constantly recorded at a constant cross head speed of v=40mm/min, deflection of s=2mm and a pre-load of Fmax=50N (Fig. 10).
Long-term tests (5000 cycles in artificial saliva=23°C) simulated an approximal wear of 5 years. Retention forces were constantly recorded.
Milled-bar-suprastructure combinations were analysed for superficial degradation (SEM).
For evaluation of the total wear the mean-retention-force [MRF] of the first and last 250 cycles were calculated and statistically compared (ANOVA, Bonferroni, P < 0.05).


Initial mean retention force differed from 5.35N [TF] to 21.68N [EG] (Tab. 2). Throughout the first cycles retention forces changed dramatically. After long-term cycling the resulting mean retention force differed from 2.41N [TF] to 18.45N [EG]. Each milled bar suprastructure combination produced a characteristic curve (Fig. 11). The change of the mean retention force (Delta F=Fmax final - Fmax initial) differed from -10.13N [EF] to +2.14N [GG] (p < 0.001). The alteration of the mean retention force differed from -54.95% [TF] to +17.09% [GG]. All combinations except GG offered retention loss. SEM-analysis revealed characteristic degradations of the corresponding material surfaces.

group initial force
final force
Δ force
Δ force
GG 12.52 14.66 2.14 117.11
EG 21.68 18.45 -3.23 85.11
TG 9.61 9.4 -0.21 97.81
ZG 6.37 6.1 -0.26 95.87
EF 21.15 11.02 -10.13 52.09
TF 5.35 2.41 -2.93 45.13
ZF 10.46 7.65 -2.8 73.19
Tab. 2: Mean retention force after 5000 cycles
Fig. 11: Long-term mean retention forces


There were differences between the initial pull-off-forces of the tested milled bar suprastructure combinations. Standardized long-term-cycling exposed specific changes of the retention characteristics and resulting pull-off-forces in regard to bar material and retentive suprastructure designs. Electroplated suprastructures showed minimal retention loss. However the manufacturing is sensitive and later maintenance is complex. Although spark eroded suprastructures loose retention force it can be reconstructed easily chairside. The use of milled zirconium bars proofed good results. All tested combinations fulfilled the basic requirements according to retention forces of established implant abutments. However, this in vitro study takes no account of inappropriate handling by the patients. According to the limitation of this in vitro study milled bars of different materials in combination with different retention concepts are functioning. To proof the different retention concepts under clinical conditions in-vivo studies are preferable.


  1. Cehreli MC, Karasoy D, kökat AM, Akca K, Eckert S: A systematic review of marginal bone loss around implants retaining or supporting overdentures. Int J Oral Maxillofac Implants 2010; 25:266-77
  2. Weinlander M, Piehslinger E, Krennmair G: Removable implant-prosthodontic rehabilitation of the edentulous mandible: five-year results of different prosthetic anchorage concepts. Int J Oral Maxillofac Implants 2010;25:589-97
  3. Bueno-Samper A, Hernandez-Aliaga M, Calvo-Guirado JL: The implant-supported milled bar overdenture: A literature review. Med Oral Patol Oral Cir Bucal 2010;15:e375-8
  4. Alsabeeha NHM, PAYNE AGT, Swain MV: Attachment systems for mandibular two-implant overdentures: A Review of in vitro investigations on retention and wear features. Int J Prosthodontics 2009;22:429-40

This Poster was submitted by Dr. Sonia Mansour.

Correspondence address:
Dr. Sonia Mansour
Martin-Luther-University Halle-Wittenberg
Department of Prosthodontics, Centre for Dentistry and Oral Medicine
Poliklinik für Prothetik
Grosse Steinstrasse 19
06108 Halle /Saale