Original study - ZZI 04/2011

Implant-retained prostheses: ball vs. conus attachments – A randomized controlled clinical trial

S. Cepa1, B. Koller1, M. Wolkewitz2, R. Kohal1

Purpose: The aim of the present study was to evaluate implant survival, peri-implant soft and hard tissue conditions, prosthodontic maintenance and patient satisfaction for implant-supported mandibular overdentures retained with ball attachments or prefabricated conical crown attachments during a 2-year period.

Materials and methods: 25 patients with edentulous mandibles received two oral implants in the mandibular interforaminal region. The denture attachment system was chosen randomly. Twelve patients received ball attachments and 13 patients received prefabricated conical crown attachments. Implant survival, peri-implant soft and hard tissue conditions such as probing depth (PD), modified plaque index (mPlI), bleeding on probing (BOP), modified gingival index (mGI), horizontal bone loss (HBL) and patient satisfaction were assessed for each patient. In addition, detailed prosthodontic maintenance interventions were monitored during the follow-up period.

Results: The implant survival rate was 100 %. There were no significant differences in PD, mPlI, BOP, mGI and HBL between the two groups. Within the two-year evaluation period prosthodontic intervention was required for 80 % of the patients in the ball attachment group and 75 % of the patients in the conical crown group. After two years, patient satisfaction in the ball group (82 %) was higher than in the conical crown group (60 %).

Conclusion: The results indicate that both attachments (ball attachment, conical crown attachment) used on two implants in the edentulous mandible show similar clinical results. However, the maintenance of both attachment groups is high. Due to the need for extensive maintenance, regular recall is fundamental for both attachment systems.

Keywords: implant-retained mandibular overdentures; SynCone; ball attachments


The management of patients with edentulous mandibles by means of implant-retained hybrid prostheses, that is, combined fixed and removable overdentures, is a simple, practicable and cost-effective solution [37]. Use of implants in the edentulous mandible improves the stability of the prosthesis and leads to an improvement in patient satisfaction compared with conventional total overdentures [3, 5, 10, 12, 17, 25, 44].

For these reasons, according to the McGill conference (2002), management with a hybrid overdenture retained on two implants should be the standard treatment of the edentulous mandible [13, 39]. This type of treatment is financially much more economical for the patient because of the very simple dental laboratory work than, for example, a fixed implant-retained restoration [38].

Implant-retained mandibular overdentures can be attached by different retaining elements such as ball attachments, locators, magnets, telescopic crowns or bars [18, 31, 32, 40, 41]. As regards maintenance, differences between splinted (bars) and non-splinted retention elements (ball heads, locator attachments etc.) have been described [6, 14, 34, 40]. However, the choice of retention element has no influence on implant survival rates [7, 11, 31, 38, 41]. In the edentulous mandible, these are 86 % to 100 % after five and ten years respectively [14, 23, 24, 26, 31].

The aim of this randomized prospective clinical study was to investigate the influence of two different retention elements (ball head and prefabricated conical crowns [SynCone]) with two interforaminal implants on different clinical parameters and horizontal bone loss. In addition, the study investigated which attachment design requires greater prosthodontic maintenance and which leads to greater patient satisfaction.

The null hypothesis states that there is no difference between SynCone attachments and ball head attachments with two interforaminal implants with regard to the aforementioned parameters.


Materials and methods

Study design

After approval of the study by Freiburg Regional Council and approval by the Ethics Committee of Freiburg University Hospital (decision number 105/04) and after obtaining written informed consent from the patients, 25 patients were treated with implant-retained mandibular prostheses in the Department of Dental Prosthetics of Freiburg University Clinic in a randomized clinical study. Either prefabricated conical crowns (ANKYLOS SynCone, DENTSPLY Friadent, Mannheim, Germany) or ball head attachments (ANKYLOS ball heads, DENTSPLY Friadent, Mannheim, Germany) were used for prosthesis retention.



The patients for this study were selected from healthy adult individuals who wanted an implant-retained restoration for their edentulous mandible. The 25 patients recruited for the study were dissatisfied with their previous full mandibular overdenture and wanted a better-fitting prosthesis. The exclusion criteria included: infectious or metabolic diseases, cardiovascular disease, pregnancy or planned pregnancy within the following twelve months, lactation, local contraindications (e. g., tumors, ulcers) to oral surgical procedures, alcohol abuse or smoking, psychological disease, non-compliance and intolerance of pre- or postoperative medication in the presence of chronic disease. All forms of opposing dentition were accepted provided these were sufficient.


Surgical procedure

Four interforaminal implants were inserted according to the manufacturer’s recommendations by one clinician (RJK) in the mandibles of 25 edentulous patients. Under local anesthesia, a mucoperiosteal flap was dissected from the region of the second left premolar to the second right premolar and the mental foramina were exposed. Two conventional implants (ANKYLOS, DENTSPLY Friadent, Mannheim, Germany) were placed in the canine region of the mandible without using a drilling template. The implants were selected according to the available bone and had a diameter of 3.5 or 4.5 mm and a length of 14 mm. For test purposes, two further smaller implants (ANKYLOS, DENTSPLY Friadent, Mannheim, Germany) were inserted between these two implants in positions 31 and 41 in artificially created bone defects. These had a diameter of 3.5 mm and a length of 8 mm. The two middle experimental implants were removed at a later time using a trephine drill to investigate two bone substitutes in another study. After relieving slits in the periosteum, the mucoperiosteal flaps were approximated tension-free with interrupted and continuous sutures. The sutures were removed ten days after implant insertion. Following suture removal, the existing lower dentures were adjusted to the new situation with a soft relining material (Soft-Liner, GC Europe, Leuven, Belgium).

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