Original study - ZZI 04/2011

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

Of the 25 patients recruited for the study, 25 underwent surgical and prosthetic treatment. In the ball head abutment group, twelve patients were fitted with overdentures. These were aged 65.2 ± 7.02 years at the time the overdentures were fitted. These twelve patients were followed up after one year. Eleven participants were followed up after two years because of one death.

13 participants were randomized to the prefabricated conical crown group. These were aged 62.9 ± 8.98 years at the time the overdentures were fitted. Twelve of these were followed up after one year. One study participant had died. Eleven patients were followed up after two years. One participant left the study as the prefabricated conical crowns were exchanged for ball heads on account of poor denture fit (Fig. 3).

 

Implant survival rates

No implant was lost in either group within 24 months. The implant survival rate after 24 months was therefore 100 %.

Clinical results

No significant differences were found between the two abutment groups for the parameters probing depth, BOP, modified gingival index, mesial HBL and distal HBL at the different examination times (p > 0.05) (Table 1–6, Fig. 4–9). The changes over time in the two groups showed no significant differences. The mean modified plaque index (mPlI) demonstrated a significant difference only at baseline (t = 0) with the ball heads (0.4 ± 0.3) and with the prefabricated conical crowns (1.2 ± 0.3) (p = 0.0322).

 

Prosthodontic maintenance

Prosthodontic intervention was required 13 times in the ball head group up to the one-year follow-up. In eleven cases, retention was too weak and was therefore improved by activation of the matrices in seven patients and exchange of the matrices in three patients. Three overdentures had to be relined.

In the SynCone group, prosthodontic maintenance treatment was required on 14 occasions. The conical crown retention was too weak in four cases. In one of these cases, new matrices were polymerized into the prosthesis. The other three patients did not want any subsequent improvement. In seven cases, the retention was too strong. In one of these cases, the prefabricated conical crowns were exchanged for ball heads. This patient was therefore withdrawn from the study. In the other cases, the overdentures were sent to the dental laboratory for improvement. The retention was reduced there by carefully rubberizing the secondary crowns. In two cases, the overdentures had to be relined. One abutment (Fig. 10) fractured. The broken abutment had to be drilled out of the implant so that it could be replaced by a new conical crown.

Further treatment was required on eight occasions in each of the study groups up to the two-year follow-up.

Loss of retention was found three times in the ball head group. To improve this, the matrices were activated in one case and in two cases the matrices were exchanged for new ones. A need for relining was found in five cases.

In the SynCone group, the retention was too weak in five cases at the two-year follow-up. One of these patients did not want any prosthodontic measures to improve denture fit. In one patient, new SynCone matrices were polymerized and in three patients the abutments were exchanged for ball heads. These patients were withdrawn from the study from this time and treated as drop-outs. In one patient, prosthetic retention was very strong. However, this patient did not want any corrective measures either. In two patients, the overdenture had to be relined.

If prosthodontic maintenance is regarded as failure, this results in the Kaplan-Meier graph seen in Figure 11. After
24 months, only 20 % of the restorations attached with ball heads are in situ unchanged, and the figure is 25 % for overdentures attached with prefabricated conical heads.

 

Patient satisfaction

All study participants were dissatisfied with their full denture prior to the start of the study. After one year, the absolute satisfaction in the ball head group was 83 % (10 of 12 patients). Satisfaction was 82 % in the prefabricated conical crown group (9 of 11 patients, 1 patient did not respond). After two years, 82 % of the patients (9 of 11 patients) in the ball head group were satisfied. In the prefabricated conical crown group, satisfaction fell to 60 % (6 of 10 patients, 1 patient did not respond) (Table 7, Fig. 12).

 

Discussion

This randomized clinical study investigated various clinical parameters, prosthodontic maintenance and patient satisfaction over a two-year period with the attachment of mandibular overdentures retained on two implants with classical ball heads compared with prefabricated conical crowns.

PAGE: 1 | 2 | 3 | 4 | 5