Overdenture treatment provides an esthetic and functional result that allows proper access for hygiene and maintenance. For implant-retained overdentures to be successful, functional loads must be distributed optimally to the mucosa and the abutments. For this purpose, impressions must record the soft tissue supporting areas simultaneously with accurate registration of the implant components. Usually, finger pressure is used to make functional impressions. This article describes an alternate pressure-free functional impression technique for implant-retained overdentures.
An overdenture impression must record the soft tissue supporting areas simultaneously with accurate positioning of the implant components.1 Functional impression technique records the alveolar mucosa in a functional state and simultaneously records the implant components in relation to the alveolar tissues.2
Three types of impression techniques have been described in the literature.3 A single-stage impression procedure is commonly used with an open or closed tray technique.4,5 A double-impression technique for overdentures retained by only 2 implants has been suggested, using a zinc oxide eugenol (ZOE) impression paste and polyether impression material.6 The third type of impression technique is a functional impression technique for implant-retained overdentures.3,7 All of these techniques require operator finger pressure. It is possible to make a functional impression without finger pressure for implant-retained overdentures by using cap attachments. Also, an implant-retained overdenture has characteristics resembling those of a complete denture with a combination of tissue support and implant retention.6 Thus, the resilience difference between implant and mucosa should be considered for the impression of implant tissue–retained overdentures.3 Therefore, the impression technique must provide an accurate resilience difference between implant and mucosa.
This article describes an alternative functional impression technique that can be used to fabricate implant-retained mandibular overdenture reinforcement with metal framework.
The step-by-step procedure for this alternative functional impression technique is as follows:
Replace healing caps (Zimmer Dental Inc, San Diego, Calif) on the osseointegrated dental implants with ball abutments (Zimmer Dental). Place ball abutment transfers (Zimmer Dental) on the ball abutments (Figure 1a).
Obtain a preliminary impression of the mandibular arch with irreversible hydrocolloid (CA 37, Cavex Holland BV, Haarlem, The Netherlands) with a stock tray.
Pour the mandibular cast with dental stone (Moldano, HeraeusKulzer GmbH, Hanau, Germany).
Place cap attachments (Zimmer Dental) parallel on ball abutments with paraskop (Bego, Bego Dental, Bremen, Germany).
Take the cast metal framework (Wironium, Bego Dental) and combine cap attachments with a self-curing acrylic resin (Meliodent, Heraeus Kulzer).
Place 1-mm-thick dental wax (Heraeus Kulzer) on the mandibular model.
Fabricate an acrylic custom tray (Heraeus Kulzer) (Figure 1b) and place the custom tray on the ball abutments in the mouth; check the relationship of soft tissues.
Border mold this impression tray with plastic impression compound (Impression Compound, Kerr Italia SpA, Salerno, Italy).
Take the impression of the alveolar mucosa with a ZOE impression paste (Cavex Outline, Cavex Holland BV, Haarlem, The Netherlands) (Figure 2a) without finger pressure.
Place ball abutment analogues (Zimmer Dental) into cap attachments (Figure 2b).
Pour the impression with Type IV stone (Begostone, Bego Dental).
The described method is technique sensitive and requires parallel placement of cap attachments. Otherwise, the probability of obtaining an erroneus impression increases. A pressure-free impression is obtained by means of retention provided through cap attachments. However, this impression method is technique sensitive for providing a perfect border relationship with various impression materials. Additionally, it is more time consuming compared with single-stage impression procedures for overdentures.
The main advantage of this technique is it provides an accurate relationship of implant components to supporting tissues without finger pressure. Delivery of the prosthesis constructed with this impression technique results in a decrease in postinsertion appliance adjustments.
Department of Prosthodontics, Ankara University, Besevler, Turkey