Technical Tips for Constructing a Maxillary Implant-Supported Overdenture by Using a Double-Impression Technique

Implant-supported overdentures offer improved retention, stability, function, proprioception, and comfort level compared with conventional dentures.1 This prosthetic application relies on a combination of soft tissue and implant support.2 The ability to achieve equitable load sharing between the implants and soft tissues may be related to the selected impression technique.

Closed- and open-tray impression techniques are most commonly used for implant-supported overdentures.3^,4 The main purpose of an implant impression is to record the relationship between implant abutments or implants and to reproduce this relationship as accurately as possible when fabricating a working cast. Implant impressions also serve a secondary but important purpose of recording soft-tissue morphology.5 

Although impression techniques are based on either direct or indirect transfer of components, different impression materials and trays can also be used, depending on the preferred impression method.6 

Mericske-Stern et al7 recommended use of double-impression techniques for overdentures retained by only 2 implants. Zinc oxide eugenol (ZOE) impression paste and polyether impression material were used in a 2-stage impression procedure when fabricating an overdenture with a combination of tissue support and implant retention.

Uludag and Sahin8 also recommended a functional impression technique for implant-retained overdentures that used a combination of ZOE and elastomeric impression materials.

The objective of this article is to describe a functional double-impression technique for the fabrication of a maxillary implant supported overdenture.

1. A preliminary impression with irreversible hydrocolloid is made and poured with dental stone. The borders of the custom tray are marked 2 mm apart from the mucobuccal fold to allow space for border molding, excluding the anterior implant region.

2. The acrylic resin custom tray is prepared (Paladur, Heraeus Kulzer GmbH, Hanau, Germany) with retention offsets on the anterior palatal side to provide retention for the elastomeric impression material (Figure 1). Wax occlusion rims are placed on the tray to functionally record the soft tissues.

3. Ball abutment transfers are inserted (Zimmer Dental Inc, Carlsbad, Calif) on ball abutments (Zimmer Dental).

4. The custom tray is border molded with modeling plastic impression compound (Kerr Italia S.p.A., Salerno, Italy).

5. The impression is made with a ZOE impression paste (S.S. White, Prima Dental Group, Gloucester, UK) in centric relation (Figure 2). The tray is removed from the patient's mouth, and excess impression paste around the implants is cleaned.

6. The tray is replaced intraorally. The impression of implants is made by injecting low viscosity vinyl polysiloxane impression material (Speedex, Coltene/Whaledent Inc, Cuyahoga Falls, Ohio) and it is supported with heavy body elastomeric impression material (Speedex, Coltene/Whaledent Inc).

7. The tray is removed from the patient's mouth, ball abutment replicas (Zimmer Dental) are placed in the impression (Figure 3), and then the impression is poured with Type IV stone (BEGO, Bremen, Germany).

8. Centric relation and vertical dimension record is obtained with a record base and occlusion rims. The casts are transferred into a semiadjustable articulator (Denar Advantage; Teledyne Waterpik, Ft Collins, Colo). The artificial teeth are arranged (Vitapan, Vita Zahnfabrik, Bad Sackingen, Germany).

9. After verifying centric relation and vertical dimension intraorally, cap attachments with metal housings (Zimmer Dental) are placed on the ball abutment replicas on the model. Undercuts are blocked out with heavy-body elastomeric impression material (Figure 4).

10. The denture is processed with conventional heat-processing technique and then finished and polished (Figure 5). It is evaluated intraorally and excellent adaptation to all the supporting tissues is verified. The denture is delivered to the patient (Figure 6).

The technique described in this article includes the use of ZOE to record the edentulous areas and the use of elastomeric impression material to transfer the implant components. Thus, a functional impression may be obtained. This results in a decrease in chair time. The use of ZOE in this technique is relatively inexpensive, and it is widely used to register edentulous ridges.9 Another advantage of using ZOE for the edentulous areas is the low viscosity of the material, which prevents the displacement of the soft tissues.9 Possible distortion because of the effect of tissue displacement may be eliminated.10 

However, implant positions may affect the technique. When the distance between the implants increases, it becomes harder to apply elastomeric impression material around the implant components.

This article describes the fabrication of a maxillary implant-supported overdenture using a functional impression technique. This impression technique is economic and sensitive and it reduces chair time.