Customized impression of an implant-supported fixed partial denture in the esthetic zone

Dr. David Furze and Mr. Ashley Byrne describe a method in which all four maxillary incisors are replaced with an implant-supported fixed partial denture

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Introduction
With the advances in implant surfaces and regenerative techniques, the survival rates of dental implants are quoted between 96% and 99%. As such, there has been a change in ethos of implant placement that should now be placed in a restoratively driven manner. The success of implant treatment is no longer merely based on the survival of the implant, but a greater influence is being placed on the esthetic result achieved. The most challenging of aspects of esthetic implant treatment lies within the soft tissue management.

Treatment planning the replacement of multiple teeth in the esthetic zone may be considered to be complicated. The number and position of the implants to be placed should carefully consider the soft tissues and, in particular, obtaining the correct papillary heights, an equivalent gingival height, and buccal soft tissue contour.

This clinical report aims to document a technique of provisional restorations to condition the soft tissue, followed by a customized fixed partial denture (FPD) impression designed to give the technical team the correct emergence profiles of both the implant and pontic sites.

Clinical report
A 55-year-old female was referred for an implant consultation (Strand on the Green Dental Surgery, London, England). Her main complaints were continued loss of post crowns, poor esthetics of her resin-bonded FPD, and the loss of bone following the extraction of her upper right lateral incisor. The patient was a non-smoker and revealed no systemic medicalproblems that would contraindicate implant therapy. On examination, she had failing restorations of her upper central incisors and her upper left lateral incisor. Bone resorption was clearly noted in the upper right lateral position. Occlusally, she was an incisal class 1 relationship and group function in lateral excursions. The unrestorable incisor teeth were removed without raising a mucoperiosteal flap, consistent with an early implant placement protocol. An immediate composite resin-bonded FPD with metal wings on both canines was modeled to support the interdental papilla and cemented using a glass ionomer cement (Fuji IX, GC). A 6-week healing period was followed by implant placement (Straumann® bone level 4.1 mm diameter, 12 mm length SLActive®, Straumann®) in the central incisor positions according to early implant protocol utilizing a surgical stent. The lateral incisor positions were not used for the implants due to the requirement of a block bone graft. The ridge was contoured using Straumann bone ceramic at both the implant and pontic sites, and a bilayered cross-linked collagen membrane (Bio-Gide®, Geistlich) in a two-layered technique. A further healing period of 3 months was observed prior to a second-stage surgical uncovering of the implants. Composite (Gradia® Direct, GC America, Inc.) was added to the palatal surfaces of both canines to return the patient to canine guidance. A closed-tray impression technique was taken in polyether (Impregum™ Penta™; 3M™ ESPE™), and a composite provisional bridge was manufactured.

Table 1

1.     The provisional FPD is removed from the patient and replaced onto the initial cast. Care is taken to ensure that there is no contact of the pontics with the cast.
2.     A light-bodied, fast-setting addition silicone (Provil® Novo CD 2, Heraeus Kulzer) impression is then taken of the apical half of the provisional FPD.
3.     The provisional FPD is then removed and replaced in the patient.
4.     Open-tray impression copings are then inserted into the cast.
5.     Bis-acrylic temporary crown and bridge material, (Integrity®, Dentsply) is used to customize the impression copings to provide an exact replica of the provisional FPD.
6.     The FPD is removed from the patient, and the customized impression coping is immediately screwed into position supporting the soft tissue contour.
7.     An open-tray polyether impression is taken (Impregum Penta; 3M ESPE).

A video of the technique may be accessed via www.brynesdental.com.

Following 6 months of tissue conditioning, a customized FPD impression was taken. The procedure is summarized in Table 1.

An irreversible hydrocolloid impression was taken of the provisional FPD in situ, and a full series of clinical photographs was emailed to the laboratory. From the customized implant FPD, impression two casts were constructed. The first was a soft tissue and the second a solid stone. An additional cast of the provisional FPD was used as a guide for the definitive case. The casts were mounted on a semi-adjustable articulator, using the previous lower to ensure the face bow recorded maintained constant. A customized an-terior guidance table was constructed using light-cured acrylic resin. A silicone index of the current provisional was taken to aid in the design of the metal work ensuring correct support of the porcelain. Two gold cylinders (Straumann bone level regular crossfit) were screwed to the cast and cut down to fit within the index. The metal work was then waxed up allowing 1.5 mm of clearance for the porcelain. The wax was sprued and invested with a phosphate investment (Fujivest® premium, GC America, Inc.) using a 25% liquid to distilled water mix. The FPD was cast in Implant 58 alloy (Cendres Metaux, Biel/Bienne, Switzerland) and allowed to bench cool. The investment was removed, and the metal heat treated in accordance to the Cendres Metaux guidelines. The metal framework was then veneered with porcelain (GC Initial™, GC America, Inc.).

The pontic and implant emergence were matched in the ceramic and consistent on both the soft tissue and stone casts. The definitive FPD is tried in at a bisque bake stage and modifications made. The definitive FPD is then torqued to 35N and access holes filled with composite.

Discussion
This use of provisional restorations to condition the tissue is now considered routine if the optimum esthetics are to be achieved. It would seem sensible to provide the technical team with every piece of information required. The use of customized impressions in single tooth replacement has been well documented, but extending the customized impression into the pontic site can further provide the technical team with accurate soft tissue information. The soft tissues collapse almost immediately following the removal of the provisional bridge. In customizing the impression copings, the soft tissues are adequately supported while the impression material sets. This information is replicated on the master casts. The accuracy of the impression technique is shown by the immediate support of the soft tissues with no blanching of the tissues at any point.

The extent of soft tissue management that may be achieved during this restorative phase is limited. It is regarded that the most important factor in achieving an esthetic result is the correct three-dimensional positioning of the implants. A correct wax-up and surgical stent are therefore required in all esthetic cases.

The choice of positioning the implants in these cases of replacing all the maxillary incisors is critical. The treatment outcome may have been greater if the implants had been placed in the lateral incisor positions. This configuration would remove the potentially hazardous position of placing two adjacent implants. In this case report, this would have required a lateral ridge augmentation procedure, and as such the central incisors sites were chosen. This esthetic risk is minimized as there will only be one midline papilla, and therefore, symmetry will not be altered in this case of placing two adjacent implants. In order to give the best potential to create a midline papilla, the implants were placed more than 3 mm apart and were of a platform-switched design. This design appears to protect the crestal bone and the subsequent overlying tissue.

This clinical report describes a simple, fast, and effective impression technique that accurately replicates the soft tissue emergence from the implant as well as the soft tissue sculpturing of the pontic site.

References available upon request.
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