Dr. Eddie Scher offers some practical advice on a metalwork protocol for single- and multiple-tooth restorations on the same arch

Implant patients’ expectations of function, comfort, and esthetics have increased, along with the reliability of endosseous implants. Three practical tips will help increase the reliability of our implant restorations, as demonstrated by a case study of a successful single-tooth implant patient (Figure 1).

Osseointegration is particularly important in patients with poor quality bone. The first tip to bear in mind is that implants placed in such alveolar bone should be progressively loaded. We should therefore leave the “torquing up” of the abutment screw until the final impression stage.

The second piece of advice for restoring a single-tooth or multiple-tooth implant in the same arch is always to provide a provisional restoration first. This allows the tissues to heal on two levels—around the coronal aspect of the crown, which can be augmented if necessary, and around the bone interface, which involves proper osseointegration of the implant, utilizing Misch’s (1995) progressive bone loading protocol.

The third practical tip involves the fact that impression and indexing techniques are becoming increasingly more reliable. The fit of the final restoration can be made even more reliable if the technician fabricates the metal coping for the definitive bonded crown using the abutment on the model before making the provisional plastic crown.

Progressive bone loading
It is important to remember that healing involves the bone and metal interface. By loading the provisional plastic crown very gently and carefully, and providing the patient with a regimen of postsurgical diet control, we can give the implant a better chance of survival in poor quality bone.

At the time of fitting the abutment after second-stage surgery, we should tighten the abutment screw only to maximum “finger pressure” tightness. This is approximately 50% of the manufacturer’s recommended torque (Figure 5). We will have the opportunity to “torque up” 3 months later, when the impression for the definitive restoration is taken. The provisional plastic crown is removed, and the screw of the implant is torqued to the manufacturer’s recommendation.

The transfer impression and the final impression
Modified impression techniques can be used to register soft tissues on the model (Attard N, Barzilay I, 2003). The purpose of such an impression is to enable the laboratory to fabricate a restoration with a superior emergence profile. We can only achieve the best function and esthetics with each implant if we consider the soft tissue contours of our patients.

Approximately 10 days after implant exposure (Figure 2), we can proceed to our transfer impression. The technician makes the abutment and the provisional plastic crown using the soft-tissue model (Figure 8). At this point, the laboratory also makes the metal coping for the bonded crown that will eventually be placed on the implant (Figure 4). The fit for this metalwork should be almost perfect, because it has been waxed up to the metal abutment, as opposed to being waxed up on a model where there are many possibilities of dimensional inaccuracy.

Impression and indexing techniques performed after second-stage implant surgery are essential for satisfying patient expectations, decreasing chair time, and increasing implant function and esthetics. We should note that by second-stage surgery impressions, gingival contours and esthetics may have changed during the bone/implant healing process.
The way we select and produce properly fitting abutments and crowns is crucial. Sometimes we must angle the implant to obtain proper anchorage in compromised bone; the angle of the implant could complicate the seating of the abutment for proper orientation with existing dentition.



After approximately 3 months and further healing, we can proceed to fabricate our definitive restoration, and at this stage, we take a normal crown impression. First, though, we place the metal coping back on the implant abutment (Figure 6). In order to be absolutely confident that the metalwork fits perfectly, we should use a little temporary cement to hold it in place.
The coping will usually remain inside the impression, and we could ask our technician to add metal tags to ensure that this happens. This method of impression taking allows the technician the possibility of providing a perfectly fitting crown.

Provisional restorations
There are two reasons why we should always make a provisional plastic crown. First, it allows the patient to have a chance to give feedback about the shape, size, color, phonetics, and esthetics of the crown. Second, it provides the soft and hard tissues the opportunity to heal.

Research tells us that we should be waiting between 2 and 3 months to make sure that there is no contraction or change of dimension of the coronal tissues. Once the provisional crown is in place (Figure 7), the soft tissue adapts to the crown’s surface (the surface itself should have been fabricated based on the indexing and impression information given to the laboratory).

Conclusion
Implant therapy success has increased over the years, as clinicians have learned to satisfy the demands of patients for esthetics, function, and cost. In addition to traditional implant protocols (such as careful planning and site preparation), improved manufacturing techniques for provisional and permanent restorations have helped us meet the needs of our patients.
Figures 8 and 9 show a successful result, having followed the above protocol.

The use of a metal coping in the second-stage impression can assist with getting the crown exactly right. Gradual loading of the implant can enhance maturation of both bone and gingival tissues before the final restorations are placed. Finally, a provisional restoration offers the patient a chance to give feedback.

These three suggestions should increase the reliability of your implant therapy.

 

Bio
Eddie Scher, BDS, LDS RCS, MFGDP, is a specialist in oral surgery and prosthodontics. He is a visiting professor of implantology at Temple University, Philadelphia, and is the chairman of the Editorial Advisory Board of Implant Dentistry Today.

Reference

Attard N, Barzilay I (2003) A modified impression technique for accurate registration of peri-implant soft tissues. J Can Dent Assoc 69:80-83.

Misch C (1995) Progressive bone loading. Dent Today 14:80-83.