The key to a successful case is careful and concise pre-treatment case planning

Which abutment, when?

An important part of the laboratory case planning is abutment selection. Implant depth

and angulation are carefully measured and the appropriate abutment is chosen and ordered. We are currently working with several implant companies and are able to work with other systems as well.

Although there seems to be a large selection of abutments on the market, most systems offer the same basic choices:

*Straight Titanium (A & B)

*Pre-Angled Titanium (D)

*Custom Cast-To Abutment (C & E)

* Some type of ceramic abutment (F)

*Direct-Impress type abutments such as Noble Biocare's Easy Abutment and Straumann's Solid abutment (see section 4, figures 2 & 3).

Ceramic abutments, when available, are the best choice when doing 

all-ceramic restorations.

Custom Cast-To Abutments are called for in situations where angulation correction over 20° is needed, in anterior porcelain-to metal restorations where a titanium silver-colored abutment collar could turn the soft tissue gray.  Also in splinted restorations where multi-angled corrections for parallelism is required, as well as in a one-piece screw-retained restorations and overdenture bar cases.

Titanium abutments are ideal for use in posterior restorations when angulation is less than 20°, fixture is not more than 2mm more subgingival than the tallest available collar.

Direct-Impress type abutments such as Noble Biocare's Easy Abutment are best used in the posterior when the has been well-placed in the center of the tooth site, angulation is not a problem (this can be checked by screwing a long guide-pin screw into the implant...this will provide a clear visual of the angulation) and the fixture head is not more than 2mm more subgingival than the tallest available collar. These abutments are usually not a good choice for anterior restorations.

SECTION 4 - IMPRESSION TECHNIQUES

If you decide to let the laboratory evaluate your case for abutment selection, then a fixture level impression is required.  Impression copings are screwed to the fixture, the fit of the component is verified with a radiograph, and an impression is taken.

            There are two types of basic metal impression copings: "open tray" (pick-up) and "closed tray" (transfer).

            A hole in the tray for screw access is required with an open tray impression coping (see figure 1, inset B). The coping is not removed from the impression until the case is completed and returned to the dentist.  This technique is recommended for splinted restorations as accuracy is slightly better than with a closed tray.

            The closed tray impression coping (see figure 1, inset A) is more popular because it is simple.  Screw it onto the fixture, verify the component’s fit to the fixture with a radiograph, and take an impression.  The downside to this technique is that the coping must be placed back in the impression attached to an analog; therefore the accuracy is slightly less than that of the open tray technique.

            For either technique, it is important to use a heavy body impression material to hold the coping firmly for an accurate model.  Also, use full-arch or quadrant impression trays.  Tri-bite trays are not appropriate when using implant impression components of any kind as the opposing can interfere with the component, causing an inaccurate bite registration and possible distortion of the impression.

            Some systems (Straumann) offer a two-piece plastic closed tray impression coping for fixture level impressions.

            When using Straumann solid abutments or similar abutment from another system it is important to use the impression components as they were designed to be used.  The abutment should be torqued down and left in the mouth to be temporized, or "capped".  The Straumann system incorporates a two-piece plastic coping (shown).  The white coping snaps on the implant shoulder and the color-coded cylinder registers the position of the abutment.  If the abutment is modified, then only the white "basket" is snapped on and injected with impression material to capture the shape of the modified abutment.  Either technique is followed by a standard pick-up impression.

            It can sometimes be difficult to obtain a good impression of implant abutment margins, so one can only benefit by using snap-on impression copings for these abutments.       

These systems, though utilizing basically the same principle, have slight variations in their specific components or instructions. So it is important to familiarize yourself with the methods being used.