How to customize implant abutments

When providing implant prosthetics and using a cementable crown, choices for the abutment head that will connect the implant fixture to the crown include stock abutments-a prefabricated abutment provided by the implant manufacturer used as is or perhaps with an alteration to its height-and custom abutments that are fabricated for that particular site.

A custom abutment can be fabricated in several methods, such as a UCLA-type abutment that allows the laboratory to control the emergence profile, the abutment height and angulation. In recent years, CAD/CAM technology has permitted custom abutments to be milled from solid titanium, providing a stronger abutment without the possibility of abutment failure that may be seen with cast UCLA abutments.

Before the introduction of the UCLA or CAD/CAM abutment, the only abutment available was a stock abutment, which either the laboratory or practitioner would mill chairside or on a model to customize to the patient. Today, this is still offered in some situations, and manufacturers have developed “milling abutments,” which essentially are a solid abutment that has bulk to it, allowing more metal to be milled from it and permitting the practitioner to change angles needed when creating a custom abutment that may not be possible with a standard stock abutment (Fig. 1).

Until recently, this in-office process was a challenge as the rotary instruments that fit standard highspeed handpieces did not efficiently cut titanium. KOMET USA introduced friction-grip carbides specifically for shaping (black ring) and finishing (red ring) titanium either intraorally or extraorally. When significant abutment customization is needed, it is easier to create the abutment extraorally, especially if a milling abutment is going to be used as these require more mass of metal to be removed.

In-office extraoral protocol

The process begins with an implant impression and fabrication of a soft-tissue model. Softissue Moulage (Kerr Lab) was injected around the crestal 3 mm of the analog and allowed to set after placing the analog on the impression head within the impression (Fig. 2).

A stone model was then poured, and models were articulated on a simple articulator (Fig. 3). A simple articulator may be used because occlusion of a final restoration is not being fabricated. The sole purpose of the articulation is to allow adjustment of the height of the abutment in relation to the opposing tooth, permitting adequate reduction to accommodate a cemented crown upon the abutment.

The milling abutment was placed into the soft-tissue model, and the fixation screw was tightened to finger tightness so that the vibration from the milling did not cause the abutment to move on the model (Fig. 4).

The gross-reduction shaping carbide (H847KRG.018) was used to reduce the occlusal surface so the buccal and lingual edge of the abutment, what will become the cusp tips of the custom abutment, have sufficient clearance (2 mm is recommended), allowing the restoration be placed over it (Fig. 5).

When occlusal clearance was achieved, the gross-reduction football-shaped carbide (H379G.023) was used to create buccal and lingual inclines on the occlusal surface. This is necessary so the laboratory can create anatomy in the final crown and have sufficient clearance (Fig. 6) plus allow for uniform thickness of the overlaying restorative materials of the crown.

Tapered gross-reduction shaping carbides (H856G.016/018 or H847KRG.016/018) were used to reduce the interproximal to the level of the soft-tissue margin (Fig. 7) as well as on the buccal and lingual surfaces (Fig. 8). It was not necessary to perform a full reduction of these surfaces at this step, but just to mark where the gingival margin was on the cast.
For orientation purposes, the abutment was marked with a marker to indicate the buccal, and then the abutment was removed from the model.

The soft-tissue material was removed from the cast, and the abutment was returned to the model, making sure to position it correctly with the buccal mark in the correct orientation.
The gross-reduction shaping carbides were then used to reduce the circumferential surfaces positioning the final margin (approximately 0.5 mm apical to the mark created when the soft-tissue material was present). The benefit of working on the model is it can be rotated in any direction and viewed from any angle to create the ideal preparation (Fig. 9). Convergence of the preparation walls (approximately 6°) should be the objective to give the crown maximum retention to the abutment.

The result of the gross-reduction carbides was a rough surface that would be difficult to capture in an impression because of surface tension between the impression material and the abutment’s surface. For this reason, the surface needs to have some polishing performed. Matching the gross reduction shaping carbides in the KOMET USA APB (Abutment Preparation Burs) Kit 4475, are titanium finishing carbides (H375R.016/018, H336.016/018 and H379.023). These were used in a similar manner to the shaping instruments by removing the rough marks on the titanium surface (Fig. 10) .
The abutments were ready for insertion into the patient (Fig. 11). Provisional crowns can be fabricated on the abutments on the soft-tissue model, before the patient’s visit, or the soft-tissue model with the custom abutments can be sent to the laboratory to have the final crowns created and delivered at the same appointment as the abutments. The impression heads and analog can be recycled, using them for subsequent patients after appropriate sterilization.

Conclusion

In-office custom implant abutments can be easily and cost-effectively fabricated using the KOMET USA APB Kit 4475. This can allow the practitioner to provide implant-fixed prosthetics within the patient’s financial means and within the boundaries of his or her insurance plan. This is not the solution to all implant-fixed prosthetic situations; however, it can be used in many cases when drastic changes in angulation are not required, specifically, in the posterior.

Dr. Kurtzman is in private general practice in Silver Spring, Md., and is a former Assistant Clinical Professor at the University of Maryland, Department of Endodontics, Prosthetics and Operative Dentistry. He can be contacted at dr_kurtzman@maryland-implants.com.