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Written by Gregori M. Kurtzman, DDS Tuesday, 01 June 2010 00:00
When using a cementable crown, implant prosthetics require that an abutment head be placed between the implant fixture and crown. Several abutment head choices are available and can be divided into stock abutments and custom abutments.1 Stock abutments are prefabricated, provided by the manufacturer, and used as is or may require height alteration. Conversely, a custom abutment is customized for that particular site in the patient, requiring a margin to be placed corresponding to the gingival margin and changes to the angulation and height.2 There is confusion among practitioners as to what “is” a custom abutment.
Provisionalization of these abutments may be necessary when the final crown is not delivered at the time the abutment is placed.3 This may be because of a need to segmentally treat the arch or alter the aesthetics and occlusion before completing the treatment.
This article will address the means to create custom in-office abutments and long-term provisionals using a moldable light-cured resin material. The provisional technique presented reduces fabrication costs while still providing a high-quality and durable result.4
Custom abutments may be fabricated by several methods. Traditionally, UCLA abutments were used to fabricate custom abutments.5 This involved adding wax to the plastic chimney of the UCLA abutment, followed by casting. This gave the dental laboratory technician the ability to control the emergence profile and the abutment’s height and angulation. More recently, CAD/CAM technology has permitted custom abutments to be created virtually and then milled from solid titanium.6 This provides a stronger abutment for the cast UCLA-type abutments. A UCLA abutment is fabricated from a gold component with a cast portion, which has a lower melting temperature than the gold component. Retention of the 2 components is mechanical, and separation can occur under load if the cast portion is too thin at the gold component.
Figure 1. Stock abutments on the implant analogs on the soft-tissue model.
Figure 2. Abutment Preparation Burs (Kit 4475 [KOMET USA]) with gross reduction carbides on the left, and finishing carbides on the right of the kit.
In today’s economic environment, laboratory costs can play a factor in acceptance of treatment. A difference of a few hundred dollars may be the decision point for some patients. Additionally, this also plays a factor when dealing with PPO insurance plans that often set the allowable fee at, or below, a UCLA or CAD/CAM abutment laboratory fee as charged to the practitioner. With this in mind, in-office custom abutment fabrication can provide a high-quality abutment at a lower cost, allowing the clinician to work within the patient’s financial and/or insurance boundaries. As a comparison, an in-office custom milled abutment will typically have a cost range between $75 and $100 (depending on the manufacturer). Whereas, the laboratory fee for a UCLA abutment is typically in the $250 range and a CAD/CAM can be more than $325 per abutment.
Before the introduction of the UCLA abutment, the only abutment available was a stock abutment, which either the dental laboratory technician or practitioner would mill; this was done chairside, or on a model creating a customized abutment. Today, this is still offered in some circumstances, and manufacturers have developed what are termed “milling abutments” to allow this to be offered in more situations. A milling abutment is essentially a solid abutment that has bulk added to it. This allows one to change angles as needed when creating a custom abutment, something that may not be possible with a standard stock abutment (Figure 1). Until recently, executing this process in the office was a challenge, as the rotary instruments we had at our disposal to fit our high-speed handpieces did not efficiently cut titanium. Friction-grip carbides in a titanium abutment adjustment kit (Figure 2). Abutments (kit 4475 [KOMET USA]) are now available specifically for shaping (black ring, golden shank) and finishing (red ring) titanium. This can be accomplished either intraorally, or extraorally. The author recommends that, unless minor customization is required, it is better to customize the abutments extraorally. This article will now address the steps for extraoral abutment customization using milling abutments.
IN-OFFICE EXTRAORAL CUSTOM ABUTMENT FABRICATION
When significant abutment customization is needed, it is easier to create the abutment extraorally versus attempting to do so intraorally. This is especially true if a milling abutment is going to be used, as these require more metal be removed. The process starts with an implant impression and fabrication of a soft-tissue model. To fabricate a soft-tissue model in the office, place the analog on the impression head within the impression and inject Soft-Tissue Moulage (Kerr Lab) 3 mm around the analog’s crestal and allow to set. A stone model is then poured and models are articulated (Figure 3).
Figure 3. Occlusal view of the stock titanium abutments showing nonparallelism.
Figure 4. Anterior view of the stock abutments on the soft-tissue model showing nonparallelism.
Figure 5. The abutments are reduced using the cross-cut carbides to indicate the gingival margin and parallelism.
Figure 6. Soft-tissue removed, casts occluded to check occlusal reduction and margins have been refined.
Figure 7. Occlusal view showing parallelism of the abutments with circumferential margins.
Figure 8. View of the abutments showing parallelism.
|Figure 9. Occluded view of the finished custom abutments.||
Figure 10. Buccal view of the finished abutment heads.
Figure 11. Lingual view of the finished abutment heads.
Figure 12. Occlusal view of the finished abutment heads showing circumferential margins.
Figure 13. Intraoral buccal view of the custom abutments.
Figure 14. Intraoral lingual view of the custom abutments.
The milling abutment is placed into the soft-tissue model. Then the fixation screw is tightened to “finger tightness” so that the milling vibration does not cause the abutment to move on the model (Figures 4 to 6). The gross-reduction carbide (H847KRG.FG.018 [KOMET USA]) is used to reduce the occlusal surface. This is done so that the buccal and lingual edge of the abutment, which will become the cusp tips of the custom abutment, have sufficient clearance (2 mm is recommended), allowing the restoration be placed over it (Figure 7). When occlusal clearance is achieved, the gross-reduction football carbide (H379G.FG.023 [KOMET USA]) is then used to create buccal and lingual inclines on the occlusal surface (Figure 8). This is necessary so that the laboratory can create anatomy in the final crown and provide sufficient clearance.
The tapered gross-reduction carbides (either the H856G.FG in 016/018 or H847KRG.FG in 016/018 [KOMET USA]) are used to reduce the interproximal to the level of the soft-tissue margin (Figure 9). This is also performed on the buccal and lingual surfaces (Figure 10). It is not necessary to perform a full reduction on these surfaces during this step, but it helps when you mark where the gingival margin is on the cast. The abutment(s) are marked with a permanent marker, indicating the buccal, and then the abutment is removed from the model. The soft-tissue material is removed from the cast, and the abutment is returned to the model, making sure it is positioned correctly with the buccal mark. The gross-reduction carbides are 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 that it can be rotated in any direction and viewed from any angle so you can create the ideal preparation. Convergence of the preparation walls at approximately 6° should be the objective, giving the crown maximum retention to the abutment.
The gross reduction carbides provide a rough surface, which will 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 finishing performed. Matching the gross-reduction carbides in the kit are titanium finishing carbides (H375R.FG.016/018, H336.FG.016/018, and H379.FG.023 [KOMET USA]). These are used to remove the rough marks on the titanium surface (Figure 11).
The abutments are now ready for insertion into the patient (Figures 12 to 14). Provisional crowns may be fabricated on the abutments on the soft-tissue model, before the patient visit or on the soft-tissue model with the custom abutments on them. Both can be sent to the laboratory to have the final crowns created and delivered during the same appointment as the abutments. The impression heads and analog can be recycled, using them for subsequent patients after proper sterilization.
FABRICATION OF LONG-TERM IMPLANT PROVISIONALS
Long-term provisionalization may be required during ongoing dental treatment for various reasons.7 This becomes especially true when implants are part of the treatment plan.8 The implant fixtures may receive provisionalization shortly after placement and be worn during the healing phase, allowing integration before final restorations are placed. Alternatively, following uncovering of the fixtures, provisionals may be utilized to mold the soft-tissue contours and develop the emergence profile of the prosthetics. With these aspects in mind, the provisional material needs to be durable enough to be utilized long-term and not succumb to the occlusal loads placed upon it.
A valuable material solution to this problem is a shape-stable, visible light-cured (VLC) resin composite material (Radica [DENTSPLY Prosthetics]). The objective was to satisfy the demand from both dental technicians and practitioners for a more durable provisional resin. Radica is a unique provisional material that is based on an oligomeric resin composition, making it moldable, and once the shape has been developed it is light-cured to harden the resin. Glass filler materials render this composite highly wear resistant9 and durable.10 The resin is provided in syringes in both dentin and enamel shades keyed to the VITA shade guide (Vident). This permits the dental technician to layer in different shades and translucencies in the material as it is shaped, before curing, and provides more natural aesthetics to the provisional. This material is typically processed using a vinyl polysiloxane matrix, on a lab-prepared model, as recommended by the manufacturer or described in the literature.11 However, the technique described below is, in the author’s opinion, more expeditious while yielding aesthetic results.
Figure 15. Rubber Sep (George Taub Products & Fusion) is applied to the customized abutments to act as a spacer for the luting material and to prevent the resin provisional from locking to the custom abutment during fabrication.
Figure 16. The provisional resin composite material (Radica [DENTSPLY Prosthetics]), in a dentin shade, is warmed and expressed over the custom abutments.
|Figure 17. The provisional resin, in an enamel shade, is warmed and expressed over the uncured dentin shade material.||Figure 18. The casts are articulated to create an impression of the opposing teeth in the warm resin.|
Figure 19. A scalpel is used to demarcate the 2 units of the provisional.
Figure 20. After the resin has reached room temperature, the provisional is removed from the abutments and the uncured resin is carved.
To provide a spacer on the custom abutments and allow removal of the provisionals from the abutments, Rubber Sep (George Taub Products & Fusion) is brushed onto the abutments and allowed to air dry (Figure 15). It is recommended that several coats be applied to ensure ease of removal of the processed provisionals from the abutments. Syringes in the selected dentin and enamel shades are placed into the warming unit and allowed to become flowable.
The selected dentin shade is expressed over the abutments and allowed to cool to room temperature (Figure 16). At room temperature the resin composite becomes “wax-like” in its handling. Some anatomical shaping can be performed at this point, using a clean composite or wax carving instrument. The selected enamel shade is then expressed from the warmed syringe over the Radica already on the abutments (Figure 17). Before the enamel shaded Radica has cooled, the casts are articulated to develop the occlusal contact points based on the opposing dentition (Figure 18). A scalpel is used to demarcate the division of the units using a mark on the cast as a guide (Figure 19). As the resin is wax-like in handling at this phase, it can be easily carved and shaped.
The provisionals may be removed from the abutments, and the Rubber Sep is peeled from inside the Radica resin. A scalpel is then used to carve the gingival embrasure area between the units and develop the appearance of individual teeth (Figure 20). Should additional material be needed, it can be added from a warm syringe and the material blended with an electric spatula (Figure 21).
Should a void be present in the uncured resin, the electric spatula is utilized to add material or flow surrounding material into the area. The spatula is also utilized to assist in blending the dentin and enamel shades to develop more natural effects. It is not advised to use an instrument heated in a flame, as this will introduce contaminants (soot) into the material before processing.
The anatomy is created and adjusted, and the provisionals are ready for processing (Figure 22). Radica VLC sealer is brushed over the finished provisional resin prior to processing (Figure 23). Sealer application eliminates any oxygen inhibited layer on the surface of the provisional and provides a glazed final surface. Should supplemental staining be desired, Radica stain powders are blended with sealer and brushed onto the surface. As these stains are very intense in color saturation, only a few particles are necessary to tint the sealer.
Figure 21. Additional resin may be added to the uncured provisional using an electric spatula.
Figure 22. Basic anatomy and form for the provisionals is created in the uncured resin.
Figure 23. Sealing resin is painted over the uncured provisional to eliminate an oxygen inhibited layer following curing.
Figure 24. The finished provisionals after curing, finalization of the anatomy and polishing.
Figure 25. Finished provisional crowns in articulation on the casts.
Figure 26. Intraoral view of the Radica provisionals.
The Radica provisional is placed into an appropriate light-curing unit (Triad 2000, Enterra, or Eclipse light-cure units [DENTSPLY Prosthetics]) and polymerization is completed.
Following removal of the processed provisional, additional shaping may be performed with diamonds (DENTSPLY Caulk) and a Sepaflex diamond disk (DENTSPLY Prosthetics) to achieve the desired final form. Polishing is similar to composite resin and can be accomplished with finishing disks (Fini [Pentron Clinical Technologies]) and soft felt wheels (DENTSPLY Prosthetics). Following polishing, another coat of the Radica sealer is applied and light-cured. The restoration is now ready for delivery with the custom abutments (Figures 24 to 26).
In-office custom implant abutments can be easily and cost effectively fabricated using the Abutment Preparation Burs Kit 4475. This allows the practitioner to provide implant-fixed prosthetics within the financial means of patients and within the boundaries of their insurance plans. Although not a solution to all implant-fixed prosthetic situations, this can be used in many cases when drastic changes in angulation are not required; specifically, in the posterior regions.
When the final prosthetics cannot be delivered at the time the implant abutments are being placed, long-term provisionalization may be indicated. Fabrication of these long-term provisionals, whether in-office or by a laboratory, will minimize chairside time and provide a durable alternative to other commonly used provisional materials. Radica allows the fabrication of these implant provisionals with the need for minimal equipment, providing durable, multishaded restorations that rival the final prosthetics aesthetically.
- Reid PE, Burke TM. Customized implant abutments: technical notes. Implant Dent. 1994;3:243-246.
- Lima Verde MA, Morgano SM, Hashem A. Technique to restore unfavorably inclined implants. J Prosthet Dent. 1994;71:359-363.
- Lodding DW. Long-term esthetic provisional restorations in dentistry. Curr Opin Cosmet Dent. 1997;4:16-21.
- Ewoldsen N, Sundar V, Bennett W, et al. Clinical evaluation of a visible light-cured indirect composite for long-term provisionalization. J Clin Dent. 2008;19:37-41.
- Chiche GJ, Pinault A. Considerations for fabrication of implant-supported posterior restorations. Int J Prosthodont. 1991;4:37-44.
- Marchack CB, Yamashita T. Fabrication of a digitally scanned, custom-shaped abutment: a clinical report. J Prosthet Dent. 2001;85:113-115.
- Burns DR, Beck DA, Nelson SK; Committee on Research in Fixed Prosthodontics of the Academy of Fixed Prosthodontics. A review of selected dental literature on contemporary provisional fixed prosthodontic treatment: report of the Committee on Research in Fixed Prosthodontics of the Academy of Fixed Prosthodontics. J Prosthet Dent. 2003;90:474-497.
- Castellon P, Casadaban M, Block MS. Techniques to facilitate provisionalization of implant restorations. J Oral Maxillofac Surg. 2005;63(9 suppl 2):72-79.
- Jain V, Platt JA, Moore BK, et al. In vitro wear of new indirect resin composites. Oper Dent. 2009;34:423-428.
- Lang R, Rosentritt M, Handel G. Fracture resistance of reinforced provisional crown & bridge restoration materials. J Dent Res 86. 2006;(Spec Iss B):Abstract No. 1973 (dentalresearch.org).
- Lin WS, Ercoli C,: A technique for indirect fabrication of an implant-supported, screw-retained, fixed provisional restoration in the esthetic zone. J Prosthet Dent. 2009;102(6):393-6.
Disclosure: Dr. Kurtzman has received honoraria in the past from the following companies whose products are mentioned in this article: DENTSPLY, KOMET USA, and Pentron.
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