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Written by Gregory Gillespie, DDS Friday, 10 September 2010 17:43
Implant restorations can be simple in theory. However, it takes careful planning and forward thinking to avoid common mistakes made by many general practitioners. Establishing an efficient protocol for implant restorations will confirm more precisely the decisions made to ensure a predictable result.1 Before the final impression, the restoration process of every implant must address a few key steps: (1) uncovering the implant, (2) tissue former placement, (3) final abutment type, and (4) impression material selection. Making the correct decision for each step prior to the impression stage will facilitate an accurate and aesthetic implant restoration.
UNCOVERING THE IMPLANT
Deciding when to uncover the implant is determined primarily by the stability of the implant body at the time of placement. Typically, the more stable the implant at placement, the shorter the time that is required for osseointegration. The bone type and quality where the implant is placed also play a significant role in this decision. Procedures ranging from immediate temporization and immediate load,2-6 to one-stage (healing cap/tissue former placement) and 2-stage (completely submerged/healing cap placement) surgeries,7,8 have all been labeled as viable options following placement of the implant body.6 The practitioner should time the loading of each implant carefully, since a miscalculation could determine success or failure of the entire implant restoration. A traditional, safe, and predictable timetable to begin loading is between 4 and 6 months post-implant body placement. However, this could require upwards of 9 months if placed in a compromised site. In addition to rigid fixation, other factors should be evaluated at the time an implant is uncovered, including:
- Absence of crestal bone loss
- Absence of pain
- Adequate zone of keratinized gingival
- Sulcus depth
- Absence of inflammation
- Proper hard-and soft-tissue contour.9
The practitioner should only proceed with the implant restoration after successful evaluation of these factors at the uncovery stage, thereby laying the foundation for long-term success.
As a teaching model, an example case will be used to demonstrate the principles discussed in this article. This particular case was an immediate placement of the implant body following extraction, and was uncovered 6 months postoperatively using a diode laser (Odyssey [Ivoclar Vivadent]) (Figures 1 and 2).
PLACEMENT OF TISSUE FORMER
Before the implant surgery ever begins, it is important to sit down with the patient and discuss the aesthetic options available. Doing so enables the practitioner to decide early on where to go for future steps after uncovery. One crucial decision is to place a tissue former, or a temporary abutment and crown, to shape the tissue before a final impression. When aesthetics are not the primary concern, manufacturers offer a variety of tissue formers to meet the needs of the majority of cases. Height and flare plus the length of time the tissue former will be in place must be determined. The patient in this example case was not concerned about aesthetics; therefore, a traditional tissue former was adequate to shape the tissue before the final impression and restoration were completed (Figure 3). The patient had been wearing a treatment partial (a “flipper”) that was adjusted in order to continue use during the fabrication of the final prosthesis (Figure 4).
When aesthetics are paramount, it is essential to prepare the tissues before the final impression is captured. Temporary abutments and crowns are used to facilitate this process. This method gives the patient and practitioner time to evaluate the perceived final result and make changes necessary to improve the overall outcome. Composite can be added or removed from the temporary crown to adjust the shape and position of tissue, especially interproximally. “Black triangles” and uneven embrasures can be corrected over a period of a few short weeks when proper attention is given to the tissue. Once the ideal shape is achieved, the final impression can then be captured,10 leaving no room for guesswork on the laboratory side of the restoration process.
FINAL IMPLANT ABUTMENT
The final abutment type is determined by the occlusion, biologic width, and the aesthetic demands of the patient. When the occlusion is straightforward, the biologic width without impingement and aesthetics are not paramount; standard abutments are sufficient for the final restoration. Such abutments often double as the impression coping. Impressions for standard, or custom abutments can be captured by either a closed- or open-tray technique. This article will only address the closed-tray technique. Establishing and following a simple, standard protocol will consistently lead to an accurate impression (each manufacturer will vary slightly):
Figure 5. Impression coping completely seated.
Figure 6. X-ray verification of complete seating of impression coping.
|Figure 7. Difficult isolation due to multiple implants and moist conditions (note: caries diagnosed and treated on teeth Nos. 22 and 27).|| |
Figure 8. Impression with EXA’lence (GC America) capturing fine detail even in areas of difficult isolation.
Figure 9. Embedded tip and initial flow of low viscosity impression material (EXA’lence).
Figure 10. Impression with EXA’lence capturing in fine detail all necessary structures.
Figure 11. Impression coping combined with analog, correctly oriented in the impression.
1. X-Ray Verification: Double-check a positive seating of the abutment with a radiograph where the connection is easily discernable.
2. Torque Abutment: Because this impression coping is also the final abutment, the practitioner must torque the abutment to the manufacturer’s specifications before taking the final impression.
3. Snap-On Impression Cap: The impression cap will snap over the final abutment with simple finger pressure. The cap will pop off with the removal of the impression. Proper placement of this cap will ensure correct alignment of the analog and accurate fit of the restoration.
4. Final Impression: This will be a closed tray impression. Due to the importance of occlusion on implants, the author recommends using a full-arch tray for implant impressions.11 Sending a bite registration to the dental laboratory also reduces the introduction of errors when occlusion is addressed.
Custom abutments are the most universally used due to the variations in biologic width, occlusion, and aesthetic demands of patients. Biologic width should be addressed even before implant placement begins.12 Impingement of biologic width by the margin of the final restoration can lead to uncontrolled bone loss and movement of the free gingival margin. Consequently, the implant margin, or even the collar of the implant, could be exposed, leaving unsightly results. Careful planning of final margin placement can predictably avoid these errors. Natural dentition has a periodontal ligament space that absorbs occlusal loads placed thereon; implants are void of this element. Therefore, occlusion on implants should be lighter than on surrounding teeth. Custom abutments can be modified to allow for sufficient material placement to compensate for occlusal differences. If the aesthetic demands of the patient are high, zirconia abutments are available.
Implant impression copings, or “transfer abutments,” are used when a custom abutment is indicated. The final impression appointment should follow certain steps to capture accurate information necessary for the final restoration:1,13-16
1. X-Ray Verification: Double check a positive seating of the impression coping with a radiograph where the connection is easily discernable. This coping will not be torqued, because it is not the final abutment (Figures 5 and 6).
2. Final Impression: This will be a closed-tray impression. Again, due to the importance of occlusion on implants, the author recommends using a full-arch tray for implant impressions along with a bite registration. Certain manufacturers also have caps for impression copings that will come off in the impression to reduce errors in abutment alignment.
3. Abutment and Analog: To facilitate accurate alignment of the abutment and analog when the impression is poured, the clinician should attach the impression coping to the implant analog after removal from the mouth and insert the entire unit into the impression.
IMPRESSION MATERIAL SELECTION
Implant impressions, just like those for crown and bridge work, have certain elements that must be captured, or the accuracy of the final restoration is compromised. The 2 most crucial elements are the tissue contours and the connection of the abutment to the implant. As previously discussed, time and attention to the tissue results in beautiful restorations, but if the contoured tissue is not correctly represented, then the efforts are worthless. If the patient needs to be anesthetized, make sure it is communicated to the laboratory for compensation. More importantly, the practitioner should choose an impression material that accurately represents the tissue in every instance.17 Such material requires excellent flow, high tear strength, and dimensional stability, like a vinyl polysiloxane (VPS).18-22 A material that is hydrophilic with good wetability is also desirable, like a polyether. The author uses a vinyl polyethersiloxane (VPES) material (EXA’lence [GC America]) that combines traits of both a VPS and a polyether for implant impressions. A VPES is reported by the manufacturer to be intrinsically hydrophilic, flowing well even in difficult-to-isolate areas (Figures 7 and 8). Impression material that flows to capture the connection of the implant and abutment, and accurately represents the surrounding tissue, is key to beautiful implant restorations.
Implementing sound techniques and materials for the final impression will lead to predictable results. An implant impression protocol should be compromised of these standardized steps:23-25
1. Inject a low-viscosity (light-body) wash material directly into sulcus around the implant. Ensure that the tip remains imbedded within the wash material throughout the dispensing procedure (Figure 9).
2. Continue injection of low-viscosity material until the implant/abutment connection and all surrounding soft tissue is completely covered.
3. High-viscosity (heavy-body/tray) material should be syringed into a full-arch tray simultaneously with low-viscosity material placement.
4. Place the full-arch tray in mouth and seat completely. Ensure full seat of the impression tray before the working time expires.
5. After complete set, remove the impression and evaluate that all necessary structures are captured adequately. Retrieve the impression coping, combine it with the analog, reorient, and place it into the impression (Figures 10 and 11). The impression is now ready for laboratory pour-up and fabrication.
Implant restorations can be predictable and aesthetic when an effective protocol is established and followed. The decisions of uncovering, tissue former placement, final abutment choice, and impression material all influence the outcome of the final restoration. Following clear guidelines will improve communication with staff, laboratory, and patients, leading to more consistent aesthetic implant restorations.
- Lee H, So JS, Hochstedler JL, et al. The accuracy of implant impressions: a systematic review. J Prosthet Dent. 2008;100:285-291.
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- Adell R, Lekholm U, Rockler B, et al. A 15-year study of osseointegrated implants in the treatment of the edentulous jaw. Int J Oral Surg. 1981;10:387-416.
- van Steenberghe D, Lekholm U, Bolender C, et al. Applicability of osseointegrated oral implants in the rehabilitation of partial edentulism: a prospective multicenter study on 558 fixtures. Int J Oral Maxillofac Implants. 1990;5:272-281.
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- Ceyhan JA, Johnson GH, Lepe X. The effect of tray selection, viscosity of impression material, and sequence of pour on the accuracy of dies made from dual-arch impressions. J Prosthet Dent. 2003;90:143-149.
- Misch CE, Misch-Dietsh F. Pre-implant prosthodontics for the partially edentulous patient: (1) overall evaluation, (2) specific criteria, and (3) pretreatment prostheses. In: Misch CE. Contemporary Implant Dentistry. 3rd ed. St. Louis, MO: Mosby Elsevier; 2007:233-275.
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- Del’Acqua MA, Arioli-Filho JN, Compagnoni MA, et al. Accuracy of impression and pouring techniques for an implant-supported prosthesis. Int J Oral Maxillofac Implants. 2008;23:226-236.
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Disclosure: Dr. Gillespie has received financial and product support from GC America.
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