28: LABORATORY PROCEDURES AS THEY PERTAIN TO IMPLANT RECONSTRUCTION

CHAPTER 28 LABORATORY PROCEDURES AS THEY PERTAIN TO IMPLANT RECONSTRUCTION

There are many options in restoring a patient’s dentition (Figure 28-1). Some are more difficult than others, but the final results are usually the same. The author has been involved in implant dentistry for the last 16 years. The largest increase in the use of implants has been over the last few years. The author’s dental lab, Jesse & Frichtel (Pittsburgh, PA), is averaging 5000 implants per year. Implant restoration has become the most successful type of restoration for technicians and dentists. The most significant reasons for this success are the very low remake factor and the dramatic cosmetic change. Over time, certain procedures have proven to be the easiest and most predictable in restoring single and multiple unit implants. In this chapter the procedures for a partially edentulous to a fully edentulous restoration are discussed.

image Partially Edentulous Reconstruction

Prior to the patient’s appointment, provide the laboratory with the specialist’s surgical instructions via email or facsimile. These instructions note the implant size, location, and manufacturer. This information will be used to forward the correct impression posts. On average, it takes up to 5 days to send the necessary impression posts for the case. Also provide the laboratory with the dentist’s name and phone number, the patient’s name, and the date of the patient’s appointment.

Appointment 1 (Impression)

At the first appointment the master impression is taken either by the closed tray or open tray technique.

Option 1: Closed Tray

IMPORTANT: Please send the following items to the laboratory: impression, impression post, x-ray of the impression posts in position, opposing model, bite, and all necessary instructions. Also be sure to include the type, size, and manufacturer of the implant.

Option 2: Open Tray

At the Laboratory

Option 1: Cement-Retained Restorations

Upon receipt of the case, the laboratory technician connects the impression posts to the analog. Most implant laboratories stock these analogs. The soft tissue material is applied around the impression posts and the analog. Then the master cast is poured. This allows the technician to remove the soft tissue from the master cast to verify an accurate seat of the restoration.

Tip: This method is preferred because the soft tissue around the implant can be taken on and off without losing information that would be lost if this area were in stone.

There are multiple options when choosing the right abutment for each implant. Most of the larger implant companies have a broad spectrum of abutments. Different choices include cuff heights, flares, and angulations in various materials such as titanium, gold colored abutments, or ceramic colored abutments.

DESIGN 1: STOCK ABUTMENTS

The author has found over the years that about 90% of all implants used are so-called “stock abutments,” which are modified to achieve the look of a custom abutment. Most often, stock abutments need only a small amount of adjustment to fit the patient’s situation. Using stock abutments ultimately results in a tremendous savings for the dentist. The average U.S. cost difference between a stock abutment and a custom abutment is about $150. In most cases, these savings do not compromise the end result of the restorations. Therefore, if you see a custom abutment instead of a stock abutment in most of your cases, one of three things could be a possibility:

If a stock abutment is used, it is likely to be designed as follows. The facial margin and lingual margin should be set 1.5 mm and 0.5 mm below the gum line, respectively. By connecting the lingual to the facial, the abutment will get a scalloped margin. Also, the technician needs to place a flat side and/or groove on the abutment. Both of these two prep features seat the crown and prevent future loosening of the crown. The shoulder preparation on the abutment gives additional stability and thickness to the porcelain, ultimately creating more color and fewer fractures on the margin.

Tip: Depending on the tooth that has to be restored, an abutment that has a significantly wider flare than the implant itself should be used. This gives enough material to create the preparation design chosen by the dentist.

DESIGN 2: CUSTOM ABUTMENTS

Custom abutments are used mainly for compromised implant placement, very large restorations (to provide better alignment of the abutments), or to change the angle of the abutment.

In today’s dental lab custom abutments are designed with the help of a computer. Before this computer technology was available, custom abutments had to be waxed and casted. After that, the crown was manufactured on top of the abutment. This process required very skilled technicians with years of experience in implant dentistry. Because the dental laboratory industry faces the loss of one third of all its technicians in the next 4-6 years, finding these skilled technicians is very difficult.

Computer-aided design is a huge part of the future of the dental lab industry. Companies such as Atlantis (Waltham, MA) and Nobel Biocare (Göteborg, Sweden) have become great partners for the laboratories. Both companies use computer technology to fabricate abutments out of materials such as titanium or zirconium with little margin of error.

Atlantis

With the Atlantis system the models are sent to the Atlantis facility. There, technicians scan the model and design the abutment with the help of computer software. The abutments are made parallel to each other and then tapered in at a 2-degree angle (Figure 28-7). This level of precision is very difficult for a lab technician to achieve. Atlantis offers polished, unpolished, or gold-plated surface options. Atlantis also offers abutments that are compatible with a wide variety of implant manufacturers so it is very likely that they have the implant abutment needed. Each abutment is saved as a computer file and can be duplicated or reordered as necessary.

Option 2: Screw-Retained Restorations

If retrievability is the driving force behind the restoration, a screw-retained restoration is a great alternative option, especially with the new substructures scanned and milled out of zirconium. Because there is no longer a metal substructure, these restorations give both a perfect fit and great cosmetics. Before scanning technology was available, the technician had to wax up the design over a UCLA abutment, which was then invested and casted. After the cast was cooled, it was divested, sandblasted, and then seated by hand to the master model. Compared to the zirconium substructures, these metal-based restorations have a much higher margin of error (Figure 28-9).

Another major use of screw-retained restorations is in cases with less than 7 mm between the head of the implant and the opposing arch, where a conventional crown cannot be cemented. Normally, a restorative height of 2 mm is required for the crown, leaving only 5 mm for the abutment. These 5 mm do not give enough surface area to cement a crown. Therefore, the only option in these compromised cases is a screw-retained crown.

With a zirconium substructure a technician still designs the frame, but instead of casting it the technician scans the framework and an off-site milling machine mills the substructure. This guarantees a very accurate fit to the master model. Because of the precision and consistency of this computer-based system, the author strongly prefers zirconium over metal substructures for these types of restorations (Figure 28-10).

Jan 7, 2015 | Posted by in Implantology | Comments Off on 28: LABORATORY PROCEDURES AS THEY PERTAIN TO IMPLANT RECONSTRUCTION
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