Inside Dental Technology
May 2014, Volume 5, Issue 5
Published by AEGIS Communications
Simplifying Cement-Retained Implant Prosthesis Retrieval
Using a screw-access marking technique to improve predictability during implant removal
Todd R. Schoenbaum, DDS, FACD Yi-Yuan Chang, BS, MDC Perry R. Klokkevold, DDS, MS
There has been much debate about screw-retained versus cement-retained implant prostheses with regards to longevity, ease of use, costs, complexity, and esthetics.1-5 The primary advantages commonly cited in favor of screw-retained prostheses are that they are easier to retrieve and do not carry the risk of retaining cement subgingivally.6 In spite of this, cement-retained prostheses continue to be a popular choice for implant restorations due to their ability to compensate for some implant angulation issues, relative ease of fabrication, predictable costs—which are generally unaffected by fluctuations in the costs of alloys—occlusal esthetics,7 decreased bacterial leakage,8 increased mean porcelain fracture loads,9 and familiar restorative cementation protocols.
Inevitably, some cemented implant restorations will need to be removed at a future date. Common prosthetic reasons for removal include: fractured porcelain; fractured or loose abutment screws; hypo-occlusion; open interproximal contacts; excessive contours; retained cement leading to peri-implantitis; failed esthetics; and unacceptable recession of the peri-implant gingiva.4,10-14 In the authors’ experience, the removal of a cemented implant prosthesis is often performed by a clinician who was not part of the original treatment team and is, therefore, unaware of the precise location of the screw access. As such, removing the cemented implant prosthesis is highly unpredictable due to the lack of standardization of techniques and materials used in implant prosthetics and the inability to identify the materials used radiographically. This ultimately leads to difficulty and unpredictability in removal, increased treatment time, and added costs for the patient.
Current Removable Methods
The existing technique for the removal of cement implant restorations is to measure the distance between landmarks and the screw-access chambers based on periapical radiographs and to make rough estimates of the screw-access line of draw on the occlusal/palatal surface of the restoration.15 If available, photographs from, or immediately after, the surgical phase can be valuable in determining the access as well. Although this is a viable technique, it can be difficult to perform accurately and does not account for buccal-lingual angulation of the implant. Cone beam computed tomography (CBCT) scans may help to resolve this issue, but are generally avoided due to increased costs and radiation exposure compared to periapical radiographs. When single-unit prostheses (and larger fixed partial dentures) are removed this way, it often results in destruction of the existing restoration. The resulting access opening is often too large or irregular to allow the restoration to be used again if desired.16 The inaccuracy of this method can also lead to significant damage to the abutment, compromising its ability to be reused if desired (Figure 1). Although it is often the only choice for removal, this “measure and estimate” technique is stressful and time-consuming for the clinician.
An alternative technique using a silicone occlusal index was developed to mark screw-access holes on cemented implant prostheses in 2007.17 In this technique, the estimated location of the screw-access holes on the occlusal surface is marked with wax, and a silicone putty matrix is formed over the top. The limitations of this technique are that the screw-access hole indication is only an estimation based on gold calipers, and that the clinician performing the removal must be in possession of the matrix.
The Authors’ Technique
The purpose of the technique detailed in this article—a modification of a technique first described by Schwedhelm in 200618—is to resolve one of the major concerns and make the retrieval of cemented implant restorations easier and more predictable. With this minor modification, the retrieval of the cement-retained implant prostheses is no more difficult than that of screw-retained units, even when the clinician creating the access was not involved in the initial treatment.
During the fabrication of the restoration, the laboratory can perform a simple modification to the prosthesis to ensure that, if needed, the future retrieval will be nearly as simple as removing a screw-retained prosthesis. By making a small indentation on the occlusal surface of a cemented restoration and clearly marking it with an opaque white (or brown) tint, the access point into the screw chamber can be easily identified. The great advantage of this technique is that the screw-access marking can be easily identified by any astute clinician at a future date, even one with no involvement with the initial treatment, ensuring simplified access and removal.
The Screw-Access Marking Technique
The technique is carried out in the laboratory as follows:
Step 1 Place the definitive abutment on the implant analog on the laboratory cast.
Step 2 Mount the cast in a surveyor (Figure 2). This is done to accurately record the path of the screw-access chamber and will allow the occlusal surface to be precisely marked, indicating the location for the screw access. The surveyor pin (Figure 3) is aligned with the screw-access chamber on the cast, ensuring that it is correctly aligned in both mesial-distal and buccal-lingual angulation.
Step 3 Align the cast so that the surveyor pin passes directly down the screw access of the abutment (Figure 4).
Step 4 Replace the surveyor pin with a fine-tip sable brush (Figure 5).
Step 5 Place the definitive restoration on the abutment. Create a small concavity with a fine diamond bur at the point of contact to ensure that the opaque stain does not wear away under function (Figure 6).
Step 6 Lower the brush (pre-loaded with the opaquing porcelain) onto the surface of the restoration (Figure 7), allowing the opaque stain (white or brown) to flow into the concavity created by the bur. The brown stain (Figure 8) is more obvious than the white stain (Figure 9), although it may be esthetically objectionable under some circumstances.
Step 7 Fire the restoration according to the manufacturer’s instructions.
Step 8 Deliver the definitive abutment, and torque to manufacturer specifications (Figure 10 and Figure 11). Note in Figure 10 that the subgingival emergence of the abutment has been stained to better match the gingival shade of the restoration, thus guarding against esthetic complications secondary to future changes in the gingiva. In Figure 11, the screw-access chamber is cleaned with 2% chlorhexidine solution, dried and obturated with polyvinyl siloxane (PVS). Note that the custom abutment in Figure 11 has been designed with the margins at approximately 0.5 mm subgingivally to ensure that removal of the excess cement is easily performed with minimal chance of retaining cement subgingivally.
Discussion: Technique Advantages and Applications
This technique is a simple and convenient way to increase the ease with which cemented implant restorations can be removed if needed. The screw-access marking is subtle enough to be esthetically and functionally unobtrusive (Figure 12 and Figure 13). The additional time required to perform the technique is minimal and requires no special training for the ceramist. If widely implemented, this technique will remove one of the major difficulties with cement-retained restorations by making their retrieval significantly more predictable and efficient. The screw-access marking technique is best indicated for cemented posterior implant restorations, particularly when implant angulation is outside of the expected range. The screw-access marking method will also work on anterior units, as long as the angulation places the screw access palatal to the incisal edge. Due to esthetic concerns, this technique is not indicated for anterior cemented restorations with a line of draw that would result in the indicator marking being placed on the facial surfaces.
Removal of cemented implant restorations—with or without the screw-access marking—does still have a risk for porcelain fracture during the creation of the access. The risk of porcelain fracture can be minimized by the clinician using appropriate burs for the material being cut (ie, fine grit diamond burs), with light intermittent pressure and water coolant. When appropriate, the prosthesis–abutment complex can be reused and the access closed as would be done for any other screw-retained restoration. This technique is not applicable for solid abutments or “one-piece” implant designs.
By creating and staining a small marking on the occlusal surface of cement-retained implant restorations, the access point to the abutment screw can be clearly identified, ensuring that any future retrieval of the prosthesis is simple and predictable, thus resolving one of the primary difficulties with cement-retained implant restorations.
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About the authors
Todd R. Schoenbaum, DDS, FACD
Assistant Clinical Professor, Division of Restorative Dentistry, Director of Continuing Education,UCLA School of Dentistry
Los Angeles, CA
Yi-Yuan Chang, BS, MDC
Staff Research Associate, Division of Restorative Dentistry, UCLA School of Dentistry
Los Angeles, CA
Perry R. Klokkevold, DDS, MS
Associate Professor, Section of Periodontics, UCLA School of Dentistry
Los Angeles, CA