In this monthly feature, Dr. Gordon Christensen addresses the most frequently asked questions from Dental Economics® readers. If you would like to submit a question to Dr. Christensen, please send an e-mail to [email protected].
Q The advertising on abutments for dental implants contains many ads on use of zirconium oxide abutments. Are ceramic abutments as strong and acceptable as metal abutments? When should they be used? Why should they be used? I am confused!A There are many questions that need to be answered about abutments connected to root-form implants. Although some of the implant companies have developed relatively easy-to-use metal abutments, many have engineered large, cumbersome abutments that need significant revision before they can be used. Nevertheless, metal abutments have served well over many years.Metal abutments are strong and dentists seldom have problems with them. Ceramic abutments have also had a successful service record and, in spite of their questioned strength, they are also very strong. Regardless of whether the abutment is ceramic or metal, the most common challenge is loosening of the screw holding the abutment, resulting in the crown or bridge being loosened from the implant. If the prosthesis has been cemented to the abutment with strong final cement, removal and destruction of the crown is necessary to gain access to the screw and to tighten it to hold the abutment to the implant. I often use provisional cement to attach the prosthesis to the abutment. In the event the screw comes loose, the prosthesis can be removed, the screw tightened, and the prosthesis recemented. Whether the abutment is ceramic or metal, the abutments still have the problem I have described.
Why use a ceramic abutment? In my opinion, there are some legitimate reasons, but also some foolish suggestions. Let’s assume that the crown or fixed prosthesis to be placed over the abutment is a relatively translucent ceramic restoration. Some examples are IPS Empress, LavaTM, Cercon®, or other popular restorations. All of the example restorations are at least somewhat translucent, and if a metal abutment is used under them, the metal imparts a gray appearance to the translucent restoration. Therefore, use of a ceramic abutment to support a translucent all-ceramic restoration is a legitimate use of the ceramic abutment.
However, let’s assume that a porcelain-fused-to-metal (PFM) crown or bridge is being used as the final restoration. In this example, the restoration is visually opaque, and the color of the abutment cannot show through the restoration. Would a ceramic abutment add any advantage when cementing a PFM restoration over the abutment? Some say yes, using the following premise. They defend the ceramic abutment by contending that it allows the portion of the abutment from the implant to the restoration margin to have a relatively tooth-colored appearance, thereby avoiding the show of gray color in the gingival tissues apical to the restoration margin. This contention is correct if the restoration is not made to extend entirely to the implant.
However, if a simple laboratory technique is used, there is no need to make a ceramic abutment in this situation. The technique — using a so-called UCLA abutment — makes the PFM restoration extend entirely over the abutment to the implant body, without any metal showing between the prosthesis and the implant body. Obviously, in this example, it would be foolish to use a ceramic abutment.
In summary, when a translucent restoration is planned to be seated on an implant abutment, a ceramic abutment makes sense. Be prepared to pay a significant fee for it from most laboratories. When a PFM restoration is planned to be placed over the abutment, there is no reason to have a ceramic abutment if the PFM restoration is extended entirely to the implant body, and if the PFM restoration has ceramic fired over it, extending to the implant body.
For detailed information on this subject, please see our newest DVD, V2326, “Successful Fixed and Removable Restorations for Dental Implants.” Contact Practical Clinical Courses at (800) 223-6569, or visit our Web site at www.pccdental.com.
Q I have had great success placing mini implants for mandibular complete dentures. There seems to be a controversy about whether or not mini implants should be placed in the maxillary arch and, if so, how many should be placed. What do you recommend?A I have been amazed at the success of the so-called “mini” or small-diameter implant (SDI) used as long-term support for dental restorations! These implants, made of the same metals as conventional diameter implants, are from 1.8 to nearly 3.0 mm in diameter. The original 1976 FDA approval of root-form implants covered implants with a diameter over 3.0 mm. FDA approval for small-diameter implants of less than 3.0 mm was first granted in 1999 to the IMTEC® company. The company’s so-called “mini” implant is now very popular. Dentatus AtlasTM implants were approved for long-term use in 2004. Both companies are finding success and eager acceptance by practitioners and patients, especially for implant-supported and implant-retained complete dentures. The minimally invasive placement procedure, lower cost, and immediate loading of SDIs has made this concept catch on rapidly in the profession.Research support on long-term use of small SDIs is building in the literature, and it is positive. Much more research is needed to validate the best techniques for these implants, both from a surgical and a prosthodontic standpoint. Most practitioners using SDIs for retention and support of removable complete dentures are using at least two implants in each of the canine areas for a total of four SDIs. Since these implants are loaded immediately, placement of four implants does not allow rotation of the implants while they are integrating with the bone over several months. I have personally placed many SDIs with success in edentulous mandibles and maxillas, as well as for removable partial dentures and fixed partial dentures. If the bone is dense and in sufficient quantity to support the SDIs, I feel from my experience that four implants are an acceptable number.
What is a sufficient quantity of bone for placement of an SDI? From my clinical experience, the following amount of bone is necessary: Four millimeters or more of bone measuring from the facial to the lingual of the ridge, and a minimum of about 10 mm of bone from the crest of the ridge to the most apical potential placement for the implant. If less bone is present, placement of more than four SDIs in the edentulous patient is probably indicated. Although I have successfully placed SDIs in 3 mm of bone from facial to lingual, this is a tenuous and difficult procedure.
See our new video (V2317 “Mini Implants for Your Practice) to assist you with those patients needing small diameter implants. For more information, contact Practical Clinical Courses at (800) 223-6569, or visit our Web site at www.pccdental.com.
Dr. Christensen is a practicing prosthodontist in Provo, Utah, and Dean of the Scottsdale Center for Dentistry. He is the founder and director of Practical Clinical Courses, an international continuing-education organization initiated in 1981 for dental professionals. Dr. Christensen is a co-founder (with his wife, Rella) and senior consultant of Clinical Research Associates which, since 1976, has conducted research in all areas of dentistry and publishes ists findings to the dental profession in the well-known "CRA Newsletter." Dr. Christensen has educational videos and hands-on courses on the above topics available through Practical Clinical Courses. Call (800) 223-6569 or (801) 226-6569.
