Response to Albrektsson T and Sennerby L: Direct bone anchorage and experimental considerations of the concept of osseointegration. International Journal of Prosthodontics 1990; Vol. 3, No. 1.
LETTER TO THE EDITOR
International Journal of Prosthodontics 1990, Vol. 3, No. 6, Pages 583-584
Readers are invited to comment on editorials, articles, and all topics of current interest to the specialty of prosthodontics. Letters should be directed to Dr Jack D Preston, editor-in-chief, and should be typed double-spaced and signed. Letters are published in the condition in which they are received, with the exception that lengthy letters may be edited to fit space requirements or to remove extraneous text. This column will not carry continuous debates on the merits of specific materials or treatment methods.
Subject: Article by Tomas Albrektsson and Lars Sennerby, Volume 3, No. 1, Jan/Feb 1990: "Direct Bone Anchorage of Oral Implants: Clinical and Experimental Considerations of the Concept of Osseointegration." The authors reach a number of conclusions in this article that are not supported by the published articles they reference or a number of articles they conveniently fail to reference.
Osseointegration or Bone Loss as Criteria of Success. Albrektsson, in an earlier article (JOMI, Vol. 1, No 1, 1986), stated what is clearly the legacy of the Brånemark research: "The Brånemark results...clearly underscore the basic concept of osseointegration as being the major, if not the exclusive reason for a successful long-term dental implant attachment."
Albrektsson and Sennerby then attempt to negate the clinical significance of this fact by applying a set of criteria proposed by Albrektsson, Zarb, et al. (JOMI 1986;1:11-25) that included: "That vertical bone loss be less than 0.2 mm annually following the implant’s first year of service."
Based on this parameter, the authors conclude: "For osseointegrated implants, it seems clear that the Brånemark fixtures meet the success criteria...Core-Vent Implants do not meet these criteria for success, and it is uncertain if the IMZ and the Calcitek hydroxyapatite-coated implants will pass..."
A review of the literature clearly demonstrates that the Brånemark Implant success rates were based on fixture stability and fixture survival, not bone loss.
1. Adell: 17 Year Study on 4,100 Brånemark Implants (J Prosthet Dent 1983;50(2):252): The anchorage function or the fixture survival rate was defined as the number of stable, prosthesis supporting, osseointegrated fixture in relation to the total number of fixtures installed.
2. Brånemark, Zarb, Albrektsson (Eds.): Tissue-Integrated Prostheses (Text, Quintessence Publ 1985): "Fixture anchorage function" and "fixture survival rate" were the criteria for success." Page 175: "The statistical basis for ascertaining the long-term prognosis of a fixture-supported prosthesis depends on two factors: (1) continuous bridge stability...(2) fixture anchorage function, which is the percentage of clinically stable and/or radiographically osseointegrated fixtures."
3. Engquist et al.: A Retrospective Multicenter Evaluation of Osseointegrated Implant Supporting Overdentures. Eleven Swedish teams documented 30% failure in Maxilla, 6% in Mandible (JOMI 1988;3(2)), Page 132: "An implant was regarded successful if the fixture had been immobile throughout the observation period and the radiographs showed no radiolucency around the fixture at the final registration." Crestal bone loss was never measured in this study: "It was not possible to register marginal bone loss with acceptable accuracy since the radiographic technique was not standardized."
Use of Bone Height Measurement as Criteria of Success. The invalidity of the Albrektsson Zarb parameter (JOMI 1986, JPD 1989) as a measurement of success becomes obvious when one considers its ramifications. For example, if an 18 mm long implant lost 1 mm of bone from time of insertion to one year following attachment of the prosthesis, and an additional 0.3 mm of bone during the implant’s second year in function, the implant would have to be called a failure based on this criteria even though it still had 16. 7 mm of its length osseointegrated. It would be ludicrous to suggest that his implant, which was supporting the prosthesis without pain or discomfort, be removed just because of applying Albrektsson and Zarb’s proposed criteria of success. If, during each of the next two years in service, the implant only lost 0.1 mm of bone height for an average of 0.13 mm for the three years following the first year of service, the implant that was a failure at two years would be a success at four years, as judged by this criteria. Success rates would never be able to be established using this criteria as they could fluctuate from year to year.
Albrektsson and Sennerby would have the profession believe that this "stricter criteria" was used to judge success or failure with Brånemark Implants so that other competitors of Nobelpharma would have to meet this contrived test also. Multicenter studies of Albrektsson et al. (J Prosthet Dent 1988;59:287-296) are referenced in this article to support this misconception but, from review of these studies, it is apparent that bone height measurements were not taken on every implant and that fixture stability or osseointegration was the overriding parameter in determining clinical success –– as it should be.
Selective use of References. Albrektsson and Sennerby state: "To date, the present authors are unaware of any scientifically controlled studies supporting the verbal claims of excellent success rates of the Core-Vent and IMZ, two frequently used osseointegrated oral implant systems."
They failed to reference an article by Kirsh and Ackerman (Dent Clin North Am, October, 1989) on a 10- year follow-up of 2,284 titanium plasma-sprayed IMZ implants, which Albrektsson was certainly aware of, as he had referenced it in a previous article. Furthermore, in criticism of Core Vent implants, the authors relied on an unpublished abstract of Moy with 100 Core-Vent implants that demonstrated 84% to 87% success rates (Maxilla-Mandible). But then, by using his own subjective criteria, Moy had predicted the final success rates would only be 58% to 68%. Albrektsson and Sennerby referenced Moy’s projected failure rates, which have never been confirmed in a subsequent abstract or published article, and incorrectly referred to these unsubstantiated, projected rates as "actual success rate." Albrektsson and Sennerby, while referencing the unpublished abstract of Moy from a 1987 meeting, failed to mention three other unpublished abstracts presented at the same meeting: Lubar with 100 consecutively placed Core Vent Implants, all over 4 years, reported 95% success, Zosky with 200 Core-Vent’s reported 93% success (96% in the Maxilla alone), and English, who conducted a survey of 672 Core-Vent users, reported on 15,150 implants with 93% success.
Malmqvist and Sennerby Study of 47 Core-Vent (43 followed for 3 to 48 months). Albrektsson and Sennerby also reference an article which Sennerby was a co-author. This study reports 33 mandibular implant(s) with 29 surviving, stable in function for 88% success rate (as best as can be determined from the published article) but then, by claiming to apply Albrektsson’s bone loss criteria, judged these same Core-Vent Implants to be only 15.6% successful. This was despite obvious deficiencies in the study. Malmqvist and Sennerby admitted in their article that: "panoramic and sometimes periapical radiographs were available...the vertical bone loss occurring during the period from surgery to prostheses connection could not be measured."
Albrektsson, in a lecture at the 1989 American Academy of Periodontics Annual Meeting, confirmed his awareness that panoramic radiographs are inadequate to measure bone loss: "You have to have individual radiographs. I think that bone loss you calculate in orthopantograms doesn’t give you much information." Malmqvist and Sennerby admit that because of inadequate radiographic documentation, they were unable to segregate initial bone loss due to surgical trauma or selection of too wide an implant from the type of annual bone loss the Albrektsson criteria sought to evaluate, so they arbitrarily allowed 2 mm in their calculations. Improper selection by the surgeon of too wide a Core-Vent Implant, which is available in 3 diameters, could cause more than 2 mm of bone loss at insertion.
Failure to Reference Patrick et al. Study of 1,605 Core-Vents. The Patrick et al. 5-year published study, which clearly states that it used osseointegration as the criteria of success, documented 1,605 consecutively placed Core-Vent Implants with an overall success of 96% (Oral Implantol, Vol. XV, No. 2, 1989). As part of the Patrick et al. study, only 7 out of 342 or 2% of the Core-Vent Implants in the partially edentulous maxilla failed for a 98% success (same for anterior and posterior arches). This included 45 freestanding, single tooth replacements, all of which achieved and maintained osseointegration. When this is compared to 7 failed Core-Vents out of only 10 placed in the maxillary partially edentulous jaws by Malmqvist, it is ludicrous for the Malmqvist-Sennerby article to blame the Core-Vent Implant’s design or surgical protocol without even considering operator error in surgical protocol or implant diameter selection for the available bone width. Since both Albrektsson and Sennerby had previously referenced the Patrick et al. study when it was only an abstract, there is no excuse for not referencing it now that it has been published in a refereed journal.
Albrektsson and Sennerby Perpetuate the Myth of Pure Titanium. Professor Frank Young, Editor of the Journal of Biomaterials, in a presentation before the 1988 NIH Consensus Conference, stated: "Commercially pure titanium has barely adequate mechanical properties (low hardness and tensile strength) for dental implant applications and, although it is a logical starting material, unalloyed metals usually are not found to be optimum...the clinical success of the titanium alloys under relatively crude conditions is remarkable."
Albrektsson and Sennerby claim that "Commercially pure titanium screws show a significantly higher proportion of mature bone in contact with the material than similar Ti-6Al-4V screws." The authors, in reaching this conclusion, rely on a study by their co-workers, Johansson et al. (J Biomed Eng 1989;11:3-8) that compared only five screws of alloy and five of pure titanium in the tibia of rabbits at the light microscope and SEM level. Albrektsson and Sennerby, while referencing an article by other Swedish researchers, Linder et al. (Acta Orthop Scand 1989;60:129-134) that refuted Johansson’s conclusions, attempt to negate the significance of the Linder article by stating that "if a quantified approach is used, there are clear differences in tissue reactions to such widely different materials." In fact, the Linder histological study, also in the tibia of rabbits, states that the sections "were also analyzed morphometrically using a Merz grid to estimate the amount of periosteal and endosteal new bone formation." In evaluating 76 implants including 38 pure titanium and 10 titanium alloy implants, only 3 implants failed to osseointegrate –– 2 were pure titanium and 1 was stainless steel. The authors concluded that, "with the exception of these 3 cases, the bony reaction was remarkably consistent; and of the recorded histologic parameters, only three showed variations."
Albrektsson and Sennerby further reference an unpublished study, co-authored by Albrektsson, which used a torque test to remove various screws. They conclude that "the torque necessary to remove CP titanium implants was also significantly higher than the corresponding removal torque of the titanium alloy implants." The logical explanation for this is that pure titanium, being a softer material than titanium alloy, machines to a rougher surface than the alloy, thus providing more mechanical resistance to unscrewing.
Conclusion. Albrektsson and Sennerby must be held accountable for misstatements and disinformation made in their articles.
Gerald A. Niznick, DMD, MSD
President, Core-Vent Corporation