Response to Malmqvist JP and Sennerby L: Clinical report on the success of 47 consectuively placed Core-Vent^® Implants followed from 3 months to 4 years. Int J Oral Maxillofac Implant 1990;5(3):53-60.

International Journal of Oral and Maxillofacial Implants 1990, Vol. 5, No. 3, Pages 211-212

TO THE EDITOR:

Subject: Article by Jay Malmqvist and Lars Sennerby, Vol. 5, No. 1, 1990: Clinical Report on the Success of 47 Consecutively Placed Core-Vent Implants Followed From 3 Months to 4 Years.

This article applies two sets of proposed criteria of success, each containing a parameter related to measurement of crestal bone loss, in judging the success of 43 Core-Vent Implants (47 less 4 lost to follow-up). Since neither of these criteria were ever used to determine success in any of the published Brånemark implant clinical studies, the article misleads the reader regarding the success of Core-Vent implants.

Schnitman-Shulman 1979 Criteria Applied to Core-Vent Implants: The Malmqvist Sennerby article applies the Schnitman-Shulman 1979 proposed criteria for implant success developed for nonosseointegrated implants. These criteria allow for "mobility of less than 1 mm in any direction" and also includes the parameter: "crestal bone loss no greater than one-third (33%) of the vertical height of the implant." If the bone loss parameter were applied to the Brånemark implant, 100% of the 10 mm and 7 mm implants would have to be considered a failure. To insert a Brånemark implant, 2mm of crestal bone is removed during countersinking, with an additional 1.5 mm of bone loss occurring in the first year following placing in function (Brånemark 1977, Adell 1983, Cox 1987). Therefore, as measured from the top of the implant, as was done with Core-Vent implants in this study, it would appear radiographically as 3.5 mm of the bone loss or 35% of the 10 mm implants and 50% of the 7 mm implants.

Albrektsson 1986 Criteria Applied to Core-Vent Implants. The Albrektsson, Zarb, et al. 1986, JOMI 1:11-25, proposed criteria includes a parameter relative to crestal bone loss: "The vertical bone loss be less than 0.2 mm annually following the implant’s first year of service."

Review of the Literature

1. Adell: 17 Year Study on 4,000 Brånemark Implants (JPD, Vol 50, No. 2, 1983, page 252): "The anchorage function or the fixture survival rate was defined as the number of stable, prosthesis supporting, osseointegrated fixtures in relation to the total number of fixtures installed."

2. Brånemark, Zarb, Albrektsson (Eds.): Tissue-Integrated Prostheses (Text, Quintessence Publishing Co, Inc, 1985): "Fixture anchorage function" and "fixture survival rate" were the criteria of 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...and (2) fixture anchorage function, which is the percentage of clinically stable and/or radiographically osseointegrated fixtures." Page 181: "It can be concluded from Table 10-2 that approximately 95% and 85% fixture survival rates were achieved for lower and upper jaws, respectively."

3. Engquist et al.: A Retrospective Multicenter Evaluation of Osseointegrated Implants Supporting Overdentures –– Eleven Swedish teams documented 30% failure in maxilla, 6% in mandible (JOMI, Vol 3, No 2, 1988). 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." Page 132: 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."

Malmqvist-Sennerby Study Lacks Scientific Objectivity. Malmqvist and Sennerby claimed to have measured crestal bone loss of 43 Core-Vent Implants in their study, but admit to not using standardized radiographic techniques: "Panoramic and sometimes periapical radiographs were available from the day of surgery and 3 to 48 months postoperatively."

The authors claim to determine implant success based on the amount of crestal bone lost without even taking into consideration the fact that if too large a diameter Core-Vent implant were selected for the width of the ridge, labial bone would be lost during the bone preparation procedure. This is quite obviously the cause of the bone loss in Figure 1 of the article, where a 5.5 mm diameter Core-Vent (6.3 mm outside thread dimension) was placed in a narrow ridge. Labial bone loss at the time of surgical preparation will not show up in an immediate postoperative radiograph because of the radiopacity of the titanium, but by 3 months, the bone mesial and distal to the implant will have resorbed to blend with the labial scalloping, creating the picture of vertical bone loss. The article admits to having inadequate radiographs to measure bone loss during this period: "The vertical bone loss occurring during the period from surgery to prostheses connection could not be measured."

Albrektsson’s proposed criteria specifically requires that bone loss due to surgical trauma and bone loss due to remodeling under function not be included in the measurement. Only the amount of annual bone loss "following the implant’s first year of service" is to be measured. Malmqvist and Sennerby did not have adequate radiographs to evaluate how much of the change in height from the top of the implant to the level of crestal bone had occurred during the submerged period and in the one year following prosthesis attachment, so they arbitrarily allowed 2 mm. Not only is this speculative, it does not even take into consideration the fact that the Core-Vent surgical protocol called for the implant to be placed 1 mm above the crest, as can be seen from the radiographs in Figures 1, 2 and 4 of the article.

Malmqvist and Sennerby state that: "The reasons for implant removal included rapidly progressing vertical bone loss, subsequent mobility of the implant." There is no documentation presented to indicate the implants lost bone and then became mobile. The more likely sequence would be that the implants failed to achieve osseointegration, which would be evidenced by mobility. If mobile implants are left in function, vertical bone loss will occur. The authors blame the design of the Core-Vent implant for the bone loss without considering that the most obvious cause was the surgeon’s selection of too wide an implant for the ridge. The authors do not consider that the failures were due to anything other than the "inexact surgical technique" which they claim to be "unavoidable...when inserting the Core-Vent implant." Malmqvist actually experienced 74% success using the same survival criteria as the Brånemark studies. This anecdotal report of 42 implants represents the learning curve of one oral surgeon with his first attempt at osseointegrated implants, and must be put in perspective by comparing it with the 5-year report of 1,605 Core-Vent implants with overall success of 96% by Drs. Patrick, Lubar, Zosky and Buchs (Oral Implantology Vol XV, No 2, 1989). As part of the Patrick et al. study, 7 out of 342, or 2% of the Core-Vent implants in the partially edentulous maxilla failed using osseointegration as the criteria (98% success), it is inappropriate for the authors to blame the implant design or surgical protocol without even considering operator error in surgical protocol, or improper implant diameter selection for the available bone width. Prosthetic overloading is also an important factor in the maintenance of crestal bone height or even in osseointegration. It is important to note that all the reported bone height measurements with the Brånemark implant were in the anterior region of edentulous jaws while many of the Core-Vent implants in this study were in the posterior of partially edentulous jaws splinted to teeth.

Based of the same set of criteria used to evaluate the Brånemark implant (i.e., osseointegration), the results reported by Malmqvist and Sennerby with Core-Vent implants placed in the lower jaw, as best as can be determined from the information contained in the article, is 88% success –– 33 implants with 4 being removed. By applying Albrektsson’s criteria, but ignoring its requirement that measurements be taken after the "implant’s first year of service," the mandibular success rate was artificially reduced 15.6%.

The Malmqvist-Sennerby article does acknowledge having reviewed the Patrick et al. abstract, but attempts to negate its significance by flatly stating: "no success criteria or follow-up routines have been reported." The Patrick et al. abstract clearly states how the patients were followed up: "During the study, 81 implants were lost to follow-up. The remaining implants and prostheses were recalled annually for clinical and radiographic examinations to check for osseointegration, gingival health and bone loss." The Patrick et al. abstract unmistakably states what criteria of success were followed: "implants that had failed to achieve osseointegration (or lost osseointegration) were removed and the successful implants were placed in function."

The authors support their findings by referencing a 1987 abstract by Moy, which has yet to be published in an article. Moy documented 84% to 87% success with Core-Vent implants, but then projected a future success rate of only 58% to 68% based on his own subjective criteria. The authors quoted the speculated rate rather than the actual rate for the three-year observation period, further misleading the reader. They failed to reference two other studies presented at the same 1987 meeting showing high success rates for Core-Vents (Lubar; Zosky and Kucey).

This analysis of the Malmqvist-Sennerby article clearly demonstrates that it is neither objective nor valid.

Dr Gerald Niznick

President, Core-Vent Corporation