Responses to Int J Oral Maxillofac Implants 1987;2(1): Kinni ME et al.: Force transfer by osseointegration implant devices (Pp 11-14); and Henry PJ: Comparative surface analysis of two osseointegrated implant systems (Pp 23-27).
LETTER TO THE EDITOR
International Journal of Prosthodontics, Vol. 3, No. 6, Pages 583-584
Your readers have been misled by information contained in two articles in the Vol 2, No. 1, 1987 issue of the Journal of Oral and Maxillofacial Implants. The first article that I take issue with is entitled, "Force Transfer by Osseointegrated Implant Devices," by Mark E. Kinni, Stephanie N. Hokama, and Angelo A. Caputo. I question the validity of this research technique because the correlation between two-dimensional stress tests in plastic and force distribution three dimensionally in bone has yet to be proven. In fact, photo-elastic stress tests have been made archaic by three-dimensional finite element analysis. One of the basic principles of implant design is that an increase in surface area will result in a corresponding decrease of stress at the interface. I viewed with suspicion the color pictures in Figures 7, 8 and 9, which represented that the solid Biotes screw implant with a 3.75mm outside thread diameter could distribute stress better than the hollow-vented Core-Vent implant with a 6.3mm outside thread diameter (5.5mm major diameter). I spoke with Dr. Caputo on March 16. He admitted, when questioned about the difference in stress patterns between the large Core-Vent implant in Figures 9 and 10 that, in fact, the picture in Figure 9 was taken at 30 lbs. of load while that in figure 10 was taken at 40 lbs. This surprised me since the article represented that all pictures were taken at 40 lbs. of load. He explained that, in this study, the pictures were taken at 10, 20, 30 and 40 lbs of load. Dr. Caputo refused to show me the different loading pictures to verify that the pictures of the Biotes implant showing minimal stress concentration were taken with the same amount of load as the Core-Vent implants.
I think it is important to note that Figure 5 examining the "unstressed models" shows the full length of the Biotes and Core-Vent implants. Figure 6, showing "stress patterns observed with 40 lb. axial load" cropped the top of the picture of the Biotes implant while it shows the full length of the Core-Vent implant. In fact, none of the figures show the top of the Biotes implants under stress. The Biotes implant, which is wider at the top, will result in undesirable high stress concentrations in the area of the crest of the ridge. Several questions raised by this study are:
1. Why did this study fail to accurately report the load under which the implants were placed at the time the pictures were taken?
2. Why were the stress concentrations at the top of the Biotes implant deliberately omitted from the pictures?
The second article which I question is entitled, "Comparative Surface Analysis of Two Osseointegrated Implant Systems," by Dr. Patrick J. Henry. Dr. Henry’s conclusion that Core Vent’s 6Al/4V titanium alloy (approximately 6% aluminum, 4% vanadium and 90% titanium) has, in fact, up to 7% iron and less than 2.57% aluminum is neither rational nor correct. The titanium alloy used in Core-Vent implant is manufactured to the very strict chemistry outlined by the American Society for Testing and Materials specifications #ASTM F 136-84. A certified chemistry report accompanies each invoice of alloy purchased by Core-Vent Corporation. The 1985 and 1986 purchases show an iron content of 0.18% and aluminum content of 6.24-6.34% (documentation available from Core-Vent Corporation). Further, Dr. Henry’s article admits that both implants were tested "in the condition supplied by the manufacturer." At the time of his testing, Core-Vent was providing the implant with a prescribed cleaning procedure to be performed by the dentist while the Biotes implant was provided pre-cleaned in titanium tubes. Core-Vent now provides its implant pre-packaged, as well. Dr. Henry’s surface analysis comparisons, therefore, are not only inaccurate, but also intentionally unfair. A simple washing with hard tap water cold increase the calcium, silicone and iron content on the surface of the implant. Core-Vent implants and Biotes implants have been tested by S. E. A. L. Laboratories in Los Angeles using Auger analysis, which is approximately 250 times more definitive than the EDAX testing procedure used by Dr. Henry. The results show the surface of Core-Vent’s alloy and Biotes’ commercially pure titanium were almost identical with no trace of iron or aluminum appearing on the surface of either material (documentation available from Core-Vent Corporation).
Dr. Henry has agreed to send 5 of the implants that he has tested directly to Dr. Frank Young, Chairman of the Department of Biomaterials at the University of South Carolina and editor of the Journal of Biomaterials. Dr. Henry and I will receive the analysis report from Dr. Young and I am sure it will confirm Dr. Henry’s misreading of the surface of the Core-Vent implant and inappropriate extrapolation of this information to his estimate of the bulk alloy.
Dr. Henry’s article further compares the grit-blasted surface of the Core-Vent implant to that of the smoother machined surface of the Biotes implant and, through references to four articles written by Brånemark and his co-workers, tries to prove the superiority of the smoother surface. One only has to read the article in this same issue of the JOMI by Steven D. Cook et al., in which reference is made to a previous article by Cook (J Biomed Mater Res 1985;19:875-901) proving that osseointegration was more likely to occur on a grit-blasted surface than on a smooth surface.
I would suggest that, in future issues of the JOMI, it would be in the profession’s best interest if articles purporting to unbiasedly compare two competing systems, be viewed with skepticism. In the editorial entitled, "Implantology ‘86" that also appeared in the same issue of JOMI, Dr. Laskin stated, "It is understandable that manufacturers praise their own products, but we would hope that we can at least turn to our professional colleagues for a less biased appraisal. Unfortunately, this, too, does not seem to be the answer at the present time."
Furthermore, it is also unfortunate that we cannot rely on our scientific journals for proper screening of inaccurate and biased reports.
Gerald A. Niznick, DMD, MSD