Response to Proceedings of Osseointegration: 10 Years in Private Practice, 1982 - 1992, held October 9 and 10, 1992, at the Lansdowne Conventoin Center, Leesburg, VA. Reported in the Internatinal Journal of Oral and Maxillofacial Implants, 1994, Volume 9, Special Supplement.
LETTER TO THE EDITOR
International Journal of Oral & Maxillofacial Implants 1995, Vol. 10, No. 1, Pages 1-2
TO THE EDITOR:
The "Special Supplement" Issue, Volume 9, 1994 of the Journal represents the transcribed proceedings of a 1992 conference limited to approximately 100 invited clinicians and scientists. Because the conference organizers restricted participation, I disagree with Dr. Laney's introductory remarks in the Journal that the "experience-based positions" of the participants "may be considered the state of osseointegration in private practice at this chronological stage of clinical application." Publications such as this "Special Supplement" of the JOMI unfortunately perpetuate the myth that if solutions to clinical problems are not provided by the three foreign implant systems, they must not be worthy of consideration.
In Topic 1, one dentist, who relies primarily on the Brånemark system, identified "loose screws" on thread-retained abutments as today’s "number one restorative problem with retrievable systems." Another dentist identified "rotational stability" as "still a big problem" with external-hex screw implants and also expressed his concerns regarding "damage to the fixture hex" and fracture of the fixture itself with single-tooth applications. He concludes that "the limitations of standard implants are now known," but continues to use Brånemark implants and 3i clones. Solutions to unstable implant/abutment connection and to fractured screw implants inherent with standard external hex implants made from commercially pure titanium have been available since 1990 with titanium or titanium alloy implants with the internal Hex-Thread Connection (Core-Vent US Patent #4,960,381). Discussions in Topic 5 emphasize the importance of a precision fit between implant and abutment in reducing center-screw loosening. To support claims of superior precision, Keith Beaty, President of 3i, included a chart (Fig. 5-4) of the diameters of external hexes on implants from six companies. This data, supposedly presented in 1992, was from a study not published until 1994 (Schulte, J Impl Dent 1994;3(1)). Such studies are easily biased by one company submitting consecutively manufactured implants while the other companies submit implants from inventory. I confirmed that the graph was misleading by measuring the hex diameter of five 3i implants of different lengths to assure that they were not consecutively made. Their tolerance range was no better than the average of four of the five competitors cited in the chart, excluding Nobelpharma, which had the highest variation in measurements.
The real issue of precision is how well a company's abutment fits on its own implants. Dr. Binon reported on such measurements at the 1993 AO Meeting. Screw-Vent’s internal hex connection demonstrated only 1.4 degrees of rotational instability compared to 4.6 degrees for 3i and 6.7 degrees for Nobelpharma components. The internal hex connection (1.5mm deep) provides 2-3 times the length of interdigitation of commercially available external hex implants, which could account for its superior stability. To entirely eliminate rotational wobble, a new concept of screw-retained abutments is needed –– intentional interference or friction fitting of the interdigitating hexes. This was first accomplished in 1992 by tapering the male hex on abutments by one degree (Core-Vent US Patent 5,334,024). This combines the frictional retention, requiring 10-20 Ncm force during tightening of the fixation screw to fully seat the abutment, with the anti rotational benefits of interdigitating hexes. The result is that 25 pounds of frictional retention is created between the abutment with zero rotational "hex play" and with approximately 4 times the compressive strength at 30 degrees than Nobelpharma's implant and abutment assembly can withstand. This friction fit concept has now been adapted to a new Swede-Vent TL Taper-Lock Implant by creating a tapered external hex on the implant (Core-Vent Patent Pending). The result is complete elimination of "hex play" with an external hex implant which Binon in Topic 5 cites as one of the main causes of screw loosening, the complication listed in Topic 1 as today’s "number one restorative problem with retrievable systems."
HA Surface Criticism
To perpetuate the mind-set that the foreign implant systems offer the only credible implant alternatives, seven of the nine panel members assigned to Topics 2 and 3, which dealt with the use of "different implant designs" and "different implant surfaces" represent these systems. Of the remaining two panel members, one had published a controversial article highly critical of HA coated cylinder implants. With these two panels so constituted, their conclusion supportive of a machined or TPS-coated implant surface and critical of HA coatings was highly predictable. What was overlooked by the panels in attributing responsibility to the HA coating for bone cratering at the crest around HA-coated cylinder implants, is that cylinders do not distribute vertical and lateral forces to the jawbone as well as screw implants (French et al., Int J Periodont Rest Dent 1989;3). What seems to be lost with all the HA bashing is that HA coatings on screw implants would offer the advantages of increased compressive load capabilities of a threaded implant and take advantage of the higher percentage of bone contact (60%) compared to only 30% with Brånemark machined surface and 50% with TPS-coated IMZ surface, as reported by Dr. Holmes in the transcribed proceedings.
The transcribed proceedings do not include the benefits of acid etching the implant surface, a process Core-Vent Corporation has used since 1986 to remove machining contaminants and loose titanium particles. Based on published research, acid etching of the titanium surface as a cleaning and roughening procedure deserves consideration in any scientific debate related to implant surface treatments, especially in light of the studies that document loose titanium particles that become imbedded in the adjacent tissues with machined surface (Schliephake H, JOMI 1993;8) and TPS surfaces (Strub JR, JOMI 1987;4).