A Response to Nobelpharma’s “Open Letter” to Oral Surgeons and Prosthodontists

In response to Nobelpharma’s “Open Letter” to all Oral Surgeons and Prosthodontists, it is Core Vent Corporation’s position that the published results of the Brånemark research are now the property of the dental profession and are subject to interpretation and reference EVEN THOUGH IT MAY BE CONTRARY TO THE COMMERCIAL INTERESTS OF THOSE NOW PROMOTING THE SALE of the implant used in this research project.

I agree completely with the statement contained in Nobelpharma’s letter that “FACTS, NOT PROMISES, SHOULD BE THE BASIS OF COMPARISON IN MATTERS OF ORAL HEALTH.”

THE PURPOSE OF THIS DETAILED REVIEW OF THE LITERATURE AND COMPARATIVE ANALYSIS IS TO ESTABLISH THE FOLLOWING FACTS:

1. The Brånemark research proved the long-term predictability of an implant that can achieve direct bone anchorage, termed “osseointegration.”

2. The Brånemark research was not the first to report on a direct bone anchorage to titanium.

3. The Brånemark research was not the first to use a submergible screw implant with internal threading for attachment of the prosthesis.

4. The Brånemark research did not prove that pure titanium had any advantages over titanium alloy in achieving and maintaining osseointegration.

5. The Brånemark research did not prove that the surface finish and geometry of their implant was the only one, or even the best one, for achieving and maintaining osseointegration.

6. The Brånemark method, according to the Swedish National Board of Health:

“…seemed not to satisfy certain clinical objective requirements regarding prosthetic treatment.”

“…should be limited to teaching institutions or hospitals with special resources.”

7. The real legacy of the Brånemark research is that, for any endosseous implant that can achieve osseointegration, “a reliable prognosis can be made in the individual case after the first year.” This is “the test of time” that is relevant in evaluating any osseointegrated implant (quotes from Nobelpharma’s “Open Letter” and the Brånemark conclusions that accompanied the letter).

8. The Core-Vent^® Implant System provides the features inherent in the Brånemark method that account for its success while additionally offering simplified surgical procedures and versatile prosthetic applications at a cost that makes “osseointegration in clinical dentistry” a reality.

REVIEW OF THE LITERATURE

The 20 years of clinical research conducted under the direction of Dr. Brånemark [1] at Gothenburg, Sweden undoubtedly has changed the way the dental profession perceives long-term predictability with endosseous implants. Dr. Brånemark and his co-workers have provided a skeptical academic community with a long-term, prospective clinical study that withstands scientific and statistical scrutiny. Published research has always served as the basis for subsequent technological advances ––the contributions of those who preceded them are recognized by way of reference. It is important to understand the evolution of the osseointegrated implant in order to ensure the future of Implant Prosthodontics in clinical dentistry.

In 1951, Leventhal [2], in experimental studies, observed that bone appeared to become anchored to titanium. In France, Chercheve, in 1958 [3], was the first to use a submergible hollow screw implant fitted into a previously bored hole created by the surgical tap of the same diameter. Benaim in 1959 [4] published his development of a solid, submergible, stainless steel screw with a vent for bone growth and with internal threading in its superior aspect for attachment of the prosthesis. Brånemark [1] started his clinical research 6 years later (1965) using a similarly designed submergible screw made from titanium instead of stainless steel to test his theory that if direct bone attachment could be achieved (versus a connective tissue interface), long-term predictability would be a reality. Linkow [5] described a three-dimensional hollow-basket implant in 1965. It was of a one-piece design with a solid post extending immediately through the oral mucosa. Straumann and Sutter [6] refined the design and insertion technique of the hollow-basket implant by incorporating an internally threaded screw in the post and by systematizing the instrumentation using trephine drills that left a bone core at the base of the receptor site.

The Core-Vent Implant [7, 8] combined the hollow-basket design with self-tapping threads to make a screw implant that had increased load distribution capabilities. By maintaining a constant major diameter throughout the entire length, the cylindrical design further increased the surface area while making it possible to shorten each Core-Vent Implant to 8 different lengths. Preparation of the 8 corresponding receptor sites is accomplished with one internally irrigated trephine instrument marked with gage lines for depth control. A two-stage bone preparation procedure was developed to facilitate this: Stage I creates a bone core that is then removed by fracturing to create a chamber for the threaded neck portion of the Core-Vent Implant. Stage II creates a bone core that is left intact. On insertion of the self-tapping screw implant, this bone core becomes encompassed by the hollow-basket lower portion, thus minimizing the amount of bone that requires regeneration in order for the jaw to totally incorporate the Core-Vent Implant. The modifiability of the length enhances load distribution by facilitating maximum use of available bone.

In addition, the Core-Vent Implant was designed to be submergible to avoid premature loading –– a hexagonal hole extending down from the superior aspect of the implant facilitates ratcheting of the self-tapping implant to place and then accepts a plastic rod for easy uncovering following the initial submerged healing period. A variety of bendable abutment heads were designed to be cemented into the hexagonal hole so that the Core-Vent Implant can be used not only for detachable fixed prosthesis as used in the Brånemark research but also free-standing single tooth replacements, abutments for fixed bridges and free-standing in the symphysis to retain overdentures –– three applications not available with the Brånemark System. Advances in the last 20 years in biomaterials (new titanium alloys and plastics), biomechanics (photoelastic and finite element studies), and computer-controlled machining now make possible more sophisticated implant designs and insertion techniques. For osseointegration to have relevance to clinical dentistry in this country, the method of connecting and supporting fixed prostheses and overdenture superstructures to the Brånemark implant would necessitate redesigning of the implant itself to allow for attachment of bendable heads.

PURE TITANIUM VERSUS TITANIUM ALLOY

The Core-Vent Implant is made from FDA-approved titanium alloy (Ti 6Al/4V), which is 60% stronger than pure titanium and with better machining properties to allow the production of even small diameters of the delicate hollow-vented design. Both pure titanium and properly prepared Ti 6Al/4V ELI (low interstitial oxygen) titanium alloy have the same titanium oxide on the surface since the aluminum and the vanadium are not self-passivating and, therefore, do not readily oxidize. As Zarb [9] stated in regard to Kasemo’s article [10], “Because the surface exposed to the biologic host system consists of a metal oxide, not a metal, it is the oxide that governs the chemistry at the implant-bio tissue interface.” Brånemark [1] discussed the research results of Morse [11], who had used titanium alloy in dental implants and reported on two specimens removed after approximately 2 years. Brånemark stated (Review of the Literature –– Interface, page 11): “The main corrosion product (on the surface) was titanium oxide, believed to be relatively inert. The used implants showed closely adherent opaque protuberances at various points on the surface and electron probe analysis revealed the presence of calcium and phosphorous, which was compatible with a designation of bony attachment.”

THE BRÅNEMARK RESEARCH

As with all research, Brånemark started out with a hypothesis –– that direct bone anchorage (later termed osseointegration) would provide long-term predictability. Because of Sweden’s socialized health care and its non-migratory population, he was able to do what no implant researcher had done previously or since. He was able to carry out a prospective, clinical study for over 15 years and proved his theory of the long-term predictability of osseointegration. To obtain valid statistics, he maintained certain controls over the period of this study. For instance, the following factors remained constant: the location of the implants in the symphysis and anterior maxilla of totally edentulous jaws, the design of the superstructure, the material, and the design of the submergible screw implant. Brånemark did not use several different designs, surfaces, or materials as controls to evaluate which was the best since he was testing his theory of osseointegration –– not testing various designs, surfaces, or materials. Brånemark [1] has stated in his report of the first 10 years results with reference to implant design and material: “The design of the implant, which has attracted a dominating interest in the literature, is of secondary importance to the mechanism of anchorage in the jaw bone…The careful handling of the tissue and the use of an inert, non-contaminated material are the prime prerequisites for osseointegration.”

COMPARE BRÅNEMARK’S 10-YEAR REPORT [1] WITH NOBELPHARMA’S INTERPRETATION

— WHAT IS OSSEOINTEGRATION?

— HOW IS OSSEOINTEGRATION ACHIEVED?

Accompanying the letter from the President of Nobelpharma was a list of 10 points entitled, “Summary and Conclusions” of the 15-year Study of Osseointegration Implants.

I disagree with only the 1st point listed.

Point #1: “Osseointegration implies a direct and intimate incorporation in the vital bone of threaded fixtures of defined finish and geometry.”

There is no need to speculate what “osseointegration implies” or what factors are essential for its achievement. Brånemark [12] defined osseointegration in his article in the August 1984 AAOMS Journal –– “Osseointegration means a direct contact, on the light-microscopic level, between living bone tissue and the implant.”

CORE-VENT IMPLANTS HAVE MET THIS CRITERIA in both animal studies and human specimens.

Nowhere in the 9 points listed on pages #122-#125 of the “Conclusions and Summary” of the 10-year report [1] is there any mention of the design, surface finish, or even the material of the implant, and no mention that the research intended on evaluating anything other than the anchorage mechanism. Point #1 of the conclusions of the 10-year results even scoffs at the preoccupation of the other researchers who have concentrated their concerns on the designs and material of the endosseous component.

Conclusion #1 stated:

To date, there remains more interest in developing new materials and designs than in evaluating tissue responses and inquiring into how tissue can be made to accept an implant. We have demonstrated that it is possible to achieve true osseointegration with careful surgical handling of bone tissue at preparation and close monitoring of healing time and load on the implant.

The 2nd Point of the list of summary and conclusions that accompanied Nobelpharma’s open letter states exactly how osseointegration is achieved.

Point #2: “Osseointegration can be achieved if the fixtures (implants) are inserted with delicate surgical technique and allowed to heal, without load, for periods of not less than 3-4 months in the lower jaw, and 5-6 months in the upper jaw.”

In the Readers’ Round Table section of the July issue of the Journal of Prosthetic Dentistry [13], I stated:

The Brånemark research did not compare various surfaces by using controlled research techniques. Likewise, the Brånemark research did not prove that the design of their fixture was the optimum one or one that could withstand functional forces without multiple splinting. The preparation technique for the Brånemark implant as outlined in the article by Kasemo [10] is standard practice for machining metal.

Dr. Zarb, a leading advocate of, and spokesman for the Brånemark System, was invited by the Editor to respond to my letter in the Journal of Prosthetic Dentistry –– HE DECLINED.

Enclosed you will find a copy of this letter to the editor. On the reverse side, I have listed the essential requirements to achieve and maintain osseointegration as proven by the Brånemark research and correspondingly, how THE CORE-VENT IMPLANT SYSTEM FULFILLS THESE REQUIREMENTS.

OSSEOINTEGRATION STANDS THE TEST OF TIME

The president of Nobelpharma stated in his letter, “We are aware that other companies have been utilizing Professor Brånemark’s work to foster interest in products that have not stood the test of time.” The 7th point of their Summary and Conclusions specifically states what is the required “test of time”:

Point #7: “A reliable prognosis can be made in the individual case after the first year.”

The physiological explanation for why this is true is also found in Point #1 of the Conclusions of the 10-year results [1]: “Roentgenologic and histologic studies clearly show that the anchoring bone is vital and remodels to fit the dynamics of the load.” If the bone accepts the load placed on the osseointegrated implant and remodels according to function, there is no physiological reason why the implant should not remain in a “steady state” indefinitely if the prosthesis allows the patient to maintain proper oral hygiene. The Core-Vent Implant maximizes the surface area by using a hollow-vented design and taking advantage of the three diameters, each modifiable to eight lengths. The stress at the interface is reduced to the point that osseointegration can be maintained during the critical initial loading period –– even when the implant is used as a free-standing replacement.

Statistical analysis by Hansson [14] indicated that implants remaining osseointegrated in function for 11 months have a lifetime predictability of 98% in the lower jaw and 94% in the upper jaw.

THIS FINDING IS THE REAL LEGACY OF THE BRÅNEMARK RESEARCH. To try to interpret the results in terms of the design and material of the implant itself –– by Nobelpharma and others personally committed to propagating the Brånemark System –– defeats the purpose and universal application of Brånemark’s research.

THE NOBELPHARMA LETTER STATES:

“Remember, THERE IS ONLY ONE BRÅNEMARK METHOD –– make no mistake!”

This is the same system that their own Swedish National Board of Health and Welfare reported [15] on 17 randomly selected cases in the Journal of Prosthetic Dentistry and found as follows:

Nine of seventeen patients showed satisfactory occlusion while eight were unstable occlusally.

Interproximal spaces were not accessible for hygiene purposes in 11 patients.

The osseointegration method seemed… not to satisfy certain clinical objective requirements regarding prosthesis treatment.

The evaluating group stated that this method should be used only by a team of specialists, not by the general practicing dentists. This means that treatment of this kind should be limited to teaching institutions or hospitals with special resources.

IMPLANT PROSTHODONTICS

Dentists around the world are achieving osseointegration on a highly consistent basis with Core Vent Implants. Since the Core-Vent Implant became commercially available almost 3 years ago, no one has reported the loss of any Core-Vent Implants once osseointegration was achieved and the implant was placed in function supporting or retaining a prosthesis. Considering that many of the Core-Vent Implants have been used free-standing to retain overdentures, osseointegration of the hollow-vented Core-Vent design can withstand forces even greater than those contemplated by Brånemark. The Core-Vent Implant System is now in use in more than 30 universities and teaching institutions in this country with several (e.g. Harvard University, Medical College of Georgia, University of Florida) using both the Brånemark and Core-Vent Systems.

As a prosthodontist, I designed the Core-Vent Implant System to implement my philosophy of Implant Prosthodontics –– maximize the benefits while minimizing the risk and expense to the patient. The Core-Vent Implant System can be used to restore the totally edentulous jaw with fixed/detachable splinting similar to the Swedish system but, since the necks of the heads are bendable and contoured, the construction of the fixed prosthesis can be carried out to the high standards of esthetics, phonetics, oral hygiene and occlusion that the American public has come to expect. The Core-Vent Implant was designed to be inserted with a minimum of instruments and each implant can be modified to 8 lengths. These cost-effective design features mean that the advantages of a predictable osseointegrated implant system providing proper prosthetics can now be translated to the benefit of a large number of patients for a fee well within the range of conventional restorative and prosthetic dentistry.

IS NOT THIS THE PURPOSE OF ALL CLINICAL RESEARCH AND DEVELOPMENT?

Sincerely,

Gerald A. Niznick, DMD, MSD

president, CORE-VENT CORPORATION

REFERENCES

1. Brånemark P-I et al.: Osseointegrated implants in the treatment of the edentulous jaw. Scandinavian Journal of Plastic and Reconstructive Surgery, September 16, 1977.

2. Leventhal G: Titanium, a metal for surgery. J Bone Joint Surg 33-A, 473, 1951.

3. Cherchève R: Les implants endo-osseux. Librarie Maloine, S.A. Paris, Pg. 291, 1962.

4. Benaim L: Presentation d’un implant tublaire endo-osseux. Journal de Stomatologie et Information Dentaire 16-7, 1959.

5. Linkow LI: Intra-osseous pins and posts and techniques thereof. United States Patent #3,499,222, filed August 17, 1965.

6. Straumann F, Sutter F: Implant for artificial tooth. United States Patent #4,180,910 filed October 13, 1978.

7. Niznick GA: Endosseous dental implant for overdenture retention, crown, and bridge support. United States Patent #4,431,416 filed April 29, 1982.

8. Niznick GA: The Core-Vent Implant System. Oral Implantology Vol X, No 3, 1982.

9. Zarb GA: Reader’s Roundtable. J Prosthet Dent Vol 52, No 1, July 1984.

10. Kasemo B: Biocompatibility of titanium implants: Surface science aspects. J Prosthet Dent 49;832, 1983.

11. Morse DR, et al.: A scanning electron microscope examination of endodontic implants. Oral Implantology 3, 139, 1972.

12. Brånemark P-I, et al.: An experimental and clinical study of osseointegrated implants penetrating the nasal cavity and maxillary sinus. J Oral Maxillofac Surg, Vol 42, No 8, August 1984.

13. Niznick GA: Reader’s Roundtable. J Prosthet Dent, Vol 52, No 1, July 1984.

14. Hansson B: Success and failure of osseointegrated implants in the edentulous jaw. Swedish Dental Journal, Supplement 1, 1977.

15. Bergman B: Evaluation of the results of treatment with osseointegrated implants by the Swedish National Board of Health and Welfare. J Prosthet Dent, Vol 50, No 1, 1983.