Controversial Issues that Effect the Dental Implant Industry
Analysis of the Shortcomings of Nobel Biocare’s® N1™ System
August 5, 2023 | Dr. Gerald Niznick
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Nobel Biocare® claims its N1™ implant is designed with a trioval neck to “reduce stress on cortical bone [compared to traditional round implants].” It makes the same claim regarding the back-tapered neck of its Nobel Active® implant. These claims and the N1 surgical protocol are based on an unsubstantiated premise that crestal bone will resorb if subjected to high (40Ncm+) implant insertion torque. There are no studies showing a correlation between insertion torque and crestal bone loss. Compression of the cortical bone is irrelevant when placing implants in the soft bone of the maxilla or extraction sockets of immediate insertion. For these applications, the trioval and back-tapered necks are counter-productive to optimizing initial stability. Furthermore, research shows that a lack of contact between the implant and the crest of the ridge contributes to bone recession. For situations where there is dense cortical bone that is preventing full seating of the implant, crestal bone drills are available to enlarge the opening to the same diameter as the implant, while still maintaining a seal at the crest.
N1 Implant includes an OsseoShaper drill with an option for one-time use OsseoShaper2 drill, adding $109 to the cost
Nobel Biocare recommends 50 rpm for preparation of the final sizing of an osteotomy with its side-cutting OsseoShaper drill. Conventional drill speeds for end-cutting spade drills is 800-1200 rpm.
Progressively enlarging the osteotomy with a series of spade drills takes little if any additional time while allowing the dentist to progressively enlarge the socket depending on the density of bone (Niznick 2000 Article). The end-cutting feature of a spade drill also controls the trajectory of the drill and avoids oversizing the socket, which can happen with side-cutting drills. Nobel’s noise/vibration comparison video is misleading – don’t go directly to the final size of a spade drill.
Nobel claims the N1 is “designed for immediate placement”. This claim is for “immediate placement,” not immediate loading. For an implant and its surgical protocol to be designed for immediate load, it must predictably achieve 35-40Ncm of implant insertion torque.- Nobel Biocare claims the N1’s surgical protocol yields “predictable insertion torque” but in fact, it yields predictable drilling torque as Nobel recommends not exceeding 40Ncm during the drilling procedure. The correlation between drilling torque and implant insertion torque is dubious. Rather than following a series of sequentially larger diameter drills to establish the appropriate socket diameter, depending on the density of the bone, the Osseoshaper drill provided with each implant may oversize the socket in soft bone, compromising stability. It often undersizes the socket in dense bone, requiring the use of a second larger diameter 1-time use drill called OsseoShaper2, which costs $109. Because the OsseoShaper is side cutting it can oversize the socket, further reducing initial implant insertion torque.
- Nobel’s claim that the N1 has a “trioval conical connection” is misleading. A conical connection consists of mating cones that gain stability by tightening the abutment’s cone into the conical-shaped internal shaft of the implant, the angle of the abutment’s bevel being slightly flatter to ensure initial contact at the opening to the internal shaft. The abutment’s Trioval surface cannot rotate within the implant’s Trioval internal shaft, so it cannot create frictional stability — it is held in place by a screw.
- Nobel claims N1’s “trioval connection [creates] …an emergence profile designed for soft tissue maintenance,” Posterior teeth are rectangular, not triangular.
Early reports on the clinical experience with the N1 implant indicated that 25% of the cases in the maxilla and 50% of the cases in the mandible required use of the OsseoShaper2 drill, which is not provided with the implant and is a single-use drill. This adds an additional $109 to the cost of the N1 implant. Nobel requires that a dentist take a course before buying N1.
Subcrestal Positioning of Implants with a Convergent Hyperbolic Collar Profile Int J Oral Maxillofac Implants 2022;37:1160-1168. “The placement of implants with a hyperbolic convergent profile collar in the subcrestal position resulted in higher buccal bone resorption and more soft tissue recession.”
Nobel Biocare includes a final sizing, tapered drill with each N1 implant. This defeats the well established concept of using a series of progressively wider diameters to enlarge the osteotomy without overheating while evaluating the density of the bone. Following use of a locator or pilot drill, the N1 surgical protocol calls for using a single “OsseoShaper” drill turning at 25rpm to create the osteotomy. This is a slower process than using an intermediate and a final sizing drill turning at 1200 rpm in dense bone. In soft bone, creating an undersized socket will allow a tapered screw implant to expand and compress the bone for increased initial stability. G. Niznick. Achieving Osseointegration in Soft Bone Oral Health, Aug. 2000
Nobel Biocare further claims that the “trioval conical connection” on the N1 implant with its matching trioval shaped abutment neck provides “optimized emergence profiles.”
Only the anterior teeth are somewhat triangular in shape. The bicuspids could be considered more rectangular, and the molars more square. Therefore, the N1 implant’s design rational has a very limited application. Emergence profile is, as its name indicates, the profile of the abutment as it emerges from the implant connection. The ideal emergence profile for anterior as well as posterior teeth can be achieved with custom cad-milled abutments that take into consideration the angle of emergence, the diameter of the implant as well as the B-L and M-D widths of the final crown to be attached to the abutment. There are no one size fits all, repeat manufactured oval shapes, that match the emergence profile of teeth. The desired emergence profile will be dictated by the tooth number being replaced, the M-D space of the missing tooth, and the diameter of the implant that was selected based on available bone width.
Nobel Biocare claims its new N1 implant is “Engineered for immediate placement and function in extraction sockets.” In immediate extraction sockets, the Trioval shape of the N1 implant just contributes to a wider gap between the implant and the bone compared to a round implant and will require more bone graft material to fill the void.
Nobel Biocare’s rationale behind the N1 design is that its “trioval implant neck reduces stress on cortical bone (compared to traditional round implants) and promotes fast osseointegration***
***This study, referenced by Nobel Biocare to support its claim of “faster osseointegration” with the N1 implant does not withstand scrutiny.
It consists of insertion torque tests in wood and histology in mice. The data demonstrated the same insertion torque for both the round and trioval implants, while lateral lateral stability of the trioval implant was slightly greater. The slight increase on bone contact after healing in the mouse model was interpreted as “faster osseointegration” and was attributed by the authors to the increased lateral stability. The study acknowledged that this increased initial stability was due to the threads of the trioval implant penetrating deeper into bone, as shown in this picture from the article. The major diameter of the threads is a factor that could easily been controlled in manufacturing the test implants, so all the study proved was that increasing the depth of penetration of threads into bone increases stability and that could affect osseointegration, i.e. the study did not prove the efficacy of a trioval implant design.
The authors further acknowledge that higher initial stability can be achieved by inserting a round tapered implant into an undersized socket. This successful technique was developed for soft bone insertions to increase stability and densify the bone. This study further claims that the Trioval shape reduces stress at the neck of the implant compared to a round implant. This can also be achieved by back-tapering the implant neck (NobelActive) as shown here but back-tapering the neck reduces initial stability.
A ”harmonized emergence profile” is one that replicates the dimensions and flare of the neck of the tooth being replaced. The neck of the trioval N1 implant is subcrestal and therefore plays little if any role in creating a natural emergence profile. The neck of the abutment is also oval shaped as it emerges from the implant’s oval internal conical connection. Its cross-sectional dimensions bear little if any relationship to the B-L and M-D dimensions of most natural teeth.
The way to ”harmonize emergence profile” is to first make a customized healing collar that supports the tissue in an immediate extraction socket or forms the tissue from a surgical opening. Shown below (left) is a shortened titanium carrier from a Legacy2 implant modified by adding acrylic to create the desired emergence profile. This can be replicated in a soft tissue model (right), followed by the fabrication of a cad milled abutment with its trans-mucosal section matching the emergence profile and dimensions of the customized healing collar.
Achilles Heel of Nobel Biocare’s New N1 Implant System
Nobel’s mantra at the end of this video is “WE FOLLOW NO ONE”. This is not accurate when you consider that I invented the internal hex connection with a lead-in bevel in 1986 (Screw-Vent – patent issued 1990) and Nobel Biocare launched the NobelActive in 2008, waiting 17 years for my conical connection patent expired. Now Nobel’s claim of “innovation” is to run a drill at 50rpm to reduce the noise compared to running at 1200rmp. It claims that the N1 Shaper drill is the monumental design innovation that allows bone cutting at slow speeds, going right to the final sizing of the osteotomy. Of course, one could run the spade drill at 50 rpm if noise were the most important factor in reducing patient stress. Real patient (and doctor) stress occurs when the implant fails to osseointegrate and we know for a fact that in soft bone, insertion of a tapered implant into an undersized socket generates higher initial stability by compressing the bone. This is important to achieve consistent osseointegration and absolutely critical for immediate loading. As shown in the comparison picture the spade drill is only end-cutting compared to the side-cutting Shaper dill. It is obvious which drill is more likely to result in an oversized socket in freehand preparation.
