I don’t use the term “paradigm shift” lightly… although when I use it I try to mean it. Why make a statement out of a simple phrase? Well, when we discuss a paradigm shift, it implies a new way of thinking challenging what we historically have accepted as the standard and usual way of doing things.
Arguably many digital technologies have been paradigm shifts for my practice, such as intraoral scanning and 3D printing. Those technologies are not changing my clinical approach to treatment but merely complementing my approach. One approach, however, has resulted in a shift in the way I diagnose, treatment plan, and deliver implant-based restorations – angled screw channels.
The reality in dental implantology is that for years we have relied upon the choice between cement-retained restorations and screw-retained restorations. This has been a long and contentious debate, often invoking deep passionate responses from clinicians saying comments like “I always use screw-retained!!” or “Keep it simple silly, cement!” The interesting side is that both arguments are valid and there are reasonable arguments for both and there are reasonable counter-arguments against. Some have advocated that off-axis implant placement can lead to significant problems; the literature has not shown that to be the case. In fact, angled implants are a core principle of many contemporary implant systems and restorative designs.
What I can say is that, in general, I almost always try to deliver a screw-retained restoration. Benefits of screw-retained restorations include: retrievability, restoring with limited occlusal height, no cement sepsis risk. The negatives of screw-retained restorations, however, include: anterior esthetics, cost, technique sensitivity, weakened occlusal table (due to the screw channel).
The most common reason I have found for clinicians using cement-retained crowns instead of screw-retained is that the screw channel is going through the anterior portion of a crown or in a position that is unfavorable for esthetics. Historically the best way to manage this challenge is simply to fabricate an abutment and then cement retained crown over the top of the abutment.
As a result, we are challenged as clinicians to place dental implants in positions that are favorable for screw-retained restorations, yet also needing to put the dental implant at an angle to compensate for the healthiest bone site. Often this occurs in the anterior but it also occurs routinely in the posterior, especially to avoid critical structures like sinus or nerve channels.
The question then comes up… why not change the angle of the way we restore screws of our implant crowns? Such an important question!
Historically angled screw channels have been limited to certain dental implant companies and/or closed prosthetic solutions. I’m a huge fan of open architecture systems and universal systems that allow any clinician or laboratory to utilize the design, equipment, and/or system.
I became acquainted with DESS via a friends of mine, Drs. Graham and Joe Meng, fellow prosthodontists who practice in Missoula, Montana. Graham was showing me some cases and I mentioned “Is that a ti-base? I’m not so sure about those things” but he quickly eased my concerns and showed me innovative workflows. I came back to my practice and started to think about where I could really use them. I instantly saw on their page, “AURUM” (now they call it a much more descriptive name “AngleBase“) and I could angle an implant screw channel up to 25 degrees and I could print/mill it by myself in my laboratory, no special dongle fees, outsourcing system, or proprietary workflow. I was instantly intrigued. (Note: neither Dr. Joe Meng, Dr. Graham Meng, nor myself have any financial relationship with DESS).
While I have mentioned one company’s solution, I feel that out of fairness I should mention there are several other companies out there that have angled screw channel options. Most of the angled screw channel abutment options available are custom fabricating abutments with angled screw channel components such as Nobel Biocare’s ASC (Angled Screw Channel), Atlantis CustomBase, and Straumann VarioBase, Blue Sky Bio Custom Abutments, and TruAbutment Angulated Screw Channel Abutments. Additionally, there are other options out there of ti-base solutions similar to the one mentioned above including Dynamic Abutment Solution and ZirkonZahn Parallel/Conical Cemented Titanium Bases.
I had a tricky case that was giving me a bit of a headache because the implant came out quite a bit to the buccal compared to the occlusal table of the adjacent teeth. I removed the healing abutment, placed a DESS Scan Body onto the implant and lightly tightened down. I scanned it using my Medit i500 intraoral scanner and export the files into exocad software for digital design. I completed the design and angled the screw towards the occlusal surface, approximately 24 degrees! I milled the crown using my VHF K5 mill with Kuraray Katana STML. A bit of stain/glaze using Jensen Dental MIYO liquid ceramics and my Whip Mix porcelain furnace. I cemented the DESS AngleBase ti-base using Panavia and off we go!
The crown dropped right in, minimal adjustments. In some of these early cases, some of my screw channels were a bit wider than I had hoped but I have since learned how to correct that. The patient is thrilled with the result, but got me thinking… could I use this approach in more complex restorations?
I did a few more single implant cases and liked how simple it was for those the routine cases. I had a challenging case coming up though – a full-arch screw-retained crown & bridge case. For myself and how I work clinically, necessity is often the mother of invention and/or development.
This patient had 8 implants placed on the mandibular arch for the purposes of crown & bridge implant dentistry – 3 separate fixed partial denture restorations (teeth 18-21; 22-27, 28-31). The left side was fairly simple to restore but the right side a bit more challenging due to the angles of implants in positions #27,28, 30, 31. I made traditional open-tray PVS impressions and then poured the dental cast into traditional Whip Mix gypsum. I placed DESS Scan Bodies onto each implant and scanned using my TRIOS intraoral scanner. I imported the files in to exocad software and planned the arch using his wax-up and changing the angles of the planned restorations with the software controls built into exocad.
After designing, I 3D printed the designed temporaries on my Nextdent 5100 3D printer and Nextdent C&B MFH resin. I fitted the final printed restorations onto AngleBase ti-bases and checked their fit on the dental cast. Some adjustments were needed, but mostly in the area where the printing supports were placed.
Over the past years I have gotten to the point now that I’m saying to myself, “why would anyone want to use anything other than an angled screw channel?” It seems like a legitimate question! The gut reaction by many in dentistry is the usual… “ti-bases don’t work” or “crowns on short ti-bases will debond!” I’ll admit… I used to think the same thing and ask similar questions until I completed many cases and have seen follow-up over time with zero de-bonds in normal situations.
I wanted to put short ti-bases to the test… I had the opportunity while filming a video at the 2019 IDS dental show:
Let’s get back to the big reason why many dentists cement crowns… anterior esthetics! I saw a patient patient who had an anterior implant in position tooth #8. He has been wearing a healing abutment for a period of time and we removed it to make a digital impression for his final crown. I placed a DESS Scan Body and scanned him using my TRIOS intraoral scanner.
After making the digital impression, I imported it into the Dental System laboratory software for design. I noticed right away that the angulation of the implant long-axis would put the screw through the incisal edge, but I was able to create a lingual access channel simply with the click of a mouse. If you are interested in seeing the software in action, I go through the case in the following video:
After designing, I milled the crown on my VHF K5 mill using a Zirlux Anterior ML disc and stained and glazed with MIYO liquid ceramics. I cemented the DESS AngleBase with Panavia. I removed the healing abutment and placed the restoration, dropped right in. I was able to torque to full manufacturer-recommended torque value. His tissues were a bit unsupported on the distal, however, overtime this will fill in nicely once the tissue has matured.
The above examples are just a few cases I have completed over my time since being exposed to angled screw channel systems. I now approach cases differently than I have before in the past because I am no longer constrained by making the decision of “Should I place this implant in the perfect restorative position even if the bone isn’t ideal there?”
Instead, I now make the decision to place implants in a position balanced between the ideal restorative and surgical position. I know now that I now can angle implants up to 25-40 degrees and correct the angles in the final prosthetic stages, ultimately still delivering a restoration that is screw-retained! Angled screw channel has truly been a paradigm shift in my implant practice.
Interested in learning more about CBCT, implant planning, 3D printing, and some amazing step-by-step guided surgery protocols in your office and/or laboratory? Check out our innovative step-by-step online digital dentistry course at www.LearnDental3D.com