Four on the Floor 101: Small-Diameter Implant Applications

INTRODUCTION
I would like to preface this article by stating that I make no claims to having mastered the art of placing small-diameter implants (SDIs). I have colleagues who have done many more cases and who have in fact served as mentors during my own development in this area. The late Dr. Sam Shatkin comes to mind as does his son Dr. Todd Shatkin, as well as Dr. Joseph Santelli, a friend and featured instructor for one of the many Shatkin First SDI (mini-implant) seminars. However, I would point out that some of baseball's best hitting coaches had paltry career numbers yet still became exceptional teachers. Let me use this analogy as a backdrop for passing along to you some of the "tricks" I've learned about denture stabilization with SDIs. Make no mistake, I've put in my course time on this subject. Background knowledge in this area is essential, as it is with any dental discipline. Ultimately, however, once that foundation is laid, the definitive teacher is jumping in and doing a live case. I recall waiting a full year after my first SDI course was taken in search of the perfect edentulous ridge to begin my journey. (Perhaps that was excessive.) Since then, and many cases later, I'm happy to relate that very little in my dental world gets the juices flowing as much as stabilizing a floppy lower denture with 4 mini dental implants (MDIs) in the course of a single morning. It's an incredibly rewarding experience for which patients are eternally grateful. That said, what follows is a collection of tips that might prove useful as you engage in your own SDI journey. I will assume a certain amount of reader familiarity with the process and focus on those areas that "eased my own pain."

WORKUP AND CASE SELECTION
Building your own confidence is crucial. The best way to kick off your SDI campaign is by choosing a patient who possesses abundant bone with firmly bound epithelialized tissue; this, as opposed to a knife-edged/movable ridge (Figures 1 and 2). The latter can come later in your SDI career. The almighty panoramic radiograph (Panoramic Corporation PC 1000) is still the film of choice when gauging how much bone is available with respect to height and quality. It can assist us in choosing the right length for our SDIs as well as in locating crucial anatomical landmarks. I've found it helpful to use a 5.0-mm diameter ball bearing (Henry Schein) secured somewhere on the denture (or pre-extraction teeth) with ordinary beading wax. This known reference in the film will allow you to get a more accurate idea of bone height (Figure 3). (Thanks to Dr. Scot Mardis for this suggestion.) Taking it up one notch, if your practice management software offers x-ray viewing options that feature a calibrated digital "ruler" (such as KDI [Carestream Dental]) this provides an even better way to measure bone height (Figure 4). As for the width of the ridge, finger-thumb palpation seems to be the most commonly used approach. Certainly you can numb your patient and use bone calipers to measure bone width, but I haven't found this necessary. And since SDIs aren't much wider than the posts we place in roots, we have a fair amount of leeway. If I'm unsure about width, I'll often take a "sample" SDI that I have handy and hold it with college pliers over the ridge while palpating, visualizing how it would be angled and located. This will usually allay my concerns. Of course a CAT scan might be the ultimate look, but this adds one more obstacle to the mix as well as increased cost. Again, this is usually not necessary so long as we confine our SDIs to the bony area in between the mental foramina. I find it most comforting when upon palpation, the bone appears to broaden beneath the tissue as opposed to diving into a lingual undercut.

Figure 1. A robust ridge with plenty of bone and an absence of redundant tissue. Figure 2. Severely atrophic ridge, perhaps necessitating an open procedure or preprosthetic
preparation.
Figure 3. A stainless steel 5.0-mm diameter ball bearing reference (Henry Schein) affixed to denture during the taking of a panoramic (Panoramic Corporation PC 1000) radiograph. Figure 4. "On-screen" computer
measurements can assist in determining bone height, albeit a 2-dimensional look.

When in doubt, and how I proceeded with all of my early cases, I would send records to Shatkin First Lab consisting of a model, a panoramic radiograph, and a photograph of the ridge. They would in turn indicate the appropriateness of the case, select implant sizes (length and diameter) and draw on the panoramic radiograph and model where to place the SDIs. On tricky cases, I continue to take this approach. Remember, 2 heads are usually better than one!

SURGICAL GUIDES
This leads us to the topic of surgical guides. Another service that Shatkin First offers, in addition to their recommendations, is a surgical stent that corresponds to those recommendations (Figure 5). In its simplest use, one can poke holes in the gingiva as dictated by the stent to locate the osteotomy sites for the SDIs. Taken one step further, when combined with an osteotomy drilling guide tool sold by Shatkin, the stent can be used to guide the actual osteotomy drill (Figure 6). The effectiveness of this approach, in my experience, depends on the definition of the ridge. If it is robust, the stent can be held firm enough to make this plausible. If ridge definition is at a minimum, it is difficult to stabilize the stent enough to allow for reliable osteotomy creation. Best to mark the spots only and free hand drill. Fixed SDI applications (the topic for another article) lend themselves well to this splint guided osteotomy approach. As you might guess, a surgical guide stabilized by teeth is simply easier to work with.

Figure 5. Small-diameter implant (SDI) surgical guide from Shatkin First. Figure 6. Surgical guide and drill guide combined during the osteotomy procedure.

With experience, you'll often be able to decide where you would like to place your SDIs and which ones to use. To that end, I still find it helpful to have an osteotomy "positional guide." In the following section, I will describe how I make them.

FABRICATING A POSITIONAL GUIDE
I use a small thermoplastic wafer (Temp Tab [All Dental Prodx]) that upon heating changes from an opaque light blue color, to clear. One or 2 wafers will usually do the trick. When fully heated in a water bath (we use a $10 electric teapot), the softened Temp Tab can then be rolled into a hotdog shape for adapting over a model of my patient's ridge. As I've predrawn where I want the SDIs to be with black pencil, I can easily see the marks through the softened clear Temp Tab. I then use a periodontal probe to create openings over the black marks on the model. Upon cooling, this guide can be taken to the mouth to transfer those SDI locations with simple bleeding points also created with a periodontal probe or similar. After removing the guide, I can digitally or with the probe inspect what lies underneath the bleeding points and adjust the position accordingly for optimal placement of the SDI (Figures 7 to 9). Also be sure that these locations are underneath an area of the denture that is of sufficient thickness to allow for placement of the retentive housings!

Figure 7. A thermoplastic material (Temp Tab [All Dental Prodx]) is used to create a "positional guide" for SDI placement. Figure 8. Positional guide in place to create bleeding point references for SDI locations.
Figure 9. Bleeding points created by introducing periodontal probe through holes in Temp Tab guide. Figure 10. Occuslal guide created with registration paste (Jet Blue Bite [Coltène/Whaledent]).

While we are talking about guides, there is one other worth mentioning: a preanesthetic occlusal index. This is simply a bite registration of the patient's habitual occlusion prior to anesthetizing the mandible. This record will ensure that the lower denture, when retrofitted with the SDI housings, will position itself back into your patient's comfort zone (Figure 10). When bilaterally blocked, as I often find necessary to do, it can be a patient challenge to find the occlusal "home base." (Despite being told numerous times at numerous seminars that local infiltration is sufficient anesthesia, patients wish to feel nothing. To accomplish this, I find bilateral blocks the most surefire way to prevent wincing during SDI placement.)

PILOT HOLE CREATION REVELATIONS
Let's talk about the actual pilot hole creation; probably the most anxiety producing aspect of the entire process. I can recall on several occasions watching my pilot drill bounce around the ridge as I tried to keep it upright and straight, praying that it would actually penetrate the site I had chosen with my bleeding point. For some reason, the seminars that I've taken never recommended the use of a small counter-sink hole to stabilize the osteotomy drill. This is easily created with a garden variety flame-shaped diamond point that need only penetrate a millimeter or so into bone to create a positive seat for your pilot drill. Needless to say, the diamond is run with a water spray. I like to use an inexpensive, presterilized, one time use, diamond point (Solo [Premier Dental Products]). This simple act will allow the operator to focus on drill orientation as opposed to fretting over cortical plate penetration. (Thanks to Drs. Ara Nazarian and Santelli for this valuable tip.)
Let me also caution about not making a pilot hole deep enough. Again, early on, I had a tendency to stop drilling short of what had been recommended. That is, I would feel cortical penetration, go a wee bit further and then stop (as opposed to penetrating two thirds of the length of the SDI, as is often recommended in the mandible). This would allow me to thread the SDI but also allow the SDI to seek its own path, resulting in undesirable angulations. Threading/seating would also be more difficult as the SDI was creating more of the "pilot hole" than I had. Simply drilling to full length (again: two thirds of the SDI length in the mandible) alleviated this issue. If you go beyond that, say full length of the SDI, it's not a deal breaker. The SDI will snug up just fine.

Figure 11. "Four on the floor" SDIs placed with square portion of the head halfway Submerged in tissue. Figure 12. Vinyl polysiloxane (Monobody [Coltène/Whaledent]) impression of SDIs within lower denture to locate drilling sites in denture. A pencil is used to mark the spots on the denture acrylic.
Figure 13. Denture ground out, ready to receive "o-ring" housings. Figure 14. Protective shims in place to prevent dreaded acrylic lock down.
Figure 15. O-ring housings in place over protective shims. Figure 16. Acrylic clear away so as to expose the rims of the o-ring housings. Metal rims are in full view.

Sequencing is also a matter of concern and preference. Early on, I placed each SDI individually, drilling one pilot hole at a time and placing each SDI nearly to full seating before beginning the next one. This was incredibly tedious. I then watched Dr. Shatkin (on a Youtube video no less) place 6 SDIs in a maxilla in less than 10 minutes. He did this by first drilling all of his pilot holes in rapid succession and then placing all of the SDIs in sequence from left side to right side. This eliminated the need to continually switch positions, instruments, drills, etc. I quickly adapted this approach and cut my placement time to a third of what it had been. (Note: Dr. Shatkin also uses Intra-Lock's engine driven approach to placing the SDIs. This too saves lots of time.)
I would like to add a final note on depth of placement. Ideally, you would like to have most of, if not all of your threads in bone. This is best accomplished if the overlying tissue is not more than 2 to 3 mm in thickness. If that is the case you will see approximately half of the square part of the head covered by tissue in "noncollared" 3M ESPE SDIs and standard Intra-Lock SDIs (Figure 11). This is desirable. If you anticipate excessive soft-tissue thickness, (4.5 or greater) it makes sense to consider having this removed by you at time of SDI placement or by a specialist prior to SDI placement. Alternatively, Intra-Lock makes an SDI with a 4-mm polished collar that can often solve this problem. They are available from Shatkin First labs.

BEWARE THE RATCHET WRENCH
I would like to say just a few words about the ratchet wrench. I own 2 of them, one that is purely a wrench that came with my first surgical kit and one that I bought after that also measures torque. Get one of these. Had I owned one, it's likely that I would have not sheared off the top of the last SDI in my first 4 on the floor case. That snap rattled me to the core. I would have known that I was challenging the torque limits of the SDI in an effort to completely seat it and instead would have backed it out and substituted a shorter one. In most cases, I now use only the thumb wrench to seat my SDIs. When in need of the torque wrench, it's a 2- to 3-click affair for final seating. If that doesn't do it...well, you now know the remedy.

HOUSING DEVELOPMENTS
I remember my first case and thinking after placing the SDIs, "Phew…the rest should be a breeze…hope there's some coffee left while I read a magazine…." Two hours later I said goodbye to my patient, hoping that I'd sufficiently brushed off all the acrylic dust from my clothes. Arguably, your immediate load responsibilities can be just as arduous as placing the SDIs themselves. Here's a technique that I now use that makes this process easier.
I take a quick vinyl polysiloxane impression (Monobody [Coltène/ Whaledent]) of the SDIs inside the denture and then use a pencil to mark through the impression as to where I should grind the holes in the denture (Figures 12 and 13). Keep in mind at all times that it is absolutely essential that a reamed-out denture sits passively over the "o-ring" housings perched atop the SDIs. Once you've made the initial openings in the denture with a round acrylic burr, an inverted cone acrylic bur is a quick way to take the remaining acrylic out. If you still feel the denture "scraping" against the housings when trying in the reamed out denture, paint the inside of the openings with pressure indicator paste and reseat. The offending hangup will be revealed. Unless the denture is absolutely passive over the housings, do not proceed. Doing so will result in the denture riding high on the SDIs after the acrylic cures, subjecting them to undue occlusal forces as well as causing more "rock" in the denture as it pivots on the SDIs. Been there, done that!
While we are on this subject, make sure to use the little plastic shims around the square portion of your SDI before picking them up (Figures 14 and 15). Failure to do so could result in acrylic locking around the SDI heads, making you "wish that you'd chosen another profession," to quote Dr. Santelli.
When it comes time to cleaning up the excess resin on your patient's newly equipped denture, be sure to remove the flash and excess resin found around the rim of the metal housings. Remove the resin until you can see the entire metallic ring (Figure 16). This will greatly reduce the possibility of post-op tissue irritation. Finally, consider using an acrylic seal coating (such as Palloseal [Heraeus Kulzer]) to make the undersurface of the denture less likely to trap and house bacteria. Your patient will have an easier time cleaning his or her denture.

A FEW ODDS AND ENDS
I believe it's helpful to keep certain concepts in mind when planning SDIs and discussing them with your patients. Chief amongst those thoughts would be the ease of removing and replacing the occasional failed SDI. Patients need to know that they can fail for a variety of reasons. They should also know that in most cases they can be replaced; possibly right away if they possess a suitable site that is adjacent to the one lost, or after the bone has healed in the very same site. Adapt a strategy for dealing with replacements. I've recently begun a protocol that covers the case for one year, during which I will replace a failed implant at no cost to the patient. After the one-year period, the patient is responsible for the cost of replacement at a discounted fee from the original cost. Fortunately, if the case is selected and planned carefully, failures are infrequent.1-3

CLOSING COMMENTS
I hope that some of the suggestions above can be of use to you. The field of MDIs is exciting and unfolding rapidly. If you haven't taken any formal seminars, there is no time like the present. Courses offered by Shatkin First, 3M ESPE, Dr. Gordon Christensen, or the Global Mini Implant Institute (to name but a few) can lay down the basics in as little as a day. If you haven't already, you may find yourself exploring SDIs as they apply to fixed restorations. The lines between MDIs and conventional implants are blurring. The conservative nature and favorable economics of the SDI are appealing to both doctor and patient. Over and out!


References

  1. Christensen GJ. The 'mini'-implant has arrived. J Am Dent Assoc. 2006;137:387-390.
  2. Christensen GJ. The increased use of small-diameter implants. J Am Dent Assoc. 2009;140:709-712.
  3. Shatkin TE, Shatkin S, Oppenheimer BD, et al. Mini dental implants for long-term fixed and removable prosthetics: a retrospective analysis of 2514 implants placed over a five-year period. Compend Contin Educ Dent. 2007;28:92-99.

Dr. Goldstein, a Fellow of the AGD and of the International Academy of Dento-Facial Esthetics, practices general dentistry in Wolcott, Conn. Recognized as one of Dentistry Today's Leaders in CE since 2002 and for his expertise in the field of dental digital photography, he lectures and writes extensively concerning cosmetics and the integration of digital photography into the general practice. He has authored numerous articles for multiple dental periodicals both in the United States and abroad. He can be reached via e-mail at This e-mail address is being protected from spambots. You need JavaScript enabled to view it or at the Web site drgoldsteinspeaks.com.

 

Disclosure: Dr. Goldstein reports no disclosures.