Chapter 12 The Best of MDIs
Q and A
This anthology has been collected from an extended time span from the ongoing MDI Online Forum and selected blogs; it was assembled by Dr. Victor Sendax and associates with consultation with traditional academic resources as needed. It is in recognition of the fact that valuable and valid answers to often perplexing clinical conundrums may be gained via unsolicited e-mail commentary and queries from patients and colleagues who are on the clinical front line. The provided summary is deemed to embody some of the most constructive contributions from this vibrant resource, but it should not be construed as definitive answers to any of the posed questions.
A. MDIs are made of high quality titanium alloy, consisting of Ti-6AL-4V. A 1997 test study at the University of Alabama at Birmingham clearly established that titanium alloy implants are significantly stronger than CP titanium products. More recently, a torque and dynamic loading study from the Medical College of Georgia at Augusta concluded that after 5,000,000 cycles of force, each ranging from 13 to 134 N at a sinusoidal rate of 8 Hz, no changes or fractures were detected in the submitted 1.8 mm × 15 mm and 1.8 mm × 13 mm MDIs.
Q. What is the approximate distance from the inferior border of the mandible after the MDI is seated? Do I want the longest implant I can get in place without contacting the cortical bone on the inferior border? Or do I want to be half or three-quarters the distance? Secondly, is there any significance to the RPMs of the bur when penetrating the cortical plate and drilling into the cancellous space? I use intraosseous anesthesia regularly and am familiar with the feel of perforating the plate, but I am aware that most implant systems suggest a very slow rotation with a high-torque motor. Will a typical air-driven slow speed hand piece be okay, or do I need an electric motor with controlled speed?
A. First of all, there is no exact specific length or distance recommended. Rather, the basic guideline should be to take advantage of as much available patient bone as possible. You are aware, however, especially in the anterior mandible, that the deep symphyseal bone can be very dense and hard to penetrate. In that event you would be better off not trying to overdo the length issue and settle for a shorter MDI rather than trying to aim for the inferior border. All you need is a crestal cortical penetration (using either a moderately high speed drill to break through or a slower speed drill if it can penetrate readily without excessive pressure or friction) only deep enough to provide a good starter opening to introduce the self-tapping implant. Then, it should be possible to readily auto-advance it with jaw support as you turn it with slow strokes into the medullary (and presumably more cancellous) bone.
Although the point is consistently not to over-instrument the patient’s bone, it is also essential to remember that you must get a good initial penetration (at the right angulation, of course) for the starter opening to allow the MDI to take hold and work its way in effectively. Also, if the initial starter penetration needs to be accomplished at a slightly higher speed for better torque control, it is only in force for a few seconds, with simultaneous water spray and with a very narrow-width drill bit, so little initial bone damage is likely to occur.
If you then follow the classic placement protocol sequence with the finger driver, the more efficient winged thumb wrench, and finally the ratchet wrench if needed to attain the final biting depth, the length of the MDI becomes ultimately less important than its stability and solidity. After the implant is securely placed, it is a mistake to over-ratchet it in dense Type I bone. It is much better to settle for a somewhat shorter implant and with the abutment head consistent with the crestal bone and soft tissue level.
Q. How much postoperative pain should my patients with MDIs expect? I know this is a relative question but it will be commonly asked. For example, is it comparable with an extraction for this type of implant, or is it usually less painful? Whereas I may prescribe hydrocodone 5 mg for an extraction, would I also expect the same level of pain control needed here? What is your usual protocol for postoperative care?
A. If there was no previous inflammation or infection in the area under treatment, there should be little postoperative pain except for the needle injection sites. Low-level analgesics like aspirin, acetaminophen, ibuprofen, and comparable NSAIDs are the only usual postoperative medicines. Warm saline rinses are also beneficial to increase circulation and blood supply to the insertion site and speed the healing process.
A. You can use chairside, immediate soft-liners over the O-ball abutment heads as the kindest, gentlest retainers until your own comfort level with the technique convinces you that, in your own hands, the Sendax MDI technique works as described. Then you can substitute O rings for more secure retention after you are convinced that the MDIs are solid and secure. You can often acquire sufficient retention with only two or three implants as well as four; therefore my recommendation is to avoid limiting yourself to any exact number in advance and allow the individual case variables help you fashion a customized decision, which also allows for what I consider a more professionally desirable complete case fee to be presented rather than the typical shopping list of charges.
A. A fibrous tissue response down the line is possible with an implant if it is subject to consistent traumatic lateral movement. Even ongoing micro-movement can be destructive to bone healing physiology. However, MDIs are placed directly through the crestal gum tissue into the underlying medullary bone with a very small starter opening, just enough to promote a self-tapping “take” and permit the auto-advancement thread design to then virtually draw the implant into the bone. This means that there is no conventional “healing period” because nothing requires a period of repair. The direct contact of implant surface to bone (osseoapposition) is accomplished immediately with minimal surgical intervention. No significant amount of bone is lost by drilling it away, as would be the case in a typical implant osteotomy procedure. The only bone loading force during a slow turning insertion phase is mostly compressive, which bone is uniquely able to tolerate within reasonable limits.
Most fundamentally, the threaded surfaces of MDIs do not have to first grow into contact with the bone; it’s already there from day one by direct osseoapposiiton, and it is mature support bone. How well the implant then bears up under diverse loading conditions may have more to do with peripheral systemic issues like medical profile and heredity. More than two decades of clinical experience with MDIs has proven the integrity and legitimacy of this unique insertion protocol and made it possible to achieve immediate and sustainable loading without significant bone loss or mobility. This is possible even in medically compromised patients in long-term applications.
A. MDIs work very well as single tooth replacement implants where space is insufficient between tooth roots for a conventional implant. MDIs can be considered long-term implants if the patented insertion protocol is followed precisely.
Q. Have you used this implant for replacement of a single mandibular incisor? I am a periodontist treating a 23-year-old woman with a congenitally missing #26 that is presently restored via a repeatedly debonded Maryland bridge. The adjacent #25 and #27 are essentially virgin teeth. Interradicular space slightly less than 4 mm makes placement of a conventional narrow diameter fixture problematic. Her restorative dentist is open to any options. Have you managed similar cases?
A. This is actually an ideal application for the MDI and we have been successful in cases with congenitally missing teeth and narrow interradicular space, with or without a previous failed Maryland bridge. Assuming you have experience in placing MDIs, follow your previous steps, taking a little extra care to get the angulation on target by taking a few progress periapicals and making any midcourse corrections as needed. A temporary crown can be placed on top of either the rectangular head or O-ball head abutments until the definitive crown is made. Some dentists are now using the CAD/CAM CEREC and comparable techniques to fabricate crown restorations over MDIs as well as via the more traditional crown techniques.
Q. I would like to place MDIs in my patient’s anterior mandible. She only has 8 mm of bone height. I was going to place the 10-mm MDIs and possibly have 1 mm through the inferior cortex. Comment please.
A. There is nothing intrinsically problematic about this strategy. The primary difficulty I see is trying to self-tap the MDI through the last few millimeters to reach the inferior cortex of the extradense symphyseal bone, leading to the likelihood of either stripping the bone or burnishing it. Also, if you do manage to penetrate or perforate through with great effort, you run the risk of the patient experiencing bone necrosis and abscess. It’s better to stop when you hit too dense a layer of apical anterior bone and even to allow a few MDI threads to remain uncovered by bone and/or gingiva if necessary. Remember, don’t over-instrument the bone! A significant number of failures can be attributed to over-instrumentation.
Q. I have a patient with a very heavy bite who has a history of fracturing several of his upper dentures. He’s asked me about MDIs. Also, what do you suggest insofar as protocol when an MDI fails? Do you replace it with a longer one? Do you go adjacent?
A. For heavy bite and temporomandibular joint parafunction cases I recommend starting with a soft liner in the O-ring caps that have been incorporated into the denture. Remove the rubber O-rings from the caps, and use a nonrunny soft liner (either powder/liquid mix or automix) in each minicap and rebase the entire intaglio (soft-tissue bearing) surface. Insert the prosthesis in the patient’s mouth over the O-ball abutment heads in centric and vertical occlusal and allow to set over the MDIs. This will give the patient a reasonably stable overdenture in which the heavy occlusion will be born mostly by the soft liner and will protect the MDI bone support from functional and/or parafunctional overloading. Eventually you can convert some or all of the O-ring caps to regular O-ring retainers as needed by the patient and if the MDIs are stable and comfortable.
As for implants that are loose or exfoliated, I recommend replacement without charge within a reasonable time frame after insertion, especially if I feel that poor bone resource is the likely cause for failure. Each clinician must be responsible for formulating a replacement charge policy based on his/her learning curve status. It applies to length, location, and number of such replacements or repositionings. It’s basically your call because you know from your x-rays and working the region far better than someone else how to proceed with reasonable confidence.
Incidentally, doctors sometimes ask if they should refund the cost for a failed MDI if the patient is unhappy. Again, this is an individual call, but I would advise approaching refunds cautiously because there is a suggestion or hint of error on your part. It’s better to focus on replacement without charge on the basis that you are still in the exploratory stage of determining where the best quality of bone for MDI support is located.
Q. I just placed my sixteenth MDI and everything went well once again. To me, the MDIs are almost scary. They’re so easy! Plus, my patients LOVE them. I’ve been charging $500 per implant and another $200 to pick up the O ring into the denture (per implant). My practice is located in a Boston suburb. Am I charging fairly? I can place two MDIs and pick up the O-ring caps in about 90 minutes start to finish.
A. Of course it’s fair if the patients think so, too. However, I would note that we typically recommend a minimum of four MDIs in the anterior mandible. One or two posterior MDIs can add significant additional retention and stability if there is available bone without the risk for encroachment on the neurovascular bundle or mental foramen.
Q. Should I have a patient having MDIs placed go without his or her dentures for any period of time after the surgery or treat it more like an immediate denture? If he or she wears it immediately after surgery, should I wait until the next day to remove it or should it come out that same evening?
A. There is no need to let the patient go without his or her prosthesis at any time unless the prosthesis itself is causing iatrogenic pressure ulcers or other comparable problems that you cannot resolve chairside by basic denture border and internal adjustments.
A. Each case is different, as you well know. Keep in mind that you need to stay well mesial to the vulnerable mental foramen and associated nerve “loops” and distal to (and superior to) any extremely dense symphyseal bone in the midline. We recommend you present the procedure to your patient as an exploratory process to test the bone quality and quantity rather than as a “tentative implant placement.” This is a professional approach, is truthful, and, importantly, less stressful for you and your patient.
Q. On a full lower denture, I placed four MDIs: three 13 mm and one 10 mm. I placed them too close together to use one of the abutment posts, allowing only three metal housings. I felt I was placing the implants into the body of the mandible through the little attached gingival I had. When I finished and was placing the housings, they were all lingually inclined, impinging on the lingual tissues. The one that could not be used because it was too close to the other implants was also so lingually inclined that it couldn’t have had a housing cap on it anyway. After 1 week the 10-mm MDI was lost. (It was positioned farthest to the left and supported one of the retention caps). Clinically I feel I had left too much cold cure acrylic around the implants and/or she bit on her denture too hard during set, which caused pretty severe tissue irritation and probably loosened the implant. Currently there are three solid implants, two with metal housings (both positioned on the right side) and one with no housing. The retention of the denture is good but the right side is solid and the left “lifts a little” during eating, making it uncomfortable to the patient. I would like to place one or two more implants on the left side to balance the retention. I would like someone to look at the case and show me the optimum position and other suggestions. The patient is fine with placing the other implants. I have a lateral cephalometric x-ray, a panoramic x-ray, and a lower study model. Please advise me how I could discuss this with someone.
A. The best bet when you want to progressively load MDIs is to use at the outset only a soft liner rebase over the implants and the entire tissue-bearing surface of the denture. This would have eliminated any starting complications in your first case by giving you time to evaluate the viability of the MDIs before committing yourself and the patient to the more efficient O-rings in their encapsulations. In fact, I use this sequencing myself in most of my own cases. Be careful to use the silicone elastomeric shims on the square 4-mm base portion of the abutment to avoid the excess acrylic locking on during O-ring cap pickups (that obviously would be the wrong way to give a patient a fixed bridge!). Also, I recommend that you enroll in a Mini Residency or MDI Seminar, if you haven’t already done so, at which time you might bring along your diagnostic materials for evaluation.
Q. How do I determine the amount or length of available bone to determine if I have enough or what length implant I would want to use? I do not have a panoramic x-ray machine, but have access to one through my local orthodontist. Would you please explain how I could take x-rays and make this evaluation for maxilla and mandibular arches? Also, could you expand on what parameters you use to judge the quality of bone? I am looking forward to using the system a lot and am already advertising for patients.
A. You have raised many pertinent questions that relate to both conventional implants and MDIs. All types of x-rays are useful guidelines for bone quality (density), quantity, and height. A panoramic unit is basic if you do implant therapy, whether it’s your own by purchase or rental, for maximum visualization ability. CT scans, tomograms, lateral plates, etc., can also be useful, but keep in mind that all these methodologies are approximations and therefore none of them give you a truly foolproof answer. Consequently, the best advice is to gain experience in estimation by doing the MDI procedures and taking evaluation x-rays to check your progress. Make midcourse corrections as needed to maximize use of available medullary and cortical bone without encroaching on any vulnerable structures, such as neurovascular bundle, mental foramen, labial, buccal and lingual plates of bone, and floor of sinus or nasal cavities. The most useful learning tool is experience doing the procedure and carefully monitoring the results. You’ll be surprised and gratified by how rapidly you’ll master the learning curve for a procedure that’s essentially simple but still embodies variable and occasionally challenging elements.
A. All implants, including MDIs, will last as long as they remain bone-integrated without mobility or infection. MDIs are the only implants on the market that can be deemed integrated immediately after insertion due to their unique, patented insertion protocol. Operating as a minimally invasive, totally self-tapping procedure, a MDI does not require a conventional osteotomy to ream out a considerable amount of bone that must be regenerated into contact with the implant surface before supportive integration can reasonably be expected. Histologic human studies have confirmed that MDIs demonstrate direct bone contact without any intervening soft tissue, and, most importantly, ongoing clinical experience has shown the ability of an integrated MDI to be able to bear functional intraoral loading without loss of integration. However, all implant systems can potentially lose bone anchorage from occlusal overloading, especially during habitual bruxism and other parafunctional, nonphysiologic activity, and local and systemic disease. Smoking has also been shown to be a prime negative factor in connection with osteoporosis and periimplantitis, leading to a greatly increased likelihood of implant failure.
If you use only a minimal starter cortex penetration and progress only 3 to 4 millimeters into underlying medullary bone, you’ll find that the MDI device auto-advances into the remaining bone until it is rock solid. This totally self-tapping, virtually nonsurgical insertion protocol will provide immediate integration without an intervening healing period. That is the core rationale for any assumption of MDI longevity.
No one can simply claim longevity. A clinician must gradually develop the essential “comfort level” required. You’ll quickly find the MDI works not only for short-term but long-term, on-going applications as well.
For implants in general as well as Sendax MDIs in particular, there should be no specific cutoff date for implant survival if the implants are in direct bone contact support. This is called osseointegration by the Brånemark definition, or as we prefer to call it, osseoapposition, because direct bone contact with MDI threads occurs immediately upon auto-advancement insertion rather than by the slow healing and bone regrowth/repair process characteristic of conventional implant systems.
Q. How do I restore the implant prosthetically? I can see that the implant has the O-ball head for a denture. What if I want to use the implant for a three-unit bridge or for a single crown? Also, are they recommended for bridges or single crowns?
A. You can still use the same O-ball head for fixed applications by blocking out the complete length of the abutment with an elastomeric shim before wax-up and casting to permit an easy “draw” of the pattern from the abutment analog. This also avoids undercut or parallelism problems. Of course, you can also use the rectangular “preppable” head MDI abutment as well as the O-ball type.
Q. I’m using the MDI Max for replacement of an upper lateral incisor. You frequently mention the use of a “shim” for casting to block out undercuts. Is the shim placed on the MDI intraorally before the impression is taken for a crown, or should I send the shim to the lab and instruct them to place it on the master plaster cast before wax-up? Will the final crown have a “positive” seat if the shape of the implant was altered by use of the shim and therefore rotates when tried in instead of fitting with a “definite” seat? You also mention that the MDI can be shaped to allow for occlusal clearance or parallelism. Any problem doing this directly in the mouth using high speed drill with water or is generation of heat from high speed drilling a concern? Comments, please.
A. The usual sequence of procedure for fixed single or multiple restorations is to take an intraoral impression in polyvinylsiloxane or comparable material, place an IMTEC analog in the MDI location, then pour up the model. (An elastomeric shim would only be used intraorally if you were doing a direct O-ring/cap pickup.) A shim can also be placed over an O-ball analog in a model to provide a spacer and undercut block-out for a wax-up. Make intraoral adjustments with moderate speed and water spray.
A. After placing O-ball MDIs, you can easily retrofit an existing maxillary or mandibular denture (or bridge) by hollowing out the acrylic for relief over the MDI(s) and following up with a soft chairside liner. When set, this will provide moderate anchorage without compromising the MDIs bone support. After you have attained your own comfort level with the system’s ability to be put into immediate function, you can switch over to the more secure O-ring retention attachments, which are included with each O-ball MDI. You might also think about O rings for medium and longer-term use rather than only as a short-term transitional solution, but that will come about naturally in the course of your familiarity and experience with the entire MDI insertion and reconstructive protocol.
Q. If I’m certain I’m going to do a “fixed” case, should I use the square- (rectangular) headed MDIs as opposed to the ball type? Also, do you often have the laboratory place the O rings at the bench rather than doing it chairside, especially for a new denture?
A. You can use either rectangular head or an O-ball head for fixed applications because they both retain well. Be sure to use the elastomeric shims for any easy draw and undercut blockout when doing direct intraoral pickups. O-ring caps can be picked up directly intraorally, or indirectly, by means of a poly impression and analogs, then lab processed.
Q. I have a lab question. I visited a dental lab in New York recently. The lab technician had a few of my MDI cases. He mentioned that on a new removable partial denture, after I place the MDIs before final impression, I can place the O-ring cap on the implants and withdraw it in the impression, place analogs inside the O-rings, and they’ll process the case. Supposedly this would save chair-time but can it be as accurate? He thinks yes; what do you think?
A. It’s apparent that your lab tech contact knows a lot about restoring MDIs. This technique works just fine, but when you ask if it’s accurate, I would respond by asking you: Accurate as compared with what other technique? An alternative would be to take a full arch heavy-bodied polyvinylsiloxane (PVS) or polyether impression of the entire jaw. A good supplemental tip is to eject some PVS medium-bodied material directly over the O-ball abutment heads before taking the impression so you get a more fully-detailed seat for the />