The following describes the manual placement of the smaller mini implants in a lower jaw in which the ridge is reasonably wide and no incision is needed. Note that all implants are placed in the anterior of the ridge, about where the six front teeth used to be located. Mini implants cannot be placed along the back part of the ridge where the molars used to be because in those locations, there is a large nerve trunk which might be injured if an implant was placed there.
On the day of Surgery, the dentist determines the correct position for each of (generally) four implants and then marks the position for each on the ridge with an indelible marker. Anesthesia is injected into the gums directly over the spots he/she made on the gums. Then the dentist begins to drill right through the gums into the bone using a 1.1 mm pilot drill in a slow speed handpiece.
After drilling the pilot hole, The dentist then begins the procedure for inserting the implant through the gums into the drilled hole. He begins by carefully aligning the implant with the original pilot hole and slowly twisting it with a finger wrench until the resistance becomes too great to continue easily. Then the dentist switches to a thumb wrench. The thumb wrench is slowly twisted until the implant is fully seated with the ball and about 1.5 mm of the shank remaining above the gums. (In the images here, a special retraction device retracts the tongue, lips and cheek so the field is kept clear and dry.)
If too much resistance to twisting the implant is met, the dentist may switch to using a specially designed ratchet wrench to finish the insertion.
The finished case looks like the images below. This is the same case viewed head on, and again, from above, using a mirror. These images were taken immediately post op. Note the lack of bleeding.
The post operative x-ray of this case looks like the image below. Note that the implants do not necessarily have to be perfectly parallel to one another.
Retrofitting the lower denture.
In order to retrofit the denture so that it snaps onto the newly placed implants, the old denture is modified so that there is a hollow in the underside corresponding to the general position of the implants.
The soft reline material must be replaced periodically, but the procedure is easy and relatively inexpensive. Some dentists prefer using this method on all their patients for the first month or two after initial placement of the implants to allow the best environment for healing, before proceeding to the long term option which is placing housings with o-rings in the denture for a more positive snap fit (see below).
The implants and the retrofit are generally billed separately, so the total cost to the patient of the soft reline option is considerably less than the total cost with permanent housings in the denture. Some patients prefer to continue indefinitely with a series of soft relines rather than placing housings since the soft material is very comfortable against the gums and new relines once or twice a year will keep the denture base so well adapted to the gums that food rarely ever gets under the denture.
The second way to retain the denture over the implants is to place a specially designed housing with a rubber o-ring over each implant. The dentist may use this option on the day of surgery when the implants are first placed, or he/she may remove the soft reline material that was placed at the time of surgery and place the housings in the denture at a later date. These housings will be transferred to the hollow that was made in the bottom of the denture in the step immediately above.
At this point, the dentist tries the denture into the mouth to see if it fits over the implants with their housings without interfering with the original fit of the denture. He keeps grinding out the hollow in the denture until the lower denture fits over the implants without changing the bite of the lower denture teeth against the upper denture. When he is satisfied that the upper and lower dentures meet in the mouth in the same relationship as they did before surgery without touching any of the implants, the dentist fills the hollow in the bottom of the denture with self curing (hard) plastic and fits the lower denture back over the implants with their housings. The patient is instructed to bite down on the dentures while the plastic pick-up material sets. Once the pickup plastic is set and finished, the lower denture looks like the image below. At this point the lower denture should snap into position over the implants.
A note about the quality of the existing denture
If the dentures are old and do not occlude (fit together) properly, it is very often advisable to have at least the lower denture either remade, relined or rebased prior to the placement of the implants. A rebase is the complete replacement of the pink plastic base of the denture with new plastic. This makes perfect sense because a firmly retained lower denture that does not fit properly with the upper denture will dislodge it and make the upper denture unwearable. Furthermore, if the lower denture has been repeatedly repaired, or the teeth keep falling out, then the modifications necessary to allow the same lower denture to engage the implants will weaken it further and make it even more prone to breakage in the future. If the dentures are much over seven years old, the patient should consider having a new set made either prior to the placement of the implants, or shortly thereafter
A note to dentists
For dentists who have never done implants, mini implants are a reasonable place to start. I would advise taking a course to begin. The easiest way to find one is to Google for "mini implant courses" For those not sure about the efficacy of minis in comparison to rootform implants, you may want to read the paper published by Gordon Christiansen (A PDF document). Below, I have included several basic facts about mini implants.
Mini implants are approved in the US and Canada for both transitional and long term use. The highest degree of success with minis is for the stabilization of upper and lower full and partial dentures.
Many clinicians are beginning to use them as abutments for crowns for lower incisors and upper lateral incisors.
No implant, including minis should be splinted (fixed) to natural teeth. Implants are solidly attached to bone by osseointegration, while natural teeth are attached to bone by the periodontal ligament. The periodontal ligament allows, and even requires, function to remain healthy. Splinting natural teeth to implants can cause the natural tooth to ankylose. An implant splinted to a natural tooth may fail as a result of the movement of the fixed splint allowed by the periodontal ligament of the natural abutment tooth.
On the other hand, partial dentures may be attached to both implants and to natural teeth without danger to either.
Mini implants are a reasonable alternative to rootform implants when cost, or lack of bone width are major considerations.
The dentist should recommend either mini or rootform implants to all patients about to go into a full lower denture, since both implant types preserve bone height. The dentist might want to invest in a set of models that show what happens to a mandible after the teeth are extracted.
Frequently asked questions
Q. How long do mini implants last?
A. No one can guarantee how long any implant will last since so many of the factors that determine the longevity of these devices are patient specific. The term "permanent" is not accurate concerning any medical or dental device, since nothing in medicine or dentistry can be guaranteed to last forever. The term "long term" is more accurate and truthful when referring to any dental appliance. Some minis done in the mid 1970's are still in function. Mini implants have been in common usage only since about the year 2000, after approval for long term use by the FDA. The vast majority of MDI minis placed since that time are still functioning well. A small percentage of implants will fail for various reasons. A failed mini implant is easily removed, and healing is generally complete. Another implant can usually be placed adjacent to the site of the failed implant immediately, or after waiting for three months, directly into the position formerly occupied by the failed implant.
The series of x-rays above shows the forerunner to the current version of the MDI mini implant. This one was placed in the lower jaw to replace a missing lower incisor in 1970. At the time it was placed, the dentist was not sure if the implant would stand on its own, so the implant tooth was splinted to the tooth next to it to stabilize it just in case the implant failed. As you can see, the opposite happened. The tooth that was supposed to stabilize it was eventually lost to gum disease, but the mini implant survived quite nicely. The last film on the right was taken in 1989 and shows that the implant has more bony support than the remaining natural tooth to the left. (That tooth has a root canal, and a second (tiny) mini implant was placed beside the original mini.) To learn more about reading dental x-rays, click here.
Q. I have heard of cases in which an implant will break while the dentist is inserting it. What happens then?
A. Unfortunately, this is a common problem when placing mini implants in the very dense bone of a heavily resorbed lower jaw. Considerable force is placed on the implant during the process of insertion. breaking an occasional mini implant during insertion is considered a "normal" complication, and since the implant is made of titanium and will actively integrate with the bone, there is no good reason to retrieve the broken piece. Most dentists simply remove any of the broken implant that remains above the bone line and then proceed to place another implant adjacent to the broken one. When the bone of the lower jaw is very heavily resorbed, I generally recommend that the patient opts for larger diameter rootform implants
Q. What if the patient smokes or drinks heavily?
A. Patients who smoke are MUCH more likely to experience implant failure. Smoking seems to affect the circulation of blood which is, of course, a factor in healing. Heavy drinking and other substance abuse negatively affects a patient's nutrition and general health. Some high functioning alcoholics have been successful with dental implants, but substance abuse is generally a contra-indication for placing any type of implant.
Q. Why does clenching or grinding on a denture increase the likelihood of implant failure?
A. Unlike natural teeth, implants are solidly attached to the bone without an intervening ligament. This means that implants do not have a natural "shock absorber" to reduce the effect of the constant forces that grinding and clenching will transmit to them. Clenching and grinding can place literally tons of pressure on the bone/implant interface. Bone is not well vascularized (i.e.. it does not have a lot of blood vessels to nourish and heal it in case of injury). The constant "shocks" experienced at the bone/implant interface due to clenching and grinding cause micro fractures and crushing of bone at the interface and these will subsequently cause the body to recognize the implant as a foreign invader. Thus the body mounts an inflammatory response, which means that it begins to replace the bone surrounding the implant with soft tissue containing lots of blood vessels in order to "reject" the implant.
People who habitually grind or clench their teeth may still be able to retain implants, but they would do better to avoid the housings with the o-rings, and remain with the soft reline option mentioned above.
Q. My mother is nearly 90 but still quite bright and active. She is frustrated because she can't eat with her lower denture. Are mini implants a good alternative for her, or is she too old?
A. Age or physical condition are not usually factors regarding the success of mini implants. Your mother is probably a candidate for minis. The short surgery, low cost and minimal post-op discomfort, as well as the ability to function against the new implants immediately, make this form of therapy ideal even for seniors with numerous physical ailments. The only common age related factors that may interfere with these cases are dementia and severe osteoporosis. Severe osteoporosis may affect the bone density and reduce the likelihood that the implants will be successfully retained. Dementia makes it difficult or impossible for the patient to cooperate during surgery, and may make it difficult for the patient to insert or remove the denture after surgery.
Q. Can a mini implant fracture or break while I am eating?
A. MDI minis are made of a special alloy of titanium (Ti6A14Va) rather than the CP titanium used in conventional implants. The use of this alloy has virtually eliminated the likelihood of fracture of these implants during normal functioning. The clinical trials of these implants prove that they can take a lot of abuse before fracturing.
For the dentist, mini implants have been discussed in the following issues of Gordon Christiansen's Clinicians Report:
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