Mini implants

In order to better understand how mini implants work, it will be helpful to read about the history and current status of standard dental implants. Mini implants have been in use since about 1970 (click here to see a case actually placed in 1970), but were not considered "permanent" implanted devices until April 1999 when they were cleared by the Food and Drug Administration.

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.

Since the FDA approved the MDI mini implant as a long term method of denture stabilization, mini implants have become increasingly popular among dentists. They are also used for supporting crowns in situations in which there is not enough room for a standard implant. The cost of a mini dental implant is generally on the order of one quarter to one third the cost of a standard dental rootform implant. (Note: MDI mini implants have also been accepted for transitional and long term use by Health Canada in Ottawa 11/9/04.)

Mini implants are 1.8 mm in diameter and come in 4 lengths. The length chosen by the surgeon is determined by the amount of bone available to retain the implant, as well as an assessment of the density of the bone. Very dense cortical bone may be better served with a shorter implant. Generally, four mini implants are placed in the anterior portion of the lower jaw. A second type of mini implant is called a Max and is 1.6 mm in diameter. Max's come in three lengths and are generally used in cases in which the bone density is low. This is most generally the case in the stabilization of upper dentures.

Unlike standard implants, mini implants allow immediate loading. This means that the patient walks out of the office on the day of surgery with a lower denture which is not only solidly stable, but can be used to eat immediately. Mini implants can often (not always) be placed in the lower jaw without cutting an incision in the gums. in other words, they can often be placed right through the gums directly into the underlying bone. Most of the time, the only anesthetic necessary is an injection directly over the position in the gums where each implant is to be placed. The old lower denture can then be retrofitted over the newly placed implants, and the patient can use the denture immediately without waiting for the three to six months necessary for a standard implant to integrate. Furthermore, because the implants are about the size of a standard wooden toothpick (they are made out of a titanium alloy), patients who have been told that there is not enough bone to accommodate standard implants can generally be fitted with minis. The entire procedure (placing the implants and retrofitting the old denture so that it is supported by the newly placed minis) takes about 90 minutes. It is generally painless, and produces very minimal post operative discomfort.

Patients can be fitted with these implants and begin using the newly stabilized denture immediately because these implants do not require months of waiting time to integrate. The implants are "screwed" firmly into the bone so integration is immediate (although further integration on a microscopic level has been shown to take place for months after the initial placement of the implant. Finally, since the procedure generally involves no major incisions, there are very few contra-indications to the surgery.

The decision about the need for making an incision before placing mini implants, and the subsequent need for sutures (stitches) after the implants are placed is made on a case by case basis. The major factor is the shape of the remaining bony ridge as determined by x-ray.

If a patient has been without lower front teeth for a very long time (decades), the bone at the top of the ridge may be quite sharp. Consequently, the pilot drill used to prepare the bone to receive the implant may slip off the top of the ridge when the hole is started.

To avoid this problem and to allow the implant to integrate into bone along its maximum length, the dentist makes an incision along the ridge, from about where the canine tooth used to be on one side to the canine position on the other side. This allows the dentist to visualize the bone, and to flatten the sharp ridge slightly in order to drill the pilot holes in precise positions.

The use of an incision does NOT preclude the immediate loading of the implants after the procedure, and the patient leaves the office wearing their denture.

The only medical conditions that absolutely preclude the placement of these implants are the following:

Uncontrolled diabetes
A history of radiation treatment to the jaws (generally for cancer)--this does not include diagnostic x-rays
Immuno-suppressed patient
Substance abuse

Factors which place the prognosis for these implants in doubt include the following: Note that these factors do not necessarily preclude the use of mini implant retained dentures. However patients who exhibit these traits are more likely to suffer complications and possible failure of one or more of the implants.

Heavy smoking and/or drinking
Sjorgren's syndrome
Alzheimer's disease (these patients may be unable to insert and remove the dentures after the implants are placed)
People who clench their teeth.
Young persons who are still growing

Even people with heart disease, high blood pressure, or other serious medical conditions usually have no difficulties retaining mini implants. Old age is NOT a factor! Persons taking anticoagulants like coumadin and wafarin need to stop taking their medication several days before the procedure only if the dentist determines that an incision will be necessary in order to place the implants. The surgery is very short (about 90 minutes) and very little bleeding occurs. Furthermore, there is generally very little post operative discomfort. Tylenol, Advil, or Aleve for the first twelve hours after surgery are often sufficient. If an incision is used, the dentist may prescribe a narcotic for the first twelve hours after the surgery. If no incision is used, many people require no pain medication at all.

What is involved?

The first visit is a general "meet and greet" during which the doctor gets the necessary information from the patient and explains to the patient what to expect. In some offices, this visit is a free consult. At a subsequent visit, the dentist will generally take two x-rays; a panorex and a lateral jaw film to assess the amount of bone available, and to determine which size implant is appropriate for the case. Many offices will charge for the x-rays, but apply the fee to the final cost of the case when it is completed. In a very few instances, we find cases in which the amount or quality of bone is not suitable even for mini implants. The old denture is assessed for suitability to receive housings with o-rings. These housings remain permanently in the denture and will engage the implants. If the denture is not suitable to receive housings, or the patient has decided to have a new one made after the implants are placed, the dentist will simply reline the old denture with soft reline material. The soft reline material engages the denture nearly as well as the housings, but should be changed every six months. If the patient is a suitable candidate, he/she is given all the information necessary in order to decide if he/she really wants to go through with the procedure, and then the patient is asked to sign an informed consent document.

The surgery

The following describes the most common type of mini implant surgery; one 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 will determine 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.

At this point, there are two ways to engage the implants in the denture. The first way is simply to fill the hollow in the base of the denture with a soft reline material. This material engages the implants fairly firmly, but allows some movement. It transmits less biting force to the implants and may be the best solution in cases in which patients smoke or clench their teeth, or in which there are other factors that may interfere with the final integration 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 three to six months 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.

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. 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. Upon rare occasions, a mini implant will break while the dentist is placing it. Considerable force is placed on the implant during the process of insertion. This 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 boneline and then proceed to place another implant adjacent to the broken one.

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 (ie. 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.

Q. How can I find a doctor who will place mini implants and retrofit my denture?

A. The Imtec corporation which manufactures the MDI mini implant system and all related instruments for their placement also offers seminars, courses and mini residencies to dentists who wish to become involved with this service. The company keeps a list of doctors who have had official education in the process. You can find a doctor (the database is worldwide) by going to their site, clicking on your language, and clicking on the link "Locate a doctor" which is located in the second toolbar near the top of the page. Use the "advanced search" option to enter your state or city. Click HERE to go to the company site.