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.
For those patients who have not yet had their teeth removed, and those who have been without teeth for less than five years, you should read my page on bone resorption (the melting away of bone after the teeth are extracted). For persons who still have their natural teeth, this page will show you why you might want to rethink your decision. For those who have recently had their teeth extracted, this page will show you why you should seriously consider getting implants before the bone melts away entirely.
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 come in four diameters (1.8mm, 2.1mm, 2.4mm and 2.9mm), and each diameter and comes in 4 lengths (10mm, 13mm, 15mm, and 18mm). The the 2.9mm diameter mini is called is called a "Hybrid" since it is nearly the diameter of the smallest available rootform implant, but can still be placed using the simplified surgical procedure shown below. Hybrids are used exclusively for the softer bone densities found in the upper arch. The smaller diameter implants are for the denser bone types. The length chosen by the surgeon is determined by the amount of vertical bone available to retain the implant. Very dense cortical bone is better served with a shorter, thinner implant. Generally, four mini implants are placed in the anterior portion of the lower jaw.
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 smaller mini 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.
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:
A history of radiation treatment to the jaws (generally for cancer)--this does not include diagnostic x-rays
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
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 warfarin 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.
Patients on immunosuppressive therapies such as methotrexate for rheumatoid arthritis may be successful with mini implants if the dose of the immunosuppressant is low, and the patient is able to take a drug holiday for at least a week before the implants are inserted and a week afterwards. Always check with your physician before doing this.
Oral bisphosphonates (for osteoporosis or Paget's disease of bone--drugs like Actonel, Boniva and Fosamax) are not considered a contraindication for implants. While implants have been known to fail in patients taking oral bisphosphonates, studies indicate a very low risk of either implant loss or BRONJ (Bisphonate Related OsteoNecrosis of the Jaw) following implant placement. This is especially true if the patient has been taking the drug for less than three years and has no other complicating factors. If the patient has been taking their bisphosphonate for more than three years, some authorities recommend a two to three month drug holiday before the implants are placed, extending to about a month post-op.
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 difference between mini, midi and maxi implants
Over the years, as larger mini implants have been introduced, the terminology for variously sized implants has become confused and a bit misleading. The following is an attempt to sort out the differences.
Mini implants are toothpick sized titanium/aluminum screws that can be placed in alveolar or cortical bone without making an incision in the overlying ridge. Just drill a hole and screw them in. They can be used in maxillary or mandibular arches with sufficient bone depth and density. They are 1.8mm, 2.1mm, or 2.4mm in diameter. They are placed using nothing more than a single pilot drill 1.1mm in diameter (sometimes slightly larger for the larger sized minis). They can be loaded immediately.
Midi implants, also called hybrid implants are larger. About 3 mm in diameter. They are about a half mm smaller than the smallest standard rootform implant. Their placement requires either a full thickness flap, or a hole cut in the soft tissue with a tissue punch. They require a pilot drill, followed by a single shaping drill. They may be loaded immediately, especially if placed in the dense bone of the lower jaw, but the companies manufacturing some brands of midi implants recommend waiting two months before loading.
Standard rootform implants (Maxi) require full thickness flaps, (or at minimum a hole cut in the soft tissue with a tissue punch), are between 3.3 and 6 mm in diameter and require a pilot drill followed by a series of larger shaping drills. They are usually loaded 4 to 6 months after placement to avoid movement of the implant during integration. Some dentists have found that they can load standard rootform implants immediately without interfering with osseointegration.
Overview of the surgery
First, if the patient has been without teeth for a very long time, bone resorption (the melting away of bone due to loss of teeth) may have reduced the depth of bone available to retain a mini implant.
Second, there may not be enough vertical bone because of the proximity of the maxillary sinuses or the mandibular canal. The sinuses are essentially holes occupying space in the jawbone above the roots of the natural back teeth. The sinuses may be quite large in some people, and they may extend too far forward to allow placement of mini implants posterior to the original location of the canine teeth. The mandibular canal contains the neurovascular bundle which supplies feeling to the lower teeth and lips. It runs just beneath the roots of the lower teeth.
Most of the time, the maximum number of mini implants that can be placed in the mandibular (lower) arch is four or five. In the maxillary (upper) arch, four or six 2.1, 2.4 or 2.9 mm mini implants are frequently used.