Traditionally, dental implants have diameters between 3.75 mm and 4.1 mm and have been scientifically proven to provide excellent long-term results. These implants are widely regarded as an industry standard and it’s extremely rare for them to fracture, even after long-term use. When choosing standard dental implants, the alveolar ridge must have sufficient horizontal crestal dimensions and there must be adequate space between the adjacent teeth or other dental implants. It’s generally thought to be advisable to have a horizontal crestal alveolar width of approximately 6 mm with a 3 mm inter-implant distance.
Mini dental implants were introduced in the 1990s. These were approximately 1.8 mm to 2 mm in diameter and were specifically designed to cause minimal disruption during placement. At first mini dental implants were intended for use as a transitional device, providing adequate stability for edentulous patients while standard diameter implants osseointegrated during a four to six-month period. Once osseointegration was complete, the mini dental implants would be removed but were discovered to have osseointegrated to the same extent as the standard dental implants. As a result, applications for mini dental implants were increased, the designs enhanced, and a greater range of diameters was developed. Narrow diameter implants (NDI) have diameters between 2.2 mm and 3 mm and often the implant surface is enhanced to help promote integration. NDI’s are also referred to as “small-diameter implants” or “SDIs” but are also called “mini dental implants” or “MDIs.”
Figures show that just 10% of patients who visit a dentist and who could benefit from dental implants will actually proceed with treatment. Sometimes patients have been told dental implant treatment isn’t suitable for them, perhaps because of inadequate room, which can often be the case when replacing lower incisors. They could have been deterred from treatment due to the need for additional procedures, such as bone augmentation. Some people are simply unwilling or unable to undergo treatment they regard as being too invasive. Often NDIs can be placed using flapless surgery, a minimally invasive technique that offers faster healing for patients. This can be a good solution for patients who cannot tolerate conventional diameter implant placement but who could cope with a shorter procedure such as flapless implant placement. It is also possible to combine the use of NDIs with traditional implants, providing far greater flexibility in treatment planning.
When you choose to offer NDIs in your practice, you will increase the range of treatments available for patients; something they may have thought impossible could become reality! Some clinicians are still unsure about the long-term viability of NDIs but a recent 14-year followup study evaluating bone loss, peri-implant bone remodeling, and esthetic outcomes reported no implant failures or prosthetic complications. Equally as importantly, patients were found to be very satisfied with their treatment.
This treatment could be suitable for edentulous patients with severely resorbed narrow ridges. NDI’s are frequently used for denture stabilization, utilizing multiple implants in the anterior jaws. Treatment can be particularly good for edentulous patients for whom financial considerations are important. Patients requiring the replacement of lower lateral, central incisors, and upper lateral incisors may benefit from this treatment. Narrow diameter implants can also be used for restoring multiple lower incisors when splinted together, and are suitable for both fixed and removable restorations. When selecting patients who might be suitable for this treatment, it’s important to consider the thickness of the soft tissue. If the tissue is thicker than approximately 2 mm, it may need to be reduced, which can be done before surgery or at the time of implant placement.
One thing you will need to decide is whether to use a single-piece or two-piece NDI. Both have their advantages and disadvantages. One advantage of using a single-piece NDI is the elimination of any micro-gap between the abutment and the implant. The disadvantage of using a single-piece NDI is that it requires exact placement, as angle correction abutments cannot be used and one-piece implants must remain out of occlusion for successful osseointegration. Ideally, NDIs should be placed as parallel as possible to help reduce the technical difficulty of placing the prosthesis and the risk of implant failure. When one-piece implants are utilized for a full-arch restoration, the implants should be splinted.
If you are not familiar with using NDIs, it’s a good idea to do some research into the various implant systems offered by manufacturers; they don’t all will make multi-unit, angle-correcting abutments. Your choice of implant system could also affect your treatment plan in other ways. For example, you will need to know if digital scans must be taken, or if healing cap sizes are available. Your dental lab may be able to help you with your selection, based on their knowledge and experience with NDIs.
Another factor is the surface area that will be in contact with bone. Where less surface area will meet with the bone, loading forces need to be considered. The existing width and height of bone also influence the forces placed on a dental implant and a lower bone height can negatively affect this. In these situations or when it’s necessary to reduce the forces on implants, your options are using longer implants, increasing the number of implants, or choosing implants where the surface texture has been increased.
If you intend to restore teeth in the esthetic zone, it is important to consider the emergence profile. Choosing an implant with too narrow a diameter can create an emergence profile that is too extreme, potentially causing esthetic and hygiene problems. This could be an issue when using one-piece implants, whereas choosing a two-piece NDI will give you the option of using a custom abutment to overcome the problem.
When treatment is planned correctly, and the NDI’s are placed and loaded properly, they can provide an excellent solution for patients who may not otherwise be suitable for dental implants, particularly given the minimally invasive nature of the surgery. While they may not replace conventional diameter implants, NDIs can be a valuable treatment for patients.
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References:
http://www.dentistrytoday.com/component/k2/item/978-small-diameter-implants