Mini-Implants in complete edentulous patients have become a treatment alternative for conventional dentures and conventional implant retained overdentures. They provide an improvement in stability and retention; they also improve subjective chewing ability and overall patient satisfaction. This article is an overview of mini-implants and their role in complete denture treatments.
In patients with edentulous arches, the ability to speak, masticate and smile is all dependent on an accurately fitting and well-retained denture. The provision of complete removable dentures that satisfy all functional and esthetic requirements is one of the challenges in dentistry. Despite overall improvements in the oral health of the population, the demand for complete removable dentures will continue as the elderly population increases. This explains the importance of continuing to provide dental students with education on the provision of complete dentures as well as the necessity to acquire and retain the expertise that will continue to be needed to provide patients with functional and esthetic complete removable dentures. A number of anatomical and physiological challenges complicate the treatment, the wearing of dentures and can result in patient dissatisfaction.1
In terms of frequency, the first therapeutically option in the complete edentulism is represented by conventional dentures. But, in a large number of cases this therapeutic option does not satisfy patient’s expectations, a number of complains being found out, primarily related to functionality and adaptation. The implant-supported overdenture brings considerable benefits, including the increase of denture stability, functional efficiency, comfort and quality of life. For this reason, not in a few cases, this treatment option has become elective.2 The main difficulties identified when the treatment plan includes implant application are correlated with an inadequate jaw morphology, due to the important bone resorption phenomena that occurs during edentulism evolution, and also to the poor bone quality, related to bone diseases that may affect elderly patients such as osteoporosis.3,4 Most times, surgical interventions prior to implants insertion are needed (bone addition, sinus lift, etc.), which are harder to accept by elderly patients, frequently with affected general status.5 Other disadvantages are related to longer duration of treatment and higher costs.2
In cases where jaw morphology does not allow the conventional implant application without helpful surgical interventions, using small-diameter implants (≤ 2,8 mm), also known as mini-dental implants (MDI) can be, most often, a treatment alternative. Among benefits2,6-13 are:
– The application method is easier and has much less intraoperative trauma.
– The possibility to be loaded immediately.
– A shorter recovery period.
– Single-stage implants.
– Lower cost.
– Narrow ridge, treatment of difficult anatomic conditions as a thin buccolingual bone dimension.
– Improved stability.
– Better functionality.
– Adaptation and higher satisfaction.
When first introduced, mini-implants were considered as a transitional device for stabilizing provisional prostheses during implant healing6, with the objective of transitioning over to standard implants when the permanent prostheses were planned for. In 1997, mini-implants were cleared by the FDA for long-term use. Mini-implants are now used for short and for long-term prosthodontic treatment.2,7,14,15
Treatment Planning and Procedure
Proper diagnosis and treatment planning are key factors in achieving predictable outcomes, which mean careful evaluation through clinical, imagistic and laboratory methods. Frequently there are identified some unfavorable conditions for implant insertion and a high degree of treatment difficulty. These issues (morphological and functional features, related to general health status, age, gender, etc.) must be linked to implants characteristics, in order to decide the particular treatment features, from surgical and prosthetic point of view. The length, diameter, number, topography, loading method of implants can present a large variety, depending on quantitative bone offer (ridge width and bone height), quality (bone density), functional features and patient’s wishes.2
It is most recommended to use minimum 4 mini-implants in the mandible and 6 in the maxillary.15,16 The necessary ridge width in order to apply a standard diameter implant must be ≥ 5 mm. Mini dental implant (≤ 2,8 mm) may be inserted also where the ridge width presents values of 3-4 mm. For the lower jaw the recommended implant is 1.8-2.1 mm diameter, a 3 mm bone width and 10 mm bone height are needed. For the upper jaw the recommended implant is 2.4 mm diameter, a 4 mm bone width and 10 mm bone height are needed.15
A new set of complete denture is fabricated for the patient. Mini-implants can be placed without surgical incision or flaps. The necks of the mini-implants are fully inserted into the soft tissue and only the abutments head are protruded into the oral cavity. Following placement of the mini-implants, a small shim is placed over each implant allowing only the o-ball of the implant to be exposed; the metal housings are then placed over them, the area is checked to make sure no undercuts are present. The tissue side of the patient’s prosthesis is relieved so that it could be seated passively over the top of the metal housings. A standard chair side self-cure acrylic mix is then prepared and placed into the denture, then seated with a functional bite into the patient’s mouth over the top of the mini implants with the metal housings attached. After an appropriate hardening time, the prosthesis is removed from the patient’s mouth and excess acrylic material trimmed. The finished prosthesis, containing the metal housings, is then replaced into the patient’s mouth for occlusal equilibration and border adjustment.8,17
In our clinical practice we regularly come across patients where it is difficult to achieve optimum denture performance due to problems associated with reduced denture retention and stability. This can be due to a number of factors, such as reduced vestibular depth, flabby ridges, hyperplasic mucosa, severe resorption, atrophic ridges, inadequate amount of saliva, xerostomia.8
From a technical viewpoint, successful prosthetic integration depends on the stability and maintenance of the prosthesis. In the past, the only strategy for preventing problems involved the use of prosthetic adhesive or retention by attachments. When using an attachment system, residual tooth roots can stabilize a denture and allow conservation of the alveolar bone structure.18
The use of dental implant to provide support and/or retention for a prosthesis offers multiple advantages when compared to the use of removable soft tissue restoration.9 Dental implants improve patient satisfaction and quality of life. However, implants have limitations related to high cost, anatomical considerations, health of the patient and the dentist’s technical ability.2,14 Mini-implant system can also be used for stabilization of a complete denture where bone status is inadequate for standard implants. The surgical procedure is less complex, quicker, less invasive, and the insertion of the implants is simpler.8
The immediate-load nature of mini-implants gives patients immediate satisfaction without delays in treatment to accommodate conventional healing, permitting full osseointegration. There is improvement in stability and retention, subjective chewing ability and overall patient satisfaction.17
As with any other type of implant, independent acute complications could appear, in particular, cases of primary implant loss or severe inflammatory reaction. Some chronic disorders, such as peri-implantitis, can be observed but rarely due to the characteristic of the “one-part” implant, which decrease this specific risk.18
This procedure requires regular inspections and replacements of retention components in the frequencies required by their producers. Occasional repair resulting from denture material damages around the nests, as well as relining and damage in the acrylic denture base might also occur. It is then necessary to remove a damaged nest or a fragment of a denture and filling the place with autopolymerizing acrylate.19
The overall MDI survival rate was 94.2% in a retrospective analysis of 2514 implants placed over a five-year period.20 Other studies reported survival rates beyond 90%.21-22 Patients should be advised of their role in maintenance, and a comprehensive recall system is mandatory to obtain satisfactory long-term results.
Mini-implants are an excellent and profitable addition to every dental practice. Mini-dental implant supported overdenture can be in complete edentulous patients a treatment alternative to both conventional dentures and conventional implant retained overdenture. This system provides an immediate and ongoing stabilization for the patient in an economical and efficient manner. It is an extremely simple and safe procedure and can be done in cases with poor bone quality as well. It opens many treatment modalities to the dentist and the patient.
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by Dr. Danielle El Hakim, Dr. Emilie El Mouchantaf, Dr. Maha Ghotmi, Dr. Pierre El Khoury