Small-Diameter Implants for Single-Unit Restorations

INTRODUCTION
By now, many dentists have heard about the use of mini dental implants (MDIs) (also referred to as small-diameter implants [SDIs]) for denture stabilization. The benefits of this procedure—in terms of greater affordability, a lower time investment, and suitability for a broader range of patients—have made it very well received by both patients and practitioners. And while some clinicians may still consider MDIs a relatively new treatment on the market, studies and meta-analysis have now proven their long-term efficacy. The benefits of the MDI procedure can also apply in cases beyond denture stabilization, as many have already discovered by using MDIs for long-term fixation of single crowns.

In fact, one of the original purposes for MDIs was to serve as a provisional support, alongside a conventional implant, for both fixed and removable prostheses.¹ Although MDIs are a newer technology than their traditional counterparts (FDA-approved in 1997, versus the late 1970s for traditional implants),¹ by now they have amassed a significant clinical track record. Studies (on MDI Mini Dental Implants [3M ESPE]), with durations ranging from one to 5 years, have found success rates between 92% and 98%.^2-4 One of the largest studies, which followed 2,514 implants (531 patients) for up to 5 years, reported a success rate of 95% for full mandibular dentures and 92% for removable partial dentures.⁵ A meta-analysis has also been published showing that survival rates for SDIs are similar to those for traditional implants.⁶

Additional data is available detailing the makeup of MDIs and their basic suitability for use in the mouth, establishing a foundation for their clinical success. These implants are made from an alpha-beta titanium alloy, a microstructured alloy that incorporates aluminum and vanadium. The addition of these materials increases tensile strength, creep strength, and elastic modulus, and also allows hardening. These properties make the alloy stronger than titanium alone.⁷ Static immersion corrosion testing has shown that implants are also resistant to corrosion, an obviously essential quality for intraoral use.⁸

In order to encourage stronger osseointegration, the surfaces of MDIs are sandblasted during manufacturing.⁹ Scanning electron microscopy analysis of the implants has been performed to confirm that the sandblasted areas are indeed effectively roughened to increase the bone-to-implant contact area.⁸ Histology data has further confirmed the efficacy of this practice, with one study demonstrating significant osseointegration at the 3-month mark, and further improvements at 6 months.¹⁰

This body of data effectively demonstrates that while MDIs are newer than conventional implants, they do have an established track record of success. With this record in hand, dentists can feel assured that this method of treatment has been proven, in both the lab and the operatory.

In addition to being clinically effective, the MDI procedure is easy to learn and less invasive than treatment with traditional implants, utilizing a simple, flapless placement technique that is straightforward for general dentists to learn and implement. Similar to complete or partial denture stabilization using MDIs, the placement protocol for single-unit cases is also quite simple. A small pilot hole is drilled and the self-tapping implant is then screwed into the bone, in most cases without creating a flap. While MDIs range in size from 1.8 to 2.9 mm, for single crowns, the largest (2.9 mm) size is recommended. Compared to traditional-diameter implants, the smaller size of MDIs makes them very useful in crown cases where either mesial-distal or buccal-lingual space is limited. With MDIs, treatment duration can also often be shorter, as the implant placement is minimally invasive with less healing time. A restoration with an MDI-supported crown is also considerably more affordable, due to both the simpler placement protocol and the fact that there is no need for a custom abutment with these one-piece implants.

The case shown here will demonstrate the simple use of an MDI for a single-unit crown in the anterior. Many dentists feel most comfortable utilizing MDIs for single-unit cases in areas where the functional demand and bite forces are lower, such as lower central or laterals and upper laterals, as will be demonstrated here.

CASE REPORT
A female in her late 50s was missing her left cuspid and lateral incisor and sought a solution to fill the gap in her smile (Figure 1). Due largely to her budget, the patient opted for treatment with a crown supported by an MDI.

CLINICAL PROTOCOL
At the implant placement appointment, the soft tissue at the implant site was probed and the thickness was recorded. Soft tissue was removed with a tissue punch, and a pilot hole was created with the drill at 1,200 to 1,500 rpm and sterile irrigation.

Figure 1. Preoperative panoramic radiograph. Patient was missing left cuspid and lateral incisor.	Figure 2. The MDI Mini Dental Implant (3M ESPE) after insertion.

The 2.9-mm MDI Mini Dental Implant (3M ESPE) was inserted into the pilot hole and tightened with the finger driver. Insertion continued with a winged thumb wrench and then an adjustable torque wrench un-til there was at least 35 Ncm of resistance (Figure 2).

Adjacent teeth were coated with petroleum jelly, and an immediate temporization cap was placed on the implant. Bis-acryl provisional material (Protemp Plus [3M ESPE]) was extruded into the restorative matrix fabricated preoperatively from the laboratory wax-up; this was then placed into the mouth and allowed to briefly set. The temporary impression and cap were then removed from the mouth to cure in the matrix for several more minutes. Excess flash was then trimmed (Figure 3). The temporary was then pressed into place on the implant without the use of any cement.

Figure 3. The provisional crown (Protemp Plus [3M ESPE]) and immediate temporization cap.	Figure 4. Shade images were captured for the final restoration.
Figure 5. An impression coping was placed on the implant.	Figure 6. The final impression with impression coping in the material.
Figure 7. An MDI analog was pressed into the impression coping.	Figure 8. A stone model was fabricated.

The patient wore the temporary for a period of 6 weeks to allow the tissue to stabilize. She then returned to the office for a final impression and shade photos (Figure 4). The temporary crown was removed and an impression coping was snapped onto the implant (Figure 5). A vinyl polysiloxane impression (Genie [Sultan Healthcare]) was taken; after setting, it was removed from the mouth, taking the impression coping with it (Figure 6). The provisional was returned into place on the implant until the cementation appointment.

At the lab, an MDI lab analog was inserted into the impression coping, and a stone model was created (Figures 7 and 8). The laboratory team used the model to create a zirconia-based crown (Lava [3M ESPE]) (Figure 9). Upon receipt of the crown in the office, the patient was recalled and the crown was cemented in place with a self-adhesive resin cement (RelyX Unicem 2 [3M ESPE]) (Figures 10 and 11).

Figure 9. The final restoration (Lava [3M ESPE]) on the stone model.	Figure 10. Radiograph showing placement of the 2.9-mm MDI.

Figure 11. Final result.

The patient was extremely pleased with the final result and very happy it could be achieved conservatively and within her budget.

CLOSING COMMENTS
As this case shows, placement of an MDI is very simple as compared to a traditional implant. The time-saving and money-saving aspects of this procedure provide benefits for both dentists and patients. Because the basics of this simplified technique can be learned, in most cases, in a one-day hands-on training seminar, dentists have the potential to add a valuable service to their practice without having to invest significant time to become trained in the procedure. This low time investment also means a lower monetary investment to get started, as it requires less time away from active practice. Once the procedure is being offered, the cost of the materials themselves is less, also making it a very fast and affordable way to add a valuable service to the practice.

From a patient’s perspective, the lower cost of MDIs is often one of the most attractive qualities of the service. This is especially pronounced in denture stabilization cases, in which not one, but 4 or more implants must be placed. Patients who receive cost estimates only for traditional implant treatments often walk away from the office, concluding that they have no choice but to continue to live with their dentures via adhesives and relines. The situation is similar, but on a smaller scale, for single-unit cases such as this one.

Without MDIs, patients are left with the option of living with their smile as is, or a choice between a bridge (requiring removal of healthy adjacent tooth structure) and a costly traditional implant. The cost savings for a single MDI are quite pronounced, and many patients are grateful to learn there is a more affordable option. In addition to its greater affordability, this minimally invasive procedure and reduced healing time required for MDI treatment are very desirable for a wide range of patients.

In addition, many practices that have implemented MDI treatment have found that the procedure can be a very effective way to boost revenue while providing excellent care. By giving patients an alternative to traditional implants that is less costly, less time consuming, and less invasive, these practices are providing an innovative service that meets a significant need in the market.

Acknowledgement
The author would like to credit Okon Dental Laboratory in Aliso Viejo, Calif, for the laboratory work in this case.

References

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8. 3M ESPE MDI Mini Dental Implants [technical data sheet]. St. Paul, MN: 3M ESPE Dental Products. Available at: tinyurl.com/pz3brkq. Accessed April 17, 2014.
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Dr. Choi graduated from the University of Southern California (USC) School of Dentistry in 1987 and has taught there for more than 10 years as an assistant clinical professor in the TMJ/Facial Pain Clinic. He has been surgically placing and restoring dental implants for many years in his private general practice in Tustin, Calif. He is a Fellow of International Congress of Oral Implantologists, a credentialed Associate Fellow of American Academy of Implant Dentistry, and a graduate of Misch International Implant Institute. He was one of the first dentists on the West Coast to place Sendax IMTEC mini dental implants for lower denture stabilization and has been conducting live surgery MDI mini-residencies in California since 2002. He has lectured extensively on various topics of implant dentistry internationally. He is the founder and director of Global Mini implant Institute, whose goal is to help dentists improve mini dental implant clinical success rate predictably and avoid complications. He can be reached via e-mail at the address rchoidds@gmail.com.

Disclosure: Dr. Choi is a paid lecturer for 3M ESPE.