Predictable Stabilization of a Lower Denture

INTRODUCTION
While ill-fitting dentures may not be considered by some as one of the most serious or health-threatening dental conditions, any dental professional who has spent time speaking with a patient living with a poorly fitting denture knows that the resultant discomfort, inconvenience, and embarrassment is often unbearable. Even after making a considerable investment in a full set of dentures, it is common for the patient to have difficulty eating and or speaking. Many patients opt not to wear one or both dentures, even when they are new, often avoiding social gatherings or eating in public as a result. The number of edentulous adults in the United States continues to rise, and by the year 2020, the number of those in need of one or 2 complete dentures is expected to increase to 37.9 million, as compared to 33.6 million in the early 1990s.¹ Statistics show that 25% of those aged 65 to 74 years are edentulous in both arches.² This illustrates the presence of a considerable and largely underserved patient base, and makes it clear that every dental practitioner should understand the particular needs of those who struggle with improperly fitted dentures.

A Conventional Solution
Conventional implants are a widely accepted and well-known treatment plan for ill-fitting dentures, but the prerequisites for this procedure can be inhibiting and may alienate many patients who are in need of a solution. A common challenge is that a large portion of the implant patient base for complete dentures is geriatric; many of these elderly patients have experienced extensive bone loss or ridge resorption, requiring invasive bone grafting prior to conventional implant placement. In addition, for many who live on a fixed income, the financial burden of the conventional implant procedure is simply untenable. This means that they may choose to live indefinitely with unsuitable dentures that significantly lower their quality of life. Other patients who are elderly, or may be among those who suffer from a variety of health conditions, find the considerable amount of recovery time daunting.

A Promising Alternative
Based on their ability to provide a sustainable solution to ill-fitting dentures with a minimally invasive procedure and lower cost, small-diameter implants (SDIs) (also referred to as mini dental implants) are quickly becoming an extremely viable alternative to the conventional implant procedure.³ SDIs were originally brought to the market as transitional devices to retain a denture while a conventional implant was allowed to osseointegrate. What many practitioners discovered was that if a patient did not return to have these transitional implants removed within 3 to 6 months, they would osseointegrate just as a conventional implant would.⁴

The US Food and Drug Administration approved SDIs for intraoral use in 1997. Conventional implants have been available far longer, and evidence supports comparable integration. All available research appears to support the use of SDIs when indicated. Histological studies at multiple intervals postinsertion have found integration via “mature and healthy” bone at the light microscope level. This finding is very positive in light of the fact that the implants are often immediately loaded.⁴ Survival rates are comparable to conventional implants and range in the 90th percentile and upward.^5-7 One recent study of 2,500 implants found a 5-year survival rate of more than 94%.⁸

Figure 1. A 330 bur was used to make 3 small openings into the intaglio surface of the denture, and then lead markers were inserted for a radiographic stent. The surface was covered with flowable composite prior to seating in mouth.	Figure 2. Panoramic radiograph shows lead markers and roots retained in the mouth.

Figure 4. Vacuum-formed stent was created out of 0.020 in guide material, then marked to guide drilling of pilot holes.	Figure 5. Going through the stent, bleeding points were made in preparation for drilling pilot holes.

Figure 6. First pilot hole was drilled.

Factors to Consider When Choosing the Small-Diameter Implant Procedure
The amount of bone present is one of the most important elements in the decision between a conventional or SDI procedure. Conventional implants require a minimum of 6.0 mm of bone width facial-lingually for insertion, and 10.0 mm or more in a coronal-apical dimension. Naturally, SDIs require much less bone in the facial-lingual dimension (about 4 mm), and can thus increase the likelihood that a patient will have adequate bone to qualify for case selection. Coronal-apical dimensions required for each implant type are similar.⁹

Another factor to consider is the patient’s health and attitude. For elderly patients or those with compromised immune systems, the minimally invasive procedure, and shortened healing time associated with SDIs is ideal. Because there are no incisions or suturing necessary, the patient will experience minimal postoperative pain and swelling, allowing one to eat comfortably within a matter of hours. Additionally, patients who are reluctant to accept an implant treatment plan for their poorly fitting dentures, due to the high cost and lengthy process of conventional implants, may be better persuaded by the less expensive and relatively fast moving SDI procedure.¹⁰

Proper Treatment Protocol
Once it has been determined that a patient is a good candidate for the SDI procedure, the practitioner must create a treatment plan outlining the number of implants to place and the ideal diameter and length needed to provide the greatest possible retention. This plan should be guided by a panoramic radiograph of the mandible superimposed by an implant length guide, which can be obtained by the manufacturer of the implants.

The risk of mandibular nerve injury is largely avoided by performing the SDI procedure in the anterior mandible. Although computed tomography software technology now exists to facilitate accurate implant placement, effective intraoral protocol can be utilized to achieve safe implant placement and avoid mandibular nerve injury without utilizing expensive software. Greenstein and Tarnow¹¹ have indicated that the mental foramen is not necessarily the most anterior extent of the inferior alveolar nerve and vessels, with up to 60% of mandibles having an anterior loop of 1.0 mm to 5.0 mm mesial to the mental foramen. Utilizing a radiographic stent to index the location of the mental foramina, relative to premeasured radiopaque markers, can be of significant assistance. The mental foramina can also be palpated by the clinician and marked with an indelible pencil, prior to determining appropriate implant location. It is well advised to place the most posterior implants at locations 7.0 mm mesial to the position of the mental foramina. This 7.0 mm zone provides for the potential of the anterior loop while maintaining room for the implant body, as well as space between the implant and the neurovascular bundle. Furthermore, this 7.0 mm zone affords reasonable protection against nerve injury.

While it is common for 4 implants to be placed at equal distances between the mental foramina to stabilize a full denture, some practitioners may decide to place additional implants to create a larger anterior-posterior or lateral spread, decreasing the chances of the dentures lifting in the back of the mouth. For example, a fifth implant may be placed in the mandibular midline, providing increased security and taking advantage of the position most anterior on the arc for a greater anterior-posterior spread. Additionally, it is important to plan the case such that if one implant were to fail, the entire case would not be a failure.

Another consideration while developing a treatment plan is whether to utilize a soft- or hard-reline material to seat the denture postimplant insertion. Surgical protocol dictates that at least 30 Ncm of torque must be achieved for each implant in order to load the case immediately by picking up the metal housings with hard-reline material. Conversely, soft-reline material allows time for the implants to integrate and immobilize, before being permanently loaded with the dentures. If a clinician is pressed for time, a soft reline allows him or her to accomplish the initial implant appointment in a shorter period of time, offering the opportunity for a second appointment to complete the hard reline.

CASE REPORT
Diagnosis and Treatment Planning
An 80-year-old male patient presented with a chief complaint of an extremely poorly-fitting lower denture. The patient’s difficulties with the denture began with its immediate insertion, after having his remaining lower teeth removed. The issues were not ameliorated by the permanent denture he received several months later. The patient complained of an inability to eat solid food, and indicated that he suffered considerable irritation. He also noted that food became lodged underneath the dentures. His frustration and discomfort was so great that he often chose not to wear the dentures at all, causing him to seek alternative treatment. The patient indicated the desire for a permanent solution to his denture discomfort, and wanted to implement the procedure within a limited amount of time.

Figure 7. Lid of implant was used to initiate insertion.	Figure 8. Finger driver was used for initial insertion of implant.
Figure 9. Insertion was continued with a winged thumb wrench.	Figure 10. Insertion was completed, using the torque wrench set at 30 Ncm to determine whether the SDI had achieved immediate and optimal retention.
Figure 11. The first implant, fully inserted.	Figure 12. All 5 implants were placed 7.5 mm apart for a large lateral spread.

Upon initial examination, it became clear that the patient likely suffered from periodontal disease for a period of time prior to extractions, as there was a considerable amount of bone loss on the alveolar ridge. The patient’s desire for a short treatment time frame, along with noticeable ridge resorption, made him an ideal candidate for SDIs.

The proposed treatment plan consisted of placing SDIs (MDI Mini Dental Implants [3M ESPE]), followed by a soft reline. The patient’s bone quality and quantity was inconsistent across the lower ridge, and several different widths and lengths of SDIs were chosen to achieve the greatest amount of retention possible.

Clinical Protocol
To determine ideal placement, a 330 bur was used to make 3 small openings in the intaglio surface of the existing denture. Next, these openings were stuffed with lead foil as markers, then covered with a flowable restorative to avoid exposing the tissue to the lead when seating in the patient’s mouth (Figure 1). A panoramic radiograph was then taken to show where the lead markers fell in relation to the alveolar ridge and the mental foramina, and then compared to a template for measuring the best length of SDI (Figures 2 and 3b). The radiograph also revealed a retained root on the mandibular left that would have to be avoided when placing the implants.

A vacuum formed stent was created out of 0.020-inch guide material and then seated in the mouth to guide the drilling of pilot holes (Figure 4). Had the patient not had an existing denture, this stent could also have been used for the radiographic index described above. Using the stent to make bleeding points at desired locations, a pilot drill was then used to penetrate the cortical plate (Figure 5). Pilot holes were drilled to a depth of about one third to one half of the threaded length of the implant (Figure 6). A 1.8-mm x 13-mm implant was placed in the pilot hole at position No. 28 (Figure 7), and inserted by a clockwise rotation with a titanium finger driver until noticeable bony resistance was felt (Figure 8). The finger driver was then replaced with a winged thumb wrench (Figure 9), and then an adjustable torque wrench, to make small incremental turns to finalize the insertion, and to measure the amount of torque required implant placement (Figure 10). In this position, only 20 Ncm of torque was achieved (Figure 11). At position No. 27, a 1.8-mm x 15-mm implant was used in hopes of achieving more retention with a longer implant. This implant was inserted entirely using the winged thumb wrench; the torque wrench was not needed. The midline generally presents denser bone due to the symphysis of the mandible, and a 1.8-mm x 13-mm implant was again used and successfully inserted using only the winged thumb wrench. One maximum thread implant at 2.4 mm x 13 mm was used at position No. 22, and the final implant was a 1.8-mm x 13-mm. The only implant exhibiting an adequate amount of torque (at least 30 Ncm) was the final implant; thus a soft reline was the most appropriate option (Figures 12 and 13).

Further supporting the soft-reline option was the decision to use a higher retention housing, in order to provide a more secure denture for the patient. Using a highly secure metal housing on an implant with a low torque reading could lead to implant failure upon removal of the denture; therefore, a soft reline was needed to allow time for the implants to osseointegrate.

Figure 13. A panoramic radiograph of the completed case showing the SDIs in place.	Figure 14. Photo taken 4.5 months postoperatively.

Figure 15. Intaglio surface of the completed denture.

The procedure was completed in 4 days, and consisted of a pre-exam meeting, surgery, one day of healing, and a final postoperative meeting. The patient returned 3 months after the postoperative meeting (Figure 14) to install the metal housings, and to have the denture permanently seated with a hard-reline material.

A final follow-up appointment was conducted 4 months later (Figure 15). The patient reported complete satisfaction with the procedure, noting that he no longer experienced pain or discomfort and was again able to eat normally.

CLOSING COMMENTS
While conventional dental implants are a widely accepted treatment for ill-fitting dentures, for many patients this procedure is out of reach due to common challenges including inadequate bone, poor health, and the inability to afford more expensive procedures when many have already struggled to pay for their initial set of dentures. Studies have shown SDIs to be a viable and reliable alternative that offers the benefits of a minimally invasive procedure and a reduced price tag.

Fully and partially edentulous Americans represent a large patient base that is struggling with the inefficiency of unstable or ill-fitting tissue-supported complete dentures; many believe that nothing can be done to make their denture experience a positive one. For these patients, the SDI procedure has the potential to improve their quality of life in a minimal time frame at an affordable cost.

When correct placement protocol is followed, the SDI procedure can be extremely rewarding for both the patient and the clinician, and offers a strong and sustainable long-term denture stabilization solution.

References

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3. De Souza MM, Ram SM, Bhanushali K. Management of atrophic mandibular ridges with mini-dental implant system—a case report. J Indian Prosthodont Soc. 2005;5:158-160.
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7. Bulard RA, Vance JB. Multi-clinic evaluation using mini-dental implants for long-term denture stabilization: a preliminary biometric evaluation. Compend Contin Educ Dent. 2005;26:892-897.
8. Shatkin TE, Shatkin S, Oppenheimer BD, et al. Mini dental implants for long-term fixed and removable prosthetics: a retrospective analysis of 2514 implants placed over a five-year period. Compend Contin Educ Dent. 2007;28:92-99.
9. Christensen GJ. Ask Dr. Christensen. Dent Econ. 2011;8:54-56,90.
10. LaBarre EE, Ahlstrom RH, Noble WH. Narrow diameter implants for mandibular denture retention. J Calif Dent Assoc. 2008;36:283-286.
11. Greenstein G, Tarnow D. The mental foramen and nerve: clinical and anatomical factors related to dental implant placement: a literature review. J Periodontol. 2006;77:1933-1943.

Dr. Schoonover received his DDS from West Virginia University in 1980 and maintains practices in Clendenin and Elkins, WVa. Dr. Schoonover is a member of several professional organizations including the ADA, where he has served as Liaison to the ADA Committee for International Affairs. Additionally, Dr. Schoonover is a master with the AGD and a frequent lecturer on the topic of small-diameter implants. He can be reached at (304) 548-7227 or via e-mail at gntldntl@frontier.com.

Disclosure: Dr. Schoonover is a nonpaid consultant for 3M ESPE’s Mini Dental Implant Division and does receive honoraria from 3M ESPE for lecturing on Mini Dental Implants.