Maximizing Denture Stability and Retention

INTRODUCTION
Mini-implants are becoming more frequently used as a treatment option for improving the retention of dentures.^1-3 When traditional implant treatment is not within the patient’s financial means, the use of mini-implants to change denture retention can provide improvement in the patient’s quality of life. In addition, patients are living longer and, since masticatory ability is tied to nutrition, patients with poorly retained dentures may suffer from nutritional deficiencies due to their inability to masticate food. As nutrition decreases, the patient’s general health is affected and their quality of life suffers.^4-6 This can be corrected with improved denture retention allowing the patient to masticate more efficiently and improve their diet.
The immediate load nature of the mini-implants gives patients immediate satisfaction without delays in treatment to accommodate conventional healing permitting full osseointegration.^7-9 As mini-implants are one piece fixtures, and are immediately loaded, it is important to avoid lateral loads on the fixtures which may lead to failure of the implants to integrate with resultant fixture loss.

MATERIALS AND TECHNIQUES

Figure 1. Comparison of the Sterngold ERA mini-implant (left) with an O ring mini-implant (right), showing the crown to implant ratio.	Figure 2. Sterngold ERA mini-implants (left to right 2.2 mm, 3.25 mm and 3.25 mm angle correction implant).

Figure 3. The ERA female angle correction heads.

The mini-implants available on the market have all utilized an O ring. Due to the height of the head needed, restorative complications can occur and lateral loads can be placed on the head during insertion/removal of the prosthesis. Sterngold has introduced a mini-implant using a smaller version of their ERA attachment. Since the supercrestal portion of the Sterngold ERA mini-implant is lower then the O ring versions of the mini-implant, divergence of the fixtures is less of an issue (Figure 1). Additionally, since less of the fixture is supercrestal, less lateral load can be placed on the fixtures during function or insertion/removal of the prosthesis. An added benefit with a lower attachment head is that less acrylic needs to be removed from the denture to accommodate the attachments male than if an O ring design is used.
The Sterngold ERA mini-implant is available in both 2.2 and 3.25 mm diameter with several lengths provided (Figure 2). The 3.25 mm diameter also allows for angle correction, should that be necessary. A lutable female correction attachment is available in 0°, 5°, 11°, and 17° angulation (Figure 3).
A key to simplifying the placement of mini-implants, as with traditional implants, is the development of a guide to position the implants in the correct buccal lingual orientation. Improper placement in the buccal/lingual plane can create restorative complications including protrusion of the attachment out of the denture flange. A surgical stent using a duplicate of the patient’s denture allows implant placement within the confines of the denture and orients the mini-implants so that the head lies under the teeth.

Laboratory Procedures
To fabricate the surgical stent, alginate (Kromopan) is mixed and placed into one half of a Lang Denture Duplicator (Lang Dental) and the patient’s denture is placed tooth side down into the alginate and allowed to set. A second batch of alginate is then mixed and placed into the tissue side of the denture sitting in the lower half of the Lang Denture Duplicator. The upper half is filled with alginate and the duplicator is closed allowing the material to set. Once set, the duplicator is opened and the denture is removed from the alginate.
Clear orthodontic acrylic (Lang Dental) is mixed to a thin consistency and poured into the mold formed in the duplicator. The duplicator is then closed and immersed in hot water. Immersion in hot water accelerates the set of the acrylic and provides a transparent denture replica when completed. Once the acrylic is cured, the clear replica denture is removed from the duplicator and the flanges are adjusted to remove any flash of material. Vertical grooves are then made on the buccal/facial surface at the sites deemed ideal for implant placement. Next, short pieces of wire are fixated in the grooves to act as radiographic markers. A panoramic radiograph is obtained and the location of vital structures, such as the maxillary sinus or the mental foramina, is identified in relation to the locations of the intended implants. Any modification of the implant locations relative to ana­tomic structures could be made at this time.
Once the final implant locations are verified, the tooth at each implant site on the clear duplicate denture stent is marked with a Sharpie pen. A 3/32-inch twist drill is used to place a pilot hole through the clear stent into the underlying stone mod­el. The stent is removed from the cast and the pilot holes in the cast are checked to verify that it is at the center of the crest and any corrections are made at this time to the pilot holes on the stent.

Clinical Procedures

Figure 4. A clear replica of the maxillary denture is inserted with pilot holes predrilled at the desired sites. A pilot drill is used to make the initial penetration into the tissue.	Figure 5. Paralleling pins are placed at the initial sites to check buccal lingual orientation. A tissue punch is then used to remove a core of soft tissue over each site.
Figure 6. Sites are prepared with an osteotomy drill paralleling it to the pins at the other sites.	Figure 7. A bone tap is introduced into the prepared sites.
Figure 8. The Sterngold ERA mini-implant is picked up on the handpiece placement tool.	Figure 9. The Sterngold ERA mini-implant is introduced and seated to depth intraorally.

The surgical stent is tried-in, and the occlusion is verified with the opposing arch. Local anesthetic is ad­ministered via infiltration into the buccal vestibule from the distal of the far right implant position through the distal to the far left implant position. A 1.6 mm pilot drill is placed into the surgical headpiece then introduced through the surgical stent at each site, piercing the soft tissue and entering the crestal bone 3 to 4 mm with sterile water irrigation (Figure 4). The surgical stent is then removed and the perforations through the gingival tissue at the implant sites are evaluated for buccal-lingual orientation.
At each site a stationary pilot drill is used to explore the osteotomy at the locations to verify that the buccal plate has not been perforated. Paralleling pins are placed into the sites and the pilot holes are deepened to a depth of the implants to be placed. A 3 mm disposable tissue punch is pressed over each perforation to the osseous crest and a gingival tissue plug is removed (Figure 5).
Paralleling pins are again placed into the implant sites and the countersink bur, for the 3.25 mm ERA mini-implant, is utilized at each site (Figure 6). In narrower ridges, a 2.2 mm diameter fixture may be selected. When higher bone density is encountered it may be necessary to use the 3.25 mm bone tap run at 45 Ncm and 20 rpm to allow placement of the im­plants to the desired depth (Figure 7).
Next, an implant carrier is placed onto the implant handpiece with torque set at 45 Ncm and a speed of 20 rpm. A ERA mini-implant package is opened and the sterile titanium cylinder containing the ERA mini-implant is removed. The im­plant carrier is snapped onto the end of the mini-implant (gold nitrite coated portion) and removed from the titanium sleeve (Figure 8). If angle correction is required, the 3.25 mm ERA mini-implant may be used which allows 0°, 5°, 11°, and 17° of correction with lutable attachment heads. If no correction is anticipated, a single piece ERA mini-implant may be used. Angle correction is not currently available with the 2.2 diameter ERA mini-fixture. (Note: Sterngold has a 510K currently in submission with the FDA for the angle correction 2.2 mm implant.) The implant is carried to the osteotomy site and under irrigation the implant is rotated apically either until the surgical unit stops at 45 Ncm or the correct depth is achieved (Figure 9).
When depth is not achieved with the handpiece, a mini-torque wrench is placed fully on the ERA attachment of the mini-implant and a clockwise rotation is applied until the implant reached correct depth. Use of the mini-wrench versus a standard torque wrench decreases the forces placed on the mini-implant due to the shorter level arm of the wrench and eliminates any deformation of the ERA attachment that may occur. Placement of the ERA mini-implants is then continued until all fixtures are placed (Figure 10).

Figure 10. Sterngold ERA mini-implants placed in the maxilla ready for placement of the ERA mini-attachments into the fixtures.	Figure 11. Plastic paralleling heads attached to the ERA mini-attachments are used to align the attachments that are luted into the Sterngold ERA mini-implants. Note mark on the fixture and angled ERA mini-attachment used to get desired position when luting.
Figure 12. Angled ERA mini-implants shown in the anterior; 3 Sterngold ERA mini-implants with 0° attachments in the posterior implant bilaterally.	Figure 13. A clear vacuform template is fabricated on the model and markings are made at the sites of the proposed implant sites.
Figure 14. The vacuformed template is placed intraorally. Markings are verified with the implant positions and corrected if needed.	Figure 15. The vacuformed template is reversed and placed into the maxillary denture to mark where the denture needs to be relieved to accommodate the attachments.
Figure 16. ERA mini attachments (male) luted in the denture with ERA Pick-up Resin.	Figure 17. Completed maxillary denture retained by 5 Sterngold ERA mini-implants.

If the angle correction ERA mini-implant is utilized, the angle correction female with the desired angle is placed on a plastic paralleling head, snapped on the ERA female, and carried to the implant fixture intraorally. Once the attachment is positioned at the desired direction, a mark (Sharpie pen) is made on the coronal of the fixture and attachment. (Care should be taken not to press the female fully into the fixture at this time.) After all of the ERA correction females have been positioned and marked, they are removed from the fixtures. The receptor on each of the ERA mini-implants is air-dried and ERA Lock Cement (Sterngold) is dispensed into the receptor area and applied to the threads on the angle correction female. The female is then inserted, tapped into the fixture, and rotated to align the previously made mark (Figure 11). Excess resin cement is wiped away with a disposable brush tip and the autocuring resin is allowed to set. Upon setting, any residual ex­cess cement is removed with a scaler (Figure 12).
On the patient’s cast, a vacuformed stent was fabricated prior to the surgical appointment. Marks are made on the cast at the pilot holes made when the clear stent was fabricated (Figure 13). This is taken intraorally and the marks are related to the actual implant positions and verified (Figure 14). Holes are then made at the verified positions on the vacuformed template. The stent is then inverted into the tissue side of the denture and a black mark made at each implant location to assist in relief of the denture acrylic in order to accommodate the ERA Micro OV metal housing (Figure 15). The ERA Micro OV males in the metal housing are placed onto each fixture and the denture is tried-in to verify clearance. Fit at this stage should be passive, with no contact with the attachment housing. Pieces of nonlatex dental dam with a central hole are placed over each mini-implant fixture and the ERA housing is snapped down over the attachment. The dam acts as a block-out preventing any acrylic from getting between the implant and soft tissue during pick-up in the denture.
The denture is dried and Stern­Vantage Varnish LC (Sterngold) primer is brushed into each receptor site in the denture and light-cured for one minute. To aid in cleanup of excess material it is advised to avoid placement of the primer in areas other than the receptor sites. ERA PickUp (Sterngold) resin is ex­pressed from an automix syringe into the receptor sites, taking care not to overfill each site. The denture is then inserted intraorally, the patient guided into occlusion, and the resin allowed to set. The patient is instructed to keep their teeth together without biting pressure to avoid tissue compression. (Tissue compression may prevent engagement of the attachments upon reinsertion of the denture intraorally.) Since the anesthetized patient will lack proprioception at this stage, an assistant should place a finger under their chin to help them remain closed while waiting for the acrylic to set.
Upon setting, the denture and the pieces of dam placed earlier are removed. Since primer is not applied outside the receptor sites, removal of excess material requires use of an acrylic bur to expose the rim of the metal housing. Any extra material can be flaked off with an instrument. A micro core cutter bur is used to remove the black processing male in each housing, and an ERA male is then snapped into each location using a micro seating tool (Figure 16). The denture is then returned to the mouth and the retention is evaluated (Figure 17).

CONCLUSION
If a patient is complaining about a lack of retention, mini-implants can provide improvement in denture retention when a stable denture can be achieved. The Sterngold ERA mini-implant provides a lower center of rotation than the O ring mini-implant design. This permits greater divergence between fixtures than can be accommodated when O ring heads are utilized and allows less required space within the acrylic of the denture.

References

1. Feine JS, Carlsson GE, eds. Implant Overdentures: The Standard of Care for Edentulous Patients. Hanover Park, IL: Quintessence Publishing, 2003.
2. Misch K, Neiva R: Small-diameter implants for optimal stabilization of implant-supported overdentures. Pract Proced Aesthet Dent. 2007;19:428-431.
3. Bulard RA: Mini implants. Part I. A solution for loose dentures. J Okla Dent Assoc. 2002;93:42-46.
4. Morais JA, Heydecke G, Pawliuk J, et al. The effects of mandibular two-implant overdentures on nutrition in elderly edentulous individuals. J Dent Res. 2003;82:53-58.
5. Steele JG. National diet and nutrition survey. People aged 65 years and over. Vol 2: Report of the oral health survey. London, England: The Stationery Office, 1998.
6. MacEntee MI, Hill PM, Wong G, et al. Predicting concerns for the mouth among institutionalized elders. J Public Health Dent. 1991;51:82-90.
7. Nazarian A: Mini dental implants: immediate gratification for patient and provider. Dent Today. 2005;24:110,112.
8. Bulard RA: Mini dental implants: enhancing patient satisfaction and practice income. Dent Today. 2001;20:82-85.
9. Ahn MR, An KM, Choi JH, et al. Immediate loading with mini dental implants in the fully edentulous mandible. Implant Dent. 2004;13:367-372.

Dr. Kurtzman is in private general practice in Silver Spring, Md and is a former assistant clinical professor at the University of Maryland, Department of Endodontics, Pros­thetics and Operative Dentistry. He has lectured both nationally and internationally on the topics of restorative dentistry; endodontics, implant surgery, and prosthetics; removable and fixed prosthetics, and periodontics. He has published more than 130 articles. He is privileged to be on the editorial board of numerous dental publications, a consultant for multiple dental companies, a former assistant program director for a University-based implant maxicourse, and he has earned Diplomat status in the International Congress of Oral Implants. He can be contacted at dr_kurtzman@maryland-implants.com.

Disclosure: Dr. Kurtzman reports no conflict of interest.

Dr. Dompkowski limits his private practice in Bethesda, Md to periodontics and implant dentistry. He received his DDS from the Medical College of Virginia/School of Dentistry, and a periodontal certificate from The Eastman Dental Center, Rochester, NY. He is also a clinical associate professor at the University of Maryland/Dental School, Baltimore, Md. He can be reached at (301) 530-5858.

Disclosure: Dr. Dompkowski reports no conflict of interest.