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Immediate Provisionalization of a Maxillary Lateral Incisor With a Dental Mini-Implant

Surgical and Prosthetic Rationale

The predictability and high success rates of single-tooth implants have been well documented.1-3 To maintain periodontal/peri-implant health, however, a minimal distance of 1.25 mm to 1.5 mm between the implant and the adjacent teeth has been advocated.4-5 Therefore, the minimal interradicular space for a particular implant should be 2.5 mm to 3 mm greater than the implant diameter.

Mini-implants are 1.8 mm to 2.5 mm in diameter and were first introduced as immediately loaded transitional implants that supported interim fixed or removable dentures during the healing phase of the definitive implant.6-11 Today, due to the development of new implant surfaces that increase the rate and magnitude of osseointegration,12-14 mini-implants are used successfully as permanent implants.15-17 The application of a mini-implant is particularly useful when the interradicular space and/or buccolingual bone width of the edentulous site are limited.

Case Presentation

A 17-year-old female presented for treatment of a congenitally missing maxillary right lateral incisor and microdontia at the maxillary left lateral incisor (Figure 1). The patient had been undergoing orthodontic treatment for two years when the treatment had to be terminated due to severe root resorption observed on the maxillary right premolar teeth. The resultant interdental and interradicular spaces of #7 were 4.5 mm while the buccolingual bone width measured 5 mm as confirmed by a periapical radiograph and a cone beam computed tomography (CBCT) image respectively (Figure 2). The interdental space at site #10 was approximately 4.5 mm as measured on a study cast. A treatment plan that included immediate provisionalization of a mini-implant (2.5 mm in diameter), a metal-ceramic crown placement at site #7, and a porcelain jacket crown on #10 was accepted by the patient and her guardian.

Fabrication of the Provisional Crown

Prior to implant placement surgery, a preliminary impression was made and diagnostic casts were fabricated. A diagnostic waxup of sites #7 and #10 was performed to ensure an aesthetically satisfactory result could be achieved. Composite resin was directly bonded on tooth #10 and shaped according to the diagnostic waxup. A new diagnostic cast and diagnostic waxup of #7 were made followed by an acrylic resin provisional shell and a surgical template which were disinfected prior to the implant surgery.

Surgical Procedure

At the time of surgery, local anesthetic was administrated at the surgical site. A circular incision was executed on the crestal ridge of site #7 and the incised soft tissue was removed. An osteotomy was made to one third of the implant length. Periapical radiographs were taken to check the angulation of the osteotomy (Figure 3). A 2.5 mm x 13 mm acid-etched threaded implant was then placed without flap reflection (Figure 4). During the implant insertion, however, a buccal perforation was noted and prompted flap reflection to examine the situation. As the apical two thirds of the implant were exposed (Figure 5), the implant was removed and replaced so that it stayed within the bony housing and emerged at an optimal angulation with 35 Ncm of insertion torque. A torque wrench was utilized to achieve the ideal corono-apical implant position, where the implant-abutment interface was 2 mm apical to the predetermined free gingival margin so that an optimal emergence profile could be established (Figure 6).  After implant stability was confirmed and the integrity of the facial bone was evaluated, the recipient site was prepared by the surgeon, who decorticated the facial bone (Figure 7). A xenograft was then applied to the perforated area and covered with collagen membrane (Figure 8). The flap was closed with absorbable antibacterial polyglactin sutures.

The metal temporary abutment was friction-fitted on the implant and modified so that the provisional crown shell could be placed passively in the appropriate position. The temporary abutment was then incorporated within the provisional crown shell using flowable composite. After completion of occlusal adjustments to clear all contacts in centric occlusion and during eccentric movement, the provisional crown was polished and cemented onto the implant (Figure 9). The implant position was confirmed with periapical radiograph and CBCT images (Figure 10).

(Continued from page 1 )

  Postoperative Instructions

Appropriate antibiotic and analgesics were prescribed for postoperative use. The patient was instructed not to brush the surgical site, but rinse gently with 0.12% chlorhexidine gluconate and was placed on a liquid diet for two weeks. Soft diet was recommended for the 6 month implant healing phase with no function on the surgical site recommended.

Definitive Restorations

Six months after the implant surgery, full coverage crowns were cemented at sites #7 and #10 with self-adhesive resin cement (Figures 11 and 12).  Tooth #10 received an all-ceramic crown with a zirconia abutment and tooth #7 received a porcelain-fused-to-metal crown with a metal abutment. At the 20-month follow-up, no complications were observed, favorable peri-implant tissue maturation was apparent, and the patient was satisfied with the treatment (Figures 13 and 14).

Discussion

In addition to space requirements, another deciding factor when considering mini-implants as definitive implants is their mechanical strength. The mini-implant used for this case was made of titanium alloy, which was 2.3 times stronger than a commercially pure titanium implant.22 Mini-implants, however, are not as strong as standard implants. Simon and Caputo reported the deformations and fractures observed when 1.8-mm–diameter mini-implants were removed with reverse torque between 27 Ncm to 35 Ncm.23 Therefore, in dense bone, it is recommended that repeated forward and backward motion be performed during mini-implant insertion to allow for bone expansion. As a result, appropriate insertion torque could be maintained during implant insertion, which would minimize the risk of fracture, deformation, and overheating of the bone.

The mini-implant used in this report has a self-drilling feature. The osteotomy was performed only up to one third of the implant length to ascertain the primary stability of the mini-implant following insertion. Due to the minimal osteotomy depth and the self-drilling feature, however, the mini-implant placement procedure can be technique sensitive, particularly when performed without flap reflection. Other caveats include the minimal buccolingual bone width and extreme alveolar bone angulation (Figure 2B). As an implant with a self-drilling feature tends to advance towards the path with least resistance, if its angulation is not properly controlled, facial cortical bone perforation could result as demonstrated by this patient treatment report. Fortunately for this case, the size and the location of the perforation (Figures 7 and 10B) did not significantly compromise the integrity of the facial bone or the initial stability of the mini-implant, and could be remedied with a bone graft and collagen membrane. Therefore, despite their small diameter, utmost care must be taken when placing these self-drilling mini-implants to avoid such surgical complications.

It is recommended that the implant platform be approximately 3 mm apical to the predetermined facial free gingival margin.24 Since the mini-implant used in this patient treatment report has a 2 mm gingival polished collar, where bone-implant contact is unlikely to be maintained, placing the implant 3 mm apical to the predetermined gingival margin may result in a high facial peri-implant mucosa dimension (~5 mm). This dimension is not stable and is prone to gingival recession, especially in patients with a thin biotype. Conversely, the mini-implant must be placed deep enough so that an optimal prosthetic emergence profile could be established. Therefore, in this situation, the mini-implant was placed 2 mm apical to the predetermined gingival margin.

Subgingival excess cement can lead to gingival inflammation and infection.25 Due to the moderately subgingival position of the implant-prosthesis junction (~2 mm), the removal of excess cement during placement of the provisional and definitive crowns can be a challenge without flap reflection. The implant head of the mini-implant used in this report consists of a square cervical portion and the ball abutment incisal portion. The square portion provides an intimate fit with the temporary and castable abutments, while the ball shape of the abutment provides space for excess cement.  Both features of this mini-implant minimize the use of cement during crown placement and decrease the incidence of excess cement.

Since the mini-implant is not as strong as a regular implant, occlusal force must be controlled. In this case report, the mini-implant was placed in the maxillary lateral incisor position where occlusal force is usually minimal. In addition, occlusal adjustment was performed on the implant restoration in order to prevent its contact with opposing teeth in centric and eccentric occlusion.

Conclusion

Mini-implants can be used to support definitive restorations when the edentulous space is limited, however their use should be preceded with careful and thorough diagnosis and treatment planning. Furthermore, the procedure is technique sensitive and meticulous execution is required to achieve desired result.

References

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