Short Implants: A Viable Alternative to Sinus Augmentation

To provide stability and long term support for dental implants, sinus lift procedure is preferred especially when there is a loss in vertical distance between the crest and the sinus floor.

INTRODUCTION

A natural sequela of the loss of maxillary molars is the loss of crestal bone height. Once teeth are removed, the remaining ridge can lose 30% to 60% of its height and width within the first 3 years. The maxillary sinus can pneumatize and become larger, and this too will result in a decrease in the remaining osseous ridge height.

When this loss of vertical distance between the crest and the sinus floor occurs, the ability to place dental implants can be compromised. When not enough bone exists to provide stability and long-term support for a dental implant and its restoration, a sinus lift procedure is indicated.

There are 3 anatomic locations for performing sinus floor grafting:

The classic Caldwell-Luc opening anterior to the zygomatic process and above the root apices of the premolar and molar teeth,1

The mid-maxillary entrance between the alveolar crest and the zygomatic process,1-2

A low position at the level of the existing alveolar ridge crest.2

In the maxillary sinus for prosthetic reasons, Boyne3 first used bone grafting to increase the volume of osseous tissue in the 1960s. Tatum4 then used an antral grafting technique for the placement of metal implants. This invasive lateral wall approach requires the surgeon to create an access window through the lateral wall of the sinus using a Caldwell-Luc Approach.5-7 Once the window is created, the wall is infractured while simultaneously elevating the sinus membrane, creating a space between the Schneiderian membrane and the floor of the sinus. A graft material is introduced into the resulting space. This technique is usually utilized when less than 5 mm of crestal bone remains.8 However, this technique, while very successful and predictable, does not come without its possible negative side effects. Infection, dehiscence, sinus perforation, and infraorbital nerve injury are all very real possibilities.

In the mid-1990s, Rosen et al9 and Summers10-11 demonstrated that the sinus floor could be lifted by the introduction of an osteotome via the implant osteotomy. This internal approach is known as the Summers approach, and it involves creating an osteotomy to within one mm of the sinus floor and then using an osteotome to upfracture the floor. Once upfractured, particulate graft material is placed into the osteotomy and pushed into the sinus. This approach has an unpredictable limit of approximately 4.0 to 5.0 mm of lift. Tears of the sinus membrane are a common side effect due to the uncontrolled fracture of sinus floor.

The unfortunate reality is that many patients will forego implant treatment if a sinus lift procedure is indicated. Either the perceived fear of the procedure or the additional cost may be the deciding factor for them.

Utilization of Short Implants

Initially, the efficacy of short implants was questioned due to longstanding implant doctrine, but in recent years, the success of short, wide-body implants has been shown. In 2004, Fugazzato et al12 demonstrated the cumulative success rates of implants less than 9 mm in length to be 95.1%. More recent studies have shown the survival rate of short implants in partially edentulous patients is similar to that of standard implants.13

The 6.0-mm Macro implant (OCO Biomedical) is a viable alternative for ridges where vertical bone height is compromised. It has aggressive threading, which allows for placement in either soft or hard bone with outstanding primary stability, has platform switching, and has a simple placement protocol.

CASE REPORT

Diagnosis and Treatment Planning

The patient was a 32-year-old male who presented with an unremarkable medical history. The maxillary right first and second molars (teeth Nos. 2 and 3) were atraumatically extracted approximately 2 years prior due to extensive decay (Figure 1). The remaining ridge, although very wide (about 11.0 mm), was compromised in the vertical dimension. CBCT scans showed posterior ridge height of 5.2 mm in the area of No. 2 (Figure 2). A compromised ridge such as this would usually have been treated with a crestal approach Summers lift, using osteotomes to upfracture the sinus floor 4.0 to 5.0 mm to accommodate an implant of 8.0 mm in length. In the No. 3 implant site, the sinus floor sloped upward as it approached the anterior wall. The ridge height in this area was 5.9 to 6.0 mm.

The treatment plan was to place two 6.0 mm x 6.0 mm Macro implants. The implant site in the No. 2 area would require a slight (1.0 mm) lift, and the No. 3 area would be able to accommodate the short implant without a lift.

Clinical Protocol

Once profound anesthesia was accomplished with the infiltration of Septocaine (Septodont) (with 1:100,000 epinephrine) on both the buccal and palatal areas, a No. 8 round bur was used to penetrate the keratinized tissue and create a divot in the crestal bone. Next, a 1.8-mm pilot drill with copious irrigation was used to create an osteotomy that extended up to the sinus floor without antral penetration (Figure 3).

Following the prescribed protocol, a 6.0-mm guided tissue punch was used to remove a concentric tissue plug around the initial pilot hole (Figure 4). Now that the crestal bone was exposed, a 3.5-mm upper osteotomy former was used first (Figure 5), followed by a 5.7-mm wide osteotomy former (Figure 6). Normally, with the OCO system, protocol allows progression from pilot to final diameter in a single step due to the unique step drill design. When using a 6.0-mm implant, it is advisable to step up in a progression in order to minimize drill “walk out” and also to lessen the possibility of heating up the bone by such a large jump in diameter. Once the osteotomy was completed on site No. 3 (Figure 7), the steps were repeated for the No. 2 site. The only difference was the use of a single 1.0-mm rubber o-ring in conjunction with a 6.0 mm depth stop to indicate the proper depth for drilling based on the CBCT measurements (Figure 8).

Both sites were flushed with sterile saline, and the patient was instructed to perform a Valsava maneuver to determine if an oral-antral communication occurred during preparation of the osteotomies. No perforation was noted, so steps were taken to place the implants.

A thin shell of bone was left at the sinus floor, and, to avoid having the bare implant body protruding into the sinus cavity, the floor was upfractured approximately 1.0 mm utilizing the dental implants.

Autogenous bone recovered from the osteotomy formers was mixed with a small amount of cortico-cancellous blend allograft material (Raptos [Citagenix]) and introduced into the osteotomies with a small paddle curette (Zoll-Dental) (Figure 9). Two 6.0 mm x 6.0 mm Macro implants were threaded into the prepared sites utilizing the attached Ultim carriers (Figure 10). Once seated, the carriers were removed and the implant driven into position with a torque wrench. Upon reaching the thin sinus floor, and mechanically pushing against it, a controlled upfracture resulted for the implant in area No. 2 (Figure 11).

The 45-Ncm rotational resistance was achieved on implant No. 2, and 47 Ncm was achieved on implant No. 3 at final insertion. These values on their own constitute enough primary stability to immediately load,14 but both implants were then checked using RFA (Osstell) (Figure 12). Implant stability quotient (ISQ) values of 68 and 72 were realized on sites Nos. 2 and 3, respectively. It is generally accepted that an ISQ value higher than 65 is sufficient to commence an immediate load (or early load) protocol per summary research by Osstell.

With outstanding primary stability achieved, 5.5 mm solid crown and bridge abutments were placed and torqued to the specified 30 Ncm (Figure 13). In approximately 5 minutes, they were retorqued to counteract any potential prestretch of the abutment threads.

Immediate temporization was carried out utilizing acrylic copings (Figure 14) and Protemp Crowns (3M ESPE). The splinted temporary crowns were cemented using Improv (OCO Biomedical), a temporary resin-based cement. The patient was dismissed with appropriate postoperative prescriptions and instructions (Figure 15).

The patient was also advised that there were no limitations for eating for the next few weeks.

After 3 weeks, the patient returned to the clinic for evaluation and the final impressions. The temporary crowns were removed and Tissue Retraction Impression Pickups (TRIPs) were placed (Figure 16). A final impression was taken using a combination of light- and heavy-body vinyl polysiloxane impression materials (Identium [Kettenbach LP]) (Figure 17). Once the impression was removed from the mouth, one-piece implant analogs were positioned back into the TRIPs. The upper and lower quadrant impressions were sent to the lab along with a bite registration (Futar [Kettenbach LP]) to fabricate individual PFM restorations (Figure 18). The temporary crowns were recemented and then the patient was dismissed.

In approximately 2 weeks, the patient returned for final seating of the restorations. After removal of the temporary crowns, all remaining temporary cement was cleaned off the abutments and the crowns checked for fit. Occlusal adjustments were carried out and the crowns were cemented (Improv [Alvelogro]) in place (Figure 19).

Excess cement was removed and verified with a radiograph (Figure 20).

CLOSING COMMENTS

Short, wide implants have allowed practitioners to place implants utilizing an atraumatic, minimally invasive, and predictable technique, done in areas where previously a traditional sinus augmentation would have been necessary. This type of treatment exposes the patient to fewer detrimental side effects and, in addition, these short implants allow for predictable, long-term success.

 

A 6.0-mm guided-tissue punch.

 

A 3.5-mm osteotomy former.

 

The 5.5-mm solid crown and bridge abutments.

 

Acrylic copings in place.

 

Analogs placed into final impression (Futar [Kettenbach LP]).