Don’t forget about one-piece implants

The set-up

“Dr. Gause makes a compelling case for the utility of one-piece dental implants, particularly in sites with limited availability of mesial-distal (interdental) bone. Eliminating the implant-abutment interface with its screw retention necessarily increases the strength and stability of the implant and its prosthesis. The trade-off is reduced prosthetic flexibility, as the angulation of the ‘abutment’ portion of the single piece can only be modified by reduction. With many manufacturers now marketing true narrow-diameter implants with customizable and/or pre-angled screw-retained abutments, and with screw or abutment failures rare in the narrow, low-stress settings that call for one-piece implants, the practitioner will have to decide on a case-by-case basis if the benefit of improved strength outweighs the liability of reduced flexibility.”-Dr. BRIEN HARVEY, TEAM LEAD

The original Brånemark system utilized a two-piece implant, which allowed the implant to be placed in one procedure, and to be restored in a secondary procedure. This allowed the implant to be placed into bone and to osseointegrate; in a secondary procedure, the implant could be accessed for prosthetic tooth replacement. More recently, it has become known that implants can be placed surgically and fitted with a provisional restoration at the time of surgery. In this case, osseointegration is facilitated by the initial stability of the implant. This created a demand for a one-piece implant.

About five years ago, one-piece implants were a hot topic in implant dentistry. Many clinicians provisionalize implants, particularly in the anterior segment of the mouth at the time of surgery. A general rule of thumb in any surgical discipline is that the less a surgeon manipulates the tissue the better it will heal. For this reason, implants that are restored with two-stage surgeries often lose more bone than implants placed with a single stage.

Why one, not two?

In terms of the fundamental tenants of implant dentistry a one-piece option makes a great deal of sense. Why is it then that one-piece implants have fallen out of favor over the past two years?

Obvious advantages of one-piece implants are:

• There is no screw inside the implant that could loosen over time.

• The interface of a narrow platform implant is generally where implant fracture occurs during surgical placement, especially due to using torquing force over 35 Newton centimeters (Ncm).

• One-piece implants can be placed in narrow spaces, which without a narrow option would only allow for the placement of a Fixed Partial Denture (FPD). If a lateral incisor is the tooth in question, the one-piece implant could be the only thing that prevents the patient from having to prepare the central incisor or the canine.

One-piece implants have a significant number of additional considerations as compared to two-piece options.

1. Because the prosthetic component, or abutment, is connected to the implant body, the implant MUST be provisionalized at the time of surgery. Initial implant stability above 25 Ncm must be achieved since there is no option to bury the implant and allow 3-5 months for osseointegration to occur.

2. In determining the angulation of the implant, the surgeon must equally consider the location of the available bone and the proposed position of the restoration. Because the maxilla and the roots of the teeth are tipped lingually, implants often are placed where there is good available bone. If the one-piece implant is straight, then the abutment component of the implant could be flared facially. This could be a near impossible restorative situation for a placed and initially stable implant.

3. There is no zirconium abutment available with one-piece implants yet, so bone recession can leave an unesthetic metal show through.

With all that being said, one-piece implants have a clear indication in implant dentistry. In many cases, they can be the difference between an implant and a bridge and can result in beautiful restorations, particularly in the lower incisor and upper lateral incisor locations.

Case 1

Patient presents with a missing tooth No. 7. Orthodontia was attempted to gain enough space to place a 3.5-mm implant, but very little space was gained and only 4.5 mm of bone was available at the crest of the ridge. The patient is a pediatric dentist, so his dental IQ was very high. He did not want a bridge. In this case, a 3.0-mm one-piece implant was a viable option.

The surgical protocol was to:

• Make sure you have an adequate understanding of the bone morphology. Undercuts must be planned for, especially if the surgery is to be flapless.

• Try in the provisional over the gingiva to get a feel for the emergence of the implant in ideal placement, and verify that the proposed angulation will leave the implant in solid bone, away from the roots of the teeth, and with the abutment in restorable position.

• Tissue punch the gingiva to create a surgical site.

• Pilot drill and verify angulation

• Osteotomy with the single prescribed drill

• Placement of the implant

• Provisionalization

• Final restoration after 3 months

Case 2

Patient presents with multiple congenitally missing laterals. Treatment plan includes veneers to create a more harmonious smile, but tooth No. 7 is replaced with a one-piece implant.

In this case, there was 4.7 mm of bone at the height of the crest from the mesial of the CEJ of No. 6 to the distal of the CEJ of No. 8. The remaining teeth can all be restored with porcelain veneers in order to improve the esthetics. The remaining challenge is how to get a lateral into the small space between Nos. 6 and 8.

This case added the additional challenge of a buccal undercut 5 mm apical to the gingival crest. This requires the implant to be placed lingually to not have a fenestration of the buccal plate. This creates angulation issues of the abutment component of the implant. The abutment portion of the implant is angled facially. If this were a two-piece implant system, an angled or UCLA abutment could be used to totally correct any angulation issue.

The solution was to slightly prep the implant back facially and to use pink porcelain to recreate the gingival color. Again, this one-piece implant provided a solution for tooth replacement in an edentulous area without preparations in adjacent teeth.

In terms of the success of one-piece implants Baer et al, found the success rate of one-piece implants to be comparable to that of implants loaded in two stages, and documented only two implant failures out of 86 documented implants placed.

In summary

One-piece implants are grossly underutilized in implant dentistry. This is not due to the fact that the implants are less successful, or to the fact that they do not have a clinical indication. One-piece implants are becoming passé due to the increased technical difficulty in terms of surgical placement and predictable restoration. This is in no way a reason to let go of an implant modality.

One-piece implants have a clear indication in esthetic and implant dentistry. They allow single-tooth replacement in areas of little available bone. They also facilitate a situation where teeth can be immediately provisionalized, thus providing an immediate sense of satisfaction to the patient. Although they are more difficult to place and restore, phasing them out of implant dentistry will cause many patients to either undergo long orthodontic treatments or to have to accept preparation of virgin adjacent teeth in a FPD.

About the author

Lee Gause, DDS, is the head of Smile Design Manhattan, one of New York’s premier providers of general, cosmetic and implant dental care. Dr. Gause’s commitment to top-notch dentistry is apparent in every facet of his work, from the comfortable and stress-free office environment to the quality of esthetics delivered. He also is a clinical associate in the Continuing Dental Education Dental Implant Program at NYU College of Dentistry.