In cases in which the maxillary sinus extension leaves minimal bone available for dental implant placement, the clinician faces at least four choices in deciding how to restore the posterior dentition. The four options for consideration are: a fixed bridge, if there are both mesial and distal potential abutments; a maxillary sinus lift (window approach); an internal sinus lift, if there is adequate bone available to lift; and short dental implants, if at least 4 mm of bone is available.
Most patients do not wish to have their existing dentition altered for a fixed bridge. This option is also dependent on the potential strength and viability of both abutments. However, because this approach is likely the least invasive and costly for the patient, it is an option that must be considered.
In the past, I frequently used maxillary sinus lifts with a window approach to increase the amount of bone available to support an implant of at least 10 mm in length. This is a more invasive method that increases the length of time to final restoration and is more costly than other approaches. I have avoided placing the implant at the time of the lift due to its relatively low 82% success rate in my practice and because it requires 6 months of healing prior to implant placement, at which time additional bone is added after osteotome creation of the osteotomy. Today, I reserve this approach for patients with less than 3 mm of crestal bone, performing fewer than 10 of these procedures each year.
Short implants have certain potential risks. Their design is often wide and tapered significantly. To place a 5-mm-wide implant requires a ridge of at least 7 mm, and preferably 9 mm, to have sufficient bone on the buccal and palatal to support the implant; otherwise, augmentation would be necessary to widen the ridge further. The posterior dentition receives the greatest amount of force in mastication. Some of this may be counteracted by increasing the number of implants, however this raises costs. If there is any crestal bone loss in the future, the tapered nature of this implant could place both the implants and restoration in jeopardy.
My first choice in areas with a low sinus but at least 2 mm to 3 mm of bone remaining is an internal sinus lift with osteotomes, a procedure I have performed more than 1,000 times in edentulous sites, with immediate implant placement at the time of extraction (Figure 1 and Figure 2). Careful use of osteotomes allows the clinician to create an entrance to lift the sinus internally and augment the area with bone material to help support the implant. An implant designed for soft bone is recommended. This procedure allows the clinician to place an implant of at least 10 mm in length with minimal trauma and little increased cost. It also decreases the amount of time needed for a final restoration from 1 year to 6 months.
According to Felice et al5 in a recent short-term 5-year randomized controlled trial, the survival rate of short dental implants is similar to that of long implants placed with sinus grafting. Many key opinion leaders like Beaumer6 and Misch7 suggest a minimum implant length of 10 mm to 12 mm should be used.
When discussing this topic, it is important to note that the definition of “short implants” has changed over the years from 8 mm to 5-6 mm due to enhanced surface treatments.5 But perhaps a more critical factor for osseointegration is surface area rather than the length of dental implants. As the diameter of an implant increases, it has more effect on surface area than the length of the implant. Therefore, the diameter of short dental implants plays a more critical role in a short implant’s long-term survival (in the posterior region only). As a result, short and wide dental implants (5 mm to 7 mm in diameter) have demonstrated excellent survival rates.
For the purposes of this article, I will address regular-diameter (4 mm) short implants (5 mm to 8 mm in length) compared to regular-diameter long implants (10 mm to 15 mm) in grafted sinus.