What is a short implant, and can it replace a sinus lift or bone grafting?

After a tooth is extracted, the jawbone becomes both thinner and lower over time. In the back of the upper jaw, on top of this, the sinus cavity expands downwards; in the back of the lower jaw there is the nerve canal that runs through the bone. As a result, there may not be enough height left for a conventional implant to fit. In this situation there are two routes: either building up the bone and placing a long implant (a sinus lift in the upper jaw, vertical bone grafting in the lower jaw) or using a short implant that fits into the remaining bone.

The limit of the word 'short' has changed over the years. Anything under 10 mm used to count as short; as implant surfaces improved, the limit came down. In 2018 the consensus conference of the International Team for Implantology (ITI) treated short implants as 6 mm or less. In the literature there are still reviews that count anything under 7 or 8 mm as 'short', and there are also studies that separately call 6 mm or less 'extra-short'. That is why, when reading the result of a study, it matters to look at which length it counted as short.

The real gain of a short implant is that it removes the burden that bone grafting brings. The ITI consensus report describes short implants as a valid option, when bone height has been lost, for avoiding the problems that additional surgery can bring. Cochrane's 2014 review also examined four studies with 102 participants: no evidence was found to show a difference between the two routes in loss of the prosthesis or the implant in the first year after loading, but there were more complications in the areas where a sinus lift was carried out. The ITI report, however, also sets out the price of this: the survival of short implants is more variable and the outcome less predictable.

The most comprehensive picture today comes from a 2024 meta-analysis. In 19 randomised trials, 2,214 implants were examined. According to evidence of moderate or high certainty, implants of 6 mm or less showed similar 5-year survival to implants of 10 mm or more in bone that needs no additional procedure and in full-mouth treatments, in both jaws; 6 mm implants were found to be usable in the upper jaw instead of a sinus lift. For the use of 4 and 5 mm implants instead of a sinus lift and the use of short implants instead of vertical bone grafting, however, the evidence is insufficient or not conclusive.

There are ten-year data too. In a multi-centre study comparing 11–15 mm implants with a sinus lift and 6 mm implants, 101 patients with a bone height of 5–7 mm were followed. At year 10, patient-level survival was 96% (2 losses) in the short implant group and 100% in the sinus lift group; the difference was not statistically significant and 21% of the patients had dropped out of follow-up. In a smaller study examining single-tooth crowns in the upper jaw, 10-year survival was found to be 89.5% in the 6 mm group and 90.9% in the 11 mm group with a sinus lift.

The negative side of the picture must be written down as well. In a meta-analysis combining nine studies with at least 5 years of follow-up, the survival of implants under 7 mm was between 86.7 and 98.5%, and that of longer ones between 95.1 and 100%; the difference was particularly marked in the upper jaw and similar in the lower jaw. With short implants there were fewer biological problems and more technical problems such as screw loosening or porcelain fracture. Another meta-analysis examining single crowns in the back of the mouth also found the survival of short implants to be lower over long follow-up and recommended caution with single crowns that are not joined to one another.

This is where the crown-to-implant ratio comes in. When the bone gets lower, the height that has been lost is added to the upper part of the tooth: the implant gets shorter and the crown on it gets longer. This lengthens the lever arm, and that is the first concern that comes to mind. A meta-analysis examining this ratio in single crowns could not find a link between the ratio and implant survival; but the qualitative data suggested that bone loss increased as the ratio grew. The most common mechanical problem was screw loosening. In other words, the ratio does not cause the implant to be lost on its own, but it makes the design and the bite adjustment more important.

The short implant is not the only option discussed when bone has been lost. When the inner part of the bone is not enough, anchoring the implant in the hard outer layer of the jaw is also a route: the corticobasal implants we use in our protocol of fixed teeth in 72 hours with the Ihde method work on this principle, and in most cases a graft or sinus lift does not come into consideration. Which route suits you is a decision made by looking at the height and width of the remaining bone on the CBCT scan, how many teeth are missing and your bite.

The distinction below was drawn according to where the published studies are strongest and weakest. Whether it suits you is determined by the CBCT scan and the examination.

The decision does not start with choosing a length; first the remaining bone is discussed, then the load, and last of all the implant itself.

1. 1

   The remaining bone is measured with a CBCT scan

   On the three-dimensional image, the height and width of the bone and the distance to the sinus or the nerve canal are read in millimetres. A panoramic X-ray is not enough on its own for this measurement, because it does not show width.

2. 2

   The options are set side by side

   A short implant, a long implant with a sinus lift or bone grafting, angled placement, and an implant that anchors in the hard layer of the jaw. More than one option should be explained to you, and the duration, additional surgery and risk of each should be compared.

3. 3

   Crown height and the bite are assessed

   You are asked how long the tooth that will go on the short implant will be, how the teeth in the opposing jaw bite together and whether there is any clenching. This information changes the number of implants and the design of the prosthesis.

4. 4

   A single crown or a joined bridge is decided on

   If there are neighbouring implants, joining the crowns to one another shares out the load. With a short implant standing on its own, the reason for the choice should be discussed separately.

5. 5

   Placement and healing

   A short implant is generally placed in a single operation, without a sinus or graft procedure. How long to wait for it to fuse with the bone and when loading will take place are determined by the dentist according to the hardness of the bone and the resistance with which the implant seats.

6. 6

   Baseline X-ray and check-up schedule

   The X-ray taken when the prosthesis is fitted is the baseline against which the bone level will be compared. Because most technical problems are seen in the first years, it is important not to skip the first check-ups.

These are not rivals to one another; in the same mouth, different routes can be chosen depending on the area.

The risks of a short implant are no different from those of a long implant, but their weights differ: fewer biological problems, more mechanical ones.

Because no graft or sinus procedure is carried out, healing is usually the healing of a single operation. The period that really calls for attention is the first years after the prosthesis is fitted.

1. The first days

   Mild swelling and tenderness are usual. Use painkillers and carry out your mouth care as your dentist has instructed; smoking impairs healing.

2. The fusing period

   The time allowed for the implant to fuse with the bone is set according to your own bone. During this period it is important not to chew anything hard on that area and not to miss check-ups.

3. The prosthesis and the baseline X-ray

   When the prosthesis is fitted, the bite is adjusted and an X-ray is taken. This film is the only record against which the bone level will be compared in future; ask for a copy.

4. The first five years

   In the 10-year multi-centre study, most technical problems were seen in the first 5 years. In these years the screw, the bite and the prosthesis in particular should be reviewed at check-ups.

The short implant itself is not a different cost item from a long implant; the difference comes from the additional procedures that are not carried out. The total is determined by the following:

The additional surgery avoided

If no sinus lift or bone grafting is carried out, the items for graft material, additional surgery and waiting time drop out. The 2019 meta-analysis found treatment cost to be lower with short implants.

Number of implants and prosthesis design

If short implants are to be joined together, more implants or a different bridge design may be needed. This changes the per-implant calculation.

Long-term maintenance

Technical problems are a little more common with short implants. The total over the years of small jobs such as replacing a screw or repairing porcelain should also be taken into account.

Imaging

The decision on a short implant is not made without a CBCT scan. Imaging is the fixed item of planning.