Managing an atrophic mandible with short implants

Once tooth gets extracted, bone remodelling starts and the residual ridge gets resorbed. Due to insufficient bone width and height caused due to resorption, many complicated procedures need to be done like sinus lifting, bone grafting, ridge split, nerve reposition etc. But unfortunately these procedures are invasive, and may not go well resulting in complications. Failure of treatment gives mental stress to operator as well as patient. To avoid this, the concept of use of short implants is now emerging. Placement of the short implants in available bone has started turning the tables.

There is no exact size of a 'short' implant. Different studies considered different implant size as short. For convenience, let us consider implant sizes less than 10 mm as short. Initially simple machined short implants were used for resorbed ridges which had higher failure rates. With increasing implant dentistry knowledge and improved implant surface design characteristics, survival rate has increased. Short implants have emerged as a possible, alternative, less complicated option for resorbed ridges. In implant science, increase in implant height increases implant to bone surface area. The area which transfers stress to the surrounding bone is known as functional surface area which is only crestal 5-7 mm. Increase in implant length does not increase this area but increased diameter of short implant provide primary stability as well as increased functional surface area.

Short implants in atrophic mandible – Review of literature

• Bruggenkat et al (1998 ) – survival rate of short implants was comparable with the longer implants from the same implant system. But it was recommended that they should be used in combination with longer implants, especially when used in the less dense bone that is often seen in the maxilla.
• Akça et al (2002) studied in a finite element analysis that in short implants, lower stress was noted compared to cantilever fixed prosthesis and therefore instead of cantilever prosthesis, shorter implants should be considered.
• Increased crown to implant ratio is the main problem for the short implants. Blanes et al (2007) showed that high success rates for short implant when crown to implant ratio was 2. No peri-implant bone loss was associated with increased crown to implant ratio.
• Esposito et al (2011)- Short implants of 5 mm in length could be a preferable choice to bone augmentation in posterior atrophic area as the treatment is faster, cheaper with less morbidity.
• Slotte et al (2012) – Short implants of 4 mm can support fixed prosthesis in severely resorbed posterior mandible ridges for 2 years with healthy peri-implant tissues.
• Pistilli et al. (2013) Short implants of 5-mm implants had shown similar results to those of longer implants placed in an augmented bone.
• Felice et al. (2014.) – The short implants have good prognosis as that of long implants placed vertically in augmented mandibles.
• Esposito et al. (2014) – 5 mm short implants achieved similar results to those of longer implants in augmented bone.
• Peixoto et al (2017) – severely resorbed mandible rehabilitated with 4 short implants placed distally at 45 degree without transcortical involvement were biomechanically more favorable, generating lower stress peaks, compared to the models with short implants of all-on-four, in upright configuration, with or without lower transcortical involvement.

Short dental implants should be recommended in cases with remaining ridge of 8–10 mm in height, which allows to place a 6-mm implant including a safety distance from the alveolar nerve of 2 mm. In cases where more than 10 mm of the bone is available, standard-length implants should be placed.

Advantages of short implants

1. Simple procedure. Complicated procedures of bone grafting, sinus lifting, nerve repositioning can be avoided.
2. Faster method.
3. Comparable survival time with long implants.
4. Can reduce stress compared to cantilevers.
5. Less skill necessary
6. Less morbidity
7. High patient acceptance as avoidance of advanced surgical procedures

Disadvantages

1. Increased crown to implant ratio

Conclusion

Insufficient alveolar bone height leads to problem for implant placement in the posterior jaws. Adjunctive surgical procedures may be required to overcome this problem. Although these procedures are proven to be successful, they may result in delayed healing, increased morbidity, and prolonged treatment period. Now a days, short dental implants have been successfully used in the situations like these with comparable survival rates with that of longer implants. Various methods are being implemented to increase the surface area and bone implant contact along with the stress reduction to the implant prosthesis. This makes short implants a viable and more predictable alternative to advanced and cumbersome surgical interventions.

References

1. Esposito M, Cannizzaro G, Soardi E, Pistilli R, Piattelli M, Corvino V, et al. Posterior atrophic jaws rehabilitated with prostheses supported by 6 mm-long, 4 mm-wide implants or by longer implants in augmented bone. Preliminary results from a pilot randomised controlled trial. Eur J Oral Implantol 2012;5:19-33.
2. YS Y et al. Short (5.0 × 5.0 mm) implant placements and restoration with integrated abutment crowns.Implant Dent. 2011 Apr;20(2):125-30.
3. Peixoto HE, Camati PR, Faot F, Sotto-Maior BS, Martinez EF, Peruzzo DC. Rehabilitation of the atrophic mandible with short implants in different positions: A finite elements study. Mater Sci Eng C Mater Biol Appl. 2017 Nov 1;80:122-128.