Clinical Application Summary:
I regularly use implants as short as 8mm in my practice without thinking twice about it. I would use 6mm implant in some cases but I like to keep things simple and stick to one implant system (I’m currently using Zimmer TSV) My caution to anyone placing short implants is to keep in mind the height of the crown you will build on top of that implant. A HUGE crown with an itty bitty implant can cause some problems–ie screw loosening & implant failure. Be mindful of the forces that will be applied to that implant–especially off axis forces during excursive movements.
What’s the literature say?
One of the challenges of dental implant surgery is placing implants in areas with deficient vertical bone or areas with maxillary sinus pneumatization or both. In areas of short bone, do you automatically have to graft?
We all know that one of the important prerequisites for implant placement is to have sufficient amount of bone height in order to meet the different structural, functional, and prosthetic challenges placed on the implant. However, in clinical practice, we’re often faced with situations in which there’s a limited bone height.
This usually happens as a consequence of edentulism. Bone augmentation techniques can often be successfully used to augment the dimensions of residual ridges. These include sinus lifts, sinus taps, GBR, and osseodensification. Many of these can be used somewhat predictably by a skilled clinician.
However, vertical ridge augmentation can be especially challenging. Lifting a sinus by 5mm is one thing, but building up an alveolar ridge crest by 5mm can be less predictable.
Also, these grafting procedures increase intraoperative & postoperative morbidity to the patient in addition to increasing treatment time and costs of the original procedure.
This might make your patient more nervous and less inclined to accept treatment. So, what’s our other option?
The use of short dental Implants
Short dental implants have received increased attention in clinical practice in cases that would otherwise require bone augmentation. In these cases, short implants have been increasingly viewed as a favorable, simple alternative in contrast to the more invasive option of grafting.
Recently, studies have added to this by showing comparable survival rates for short and long dental implants in contrast to previous studies that indicated lower survival rates for short implants. This is related to developments in the manufacturing of implants such as implant designs and surface treatments as well as to developments in clinical protocols for implant surgeries and prosthetic rehabilitation. (Quieroz et al. 2015; Monje et al. 2013).
The Survival Rate of short vs. long implants:
The literature provides varying theories about survival rates:
- Studies show similar survival rates for short and long implants (Monje et al. 2013).
- Studies demonstrate lower survival rates for short implants in comparison with long implants (Herman et al. 2005; Queiroz et al. 2015).
- Studies indicate that survival rate is not related to the length of an implant (Romeo et al. 2004; Mijiritsky et al. 2013)
WTF? Why are these studies contradicting each other?
As we can see above, there are three main theories about the relationship between implant length and survival rates. In order to better understand these theories, let’s take a closer look:
The first study indicates a similar survival rate for short and long implants. (This one is a study by Monje et al. 2013, in which they reviewed the literature (1997 – 2013) to evaluate 1,955 implants during a 14-years follow-up period) The authors concluded that short implants are just as predictable as long implants.
This increase in survival rates and decrease in failure rates was attributed to the compensation for the reduction in implant length through making implant modifications such as implant diameter, surface treatments, and modifying implant thread geometry.
The second study indicates a lower survival rate for short implants in comparison with long implants. In a study by Hermann et al. 2005, which examined a research database of 1,305 implants during a 5-year follow-up period, it was concluded that implant length correlates significantly with implant success rates. Therefore, longer implants have higher success rates in comparison with short implants.
However, the authors of this study indicated that implant-related modifications, such as implant surface texture, implant diameters, and implant design were not included in their study. As mentioned in the first theory, it is these implant-related modifications that are responsible for the compensation of the reduction of the length of implants. Therefore, disregarding these implant modifications will not paint the full picture–as we have seen from the first study that these modifications are significant.
The third study indicates no relation between implant length and survival rate. In a study by Mijiritsky et al.2013, to assess the survival rate of short implants during the first 2 years of function, it was found that during this period, implant length and diameter are not related to the survival rate of an implant.
However, the authors acknowledge the short-term follow-up of the implants and recommend further follow-up for their results. Therefore, the lack of long-term follow up for this study would make it difficult to validate such results accurately.
Short implants have come a long way. Design innovations have allowed for favorable prognosis and better predictability for short implants. However, further research is still required to determine various aspects related to short implants such as favorable size and distribution as well as favorable prosthesis parameters.
Now, what classifies an implant as short vs long? That’s a topic for another post :/
Hermann et al. Evaluation of Patient and Implant Characteristics as Potential Prognostic Factors for
Oral Implant Failures. Int J Oral Maxillofac Implants. 2005 Mar-Apr;20(2):220-30.
Mijiritsky et al. Implant Diameter and Length Influence on Survival: Interim Results During the First 2 Years of Function of Implants by a Single Manufacturer. Implant Dent. 2013 Aug;22(4):394-8.
Monje et al. Are Short Dental Implants (<10 mm) Effective? A Meta-Analysis on Prospective Clinical Trials. J Periodontol. 2013 Jul;84(7):895-904.
Queiroz et al. Clinical study on survival rate of short implants placed in the posterior mandibular region: resonance frequency analysis. Clin Oral Implants Res. 2015 Sep;26(9):1036-42.