The subject of implant diameters always brings with it some level of controversy. A recent study investigated the effect of implant diameter on fatigue strength using static and cyclic load test, by comparing four different implant systems, ranging from 2.3 to 4.0. The conclusion:

Implant diameter has an effect on the ability to withstand both static and cyclic loads within Dentium implant systems, The ultimate failure load (UFLs) and fatigue cycles decreased as the implants diameter became smaller.

This, of course, is only one study, but we are curious if anyone has actually measured the failure rate of various implant diameters in their practice? Does the failure rate increase as the diameter of implants decreases?

1. Implant Dent. 2017 Feb;26 Effect of Implant Diameter on Fatigue Strength. Song SY et al.

This is an interesting article. I would like to read the full text if that could be posted. I believe that titanium alloy even in small diameter implants can tolerate most occlusal loads delivered by most patients over many years of service with appropriate occlusal schemes. However, the ability of the supporting bond and vegetative intraosseous bacteria are probable more important for implant longevity.

Dennis Flanagan DDS MSc

I agree with dr.Flanagan’s curiousity. There are some literatures on small diameter implants but many of them are not conclusive. I’d like to know how important the diameter of an implant really is when it comes to long term longevity, not from anecdotal studies but more organized science with more definitive data..

The answer is straightforward.

Consider a circular beam subjected to bending, with a radius R. Its moment of inertia is I=pi*R^4/4. The maximum stress on the outer fiber is dictated by (linear elasticity) the ration c/I where c=R/2.

The ratio becomes 2/pi*R^3.

Therefore, the maximum stress will depend on 1/R^3.

Meaning that for a given bending moment the stress will be smaller when the diameter increases.

And we know that smaller repetitive loads improve fatigue endurance of a structure….

Dentistry is biomedical engineering. Math should be a huge part of clinical analysis. There may be a large decrease in clinical failures after a complete math workup.

I can only agree with you. Perhaps “math” is a frightening word to some of us, so better call it “biomechanical engineering”.

Indeed some concepts that are well known in engineering mechanics seem to be ignored by the clinical community, which is not a sin at all, but when this is deliberate, it becomes a pity.

Sometimes, work that we would like to publish in dentistry journals are poorly received whereas they are highly appreciated in biomechanics journals. Unfortunately, it seems like the clinical community does not look at those journals. I believe time has come for a closer cooperation between our 2 communities.

Clinical data IS going to be more relevant than mathmatical statement. To above poster who posted the answer as ” straight forward”. There is much debate about whether you can use 3.5 mm implant for a first molar replacement still due to conflicting anecdotal daya out there. Your math equation is accurate but certainly doesn’t provide straight foward answer to this ongoing clinical issue. Math should be supporting mean to clinical data but we can’t retrieve any definitive answer to possible longevity of implants just from math alone as everyone’s bite force varies.

And we know that smaller repetitive loads improve fatigue endurance of a structure….

That does not cover biological issues. Only mechanical