The Importance Of Considering Bite Force In Prosthetic Case Planning And Implant Selection

enero 24, 2018

Injerto óseo sintético, implante dental, MimetikOss

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Being able to properly chew foods is something that the majority of us take for granted, yet for many who are missing several or more teeth, the reality is that this simple task is often a struggle. So much so, that many alter their dietary intake to accommodate the foods they can eat, rather than foods they really enjoy or know that are good for them. Clearly when this happens it's a 'quality of life' issue but fortunately, one that can be addressed utilising implant-based restorations.

While replacing a 'like for like' restoration to improve dentition (and therefore chewing functionality) may seem like a clear task, the mechanical factors surrounding the act of chewing are largely unknown.

So what does this mean for dentists?

For dentists looking to place any type of implant-based restoration, the initial force of a patient's natural bite can and does have a significant impact on implant success. This is backed up by the fact that studies in the past have indicated that most patients needing implant restorations were able to generate a bite force somewhere in the range of 50 – 900N. While that evidence is perhaps nothing new, where it gets interesting is that more recent studies have shown that for some patients, it's normal to exceed levels greater than 900N.

A case in point was one 70 year old male who was seeking a fixed partial denture to facilitate better chewing. After a complete oral, clinical, and radiographic examination was carried out, a long-span, fixed partial denture was placed. This was supported with two implants. After 3 months of use, the anterior-most implant failed. A bite force measurement was taken and surprisingly, the result was found to be somewhere closer to 1200N.

Bite force measurement in patient mouth (source: Bite force and dental implant treatment: a short review. Flanagan D.)

To counteract the problem, after removal and debridement of the failed implant, a larger, longer diameter (4.7 x13mm) implant was placed. After successful osseointegration, the new denture was positioned and the patient up until now, hasn't experienced any implant failure or further bone loss.

Here's what we do know...

When teeth are missing, any loss does not reduce bite force capability. Therefore, the predominant force of a jaw bite is muscle dependent and not tooth dependent. While a well-designed occlusal loading scheme is paramount to treatment planning, it's worth remembering that human mastication is usually periodical, multi-directional, and of varying magnitudes. Despite this, if the patient's maximum bite force is recorded in the planning stages, it's possible to control these forces by combining the right number and type of implants, the right positioning to minimise impact, and the right density of bone.

What about the problematic anterior maxilla area?

Naturally the anterior maxilla is the predominant area where the vast majority of off-axial loading takes place. Off-axial loading can be detrimental for any implant at the best of times, but even more so when it isn't embedded into adequate bone. If the clinician suspects the possibility of overload potential, then it's advisable for them to firstly measure and record the maximal bite force that the patient can generate. The reason?

It's well-documented that a patient with a low bite force will often manage a successful implant, in spite of any eating habits or para-functions, and, even on some occasions, with poor anatomical bone structure. However when bite force is excessive, then this should always indicate the outcome including:

  •         Using longer or wider diameter implants and...
  •         Any correct occlusal design features that can adequately resist the load.

But that's not all...

Just to complicate matters further, there are other considerations that also need to be taken into account when deciding whether it's safe to place implants into a particular area. In other words - determining the strength of a jaw bite shouldn't be the only underlying reason....

Other factors for example can work in tandem with bite force to cause overload to any implant supported structure. Consider the patient who has a chronic popcorn habit - even though their bite force alone might not be perceived as excessive, when you combine this with their habit of continually crunching on any hard un-popped kernels, it might be sufficient to cause untold damage. Equally, what about the habitual nail biter? Again, they mightn't have an overly-excessive bite force, but add this to their likening for hard fingernails and it may be sufficient enough to eventually cause an implant to fail.

So what's the key takeaway?

Restoring full chewing capability should always be the number one goal of any implant-based restoration. As such a patient's bite force should play an integral part in the prosthetic case planning and implant selection. However, while a high bite force should indicate a greater risk of a component fracture; para-functional and dietary habits should also play a key role in determining the implant size, implant number, and the occlusal features that will help to resist the load. On the contrary, in spite of any para-functional and/or dietary habits, there is evidence to support the fact that some people who have naturally low biting forces can still experience a successful long-term outcome, irrespective of having poor anatomical bone qualities.

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