DentalTech Forum

Wolff’s Law: Under normal physiological stress, bone mass stabilizes at normal levels.  Under excessive stress, mass increases, and under low stress, bone resorbs.

We have the concept of Wolff’s Law from orthopedic theory.  Wolff’s Law refers to the correlation between bone regeneration and behavior with physiological force.  When force applied to bone structures are within physiological norms, the bone responds by achieving and stabilizing with physiologically normal mass and density.  When force is below normal, bone responds by resorbing or shrinking.  When force is excessive, bone responds by growing to above-normal mass and density.  We would typically expect to see atrophy in the ridge with the ridge is not engaged in mastication.  When the ridge is excessively engaged, we would see reapposition.  When the ridge is engaged normally, we would expect to see normal and stable bone mass and density.  This concept is actually what allows implants to work as well as they do.  The implant creates a normal environment for the supporting bone.  While no partial will replicate this exactly, the tissue-bearing partial comes closer than the tooth-supported partial.  The only factor to consider is balancing the force distribution over the edentulous ridge, not whether or not to engage it at all.

Wolff's Law and bone's structural adaptations to mechanical usage: an overview for clinicians

Harold M. Frost, MD^a

ABSTRACT

Basic Multicellular Unit-based bone remodeling can lead to the removal or conservation of bone, but cannot add to it. Decreased mechanical usage (MU) and acute disuse result in loss of bone next to marrow; normal and hypervigorous MU result in bone conservation. Bone modeling by resorption and formation drifts can add bone and reshape the trabeculae and cortex to strengthen them but collectively they do not remove bone. Hypervigorous MU turns this modeling on, and its architectural effects then lower typical peak bone strains caused by future loads of the same kind to a threshold range. Decreased and normal MU leave this modeling off. 

Where typical peak bone strains stay below a 50 microstrain region (the MESr) the largest disuse effects on remodeling occur. Larger strains depress it and make it conserve existing bone. Strains above a 1500 microstrain region (the MESm) tend to turn lamellar bone modeling drifts on. By adding to, reshaping and strengthening bone, those drifts reduce future strains under the same mechanical loads towards that strain region. Strains above a 3000 microstrain region (the MESp) can turn woven bone drifts on to suppress local lamellar drifts but can strengthen bone faster than lamellar drifts can. Such strains also increase bone microdamage and the remodeling that normally repairs it.

Those values compare to bone's fracture strain of about 25,000 microstrain.

Department of Orthopaedic Surgery, Southern Colorado Clinic. American Academy of Orthopaedic Surgeons; Association of Bone and Joint Surgeons; Adjunct Professor of Anatomy, Purdue University; Adjunct Professor of Radiobiology, University of Utah

KEY WORDS: Bone, Wolff's Law, Biomechanics, Remodeling, Modeling, Mechanical influences, Endoprostheses, Orthodontics, Orthopaedics.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=

PubMed&list_uids=8060014&dopt=Abstract