Unworn teeth are less resistant to noncarious lesions

Modern lifestyles have made teeth more vulnerable to noncarious cervical lesions because reduced wear has changed their biomechanics, a new study suggests.

Using computer simulation of chewing stresses, researchers at the University of Leipzig and the University of Frankfurt in Germany found that the stress concentrated in the cervical area of unworn teeth.

They published their findings in April in PLoS ONE.

Led by Stefano Benazzi, PhD, from the Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany, the researchers hypothesize that teeth evolved to be strong in an environment where they were being worn down.

Until industrialization, our ancestors ate tougher, grittier foods that wore down the cusps of their teeth. The less-worn teeth we have now distribute the loads of chewing differently, the researchers said.

“I think there are a lot of clinical implications,” coauthor Ottmar Kullmer, PhD, from the Department of Palaeoanthropology and Messel Research, Senckenberg Research Institute, Frankfurt am Main, Germany, told. “It seems very important to consider the dynamics of natural tooth wear and occlusal contacts for the reconstruction of tooth surfaces.”

For the study, Dr. Benazzi and colleagues used skulls gathered in South Africa in 1907 and 1909. The ages at death of 2 of the individuals from which the skulls were taken were 15 to 20 years. The ages of the other 2 were about 30 years each.

This gave the researchers examples of teeth at different levels of wear.

To understand the process by which teeth wear down, they created models for the teeth from the 2 individuals who died youngest.

They used polysiloxane impressions of the dentition to make stone crowns of the lower right second premolars and mounted the crowns with wax in their best-fit occlusal position.

They then set the dental arches in a dental articulator, using geometry details from the original jaws of the specimens. They moved the upper arm of the dental articulator in occlusion, wearing down the dental stone casts until they had produced flat facets.

The researchers then scanned these stone teeth using an optical topometery system. They also scanned the complete dental arches in maximum intercuspation and scanned the skulls, using microcomputed tomography.

The authors segmented the lower right second premolars as well as the supporting periodontal ligament, trabecular, and cortical bone from each skull to refine their digital models, and then scanned them.

They used these scans to create digital models of teeth at various stages of wear. Using Occlusal Fingerprint Analyser software, they analyzed the motion of the teeth against each other.

The software calculated the distribution of the load according to the occlusal contact areas, estimating stress patterns.

The researchers found that during maximum intercuspation, the slightly worn premolars contacted each other mainly on the buccal cusps and in the distal margin of the occlusal surface.

The steepness of the buccal cusp directed the load obliquely with respect to the axis of the tooth, so that the buccal side of the tooth experienced high tensile stresses, affecting the cervical half of the tooth and the lower third of the crown. This could account for both cervical lesions and root fracture, the researchers note.

In contrast, in worn teeth, contact areas covered a larger portion of the occlusal surface, resulting in a less localized pattern of stress directed almost parallel to the longitudinal access of the tooth into the root’s apex.

Because the force was more axial in the worn teeth, the tensile stresses were reduced and affected the lateral sides of the teeth, mainly distally instead of buccally. This could account for the absence of noncarious cervical lesions in samples of teeth from early modern humans, as well as their presence in contemporary teeth.

Although the results need to be confirmed, the researchers note, the data suggest that lack of wear could contribute to malocclusion.

Clinicians may want to take these factors into consideration, for example, in the design of implants and other restorations, Dr. Kullmer told Medscape Medical News.

Asked to comment, Mark Wolff, DDS, PhD, chair of cariology and comprehensive care at New York University in New York City, said the research was done well. “It’s actually a beautiful paper.”

However, he questioned whether clinicians would want to make flatter restorations based on concerns about noncarious cervical lesions. These lesions are generally not a big problem, he said.

“In rare occasions they cause sensitivity, and in very rare occasions they cause tooth loss,” he told. “But they are much more an aesthetic issue than a functional issue.”

In addition, cusps have some functions, such as piercing food and guiding occlusion, so designing restorations without them could be disadvantageous for chewing.

That does not mean the article has no implications for restorations, he said. “Could you make material that would absorb the shock and wear less? You would wind up in a scenario where you get less of these noncarious lesions.”

This research is supported by the Senckenberg Research Institute Frankfurt am Main, the Deutsche Forschungsgemeinschaft, and the Max Planck Society. One coauthor owns the Dental Workshop Bensheim. The authors and Dr. Wolff have disclosed no other relevant financial relationships.