Physical properties of human premolar cementum: hardness and elasticity

AIMS: To determine if the cementum on the maxillary right and left first premolars has identical physical properties. METHODS: Ten normal maxillary first premolar teeth, extracted from five orthodontic patients with a mean age of 14.0 years, were used. The teeth had not been subjected to an orthodontic force. The hardness and elastic modulus of the cementum were measured on the buccal and lingual surfaces of the roots at three locations: cervical third, middle third and apical third. RESULTS: There were no significant side-to-side differences in cementum hardness (Mean side-to-side difference: 0.0063 GPa; SD: 0.0279; p = 0.525) or elastic modulus (Mean side-to-side difference: -0.027 GPa; SD: 0.111; p = 0.814). The hardness and elastic modulus of the cementum decreased from cervical to apical regions on both root surfaces. CONCLUSIONS: Similar physical properties of the cementum on the maxillary right and left first premolars suggest that intra-arch comparisons can be used to investigate root resorption caused by orthodontic forces.5 page(s

Changes in the physical properties of human premolar cementum after application of 4 weeks of controlled orthodontic forces

This study was performed to assess the relationship between the magnitude of orthodontic force and physical properties of individual human cementum, and to identify the sites that may be predisposed to root resorption. The findings may assist in relating physical properties of dental root cementum and its susceptibility to root resorption. Sixteen maxillary first premolar teeth were selected in eight orthodontic patients (three males and five females), mean age 14.8 years (range 11.2–17.5 years), requiring first premolar extractions. In each patient, a light orthodontic force of 25 cN was applied buccally using a sectional archwire on the first premolar on one side, while a heavy force of 225 cN was applied to the contralateral side. The teeth were extracted 4 weeks after initial force application. Hardness and elastic modulus were measured on the buccal and the lingual surfaces of the cementum at the cervical, middle, and apical third of the root. The results showed that the mean hardness and elastic modulus of cementum in the light force group were greater than in the heavy force group at all positions. There were highly significant differences in both hardness and elastic modulus between the heavy and light force groups (P < 0.01). The mean hardness and elastic modulus of cementum gradually decreased from the cervical to the apical regions for buccal as well as lingual surfaces in both groups. There was, however, an insignificant difference between hardness and elastic modulus on the buccal surface compared with the lingual surface (P < 0.05). It was concluded that the hardness and elastic modulus of cementum were affected by the application of orthodontics forces.6 page(s

Fundamental Structure and Properties of Enamel, Dentin and Cementum

In this chapter, the fundamental structure of dental tissue at different scale levels and its concurrent role in determining the mechanical properties of the tooth are discussed. The main emphasis is on the role of the organic phase in determining the mechanical properties of enamel and dentin. In this regard, the results of nanoindentation experiments following different treatments of enamel and dentin are presented. These treatments include selective removal of matrix proteins and water of enamel and dentin tissue. The findings indicate that peptides and organic remnants not only play a significant role in the formation and structure of enamel and dentin, but also they regulate the mechanical response and functional integrity of the tooth tissue. In addition, these findings provide a basis for further investigation of the adverse effect of some current clinical treatments, such as bleaching, on the health and properties of dental tissue