Birefringence of the Secretory-Stage Enamel Organic Extracellular Matrix from Rats Submitted to Successive Injections of Bisphosphonates

Abstract

The aim of the present study was to assess birefringence of the secretory-stage enamel organic extracellular matrix (ECM) and mechanical properties of mature enamel from rats treated with bisphosphonates. Longitudinal sections were obtained from upper incisors of rats that had been submitted to injections of bisodic etidronate (8 mg/Kg/day), sodium alendronate (30 microg/Kg/day), or sodium chloride as control (8 mg/Kg/day) for 42 days. Sections were immersed in 80% glycerin for 30 min and optical retardation of birefringence brightness in the secretory-stage enamel organic ECM was determined in nanometers. Etidronate-treated rats exhibited extensive morphological changes in the secretory-stage enamel organic ECM inclusive nonbirefringent conspicuous incremental lines, but presented optical retardation values similar to those showed by control rats (p > 0.05). Birefringence of secretory enamel organic ECM from etidronate rats presented an irregular aspect. Alendronate-treated rats did not show morphological alterations in the secretory-stage enamel organic ECM, however, they presented significant reduction in optical retardation of birefringence brightness when compared with control and etidronate rats (p < 0.01). Alendronate and etidronate groups exhibited reductions of approximately 6-10% in mature enamel cross-sectional microhardness when compared with control group (p < 0.01). Scanning electron microscopy analysis showed extensive alterations in mature enamel only from etidronate group with absence of enamel rods. The present work shows that bisphosphonates can affect the birefringence of the secretory-stage enamel organic ECM. The results presented here suggest that alterations in the supramolecular organization of the secretory-stage enamel organic ECM are a plausible mechanism by which environmental factors may cause enamel defects.

Intermittent Parathyroid Hormone Administration Improves Periodontal Healing in Rats

“…Birefringence is the anisotropy caused by the difference between the two refractive indices of a substance, and it occurs as a consequence of ordered polymerization of macromolecules, such as organic matrix of enamel and collagen fibers in the periodontium 22,23 . One of the key functional characteristics of the acellular cementum is the insertion of collagen fibers from the PDL, the so‐called Sharpey fibers 23 .…”

Systemically alendronate was incorporated into dental tissues but did not cause morphological or mechanical changes in rats teeth

“…For instance, the effects of etidronate (HEBP), a nonaminobisphosphonate, on collagen fibrillogenesis, matrix synthesis, and mineralization of dentin have been reported (Beertsen et al,1985; Larsson,1974; Ogawa et al,1989; Sakai et al,1999; Takano et al,1998). HEBP has also been shown to affect enamel mineralization (Espírito Santo et al,2010; Fouda et al,1989, 1991, 1992; Weile et al,1990, 1993), ameloblast morphology (Fejerskov et al,1990; Josephsen et al,1990), and ameloblast functions, including effects on protein synthesis and secretion (Fuangtharnthip et al,2000; Yamada et al,2000), with development of hypoplasia and formation of subameloblastic cysts (Fejerskov et al,1990; Fouda et al,1989, 1991, 1992; Simmelink,1987). …”

“…In the present study, the DXA analysis revealed an increase in the bone mineral density of the proximal tibial metaphysis after exposure to sodium alendronate, which confirms previous reports (Freundlich and Alon,2008; Inoue et al,2008; Kawate et al,2010). Despite being widely used, few studies evaluated the effect of sodium alendronate in dental hard tissue formation in vivo, and those available are limited to enamel (Espírito Santo et al,2010; Massa et al,2006). …”

“…Finally, the analysis of the enamel and dentin by BFM showed no morphological alterations in the extracellular matrix. A recent study (Espírito Santo et al,2010) evaluated the birefringence of enamel organic extracellular matrix during the secretory stage and the mechanical properties of the enamel of maxillary incisors of rats treated with subcutaneously injected sodium alendronate (30 μg/kg/day). The morphological alterations in the extracellular matrix reported by those authors were not observed in the present study probably because they evaluated immature enamel while we evaluated mature enamel in addition to using different alendronate dose and route of drug administration.…”

“…Although the mechanism of action of sodium alendronate has been extensively investigated in bone (Azaras and Rezvani, 2010; Diab et al,2009; Enjuanes et al,2010; Ward et al,2011), little is known about its effects in the formation of mineralized dental tissues, limited to enamel (Espírito Santo et al,2010; Massa et al,2006). To the best of our knowledge there are no studies investigating the effects of sodium alendronate on dentin.…”