Adaptive properties of human cementum and cementum dentin junction with age - PubMed (original) (raw)

Adaptive properties of human cementum and cementum dentin junction with age

Andrew T Jang et al. J Mech Behav Biomed Mater. 2014 Nov.

Abstract

Objectives: The objective of this study was to evaluate age related changes in physical (structure/mechanical properties) and chemical (elemental/inorganic mineral content) properties of cementum layers interfacing dentin.

Methods: Human mandibular molars (N=43) were collected and sorted by age (younger=19-39, middle=40-60, older=61-81 years). The structures of primary and secondary cementum (PC, SC) types were evaluated using light and atomic force microscopy (AFM) techniques. Chemical composition of cementum layers were characterized through gravimetric analysis by estimating ash weight and concentrations of Ca, Mn, and Zn trace elements in the analytes through inductively coupled plasma mass spectroscopy. The hardness of PC and SC was determined using microindentation and site-specific reduced elastic modulus properties were determined using nanoindentation techniques.

Results: PC contained fibrous 1-3 µm wide hygroscopic radial PDL-inserts. SC illustrated PC-like structure adjacent to a multilayered architecture composing of regions that contained mineral dominant lamellae. The width of the cementum dentin junction (CDJ) decreased as measured from the cementum enamel junction (CEJ) to the tooth apex (49-21 µm), and significantly decreased with age (44-23 µm; p<0.05). The inorganic ratio defined as the ratio of post-burn to pre-burn weight increased with age within primary cementum (PC) and secondary cementum (SC). Cementum showed an increase in hardness with age (PC (0.40-0.46 GPa), SC (0.37-0.43 GPa)), while dentin showed a decreasing trend (coronal dentin (0.70-0.72 GPa); apical dentin (0.63-0.73 GPa)).

Significance: The observed physicochemical changes are indicative of increased mineralization of cementum and CDJ over time. Changes in tissue properties of teeth can alter overall tooth biomechanics and in turn the entire bone-tooth complex including the periodontal ligament. This study provides baseline information about the changes in physicochemical properties of cementum with age, which can be identified as adaptive in nature.

Keywords: Adaptive properties; Age; Cementum; Cementum dentin junction (CDJ); Dentin.

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Figures

Figure 1

(a) Age ranges of younger, middle, and older humans from whom teeth obtained were used for microscopy (second row; mean +/− standard deviation), microindentation, nanoindentation, and inductively coupled plasma mass spectroscopy (ICP-MS) (third row; mean +/− standard deviation). Sample size of each group is shown in parentheses. (b) Transmission light microscopy images of sectioned molars demonstrate the clear fibrous cementum-dentin junction (CDJ). (c) Representative graphs of cementum width vs. anatomical location show a two-step increase in cementum thickness when measured from the cementum enamel junction (CEJ) to the root apex regions, that is, along the length of the root. (d) Graph of average cementum width across age groups for primary cementum (PC) and secondary cementum (SC) regions. In general, SC was thicker than PC and cementum thickness generally increased as a function of age. Statistical significant (p<0.05) relationships are indicated with an asterisk (*). (e) The thickness of the collagenous band indicative of the CDJ within the PC and SC regions decreased with age. Additionally, a decrease in apical CDJ width compared to the coronal CDJ in younger group was observed. However the CDJ width for middle and older groups was not different.

Figure 2

(a) Isolated cementum rings for ICP-MS analysis were sorted by anatomical location and tooth specimen (PC – primary cementum, SC – secondary cementum). Confirmation of dentin removal was performed by checking for any remnant dentin by using a light microscope for all specimens as shown at several magnification (a1 and a2). (b) Graph highlights inorganic ratio (ash weight/preburn weight) of cementum as measured in this study vs. age relative to reported values (dashed lines) for mineralized tissues enamel (E), dentin (D), and alveolar bone (B), including cementum (C) [1]. (c) A table of inorganic ratio and percentage of elemental composition (by weight) for calcium, magnesium, and zinc is shown for all age groups in primary and secondary cementum (PC, SC) types. The elemental standard (NIST 1400-bone ash) used for analysis is also included.

Figure 3

(a) Schematic of a tooth highlighting a region (rectangle) that was ultrasectioned for imaging using light (a1) and atomic force microscopy techniques (b, c). The surface of the ultrasectioned block contains regions that were imaged using an AFM (red squares with solid and dashed lines). AFM micrographs illustrate fibrous CDJ region in primary cementum (b) and in secondary cementum (c) under hydrated conditions. (c) The structure of secondary cementum includes lamellae, PDL-inserts (arrows), and the CDJ (the zone between the dashed lines). Incremental lines indicating growth are shown asterisk (*) with about a 10 – 40 µm spacing between each line.

Figure 4

Knoop hardness variations were grouped by age and location (from edge of the root through cementum (C) and into dentin (D)). (a) Hardness data from microindentation was graphed against age (Y: younger, M: middle, O: older) and from the cementum enthesis (edge of the root where the periodontal ligament meets cementum to dentin in order to depict the increase in hardness with age. Note that 1” – 9” represent hardness values for PC, CDJ, D, and 1’–9’ represent hardness values for SC, corresponding CDJ, and D. (b) Averages for each age and general trends were calculated to illustrate a gradual shift in material hardness between cementum and dentin. Grey zones represent 95% upper and lower bounds for all age groups.

Figure 5

Plotted graphs (a) and table values (b, averages (standard deviations)) illustrate hardness values across the enthesis (En, PDL-cementum interface), cementum (C), cementum dentin junction (CDJ), and dentin (D). (b) shows an increasing trend in hardness as a function of age. Incremental changes in hardness between regions illustrate a mechanical continuum across these tissues. Notice that both cementum and dentin show similar age related trends in the apical and coronal regions while dentin exhibits an age and location interaction effect. 1°: Primary Cementum, 2°: Secondary Cementum.

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Adaptive properties of human cementum and cementum dentin junction with age - PubMed (original) (raw)