Journal of Dental Research http://jdr.sagepub.com/
The Inorganic Components of Cementum- and Enamel-related Dentin in the Rat Incisor J. Steinfort, B.M. Deblauwe and W. Beertsen J DENT RES 1990 69: 1287 DOI: 10.1177/00220345900690061301 The online version of this article can be found at: http://jdr.sagepub.com/content/69/6/1287
Published by: http://www.sagepublications.com
On behalf of: International and American Associations for Dental Research
Additional services and information for Journal of Dental Research can be found at: Email Alerts: http://jdr.sagepub.com/cgi/alerts Subscriptions: http://jdr.sagepub.com/subscriptions Reprints: http://www.sagepub.com/journalsReprints.nav Permissions: http://www.sagepub.com/journalsPermissions.nav Citations: http://jdr.sagepub.com/content/69/6/1287.refs.html
>> Version of Record - Jun 1, 1990 What is This?
Downloaded from jdr.sagepub.com at DALHOUSIE UNIV on July 11, 2014 For personal use only. No other uses without permission.
The Inorganic Components of Cementum- and Enamel-related Dentin in the Rat Incisor J. STEINFORT, B.M. DEBLAUWE, and W. BEERTSEN Experimental Oral Biology Group, Department of Periodontology, Academic Centre for Dentistry Amsterdam (ACTA), Louwesweg 1, 1066 EA Amsterdam, The Netherlands
Recently, we have shown that, in rodent incisors, the crownand root-analogue dentin (enamel- and cementum-related dentin) show differences in mineralization rates (Beertsen and Niehof, 1986) and composition of the organic matrices (Steinfort et al., 1989). It was the aim of the present study to determine whether these differences were accompanied by differences in the inorganic components. Rat incisors were analyzed by means of hardness measurements, microradiography, and the determination of Ca, Mg, and P04 content. The outer circumpulpal dentin layer of the enamel-related dentin (ERD) was considerably harder and denser than the comparable layer of the cementum-related dentin (CRD). Concomitantly, a higher Ca and P04 content was found for the ERD than for the CRD, while the reverse occurred with respect to Mg. From the apical end of the incisor toward the incisal edge, the Ca/PO4 ratio tended to decrease for both ERD and CRD, while the Mg/PO4 ratio increased. All differences appeared to be statistically significant. It is concluded that differences in the non-collagenous organic matrix were accompanied by differences in the inorganic components. More specifically, a relatively high content of highly phosphorylated phosphoproteins (ERD) was associated with a higher Ca and a lower Mg content. J Dent Res 69(6):1287-1292, June, 1990
Introduction. The role of noncollagenous proteins in the mineralization of hard tissues is poorly understood. Based on in vitro studies, a number of functions-such as initiation as well as inhibition of crystal growth, determination of crystal habits, and ion transport-have been ascribed to various organic matrix com-
/
ponents (Linde, 1985; Addadi and Weiner, 1985; Boskey, 1989). Confirmation in vivo, however, has not been obtained so far. We have attempted to explore the possible role in dentin mineralization of the organic matrix by comparing local variations in its composition with variations in the composition of the mineral phase. There is evidence to suggest that rodent incisor dentin consists of two distinct compartments, one related to the enamel (ERD) and the other to the cementum (CRD). The two compartments show differences in mineralization rate (Beertsen and Niehof, 1986) and in phosphoprotein composition (Steinfort et al., 1989). Certain differences in the inorganic components have already been reported. Rasmussen (1972) found that the mineral content was higher in the ERD than in the CRD. Furthermore, in the ERD, random orientation of crystals and the presence of calcospherites have been described in contrast to the CRD, where the crystals are oriented parallel to the tooth axis (Mishima and Sakae, 1986; Mishima et al., 1988). The present investigation focuses on the calcium and magnesium content of the two dentins in relation to physical parameters like hardness and density.
Materials and methods. Hardness measurements. Preparation ofslices. -Fifteen female Wistar rats (four months old) were killed by an overdose of Nembutal (injected intracardially), and the left and right lower jaws were dissected out. Marks were made at the outer surface of each mandible, indicating incisal, apical, and middle cross-sectional planes that were used for hardness determinations (Fig. 1). After removal of the jaw bone, the incisors were enclosed in Vertex (PMMA). Cross-sectional slices (1.75 mm thick) at the incisal, middle, and apical levels were prepared cementum
cementum-related dentin (CRD) pulp
7!
enamel-related dentin (ERD) enamel
a)
Inclsal
b)
Cross-section of rat lower Incisor
apical
I
middle Fig. 1-Rat lower incisor, cross-sectioned at three levels,
Received for publication July 4, 1989 Accepted for publication January 15, 1990
as
indicated.
Fig. 2-(a) Cross-section of rat lower incisor, showing the enamel- and the cementum-related dentin portions. Hardness and mineral density were measured in three concentric (circumpulpal) dentin zones at ten sites each. Zones I and II were located 60 and 120 pum, respectively, from the outer dentin border, whereas zone III was chosen at 60 pum from the dentin mineralization front. (b) Isolation of ERD and CRD for the determination of calcium, phosphate, and magnesium. After the enamel was ground away, the ERD and CRD were separated.
Downloaded from jdr.sagepub.com at DALHOUSIE UNIV on July 11, 2014 For personal use only. No other uses without permission.
1287
1288
J Dent Res June 1990
STEINFORT et al.
dentin hardness apical level 90 70
11
I
III
middle level 9o 70
60
30 III
I
incisal level
III
o~ ERD
4
-~ ORD
Fig. 3-Dentin hardness (mean + s.d.; n = 10) as measured at three cross-sectional levels of the rat lower incisor. k.u., Knoop units; x-axis represents distance from the dentin-enamel (ERD) or dentin-cementum (CRD) junction (open arrows): zone I, at 60 Arm from the outer dentin border; zone II, at 120 pm from the outer dentin border; zone III, at 60 um from the dentin mineralization front (closed arrows). ERD and CRD were found to be statistically different in hardness: (a) p
The Inorganic Components of Cementum- and Enamel-related Dentin in the Rat Incisor J. Steinfort, B.M. Deblauwe and W. Beertsen J DENT RES 1990 69: 1287 DOI: 10.1177/00220345900690061301 The online version of this article can be found at: http://jdr.sagepub.com/content/69/6/1287
Published by: http://www.sagepublications.com
On behalf of: International and American Associations for Dental Research
Additional services and information for Journal of Dental Research can be found at: Email Alerts: http://jdr.sagepub.com/cgi/alerts Subscriptions: http://jdr.sagepub.com/subscriptions Reprints: http://www.sagepub.com/journalsReprints.nav Permissions: http://www.sagepub.com/journalsPermissions.nav Citations: http://jdr.sagepub.com/content/69/6/1287.refs.html
>> Version of Record - Jun 1, 1990 What is This?
Downloaded from jdr.sagepub.com at DALHOUSIE UNIV on July 11, 2014 For personal use only. No other uses without permission.
The Inorganic Components of Cementum- and Enamel-related Dentin in the Rat Incisor J. STEINFORT, B.M. DEBLAUWE, and W. BEERTSEN Experimental Oral Biology Group, Department of Periodontology, Academic Centre for Dentistry Amsterdam (ACTA), Louwesweg 1, 1066 EA Amsterdam, The Netherlands
Recently, we have shown that, in rodent incisors, the crownand root-analogue dentin (enamel- and cementum-related dentin) show differences in mineralization rates (Beertsen and Niehof, 1986) and composition of the organic matrices (Steinfort et al., 1989). It was the aim of the present study to determine whether these differences were accompanied by differences in the inorganic components. Rat incisors were analyzed by means of hardness measurements, microradiography, and the determination of Ca, Mg, and P04 content. The outer circumpulpal dentin layer of the enamel-related dentin (ERD) was considerably harder and denser than the comparable layer of the cementum-related dentin (CRD). Concomitantly, a higher Ca and P04 content was found for the ERD than for the CRD, while the reverse occurred with respect to Mg. From the apical end of the incisor toward the incisal edge, the Ca/PO4 ratio tended to decrease for both ERD and CRD, while the Mg/PO4 ratio increased. All differences appeared to be statistically significant. It is concluded that differences in the non-collagenous organic matrix were accompanied by differences in the inorganic components. More specifically, a relatively high content of highly phosphorylated phosphoproteins (ERD) was associated with a higher Ca and a lower Mg content. J Dent Res 69(6):1287-1292, June, 1990
Introduction. The role of noncollagenous proteins in the mineralization of hard tissues is poorly understood. Based on in vitro studies, a number of functions-such as initiation as well as inhibition of crystal growth, determination of crystal habits, and ion transport-have been ascribed to various organic matrix com-
/
ponents (Linde, 1985; Addadi and Weiner, 1985; Boskey, 1989). Confirmation in vivo, however, has not been obtained so far. We have attempted to explore the possible role in dentin mineralization of the organic matrix by comparing local variations in its composition with variations in the composition of the mineral phase. There is evidence to suggest that rodent incisor dentin consists of two distinct compartments, one related to the enamel (ERD) and the other to the cementum (CRD). The two compartments show differences in mineralization rate (Beertsen and Niehof, 1986) and in phosphoprotein composition (Steinfort et al., 1989). Certain differences in the inorganic components have already been reported. Rasmussen (1972) found that the mineral content was higher in the ERD than in the CRD. Furthermore, in the ERD, random orientation of crystals and the presence of calcospherites have been described in contrast to the CRD, where the crystals are oriented parallel to the tooth axis (Mishima and Sakae, 1986; Mishima et al., 1988). The present investigation focuses on the calcium and magnesium content of the two dentins in relation to physical parameters like hardness and density.
Materials and methods. Hardness measurements. Preparation ofslices. -Fifteen female Wistar rats (four months old) were killed by an overdose of Nembutal (injected intracardially), and the left and right lower jaws were dissected out. Marks were made at the outer surface of each mandible, indicating incisal, apical, and middle cross-sectional planes that were used for hardness determinations (Fig. 1). After removal of the jaw bone, the incisors were enclosed in Vertex (PMMA). Cross-sectional slices (1.75 mm thick) at the incisal, middle, and apical levels were prepared cementum
cementum-related dentin (CRD) pulp
7!
enamel-related dentin (ERD) enamel
a)
Inclsal
b)
Cross-section of rat lower Incisor
apical
I
middle Fig. 1-Rat lower incisor, cross-sectioned at three levels,
Received for publication July 4, 1989 Accepted for publication January 15, 1990
as
indicated.
Fig. 2-(a) Cross-section of rat lower incisor, showing the enamel- and the cementum-related dentin portions. Hardness and mineral density were measured in three concentric (circumpulpal) dentin zones at ten sites each. Zones I and II were located 60 and 120 pum, respectively, from the outer dentin border, whereas zone III was chosen at 60 pum from the dentin mineralization front. (b) Isolation of ERD and CRD for the determination of calcium, phosphate, and magnesium. After the enamel was ground away, the ERD and CRD were separated.
Downloaded from jdr.sagepub.com at DALHOUSIE UNIV on July 11, 2014 For personal use only. No other uses without permission.
1287
1288
J Dent Res June 1990
STEINFORT et al.
dentin hardness apical level 90 70
11
I
III
middle level 9o 70
60
30 III
I
incisal level
III
o~ ERD
4
-~ ORD
Fig. 3-Dentin hardness (mean + s.d.; n = 10) as measured at three cross-sectional levels of the rat lower incisor. k.u., Knoop units; x-axis represents distance from the dentin-enamel (ERD) or dentin-cementum (CRD) junction (open arrows): zone I, at 60 Arm from the outer dentin border; zone II, at 120 pm from the outer dentin border; zone III, at 60 um from the dentin mineralization front (closed arrows). ERD and CRD were found to be statistically different in hardness: (a) p
