Korean J Orthod.  2017 Nov;47(6):365-374. 10.4041/kjod.2017.47.6.365.

The relationships between the arrangement of teeth, root resorption, and dental maturity in bovine mandibular incisors

  • 1Department of Orthodontic Science, Division of Oral Health Sciences, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan. y.matsumoto.orts@tmd.ac.jp


The objective of this study is to investigate the eruption pattern and root resorption of the bovine anterior dentition in relation to growth-related parameters based on dental maturity.
A cross-sectional study was conducted on 110 bovine anterior mandibles by using standard radiography, cone-beam computed tomography (CBCT), and actual measurements. We determined the relationships between the stages of dental maturity by using a modification of Demirjian's method and various growth-related parameters, such as the activity of the root-resorbing tissue and mobility of the deciduous teeth. The correlation of growth-related parameters with interdental spacing and distal unusual root resorption (DRR) of the deciduous fourth incisor was assessed. The cause of mesial unusual root resorption (MRR) of the deciduous fourth incisor was determined on the basis of the arrangement of the permanent third incisor.
An independent t-test and chi-square test indicated significant differences in growth-related parameters associated with dental arch length discrepancy and factors related to the shedding of deciduous teeth between the low and high dental maturity groups. The samples with interdental spacing and DRR showed a larger sum of mesiodistal permanent crown widths and higher dental maturity than did the respective controls. Samples with MRR tended to show a lingually rotated distal tip of the adjacent tooth crown.
Dental maturity has relevance to the interdental spaces and unusual root resorption of mixed dentition. The position of the adjacent tooth crown on CBCT may be correlated with the occurrence of unusual root resorption of the incisor.


Growth and development; Root resorption; Ectopic eruption; Computed tomography

MeSH Terms

Cone-Beam Computed Tomography
Cross-Sectional Studies
Dental Arch
Dentition, Mixed
Growth and Development
Root Resorption*
Tooth Crown
Tooth, Deciduous


  • Figure 1 Anterior deciduous and permanent teeth of the cattle, measurements on cone-beam computed tomographic images, classification with respect to spaced dentition, and distal unusual root resorption of the fourth deciduous incisor root (DRR). A, Lingual view; B, standard radiographic image in the same position; C, section in the sagittal direction; D, section in the coronal direction; E, section in the horizontal direction; F, non-spacing group; G, spacing group; H, non-DRR group; I, DRR group. In the sagittal direction, from the plane perpendicular to the Frankfurt plane, the shortest distance between the root surface of D3 and crown of P3 is measured (C). In the coronal direction, from the plane perpendicular to the Frankfurt plane, the narrowest thickness of the periodontal ligament space in the D4 distal root surface is measured (D). In the horizontal directions, in the area parallel to the Frankfurt plane, the longest mandibular bone width and angulation of the P3 crown are measured (E). Black line, mandibular bone width; vertical white line, median suture line; horizontal white line, mesio-distal line of the P3 crown; white angle, angulation of the P3 crown (E). Based on the aspect of spaced dentition, the samples are classified into two groups. The non-spacing group (F) shows no interdental spaces in the deciduous dentition. The spacing group (G) has interdental spaces between the deciduous teeth. Based on the occurrence of DRR, the samples are classified into two groups: non-DRR (H) and DRR groups (I). DRR occurs at the site wherein the distal root surface of D4 is in contact with the alveolar bone. P1, First anterior permanent incisor; P2, second permanent incisor; P3, third anterior permanent incisor; P4, fourth anterior permanent incisor; D2, second deciduous incisor; D3, third deciduous incisor; D4, fourth deciduous incisor.

  • Figure 2 Comparison between the unaffected controls and the samples with mesial unusual root resorption of the fourth deciduous incisors (MRR) by using cone-beam computed tomographic three- and two-dimensional images. The vertical position of the P3 crown and resorption degree of the D3 root are similar in both samples. The distal tip of the P3 crown is located on the labial side with respect to the D4 root in normal samples (A), and the lingual side in MRR samples (B). The contact between the distal tip of the P3 crown and the D4 root surface occurs only in MRR samples in the coronal section (C, D). Angulation of the P3 crown is higher in the samples with MRR (F) than in the normal samples (E) in the horizontal section. Horizontal line in (E) and (F), mesio-distal line of the P3 crown; vertical line in (E) and (F), a line parallel to the median suture line.

  • Figure 3 Comparison of chronological age based on dental maturity, spacing aspect, and root-resorbing aspect (A), and comparison of mandibular bone width in the same age range (B). A significant difference between the low and high dental maturity groups is observed (low maturity, 27.3 ± 1.3 months; high maturity, 28.3 ± 1.1 months). However, no significant difference (NS) is observed between the spacing and non-spacing groups (non-spacing, 26.5 ± 1.3 months; spacing, 26.7 ± 1.3 months), and between the distal unusual root resorption (DRR) group and the non-DRR group (non- DRR, 27.8 ± 1.4 months; DRR, 28.1 ± 1.0 months). In the same age range, the mandibular width is higher in the highmaturity than low-maturity samples. The samples with high maturity show a tendency towards a high skeletal growth status (*p < 0.05, **p < 0.001).


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