Changes in the Distribution of Periodontal Nerve Fibers during Dentition Transition in the Cat.

The periodontal ligament has a rich sensory nerve supply which originates from the trigeminal ganglion and trigeminal mesencephalic nucleus. Although various types of mechanoreceptors have been reported in the periodontal ligament, the Ruffini ending is an essential one. It is unknown whether the distribution of periodontal nerve fibers in deciduous teeth is identical to that in permanent teeth or not. Moreover, morphological changes in the distribution of periodontal nerve fibers during resorption of deciduous teeth and eruption of successional permanent teeth in diphyodont animals have not been reported in detail. Therefore, in this study, we examined changes in the distribution of periodontal nerve fibers in the cat during changes in dentition (i.e., deciduous, mixed and permanent dentition) by immunohistochemistry of protein gene product 9.5. During deciduous dentition, periodontal nerve fibers were concentrated at the apical portion, and sparsely distributed in the periodontal ligament of deciduous molars. During mixed dentition, the periodontal nerve fibers of deciduous molars showed degenerative profiles during resorption. In permanent dentition, the periodontal nerve fibers of permanent premolars, the successors of deciduous molars, increased in number. Similar to permanent premolars, the periodontal nerve fibers of permanent molars, having no predecessors, increased in number, and were densely present in the apical portion. The present results indicate that the distribution of periodontal nerve fibers in deciduous dentition is almost identical to that in permanent dentition although the number of periodontal nerve fibers in deciduous dentition was low. The sparse distribution of periodontal nerve fibers in deciduous dentition agrees with clinical evidence that children are less sensitive to tooth stimulation than adults

PGP9.5-immunoreactive nerve fibers in a deciduous second molar and succeeding permanent second molar in a 5-month-old cat (a).

<p>b-e: Higher magnification views of boxed areas in a. b: In the periodontal ligament under the resorbing root of deciduous second molar, PGP9.5-immunoreactive thick nerve fibers are detected as having a dot-like appearance. c: Many PGP9.5-immunoreactive nerve fibers are randomly distributed in the cervical area of the periodontal ligament of the permanent premolar. d: At the apical part of the distal side of the periodontal ligament of the distal root of the permanent second premolar, thick nerve fibers and thin varicose nerve fibers are running coronally. e: In the furcation area of the permanent premolar, PGP9.5-immunopositive thick nerve fibers (arrowheads) and thin nerve fibers with varicosity (arrows) are found. AB: alveolar bone, D1: dentin of primary teeth, D2: dentin in permanent teeth, P: pulp. Scale bars: 200 μm in a, and 50 μm in b, which is applicable to c-e.</p

Schematic drawing for quantitative analysis.

<p>The percentage of PGP 9.5 immunoreactive areas was measured in the cervical (C), middle (M) and apical (A) portions of distal side of distal root of deciduous second molar (m₂) of the 2-month-old cat and permanent second premolar (P₂) of the 5-month-old cat, and mesial side of mesial root of permanent first molar (M₁) of the 5- and 12-month-old cats at the length of 800 μm (dotted area).</p

PGP9.5-immunoreactivities in the periodontal ligament of the lower second deciduous molar of the 2-month-old cat.

<p>a; Low-powered image of the root apex. A few nerve fibers are found in the periodontal ligament (PDL). C; cementum, AB; alveolar bone. b; High-powered image of the boxed area in a. Thick nerve fibers run along the periodontal ligament. They are less ramified and do not terminate in the cementum. c-e: Double-labeling for PGP9.5 (c) and S100 (d), and merged image (e) in the periodontal ligament in a 2-month-old lower second deciduous molar. Rounded S100-positive cells (arrowheads in d, e) are associated with PGP9.5-immunoreactive nerve fibers. Scale bars: 100 μm in a, 50 μm in b, 20 μm in e (also applied for c and d)</p

PGP9.5 immunoreactivity in the periodontal ligament of the permanent premolar (a) and molar (b) in a 12-month-old cat.

<p>Many thick PGP9.5-immunoreactive thick nerve terminals are observed. They are less expanded. C: cementum Scale bars: 50 μm</p

Double-labeling images for PGP9.5 (a, d) and S100 (b) or S100β(e), and merged images (c, f) in the apical periodontal ligament of deciduous second molar of 2-month-old cat (2mo; a-c) and cervical portion of erupting permanent second premolar of 5-month-old cat (5mo; d-f).

<p>a-c: PGP 9.5-immunoreactive nerve fibers (a, c) accompanying S-100 immunoreactive structures (b, c) are observed without interruption in the ligament of 2-month-old-cat. d-f: PGP9.5-immunoreactive nerve fibers show a dot-like appearance (d, f), while continuity of S100 structures is recognized (e, f) in 5-month-old cat. Scale bar: 50 μm.</p