Takashi Oikawa

Time-lapse observation of rat periodontal ligament during function and tooth movement, using microcomputed tomography

The aim of this study was to observe the time-lapse changes in the rat periodontal ligament (PDL) during function and tooth movement. Under Nembutal anaesthesia, time-lapse changes in the thickness of the PDL of the first molars were investigated in five 12-week-old adolescent rats with microcomputed tomography. Three-dimensional (3D) images were reconstructed from the data. Histological observation was also performed, using undecalcified frozen sections of the maxillary first molar area. The PDL appeared as a radiolucent furrow on the 3D images. A slight change in the thickness of the PDL was observed 1 hour after initiation of orthodontic force loading, which became significant after 6 hours, with the appearance of pressure-tension zones during the tooth movement. These changes were more significant 3 days after orthodontic loading. Histological observation of the lingual cervical PDL (pressure zone) in nine 12- to 13-week-old rats demonstrated that the periodontal space had become narrow and the cellular elements appeared to be densely packed in the narrowed PDL 6 hours after orthodontic loading. Degeneration of tissues appeared 3 days after loading. Observation of the buccal cervical PDL (tension zone) demonstrated that the PDL was extended 6 hours after orthodontic force loading, and the extension continued for up to 3 days. Alkaline phosphatase activity was distributed in the PDL, except for the degenerating tissues in the pressure zone 3 days after loading. The results suggest that the periodontal reaction was initiated within 6 hours after orthodontic force loading, which was related to the structural changes of the PDL. The changes probably induced an early response in individual cells of the PDL.

Elimination of transverse dental compensation is critical for treatment of patients with severe facial asymmetry

This case report describes the importance of eliminating transverse dental compensation during preoperative orthodontic treatment for a patient with severe facial asymmetry. The patient, a 17-year-old Japanese woman, had severe facial asymmetry involving the maxilla and the mandible, and extreme transverse dental compensation of the anterior and posterior teeth in both arches. Therefore, the main treatment objectives were elimination of the transverse dental compensation by orthodontic treatment and correction of the morphology of the maxilla and the mandible by orthognathic surgery. The preoperative orthodontic treatment resulted in sufficient elimination of the transverse dental compensation and movement of the teeth into their proper positions so that basal bone firmly supported them. LeFort I osteotomy and sagittal split ramus osteotomy were performed to correct the skeletal morphology. Facial asymmetry was dramatically improved, and a favorable occlusion was obtained. At 1 year 8 months after the surgical orthodontic treatment, the facial symmetry and occlusion remained favorable. The results suggest that sufficient elimination of transverse dental compensation in the maxillary and mandibular arches during preoperative orthodontic treatment is requisite for successful treatment of severe facial asymmetry.

Laser capture microdissection of rat periodontal ligament for gene analysis

The periodontal ligament (PDL) is a connective tissue interposed between two hard tissues, viz., the root of a tooth and the alveolar bone, which makes it difficult to obtain directly. In the study reported here, PDL, subgingival connective tissue and pulp of rat molars were extracted directly by laser capture microdissection and the gene expression of TGF-β1 on the microdissected PDL was examined. The maxillae of rats were dissected and rapidly immersed in isopentane cooled with liquid nitrogen. Serial frontal sections of the rat first molar area were used for immunohistochemistry and for laser capture microdissection to localize the TGF-β1 gene. Gene expression and immunohistochemical localization of TGF-β1 also were examined in the pulp and subgingival connective tissues. TGF-β1 was located immunohistochemically in the fibroblasts in the PDL. A considerable amount of RNA was obtained by laser capture microdissection of these three tissues for analysis of gene expression. The reverse transcription- polymerase chain reaction demonstrated that glyceraldehyde 3-phosphate dehydrogenase was amplified in all three tissues, and that TGF-β1 was detected in the PDL. Laser capture microdissection makes it possible to analyze the gene expression of PDL and expression of TGF-β1in the PDL suggests that this gene could function in maintaining PDL.

Mechanism of active eruption of molars in adolescent rats

The mechanism of active eruption of molars was examined in 36 male adolescent Wistar rats. Histological, histochemical [tetracycline (TC) labelling and alkaline phosphatase (ALP) activity], and immunohistochemical [transforming growth factor (TGF)-β1, -β2, and -β3] investigations were conducted of the rat molar areas. Real-time reverse transcription-polymerase chain reaction (RT-PCR) for mRNA of TGF-β was performed on the periodontal ligament (PDL) dissected out by laser capture microdissection. TC labelling lines showed that a considerable amount of bone formation occurred in the alveolar crest region, apical region, and intraradicular septum, indicating that the maxillary molars had moved downward. However, the periodontal fibres revealed a regular arrangement (alveolar crest, horizontal and oblique fibres) during the experimental period. This suggests that new formation of alveolar crest fibres and rearrangement of the periodontal fibres occurred in the PDL. ALP activity was intense on the bone surface and in the PDL. TGF-β1 was also detected in osteoblasts and fibroblasts but less so in cementoblasts. Real-time RT-PCR also demonstrated significant expression of mRNA of TGF-β1 in the PDL, indicating that TGF-β1 was involved in active eruption. These results suggest that active eruption occurs in adolescent rats and can be managed by TGF-β1.

Histology and tetracycline labeling of a single section of alveolar bone of first molars in the rat

We observed the histology and tetracycline (TC) labeling in a single frontal section of alveolar bone of upper first molars of adolescent rats. A single injection of TC was administered intraperitonealy in adolescent rats. After three weeks, the upper jaws were immersed rapidly in liquid nitrogen and sectioned. Five micrometer unfixed, undecalcified frozen sections were cut and observed by light and fluorescence microscopy. Frontal sections of the upper first molar area revealed that the structural relationships among the roots, the periodontal ligament and the alveolar bone, and also between the cervical enamel and the attachment epithelium were well preserved. The TC labeling lines in the sections were very clear and distinguished new bone from old bone. The brightness of the lines differed among regions. An analysis of the brightness in the same section suggested a difference in the bone forming activity at the time of injection.

Reconstruction of a collapsed dental arch in a patient with severe periodontitis.

This case report describes the significance of orthodontic treatment in reconstruction of a collapsed dental arch and a malocclusion associated with severe periodontitis. A Japanese man (age, 40 years 7 months) had an anterior crossbite, a collapsed occlusion, and severe periodontitis. Orthodontic treatment included the following steps: (1) correction of the anterior crossbite, labial movement of the maxillary incisors, and intrusion and retraction of the mandibular incisors; (2) correction of the posterior crossbite on the left side, buccal movement of the maxillary left canine and first premolars, and intrusion and retraction of the mandibular first premolar into the space of the mandibular left canine; (3) correction of the crowding of the mandibular right buccal segment and alignment of the teeth after extraction of the mandibular right first molar with a periapical lesion; and (4) improvement of the occlusion, with reconstruction of an acceptable occlusion. When combined with restorative and prosthodontic treatment, a fairly good occlusion was obtained. Reevaluation of the treatment after 11 years showed that the occlusion and periodontal condition were maintained well without deepening of the pockets and further bone loss. Orthodontic treatment with a systematic approach helped to recover the occlusion and prevented the recurrence of periodontitis by acquiring a good oral environment and motivating the patient to maintain oral health.

Tooth movement limited to periodontal ligament width using interrupted orthodontic force

Abstract A new orthodontic appliance with ratchet mechanism (ratchet bracket) was used in experimental animals and clinically, in order to assess tooth movement limited to periodontal ligament (PDL) width, using interrupted orthodontic force. After experimental tooth movement using two beagle dogs’ third incisors, active bone formation was seen at the tension region on fluorescent images, and blood vessels could be seen in the maximal compressed region. No obvious signs of root resorption were seen on the outline of the roots in micro-CT images. The average distal movement of 10 upper canines in six female patients was 1.9 mm (S.D. 0.21) in a month, and 5.5 mm in 102 days, which was the longest period. No patient complained of spontaneous pain during tooth movement or pain on biting. Dental radiography revealed long and thick lamina dura on the tension side of the canines, suggesting bodily tooth movement and a relatively dense bone formation. There was no obvious sign of root resorption in any canines. These results suggested that an interrupted orthodontic force controlled to a distance of 0.26 mm using ratchet mechanism may cause tooth movement without serious damage or pain.