Re-innervation in the canine periodontal ligament of replanted teeth using an antibody to protein gene product 9.5: an immunohistochemical study

Low-intensity pulsed ultrasound attenuates replacement root resorption of avulsed teeth stored in dry condition in dogs

This study aimed to investigate the effects of low-intensity pulsed ultrasound (LIPUS) on replacement root resorption after replantation of avulsed teeth stored in a dry condition in dogs. A total of 73 premolar roots from four male mongrel dogs were intentionally avulsed with forceps and divided into four groups—HN, HL, DN, and DL—according to storage conditions and whether or not they received LIPUS treatment. Thirty-eight roots were kept in Hanks’ Balanced Salt Solution for 30 min (HN and HL groups), whereas the remaining 35 roots were left to dry in the air for an hour (DN and DL groups) prior to replantation. Following replantation, the roots in the HL and DL groups (21 and 18 roots, respectively) received a 20-min daily LIPUS treatment for 2 weeks. The animals were euthanized 4 weeks after the operation. Micro-computed tomography images were acquired for each root and the amount of replacement root resorption was measured three-dimensionally. Histological assessments were also carried out. There was significantly less replacement root resorption for the roots in the DL group compared to the DN group (p < 0.01). Histological findings in the DN group demonstrated evident replacement root resorption, whereas the DL group revealed less severe resorption compared to the DN group. Within the limitations, these results suggest that LIPUS could attenuate the replacement resorption of avulsed teeth stored in a dry condition, thereby improving their prognosis.

Periodontal tactile sensation and occlusal loading condition of autotransplanted teeth: A retrospective pilot study

PURPOSE

The objectives of this retrospective pilot study were: (1) to examine the occlusal properties (periodontal tactile sensation, occlusal force support ability, dynamic tooth mobility, occlusal force, contact area, preferred chewing side and main occluding area) of autotransplanted teeth with no clinical complications after transplantation (postoperative periods from 1 to 7 years).

METHODS

Three groups were formed from 20 subjects (23 teeth in each group): autotransplanted teeth (ATP group), teeth contralateral to the recipient site (control group A), and teeth contralateral to the donor site (control group B).

RESULTS

The tactile detection threshold of the ATP group was higher than both the control groups, and the individual occlusal force was significantly lower than control group A. The occlusal force ratio and the occlusal contact area ratio were significantly lower in the ATP group than in both control groups, while the mobility was similar in all groups. Eight out of 20 subjects chose the autotransplanted teeth side as the preferred chewing side. Especially when the recipient site was the first molar, the ATP of these subjects were included in the main occluding area. The pocket depth of the three groups was within the normal range.

CONCLUSIONS

These results demonstrate that teeth autotransplantation can achieve a mastication efficiency and periodontal condition similar to normal teeth; however, without proper healing, the periodontal sensation of autotransplanted teeth may be inferior to that of normal teeth (<250).

Sensory innervation around immediately vs. delayed loaded implants: a pilot study

Although neurophysiological and psychophysical proof of osseoperception is accumulating, histomorphometric evidence for the neural mechanisms of functional compensation following immediate and delayed implant loading is still lacking. For this randomized split-mouth study, six mongrel dogs randomly received one of four treatment protocols at 36 implant-recipient sites over 16 weeks (third maxillary incisor, third and fourth mandibular premolar): immediate implant placement and immediate loading (IIP+IL); delayed implant placement and delayed loading (DIP+DL); delayed implant placement and immediate loading (DIP+IL); and natural extraction socket healing (control). Histomorphometry was performed in the peri-implant bone and soft tissues within 300 µm around the implants. Immunocytochemistry and transmission electron microscopy were used to confirm the presence of neural structures and to reveal their ultrastructural characteristics, respectively. Myelinated nerve fibres densely populated the peri-implant crestal gingival and apical regions, although they were also identified in the woven bone and in the osteons near the implant threads. Compared with the control group in the mandible, the group that received IIP+IL showed a higher innervation (in N⋅mm⁻², 5.94±1.12 vs. 3.15±0.63, P<0.001) and smaller fibre diameter (in µm, 1.37±0.05 vs. 1.64±0.13, P=0.016), smaller axon diameter (in µm, 0.89±0.05 vs. 1.24±0.10, P=0.009) and g-ratio (0.64±0.04 vs. 0.76±0.05, P<0.001) in the middle region around the implants. Compared with DIP+IL in the mandible, IIP+IL had a higher nerve density (in N⋅mm⁻², 13.23±2.54 vs. 9.64±1.86, P=0.027), greater fibre diameter (in µm, 1.32±0.02 vs. 1.20±0.04, P=0.021), greater axon diameter (in µm, 0.92±0.01 vs. 0.89±0.03, P=0.035) and lower g-ratio (0.69±0.01 vs. 0.74±0.01, P=0.033) in the apical region around the implants. It may be assumed that the treatment protocol with IIP+IL is the preferred method to allow optimized peri-implant re-innervation, but further functional measurements are still required.

Tissue-engineered ligament: implant constructs for tooth replacement

AIM

A tissue-engineered periodontal ligament (PDL) around implants would represent an important new therapeutic tool to replace lost teeth. The PDL is the key to tooth anchoring; it connects tooth root and alveolar bone, and it sustains bone formation.

MATERIALS AND METHODS

Cells were isolated from PDL and cultured in a bioreactor on titanium pins. After the formation of multiple cellular layers, pins were implanted in enlarged dental alveolae.

MAIN OUTCOME MEASURES

Cell-covered implants integrated without adverse effects, and induced bone in their vicinity.

RESULTS

A histological examination of a dog model revealed that cells were arranged in a typical ligament-like fashion. In human patients, product safety was ascertained for 6-60 months. Probing and motility assessments suggested that the implants were well integrated with mechanical properties similar to those of teeth. Radiographs demonstrated the regeneration of deficient alveolar bone, the development of a lamina dura adjacent to a mineral-devoid space around the implant and implant migration in an intact bone structure.

CONCLUSIONS

New tissue consistent with PDL developed on the surface of dental implants after implantation. This proof-of-principal investigation demonstrates the application of ligament-anchored implants, which have potential advantages over osseointegrated oral implants.

The biomechanical properties of the healing periodontium of replanted rat mandibular incisors

One of the most important aspects in tooth replantation seems to be restoration of the tooth support function of the healing periodontal ligament (PDL). We examined the support function, as measured by the mechanical properties, of the healing PDL at 7, 14, and 21 days after replantation of the left mandibular incisor in rats. From each dissected left mandible, a transverse section(650 microm in thickness) of the incisor was cut through an axis near the labial alveolar crest. Each section was intrusively loaded at a rate of 5 mm min(-1), and the shear stress-strain curve for the PDL was analyzed. Mechanical measures of the healing PDL showed gradual improvement after replantation. By 21 days, the mechanical strength returned to 53% of the control value; the extensibility, to 85%; the stiffness, to 61%; and the toughness, to 52%. The healing PDL exhibited reattachment of fibers in the middle region of the PDL, and the birefringent collagen fibers appeared to have regained the functional orientation by 14 days. The ratios occupied by the birefringent collagen fibers in the tooth-related, middle, and bone-related areas of the healing PDL gradually improved and returned to 78, 51, and 48% of the respective control values by 21 days. These results suggest that the support function of the healing PDL is gradually restored and that the biomechanical restoration is closely related to the reorganization and reorientation of collagen fiber bundles in replanted rat incisors.

Effect of denervation on healing after tooth replantation in the ferret

Studies have shown that the sensory nerves participate in inflammation and immune responses and possess trophic-facilitating wound healing in general. Tooth avulsion represents a pulpal and periodontal injury, and the mechanisms involved in the healing responses subsequent to replantation of teeth are still unclear. The objective of this study was to investigate the healing responses after denervation and replantation of teeth. Unilateral denervation was performed in 15 ferrets by axotomy of the inferior alveolar nerve, 5 days before extraction of the first lower premolars. Six weeks later the mandibles were excised and processed for histological evaluation. Immunohistochemistry was performed using antibodies against the sensory neuropeptides substance P (SP) and calcitonin gene-related peptide (CGRP), and measurements of root resorption and ankylosis were performed in four sections from each replanted tooth. After 6 weeks substantial reinnervation was observed in the jaws. Immunoreactivity in the pulp was observed in only two replanted teeth on the denervated side, compared with four on the innervated side. Total pulp necrosis appeared in 10 replanted teeth on the denervated side and in 5 on the innervated, indicating that sensory nerves promote survival of the pulp after replantation. SP-immunoreactive (IR) fibers were more frequently observed in the resorptive lacunae than CGRP-IR fibers. However, resorptive areas lacking IR fibers were frequently found along the root surface. Root resorption averaged 0.062 +/- 0.029 mm2 on the innervated side compared to 0.016 +/- 0.0043 mm2 on the denervated (P< 0.02). Ankylosis was observed in four of the replanted teeth on the innervated side (169.3 +/- 49.7 microm) and in six on the denervated side (332.56 +/- 193.2 microm) (P = 1). It is concluded that the sensory nerves promote root resorption after pulpoperiodontal injuries but have less influence on the osteoblastic activity expressed by ankylosis.

Morphological and cytochemical characteristics of periodontal Ruffini ending under normal and regeneration processes

Current knowledge on the Ruffini endings, primary mechanoreceptors in the periodontal ligament is reviewed with special reference to their cytochemical features and regeneration process. Morphologically, they are characterized by extensive ramifications of expanded axonal terminals and an association with specialized Schwann cells, called lamellar or terminal Schwann cells, which are categorized, based on their histochemical properties, as non-myelin-forming Schwann cells. Following nerve injury, the periodontal Ruffini endings of the rat incisor ligament can regenerate more rapidly than Ruffini endings in other tissues. During regeneration, terminal Schwann cells associated with the periodontal Ruffini endings migrate into regions where they are never found under normal conditions. Also during regeneration, alterations in the expression level of various bioactive substances occur in both axonal and Schwann cell elements in the periodontal Ruffini endings. Neuropeptide Y, which is not detected in intact periodontal Ruffini endings, is transiently expressed in their regenerating axons. Growth-associated protein-43 (GAP-43) is expressed transiently in both axonal and Schwann cell elements during regeneration, while this protein is localized in the Schwann sheath of periodontal Ruffini endings under normal conditions. The expression of calbindin D28k and calretinin, both belonging to the buffering type of calcium-binding proteins, was delayed in periodontal Ruffini endings, compared to their morphological regeneration. As the importance of axon-Schwann cell interactions has been proposed, further investigations are needed to elucidate their molecular mechanism particularly the contribution of growth factors during the regeneration as well as development of the periodontal Ruffini endings.