Effects of alendronate on restoration of biomechanical properties of periodontium in replanted rat molars

OBJECTIVE: We examined the effect of the pretreatment of roots with alendronate on the restoration of the support function of the healing periodontal ligament in replanted rat molars. METHODS: The left maxillary first molars were extracted, placed in 0.9% NaCl containing 1 mm alendronate (alendronate group) or 0.9% NaCl (control group) for 5 min, and were replanted into their sockets. Groups of animals were killed at 7, 14, and 21 days after replantation. Normal control rats were also killed on the same days. The force required to extract the replanted or normal tooth from its socket was measured, and a load-deformation curve was developed and analyzed. Micro-computed tomography and histologic analyses were also made. RESULTS: The mechanical properties of the healing periodontal ligament in the alendronate group were gradually restored from 7 to 21 days. However, fractures of the roots and bones during mechanical testing occurred in most of the replanted teeth in the control group at 21 days. The rates of restoration of the mechanical strength, extensibility, stiffness, and toughness for the alendronate group at 21 days were 67, 98, 74, and 68% of the normal controls, respectively. Micro-computed tomography and histologic observations revealed that bone-like structures within the pulp and ankylosis between the roots and socket bones occurred commonly in the control group, but were uncommon in the alendronate group. CONCLUSIONS: Our findings suggest that the pretreatment with alendronate inhibits the formation of abnormal mineralized tissues and results in better restoration of the support function of the healing periodontal ligament in replanted teeth.     

The effect of topical minocycline on replacement resorption of replanted monkeys' teeth

Abstract – Tetracycline has been reported to possess antiresorptive properties in addition to antimicrobial actions. Systemic administration of tetracycline showed variable results in the control of replacement resorption after replantation with good results in half of the cases, and almost no healing in the rest. The purpose of this study was to evaluate histologically the effect of topically applied minocycline on replacement resorption of replanted monkeys' teeth. Thirty‐two roots from seven monkeys were endodontically treated aseptically to prevent inflammatory resorption of pulpal origin, a common sequela after avulsion injury. Teeth were then extracted as atraumatically as possible. Teeth in the negative control group (10 roots) were replanted almost immediately, while teeth in the positive control group (12 roots) were allowed to bench‐dry for 1 h prior to replantation, both without further treatment. Teeth in the experimental group (10 roots) were bench‐dried for 1 h, rinsed with saline, and then immersed in 1 ml of 50 mg ml^?1 minocycline hydrochloride for 5 min before replantation. No splinting was used. After 12 weeks, the animals were sacrificed and histological sections were prepared and evaluated according to a morphometric analysis modified from that described by Andreasen (1987) as complete healing, inflammatory resorption, and replacement resorption. Kruskal–Wallis test showed significant differences among the three groups in all the three healing categories. Further analysis with Mann–Whitney U‐test showed teeth in the negative control group to have significantly higher complete healing and significant lower unfavorable healing, comprising of replacement resorption and inflammatory root resorption than the positive control group and the minocycline group. Topical application of minocycline to the root surface appeared to result in slightly higher occurrence of complete healing (32.46%) compared to the delayed replantation group with no minocycline treatment (positive control) (16.58%), but the difference was not statistically significant (P = 0.09).     

Regeneration of calcitonin gene-related peptide immunoreactive nerves in replanted rat molars and their supporting tissues.

First maxillary right molars in 66 rats were elevated and replanted and the pulps allowed to regenerate for 1-90 days. The contralateral tooth served as control. Regeneration of nerves in the pulp and periodontium was studied by CGRP-immunohistochemistry and the avidin-biotin-peroxidase method. The pulp and periodontium of the controls were richly supplied with CGRP-labelled nerves. One day after replantation the pulp was completely devoid of CGRP-immunoreactive nerves. After 2 days, axon sprouts were present in the apical, regenerated pulp and in the periodontium. From 3-7 days CGRP-immunoreactive axons were regularly seen to have regenerated in front of the cellular inflammation in the pulp. After 10 days, the pulps were reinnervated up to the horns, although more sparsely than in the controls. From day 20-90 there was a marked divergence in pulpal healing: 17 pulps formed irregular postoperative dentine with a gradual increase in nerve density; 16 pulps remained sparsely innervated and were gradually replaced by bone. Root resorption was most extensive in the teeth with bone replacement of pulp. The soft tissue adjacent to extensive resorbing areas had many more CGRP-labelled axons than in the controls. The reinnervation of the regenerating pulp occurred at the same time as pulpal wound healing, but did not achieve the innervation density of the controls.     

Long-term effects of local pretreatment with alendronate on healing of replanted rat teeth

Background and Objective:  Our previous study showed that topical alendronate, an inhibitor of bone resorption, reduces root resorption and ankylosis for 21 d after replantation of rat teeth. The aim of the present study was to evaluate the long-term inhibitory effects of topical alendronate in the replanted teeth.
Material and Methods:  The rat maxillary first molars were extracted, placed in saline containing 1 m m alendronate (alendronate group) or saline (saline group) for 5 min and then replanted. The maxillae were dissected at 60 and 120 d. Microcomputed tomography horizontal sections at three root levels were analyzed for root and bone resorption, ankylosis and pulp mineralization.
Results:  In the alendronate group at 60 and 120 d, the frequencies of resorption of roots and bone were lower than those in the saline group. The p values show statistical significances of lower frequencies in the alendronate group than in the saline group by chi-square test (see Table 1 ). Ankylosis and pulp mineralization occurred in the alendronate and saline groups. Bone marrow spaces were narrowed in conjunction with bone tissue expansion around the replanted teeth in the alendronate group.  

  Table 1.  Percentage of sites with ankylosis, root resorption, bone resorption and pulp mineralization for the alendronate and saline groups at 60 and 120 d after tooth replantation     

7.

The effects of bisphosphonates on osteoblasts in vitro     

Naidu A  Dechow PC  Spears R  Wright JM  Kessler HP  Opperman LA 《Oral surgery, oral medicine, oral pathology, oral radiology, and endodontics》2008,106(1):5-13

     

8.

Effect of topical alendronate on root resorption of dried replanted dog teeth   总被引：5，自引：0，他引：5  

L. Levin  E. C. Bryson  D. Caplan  M. Trope 《Dental traumatology》2001,17(3):120-126

Abstract – Alendronate (ALN) is a third generation bisphosphonate with demonstrated osteoclast inhibitory activity that may slow down the resorptive process after severe traumatic injuries. Eighty-two premolar roots of five mongrel dogs were endodontically treated and restored, extracted and treated as follows: 70 roots were bench dried for either 40 or 60 min. Thirty-eight of these roots were then soaked for 5 min in a 1 mM solution of ALN in Hanks' Balanced Salt Solution (HBSS) and replanted. Thirty-two roots were soaked for 5 min in HBSS and replanted. In the remaining 12 roots which were not exposed to the bench drying procedure, a 0.5 mM deep lingual mid-root cemental defect was made. Six of these roots were soaked in a 1 mM solution of ALN in HBSS for 5 min and replanted. The other six roots were soaked for 5 min in HBSS and replanted. Historical negative and positive controls were used from similarly treated teeth in our previous studies. After 4 months the dogs were killed and the roots prepared for histological evaluation. Five-μm-thick cross-sections of the root and surrounding tissue taken every 70 μm were evaluated for healing according to the criteria of Andreasen. In the 12 roots with cemental defects, healing with cementum of the damaged root surface was evaluated. In addition, residual root mass was also measured to determine the extent of root structure loss for each soaking method. Cemental healing took place in all 12 artificially damaged roots, indicating that these soaking media did not inhibit cementogenesis. The alendronate-soaked roots had statistically significantly more healing than the roots soaked in HBSS without alendronate. This improvement in healing was seen in all dogs except one and in all teeth except the first premolar. Soaking in alendronate also resulted in significantly less loss in root mass due to resorption compared to those teeth soaked in HBSS without alendronate.     

9.

Orthodontic effects of bisphosphonates     

《Dental Abstracts》2010,55(5):237

     

10.

卡介苗多糖核酸局部治疗顽固性糜烂型OLP预试验结果分析   总被引：2，自引：1，他引：1  

郑华  申俊  徐小萌  周红梅  李秉琦 《临床口腔医学杂志》2005,21(7):438-439

目的:试用卡介苗多糖核酸(BCGPSN)局部治疗口腔扁平苔藓(OLP),拟通过较高的药物浓度来直接调节局部免疫,以期获得更好更持久的疗效。本文仅对预试验疗效趋势进行分析。方法:选择15例顽固性糜烂型OLP患者,用BCGPSN注射液行病损基底封闭,0.25～0.5ml/次,隔日1次,注射1～6次,观察其初步疗效及可能的不良反应。结果:经过1～6次治疗,有13例患者的局部病损愈合,在治疗完成后15d和30d,各有1例复发,仅有1例出现轻微不良反应。结论:用BCGPSN基底封闭治疗顽固性糜烂型OLP有一定疗效趋势和可行性,但尚需进行正规的临床试验来加以论证。     

11.

The effects of orthodontic force on replanted teeth: a radiographic survey     

J G Graupner 《American journal of orthodontics》1972,62(5):544-545

     

12.

The clinical effects of topical application of a topical anesthesia benzocaine (Hurricaine Gel and Liquid)     

T Shioiri  Y Arisawa  E Miyakawa  K Ishibashi  K Asada  T Hayakawa  Y Amemiya 《Nippon Shishubyo Gakkai kaishi》1983,25(4):882-887

     

13.

Possibility of application of calcium carbonate in pulpotomy of rat molars     

Pengjun Lu  Kiyoshi Arai  Noboru Kuboyama 《Pediatric Dental Journal》2010,20(1):45-56

We investigated restitution processes in mechanically exposed rat molar pulp during pulpotomy with calcium carbonate (CC). The results of the CC treatment were then compared with Calvital^®-containing calcium hydroxide (CH). Micro-computerized tomography (micro-CT), hematoxylin and eosin (H&E) staining and immunoreactivity for nestin, dentin matrix protein-1 (DMP-1) and osteopontin (OPN) were also analyzed. The increment of dentinlike calcified tissue in the pulp was observed by micro-CT. Both CC and CH groups induced pulpotomy resulted in changes associated with inflammation followed by progressive odontoblasts differentiation, dentin matrix secretion and dentin-like bridge formation. Necrotic layer formation and moderate to severe inflammation occurred during the early stages in the CH group. Necrotic layer formation was not observed in the CC group and only associated with mild to moderate inflammation. Immunoreactivity of nestin was observed earlier in the CC group than the CH group. In the CC group, immunoreactivity of DMP-1 was identified beneath the amputated site after 7 days, before increasing until 28 days, and immunoreactivity of OPN was observed in the dentin-like bridge at 28 days, which was also similar to the CH group. These findings suggested that the primary processes of reparative dentinogenesis after pulpotomy with CC may involve natural pulpal wound-healing mechanisms that are similar to the restitution processes observed during pulpotomy with CH. However, CC may prove to be less irritation and more calcified tissue formation than traditional CH-based materials when used as a pulpotomy agent.     

14.

同时应用雌激素和二膦酸盐对骨质疏松大鼠种植体骨结合的累加效应     

王买全  李运峰 《实用口腔医学杂志》2016,(5):640-644

目的:研究在切除卵巢的大鼠体内,局部应用二膦酸盐(BPs)和全身应用雌激素,对有羟基磷灰石(HA)涂层的种植体骨结合的影响.方法:20只雌性大鼠接受双侧卵巢切除术12周后,在每只大鼠的双侧胫骨近端各植入1颗含有HA涂层的种植体,植入左侧胫骨的种植体携带BPs,植入右侧胫骨的种植体不含BPs.大鼠平均分成2组,其中一组接受17β-雌二醇(E)皮下注射,另一组注射安慰剂.4组大鼠分别为:对照组、雌激素组(E组)、二膦酸盐组(BPs组)、雌激素+二膦酸盐组(E+ BPs组).种植手术12周后,手术取出带有种植体的胫骨,用显微CT和推出试验来评估骨结合效果.结果:E+BPs组与空白对照组相比,种植体周围的相对骨体积增加了2.3倍,骨结合率增加了1.9倍,最大推出力增加了3.3倍.E组和BPs组种植体的固位力也增加了,但效果弱于E+BPs组.结论:全身应用雌激素和局部应用BPs对涂有HA涂层的种植体的骨结合具有累加效果.     

15.

Effect of topical application of citric acid in the treatment of furcation involvement in human lower molars     

Ricardo J.  Parori Maria E.  Esper 《Journal of clinical periodontology》1984,11(10):644-651

Abstract Improvement of new attachment procedures using topically applied citric acid was tested in human beings. Furcation involvement and the adjacent proximal area were surgically exposed. Saline was used as placebo drug. Baseline pocket depth and attachment levels were scored prior to surgery and bone level recorded at the time of surgery. After 1, 3 and 6 months, the clinical parameters were re-scored and at that time, a re-entry operation allowed a new measurement of the bone level. In the post-operative experimental periods, there was an improvement of all clinical parameters in both the control and experimental groups. Pocket depth reduction was consistent; the gain in the attachment level compared to the baseline examination in the experimental group and the improvement in the bone height level were statistically significant within the 6-month post-operative interval; however, in both the furcation and proximal areas, no statistically significant differences could be detected on comparing experimental and control groups.     

16.

The topical application of fluoride.     

B Jenkison 《New Zealand School Dental Service gazette》1976,37(1):6-7

     

17.

Fluoride uptake and caries rate in hamster molars after topical fluoride application followed by acidulation.     

A Nathaniel  I Gedalia  J Anaise  L Daphni 《Journal of dental research》1978,57(3):534-537

Daily topical application of 2% NaF on hamster molars for 4 days in vivo, followed by acidulation (grapefruit beverage, pH 3.3) resulted in a lower caries rate than NaF followed by water application. Fluoride uptake was somewhat higher, but not significantly so in the acidulated group.     

18.

The effects of orthodontic forces on the mechanical properties of the periodontal ligament in the rat maxillary molars     

H R Ki 《American journal of orthodontics and dentofacial orthopedics》1990,98(6):533-543

Previous studies have shown that the mechanical strength of the periodontal ligament decreased markedly after the application of an orthodontic force to the rat mandibular first molar. However, the effects of orthodontic forces on the mechanical properties of the periodontal ligament of the other teeth in the same dental arch have not been examined. Furthermore, a detailed analysis of the mechanical parameters has not been made. The purpose of the present study was to analyze mechanical parameters such as maximum shear load, maximum deformation, elastic stiffness, and failure energy in shear, estimated from the load-deformation curves obtained by extracting the rat maxillary molars from their sockets after application of an orthodontic force for 5 days. It was found that the mechanical properties of the periodontal ligament of the rat maxillary molars varied considerably among control teeth in the same dental arch. Decreases in the mechanical properties of the periodontal ligament of the experimental teeth were greatest in the first, less in the second, and least in the third molars. Significant correlations were found between the maximum load and the failure energy and between the maximum deformation and the failure energy in all teeth. It was concluded that orthodontic force affected not only the mechanical properties of the periodontal ligament of the teeth to which the force had been applied but also the mechanical properties of distant teeth.     

19.

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

Josuke Shinohara  Tatsuya Shibata  Akemi Shimada  Koichiro Komatsu 《Dental traumatology》2004,20(4):212-221

Abstract –  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 µm 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.     

20.

The effect of topical fluoride application on porcelain restorations     

Venita J. Sposetti D.M.D.  Chiayi Shen Ph.D.  Alan C. Levin B.D.S.   《The Journal of prosthetic dentistry》1986,55(6):677-682

     

Effect of topical alendronate on root resorption of dried replanted dog teeth

Abstract – Alendronate (ALN) is a third generation bisphosphonate with demonstrated osteoclast inhibitory activity that may slow down the resorptive process after severe traumatic injuries. Eighty-two premolar roots of five mongrel dogs were endodontically treated and restored, extracted and treated as follows: 70 roots were bench dried for either 40 or 60 min. Thirty-eight of these roots were then soaked for 5 min in a 1 mM solution of ALN in Hanks' Balanced Salt Solution (HBSS) and replanted. Thirty-two roots were soaked for 5 min in HBSS and replanted. In the remaining 12 roots which were not exposed to the bench drying procedure, a 0.5 mM deep lingual mid-root cemental defect was made. Six of these roots were soaked in a 1 mM solution of ALN in HBSS for 5 min and replanted. The other six roots were soaked for 5 min in HBSS and replanted. Historical negative and positive controls were used from similarly treated teeth in our previous studies. After 4 months the dogs were killed and the roots prepared for histological evaluation. Five-μm-thick cross-sections of the root and surrounding tissue taken every 70 μm were evaluated for healing according to the criteria of Andreasen. In the 12 roots with cemental defects, healing with cementum of the damaged root surface was evaluated. In addition, residual root mass was also measured to determine the extent of root structure loss for each soaking method. Cemental healing took place in all 12 artificially damaged roots, indicating that these soaking media did not inhibit cementogenesis. The alendronate-soaked roots had statistically significantly more healing than the roots soaked in HBSS without alendronate. This improvement in healing was seen in all dogs except one and in all teeth except the first premolar. Soaking in alendronate also resulted in significantly less loss in root mass due to resorption compared to those teeth soaked in HBSS without alendronate.     

卡介苗多糖核酸局部治疗顽固性糜烂型OLP预试验结果分析

目的:试用卡介苗多糖核酸(BCGPSN)局部治疗口腔扁平苔藓(OLP),拟通过较高的药物浓度来直接调节局部免疫,以期获得更好更持久的疗效。本文仅对预试验疗效趋势进行分析。方法:选择15例顽固性糜烂型OLP患者,用BCGPSN注射液行病损基底封闭,0.25～0.5ml/次,隔日1次,注射1～6次,观察其初步疗效及可能的不良反应。结果:经过1～6次治疗,有13例患者的局部病损愈合,在治疗完成后15d和30d,各有1例复发,仅有1例出现轻微不良反应。结论:用BCGPSN基底封闭治疗顽固性糜烂型OLP有一定疗效趋势和可行性,但尚需进行正规的临床试验来加以论证。     

Possibility of application of calcium carbonate in pulpotomy of rat molars

We investigated restitution processes in mechanically exposed rat molar pulp during pulpotomy with calcium carbonate (CC). The results of the CC treatment were then compared with Calvital^®-containing calcium hydroxide (CH). Micro-computerized tomography (micro-CT), hematoxylin and eosin (H&E) staining and immunoreactivity for nestin, dentin matrix protein-1 (DMP-1) and osteopontin (OPN) were also analyzed. The increment of dentinlike calcified tissue in the pulp was observed by micro-CT. Both CC and CH groups induced pulpotomy resulted in changes associated with inflammation followed by progressive odontoblasts differentiation, dentin matrix secretion and dentin-like bridge formation. Necrotic layer formation and moderate to severe inflammation occurred during the early stages in the CH group. Necrotic layer formation was not observed in the CC group and only associated with mild to moderate inflammation. Immunoreactivity of nestin was observed earlier in the CC group than the CH group. In the CC group, immunoreactivity of DMP-1 was identified beneath the amputated site after 7 days, before increasing until 28 days, and immunoreactivity of OPN was observed in the dentin-like bridge at 28 days, which was also similar to the CH group. These findings suggested that the primary processes of reparative dentinogenesis after pulpotomy with CC may involve natural pulpal wound-healing mechanisms that are similar to the restitution processes observed during pulpotomy with CH. However, CC may prove to be less irritation and more calcified tissue formation than traditional CH-based materials when used as a pulpotomy agent.     

同时应用雌激素和二膦酸盐对骨质疏松大鼠种植体骨结合的累加效应

目的:研究在切除卵巢的大鼠体内,局部应用二膦酸盐(BPs)和全身应用雌激素,对有羟基磷灰石(HA)涂层的种植体骨结合的影响.方法:20只雌性大鼠接受双侧卵巢切除术12周后,在每只大鼠的双侧胫骨近端各植入1颗含有HA涂层的种植体,植入左侧胫骨的种植体携带BPs,植入右侧胫骨的种植体不含BPs.大鼠平均分成2组,其中一组接受17β-雌二醇(E)皮下注射,另一组注射安慰剂.4组大鼠分别为:对照组、雌激素组(E组)、二膦酸盐组(BPs组)、雌激素+二膦酸盐组(E+ BPs组).种植手术12周后,手术取出带有种植体的胫骨,用显微CT和推出试验来评估骨结合效果.结果:E+BPs组与空白对照组相比,种植体周围的相对骨体积增加了2.3倍,骨结合率增加了1.9倍,最大推出力增加了3.3倍.E组和BPs组种植体的固位力也增加了,但效果弱于E+BPs组.结论:全身应用雌激素和局部应用BPs对涂有HA涂层的种植体的骨结合具有累加效果.     

Effect of topical application of citric acid in the treatment of furcation involvement in human lower molars

Abstract Improvement of new attachment procedures using topically applied citric acid was tested in human beings. Furcation involvement and the adjacent proximal area were surgically exposed. Saline was used as placebo drug. Baseline pocket depth and attachment levels were scored prior to surgery and bone level recorded at the time of surgery. After 1, 3 and 6 months, the clinical parameters were re-scored and at that time, a re-entry operation allowed a new measurement of the bone level. In the post-operative experimental periods, there was an improvement of all clinical parameters in both the control and experimental groups. Pocket depth reduction was consistent; the gain in the attachment level compared to the baseline examination in the experimental group and the improvement in the bone height level were statistically significant within the 6-month post-operative interval; however, in both the furcation and proximal areas, no statistically significant differences could be detected on comparing experimental and control groups.     

Fluoride uptake and caries rate in hamster molars after topical fluoride application followed by acidulation.

Daily topical application of 2% NaF on hamster molars for 4 days in vivo, followed by acidulation (grapefruit beverage, pH 3.3) resulted in a lower caries rate than NaF followed by water application. Fluoride uptake was somewhat higher, but not significantly so in the acidulated group.     

The effects of orthodontic forces on the mechanical properties of the periodontal ligament in the rat maxillary molars

Previous studies have shown that the mechanical strength of the periodontal ligament decreased markedly after the application of an orthodontic force to the rat mandibular first molar. However, the effects of orthodontic forces on the mechanical properties of the periodontal ligament of the other teeth in the same dental arch have not been examined. Furthermore, a detailed analysis of the mechanical parameters has not been made. The purpose of the present study was to analyze mechanical parameters such as maximum shear load, maximum deformation, elastic stiffness, and failure energy in shear, estimated from the load-deformation curves obtained by extracting the rat maxillary molars from their sockets after application of an orthodontic force for 5 days. It was found that the mechanical properties of the periodontal ligament of the rat maxillary molars varied considerably among control teeth in the same dental arch. Decreases in the mechanical properties of the periodontal ligament of the experimental teeth were greatest in the first, less in the second, and least in the third molars. Significant correlations were found between the maximum load and the failure energy and between the maximum deformation and the failure energy in all teeth. It was concluded that orthodontic force affected not only the mechanical properties of the periodontal ligament of the teeth to which the force had been applied but also the mechanical properties of distant teeth.     

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

Abstract –  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 µm 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.