Effects of tooth function on adjacent alveolar bone and Sharpey's fibers of the rat periodontium

There is little information about the effects of short-term non-hypo-, and hyperfunction of teeth on the 1) mineralization patterns of intrinsic and extrinsic (Sharpey's) fibers and 2) mean number and diameter of Sharpey's fibers of adjacent alveolar bone. The mineral density of intrinsic and Sharpey's fibers and the size and number of Sharpey's fibers could indicate the relative strength of the attachment of a tooth to bone in various functional situations. In the present study, non- and hypofunctional situations were created by selective extraction of right molar teeth of the rat; the contralateral teeth were placed in hyperfunction by the surgery. In non- and hypofunctionals, intrinsic and Sharpey's fibers of the crestal third of the alveolus were less densely mineralized than in hyperfunctionals or untreated controls. Mean Sharpey's fiber diameters were significantly greater and their mean number/unit area significantly less in non- than in hypo- or hyperfunctionals or untreated controls (P less than 0.001). Mean Sharpey's fiber diameters in hyperfunctionals were significantly less than in untreated controls (P less than 0.05). Hypofunction ameliorated the effects of nonfunction on mean diameter and number of Sharpey's fibers, but had little effect on the density of mineralization of either the intrinsic or Sharpey's fibers of the alveolus, suggesting that their mineralization may be controlled by factors other than occlusal forces from the adjacent teeth. Thus changes in the stress/strain environment within the periodontium, coincident to altered occlusal function of the adjacent teeth, rapidly affects the morphology of intrinsic and Sharpey's fibers of alveolar bone and ensures that adequate tooth support is maintained in the new functional situation.     

Effects of hypofunction on the distribution of 3H-proline in the transseptal fibers of the periodontium of the rat

There is little information concerning the effect of altered occlusal forces on the turnover of collagenous proteins of transseptal fibers of the periodontium. In the present study, hypofunction was induced in rats by extraction of the maxillary teeth, allowing the mandibular teeth to supererupt (hypofunctional side, herein). The contralateral side served as an internal control, although it was likely experiencing occlusal hyperfunction (hyperfunctional side, herein). Untreated animals were also studied (external controls, herein). Animals were injected with 3H-proline and silver grains were counted on radioautographic preparations. The study demonstrated significant differences in the synthesis and degradation of collagenous proteins coincident to altered occlusal function; 3H-proline was most heavily incorporated into the transseptal fibers of hyperfunctional and least rapidly into the external control tissues (P less than .001). Significant differences in grain counts were evident during the first 3 weeks after injections. Collagenous proteins were degraded most rapidly in transseptal fibers of the hyperfunctional and least rapidly in hypofunctional tissues (P less than .001). The study also demonstrated regional variability in the turnover of labeled collagenous proteins, that is, proteins were synthesized and degraded most rapidly in the middle third and least rapidly in the mesial third of the ligament (P less than .001). "Whole" counts (mean of counts over middle, mesial, and distal thirds) were not similar to those of any specific region and could provide erroneous information concerning remodeling of collagenous proteins of transseptal fibers. Transseptal fibers, labeled by the 3H-proline pulse, migrated occlusally with the teeth; new transseptal fibers and bone were formed at the crest of the interdental septum.     

牵张成骨区成骨方式的有限元分析

背景：有研究报道牵张间隙内存在软骨内成骨及膜内成骨两种成骨方式,也有研究认为在只有轴向牵张力作用而无其他方向外力干扰情况下,牵张新骨仅以膜内成骨一种方式成骨。 目的：研究不同咬合状态下牵张区新生组织所处的力学环境,并验证该环境是否具有诱导和促进成软骨的能力,解释成骨方式不一致的矛盾。 方法：建立下颌骨双侧牵张成骨模型,设定牵开距离为1 cm,固定后4周,在骨面咀嚼肌附着部位施加肌肉力来模拟实际咀嚼运动。选择双侧后牙咬合、左侧磨牙咬合及前牙咬合状态进行模拟分析,考察压应力/张应力、剪应力、范式应力变化。 结果与结论：①双侧后牙咬合状态：范式应力及剪应力自舌侧向颊侧力值有所增加。自远中舌侧下缘至远中颊侧上缘,压应力逐渐转为张应力。②前牙咬合状态：范式应力及剪应力自舌侧面逐渐向颊侧减小。压应力/张应力在舌侧面压应力较大,向颊侧逐渐减小,过渡为张应力。③左侧磨牙咬合状态：左侧牵张区各应力和双侧后牙咬合状态下的各应力分布特点很相近,但最大值均要比双侧后牙咬合状态下的相应力值小。右侧牵张区范式应力在远中面的上缘和下缘出现应力最大值,近中颊侧下缘出现应力最小值,之间为过渡区。剪应力与范式应力特点相似。压应力/张应力则主要出现在近中下缘。说明在固定早期若牵张器不够稳定,咀嚼运动可以在新生组织内形成一个促使软骨形成的力学环境,为成骨方式不一致的矛盾指出了明确的答案。     

Effect of occlusal functional forces on incisor socket morphology and location in the rat mandible

The effect of functional occlusal stress on dimensional alterations of the rat incisor socket and mandible were studied from roentgenograms. In 12 rats, the lower left incisor was shortened twice weekly, whereas the lower right incisor was allowed to remain in contact with both upper incisors. Thus, the right incisors were subjected to hyperfunction, and the left ones, to hypofunction. The lower incisors of 16 rats with normal occlusal contact served as control. Following an experimental period of 3 months, the animals were killed and standardized radiographs were taken of the cleaned mandibles. Socket and mandibular dimensions were measured on magnified tracings of the roentgenograms. Socket area, its posterior length, posterior mandibular length, and gonial angle changed in the same direction under both hyper- and hypofunction. The anterior socket was relocated in opposite directions: under hyperfunction, it assumed a more inferior position, whereas in hypofunction, it moved superiorly. The angulation of the socket became significantly more acute under hyperfunction, whereas in hypofunction, this parameter remained unchanged. It is concluded that altered functional demands affect the morphology of the incisor socket and its location within the mandibular borders.     

Elastic system fibers in rat incisor periodontal ligament - immunohistochemical study using sections of fresh-frozen un-demineralized tissues

The aim of this study was to examine the localization and distribution of the components of elastic system fibers in the periodontal ligament of continuously erupting rat incisors in an effort to understand the mechanism of the eruption of the tooth. Sections of fresh-frozen, un-demineralized incisors of the rat mandible were prepared for immunohistochemical localization of elastin, fibrillin-2 and microfibril-associated glycoprotein-1 (MAGP-1). The structure of the periodontal ligament was well preserved in sections of fresh-frozen tissues. At the basal region of the ligament, intense immunolabelling for fibrillin-2 and MAGP-1 was observed as dot-like structures (transversely sectioned fibers) mainly on the tooth side of the ligament close to the cementum. These dot-like structures gradually increased in number towards the incisal area and were distributed throughout the tooth side of the ligament. This pattern of distribution was the same as that of reported oxytalan fibers. Elastin-immunopositive fibers were also detected in the ligament, although the labelling was limited and distribution was sparse. In conclusion, both fibrillin-2 and MAGP-1 immunopositive fibers may serve as a scaffold for deposition of tropoelastin during elastogenesis in the periodontal ligament. They may also provide guidance for the migration of fibroblasts to the occlusive side, which generates contractile forces for the movement of the tooth for continuous eruption of incisors.     

Effects of orthodontic forces on the morphology and diameter of Sharpey fibers of the alveolar bone of the rat

There is little information available concerning the effects of functional and therapeutic forces on Sharpey fibers and adjacent bone matrix. In the present study, springs were placed between the left first and second maxillary molar teeth of rats and retained for 1, 2, 3, 4, or 5 days. The right side served as a control. Tissues from sham-operated, untreated animals were also studied. Maxillae were removed, fractured, rendered anorganic with sodium hypochlorite, and then examined by scanning electron microscopy (SEM). Some tissues were demineralized and examined by high-voltage electron microscopy (HVEM). Sharpey fibers were studied at the alveolar wall and at the midline of the interdental septum (intra-septal Sharpey fibers). In 5-day experimental tissues, SEM showed intra-septal Sharpey fibers had either a reduced number of, or lacked, unmineralized cores. Unit collagen fibrils in 5-day tissues viewed by HVEM were densely packed into Sharpey fibers which had no afibrillar areas. Sharpey fibers at the alveolar wall demonstrated no observable changes in morphology or in pattern of mineralization. After 5 days of spring placement, the mean diameters of intra-septal fibers were significantly less than those at the alveolar wall (p less than 0.001). The disparity in Sharpey fiber diameters of treated and untreated control animals suggests that untreated controls are essential to the design of studies of rodent tooth movement. This study suggests that orthodontic tooth movement produces changes in the morphology and mineralization patterns of Sharpey fibers which might affect the mechanical strength of the periodontium.     

Relationships between tooth eruption, occlusion and alveolar bone resorption: histochemical and cytological studies of bone remodeling on rat incisor alveolar bone facing the enamel after root resection

The labial side of rat incisor alveolar bone facing the enamel is continuously resorbed as the result of compressive force produced by the occlusion and eruption of incisors. In order to clarify the relationship between this mechanical compressive force and the bone cells involved in bone remodeling, we examined morphological changes occurring in the alveolar bone once the compressive force was eliminated by the removal of the proliferative odontogenic base (root resection according to Berkovitz and Thomas, 1969). After root resection, the incisor migrated halfway along the socket. On the crestal part where incisor still existed, active osteoclasts were prominent on the bone surface, and flattened mononuclear cells lay close upon active osteoclasts. Sinusoidal blood vessels or capillaries were observed at short distances from the bone surface. On the basal part where socket was vacant, osteoblasts lined up on the newly formed bone, and the osteogenic cell layer lay on the osteoblasts. Between the two parts, which correspond to the reversal phase proposed by Baron (1977), osteoblastic cells with developed cell organelles increased in number and the distance between blood vessels and bone surface increased. Osteoclasts reduced their activities, and osteoblastic cells often wedged themselves between the osteoclasts and bone surface. These findings indicate that the elimination of compressive force mediated by incisors leads to the activation of osteoblastic cells and inactivation of osteoclasts, which results in a conversion from bone resorption to bone formation. Thus, osteoblastic cells may play an important role in controlling osteoclastic activity in conversion from bone resorption to bone formation, partly by a direct effect and partly by controlling the access of blood vessels to the bone surface.     

A method for sampling the stages of amelogenesis on mandibular rat incisors using the molars as a reference for dissection

A method for locating specific stages of amelogenesis on continuously erupting incisors was devised for rats weighing 101 +/- 5 g (n = 32). The technique is based on reflecting reference lines from the mandibular molars as perpendiculars to the labial surface of mandibular incisors. From these reference lines additional measurements are then made along the midline of the labial surface of the incisor in an apical or incisal direction to find the site desired for sampling. Histological studies on 24 decalcified incisors split into segments by using such reference lines and reconstructed by morphometry indicated that a reference line reflected from the contact point between the 2nd and 3rd molars crossed the enamel organ and adjacent enamel at 3,181 +/- 329 microns incisal to the start of the secretory zone of amelogenesis. A reference line from the 2nd and 1st molars crossed the enamel organ and enamel at 1,238 +/- 424 microns incisal to the start of the maturation zone of amelogenesis, while a reference line from the mesial side of the 1st molar crossed the enamel organ and enamel almost exactly where the enamel becomes completely soluble following prolonged decalcification in EDTA. Although reference lines were reproducible within a group of male rats having similar body weights, the linear distance between the apical end of the incisor and the point at which they crossed the tooth increased at a rate of 1 mm per 159 g for rats between 50 and 300 g body weight. This suggests that molars do not maintain a fixed relationship to incisors over time, and extreme care must be taken to standardize an experiment to a specific body weight when using this method.     

A light and electron microscopic study on pulpal nerve fibers in the lower incisor of the mouse.

Light and electron microscopic studies were made on pulpal nerve fibers in mouse lower incisors, typical continuously growing teeth. Serial sections, from the apex of the odontogenic sheath to the incisal edge of the apical foramen, were examined by light microscopy to identify myelinated fibers passing through the apical foramen. The fine structure of the pulpal nerves was examined by electron microscopy at three sites: 1) the level at the incisal edge of the apical foramen; 2) a level 5 mm incisal from the apex of the odontogenic sheath; and 3) the level where the incisor comes out of the alveolar bone. No myelinated fibers were found passing through the apical foramen; they were also lacking at the three levels of the pulp. At level 2, unmyelinated axons were seen in close contact with smooth muscle fibers of arterioles. At level 3, nerve fibers were difficult to distinguish from processes of fibroblasts and odontoblasts. Degenerating axons were present in Schwann cells, and fine unmyelinated axons running through the odontoblast cell layer were seen. Various types of unmyelinated axons were observed in the apical region (level 1). These axons were classified into 6 types on the basis of their fine structures: Type I, bundles of unmyelinated axons completely or partly ensheathed by Schwann cell cytoplasm (mature type); Type II, bundles of unmyelinated axons in a space formed by a Schwann cell membrane (regenerating type); Type III, bundles of unmyelinated axons ensheathed not by a Schwann cell, but merely by a basal lamina (regenerating type); Type IV, single axons in direct contact with the basal lamina (regenerating or terminal type); Type V, naked, electron-dense axons with many vesicles and mitochondria (growth cone-like type); and Type VI, electron opaque axons, due to loss of axonal organellae (degenerating type). The significance of these structures is discussed in relation to the continuous growth of the rodent incisor.     

有限元应力分析不同桩核修复上中切牙牙冠的斜型缺损

背景：采用纤维桩树脂核修复上中切牙近中或远中缺损可达到与牙本质接近的弹性模量,并可实现良好的美学效果,但当牙体组织大量缺损无法制备出完整的牙本质肩领时,使用纤维桩树脂核修复后桩核脱落、折断的可能性增大。 目的：通过三维有限元法对比分析分别采用镍铬铸造桩核、金钯铸造桩核及纤维桩树脂核修复牙冠近远中斜行缺损后的应力分布状态。 方法：挑选一颗牙体完好无损及解剖值符合中国牙体解剖平均数据的成人离体上中切牙,使用牙科专用锥形束CT扫描后,应用ABAQUS软件根据牙冠和牙本质肩领近远中斜行缺损量逆向建立牙冠斜型缺损类型的牙体-纤维桩核(镍铬桩核或金钯桩核)-全瓷冠的三维有限元模型,该模型牙冠近远中斜行缺损,牙本质肩领部分缺失;分别采用镍铬铸造桩核、金钯铸造桩核及纤维桩树脂核修复后,使用ABAQUS进行三维有限元分析,对比加载后的应力分布状态。 结果与结论：上颌中切牙牙冠近远中斜形缺损,使用纤维桩树脂核修复时粘接剂层面和桩层面上的应力峰值明显低于使用镍铬或金钯桩核修复时的情况,说明牙本质肩领部分缺失的牙冠近远中斜行缺损使用金钯桩核,镍铬桩核牙根折断的可能性增大;3种桩核修复模型后牙本质层面的应力峰值基本一致。结果表明牙本质肩领部分缺失的牙冠近远中斜行缺损使用纤维桩树脂核修复效果最佳。     

贵州省氟斑牙前牙色度值的测量分析

背景：在口腔烤瓷修复中应用维他经典比色板和维他三维能手比色板比色时不能完全覆盖所有天然牙颜色构成的空间范围,对氟斑牙色度的覆盖范围更少。 目的：分析贵州省氟斑牙色度值的分布规律和特征及与正常牙色度值分布的差别。 方法：从贵州省氟中毒人群中随机抽取氟斑牙患者317例作为实验组,共计634颗上颌中切牙;随机抽取204名健康人群的正常天然牙作为对照组,共记408颗上颌中切牙,采用国际照明委员会(CIE)推荐的CIE_1976(L*a*b*)表色系统,用Shade Eye-NCC电脑比色仪测定其色度学各要素(L*、a*、b*)值。 结果与结论：实验组氟斑牙上颌中切牙色度值范围较对照组大,其中氟斑牙明度均值L*显著小于对照组(P < 0.05),a*、b*均值明显高于对照组(P < 0.05)。实验组氟斑牙上颌中切牙9个区明度L*值在颈部Ⅱ区最高,切部Ⅸ区最低,从颈部、中部到切部逐渐降低;唇面近中1/3的a*、b*值均大于远中1/3,且同一受试者左右两侧中切牙的颜色参数差异无显著性意义(P < 0.05)。表明与与天然牙相比,氟斑牙色度值分布较为松散,色度学各要素分布范围广,颜色较正常牙暗且偏红偏黄。     

A unique localization of mechanoreceptors in the periodontal tissue of guinea pig teeth

This study describes the unique distribution of Ruffini endings (RE) in the periodontal tissues of the guinea pig teeth with special references to their presence in the enamel-related aspects of the continuously growing incisors and molars. In guinea pig incisors, immunohistochemistry for PGP 9.5 and glia specific S-100 protein revealed a condensed distribution of well-developed RE in the bone-related part of the lingual periodontal ligament as has been reported in many other rodents. In most cases, some RE-like nerve elements characterized by dendritic ramification and rounded terminal Schwann cells were found to be located in the labial, enamel-related regions, where no periodontal ligament-like fiber arrangement was established. In the molar periodontal ligament, well-developed RE-like nerve elements were also distributed in the enamel-related part, but in intimate relation to thick periodontal fiber bundles inserted in the cementum pearls grown on the enamel surface. In some cases, few RE were located in the apical region of the alveolar socket, where no periodontal fiber bundles could be identified. Our data provide the first morphological evidence of the presence of RE-like nerve elements in the enamel-related, fibrous connective tissue of continuously erupting rodent incisors. These data indicate that RE in guinea pig periodontal tissues have variable spatial correlation to the surrounding fibers, implicating their diverse mechanoreceptive properties depending on the anatomical location.     

The spatial distribution of focal stacks within the inner enamel layer of mandibular mouse incisors

Focal stacks are an alternative spatial arrangement of enamel rods within the inner enamel of mandibular mouse incisors where short rows comprised of 2–45 enamel rods are nestled at the side of much longer rows, both sharing the same rod tilt directed mesially or laterally. The significance of focal stacks to enamel function is unknown, but their high frequency in transverse sections (30% of all rows) suggests that they serve some purpose beyond representing an oddity of enamel development. In this study, we characterized the spatial distribution of focal stacks in random transverse sections relative to different regions of the inner enamel and to different locations across enamel thickness. The curving dentinoenamel junction (DEJ) in transverse sections complicated spatial distribution analyses, and a technique was developed to “unbend” the curving DEJ allowing for more linear quantitative analyses to be carried out. The data indicated that on average there were 36 ± 7 focal stacks located variably within the inner enamel in any given transverse section. Consistent with area distributions, focal stacks were four times more frequent in the lateral region (53%) and twice as frequent in the mesial region (33%) compared to the central region (14%). Focal stacks were equally split by tilt (52% mesial vs. 48% lateral, not significant), but those having a mesial tilt were more frequently encountered in the lateral and central regions (2:1) and those having a lateral tilt were more numerous in the mesial region (1:3). Focal stacks having a mesial tilt were longer on average compared to those having a lateral tilt (7.5 ± 5.6 vs. 5.9 ± 4.0 rods per row, p < 0.01). There was no relationship between the length of a focal stack and its location within the inner enamel. All results were consistent with the notion that focal stacks travel from the DEJ to the outer enamel the same as the longer and decussating companion rows to which they are paired. The spatial distribution of focal stacks within the inner enamel was not spatially random but best fit a null model based on a heterogenous Poisson point process dependent on regional location within the transverse plane of the enamel layer.     

Displacements of precious and nonprecious dental bridges utilizing endosseous implants as distal abutments

An investigation was conducted to establish qualitative trends regarding to relative displacements exhibited by the distal and mesial abutments in a five-unit fixed dental bridge as a function of bridge material and implant design utilized in the distal abutment site. Both Au and Ni-based bridge systems utilizing double, natural-tooth mesial abutments and three types of distal abutments (natural second molar, blade dental implant, and hollow-basket implant) were tested on a dried human mandible and subjected to a controlled force applied distally. Dial gauges were positioned around each abutment site bilaterally to provide displacement data in the x(mesial/distal), y(buccal/lingual, and z(occlusal/gingival) directions. The results indicate some significant differences exist in the displacement profiles exhibited by the bridge systems as a function of both bridge material and abutment type.     

Polarized light microscopic analyses of collagen fibers in the rat incisor periodontal ligament in relation to areas,regions, and ages

We prepared decalcified sagittal sections (20 microm thick) from the incisal, middle, and basal regions of the mandibular incisor of male Wistar rats aged 2, 6, 12, and 24 months, and examined the sections using polarized light microscopy. Most of the birefringent fibers appeared to run obliquely across the periodontal ligament. Birefringent fibers running parallel to the long axis of the incisor were also found in the intermediate area of the ligament. Similar fiber architecture was observed in all four age groups. Quantitative analysis showed that the retardation values of collagen were higher in the bone- and tooth-related areas and lower in the intermediate area of the ligament. The values for the bone- and tooth-related areas increased from the basal toward the incisal regions in all four age groups. Age-related changes in the retardation values were found only in the incisal region of the incisor. In the incisal region, the values for the bone- and tooth-related areas increased markedly from 2-24 months of age, whereas those for the intermediate area increased slightly but significantly with age. Our findings indicate that the degrees of molecular organization and alignment of collagen fibers in the bone- and tooth-related areas of the ligament are higher than those in the intermediate area and increase near the incisal region and with age. It is also suggested that the collagen fibers in the intermediate area remain immature along the long axis of the incisor throughout the life span of the animal.     

Characteristics of the transverse 2D uniserial arrangement of rows of decussating enamel rods in the inner enamel layer of mouse mandibular incisors

The 2D arrangement of rows of enamel rods with alternating (decussating) tilt angles across the thickness of the inner layer in rat and mouse incisor enamel is well known and assumed to occur in a uniform and repetitive pattern. Some irregularities in the arrangement of rows have been reported, but no detailed investigation of row structure across the entire inner enamel layer currently exists. This investigation was undertaken to determine if the global row pattern in mouse mandibular incisor enamel is predominately regular in nature with only occasional anomalies or if rows of enamel rods have more spatial complexity than previously suspected. The data from this investigation indicate that rows of enamel rods are highly variable in length and have complex transverse arrangements across the width and thickness of the inner enamel layer. The majority of rows are short or medium in length, with 87% having < 100 rods per row. The remaining 13% are long rows (with 100–233 rods per row) that contain 46% of all enamel rods seen in transverse sections. Variable numbers of rows were associated with the lateral, central and mesial regions of the enamel layer. Each region contained different ratios of short, medium and long rows. A variety of relationships was found along the transverse length of rows in each region, including uniform associations of alternating rod tilts between neighboring rows, and instances where two rows having the same rod tilt were paired for variable distances then moved apart to accommodate rows of opposite tilt. Sometimes a row appeared to branch into two rows with the same tilt, or conversely where two rows merged into one row depending upon the mesial‐to‐lateral direction in which the row was viewed. Some rows showed both pairing and branching/merging along their length. These tended to be among the longest rows identified, and they often crossed the central region with extensions into the lateral and mesial regions. The most frequent row arrangement was a row of petite length nestled at the side of another row having the same rod tilt (30% of all rows). These were termed ‘focal stacks’ and may relate to the evolution of uniserial rat and mouse incisor enamel from a multilayered ancestor. The mesial and lateral endpoints of rows also showed complex arrangements with the dentinoenamel junction (DEJ), the inner enamel layer itself, and the boundary area to the outer enamel layer. It was concluded that the diversity in row lengths and various spatial arrangements both within and between rows across the transverse plane provides a method to interlock the enamel layer across each region and keep the enamel layer compact relative to the curving DEJ surface. The uniserial pattern for rows in mouse mandibular incisors is not uniform, but diverse and very complex.     

Polarized light microscopic analyses of collagen fibers in the rat incisor periodontal ligament in relation to areas,regions, and ages

We prepared decalcified sagittal sections (20 μm thick) from the incisal, middle, and basal regions of the mandibular incisor of male Wistar rats aged 2, 6, 12, and 24 months, and examined the sections using polarized light microscopy. Most of the birefringent fibers appeared to run obliquely across the periodontal ligament. Birefringent fibers running parallel to the long axis of the incisor were also found in the intermediate area of the ligament. Similar fiber architecture was observed in all four age groups. Quantitative analysis showed that the retardation values of collagen were higher in the bone‐ and tooth‐related areas and lower in the intermediate area of the ligament. The values for the bone‐ and tooth‐related areas increased from the basal toward the incisal regions in all four age groups. Age‐related changes in the retardation values were found only in the incisal region of the incisor. In the incisal region, the values for the bone‐ and tooth‐related areas increased markedly from 2–24 months of age, whereas those for the intermediate area increased slightly but significantly with age. Our findings indicate that the degrees of molecular organization and alignment of collagen fibers in the bone‐ and tooth‐related areas of the ligament are higher than those in the intermediate area and increase near the incisal region and with age. It is also suggested that the collagen fibers in the intermediate area remain immature along the long axis of the incisor throughout the life span of the animal. Anat Rec 268:381–387, 2002. © 2002 Wiley‐Liss, Inc.     

Calcitonin gene-related peptide-immunoreactive nerves and neuroendocrine cells after lung transplantation in the rat.

Bronchial innervation is interrupted at lung transplantation. Nerve fibers with cell bodies above the section, such as sensory C fibers, should degenerate. Using histofluorescence, we evaluated calcitonin gene-related peptide (CGRP) immunoreactivity in syngeneic Lewis rats 1 and 5 mo after unilateral lung transplantation and in controls. CGRP-immunoreactive (IR) neuroendocrine cells were located within the epithelium of large and small bronchi. At 1 mo after transplantation, their number had significantly increased in large bronchi and had normalized 5 mo after transplantation. The density of CGRP-IR fibers in control lungs gradually decreased from large (0. 35 +/- 0.02 micron/micron basal lamina) to small (0.23 +/- 0.02) and peripheral bronchi (0.12 +/- 0.01). At 1 mo after lung transplantation, few CGRP-IR fibers were observed in large bronchi (0.17 +/- 0.02), fewer in small bronchi (0.04 +/- 0.01) (P < 0.01), and none in peripheral bronchi. At 5 mo after lung transplantation, transplanted lungs still had fewer CGRP-IR fibers in large (0.22 +/- 0.02) and small (0.11 +/- 0.02) bronchi (P < 0.02) than did controls, but there were, nonetheless, more in the small bronchi than at 1 mo after transplantation (P < 0.01). Additionally, few CGRP fibers were present in the peripheral bronchi (0.03 +/- 0.01) (P < 0.01). These results clearly demonstrate the occurrence of denervation followed by partial reinnervation with CGRP-IR fibers after transplantation in rat lung.