Palisade technique as an effective endoscopic submucosal dissection tool for large colorectal tumors.

Background and study aims Endoscopic submucosal dissection (ESD) has become the standard treatment for colorectal ESD, but large colorectal tumors remain difficult to remove. We developed a new method, called the palisade technique, by modifying the multiple tunneling technique. In this method, a palisade of submucosal tissue is left beneath the tumor to anchor a dissected specimen, maintaining effective submucosal traction. Patients and methods The study included 11 patients with large colorectal tumors that were over half the circumference of the colorectal lumen which were treated using the palisade technique from August 2017 to October 2019. Overall resection outcomes were assessed. Results All 11 lesions were removed en bloc. The R0 resection rate was 45.6 % because of marginal burning of the specimen, but no local recurrence was found after a median observation period of 31 months. The median submucosal dissection time (SDT) and submucosal dissection speed (SDS) were 170 minutes and 23.1 mm 2 /min, respectively. One case of post-ESD hemorrhage was successfully managed endoscopically, and two cases of post-colorectal ESD coagulation syndrome were managed conservatively. Conclusion The palisade technique can be an effective and safe technique for treating large colorectal tumors that extend over half the luminal circumference.

Effects of masticatory muscle force on temporomandibular joint disc growth in rats.

Biomechanical factors in masticatory function are related to the development of the mandible and the condyle. Previous studies have reported that reduced masticatory muscle force influences mandibular bone formation and chondroblastic proliferation. We examined the importance of compressive force in temporomandibular joint (TMJ) disc growth by reducing the masticatory load. Thirty 3-week-old male Wistar rats were used in this study. In the experimental group, the masseter muscles were bilaterally resected to evaluate the influence of masticatory muscle force on morphology and composition of TMJ disc during growth. No surgery was performed in the control group. The thickness of the TMJ disc was measured to evaluate the morphological changes. The localization of type I collagen and decorin was performed by immunostaining to examine compositional change. Cell proliferation in the disc was identified by insulin-like growth factor-1 receptor (IGF-1r) immunostaining. The disc thickness at each region in the experimental group was reduced compared to the control group. While in the control group, type I collagen and decorin were identified throughout the disc, it was concentrated on the superior portion of the disc at the anterior and posterior bands in the experimental group. The expression of IGF-1r immunopositive cells in the experimental group was also significantly lower than in the control. We conclude that masticatory muscle force is closely related to TMJ disc morphology and composition during growth.

The influence of masseter activity on rat mandibular growth.

Many studies have shown that mandibular and condylar growth is affected by compressive forces on mandibular bone and the condyle. It has been reported that chondroblastic differentiation and proliferation in chondrocytes play important roles in condylar growth. However, the influence of reduced compressive force on chondroblastic proliferation and mandibular bone formation is not fully understood. Thirty-six 3-week-old male Wistar rats were used in this study. In the experimental group, the masseter muscles were bilaterally resected to evaluate the influence of masticatory force on mandibular and condylar bone morphology. Six weeks after the operation, while the rats were in the pubertal growth stage, lateral X-rays were taken to analyze the skeletal pattern of the mandible. The form of the condyle and the thickness of the chondroblastic layers were evaluated by toluidine blue staining. Chondroblastic proliferation was identified by insulin-like growth factor-1 receptor (IGF-1r) immunostaining and bone resorption of the condyle was assessed by measuring tartrate-resistant acid phosphatase (TRAP) activity. Lateral X-rays of the mandible showed that rats in the experimental group tended to have large mandibular plane angles. The chondroblastic layer in the condyles of the experimental group rats was thinner than in the control group. The expression of IGF-1r immunopositive cells in the experimental group was significantly lower than in the control chondrocytes, and the number of TRAP-positive cells was significantly higher in the condylar bone of the experimental group. We conclude that masseter muscle activity is closely related to mandibular morphology during growth.

Effects of occlusal loading on alveolar bone remodeling and changes in the distribution of neuropeptides after tooth replantation in rats.

Biomechanical and biochemical factors are involved in bone remodeling. Occlusal loading is a well-known mechanical modulator of alveolar bone remodeling. Neuropeptides, such as vasoactive intestinal peptide (VIP) and calcitonin generelated peptide (CGRP), have been described within the biochemical bone regulators. In this study, the influences of occlusal loading on the alveolar bone remodeling and the distribution of VIP- and CGRP-immunoreactive (IR) fibers were investigated 1, 3 and 5 days after tooth replantation in rats. At day 5, occlusal loading induced a significant increase (p<0.05) in osteoclast number and osteoblast surface compared to those in the nonoccluded group. VIP-IR fibers were observed beside osteoblastic layers and their distribution was significantly enhanced (p<0.05) at day 5 in the occluded group, compared to the non-occluded group. Although there was immunoreactivity for CGRP in the periodontal ligament and alveolar bone apically, CGRP-IR fibers were not detected above the furcation. These results suggest that, after tooth replantation in rats, occlusal loading induced an increase in osteoclast and osteoblast formation, and that VIP might play a functional role in osteoblasts.

Influence of estrogen cycle on temporomandibular joint synovial membrane in rat with deviated mandible.

Temporomandibular disorders (TMD) are known to be more prevalent and severe in women than in men, especially in those who are in their reproductive age. In those patients reproductive hormones may play a vital role in the host adaptive capacity of the temporomandibular joint (TMJ). In order to clarify the relationship between TMD prevalence and estrogen cycle, a mandible deviated animal model was carried out, and the expression of inducible nitric oxide synthase (iNOS), an essential enzyme in the pathogenesis of inflammatory arthritis, was investigated in the rat's synovial tissue. An appliance was attached to the rat's incisors to produce a lateral deviation of the mandible during the metestrus phase, and the animals were sacrificed in the proestrus and estrus phase, when the estrogen was at the highest and lowest level, respectively. Immunostaining was then performed for 2 consecutive estrous cycles to demonstrate iNOS expression in the synovial membrane of the TMJ. The immunoreactivity for iNOS was more intense in the synovial membrane on the contralateral side in the proestrus phase (estrogen peak phase). These observations suggest that iNOS expression in the synovial membrane with mandibular deviation may be exacerbated in the presence of estrogen.

Functional lateral deviation of the mandible and its positional recovery on the rat condylar cartilage during the growth period.

The objective was to examine the effects of a lateral functional shift of the rat mandible and the effects of a shift release on the condylar cartilage during the growth period. Fifty 5-week-old male Wistar rats were initially divided into three groups: shift, recovery, and control. At 5 weeks of age, each animal in the shift and recovery groups received an appliance designed to produce a lateral functional shift of the mandible to the left side. For the recovery group, the appliance was removed after 2 weeks. For the shift group, the appliance was used for 4 weeks. Total cartilage thickness, 5-bromo-2'-deoxyuridine-labeling index, and toluidine blue and tartrate-resistant acid phosphatase-positive cell number in the condylar cartilage at 1, 2, 3, and 4 weeks were compared with those in age-matched controls that had no appliances. In the shift group at 2 weeks, the cartilage thickness and labeling index increased in the central region on the contralateral side, whereas these decreased in the lateral region on the ipsilateral side. However, in the recovery group, 1 to 2 weeks after appliance removal, the cartilage thickness and labeling index in both investigated regions became similar to the control groups. These results emphasize the importance of early treatment to normalize occlusion and create appropriate conditions for normal occlusal development.

Occlusal forces promote periodontal healing of transplanted teeth and prevent dentoalveolar ankylosis: an experimental study in rats.

The process of healing periodontal ligaments (PDL) after transplantation has been widely examined, but the mechanism for preventing dentoalveolar ankylosis is still unclear. In this study, we focused on the role of mechanical stimuli in preventing ankylosis using an animal model of tooth transplantation assessed by histologic observation and evaluation of proliferating PDL cells. Five-week-old Sprague-Dawley male rats were divided into occluded and nonoccluded groups. The right maxillary first molars were replanted in both groups, and histologic observations were carried out after one or two weeks. The proliferative activity of PDL cells was also examined by assessing the distribution of 5-bromo-2'-deoxyuridine (BrdU). After two weeks in the nonoccluded group, ankylosis was clearly detected and PDL stricture was obvious, whereas no severe bone or root resorption was observed. On the other hand, the occluded group showed an enlarged and thickened PDL with extensive root resorption, but no ankylosis. Based on these findings, the replanted teeth were given a one-week healing period and then occlusion recovery was assessed, which resulted in decreased ankylosis and root resorption. The proliferative activity of PDL cells in the occluded group was generally higher than in the nonoccluded group. The activity of PDL cells in the recovery group was also higher than that of the nonoccluded group. These results suggest that occlusal stimuli promoted the regeneration of the PDL and prevented dentoalveolar ankylosis, whereas excessive initial force might cause severe root and bone resorption.

Age-related changes and the possible adaptability of rat jaw muscle spindles: immunohistochemical and fine structural studies.

Afferent signals from jaw muscle spindles contribute to the feedback mechanism that regulates mastication. The integrity and adaptability of this proprioceptor to age-related changes of the surrounding structures are therefore essential to maintain an appropriate masticatory function throughout life. In this study, we examined muscle spindles obtained from temporal and masseter muscles of 10-week-, 12-, 18-, and 24-month-old Wistar rats, employing immunohistochemistry for protein gene product 9.5 (PGP 9.5) or growth-associated protein (GAP-43) in addition to transmission electron microscopy, in order to investigate their morphological changes in relation to the effect of aging on the adaptive potential of the receptors. Immunohistochemistry for PGP 9.5 showed virtually similar reactions at sensory nerve terminals in all age groups. On the other hand, immunoreactivity for GAP-43 in the sensory nerve ending of the muscle spindles was found 2 and 3 weeks after birth but became almost undetectable by 10 weeks. However GAP-43 immunoreactions occasionally reappeared in those of spindles in 12- and 18-month old animals, and vanished again by 24 months of age. Electron microscopic observations also revealed age-related morphological changes in the intrafusal muscle fibers of the rats in 12-month and older groups. The extent of degenerative and/or atrophic alterations of intrafusal fibers increased with age and involved the nerve elements of spindles by 24 months. These findings indicate that the adaptation potential of rat jaw muscle spindles is well preserved until middle age, but diminishes in elderly animals. Structural changes of muscle spindles in elderly animals probably contribute to the deterioration of the muscular function.

Changes in response properties of periodontal mechanoreceptors after experimental orthodontic tooth movement in rats.

Using an in vitro preparation, we investigated chronological changes in response properties of periodontal mechanoreceptors (PMRs) in the rat right mandibular first molar (M1) after experimental orthodontic tooth movement. Orthodontic force was applied to M1 for 14 days by activating 24.5 mN superelastic titanium-nickel alloy closed coil springs anchored to the mandibular incisors. Experiments were performed on days 3, 7, 10, and 14 during application of orthodontic force and on days 7, 14, 21, and 28 after removal of orthodontic force. The rats without application of orthodontic force were used as control group. In each group, direct mechanical stimulation using von Frey hairs and electrical stimulation was applied to the distal root of M1. Results showed that compared with controls (1) the mechanical thresholds were significantly lower during application of orthodontic force; however, no significant difference was found after removal of force application and (2) conduction velocities were significantly lower from day 7 during application of orthodontic force to day 14 after removal of orthodontic force; however, no significant difference was found on days 21 and 28 after removal of orthodontic force. These results suggest that the PMRs, although having some of their response properties altered during orthodontic force application, were able to recover and adapt to the newly acquired intraoral condition after removal of the orthodontic force.

Growth-associated protein-43 immunohistochemical and ultrastructural changes in jaw muscle spindles of the rat following loss of occlusion.

The effects of complete loss of occlusion on the structural and functional status of these muscle spindles were investigated by immunohistochemistry either for protein gene product 9.5 (PGP 9.5) or growth-associated protein-43 (GAP-43) by light and electron microscopy. All the upper molars of 4-week-old Wistar rats were extracted and the erupted portions of the upper and lower incisors of the same animals were cut-off at the level of the interdental papilla every other day. In a control group, immunoreactivity for GAP-43 was positive in the developing annulospiral endings of 2-week-old rats, but was not detected in any of the muscle spindles after 3 weeks of age. At 4 weeks of age, the PGP 9.5 immunostained spindles had well-differentiated annulospiral endings. Ultrastructurally, these afferent endings showed lenticular or circular profiles in cross-sections, and were differentially indented into the intrafusal-fibres. The inner surfaces of the terminals formed rather smooth myoneural junctions, while the outer surfaces were covered only by basal lamina continuous with that of the underlying intrafusal muscle fibres. After the experimental elimination of occlusal contact, GAP-43 immunoreactivity reappeared in some nerve endings of muscle spindles by 3 days, and persisted for at least 28 days. During this period, the afferent-terminals exhibited various fine structural abnormalities such as irregular outlines and invaginated neuromuscular interfaces. Some sensory-terminal (ST) profiles were completely engulfed by intrafusal-fibres. However, GAP-43 expression and ultrastructural alterations became undetectable within a week of the end of incisal cutting and the recovery of incisal-contact. These data indicate that remodelling of nerve terminals in muscle spindles, as assessed by GAP-43 expression and ultrastructural changes, occurs soon after a loss of occlusion, and ceases if incisal-contact is restored. It is concluded that possible changes in jaw muscle function, as well as a sudden loss of proprioceptive sensory input from the periodontal mechanoreceptors of molars and incisors, induce the structural reorganisation of nerve terminations in jaw muscle spindles that is associated with the appearance and disappearance of GAP-43 immunoreactivity.