[A Case of Laparoscopic Repair for Hiatal Hernia Occurred Five Years after Esophagectomy for Esophageal Cancer]

A 70s man underwent minimally invasive esophagectomy and gastric conduit reconstruction via the posterior mediastinal route for early esophageal cancer 5 years ago. Three days prior to hospital visit, he presented with abdominal fullness, left chest pain, and vomiting. A CT revealed a postoperative hiatal hernia, and emergency surgery was performed laparoscopically. The laparoscopic findings showed that the transverse colon had prolapsed into the left thoracic cavity through the esophageal hiatus on the left side of the gastric conduit. The transverse colon had no sign of necrosis. The diaphragmatic defect was closed with unabsorbable suture. Increased bowel motility due to postoperative fat loss in the mesentery and intra-abdominal pressure are thought to be causes of the hernia. In addition, decreased adhesion formation due to endoscopic surgery may be a contributing factor. Although there is no unanimous opinion regarding the suture fixation of the conduit to the diaphragm after esophagectomy, it should be performed to prevent a herniation. Postoperative hiatal hernia occurs more than 5 years after the surgery is relatively rare, but its occurrence should be noted.

Ultrasonic Cleaning for Irrigating Purulent Substances during Laparoscopic Gastrointestinal Surgery

To improve the outcome of laparoscopic gastrointestinal surgery, improvement in the technology for removing purulent substances from the abdominal cavity is required. Ultrasonic cleaning technology may be suitable for the task. However, it is necessary to examine cleaning efficiency and safety through model tests that can lead to clinical trials for practical use. Nine surgical specialists first estimated the distribution of the actual attachment of purulent substances using videos of removing pus-like model dirt as an evaluation scale. Subsequently, cleaning tests were conducted using a small-size shower with model dirt that was somewhat difficult to remove, and its suitability as a model sample was confirmed. A mixture of miso and other substances was attached to a silicon sheet to prepare a test sample. The model dirt could be removed within a few seconds by cleaning using a probe-type ultrasonic homogenizer while the test sample was submerged in water. This performance greatly surpassed that of water flow cleaning under increased water pressure. An ultrasonic cleaner that is useful for irrigation during laparoscopic surgery will be suitable for practical use in laparoscopic surgery.

[Laparoscopic Local Gastrectomy for Gastric Schwannoma and Extramurally Developed Gastric GIST]

Among gastric submucosal tumors, neurogenic tumors are considered to be rare diseases. We experienced a case of laparoscopic local gastrectomy of gastric schwannoma coexisting with extramurally developed gastric GIST found accidentally during surgery. A 61-year-old man was pointed out a gastric submucosal tumor with a diameter of 15 mm in a medical checkup. Endoscopic ultrasound-guided fine needle aspiration(EUS-FNA)was performed, and immunostaining showed that c-kit(-), CD34(-), S-100(+), SMA(-), MIB-1<2%. Diagnosis was gastric schwannoma. We performed laparoscopic local gastrectomy. During the surgery another extramural nodule was accidentally found with a diameter of 8 mm at the anterior wall of the gastric body near lesser curvature. Immunostaining showed c-kit(+), CD34(+)and was diagnosed GIST. Because a gastric schwannoma coexisting with GIST is a rare case, we decided to report it by adding discussion with some literatures.

[A Case of Liver Metastasis 28 Years after Resection for Gastrointestinal Stromal Tumor of Duodenum]

A 69-year-old woman underwent a pancreaticoduodenectomy at the age of 41 years for a submucosal tumor of duodenum, which was diagnosed as leiomyoma at that time. Twenty eight years later, a liver tumor, which is 10 cm in a diameter, was identified on an abdominal ultrasonography. The left hepatectomy was undertaken. Immunohistochemical examination indicated that the tumor was positive for c-kit and diagnosed as a gastrointestinal stromal tumor(GIST). The pathological reexamination revealed the primary tumor was also positive for c-kit and diagnosed as GIST. Therefore, the liver tumor was considered as a metastasis of the duodenal GIST, which was resected 28 years earlier.

Physical vapor deposition using a coaxial ion acceleration method

A novel physical vapor deposition method involving electromagnetic acceleration using a set of coaxial electrodes has been developed. In this study, the coaxial ion acceleration method is applied for a diamond-like carbon (DLC) thin film formation. In the developed method, the central electrode made of the deposition material is sputtered by the noble gas plasma current and accelerated toward the deposition chamber. Because the sputtered ions are accelerated by the Lorentz self-force, the ion injection energy can be controlled separately from the plasma temperature. In addition, the gaseous hydrocarbon, which is commonly used for DLC formation, is not required since a noble gas is used as the discharge gas.

OLFM4 Enhances STAT3 Activation and Promotes Tumor Progression by Inhibiting GRIM19 Expression in Human Hepatocellular Carcinoma

Olfactomedin 4 (OLFM4) induces signal transducer and activator of transcription 3 (STAT3) activation by inhibiting gene associated with retinoid‐interferon‐induced mortality 19 (GRIM19), a strong STAT3 suppressor gene; however, the mechanisms of OLFM4 for regulating GRIM19‐STAT3 cascade in hepatocellular carcinoma (HCC) remain unclear. The functions and regulations of OLFM4, GRIM19, and STAT3 activation in HCC progression were evaluated using surgical specimens collected from 111 HCC patients or 2 HCC cell lines in vitro. Moreover, the cancer stem cell–like property of OLFM4 mediated by leucine‐rich repeat‐containing G protein‐coupled receptor 5 (LGR5), known as an intestinal stem cell marker, was investigated. OLFM4 was increased in HCC compared with adjacent liver tissue. The multivariate analysis revealed that high OLFM4 expression was an independent factor for poor prognosis. OLFM4 expression was negatively correlated with GRIM19 expression and positively correlated with STAT3 activation in HCC, thereby increasing cell cycle progression. OLFM4 knockdown in HCC cells increased GRIM19 expression and inhibited STAT3 activation; however, after double knockdown of GRIM19 and OLFM4, STAT3 activation decreased by OLFM4 knockdown was increased again. OLFM4 knockdown increased cell apoptosis, inhibited cell proliferation, and suppressed cancer stem cell–like property in HCC cells. The incidence of hematogenous recurrence was higher in HCC patients with high OLFM4 expression, suggesting that anoikis resistance of HCC was enhanced by OLFM4. In clinical cases, LGR5 expression and CD133 expression was correlated with OLFM4 expression in HCC, leading to poor patient prognosis. In vitro, LGR5 enhanced cancer stem cell–like property by up‐regulating OLFM4 through the Wnt signaling pathway. Conclusion: OLFM4 is induced by the LGR5‐Wnt signaling pathway and is strongly associated with aggressive tumor progression and poor prognosis in HCC by regulating STAT3‐induced tumor cell proliferation and cancer stem cell–like property. Therefore, OLFM4 is a novel prognostic predictor and a potential therapeutic target for patients with HCC.

[Surgical Cases of Rupture of Hepatocellular Carcinoma after Transcatheter Arterial Embolization]

Rupture of hepatocellular carcinoma(HCC)is a disease wherein the prognosis is poor. In this study, we investigated cases of rupture of HCC that we encountered over 18 years. The age of onset ranged 48-76 years(67 years on average). The patients included 5 males and 1 female. All the cases experienced onset with rapid abdominal pain or loss of consciousness. Shock conditions appeared in 3 cases. Arrest of bleeding was possible by transcatheter arterial embolization(TAE)in all the cases. Subsequently, systemic search and evaluation of hepatic functional reserve were conducted. Hepatectomy was performed in all the cases. No notable complications occurred after the surgery. Two patients with recurrent peritoneal dissemination died of the original disease within 2 years. In the other 3 patients, recurrence has not occurred, and 2 of them have achieved long-term recurrence-free survivals for 4 years or longer. Therefore, based on the findings, we consider that longterm survival can be expected, depending on individual cases.

[Simultaneous Resection of Sigmoid Colon Cancer and Synchronous Liver Metastasis by Laparoscopic Surgery]

We report the case of a patient with sigmoid colon cancer with synchronous liver metastasis who underwent simultaneous sigmoid colectomy and partial hepatectomy by laparoscopic surgery. A 70-year-old man with positive fecal occult blood was diagnosed with sigmoid colon cancer and referred to our hospital. Staging computed tomography (CT) revealed a solitary liver metastasis in segment 6, confirmed by magnetic resonance imaging (MRI). He underwent simultaneous laparoscopic sigmoid colectomy and partial hepatectomy. The patient's postoperative recovery was uneventful and he was discharged 12 days later. The patient was alive without recurrence 4 months after surgery. Laparoscopic surgery is an accepted mode of treatment for colorectal cancer. However, the use of laparoscopy in liver surgery is still limited. There have only been few case reports of combined laparoscopic colorectal and liver resection. Simultaneous laparoscopic colectomy and hepatectomy is feasible for selected colorectal cancer patients with liver metastases. It may provide significant decrease in morbidity, length of hospitalization time, and intraoperative blood loss, without compromising curability or increasing mortality. Further studies are needed to confirm the feasibility of this approach.

[A Case of a Metastatic Liver Tumor from a Thymic Carcinoma Detected During a Cesarean Section]

A 40-year-old pregnant woman who had previously been diagnosed with uterine myoma underwent cesarean section. During the operation, a tumor thought to be uterine myoma was found to be an extrauterine tumor arising from the upper abdomen. After the delivery of the fetus, a staging CT scan was performed, which revealed a huge, 18 cm, hepatic tumor in the left lateral segment, a mediastinal tumor with calcification, and multiple lung nodules. She underwent a left hepatic lobectomy and a wedge resection 8 days after the delivery. The initial pathological diagnosis was moderately differentiated neuroendocrine tumor (NET). However, as a primary hepatic NET is extremely rare, further immunohistochemical staining was performed. The tumor was positive for p63, CD5, c-kit, and bcl-2, indicating a diagnosis of thymic carcinoma with liver and lung metastases.

[Successful Surgical Treatment for Hepatocellular Carcinoma with Portal Vein Tumor Thrombus after Favorable Response to Irradiation and Transcatheter Arterial Chemoembolization]

Here, we describe the surgical treatment of a patient with hepatocellular carcinoma(HCC)with portal vein tumor thrombus (PVTT) after irradiation and transcatheter arterial chemoembolization (TACE). A 51-year-old man was being followed-up for HBV-related liver cirrhosis and HCC that was previously treated by radio-frequency ablation (RFA) and TACE. A follow up CT study revealed recurrence of HCC in segment 6 of the liver with PVTT extending to the right branch. As early recurrence was likely after resection and due to insufficient hepatic functional reserve, primary radiotherapy for PVTT was performed followed by TACE. After non-surgical treatment, a favorable tumor response was observed with no evidence of intrahepatic disease within the left lobe of the liver, and the volume of the future liver remnant increased, allowing us to perform splenectomy and right hemihepatectomy combined with portal vein resection/reconstruction.

Effect of Sample Collection Site on Semen Parameters of Healthy Young Volunteers

The effect of sample collection site on semen parameters in ten men aged between 22 and 24 years was investigated. Sperm was collected at two sites: in a university hospital restroom for general use and in a one-person hospital room. Samples were collected from the same individual twice, with an interval of two weeks between collections. Semen parameters for the two sites were compared. Samples were collected after a minimum of three days and not longer than seven days of sexual abstinence. Sperm concentration did not differ significantly between the university hospital restroom location (86.8 +/- 25.4 x 10(6)/ml; mean +/- standard deviation) and the private hospital room (97.1 +/- 72.0 x 10(6)/ml). There was no difference in the total motile sperm count or daily sperm production between the collection sites. These results suggest that the collection site has little effect on semen parameters.

INDIVIDUAL VARIATION IN SEMEN PARAMETERS OF HEALTHY YOUNG VOLUNTEERS

Individual variation in semen parameters was investigated in healthy young volunteers. Semen samples were collected approximately once a month over a one-year period for a total of 93 samples (5 to 10 samples per subject) from 12 volunteers in their twenties. Semen analysis was carried out according to the WHO Manual. The amount of variation in each semen variable was calculated for each subject by dividing the maximum value by the minimum value. The results showed that the semen volume varied by 1.9+/-0.8 fold (1.3 to 4.2 fold), the sperm concentration by 4.8+/-4.3 fold (1.5 to 17.2 fold), the percentage of sperm with forward progression by 2.8+/-1.4 fold (1.6 to 6.4 fold), the percentage of sperm with rapid linear progression by 3.4+/-2.6 fold (1.7 to 10.9 fold), the percentage of sperm with normal morphology by 1.9+/-0.4 fold (1.3 to 2.4 fold), and the percentage of live sperm by 1.5+/-0.4 fold (1.1 to 2.6 fold). A between-group comparison showed significant differences in all of the variables except the percentage of sperm with normal morphology. These results suggest multiple and considerable semen analyses are needed when evaluating semen parameters.

Gonadal function in patients with testicular germ cell tumors

The gonadal function of 18 patients with testicular germ cell tumors was evaluated. Seminal parameters after orchiectomy were examined in 15 patients. Six of them were available for follow-up observation after 2 or 3 courses of adjuvant chemotherapy. Serum gonadal hormones before and after orchiectomy were evaluated in 7 patients (testosterone and PRL were not examined in one patient). Five of 15 (33.3%), 8 of 15 (53.3%), 13 of 15 (86.7%), 7 of 13 (53.8%), and 9 of 12 (75.0%) had abnormal values in seminal volume, sperm concentration, motility, morphology, and vitality, respectively. The sperm concentration gradually improved after chemotherapy following orchiectomy in 5 of 6 (83.3%) patients. In all the patients examined, serum levels of follicular stimulating hormone (FSH), luteinizing hormone (LH), and prolactin (PRL) increased after orchiectomy. Serum levels of testosterone increased in 4 patients, but decreased in 2 after orchiectomy. These findings suggest that several factors, including preexisting intrinsic defect and disturbance of the hypothalamus-pituitary-gonadal axis, are involved in the deterioration of gonadal function in patients with testicular germ cell tumors.

Clinical study of testicular germ cell tumors

A clinical statistical analysis on 65 patients with 68 testicular germ cell tumors was performed. Thirty-six testes (53.7%) had seminomas and the remainder non-seminomatous germ cell testicular tumors (NSGCTTs). Of the seminomas, 31 (88.6%) were in stage I and the others showed distant metastases at presentation. Of the 32 NSGCTTs, 22 (68.8%) were in stage I. The average ages of the patients with seminomas and NSGCTTs were 40.4 and 29.9 years, respectively. Thirty-nine patients (60.0%) had tumors on the right side, 23 (35.4%) on the left and 3 (4.6%) in both testes. Five patients had a past history of cryptorchidism. Chief complaints in 49 patients (73.1%) were a painless scrotal mass. The interval from clinical onset to presentation was longer in seminoma patients than in NSGCTT patients (10.9 months on average versus 3.4 months). Immunosuppressive acidic protein (IAP) was a useful diagnostic tumor marker as well as alpha-feto protein (AFP), beta-human chorionic gonadotropin (beta-hCG) and lactic dehydrogenase (LDH). We adopted a surveillance policy in more than half of the stage I patients and obtained acceptable results. In the remaining cases, therapies including combination chemotherapy, radiation and salvage operation were performed after orchiectomy. The three-year survival rate was 98.0, 100.0 and 26.7%, for stage I, II and III patients respectively.

[A case of Down's syndrome associated with testicular seminoma]

Down's syndrome is an inherited disorder caused by trisomy of chromosome 21. In patients with Down's syndrome, an increased risk of leukemia has been observed. Recently, the coincidence of testicular cancer with this syndrome has been also emphasized. We present a case of Down's syndrome associated with testicular seminoma. This is the 19th case of Down's syndrome associated with testicular tumor in Japan.

Very early face mask therapy in Class III children

The purpose of this study was to examine the effects of very early face mask therapy in children with Class III malocclusion. At pretreatment (T0), 40 female subjects who were eventually treated showed a more severe Class III pattern (ANB 0.1 degrees) than did 28 skeletal Class III female subjects who remained untreated (ANB 0.4 degrees), as observed in the Wits analysis. Posttreatment results (T1) showed significant (p<0.01) anterior advancement of the maxillary components, backward rotation of the mandible without increased lower anterior facial height, and an improved incisor relationship. Comparison of posttreatment (T1) and postretention (T2) records, however, revealed no increase in SNA in the treated group. SNA did increase in the untreated group, with no significant difference in ANB angle. The x-components of B-point and Me showed a significant (p<0.05) difference between the two groups. At postretention (T2), N-S-Ba, N-S-Ar, and CC-Ba tended to increase more in the treated group than in the untreated group.

Mechanism of DNA gyrase-mediated illegitimate recombination: characterization of Escherichia coli gyrA mutations that confer hyper-recombination phenotype

To study the mechanism of DNA gyrase-mediated illegitimate recombination in Escherichia coli, we isolated temperature-sensitive gyrA mutants that confer spontaneous illegitimate recombination and spontaneous induction of lambda prophage at higher frequencies than that in the wild-type. After reconstruction of single mutations by targeted mutagenesis, we confirmed that two single mutations, gyrAL492P and gyrAL488P, and a double mutation, gyrAI203V+gyrAI205V, show the same properties as those described above. With respect to the phenotypes of hyper-recombination and higher induction of lambda prophage, these mutations were dominant over the wild-type. Analysis of recombination junctions of lambdabio transducing phages formed spontaneously in these mutants showed that the parental E. coli bio and lambda recombination sites have a homologous sequence of only 0. 7 base-pair on average, indicating that homology is not required for this illegitimate recombination. Analysis of nucleotide sequences of mutant gyrA genes revealed that the gyrAL492P and gyrAL488P mutations contain amino acid substitutions of Leu492-->Pro and Leu488-->Pro, respectively, which correspond to the alpha18 helix in the breakage-reunion domain of DNA gyrase A subunit. The gyrAI203V and gyrAI205V mutations contain Ile203-->Val and Ile205-->Val, respectively, which correspond to the alpha10' helix, also in the breakage-reunion domain of DNA gyrase A subunit. Biochemical analysis indicated that the GyrA63 protein that contains the L492P mutation has an apparently normal supercoiling activity, but it also produces a small amount of linear DNA in the absence of DNA gyrase inhibitor during the supercoiling reaction, suggesting that the mutant DNA gyrase may have a defect at the step of religation or a defect in the subunit interaction. These results suggest that the recombination is induced by defects of religation and/or dimer formation in the mutant DNA gyrases, implying that two alpha helices, alpha10' and alpha18, of DNA gyrase A subunit have crucial roles in subunit interaction and/or resealing of DNA.

Super pulse CO2 laser for bracket bonding and debonding

A super pulse and a normal pulse CO2 laser were used to carry out enamel etching and bracket debonding in vitro and in vivo. The shear bond strength of the orthodontic brackets attached to laser-etched and conventional chemically-etched extracted premolars was measured. The pulp cavity temperature was also measured using the same laser irradiation conditions as the shear test. Both super pulse and normal pulse CO2 laser etching resulted in a lower shear bond strength (super pulse: 6.9 +/- 3.4 kg, normal pulse: 9.7 +/- 5.2 kg) than that of chemical etching (15.3 +/- 2.8 kg). Furthermore, the super pulse CO2 laser was able to create debonding at 2 watts within a period of less than 4 seconds (2.9 +/- 0.9 seconds). The super pulse, when irradiating the ceramic brackets from above, during debonding showed a 1.4 degrees C temperature increase in the dental pulp at 2 watts and an increase of 2.1 degrees C at 3 watts. While etching, directly irradiating the enamel surface at 3 watts, the dental pulp showed a temperature increase of 3.5 degrees C. These temperature increases were within the physiologically acceptable limits of the pulp. These results indicate that, in orthodontic treatments, super pulse CO2 laser debonding is more useful than laser etching.

Ultrastructural features of odontoclasts that resorb enamel in human deciduous teeth prior to shedding

Three dental hard tissues, i.e., cementum, dentin, and enamel, are resorbed by multinucleated cells referred to as "odontoclasts." These cells have morphological and functional characteristics similar to those of bone-resorbing osteoclasts. However, concerning enamel resorption, which is a process that may occur during tooth eruption, satisfactory ultrastructural data on odontoclastic resorption are still lacking. Ultrastructural and histochemical characteristics of odontoclasts resorbing enamel of human deciduous teeth prior to shedding were examined by means of light microscopy and transmission and scanning electron microscopy. Odontoclasts that that resorbed enamel were tartrate-resistant acid phosphatase (TRAP)-positive multinucleated giant cells that were essentially the same as those that resorbed dentin and cementum. Ultrastructurally, they had numerous mitochondria, lysosomes, and free polysomes in their cytoplasm. In addition, they were characteristically rich in large cytoplasmic vacuoles containing enamel crystals in the cytoplasm opposite the ruffled border. Although they extended a well-developed, ruffled border against enamel surface, a clear zone--an area typically devoid of organelles--was rarely seen in these cells. In many cases, the cells were in very close contact with the enamel surface by the peripheral part of their cytoplasm. The enamel prisms at the resorption surface contained more loosely packed and electron-lucent enamel crystals compared with those of unresorbed, intact enamel. Furthermore, numerous thin needle- or plate-like enamel crystals that were liberated from the enamel matrix were found in the extracellular channels of the ruffled border and in various-sized cytoplasmic vacuoles in their cytoplasm. The superficial layer of the enamel matrix undergoing odontoclastic resorption stained positively with toluidine blue and for TRAP activity. The results of the present study suggest that odontoclasts resorbing enamel secrete acids as well as organic components, including hydrolytic enzymes, into the resorption zone underlying their ruffled border and that they phagocytose crystals that have been liberated from the partially demineralized enamel matrix by acids, subsequently dissolving them intracellularly.

Quantitative evaluation of newly formed bone in the alveolar wall surrounding the root during the initial stage of experimental tooth movement in the rat

By using a chronological lead-labelling technique and computer image analysis the volume of this newly formed bone was evaluated. Rat maxillary first molars were moved mesially by a fixed, closed coil-spring appliance for 6 days using three different magnitudes of initial tensile force (27, 60 and 136 g). Sham-treated rats wearing an inactivated appliance were used for the control study. All animals were injected twice intraperitoneally with lead-disodium EDTA, 3 hr before the beginning and 3 hr before the end of treatment. The unit volumes of newly formed bone (mm3/mm2) were assessed with reference to lead-labelling lines in the alveolar walls of the root socket by computer image analysis. In the control group, two distinct lead-labelling lines indicated continuous bone formation on the mesial side of the root sockets, but only a jagged line was found on the distal side. After experimental mesial tooth movement, only a single lead line could be found on the mesial/pressure side of the root sockets; on the distal/tension side, a wide layer could be detected between the two lead lines. The volume of newly formed bone on the distal/tension side in the experimental groups was significantly greater than that in the control group. However, there was no significant difference in the volumes of newly formed bone among the three experimental groups. The study demonstrates that the volume of newly formed bone in the alveolar walls during the initial stage of tooth movement can be quantified and that the magnitude of the tensile force of tooth movement may not influence directly the volume of newly formed bone in the alveolar wall on the tension side.

Short-homology-independent illegitimate recombination in Escherichia coli: distinct mechanism from short-homology-dependent illegitimate recombination

We have shown elsewhere that there is no, or very little, homology at the recombination sites in DNA gyrase-mediated illegitimate recombination in vitro. On the other hand, many reports have indicated that illegitimate recombination takes place between sequences with a short homology. To clarify this contradiction, we analyzed the mechanism of DNA gyrase-mediated illegitimate recombination in vivo, by isolating a temperature-sensitive gyrA mutant (gyrAhr1) that causes spontaneous illegitimate recombination at a higher frequency than that of the wild-type. This mutant also causes spontaneous induction of lambda prophage. It is therefore suggested that the gyrAhr1 mutation induces strand breaks in the chromosome, resulting in the formation of illegitimate recombinants. Analysis of the recombination junctions of lambdabio transducing phages formed spontaneously in the gyrAhr1 mutant revealed that the Escherichia coli bio and lambda recombination sites have an average homologous sequence of only 1.3 base pairs. This is the first indication that homology in vivo is not required for illegitimate recombination. On the other hand, a short homology of 8.4 bp, on average, was found in the junctions of lambdabio transducing phages formed spontaneously in the wild-type bacteria. When the gyrAhr1 mutant was irradiated with UV, short homologies were also detected in the junctions. We concluded that illegitimate recombination, which takes place spontaneously in the gyrAhr1 mutants, is distinguishable from spontaneous recombination in the wild-type and from UV-induced recombination in the mutant with regard to the requirement for short homology. We propose that short-homology-independent illegitimate recombination is mediated by subunit exchange between DNA gyrase, while short-homology-dependent recombination is triggered by double-strand breaks and completed by processing, annealing, and ligation of DNA ends.

Cytodifferentiation of the odontoclast prior to the shedding of human deciduous teeth: an ultrastructural and cytochemical study

BACKGROUND

In human deciduous teeth, odontoclastic resorption takes place at the pulpal surface of the coronal dentine prior to shedding, and this resorption shows clear time-related histological changes (Sahara et al., 1992).

METHODS

Using this phenomenon as an observation system, we examined the cytodifferentiation of human odontoclasts by light and electron microscopy. For a histochemical marker of odontoclast differentiation and function, tartrate-resistant acid phosphatase (TRAP) activity was determined by light and electron microscopic enzyme histochemistry.

RESULTS

As root resorption neared completion, TRAP-positive mononuclear cells were initially detected in the pulp chamber. They had abundant mitochondria, small lysosomes, and moderately developed rough endoplasmic reticulum throughout their cytoplasm. In these mononuclear cells, TRAP activity was localized in compartments of the biosynthetic pathway, i.e., in cisternae of the endoplasmic reticulum and Golgi lamellae, as well as small lysosomes. The TRAP-positive mononuclear cells first made contact with the predentine surface by their elongated cellular processes. After attachment, they spread out along the predentine surface and developed specialized membrane structures, clear zones, and ruffled borders. Next, they fused with each other on the predentine surface and formed typical multinucleate odontoclasts. After termination of their resorption function, the odontoclasts lost their ruffled borders and became detached from the resorbed surface. Most of the detached odontoclasts had numerous large pale vacuoles and secondary lysosomes and appeared to be in the process of degeneration.

CONCLUSIONS

The present study demonstrates that: (1) odontoclasts differentiated from TRAP-positive mononuclear cells, which presumably originate from circulating progenitor cells, (2) membrane specialization of odontoclasts, i.e., development of a clear zone and ruffled border, is induced following their contact with the resorption surface, (3) multinucleation of odontoclasts takes place only after their attachment to the resorption surface, (4) mature multinucleate odontoclasts can resorb predentine as well as dentine in the same way as osteoclasts resorb bone, and (5) at the end of the resorption, odontoclasts gradually lose their ruffled borders and become detached from the resorbed surface.

Odontoclastic resorption of the superficial nonmineralized layer of predentine in the shedding of human deciduous teeth

Resorption by odontoclasts of a superficial nonmineralized layer of predentine that occurs in prior to the shedding of human deciduous teeth was studied by light and electron microscopy. As resorption of the tooth roots neared completion, multinucleate cells appeared on the predentine surface of the coronal dentine between the degenerated odontoblasts, excavated characteristic resorption lacunae in the nonmineralized predentine. These multinucleate cells had the same ultrastructural characteristics as odontoclasts and histochemical demonstration of tartrate-resistant acid phosphatase activity in the multinucleate cells revealed intense staining in numerous small granules identified as lysosomes. Occasionally, the multinucleate cells simultaneously resorbed both nonmineralized and calcospherite-mineralized matrix in the predentine. The study demonstrates that multinucleate odontoclasts can resorb nonmineralized predentine matrix in vivo, probably in the same way as they resorb demineralized organic matrix in the resorption zone underlying their ruffled border.

A histological study of the exfoliation of human deciduous teeth

For clarification of the histological details of the shedding of human deciduous teeth, exfoliated and extracted deciduous teeth were examined by light and electron microscopy. After the roots were completely resorbed, the dentogingival junction migrated along the inner resorbing surface and finally reached the pulpal surface of the crown. At the same time, the gingival epithelium also proliferated and migrated under the crown of the deciduous tooth in such a way that part of it lined the residue of the pulp and another part lined the surface overlying the erupting successional tooth. This phenomenon took place from various sides of the tooth surface. Therefore, just before exfoliation, the migrated gingival epithelium formed narrow necks of tissue, and the crown was only superficially attached to the gingiva by them. The final shedding of the tooth appeared to occur by a tearing of these narrow tissue regions. The results of the present study suggest that the dento-gingival junction as well as gingival epithelium play important roles in the process of exfoliation of human deciduous teeth.

Cementum-like tissue deposition on the resorbed pulp chamber wall of human deciduous teeth prior to shedding

In the later stage of exfoliation in human deciduous teeth, odontoclastic resorption takes place at the pulpal surface of the coronal dentin. However, this resorption does not continue until the teeth are shed, and the resorbed pulp chamber wall is usually repaired by cementum-like tissue deposition. In this study, we examined the formation and characteristics of the cementum-like hard tissue on the resorbed dentin surface in the pulp chamber of deciduous teeth prior to shedding. The site and degree of deposition of newly formed cementum-like tissue on the resorbed pulp chamber wall varied from tooth to tooth. Furthermore, they also showed compositional and structural variations. Generally, however, the matrix of the cementum-like tissue was composed of intrinsic collagen fibers, acellular or cellular. There was a tendency for acellular cementum-like tissue to be deposited on small and shallow resorption bays, whereas the cellular type was found on larger and deeper ones. In both cases, the surface of the deposited cementum-like tissue on the resorbed dentin surface usually became flat. However, unlike the cementum repair of resorbed areas on the root surface, no acellular extrinsic fiber cementum-like tissue was found on the resorption pulp chamber wall. Although the role of the repair of the resorbed pulp chamber wall with cementum-like tissue deposition just before shedding is unknown, it might play some role in the retention of deciduous teeth until shedding.