Preoperative MRI for predicting pathological changes associated with surgical difficulty during laparoscopic cholecystectomy for acute cholecystitis.

BACKGROUND: Severe inflammation with necrosis and fibrosis of the gallbladder in acute cholecystitis increases operative difficulty during laparoscopic cholecystectomy. This study aimed to assess the use of preoperative MRI in predicting pathological changes of the gallbladder associated with surgical difficulty. METHODS: Patients who underwent both preoperative MRI and early cholecystectomy for acute cholecystitis between 2012 and 2018 were identified retrospectively. On the basis of the layered pattern of the gallbladder wall on MRI, patients were classified into three groups: high signal intensity (HSI), intermediate signal intensity (ISI), and low signal intensity (LSI). The endpoint was the presence of pathological changes of the gallbladder associated with surgical difficulty, such as necrosis, abscess formation and fibrosis. RESULTS: Of 229 eligible patients, pathological changes associated with surgical difficulty were found in 17 (27 per cent) of 62 patients in the HSI group, 84 (85 per cent) of 99 patients in the ISI group, and 66 (97 per cent) of 68 patients in the LSI group (P < 0·001). For detecting these changes, intermediate to low signal intensity of the gallbladder wall had a sensitivity of 90 (95 per cent c.i. 84 to 94) per cent, specificity of 73 (60 to 83) per cent and accuracy of 85 (80 to 90) per cent. CONCLUSION: Preoperative MRI predicted pathological changes associated with surgical difficulty during laparoscopic cholecystectomy for acute cholecystitis.

ANTECEDENTES: La inflamación grave con necrosis y fibrosis de la vesícula biliar en la colecistitis aguda aumenta la dificultad quirúrgica durante la colecistectomía laparoscópica. Este estudio tuvo como objetivo evaluar el uso de la resonancia magnética preoperatoria (magnetic resonance imaging, MRI) para predecir los cambios patológicos de la vesícula biliar asociados con la dificultad quirúrgica. MÉTODOS: Los pacientes que se sometieron tanto a MRI preoperatoria como a colecistectomía precoz por colecistitis aguda entre 2012 y 2018 fueron identificados retrospectivamente. En base a la distribución en capas de la pared de la vesícula biliar en la MRI, los pacientes se clasificaron en tres grupos: (1) intensidad de señal alta (high signal intensity, HSI), (2) intensidad de señal intermedia (intermediate signal intensity, ISI) y (3) intensidad de señal baja (low signal intensity, LSI). El objetivo final fue la presencia de cambios patológicos en la vesícula biliar asociados con la dificultad quirúrgica, tales como necrosis, formación de abscesos y fibrosis. RESULTADOS: De los 229 pacientes elegibles, se documentaron cambios patológicos asociados con dificultad quirúrgica en 17 (27,4%) de 62 pacientes en el grupo HSI, 84 (84,8%) de 99 pacientes en el grupo ISI y 66 (97,1%) de 68 pacientes en el grupo LSI (P < 0,001). Para detectar estos cambios, la intensidad de señal de intermedia a baja de la pared de la vesícula biliar tuvo una sensibilidad del 89,8% (i.c. del 95% 84,2%-94,0%), una especificidad del 72.6% (i.c. del 95% 59,8%-83,1%) y una precisión del 85,2% (i.c. del 95% 79,9%-89,5%). CONCLUSIÓN: La MRI preoperatoria predijo los cambios patológicos asociados con la dificultad quirúrgica durante la colecistectomía laparoscópica por colecistitis aguda.

Randomized clinical trial of single skin sterilization with a povidone-iodine applicator versus conventional skin sterilization in abdominal surgery.

Background: The efficacy of widely used povidone-iodine applicators for skin sterilization in abdominal surgery is unclear. The aim of this trial was to evaluate whether sterilization with a povidone-iodine applicator was not inferior to a conventional sterilization method. Methods: Patients undergoing elective abdominal surgery were assigned randomly to receive single sterilization with the applicator or conventional sterilization. The primary endpoint was wound infection rate. Secondary endpoints were rate of organ/space surgical-site infection (SSI), adverse effects of povidone-iodine, amount of povidone-iodine used and total cost of sterilization. Results: Of 498 patients eligible for the study between April 2015 and September 2017, 240 were assigned and analysed in the applicator group and 246 in the conventional group. Wound infection was detected in 16 patients (6·7 per cent) in the applicator group and 16 (6·5 per cent) in the conventional group (absolute difference 0·0016 (90 per cent c.i. -0·037 to 0·040) per cent; P = 0·014 for non-inferiority). There was no difference between the groups in the organ/space SSI rate (11 patients (4·6 per cent) in the applicator group and 16 (6·5 per cent) in the conventional group. Both the amount of povidone-iodine used and the total cost of sterilization were higher in the conventional group than in the applicator group (median 76·7 versus 25 ml respectively, P < 0·001; median €7·0 versus €6·4, P < 0·001). Skin irritation was detected in three patients in the conventional group. Conclusion: In abdominal surgery, this povidone-iodine applicator was not inferior to conventional sterilization in terms of the wound infection rate, and it is cheaper. Registration number: UMIN000018231 (http://www.umin.ac.jp/ctr/).

Comparison between dexmedetomidine and midazolam as a sedation agent with local anesthesia in inguinal hernia repair: randomized controlled trial.

PURPOSE: In Japan, inguinal hernia repair is widely performed with local anesthesia. The objective of this study was to evaluate safety and efficacy of intravenous dexmedetomidine as a sedation agent with local anesthesia in inguinal hernia repair. METHODS: We performed this randomized, single-blind study for 200 patients who were scheduled to undergo inguinal hernia repair with local anesthesia. Patients were randomly divided into two groups (dexmedetomidine group: Group D, midazolam group: Group M). The primary outcome was to evaluate the safety of intravenous dexmedetomidine. Secondary outcomes were to analyze results of operators' surveys and patients' questionnaires and evaluate implementation of conscious sedation. RESULTS: Incidence of respiratory depression was significantly higher in Group M than Group D (p = 0.03). Other adverse events examined did not differ significantly. All three operators' questionnaires indicated that results were better in Group D than Group M. More than 70% of patients in both groups were satisfied with the surgery. More than 80% of Group D patients and 74% of Group M patients achieved a state of conscious sedation. CONCLUSION: This study demonstrated that intravenous dexmedetomidine during hernia repair with local anesthesia is safe and the results were satisfactory to both operators and patients.

Prognostic impact of lymph node metastasis in distal cholangiocarcinoma.

BACKGROUND: The aim of the study was to investigate the prognostic impact of lymph node metastasis in cholangiocarcinoma using three different classifications. METHODS: Patients who underwent pancreaticoduodenectomy for distal cholangiocarcinoma in 24 hospitals in Japan between 2001 and 2010 were included. Survival was calculated by means of the Kaplan-Meier method and differences between subgroups were assessed with the log rank test. The Cox proportional hazards model was used to identify independent predictors of survival. χ(2) scores were calculated to determine the cut-off value of the number of involved nodes, lymph node ratio (LNR) and total lymph node count (TLNC) for discriminating survival. RESULTS: Some 370 patients were included. The median (range) TLNC was 19 (3-59). Nodal metastasis occurred in 157 patients (42·4 per cent); the median (range) number of involved nodes and LNR were 2 (1-19) and 0·11 (0·02-0·80) respectively. Four or more involved nodes was associated with a significantly shorter median survival (1·3 versus 2·2 years; P = 0·001), as was a LNR of at least 0·17 (1·4 versus 2·3 years; P = 0·002). Involvement of nodes along the common hepatic artery, present in 21 patients (13·4 per cent), was also associated with a shorter survival (median 1·3 versus 2·1 years; P = 0·046). Multivariable analysis among 157 node-positive patients identified the number of involved nodes as an independent prognostic factor (risk ratio 1·87; P = 0·002). CONCLUSION: The number of involved nodes was a strong predictor of survival in patients with distal cholangiocarcinoma.

Utilization of third molars in the orthodontic treatment of skeletal class III subjects with severe lateral deviation: case report.

AIM: This clinical report discusses the importance and use of third molars in the adult patient by presenting a case in which their use during orthodontic treatment allowed occlusal improvement. SUBJECT AND TREATMENT PLAN: The patient was a Japanese adolescent boy who had a skeletal Class III malocclusion with severe lateral deviation of the mandible, significant loss of posterior occlusal vertical dimension, due to premature loss of the maxillary and mandibular left first molars, and furthermore, both first molars had advanced carious lesions that had resulted in reduced crown heights and bilateral chewing surfaces. The mandible had shifted to the left, with a bilateral chewing pattern and a lack of posterior vertical alveolar height, which in turn had produced an abnormal occlusal plane and curve of Spee. The maxillary arch was expanded, the maxilla was moved downward and forward, and the mandible was moved slightly backward and rotated open to increase posterior vertical alveolar and crown height. The reconstruction of a functional occlusal plane was achieved by uprighting the posterior teeth to correct asymmetric posterior vertical alveolar and crown height, using a full multibracket system incorporating four third molars and closing the space from the missing first molars and extraction of the questionable first molars. RESULTS: A normal overbite and overjet and adequate posterior support and anterior guidance were established, achieving a better intercuspation of the posterior teeth. A favorable perioral environment was created, with widened tongue space to produce an adequate airway. A well-balanced lip profile and almost symmetric face were achieved using the four wisdom teeth without extraction of the four premolars. Subsequent mandibular growth, with development of posterior vertical alveolar height and temporomandibular joint adaptation, has resulted in an almost symmetric posterior vertical height and joint structure between right and left sides. These factors have contributed to the occlusal stability maintained for more than 5 years. CONCLUSION: In the growing patient, with missing and/or early advanced caries of the first molars, it may be more beneficial to plan occlusal improvement through extraction of the questionable first molar rather than premolar extraction. This method of treatment can equalize posterior vertical dimension and does not restrict tongue space. In addition, this treatment method addresses the clinician's concern about postorthopedic relapse due to tongue habits and eruption of the third molars.

Solubility properties of human tooth mineral and pathogenesis of dental caries.

Dental research over the last century has advanced our understanding of the etiology and pathogenesis of caries lesions. Increasing knowledge of the dynamic demineralization/remineralization processes has led to the current consensus that bacteria-mediated tooth destruction can be arrested or even to some degree reversed by adopting fluoride and other preventive measures without using restorative materials. Our experimental approach provided new insight into the stoichiometries and solubility properties of human enamel and dentin mineral. The determination of the solubility product constant on the basis of the stoichiometric model (Ca)5.x(Mg)q(Na)u(HPO4)v(CO3)w(PO4)3.y(OH,F)1.z, verifies the difference in their solubility properties, supporting the phase transformation between tooth mineral and calcium phosphates in a wide range of fluid compositions as found in the oral environment. Further refinement of the stoichiometry and solubility parameters is essential to assess quantitatively the driving force for de- and remineralization of enamel and dentin in the oral fluid environment. Prediction of the effects of a combination of inhibitors and accelerator(s) on remineralization kinetics is also required. In order to develop devices efficient for optimizing remineralization in the lesion body, it is a critical question how, and to what extent, fluoride can compensate for the activity of any inhibitors in the mineralizing media.

Dental fluorosis: chemistry and biology.

This review aims at discussing the pathogenesis of enamel fluorosis in relation to a putative linkage among ameloblastic activities, secreted enamel matrix proteins and multiple proteases, growing enamel crystals, and fluid composition, including calcium and fluoride ions. Fluoride is the most important caries-preventive agent in dentistry. In the last two decades, increasing fluoride exposure in various forms and vehicles is most likely the explanation for an increase in the prevalence of mild-to-moderate forms of dental fluorosis in many communities, not the least in those in which controlled water fluoridation has been established. The effects of fluoride on enamel formation causing dental fluorosis in man are cumulative, rather than requiring a specific threshold dose, depending on the total fluoride intake from all sources and the duration of fluoride exposure. Enamel mineralization is highly sensitive to free fluoride ions, which uniquely promote the hydrolysis of acidic precursors such as octacalcium phosphate and precipitation of fluoridated apatite crystals. Once fluoride is incorporated into enamel crystals, the ion likely affects the subsequent mineralization process by reducing the solubility of the mineral and thereby modulating the ionic composition in the fluid surrounding the mineral. In the light of evidence obtained in human and animal studies, it is now most likely that enamel hypomineralization in fluorotic teeth is due predominantly to the aberrant effects of excess fluoride on the rates at which matrix proteins break down and/or the rates at which the by-products from this degradation are withdrawn from the maturing enamel. Any interference with enamel matrix removal could yield retarding effects on the accompanying crystal growth through the maturation stages, resulting in different magnitudes of enamel porosity at the time of tooth eruption. Currently, there is no direct proof that fluoride at micromolar levels affects proliferation and differentiation of enamel organ cells. Fluoride does not seem to affect the production and secretion of enamel matrix proteins and proteases within the dose range causing dental fluorosis in man. Most likely, the fluoride uptake interferes, indirectly, with the protease activities by decreasing free Ca(2+) concentration in the mineralizing milieu. The Ca(2+)-mediated regulation of protease activities is consistent with the in situ observations that (a) enzymatic cleavages of the amelogenins take place only at slow rates through the secretory phase with the limited calcium transport and that, (b) under normal amelogenesis, the amelogenin degradation appears to be accelerated during the transitional and early maturation stages with the increased calcium transport. Since the predominant cariostatic effect of fluoride is not due to its uptake by the enamel during tooth development, it is possible to obtain extensive caries reduction without a concomitant risk of dental fluorosis. Further efforts and research are needed to settle the currently uncertain issues, e.g., the incidence, prevalence, and causes of dental or skeletal fluorosis in relation to all sources of fluoride and the appropriate dose levels and timing of fluoride exposure for prevention and control of dental fluorosis and caries.

Histopathological studies on virulence of dipeptidyl aminopeptidase IV (DPPIV) of Porphyromonas gingivalis in a mouse abscess model: use of a DPPIV-deficient mutant.

To elucidate the role of dipeptidyl aminopeptidase IV (DPPIV) in the virulence of Porphyromonas gingivalis, mice were infected with either a wild-type strain or a DPPIV-deficient mutant using an abscess model. Histopathological analysis of the resulting lesions indicated that DPPIV participates in virulence through the destruction of connective tissue and the less effective mobilization of inflammatory cells.

The secretion of amelogenins is associated with the induction of enamel and dentinoid in an ameloblastic fibro-odontoma.

Ameloblastic fibro-odontoma is the unique entity of epithelial-ectomesenchymal odontogenic tumors, which is characterized by enamel formation in addition to dentine. We examined immunohistochemically a case of this tumor in which enamel having prism structures was developed in the absence of odontoblast differentiation but was in contact with mesenchymal matrices. Histological examination showed diverse morphological features of epithelial tumor cells, e.g., cuboidal cells comprising tooth bud-like projections, ameloblast- and stellate reticulum-like cells, and residual cells in forms of extended cords or islands of odontogenic epithelium. Immunostaining with anti-amelogenin sera proved that the intracellular production of amelogenins was initiated at the tooth bud-like stage. The secreted amelogenins were detected almost exclusively in the induced enamel and dentinoid areas, as well as in the core region of cementicle-like spheres deposited in the encapsulating stroma. The results obtained indicate that the odontogenic tumor epithelia and its products, i.e., amelogenins, participate in multifaceted aspects of dental hard tissue formation that takes place during oncogenesis.

Sexual dimorphism of porcine amelogenins: male-specific amelogenins have strong adsorption properties onto apatite crystals.

The present studies were undertaken to investigate the sexual dimorphism of porcine amelogenins and to gain information as to whether excesses of male amelogenins, if any, possess functional significance in protein-crystal interactions. Enamel proteins, including the intact full-length amelogenins and their degraded polypeptides, were isolated from the secretory enamel of male and female pigs. To identify the amelogenins among the separated pools of male- and female-matrix proteins, rabbit anti-C13 and C25 peptide sera were used, which reacted specifically with the conserved C-terminal domain. Immunoblotting showed that a few extra members of the amelogenins, sharing common epitopes at the C-terminus, were recognized in male products. The apparent yield of the male amelogenins was only marginal, on the basis of their stained intensities on the gel, but the secreted male amelogenins demonstrated selective (probably the strongest among the amelogenins) adsorption properties onto apatite crystals. Reflecting the general symmetric electrophoretic profiles of the male- and female-enamel proteins in toto, there were no sex-linked differences in the protein-crystal interaction and the resulting regulatory function of crystal precipitation.

Nonsurgical and nonextraction treatment of skeletal Class III open bite: its long-term stability.

Two female patients, aged 14 years 5 months and 17 years 3 months with skeletal Class III open bite and temporomandibular dysfunction are presented. They had previously been classified as orthognathic surgical cases, involving first premolar removal. The primary treatment objective was to eliminate those skeletal and neuromuscular factors that were dominant in establishing their malocclusions. These included abnormal behavior of the tongue with short labial and lingual frenula, bilateral imbalance of chewing muscles, a partially blocked nasopharyngeal airway causing extrusion of the molars, with rotation of the mandible and narrowing of the maxillary arch. Resultant occlusal interference caused the mandible to shift to one side, which in turn produced the abnormal occlusal plane and curve of Spee. As a result, the form and function of the joints were adversely affected by the structural and functional asymmetry. These cases were treated by expanding the maxillary arch, which brought the maxilla downward and forward. The mandible moved downward and backward, with a slight increase in anterior facial height. Intruding and uprighting the posterior teeth, combined with a maxillary protraction, reconstructed the occlusal plane. A favorable perioral environment was created with widened tongue space in order to produce an adequate airway. Myofunctional therapy after lingual and labial frenectomy was assisted by vigorous gum chewing during and after treatment, together with a tooth positioner. Normal nasal breathing was achieved.

Case report of malocclusion with abnormal head posture and TMJ symptoms.

Abnormal cervical muscle function can cause abnormal head posture, adversely affecting the development and morphology of the cervical spine and maxillofacial skeleton, which in turn leads to facial asymmetry and occlusal abnormality. There can be morphologic abnormalities of the mandibular fossa, condyle, ramus, and disk accompanying the imbalance of the cervical and masticatory muscles activities. Two normally growing Japanese female patients with Class II Division 1 malocclusion presented with TMJ symptoms and poor head posture as a result of abnormal sternocleidomastoid and trapezius cervical muscle activities. One patient underwent tenotomy of the two heads of the sternocleidomastoid muscle and the other patient did not. In addition to orthodontics, the 2 patients received physiotherapy of the cervical muscles during treatment. Both were treated with a functional appliance as a first step, followed by full multi-bracketed treatment to establish a stable form of occlusion and to improve facial esthetics with no head gear. This interdisciplinary treatment approach resulted in normalization of stomatognathic function, elimination of TMJ symptoms, and improvement of facial esthetics. In the growing patients, the significant response of the fossa, condyle, and ramus on the affected side during and after occlusal correction contributed to the improvement of cervical muscle activity. Based on the result, early occlusal improvement, combined with orthopedic surgery of the neck muscles or physiotherapy to achieve muscular balance of the neck and masticatory muscles, was found to be effective. Two patients illustrate the potential for promoting symmetric formation of the TMJ structures and normal jaw function, with favorable effects on posttreatment growth of the entire maxillofacial skeleton.

Small-angle X-ray scattering and computer-aided molecular modeling studies of 20 kDa fragment of porcine amelogenin: does amelogenin adopt an elongated bundle structure?

Amelogenins, which are major matrix constituents in the developing tooth, play a regulatory role in the process of enamel crystal formation. Porcine amelogenin with 173 amino acid residues is rich in proline, glutamine, leucine, and histidine. We utilized the small-angle X-ray scattering (SAXS) technique to examine the solution structure of porcine amelogenin. Samples used were two porcine amelogenins with apparent molecular weights of 20 kDa (amino acids 1 to 148) and 13 kDa (amino acids 46 to 148) on SDS-PAGE. Prior to SAXS measurements, the protein samples were dissolved in 2% (v/v) acetic acid to give a concentration range up to 10 mg/ml. Comparison between Rg (the overall radius of gyration) and Rc (the cross-sectional radius of gyration) revealed that the 20 kDa amelogenin exists in this solution as asymmetric particles with a length of about 15 nm, presumably corresponding of dimers. Based on these experimental data and computer-aided molecular modeling studies, we propose that the 20 kDa amelogenin adopts an elongated bundle structure which mainly consists of extended structures similar to polyproline II and/or beta-strand, interspersed with beta-turn or loop.

Enamel mineralization and an initial crystalline phase.

In this communication, we summarized our recent experimental approaches to an unsettled issue, i.e., the nature and role of an acidic precursor in enamel mineralization. The objectives we specially focused our attention on are: the composition, structure and high resolution images of enamel crystals at various developmental stages, thermodynamic and kinetic consideration of octacalcium phosphate (OCP) vs hydroxyapatite (HA) precipitation in physiological media simulating the enamel fluid, reversible changes in the composition and structure of OCP, effects of fluoride at low concentrations and enamel proteins on OCP hydrolysis, and adsorption of enamel proteins onto OCP and fluoridated hydrolysates at neutral pH and room temperature. On the basis of all experimental evidence, we propose that enamel crystal growth comprises two events: the two-dimensional growth of an OCP-like precursor in a narrow outermost zone adjacent to the ameloblasts and the subsequent overgrowth of apatite units on the template under discrete fluid environment in the underlying region distant from the cell layer. The experimental data also support the concept that the whole process of enamel mineralization is modulated substantially through interaction between enamel proteins and crystals including the acidic precursor.

The effect of fluoride on apatite structure and growth.

Fluoride participates in many aspects of calcium phosphate formation in vivo and has enormous effects on the process and on the nature and properties of formed mineral. The most well-documented effect of fluoride is that this ion substitutes for a column hydroxyl in the apatite structure, giving rise to a reduction of crystal volume and a concomitant increase in structural stability. In the process of enamel mineralization during amelogenesis (a unique model for the cell-mediated formation of well-crystallized carbonatoapatite), free fluoride ions in the fluid phase are supposed to accelerate the hydrolysis of acidic precursor(s) and increase the driving force for the growth of apatitic mineral. Once fluoride is incorporated into the enamel mineral, the ion likely affects the subsequent mineralization process by reducing the solubility of the mineral and thereby modulating the ionic composition in the fluid surrounding the mineral, and enhancing the matrix protein-mineral interaction. But excess fluoride leads to anomalous enamel formation by retarding tissue maturation. It is worth noting that enameloid/enamel minerals found in vertebrate teeth have a wide range of CO3 and fluoride substitutions. In the evolutionary process from elasmobranch through enameloid to mammalian enamel, the biosystems appear to develop regulatory functions for limiting the fluoridation of the formed mineral, but this development is accompanied by an increase of carbonate substitution or defects in the mineral. In research on the cariostatic effect of fluoride, considerable emphasis is placed on the roles of free fluoride ions (i.e., preventing the dissolution and accelerating the kinetics of remineralization) in the oral fluid bathing tooth mineral. Fluoride also has been used for the treatment of osteoporosis, but much still remains to be learned about maximizing the benefit and minimizing the risk of fluoride when used as a public health measure.

Disturbed enamel mineralization in a rat incisor model.

Possession of full-thickness hard enamel appears to be one of the indispensable life-saving characteristics of rats. Previous studies by Suga and his colleagues and by others demonstrated that various types of malformation are evoked in continuously erupting rat incisors. In the current report, we directed our effort to oversee various types of enamel malformation caused experimentally in rat incisors. We surveyed the specimens collected by Suga and his colleagues, as well as specimens we obtained. From the results, it is conceivable that perturbation of the programmed sequential events during enamel development is a major factor in the establishment of enamel malformation. Animal studies with either 1-hydroxyethylidene-1,1-bisphosphonate (HEBP) or a multidentate phosphonic acid (EDTPO) confirmed that dentin mineralization provides a certain inductive effect on the secretion of enamel matrix and subsequent enamel crystallization. Our recent studies using anti-microtubular agents led to the conclusion that the acceleration of mineralization in outer enamel is a type of enamel malformation, most likely due to disruption of the cellular regulation of calcium transport under severe toxic regimens. In future work, experimental approaches combining measurements of kinetic factors with static observation of enamel lesions are required before we can gain a comprehensive understanding of the pathogenesis of disturbed enamel mineralization. The kinetic factors to be considered include the rates of tissue apposition and tooth eruption which determine the total volume of tooth substance formed, and the rate of mineral accretion. Furthermore, information as to the composition, crystallinity, solubility, and mechanical properties of enamel defects is needed before we can assess the susceptibility of teeth having those lesions to caries and other physico-chemical attacks in the oral environment.

Recent observations on enamel crystal formation during mammalian amelogenesis.

BACKGROUND: Enamel mineralization taking place during amelogenesis is a unique model to investigate carbonatoapatite formation in vivo. The abundance of proteinaceous crystal growth inhibitors, in particular amelogenins, contributes significantly to the mineralization process. Their putative roles are to prevent random proliferation of crystal nuclei and to regulate the growth kinetics and orientation of the formed enamel crystals. METHODS: The enamel fluid surrounding the forming enamel crystals contains high concentrations of carbonate and magnesium ions, both of which seem to modulate the mineralization process. Particularly, Mg ions can adsorb onto enamel crystal surfaces in a manner to compete with Ca ions. Enamel mineral formed during amelogenesis is featured as calcium-deficient, acid phosphate-rich carbonatoapatites. Currently the most putative stoichiometry model for enamel mineral is (Ca)5-x(HPO4)v(CO3)w(PO4)3-x (OH)1-x. RESULTS: Very significant changes in the morphology, stoichiometry, and solubility of enamel crystals occur during the various stages of amelogenesis. The early enamel mineralization comprises two events: the initial precipitation of the well-documented thin ribbons and the subsequent overgrowth of apatite crystals on those templates. The thin ribbons precipitated in the vicinity of the secretory ameloblasts have the highest contents of acid phosphate, particularly in the form of exchangeable species, whereas both the exchangeable and unexchangeable acid phosphate decrease concomitantly with the progress of the apatite overgrowth and the appearance of elongated hexagonal crystals in the late secretory stages. CONCLUSIONS: Those morphological and compositional features seem to be consistent with the formation of precursors, such as octacalcium phosphate.

Reversible structural changes of octacalcium phosphate and labile acid phosphate.

Acid phosphate is one of the major impurities incorporated into bioapatites, and its quantity and environment in forming mineral have been used as diagnostic probes to pursue acidic precursor(s). Currently, little is known about the structural feature of nonstoichiometric octacalcium phosphate (OCP), which has been advocated to be, most plausibly, mineral salt initially formed during amelogenesis. In the present report, we attempt to define the state of acid phosphate in OCP crystals which were Ca-deficient and contained 40% total phosphate as acid phosphate. We assessed fractions of acid phosphate in discrete environments by extracting the crystals in either deionized water, 10 mmol/L NaOH solution (initial pH 11), or 150 mmol/L Tris buffer at pH 7.4. Solid samples before and after the treatments were examined by chemical analyses and x-ray diffraction. The results indicated that successive extractions with use of the alkaline solution brought about a reversible change (not hydrolysis) in the interior structure of OCP, which accompanied a marked decrease in acid phosphate. A substantial part of the lost acid phosphate was restored during subsequent treatments at neutral pH, and, intriguingly, this restoration accompanied a re-ordering of OCP structure. The data suggested that the acid phosphate in OCP is separated into three pools: (a) a stable pool corresponding to roughly 50 to 60% of the total acid phosphate, (b) a reversibly exchangeable pool corresponding to 25 to 30% of the acid phosphate which may exist either in the water layer or on crystal surfaces, and (c) an unstable (or irreversibly lost) pool corresponding to 15 to 20% of the acid phosphate, a part of which might be explained by the presence of excess hydrogen in OCP. The present work supports the concept that protons and, to a lesser magnitude, phosphate species can diffuse into and out of the OCP lattice prior to initiation of its hydrolytic transition into apatite.

Confocal laser scanning microscopic studies on alveolar bone remodeling with orthodontic tooth movement and retention.

Alveolar bone reconstruction in growing dog during the retention period following orthodontic tooth movement was studied. Three beagle dogs (8-10 kg body weight, about one-year-old) were used and two of the animals were subjected to histological observation. The upper 2nd and lower 3rd premolars on both sides were extracted prior to the orthodontic treatments. After a healing period of one month, the upper 3rd premolar and the lower 4th premolar on the right side were moved mesially with a conventional orthodontic force for 8 weeks, and then retained in their new position for 4 weeks. The contralateral corresponding premolars were used as control. The alveolar bone was double-labeled with tetracycline (TC) during the movement and calcein (Cal) during the retention period. Alveolar bone structure and labeling patterns were examined by contact microradiography, conventional fluorescence microscopy, and confocal laser scanning microscopy (CLSM). Optimizing the separation of TC and Cal labelings in the alveolar bone was attained by the simultaneous use of ultraviolet (364 nm) and argon (488 nm) laser sources for excitation of TC and Cal, respectively. Cal labeling, indicative of new bone deposition showed two distinct patterns: lamination at the periodontal surface and rings circumscribing the vascular canal. The cementum surface also exhibited active deposition during the experimental period. Bone formation was affected by slight changes in magnitude and direction of orthodontic or occlusal forces. CLSM is valuable in deciphering the process of alveolar bone remodeling.