Hydrodynamic properties of biomimetic shark skin: effect of denticle size and swimming speed.

Biomechanists and biologists alike have yet to fully understand the complex morphology and function of shark denticles, morphologically intricate tooth-like structures embedded into the skin of sharks. Denticles vary in many ways (such as size and shape) depending on shark species, and studies on denticle hydrodynamics have suggested that they may aid in drag reduction as well as increase both lift and thrust. Although previous studies have analyzed the effect of different denticle patterns on hydrodynamic performance, no previous work has focused on the effects of denticle size. Here, we report on the hydrodynamic properties of 3D printed shark skin foils with rigid denticles embedded into a flexible substrate. The patterning of these denticles was based on previously reported designs exhibiting the greatest hydrodynamic performance (which also most closely mimics real shark skin). The size of the denticles and the speed of the flow were varied, and the foils were evaluated under both static and dynamic conditions. Static tests showed drag reduction compared to a smooth control foil (without denticles) for the smallest denticle size, while medium and large denticles exhibited increased drag. Under dynamic testing conditions, the smallest denticles increased the self-propelled swimming speed, while the largest denticles reduced swimming performance. At higher speeds, the smallest denticles were also able to reduce power consumption compared to the control, demonstrating that their hydrodynamic effect depends on both denticle size and swimming speed. Our results thus provide new insights into the role of denticle size in shark swimming hydrodynamics across a range of locomotory modes, while simultaneously providing new design guidelines for the production of high performance low drag surface coatings for aquatic and aerospace applications.

Pulp stones: a review.

Pulp stones are a frequent finding on bitewing and periapical radiographs but receive relatively little attention in textbooks. A review of the literature was therefore performed, initially using the PubMed database and beginning the search with 'pulp calcifications' and 'pulp stones'. Each term provided more than 400 references, many of which related to pulp calcification in general rather than pulp stones, and focussed largely on the problems these changes presented to clinicians. A manual search using references from this source was carried out. Contemporary textbooks in endodontology were also consulted, and an historic perspective gained from a number of older books and references. The factors involved in the development of the pulp stones are largely unknown. Further research may determine the reasons for their formation, but with current endodontic instruments and techniques this is unlikely to alter their relevance to clinicians.

A novel role for Twist-1 in pulp homeostasis.

The molecular mechanisms that maintain the equilibrium of odontoblast progenitor cells in dental pulp are unknown. Here we tested whether homeostasis in dental pulp is modulated by Twist-1, a nuclear protein that partners with Runx2 during osteoblast differentiation. Our analysis of Twist-1(+/-) mice revealed phenotypic changes that involved an earlier onset of dentin matrix formation, increased alkaline phosphatase activity, and pulp stones within the pulp. RT-PCR analyses revealed Twist-1 expression in several adult organs, including pulp. Decreased levels of Twist-1 led to higher levels of type I collagen and Dspp gene expression in perivascular cells associated with the pulp stones. In mice heterozygous for both Twist-1 and Runx2 inactivation, the phenotype of pulp stones appeared completely rescued. These findings suggest that Twist-1 plays a key role in restraining odontoblast differentiation, thus maintaining homeostasis in dental pulp. Furthermore, Twist-1 functions in dental pulp are dependent on its interaction with Runx2.

A clinical classification of the status of the pulp and the root canal system.

Many different classification systems have been advocated for pulp diseases. However, most of them are based on histopathological findings rather than clinical findings which leads to confusion since there is little correlation between them. Most classifications mix clinical and histological terms resulting in misleading terminology and diagnoses. This in turn leads to further confusion and uncertainty in clinical practice when a rational treatment plan needs to be established in order to manage a specific pathological entity. A simple, yet practical classification of pulp diseases which uses terminology related to clinical findings is proposed. This classification will help clinicians understand the progressive nature of the pulp disease processes and direct them to the most appropriate and conservative treatment strategy for each condition. With a comprehensive knowledge of the pathophysiology of pain and inflammation in the pulp tissues, clinicians may accomplish this task with confidence.

Stimulatory effects of hydroxyl radical generation by Ga-Al-As laser irradiation on mineralization ability of human dental pulp cells.

The present study was conducted to investigate the effects of Ga-Al-As laser irradiation on the mineralization ability of human dental pulp (HDP) cells. HDP cells in vitro were irradiated once with a Ga-AL-As laser at 0.5 W for 500 s and at 1.0 W for 500 s in order to investigate free radicals as one mechanism for transmission of laser photochemical energy to cells. Production of the hydroxyl radical (*OH) was measured using the ESR spin-trapping method and was found to be increased by laser irradiation. The DMPO-OH was not detected in the presence of dimethyl sulfoxide (DMSO), a *OH scavenger. The formation of calcification nodule was also investigated by von Kossa staining. The number of calcified nodules was increased by 1.0 W-laser irradiation. Alkaline phosphatase (ALP) activity was higher in the 1.0 W-laser irradiation group. Expression of mRNAs for heat shock protein 27, bone morphogenetic proteins (BMPs) and ALP were greater in the 1.0 W-laser irradiation group. Expression of BMPs in the conditioned medium was also higher in the 1.0 W-laser irradiation group. In particular, DMSO decreased the number of calcified nodule produced by 1.0 W-laser irradiation. These results supposed that the mineralization of HDP cells is stimulated by laser irradiation, and that *OH generated by laser irradiation is a trigger for promotion of HDP cell mineralization.

Human dental pulp cell culture and cell transplantation with an alginate scaffold.

Many studies on tissue stem cells have been conducted in the field of regenerative medicine, and some studies have indicated that cultured dental pulp mesenchymal cells secrete dentin matrix. In the present study we used alginate as a scaffold to transplant subcultured human dental pulp cells subcutaneously into the backs of nude mice. We found that when beta-glycerophosphate was added to the culture medium, dentin sialophosphoprotein mRNA coding dentin sialoprotein (DSP) was expressed. An increase in alkaline phosphatase, which is an early marker for odontoblast differentiation, was also demonstrated. At 6 weeks after implantation the subcutaneous formation of radio-opaque calcified bodies was observed in situ. Immunohistochemical and fine structure studies identified expression of type I collagen, type III collagen, and DSP in the mineralizing transplants. Isolated odontoblast-like cells initiated dentin-like hard tissue formation and scattered autolyzing apoptotic cells were also observed in the transplants. The study showed that subcultured dental pulp cells actively differentiate into odontoblast-like cells and induce calcification in an alginate scaffold.

O processo de calcificaçäo pulpar / The process of pulpal calcification

Ao longo do tempo, a polpa dentária sofre alteraçöes decorrentes da própria fisiologia pulpar frente ao processo de envelhecimento tecidual e em reposta a estímulos irritantes, tais como cárie, doença periodontal, traumatismos ou procediemntos de restauraçöes dentárias. Essas alteraçöes variam conforme estímulo. Ocorre deposiçäo de tecido mineralizado, tanto na periferia da câmara pulpar, como no interior do tecido conjuntivo pulpar sob a forma de nódulos. Isso acarreta uma reduçäo progressiva no espaço pulpar, podendo levar ao fechamento total do canal radicular, isquemia pulpar, necrose e osteíte periapical. Frente ao trauma do feixe vásculo-nervoso apical, indica-se controle radiográfico periódico e a necessidade de intervençäo endodôntica quando houver diminuiçäo do volume do canal comparado ao elemento vizinho

[Pitfalls to avoid in the cleaning and shaping of the pulp canal]. / Pièges à éviter lors du nettoyage et de la mise en forme de la cavité pulpaire.

Chemomechanical instrumentation of the root canal system is without doubt the most important but most challenging part of endodontic treatment. The first essential in cleaning and shaping is gaining direct access to the root canals. A properly prepared endodontic access opening can eliminate many of the technical problems encountered in root canal treatment. Excessive calcification in the root canal system and performing root canal treatment through existing artificial crowns however can be a challenge for the clinician. Secondly, enlargement of a curved root canal often results in loss of working length, incomplete removal or extrusion of the root canal content and unwanted alterations in the canal shape, such as transportation (stripping, zipping, elbow formation), ledge formation and perforation. This article focuses on the causes and effects of procedural errors during root canal cleaning and shaping. Each of these complications is addressed in a manner designed to prevent problems rather than to manage them once they are recognized. Throughout the immense amount of literature published the last 30 years on this topic, concensus is obtained concerning the preferential procedure of cleaning and shaping the root canal.

Evaluación clínica y radiográfica de autotrasplantes y reposiciones dentales / Clinical and radiographic evaluation of autotransplantations and dental repositions

Se realizó un estudio prospectivo de 8 autotrasplantes y 2 reposiciones dentales en 8 pacientes que consultaron entre agosto de 1994 y abril de 1996, los que se controlaron en el período de un año. Se evaluaron parámetros clínicos como dolor, cambio de color, sangrado, movilidad e índice de Russell, también se evaluaron parámetros radiográficos como espacio del ligamento periodontal, reabsorción radicular interna y externa, obliteración de la cámara pulpar y estadio de desarrollo radicular. Todos los casos se realizaron de diferentes dientes donantes a diferentes sitios receptores, notándose que los autotrasplantes más frecuentemente realizados son del tercer molar al primer molar y las reposiciones en zona de premolares. La tasa de supervivencia fue del 100 por ciento a los seis meses y del 75 por ciento a los 12 meses, teniendo en cuenta que no todos los casos han completado los períodos de control. Uno de los autotrasplantes no sobrevivió aunque se le intentó realizar tratamiento pulpar con hidróxido de calcio. Los resultados iniciales de este estudio piloto demuestran que los autotrasplantes y las reposiciones dentales son alternativas de tratamiento con altos porcentajes de éxito en caso de pérdida dentaria o alteración en la erupción por malposición

Iatrogenia en endodoncia / Iatrogenia in endodontics

Ya sea por descuido, falta de atención o prisa, el profesional puede ocasionar alguna iatrogenia que irá a dificultar la limpieza de los conductos así como la correcta obturación

Characteristics and effects of calcified degenerative zones on the formation of hard tissue barriers in amputated canine dental pulp.

The purpose of this research was to study under undecalcified conditions the presence, ultrastructural features, and contributions of the degenerative zone beneath the necrotic zone and whether it had effects on the formation of reparative dentin in canine incisors and premolars. The research was conducted over a period of 14 days after experimental pulpotomy using calcium hydroxide as a pulp-capping agent. On the first day following pulp exposure and capping with calcium hydroxide, electron-dense spherical bodies were observed under the necrotic zone. Energy dispersive X-ray point analysis confirmed that these electron-dense deposits contained calcium and phosphorus. By the third day, varying amounts of minute von Kossa-positive granules could be observed light-microscopically between the two zones of necrosis and underlying vital pulp tissue. Migration and proliferation of pulpal cells, most probably mesenchymal cells, were observed adjacent to the von Kossa-positive zone. The ultrastructure of the von Kossa-positive zone consisted of degenerated cells, electron-dense spherical bodies, and electron-dense shortened dilating fibrils. By the seventh day, short cylindrical-shaped cells collected at the coronal end of the vital pulp tissue. By the fourteenth day, the specimens having a uniform von Kossa-positive zone exhibited rapid differentiation of odontoblasts and tubular dentin formation. In contrast, only some specimens having an irregular von Kossa-positive zone exhibited osteodentin formation and the beginning of odontoblast differentiation beneath the osteodentin. These findings suggest that this calcified degenerative zone has an important effect on the reparative process of pulp tissue after pulpotomy.

Progressive changes in the pulpo-dentinal complex and their clinical consequences.

With changes in the age structure and oral health in the population, changes in the pulpo-dentinal complex are becoming more relevant clinically. Age-related changes in the structure of dentine and pulp are reviewed. The influence of these changes on restorative dentistry are considered with particular emphasis on endodontics and the use of adhesive restorative materials.

Replantation of 400 avulsed permanent incisors. 2. Factors related to pulpal healing.

Four hundred avulsed and replanted permanent teeth were examined for pulpal healing. In 110 teeth, the apical foramen was either open or half-open. In 16 teeth, the pulps were extirpated prophylactically. Thus, pulpal revascularization was considered possible in 94 teeth. Revascularization occurred in 32 teeth (34%). Pulp necrosis could usually be demonstrated after 3 weeks. Positive pulpal sensibility and radiographis signs of pulp canal obliteration were usually observed after 6 months. The effect of various clinical factors was examined, such as sex, age, type of tooth replanted, stage of root formation, type and length of extra-alveolar storage, clinical contamination of the root surface, type of cleansing procedure of the root surface, type and length of splinting and the use of antibiotics. Finally, the width of the apical foramen and the length of the root canal were measured on radiographs taken at the time of injury. A multivariate statistical analysis revealed that pulpal revascularization was more frequent in teeth with shorter distances from the apical foramen to the pulp horns. Furthermore, that wet storage (saliva and/or saline) for more than 5 min decreased the chance of pulpal revascularization; whereas dry extraalveolar storage had a monotonous effect on pulpal revascularization, i.e. decreasing chance of revasculatization with increasing length of the extraalveolar dry storage. Based on these findings, immediate replantation after brief cleansing in either tap water or saline is recommended.

Age-related changes of the dental pulp complex and their relationship to systemic aging.

The dental pulp and its associated structures, the dentin and the cementum, are discussed. Because many of the age-related pulpal changes have components considered in several of the current theories of aging, these theories are briefly reviewed. Part 2 describes the age-related changes of the dental pulp, the dentin, and the cementum (the dental pulp complex). An attempt is made to differentiate inherent aging changes from physiologic defensive changes and pathologic irritant-induced changes. Part 3 describes the relationship of age-induced changes in the dental pulp complex to components of the current aging theories together with a unified concept of the dental pulp complex aging. Part 4 considers whether dental pulp complex aging can be used as a biomarker for generalized aging. Whether age-related changes of the dental pulp complex can be altered by interventions is discussed.

[Aging of the dental pulp]. / Vieillissement de l'organe pulpo-dentinaire.

During life, the modifications of the dental pulp are important mostly in the root portion. This area, more than the coronal part of the tooth is submitted to involution and histologic dedifferentiation. Fibrosis and calcification occur leading to severe difficulty in performing endodontic treatment.

The effect of aging on tooth morphology: a study on impacted teeth.

The effect of age on dental tissues was studied on histologic sections of totally impacted teeth obtained from patients between 11 and 76 years of age. Impacted teeth were used in order to obviate the influence of the environmental effects prevalent in the oral cavity. The presence of concentric denticles and diffuse calcifications was determined, and the width of secondary dentin, predentin, and cementum was measured. The width of predentin and cementum increased linearly with age, whereas the aging process of secondary dentin formation and diffuse calcifications followed a different pattern. The incidence of concentric denticles was identical for all age groups.