Cranial suture biology and dental development: genetic and clinical perspectives

Cranial trephination and infectious disease in the Eastern Mediterranean: The evidence from two elite brothers from Late Bronze Megiddo, Israel

Here we present the paleopathological profiles of two young adult males, identified as brothers through ancient DNA analysis, who were buried together beneath the floor of an elite early Late Bronze Age I (ca. 1550-1450 BC) domestic structure at the urban center of Megiddo (modern Israel). Both individuals displayed uncommon morphological variants related to developmental conditions, and each exhibited extensive bone remodeling consistent with chronic infectious disease. Additionally, one brother had a healed fracture of the nose, as well as a large square piece of bone cut from the frontal bone (cranial trephination). We consider the potential etiologies for the appearance of the skeletal anomalies and lesions. Based on the bioarchaeological context, we propose that a shared epigenetic landscape predisposed the brothers to acquiring an infectious disease and their elite status privileged them enough to endure it. We then contextualize these potential illnesses and disorders with the trephination procedure. The infrequency of trephination in the region indicates that only selected individuals could access such a procedure, and the severity of the pathological lesions suggests the procedure was possibly intended as curative to deteriorating health. Ultimately, both brothers were buried with the same rites as others in their community, thus demonstrating their continued integration in society even after death.

Evaluation of dental maturity in Muenke syndrome, Saethre-Chotzen syndrome, and TCF12-related craniosynostosis

OBJECTIVES

To determine whether dental maturity (dental development) was delayed in patients with Muenke syndrome, Saethre-Chotzen syndrome, and TCF12-related craniosynostosis, compared with a Dutch control group without syndromes.

MATERIALS AND METHODS

This study included 60 patients (38 patients with Muenke syndrome, 17 patients with Saethre-Chotzen syndrome, and 5 with TCF12-related craniosynostosis), aged 5.8-16.8 years that were treated at the Department of Oral Maxillofacial Surgery, Special Dental Care, and Orthodontics, in Sophia Children's Hospital, Erasmus University Medical Center, Rotterdam, the Netherlands. Dental age was calculated according to Demirjian's index of dental maturity. The control group included 451 children without a syndrome.

RESULTS

Compared with the control group, dental development was delayed by an average of one year in 5- to 8-year-old patients with Muenke syndrome (P = 0.007) and in 8- to 10-year-old patients with Saethre-Chotzen syndrome (P = 0.044), but not in patients with TCF12-related craniosynostosis.

CONCLUSIONS

Our results indicated that dental development was delayed by one year, on average, in patients with Muenke syndrome and Saethre-Chotzen syndrome, compared with a Dutch control group without syndromes.

IMPLICATIONS

Our findings have improved the understanding of dental development in patients with Muenke and Saethre-Chotzen syndrome. These results can provide guidance on whether the orthodontist needs to consider growth disturbances related to dental development.

Influences of the IL-6 cytokine family on bone structure and function

The IL-6 family of cytokines comprises a large group of cytokines that all act via the formation of a signaling complex that includes the glycoprotein 130 (gp130) receptor. Despite this, many of these cytokines have unique roles that regulate the activity of bone forming osteoblasts, bone resorbing osteoclasts, bone-resident osteocytes, and cartilage cells (chondrocytes). These include specific functions in craniofacial development, longitudinal bone growth, and the maintenance of trabecular and cortical bone structure, and have been implicated in musculoskeletal pathologies such as craniosynostosis, osteoporosis, rheumatoid arthritis, osteoarthritis, and heterotopic ossifications. This review will work systematically through each member of this family and provide an overview and an update on the expression patterns and functions of each of these cytokines in the skeleton, as well as their negative feedback pathways, particularly suppressor of cytokine signaling 3 (SOCS3). The specific cytokines described are interleukin 6 (IL-6), interleukin 11 (IL-11), oncostatin M (OSM), leukemia inhibitory factor (LIF), cardiotrophin 1 (CT-1), ciliary neurotrophic factor (CNTF), cardiotrophin-like cytokine factor 1 (CLCF1), neuropoietin, humanin and interleukin 27 (IL-27).

Non-syndromic craniosynostosis in children: Scoping review

BACKGROUND

Craniosynostosis (CS) is a complex condition consisting of the early fusion of one or more cranial sutures in the intrauterine stage. The affected infant exhibits abnormal head shape at time of birth or shortly thereafter. It can be observed in normal individuals (non-syndromic CS or NSCS) or as a part of a multisystem syndrome. The purposes of the present article were to carry out a scoping review on Non-Syndromic CS and to discuss the most important findings retrieved.

MATERIAL AND METHODS

The steps of this scoping review were as follows: first, to pose a research question; second, to identify relevant studies to answer the research question; third, to select and retrieve the studies; fourth, to chart the critical data, and finally, to collate, summarize, and report the results from the most important articles. Relevant articles published over a 20-year period were identified and retrieved from five Internet databases: PubMed; EMBASE; Cochrane Library; Google Scholar, and EBSCO.

RESULTS

Fourteen articles were finally included in the present scoping review. The following four most important clinical issues are discussed: (i) normal cranial development, clinical manifestations, and pathogenesis of NCSC; (ii) clinical evaluation of NCSC; (iii) treatment and post-surgical follow-up; and (iv) additional considerations.

CONCLUSIONS

NSCS may be present with associated head shapes. Multiple early surgical reconstructive options are currently available for the disorder. Pediatric Dentistry practitioners must be familiarized with this condition and form part of a multi-approach health team as those responsible for the opportune oral health care of the affected child.

Multiple supernumerary teeth in a likely syndromic individual from prehistoric Illinois

OBJECTIVE

This paper reports the first published case of a prehistoric human with five or more supernumerary teeth. Such cases are often neglected in paleopathology, in part due to a gap between the medicodental and anthropological literature leading to the view in anthropology that supernumerary teeth are curious anomalies rather than pathologies.

DESIGN

Reconstruction and pathological description of the skeletal remains were performed according to standard osteological protocols. Each supernumerary tooth was categorized based on its morphology, location, and orientation. The dental characteristics of the individual were compared to published norms for incidences of syndromic and non-syndromic supernumerary teeth and a differential diagnosis was subsequently performed.

RESULTS

Six supernumerary teeth and one deciduous tooth were identified. Additionally, the individual suffered from impacted teeth, dilacerated roots, and extensive sutural anomalies (including retention of the metopic suture into adulthood and an unusually high number of sutural bones). The morphology and location of the supernumerary teeth, in conjunction with the suite of other symptoms, are highly unusual among non-syndromic patients and therefore are indicative of a complex genetic disorder.

CONCLUSIONS

The individual reported here almost certainly suffered from a genetic disorder or syndrome resulting in extensive dental and sutural abnormalities. Despite a lack of post-cranial involvement, a tentative diagnosis of Cleidocranial Dysplasia was made on the basis that mutations in the RUNX2 gene may cause the dental symptoms without any pathology of the clavicle.

Craniofacial Tissue Engineering

The craniofacial complex is composed of fundamental components such as blood vessels and nerves, and also a variety of specialized tissues such as craniofacial bones, cartilages, muscles, ligaments, and the highly specialized and unique organs, the teeth. Together, these structures provide many functions including speech, mastication, and aesthetics of the craniofacial complex. Craniofacial defects not only influence the structure and function of the jaws and face, but may also result in deleterious psychosocial issues, emphasizing the need for rapid and effective, precise, and aesthetic reconstruction of craniofacial tissues. In a broad sense, craniofacial tissue reconstructions share many of the same issues as noncraniofacial tissue reconstructions. Therefore, many concepts and therapies for general tissue engineering can and have been used for craniofacial tissue regeneration. Still, repair of craniofacial defects presents unique challenges, mainly because of their complex and unique 3D geometry.

Evaluation of the maxillofacial morphological characteristics of Apert syndrome infants

Apert syndrome is a rare craniosynostosis syndrome characterized by irregular craniosynostosis, midface hypoplasia, and syndactyly of the hands and feet. Previous studies analyzed individuals with Apert syndrome and reported some facial and intraoral features caused by severe maxillary hypoplasia. However, these studies were performed by analyzing both individuals who had and those had not received a palate repair surgery, which had a high impact on the maxillary growth and occlusion. To highlight the intrinsic facial and intraoral features of Apert syndrome, five Japanese individuals with Apert syndrome from 5 years and 2 months to 9 years and 10 months without cleft palate were analyzed in this study. A concave profile and a skeletal Class III jaw-base relationship caused by severe maxillary hypoplasia were seen in all patients. The patients exhibited anterior and posterior crossbites possibly due to a small dental arch of Maxilla.

Tooth agenesis and orofacial clefting: genetic brothers in arms?

Tooth agenesis and orofacial clefts represent the most common developmental anomalies and their co-occurrence is often reported in patients as well in animal models. The aim of the present systematic review is to thoroughly investigate the current literature (PubMed, EMBASE) to identify the genes and genomic loci contributing to syndromic or non-syndromic co-occurrence of tooth agenesis and orofacial clefts, to gain insight into the molecular mechanisms underlying their dual involvement in the development of teeth and facial primordia. Altogether, 84 articles including phenotype and genotype description provided 9 genomic loci and 26 gene candidates underlying the co-occurrence of the two congenital defects: MSX1, PAX9, IRF6, TP63, KMT2D, KDM6A, SATB2, TBX22, TGFα, TGFβ3, TGFβR1, TGFβR2, FGF8, FGFR1, KISS1R, WNT3, WNT5A, CDH1, CHD7, AXIN2, TWIST1, BCOR, OFD1, PTCH1, PITX2, and PVRL1. The molecular pathways, cellular functions, tissue-specific expression and disease association were investigated using publicly accessible databases (EntrezGene, UniProt, OMIM). The Gene Ontology terms of the biological processes mediated by the candidate genes were used to cluster them using the GOTermMapper (Lewis-Sigler Institute, Princeton University), speculating on six super-clusters: (a) anatomical development, (b) cell division, growth and motility, (c) cell metabolism and catabolism, (d) cell transport, (e) cell structure organization and (f) organ/system-specific processes. This review aims to increase the knowledge on the mechanisms underlying the co-occurrence of tooth agenesis and orofacial clefts, to pave the way for improving targeted (prenatal) molecular diagnosis and finally to reflect on therapeutic or ultimately preventive strategies for these disabling conditions in the future.

Occlusal Relations in Patients With Scaphocephaly

Scaphocephaly results from a premature fusion of the sagittal suture. Usually, cranial vault corrective surgery is performed during the first year of life. There is currently no scientific data regarding occlusion of scaphocephalic patients, or the potential effect of craniovault surgery on the occlusion. The aims were to describe occlusion in scaphocephalic patients and compare with a general pediatric population, and to compare the difference in occlusion of surgically versus unoperated treated scaphocephalic subgroup. A total of 91 scaphocephalic patients (71 boys aged between 2 and 11 y) seen at the Craniofacial Clinic of CHU Ste-Justine's formed the experimental group. All patients received an orthodontic assessment. Among them, 44 underwent craniovault surgery, whereas 47 remained unoperated. Thirty-eight (33 boys; 17 operated) had lateral cephalometric radiographies, some of them also had cephalometric growth follow-ups. Clinical values for dental classification and overjet indicate an increased prevalence of class II malocclusions in scaphocephalic patients. However, interestingly enough, cephalometric values indicative of skeletal class II malocclusions (ie, N-A perp HP, N-B perp HP, N-Pog perp HP, Wits, N-A-Pog) remained within normal limits. Some cephalometric values present statistically significant differences between operated and unoperated patients (ANS-PNS t2, P = 0.025; /1-FH t2, P = 0.028), but these are individual variations not related to scaphocephaly. Maxillary width of scaphocephalic children remains within normal limits. Scaphocephalic patients clinically presented more class II malocclusions compared with normal children. Radiographic values remain, however, within normal limits for both anteroposterior and transverse dimensions. Corrective craniovault surgery did not affect occlusion in these patients.

The dental development in patients with Aperts syndrome

OBJECTIVES

The aim of this retrospective study was to quantify the level of dental developmental delay in a group of patients with Aperts syndrome when compared to matched controls.

METHODS

Twenty-six Dental Panoramic Tomographic (DPT) radiographs of patients with Apert syndrome attending Great Ormond Street Hospital were compared to controls (n = 29) from the Eastman Dental Hospital, UK. Dental development was assessed using the staging systems of Demirjian and Haavikko, and dental age (DA) was estimated using the weighted averages method.

RESULTS

Dental age, as estimated using the 12 stages of Haavikko and eight stages of Demirjian, suggested no statistical evidence of developmental delay between the Aperts and control group.

CONCLUSIONS

The hypothesis 'that there is no difference in the dental development of subjects with Apert syndrome, when compared to a group of matched controls', was accepted.

Preclinical evidence of potential craniofacial adverse effect of zoledronic acid in pediatric patients with bone malignancies

High doses of zoledronic acid (ZOL), one of the most potent inhibitors of bone resorption, are currently evaluated in phase III clinical trials in Europe for the treatment of malignant pediatric primary bone tumors. The impact of such an intensive treatment on the craniofacial skeleton growth is a critical question in the context of patients with actively growing skeleton; in particular, in light of our previous studies evidencing that endochondral bone formation was transiently disturbed by high doses of ZOL. Two protocols adapted from pediatric treatments were developed for newborn mice (a total of 5 or 10 injections of ZOL 50μg/kg every two days). Their impact on skull bones and teeth growth was analyzed by X-rays, microCT and histology up to 3months after the last injection. ZOL administrations induced a transient delay of skull bone growth and an irreversible delay in incisor, first molar eruption and root elongation. Other teeth were affected, but most were erupted by 3months. Root histogenesis was severely impacted for all molars and massive odontogenic tumor-like structures were observed in all mandibular incisors. High doses of ZOL irreversibly disturbed teeth eruption and elongation, and delayed skull bone formation. These preclinical observations are essential for the follow-up of onco-pediatric patients treated with ZOL.

Dental Maturation in Children with the Syndrome of Crouzon and Apert

Purpose

Developing teeth are used to assess maturity and estimate age in a number of disciplines. The purpose of this investigation was to study the dental maturation in children with Crouzon or Apert syndrome compared with nonsyndromic controls.

Patients and Methods

Records of 40 children with Crouzon syndrome (18 boys and 22 girls, aged 4.0 to 17.9 years) and 28 children with Apert syndrome (10 boys and 18 girls, aged 3.9 to 15.1 years) were referred to the Department of Orthodontics, Cleft Palate Team and Craniofacial Team, Erasmus MC–Sophia. Data from syndromic children were compared with data from 451 nonsyndromic children (225 boys and 226 girls, aged 2.9 to 16.9 years). From panoramic radiographs, dental maturation was determined for patients with Crouzon and Apert syndromes and compared with data collected from control children. Logistic functions were constructed for dental maturation over time for syndromes and gender.

Results

Statistically significant gender differences in dental maturation scores were found for girls with Crouzon ( P < .05) and Apert syndrome ( P < .05). Patients with Apert syndrome demonstrated a significantly delayed dental maturation ( P < .05), while patients with Crouzon syndrome showed a nonsignificant delay.

Conclusions

Dental maturation in patients with Apert syndrome was more delayed than in patients with Crouzon syndrome. The delay of tooth formation in patients with Crouzon or Apert syndrome suggests a possible common genetic association.

Msx1 role in craniofacial bone morphogenesis

The homeobox gene Msx1 encodes a transcription factor that is highly expressed during embryogenesis and postnatal development in bone. Mutations of the MSX1 gene in humans are associated with cleft palate and (or) tooth agenesis. A similar phenotype is observed in newborn mice invalidated for the Msx1 gene. However, little is known about Msx1 function in osteoblast differentiation and bone mineralization in vivo. In the present study, we aimed to explore the variations of individualized bone shape in a subtle way avoiding the often severe consequences associated with gene mutations. We established transgenic mice that specifically express Msx1 in mineral-matrix-secreting cells under the control of the mouse 2.3kb collagen 1 alpha 1 (Col1α1) promoter, which enabled us to investigate Msx1 function in bone in vivo. Adult transgenic mice (Msx1-Tg) presented altered skull shape and mineralization resulting from increased Msx1 expression during bone development. Serial section analysis of the mandibles showed a high amount of bone matrix in these mice. In addition, osteoblast number, cell proliferation and apoptosis were higher in Msx1-Tg mice than in controls with regional differences that could account for alterations of bone shape. However, Von Kossa staining and μCT analysis showed that bone mineralization was lower in Msx1-Tg mice than in controls due to alteration of osteoblastic differentiation. Msx1 appears to act as a modeling factor for membranous bone; it stimulates trabecular bone metabolism but limits cortical bone growth by promoting apoptosis, and concomitantly controls the collagen-based mineralization process.

PAX9 polymorphism and susceptibility to sporadic non-syndromic severe anodontia: a case-control study in southwest China

Our research aimed to look into the clinical traits and genetic mutations in sporadic non-syndromic anodontia and to gain insight into the role of mutations of PAX9, MSX1, AXIN2 and EDA in anodontia phenotypes, especially for the PAX9.

Initiation of early osteoblast differentiation events through the direct transcriptional regulation of Msx2 by FOXC1

Hierarchal transcriptional regulatory networks function to control the correct spatiotemporal patterning of the mammalian skeletal system. One such factor, the forkhead box transcription factor FOXC1 is necessary for the correct formation of the axial and craniofacial skeleton. Previous studies have demonstrated that the frontal and parietal bones of the skull fail to develop in mice deficient for Foxc1. Furthermore expression of the Msx2 homeobox gene, an essential regulator of calvarial bone development is absent in the skull mesenchymal progenitors of Foxc1 mutant mice. Thus we sought to determine whether Msx2 was a direct target of FOXC1 transcriptional regulation. Here, we demonstrate that elevated expression of FOXC1 can increase endogenous Msx2 mRNA levels. Chromatin immunoprecipitation experiments reveal that FOXC1 occupies a conserved element in the MSX2 promoter. Using a luciferase reporter assay, we demonstrate that FOXC1 can stimulate the activity of the both human and mouse MSX2 promoters. We also report that reducing FOXC1 levels by RNA interference leads to a decrease in MSX2 expression. Finally, we demonstrate that heterologous expression of Foxc1 in C2C12 cells results in elevated alkaline phosphatase activity and increased expression of Runx2 and Msx2. These data indicate that Foxc1 expression leads to a similar enhanced osteogenic differentiation phenotype as observed with Msx2 overexpression. Together these findings suggest that a Foxc1->Msx2 regulatory network functions in the initial stages of osteoblast differentiation.

Patterns of tooth agenesis in patients with crouzon or apert syndrome

PURPOSE

Dental agenesis is the most common anomaly of dental development and can be a component of a congenital syndrome. The purpose of this study was to evaluate the prevalence of agenesis and to describe patterns of tooth agenesis in patients with Crouzon or Apert syndrome compared with nonsyndromic controls.

PATIENTS AND METHODS

Longitudinal records of 67 patients with Crouzon syndrome (n = 39) or Apert syndrome (n = 28) from the Erasmus Medical Centre were examined. Syndromic patients were compared with patients in a nonsyndromic control group (n = 284).

RESULTS

Prevalence of tooth agenesis in patients with Crouzon syndrome (35.9%) and patients with Apert syndrome (46.4%) was significantly higher than the prevalence in control subjects (27.5%) (P < .005). In all groups third molars were the most likely to be agenetic. Tooth agenesis excluding third molars was significantly higher in syndromic patients than in control subjects (P < .001). Bilateral agenesis of mandibular second premolars occurred significantly more often in patients with Crouzon and Apert syndrome than in control subjects (P < .001).

CONCLUSIONS

Tooth agenesis is more prevalent in patients with Crouzon or Apert syndrome than in control subjects. Tooth agenesis and mandibular symmetrical patterns of second premolar agenesis are more prevalent in syndromic patients.

Dental approach to craniofacial syndromes: how can developmental fields show us a new way to understand pathogenesis?

The paper consists of three parts. Part 1: Definition of Syndromes. Focus is given to craniofacial syndromes in which abnormal traits in the dentition are associated symptoms. In the last decade, research has concentrated on phenotype, genotype, growth, development, function, and treatment. Part 2: Syndromes before Birth. How can the initial malformation sites in these syndromes be studied and what can we learn from it? In this section, deviations observed in syndromes prenatally will be highlighted and compared to the normal human embryological craniofacial development. Specific focus will be given to developmental fields studied on animal tissue and transferred to human cranial development. Part 3: Developmental Fields Affected in Two Craniofacial Syndromes. Analysis of primary and permanent dentitions can determine whether a syndrome affects a single craniofacial field or several fields. This distinction is essential for insight into craniofacial syndromes. The dentition, thus, becomes central in diagnostics and evaluation of the pathogenesis. Developmental fields can explore and advance the concept of dental approaches to craniofacial syndromes. Discussion. As deviations in teeth persist and do not reorganize during growth and development, the dentition is considered useful for distinguishing between syndrome pathogenesis manifested in a single developmental field and in several fields.

Craniosynostosis in pycnodysostosis: broadening the spectrum of the cranial flat bone abnormalities

Pycnodysostosis is a rare autosomal recessive skeletal dysplasia caused by the absence of active cathepsin K, which is a lysosomal cysteine protease that plays a role in degrading the organic matrix of bones, acting in bone resorption and bone remodeling. The disease is primarily characterized by osteosclerosis, bone fragility, short stature, acro-osteolysis, and delayed closure of the cranial sutures. A differing feature, cranial synostosis, has occasionally been described in this disorder. We reviewed six unrelated patients with pycnodysostosis (mean age of 10 years and 4 months) in order to evaluate the presence of craniosynostosis. In addition to the typical findings of the condition, they all presented premature fusion of the coronal suture. Although none of them showed signs of cranial hypertension, one patient had had the craniosynostosis surgically corrected previously. These data suggest that the cranial sutures in pycnodysostosis can display contradictory features: wide cranial sutures, which are commonly described, and craniosynostosis. The clinical impact of this latter finding still remains to be elucidated. Further studies are necessary to address more precisely the role of cathepsin K in suture patency.

Osteogenic potential of mandibular vs. long-bone marrow stromal cells

Although fundamentally similar to other bones, the jaws demonstrate discrete responses to developmental, mechanical, and homeostatic regulatory signals. Here, we hypothesized that rat mandible vs. long-bone marrow-derived cells possess different osteogenic potential. We established a protocol for rat mandible and long-bone marrow stromal cell (BMSC) isolation and culture. Mandible BMSC cultures formed more colonies, suggesting an increased CFU-F population. Both mandible and long-bone BMSCs differentiated into osteoblasts. However, mandible BMSCs demonstrated augmented alkaline phosphatase activity, mineralization, and osteoblast gene expression. Importantly, upon implantation into nude mice, mandible BMSCs formed 70% larger bone nodules containing three-fold more mineralized bone compared with long-bone BMSCs. Analysis of these data demonstrates an increased osteogenic potential and augmented capacity of mandible BMSCs to induce bone formation in vitro and in vivo. Our findings support differences in the mechanisms underlying mandible homeostasis and the pathophysiology of diseases unique to the jaws.

Recognizing craniosynostosis

Craniosynostosis is characterized by the fusion of sutures. It presents with an abnormal head shape. This article examines this defect and discusses its embryologic origin. A systemic physical assessment guide serves as a tool to enhance early recognition of this defect. Pictorial examples increase understanding of the defect. A discussion of treatment and nursing implications, with an emphasis on family support, is provided.

Mechanism of skull suture maintenance and interdigitation

Skull sutures serve as growth centers whose function involves multiple molecular pathways. During periods of brain growth the sutures remain thin and straight, later developing complex fractal interdigitations that provide interlocking strength. The nature of the relationship between the molecular interactions and suture pattern formation is not understood. Here we show that by classifying the molecules involved into two groups, stabilizing factors and substrate molecules, complex molecular networks can be modeled by a simple two-species reaction-diffusion model that recapitulates all the known behavior of suture pattern formation. This model reproduces the maintenance of thin sutural tissue at early stages, the later modification of the straight suture to form osseous interdigitations, and the formation of fractal structures. Predictions from the model are in good agreement with experimental observations, indicating that the model captures the essential nature of the interdigitation process.

Osteoclasts have multiple roles in bone in addition to bone resorption

Osteoclasts are the cells that degrade bone to initiate normal bone remodeling and mediate bone loss in pathologic conditions by increasing their resorptive activity. They are derived from precursors in the myeloid/ monocyte lineage that circulate in the blood after their formation in the bone marrow. These osteoclast precursors (OCPs) are attracted to sites on bone surfaces destined for resorption and fuse with one another to form the multinucleated cells that resorb calcified matrixes under the influence of osteoblastic cells in bone marrow. Recent studies have identified functions for OCPs and osteoclasts in and around bone other than bone resorption. For example, they regulate the differentiation of osteoblast precursors and the movement of hematopoietic stem cells from the bone marrow to the bloodstream; they participate in immune responses, and secrete cytokines that can affect their own functions and those of other cells in inflammatory and neoplastic processes affecting bone. Here, we review these findings, which define new roles for osteoclasts and OCPs in the growing field of osteoimmunology and in common pathologic conditions in which bone resorption is increased.

Dental agenesis: genetic and clinical perspectives

Dental agenesis is the most common developmental anomaly in humans and is frequently associated with several other oral abnormalities. Whereas the incidence of missing teeth may vary considerably depending on dentition, gender, and demographic or geographic profiles, distinct patterns of agenesis have been detected in the permanent dentition. These frequently involve the last teeth of a class to develop (I2, P2, M3) suggesting a possible link with evolutionary trends. Hypodontia can either occur as an isolated condition (non-syndromic hypodontia) involving one (80% of cases), a few (less than 10%) or many teeth (less than 1%), or can be associated with a systemic condition or syndrome (syndromic hypodontia), essentially reflecting the genetically and phenotypically heterogeneity of the condition. Based on our present knowledge of genes and transcription factors that are involved in tooth development, it is assumed that different phenotypic forms are caused by different genes involving different interacting molecular pathways, providing an explanation not only for the wide variety in agenesis patterns but also for associations of dental agenesis with other oral anomalies. At present, the list of genes involved in human non-syndromic hypodontia includes not only those encoding a signaling molecule (TGFA) and transcription factors (MSX1 and PAX9) that play critical roles during early craniofacial development, but also genes coding for a protein involved in canonical Wnt signaling (AXIN2), and a transmembrane receptor of fibroblast growth factors (FGFR1). Our objective was to review the current literature on the molecular mechanisms that are responsible for selective dental agenesis in humans and to present a detailed overview of syndromes with hypodontia and their causative genes. These new perspectives and future challenges in the field of identification of possible candidate genes involved in dental agenesis are discussed.

Memory encoded throughout our bodies: molecular and cellular basis of tissue regeneration

When a sheep loses its tail, it cannot regenerate it in the manner of lizards. On the other hand, it is possible to clone mammals from somatic cells, showing that a complete developmental program is intact in a wounded sheep's tail the same way it is in a lizard. Thus, there is a requirement for more than only the presence of the entire genetic code in somatic cells for regenerative abilities. Thoughts like this have motivated us to assemble more than just a factographic synopsis on tissue regeneration. As a model, we review skin wound healing in chronological order, and when possible, we use that overview as a framework to point out possible mechanisms of how damaged tissues can restore their original structure. This article postulates the existence of tissue structural memory as a complex distributed homeostatic mechanism. We support such an idea by referring to an extremely fragmented literature base, trying to synthesize a broad picture of important principles of how tissues and organs may store information about their own structure for the purposes of regeneration. Selected developmental, surgical, and tissue engineering aspects are presented and discussed in the light of recent findings in the field. When a sheep loses its tail, it cannot regenerate it in the manner of lizards. On the other hand, it is possible to clone mammals from somatic cells, showing that a complete developmental program is intact in a wounded sheep's tail the same way it is in a lizard. Thus, there is a requirement for more than only the presence of the entire genetic code in somatic cells for regenerative abilities. Thoughts like this have motivated us to assemble more than just a factographic synopsis on tissue regeneration. As a model, we review skin wound healing in chronological order, and when possible, we use that overview as a framework to point out possible mechanisms of how damaged tissues can restore their original structure. This article postulates the existence of tissue structural memory as a complex distributed homeostatic mechanism. We support such an idea by referring to an extremely fragmented literature base, trying to synthesize a broad picture of important principles of how tissues and organs may store information about their own structure for the purposes of regeneration. Selected developmental, surgical, and tissue engineering aspects are presented and discussed in the light of recent findings in the field.