Mechanobiology of orthodontic tooth movement: An update.

The purpose of this review is to provide an update on the changes at the cellular and tissue level occurring during orthodontic force application. For the understanding of this process, knowledge of the mechanobiology of the periodontal ligament and the alveolar bone are essential. The periodontal ligament and alveolar bone make up a functional unit that undergoes robust changes during orthodontic tooth movement. Complex molecular signaling is responsible for converting mechanical stresses into biochemical events with a net result of bone apposition and/or bone resorption. Despite an improved understanding of mechanical and biochemical signaling mechanisms, it is largely unknown how mechanical stresses regulate the differentiation of stem/progenitor cells into osteoblast and osteoclast lineages. To advance orthodontics, it is crucial to gain a better understanding of osteoblast differentiation from mesenchymal stem/progenitor cells and osteoclastogenesis from the hematopoietic/monocyte lineage

Cellular and Molecular Biology of Orthodontic Tooth Movement

Orthodontic tooth movement is the result of a goal‐oriented application of an external force to a complex biological system. For a proper understanding of the processes underlying this complicated system, knowledge of its constituents is necessary. Therefore, this chapter begins with a description of the morphology and physical characteristics of fiber systems and the ground substance of the extracellular matrix, and a description of the different cell types involved in the synthesis and turnover of this matrix. Also, the biomechanical characteristics of the periodontal ligament are described. Orthodontic tooth movement is a result of mutual interactions between cells and between cells and the extracellular matrix. General systems of cell–cell and cell–matrix interactions are described in detail. Tooth movement and the different phases that can be distinguished in this process are explained. Each phase is characterized by specific cell biological regulatory systems. Particular attention will be given to the linear phase in which a mechanosensory system is responsible for a cascade of events that ultimately leads to bone resorption at the leading side and bone deposition at the trailing side of the moving tooth

The Biological Background of Relapse of Orthodontic Tooth Movement

Recent years have shown increased interest and research activity in retention procedures, and a number of clinical trials have tested retainer wear and effectiveness. In contrast, published data on the biological basis of relapse after a successful course of orthodontic treatment are still scarce. The majority of the studies on this issue are descriptive and led to the hypothesis that relapse is caused by the fibrous structures within the supporting tissues of the teeth. That would suggest that retention is needed until these structures are completely reorganized. However, there is considerable evidence that the rate of collagen turnover in the periodontal ligament is extremely fast, and that the gingival fibers, and especially the transseptal fibers, are remodeled rapidly. Therefore, it is concluded that collagen turnover is probably not the important factor in the etiology of relapse, and other extracellular matrix components may contribute significantly to this process. There is a definite need for more experimental and well‐designed clinical studies to elucidate the biological basis of relapse. This process will be time consuming, but only if the etiology has been unraveled, we will be able to design evidence‐based retention strategies

Update on 13 Syndromes Affecting Craniofacial and Dental Structures

Care of individuals with syndromes affecting craniofacial and dental structures are mostly treated by an interdisciplinary team from early childhood on. In addition to medical and dental specialists that have a vivid interest in these syndromes and for whom these syndromes are of evident interest, experts of scientific background—like molecular and developmental geneticists, but also computational biologists and bioinformaticians—, become more frequently involved in the refined diagnostic and etiological processes of these patients. Early diagnosis is often crucial for the effective treatment of functional and developmental aspects. However, not all syndromes can be clinically identified early, especially in cases of absence of known family history. Moreover, the treatment of these patients is often complicated because of insufficient medical knowledge, and because of the dental and craniofacial developmental variations. The role of the team is crucial for the prevention, proper function, and craniofacial development which is often combined with orthognathic surgery. Although the existing literature does not provide considerable insight into this topic, this descriptive review aims to provide tools for the interdisciplinary team by giving an update on the genetics and general features, and the oral and craniofacial manifestations for early diagnosis. Clinical phenotyping together with genetic data and pathway information will ultimately pave the way for preventive strategies and therapeutic options in the future. This will improve the prognosis for better functional and aesthetic outcome for these patients and lead to a better quality of life, not only for the patients themselves but also for their families. The aim of this review is to promote interdisciplinary interaction and mutual understanding among all specialists involved in the diagnosis and therapeutic guidance of patients with these syndromal conditions in order to provide optimal personalized care in an integrated approach

Age-related changes of dental pulp tissue after experimental tooth movement in rats

It is generally accepted that the effect of orthodontic tooth movement on the dental pulp in adolescents is reversible and that it has no long-lasting effect on pulpal physiology. However, it is not clear yet if the same conclusion is also valid for adult subjects. Thus, in two groups of rats, aged 6 and 40 weeks respectively, 3 molars at one side of the maxilla were moved together in a mesial direction with a standardized orthodontic appliance delivering a force of 10 cN. The contralateral side served as a control. Parasagittal histological sections were prepared after tooth movement for 1, 2, 4, 8, and 12 weeks. The pulp tissue was characterized for the different groups, with special emphasis on cell density, inflammatory cells, vascularity, and odontoblasts. Dimensions of dentin and the pulpal horns was determined and related with the duration of orthodontic force application and age ware evaluated. We found that neither in young nor in adult rats, force application led to long-lasting or irreversible changes in pulpal tissues. Dimensional variables showed significant age-related changes. In conclusion, orthodontic tooth movement per se has no long-lasting or irreversible effect on pulpal tissues, neither in the young nor in the adult animals