Genetic Factors and Tooth Movement

Genetics of Dentofacial and Orthodontic Abnormalities

The development of craniofacial complex and dental structures is a complex and delicate process guided by specific genetic mechanisms. Genetic and environmental factors can influence the execution of these mechanisms and result in abnormalities. An insight into the mechanisms and genes involved in the development of orofacial and dental structures has gradually gained by pedigree analysis of families and twin studies as well as experimental studies on vertebrate models. The development of novel treatment techniques depends on in-depth knowledge of the various molecular or cellular processes and genes involved in the development of the orofacial complex. This review article focuses on the role of genes in the development of nonsyndromic orofacial, dentofacial variations, malocclusions, excluding cleft lip palate, and the advancements in the field of molecular genetics and its application to obtain better treatment outcomes.

Interfacing the basic sciences and clinical orthodontics

Translational research aims to move knowledge generated from basic science and apply it to the clinical setting. As orthodontists, we continually strive for faster, safer and alternative clinical therapies in our goal to improve our patient outcomes and experiences. Our clinical questions may be answered by benchtop research and the ensuing translational research involving relevant animal models and robust clinical trials.

Heredity, Genetics and Orthodontics - How Much Has This Research Really Helped?

Uncovering the genetic factors that correlate with a clinical deviation of previously unknown etiology helps to diminish the unknown variation influencing the phenotype. Clinical studies, particularly those that consider the effects of an appliance or treatment regimen on growth, need to be a part of these types of genetic investigations in the future. While the day-to-day utilization of "testing" for genetic factors is not ready for practice yet, genetic testing for monogenic traits such as Primary Failure of Eruption (PFE) and Class III malocclusion is showing more promise as knowledge and technology advances. Although the heterogeneous complexity of such things as facial and dental development, the physiology of tooth movement, and the occurrence of External Apical Root Resorption (EARR) make their precise prediction untenable, investigations into the genetic factors that influence different phenotypes, and how these factors may relate to or impact environmental factors (including orthodontic treatment) are becoming better understood. The most important "genetic test" the practitioner can do today is to gather the patient's individual and family history. This would greatly benefit the patient, and augment the usefulness of these families in future clinical research in which clinical findings, environmental, and genetic factors can be studied.

Experimentally determined mechanical properties of, and models for, the periodontal ligament: critical review of current literature

Introduction. This review is intended to highlight and discuss discrepancies in the literature of the periodontal ligament's (PDL) mechanical properties and the various experimental approaches used to measure them. Methods. Searches were performed on biomechanical and orthodontic publications (in databases: Compendex, EMBASE, MEDLINE, PubMed, ScienceDirect, and Scopus). Results. The review revealed that significant variations exist, some on the order of six orders of magnitude, in the PDL's elastic constants and mechanical properties. Possible explanations may be attributable to different experimental approaches and assumptions. Conclusions. The discrepancies highlight the need for further research into PDL properties under various clinical and experimental loading conditions. Better understanding of the PDL's biomechanical behavior under physiologic and traumatic loading conditions might enhance the understanding of the PDL's biologic reaction in health and disease. Providing a greater insight into the response of the PDL would be instrumental to orthodontists and engineers for designing more predictable, and therefore more efficacious, orthodontic appliances.

Pathways in external apical root resorption associated with orthodontia

To review studies investigating if genetic factors play a role in external apical root resorption (EARR) during orthodontic treatment. Heritability estimation in human sib-pairs, comparison of multiple inbred mouse strains, human sib-pair linkage and parents-child trio association studies, and two gene (Il-1b, and P2rx7) knock out mouse models. Heritability for EARR of the maxillary central incisors concurrent with orthodontic treatment is 0.8. DBA/2J, BALB/cJ, and 129P3/J inbred mouse strains are highly susceptible (p < .05) to histological root resorption (RR) associated with orthodontic force (RRAOF), whereas A/J, C57BL/6J and SJL/J mice are resistant. Non-parametric sibling pair linkage analysis identified evidence of linkage (LOD = 2.5; p = 0.02) of EARR with microsatellite D18S64 (tightly linked to TNFRSF11A, also known as RANK). There is significant linkage disequilibrium of IL-1B (p = 0.0003), and OPG (p = 0.003) with EARR. RRAOF increases in Il1b KO (p < or = 0.013), and increases in P2rx7 KO (p < 0.02) mice compared to wild-type. Genetic factors play a marked role in EARR concurrent with orthodontic force, accounting for one-half to two-thirds of the variation. Two pathways for this may involve: 1) activation control of osteoclasts through the ATP/P2XR7/IL-1B inflammation modulation pathway; and 2) RANK/RANKL/OPG osteoclast activation control. Histological RR occurs and is typically healed. If resorption outpaces healing, then EARR develops. Normal and parafunctional forces, as well as orthodontic forces, may add to or interact with the individual's susceptibility to pass the threshold of developing EARR.