Stability of tooth position in the broader sense considers all the forces that may act on the tooth. Reitan reported that significant forces remained in the periodontium after tooth movement, and he carried out research that demonstrated residual stretching of the crestal periodontal fibers more than 7 months after tooth movement. Brain demonstrated that severing the fibers reduced the relapse in tooth position in dogs. Edwards published a series of papers exploring the effects of surgical transection of the gingival fibers on tooth stability, recommending that circumferential fiberotomy be performed in order to increase posttreatment tooth stability. Other researchers have suggested ways to increase the stability of the incisors, which are typically most prone to relapse. Peck and Peck recommended that interproximal reduction be done to broaden the contact point. Boese also recommended interproximal reduction as part of a four-pronged approach to retention.
Orthodontic tooth movement results from applied forces to the teeth evoking cellular responses in the teeth and their surrounding tissues, including the periodontal ligament, alveolar bone and gingiva. It is advantageous for the orthodontist to be well informed of the detailed process of the biological events that unfold during tooth movement, since some of these details may differ from one person to another due to biological differences such as periodontal metabolism or alveolar bone density. This led us to emphasize that orthodontics is a field of endeavor where the integration of mechanics and biology is materialized, and to affirm the fact that tooth movement is conducted in individual human beings, each composed of a unique and intricate physiological system. Biological variations may be the foundation of the differences that are frequently observed in the outcomes of orthodontic treatment in particular with reference to treatment duration between patients with similar malocclusions and who were treated identically. A wide diversity of clinical trials has been carried out to control the tissue resistance to facilitate orthodontic tooth movement, which involves biomechanical, pharmaceutical, surgical, electrical regimens or tissue engineering technology. The term 'Corticision' is a neologism which indicates 'cortical bone incision'. It is a minimally invasive periodontal procedure without flap elevation, thus accelerating tooth movement with an enhanced turnover rate of the surrounding structures. This chapter introduces the technical procedure, and the biological background of how such a minor surgical procedure can receive the accelerated tooth movement with impunity and thereby shorten the duration of treatment.
Surgical techniques for the acceleration of the orthodontic tooth movement have been tested for more than 100 years in clinical practice. Since original methods have been extremely invasive and have been associated with increased tooth morbidity and various other gaps, the research in this field has always followed an episodic trend. Modern approaches represent a well-refined strategy where the concept of the bony block has been abandoned and only a cortical plate around the orthodontic tooth movement has been desired. Selective alveolar decortication has been a reproducible gold standard to this end. Its proposed mechanism has been the induction of rapid orthodontic tooth movement through the involvement of the periodontal ligament. More recent techniques included further refinement of this procedure through less invasive techniques such as the use of piezoelectricity and corticision. This chapter focuses on the evolution of the surgical approaches and the mechanistic concepts underlying the biological process during the surgically accelerated orthodontic tooth movement.
Bone is masterfully programmed to repair itself through the coupling of bone formation following bone resorption, a process referred to as coupling. In inflammatory or other conditions, the balance between bone resorption and bone formation shifts so that a net bone loss results. This review focuses on four pathologic conditions in which remodeling leads to net loss of bone, postmenopausal osteoporosis, arthritis, periodontal disease, and disuse bone loss, which is similar to bone loss associated with microgravity. In most of these there is an acceleration of the resorptive process due to increased formation of bone metabolic units. This initially leads to a net bone loss since the time period of resorption is much faster than the time needed for bone formation that follows. In addition, each of these processes is characterized by an uncoupling that leads to net bone loss. Mechanisms responsible for increased rates of bone resorption, i.e. the formation of more bone metabolic units, involve enhanced expression of inflammatory cytokines and increased expression of RANKL. Moreover, the reasons for uncoupling are discussed which range from a decrease in expression of growth factors and bone morphogenetic proteins to increased expression of factors that inhibit Wnt signaling.
Tissue reaction to orthodontic force has been a subject of research with the purpose of providing the orthodontists with information necessary for the application of a force system that can generate a maximum of tooth movement and modeling of the alveolar process with a minimum of damage. Traditionally, the studies of bone biological reactions have been distinguishable from those performed by bone biologists. This has led to a controversy regarding both the terminology and perception of the reaction to mechanical perturbation. The present chapter, with its basis in bone biology, surveys the attempts by orthodontists to optimize the tissue reaction and shorten treatment time.
Pain and discomfort are prevalent symptoms among the vast majority of patients with fixed orthodontic appliances and is the most disliked aspect of treatment. The periodontium is a highly innervated structure that also provides the necessary trophic factors, such as nerve growth factor, which promote neuronal survival, maintenance and axonal growth, via interaction with specific nerve surface receptors, such as TrkA. Various types of nerves are found in the periodontium, including thinly myelinated and unmyelinated sensory fibers that express the neuropeptides substance P and calcitonin gene-related peptide among others. Tooth movement activates peripheral sensory nerve endings, which transmit painful signals to the brain after being processed at the trigeminal spinal nucleus, resulting in local expression of pain related genes, such as c-Fos. Concurrently, an attendant inflammatory process is detected in the trigeminal spinal nucleus, including activation of astrocytes, microglia and neurons. This complex neurologic reaction to tooth movement mediates orthodontic pain and also serves a source of neurogenic inflammation exhibited in the trigeminal spinal nucleus and the periodontium. Activated periodontal sensory fibers release neuropeptides in the periodontal environment, which in turn induce a local inflammatory cascade aiding in alveolar bone turnover and tooth movement per se. Control of pain with nonsteroidal anti-inflammatory drugs and other prescription or over-the-counter pain killers effectively reduce this neurologic reaction and alleviate the attendant pain, but also reduce the neurogenic inflammatory component of orthodontic tooth movement causing a slowdown in bone turnover and consequently delaying orthodontic treatment.
The periodontal ligament (PDL) and alveolar bone are two critical tissues for understanding orthodontic tooth movement. The current literature is replete with descriptive studies of multiple cell types and their matrices in the PDL and alveolar bone, but is deficient with how stem/progenitor cells differentiate into PDL and alveolar bone cells. Can one type of orthodontic force with a specific magnitude and frequency activate osteoblasts, whereas another force type activates osteoclasts? This chapter will discuss the biology of not only mature cells and their matrices in the periodontal ligament and alveolar bone, but also stem/progenitor cells that differentiate into fibroblasts, osteoblasts and osteoclasts. Key advances in tooth movement rely on further understanding of osteoblast and fibroblast differentiation from mesenchymal stem/progenitor cells, and osteoclastogenesis from the hematopoietic/monocyte lineage.
Osteotomies and corticotomies used in combination with orthodontic tooth movement can activate different bone responses that may be exploited to accelerate tooth movement. Segmental osteotomies around dental roots can create a tooth-bearing transport disk that may be distracted and positioned with orthodontic appliances and archwires. In difficult craniofacial repairs, alveolar segments can be guided into position with archwires and orthodontic mechanics. The corticotomy extending into the marrow space can activate bone injury repair mechanisms that accelerate bone turnover as the alveolar bone surrounding the dental roots transitions from a demineralization phase to a fibrous replacement phase and, finally, a mineralization phase. The controlled demineralization and replacement of alveolar bone provides a window of opportunity for roots to move though less dense bone prior to remineralization. Although the corticotomies and osteotomies are minor surgeries compared to orthognathic surgery, the goal of future research is to produce similar bone responses by using smaller surgeries or by eliminating the surgeries altogether.
Piezocision™-assisted orthodontics is an innovative, minimally invasive surgical procedure designed to help achieve rapid orthodontic tooth movement while correcting/preventing mucogingival defects by adding bone and/or soft tissues. Microsurgical interproximal openings are done in the buccal gingiva to let the piezoelectric knife create the bone injury that will lead to transient demineralization and subsequent accelerated tooth movement. This technique can be used for the whole mouth, the cuts being simultaneously performed at the maxilla and the mandible (generalized Piezocision) or for segments of the dentition (localized Piezocision) to achieve specific localized results (intrusion, extrusion, distalization of teeth, etc.).
Photobiomodulation is discussed to be a noninvasive method to accelerate orthodontic tooth movement. The stimulatory effect of low-level laser therapy is well known and includes enhancement in tissue growth and tissue regeneration, resolvement of inflammation and pain. In recent research projects, the effect of laser therapy was tested regarding the stimulatory effect on bone remodeling with the potential to influence the tooth movement rate. The results are divers. The effect of laser regarding the reduction of the postadjustment pain could be proved, but not all authors describe the acceleration of tooth movement. Depending on the protocol, low-level laser therapy with low dosage increases the amount of tooth movement while high dosage seems to result in inhibitory effects. In conclusion, future studies are necessary to find the right protocol delivering beneficial results regarding the influence on bone remodeling and tooth movement to implement this therapy in daily orthodontic routine.
It is a well-known concept that bone remodeling occurs during orthodontic tooth movement. The orthodontic literature is vastly full of information about the changes occurring on the periodontal ligament level. However, changes occurring in the alveolar bone are being elucidated. The purpose of this chapter is to present some of the studies describing the bone changes associated with orthodontic tooth movement. Initiation of osteoclastogenesis requires inflammation in the adjacent area. Tissue biomarker RANKL responds to the compressive forces. Conversely, an increase in osteoprotegrin biomarker causes a decrease in RANKL and inhibits tooth movement. Osteocyte activity during tooth movement is not well understood. Emerging studies are showing the effect of osteocytes on orthodontic tooth movement. Nitric oxide (NO), produced by osteocytes, is an important regulator of bone response to loading and has been shown to mediate osteoclast activity. iNOS (which produces NO) has been shown to mediate inflammation-induced bone resorption on the compression side. Several molecules have been linked to osteogenesis in tooth movement: TGF-β, BSP, BMPs and epidermal growth factor. Osteogenesis on the tension side is not well understood. Studies have shown increase in the expression of Runx2 on the tension side. Additionally, eNOS (produces NO) mediates bone formation on the tension side. The concept of osteoclastogenesis and osteogenesis is being unraveled.
The regional acceleratory phenomenon (RAP) is a tissue reaction to a noxious stimulus that increases the healing capacities of the affected tissues. It is typical not only of hard tissues such as bone and cartilage, but also of soft tissues. The RAP is characterized by acceleration of the normal cellular activities, as an 'SOS' phenomenon of the body that has to respond to the new perturbation. In the alveolar bone, the RAP is characterized, at a cellular level, by increased activation of the basic multicellular units (BMUs), thereby increasing the remodeling space. At the tissue level, the RAP is characterized by the production of woven bone, with the typical unorganized pattern, that will be reorganized into lamellar bone at a later stage. In the alveolar bone, the RAP occurs typically in the healing process of the alveolar sockets after tooth extraction, in periodontal disease, after surgery and trauma and during orthodontic tooth movement. In relation to orthodontic tooth movement, the RAP can be seen as a tissue response to the mechanical cyclical perturbation that induces the formation of microdamage that has to be removed to avoid their accumulation and the following bone failure. The adaptation to the new orthodontically induced mechanical environment is ensured by an increased activation of the BMU that returns to normal levels after few months.
Bone remodeling is a highly coordinated process responsible for bone resorption and formation. It is initiated and modulated by a number of factors including inflammation, changes in hormonal levels and lack of mechanical stimulation. Bone remodeling involves the removal of mineralized bone by osteoclasts followed by the formation of bone matrix through osteoblasts that subsequently becomes mineralized. In addition to the traditional bone cells (osteoclasts, osteoblasts and osteocytes) that are necessary for bone remodeling, several immune cells such as polymorphonuclear neutrophils, B cells and T cells have also been implicated in bone remodelling. Through the receptor activator of nuclear factor-x03BA;B/receptor activator of the NF-x03BA;B ligand/osteoprotegerin system the process of bone resorption is initiated and subsequent formation is tightly coupled. Mediators such as prostaglandins, interleukins, chemokines, leukotrienes, growth factors, wnt signalling and bone morphogenetic proteins are involved in the regulation of bone remodeling. We discuss here cells and mediators involved in the cellular and molecular machanisms of bone resorption and bone formation.
The earliest report on orthodontic tooth movement in the English literature was published in 1911. Oppenheim carried out studies on baboons to determine what histologic changes occurred during tooth movement. Reitan and many others carried out research into the nature of tooth movement. The pressure-tension model of tooth movement developed from these studies, whereby the two sides of the tooth responded to forces as if in isolation. A second theory, proposed by Stuteville in 1938, was the hydraulic theory of tooth movement. In this theory, fluid from the vasculature, lymphatic system and intercellular spaces responds to the forces of tooth movement, damping the force and limiting movement. Bien and Baumrind expanded on this theory with their own studies in the 1960s. It is clear that both the pressure-tension and fluid flow concepts have merit, but considerable work needs to be done to ascertain the details so that tooth movement can be managed and controlled.
Reconstruction of maxillofacial bones has proven to be complex due to the aesthetic requirements and functional demands of the jaw. Although autogenous bone grafts and a wide range of biomaterials are routinely used for facial bone reconstruction, these methods are associated with a number of drawbacks, including the limited availability of autogenous grafts and the morbidity associated with bone graft harvesting, whilst biomaterials are also linked with a high failure rate. These limitations have inspired the search for innovative techniques for bone bioengineering and the development of more reliable biomaterials. Tissue engineering approaches yield powerful tools for long-term satisfying results enabling customized reconstruction and the support of natural healing processes. There is no doubt that further advances in tissue engineering are essential to achieve reliable and satisfactory clinical outcomes for patients. This chapter will highlight the clinical application of biomaterials and provide an overview of the current scientific concepts in the field.
The successful clinical application arising from advances in polymer and macromolecular sciences in different fields of medicine has opened new explorative approaches for the future design and development of the ever more sophisticated bio-/nanotechnologies that are needed to realise the full potential of modern dentistry. In this chapter, the most recent polymer therapeutic approaches for alveolar ridge augmentation, bone grafts, periodontal disease, restorative materials and scaffolds or carriers for cell-based therapies are presented highlighting the potential of either synthetic or natural polymers, such as polyesters, polyolefins, polyacrylates or chitosan for example, being tailored and engineered to yield a range of properties valuable in the design and development of dental polymer therapeutics.
The use of titanium dental implants has consistently changed the way of rehabilitating patients in modern dentistry and can count on high long-term survival and success rates. With respect to its introduction in the late 1960s, clinical indications for implant therapy have been significantly extended and optimal results have been achieved, even in clinical conditions formerly considered as unfavourable. Such evolution owes a lot to the significant progress made in the field of titanium surfaces. The topographical and chemical modification of traditional titanium surfaces has led to a real epochal shift in implant dentistry. Depending on the type and characteristics of the surface treatment applied, a wide range of implants has been produced, which have contributed to the success but also increased the risk of confusion in implant selection criteria for the clinician. This chapter, which provides an updated analysis of the relevant literature, the characteristics of modern implant surfaces, the biological principles underlying their role in promoting osseointegration and the scientific evidence about their clinical use are analyzed and presented.
