Introduction
The human body consists of different systems, organs, tissues and cells that are crucial to its functioning. Their interaction leads to the survival of the species and its adaptation to the environment. The skeletal system plays an important role in the support of the body and forms a structure on which other organs are supported (Renaud, Auffray & De La Porte 2010). Researchers describe two types of bones that make up this system, including compact and spongy bone (Renaud, Auffray & De La Porte 2010). Additionally, available evidence points to different mechanisms of formation and functioning of these bones (Martinez-Maza, Rosas & Nieto-Díaz 2013). One of the important bones in oral biology is the jawbone that has a special role in dentition and face structure. Consequently, this essay describes the complex process of the remodeling of the compact bone of the jaw.
The Jawbone and its Significance
The Mandible is part of the bones of the face. This bone is the strongest of the face bones with the special function of dentition (Martinez-Maza, Rosas & Nieto-Díaz 2013). The mandible is specially designed to accommodate the teeth with the two main parts being the body and the two rami (Martinez-Maza, Rosas & Nieto-Díaz 2013). In addition, the development of the different parts of the bone occurs at different times and through different processes. The osteogenesis of the jawbone is unique with ossification taking place at different centers (Martinez-Maza, Rosas & Nieto-Díaz 2013). Consequently, there are different structures that result from these ossification centers.
The jawbone goes through different processes during growth. First, the growth of secondary cartilage increases the overall size of the structure with the condylar distance increasing daily. Secondly, the alveolar process leads to an additional growth of the teeth (Martinez-Maza, Rosas & Nieto-Díaz 2013). According to Anderson, Renaud and Rayfield (2014), the teeth allow for a further increase in the height of this bone. The last step in development is the apposition and resorption of the subperiosteal bone that results in the different landmarks on the bone. The process of remodeling in this bone is similar to that of other bones in the body and is influenced by various structural forces, chemicals, and genes. This process is discussed in general in the next section followed by a discussion of the specific remodeling process of the jawbone.
The Process of Remodeling
Although the bone appears solid, this structure is alive with different types of cells participating in its formation and functioning. The skeleton is in a continuous process of breakdown and formation with new bone being formed, as old bone is recycled or redistributed (Zimmerman, Meunier, Katz & Christel 1990). Bone remodeling entails the renewal and repair of bone in the body. According to researchers, the process of remodeling is very complex involving several processes, chemical receptors, and cells. The introduction of advanced techniques such as the use of the ultrasound has enabled researchers to study the process of bone remodeling (Zimmerman, Menunier, Katz & Christel 1990). Zimmerman, Menunier, Katz and Christel (1990) used this technique to describe the process of cortical bone remodeling in patients that has total hip arthroplasty. Their Scanning Acoustic Microscope (SAM) allowed them to demonstrate the microstructural remodeling in the bones.
Bone resorption takes place when the mineral matrix is broken down by the special cells called osteoclasts. These cells have special chemicals and receptors that play the crucial role of breaking down all types of bone. The temporal and special regulation of this process is tightly regulated (Zimmerman, Menunier, Katz & Christel 1990). The balance between the various processes that are in remodeling changes with age. Consequently, younger individuals have a bone mass that is almost constant. However, an increase in age leads to alteration of this balance with subsequent increase in the bone turnover (Zimmerman, Menunier, Katz & Christel 1990). When turnover exceeds the rate of formation of new bone, the density reduces, and the individual becomes osteoporotic.
The observations made by different researchers have led to the development of different interventions in the treatment of osteoporosis. According to Gallagher and Sai (2010), the mastery of the process of remodeling can be used to influence treatment of this disease of the elderly whose mainstay of management has been the use of bisphosphonates (Gallagher & Sai 2010). Monoclonal antibodies were developed as inhibitors of the substances and process in remodeling. Consequently, the understanding of the process of bone remodeling is crucial in the management of osteoporosis and other bone-related conditions.
According to Hadjidakis and Androulakis (2006), the process of remodeling is continuous and occurs throughout the lifetime of an individual. Osteolysis by the osteoclasts is followed by new bone formation.. These authors describe the process of remodeling in three phases: resorption, reversal, and formation. In resorption, old bone is broken down by the osteoclasts with the different constituents being returned to the body system. This process is followed by reversal where the mononuclear cells are transported to the bone surface. Finally, the osteoblasts take over to replace the bone (Hadjidakis & Androulakis 2006).
The important of remodeling is to change the architecture of the bone to suit the changing mechanical needs. Additionally, this process leads to bone repair as occurs after a fracture (Schindeler, McDonald, Bokko & Little 2008). Schindeler, McDonald, Bokko and Little (2008) state that the process of bone repair takes place through the remodeling process after a fracture. The four main stages in the healing process eventually lead to bone remodeling. The callus formed in the process of bone healing is usually shapeless and does not reflect the function of the bone. However, remodeling ensures that the bone formed is adapted to its function with time (Schindeler, McDonald, Bokko & Little 2008). Additionally, catabolic and anabolic processes adjust to make the bone stronger and contribute to the remodeling process (Schindeler, McDonald, Bokko & Little 2008).
Aside from repair of the bone, resorption also serves to remove old bone that may be functionally obsolete and is prone to fractures (Hadjidakis & Androulakis 2006). Some damages in bone also occur because of daily activities, and remodeling also serves to repair these micro-damages. Hadjidakis and Androulakis (2006) also state that bone remodeling is important in calcium homeostasis. The skeletal system is the main depot for calcium in the body, and this calcium is released into the bloodstream whenever there is any need. In addition, the calcium stored in bone is necessary to balance other electrolytes such as potassium and magnesium (Hadjidakis & Androulakis 2006).
Regulation of Remodeling
The processes regulating bone remodeling have been the subject of many studies. According to Hadjidakis and Androulakis (2006), this regulation takes place both at the local and systemic levels. The systemic regulation of remodeling occurs in response to several hormones and chemicals. Calcium homeostasis is the main reason for the regulation of the bone remodeling process (Wong, Zengin, Herzog & Baldock 2008). Consequently, hormones crucial in calcium regulation such as the parathyroid hormone (PTH) calcitriol, and growth hormone participate in the regulation of bone remodeling (Hadjidakis & Androulakis 2006). In addition to these hormones, the other chemicals important in the regulation of remodeling include the systemic cytokines, tumor growth factor-beta (TGF-beta), prostaglandins, and the bone morphogenic proteins (BMPs) (Hadjidakis & Androulakis 2006).
Newer cytokines and other factors involved in bone remodeling regulation have also been discovered. However, researchers are yet to find all the substances involved in the regulation of this complex process. Skeletal integrity is maintained through several processes that also ensure there is regulation of the remodeling process (Hadjidakis & Androulakis 2006). Ito and colleagues (2005) developed a mouse model that demonstrated the regulation of the bone remodeling process. These researchers showed the genes necessary in the healing process and manipulated them to promote remodeling of bone (Ito et al. 2005). Their method involved the combination of rAAV-RANKL and the rAAV-VEGF to promote vascularization and remodeling in bone (Ito et al. 2005). These are necessary for the repair process.
In addition to the systemic controls of bone remodeling, other local controls are necessary. Henriksen, Neutzsky-Wulff, Bonewald and Karsdal (2009) state that some process on the bone and within the skeletal system control the process of remodeling. The local controls of bone remodeling include biochemical and mechanical processes. The mechanical stresses on a bone influence the process by determining the direction of remodeling and the amount of remodeling that takes place (Henriksen, Neutzsky-Wulff, Bonewald & Karsdal 2009). The areas that need support receive the most cortical bone while other areas of the bone that are not used a lot are resorbed (Henriksen, Neutzsky-Wulff, Bonewald & Karsdal 2009).
Cell-cell interaction together with the molecular interaction of the bone cells results in the regulation of the bone remodeling process (Georges et al. 2008). Local factors involved in the regulation of remodeling include the proteases and the other chemicals in the integrin family (Georges et al. 2008). According to Georges et al. (2008), the location of the proteases on the membrane of the cell or other areas influence the contact of cells involved in remodeling.
There is plenty of evidence to support the theory that mechanical forces play a central role in the remodeling process. According to Kameo, Adachi and Hojo (2011), a mechanosensory system consisting of osteoclasts and osteocytes within the bone matrix influence bone remodeling. Bone leading stimulates the process of remodeling in the direction of the force (Kameo, Adachi & Hojo (2011). Additionally, the amount of force determines the amount of remodeling and bone deposition that takes place within the affected bones. In the jawbone, the main forces that influence remodeling are those from the process of chewing. These influence the amount of remodeling and the areas that are most affected. The methods used to study these forces influencing remodeling include the piezoelectricity poromechanics (Lemaire, Capiez-Lernout, Kaiser, Naili & Sansalone 2011).
The remodeling of cortical bone occurs in several steps that are sensitive to the forces acting on the bone (Knothe Tate, Dolejs, McBride, Miller & Knothe, 2013). The development of skeletal bone takes place in several ways that are also sensitive to the neurochemicals surrounding these structures. According to Knothe and colleagues (2011), the remodeling process of compact bone takes place in the direction of the force applied to it. As a result, the bones that bear the largest forces in the body are the most remodeled with active deposition of bone matrix.
Remodeling of the Compact JawBone
The process followed in the remodeling o the jawbone is not different from that of any other compact bones in the body. The remodeling of this bone is influenced by several local and systemic factors in the body (Sims & Gooi 2008). Like in other bones, the remodeling of the mandible occurs when the osteoclasts break down bone and interact with other cells such as the osteoblasts to form new bone (Sims & Gooi 2008). Sims and Gooi (2008) state that remodeling in the bone takes place after the signals responsible for the resorption of existing bone permit the breakdown of the bone. Mineralization follows the breakdown of the bone with new bone being formed. For this remodeling to occur, the two main types of cells responsible for remodeling have to be in constant communication (Matsuo & Irie 2008). This communication is mediated through neurochemicals and the co-stimulatory molecules (Matsuo & Irie 2008).
Remodeling of the mandible is especially necessary during the growth of this bone and its adjustment to function. Remodeling occurs at several areas of this bone in the process of shaping it and strengthening areas that are necessary for chewing (Fanghänel et al. 2006). The first thing that occurs is the resorption of bone from places that it is not utilized. The bone mineral from these places is deposited in other areas and used to strengthen these areas. According to Lian and colleagues (2011), the resorption of bone from the inner part of the mandible is followed by the deposition of this bone on the external surface. Consequently, this remodeling process leads to an increase in the transverse dimension of the bone (Anderson, Renaud & Rayfield 2014).
The other remodeling process that takes place in the mandible leads to an alteration in the thickness of the ramus of this bone. First, the anterior border of this part of the mandible is broken down through resorption. The resultant bone matrix is deposited on the posterior border with a resultant change in the ramus thickness (Anderson, Renaud & Rayfield 2014). A similar process occurs in the coronoid process of the mandible resulting to its displacement. First, the posterior border of this structure is eroded through the process of resorption. This is followed by a deposition of new bone on the anterior border resulting in the displacement of the structure (Lian et al. 2011).
The changes described are crucial in the dentition of an individual. However, the jawbone also plays a role in the facial anatomy and appearance. Consequently, the process of remodeling of the mandible leads to new bone formation in the face and defines the appearance of an individual. For example, the deposition of new bone on the chin results to a distinct lower face that is unique to many individuals of different races and ethnicities (Martinez-Maza, Rosas & Nieto-Díaz 2013). The amount of remodeling that takes place in this bone influences the facial structures formed.
Bone remodeling in the mandible is responsible for the age-related changes that are evident in the bone (Martinez-Maza, Rosas & Nieto-Díaz 2013). Consequently, the mandible of a newborn is different from that of a teenager and an elderly individual. The remodeling of the coronoid process and the condyles influences the appearance of this bone. The fusion of the two bones of the mandible is also influenced by the remodeling process. The other changes that occur in this structure also allow for the development of more teeth as the person ages (Zhao et al. 2013). During the early years, the process of resorption is greater than that of matrix deposition. However, the two process in remodeling become almost equal in teenage as one approaches adulthood (Renaud, Auffray & De La Porte 2010). In the elderly, remodeling changes with more resorption that bone deposition, resulting in bone erosion and osteoporosis. Consequently, the teeth become weak and fall off while the alveolar process is absorbed (Renaud, Auffray & De La Porte 2010). The process of remodeling is an important determinant of mandibular growth and shape.
Conclusion
In conclusion, the human skeleton is alive with numerous physiological and chemical activities taking place. This essay evaluates the remodeling of bone that leads to new bone formation and reshaping. The jawbone is a bone structure whose development and shape is influenced by remodeling. Some of the cells involved in remodeling include the osteoclasts and the osteoblasts. The paper also describes the local and systemic controls of bone remodeling with a particular focus on the jawbone.
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