The facts about working of the braces have always been on the minds of the persons, thinking about undergoing correction of the deformities of their teeth by the use of the orthodontics branch of dentistry. Let me tell you that even though our teeth are one among the strongest things in the world, force applied over a planned duration of time can move them easily. The orthodontic braces work by applying particular value of force which is sufficient to apply the force on the teeth to align them properly in shape and to correct the deformities which act as a hindrance to a beautiful smile. The arch wires placed in the slots of the brackets a part of braces which are bonded securely to the teeth with the use fluoride releasing glue in place of the earlier used wire bands. The fluoride glue is very useful in reducing the amount of caries. The arch wires adapted on to the braces help in the application of forces, which lead to mainly five kind of tooth movement.
1. First being rotation which is one of the toughest types of tooth movement when force is applied on the mid-point of the root of the tooth.
2. Translation which is also called as the bodily movement of the tooth.
3. A combination of bodily and the spinning or rotational movement of the tooth is one of the most simple and common movements of the teeth.
4. Intrusion or the movement of the teeth towards the bone is a part of orthodontics.
5. Extrusion known to be the simplest movement of the teeth is movement of the teeth out of the bone.
Braces which are used in the field of orthodontics consist of the following parts
Brackets which are made up of metal or ceramic and they are attached to each tooth.
A glue (especially fluoride containing glue) or metal band is involved which helps in the attachment of the bracket to the tooth.
An arch wire which is the main component of application of the force on the teeth is places in the bracket.
One of the latest advances today is the nickel titanium wires activated by heat which react to body’s natural temperature. The temperature of the body causes the causes the wires to produce a gentle but constant force. These new advances reduce the frequencies of adjustments and orthodontist visits. The nickel titanium wires activated by heat are more efficient than the stainless steel wires and are quite popular among the young orthodontic patients and also the pain associated with them is less as compared to stainless steel wires. Arch wires have a very efficient property of elasticity and then there are nickel titanium wires with the property of shape memory that is they tend to get back to the same shape as they were before bending also so they want to retain their normal straight shape. The wires commonly used these days are the twist wires having resemblance to a small cable. The wants to remain straight even after it is put into your mouth to keep the braces in place in your mouth. The mouth temperature is 20-25 degrees more than the room temperature, this enhances the tendency of the wire to be stiff and in the process provides the forces necessary for bringing about the biomechanical process of bone remodeling and make the orthodontic tooth movement possible.
Ligature wires or elastic rings (o-rings) are used for binding the arch wire with the bracket firmly. The ligatures are adjusted and if needed are changed at each follow up visit. But recently used self binding brackets don’t need adjustments.
The movement of the teeth is caused by the pressure applied on the brackets and the teeth. Springs and rubber bands are also used to exert force in required amount and direction in some cases. Braces are the components exerting constant force over a period of time leading to the movement of the teeth in the required particular directions. The use of extra oral appliances like the head gear may also be needed in some cases especially the adults to complete the treatment in said form and time.
The teeth are surrounded by the gum tissue all around and the periodontal membrane is present around the root portion of the teeth and alveolar bone surrounds the root portion of the teeth and periodontal membrane joins the cementum of the tooth with the alveolar bone.
The pressure applied by the braces on the teeth causes the stretch of periodontal membrane on one side and compression on the other side of the periodontal membrane. The process scientifically called as bone remodeling leads to growth of bone in the new position.
Movement of the Teeth via the Process of Bone Remodeling
Bone is a tissue made up of cells called as the osteoblasts or the bone forming cells and the osteoclasts or the bone eating cells, both of which are involved in the process of bone remodeling i.e. a biomechanical process which makes bone stronger by bone deposition in stress bearing areas and bone is made weaker in areas of no load by bone resorption. The osteoclasts or the bone dissolving cells are responsible for bone resorption and osteoblasts or the bone forming cells are responsible for the bone deposition process and both combined together lead to bone re-modeling. The bone density is increased by this process.
The teeth are placed in the bone and are the roots are connected to the bone is periodontal membrane and the force applied by the arch wires pushes the tooth in the desired direction and creates stress in this periodontal membrane. The stress produced in this ligament leads to compromised blood supply in it and the biological response leads to bone remodeling which causes bone resorption by osteoclasts on one side and bone deposition by osteoblasts on the other side. The bone resorption is possible in two different ways known as the direct resorption from the cells lining the alveolar bone and indirect resorption or the retrograde resorption from the activity of osteoclasts in the surrounding bone marrow. The retrograde resorption takes place in case of excessive stress for a longer time which causes diminished blood supply of the periodontal ligament and necrosis after that. This necrosis or hyalinization leads to resorption of a larger area then deposition which is also referred as negative balance by the orthodontists occur whenever there is the application of the force to produce indirect resorption. The acellular periodontal ligament undergoes retrograde resorption under the effect of the desired stress on the enamel of the teeth for the desired amount of the teeth. Deposition of bone is also very important as without it tooth movement is not possible. If bone deposition does not occurs on the side opposite to that of tooth movement there would occur gaps on that side and teeth will become loose. These gaps make the tooth movement difficult and hamper proper treatment. A patient should understand the concept of the bone deposition and bone resorption. All these movements occur due to the compression and biological changes in the periodontal ligament all due to the forces applied.
The periodontal ligament acts as a joining b/w teeth and surrounding alveolar bone. Pressure created b/w the periodontal ligament and the alveolar bone leads to the production of osteoclasts and one lysis occurs and normal gap is created b/w the teeth and the alveolar bone. The tension created in the ligament on the distal side of the teeth causes the osteoblasts to make new bone in the direction opposite to that of the tooth movement and re- establish the normal gap b/w the teeth and the bone. The force required is only a part of the maximum. Then there are the brackets and the arch wire are the creators of the artificial force which sustains the pressure. The process of force transmission is complete with the placement of the arch wires in the braces placed on the teeth. This transmission leads to the transfer of force from the braces to the teeth and cause bone remodeling to take place and move the teeth in new functionally and aesthetically desired orthodontic positions.
The process of bone resorption caused by the osteoblasts takes about 72 days to get completely going and bone deposition process by the osteoblasts takes about 90 days to start the action in full swing. The stabilization of the result achieved takes about 10 months which makes it necessary to wear the retainer to avoid relapse to the old uncorrected or some in b/w undesirable position after the completion of treatment.
The movement seen in the tooth is about a millimeter in a month which is accounted by the orthodontists but it can vary from individual to individual, depending upon the type of treatment, the type of movement and correction needed and also the type of appliance and technique used. An understanding is required.
Now after this knowledge on the working of braces one can easily go ahead with procedure of wearing braces to have a wonderful smile.