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Orthodontic tooth movement ppt.
 

Orthodontic tooth movement ppt.

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Orthodontic tooth movement ppt.

Orthodontic tooth movement ppt.

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    Orthodontic tooth movement ppt. Orthodontic tooth movement ppt. Presentation Transcript

    • Orthodontic tooth movement Abdurrahman Mosaad Orthodontics department Armed forces medical complex – Kobry al Qubba
    • In the name of Allah , most gracious , most merciful
    • # What is orthodontics : = Orthodontics is the specialty of dentistry with the management and treatment of malocclusion. concerned =In the majority of cases, a malocclusion does not in itself represent a disease state, but rather a variation from what is considered ideal
    • - Andrew’s keys for ideal occlusion
    • - The nature of orthodontic tooth movement : = it has a bio – mechanic nature. = solely based upon stress- strain occurs in the PDL environment = the orthodontic tooth movement results from forces delivered to the teeth
    • = the forces are delivered via orthodontic app. Either fixed or removable = PDL undergoes biological respond upon the mechanical application of a force i.e to achieve a precise biological respond the mechanical forces to be delivered should be precise
    •  = Knowledge of the mechanical principles governing forces is necessary for the control of orthodontic treatment  = The proper application of biomechanics principles increases treatment efficiency through improved planning and delivery of care
    • = Knowledge of the mechanical principles governing forces is necessary for the control of orthodontic treatment = The proper application of biomechanics principles increases treatment efficiency through improved planning and delivery of care
    • 1 = center of resistance. - All objects have a center of mass. - This is the point through which an applied force must pass for a free object to move linearly without any rotation, - i.e., the center of mass is an object’s “balance point.”
    • analytic studies have determined that the center of resistance for single-rooted teeth with normal alveolar bone levels is about 1/4 to 1/3 the distance from the cementoenamel junction (CEJ) to the root apex.
    • Location of the center of resistance depends on the alveolar bone height and root length . = Location of the center of resistance with alveolar bone loss = with a shortened root
    • 2 - Forces = they are actions applied to bodies = they equals ( mass X acceleration) F =ma = in clinical orthodontics its unit is Grams = forces has the characteristics of vectors i.e magnitude & direction Note : the diagram shows that the force vectors characteristics – magnitude , point of origin & direction
    • = 2 vectors could added by placing one vector at the head of the another i.e sum of them called resultant = a vector could be resolved into components along x , y & z axes
    • = Clinically the determination of the horizontal, vertical, and transverse components of a force improves the understanding of the direction of tooth movement = An important point of view that the orthodontic tooth movement is not applied on the center of rotation of the tooth as it is usually delivered through the tooth crown
    • = as the orthodontic forces are delivered through the tooth crown they will not produce a pure linear movement ,, some rotational movement will be present ,, those rotational movements are called Moment of the force = The moment of the force is the tendency for a force to produce rotation.
    • = Its direction is found by following the line of action around the center of resistance toward the point of origin =It is determined by multiplying the magnitude of the force by the perpendicular distance of the line of action to the center of resistance
    • = The importance of the moment of a force is often not recognized in clinical orthodontics, but awareness of it is needed to develop effective and efficient appliance designs
    • Clinical examples of moments of the forces
    • 3 – Couple - A couple is two parallel forces of equal magnitude acting in opposite directions and separated by a distance (i.e. different lines of action) - The magnitude of a couple is calculated by multiplying the magnitude of force(s) by the distance between them
    • Couples result in pure rotational movement about the center of resistance
    • clinical examples of couples
    • 4 – Torque = Torque is a common synonym for moment (both moments of forces and of couples) = Torque is erroneously described in terms of degrees by many orthodontists.
    • = The appropriate unit for the applied torque is gram/millimeters (force × distance). It is the description of the moments that more accurately describes the rotational components of a force system and appliance design
    • Orthodontic wire bends -1st order -- 2nd order -- 3rd order
    • # Anchorage -Anchorage is the site of delivery from which force is exerted - degree of resistance to displacement offered by an anatomic unit for the purpose of tooth movement.
    • # Classification of ortho. Anchorage -acc. to manner of force application : * simple * stationary * reciprocal - according to jaws involved : * intermaxillary * intramaxillary - according to site : * intraoral * extaraoral * muscular - according to anchorage units : * primary * compound *reinforced (multiple)
    • # anchorage planning : -Increasing no. of teeth to be move requires more anchorage - teeth having more surface area requires more anchorage - bodly movement requires more anchorage - prolonged tx. Plan requires more anchorage - vertical growth pattern requires more anchorage due to the less tonicity of muscles - N.B. Good occlusion = Good anchorage
    • # Anchorage loss : -Its is the unwanted tooth movements during orthodontics that cause space loss -Maximum anch. * anch. Demand is very high *not more than ¼ of ext space should be lost * augmentation of anchor units is usually done -Moderate anch. * ¼ - ½ of ext space should be lost - Minimum anch. * more than ½ ext space could be lost
    • Maximum anch.
    • Moderate anch.
    • Minimum anch.
    • # Equivalent Force systems = A useful method for predicting the type of tooth movement that will occur with appliance activation is to determine the equivalent force system at the tooth’s center of resistance = The force system at the center of resistance accurately reflects the type of movement
    •  eg. Intrusion arch force system
    • # Types of tooth movement : 1 – tipping ( controlled & uncontrolled) 2 – translation ( bodily ) 3 – root movement 4 - rotation 5 - intrusion & extrusion
    • -The relationship between the applied force system and the type of movement can be described by the moment/force ratio -The movement that occurs is dependent on the (moment/force ) ratio #and# the quality of the periodontal Support
    • 1- Tipping : * simplest orthodontic movement * controlled occurs about the tooth apex *uncontrolled occurs about CER * Force needed is about 50 – 75 gm.
    • Controlled tipping
    • Uncontrolled tipping
    • 2- Translation : * all PDL is uniformly loaded with the force * Force needed is about 100 – 150 gm.
    • 3 – Rotation : * needs high force * occurs around the CER * Force needed is about 50 – 100 gm.
    • 4 – Extrusion : * needs to produce tension in the PDL ligaments * Force needed is about 50 gm.
    • 5 – Intrusion : * forces are nearly at the apex * needs minimum force application * Force needed is about 15 – 25 gm.
    • 6- Root movement : * usually expressed as torque * the crown is held stationary and the root moves * CER is the bracket itself * done by increasing the Moment/Force ratio
    • Moment / Force ratios needed for different kinds of tooth movement : 1 – tipping * controlled 5:1 * uncontrolled 7 : 1 2 – translation 10 : 1 3 – root movement 12 : 1
    • Types of orthodontic forces acc. to Duration - continuous - interrupted - intermitted
    • * Threshold --- 6 hrs per day. * No tooth movement if forces are applied less than 6 hrs/d. * From 6 to 24 hrs/d, the longer the force is applied, the more the teeth will move.
    • - Continuous force : * achievable via fixed orthodontics *Never declines to zero.
    • - Interrupted force : * force starts heavy then decline to optimal after that may reach zero . *achievable via removable appliance. * produces some kind of undermining resorption . * reactivated every specific time .
    • -Intermittent forces : * declines to zero * very high force 250 – 500 gm.( anch – dist ) * achievable via extraoral appliance * needs at least 12 hrs/day to be effective * 14 hrs/day is optimal
    • -Force level : * Light, continuous forces are currently considered to be most effective in inducing tooth movement. *Heavy forces cause damages and fail to move the teeth. N.B. Optimal force : “High enough to stimulate cellular activity without completely occluding blood vessels in the PDL”
    • Heavy Forces Tooth movement (mm) * B.V of PDL is totally occluded --then * causes cellular necrosis within the bone --then * hyalinization i.e undermining resorption occur Phase 3 Phase 2 Phase 1 Time (Arbitrary Unit)
    • • • Tooth mov. Light, continuous forces Osteoclasts formed Phase 2 *Removing lamina dura. *Tooth movement begins Time *This process is called “FRONTAL RESORPTION”. ( remodeling process ) Phase 3
    • -Phases of orthodontic tooth movement :- * Displacement - no clinical movement - instantaneous * Delay – no clinical movement - short ( partial B.Vs occ. ) or long 1-2 weeks ( more B.Vs occ. ) * Acceleration – rapid tooth displacement - differs among individuals
    • Tooth movement (mm) Phase 3 Phase 2 Phase 1 Time (Arbitrary Unit)
    • Orthodontic tooth movement adverse effects : * Pulp - transient inf. response , can cause loss of vitality - in cases of compromised tooth ,, heavy force ,, wrong mech. * Root - usually repaired by cementum during rest periods - resorption may occur up to 2 mm. in permanent cases - At risk : thin roots ,, heavy force ,,
    • Material considerations : 1 – orthodontic wires *material of the wire * effect of increasing wire diameter 2 – orthodontic brackets * edgewise vs pre-adjusted (roth) * self ligating brackets * size of slots * interbracket distance * torque of the brackets
    • force deflection Modulus of elasticity of the wire
    • 100% 200% 300% 400% Percentage increase in stiffness  14’’ 50gm  16’’ 85gm 71% increase  18’’ 137gm 173% increase 14’’ 16’’ 18’’ 20’’ 22’’ Wire diameter Effect of increasing wire diameter
    • Torque selection of lower teeth brackets
    • Torque selection of upper teeth brackets
    • Finally : Optimal force is the lightest force that will move a tooth to a desired position in the shortest possible time without iatrogenic effects So ,,, we should think optimal ,, it is orthodontics so we ( work smarter not harder ) 
    • Thank You 