A high force magnitude would not result in higher magnitude of intrusion. In order to achieve low magnitude for pure intrusion, a wire with low load-deflection rate should be used. Higher force can result in various side-effects on teeth and are listed below Increased rate of root resorption Rate of intrusion does not increase with increased force Extrusion of the posterior teeth Steepening of upper arch plane of occlusion Flattening of lower arch plane of occlusion Another concept of force that is critical in understanding the concept of intrusion mechanics is that equal and opposite forces are produced at incisors and at molars. For example, a 40g force that's acting to intrude the lower incisors is being counteracted by 40g of force being produced to extrude the posterior molars where the other end of intrusion arch is being engaged. Thus it is important to use a wire that has a low load-deflection rate which gives a constant force of intrusion on the teeth and prevents the side-effect. Many different orthodontists have suggested forces that may be ideal for intrusion. 1978, Bench et al. suggested an intrusive force of 15-20g per lower incisor and 60-80g for all four lower incisors. Liu et al. proposed in 1981 to use force of 100g for all four incisors. Side-effects Whether using segmental or continuous arch method, side-effects are still observed when intruding teeth. Incisal flaring When using intrusion arch which is normally has its point of application buccal to center of resistance, a counter-clockwise moment will be observed at the center of resistance which will move the crown labial and root lingual. This will lead to flaring of the incisors where crown will move buccally/facially and root will move lingually. The greater the distance of the bracket from the center of resistance of a tooth, the greater the moment observed to top the incisors buccally. This may appear as intrusion but is called a pseudo-intrusion where the teeth are being tipped and not translated apically through the bone. In cases such as extraction cases where space closure is desired, retraction of incisors to correct its inclination can be first achieved and then intrusion applied when the incisors are upright. Another way to control the side-effect is to do intrusion-retraction which simultaneously achieves space closure but also prevents the dumping of the incisors. Lingual crown tip on molars A certain intrusive force acting on the