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Lawrence Andrews:

 Developed the preadjusted edgewise appliance in 1970.

 Also developed Andrews’ six keys to occlusion.

 Is an American orthodontist who has now retired from patient care, although he still takes part in research and education.

 His son Will A. Andrews followed in his footsteps and joined the practice that Lawrence established in 1958 called Point Loma in San Diego, California.

Preadjusted edgewise appliance (Figure 1.5):

 Another name for this is the straight‐wire appliance.

 It is used on patients for either their first stage of treatment or the second stage following removable or functional appliances.

 These brackets are called ‘preadjusted’ edgewise brackets because they are thicker in the horizontal dimension, and are also different from one another due to the inbuilt prescriptions designed specifically for each individual tooth.Figure 1.5 Preadjusted edgewise brackets.

 The inbuilt prescriptions within the brackets are:In and out: first‐order bendTip: second‐order bendTorque: third‐order bend.

 Because of the inbuilt prescriptions within the brackets they became very popular, as it meant wire bending was minimised and in some cases not needed at all.

 For the inbuilt prescriptions to be achieved on each tooth, the brackets are manufactured in a certain way:In and out (first‐order bend): to achieve this, the base of the bracket is manufactured differently. For example, lateral incisors sit slightly back from the central incisors, therefore the base of this bracket will be thicker than the brackets for the central incisors.Tip (second‐order bend): each bracket slot is cut at a certain angulation to help achieve the correct angulation for each individual tooth; this differs for each bracket.Torque (third‐order bend): each bracket has different torque percentages within the bracket slot. The thicker the wire, the more torque is created. If the desired torque is not achieved, bends within archwires can be placed to help with this type of movement.

 Preformed archwires are used with this appliance, as this allows teeth to move gradually from their original position into their desired position.

 Brackets come in different slot sizes:0.018 × 0.025 in., with the working wire being used = 16 × 22 ss (stainless steel)0.022 × 0.028 in., with the working wire being used = 19 × 25 ss (more commonly used).

 Depending on the degree of crowding the patient presents with, the appliance can be used on non‐extraction or extraction cases.

 Still in good use today, the preadjusted edgewise appliance has three common bracket prescriptions:AndrewsRothMBT = McLaughlin, Bennett, Trevisi.

 Different orthodontists created these three common bracket prescriptions. It was known that each orthodontist had different views on how much torque should be built within the bracket slot. Therefore, each bracket prescription contains different values of torque, with MBT containing the highest value of torque out of the three.

Advantages of the edgewise appliance:

 Reduced chair time.

 Amount of wire bending is minimised.

 Sliding mechanics for tooth movement.

 Good finishing.

Disadvantages:

 Larger inventory of brackets is required, as each individual tooth has different requirements of in and out, tip and torque.

 Ignores individual biological variation.

 Increased friction has implications and increases anchorage considerations.