Lecture 6-Space analysis and extraction.pdf - ORTHODONTICS...

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1 ORTHODONTICS Lecture 6 Dr. Akram Alyessary Space analysis Space analysis is a process that allows an estimation of the space required in each arch to fulfil the treatment aims. Space planning is carried out in two phases: the first is to determine the space required and the second calculates the amount of space that will be created during treatment. It must be stressed that space analysis can act only as a guide, as many aspects of orthodontics cannot be accurately predicted, such as growth, the individual patient s biological response and patient compliance. Before undertaking a space analysis, the aims of the treatment should be determined as this will affect the amount of space required or created. Calculating the space requirements Space is required to correct the following: Crowding Incisor anteroposterior change (usually obtaining a normal overjet of 2 mm) Levelling of occlusal curves Arch contraction (expansion will create space) Correction of upper incisor angulation (mesiodistal tip) Correction of upper incisor inclination (torque) The space requirements to correct incisor angulation and inclination are usually minimal. Crowding The amount of crowding present can be calculated by measuring the mesiodistal widths of any misaligned teeth in relation to the available space in the arch (Figure 1). The amount of crowding present is often classified as: Mild (<4 mm) Moderate (4 8 mm) Severe (>8 mm)
2 Figure 1: Assessment of crowding. These photographs show the method of assessing the degree of crowding by measuring the width of the misaligned tooth compared with the amount of available space in the arch. In this example, the first photograph shows that the width of the tooth is 6 mm and the second photograph shows that the amount of space available in the arch for this tooth is 4 mm. This suggests crowding of 2 mm for this tooth. Incisor anteroposterior change It is often necessary to alter the anteroposterior position of the upper incisors, particularly when reducing an overjet. If incisors are retracted, this requires space; if incisors are proclined then space is created. The aim is to create an overjet of 2 mm at the end of treatment. Every millimetre of incisor retraction requires 2 mm of space in the dental arch. Conversely, for every millimetre of incisor proclination 2 mm of space are created in the arch. For example, if a patient presented with an overjet of 6 mm and the incisors needed to be retracted to create a normal overjet of 2 mm, then this would require space. Every millimetre of retraction requires 2 mm of space. So to reduce the overjet by 4 mm would require 8 mm of space. Levelling occlusal curves Where there is no occlusal stop the lower incisors may over-erupt. This may result in an occlusal curve which runs from the molars to the incisors and is known as a Curve of Spee as seen in Figure 2. The amount of space required to level an increased curve of Spee is controversial, as it is affected by a number of factors, such as the shape of the archform and tooth shape. However, as a guide Table 1 gives an estimation of the space required.

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