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Orthodontic diagnosis is complex and multifactorial, and an initial space analysis informing a decision whether or not to extract teeth, is consistently highlighted as the most significant diagnostic factor, with other clinical factors being secondary. Although most clinicians are taught a method of space analysis, few subsequently place their confidence in any formal method and furthermore may not consider the space implications of the curve of Spee. A survey of orthodontists revealed a surprising variability in the assessment of crowding, as well as a tendency to make a different diagnostic decision on the same case sometime later. This two-part series explores the current status of space analysis and suggests how we may be able to limit the potential for making poor extraction decisions. Part 1 explored the various factors that need to be considered in an orthodontic space analysis, and in particular, the space implications of the curve of Spee. Part 2 examines the various methods and tools available to the clinician in assessing orthodontic crowding. We also look at ways in which potentially poor extraction decisions may be mitigated in clinical practice.
CPD/Clinical Relevance: To help understand the clinical significance of space analysis as the key diagnostic factor informing a decision whether to extract teeth or not.
Article
The first part of this two-part series, explored the various factors that need to be considered in an orthodontic space analysis, and in particular, the space implications of the curve of Spee.1 Here we will explore the various methods and the tools available for the clinician. We will also look at the ways in which potentially poor extraction decisions may be mitigated in clinical practice.
Although there are published average sizes of teeth, to accurately measure the all-important mesio-distal tooth widths, either a ruler, dividers and a ruler, or manual/digital calipers are required (Figure 1). However, as already highlighted, the challenge with using these instruments is being able to accurately position them at the mesial and distal contact points of the teeth. Nonetheless, some form of mesio-distal tooth width measurement is required in the following methods of space analysis.
The brass wire method was a technique originally intended to monitor tooth movement, but it was later adapted by Nance2 as a method of quantifying crowding. This technique (still taught in some US dental schools) involves placing a brass wire around the lower arch on the occlusal surfaces, above the estimated positions of the contact points, while maintaining a smooth curve. It is assumed that by subtracting this wire length from the total mesio-distal widths of the teeth it is possible to quantify the crowding. However, a wire placed into the curve of Spee will be longer than the potential post-treatment flat arch length, therefore underestimating the degree of crowding.
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