**2.4 Results**

The results of this experiment were published by Rafeek et al., (2010). There were no undercuts detected on any of the laboratory specimens as compared to the clinical specimens where 12.5% were undercut. The overall mean taper for the laboratory specimens was 22.5° (BL) and 14.5° (MD). The overall mean taper for the clinical specimens was 24.2° (BL) and 19.6° (MD). Table 1 shows the percent of specimens falling within the ideal taper range of 4° – 14°.


Table 1. Shows the percentage of tapers falling within the ideal range of 4° – 14°.

Although the mean tapers achieved in the laboratory compared to the clinic were lower, there was no significant difference detected between the mean tapers achieved (p>0.05) except for the MD taper of posterior teeth (p<0.05).

#### **2.5 Discussion**

The overall mean tapers achieved were higher than the recommended range of 4°-14° however the results were similar to many other clinical studies involving dental students. Table 2 summarises the comparisons of mean taper achieved in this study versus those measured with traditional devices.


Table 2. Comparison of mean bucco-lingual (BL) and mesio-distal (MD) tapers of Clinical and Laboratory specimens with this study and studies utilising traditional methodology.

The comparisons of these data demonstrate that dental students in the Trinidad dental school have produced tapers that are comparable to dental students in many other dental schools around the world (Noonan & Goldfogel, 1991; Sato et al., 1998; Patel et al., 2005; Ayad et al., 2005; Mack, 1980). The dental students in the metrology study not only achieved mean tapers comparable to other students but also to dentists in a US study (Nordlander et al., 1988).

Because of the varying methods used to measure taper in the past, one must compare data with caution, however, it would appear from this work that measurements made by 3-D coordinate metrology are in close range of several studies previously undertaken. The traditional methodologies however do involve forming a two dimensional profile from the three dimensional die replica. This in itself can introduce error. This 3-D coordinate metrology is unique in that it is truly 3-D free-form surface digitisation, rather than 2-D profiling. The software is also able to use the image in a particular requested plane, therefore the taper angles can be calculated in the same plane for each of the samples. This reduces the possible error in angle calculation due to the samples being misaligned. It would be useful to measure the taper of the dies using traditional devices and then measure the taper of the same dies using CMM and compare the data to determine how closely they measure up.
