الملخص
<p style="direction: ltr;"><strong>ABSTRACT</strong></p>
<p style="direction: ltr;"><strong>Statement of the Problem:</strong> Clinicians must ensure that tooth preparation for extra - coronal restorations have adequate resistance form to Improve the long - term success of the restoration. Among the factors affecting resistance form of cemented full coverage restorations are total occlusal convergence (TOC), occluso - cervical dimension (OCD), and occluso - cervical to facio- lingual ratio (OC / FL ratio).</p>
<p style="direction: ltr;"><strong>Purpose:</strong> The purpose of this prospective study was to evaluate mesio - distal total occlusal convergence (MD - TOC), faclo - lingual total occlusal convergence (FL - TOC), OCD, and OC / FL ratio of posterior teeth preparations for cemented full coverage single crowns carried out by students at different stages of their training at the College of Dentistry, Ajman University.</p>
<p style="direction: ltr;"><strong>Material and Methods</strong>: Resistance features of 344 teeth preparations consecutively performed, under normal working conditions, by students at preclinical third year, clinical fourth year, Internship program, and Master of Science in Restorative Dentistry program were evaluated. Two dies of each tooth preparation were obtained. The first die of each tooth preparation was sectioned in meslo - distal direction, whereas the second die was sectioned in facio - lingual direction. Dies sectioned in mesio - distal direction were used for measurements of MD - TOC. On the other hand, dies sectioned in facio - lingual direction were used for measurements of FL - TOC, OCD, and OC / FL ratio. Measurements of TOC were carried out on images obtained using the Dino lite pro digital microscope at a magnification of 20 X. Measurements of OCD and OC / FL ratio were carried out on images obtained using stereomicroscope at a magnification of 8X.</p>
<p style="direction: ltr;"><strong>Results:</strong> The overall mean of MD - TOC and FL - TOC achieved by all students were 20.83 ± 10.023 ° and 22.20 ± 9.80 ° respectively. The overall OCD and OC / FL ratio achieved by all students were 3.9409 ± 1.473 mm and 0.52 ± 0.155 respectively. MD - TOC achieved by students at third and fourth years as well as interns and master students were 15.52 ± 7.978 °, 23.11 ± 9.619 °, 24.96 ± 10.999 °, 18.91 ± 8.425 ° respectively. Statistical analysis revealed that undergraduate third year preclinical students and postgraduate masters ' students achieved significantly lower MD - TOC than undergraduate fourth year and internship students. FL - TOC achieved by students at third year (17.98 ± 8.775 °) were significantly lower than those achieved by fourth year (23.45 ± 9.282 °) and interns (25.66 ± 10.703 °). Furthermore, FL - TOC achieved by master students (20.26 ± 8.969 °) were significantly lower than those achieved by interns. Both MD - TOC and FL - TOC achieved by third year and masters ' students were within the recommended 20 ° TOC, On the other hand, MD - TOC and FL - TOC achieved by fourth year and interns were higher than the recommended values. OC / FL ratio achieved by third year (0.56 ± 0.152), fourth year (0.51 ± 0.152), Interns (0.46 ± 0.139), and masters ' students (0.51 ± 0.160) were higher than the recommended 0.4 values. The TOC achieved by male students (MD - TOC of 19.17 ± 9.864 °; FL - TOC of 20.08 ± 9.070 °) were significantly lower than those achieved by female students (MD - TOC of 22.20 ± 9.972 °; FL - TOC of 23.74 ± 10.043 °), however there was no difference in OC / FL ratio of teeth prepared by both genders.</p>
<p style="direction: ltr;"><strong>Conclusions</strong>: During teeth preparations of cemented full coverage posterior single crowns under normal working conditions, both undergraduate third year preclinical and masters ' students were able to achieved lower TOC than fourth year and internship students at Ajman University. Posterior teeth preparations made by third year and masters ' students were within the recommended 20 ° for TOC. On the other hand, preparations made by fourth year and Internship students had higher TOC than the recommended values. All students at College of Dentistry, Ajman University were able to achieve higher OC / FL ratio than the recommended values. Furthermore, male students achieved lower TOC than female students.</p>
