Hölttä P, Nyström M, Evälahti M, Alaluusua S
Department of Pedodontics and Orthodontics, Institute of Dentistry, Hospital for Children and Adolescents, University of Helsinki, Finland.
Eur J Orthod. 2004 Oct;26(5):491-7. doi: 10.1093/ejo/26.5.491.
An unfavourable root-crown (R/C) ratio caused by short dental roots may result from a developmental deficiency, root resorption after orthodontic treatment, or dental trauma. In the assessment of root shortening, subjective grading has often been used. For objective tooth measurements, varying materials and methods may make the results impossible to compare. This study used a simple, objective method to assess the R/C ratio (relative root length) of mature permanent teeth from panoramic radiographs (PRGs), tested its reproducibility and calculated the mean values of R/C ratios and their variations in a healthy Caucasian (Finnish) population. Two thousand seven hundred and seventy-nine teeth were measured on 108 PRGs. The intra- and inter-examiner reproducibility of the assessment method was good (Pearson correlation coefficients 0.87 and 0.83, respectively; P < 0.001) and the mean R/C ratios did not differ between the repeated measurements (P > 0.05). The biological variance in all cases exceeded the error variance for each tooth. These facts suggest that the method reported in this study can be used in the assessment of the relative root length of 'normal' teeth and its alterations in teeth with developmental or acquired aberrations of dental roots. Males, overall, tended to have higher R/C ratios than females; P-values varied from non-significant to less than 0.01. With the exception of the permanent lateral incisors in males and the permanent second molars in both genders, the ratios of the antagonist teeth were significantly greater in the mandible than in the maxilla (P < 0.05 for the lateral incisors of females; P < 0.001 for all other teeth). Consequently, in quantifying root shortening in developmentally short-rooted teeth, tooth- and gender-specific reference values should be employed. The Finnish R/C data reported here for all teeth except third molars could be used for comparison with other populations, patient groups or individuals where crown-root aberrations are suspected.
牙根过短导致的不良根冠比（R/C）可能源于发育缺陷、正畸治疗后的牙根吸收或牙外伤。在评估牙根缩短时，常采用主观分级。对于客观的牙齿测量，不同的材料和方法可能导致结果无法比较。本研究采用一种简单、客观的方法，通过全景X线片（PRG）评估成熟恒牙的R/C比（相对根长），测试其可重复性，并计算健康高加索（芬兰）人群的R/C比平均值及其变化。在108张PRG上测量了2779颗牙齿。该评估方法的检查者内和检查者间可重复性良好（Pearson相关系数分别为0.87和0.83；P<0.001），重复测量的平均R/C比无差异（P>0.05）。所有病例的生物学变异均超过每颗牙齿的误差变异。这些事实表明，本研究报道的方法可用于评估“正常”牙齿的相对根长及其在牙根发育或后天异常牙齿中的改变。总体而言，男性的R/C比往往高于女性；P值从无显著性差异到小于0.01不等。除男性的恒侧切牙和两性的恒第二磨牙外，下颌拮抗牙的比值显著大于上颌（女性侧切牙P<0.05；所有其他牙齿P<0.001）。因此，在量化发育性短根牙的牙根缩短时，应采用牙齿和性别特异性的参考值。这里报道的除第三磨牙外所有牙齿的芬兰R/C数据可用于与其他怀疑有冠根异常的人群、患者组或个体进行比较。
