Evaluation of the Selected Root-to-Crown Ratio of Crowned Teeth in a Hospital Setting: A Cross-sectional Study

Aims: The root-to-crown (R/C) ratio is envisaged to influence the longevity of crowned teeth. The purpose of this study is to measure the selected R/C ratio of crowned teeth at the Royal Dental Hospital of Melbourne, and to evaluate the effect of tooth category and location on the R/C ratio.

Study Design: Retrospective study.

Place and Duration of Study: Melbourne Dental School and the Royal Dental Hospital of Melbourne, between February 2014 and July 2015.

Methodology: Peri-apical radiographs of patients treated with single tooth crowns were retrieved. The radiographs were confirmed to be of diagnostic quality and covered the entire crowned tooth. All the selected radiographs were scanned and converted to digital radiographs. With the aid of image manipulation software, the crown and root lengths were measured along the long axis of the tooth. The bone crest level separated the crown and the root. Subsequently, the R/C ratio was established. In addition, the mean R/C ratio was calculated for all the teeth and for every single tooth category. The impact of tooth type and location within the arch on the R/C ratio was statistically evaluated.

Results: A total of 257 crowned teeth were included. The mean R/C ratio was 1.43. Canines had the lowest R/C ratio followed by molars, incisors and premolars respectively. The significant difference existed between incisors and premolars (P = .04), and between premolars and molars (P = .01). In general, the maxillary anterior region exhibited a greater R/C ratio than the mandibular anterior region. However, for the posterior region, the mandibular teeth had a slightly greater R/C ratio than the maxillary teeth.

Conclusion: The implemented R/C ratio of the crowned teeth in this study was close to the recommended ratio of 1.5. Although differences exist between the different tooth categories, the actual difference is minimal. Thus it is difficult to set the R/C ratio recommendation for each tooth category.