AIM First, to examine the impact of the residual volume of coronal tooth structure in posterior teeth measured with an intra-oral scanner on the 4-year clinical survival of root canal retreated teeth. Secondly, to assess retrospectively the effectiveness of the Dental Practicality Index (DPI) in predicting the survival of root canal retreated teeth. METHODOLOGY A total of 156 posterior root canal treated teeth (140 patients) had baseline periapical radiographs (PA) and cone-beam computed tomography (CBCT) scans taken prior to root canal retreatment. These teeth were followed up with a clinical examination at 1, 2, 3 and 4 years (T12, T24, T36 and T48) with periapical radiographs and CBCT images taken at T12, and PA taken at T24, T36 and T48 where appropriate. Root canal retreated teeth were dichotomized into 'survived' versus 'extracted'. Fisher's exact test was used to determine the association between the volume of remaining coronal tooth structure and the 4-year tooth survival. The Dental Practicality Index for each tooth was established using the preoperative clinical and radiographical data. Fisher's exact test was used to establish a relationship between categorical variables, the total score of DPI vs tooth outcome. RESULTS The percentage of extractions associated with teeth with <29.5% remaining coronal tooth structure was 3 times higher (12.5%) compared to that of teeth with a residual tooth structure > 29.5% (3.5%), but with no significant difference (P = 0.073). There was a significant correlation between the outcome of root canal retreatments at 1 year, assessed by both PA and CBCT, and the 4-year survival (Fisher's exact test, P = 0.007 and P = 0.001, respectively). Teeth with DPI scores ≥ 6 were more likely to be extracted than teeth with DPI score < 6 (18.8% vs. 3.9%) (Fisher's exact test, P = 0.045). CONCLUSION Teeth with <30% of remaining tooth structure were associated with a survival rate above 80% and teeth with more than 30% of residual tooth structure survived in more than 94% of the cases. The radiographic outcome of root canal treatment can also help to predict tooth survival with teeth having an unfavourable outcome at 1 year more likely to be extracted within 4 years of completion of treatment. The DPI score can potentially be used to identify teeth with failed root canal treatment, which are likely to be extracted following retreatment and cuspal coverage.

中文翻译：

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一项前瞻性研究，研究了冠状牙齿结构丢失对根管后退牙齿的4年临床存活率的影响，并对牙科实用性指数进行了回顾性验证。

目的首先，研究用口腔内扫描仪测量后牙冠状牙齿结构的残余体积对根管治疗后牙齿的4年临床存活率的影响。其次，回顾性评估牙科实用性指数（DPI）在预测后牙根管存活方面的有效性。方法总共156根后根管治疗的牙齿（140例患者）在根管再治疗前进行了根尖周放射线照相（PA）和锥束计算机断层扫描（CBCT）扫描。对这些牙齿进行1、2、3和4年（T12，T24，T36和T48）的临床检查，并在适当的时候在T12拍摄根尖周X光片和CBCT图像，在T24，T36和T48拍摄PA。将根管后退牙齿分为“存活”与“ 提取”。Fisher精确测试用于确定剩余冠状牙齿结构的体积与4年牙齿存活率之间的关联。使用术前临床和影像学数据确定每颗牙齿的牙科实用性指数。Fisher精确检验用于建立分类变量，DPI总分与牙齿结局之间的关系。结果与剩余冠状牙结构> 29.5％的牙齿相比，与冠状残齿> 29.5％（3.5％）的牙齿相比，拔牙百分比高出3倍（12.5％），但无显着性差异（P = 0.073）。PA和CBCT评估的1年根管再治疗结果与4年生存率之间存在显着相关性（Fisher精确检验，P = 0。007和P = 0.001）。DPI得分≥6的牙齿比DPI得分<6的牙齿更容易拔牙（分别为18.8％和3.9％）（Fisher精确检验，P = 0.045）。结论剩余牙齿结构少于30％的牙齿的存活率高于80％，而剩余牙齿结构超过30％的牙齿的存活率超过94％。根管治疗的放射学结果也可以帮助预测牙齿的存活，其中在治疗完成后4年内有1年不良结果的牙齿更有可能被拔出。DPI分数可潜在地用于识别根管治疗失败的牙齿，这些牙齿很可能在再治疗和and骨覆盖后被拔出。DPI得分≥6的牙齿比DPI得分<6的牙齿更容易拔牙（分别为18.8％和3.9％）（Fisher精确检验，P = 0.045）。结论剩余牙齿结构少于30％的牙齿的存活率高于80％，而剩余牙齿结构超过30％的牙齿的存活率超过94％。根管治疗的放射学结果也可以帮助预测牙齿的存活，其中在治疗完成后4年内，有1年不良结果的牙齿更有可能被拔出。DPI分数可潜在地用于识别根管治疗失败的牙齿，这些牙齿很可能在再治疗和and骨覆盖后被拔出。DPI得分≥6的牙齿比DPI得分<6的牙齿更容易拔牙（分别为18.8％和3.9％）（Fisher精确检验，P = 0.045）。结论剩余牙齿结构少于30％的牙齿的存活率高于80％，而剩余牙齿结构超过30％的牙齿的存活率超过94％。根管治疗的放射学结果也可以帮助预测牙齿的存活，其中在治疗完成后4年内，有1年不良结果的牙齿更有可能被拔出。DPI分数可潜在地用于识别根管治疗失败的牙齿，这些牙齿很可能在再治疗和and骨覆盖后被拔出。30％的剩余牙齿结构与80％以上的存活率相关，而剩余牙齿结构超过30％的牙齿在94％以上的病例中存活。根管治疗的放射学结果也可以帮助预测牙齿的存活，其中在治疗完成后4年内，有1年不良结果的牙齿更有可能被拔出。DPI分数可潜在地用于识别根管治疗失败的牙齿，这些牙齿很可能在再治疗和and骨覆盖后被拔出。30％的剩余牙齿结构与80％以上的存活率相关，而剩余牙齿结构超过30％的牙齿在94％以上的病例中存活。根管治疗的放射学结果也可以帮助预测牙齿的存活，其中在治疗完成后4年内，有1年不良结果的牙齿更有可能被拔出。DPI分数可潜在地用于识别根管治疗失败的牙齿，这些牙齿很可能在再治疗和and骨覆盖后被拔出。根管治疗的影像学结果也可以帮助预测牙齿的存活，其中在治疗完成后4年内有1年不良结果的牙齿更有可能被拔除。DPI评分可潜在地用于识别根管治疗失败的牙齿，这些牙齿很可能在再治疗和and骨覆盖后被拔出。根管治疗的影像学结果也可以帮助预测牙齿的存活，其中在治疗完成后4年内有1年不良结果的牙齿更有可能被拔除。DPI评分可潜在地用于识别根管治疗失败的牙齿，这些牙齿很可能在再治疗和and骨覆盖后被拔出。