Hayes A, Duvall N, Wajdowicz M, Roberts H
Oper Dent. 2017 May/Jun;42(3):327-334. doi: 10.2341/16-097-L.
The purpose of this study was to evaluate the effect of endocrown pulp chamber extension on mandibular molar fracture resistance.
A total of 36 recently extracted mandibular third molars of approximate equal size were sectioned at the facial lingual height of contour followed by endodontic access into the pulp chamber. The specimens were then randomly divided into three groups (n=12) and pulpal and root canal contents removed. Pulp chamber floors were established at 2, 3, and 4 mm from the occlusal table using a three-step etch-and-rinse adhesive and a flowable resin composite. The prepared specimens were then embedded in auto-polymerizing denture base resin with surface area available for adhesive bonding determined using a digital recording microscope. Specimens were restored using a standardized template with a chairside computer-aided design/computer-aided manufacturing unit with the endocrown milled from a lithium disilicate glass-ceramic material. Restoration parameters of occlusal table anatomy and thickness were standardized with the only parameter difference being the pulp chamber extension depth. The endocrown restorations were luted with a self-adhesive resin luting agent and tested to failure after 24 hours on a universal testing machine, with force applied to the facial cusps at a 45° angle to the long axis of the tooth. The failure load was converted into stress for each specimen using the available surface area for bonding. Mean failure load and stress among the three groups was first subjected to the Shapiro-Wilk and Bartlett tests and then analyzed with an analysis of variance with the Tukey post hoc test at a 95% confidence level (p=0.05).
The 2- and 4-mm chamber extension groups demonstrated the highest fracture resistance stress, with the 3-mm group similar to the 2-mm group. The 3- and 4-mm chamber extension group specimens demonstrated nearly universal catastrophic tooth fracture, whereas half the 2-mm chamber extension group displayed nonrestorable root fractures.
Under the conditions of this study, mandibular molars restored with the endocrown technique with 2- and 4-mm pulp chamber extensions displayed greater tooth fracture resistance force as well as stress. All groups demonstrated a high number of catastrophic fractures, but these results may not be clinically significant because the fracture force results are higher than normal reported values of masticatory function.
本研究旨在评估髓腔冠部延伸对下颌磨牙抗折性的影响。
选取36颗近期拔除的大小近似的下颌第三磨牙，在牙冠的颊舌侧外形高点处进行切割，然后进行开髓进入髓腔。将标本随机分为三组（n = 12），去除牙髓和根管内容物。使用三步酸蚀冲洗粘结剂和流动树脂复合材料，在距咬合面2、3和4 mm处建立髓腔底。然后将制备好的标本嵌入自凝义齿基托树脂中，使用数字记录显微镜确定可供粘结的表面积。使用椅旁计算机辅助设计/计算机辅助制造单元，通过标准化模板对标本进行修复，髓腔冠由二硅酸锂玻璃陶瓷材料铣削而成。咬合面解剖结构和厚度的修复参数进行了标准化，唯一的参数差异是髓腔延伸深度。髓腔冠修复体用自粘结树脂粘结剂粘结，在万能试验机上放置24小时后进行破坏试验，以与牙齿长轴呈45°角的力施加于颊尖。使用可供粘结的表面积将每个标本的破坏载荷转换为应力。首先对三组的平均破坏载荷和应力进行Shapiro-Wilk和Bartlett检验，然后在95%置信水平（p = 0.05）下用方差分析和Tukey事后检验进行分析。
2 mm和4 mm髓腔延伸组显示出最高的抗折应力，3 mm组与2 mm组相似。3 mm和4 mm髓腔延伸组的标本几乎全部发生灾难性牙齿折断，而2 mm髓腔延伸组有一半出现不可修复的牙根折断。
在本研究条件下，采用髓腔冠技术修复且髓腔延伸2 mm和4 mm的下颌磨牙显示出更大的抗折力和应力。所有组均出现大量灾难性折断，但这些结果可能在临床上无显著意义，因为折断力结果高于正常报道的咀嚼功能值。
