Harsha Madhavareddy Sri, Praffulla Mynampati, Babu Mandava Ramesh, Leneena Gudugunta, Krishna Tejavath Sai, Divya G
General Practitioner, Consultant Endodontist, Guntur, Andhra Pradesh, India.
Senior Lecturer, Department of Conservative Dentistry and Endodontics, Drs Sudha and Nageswara Rao Siddhartha Institute of Dental Sciences, Vijayawada, Andhra Pradesh, India.
J Clin Diagn Res. 2017 May;11(5):ZC45-ZC48. doi: 10.7860/JCDR/2017/25305.9856. Epub 2017 May 1.
Cavity preparations of posterior teeth have been frequently associated with decreased fracture strength of the teeth. Choosing the correct indirect restoration and the cavity design when restoring the posterior teeth i.e., premolars was difficult as it involves aesthetic, biomechanical and anatomical considerations.
To evaluate the fracture resistance and failure pattern of three different cavity designs restored with monolithic zirconia.
Human maxillary premolars atraumatically extracted for orthodontic reasons were chosen. A total of 40 teeth were selected and divided into four groups (n=10). Group I-Sound teeth (control with no preparation). Group II-MOD Inlay, Group III-Partial Onlay, Group IV-Complete Onlay. Restorations were fabricated with monolithic partially sintered zirconia CAD (SAGEMAX- NexxZr). All the 30 samples were cemented using Multilink Automix (Ivoclar) and subjected to fracture resistance testing using Universal Testing Machine (UTM) (Instron) with a steel ball of 3.5 mm diameter at crosshead speed of 0.5 mm/minute. Stereomicroscope was used to evaluate the modes of failure of the fractured specimen. Fracture resistance was tested using parametric one way ANOVA test, unpaired t-test and Tukey test. Fracture patterns were assessed using non-parametric Chi-square test.
Group IV (Complete Onlay) presented highest fracture resistance and showed statistical significant difference. Group II (MOD Inlay) and Group III (Partial Onlay) showed significantly lower values than the Group I (Sound teeth). However, Groups I, II and III presented no significant difference from each other. Coming to the modes of failure, Group II (MOD Inlay) and Group III (Partial Onlay) presented mixed type of failures; Group IV (Complete Onlay) demonstrated 70% Type I failures.
Of the three cavity designs evaluated, Complete Onlay had shown a significant increase in the fracture resistance than the Sound teeth.
后牙的窝洞预备常常与牙齿折裂强度降低相关。在修复后牙即前磨牙时，选择正确的间接修复体和窝洞设计很困难，因为这涉及美学、生物力学和解剖学方面的考量。
评估用整块氧化锆修复的三种不同窝洞设计的抗折性和失败模式。
选择因正畸原因无创伤拔除的人类上颌前磨牙。共选取40颗牙齿并分为四组（n = 10）。第一组——完整牙齿（未做预备的对照）。第二组——MOD嵌体，第三组——部分高嵌体，第四组——完整高嵌体。修复体用整块部分烧结的氧化锆CAD（SAGEMAX - NexxZr）制作。所有30个样本用Multilink Automix（义获嘉）粘结，并用万能试验机（UTM）（英斯特朗）以0.5毫米/分钟的十字头速度使用直径3.5毫米的钢球进行抗折性测试。用体视显微镜评估断裂标本的失败模式。使用参数单因素方差分析、非配对t检验和Tukey检验对抗折性进行测试。使用非参数卡方检验评估断裂模式。
第四组（完整高嵌体）表现出最高的抗折性，且显示出统计学上的显著差异。第二组（MOD嵌体）和第三组（部分高嵌体）的值明显低于第一组（完整牙齿）。然而，第一组、第二组和第三组之间彼此无显著差异。关于失败模式，第二组（MOD嵌体）和第三组（部分高嵌体）呈现混合型失败；第四组（完整高嵌体）显示70%为I型失败。
在评估的三种窝洞设计中，完整高嵌体的抗折性比完整牙齿有显著提高。
