| Summary: | 碩士 === 國立臺灣大學 === 臨床牙醫學研究所 === 88 === Vertical root fracture（VRF）is difficult in diagnosis and treatment. According to the literature review, VRF occurs more frequently in teeth that have received endodontic treatment. There are some studies working on the possible causes of vertical root fractures, but the etiologies of this disease still remained uncertain. Besides, VRF can also be found clinically in non-endodontically treated teeth. The relative literature is sparse, therefore, its possible causes are yet to be known. Understanding the factors that predispose a tooth to fracture is essential to develop thorough concept of diagnosis, treatment, and prevention. The specific aims of this study were as follows: 1. the characteristics of VRF by clinical survey; 2. to observe the fracture characteristics; 3. to understand more comprehensive in its possible etiologies and mechanisms; 4. to compare the biomechanical properties of dentin in VRF teeth with those of normal ones.
One hundred and twenty teeth with the diagnosis of VRF were included in this study. The patients’ dental history, clinical manifestation, and radiographic findings were recorded. All the fractured teeth were divided into 6 groups: 1. Group ED endodontically treated teeth, operative restorations without posts; 2. Group EC endodontically treated teeth, crowns or bridges reconstruction without posts; 3. Group EPC endodontically treated teeth, crowns or bridges reconstruction with posts; 4. Group N non-endodontically treated teeth without any restorations; 5. Group ND non-endodontically treated teeth with operative restorations; 6. Group NC non-endodontically treated teeth with crowns or bridges reconstruction. Stereomicrographic observation and SEM fractographic study were utilized to determine the directions of crack initiation and propagation, and the fracture patterns. Vickers microhardness and elastic modulus of dentin were determined by the dynamic microindentation test in order to understand the differences of mechanical properties between vertical root fractured teeth and normal ones.
The results revealed that: 1. 87% VRF occurred in endodontically treated teeth with crowns or bridges reconstruction. It implies that restorations such as full crowns or bridges do not prevent VRF. 2. Fractures extended primarily buccolingually not only in endodontically treated teeth but in non-endodontically ones. 3. Most fractures extended to reconstructed crown margins in group EC, EPC, and NC. However, in group ED, N, and ND, fractures never extended within 0.5㎜ to CEJ. It appears that DEJ may play an important role in resisting crack propagation. 4. VRF is chronic fracture as well as a fatigue fracture. 5. The change of biomechanical properties of root dentin seems not to affect the occurrence of vertical root fracture.
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