The Effect of Different Cavity Designs and Temporary Filling Materials on the Fracture Resistance of Upper Premolars Hacer Balkaya, DMD, PhD,* H€ useyin Sinan Topc ¸uo glu, DMD, PhD, † and Sezer Demirbuga, DMD, PhD* Abstract Introduction: The aim of this study was to compare the fracture resistance of upper premolars undergoing root canal treatment that had been temporarily restored with 4 different temporary filling materials. Methods: This study was based on 120 extracted upper premolars. Eight teeth were left intact and served as the negative control group. Mesio-occluso-distal cavities with 2 different designs were prepared for the rest of the teeth (for group 1 a width of one third of the intercuspal dis- tance and for group 2 a width of two thirds of the inter- cuspal distance). Then, the endodontic access cavities were prepared, and the root canals instrumented with Revo-S rotary files (MicroMega, Besancon, France). Thereafter, a total of 16 teeth consisting of 8 each from group 1 and group 2 served as the positive control group and did not have any temporary filling material. The teeth were randomly divided into 4 subgroups (n = 12) according to the temporary filling material: Cavit G (3M ESPE, St Paul, MN), Coltosol F (Colt ene/Whale- dent AG, Altst€ atten, Switzerland), Intermediate Restor- ative Material (Dentsply Sirona, Konstanz, Germany), or DiaTemp (DiaDent Europe BV, Almere, Netherlands). Each specimen was then subjected to a fracture resis- tance test using a universal testing machine until the fracture occurred. The force required to fracture each specimen was recorded, and the data were statistically analyzed. Results: The negative control group showed the highest fracture resistance values compared with the other groups, whereas the positive control groups showed the lowest fracture resistance values. There were no statistically significant differences in the frac- ture resistance of upper premolar teeth undergoing root canal treatment among Cavit G, Intermediate Restorative Material, Coltosol F, and DiaTemp, regard- less of the cavity width (P > .05). Conclusions: The cav- ity design was found to be an effective factor on the fracture resistance of upper premolar teeth undergoing root canal treatment. The temporary filling materials tested did not affect the fracture resistance. (J Endod 2019;-:1–6) Key Words Fracture resistance, root canal treatment, temporary filling material A temporary filling ma- terial is often placed in the access cavities of endodontically treated teeth to seal the root canal between endodontic ap- pointments or until a per- manent restoration takes place (1). During endodontic therapy, a good temporary filling material has to prevent the root canal system from contamination by saliva, fluids, and microorganisms (2). It must also protect teeth against fractures that may be caused by chewing forces between appointments. Vertical root fracture, which may occur during or after endodontic treatment, is a challenging complication that has several predisposing factors such as dehydration of dentin, loss of hard tissue, undesirable effects of irrigation solutions, and excessive pressure during filling procedures (3–5). It is well-known that the prognosis of a tooth with a vertical root fracture is poor, often requiring hemisection or extraction of the tooth, especially when there is severe associated bone loss or a deep periodontal pocket (6, 7). Therefore, after the completion of root canal treatment (RCT), clinicians aim to reinforce the remaining tooth structure between appointments. There are several studies evaluating the effects of different variables including the endodontic rotary file system, intracanal medicament (8, 9), obturation technique (10), permanent coronal restoration type (11, 12), and irrigation solution volume and concentration (5) on the fracture resistance of teeth during RCT procedures. To the best of our knowledge, there are no studies evaluating the effect of various tempo- rary filling materials on the fracture resistance of teeth undergoing RCT with 2 different cavity designs. Therefore, the aim of this study was to evaluate the effects of 4 different From the Departments of *Restorative Dentistry and † Endodontics, Faculty of Dentistry, Erciyes University, Kayseri, Turkey. Address requests for reprints to Dr Hacer Balkaya, Department of Restorative Dentistry, Faculty of Dentistry, Erciyes University, 38039, Melikgazi, Kayseri, Turkey. E-mail address: dhacer89@hotmail.com 0099-2399/$ - see front matter Copyright ª 2019 American Association of Endodontists. https://doi.org/10.1016/j.joen.2019.01.010 Significance The current study determined that the cavity design affected the fracture resistance of upper premolar teeth undergoing root canal treatment, whereas the type of temporary filling material did not. Basic Research—Technology JOE — Volume -, Number -, - 2019 The Fracture Resistance of Upper Premolars 1