Objective: This study aimed to evaluate the effect of access cavity design on the amount of apically extruded debris in maxillary molars. Methods: Twenty-eight extracted maxillary molars were selected for this study. Inclusion criteria were caries-free teeth with mature roots and similar mesiobuccal root dimensions. The samples were randomly assigned into two groups, as follows: conservative endodontic cavity (CEC) and traditional endodontic cavity (TEC). Mesiobuccal canals of the teeth were instrumented using Reciproc instruments. Preweighed plastic tubes were used for collecting the apically extruded debris. The weights of plastic tubes (pre-and post-instrumentation) were determined using an electronic balance. The data were analyzed with an independent sample t-test, and a P-value < 0. 05 was considered statistically significant. Results: The weight of apically extruded debris was significantly lower in the TEC group than in the CEC group (P =0. 003). Conclusions: The results of this in vitro study demonstrated that TEC preparation was superior to the CEC approach in terms of minimizing apical extrusion of debris.

Introduction & Objective: Preparation of access cavity to root canal is a critical phase in endodontic treatment. The purpose of this study was to evaluate the effect of access cavity location (labial or palatal) on fracture resistance of endodontically treated maxillary central teeth.Materials & Methods: In this experimental laboratorial study, 84 intact human maxillary central incisors with similar dimensions were selected. The teeth were divided into 4 test groups as follows: Group 1: teeth without access cavity (control group); Group 2: teeth with labial access; Group 3: teeth with palatal access; and Group 4: teeth with labial & palatal accesses. Root canals were cleaned and lateral condensation technique was used to obdurate the canals and root canal therapy was completed. The access cavities were restored with a light cured microhybrid resin composite. Continuous compressive force at a crosshead speed of 2 mm/min was applied by a testing machine. Load at fracture was recorded in MPa. Modes of fracture were assessed using stereomicroscope at X20 magnification. Data was analyzed using One-Way analysis of Variance and Tukey HSD tests.Results: Means and standard deviations of fracture resistance for the 4 tested groups were: G1: 1172.2±224.05N, G2:990.4±199.324 N, G3: 861.95±237.089N and G4:784.27±221.586 N. There was significant difference in fracture resistance values between G1 (control) and each tested group (P<0.05). Mean fracture resistance for the test group with labial access was higher than the test group with palatal access but no significant difference was observed. Group 2 showed statistical difference compared with group 4 (P=0.017) but there is no significance between group 3 and group 4(P=0.666). Fracture modes in all groups were an oblique pattern and maximum and minimum of unfavorable fractures were seen in the control group with 48% and group 3 with 5%.Conclusion: Preparation of access cavity reduces tooth fracture resistance. Palatal and labial& palatal accesses decrease considerably tooth fracture of resistance.

Introduction: Implant-supported prostheses can be screw-type or can be cemented onto the abutment. Use of permanent cements, which are used in conventional prostheses, is not recommended for implant-supported prostheses. These cements are very strong and do not allow easy removal of the prosthesis. By using temporary cements not only permanent cement faults will be eliminated but also prosthesis can be retrieved as needed. The aim of this study was to evaluate the effect of screw access filling material and cement on the retention of implant cemented crowns. Materials & Methods: In this in vitro study, 5 angulated abutments (15° ) were screwed onto the analogue and ten crowns were fabricated for each of them. Four filling materials, Coltosol, composite resin, Teflon tape and silicone, were used to fill the access cavity and one abutment was left empty (only the screw was covered). Two temporary cements (Temp Bond and Temp Bond NE) were used to cement the crowns. The force required to remove the crowns was measured with a universal testing machine at a crosshead speed of 5 mm/min. Data were analyzed with ANOVA and Tukey test (α = 0. 05). Results: In all the samples, the force required to separate the casting crowns from the abutment were higher in Temp Bond NE group and this difference was statistically significant (p value = 0. 007). In addition, the difference between the access filling material was statistically significant (p value ˂ 0. 001). Therefore in each group, Coltosol, empty, composite resin, Teflon and the condensational silicone exhibited the highest means of separating force in ascending order. Conclusion: Retention of implant-supported crowns was influenced by types of filling material, access cavity and cement used.

Introduction: This invitro study aims to compare the discoloration in endodontically treated and restored anterior teeth with a traditional endodontic cavity (TEC), conservative endodontic cavity (CEC), and “ninja” or ultraconservative (NEC) endodontic access cavity. Materials and Methods: In this experimental laboratory study conducted in Shiraz Dental Faculty in 2018, 46 intact human maxillary anterior teeth were randomly assigned to 5 groups. Three experimental groups, TEC, CEC, NEC (n = 12), and two control groups: positive (D) and negative (E) control groups (n = 5). Discoloration was assessed at the baseline (T = 0), after preparing the access cavity (T = 1), after endodontic treatment and restoration (T = 2), after one week (T = 3), after one month (T = 4), after three months (T = 5) and after six months (T = 6). Statistical analysis was performed using multi-sample repeated measures analysis of variance, one-way ANOVA, and Tukey test. Results: In all groups, significant changes were observed in the discoloration over time (p value < 0. 05). The NEC group had a significantly higher level of discoloration in ∆E1 (after preparing access cavity) and ∆E2 (after endodontic treatment and restoration). The NEC group had a significantly higher level of discoloration in ∆E3 (1 week) than The TEC group (p value < 0. 05). ∆E4 (1 month), ∆E5 (3 months), ∆E6 (6 months) were not significantly different between the three experimental groups. The highest level of discoloration pertained to ∆E6 (1 month later) in all groups. Conclusion: Despite statistically significant differences in the groups up to the first week, there is no significant difference in tooth color change with standard, conservative, and ultraconservative access cavities in the time intervals of 1 month, two months, and six months.