Microhardness evaluation of root dentin after using resin sealer solvents

Background. This study aimed to assess the effects of methyl ethyl ketone (MEK) and ethyl acetate (EA) on dentin microhardness, used as resin sealer solvents. Methods. Eighty halves of single-rooted teeth were randomly divided into four groups to apply MEK, EA, chloroform, or saline solution. Vickers hardness values were measured for three root levels before and after the direct application of solvents for 5 and 15 minutes or a 1-minute application with ultrasonic agitation. The results were analyzed using repeated-measures ANOVA, and adjustments were made for comparisons with Bonferroni tests. Results. The dentin microhardness decreased in all the solvent groups (P<0.05). The changes in microhardness increased with prolonged exposure times, except for the saline solution group. Chloroform exhibited the most significant decrease in value. Furthermore, ultrasonic agitation elicited a more substantial decline in values. Conclusion. MEK and EA might be preferred over chloroform as a solvent for resin sealers because they offer an attenuated decrease in dentin microhardness and do not have gutta-percha-dissolving properties.

Stability of dental implants with sandblasted and acid-etched (SLA) and modified (SLActive) surfaces during the osseointegration period

Background. The surface properties of implants are effective factors for increasing the osseointegration and activity of osteoprogenitor cells. This study compared the stability of dental implants with sandblasted and acid-etched (SLA) and modified surfaces (SLActive) using the resonance frequency analysis (RFA). Methods. In a split-mouth design, 50 dental implants with either SLA surface properties (n=25) or modified (SLActive) surface properties (n=25) were placed in the mandibles of 12 patients with a bilateral posterior edentulous area. Implant stability was measured using RFA (Osstell) at implant placement time and every week for 1, 2, and 3 months before the conventional loading time. Results. One week following the implantation, implant stability increased from 70 to 77.67 for SLA and from 71.67 to 79 for SLActive (P<0.05). Stability improved each week except in the 4th week in SLActive surface measurements. No significant differences were observed between the groups at 2 and 3 months (P>0.05). Conclusions. For both implant surfaces, increased stability was observed over time, with no significant differences between the groups.

Comparison of infiltration (INF) and inferior alveolar nerve block (IANB) injection techniques in bilateral therapeutic removal of mandibular premolars

Background. The present study aimed to evaluate and compare the anesthetic effect of infiltration (INF) and inferior alveolar nerve block (IANB) techniques for bilateral therapeutic extraction of mandibular premolars. Methods. One hundred patients requiring bilateral therapeutic removal of mandibular premolars were included in the study. For the extraction of the mandibular right premolar tooth, INF was used, and after one week, the mandibular left premolar tooth was extracted using the IANB. The effect of anesthesia between the two techniques was compared and evaluated by ANOVA using SPSS. Results. INF was successful in 78% of cases, whereas IANB was successful only in 22% of cases. Furthermore, INF had a significantly better anesthetic effect than IANB (P<0.05). During pain assessment during the anesthetic drug injection and the procedure, two patients in the INF and five patients in the IANB group reported minimal pain during extraction (P>0.05). The onset of the anesthetic effect was faster in the INF group, while the duration of the effect was longer in the IANB group. Conclusion. INF was a more efficacious local anesthetic technique with high success rate than the IANB technique.

Correlation between mandibular third molar and mandibular incisor crowding: A retrospective CBCT-based study

Background. Late mandibular incisor crowding is a fairly common phenomenon experienced by growing adults. The etiology of late mandibular incisor crowding, however, is controversial and inconclusive. Hence, this study aimed to investigate the correlation between mandibular third molar and mandibular incisor crowding using Cone-beam computed tomography (CBCT) data. Methods. The study consisted of 40 samples of CBCT images divided into two groups (n=20). Group A comprised CBCT images without third molars, and group B included CBCT images with third molars. The images were observed in the axial view and manually marked to calculate the amount of crowding using Little’s irregularity index. The obtained values were statistically analyzed using Pearson’s correlation test. SPSS 23 was used for statistical analysis. Results. The results showed a positive correlation between the mandibular third molars and mandibular incisor crowding, which was significant (P=0.033). The mean Little’s irregularity index score for groups A and B were 4.26 and 6.799, respectively (P=0.033). Conclusion. The positive correlation between the two groups suggests an association between the mandibular third molars and mandibular incisor crowding.

A 3-dimensional finite element analysis to evaluate the impact of force direction, insertion angle, and cortical bone thickness on mini-screw and its surrounding bone

Background. The present study aimed to assess the stress and strain distribution on mini-screws and the surrounding bone in cases of different cortical bone thicknesses (CBTs), mini-screw insertion angles, and force directions using finite element analysis (FEA). Methods. Inventor professional version 8 software was used to construct 24 three-dimensional assemblies of mini-screws inserted with different insertion angles (30º, 60º, and 90º) in alveolar bone blocks with different CBTs (0.5, 1, 1.5, and 2 mm). The models simulated mini-screws inserted in bones with different CBTs and different insertion angles. A 2-N load was applied in two directions to mini-screw heads. The resultant stresses of the applied load were collected from the output of the ANSYS program. Results. The results indicated that force direction affected bone strains as the horizontal force generated more strains on cortical bone than the oblique one. Force applied to 60º inserted mini-screws generated much more strains on cortical bone than 90º and 30º inserted mini-screws. In a 60º inserted mini-screw, the horizontal force generated about 45% more strains on cortical bone than the oblique one. The exerted microstrain on bone decreased as CBT increased. Conclusion. It can be concluded that inserting mini-screws at 60º to the bone surface should be avoided as it generates much more strains on cortical bone than 90º and 30º, especially when a force parallel to the bone surface is applied.

Effect of RaCe, ProTaper, and V-Taper rotary systems on dentinal crack formation during endodontic treatment: An in vitro study

Background. Prevention of dentinal crack formation is of utmost importance in endodontic treatment. This study aimed to evaluate the effect of RaCe, ProTaper, and V-Taper rotary systems on dentinal crack formation in three root regions during endodontic treatment. Methods. Seventy human mandibular first molars were selected randomly, and their distal roots were used. Ten samples were assigned to the control group, and sixty samples were assigned to three groups (n=20). Each group was prepared with RaCe, ProTaper, or V-Taper rotary files according to the manufacturers’ instructions. A stereomicroscope was used to view cracks at ×40 magnification. Friedman’s, chi-squared, and Kruskal-Wallis tests were used for statistical analysis of data (P<0.05). Results. A comparison of the three rotary systems did not reveal any significant differences in the number of cracks between the three root thirds evaluated (P>0.05). A comparison of the number of cracks in the coronal, middle, and apical thirds in each rotary system showed that the number of cracks in the middle third was fewer than that in the two other thirds only in the V-Taper group (P<0.05), with no significant differences in the ProTaper and RaCe groups between the different root regions (P>0.05). Conclusion. The application of RaCe, ProTaper, and V-Taper rotary files resulted in a similar rate of crack formation in endodontic treatment. V-Taper files created the minimum number of cracks in the middle third.

Electromyographic activity of the masseter muscle in individuals with group function and canine guidance

Background. There is no general consensus in restorative dentistry about which lateral guidance should be established. Some studies have shown that canine guidance decreases the tension of masticatory muscles. Others have reported that group function might achieve a better physiologic distribution of occlusal forces. Also, some reports have shown that both guidances are equally acceptable. Despite all discussions, clinical evidence of one guidance being superior to another is limited. Thus, this study aimed to analyze the electromyographic (EMG) activity of masseter muscles in individuals with group function and canine guidance. Methods. Twenty volunteers of both genders, aged 20-25, were divided into two groups: GF (group function guidance, n=10) and CA (canine guidance, n=10). EMG activity of masseters was captured using surface electrodes during habitual maximum intercuspation (HMI) and right and left lateral jaw movements and recorded using EMG amplitude values (RMS – root means square). Student’s t-test was used to compare mean RMS values between the groups and lateral movements in each group. Results. During HMI, there was no difference in masseter EMG activity between the groups. Both masseters showed higher activity in group GF only on the right side during lateral movements, while the left masseter exhibited higher activity on the nonworking side in both groups. The activity of both masseters distributed by tooth was higher in group CA. Conclusion. During tooth restorative procedures, any guidance is acceptable considering HMI. However, group function guidance is more favorable during lateral movements due to greater dissipation of occlusal pressures.

Comparison of radiographic changes in the alveolar crest after extraction of fully and partially erupted premolars during orthodontic treatment: A retrospective analytical study

Background. The alveolar process plays an essential role in providing dental support and gradually disappears with tooth loss. Space deficiency can cause one premolar to remain semi-erupted adjacent to a fully-erupted premolar. During orthodontic treatment, each of these premolars can be extracted. This retrospective study aimed to compare radiographic changes of the alveolar crest due to orthodontic movements of fully-erupted and semi-erupted premolars into the extraction sites before and after treatment. Methods. The patients were divided into the fully-erupted premolar extraction (first) group and the semi-erupted premolar extraction (second) group. The distance between the cementoenamel junction (CEJ) and the alveolar crest, from the distal aspect of the canine to the mesial aspect of the first molar, was measured on panoramic radiographs of 78 patients (39 from each group) before and after treatment with a digital caliper. Changes in the alveolar crest were compared between the two groups. Finally, the height differences of the alveolar crest in mesial and distal aspects of the remaining premolars in both groups were calculated at the end of treatment. Descriptive statistical analyses and paired and independent t tests were used in the study. Results. The distance from the CEJ to the alveolar crest at mesial and distal aspects in the first group and the distal aspect of the extraction site in the second group increased significantly. However, changes at the mesial aspect were not significant in the second group. Comparing the alveolar crest height between the two groups and between the mesial and distal aspects of the remaining premolar tooth indicated no significant differences. Conclusion. No significant difference was observed between the extraction of a fully-erupted or semi-erupted premolar to obtain greater alveolar height.

Effect of laser-microtexturing on bone and soft tissue attachments to dental implants: A systematic review and meta-analysis

Background. It is critical to understand laser-microtextured implant collars’ influence on peri-implant pocket depths and marginal bone levels, especially in crucial areas. The present review investigated the peri-implant marginal bone loss (MBL) and pocket depths and failure rates of dental implants with laser-microtextured collars. Methods. An electronic search was run in the PubMed and Embase databases until September 15, 2019. Randomized and prospective clinical studies comparing peri-implant MBL and pocket depths and failure rates between implants with laser-microtextured and machined collar surfaces were included. Five studies (two cohort studies and three RCTs) were included in the meta-analysis after the inclusion and exclusion criteria and qualitative assessments were applied. The risk ratio of osseointegrated implant failure and mean differences in peri-implant MBL and pocket depths were calculated using the Comprehensive Meta-Analysis (CMA) software. Results. Implants with laser-microtextured collars exhibited significantly better marginal bone level scores (P<0.001; MD: 0.54; 95% CI: 0.489‒0.592) and a significant reduction in peri-implant probing depths than implants with machined collars (P<0.001; MD: 1.01; 95% CI: 0.90‒1.13). The assessed studies showed that 17 out of 516 implants failed (3.29%), comprising nine implants with machined (3.62%) and eight implants with laser-microtextured collars (2.98%). However, no significant differences were detected in the implant neck surface characterization (P=0.695; RR: 1.205; 95% CI: 0.472‒3.076). Conclusion. This study suggests that laser-microtexturing of implant collar significantly affected the peri-implant MBL and probing depths. Although no significant differences were noted in implant failure rates between implants with laser-microtextured and machined collar surfaces, the peri-implant MBL and probing depths with laser-microtextured collars were significantly lower than the machined collars.

Risk factors for actinic cheilitis: A meta-analysis

Background. Actinic cheilitis (AC) is a potentially malignant disorder characterized by chronic lip inflammation, especially the lower lip, associated with accumulative exposure to solar radiation. The present study aimed to assess the possible risk factors related to AC. Methods. A search for studies on AC risk factors was conducted in the following databases: PubMed (MEDLINE, Cochrane Library), Web of Science (WoS), and Google Scholar. For dichotomous outcomes, the estimates of the effects of intervention were expressed as odds ratios (ORs) using Mantel-Haenszel (M-H) method, and for continuous outcomes, the estimates of the effects of intervention were expressed as mean difference (MD) using the inverse variance (IV) method, both with 95% confidence intervals. Results. Twelve studies were considered in this meta-analysis. The factors from the highest to lowest risk of AC were having a low skin phototype (OR: 3.30), age >50 years (OR: 3.01), having high sun exposure, cumulative throughout life (OR: 2.13) as daily (OR: 2.00), being male (OR: 1.78), and being a drinker (OR: 1.56) or smoker (OR: 1.32). However, the use of sunscreen creams and caps/hats to protect against the sun were factors with no significant influence on the AC risk. Conclusion. Chronic sun exposure in subjects with low skin phototypes is the main risk factor for AC.