The Effects of Different Attachment Types and Positions on Rotation Movement in Clear Aligner Treatments: A Finite Element Analysis.

Aim Rotation of the mandibular premolars during aligner treatment is a difficult movement to achieve accurately. The purpose of this study is to compare the effects of different attachment types and positions used in clear aligner treatments on the rotation movement and retention of clear aligners in the rotated first premolar teeth. The study also addressed the stress values in periodontal ligaments (PDLs) with finite element analysis. Materials and methods For purposes of this research, we created a mandibular tooth model and modeled the premolar tooth with a 30° rotation. Twelve separate groups were created by attaching horizontal rectangular, vertical rectangular, ellipsoid, and semi-ellipsoid attachments to the premolar tooth in buccal, lingual, and combined buccal and lingual ways. A model without attachments was created to be used as the control group. An activation movement of 0.25 mm was applied to the first premolar tooth in all 12 models. The study evaluated clear aligner displacement, von Misses stress on the PDL, and tooth displacements using the finite element stress analysis method. Results It was found that the group with horizontal rectangular attachments placed on both the buccal and lingual sides had the highest stress value in the PDL (0.1971 MPa) and the highest displacement in the tooth (0.1267 mm). Conversely, the group with semi-ellipsoid attachments placed both buccally and lingually had the least displacement movement in clear aligners (0.1441 mm). Conclusion The results indicate that groups with attachments provided better retention than groups without attachments. Models with horizontal, rectangular attachments showed significantly more tooth displacement compared to other models. Horizontal rectangular attachments placed buccally and lingually combined to provide tooth movement in rotated mandibular first premolars can be recommended for clinical use.

Endodontic Management of a Mandibular Second Premolar with Three Root Canals and Taurodontism: A Case Report.

A complete understanding of canal morphology is essential to achieve successful endodontic treatment. Although mandibular second premolars are reported to have usually only one root canal at the apex, in this case we reported a mandibular second premolar with three root canals and taurodont morphology. A patient was referred to the endodontic department at Mashhad Faculty of Dentistry with a chief complaint of pain in her mandibular right second premolar tooth. The diagnosis of pulpal necrosis and chronic apical periodontitis was established. The initial radiograph showed a taurodont premolar with two roots. However, with cone-beam computed tomography assistance, three root canals were confirmed. The root canal treatment process was successfully managed with a dental operating microscope. Using cone-beam computed tomography and a dental operating microscope greatly facilitated the determination of tooth morphology and successful following nonsurgical endodontic treatment.

Cone beam computed tomography evaluation of c-shaped canal morphology in mandibular premolar teeth.

Purpose: The aim of this study was to evaluate the prevalence and the morphology of c-shaped root canal(s) in mandibular premolars using cone beam computed tomography (CBCT) images. Materials and methods: CBCT images of 1095 mandibular premolars were examined at coronal, middle, and apical levels of the root canals. The type, the level, and the position (buccal or lingual) of the c-shaped anatomy were recorded. Absolute counts and percentages of different groups and subgroups of C-shape morphologies were calculated. The Chi-square test was used to compare the prevalence of C-shaped morphology between mandibular first and second premolars. The Z-test for proportions in independent groups was used to analyze the differences in mandibular C-shaped premolar proportions between location (left and right side) and tooth (first or second premolars) (p=0.05). Results: C-shaped root canal morphology was present in 44 teeth. The percentage of c-shaped morphologies was 6.9% and 1.6% in mandibular first and second premolars, respectively. Comparison of the first and the second premolars showed that C1 type (p=0.008) and C4b type (p=0.013) configurations are more common in the first premolars at the coronal level. In contrast, the C2 type configuration showed significantly higher prevalence in the second premolars (p=0.009). Additionally, the C4c type configuration was significantly frequent on the right premolars at the coronal level (p=0.038). Conclusion: C-shape canal morphology is a rare but complex anatomic feature in mandibular premolars. Therefore, clinicians should be aware of this complex root canal anatomy for the success of endodontic treatment in mandibular premolar teeth.

Influence of endodontic access cavity design on mechanical properties of a first mandibular premolar tooth: a finite element analysis study.

OBJECTIVES: This study aimed to investigate the influence of access cavity designs on the mechanical properties of a single-rooted mandibular first premolar tooth under various static loads using a finite element analysis. MATERIALS AND METHODS: 3-dimensional FEA designs were modeled according to the access cavity designs: an intact tooth (control), traditional access cavity (TEC-I), traditional access cavity with Class-II mesio-occlusal cavity design (TEC-II), conservative access cavity (CEC), ninja access cavity (NEC), caries-driven access cavity (Cd-EC), buccal access cavity (BEC) and bucco-occlusal access cavity (BOEC). After the simulated access cavity preparations, root canal treatment was simulated and three different static loads which mimicked oblique and vertical mastication forces were applied to the models. The stress distribution and maximum Von Misses stress values were recorded. The maximum stress values were obtained on both enamel and dentin under multi-point vertical loads. RESULTS: The maximum stress values were obtained on both enamel and dentin under multi-point vertical loads. Under all load types, the minimum stress distribution was observed in the control group, followed by CEC, NEC and BEC designs. The highest stress concentration was detected in Cd-EC and TEC-II designs. Under single-point vertical loading, the stress was mostly concentrated in the lingual PCD area, while under multi-point vertical loading, the entire root surface was stress-loaded except for the lingual apical third of the root. CONCLUSION: Preserving tooth tissue by simulating CEC, NEC and BEC access cavities increased the load capacity of a single-rooted mandibular first premolar following simulated endodontic treatment.

Mandibular Second Premolar Agenesis: A Retrospective Cross-sectional Study from Palestine.

Objectives: This retrospective study aimed to determine the prevalence of congenitally missing mandibular second premolars. Materials and Methods: A total of 1,843 radiographs were collected from five different cities in Palestine. Two experienced dentists independently examined the panoramic radiographs and demographic data (age and gender). Results: Among the 1,843 radiographs, 1,039 were for females (57.37%) and 804 were for males (43.63%); 13 cases had at least one congenitally mandibular second premolar. The prevalence of congenitally missing mandibular second premolars in the study population was 0.7%. There was no significant association between gender and mandibular second premolar agenesis. Unilateral agenesis was more common than bilateral, and the left side had more cases of congenitally missing mandibular second premolars than the right side. Conclusions: The prevalence of congenitally missing mandibular second premolars in this study population was 0.7%, within the range reported in other populations.

Fracture resistance of post and core in immediate and delayed post space in trauma simulated teeth.

INTRODUCTION: This research aims to assess and analyze the fracture resistance of GC Everstick post with separate composite core buildup and Edelweiss prefabricated resin composite post and core single unit into immediate and delayed post space prepared teeth. METHODS: A total of 120 extracted human mandibular premolars have been subjected to a standardized protocol of mechanical trauma to simulate tooth fracture. Teeth samples were randomly divided into four groups (n = 30) on the basis of time taken for the preparation of post space (approximately following root canal obturation and 24 h after root canal obturation) for the single unit Edelweiss post and core system and GC post with separate core buildup. Compressive load has been utilized to do the analysis necessary to establish the fracture resistance using a universal testing machine. The fracture force calculated was in Newtons (N), and a stereomicroscope was utilized for investigating the common causes of failure. RESULTS: In an immediate post space prepared tooth, the GC post exhibited a mean failure load of 970.584 N. In contrast, the Edelweiss post, and core system showed a significantly higher mean failure load of 1250.349 N. In delayed post space prepared tooth, the GC Everstick post exhibited a mean failure load of 950.287 N. In contrast, the Edelweiss post, and core system showed a significantly higher mean failure load of 1229.348 N. CONCLUSION: This study aims to assess and analyze the fracture resistance of the GC Everstick post with separate composite core buildup and the Edelweiss prefabricated resin composite post and core single unit in immediate and delayed post space prepared teeth. The study results showed that the failure modes in both groups were non-catastrophic in nature. These findings suggest that the Edelweiss post and core system may be a more suitable option for restoring teeth that have been subjected to traumatic conditions. The study provides valuable information for dental professionals in their decision-making process for post and core restoration techniques in teeth that have been subjected to trauma.

Apexification of dens evaginatus in a mandibular premolar: A case report.

Key Clinical Message: Dens evaginatus is an uncommon dental anomaly presenting on mandibular premolar teeth. Affected teeth are difficult to diagnose and manage, and often demonstrate immature apices requiring complex endodontic treatment approaches. Abstract: Dens evaginatus (DE) is an uncommon anomaly affecting mandibular premolars, frequently requiring endodontic intervention. This report documents the treatment of an immature mandibular premolar presenting with DE. Early diagnosis and preventive strategies remain the preferred management for these anomalies, however endodontic approaches may be successfully applied to retain these teeth.

A case of peripheral odontogenic fibroma arising in the mandibular premolar region of a teenager.

Peripheral odontogenic fibroma (POdF) is a rare, benign ectomesenchymal tumor. Herein, we report a case of a 15-year-old female patient who developed POdF in the mandible. The lesion was resected along with the periosteum. Histopathological findings revealed a small mass and cord-like epithelium. There was no recurrence 16 months postoperatively.

Shape and anatomical relationship of the mental foramen to the mandibular premolars in an Indian sub-population: a retrospective CBCT analysis.

Objectives: This study assessed the shape and anatomical relationship of the mental foramen (MF) to mandibular posterior teeth in an Indian sub-population. Materials and Methods: In total, 475 existing cone-beam computed tomography records exhibiting 950 MFs and including the bilateral presence of mandibular premolars and first molars were assessed. Images were evaluated 3-dimensionally to ascertain the position, shape, and anatomical proximity of MFs to mandibular teeth. The position and shape of MFs were measured and calculated. The Pythagorean theorem was used to calculate the distance between the root apex of the mandibular teeth and the MF. Results: MFs exhibited a predominantly round shape (left: 67% and right: 65%) followed by oval (left: 30% and right: 31%) in both males and females and in different age groups. The root apices of mandibular second premolars (left: 71% and right: 62%) were closest to the MF, followed by distal to the first premolars and mesial to the second premolars. The mean vertical distance between the MF and the nearest tooth apex calculated on sagittal sections was 2.20 mm on the right side and 2.32 mm on the left side; no significant difference was found according to sex or age. The distance between the apices of the teeth and the MF was ≥ 4 mm (left; 4.09 ± 1.27 mm and right; 4.01 ± 1.15 mm). Conclusions: These findings highlight the need for clinicians to be aware of the location of the MF in treatment planning and while performing non-surgical and surgical endodontic procedures.

Prevalence of complex root canal morphology in the mandibular first and second premolars in Thai population: CBCT analysis.

BACKGROUND: Mandibular premolars demonstrate high variability in root canal morphology, especially mandibular first premolars. The purposes of this study were to determine the prevalence of root canal configurations of mandibular premolars according to Vertucci classification in a Thai population. METHODS: Total of 1159 CBCT images of Thai patients who received radiographic imaging at the Department of Radiology, Faculty of Dentistry, Chulalongkorn University in 2017-2018 was evaluated. The data were reported using descriptive statistics and the relationship between the prevalence of the root canal complexities and sex was analyzed using the chi-squared test. RESULTS: The most common root canal configuration was Vertucci type I, with a 63.1% and 98% prevalence in the mandibular first and second premolars, respectively. More than 98% of mandibular premolars had a single root. The prevalence of a bifurcation was 28.5% and 1.5% in the mandibular first and second premolars, respectively. The prevalence of a trifurcation was 3.2% in the mandibular first premolar. A C-shaped root canal was observed at 23.7% and 0.7% in the mandibular first and second premolars, respectively. The level of branching was mostly found at the middle 1/3 of the root. Bilateral appearance of the same root canal configuration was identified in 80.3% and 95.9% in the mandibular first and second premolars, respectively. There was no relationship between sex and the prevalence of a bifurcation, trifurcation, or C-shaped root canal. CONCLUSION: Mandibular first premolars have more root canal complexities than mandibular second premolars. Horizontal tube shift x-ray technique, CBCT, dental operating microscope, and knowledge of root canal configurations have an important role in root canal identification in mandibular premolar with suspected complex root canal morphology.

Worldwide Prevalence of a Lingual Canal in Mandibular Premolars: A Multicenter Cross-sectional Study with Meta-analysis.

INTRODUCTION: The presence of multiple root canals is an important morphologic aspect of mandibular premolars. This study aimed to perform a worldwide analysis on the prevalence of a lingual canal in mandibular premolars and to evaluate its influence on patients' demographics in 23 countries using cone-beam computed tomographic images. METHODS: Observers from 23 countries were instructed to evaluate cone-beam computed tomographic images of 300 first and 300 second premolars (13,800 teeth) regarding the presence of a lingual canal, canal configuration, and data related to patients' ethnicity, age, and sex following a standardized screening methodology. Intra- and interrater evaluations were performed using the Cohen kappa test and intraclass correlation coefficient. Proportion and odds ratio forest plots were calculated in order to compare groups. Statistical significance was set at 5%. RESULTS: Both kappa and intraclass correlation coefficient values were above 0.60, and the percentage of agreement was 94.9% (first premolar) and 97.8% (second premolar). A significant statistical difference was observed between the worldwide proportion of a lingual canal in mandibular first (23.8%; range, 12.0%-32.7%) and second (5.3%; range, 1.0%-15.3%) premolars (P < .05). Asians and patients over 60 years old were associated with the lowest proportions of a lingual canal (P < .05), whereas Africans and younger groups were associated with the highest proportions (P < .05). The prevalence of a lingual canal in males (27.9%) was higher than females (20.0%) for the first premolar only (P < .05). Males were associated with 1.533 and 1.597 higher odds of presenting a lingual root canal in the first and second premolars, respectively. CONCLUSIONS: The worldwide proportion of a lingual root canal was 23.6% and 5.3% for the first and second premolars, respectively. Ethnicity, geographic region, age, and sex had an influence on the outcomes.

Effect of canal preparation with XP-endo Shaper and ProTaper Next on root canal geometry and dentin thickness of mandibular premolars with radicular grooves and two canals: a micro-CT study.

OBJECTIVES: This study aimed to evaluate the effects of different shaping protocols on the root canal geometry and remaining dentin thickness of mandibular premolars with radicular grooves (RG) and two canals by means of micro-CT. MATERIALS AND METHODS: Mandibular premolars with RG and two canals were matched based on their similar morphological dimensions and assigned to 2 experimental groups according to the canal preparation (n=8): XP-endo Shaper (XPS) and ProTaper Next (PTN) systems. Before and after preparation, morphometric measurements of the volume, surface area, structure model index, area, perimeter, roundness, major and minor diameters, as well as untouched canal walls, canal transportation, and dentin wall thickness were evaluated. Data were statistically compared within and between groups using the independent sample t test (α=5%). RESULTS: XPS revealed less changes in volume, surface area, area, perimeter, and major and minor diameters (P<0.05). There was no significant difference in structure model index (SMI), roundness, and percentage of untouched canal walls between groups (P>0.05). XPS resulted in less apical canal transportation and a higher remaining dentin thickness toward the RG compared to PTN in lingual canals (P<0.05). CONCLUSIONS: XPS revealed fewer changes in root canal geometry as well as lower transportation and a greater remaining dentin thickness in the lingual canals toward the RG compared to PTN. CLINICAL RELEVANCE: Internal and external anatomical characteristics of mandibular premolars might have an influence on biomechanical preparation. Considering the risk of perforation, the canal preparation using XPS appears to be more conservative compared to PTN.

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.

Endodontic Treatment of C-shaped Mandibular Premolars: A Case Report and Review of Literature.

Our article aimed to present a curious case of a mandibular premolar with a C-shaped root canal and to review the available literature on this anatomical variation. Mandibular premolar teeth account for the greatest endodontic challenges in the course of treatment on account of the morphological variations in their root canal systems, including extra root(s)/canal(s) or a C-shaped configuration. A 20-year-old female patient was referred to the Department of Endodontics of Mashhad Faculty of Dentistry, suffering from abscess, and pain while chewing. On examination the culprit was found to be the left mandibular first premolar. Following special tests and periapical radiography, we found an amalgam restoration proximate to the non-vital pulp chamber, as well as an unusually complex root canal anatomy with periapical radiolucency. A non-surgical root canal treatment with the aid of a dental operating microscope was considered as the treatment plan. Clinicians should always anticipate the presence of a C-shaped configuration in mandibular premolars, and make use of all the available tools to locate and treat such cases. A substantial knowledge of root canal anatomy would be prudent to ensure a successful outcome ensuing surgical and non-surgical root canal treatments.

Fracture strength of endodontically treated teeth restored with different fiber post and core systems.

The aim of this study was to investigate the effects of different post and core systems, CAD/CAM crown placement on fracture strength of endodontically treated mandibular premolar teeth. One hundred forty single-rooted premolar teeth were randomly divided into a control group and six experimental groups as follows: control group (Group 1); FiberSite post luting with Clearfil DC Core Plus (Group 2); RelyX Fiber post luting and core build up with Clearfil DC Core Plus (Group 3); RelyX Fiber post luting with Clearfil DC Core Plus and core build up with Filtek Bulk Fill Posterior (Group 4); specimens that received CAD/CAM crowns after the same procedures performed in Groups 2, 3, and 4, respectively (Groups 5, 6, and 7). Fracture strength tests were performed, and the failure modes were recorded. Data were statistically analyzed using one-way ANOVA and post hoc Tukey tests. The highest fracture resistance was observed in the control group and among the experimental groups in Group 4. Groups 3 and 5 showed similar fracture resistance followed by Group 2. The lowest fracture resistances were seen in the samples of Groups 6 and 7. While the fracture strength of Group 2 increased after the crown placement (Group 5), the fracture strength of Group 3 and Group 4 decreased (P < 0.05). While the specimens in Groups 1, 2, 3, and 4 predominantly showed favorable failure, unfavorable failure was more frequent in Groups 5, 6, and 7.

Stress distribution in a mandibular premolar after separated nickel-titanium instrument removal and root canal preparation: a three-dimensional finite element analysis.

OBJECTIVE: This study used finite element analysis (FEA) to assess the von Mises stresses of a mandibular first premolar after removing a separated instrument with an ultrasonic technique. METHODS: FEA models of the original and treated mandibular first premolar were reconstructed, and three models (the original canal, size 30/taper 0.04 canal, and separated instrument removal canal) were created. Two-direction (vertical and lateral) loading patterns were simulated with a 175-N force. The maximum von Mises stresses of the models within the roots from the apex to the cervical region were collected and summarized. RESULTS: Under vertical and lateral loads, all maximal values in the three models were localized in the straight-line access region. Compared with the original model (model 1), the treated models (models 2 and 3) had greater maximum stress values from the apex to the cervical region. Greater differences in the maximum von Mises stresses between models 2 and 3 were present in the straight-line access region. CONCLUSIONS: Separated instrument removal caused changes in stress distribution and increases in stress concentration in the straight-line access region of roots.

Endodontic management of mandibular second premolar with three canals.

Mandibular premolar can present a complex pulp anatomy. Apart from the usual single root and single canal a many other variations may be seen. Hence not only a thorough knowledge of the root canal anatomy but also it's variations are indispensable pre requisites for the success of any endodontic treatment. Good magnification and CBCT scans will definitely be beneficial for successful endodontic treatment. The present case provides evidence that mandibular premolars may have more than one canal.

Effect of large instrument use on shaping ability and debris extrusion of rotary and reciprocating systems.

AIM: The aim of the present study was to evaluate the effect of large instrument use on the shaping ability and apical debris extrusion of rotary and reciprocating systems in oval-shaped root canals. METHODS: Forty-five mandibular premolars, with an 18-mm long, oval-shaped single canal, and apical diameter ranging from 300 to 350 µm, were separated into three groups (n=15), according to the system used: ProTaper Universal group, F5 (0.50/0.05); ProTaper Next (PTN group), X5 (0.50/0.06); and Reciproc (RC group), R50 (0.50/0.05). Cone-beam computed tomography was performed before and after preparation to analyze apical transportation (AT), centering ability (CA), and change in root canal diameter (CRCD). For evaluating apical debris extrusion, the roots were coupled to pre-weighed glass receptacles to collect the extruded debris during preparation. RESULTS: All systems promoted AT and apical debris extrusion; the latter was higher for the PTN group (P<.05). No system presented perfect CA. The RC group demonstrated the largest CRCD (P<.05). CONCLUSIONS: As consequences of their use, the large instruments promoted undesirable AT and debris extrusion, irrespective of the system used to perform root canal preparation. Moreover, no system was able to remain perfectly centralized within the root canal.

Effect of ferrule on the fracture resistance of mandibular premolars with prefabricated posts and cores.

PURPOSE: This study evaluated fracture resistance with regard to ferrule lengths and post reinforcement on endodontically treated mandibular premolars incorporating a prefabricated post and resin core. MATERIALS AND METHODS: One hundred extracted mandibular premolars were randomly divided into 5 groups (n=20): intact teeth (NR); endodontically treated teeth (ETT) without post (NP); ETT restored with a prefabricated post with ferrule lengths of either 0 mm (F0), 1 mm (F1), or 2 mm (F2). Prepared teeth were restored with metal crowns. A thermal cycling test was performed for 1,000 cycles. Loading was applied at an angle of 135 degrees to the axis of the tooth using a universal testing machine with a crosshead speed of 2.54 mm/min. Fracture loads were analyzed by one-way ANOVA and Tukey HSD test using a statistical program (α=.05). RESULTS: There were statistical differences in fracture loads among groups (P<.001). The fracture load of F2 (237.7 ± 83.4) was significantly higher than those of NP (155.6 ± 74.3 N), F0 (98.8 ± 43.3 N), and F1 (152.8 ± 78.5 N) (P=.011, P<.001, and P=.008, respectively). CONCLUSION: Fracture resistance of ETT depends on the length of the ferrule, as shown by the significantly increased fracture resistance in the 2 mm ferrule group (F2) compared to the groups with shorter ferrule lengths (F0, F1) and without post (NP).