Biomechanical Evaluation of the Mandibular First Molar After Simulated Occlusal Wear Using 3D Finite Element Analysis

PURPOSE：This study aimed to investigate the biomechanical basis of vertical tooth fracture occurring in the mesial root of the mandibular first molar. METHODS：We used 3D finite elements to analyze the stress distribution and transient displacement of the mandibular first molar after occlusal surface wear and tooth tilt. Based on four degrees of wear within each of the surface wear and tooth tilt groups, eight models were established in addition to the control model. A simulated bite force of 200 N was loaded on the occlusal surface, and nonlinear finite element analysis was used to explore the biomechanical basis of vertical root fracture. RESULTS：When the distal tipping angle of the abrasion plane of the mandibular first molar increased from 5° to 15°, the angle between the instantaneous displacement contours and the long axis of the tooth decreased. Meanwhile, the mesial root was found to suffer the highest stress concentration, and the possibility of longitudinal root fracture was increased. CONCLUSION: By evaluating the biomechanical effect of tooth wear and occlusal loading, we are able to identify some clinical interventions that may prevent vertical tooth fracture.

Complexities in endodontics: A case series

There are cases in the endodontic treatment which are a real challenge. There are teeth with different anatomies of the root canals of different teeth and their treatment. There are most of the cases which are sevely carious and has lost more than 50% of the tooth structure. Patients usually lose their teeth because these problems. The aim of this study is to investigate several cases with different root canal anatomies like in open apex with blunderbuss canals in maxillary central incisors or mandibular premolar and molars with severly decayed crown tooth structures and their management. one case with severly decayed lower mandibular premolar i.e 45, one case of maxillary first molar with severly decayed crown structure i.e 16, a case of severly decayed mandibular first molar i.e 36, Three Cases of maxillary central incisors with immature open apex and blunderbuss canals w.r.t 21. Results are observed after several years. In performing a root canal treatment on such teeth, one should appreciate the complexity of the root canal system, canal obliteration and configuration, and the potential for regenerating the original anatomy of the tooth either Endodontic or Post Endodontic. Knowledge of the phenomenon of the complexity of the root canal system, canal obliteration and configuration, and the potential for regenerating tooth anatomies with the help of rebond fibres, MTA and Composite restorations, this will improve the medical practice of the general dental practitioner.

Effects of Obesity on Bone Healing in Rats

Although the association between periodontitis and obesity is well explored, it is unclear whether obesity is associated with a worse therapeutic outcome after periodontal treatment. The aim of this study was to investigate the effects of obesity on bone healing with and without the application of regeneration-promoting molecules. A standardized bone fenestration-type defect was created over the root of the mandibular first molar in 15 Wistar rats. Ten animals received a high-fat, high-sucrose diet (HFSD), while the remaining five animals were fed a standard diet. During surgery, the fenestration defects from half of the HFSD-fed, i.e., obese animals, were treated with regeneration-promoting molecules (enamel matrix derivative; EMD). After four weeks, bone healing was evaluated by histomorphometry, TRAP staining and immunohistochemistry for RUNX2 and osteopontin. The analyses revealed that the spontaneous healing of the periodontal defects was compromised by obesity. Application of EMD partially compensated for the negative effect of obesity. Nevertheless, EMD-stimulated bone healing in obese animals was not better than the spontaneous healing in the obesity-free control group, indicating that obesity may also inhibit the stimulatory effects of regeneration-promoting molecules. Our results show that obesity can negatively influence bone healing and suggest that bone healing may be compromised in humans.

The potential of cassava leaves extract in gingival fibroblasts of periodontitis of rats with ovarian dysfunction

Introduction: The prevalence of periodontitis has reached 42.8% in Indonesia. One contributing factor is Porphyromonas gingivalis. The ovarian dysfunction caused by ovariectomy procedures may also cause periodontitis. Post ovariectomy conditions resemble menopause, lowering the production of estrogen and progesterone hormones, leaving patients vulnerable to periodontitis. To prevent the side effects of the treatment, herbal ingredients are commonly used. The extract of cassava leaves is known to have pharmacological effects as an antioxidant and, thus, can be applied as a medicine for periodontitis. Methods: A total of 21 rats were divided into three groups, (1) control: healthy rats; (2) Group P.1: P. gingivalis-induced rats; (3) Group P.2: ovariectomized rats. Groups P.1 and P.2 were further divided into three subgroups that were administered cassava leaves extract at a dosage of 179.2 mg/ kg BW, aquades and vitamin C. Rats were euthanized at day eight after the initial treatment to collect left mandibular first molar. The mandibular sections were immunohistochemically stained to quantify SOD expression using light microscope while the Image J software was used. Fibroblast cells expressing SOD are characterized by brown coloration in the cytoplasm and darker nucleus. Results: In periodontitis conditions, either due to P.gingivalis induction or ovarian dysfunction, fibroblast cells in rats given cassava leaves extract expressed higher SOD than rats given aquades, but still lower than rats given vitamin C. The result of the one way ANOVA test showed p value of 0,00, which means that there is a significant difference in all groups. Conclusion: Cassava leaves extract demonstrated the potential to increase the antioxidant expression in P. gingivalis-induced and ovarian dysfunction rats.

The Effect of Implant Length and Diameter on Stress Distribution around Single Implant Placement in 3D Posterior Mandibular FE Model Directly Constructed Form In Vivo CT

A three-dimensional (3D) finite element (FE) model of the mandibular bone was created from 3D X-ray CT scan images of a live human subject. Simulating the clinical situation of implant therapy at the mandibular first molar, virtual extraction of the tooth was performed at the 3D FE mandibular model, and 12 different implant diameters and lengths were virtually inserted in order to carry out a mechanical analysis. (1) High stress concentration was found at the surfaces of the buccal and lingual peri-implant bone adjacent to the sides of the neck in all the implants. (2) The greatest stress value was approximately 6.0 MPa with implant diameter of 3.8 mm, approx. 4.5 MPa with implant diameter of 4.3 mm, and approx. 3.2 MPa with implant diameter of 6.0 mm. (3) The stress on the peri-implant bone was found to decrease with increasing length and mainly in diameter of the implant.

Unerupted Supernumerary Mandibular Fourth Premolar in a dog

A 2.5-year-old intact male Irish setter was presented for a draining tract associated with the right mandibular first molar tooth (409). Conscious oral examination yielded two draining tracts associated with the right mandibular first molar tooth. No obvious missing teeth or other gross abnormalities associated with the oral cavity were observed. Upon anesthetized radiographic evaluation, the presence of an unerupted, abnormally positioned, supernumerary premolar tooth was observed. The following article describes the extraction of the right mandibular first molar tooth (409) as well as the unerupted supernumerary premolar tooth with associated supernumerary root and the diagnostic approach taken for this uncommon abnormality.

Intraoral scanner-based monitoring of tooth wear in young adults: 12-month results

Objectives To investigate tooth wear in young adults, intraoral scanning was used for digital monitoring of the mandibular first molar over 12 months. A possible influence of aetiological factors obtained by a questionnaire on tooth wear was investigated. Materials and methods A total of 109 participants (mean age at the start of the study: 21.0 ± 2.2 years) were included in this clinical study. At baseline (T0), an intraoral scan (Trios 3, 3Shape) of the study tooth (FDI # 36 or #46) was conducted. After a mean observation period of 373 ± 19 days, a second intraoral scan (T1, n = 94) of the same tooth as at T0 was performed and standard tessellation language datasets were superimposed with 3D analysis software (GOM Inspect). The occlusal surface of the study tooth was divided into 7 areas (5 cusps, 2 ridges) and maximum vertical substance loss was measured between T0 and T1 (n = 91). Three types of tooth wear were defined: cupping (C), facet (F) and combined cupping-facet (CF). Furthermore, a questionnaire on aetiological factors, such as dietary behaviour, was filled out at T0. Data were analysed with non-parametric tests (p < 0.05). Results Only one study tooth exhibited no tooth wear at T0, whereas 3 teeth showed C, 47 teeth F and 40 teeth CF. A progression of vertical substance loss for all three types was shown. Most affected were the mesiobuccal cusps (43, 38/47 µm; median, 95%CI) followed by distobuccal (36, 33/39 µm), mesiolingual (35, 26/40 µm), distolingual (34, 27/36 µm) and distal (31, 25/34 µm). On mesial and distal ridges, only F was detected with the lowest vertical substance loss of all areas (mesial ridge: 0, 0/0 µm; distal ridge: 0, 0/0 µm). An association between aetiological factors and loss values could not be shown. Conclusions All study teeth showed clear signs of wear, and after only 1 year, further substance loss was detectable. This result is of significance for young adults. Clinical relevance Since data of young adults regarding tooth wear are scarce, the results give a first idea of the amount of vertical loss per year and its relation to aetiological factors such as dietary behaviour. Therefore, further studies over a longer observation period are highly recommended.

The Effect of Rotation Speed of XP-endo Shaper on Apically Extruded Debris During Endodontic Procedures: an In Vitro Study

The aim of this study was to evaluate the effect of using a higher rotation speed with the XP-endo Shaper (XPS) on apically extruded debris and operation time during endodontic treatment and retreatment procedures. Sixty mesial roots of mandibular first molar teeth were randomly assigned to four groups (Initial treatment groups: XPS used at 1000 or 3000rpm rotation speeds and Retreatment groups: XPS used at 1000 or 3000rpm rotation speeds). During the initial treatment and retreatment procedures preweighed eppendorf tubes were used to collect apically extruded debris, and the operation time was recorded in seconds. The extruded debris was quantified by subtracting the preinstrumentation from the postinstrumentation weight of the Eppendorf tubes. Data were analysed using two-way ANOVA at a significance level of 0.05. In all groups, the use of the XPS at 1000 or 3000rpm rotation speeds had no statistically significant effect on the amount of apically extruded debris (p>0.05). The use of the XPS at a 3000rpm rotation speed significantly decreased the instrumentation time (p<0.05). In summary, the use of the XPS at high rotation speeds in initial treatment and retreatment procedures did not have a significant effect on the amount of apically extruded debris but significantly decreased the operation time.