Comparison of ultimate force revealed by compression tests on extracted first premolars and FEA with a true scale 3D multi-component tooth model based on a CBCT dataset.

OBJECTIVE: The aim of this study was to develop a new method for creating a multi-component and true scale 3-dimensional (3D) model of a human tooth based on cone-beam computed tomography (CBCT) images. MATERIALS AND METHODS: First maxillary premolar tooth model was reconstructed from a patient's CBCT images. The 2D serial sections were used to create the 3D model. This model was used for finite element analysis (FEA). Model validation was performed by comparing the ultimate compressive force (UF) obtained experimentally using a universal testing machine and from simulation. The simulations of three component-omitting models (silicone, cementum, and omitting both) were performed to analyze the maximum (max.) principal stress and stress distribution. RESULTS: The simulation-based UF indicating tooth fracture was 637 N, while the average UF in the in vitro loading was 651 N. The discrepancy between the simulation-based UF and the experimental UF was 2.2%. From the simulation, the silicone-omitting models showed a significant change in max. principal stress, resulting in a UF error of 26%, whereas there was no notable change in the cementum-omitting model. CONCLUSION: This study, for the first time, developed a true scale multi-component 3D model from CBCT for predicting stress distribution in a human tooth. CLINICAL RELEVANCE: This study proposed a method to create 3D modeling from CBCT in a true scale and multi-component manner. The PDL-like component-omitting simulation led to a higher error value of UF, indicating the importance of multi-component tooth modeling in FEA. Tooth 3D modeling could help determine mechanical failure in dental treatments in a more precise manner.

The effect of iloprost on cell proliferation and angiogenesis-related gene expression in human periodontal ligament cells.

Periodontal ligament is considered a rich source of mesenchymal stem cells for pulp regeneration. This study investigated the effect of iloprost, a prostacyclin analog, on cell proliferation and the expression of angiogenesis-related genes in human periodontal ligament cells (hPDLs) in vitro. The hPDLs were treated with 10-9-10-6 M iloprost for 1, 6 and 24 h. Cell proliferation was determined by an MTT assay. Vascular endothelial growth factor (VEGF), alpha-1 type I collagen (COL1), and basic fibroblast growth factor (bFGF) mRNA expression were determined by semi-quantitative and qPCR. ELISA was employed for assessment of VEGF expression. Immunofluorescence staining for COL1 protein expression was performed. A prostacyclin receptor (IP) antagonist was used to verify the signaling pathway. The Kruskal-Wallis and Tukey significant difference tests were used to analyze the results. From the results, iloprost treatment did not affect cell morphology or proliferation. Iloprost induced the upregulation of VEGF and COL1 mRNA levels as shown by PCR. The effect of iloprost on bFGF mRNA expression was not observed. The immunofluorescence assay revealed that COL1 protein expression was increased in the iloprost groups. Pretreating the hPDLs with the IP antagonist significantly suppressed the enhancing effect of iloprost on VEGF and COL1 mRNA expression and suppressed COL1 protein expression. In conclusion, iloprost promoted mRNA and protein expression of VEGF and COL1, but not of bFGF in hPDL cells. The increased effect of iloprost was abolished by IP receptor antagonist pretreatment. Iloprost might be a promising agent in dentin-pulp regeneration.

Oral Functional Behaviors and Tooth Factors Associated with Cracked Teeth in Asymptomatic Patients.

INTRODUCTION: A cracked tooth may occur due to excessive applied force or tooth weakness. However, there is scant information concerning the cracked tooth risk factors. This study aimed to explore the oral functional behaviors and tooth factors associated with posterior cracked teeth. METHODS: Fifty-six patients underwent their oral functional behavior assessment via a questionnaire. The intraoral parameters at the patient level (remaining teeth, occluding tooth pairs, overbite, overjet, and occlusal guidance type) and tooth level (remaining marginal ridge number, restored surface number, restorative materials, and cuspal inclination) were examined. The posterior teeth were stained with methylene blue dye and inspected for cracks using a microscope. The correlations between each patient-level parameter and the cracked tooth number/subject were determined using linear regression analysis. The cracked teeth were matched with their contralateral noncracked teeth, and binary regression analysis was used to analyze the association between tooth-level parameters and a cracked tooth. Multivariate regression analysis was performed if more than 1 parameter had a P value ≤.1. RESULTS: One hundred thirty-five cracked teeth were found. Eating hard food was significantly related to the cracked tooth number (P < .05). In molars, the occlusal surface restoration and cuspal inclination were significantly related to a cracked tooth, except the mesiobuccal cusp. In the multivariate analysis, the distolingual cusp inclination significantly predicted a cracked tooth (P < .05). In premolars, the lingual cusp inclination was associated with a cracked tooth (P < .05). CONCLUSIONS: Eating hard food, occlusal surface restoration, and steep cuspal inclination were associated with posterior cracked teeth.

Resin Composite Core and Fiber Post Improved the Fracture Parameters of Endodontically Treated Maxillary Premolars with Wedge-shaped Cervical Lesions.

INTRODUCTION: The aim of this study was to evaluate the fracture resistance and fracture patterns of endodontically treated maxillary premolars with wedge-shaped cervical lesions restored with a resin composite core with or without a fiber post under nonaxial loading. METHODS: Sixty extracted human maxillary premolars with 2 root canals were randomly allocated into 4 groups (n = 15). Forty-five teeth were prepared with a wedge-shaped lesion at the buccal cervical area and root canal treatment. There were 3 restoration groups: no restoration, restoration with a resin composite core, and restoration with a resin composite core and a fiber post. Intact teeth served as the control group. All teeth were subjected to thermocycling and cyclic loading. A 45° compressive load was applied to the palatal plane of the buccal cusp until tooth fracture. The fracture resistance and facture patterns were analyzed using 1-way analysis of variance and the chi-square test (α = 0.05), respectively. RESULTS: The no restoration group demonstrated the lowest fracture resistance and was significantly different from the other groups (P < .001). The intact teeth presented the highest fracture resistance, which was not significantly different from the restoration with a resin composite core and a fiber post group (P > .05). The failure patterns were significantly different between groups (P < .001). Most intact teeth fractured coronally to the cementoenamel junction level, whereas most teeth in the other groups fractured at the gingival margin of the cervical lesion. CONCLUSIONS: Endodontically treated maxillary premolars with wedge-shaped cervical lesions restored with fiber posts and a resin composite cores had a fracture resistance equivalent to intact teeth. However, their fracture patterns were not improved by the fiber post and a resin composite core.