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Background Preservation of a healthy periodontium is critical for the long-term success of restored teeth. In cases of extensive caries, tooth fracture, inadequate crown length, and increased esthetic demands, the restorative margins need to be placed apical to the gingival margin. Violation of the biological width due to dental trauma frequently appears in clinical practice. There are three treatment options for preserving biological width and the ferrule effect: crown lengthening, orthodontic extrusion, and surgical extrusion. This case report describes the surgical intervention and fixed prostheses for crown-root fractured maxillary incisors in a growing patient. Case presentation A fourteen-year-old boy was referred from Department of Oral and Maxillofacial Surgery and visited the Department of Pediatric Dentistry after emergency dental treatment. He got hit with a baseball bat and his upper right central and lateral incisors were fractured with pulp exposure. A vertical fracture line extended 2 mm below gingival margin was observed. Surgical extrusion and conventional root canal treatments were performed on both fractured teeth. Surgical crown lengthening was additionally done to preserve the biological width and to make sure of the ferrule effect. Then, these teeth were finally restored with porcelain fused metal crowns. Conclusions Surgical extrusion and crown lengthening may be considered the most effective treatments to save the teeth instead of coronectomy or extraction for severely fractured teeth. The case described here showed satisfactory esthetic and periodontal outcomes during two years of follow-up, and the patient was satisfied that he could retain his natural teeth.

The present study explores bone healing patterns induced by orthodontic (OE) and surgical extrusion (SE) of structurally compromised teeth, where extrusion techniques are commonly used in rehabilitation. Changes in the trabecular bone were assessed by means of fractal analysis (FA) of consecutive periapical radiographs. (2) The present study is a retrospective case–control study. Pre- and post-treatment periapical radiographs from 44 adults undergoing orthodontic (OE) or surgical extrusion (SE) were retrieved. The radiographs were taken at T0 (pre-treatment), T1 (post-treatment), T2 (3-month follow-up), and T3 (6-month follow-up). Bone density (fractal dimension, FD) was analyzed in the apical and proximal bone regions (ROIs) of the extruded teeth, and both intra-group and inter-group differences were examined. (3) In all the regions of interest (ROIs), statistically significant intra-group differences in terms of bone density (FD) for both groups were found. In the OE group, the FD value increased, respectively, at T1, T2, and T3 in the apical ROI, compared to T0. For the proximal ROI, nearly the same trend was observed, respectively, at T1, T2, and T3 versus T0. As for the SE group, a statistically significant increase in the apical ROI was noted at T1, T2, and T3 when compared to T0. The same trend was registered in the proximal ROI compared to T0. However, no statistically significant inter-group differences in FD were detected between the two groups. (4) Orthodontic extrusion and surgical extrusion both resulted in an increased bone density (FD) despite the different healing patterns. Further prospective studies with a longer follow-up in this field are required.

The purpose of this study was to compare the effect of ferrule with different heights on the stress distribution of dentin and the restoration-tooth complex, using the finite element stress analysis method. Three-dimensional finite element models simulating an endodontically treated maxillary central incisor restored with an all-ceramic crown were prepared. Three-dimensional models were varied in their ferrule height (NF: no ferrule, 1F: 1-mm ferrule, and 2F: 2-mm ferrule). A 300-N static occlusal load was applied to the palatal surface of the crown with a 135° angle to the long axis of the tooth. In addition, two post and core materials with different elastic modulus were evaluated. The differences in stress transfer characteristics of the models were analyzed. Maximum stresses were concentrated on force application areas (32.6–32.8 MPa). The stress values observed with the use of a 2-mm ferrule (14.1/16.8 MPa) were lower than the no-ferrule design (14.9/17.1 MPa) for both the glass fiber-reinforced and zirconium oxide ceramic post systems, respectively. The stress values observed with zirconium oxide ceramic were higher than that of glass fiber-reinforced post system. The use of a ferrule in endodontically treated teeth restored with an all-ceramic post-and-core reduces the values of von Mises stresses on tooth-restoration complex. At rigid zirconium oxide ceramic post system, stress levels, both at dentin wall and within the post, were higher than that of fiber posts.

To our knowledge there is no data about the mechanical performance of indirect restoration adhesively cemented on teeth without an adequate build-up to provide the correct geometrical configuration. The aim of this study was to compare the fracture strength of human teeth restored with lithium disilicate onlays, with and without fiber post build-up. Methods: Twenty human mandibular molars were horizontally sectioned and divided into two groups (n = 10). No treatment was applied in group A. Teeth in group B were endodontically treated, built-up using fiber post and composite core and prepared with a circumferential chamfer providing a 1 mm circumferential ferrule. Lithium disilicate onlays were pressed and luted on teeth using dual-curing luting composite. Teeth were tested under static load. Failures were classified as restorable or not restorable. Failure loads were analyzed with one-way analysis of variance. Failure modes were compared using Pearson’s Chi-square tests. Results: The mean fracture loads were 1383.5 N for group A and 1286.3 N for group B. No difference was found (p = 0.6). Ninety per cent of fractures were classified as not restorable in both groups, with no difference (p = 0.8). Conclusions: For teeth restored with adhesive procedures and lithium disilicate onlays, the presence of build-up with fiber post to provide retention and resistance form does not influence the fracture strength.

A high-sensitivity fiber optic temperature sensor based on the enhanced harmonic Vernier effect (HVE) is proposed, which consists of two Fabry–Perot interferometers (FPI) that are sensitive to temperature and connected in parallel. FPI 1 is a polydimethylsiloxane (PDMS) cavity formed by filling a ceramic ferrule with PDMS, and FPI 2 is an air-cavity formed by inserting a single-mode fiber into a ceramic ferrule coated with PDMS film on the end face. FPI 1 and FPI 2 have opposite temperature responses and an approximate 2-fold free spectral range (FSR) relationship. As the temperature rises, the interference spectrum of FPI 1 gradually red-shifts, while the interference spectrum of FPI 2 gradually blue-shifts, resulting in an enhanced HVE. Its temperature sensitivity is much higher than that of a single FPI, and the amplification rate is significantly higher than that of ordinary Vernier effect. Two enhanced HVE sensors S 1 and S 2 are developed using this method, but there is a certain difference in their FSR detuning. The experimental results reveal that within the temperature range of 30–35 °C, the temperature sensitivity of S 1 and S 2 reach − 44.39 nm/°C and − 23.14 nm/°C, respectively. Both S 1 and S 2 have extremely high temperature sensitivity, but FSR detuning has a significant impact on sensitivity amplification. Additionally, the proposed enhanced HVE sensor has good repeatability and stability in measuring temperature.

Background The purpose of this study was to evaluate the effect of ferrule design on the fracture resistance of endodontically treated mandibular first premolars after simulated crown lengthening and orthodontic forced eruption methods restored with a fiber post-and-core system. Methods Forty extracted and endodontically treated mandibular first premolars were decoronated to create lingual-to-buccal oblique residual root models, with a 2.0 mm height of the lingual dentine wall coronal to the cemento-enamel junction, and the height of buccal surface at the cemento-enamel junction. The roots were divided randomly into five equal groups. The control group had undergone incomplete ferrule preparation in the cervical root, with 0.0 mm buccal and 2.0 mm lingual ferrule lengths (Group F0). Simulated surgical crown lengthening method provided ferrule preparation of 1.0 mm (Group CL/F1) and 2.0 mm (Group CL/F2) on the buccal surface, with ferrule lengths of 3.0 mm and 4.0 mm on the lingual surface, respectively. Simulated orthodontic forced eruption method provided ferrule preparation of 1.0 mm (Group OE/F1) and 2.0 mm (Group OE/F2) on the buccal surface and ferrule lengths of 3.0 mm and 4.0 mm on the lingual surface, respectively. After restoration with a glass fiber post-and-core system and a cast Co-Cr alloy crown, each specimen was embedded in an acrylic resin block to a height on the root 2.0 mm from the apical surface of the crown margin and loaded to fracture at a 135° angle to its long axis in a universal testing machine. Data were analyzed statistically using two-way ANOVA with Tukey HSD tests and Fisher’s test, with α = 0.05. Results Mean fracture loads (kN) for groups F0, CL/F1, CL/F2, OE/F1 and OE/F2 were as follows: 1.01 (S.D. = 0.26), 0.91 (0.29), 0.73 (0.19), 0.96 (0.25) and 0.76 (0.20), respectively. Two-way ANOVA revealed significant differences for the effect of ferrule lengths ( P  = 0.012) but no differences for the effect of cervical treatment methods ( P  = 0.699). The teeth with no buccal ferrule preparation in control group F0 had the highest fracture resistance. In contrast, the mean fracture loads for group CL/F2 with a 2.0-mm buccal and 4.0-mm lingual ferrule created by simulated crown lengthening method were lowest ( P  = 0.036). Conclusions Increased apically complete ferrule preparation resulted in decreased fracture resistance of endodontically treated mandibular first premolars, regardless of whether surgical crown lengthening or orthodontic forced eruption methods been used.