Does Resin Cement Type and Cement Preheating Influence the Marginal and Internal Fit of Lithium Disilicate Single Crowns?

This paper assesses the effect of cement type and cement preheating on the marginal and internal fit of lithium disilicate single crown. Methods: 40 maxillary premolars were selected, restored with lithium disilicate single crowns. Teeth were randomly assigned into four groups (n = 10) based on cement type (Panavia SA or LinkForce) and preheating temperature (25 °C or 54 °C). After fabrication of the restoration, cements were incubated at 25 °C or 54 °C for 24 h, and each crown was cemented to its corresponding tooth. After 24 h, all specimens were thermally aged to (10,000 thermal cycles between 5 °C and 55 °C), then load cycled for 240,000 cycles. Each specimen was then sectioned in bucco-palatal direction and inspected under a stereomicroscope at x45 magnification for marginal and internal fit evaluation. The data were statistically analyzed (significance at p ≤ 0.05 level). Results: At the mid-buccal finish line, mid-buccal wall, palatal cusp, mid-palatal wall, mid-palatal finish line, and palatal margin measuring points, there was a significant difference (p ≤ 0.05) between the lithium disilicate group cemented with Panavia SA at 25 °C and the group cemented with LinkForce at 25 °C, while there was no significant difference (p > 0.05) at the other points. At all measuring points, except at the palatal cusp tip (p = 0.948) and palatal margin (p = 0.103), there was a statistically significant difference (p ≤ 0.05) between the lithium disilicate group cemented with Panavia SA at 54 °C and the group cemented with LinkForce at 54 °C. Regardless of cement preheating, statistically significant differences were found in the buccal cusp tip, central groove, palatal cusp tip, and mid-palatal wall (p ≤ 0.05) in the lithium disilicate group cemented with Panavia SA at 25 °C and 54 °C, as well as the mid-palatal chamfer finish line and palatal margin in the LinkForce group cemented with Panavia SA at 25 °C and 54 °C. At the other measurement points, however, there was no significant difference (p > 0.05). Conclusions: The type of resin cement affects the internal and marginal fit of lithium disilicate crowns. At most measuring points, the cement preheating does not improve the internal and marginal fit of all lithium disilicate crowns.

Relatively low tooth replacement rate in a sauropod dinosaur from the Early Cretaceous Ruyang Basin of central China

Tooth replacement rate is an important feature related to feeding mechanics and food choices for dinosaurs. However, only a few data points are available for sauropod dinosaurs, partially due to rarity of relevant fossil material. Four somphospondylan sauropod species have been recovered from the Lower Cretaceous Aptian–Albian Haoling Formation in the Ruyang Basin, Henan Province of central China, but no cranial material has been reported except for a single crown. Here we report the discovery of the rostral portion of a left dentary with replacement teeth in its first five alveoli. Comparative anatomical study shows the partial dentary can be assigned to a member of early diverging somphospondylans. The non-destructive tooth length-based approach to estimating tooth formation time and replacement rate is adopted here. The estimated tooth replacement rate is 76 days, faster than that of Brachiosaurus (83 days) and much lower than typical late diverging lithostrotian titanosaurians (20 days). Thus, this discovery adds an intermediate tooth replacement rate in the evolution of titanosauriform sauropods and supports the idea that evolution of tooth replacement rate is clade-specific. This discovery also provides more information to understand the Ruyang sauropod assemblage, which includes one of the most giant dinosaurs to have walked our Earth (Ruyangosaurus giganteus).

Stress distribution in prosthetic abutments: a finite element analysis comparison of conical and UCLA abutments

The effect of prosthetic abutment type on single-screwed prostheses in posterior mandibular molar rehabilitations is not yet known. Thus, the aim of this study was to evaluate the distribution of stresses in the crowns, prosthetic components, implant and bone in implant-supported restorations with or without a prosthetic abutment, maintaining an equal total height of the implant-crown set. Virtual 3-dimensional (3D) finite element models were constructed, the models were designed to represent a posterior single crown rehabilitation with a screwed retention system and external hexagon implants placed in the lower first molar region. Two rehabilitation methods were designed to simulate a monolithic zirconia crown screwed onto a conical abutment, which was screwed onto an external hexagon implant (M1); and a monolithic zirconia crown screwed directly onto the external hexagon implant using an UCLA abutment (M2). An axial load of 200 N was simulated and applied axially in the occlusal region of the restoration divided into 5 points. The quantitative and qualitative description of the maximum principal stress for crowns, von Mises stress for screws, conical abutment and implant; and minimal principal stress for cortical and medullary bone were evaluated. M1 presented similar stress distribution for crowns, cortical and medullary bone compared to M2. Conversely, the stress values were considerably higher for crowns screw and implants in the M2 group. In conclusion, single implant-supported rehabilitations of mandibular first molars using external hexagon implants presented better stress distribution on the crown screw and implants for the M1 group compared to M2.

Individual tree extraction from terrestrial laser scanning data via graph pathing

Background Individual tree extraction from terrestrial laser scanning (TLS) data is a prerequisite for tree-scale estimations of forest biophysical properties. This task currently is undertaken through laborious and time-consuming manual assistance and quality control. This study presents a new fully automatic approach to extract single trees from large-area TLS data. This data-driven method operates exclusively on a point cloud graph by path finding, which makes our method computationally efficient and universally applicable to data from various forest types. Results We demonstrated the proposed method on two openly available datasets. First, we achieved state-of-the-art performance on locating single trees on a benchmark dataset by significantly improving the mean accuracy by over 10% especially for difficult forest plots. Second, we successfully extracted 270 trees from one hectare temperate forest. Quantitative validation resulted in a mean Intersection over Union (mIoU) of 0.82 for single crown segmentation, which further led to a relative root mean square error (RMSE%) of 21.2% and 23.5% for crown area and tree volume estimations, respectively. Conclusions Our method allows automated access to individual tree level information from TLS point clouds. The proposed method is free from restricted assumptions of forest types. It is also computationally efficient with an average processing time of several seconds for one million points. It is expected and hoped that our method would contribute to TLS-enabled wide-area forest qualifications, ranging from stand volume and carbon stocks modelling to derivation of tree functional traits as part of the global ecosystem understanding.

Comparison of the Accuracy of Intraoral Scanners Based on the Type of Tooth Preparation for a Single Crown

The purpose of this study was to evaluate the accuracy of intraoral scanners in 10 abutments (five premolars and five molars) obtained in a dental clinic and to analyze the impacts of the volume and area of abutments on scanning accuracy. Abutment casts were scanned five times with a 3D contact scanner (DS10; Renishaw plc). The five scan files were lined up and then merged, and one high-resolution computer-aided design reference model (CRM) was obtained. To obtain a computer-aided design test model (CTM), three types of intraoral scanners (CS3600 (Carestream Dental), i500 (Medit), and EZIS PO (DDS)) and one type of laboratory scanner (E1; 3Shape) were employed. Using 3D analysis software (Geomagic control X; 3D Systems), the accuracy of the scanners was evaluated, including optimal overlap by optimal alignment. The conformity of the overlapped data was calculated by the root mean square (RMS) value, using the 3D compare function for evaluation. As for statistical analysis, testing was conducted, using one-way and two-way ANOVA and the Tukey HSD test (α = 0.05) for the comparison of the groups. To analyze the correlations of the volume and area of the abutments with accuracy, Pearson’s correlation analysis was conducted (α = 0.00625). Both premolar and molar abutments showed a lower RMS value on the laboratory scanner than on the intraoral scanners, and the RMS value was lower in premolars than in molars (p < 0.001). In the intraoral scanner group, CS3600 showed the best accuracy (p < 0.001). There were significant positive correlations for the volume and area of the abutments with accuracy (p < 0.001). The type, volume, and area of the clinically applicable abutments may affect the accuracy of intraoral scanners; however, the scanners used in the present study showed a clinically acceptable accuracy range, regardless of the type of abutment.

Bone Stress Evaluation with and without Cortical Bone Using Several Dental Restorative Materials Subjected to Impact Load: A Fully 3D Transient Finite-Element Study

Statement of problem. Previous peri-implantitis, peri-implant bone regeneration, or immediate implant placement postextraction may be responsible for the absence of cortical bone. Single crown materials are then relevant when dynamic forces are transferred into bone tissue and, therefore, the presence (or absence) of cortical bone can affect the long-term survival of the implant. Purpose: the purpose of this study is to assess the biomechanical response of dental rehabilitation when selecting different crown materials in models with and without cortical bone. Methods: several crown materials were considered for modeling six types of crown rehabilitation: full metal (MET), metal-ceramic (MCER), metal-composite (MCOM), peek-composite (PKCOM), carbon fiber-composite (FCOM), and carbon fiber-ceramic (FCCER). An impact-load dynamic finite-element analysis was carried out on all the 3D models of crowns mentioned above to assess their mechanical behavior against dynamic excitation. Implant-crown rehabilitation models with and without cortical bone were analyzed to compare how the load-impact actions affect both type of models. Results: numerical simulation results showed important differences in bone tissue stresses. The results show that flexible restorative materials reduce the stress on the bone and would be especially recommendable in the absence of cortical bone. Conclusions: this study demonstrated that more stress is transferred to the bone when stiffer materials (metal and/or ceramic) are used in implant supported rehabilitations; conversely, more flexible materials transfer less stress to the implant connection. Also, in implant-supported rehabilitations, more stress is transferred to the bone by dynamic forces when cortical bone is absent.

Temporary adhesive bridge restoration of the upper anterior teeth lost due to trauma: Three case reports

Aim: Traumatic dental injuries at the anterior region of the maxilla occur frequently in children and adults. In this case report, we aimed to describe the temporary aesthetic restoration of the upper lateral incisor with a fiber-reinforced bridge by using the original tooth crown, which had avulsed after dental trauma. Methodology: Case 1: A 14-year-old girl with an avulsion in tooth #11 due to trauma visited our clinic. During the examination, it was seen that the wound had healed, and there was no luxation in teeth #21 and #12. Since the patient could not undergo prosthetic procedures, for reasons including implants, and did not want a removable prosthesis, a single crown supported by acrylic tooth fibers was constructed. Case 2: A 17-year-old male patient was referred to our clinic because of an avulsed left lateral incisor tooth, which was traumatized 15 days before visiting the clinic. His medical history revealed that his parents had found the tooth two hours after the trauma. However, the emergency clinic that he had previously visited did reimplant that tooth and repaired it with fiber-reinforced composite. Case 3: In the examination of a 12-year-old male patient who applied to our clinic due to trauma, it was observed that tooth #11 had an avulsion and tooth #12 had a crown fracture. Root canal treatment was performed. A crown was made for the patient by supporting the fiber inside the canals of tooth #11 and tooth #21. It was revised aesthetically with the support of the crown of the other tooth. Conclusion: Avulsion after anterior trauma affects patients’ appearance aesthetically; thus, patients want to be treated as soon as possible. Function, phonation, and aesthetics must be quickly provided for a loose anterior tooth. Fiber-reinforced adhesive bridge techniques may be considered as a temporary treatment for providing an aesthetically appealing appearance until the completion of permanent prosthetic treatment. How to cite this article: Şahin M, Toptancı İR. Temporary adhesive bridge restoration of the upper anterior teeth lost due to trauma: Three case reports. Int Dent Res 2021;11(Suppl.1):285-91. https://doi.org/10.5577/intdentres.2021.vol11.suppl1.42 Linguistic Revision: The English in this manuscript has been checked by at least two professional editors, both native speakers of English.