Tooth Area Research Articles

Growth allometry and dental topography in Upper Triassic conodonts support trophic differentiation and molar-like element function

AbstractConodont elements have high rates of morphological evolution, but the drivers of this disparity are debated. Positive allometric relationships between dimensions of food-processing surfaces and entire P1 elements have been used to argue that these elements performed mechanical digestion. If involved in food processing, the surface of the element should grow at a rate proportional to the increase in energy requirements of the animal. This inference of function relies on the assumption that the energy requirements of the animal grew faster (≅ mass0.75) than the tooth area (≅ mass0.67). We reevaluate this assumption based on metabolic rates across animals and calculate the allometry in platform-bearing P1 elements of Late Triassic co-occurring taxa, Metapolygnathus communisti and Epigondolella rigoi, using 3D models of ontogenetic series. Positive allometry is found in platform and element dimensions in both species, supporting a grasping-tooth hypothesis, based on the assumption that metabolic rate in conodonts scaled with body mass similarly to that in fish and ectotherms. We also calculate the curvature of the P1 platform surface using the Dirichlet normal energy (DNE) as a proxy for diet. DNE values increase with body mass, supporting the assumption that conodont metabolic rates increased faster than mass0.67. We finally find that adults in both taxa differ in their food bases, which supports trophic diversification as an important driver of the remarkable disparity of conodont elements.

Biomechanical influence of narrow-diameter implants placed at the crestal and subcrestal level in the maxillary anterior region. A 3D finite element analysis.

To evaluate the tendency of movement, stress distribution, and microstrain of single-unit crowns in simulated cortical and trabecular bone, implants, and prosthetic components of narrow-diameter implants with different lengths placed at the crestal and subcrestal levels in the maxillary anterior region using 3D finite element analysis (FEA). Six 3D models were simulated using Invesalius 3.0, Rhinoceros 4.0, and SolidWorks software. Each model simulated the right anterior maxillary region including a Morse taper implant of Ø2.9mm with different lengths (7, 10, and 13mm) placed at the crestal and subcrestal level and supporting a cement-retained monolithic single crown in the area of tooth 12. The FEA was performed using ANSYS 19.2. The simulated applied force was 178N at 0°, 30°, and 60°. The results were analyzed using maps of displacement, von Mises (vM) stress, maximum principal stress, and microstrain. Models with implants at the subcrestal level showed greater displacement. vM stress increased in the implant and prosthetic components when implants were placed at the subcrestal level compared with the crestal level; the length of the implants had a low influence on the stress distribution. Higher stress and strain concentrations were observed in the cortical bone of the subcrestal placement, independent of implant length. Non-axial loading influenced the increased stress and strain in all the evaluated structures. Narrow-diameter implants positioned at the crestal level showed a more favorable biomechanical behavior for simulated cortical bone, implants, and prosthetic components. Implant length had a smaller influence on stress or strain distribution than the other variables.

Patients' preferences in dental care: A discrete-choice experiment and an analysis of willingness-to-pay.

Dental diseases are a major problem worldwide. Costs are a burden on healthcare systems and patients. Missed treatments can have health and financial consequences. Compared to other health services, dental treatments are only covered in parts by statutory health insurance (SHI). Using the example of dental crowns for a cost-intensive treatment, our study aims to investigate whether (1) certain treatment attributes determine patients' treatment choice, and (2) out-of-pocket payments represent a barrier to access dental care. We conducted a discrete-choice-experiment by mailing questionnaires to 10,752 people in Germany. In presented scenarios the participants could choose between treatment options (A, B, or none) composed of treatment attribute levels (e.g., color of teeth) for posterior (PT) and anterior teeth (AT). Considering interaction effects, we used a D-efficient fractional factorial design. Choice analysis was performed using different models. Furthermore, we analyzed willingness-to-pay (WTP), preference of choosing no and SHI standard care treatment, and influence of socioeconomic characteristics on individual WTP. Out of n = 762 returned questionnaires (response rate of r = 7.1), n = 380 were included in the analysis. Most of the participants are in age group "50 to 59 years" (n = 103, 27.1%) and female (n = 249, 65.5%). The participants' benefit allocations varied across treatment attributes. Aesthetics and durability of dental crowns play most important roles in decision-making. WTP regarding natural color teeth is higher than standard SHI out-of-pocket payment. Estimations for AT dominate. For both tooth areas, "no treatment" was a frequent choice (PT: 25.7%, AT: 37.2%). Especially for AT, treatment beyond SHI standard care was often chosen (49.8%, PT: 31.3%). Age, gender, and incentive measures (bonus booklet) influenced WTP per participant. This study provides important insights into patient preferences for dental crown treatment in Germany. For our participants, aesthetic for AT and PT as well as out-of-pocket payments for PT play an important role in decision-making. Overall, they are willing to pay more than the current out-of-pockt payments for what they consider to be better crown treatments. Findings may be valuable for policy makers in developing measures that better match patient preferences.

Bacterial Colonization and Proliferation in Primary Molars following the Use of the Hall Technique: A Confocal Laser Scanning Microscopy Study.

Restorative dentistry aims to create a favorable environment to arrest caries with minimal operative intervention. The Hall technique (HT) involves the seating and cementation of stainless steel crowns (SSC) on primary molars without any tooth preparation, caries removal, or local anesthesia. In this manner, it entombs bacteria and arrests caries' progress. We compared bacterial distribution and quantity among primary molars affected with caries and restored with SSC using the HT (n = 10), the conventional technique (CT; n = 10), or not restored at all (control; n = 10). The teeth were contaminated with Enterococcus faecalis to mimic the clinical situation in the oral cavity and then incubated for 21 days. They were then cut mesiodistally and evaluated with confocal laser scanning microscopy. Total bacterial load (live + dead) in the mesial and distal areas of the crown showed no significant difference between the groups (p = 0.711), but there were significantly more dead than live bacteria in the CT and control groups versus the HT group (p = 0.0274 and p = 0.0483, respectively). Inside the pulp chamber and the crown area, the total bacterial load was significantly higher in the HT compared to the CT group (p < 0.001). Significantly more dead than live bacteria were observed in all tooth areas treated with the HT (p = 0.0169). Bacterial penetration depth was significantly correlated with bacterial load (p = 0.0167). In conclusion, although more bacteria were present in teeth that had undergone the HT versus those treated with the CT, they were mainly unviable. Additionally, the CT and the HT showed a similar performance in terms of marginal leakage, indicating that complete caries removal is not essential to achieve good sealing.

Variability in molar crown morphology and cusp wear in two Western chimpanzee populations.

Chimpanzees (Pan troglodytes) possess a relatively generalized molar morphology allowing them to access a wide range of foods. Comparisons of crown and cusp morphology among the four subspecies have suggested relatively large intraspecific variability. Here, we compare molar crown traits and cusp wear of two geographically close populations of Western chimpanzees, P. t. verus, to provide further information on intraspecific dental variability. Micro-CT reconstructions of high-resolution replicas of first and second molars of two Western chimpanzee populations from Ivory Coast (Taï National Park) and Liberia, respectively were used for this study. First, we analyzed projected tooth and cusp 2D areas as well as the occurrence of cusp six (C6) on lower molars. Second, we quantified the molar cusp wear three-dimensionally to infer how the individual cusps alter with advancing wear. Both populations are similar in their molar crown morphology, except for a higher appearance rate of a C6 in Taï chimpanzees. In Taï chimpanzees, lingual cusps of upper molars and buccal cusps of lower molars possess an advanced wear pattern compared to the remaining cusps, while in Liberian chimpanzees this wear gradient is less pronounced. The similar crown morphology between both populations fits with previous descriptions for Western chimpanzees and provides additional data on dental variation within this subspecies. The wear pattern of the Taï chimpanzees are in concordance with their observed tool rather than tooth use to open nuts/seeds, while the Liberian chimpanzees may have consumed hard food items crushed between their molars.

Exploiting multimodal CNN architecture for automated teeth segmentation on dental panoramic X-ray images.

Panoramic X-ray images are the major source used in field of dental image segmentation. However, such images suffers from the disturbances like low contrast, presence of jaw bones, nose bones, spinal bone, and artifacts. Thus, to observe these images manually is a tedious task, requires expertise of dentist and is time consuming. Hence, there is need to develop an automated tool for teeth segmentation. Recently, few deep models have been developed for dental image segmentation. But, such models possess large number of training parameters, thus making the segmentation a very complex task. Also, these models are based only on conventional CNN and lacks in exploiting multimodal CNN features for dental image segmentation. Thus, to address these issues, a novel encoder-decoder model based on multimodal-feature extraction for automatic segmentation of teeth area is proposed. The encoder has three different CNN based architectures: conventional CNN, atrous-CNN, and separable CNN to encode rich contextual information. Whereas decoder contains a single stream of deconvolutional layers for segmentation. The proposed model is tested on 1500 panoramic X-ray images and uses very less parameters when compared to state-of-the-art methods. Besides this, the precision and recall are 95.01% and 94.06%, which out performs the state-of-the art methods.

ИССЛЕДОВАНИЕ МИНЕРАЛИЗАЦИИ ТВЕРДЫХ ТКАНЕЙ ЗУБОВ, ПОРАЖЕННЫХ ЛУЧЕВЫМ КАРИЕСОМ, С ПОМОЩЬЮ МЕТОДА РАМАН-ФЛЮОРЕСЦЕНТНОЙ ДИАГНОСТИКИ

Subject. Mineralization of hard tissues of teeth affected by radiation caries in patients after radiation therapy of malignant neoplasms.&#x0D; Objectives. To develop a digital method for diagnosing radiation caries based on Raman fluorescence technology.&#x0D; Methodology. The study was conducted at the Department of Orthopedic Dentistry and Orthodontics of South Ural State Medical University. The study was conducted on two groups of people (cohorts) comparable in sex and age, who voluntarily agreed to take part in it. The main group consisted of 20 people (patients with radiation caries), the comparison group – 20 people (without radiation caries). The main research method was the study of Raman fluorescence of tooth areas using the «InSpectr» hardware-software complex with diagnostic sensitivity according to the integral concentration of aerobic-anaerobic microbial suspension up to 109 KOE/ml. A study was made of teeth in the pathological area in patients of the main group, and in the intact area in patients of the comparison group.&#x0D; Results. Raman fluorescent diagnostics of the intact tooth surface and the surface with a pathological focus made it possible to clearly see the difference in mineralization in digitized indicators. So, for example, according to the indicators of patients with damage to the teeth by radiation caries, it can be concluded that the indicators of mineralization in the focus affected by radiation caries ( y = 172 ± 0.04, x = 963 cm-1) are lower than those of the intact area (y = 1174 ± 0.071, x = 963 cm-1)&#x0D; Conclusion. The method of Raman fluorescence diagnostics can be used in the diagnosis of radiation caries, since there is a potential difference between the healthy and the affected areas of the hard tissues of the tooth. On the basis of the study, the author recommends using the «InSpectr» hardware-software complex for diagnosing radiation caries.

Analysis of morphometric changes in the anterior alveolar bone in bimaxillary protrusion adult patients after retraction with cone-beam CT

Objective: To measure and analyze the morphometric changes in the anterior alveolar bone during treatment and retention stage after retraction in bimaxillary adults using cone-beam CT(CBCT). Methods: Fifteen adult patients, four males and 11 females, aged 19 to 28 years[(22.2±3.1) years], who have completed orthodontic treatment and extracted four first premolar teeth for retraction in the Department of Orthodontics, The Affiliated Stomatological Hospital of Nanchang University from January 2016 to December 2018 were selected. CBCT was taken to assess the labial and palatal vertical bone level, total bone thickness at crest area, middle root area and apical area in pre-treatment (T1), post-treatment (T2) and at follow-up (maintained for more than two years) (T3). The differences in alveolar bone morphology at different stages were compared by single factor repeated measure ANOVA, and Pearson correlation analysis was performed on the amount of alveolar bone change in treatment stage and retention stage. Results: There were statistically significant differences in the alveolar bone height of the palatal side of maxillary anterior teeth, the labial side of maxillary lateral incisors and canine among three time points (P<0.05). The height difference of palatal alveolar bone of anterior teeth in T1-T2 stage was statistically significant (P<0.05). Palatal alveolar bone of upper and lower central incisors decreased by (1.52±0.32) and (4.96±0.46) mm, respectively. The height difference of anterior palatal alveolar bone was statistically significant in T2-T3 stage(P<0.05), the palatal alveolar bone height of central incisors increased by (1.20±0.27) and (3.14±0.35) mm respectively. The height difference of palatal alveolar bone in the anterior teeth of T1-T3 stage was statistically significant (P<0.05), and the height of palatal alveolar bone of central incisors was decreased (0.33±0.11) and (1.82±0.39) mm, respectively. There were statistically significant differences in the thickness of the cervical and middle root alveolar bone of anterior teeth among three time points (P<0.05). The difference of alveolar bone thickness of the cervical and middle root of anterior teeth at T1-T2 was statistically significant (P<0.05). decreased by (0.63±0.10) and (0.67±0.09) mm in lateral incisors, respectively. In the T2-T3 stage, the alveolar bone thickness of the crest area of the lower anterior teeth was significantly different (P<0.05), the alveolar bone thickness of mandibular central incisor crest area increased (0.09±0.03) mm. There were statistically significant differences in alveolar bone thickness in crest area and middle root of the incisors during T1-T3 stage (P<0.05), among which the middle root decreased by (0.38±0.16) mm and (0.63±0.13) mm, respectively. There was no statistically significant difference in other areas (P>0.05). The change of alveolar bone height in palatal side of upper anterior teeth at T2-T3 was very strongly negatively correlated with the change in T1-T2. The change of alveolar bone height in labial side of upper anterior teeth and lingual side of lower anterior teeth and the thickness of incisor root and neck were moderately strongly negatively correlated (r≤-0.8, P<0.001), the change of alveolar bone height in labial side of upper anterior teeth and lingual side of lower anterior teeth and the thickness of incisor crest area were moderately strongly negatively correlated (-0.8<r≤-0.4, P<0.05). Conclusions: For adult patients after retraction, anterior alveolar bone decreased significantly. In the retention stage, the same degree of bone apposition will occur, but still have alveolar bone loss compared with pre-treatment. The amount of alveolar bone change in the retention stage correlated with the amount of alveolar bone change in the treatment stage.

Evaluation of the accuracy of T-scan system and Cerec Omnicam system used in occlusal contact assessment

PurposeThe objective of the present study was to determine the accuracy of T-scan system and Cerec Omnicam system with respect to the evaluation of occlusal contact by quantitatively comparing the occlusal contact areas and the overlapping ratios of occlusal contact areas obtained from these systems. Material and methodsThe occlusal contact of 20 adolescents with normal occlusion was measured with the T-scan system and the Cerec Omnicam system, respectively. The occlusal contact areas in the intercuspal position were then quantified with Adobe Photoshop CS6 Software. The same procedure was repeated for each subject using with 8 μm articulating paper as the control group. The overlapping ratio of T-scan system and Cerec Omnicam system was calculated respectively, which is defined as the ratio of overlapping areas comparing with those obtained from articulating paper. To examine the accuracy of T-scan system and Cerec Omnicam system, the Paired t-test was applied. The reproducibility of T-scan system was evaluated with Wilcoxon matched-pairs signed-ranks test by comparing the occlusal contact areas between two repeated measurements. In all statistical analysis, the level of significance was set to α = 0.05. ResultsResults demonstrated measured occlusal contact areas were significantly different between those obtained between T-scan system and Cerec Omnicam system (P < 0.05). The tooth position of two-dimensional virtual dental arch established by T-scan system based on the width of the central incisor was in disagreement with the actual tooth position. The overlapping ratios obtained from Cerec Omnicam system were higher than those obtained from the T-Scan system (P < 0.05). The sensitivity of T-Scan system in anterior teeth area decreased when sensors are used more than once (P < 0.05). ConclusionsIn the intercuspal position, the accuracy of Cerec Omnicam system for occlusal contact assessment is higher than that of T-scan system. The T-scan system demonstrates good reproducibility in the premolar region and the molar region, but poor reproducibility in the anterior teeth region. Clinical implicationsIn the intercuspal position, Cerec Omnicam system is more accurate than T-scan system, which can quantitatively analyze occlusal relationship in terms of number, position, size and distribution of occlusal contact points. When evaluating occlusal contacts, the accuracy of T-scan system in anterior teeth region is significantly lower than that of premolar and molar regions.

Semi-Automated Planimetric Quantification of Dental Plaque Using an Intraoral Fluorescence Camera.

Dental plaque accumulation is quantified using clinical indices or, otherwise, the planimetric plaque index (PPI),which measures the relative area of a tooth that is covered by plaque deposits. Compared to clinical indices, the PPI has a higher discriminatory power, but traditional planimetry is a time-consuming analysis, as the plaque-covered and clean tooth areas have to be determined manually for each image using image-processing software. Here, we present a method for the semi-automated planimetric quantification of dental plaque, which allows for the rapid processing of up to 1,000 images simultaneously. The method exploits the enhanced contrast between disclosed plaque, sound tooth surfaces, and soft tissues in fluorescence images acquired with an intraoral camera. Careful execution of the clinical procedures and accurate image acquisition are crucial steps for the successful semi-automated identification of the plaque-covered areas. The method is suitable for planimetry on sound facial and oral tooth surfaces, on most composite resin restorations, and on teeth with orthodontic brackets, but not on metallic restorations. Compared to traditional PPI recordings, semi-automated planimetry considerably reduces the amount of time spent on the analysis, as well as the subjective human input, thus increasing the reproducibility of planimetric measurements.

The Effect of Heat-Polymerizing Method on Color Stability of Acrylic and Composite Resin Denture Teeth

Objectives: The purpose of this study was to investigate the color stability of acrylic and composite denture teeth after heat-polymerization method. Methods: Three different brands of acrylic denture teeth: Livera Alpha (LA), Yamahashi (YA) and Major Dent (MA) and 2 different brands of composite denture teeth: Yamahashi PX (YC) and Endura (EC) were tested. Ten maxillary central incisors from each group were pressed onto putty-type polyvinyl siloxane in order to measure color in the same area of denture teeth. Color, at cervical third and incisal third, was recorded by spectrophotometer in CIE L*a*b system. All specimens were undergone heat-polymerization of heat-curing acrylic resin. After flask cooling for 24 hours, the specimens were removed. The color measurement was performed at the same area of each specimen. Color differences (∆E) was calculated. A ∆E of ≤3.3 was considered clinically acceptable. The data were evaluated by 3-way repeated-measures ANOVA and Tukey HSD test (α =0.05). Results: The ∆E of LA, YA, EC, MA and YC at incisal third were 4.41±0.56, 2.45±0.60, 0.76±0.57, 0.75±0.24 and 0.63±0.24 respectively. At cervical third, the ∆E of LA, YA, EC, MA and YC were 4.59±1.26, 2.44±1.08, 0.59±0.36, 0.81±0.61 and 1.22±0.78 respectively. The highest ΔE values were found in LA. These values were significantly higher than those obtained from other brands (p&lt;0.05) and beyond clinically acceptable level. Conclusions: After heat-polymerization, the color of LA changed significantly at both incisal and cervical areas. On the other hand, color stability of YA, EC, MA and YC were clinically acceptable.

Understanding the Influence of Patient Factors on Accuracy and Decision-Making in a Diagnostic Accuracy Study with Multiple Raters-A Case Study from Dentistry.

In diagnostic accuracy studies, the test of interest is typically applied only once in each patient. This paper illustrates some possibilities that arise when diagnoses are carried out by a sufficiently large number of multiple raters. In a dental study, sixty-one examiners were asked to diagnose 49 tooth areas with different grades of tissue loss (minor, moderate, and advanced) to decide whether dentine was exposed (positive status) or not (negative status). The true status was determined by histology (reference). For each tooth, the rate of correct decisions reflecting the difficulty to diagnose this tooth and the positive rate reflecting the perception of the tooth by the raters was computed. Meta-analytical techniques were used to assess the inter-tooth variation and the influence of tooth-specific factors on difficulty or perception, respectively. A huge variation in diagnostic difficulty and perception could be observed. Advanced tissue loss made diagnoses more difficult. The background colour and tissue loss were associated with perception and may hint to cues used by the raters. The use of multiple raters in a diagnostic accuracy study allows detailed investigations which make it possible to obtain further insights into the decision-making process of the raters.

Deep learning-based prediction of mandibular growth trend in children with anterior crossbite using cephalometric radiographs

BackgroundIt is difficult for orthodontists to accurately predict the growth trend of the mandible in children with anterior crossbite. This study aims to develop a deep learning model to automatically predict the mandibular growth result into normal or overdeveloped using cephalometric radiographs.MethodsA deep convolutional neural network (CNN) model was constructed based on the algorithm ResNet50 and trained on the basis of 256 cephalometric radiographs. The prediction behavior of the model was tested on 40 cephalograms and visualized by equipped with Grad-CAM. The prediction performance of the CNN model was compared with that of three junior orthodontists.ResultsThe deep-learning model showed a good prediction accuracy about 85%, much higher when compared with the 54.2% of the junior orthodontists. The sensitivity and specificity of the model was 0.95 and 0.75 respectively, higher than that of the junior orthodontists (0.62 and 0.47 respectively). The area under the curve value of the deep-learning model was 0.9775. Visual inspection showed that the model mainly focused on the characteristics of special regions including chin, lower edge of the mandible, incisor teeth, airway and condyle to conduct the prediction.ConclusionsThe deep-learning CNN model could predict the growth trend of the mandible in anterior crossbite children with relatively high accuracy using cephalometric images. The deep learning model made the prediction decision mainly by identifying the characteristics of the regions of chin, lower edge of the mandible, incisor teeth area, airway and condyle in cephalometric images.

Effect of tooth head modification on the performance of a scroll expander for ORC waste heat recovery system

In order to cope with the energy crisis and improve energy efficiency, the use of organic Rankine cycle (ORC) to convert low-quality heat energy into electricity and use it is an effective method. Based on the ORC waste heat recovery system of vehicle engine, this paper explores the flow heat transfer and deformation law of the core component scroll expander under different tooth head corrections. Deformation has a significant impact on the performance of the expander. In this study, several flow-thermal-solid coupling models based on double circular arc correction and double circular arc plus straight-line correction are established. The effects of tooth head correction on the strength and stiffness of tooth head, flow field distribution of suction chamber and deformation characteristics of tooth head are studied. Finally, the deformation law of scroll tooth head with different correction angles was discussed. The results show that the EA-SAL correction makes the wall curvature of the tooth head change greatly, and the flow field in the center of the tooth head becomes more uneven and complicated. The tooth head area under EA-SAL modification is larger, and the tooth head strength and stiffness are improved by about 6%. Within a certain angle range, the tooth head deformation after EA-SAL correction is slightly larger than that after PMP correction, but the difference between them decreases and even reverses with the increase of angle. The maximum deformation of the EA-SAL modified tooth head under internal pressure is about 20% smaller than that of PMP. With a given initial correction angle ∅, the deformation of the corrected tooth head caused by a pressure or temperature load reduces when the correction angle γ is reduced, Therefore, reducing the correction angle properly is helpful to reduce the deformation of the tooth head.

Effect of Temporary Cement, Surface Pretreatment and Tooth Area on the Bond Strength of Adhesively Cemented Ceramic Overlays—An In Vitro Study

Several viewpoints have been reported regarding the effect of temporary cements, different surface pretreatment protocols before adhesive cementation, and predictive factors. This in vitro study tested if temporary cement, pretreatment of the tooth surface, the size of enamel or dentine influence adhesive cementation to zirconia ceramics. Twenty premolars were prepared for determination of enamel and dentin area, bond strength test and failure analysis. The samples were divided into two groups: untreated prior adhesive cementation (n = 10) and with temporary cementation done, pretreated prior adhesive cementation (n = 10). Zirconia overlays (Katana Zirconia STML) were cemented on the grounded flat teeth surfaces using Panavia V5. An additional six premolars underwent dentine tubule analysis with SEM to detect temporary cement residues after temporary cementation on an untreated tooth surface (n = 3) and on a pretreated surface (n = 3). The independent sample t-test was used to compare the two groups and the means of the total tooth, dentin or enamel areas did not differ significantly between the untreated and pretreated specimens. The mean tensile bond strength was significantly (p = 0.005) higher in the pretreated specimens (337N) than in the untreated ones (204N). The overall multivariable linear regression model with three predictors (surface pre-treatment, enamel area and dentine area) was significant (p = 0.003), among which the size of enamel was the strongest predictor (β = 0.506; p = 0.049), followed by the pretreatment effect (β = 0.478; p = 0.001) and the size of dentin area (β = -0.105; p = 0.022).

Marginal bone loss associated with unilateral free end mandibular implant supporting superstructures constructed with different occlusal schemes

AimsThis study was designed to evaluate the amount of bone resorption related to implant in free end saddle in response to different occlusal designs.Patients and methodsTwenty patients with unilateral free end saddle in the lower arch till the second premolar were selected and received delayed single dental implants replacing the first molar tooth. They were divided into two main groups according to the implant superstructure deign (n = 10). Group 1: implant-supported fixed dental prosthesis which follow the principals of implant protected occlusion, and with the occlusal contact area of the crown smaller than the occlusal contact area of adjacent tooth. Group 2: implant-supported fixed dental prosthesis which follow the principals of implant protected occlusion, and with the occlusal contact area of the crown larger than the occlusal contact area of adjacent tooth. Patients were evaluated for the amount of marginal bone level at the time of crown insertion, after 3 and 6 months of function.ResultsThere was a statistically significant change by time in marginal bone loss in both groups especially during the first 3 months. However, there was no statistically significant difference between marginal bone loss regarding the two groups.ConclusionIt was concluded that increasing the occlusal contact area of the implant superstructure has no effect on marginal bone loss.

Autotransplantation of a horizontally oriented fragment of the root of a removed tooth to preserve alveolar tissues

To develop a method to contain atrophy of the alveolar bone and surrounding soft tissues in the area of many cortical teeth in the first 3 months after removal for subsequent installation of a dental implant. A description of a method for containing atrophy of the alveolar bone and surrounding soft tissues after removal of the first molar of the mandible 3 months after tooth extraction is presented. The method consists in closing the mouth of the well with a horizontally oriented fragment of the root of the removed tooth with a preserved section of the ligamentous apparatus. An X-ray assessment of bone restoration in the lumen of the well was carried out according to the Hounsfield coefficient and an assessment of the condition of soft tissues in the area of surgery 3 months after removal. For histological assessment of bone maturity, bone was taken from the implantation area 14 weeks after tooth extraction. The technique allowed to preserve the quality of soft tissues close to the original; on three-dimensional X-ray images in the lumen of the well, bone restoration sufficient for the installation of a dental implant is diagnosed, the zonal value of the Hounsfield coefficient is more than 300 units; histologically, a well-developed network of coarse-fibrous trabeculae is determined with the beginning of reconstruction into lamellar bone, regeneration of the alveolar process occurs by intramembranous ossification. The proposed technique contributes to the preservation of the qualities of the marginal gum in the healing zone after tooth extraction and the formation of sufficient bone maturity in the lumen of the well.

Research on the design and bearing characteristics of shipborne spiral elevator in specific small space

This work aims at the problem that the temperature rise, gluing or wear of the thread sliding friction pair under fast and heavy load make it difficult to estimate the service life of the equipment. Based on the numerical simulation method and the heat balance theory of the screw friction pair, the bearing characteristics of a self-designed shipborne multi-section free-telescopic screw elevator are studied. The results show that the stress of the thread tooth is mainly concentrated in the root area of the thread tooth, and the load of the thread is mainly concentrated in the first three threads of the meshing thread. When the friction coefficient is more than 0.3, the friction temperature rise will lead to gluing failure. Therefore, a good lubrication environment can effectively reduce the friction coefficient of the thread and reduce the screw contact surface gluing failure caused by the friction torque work heating.

Shear bond strength between denture teeth and denture base using different bonding resins and tooth surface treatments

Aim of studyThe aim of the present study was to evaluate the influence of surface treatments of the ridge lap area of PMMA acrylic denture teeth on their shear bond strength with different bonding resins to denture base milled from prefabricated PMMA block, in a two-way factorial experiment. The traditional heat-curing method was included as a reference method to compare to the proposed new method that employs digital technology. Materials and methodsFifty-four cylindrical rods were prepared from two different types of PMMA based denture resin; one specially designed for the computer-aided design and computer-aided manufacturing (CAD/CAM) milling method (groups A, n = 18 and B, n = 18) and a conventional heat-curing resin (group C, n = 18). A central maxillary incisor was selected as the experimental tooth. The specimens of each group A, B, and C were divided equally into three subgroups (a, b, c; n = 6 for every subgroup) according to three surface conditionings (no treatment, sandblasting, sandblasting plus methyl-methacrylate application, respectively). A specially designed bonding resin for digital dentures was used in group A, and a common self-curing resin for repairs in group B, while in group C the specimens were prepared by the conventional heat-curing method. Shear bond strength was determined using an electro-mechanic loading frame (MTS Insight) with a cross-head speed to 1 mm/min. ResultsThere was a statistically significant interaction between the construction method (A, B, C) and tooth surface treatment (a, b, c) (p = 0.026). After eliminating one subgroup, the effect of tooth surface treatment was not significant (p = 0.42). ConclusionsSurface treatment seems not to affect the teeth-base bond. Denture teeth bonded to a CAD/CAM denture base using PMMA self-curing resin for repairs (group B) showed the highest bond strength compared to groups A and C. Clinical significanceIn terms of bond strength, the digital denture construction method can be successfully used in everyday clinical and laboratory practice and replace effectively the conventional heat curing method.

Dental implant placement in the area of ectopic and impacted teeth

The paper presents two clinical cases demonstrating the effectiveness of using surgical templates for the installation of dental implants in the areas of ectopic and impacted teeth in case of patient's disagreement on their removal or other methods of treatment.