Linear Deviation Research Articles

Evaluating the Effects of Dynamic Navigation on the Accuracy and Outcomes of the Autogenous Bone Ring Technique for Vertical Ridge Augmentation: A Pilot Randomized Controlled Trial.

Autogenous bone ring technique (BRT) is a one-stage vertical augmentation approach with simultaneous implant placement. The aim of this study was to compare the accuracy and efficacy of autogenous BRT assisted by dynamic navigation (DN) with freehand approach (FA) for vertical ridge augmentation. Twenty-four patients eligible for autogenous BRT were randomly assigned to DN or FA groups. Digital preoperative design was conducted for both groups. BRT surgeries were executed with or without the aid of DN in the two groups. Accuracy outcomes evaluated angular and linear deviations at the bone ring in the donor site (BR-D), recipient site (BR-R), and implant entry/apex between planned and actual positions revealed by cone-beam computed tomography. Vertical augmentation-related outcomes, surgical complications, and patient-reported outcomes were assessed over 6 months. Twenty-four patients underwent surgery while one was lost to follow-up. The DN group showed significantly lower mean (SD) BR-R angular (3.58 [2.07] vs. 8.77 [4.20]°) and entry deviation (1.43 [0.51] vs. 2.01 [0.70] mm). For BR-D, the DN group had significantly lower angular (4.80 [2.62] vs. 12.97 [6.26]°), entry (1.45 [0.96] vs. 3.52 [1.54] mm), and apex deviation (1.28 [0.64] vs. 3.50 [1.47] mm) compared to the FA group. Implant angular deviation (3.74 [2.14] vs. 9.17 [4.39]°) and apex deviation (1.75 [0.44] vs. 2.35 [0.82] mm) was significantly lower in the DN group. In the FA group, one patient exhibited temporary lower lip hypoesthesia. No significant differences were observed in vertical bone gain, resorption, or patient-reported outcomes. Compared to FA, DN may improve the accuracy of autogenous BRT procedures for vertical ridge augmentation while minimizing invasiveness. This study was registered at the Chinese Clinical Trial Registry (https://www.chictr.org.cn; Registration No. ChiCTR2200065585; registration date: 2022/11/09).

A Novel Pedicle Screw Placement Surgery Based on Integration of Surgical Guides and Augmented Reality.

Augmented reality is a new technology that, when applied to spinal surgery, offers the potential for efficient, safe, and accurate placement of pedicle screws. This study investigated whether augmented reality combined with a guide board improved the safety and accuracy of pedicle screw placement compared to traditional freehand screw placement. Four trainers were divided into augmented reality navigation and freehand groups. Each group consisted of a novice and an experienced spine surgeon. A total of 80 pedicle screws were implanted. First, the AR group reconstructed the three-dimensional (3D) model and planned the screw insertion route according to the computed tomography (CT) data of L2 lumbar vertebrae. Next, the Microsoft HoloLens 2 was used to identify the vertebral model, and the planned virtual path was superimposed on the real cone model. Then, the screw was placed according to the projected trajectory. Finally, Micron Tracker was used to measure the deviation of screws from the preoperatively planned trajectory, and pedicle screws were evaluated using the Gertzbein-Robbins scale. In the augmented reality group, the linear deviation of the experienced doctors and novices was 1.59 ± 0.39 and 1.73 ± 0.52 mm, respectively, and the deviation angle was 2.72 ± 0.61 and 2.87 ± 0.63 degrees, respectively. In the freehand group, the linear deviation of the experienced doctors and novices was 2.88 ± 0.58 and 5.25 ± 0.62 mm, respectively, and the deviation angle was 4.41 ± 1.18 and 7.15 ± 1.45 degrees, respectively. The screw placement accuracy rate was 97.5% in the augmented reality navigation group and 77.5% in the freehand group. Augmented reality navigation improves the accuracy and safety of pedicle screw implantation compared with the traditional freehand method and can assist inexperienced doctors in successfully completing the surgery.

Accuracy of digital and conventional implant impressions in edentulous jaws: A clinical comparative study.

This clinical study aimed to evaluate the accuracy of digital and conventional implant impressions in a fully edentulous maxilla and mandible. A 53-year-old edentulous patient with four maxillary and two mandibular implants was selected. Ten intraoral scans (IOS) and a conventional impression per jaw were taken. Clinically verified upper and lower plaster models were digitized using both optical (reference data, n = 10 per model) and tactile laboratory scanner (n = 10 per model). Accuracy was evaluated by comparing the precision and linear/angular deviations of the implants with the reference data. Statistical analyses were conducted using Student's t-test and Kruskal-Wallis test (α = 0.05). In the maxilla, the most significant linear deviations exceeding the 100 µm threshold were found with IOS between implants 1-4. In the mandible, all linear deviations remained below 55 µm. Angular deviations between implants after IOS ranged from 0.01° to 0.40° in the mandible and <0.01° to 1.86° in the maxilla. After tactile scanning, linear deviations did not exceed 100 µm threshold (except in one distance) and angular deviations ranged from 0.04° to 0.54° (mandible) and <0.01° to 2.50° (maxilla). The optical scanner demonstrated significantly higher precision (p < 0.001) compared to the IOS and tactile scanner. Given the significant deviations observed, especially in the maxilla, the optical scanner following conventional impressions remained the preferred method for fully edentulous cases due to its superior accuracy. IOS could be a viable alternative particularly for shorter distances in the edentulous jaw, although the clinical implications of these deviations need to be investigated in future studies.

Enhancing activity and selectivity of palladium catalysts in ketone α-arylation by tailoring the imine chelate of pyridinium amidate (PYA) ligands.

Even though α-arylation of ketones is attractive for direct C-H functionalization of organic substrates, the method largely relies on phosphine-ligated palladium complexes. Only recently, efforts have focused on developing nitrogen-based ligands as a more sustainable alternative to phosphines, with pyridine-functionalized pyridinium amidate (pyr-PYA) N,N'-bidentate ligands displaying good selectivity and activity. Here, we report on a second generation set of catalyst precursors that feature a 5-membered N-heterocycle instead of a pyridine as chelating unit of the PYA ligand to provide less steric congestion for the rate-limiting transmetalation of the enolate. To this end, new heterocycle-functionalized PYA palladium(ii) complexes containing an oxazole (5b), N-phenyl-triazole (5c), N-methyl pyrazole (5d), N-phenyl-pyrazole, (5e), N-xylyl-pyrazole (5f), and N-isopropyl-pyrazole (5g) were synthesized compared to the parent pyr-PYA complex 5a. Less packing of the palladium coordination sphere was evidenced from solid state X-ray diffraction analysis. While the catalytic activity of the oxazole system was lower, all other complexes showed higher activity. In particular, complex 5g comprised of an electron-donating and sterically demanding iPr-pyrazole chelating PYA ligand is remarkably stable towards air and moisture and shows outstanding catalytic activity with complete selectivity (>99% yield) and turnover frequencies up to 1200 h-1, surpassing that of parent 5a by one order of magnitude and rivalling the most active phosphine-based palladium systems. Kinetic studies demonstrate a first order rate-dependence on palladium and the substrate. Some deviation of linearity together with poisoning experiments suggest a mixed homogeneous/heterogeneous pathway, though the reproducible kinetics of in situ catalyst recycling experiments strongly point to a molecularly defined active species, demonstrating the high potential of PYA-based ligands.

Longitudinal analysis of anthropometric measures over 5 years in patients with Friedreich ataxia in the EFACTS natural history study.

Friedreich ataxia is a rare neurodegenerative disorder caused by frataxin deficiency. Both underweight and overweight occur in mitochondrial disorders, each with adverse health outcomes. We investigated the longitudinal evolution of anthropometric abnormalities in Friedreich ataxia and the hypothesis that both weight loss and weight gain are associated with faster disease progression. Participants were drawn from the European Friedreich's Ataxia Consortium for Translational Studies (EFACTS). Age- and sex-specific BMI and height scores were calculated using the KIGGS-BMI percentiles for children. Height correction was applied for scoliosis. Longitudinal data were analysed using linear mixed effects models and incremental standard deviation scores and growth mixture models identified subclasses with varying BMI trajectories. Five hundred and forty-three adults and fifty-nine children were assessed for up to 5 years. In children, severe underweight (26%), underweight (7%), severe short stature (16%) and short stature (23%) were common. The corrected BMI percentile was stable in children, although 48% had negative incremental BMI scores over 1 year and 63% over 3 years versus 10%/year in a normal reference cohort. Overweight was common in adults (19%), with a slight increase in BMI over time. Longer GAA repeat size was linked to lower BMI in adults. Weight trajectory was not associated with ataxia progression in adults. Significant anthropometric abnormalities were identified, with underweight and short stature prevalent in children and overweight in adults. These findings highlight the need for regular nutritional monitoring and interventions to manage underweight in children and promote healthy weight in adults.

Accuracy of Full-Arch Intraoral Scans Versus Conventional Impression: A Systematic Review with a Meta-Analysis and a Proposal to Standardise the Analysis of the Accuracy.

Objectives: The aim of this study was to systematically revise the state of art of the accuracy of digital and conventional impressions in clinical full-arch scenarios. Methods: Electronic and manual searches were conducted up to December 2024. Only trials comparing the accuracy of digital versus conventional impressions were selected by two independent reviewers. Accuracy was evaluated by analysing the fit of the prostheses obtained through conventional workflows and those obtained from digital workflows using intraoral scanners. Alternatively, accuracy was assessed by comparing the standard tessellation language data acquired from intraoral scanning with those obtained from scanning the physical model. The risk of bias was assessed using the Quality Assessment of Diagnostic Accuracy Studies tool. Meta-analysis was conducted to pool the mean differences from the included studies, with heterogeneity tested by Cochran's Q test and quantified by the I2 index. Results: We included 9 relevant studies from a total of 2535 identified studies. The risk of bias was evaluated as low, and the main results of all the included articles reported similar accuracy between digital and conventional impressions. Random effects meta-analysis resulted in a pooled mean difference of 152.46 (95% C.I. = 76.46-228.46, p-value < 0.001, I2 = 93.48%). Conclusions: In conclusion, the results of the present systematic review reveal contradictory findings regarding the accuracy of digital impressions. However, most studies analysing the clinical performance of prostheses obtained through digital impressions suggest that their accuracy falls within clinically acceptable thresholds. Future research should report comparable outcomes and focus attention on linear deviations, comparing differences between conventional and digital impressions not in absolute terms, but relative to the distance measured.

Safety and Accuracy of Guided Interradicular Miniscrew Insertion: A Systematic Review and Meta-Analysis.

Background: Achieving ideal anchorage is crucial in orthodontics for controlled tooth movement. Miniscrews (MSs) have improved skeletal anchorage, but freehand placement poses risks like root damage and limited precision. Guided techniques, including radiographic guides and computer-assisted methods (static [sCAS] and dynamic [dCAS]), were developed to enhance accuracy and safety. Objective: This systematic review and meta-analysis aimed to evaluate the safety and accuracy of MS placement using different guidance approaches. Materials: A systematic search up to March 2024 identified studies on guided MS insertion, assessing safety (root contact/damage) and accuracy (angular, coronal, and apical deviations) of guided vs. freehand placement. Two reviewers assessed the risk of bias and study quality using RoB 2 for RCTs, NOS for cohort studies, and an adapted tool for pre-clinical studies. Random-effects meta-analysis was performed for studies with common parameters, and safety outcomes were pooled using logit-transformed proportions. Heterogeneity was evaluated with I² and χ² tests. Results: Eleven studies (652 MSs) were included, though no dCAS studies were analyzed. The only RCT had "some concerns" regarding risk of bias, cohort studies ranged from medium to low quality, and most pre-clinical studies had high bias risk. sCAS significantly reduced root damage compared to freehand methods (OR = 0.11; 95% CI: 0.04-0.36; p < 0.001; I² = 1%) and reduced angular and linear deviations. Due to heterogeneity, no quantitative synthesis of accuracy outcomes was performed. Conclusions: sCAS improves the safety and accuracy of MS insertion compared to freehand and radiographic guide methods. These results highlight the clinical benefits of sCAS in orthodontics. Future studies should refine protocols and explore dCAS for further accuracy improvements.

Accuracy of digital jaw relation determination in different occlusal conditions - an in vitro study.

In orthodontics, accurate registration of jaw relationships is essential for correct diagnosis and treatment planning. Therefore, accuracy of the digital spatial registration of maxillary and mandibular models and - for the first time-the influence of dentition stage and malocclusion type on this procedure were investigated under controlled conditions. Eight pairs of jaw models, representing different occlusal and developmental statuses (m1-m8), were scanned using two IOS types (PS: Primescan; TR: Trios4). Buccal scans for registering maxillary and mandibular models were repeated (n = 3). Reference scans were obtained using a desktop scanner (RDS; Ceramill Map 600). Arch-specific 3D coordinate systems were used to calculate the linear and angular deviations among different registrations. Trueness of registration by PS and TR was calculated using a statistical mixed-effect model (random-effect: model-type). Precision values of IOS registrations across m1-m8 were characterized as standard deviations (SDs). As maximum deviations compared to RDS, PS showed caudal translation (0.11 ± 0.02mm), while TR showed ventral translation (0.08 ± 0.06mm), of the maxillary relative to the mandibular model. Maximum rotational values were calculated for tilting around the transverse axis (PS: anteinclination (0.25 ± 0.16°), TR: retroinclination (0.27 ± 0.16°)). These deviations varied with the malocclusion type. The lowest IOS precision was recorded for sagittal translation (PS: 0.013 ± 0.005mm, TR: 0.021 ± 0.010mm) and rotation around the transverse axis (PS: 0.051 ± 0.013°, TR: 0.076 ± 0.031°). Registrations using buccal IOS scans showed quantifiable but clinically negligible 3D deviations from reference scan registrations, whereby the type of tooth and jaw misalignment did not appear to have a clinically relevant influence. Therefore, the examined IOSs appear to be suitable for digital jaw relation determination in everyday clinical orthodontic practice.

A Comparative Prospective Study on the Accuracy and Efficiency of Autonomous Robotic System Versus Dynamic Navigation System in Dental Implant Placement.

This study aimed to evaluate the efficiency of and discrepancies between planned and final implant positions using dynamic computer-assisted implant surgery (d-CAIS) and autonomous robotic computer-assisted implant surgery (r-CAIS) in clinical practice. The study included 83 patients, who received 135 implants between December 2022 and March 2024 (r-CAIS group: 43 patients with 71 implants; d-CAIS group: 40 patients with 64 implants). Cone-beam computed tomography scans taken before and after surgery assessed linear and angular deviations between the groups in both 2D and 3D spaces. The duration of surgery was also analysed. The angular deviation between d-CAIS and r-CAIS was 3.61° ± 1.65° versus 1.62° ± 0.93° (p < 0.001), the platform deviation was 1.12 ± 0.51 mm versus 0.50 ± 0.19 mm (p < 0.001) and the apex deviation was 1.36 ± 0.57 mm versus 0.58 ± 0.21 mm (p < 0.001). The d-CAIS group experienced significantly longer drilling and implant placement times compared to the r-CAIS group (10.6 ± 3.8 vs. 8.3 ± 3.4 min, p < 0.01), while preparation time showed no statistical difference between the groups (7.2 ± 3.3 vs. 6.2 ± 2.7 min, p > 0.05). The robotic system demonstrated higher accuracy and efficiency of implant placement than the dynamic navigation system in partially edentulous patients.

Learning Curve for Dynamic Navigation Procedure during Endodontic Management of Permanent Maxillary Anterior Teeth with Pulp Canal Calcification: A Risk-Adjusted Cumulative Summation Analysis of a Single Operator's Experience.

The dynamic navigation system (DNS) in endodontics presents a significant learning curve. This cross-sectional study aimed to assess the number of cases required to achieve consistent performance in DNS-assisted treatment of maxillary anterior teeth with pulp canal calcification. A series of DNS procedures were performed on 45 calcified maxillary anterior teeth with pulp necrosis by a single endodontist who had no prior clinical DNS experience. Preoperative cone-beam computed tomography was obtained. After trace registration and calibration, drilling was executed using a low-speed bur. Once the canal was located and scouted to the working length, a postoperative cone-beam computed tomography was taken immediately. Angular deviation (AD), linear deviation (LD), and operating time (OT) were measured. The learning curve was evaluated using the risk-adjusted cumulative sum analysis method. The overall success rate in locating canals was 93.33% (95% CI 80.7, 98.3). The mean (±SD) for AD, LD and OT was 3.21±2.23°, 0.52±0.33mm and 34.14±13.18minutes, respectively. For AD, 2 distinct peaks were observed at the 5th and 18th cases, identifying 3 learning phases: Phase I (cases 1-5), Phase II (cases 6-18), and Phase III (cases 19-45). Similarly, LD exhibited peaks at the 13th and 28th cases. Two peaks for OT were identified at the 7th and 26th cases. Achieving technical proficiency in locating calcified canals using DNS required approximately 18 to 28 cases, indicating a significant learning curve that must be overcome for optimal accuracy.

Serial Robot Kinematic Calibration Using a Novel Linear Finite Screw Deviation Model

Serial Robot Kinematic Calibration Using a Novel Linear Finite Screw Deviation Model

The Use of Dynamic Navigation for the Placement of Zygoma Implants: A Cadaver Study to Compare Accuracy.

This study aimed to compare the angular, platform, and apical deviation of zygoma implants placed with the aid of a dynamic navigation (DN) device compared with the implants placed freehand. Eight cadaver heads were used for the study. Preoperative cone beam computerized tomography (CBCT) scans were made for the heads, and an implant-planning software was used to plan zygoma implants bilaterally in each scanned head. A total of 16 zygoma implants were placed using each surgical technique. Postimplant CBCT scans were merged with the preoperative plan to evaluate and compare the accuracy of the implants using each technique. Angular and linear deviations of the implants were measured and compared. The effect of implant length and position on the deviation was also investigated. The results showed a mean angular deviation of 2.44° ± 1.10° for implants placed using DN compared with 6.63° ± 4.81° for implants placed freehand. The mean apical deviation for implants placed using DN and for implants placed freehand was 2.14 ± 1.02 mm and 3.80 ± 2.49 mm, respectively. Finally, the mean platform deviation for implants placed using DN and for implants placed freehand was 1.66 ± 0.9 mm and 2.81 ± 2.1 mm, respectively. The analysis showed a significant difference between the two techniques in angular and apical deviation (p = .001 and .029, respectively). Zygoma implants placed with a DN device resulted in less apical and angular deviation than implants placed freehand.

Study on Real-Time Detection of Lightweight Tomato Plant Height Under Improved YOLOv5 and Visual Features

Tomato cultivation is relatively dense, and the main stem is easily submerged in a background environment with small color difference. The semi-enclosed planting space and fast growth cycle are both limitations that cannot be ignored in detection technology. The accuracy and real-time performance of plant height detection are of great practical significance. To this end, we are committed to improving YOLOv5 and proposing a lightweight real-time detection method for plant height by combining visual features of tomato main stems. Here, we improved the backbone, neck, head, and activation functions of YOLOv5, using CSP dark net53-s as the backbone structure and introducing a focus structure to reduce the number of GE modules. We replaced all CSP2_X structures in neck and head with GE modules, embedded interactive multi-head attention, and replaced YOLOv5’s framework function and attention activation function. We defined visual features such as the color of the main stem of tomato plants in the preprocessed image; input improved YOLOv5; and completed plant height detection through effective feature map fusion, main stem framing, and scale conversion. The experimental results show that the linear deviation between the plant height detection value and the actual value of the proposed method is always less than 3 cm, and the detection FPS can reach up to 67 frames per second, with superior timeliness, which can effectively achieve lightweight real-time detection.

Accuracy of Photogrammetry, Intraoral Scanning, and Conventional Impression for Multiple Implants: An InVitro Study.

This invitro study compared the accuracy of conventional impressions (CNVs), photogrammetry (PG), and intraoral scanning (IOS) for recording implant impressions of edentulous segments, ranging from part to complete arches by different evaluation methods. The master model for an edentulous maxillary arch was created with six implants (a-f). CNVs, PG, and IOS were used for impressions. Three impression ranges (bcde, bcdef, and abcdef) were chosen for analysis. The best-fit algorithm, absolute linear deviation, and angular deviation were used for evaluation. Trueness and precision were analyzed by two-way ANOVA and the Kruskal-Wallis test, respectively. The accuracy of multiple implant impressions was significantly influenced by the impression method and impression range (p < 0.05) regardless of the evaluation methods used. At smaller ranges (bcde and bcdef), there was no difference in the trueness of the three impression methods, whereas at a larger range (abcdef), both PG and CNV exhibited similar trueness, which was significantly higher than that of IOS(p < 0.05). The precision of PG was significantly better than that of CNV and IOS in most of cases (p < 0.05). As the range expanded, the trueness and precision of PG and IOS decreased (p < 0.05), whereas the accuracy of CNV remained stable. In the case of large-range impressions, PG demonstrated a similar degree of trueness and better precision compared with CNVs, whereas the trueness and precision of the intraoral scanning were worse. This indicated that PG might be a promising method for multiple implant impressions.

Influence of Bone Conditions on the Accuracy of Implant Placement.

This study aimed to assess the influence of cortical bone thickness, bone density, and residual ridge morphology in the posterior mandibular area on the accuracy of implant placement using tooth-supported digital guides. The research included 75 implants from 55 patients. Each patient underwent a cone-beam computed tomography (CBCT) scan for image analysis. Simplant® Pro 17 software (SIMPLANT Pro 17.01) was utilized to measure cortical bone thickness, bone density, and residual ridge morphology at the implant sites. Subsequently, 3Shape Trios software (3Shape TRIOS Design Studio 1.7.19.0) was applied to delineate optimal implant positions and design tooth-supported surgical guides. After implant treatment, the linear and angular deviations from the planned placement were quantified. Multiple linear regression, Kruskal-Wallis test, Conover-Iman test, and Bonferroni adjustment were conducted to investigate the impact of bone characteristics on implant placement precision. The tooth-supported digital guides used in this study were sufficient to fulfill the precision criteria for implant treatment. Bone density was found to significantly influence the buccal-lingual angular deviation, mesio-distal linear deviation, and mesio-distal angular deviation (p < 0.05). Additionally, significant variances were noted in the coronal deviation, apical deviation and depth deviation in buccal-lingual orientation, coronal deviation, and apical deviation in mesio-distal orientation across various residual ridge morphologies (p < 0.05). Low bone density and S-shape morphology may affect the accuracy of implant placement using tooth-supported surgical guides.

Investigation of the influence of linear and angular deviations of UAVS on the change in parallaxes of images of the underlying surface obtained in the mode of rectilinear horizontal flight

The purpose of the research is assessment of the joint and separate influence of linear and angular deviations of the UAV from the trajectory of rectilinear horizontal flight on the change in parallax images of the underlying surface. Methods. Quantitative estimates are based on a study of the sensitivity of a model describing the functional relationship between the parameters of UAV deviations from a given trajectory and changes in the longitudinal and transverse parallaxes of overlapping images of the underlying surface caused by these deviations.Results. The difference of longitudinal parallaxes in the absence of linear deviations of the UAV, regardless of the sign of the ordinate of the point in the overlap zone, is always positive and increases with an increase in the level of angular deviations, and transverse deviations are negative and decrease, and the value of the first is three times greater than the second. The difference of the transverse parallaxes in the absence of angular deviations of the UAV at a positive ordinate point in the overlap zone is positive, and the longitudinal parallaxes are negative, and at a negative ordinate, on the contrary. At the same time, regardless of the sign of the ordinate of the point in the overlap zone, with an increase in the level of linear deviations of the UAV, the first increases, the second decreases, and the value of the first is four times greater than the secon.Conclusion. The magnitude of the parallax differences depends on the levels of linear and angular deviations of the UAV that occurred at the time of registration of the inclined image, and the sign depends on the sign of the ordinate of the corresponding point in the overlap zone of the second pair of images. In this case, the difference of longitudinal parallaxes is always directly proportional to the level of angular deviations and inversely proportional to the level of linear deviations, and transverse parallaxes is directly proportional to the level of angular deviations at negative values of the ordinate of the point and inversely proportional at its positive values.

Influence of the color of 3D-printed scan aids on the trueness of complete arch digital scans.

To determine the influence of using 3D-printed scan aids in varying colors on the trueness of digital scans. A master cast with five multi-unit analogues was scanned. The acquired dataset was exported to standard tessellation language (STL) file format to serve as the reference STL. 3D printing of the prototype in five distinct colors (beige [SABEIGE], grey [SAGREY], white [SAWHITE], red [SARED], and blue [SABLUE]) of polylactic acid filament was executed. The experimental STLs of each color group were aligned to the reference STL. RMS values were solely computed for the scan bodies. Based on the centers of the created best-fit and offset planes, scan bodies were converted into virtual cylinders. Cartesian coordinates of each cylinder were acquired. Subsequently, angular (AD) and linear deviation (LD) values were calculated. LD was further examined separately along the x, y, and z axes. Data were statistically analyzed. According to the results of one-way ANOVAs, significant differences were detected among color groups on AD, LD, RMS estimate error, ∆x, ∆y, and ∆z data. The lowest AD and LD values were exhibited by the SAGREY group in all implant sites. The SAGREY group was followed by the SABEIGE, SAWHITE, SARED, and SABLUE groups. The SAGREY outperformed the other groups in terms of trueness. Although the LD values of all color groups were below the threshold value (<100 µm), only the AD values of the SAGREY, SABEIGE, and SAWHITE groups were clinically acceptable (<0.5°).

Rainfall Variability, Flood Hazards and Adaptation Strategies in Douala IV and V Municipalities, Littoral Region of Cameroon

Excessive rainfall resulting to floods remain a thorny problem in developing countries including Cameroon. This follows the negative impacts of floods on the population, infrastructure and public services. This study examines rainfall variability, population vulnerability to floods and measures put in place by the population and other stakeholders to adapt to the situation in the Douala IV and V municipalities in Littoral Cameroon. The study exploits both primary and secondary sources data for its realization. Heads of households, quarter’s heads, municipal authorities and its personnel, and public administrative officials were contacted for data collection. The data focused on floods manifestation, their effects on the city, and adaptation strategies put in place to mitigate the negative outcomes. Data from semi structured interview conducted were analyzed using content analysis methods. Sociological and spatial data also collected were analyzed using remotely sensed techniques and statistical tools such as SPSS and Microsoft excel. Climatic data were collected from the urban council, the meteorological units in the town and the National Observatory on Climate Change of Cameroon. Sequential analyses (linear trend curves, standard deviations, and cumulative balances) were used to evaluate the evolution of rainfall and correlation to floods events. The result revealed that floods in Douala IV and V result from rainfall variability, characterized by deficit and excessive rains in the months of June, July, August and September. These heavy rains accompanied by human induced factors such as uncontrolled urbanization, anarchy in construction and occupation of wetlands, poor waste management, pollution of water ways and lack of drains for stagnant water evacuation leads to floods. Also, natural drivers such as the low relief of the area, a dense hydrographic network and contact with the Atlantic Ocean via the Wouri estuary result to floods. These floods are a problem to the health of the population, public services and infrastructure and sustainability of the city. Faced with the numerous damages caused by floods, remediation strategies such as: the construction of traditional dikes, solid house foundations, water embankments, and periodic weather forecasting by the National Observatory on Climate Change of Cameroon to reduce the negative outcomes of flooding has been ineffective in reduction of floods outcomes. Consequently, floods still remains a concern in Douala town. Good environmental practices such as civil education on hygiene and sanitation, periodic cleaning of drains, combats on deforestation of mangroves and afforestation campaigns, government investment on decentralization of waste collection and management will be productive in reducing the effects of floods in Douala. The implementation of all these remedial measures will not only ensure the safety of vulnerable civilian populations but the protection of their activities.

Accuracy of a facebow record: A comparison between a conventional facebow and a smartphone 3D scanner

Statement of problemAccurately transferring the maxillary cast to the articulator is an essential step in most prosthodontics procedures in both digital and conventional workflows. Recently, the use of a smartphone 3-dimensional (3D) scanner-based virtual facebow record has been reported, but its accuracy is unclear. PurposeThe purpose of this clinical study was to compare the trueness and precision of a virtual facebow record made with a smartphone 3D scanner with that of a conventional facebow technique. Material and methodsOne hundred facebow records were obtained from 10 participants using a virtual facebow record made with a smartphone 3D scanner (VFR_SP) and with a conventional facebow record (CFR) (n=10). In the VFR_SP group, a printed facebow fork was used to obtain virtual facebow records by using a smartphone-based face scanner. For the CFR group, an analog facebow record was obtained and scanned by using an industrial scanner. A cone beam computed tomography (CBCT) scan with an aligned maxillary arch scan was used as the control for each participant. Three reference points were placed on the maxillary arch scan on the right first molar, left central incisor, and left first molar. Scans from each group were superimposed on the CBCT scan to determine trueness. Scans within each group were also superimposed on each other to determine precision. Linear deviation at the 3 reference points and the angular deviation of occlusal planes were measured using a Python script. The trueness and precision of the 2 groups were compared by using a linear mixed model to account for repeated measures (α=.05). ResultsNo significant linear trueness differences between the 2 groups were found (P>.05). However, the VFR_SP group showed significantly less angular deviation: 1.53 degrees for the virtual facebow and 2.03 degrees for the conventional facebow group (P=.046). Regarding precision, the VFR_SP group showed significantly less linear deviation: 1.59 mm for the virtual facebow group and 2.33 mm for the conventional facebow group (P<.001), as well as angular deviation: 1.03 degrees for the virtual facebow group and 2.17 degrees for the conventional facebow (P<.001). ConclusionsThe VFR_SP group showed better accuracy compared with the CFR group. Further research with a larger sample size is needed.

Study of the Technical and Operational Parameters of Injectors Using Biogas Fuel

Using biogas fuel in a modern internal combustion engine equipped with gas equipment of the fourth and fifth generations can create several difficulties. This is due to the low heat of combustion of untreated biogas, the presence of moisture, and the specifics of the injectors. The main problem of the studies we considered is that there are no data on the operating parameters of biogas fuel injectors. Studies on the parameters of the Matrix, Barracuda, Valtek, Hana, and Keihin injectors in relation to biogas fuel were carried out according to performance indicators, the linearity of operation, the resistance of the injectors, the ability to maintain factory parameters, and service life. According to the indicators of performance and linearity of work, Valtek injectors have the highest deviation in productivity and linearity of work, with an average of 38.8%, and the lowest deviation of Barracuda injectors is 7.5%. Keihin (15.3%) and Hana injectors (19.1%) also showed good performance indicators, and therefore can be used effectively for biogas fuel systems. As a result of research on the response time of the injectors, it was established that the best indicators were found for Hana (1.75 ms) and Keihin (1.99 ms) injectors. Valtek injectors showed good response rates (2.07 ms), as did Barracuda injectors (2.19 ms), but the highest response time was found in Matrix injectors, with 2.44 ms. Keihin injectors had the lowest average resistance value of 1.25 ohms, and Valtek injectors had the highest resistance value of 3 ohms. According to the research results, Keihin, Matrix, and Barracuda injectors provide the best ability to maintain factory performance when using biogas fuel at 2 to 5%, and Valtek had the worst performance up to 20%. Keihin, Barracuda, and Hana experimental injectors had the highest service life, which is from 200 to 250 thousand km of car mileage. The lowest indicators were found for Valtek and Matrix injectors, the service life of which varies from 70 to 100 thousand km of mileage.