Vertical Shrinkage Research Articles

Study on the dry shrinkage characteristics and size effect of swell-shrink characteristic soil.

Swell-shrink characteristic soils exhibit a high susceptibility to cracking during the drying process, which poses a significant risk of various geological disasters. Among these, the occurrence of drying shrinkage acts as a prerequisite for the cracking phenomenon. Therefore, it is of utmost importance to comprehend the specific characteristics associated with the drying shrinkage mechanism. To investigate the drying shrinkage behavior of swell-shrink characteristic soils, a series of drying shrinkage experiments were conducted on long strip samples of red clay and expansive soil. Utilizing three-dimensional digital image correlation (DIC) technology, the surface displacement, strain, and anisotropic shrinkage rates of the soil samples during the drying process were obtained, and the size effect on the drying shrinkage of swell-shrink characteristic soil were analyzed. The research findings are as follows: The displacement development of the soil samples in the X and Y directions can be divided into two stages: a linear growth stage and a stable displacement stage. In the Z direction, the soil surface deformation can be divided into three stages: soil surface arching, vertical shrinkage, and shrinkage stabilization. The drying shrinkage of swell-shrink characteristic soil exhibits anisotropy, with the vertical shrinkage rate being the largest, followed by the longitudinal and then the transverse directions. Additionally, the soil sample shrinkage exhibits a size effect, whereby the shrinkage rates in all directions increase with increasing sample width and thickness. During the drying shrinkage process, the stress state on the soil surface evolves from initial tensile strain to subsequent compressive strain. The strain at different positions and times within the soil sample is not uniform, resulting in the non-uniformity and anisotropy of the sample shrinkage. This study provides important insights into the cracking mechanism of swell-shrink characteristic soils and serves as a valuable reference for related laboratory experiments, which will contribute to better prediction and control the geological hazards caused by the drying shrinkage of swell-shrink characteristic soils.

Controlled shrinkage of cellulose nanofibril films to enhance mechanical and barrier properties

Standalone cellulose nanofibril (CNF) films have a natural tendency to shrink upon drying from wet conditions due to capillary drying stresses. This shrinkage happens in both the radial direction, and the vertical direction. In this study, we prepared two types of CNF films- one in a restrained condition that did not allow shrinkage in the radial direction but enabled it in the vertical direction and another with 11 % radial shrinkage but limited vertical shrinkage. The radial shrinkage led to a more porous structure than the vertical shrinkage, which brought about poorer oxygen/moisture barrier performance. However, the density and oxygen permeability of the films converged to a similar value upon a simple thermocompression process. Radial shrinkage resulted in 140 % and 90 % higher strain at break and toughness in films with a significant sacrifice in strength and modulus. Scanning electron microscopy revealed that radial shrinkage formed wavy layers in the core structure leaving more free space, whereas vertical shrinkage formed flatter layers. Radial shrinkage is likely to produce a thicker individual layer in the core structure of CNF films than vertical shrinkage. The insight from this study will help tune the mechanical and barrier performance of CNF films and their composites.

Half- and full-grafting alveolar ridge preservation with different sealing materials: A three-arm randomized clinical trial.

The objective of this study is to investigate the effect of different alveolar ridge preservation (ARP) approaches on bone resorption and their potential for facilitating implant placement. Patients who underwent one or two tooth extractions with a desire for restoration were included in the study. The participants were randomly assigned to one of three groups for ARP. The groups were as follows: (1) Half grafting of bovine bone mineral (DBBM-C) covered with non-resorbable dense polytetrafluoroethylene (dPTFE) membrane (Test 1 group); (2) Half grafting of bovine bone mineral (DBBM-C) covered with collagen membrane (Test 2 group); and (3) Full grafting with collagen membrane (DBBM-C + Collagen membrane) as the Control group. After 6-month healing period, the evaluation encompassed clinical, radiographic, implant-related outcomes, and the factors contributing to hard and soft tissue alterations. Enrollment in this study comprised 56 patients. At the 6-month follow-up, radiographic analysis in computed beam computed tomography images was conducted for 18, 19, and 19 patients with 18, 20, and 20 tooth sites in Test 1, Test 2, and Control groups, respectively. Additionally, a total of 15, 17, and 17 patients with 15, 18, and 17 implants were evaluated. Based on radiographic analysis, all groups showed limited ridge resorption at 1 mm from crest horizontally (Test 1: 1.29 ± 1.37; Test 2: 1.07 ± 1.07; Control: 1.54 ± 1.33 mm, p = 0.328), while the Control group showed greater radiographic bone height gain in mid-crestal part vertically (Test 1: 0.11 ± 1.02; Test 2: 0.29 ± 0.83; Control: -0.46 ± 0.95 mm, p = 0.032). There were no significant intergroup differences in terms of keratinized mucosal width, bone density, insertion torque, and the need of additional bone graft. However, the use of a dPTFE membrane resulted in a significantly higher vertical mucosal thickness (Test 1: 2.67 ± 0.90; Test 2: 3.89 ± 1.08; Control: 2.41 ± 0.51 mm, p < 0.001). The study showed comparable dimensional preservation with limited vertical shrinkage, while thin buccal bone plate, non-molar sites, and large discrepancy between buccal and palatal/lingual height may contribute to greater shrinkage. Thicker mucosa with dPTFE membrane required further investigation for interpretation. NCT06049823. This clinical trial was not registered prior to participant recruitment and randomization.

Reactivation of an old landslide in north–central Iran following reservoir impoundment: Results from multisensor satellite time-series analysis

Water impoundment combined with more frequent precipitation extremes due to climate change increases landslide hazards on the slopes surrounding dam reservoirs. In situ monitoring systems in these potential landslide-prone areas are often unavailable, making landslide failures challenging to forecast. This paper describes a multisensor and multivariate remote sensing approach using data from Envisat, Sentinel-1, Landsat and PlanetScope satellites to reconstruct the spatiotemporal evolution of the mechanism and causes of the March 2019 landslide failure backside of the dam reservoir in Hoseynabad-e Kalpush village, north–central Iran. Statistical analysis and time series clustering are performed to derive the main landslide kinematic features from multitemporal interferometric synthetic aperture radar (MT-InSAR) analysis. We also exploit GIS and wavelet analysis to correlate potential external driving factors with landslide kinematics. Envisat and Sentinel-1 MT-InSAR analyses revealed that a previously stable old landslide was reactivated following reservoir impoundment in early 2013. As the reservoir water level rose during the following years up to 34 m in 2019, the landslide displacement rate gradually increased from 3.5 cm/yr to 8.4 cm/yr, and the destabilization gradually propagated upslope. At this stage, seasonal precipitation effects were detected only in the vertical component, indicating swelling and shrinkage movements of the shallower soil layer. The reactivated landslide accelerated and catastrophically failed following the exceptional precipitation in early 2019, producing a horizontal shift of >40 m, detected with optical image digital correlation. In the aftermath, the landslide continued to move with a decreasing trend until final stabilization in October 2021. Our study demonstrates how combined observations derived from multisensor satellite remote sensing data can be used to assess landslide precursors and kinematics, as well as the influence of climatic and anthropogenic factors on the instability of slopes surrounding water reservoirs. This is especially relevant in data-scarce areas.

Coupled thermo-hydro-mechanical model for simulating thermal history-induced voids in buffer material

The thermo-hydro-mechanical processes in a deep geological repository (DGR) influence the bentonite buffer’s long-term performance. The buffer’s temperature evolution over a repository’s service life imposes a thermal history in the DGR. The developed thermal history cause shrinkage of the buffer and generates the technological voids (i.e., annular gaps) in a DGR. The void formed compromises the intimate contact between the dissimilar materials within the DGR and thus impedes the containment ability of the buffer in the long run. Therefore, to investigate the complex coupled processes involved, the present study developed a coupled thermo-hydro-mechanical (THM) model to evaluate thermal history’s influence on buffer’s hydro-mechanical performance. The developed THM model was validated using data from an infiltration test conducted under isothermal conditions. Furthermore, the THM simulations on thermal history indicated radial and vertical shrinkage within bentonite. The formed voids were sealed due to rehydration occurring through the bottom boundary. The hydro-mechanical parameters, such as swell deformation in radial and vertical directions, porosity, permeability, water intake, and swell pressure, were assessed during the hydration process. A sudden increase in the swell pressure was observed when the void gets sealed completely due to rehydration. The rate and magnitude of swell pressure generated were proportional to the peak temperature imposed at the non-yielding boundaries and the consequent void size formed. The increased swell pressures could have impaired the structural integrity of the waste contained canister at a DGR scale. Given this, the implications were comprehended based on the outcome of numerical investigations for the plausible adverse effects inside a DGR due to thermal history.

Quantitative analysis of desiccation crack evolution based on digital image correlation

Red clay is prone to cracking in desiccating environments, with criss-cross cracks compromising soil structures and inducing slope instability. Under natural hygrothermal conditions, a desiccation test of red clay slurry was performed with a self-made device and digital image correlation (DIC) technology to study the crack evolution and quantitatively analyse the relationships between moisture content, displacement, strain and cracks. The results showed that cracks were usually initiated by subdividing and intersecting with other cracks at right angles. The main cracks were initiated first and had the longest duration; the stabilised main cracks were longer and wider than secondary cracks. DIC technology was used to monitor crack evolution dynamically. Based on the areas of strain concentration, the locations of early-initiated cracks and propagation trends could be preliminarily predicted. The failure strain in cracking was related to the moisture content, while crack evolution was related to the Atterberg limits of the red clay. The soil shrinkage exhibited anisotropic behaviour, with greater vertical shrinkage at the soil clod centre compared with the edges. In contrast, the horizontal displacement and maximum principal strain at the soil clod centre were smaller than those at the edges. These findings contribute to providing guidance for formulating engineering geological hazard control measures.

3D Facial Changes Between Maximal Intercuspal Position and Physiologic Rest Position.

To evaluate the soft tissue changes of the face between two positions of occlusion: maximal intercuspal position (MIP) and physiologic rest position (RP). In this study, facial surface scans of 83 volunteers in two mandibular positions (MIP and RP) were obtained using a 3D optical scanner. On each 3D image, 21 cephalometric soft tissue landmarks were identified and then compared using t test for various facial parameters (widths, heights, depths, angles, and ratio). Additionally, a regional analysis of the facial surface differences in each patient between the two mandibular positions was performed using a whole scan shell best-fit method and the regional forehead best-fit method. In MIP, facial heights with the nasion-gnathion distance shortened by approximately 1.2 mm (due to the vertical shrinkage of both lips together by 0.8 mm), and the mouth width was significantly widened, while other facial widths displayed no change. The labiomental angle and the upper vermilion arch were altered correspondingly, and regional analysis confirmed the findings with evident changes in the mandibular and subnasal areas with deviations amplified toward the facial midline. By applying 3D facial-scanning technology, this study displayed changes of facial appearance in different mandibular positions (MIP and RP), highlighting the need to instruct and monitor the patient's mandibular position more consistently to achieve accurate and repeatable data in a 3D facial analysis.

Environmental and human facets of the waterweed proliferation in a Vast Tropical Ramsar Wetland-Vembanad Lake System.

The Vembanad Lake and its associated low-lying areas and network of canals (hereafter VBL) form the major part of India's second-largest Ramsar wetland (1512 km2) located in Kerala State alongIndia's southwest coast. The extensive VBL has a large fishery, inland waterways, and popular tourist attractions that support the livelihoods of thousands of people. Over the last several decades, the proliferation of water weeds in the VBL has alarmingly increased, causing many adverse ecological and socioeconomic effects. This study based on a review and synthesis of long-term data introduced the environmental and human dimensions of water weed proliferation in the VBL. Eichhornia (= Pontederia) crassipes, Monochoria vaginalis, Salvinia molesta, Limnocharis flava, Pistia stratiotes, and Hydrilla verticillata are the most troublesome water weeds in the VBL, with the first three being the most widespread. They were mostly imported to India long ago before becoming a part of the VBL.These weeds harmed water quality, waterways, agriculture, fisheries, disease vector management, as well as the vertical and horizontal shrinkage of the VBL through increased siltation and faster ecological succession. The inherently fragile VBL was harmed by extensive and long-term reclamation, the construction of saltwater barrages, and many landfill roads that crisscross water bodies serving as coastal dams, creating water stagnation by blocking natural flushing/ventilation by periodic tides from the adjacent southeastern Arabian Sea. These ecological imbalances were exacerbated by excessive fertiliser use in agricultural areas, as well as the addition of nutrient-rich domestic and municipal sewage, which provided an adequate supply of nutrients and a favourable habitat for the expansion of water weeds. Furthermore, because of recurrent floods and a changing ecology in the VBL, the water weed proliferation has become a more significant problem, with the potential to disrupt their current distribution pattern and spread in the future.

Laboratory modeling of thermal and temporal cracking in swelling clays

Crack development in a changing environment is the controlling factor for the stability and strength of expansive soils. Expansive soils exhibit large volumetric changes with changes in their moisture conditions that may occasionally lead to reduced bearing capacity and foundation failures. This study purports to model crack initiation and its spatial progression in relation to the moisture content and drying period, respectively. Volumetric soil shrinkage is determined using high-definition digital camera imaging and Vernier scale methods, while the soil settlement under vertical shrinkage deformation could be captured through a tensile stress model for soils. It was revealed that a small change in suction could trigger crack initiation, which would propagate further under different environmental conditions. Furthermore, it was observed that the crack volume increased rapidly at specific moisture content and could penetrate as deep as 1 m after nearly 1.5 months that is fully consistent with the current model predictions. A comparison between the performance of the model proposed in this study and that of two existing models shows that the former predicts the vertical shrinkage strain values in closer agreement with those observed experimentally and is less conservative than those predicted by both models. Nevertheless, the findings from this study could be used to quantify the detrimental behavior of expansive soil present in pavement subgrades and shallow foundations for lightweight structures.

Stability and optimization of small-spacing two-well (SSTW) gas storage salt caverns in bedded salt formation

Many rock salts in China have a bedded structure, consisting of several thin interlayers and salt layers. To eliminate the limitations of the conventional single-well gas storage caverns, the small-spacing two-well (SSTW) salt caverns can be utilized. In this paper, under the geological conditions of Pingdingshan salt formation in Henan province, China, a geomechanical model was established to evaluate the stability of the SSTW salt cavern. The deformation, volume shrinkage rate, and safety factor were used for the cavern stability evaluation. The optimal cavern roof shape, two-well spacing, and cavern roof height were determined by analyzing the salt cavern stability under constant pressure conditions. Based on the optimal salt cavern morphology, the stability of the salt cavern and interlayers under various injection and withdrawal cycle frequencies are investigated. The results show that the rampant arch-shaped SSTW salt cavern has good feasibility in Pingdingshan salt formation. The cavern roof vertical displacement and volume shrinkage decrease with the increase of cavern roof height, and it is suggested that the ratio of cavern roof height to cavern height is at least 0.26. With the continuous increase of the two-well spacing, the cavern volume shrinkage also increases. It is recommended that the ratio of the two-well spacing to the single cavern radius should be no more than 0.625. The increase in cycle frequency reduces the duration of salt caverns under low-pressure conditions, thus improving the mechanical stability of the cavern and interlayers. This paper provides design and operation parameters for the SSTW salt cavern in Pingdingshan salt formation and can also be a reference for the construction of other SSTW salt caverns.

Spatial Variability during Shrinkage Testing of Expansive Clays

Civil infrastructure constructed with, buried in, or underlain by expansive clays is affected by high volumetric changes, especially because large-scale facilities are spatially distributed. This research focused on determining spatial variability during the shrinkage testing of expansive clays. An initially saturated sample (600 mm in diameter) of a high-plasticity clay was exposed to desiccation and thoroughly monitored over five months. The results indicated an expansive clay (30% smectite and 14% illite) in alkaline-pore water (695 mg/L Na+ and 1150 mg/L SO42−) for developing a dispersive soil fabric. The vertical shrinkage in the intact-soil portion was unchanged (remaining at 114 × 106 mm3) in the first 10 days, sharply decreased the initial volume by 30% (up to 280 mm or 80 × 106 mm3) in 68 days, and slowly decreased the initial volume by 40% (up to 240 mm or 68 × 106 mm3) in 145 days. Furthermore, the soil temperature was found to be 10% lower than the air temperature, whereas the relative humidity within the cell was found to be 30% higher than that outside the cell. The soil showed an initial prominent central ridge with a few cracks that gradually evolved into a distinct crack pattern with equal-sized and irregular soil chunks. The average soil surface showed no volume reduction up to 18 days and a subsequent linear reduction, reaching 25% of the initial soil volume by the end of the test.

Physical properties of wood-based materials for liquid deposition modeling

Purpose The purpose of this study is to quantify the vertical shrinkage rates and the mechanical strength of three-dimensional (3D) printed parts for a variety of wood-based materials for liquid deposition modeling. Design/methodology/approach The overall hypothesis was that a well-chosen combination of binders, fibers and fillers could reduce shrinkage in the Z dimension and increase compressive and flexural strength (DIN 52185, 52186). To test this assumption, eight sub-hypotheses were formulated. Mixtures of the ingredients were chosen in different ratios to measure the performance of prints. For time efficiency, an iterative heuristic approach was used – not testing all variations of all variables in even increments, but cutting off lines of testing when mixtures were clearly performing poorly. Findings The results showed that some mixtures had high dimensional accuracy and strength, while others had neither, and others had one but not the other. Shrinkage of 3D printed objects was mainly caused by water release during drying. An increase of the wood as well as the cement, sand, salt and gypsum content led to reduced vertical shrinkage, which varied between 0 and 23%. Compressive and flexural strength showed mixed trends. An increase in wood and salt content worsened both strength properties. The addition of fibers improved flexural, and the addition of cement improved compression strength. The highest strength values of 14 MPa for compressive and 8 MPa for flexural strength were obtained in the test series with gypsum. Originality/value This paper is an important milestone in the development of environmentally friendly materials for additive manufacturing. The potential of many ingredients to improve physical properties could be demonstrated.

The Effect of Initial Water Content and Density on the Swelling-Shrinkage and Cracking Characteristics of Compacted Clay

The swelling-shrinkage and cracking characteristics of compacted clay under the coupling effect of initial conditions are rarely studied. The dry-wet cycle test of compacted clay with varying initial water contents and densities was performed in this study; the size and cracking conditions were investigated. The results showed that when the initial moisture content was 21% and the dry density was 1.65 g/cm3, the longitudinal expansion amount of the compacted clay was relatively small. However, it was rather large when the initial water content was 17% and 19%. Under the same dry density, the final vertical shrinkage ratio of the sample with a water content of 21% was the smallest, while that of the samples with a water content of 23% and 25% was rather big. Under the same water content, the final vertical shrinkage ratio decreased with the increase in dry density. After three wetting-drying cycles, compacted clay with a dry density of 1.65 g/cm3 and an optimal initial water content of 21% produced the fewest cracks and had the lowest cracking factor (CF) (only 7.58%). The compacted clay specimens with the dry densities of 1.55 g/cm3 and 1.60 g/cm3 had rather significant cracking at the same initial moisture content of 21%. The mercury intrusion porosimetry (MIP) test demonstrated that in the first two dry and wet cycles, the distribution of large pores decreased and that of tiny pores increased. After the third cycle, the distribution of small and medium pores decreased slightly. The results of this study will provide theoretical guidance for selecting cover soils in landfills.

Experimental characterization of desiccation cracking mechanisms in clayey soils

Desiccation cracking in clayey soils is a complex phenomenon investigated by researchers over many decades. Understanding and mitigating this issue will have a significant influence on the performance of raw earth construction materials and geotechnical engineering. In the current study, the digital image correlation technique was used to provide a thorough insight about the shrinkage anisotropy and the cracking mechanisms during drying. A series of free shrinkage tests were performed on an initially saturated slurries in order to assess the effects of the intrinsic characteristics of the material, the surface tension, the sample thickness and the geometric boundary conditions on the crack initiation and propagation in clays. The results show that increasing sample thickness prevents cracks formation in a non-swelling clay and delays it in a swelling clay. A vertical uplift was observed in the swelling clay due to a concave bending of the material during the desiccation shrinkage. An important anisotropy in the vertical shrinkage was observed compared to the horizontal shrinkage. The geometric boundary conditions indirectly influence the internal drying stress that becomes anisotropic. The intrinsic characteristics have a greater effect on the shrinkage behavior of the material than the hygrothermal and geometric boundary conditions.

Effect of initial water content and dry density on the self-healing of desiccation cracks in compacted hipparion red clay

The self-healing of desiccation cracks in compacted clayey soils is important for mechanism revelation of cracking behavior in compacted soils. Although the crack self-healing behavior has been found, the influence of soil physical indices on it is still unclear, especially initial water content and dry density of specimen. This study aims to identify and evaluate the effect of initial water content and dry density on self-healing of desiccation cracks. Firstly, a series of desiccation tests were conducted on compacted Hipparion red clay specimens under different initial conditions. Secondly, the two-dimensional morphology of desiccation cracks and strain field changes on specimen surface were examined using the pore and crack analysis system and digital image correlation techniques. The result shows that the desiccation cracks on specimen surface exhibits self-healing behavior during drying. Based on the observed crack self-healing behavior, the desiccation cracking of compacted Hipparion red clay undergoes four stages including initiation, development, self-healing, and stabilization. During the self-healing stage, the critical water content for occurrence of crack self-healing and the crack self-healing amount referring to the crack ratio reduction from peak value to the stable value, are dry density dependent and water content dependent variables. In particular, the higher the initial water content and the lower the dry density of compacted specimen are, the larger the crack self-healing amount is. This crack self-healing difference in specimen with different initial conditions is caused by the vertical anisotropic shrinkage of substrate soil below non-propagating cracks due to its pore structure difference. This study provides a new perspective on the mechanism of desiccation crack in clayey soils affected by initial conditions.

Macrocycle Network-Aided Nanopatterning of Inorganic Resists on Silicon

Inorganic resists have emerged as promising candidates in semiconductor industries to realize sub-10 nm node technology. However, controlling vertical shrinkage of resist films during the pattern development process, particularly for ultralow thin film applications, is among the highly pressing limitations of inorganic resists along with pattern roughness and poor resist shelf-life characteristics. Tin-based clusters and small molecules have been recently introduced as resist materials. They possess a high absorption coefficient and fast solubility transitions under irradiation exposure. As we investigated, n-butylstannoic acid (BTA) showed ∼38% vertical shrinkage when its film was exposed with deep ultraviolet photons (DUV, ∼254 nm) and could pattern features of ∼120 nm. We hypothesized and experimentally validated an approach that provided control on shrinkage issues, along with improving its patterning potential to sub-15 nm regime. In our approach, BTA was embedded into a polyhydroxy organic host matrix composed of noria (water-wheel-like macrocycle) derivatives. The rigid molecular cage structure and photo-inert nature of noria (N-Me) were utilized as the host matrix that apprehended the inorganic resist material within its intermolecular space. Ultrathin films (∼20 nm) were coated on silicon, and various nanofeatures including 10 nm lines, meshlike grids with 10 nm width, complex patterns, and so forth were patterned using electron beam and helium ion beam lithography. Most importantly, we were able to drastically reduce the vertical shrinkage to ∼13% with respect to initial thickness, which substantiates the potential of our hypothesis. We also noticed good shelf-life (6 months), good etch resistance, and low line edge roughness (LER)/line width roughness (LWR) for the developed resist composition.

Satellite Observed Sensitivity of Tropical Clouds and Moisture to Sea Surface Temperature on Various Time and Space Scales: 2. Focus on Marine Low Level Clouds

AbstractThis study examines how satellite observed relative humidity (RH) profiles, cloud covers, and cloud altitudes vary with sea surface temperature (SST) in low cloud regions on different temporal and spatial scales over the tropical oceans (30°N–30°S). We split low clouds into optically opaque and optically thin clouds and characterize for the first time their altitude variations with SST using space lidar observations. On the process scale, the median instantaneous observations at high spatial resolution show simultaneously decreasing low opaque cloud top altitude, decreasing low opaque cloud cover, increasing middle‐tropospheric RH, and decreasing lower‐tropospheric RH with SST. Collectively, these observational results suggest decreasing opaque marine boundary layer cloud cover and enhanced mixing between the middle and lower troposphere with SST on the process scale, consistent with previous Large‐Eddy Simulation studies. The covariations between opaque cloud cover and RH with SST are quantified on all time and space scales (from the process scale to the annual tropical mean scale). Meanwhile, on the process scale, low optically thin clouds, coexisting with opaque clouds, rise with SST (consistent with the literature mechanism), while the low optically thin cloud cover is insensitive to SST (not consistent with the literature mechanism). These results are then compared to a general circulation model, which captures the observed sign of change of opaque cloud cover and middle‐tropospheric RH with SST but fails to reproduce the observed vertical shrinkage of low opaque clouds with SST and the variations of low thin clouds with SST.

Dimensional changes of keratinized mucosa after accordion versus conventional free gingival graft around dental implants: A randomized two-arm parallel clinical trial.

Free gingival graft (FGG) is the most effective way to increase the apico-coronal width of the keratinized mucosa. In case of limited donor tissue, the accordion technique can be used. This study compared FGG for dimensional and clinical changes using accordion and conventional methods. Ninety-four implants with keratinized tissue deficiency (<2mm) were randomly assigned to treatment with accordion (49 implants) and conventional (45 implants) FGG. Endpoints including apico-coronal keratinized tissue width, vertical shrinkage, vestibular depth, probing depth, bleeding on probing, and plaque index were measured. The graft harvesting and recipient bed preparation method were similar in the two groups, and the only difference was the graft length. FGG was harvested with a length 40% shorter than the mesiodistal length of the recipient area in the accordion method and as much as the recipient area in the conventional method. vertical graft shrinkage 1, 3, and 6months following conventional graft placement was 12.04±14.99, 17.12±20.40, and 23.29±24.63 percent, respectively. In the accordion graft group, the shrinkage was significantly greater with 30.10±16.12, 36.99±15.51, and 43.75±18.78 percent at 1, 3, and 6months, respectively (p-value<.001). Other factors did not show a clinically significant difference between the two groups. Comparison of vertical shrinkage changes shows that the shrinkage rate in the accordion group is significantly higher than the conventional group. IRCT20190721044296N1 (Evaluation of dimensional changes of peri-implant attached mucosa following the treatment of free gingival graft by conventional and accordion methods; randomized clinical trial two-arm parallel).

Experimental Investigation on the Impact of Drying–Wetting Cycles on the Shrink–Swell Behavior of Clay Loam in Farmland

Soil shrink–swell behavior is a common phenomenon in farmland, which usually alters the process of water and solute migration in soil. In this paper, we report on a phenomenological investigation aimed at exploring the impact of drying–wetting cycles on the shrink–swell behavior of soil in farmland. Samples were prepared using clay loam collected from farmland and subjected to four drying–wetting cycles. The vertical deformation of soil was measured by a vernier caliper, and the horizontal deformation was captured by a digital camera and then calculated via an image processing technique. The results showed that the height, equivalent diameter, volume and shrinkage-swelling potential of the soil decreased with the repeated cycles. Irreversible deformation (shrinkage accumulation) was observed during cycles, suggesting that soil cracks might form owing to previous drying rather than current drying. The vertical shrinkage process consisted of two stages: a declining stage and a residual stage, while the horizontal shrinkage process had one more stage, a constant stage at the initial time of drying. The VG-Peng model fit the soil shrinkage curves very well, and all shrinkage curves had four complete shrinkage zones. Drying–wetting cycles had a substantial impact on the soil shrinkage curves, causing significant changes in the distribution of void ratio and moisture ratio in the four zones. However, the impact weakened as the number of cycles increased because the soil structure became more stable. Vertical shrinkage dominated soil deformation at the early stage of drying owing to the effect of gravity, while nearly isotropic shrinkage occurred after entering residual shrinkage. Our study revealed the irreversible deformation and deformation anisotropy of clay loam collected from farmland during drying–wetting cycles and analyzed the shrink–swell behavior during cycles from both macroscopic and microscopic points of view. The results are expected to improve the understanding of the shrink–swell behavior of clay loam and the development of soil desiccation cracks, which will be benefit research on water and solute migration in farmland.

Dimensional and histomorphometric evaluation of biomaterials used for alveolar ridge preservation: a systematic review and network meta-analysis.

This systematic review and network meta-analysis aimed to answer to the following questions: (a) In patients undergoing alveolar ridge preservation after tooth extraction, which grafting material best attenuates horizontal and vertical ridge resorption, as compared to spontaneous healing?, and (b) which material(s) promotes bone formation in the extraction socket? The MEDLINE, SCOPUS, CENTRAL, and EMBASE databases were screened in duplicate for RCTs up to March 2021. Two independent authors extracted the data and assessed the risk of bias of the included studies. Primary outcomes were ridge horizontal and vertical dimension changes and new bone formation into the socket. Both pairwise and network meta-analysis (NMA) were undertaken to obtain estimates for primary outcomes and compare different grafting materials. Eighty-eight RCTs were included, with a total of 2805 patients and 3073 sockets. Overall, a total of 1740 sockets underwent alveolar ridge preservation with different materials (1432 were covered by a membrane). Pairwise meta-analysis showed that, as compared to spontaneous healing, all materials statistically significantly reduced horizontal and vertical shrinkage. According to the multidimensional scale ranking of the NMA, xenografts (XG) and allografts (AG), alone or combined with bioactive agents (Bio + AG), were the most predictable materials for horizontal and vertical ridge dimension preservation, while platelet concentrates performed best in the percentage of new bone formation. Alveolar ridge preservation is effective in reducing both horizontal and vertical shrinkage, as compared to untreated sockets. NMA confirmed the consistency of XG for ridge dimension preservation, but several other materials and combinations like AG, Bio + AG, and AG + alloplasts, produced even better results than XG in clinical comparisons. Further evidence is needed to confirm the value of such alternatives to XG for alveolar ridge preservation. Bio + AG performed better than the other materials in preserving ridge dimension and platelet concentrates in new bone formation. However, alloplasts, xenografts, and AG + AP performed consistently good in majority of the clinical comparisons. XG and Bio + AG demonstrated significantly better performance in minimizing post-extraction horizontal and vertical ridge dimension changes as compared with other grafting materials or with spontaneous healing, even if they presented the worst histological outcomes. Allografts and other materials or combinations (AG + AP) presented similar performances while spontaneous healing ranked last.