Experimental observation of curved light-cones in a quantum field simulator.

We investigate signal propagation in a quantum field simulator of the Klein-Gordon model realized by two strongly coupled parallel one-dimensional quasi-condensates. By measuring local phononic fields after a quench, we observe the propagation of correlations along sharp light-cone fronts. If the local atomic density is inhomogeneous, these propagation fronts are curved. For sharp edges, the propagation fronts are reflected at the system's boundaries. By extracting the space-dependent variation of the front velocity from the data, we find agreement with theoretical predictions based on curved geodesics of an inhomogeneous metric. This work extends the range of quantum simulations of nonequilibrium field dynamics in general space-time metrics.

Spatial confinement: A spur for axonal growth.

The concept of spatial confinement is the basis of cell positioning and guidance in in vitro studies. In vivo, it reflects many situations faced during embryonic development. In vitro, spatial confinement of neurons is achieved using different technological approaches: adhesive patterning, topographical structuring, microfluidics and the use of hydrogels. The notion of chemical or physical frontiers is particularly central to the behaviors of growth cones and neuronal processes under confinement. They encompass phenomena of cell spreading, boundary crossing, and path finding on surfaces with different adhesive properties. However, the most universal phenomenon related to confinement, regardless of how it is implemented, is the acceleration of neuronal growth. Overall, a bi-directional causal link emerges between the shape of the growth cone and neuronal elongation dynamics, both in vivo and in vitro. The sensing of adhesion discontinuities by filopodia and the subsequent spatial redistribution and size adaptation of these actin-rich filaments seem critical for the growth rate in conditions in which adhesive contacts and actin-associated clutching forces dominate. On the other hand, the involvement of microtubules, specifically demonstrated in 3D hydrogel environments and leading to ameboid-like locomotion, could be relevant in a wider range of growth situations. This review brings together a literature collected in distinct scientific fields such as development, mechanobiology and bioengineering that highlight the consequences of confinement and raise new questions at different cellular scales. Its ambition is to stimulate new research that could lead to a better understanding of what gives neurons their ability to establish and regulate their exceptional size.

Actin cytoskeletal dynamics do not impose an energy drain on growth cone bioenergetics.

The regulation of the intracellular level of ATP is a fundamental aspect of bioenergetics. Actin cytoskeletal dynamics have been reported to be an energetic drain in developing neurons and platelets. We addressed the role of actin dynamics in primary embryonic chicken neurons using luciferase assays, and by measurement of the ATP/ADP ratio using the ratiometric reporter PercevalHR and the ATP level using the ratiometric reporter mRuby-iATPSnFR. None of the methods revealed an effect of suppressing actin dynamics on the decline in the neuronal ATP level or the ATP/ADP ratio following shutdown of ATP production. Similarly, we find that treatments that elevate or suppress actin dynamics do not alter the ATP/ADP ratio in growth cones, the subcellular domain with the highest actin dynamics in developing neurons. Collectively, the data indicate that actin cytoskeletal dynamics are not a significant energy drain in developing neurons and that the ATP/ADP ratio is maintained when energy utilization varies. Discrepancies between prior work and the current data are discussed with emphasis on methodology and interpretation of the data.

The photobiology of the human circadian clock.

SignificanceThe function of our biological clock is dependent on environmental light. Rodent studies have shown that there are multiple colors that affect the clock, but indirect measures in humans suggest blue light is key. We performed functional MRI studies in human subjects with unprecedented spatial resolution to investigate color sensitivity of our clock. Here, we show that narrowband blue, green, and orange light were all effective in changing neuronal activity of the clock. While the clock of nocturnal rodents is excited by light, the human clock responds with a decrease in neuronal activity as indicated by a negative BOLD response. The sensitivity of the clock to multiple colors should be integrated in light therapy aimed to strengthen our 24-h rhythms.

Septins mediate a microtubule-actin crosstalk that enables actin growth on microtubules.

Cellular morphogenesis and processes such as cell division and migration require the coordination of the microtubule and actin cytoskeletons. Microtubule-actin crosstalk is poorly understood and largely regarded as the capture and regulation of microtubules by actin. Septins are filamentous guanosine-5'-triphosphate (GTP) binding proteins, which comprise the fourth component of the cytoskeleton along microtubules, actin, and intermediate filaments. Here, we report that septins mediate microtubule-actin crosstalk by coupling actin polymerization to microtubule lattices. Superresolution and platinum replica electron microscopy (PREM) show that septins localize to overlapping microtubules and actin filaments in the growth cones of neurons and non-neuronal cells. We demonstrate that recombinant septin complexes directly crosslink microtubules and actin filaments into hybrid bundles. In vitro reconstitution assays reveal that microtubule-bound septins capture and align stable actin filaments with microtubules. Strikingly, septins enable the capture and polymerization of growing actin filaments on microtubule lattices. In neuronal growth cones, septins are required for the maintenance of the peripheral actin network that fans out from microtubules. These findings show that septins directly mediate microtubule interactions with actin filaments, and reveal a mechanism of microtubule-templated actin growth with broader significance for the self-organization of the cytoskeleton and cellular morphogenesis.

The evolutionary history and spectral tuning of vertebrate visual opsins.

Many animals depend on the sense of vision for survival. In eumetazoans, vision requires specialized, light-sensitive cells called photoreceptors. Light reaches the photoreceptors and triggers the excitation of light-detecting proteins called opsins. Here, we describe the story of visual opsin evolution from the ancestral bilaterian to the extant vertebrate lineages. We explain the mechanisms determining color vision of extant vertebrates, focusing on opsin gene losses, duplications, and the expression regulation of vertebrate opsins. We describe the sequence variation both within and between species that has tweaked the sensitivities of opsin proteins towards different wavelengths of light. We provide an extensive resource of wavelength sensitivities and mutations that have diverged light sensitivity in many vertebrate species and predict how these mutations were accumulated in each lineage based on parsimony. We suggest possible natural and sexual selection mechanisms underlying these spectral differences. Understanding how molecular changes allow for functional adaptation of animals to different environments is a major goal in the field, and therefore identifying mutations affecting vision and their relationship to photic selection pressures is imperative. The goal of this review is to provide a comprehensive overview of our current understanding of opsin evolution in vertebrates.

Multicompartment imaging of the brain using a comprehensive MR imaging protocol.

In this study, we describe a comprehensive 3D magnetic resonance imaging (MRI) protocol designed to assess major tissue and fluid components in the brain. The protocol comprises four different sequences: 1) magnetization transfer prepared Cones (MT-Cones) for two-pool MT modeling to quantify macromolecular content; 2) short-TR adiabatic inversion-recovery prepared Cones (STAIR-Cones) for myelin water imaging; 3) proton-density weighted Cones (PDw-Cones) for total water imaging; and 4) highly T2 weighted Cones (T2w-Cones) for free water imaging. By integrating these techniques, we successfully mapped key brain components-namely macromolecules, myelin water, intra/extracellular water, and free water-in ten healthy volunteers and five patients with multiple sclerosis (MS) using a 3T clinical scanner. Brain macromolecular proton fraction (MMPF), myelin water proton fraction (MWPF), intra/extracellular water proton fraction (IEWPF), and free water proton fraction (FWPF) values were generated in white matter (WM), grey matter (GM), and MS lesions. Excellent repeatability of the protocol was demonstrated with high intra-class correlation coefficient (ICC) values. In MS patients, the MMPF and MWPF values of the lesions and normal-appearing WM (NAWM) were significantly lower than those in normal WM (NWM) in healthy volunteers. Moreover, we observed significantly higher FWPF values in MS lesions compared to those in NWM and NAWM regions. This study demonstrates the capability of our technique to volumetrically map major brain components. The technique may have particular value in providing a comprehensive assessment of neuroinflammatory and neurodegenerative diseases of the brain.

Melanopsin-mediated amplification of cone signals in the human visual cortex.

The ambient daylight variation is coded by melanopsin photoreceptors and their luxotonic activity increases towards midday when colour temperatures are cooler, and irradiances are higher. Although melanopsin and cone photoresponses can be mediated via separate pathways, the connectivity of melanopsin cells across all levels of the retina enables them to modify cone signals. The downstream effects of melanopsin-cone interactions on human vision are however, incompletely understood. Here, we determined how the change in daytime melanopsin activation affects the human cone pathway signals in the visual cortex. A 5-primary silent-substitution method was developed to evaluate the dependence of cone-mediated signals on melanopsin activation by spectrally tuning the lights and stabilizing the rhodopsin activation under a constant cone photometric luminance. The retinal (white noise electroretinogram) and cortical responses (visual evoked potential) were simultaneously recorded with the photoreceptor-directed lights in 10 observers. By increasing the melanopsin activation, a reverse response pattern was observed with cone signals being supressed in the retina by 27% (p = 0.03) and subsequently amplified by 16% (p = 0.01) as they reach the cortex. We infer that melanopsin activity can amplify cone signals at sites distal to retinal bipolar cells to cause a decrease in the psychophysical Weber fraction for cone vision.

Preparation of Activated Biocarbons from Cones and their Potential Application for Adsorption of Antibiotics (Tetracycline).

The pine cones (PC), spruce cones (SC) and fir cones (FC) were used for biocarbons preparation. Chemical activation with sodium hydroxide was applied to prepare activated biocarbons. All the materials under investigation were characterized by the N2 adsorption, scanning electron microscopy (SEM), elemental analysis (CHNS), infrared spectroscopy (ATR FT-IR), and the Boehm's titration method. Moreover, pHpzc (the point of zero charge) was determined. It was shown that cones are a good, cheap precursor from which biocarbons with a developed porous structure, characterized by good adsorption properties, can be obtained. All the obtained adsorbents are characterized mainly by a microporous structure. Moreover, they contain both acidic and basic surface functional groups (acidic ones prevail over basic ones). The tested activated biocarbons have large specific surface area values ranging from 578 to 1182 m2 g-1. The efficacy of selected materials in the adsorption of an essential contaminant of increasing concern, tetracycline (TC), was investigated. The experimental data were described using the Langmuir and Freundlich adsorption isotherm models. The maximum adsorption capacity of the tested biocarbons ranges from 200 to 392 mg g-1. Thermodynamic studies proved that adsorption is a spontaneous and endothermic process. In summary, economical and environmentally friendly adsorbents were obtained.

Ribosomal Protein Dynamics and Its Association with Actin Filaments and Local Translation in Axonal Growth Cones of Dorsal Root Ganglia Neurons.

Local translation in growth cones plays a critical role in responses to extracellular stimuli, such as axon guidance cues. We previously showed that brain-derived neurotrophic factor activates translation and enhances novel protein synthesis through the activation of mammalian target of rapamycin complex 1 signaling in growth cones of dorsal root ganglion neurons. In this study, we focused on 40S ribosomal protein S6 (RPS6), 60S ribosomal protein P0/1/2 (RPP0/1/2), and actin filaments to determine how localization of ribosomal proteins changes with overall protein synthesis induced by neurotrophins. Our quantitative analysis using immunocytochemistry and super-resolution microscopy indicated that RPS6, RPP0/1/2, and actin tend to colocalize in the absence of stimulation, and that these ribosomal proteins tend to dissociate from actin and associate with each other when local protein synthesis is enhanced. We propose that this is because stimulation causes ribosomal subunits to associate with each other to form actively translating ribosomes (polysomes). This study further clarifies the role of cytoskeletal components in local translation in growth cones.

Spatially-dependent model for rods and cones in the retina.

We develop a mathematical model for photoreceptors in the retina. We focus on rod and cone outer segment dynamics and interactions with a nutrient source associated with the retinal pigment epithelium cells. Rod and cone densities (number per unit area of retinal surface) are known to have significant spatial dependence in the retina with cones located primarily near the fovea and the rods located primarily away from the fovea. Our model accounts for this spatial dependence of the rod and cone photoreceptor density as well as for the possibility of nutrient diffusion. We present equilibrium and dynamic solutions, discuss their relation to existing models, and estimate model parameters through comparisons with available experimental measurements of both spatial and temporal photoreceptor characteristics. Our model compares well with existing data on spatially-dependent regrowth of photoreceptor outer segments in the macular region of Rhesus Monkeys. Our predictions are also consistent with existing data on the spatial dependence of photoreceptor outer segment length near the fovea in healthy human subjects. We focus primarily on the healthy eye but our model could be the basis for future efforts designed to explore various retinal pathologies, eye-related injuries, and treatments of these conditions.

Distinct contribution of cone photoreceptor subtypes to the mammalian biological clock.

Ambient light detection is important for the synchronization of the circadian clock to the external solar cycle. Light signals are sent to the suprachiasmatic nuclei (SCN), the site of the major circadian pacemaker. It has been assumed that cone photoreceptors contribute minimally to synchronization. Here, however, we find that cone photoreceptors are sufficient for mediating entrainment and transmitting photic information to the SCN, as evaluated in mice that have only cones as functional photoreceptors. Using in vivo electrophysiological recordings in the SCN of freely moving cone-only mice, we observed light responses in SCN neuronal activity in response to 60-s pulses of both ultraviolet (UV) (λmax 365 nm) and green (λmax 505 nm) light. Higher irradiances of UV light led to irradiance-dependent enhancements in SCN neuronal activity, whereas higher irradiances of green light led to a reduction in the sustained response with only the transient response remaining. Responses in SCN neuronal activity decayed with a half-max time of ∼9 min for UV light and less than a minute for green light, indicating differential input between short-wavelength-sensitive and mid-wavelength-sensitive cones for the SCN responsiveness. Furthermore, we show that UV light is more effective for photoentrainment than green light. Based on the lack of a full sustained response in cone-only mice, we confirmed that rapidly alternating light levels, rather than slowly alternating light, caused substantial phase shifts. Together, our data provide strong evidence that cone types contribute to photoentrainment and differentially affect the electrical activity levels of the SCN.

Are Flexible Metaphyseal Femoral Cones Stable and Effective? A Biomechanical Study on Hinged Total Knee Arthroplasty.

BACKGROUND: Cones currently available in the market are rigid, and unless they are custom-specific designed, are unable to correctly adapt to the shape of the patient's bone. Therefore, flexible metaphyseal cones have been recently introduced to reduce potential bone trauma during implantation. Even if a preliminary clinical study on their use has shown promising results, no biomechanical study evaluates and quantifies their mechanical efficacy and safety. METHODS: Two commercial versions of flexible cones were analyzed in this study using finite element analysis, based on a previously validated model. Each cone geometry was modeled both as flexible and as rigid, and implanted following surgical guidelines. Three activities were simulated in this study and compared among configurations: surgical impaction, walking, and chair rise. RESULTS: During impaction, results showed considerably reduced stress in the flexible cones in comparison with rigid ones; the stress resulted was also better distributed and more homogeneous all over the cortical bone, with lower bone peaks. Considering the 2 different activities, the analysis did not show any remarkable differences between flexible and rigid cones both in terms of bone stress and implant micromotion. CONCLUSIONS: The findings demonstrate that metaphyseal flexible cones allow macrodeformation during impaction due to their flexibility, and therefore, are safer in comparison with rigid cones. However, for the daily tasks investigated, results showed no major differences between rigid and flexible cones in terms of bone stress, implant stability, and micromotion. Therefore, their mechanical performances can be considered similar to the rigid cone.

Porous Tantalum Metaphyseal Cones for Severe Femoral and Tibial Bone Defects in Revision Total Knee Arthroplasty are Reliable for Fixation at Mean 5-Year Follow-Up.

BACKGROUND: Porous tantalum metaphyseal cones may facilitate reconstructions of severe bone defects during revision total knee arthroplasty (TKA), but there remains a paucity of data on their outcomes at mean 5 years of follow-up. This study reports the component survivorship, patient satisfaction, functional outcomes, radiographic osseointegration, and complications of revision TKA with porous tantalum metaphyseal cones at mid-term (mean 5-year) follow-up. METHODS: This study included 152 patients who had a mean age of 66 years (range, 33 to 86 years) undergoing revision TKA with porous tantalum metaphyseal cones. Indications for surgery included aseptic loosening (n = 87, 57.3%), second-stage reimplantation for infection (n = 42, 27.6%), osteolysis with well-fixed components (n = 20, 13.2%), and periprosthetic fracture (n = 3, 2.0%). Component survivorship, clinical outcomes, radiographic outcomes, and any complications were recorded. The mean follow-up time was 5.6 years (range, 2.2 to 13.7). RESULTS: Survivorship was 100% when the end point was revision of the metaphyseal cone (no cones were revised) and 83.8% (95% confidence interval: 77.9 to 90.2%) when the end point was reoperation for any reason at 5-year follow-up. Reoperations were performed for infection (n = 10), instability (n = 4), periprosthetic fracture (n = 2), and quadriceps rupture/dehiscence (n = 3). The mean patient satisfaction score was 78.8 ± 11.3 and the mean Forgotten Joint Score was 62.2 ± 16.7 at the final follow-up. The preoperative median University of California at Los Angeles score improved from 2 (interquartile range 2 to 3) to 6 points (interquartile range 5 to 6) (P < .001), and the preoperative Oxford knee score improved from 15.2 ± 3.8 to 39.4 ± 5.1 points (P < .001) at the final follow-up. All metaphyseal cones showed radiographic evidence of osteointegration without any subsidence or loosening. CONCLUSIONS: Porous tantalum metaphyseal cones enabled robust reconstructions of severe femoral and tibial bone defects during revision TKA. These reconstructions were associated with excellent survivorship, improvements in functional outcomes, and reproducible radiographic osseointegration at mean 5-year follow-up. The most common reasons for reoperation were infection and instability.

Outcomes of Metaphyseal Cones and Stem Fixation Following Rotating Hinge in Complex Primary and Revision Total Knee Arthroplasty.

BACKGROUND: Although hinged prostheses have been used successfully in complex revision total knee arthroplasty (TKA), concerns exist regarding early failure due to aseptic loosening and other mechanical complications. The use of metaphyseal cones and hybrid cement fixation have been studied in unlinked constrained primary or revision TKA, but their impact on the survivorship of hinged prostheses has yet to be investigated. METHODS: We identified a consecutive series of 164 hinged prostheses and collected data on demographics, indications, complications, and re-revisions in patients who had fully cemented versus hybrid stems, with and without metaphyseal cones. A multivariate analysis was performed to identify independent variables associated with re-revision as the primary end point. RESULTS: In total, 84 patients (51.2%) had fully cemented stems, and 80 patients (48.8%) had hybrid stems. Cones were used in 73 patients (44.5%). At a mean follow-up of 3.4 ± 2.2 years, 42 patients underwent re-revision (25.8%), most commonly for infection (12.2%), followed by loosening (6.7%) and periprosthetic fracture (3.7%). Patients who had fully cemented stems had lower re-revision rates than hybrid fixation constructs (19 versus 26%, P = .043). Using multivariable regression, a construct with hybrid fixation with cones (odds ratio = 2.39; P = .037) was an independent risk factor for failure. Utilization of cones alone did not have an effect on re-revision rates at 3.4-year follow-up. CONCLUSIONS: While we found no difference with the use of cones, patients undergoing revision TKA with a hinge prosthesis and fully cemented stems had better overall survivorship than hybrid stems.

Metaphyseal Fixation Using Cones and Sleeves for Severe Proximal Tibial Bone Loss.

BACKGROUND: Tibial bone defects are commonly encountered in revision total knee arthroplasty (rTKA) and can be managed with metaphyseal cones or sleeves. Few studies have directly compared tibial cones and sleeves in rTKA, and none have limited this comparison to the most severe tibial defects. The purpose of this study was to evaluate and compare the outcomes of metaphyseal cones and sleeves for tibial reconstruction in rTKA regarding implant fixation and clinical outcomes. METHODS: A retrospective review was conducted on patients undergoing rTKA in which metaphyseal cones or sleeves were utilized for addressing metaphyseal bone loss (34 cones and 18 sleeves). Tibial bone loss was classified according to the Anderson Orthopaedic Research Institute bone defect classification, with types 2B and 3 being included. Patient-reported outcomes and postoperative complications were collected, and a radiographic evaluation of osseointegration or loosening was performed. RESULTS: There were 52 knees included (34 cones, 18 sleeves), with a median follow-up of 41.0 months. All-cause implant survival was 100% at 2 years and 96% (95% confidence interval: 76 to 99%) at 4 years, with 98% of tibial components demonstrating osseointegration at the final follow-up. During follow-up, there were a total 11 revisions, of which 1 sleeve was revised secondary to implant loosening. Tibial sleeves had a higher risk of revision compared to tibial cones (P < .01), and sleeves fixed with a hybrid technique were more likely to need revision than cones fixed by the same method (P = .01). CONCLUSIONS: Porous metaphyseal tibial cones and tibial metaphyseal sleeves both performed well at a 41-month median follow-up with no difference in aseptic survivorship between the 2 constructs. Both demonstrate high rates of osseointegration, low rates of aseptic failure, and significant improvement in Knee Society Scores in patients with severe tibial defects in rTKA.

Tips and Tricks to Save You During Revision Total Knee Arthroplasty.

The number of revision total knee arthroplasties (TKAs) performed annually continues to rise. This article is a summary of a symposium on revision TKAs presented at the 2023 American Association of Hip and Knee Surgeons annual meeting. It will provide an overview of the surgical tips and tricks for exposure and component removal, use of metaphyseal fixation and stems to manage bone loss and optimize fixation, constraint in TKA, as well as how to manage extensor mechanism disruptions with a synthetic mesh reconstruction. LEVEL OF EVIDENCE: V.

Are Proud Tibial Cone Constructs an Effective Alternative to Those That are Fully Seated in Revision Total Knee Arthroplasty?

BACKGROUND: This study compared the clinical, radiographic, and patient-reported outcomes between patients treated with the traditional fully seated tibial cone construct and those with the novel proud tibial cone construct in revision total knee arthroplasty (rTKA). METHODS: This was a retrospective study of 56 adult patients who had a minimum 2-year follow-up and underwent rTKA with either the fully seated (n = 18 knees) or proud (n = 42 knees) tibial cone construct between 2010 and 2020. The electronic medical record was reviewed for demographic, clinical, and radiographic data. Knee Injury and Osteoarthritis Outcome Scores (KOOS) were collected. RESULTS: All patients had improved mechanical alignment postoperatively regardless of surgical technique. All patients showed good evidence of osseointegration without loss of fixation at the latest follow-up. There were no significant differences in the complication rate or re-revision rate between the groups. KOOS Function in Sport and Recreation (Sport/Rec) scores were significantly higher for patients treated with the fully seated construct (mean 57 [range, 20 to 95] versus 38 [range, 0 to 75], P = .04); however, no significant differences were present for the other KOOS subscales or KOOS Jr. CONCLUSION: The proud tibial cone construct may be an effective alternative to the fully seated construct in the setting of severe bone loss in rTKA. The proud construct avoids a proximal tibial cut, and thus is a bone-preserving technique that provides good fixation, reduces operative time, prevents potential iatrogenic injuries, decreases the need for tibial augments, saves costs, and improves the ease of restoring joint height.

Porous Tantalum Tibial Metaphyseal Cones in Revision Total Knee Arthroplasty: Excellent 10-Year Survivorship.

BACKGROUND: Highly porous metal tibial metaphyseal cones (TMCs) are commonly utilized in revision total knee arthroplasty (TKA) to address bone loss and obtain biologic fixation. Mid-term (5 to 10 year) studies have previously demonstrated excellent survivorship and high rates of osseointegration, but longer-term studies are lacking. We aimed to assess long-term (≥ 10 year) implant survivorship, complications, and clinical and radiographic outcomes after revision TKA with TMCs. METHODS: Between 2004 and 2011, 228 revision TKAs utilizing porous tantalum TMCs with stemmed tibial components were performed at a single institution and were retrospectively reviewed. The mean age at revision was 65 years, the mean body mass index was 33, and 52% were women. Implant survivorship, complications, and clinical and radiographic outcomes were assessed. The mean follow-up was 6.3 years. RESULTS: The 10-year survivorship free of aseptic loosening leading to TMC removal was 97%, free of any TMC removal was 88%, free of any re-revision was 66%, and free of any reoperation was 58%. The most common indications for re-revision were periprosthetic joint infection, instability, and aseptic femoral component loosening. The 10-year nonoperative complication rate was 24%. The mean Knee Society scores increased from 38 preoperatively to 69 at 10 years. There were 8 knees that had evidence of partial, progressive tibial radiolucencies at 10 years. CONCLUSIONS: Porous tantalum TMCs demonstrated persistently durable longer-term survivorship with a low rate of implant removal. The rare implant removals for component loosening or instability were offset by those required for periprosthetic joint infection, which accounted for 80% of cone removals. Porous tantalum TMCs provide an extremely reliable tool to address tibial bone loss and achieve durable long-term fixation in revision TKA. LEVEL OF EVIDENCE: IV.

Impact of low-fusion gutta-percha cones used in variations of the continuous wave condensation technique with filling sealers based on bioceramic compounds on the quality of root canal filling.

To evaluate the impact on the quality of filling with of low-fusion and conventional gutta-percha cones. Thirty-six maxillary canines were prepared and divided into three groups: I-conventional cone with Downpack at 200 °C at 4 mm from the WL; II-low-fusion cone with Downpack at 100 °C up to 4 mm from the WL; III-low-fusion cone with Downpack at 100 °C up to 7 mm from the WL. Temperature variations were measured in thirds on the external surface of the root. The bond strength was evaluated using the push-out test. The adhesive interface was analyzed by scanning electron microscopy. The bond strength and the temperature variation data were analyzed using analysis of variance and the failure type using the chi-square test. The low-fusion cone group with 7 mm Downpack showed higher bond strength (4.2 ± 2.7) compared with conventional cones (2.8 ± 1.6) and low-fusion cones with 4 mm Downpack (2.9 ± 1.6) (p < 0.05), with occurrence of a higher number of adhesive failures to the filling material and mixed failures. Relative to temperature variation, there was less temperature change in the apical third, in the low-fusion cone with Downpack 7 mm (1.0 ± 1.0) (p < 0.05). The use of low-fusion cones allowed the continuous wave condensation technique to be performed at a lower depth of Downpack at 100 °C at 7 mm, with less heating in the apical third, without compromising the quality of filling. Using gutta-percha cones with low fusion, which permits a lower condensation temperature and reduced Downpack depth, maintains the quality of filling, in order to minimize possible damage to the periapical tissues.