Accessory Cone Research Articles

New insights into the retinal microstructure-diurnal activity relationship in the African five-lined skink (Trachylepis quinquetaeniata) (Lichtenstein, 1823)

BackgroundThe retinae of diurnal vertebrates have characteristics. Most lizards are strictly diurnal, and their retinal morphology is still unknown.Materials and methodsThe retina of the African five-lined skink (Trachylepis quinquetaeniata) was studied using light and transmission electron microscopy.ResultsThe retina's ten layers were all detected. The inner nuclear layer was the thickest by an average of 67.66 μm, and the inner plexiform layer was 57.564 μm. There were elliptical, long cylindrical, and spherical melanosomes (small and large) in the pigment epithelial layer of the retina. The cylindrical melanosomes had a large area on the lateral surfaces of cones to increase light scatter absorption. The photoreceptor layer of the retina had cones only. There were single and double cones, with the double cones consisting of principal and accessory cones. The cones had inner and outer segments separated by oil droplets. A spherical paraboloid body existed between the limiting membrane and the ellipsoid. All single cones had a paraboloid, and double cones had a large paraboloid in the accessory cone. The presence of paraboloids and large ellipsoids with mitochondria of varying sizes may have helped focus the light on cone segments.ConclusionThe African five-lined skink's eye was light-adapted due to a variety of retinal specializations related to the demands of its diurnal lifestyle in its environment.

Desafios enfrentados por estudantes de graduação em odontologia durante o tratamento de canal radicular: um estudo de pesquisa

Abstract Introduction root canal treatment is a challenging procedure often first encountered by undergraduate dental students, leading to various difficulties and mistakes. Objective this study aimed to identify the specific difficulties encountered by undergraduate dental students during root canal treatment and the frequency of mistakes they committed in relation to these difficulties. Material and method this study employed a cross-sectional survey design. A cohort of 60 third-year students completed a self-administered questionnaire consisting of 27 questions addressing various aspects of endodontic treatment and 11 key areas of root canal procedures. The response options for each question were based on a 4-point Likert scale. Data analysis was performed using Python programming language and heatmaps were created using the seaborn library to better understand the distribution of the data. Result students encounter challenges in developing tactile sensation, accessory cone placement, and accurately reaching the apex during canal location. Dental schools should focus on improving students' tactile skills and methods to reach the apex to enhance the effectiveness of root canal treatment education. In contrast, students reported fewer mistakes in rubber dam application and safety measures during treatment. Dental educators should emphasize proper instrument use and safety precautions during root canal treatment. Interestingly, students did not perceive these areas as problematic despite committing mistakes. Conclusion this study provides valuable insights into the challenges and mistakes encountered by undergraduate dental students during root canal treatment. Dental educators should address these issues to improve students' skills and techniques and provide optimal patient care.

Theoretical distribution of gutta-percha within root canals filled using cold lateral compaction based on numeric calculus.

This study aimed to present a new method based on numeric calculus to provide data on the theoretical volume ratio of voids when using the cold lateral compaction technique in canals with various diameters and tapers. Twenty-one simulated mathematical root canal models were created with different tapers and sizes of apical diameter, and were filled with defined sizes of standardized accessory gutta-percha cones. The areas of each master and accessory gutta-percha cone as well as the depth of their insertion into the canals were determined mathematically in Microsoft Excel. When the first accessory gutta-percha cone had been positioned, the residual area of void was measured. The areas of the residual voids were then measured repeatedly upon insertion of additional accessary cones until no more could be inserted in the canal. The volume ratio of voids was calculated through measurement of the volume of the root canal and mass of gutta-percha cones. The theoretical volume ratio of voids was influenced by the taper of canal, the size of apical preparation and the size of accessory gutta-percha cones. Greater apical preparation size and larger taper together with the use of smaller accessory cones reduced the volume ratio of voids in the apical third. The mathematical model provided a precise method to determine the theoretical volume ratio of voids in root-filled canals when using cold lateral compaction.

Light and electron microscopic studies on the pigmented epithelium and photoreceptors of the retina of common buzzard (Buteo buteo)

The current study is essentially carried out to reveal the histological and ultra-structural details of the retinal pigmented epithelium (RPE) and photoreceptors cell layers of a common buzzard (Buteo buteo). The recorded results revealed that the neural retina of common buzzard consisted of seven distinct cell layers. The inner nuclear layer was markedly revealed as the thickest one among these layers. A highly melanized RPE was recorded in between the choroid and neural retina. Histologically, the RPE was represented by a single layer of cuboidal epithelial cells with centrally located nucleus. Ultrastructurally, the RPE cells showed numerous melanosomes, mitochondria, phagosomes, myeloid bodies, smooth endoplasmic reticulum (SER), but very rare rough endoplasmic reticulum (RER). The photoreceptor cell layer was represented by three categories of photoreceptor cells: few single rods, numerous single and double cones. Each double cone consisted of a short accessory cone and a long principle cone. The photoreceptor outer segment consisted of bi-membranous discs that are enclosed by outer membrane. Moreover, the inner segment of rods consisted of an ellipsoid and an inner hyperboloid. The hyperboloid was rich with RER, polysomes, Golgi apparatus and autophagic vacuoles. Furthermore, the inner segment of single cone and accessory cone consisted of an ellipsoid, paraboloid and myoid regions, while, the inner segment of principle cone lacked the paraboloid regions. At the proximal end of each inner segment for all types of cones, there was a large heterogeneous oil droplet. The paraboloid region was markedly rich with glycogen granules. The myoid region exhibited the same organelles but with little glycogen granules when compared with hyperboloid.

Effect of filling technique and root canal area on the percentage of gutta‐percha in laterally compacted root fillings

To determine the influence of filling technique and root canal area on the percentage of gutta-percha (PGP) in laterally compacted root fillings. Sixty extracted canine teeth were accessed and the root canals instrumented to the same size. They were then divided in three groups and filled with laterally compacted gutta-percha cones and AH Plus using different techniques. A variation of cold lateral compaction using a sequence of spreaders prior to accessory cone placement was compared to two commonly-used techniques. Twenty additional canines with prepared root canals were used as negative controls in which gutta-percha was introduced into the canals but no compaction applied. The roots were sectioned horizontally at 3 and 6 mm from the apex and micro-photographs taken. Using software, the area of the canals and gutta-percha at each level were measured and PGP calculated. A Multivariate analysis was used to determine the variables influencing PGP. A linear regression test was used to verify the variation in PGP explained by canal area. At each level the largest canal was two to three times wider than the smallest. Canal area significantly influenced the PGP at both levels (P < 0.05), however, the variation in PGP was only partially explained by canal area (r(2) = 0.154, 6 mm; r(2) = 0.119, 3 mm). The PGP at the 3 mm level was lower than at 6 mm (P = 0.003). The spreader-sequence technique achieved a higher PGP than the other two techniques (P = 0.00002). The control group had the lowest area of GP. Variations in root canal filling technique and canal area influenced the percentage of gutta-percha of laterally compacted root fillings. The percentage of gutta-percha was lower at the 3 mm level compared to the 6 mm level.

Comparison of first accessory cone penetration after using stainless-steel and ni-ti spreaders in curved resin blocks.

The purpose of this study was to compare first accessory gutta-percha penetration after the use of nickel-titanium (Ni-Ti) or stainless-steel spreaders in curved resin blocks. Forty resin blocks with 30º and 45º curvatures (20 blocks for each) were prepared and #30 master cones were placed in canals. In part one, under 20 Newton pressure, Ni-Ti or stainless-steel spreaders were placed alongside the master cone and their penetration was measured with a millimeter ruler. In part two, after removing the spreader, one of the accessory cones (#15, #20 or MF) was substituted in the canal and its penetration was measured. The Mann-U Whitney test was used for the final evaluation. In both curvatures, the penetration of Ni-Ti spreaders were significantly more than stainless-steel spreaders (p<0.005). Penetration of the first accessory cones (#15 and MF) in Ni- Ti spreader group were also significantly more than stainless-steel group (p<0.05) (in both curvature groups). This study showed that Ni-Ti spreaders and #15 accessory cones penetrated deeper in curved canals than stainless spreaders and #15 accessory cones. Therefore, the use of NiTi spreader in lateral condensation technique is suggested for better results.

Evaluation of the 17-kDa Prenyl-binding Protein as a Regulatory Protein for Phototransduction in Retinal Photoreceptors

The mammalian rod photoreceptor phosphodiesterase (PDE6) holoenzyme is isolated in both a membrane-associated and a soluble form. Membrane binding is a consequence of prenylation of PDE6 catalytic subunits, whereas soluble PDE6 is purified with a 17-kDa prenyl-binding protein (PDEdelta) tightly bound. This protein, here termed PrBP/delta, has been hypothesized to reduce activation of PDE6 by transducin, thereby desensitizing the photoresponse. To test the potential role of PrBP/delta in regulating phototransduction, we examined the abundance, localization, and potential binding partners of PrBP/delta in retina and in purified rod outer segment (ROS) suspensions whose physiological and biochemical properties are well characterized. The amphibian homologue of PrBP/delta was cloned and sequenced and found to have 82% amino acid sequence identity with mammalian PrBP/delta. In contrast to bovine ROS, all of the PDE6 in purified frog ROS is membrane-associated. However, addition of recombinant frog PrBP/delta can solubilize PDE6 and prevent its activation by transducin. PrBP/delta also binds other prenylated photoreceptor proteins in vitro, including opsin kinase (GRK1/GRK7) and rab8. Quantitative immunoblot analysis of the PrBP/delta content of purified ROS reveals insufficient amounts of PrBP/delta (<0.1 PrBP/delta per PDE6) to serve as a subunit of PDE6 in either mammalian or amphibian photoreceptors. The immunolocalization of PrBP/delta in frog and bovine retina shows greatest PrBP/delta immunolabeling outside the photoreceptor cell layer. Within photoreceptors, only the inner segments of frog double cones are strongly labeled, whereas bovine photoreceptors reveal more PrBP/delta labeling near the junction of the inner and outer segments (connecting cilium) of photoreceptors. Together, these results rule out PrBP/delta as a PDE6 subunit and implicate PrBP/delta in the transport and membrane targeting of prenylated proteins (including PDE6) from their site of synthesis in the inner segment to their final destination in the outer segment of rods and cones.

Analysis of the film thickness of a root canal sealer following three obturation techniques.

The aim of this study was to obtain a quantitative analysis of the film thickness of a root canal sealer formed after filling by three different techniques. Thirty human maxillary incisors were selected and access cavities were prepared using high-speed diamond stones and water spray. A size #15 K-Flexofile was introduced in the canal of each specimen until it was seen just at the apical foramen. The working length was determined to be 1 mm short of that position and the canals were prepared to an apical size of #45 K-Flexofile. Copious irrigation with 5.25% NaOCl (sodium hypochlorite) was used during and after instrumentation. The samples were divided into three groups and obturated as follows: G1 - lateral condensation, G2 - lateral condensation with an accessory cone, and G3 - continuous wave of condensation. The samples were evaluated in the cervical, middle and apical thirds. The film thickness of the root canal sealer was measured through a microscopic evaluation. Statistical analysis was obtained using the Wilcox test. Statistical analysis showed significant differences between G3 and G1, G3 and G2 (p < 0.05). In general, the lowest film thickness was observed in the continuous wave of condensation (G3). Lateral condensation with an accessory cone (G2) and lateral condensation (G1) demonstrated poorer results in this study, showing a higher film thickness. The small film thickness of the sealer obtained by the continuous wave of condensation technique may increase the clinical performance of this technique.

Effect of Spreader and Accessory Cone Size on Density of Obturation Using Conventional or Mechanical Lateral Condensation

A simulated curved root canal in a resin block was enlarged to size 40 and used to compare the depth of accessory cone penetration and weight of obturation occurring with the use of different obturation techniques and spreader-accessory cone combinations. Twelve groups, each consisting of 10 obturations, were created. A conventional lateral condensation technique was used in six groups and a mechanical lateral condensation (MLC) technique was used in six matched groups. The six spreader-accessory cone combinations were either Fine-Medium or Fine nickel-titanium finger spreaders with either Fine, Medium-Fine, or size 25 accessory cones. Seven accessory cones were placed in every obturation. The depth of each accessory cone penetration into the canal was measured. After each obturation the gutta-percha was removed, sectioned, and the resulting mass was weighed. The means for each variable were determined and compared. MLC fills were significantly heavier and had greater depth of penetration on average than conventional lateral condensation. The best combination for heavy fills was MLC, Fine-Medium spreaders, and Fine accessory cones. The greatest mean accessory cone depth occurred with MLC, Fine-Medium spreaders, and size 25 accessory cones.

Gutta-Percha Softening: “Hemo-De” as a Xylene Substitute

The putative hazardous nature of chloroform and xylene implies that safer substitutes should be considered. Standard cylindrical gutta-percha samples were immersed in Hemo-De, a xylene substitute, for 60 s at 37 degrees C. Weight loss of a sample, after drying, was used as a measure of its solubility. Master and accessory cone gutta-percha of three brands were compared. The highest solubility of all kinds of gutta-percha was in chloroform, which served as a positive control. The average solubility of all samples in xylene and Hemo-De was 61% and 52% of that in chloroform, respectively. DMS gutta-percha was more soluble than of Hygienic and DeTrey. Master cone gutta-percha of all brands was more soluble than that of their accessory cones. These results indicate that (a) large differences exist in the solubility of gutta-percha and (b) Hemo-De dissolved gutta-percha in a range similar to that of xylene and may be considered as a potential substitute for this organic solvent.

Comparison of Nickel-Titanium and Stainless-Steel Spreader Penetration and Accessory Cone Fit in Curved Canals

The purpose of this study was to compare nickel-titanium and stainless-steel spreader penetration in curved canals. Twenty prepared plastic blocks with a 30 degrees curvature were used for each part of the study. In part 1, the force required to insert each spreader to within 1 mm of working length in an empty canal was measured. In part 2, the force required to insert each spreader to within 3 mm of working length was measured in a canal containing a master cone. In part 3, the depth of penetration of each spreader with a master cone in place using a 1.5 kg force was measured. Additionally, in part 3, the depth of penetration of the first accessory cone was measured. The results from part 1 showed that a nickel-titanium spreader required significantly less force than a stainless-steel spreader (0.30 kg vs. 0.59 kg). In part 2, a nickel-titanium spreader required significantly less force than a stainless-steel spreader (1.56 kg vs. 2.42 kg). In part 3, a nickel-titanium spreader penetrated significantly deeper than a stainless-steel spreader (15.0 mm vs. 14.0 mm). There was no significant difference in the depth of penetration of the first accessory cone used after either spreader (0.8 mm vs. 0.7 mm). Therefore, the potential for vertical root fracture in curved canals during lateral condensation may be minimized by using nickel-titanium spreaders.

Fine structure of the retinal photoreceptors of the emu (Dromaius novaehollandiae)

The retinal photoreceptors of the emu (Dromaius novaehollandiae) consist of rods, single cones and double (unequal) cones present in a ratio of about 10:1:4 respectively. The rods are long slender cells which are felt to undergo retinomotor movements. The rod outer segment is a stack of bimembranous discs which display shallow peripheral incisures and are all of the same diameter. The rod inner segment displays an ellipsoid of mitochondria, much rough endoplasmic reticulum (ER), numerous polysomes and a prominent hyperboloid of glycogen. Single cones show a tapered outer segment, no oil droplet but a large ellipsoid with several small lipid droplets and a paraboloid of glycogen. Double cones consist of a chief member which displays a single large heterogeneous oil droplet and no paraboloid, and an accessory cone which has no oil droplet but again several small lipid droplets and a large paraboloid. All cones show a large ellipsoid, plentiful polysomes, rough ER, Golgi zones and autophagic vacuoles. Along the length of the contiguous membranes of the two members of the double cones are scattered membrane densifications. The cones are not believed to undergo retinomotor movements in the emu. Rod photoreceptors are relatively small in diameter and hence are closely packed, while the larger cones are not as abundant. Rods and cones (both types) display both invaginated (ribbon) synapses as well as numerous superficial (conventional) synaptic sites.

Retinal Photoreceptor Fine Structure in the Great Blue Heron (Ardea herodias)

The morphology of the retinal photoreceptors of the great blue heron (Ardea herodias) has been investigated by light and electron microscopy. They consist of rods, single cones and double (unequal) cones present in a ratio of about 2:1:1 respectively. The rods are slender elongated cells with outer segments that reach to the retinal epithelial (RPE) cells and are surrounded by pigment-rich apical processes of the RPE cells in the light-adapted state. The rod inner segment displays an ellipsoid of mitochondria, an hyperboloid of glycogen, much rough ER, numerous polysomes, Golgi zones and autophagic vacuoles. The rod nucleus is located deep in the outer nuclear layer and the rod synaptic pedicle displays both invaginated and superficial synaptic sites. Single cones display a slightly tapered outer segment, a large electron lucent oil droplet and an ellipsoid of mitochondria in the apex of the inner segment. Double cones consist of a long thin chief member which shows an electron dense oil droplet and a shorter, stouter accessory cone with no oil droplet but a paraboloid of glycogen below the ellipsoid. As in the single cone, polysomes, RER and Golgi zones are present in the myoid region of both members of the double cone. All photoreceptor types have a connecting cilium joining inner and outer segments. Near the external limiting membrane, the chief and accessory cones show intercellular junctions. All cone photoreceptors are relatively small in diameter and hence tightly packed. While rods are felt to undergo retinomotor movements, cones are felt to move minimally or not at all. Both single and double cones display several invaginated (ribbon) synapses as well as numerous superficial (conventional) synaptic sites.

Retinal Photoreceptor Fine Structure in the Red‐Tailed Hawk (Buteo jamaicensis)

The retinal photoreceptors of the red-tailed hawk (Buteo jamaicensis) consist of rods, single cones and double (unequal) cones present in a ratio of about 2:1:5. In the light-adapted state, the rods are slender elongated cells with outer segments that reach to the retinal epithelial (RPE) cells. The inner segment displays an ellipsoid of mitochondria, plentiful polysomes, some rough ER and Golgi zones. The rod nucleus is located deep within the outer nuclear layer and the synaptic spherule displays both invaginated (ribbon) and superficial (conventional) synaptic sites. Single cones show a thin tapering outer segment, a large electron lucent oil droplet at the apex of the inner segment and an ellipsoid of mitochondria. Double cones consist of a larger chief member which displays a thin tapering outer segment and an electron dense oil droplet as well as a smaller accessory cone which shows no oil droplet, an ellipsoid and a paraboloid of glycogen. As in the single cone, polysomes, RER and Golgi zones are also noted in the inner segments of both members of the double cone. Near the external limiting membrane the chief and accessory cones show membrane specializations indicative of junctions on their contiguous surfaces. All cone photoreceptors are of a smaller diameter than is normally reported for avian species. Both single and double cones display several invaginated synapses as well as numerous superficial synaptic sites.

Histology and microspectrophotometry of the photoreceptors of a crocodilian, Alligator mississippiensis

The photoreceptors in the retina of Alligator mississippiensis were examined by means of in situ , single cell microspectrophotometry and scanning electron microscopy (SEM). The retina is characterized by a system of four cone visual pigments. One type of single cone contains a visual pigment with absorbance maximum ( λ max ) at 535 nm. A second type contains a visual pigment absorbing maximally at 444 nm. The principal member of the double cone has a visual pigment with λ max at 566 nm whereas the accessory member’s visual pigment absorbs maximally at 503 nm. There is only one rod pigment and it is virtually identical to that within the accessory cone, absorbing maximally at 501 nm. All visual pigments are based on the retinal or vitamin A 1 chromophore. SEM confirms that the alligator retina is duplex with rods dominating but cones present in significant numbers. There is a wide range of photoreceptor shapes and sizes throughout the retina

Evaluation of size variation between endodontic finger spreaders and accessory gutta-percha cones

The diameter of nine sizes of three brands of endodontic spreaders was measured at D1 and D16 and compared with corresponding sizes of six brands of accessory gutta-percha cones. Two evaluators independently measured 20 randomly selected samples of each size of finger spreader and accessory gutta-percha cone. A standardized method of measurement was used for all samples and the interrater reliability was found to be extremely high using this methodology. Results indicated that very few of the diameters corresponded when like sizes of finger spreaders and accessory gutta-percha cones were compared. We concluded that there is a need for standardization by the manufacturer of finger spreaders so that accessory gutta-percha cones will fit into the space created by corresponding sized finger spreaders.

Compatibility of accessory gutta-percha cones used with two types of spreaders

This study assessed the apical seal produced in 60 extracted single-rooted human teeth by laterally condensing fine-fine or #25 gutta-percha accessory cones with a D11-T spreader or a #30 finger spreader. The amount of vertical load (1.5 kg) applied to the spreader, the time of spreader contact with the gutta-percha, and the time between spreader withdrawal and insertion of the next accessory cone were rigidly controlled. India ink was used as an indicator of leakage. After clearing the teeth, the extent of ink penetration into the obturated root canal was determined at a magnification of ×15 with a binocular dissecting microscope equipped with a measuring grid. The presence of voids and the degree of fusion of accessory cones to the master cone were subjectively evaluated. The difference in leakage among the four experimental groups was not significant (analysis of variance, p>0.05). Fine-fine accessory cones were used in 9 of 10 teeth demonstrating overextension of guttapercha. Fewer voids and better fusion of the guttapercha were seen in canals obturated with #25 accessory cones condensed with either the D11-T or the #30 finger spreader. This study assessed the apical seal produced in 60 extracted single-rooted human teeth by laterally condensing fine-fine or #25 gutta-percha accessory cones with a D11-T spreader or a #30 finger spreader. The amount of vertical load (1.5 kg) applied to the spreader, the time of spreader contact with the gutta-percha, and the time between spreader withdrawal and insertion of the next accessory cone were rigidly controlled. India ink was used as an indicator of leakage. After clearing the teeth, the extent of ink penetration into the obturated root canal was determined at a magnification of ×15 with a binocular dissecting microscope equipped with a measuring grid. The presence of voids and the degree of fusion of accessory cones to the master cone were subjectively evaluated. The difference in leakage among the four experimental groups was not significant (analysis of variance, p>0.05). Fine-fine accessory cones were used in 9 of 10 teeth demonstrating overextension of guttapercha. Fewer voids and better fusion of the guttapercha were seen in canals obturated with #25 accessory cones condensed with either the D11-T or the #30 finger spreader.

Immunocytochemical localization of rhodopsin-like immunoreactivity in the outer segments of the rods and single cones of chick retina.

Photoreceptor cells in chick retina consist of a rod and five types of cones. Immunocytochemical techniques have pinpointed rhodopsin-like immunoreactivity in the outer segments of some single cones as well as in rods. The antibody used in our study was raised against bovine rhodopsin purified by SDS-polyacrylamide gel electrophoresis. No rhodopsin-like immunoreactivity was found in the principal and accessory cone. Epon-embedded, semi-thin sections also were treated with potassium hydroxide to remove epoxy resin and then subjected to immunoreaction with the antibody. With this method the same results were obtained repeatedly, and the possibility of staining failure in double cones and some single cones due to insufficient permeability was avoided. Electron microscopy revealed that the oil droplets of stained single cones are slightly smaller and are located in a more vitreal position than those of unstained single cones. The stained single cones are presumed to be types II and III single cones. In the inner segment, especially in the Golgi region and the rER, no staining was seen. Only slight staining was found in the connecting cilium and in the small vesicular or granular structure between the oil droplet and the plasma membrane facing the heavily stained outer segment. This suggests that opsin is incorporated into the plasma membrane in the distal portion of the inner segment.

Pigment types, densities and concentrations in cone oil droplets of Emydoidea blandingii.

The peak optical densities (Dp) of colored oil droplets in the retinal cones of the turtle, Emydoidea blandingii, were found to range from 1.2 to 8.8 for yellow droplets, 3.2 to 11.4 for orange, and 8.8 to 58 for red. The yellow droplets' spectra matched that of zeaxanthin, the red and orange matched astaxanthin. One type of clear droplet absorbed negligibly in the visible spectrum. A second type had a Dp approximately 0.9 somewhere between 370 and 400 nm. The accessory cone had no oil droplet, but its ellipsoid contained a pigment with the absorption spectrum of zeaxanthin and Dp approximately 1.1.

Optics of retinal oil droplets: a model of light collection and polarization detection in the avian retina.

A wave optical model was used to analyse the scattering properties of avian retinal oil droplets. Computations for the near field region showed that oil droplets perform significant light collection in cone photoreceptors and so enhance outer segment photon capture rates. Scattering by the oil droplet of the principal cone of a double cone pair, combined with accessory cone dichroic absorption under conditions of transverse illumination, may mediate avian polarization sensitivity.