Potential of Ocotea indecora (Schott) Mez essential oil nanoemulsion in schistosomiasis control: Molluscicidal effects

Schistosomiasis is a neglected disease transmitted through contaminated water in populations with low basic sanitation. The World Health Organization recommends controlling the intermediate host snails of the Biomphalaria genus with the molluscicide niclosamide. This work aims to evaluate the biocidal potential of the nanoemulsion prepared with the essential oil of Ocotea indecora leaves for the control of the mollusk Biomphalaria glabrata, intermediate host of the Schistosoma mansoni, the etiologic agent of schistosomiasis.

Characterization of bergamot essential oil: chemical, microbiological and colloidal aspects

Citrus bergamia is a citric species known as bergamot. The species is widely used due to its derivatives, such as juices, extracts, and essential oil. Specifically, the bergamot essential oil (BEO) is of great interest, with a chemical composition rich in terpenes and esters. Considering its chemical composition, bioactivity, and great economic potential, the characterization of BEO should be studied. However, this essential oil is almost unexplored in terms of a characterization associated with colloids. Chemical characterization was carried out by gas-chromatography coupled to a mass spectrometer and by gas-chromatography coupled to a flame ionization detector. Antibacterial activity against Staphylococcus aureus and Escherichia coli was carried out to confirm the bioactivity of this important essential oil. Dynamic light scattering analysis was performed to create a pattern of droplet size distribution of BEO. Major compounds of BEO were linalyl acetate, limonene, and linalool. The BEO was active against E. coli and presented a MIC value of 2.000 µg/mL, while values of MIC and MBC higher than 2.000 µg/mL were observed for S. aureus. The dynamic light scattering analysis revealed a mean hydrodynamic diameter of 65.7 ± 2.2 nm. After a 1:10 dilution it was observed reduction of mean diameter and enhancement of the percentagem of low size droplets, resepctively 44.1 ± 1.2 nm and 14.5 ± 0.5 nm (28.8 ± 1.2%). Higher droplets and reduced polydispersity index were observed after 1:100 dilution. In the present study, the chemical characterization was in accordance with the species, as the characteristic chemical markers of the species were found. Moreover, it has presented antibacterial activity as expected for the BEO. The analysis of the colloid showed a pattern of droplet size distribution following the Ostwald ripening mechanism after dilution.

Larvicidal Effect of Hyptis suaveolens (L.) Poit. Essential Oil Nanoemulsion on Culex quinquefasciatus (Diptera: Culicidae)

Mosquitoes can be vectors of pathogens and transmit diseases to both animals and humans. Species of the genus Culex are part of the cycle of neglected diseases, especially Culex quinquefasciatus, which is an anthropophilic vector of lymphatic filariasis. Natural products can be an alternative to synthetic insecticides for vector control; however, the main issue is the poor water availability of some compounds from plant origin. In this context, nanoemulsions are kinetic stable delivery systems of great interest for lipophilic substances. The objective of this study was to investigate the larvicidal activity of the Hyptis suaveolens essential oil nanoemulsion on Cx. quinquefasciatus. The essential oil showed a predominance of monoterpenes with retention time (RT) lower than 15 min. The average size diameter of the emulsions (sorbitan monooleate/polysorbate 20) was ≤ 200 nm. The nanoemulsion showed high larvicidal activity in concentrations of 250 and 125 ppm. CL50 values were 102.41 (77.5253−149.14) ppm and 70.8105 (44.5282−109.811) ppm after 24 and 48 h, respectively. The mortality rate in the surfactant control was lower than 9%. Scanning micrograph images showed changes in the larvae’s integument. This study achieved an active nanoemulsion on Cx. quinquefasciatus through a low-energy-input technique and without using potentially toxic organic solvents. Therefore, it expands the scope of possible applications of H. suaveolens essential oil in the production of high-added-value nanosystems for tropical disease vector control.

Potential implications of vouacapan compounds for insecticidal activity: an in silico study

BACKGROUND

From the fruits and seeds of the species of Pterodon, it is possible to obtain two main products: the essential oil and oleoresin. In oleoresin, numerous vouacapan compounds have been demonstrated to have biological potential, including insecticidal activity.

OBJECTIVE

In silico studies were performed to identify potential candidates for natural insecticides among the vouacapans present in the genus Pterodon.

MATERIALS AND METHODS

Molecular docking and molecular dynamics studies were performed to analyze the interaction of vouacapan compounds with acetylcholinesterase of Drosophila melanogaster. Pharmacokinetic parameters regarding physicochemical properties, plasma protein binding, and activity in the central nervous system were evaluated. The toxicological properties of the selected molecules were predicted using Malathion as the reference compound.

RESULTS

6α,7β-dimethoxivouacapan-17-ene (15) showed a high number of interactions and scores in molecular docking studies. This result suggests that this compound exhibits an inhibitory activity of the enzyme acetylcholinesterase. Regarding physicochemical properties, this compound showed the best results, besides presenting low cutaneous permeability values, suggesting null absorption. Molecular dynamics studies demonstrated few conformational changes in the structure of the complex formed by compound 4 and acetylcholinesterase enzyme throughout the simulation time.

CONCLUSION

It was determined that compound 4 (vouacapan 6α,7β,17β,19-tetraol) is an excellent candidate for usage as a natural insecticide.

A Low Energy Approach for the Preparation of Nano-Emulsions with a High Citral-Content Essential Oil

Pectis elongata is found in the northern and northeastern regions of Brazil. It is considered a lemongrass due to its citric scent. The remarkable citral content and the wide antimicrobial properties and bioactive features of this terpene make this essential oil (EO) eligible for several industrial purposes, especially in cosmetics and phytotherapics. However, to address the problems regarding citral solubility, nano-emulsification is considered a promising strategy thanks to its improved dispersability. Thus, in this paper we propose a low-energy approach for the development of citral-based nano-emulsions prepared with P. elongata EO. The plant was hydrodistillated to produce the EO, which was characterized with a gas chromatograph coupled to mass spectrometry. The nano-emulsion prepared by a non-heated water titrating (low-energy) method was composed of 5% (w/w) EO, 5% (w/w) non-ionic surfactants and 90% (w/w) deionized water and was analyzed by dynamic light scattering. Levels of citral of around 90% (neral:geranial—4:5) were detected in the EO and no major alteration in the ratio of citral was observed after the nano-emulsification. The nano-emulsion was stable until the 14th day (size around 115 nm and polydispersity index around 0.2) and no major alteration in droplet size was observed within 30 days of storage. Understanding the droplet size distribution as a function of time and correlating it to concepts of compositional ripening, as opposing forces to the conventional Ostwald ripening destabilization mechanism, may open interesting approaches for further industrial application of novel, low-energy, ecofriendly approaches to high citral essential oil-based nano-emulsions based on lemongrass plants.

Efficacy of nanoemulsion with Pterodon emarginatus Vogel oleoresin for topical treatment of cutaneous leishmaniasis

Cutaneous leishmaniasis (CL) is a neglected tropical skin disease caused by the protozoan genus Leishmania. The treatment is restricted to a handful number of drugs that exhibit toxic effects, limited efficacy, and drug resistance. Additionally, developing an effective topical treatment is still an enormous unmet medical challenge. Natural oils, e.g. the oleoresin from P. emarginatus fruits (SO), contain various bioactive molecules, especially terpenoid compounds such as diterpenes and sesquiterpenes. However, its use in topical formulations can be impaired due to the natural barrier of the skin for low water solubility compounds. Nanoemulsions (NE) are drug delivery systems able to increase penetration of lipophilic compounds throughout the skin, improving their topical effect. In this context, we propose the use of SO-containing NE (SO-NE) for CL treatment. The SO-NE was produced by a low energy method and presented suitable physicochemical characteristic: average diameter and polydispersity index lower than 180 nm and 0.2, respectively. Leishmania (Leishmania) amazonensis-infected BALB/c mice were given topical doses of SO or SO-NE. The topical use of a combination of SO-NE and intraperitoneal meglumine antimoniate reduced lesion size by 41 % and tissue regeneration was proven by histopathological analyses. In addition, a reduction in the parasitic load and decreased in the level of IFN-γ in the lesion may be associated, as well as a lower level of the cytokine IL-10 may be associated with a less intense inflammatory process. The present study suggests that SO-NE in combination meglumine antimoniate represents a promising alternative for the topical treatment of CL caused by L. (L.) amazonensis.

Repellency effect of Pilocarpus spicatus A. St.-Hil essential oil and nanoemulsion against Rhipicephalus microplus larvae

Rhipicephalus microplus, the cattle tick, is a major cause of economic losses in bovine production. Due to the widespread acaricidal resistance to commercially available products, as well as their toxicity and environmental impact, alternative control methods are required. Nanoformulations produced from plant extracts as bioactive substances are very promising as innovative acaricidal agents. Thus, the aim of this study was to evaluate the in vitro repellent activity of Pilocarpus spicatus essential oil and its nanoemulsion against R. microplus, using larval repellent test (RT). The essential oil was extracted by hydrodistillation, using a Clevenger-type apparatus. The nanoemulsion was prepared with 5% essential oil, 5% tween 80, and 90% water, using the phase inversion method (50 mg/mL). Limonene was the major component (46.8%) of the essential oil, as determined by gas chromatography-mass spectrometry (GC/MS) and confirmed by flame ionization detection (GC/FID). According to the RT results, the essential oil had a repellent activity greater than 69%, from concentrations of 3.12 mg/mL (69.81 ± 10%) to 50 mg/mL (98.10 ± 0.6%), whereas the nanoemulsion at 50 mg/mL presented repellent activities of 97.14 ± 1.37% and 97.89 ± 0.52% 6 and 10 h after treatment, respectively. These values regarding to total repellency were very close to those calculated for mortality corrected by Abbott's formula. The phase inversion method preserved the chemical and physical characteristics of the essential oil since both reached an equal repellent effect at the same concentration. Therefore, P. spicatus essential oil and nanoemulsion had excellent repellent activities against R. microplus larvae, demonstrating its potential for future use as an alternative for tick control.

Effects of a nanoemulsion with Copaifera officinalis oleoresin against monogenean parasites of Colossoma macropomum: A Neotropical Serrasalmidae

Monogeneans are ectoparasites that may cause losses in production and productivity in the aquaculture of Colossoma macropomum. Chemotherapeutics used in aquaculture usually have major adverse effects on fish; hence, the use of essential oils has been considered advantageous, but these are not soluble in water. Thus, the use of nanostructures to enhance water solubility of compounds and improve bioactivity may be very promising. This study investigated the antiparasitic activity of nanoemulsion prepared with Copaifera officinalis oleoresin (50, 100, 150, 200 and 300 mg/L), against monogenean parasites from the gills of C. macropomum. The particle size distribution and zeta potential suggested that a potentially kinetic stable system was generated. The nanoemulsion from C. officinalis oleoresin achieved high efficacy (100%) at low concentrations (200 and 300 mg/L) after 15 min of exposure. This was the first time that a nanoemulsion was generated from C. officinalis oleoresin using a solvent-free, non-heating and low-energy method. Moreover, this was the first time that an antiparasitic against monogeneans on fish gills, based on nanoemulsion of C. officinalis oleoresin, was tested.

Nanoemulsion from essential oil of Pterodon emarginatus (Fabaceae) shows in vitro efficacy against monogeneans of Colossoma macropomum (Pisces: Serrasalmidae)

Outbreaks of diseases pose a major threat to sustainable aquaculture development worldwide. Application of herbal products to combat parasitic diseases provides an alternative approach for sustainable aquaculture. This study investigated the in vitro antiparasitic effects of an oil-in-water nanoemulsion prepared using the essential oil from Pterodon emarginatus, against monogeneans infesting Colossoma macropomum. Gill arches from C. macropomum (47.6 ± 14.5 g and 13.5 ± 1.4 cm) that were naturally parasitized by Anacanthorus spathulatus, Notozothecium janauachensis and Mymarothecium boegeri were immersed in different dispersions of the P. emarginatus nanoemulsions (0, 50, 100, 200, 400 and 600 mg/L). The major compounds presented in the essential oil of P. emarginatus were β-elemene, β-caryophyllene and α-humulene. Characterization of these nanoemulsions showed that they have a small mean droplet size and low polydispersity index, which is concordant with stable systems. In this in vitro trial, the P. emarginatus nanoemulsion concentrations of 100, 200, 400 and 600 mg/L presented 100% helminthic efficacy against monogeneans of the gills of C. macropomum. The highest two concentrations used (400 and 600 mg/L) were seen to immobilize the parasites after only 15 min. Therefore, it would be worthwhile testing these concentrations in therapeutic baths against monogeneans of C. macropomum.

Development and Characterization of Cassia grandis and Bixa orellana Nanoformulations

Cassia grandis and Bixa orellana are important plant species with folk use and great potential for phytopharmaceuticals. Nanodispersions are disperse systems of insoluble or immiscible substances in a liquid medium that may be prepared with or without coating polymers. To our knowledge, no studies were carried in order to achieve coating-polymer free nanoformulations using B. orellana extract or any C. grandis-based nanoformulations. Thus, on the present study we aimed to develop C. grandis nanoformulations using three different coating polymers (Eudragit® L 100 55, PEG 4000 and Kollicoat®), while B. orellana nanodispersions were obtained using different surfactants (polysorbate 80, polysorbate 20, polyethylene glycol 400 monooleate, polyethylene glycol 600 monooleate, polyethylene glycol 400 dioleate and polyethylene glycol 600 dioleate) as coating polymer-free nanoformulations. Characterization of nanoformulations was performed by different parameters, including particle size, polydispersity index and zeta-potential. Our results suggested that some optimal nanoformulations were obtained for both plant species. Moreover, possible stable behavior was observed during storage period for C. grandis (30 days) and B. orellana (21 days). On this context, the present study contributes to nanobiotechnology development of phytopharmaceuticals, allowing achievement of novel nano-delivery systems with two important folk medicinal plant extracts and making them potential products for innovative phytopharmaceuticals.

Pterodon emarginatus oleoresin-based nanoemulsion as a promising tool for Culex quinquefasciatus (Diptera: Culicidae) control

BACKGROUND

Preparation of nanoformulations using natural products as bioactive substances is considered very promising for innovative larvicidal agents. On this context, oil in water nanoemulsions develop a main role, since they satisfactorily disperse poor-water soluble substances, such as herbal oils, in aqueous media. Pterodon emarginatus, popularly known as sucupira, has a promising bioactive oleoresin. However, to our knowledge, no previous studies were carried out to evaluate its potential against Culex quinquefasciatus, the main vector of the tropical neglected disease called lymphatic filariasis or elephantiasis. Thus, we aimed to investigate influence of different pairs of surfactants in nanoemulsion formation and investigate if a sucupira oleoresin-based nanoemulsion has promising larvicidal activity against this C. quinquefasciatus. We also evaluated morphological alteration, possible mechanism of insecticidal action and ecotoxicity of the nanoemulsion against a non-target organism.

RESULTS

Among the different pairs of surfactants that were tested, nanoemulsions obtained with polysorbate 80/sorbitan monooleate and polysorbate 80/sorbitan trioleate presented smallest mean droplet size just afterwards preparation, respectively 151.0 ± 2.252 and 160.7 ± 1.493 nm. They presented high negative zeta potential values, low polydispersity index (<0.300) and did not present great alteration in mean droplet size and polydispersity index after 1 day of preparation. Overall, nanoemulsion prepared with polysorbate 80/sorbitan monooleate was considered more stable and was chosen for biological assays. It presented low LC50 value against larvae (34.75; 7.31-51.86 mg/L) after 48 h of treatment and some morphological alteration was observed. The nanoemulsion did not inhibit acetylcholinesterase of C. quinquefasciatus larvae. It was not toxic to green algae Chlorella vulgaris at low concentration (25 mg/L).

CONCLUSIONS

Our results suggest that optimal nanoemulsions may be prepared with different surfactants using a low cost and low energy simple method. Moreover, this prototype proved to be effective against C. quinquefasciatus, being considered an ecofriendly novel nanoproduct that can be useful in integrated control programs of vector control.

Development of a Larvicidal Nanoemulsion with Pterodon emarginatus Vogel Oil

Pterodon emarginatus Vogel is a Brazilian species that belongs to the family Fabaceae, popularly known as sucupira. Its oil has several biological activities, including potent larvicidal property against Aedes aegypti. This insect is the vector of dengue, a tropical disease that has been considered a critical health problem in developing countries, such as Brazil. Most of dengue control methods involve larvicidal agents suspended or diluted in water and making active lipophilic natural products available is therefore considered a technological challenge. In this context, nanoemulsions appear as viable alternatives to solve this major problem. The present study describes the development of a novel nanoemulsion with larvicidal activity against A. aegypti along with the required Hydrophile Lipophile Balance determination of this oil. It was suggested that the mechanism of action might involve reversible inhibition of acetylcholinesterase and our results also suggest that the P. emarginatus nanoemulsion is not toxic for mammals. Thus, it contributes significantly to alternative integrative practices of dengue control, as well as to develop sucupira based nanoproducts for application in aqueous media.

Laboratory evaluation of the effects of Manilkara subsericea (Mart.) Dubard extracts and triterpenes on the development of Dysdercus peruvianus and Oncopeltus fasciatus

BACKGROUND

Studies were carried out to evaluate the effects of Manilkara subsericea extracts and triterpenes on the development of two species of agricultural pest insects, Oncopelus fasciatus and Dysdercus peruvianus.

RESULTS

All treatments of insects with M. subsericea extracts induced mortality, delayed development and inhibited moulting. Some extracts assayed (FH, FB and FD in D. peruvianus, and FH, FB and FEA in O. fasciatus) also produced body deformities in the few adults that emerged. Other extracts (FH, FEA, FB, FD and LET in both insects), however, induced either permanent (overaged) or extranumerary nymphs, both of which were unable to achieve the adult stage and reproductive status. The insects were also treated with triterpenes (α- and β-amyrin acetates) which showed high lethality at 30 days after treatment and delayed the intermoult period so that overaged nymphs were detected.

CONCLUSION

The results indicate that extracts and triterpenes from Manilkara subsericea act as potent growth inhibitors of phytophagous hemipteran nymphs. It is also concluded that the mixture of several different molecules in the extracts used produces synergic effects that do not occur after using the triterpenes (PFT) alone. These secondary metabolites in the M. subsericea extracts can potentially be used in integrated control programmes against crop pests.

The significance of major connectors and denture base mucosal contacts on the functional strain patterns of maxillary removable partial dentures

The purpose of this study was to investigate the biomechanical significance of major connectors and base mucosal contacts on the mechanical behaviour of maxillary removable partial dentures in vivo. Six subjects wearing maxillary dentures retained by conical crowns were selected for the study. Reflective photoelasticity and strain gauges were used to monitor the development of strain/stress during functional loading. Loading tests were performed initially with a denture design including a palatal major connector and denture bases and then repeated after removal of the major connectors and denture base alveolar muccosa contacts. The palatal major connector and the denture bases mucosal contacts contribute significantly to the rigidity and stability of removable partial dentures retained by conical crowns.

Jaw-closing muscles: electromyographic activity of human subjects with reduced periodontal support

The aim of this study was to compare the electromyographic (EMG) activity of jaw-closing muscles of individuals with normal and reduced periodontal bone support. Fourteen adult subjects with more than 24 remaining teeth and low levels of periodontal inflammation, were selected for the study. Subjects of the control group had 90% of the periodontal bone support left, while other subjects presented a reduction of 52% of the original periodontal bone. Chewing experiments were performed using silicone tablets, carrots and white bread. The EMG of masseter and anterior temporal muscles was performed bilaterally, using bipolar surface electrodes, and the EMG amplitude was full wave rectified, integrated and the area extension under the curve was used to access muscle activity. The results of the chewing experiments did not show any statistically significant difference in the EMG activity of the study groups, irrespective of the chewing stuff. The height of periodontal bone support did not seem to influence the electroactivity of jaw-closing muscles, indicating that reduced periodontal support might equally be able to withstand masticatory loads. Hence, individuals with reduced periodontal bone support revealed a similar EMG activity compared to subjects with normal periodontal bone support.

Accuracy, detail reproduction, and hardness of gypsum casts produced from silicone impressions treated with glow discharge

Plasma treatment has been reported to improve the wettability of silicone impression materials. This study investigated whether plasma treatment of silicone impressions influenced the linear dimensional accuracy, detail reproducibility, and surface hardness of models produced from a type IV dental die stone. Five silicone impressions materials were used in this study. Linear dimensional accuracy and detail reproduction were tested according to ISO standards. Surface hardness was evaluated with a Vickers hardness test. The results indicated that plasma-treated impressions from Xantopren and Provil silicone impression materials had significantly smaller dimensional change than their respective controls, and the other materials were not influenced. The detail reproduction was superior in casts produced from plasma-treated impressions from President silicone. Surface hardness was not influenced by the treatment. Plasma treatment of silicone impressions has no negative influence on the tested physical properties of die stone models.

Surface properties of elastomeric impression materials

This study investigated the wettability of commonly used elastomeric impression materials and their gypsum castability. The wettability was evaluated by determining the contact angles of drops of a CaSO4 aqueous solution on flat impression surfaces. Gypsum castability was determined by counting the number of voids formed in die stone casts made from impressions of a critical die. All specimens used in this study were exposed to saliva to simulate clinical conditions, where materials spontaneously acquire salivary origin biofilms. The results indicate that the condensation silicones and conventional addition silicones exhibited the largest contact angles and the highest number of voids. The new generation of 'hydrophilic' addition silicones had higher wettability than the conventional silicones and an improved gypsum castability, comparable to that of the polyether materials.

Effect of salivary films on the surface properties of elastomeric impression materials

Impression materials exposed to the oral cavity are subjected to spontaneous adsorption of salivary films. The aim of this study was to evaluate the effect of adsorbed salivary films on some surface properties of one condensation, four addition silicone and one polyether impression materials. The results showed that adsorbed salivary films caused an increase in the critical surface tension and in the polarity ratios for all materials tested. A reduction in the number of voids in die stone casts was also noticed, along with an improvement in the gypsum compatibility with the impression materials tested. It can be concluded that the presence and effect of salivary films should be taken into consideration when studying the surface properties of elastomeric impression materials.

Effect of plasma treatment on the wettability of elastomeric impression materials

This study investigated the effect of "plasma treatment" on the wettability of impression materials and void formation in die stone casts. Four addition reaction silicones, one condensation reaction silicone, and one polyether impression material were used. Wettability was determined before and after plasma treatment by contact angle registration of a saturated aqueous solution of calcium sulfate (CaSO4) on flat surfaces made from the tested impression materials. Two groups of surfaces were used for each material. The surfaces in one of the groups were exposed to saliva for 5 minutes. The same impression materials were used to produce four groups of die stone casts from a master die. Two groups were produced from impressions that had been exposed to milk. One group from the exposed and one from the bare surfaces were plasma-treated before pouring. Voids in the stone casts were counted under a stereoscopic microscope. The results indicated that after plasma treatment, the drop of CaSO4 solution completely spread over the addition type silicone surfaces. The corresponding die stone casts were found to be void free. It was concluded that plasma treatment produced high-energy impression surfaces that result in void-free die stone casts from the addition type silicone materials.

Masticatory efficiency of patients treated with implant retained fixed bridges in the upper jaw over a 2-year period

The aim of this study was to investigate the effect of the rehabilitation of the upper jaw with a fixed bridge supported by Brånemark implants upon patient's masticatory efficiency. Five patients wearing complete dentures in the upper jaw were selected for the study. Chewing tests using Optosil tablets were performed before fixture installation, immediately after bridge connection and 2 years after bridge delivery. The results indicated that treatment with fixed bridges retained by osseointegrated implants did not give immediate improvements in masticatory efficiency. Only after the subjects had enough time to adapt to the reconstruction was an improvement in the masticatory efficiency index observed.

Surface properties and castability of elastomeric impression materials after plasma cleaning

The wettability of impression materials is an important requirement for accurate reproduction of intraoral structures. The aims of this study were to evaluate the effect of plasma cleaning on critical surface tension and die stone castability of five silicone impression materials. Critical surface tension was calculated using a contact angle analysis according to Zisman (1964), before and after plasma cleaning. Die stone casts were produced from impressions of a master die and the area extension of the reproduction was measured planimetrically. The results showed a general increase in the critical surface tension and in the polar force component of the composite free energy for materials treated with plasma cleaning. An improvement in castability of all materials was also noted.

The orientation and direction of rods in dental enamel

Enamel rods are commonly accepted as perpendicularly oriented to the tooth surface and this concept has influenced the design of cavity preparations. This investigation studied the orientation and direction of enamel rods at the outer third of the enamel plate. Fifteen human molars were randomly selected and sectioned in the buccolingual, mesiodistal, and coronal directions. Angulations of the rods at the outer surface were measured by use of a protractor superimposed on the micrographs taken by scanning electron microscope. The mean angulation for axial surfaces was 60 degrees. The enamel rods were consistently parallel to the long axis of the tooth with 55-degree mean angulation. The conclusion was that enamel rods are not perpendicular to the surface except at the edge of the cusps and occasionally at the cervical area.