Effect of degree of conversion on the surface properties of polymerized resin cements used for luting glass fiber posts.

STATEMENT OF PROBLEM: Lack of conversion of resin cements for luting glass fiber posts in deeper levels of the root canal may compromise clinical performance. PURPOSE: The purpose of this in vitro study was to evaluate the effect of the degree of conversion on the surface properties of dual-polymerized resin cements used for cemented glass fiber posts according to the root level. MATERIAL AND METHODS: Fifty maxillary central incisor teeth were endodontically treated, and glass fiber posts were cemented using the following systems: self-adhesive dual-polymerized resin luting cement (RelyX U200) and dual-polymerizing flowable core and a post luting system (Rebilda DC) with a self-etching adhesive (Futurabond DC). The degree of conversion was determined via attenuated total reflectance and Fourier transform infrared spectroscopy, and surface microhardness and cement film thickness were measured. The intraradicular fit was evaluated with microscopy. All tests were performed in the coronal, middle, and apical third of the root canal. Statistical analysis was done with ANOVA and the multiple comparison Tukey test (α=.05). RESULTS: The degree of conversion was higher in the coronal third using Rebilda DC (65.3 ±4.8%) than RelyX U200 (38.7 ±5.3%) (P<.05); on both resin cements, these values decreased from the coronal to the apical third (30.9 ±3.7%, 61.9 ±8.7%, respectively). The cement film thickness was higher for RelyX U200 in the 3 thirds than for Rebilda DC; significant differences (P<.05) were recorded in both cementing systems in the coronal and apical thirds. In the middle third, no significant differences were observed (P>.05). The mean surface microhardness values increased in the coronal thirds and decreased with increasing root canal depth. The marginal seal in the coronal thirds and the intraradicular fit in the middle thirds showed closer adaptation; however, some tags were observed in the interface resin cement and radicular dentin. Gap and tag formations were observed in the apical third. CONCLUSIONS: Depending on the root canal third, the surface properties of dual-polymerized resin cements are influenced by the degree of conversion.

Effect of short fiber-reinforced composite combined with polyethylene fibers on fracture resistance of endodontically treated premolars.

STATEMENT OF PROBLEM: Whether direct coronal restorations of endodontically treated teeth with short fiber-reinforced composite combined with polyethylene fibers provide adequate mechanical strength is unclear. PURPOSE: The purpose of this in vitro study was to compare the fracture strength of endodontically treated premolars with standardized mesio-occluso-distal (MOD) preparations restored with short fiber-reinforced composite (SFRC) combined with polyethylene Ribbond fibers (PRFs). MATERIAL AND METHODS: A total of 40 premolars were selected and distributed into 4 groups (n=10) as follows: group restored with SFRC (EverX Posterior), group restored with PRF (Ribbond fibers), and group restored with the combination PRF+SFRC, all followed by a conventional composite resin (IPS Empress Direct). MOD preparations and endodontic treatments were prepared except in the control group (intact teeth). MOD preparations and endodontic treatments were prepared except in the control group (intact teeth). Specimens were loaded using a universal testing machine until fracture occurred at a crosshead speed of 0.5 mm/min, and the failure type and fracture patterns was reported descriptively. The mean values of the groups were analyzed by using the Shapiro-Wilk test and 1-way ANOVA tests (α=.05). RESULTS: Restoration with PRF+SFRC provided the highest mean ±standard deviation fracture resistance (288.2 ±73.5 N). Restoration with just PRF had the lowest values (192.4 ±25.4 N), which were statistically different from those of SFRC and PRF+SFRC (P<.05). The predominant mode of failure was mixed, and all fracture patterns were favorable. CONCLUSIONS: Reinforcing endodontically treated premolars with MOD cavities with Ribbond fibers followed by a conventional composite resin enhanced fracture resistance and may be suitable for the direct coronal restoration of large posterior cavities in stress-bearing areas.

Knowledge about COVID-19 and perception of health safety among mexican dental students / Conocimiento sobre COVID-19 y percepción de seguridad en la salud de estudiantes mexicanos de odontología

This study aimed: 1) to investigate sources of information used by students to learn about COVID-19, 2) to investigate levels of knowledge about COVID-19 and about conditions for the treatment of patients during the COVID-19 lockdown, and 3) to evaluate students' perceptions of safety regarding their return to in-person activities at the School of Dentistry. Dental students answered a questionnaire (29 items; n=371) that explored the aims of the study, based on a Likert scale (Cronbach's alpha, 0.778). Data were tested with the Mann-Whitney U test and Kendall's Tau-c. Dental students received information about COVID-19 from the Mexican Health Ministry as their first source (45.28%). Students had good knowledge about the main characteristics of COVID-19, and 59.3% of students had excellent knowledge about the factors relevant to dental treatment of patients. Half of the students said they felt safe regarding a possible return to in-person activities at the dental school, while the other half did not. Statistically significant differences were noted between the students' scholar year and their level of knowledge (P<0.001) and between their perception of safety (very unsafe, unsafe, safe, and very safe) and scholar year (P=0.000). Dental students had good knowledge about COVID-19 and about the dental care for patients during the lockdown. Half of the dental students felt unsafe about a possible return to in-person school activities.

Los objetivos del estudio fueron 1) investigar que fuentes de información usaron los participantes para conocer sobre la COVID-19, 2) evaluar cuál es el nivel de conocimiento que tienen sobre COVID-19 y la atención a pacientes durante la contingencia, y 3) evaluar la percepción de seguridad sobre el regreso a actividades presenciales en la facultad. Estudio transversal. Se aplicó un cuestionario en línea (29 ítems; n=371) que exploró cada objetivo e incluyó una escala de Likert (Alfa de Cronbach de 0.778). Los datos fueron analizados con las pruebas de U de Mann Whitney y con Tau-c de Kendall. La mayoría de los participantes obtuvieron información sobre la COVID-19 a través de la Secretaría de Salud (45.28%), tuvieron un conocimiento bueno sobre las generalidades de la COVID-19 y el 59.3% tuvo un conocimiento excelente sobre la atención a pacientes. La mitad de los encuestados tuvo una percepción de inseguridad en un posible regreso a actividades en la facultad. Hubo diferencia estadística significativa para la asociación entre año escolar y grado de conocimiento (p<0.001) y entre la percepción en la seguridad en el regreso a actividades (muy inseguro, inseguro, seguro y muy seguro) y el grado escolar (P=0.000). Los participantes tuvieron buen conocimiento sobre las generalidades de la COVID-19 y sobre la atención a pacientes en situación de contingencia. La mitad de los EO sienten inseguridad sobre un posible regreso a actividades.

Learning of the mental nerve block technique with dental anaesthesia simulation models builds motor skills and confidence in dental students.

INTRODUCTION: We compared the motor learning, self-confidence whilst performing an anaesthesia technique and the perception of confidence between a group of students trained (G1) with two distinct dental anaesthesia simulation models (DASM) and a group of students (G2) not trained with DASM. MATERIALS AND METHODS: The G1 students (n = 22) were trained with a learning protocol including a DASM for simulating a puncture and a DASM for simulating an injection of dental anaesthesia. The G2 students (n = 22) received no such training. Both groups performed the mental nerve block (MNB) in a clinical setting, after which the average working time (motor learning), number of times help was requested for performing the MNB (self-confidence) and the scores of a Likert Scale questionnaire (perception of confidence) between the groups were compared with a t test. RESULTS: Compared with G2, the G1 students showed a shorter average working time (G1, 7:30 ± 0:54 min; G2, 9:06 ± 2:27 min; P = .017). Hence, G1 students had better motor skills. They also requested help when performing the MNB fewer times than the G2 students (G1, 2.2 ± 0.5 times; G2, 4.6 ± 1.95 times; P < .001). On the other hand, the G1 students demonstrated better perception of confidence (Likert Scale questionnaire) when performing the MNB compared with the G2 students (P = .007). CONCLUSION: The learning protocol with two different DASMs had a positive effect on the motor skills and the confidence of dental students performing the mental nerve block.

Impact of Two Distinct Dental Anesthesia Simulation Models on the Perception of Learning by Students / Impacto de dos distintos modelos de simulación para anestesia dental en la percepción del aprendizaje en estudiantes

ABSTRACT We evaluated an infiltration anesthesia simulation model (IAM) and a conduction anesthesia simulation model (CAM) on the perception of learning by Mexican dental students. Our aim was to compare the perception of learning by dental students trained with two distinct dental anesthesia simulation model (DASM) with dental students who were not trained with a DASM. 3 groups participated in the study: G1 (N=12 students) learned to block the mental nerve (BMN) by participating in a theoretical lecture (stage 1) and a clinical demonstration (stage 2); G2 (N=12 students) learned the BMN by participating in the stage 1, stage 2, and training with the CAM; G3 (N=12 students) learned the BMN by participating in the stage 1, stage 2, and training with the IAM. The groups performed the BMN in a clinical exercise. Working-time of all participants was timed. Perception of learning for all participants was evaluated with a 5-point Likert Scale. The results showed that statistically significant differences were found between score of G1 and score of G2 and score of G3 (P<0.05). No statistically significant differences were found between scores of G2 and scores of G3. G1, G2 and G3 showed an average working-time of 12:42 minutes, 9.75 minutes and 8:03 minutes, respectively (P<0.05). We concluded that the IAM and CAM showed a positive impact on the perception of learning, and the students trained with the IAM showed a shorter working time compared with the students trained with the CAM.

RESUMEN En este estudio se evaluó el impacto de un modelo de simulación de anestesia dental por infiltración (IAM) y de un modelo de simulación de anestesia dental por bloqueo (CAM) en la percepción del aprendizaje en estudiantes mexicanos en estomatología. El objetivo fue comparar la percepción en el aprendizaje de estudiantes que entrenaron empleando dos distintos modelos de simulación de anestesia dental con estudiantes que no recibieron entrenamiento empleando algún modelo de simulación de anestesia dental. Participaron 3 grupos en el estudio: G1 (n=12) aprendieron el bloqueo del nervio mentoniano (BNM) al participar en una clase teórica (sesión 1) y en una demostración clínica (sesión 2); G2 (n=12) aprendieron la técnica de anestesia del BNM al participar en la sesión 1, sesión 2 y entrenando con el CAM; G3 (n=12) aprendieron la técnica del BNM al participar en la sesión 1, sesión 2 y entrenando con el IAM. Los grupos aplicaron la técnica del BNM en un ejercicio clínico. Se midió el tiempo de trabajo de los participantes. La percepción del aprendizaje de los participantes se evaluó con una Escala de Likert de 5 ítems. Los resultados mostraron diferencias estadísticamente significativas entre los valores del G2 y del G3 en comparación con el G1. No se encontraron diferencias estadísticas entre los valores del G2 y del G3. El tiempo de trabajo para el G1, G2 y G3 fue respectivamente de: 12:42 minutos, 9.75 minutos y 8:03 minutos, (P<0.05). Se concluyó que el IAM y el CAM mostraron un impacto positivo en la percepción del aprendizaje; los estudiantes entrenados con el IAM mostraron un tiempo de trabajo más corto en comparación con los estudiantes entrenados con el CAM.