Dental Hypotheses
Volume:11 Issue: 4, Oct-Dec 2020

Evaluation of the marginal adaptation of root-end filling materials to root canal walls provides invaluable information on their sealing ability. Different materials, such as Mineral Trioxide Aggregate (MTA), have been used for root-end fillings. Recently, elements such as RetroMTA or Biodentine have been introduced to overcome the drawbacks of MTA. This research was carried out to evaluate the marginal adaptation of root-end filling materials, RetroMTA, Biodentine, and ProRoot MTA, using an experimental method.

In this experimental research, 45 single-rooted teeth were prepared and obturated; then, 3 mm of the apical third of the roots were resected, and root-end cavities were prepared using a standard ultrasonic method. The teeth were randomly divided into three groups and filled with RetroMTA, Biodentine, and ProRoot MTA. After a week, epoxy resin replicas of the root-ended surfaces were provided after a longitudinal section. The size of gaps between the filling material and the canal walls were measured with SEM at longitudinal and transverse sections at eight points and compared between the three filling materials using one-way ANOVA.

The mean gaps between the filling material and canal wall in Biodentine, Retro-MTA, and MTA ProRoot groups in longitudinal sections were rated at 4.49mm, 8.55mm, and 14.34mm, respectively (P=0.007). However, no significant differences were identified between the three filling materials in transverse sections.

The best marginal adaption in longitudinal sections were identified in Biodentine, RetroMTA, and MTA ProRoot, respectively. However, in transverse sections, there were no significant differences between the three materials.

The aim of this study was to test and find connection between three different parameters of acrylic resins: cytotoxicity, residual monomer content in the material and flexural strength.

Superacryl Plus (SpofaDental, Czech Rep.) acrylic material has been polymerized in three different ways, short-time polymerization (45 minutes), normal time (90 minutes) and long-time (7 hours 30 minutes). Flexural strength was tested in compressive instrument Shimadzu for 65 × 10 × 3.3 mm samples. Then after 24 hours the samples were broken. In 50 mm diameter and 1 mm thick samples, residual monomer was determined by gas chromatography (according to ISO standard), and the last series of the sample was used to perform cytotoxicity tests (5 mm diameter). Statistical analysis: Data were analyzed by two-way ANOVA (in GraphPad Software Inc., San Diego, CA, USA), with p-value < 0.05 as statistically significant.

The results from the tests show that the greatest inhibition in the development of cell cultures (VERO CCL-81) by MTT assay), was observed for the sample polymerized in the first short-time method (73.49±10%). The material also had the largest content of residual monomer 2.02±0.08% (p-value < 0.01) and lowest flexural strength 71.53±2.26 MPa. Hardened acrylic resins over 60 minutes do not adversely affect cell cultures (undisturbed growth 83.18±10.72%). The residual monomer content was below 1% (p-value < 0.01) and the mechanical resistance to fracture was over 80 MPa (p-value < 0.01).

The use of a short polymerization method of acrylic materials can adversely affect both the mechanical properties of the prosthesis itself and its biocompatibility. From a clinical point of view, it is important to take care about the polymerization times of acrylic. Dentures for allergic patients should be carried out in long-term polymerization when the content of residual monomer is as low as possible.

Composite resins have developed in past years, however, failures may occur which needs whole restoration repairing. this study aimed to evaluate the effect of different surface treatments on shear bond strength of new to old composite restorations.

A total of 60 blocks of Z250 composite resin were divided to four groups 1) no surface preparation (control group), 2) abrasion through aerosols using 50-micron aluminum oxide particles, 3) abrasion through diamond milling with 125-micrometer particles, 4) surface preparation using hydrofluoric acid. Shear bond strength in different methods such as etching with hydrofluoric acids (with and without silanization), air abrasion, and diamond milling was compared with the control group. All data were analyzed using the Kolmogorov-Smirnov test and one-way analyses of variance (ANOVA) and Tukey’s post hoc test.

In comparing the groups with each other, it was found that shear bond strength in Hydrofluoric acid and silanization group was significantly higher than control (P=0.017).

The effects of etching with hydrofluoric acid and silanization in increasing shear bond strength between aged and new composite resins are superior to control, which could be a suitable repair protocol to obtain optimal repair bond strength.

The aim of this in vitro study was to evaluate the effect of modification of the attachment on stress transmitted to the abutment tooth and residual ridges in lower unilateral distal extension partial dentures.

An acrylic lower unilateral distal extension cast with the first premolar as the main abutment was constructed. Three types of commonly used extracoronal castable attachments were selected, namely: (1) Preci-vertix standard, CEKA attachment, (2) Preci-sagix mini size, CEKA attachment, (3) OT–cap normal, Rhein 83. They underwent a simple new modification and their effect on stress distribution was studied. Six attachment retained removable partial dentures were constructed: among them, three with nonmodified attachments, and three with modified attachments. Four strain gauges were installed on the acrylic cast to measure the microstrain induced around the abutment tooth and residual ridges. A unilateral static vertical load of 300 Newton was applied on the first premolar and the first molar at a crosshead speed of 2 mm/min and microstrain was recorded using specific miniature Universal Testing Machine. Data were collected and analyzed using the Wilcoxon test for comparison between attachments before and after modification.

The highest microstrain was recorded for modified OT cap and modified Preci-sagix attachment around the abutment tooth and residual ridges respectively. While modified PV attachment showed the lowest microstrain around abutment and residual ridges.

Maximum strain induced around the tooth and residual ridges in cases of OT cap and Preci-sagix attachments. Among all attachments, the use of Preci-vertix showed better stress distribution around both abutment and residual ridges

In the present scenario, the pandemic of coronavirus disease 2019 (COVID-19), which is responsible for simple upper respiratory infection to fatal pneumonia and multi-organ failure has become a major public health challenge and a public health emergency of international concern. Apart from secondary and tertiary care, it is very much essential to provide primary care, prevention, and early detection. To prevent the virus from the human-human transmission and to control the situation, the protocols vary at various setups. Due to the uniqueness of dental settings and practice, the risk of cross-infection can be high between patients and dental practitioners. Establishment of strict and effective infection control protocol is necessary owing to the varying sustainability of the virus on different surfaces. The area of concern for a dental professional is the oral cavity and upper respiratory region where the host recipient cell receptor, angiotensin-converting enzyme receptor 2, is present abundantly acts as the host cell entry route for the coronavirus. Dental professionals play an important role in preventing the transmission of SARS-CoV-2; we aim to review the infection control measures in dental practice.

School shutdowns in the United States due to Covid-19 forced many dental schools who rely on in-person learning to search for alternatives that maintain the quality of their institution’s education. Two online alternatives include the remote learning model, which aims to replicate the live classroom experience, and prerecorded learning that provides the course material in a lump sum for students to review at their own pace. Administering didactic learning in an online format contains challenges such as technological limitations and disparities between studenthome environments. Overcoming these obstacles and successfully replicating the live classroom experience relies on the preservation of student-teacher engagement to assess student comprehension. Moving forward, dental schools should consider opting to maintain aspects of online alternatives to allow students to allocate more or less time to tasks based on individual needs versus continuing the standardized lecture blocks used with in-person classroom learning.