Polymerization shrinkage and spherical glass mega fillers: effects on cuspal deflection

Influence of internal angle and shape of the lining on residual stress of Class II molar restorations

Polymerization shrinkage is a major side effect of resin composite materials that affects the success and longevity of caries restorations. This study was to analyze the effect of the internal angle and shape of the lining on the shrinkage residual stress of dental restorations in Class II mesio-occlusal-distal (MOD) cavities through finite element analysis (FEA). A 3D reconstructed model of a human mandibular first molar was created from micro-CT images, and then the tooth was prepared as a Class II MOD cavity. 3D models of four regular internal corner shapes of Class II MOD cavities with different internal angles of lining and one 90° filleted corner model were created. The thermal expansion technique was applied to approximate the shrinkage impact of composite resin polymerization in the FE software ABAQUS. Von Mises stress was taken as a metric. The results showed that the level of residual stresses in the Class II MOD cavities was greatly dependent on the internal angle of the lining. The maximum von Mises stress in tooth tissue decreased as the internal angle of the lining increased. The internal shapes of the lining had no obvious effect on the stress, and the filleted corner model had less stress. This lining strategy is appropriate for Class II MOD cavities with serious loss of tooth tissue.

Change in the Shrinkage Forces of Composite Resins According to Controlled Deflection

The aim of this study was to investigate how the polymerization shrinkage forces of composite resins change with change in deflection. Five composites, SDR (Dentsply Caulk, Milford, DE, USA), EcuSphere-Shape (DMG, Hamburg, Germany), Tetric N-Ceram Bulk Fill (Ivoclar Vivadent, Schaan, Liechtenstein), CLEARFIL AP-X (Kuraray Noritake Dental Inc., Sakazu, Kurashiki, Okayama, Japan), and Filtek Z350 XT (3M Dental Products, St Paul, MN, USA), were tested in this experiment. The polymerization shrinkage forces of the composites were measured using a custom-made tooth-deflection-mimicking device and software (R&B Inc, Daejon, Korea). In all measurements, six modes were tested: maximum-deflection, zero-deflection, and four deflection-controlled modes. For each deflection mode, the shrinkage forces were recorded continuously every 0.1 second for 180 seconds. Polymerization shrinkage and flexural modulus were also measured. Eight specimens of each material were allocated for each test. For each material, six groups of shrinkage force values were compared using one-way ANOVA and Tukey post hoc tests at a 95% confidence level. The polymerization shrinkage force of each material in each of the six deflection modes was analyzed with 95% confidence using one-way ANOVA and Tukey post hoc tests. The relationship between the force measured in the six deflection modes and the linear polymerization shrinkage and flexural modulus was analysed with 95% confidence using Pearson correlation analysis. For each material, the following held true: the shrinkage force was highest in zero-deflection mode, the force decreased as deflection increased, and the smallest force appeared in maximum-deflection mode (p<0.05). There was a high negative correlation between allowable deflection and shrinkage force in all materials.

A new spiral dental implant: a tool for oral rehabilitation of difficult cases

Spiral dental implant (SDI) is an implant with a conical internal helix that confers the characteristic of self-drilling, self-tapping, and self-bone condensing. These proprieties offer better control during insertion of SDI giving a high primary stabilization, even in poor quality bone. A shorter diameter of SDI results in reduced drilling during insertion and consequently less trauma and minimal bone loss. To address the research purpose, the investigators designed a retrospective cohort study. The study population was composed of 25 patients, 11 males and 14 females that have been treated by Dr. Balan with 187 SDI positioned in mandible and into maxilla bone. The implants were placed during the years 2013 to 2014 in Dr. Balan clinic. All patients underwent the same surgical protocol. Several variables are investigated: demographic (age and gender), anatomic (upper/lower jaws and tooth site), implant (length and diameter and type) variables, edentulism (partial or total), and comorbid status of health (i.e.: hypothyroidism, parodontitis, hypertension, diabetes, presence of cancer, heart disease, hepatitis and rheumatologic disease). Pearson Chi-Square test was used to investigate variables and p < 0.05 was considered statistically significant. Statistically it has been shown that females have a higher possibility of unsuccessful respect of male, with a "p value" of 0.014. Another important impact factor for success of implant insertion has been represented by concomitants pathologies: cancer represents the most negative high factor risk with a percentage of unsuccessful of 50%, followed by heart disease (15%), and diabetes (3.7%). SDIs are reliable tools for difficult cases of oral rehabilitation. They have a higher success and survival rate, which means stable results over time. No differences were detected among SDI lengths, implant/crown ratio. In addition, the insertion of SDIs in banked bone can be performed without adverse effects. Finally, flapless and computer tomography-planned surgery does not significantly increase the clinical outcome of SDIs in complex rehabilitation. Cancer represents the most important variable to consider when a patient wants to do oral rehabilitation because of its high risk of unsuccessful.

Risk assessment of colonization of legionella spp. in dental unit waterlines

The aerosol produced during the use of dental instruments can spread pathogens potentially harmful to health. Most of the pathogens found in hydraulic system are Gram-negative aerobic heterotrophic environmental bacterial species exhibiting very low pathogenicity, although they may be of concern in the treatment of vulnerable patients, such as immunocompromised, medically compromised individuals and dental team. Dental team can be exposed to pathogenic microorganisms including cytomegalovirus, hepatitis B virus, hepatitis C virus, herpes simplex virus and Legionella spp. Legionella spp. are ubiquitous in hydraulic system, in fact surveys have shown that the percentage of samples taken at different dental chairs that were positive for Legionella spp. and ranged from 0 to 100%. The concentration of Legionella spp. in hydraulic system may reach 1000 organisms per ml. The primary route of Legionella spp. transmission is inhalation or aspiration of environmentally contaminated aerosols. All dentists are required to conduct a statutory risk assessment of their hydraulic system, in fact to comply with their legal duties, dentists must identify and assess the sources of risk and prepare a scheme for preventing and controlling risks. Moreover, they must monitor the quality of their hydraulic system at least annually to ensure that they are "legionellae free".