Nikolaos Poulis

In the present study, an aero pneumatic fatigue testing machine for complete dentures was designed, fabricated, and tested for the evaluation of the fatigue life of reinforced complete upper denture (CUD). On completion and testing, it was observed that the machine has the potential of generating reliable number of cyclic data. The machine’s performance was evaluated using test specimens of identical CUDs that were machined in conformity with standard procedures. The fatigue machine compressed the lower dental arch over the upper denture-specimen in centric occlusion, in the same way that the two masticatory muscles pull the lower jaw over the upper jaw during chewing. The incorporation of glass fibres into the CUD using a sandwich technique quadruples the lifespan of the denture (P = 0.004). The low standard deviation, along with the low coefficient of variation (CV) of the group of unreinforced dentures shows the repeatability of the results and the reliability of the machine. The high standard deviation and coefficient of variation of reinforced dentures was expected, since a high variation of results is usually recorded in fibre reinforcement cases. This research confirmed the view that the crack during denture fracture initiates in the anterior palatal area and propagates to the posterior.

This paper focuses on introducing a new biomechanical method for estimating the fracture strength of complete upper dentures (CUDs) and evaluating which notch mode has the greatest impact on their strength reduction. Forty identical CUDs were constructed according to a previously applied methodology, and it was divided into four groups of ten specimens. This is dependent on the location and size of the notches in the labial region of the denture. The upper grip of a universal testing machine was replaced by a newly designed and constructed loading element for simulating the intraoral denture loading conditions. The fracture load and the deflection at fracture were measured, while the fracture energy was calculated (product of the load to the deflection) under compression. The measurement of fracture energy through the present novel method leads to more precise outcomes. The highest impact on the reduction of CUDs strength was for the combination group 4 with both the midline (incisal) diastema and deepened labial fraenal notch. Nevertheless, it gradually reduced for group 2 with midline (incisal) diastema, group 3 with deep labial fraenal notch, and group 1 with initial-shallow labial fraenal notch (P<0.001). The conditions for groups 2 and 4 strongly require reinforcement of the denture bases.

In recent years, a gradual transition from passive teaching to active learning has intensified in higher education. Critical thinking and deep learning is promoted, as opposed to surface learning. The Teaching Excellence Framework guidance for higher education associates learning with research, thus research skills acquisition is fundamental. An innovative collaborative research project, leading to individually composed assignments, was implemented in a research methodology module, aiming at developing an undergraduate research skill set and writing performance. The results were satisfactory showing positive student response to the newly implemented approach. Critical thinking, deep learning, autonomy, peer-support and collaboration are mostly what the undergraduate students can benefited from, through this innovative learning approach.

Introduction: Surface integrity of dental elastomeric impression materials that are subjected to disinfection is of major importance for the quality of the final prosthetic restorations.
Aim: The aim of this qualitative Scanning Electronic Microscopy (SEM) study was to reveal the effects of immersion or ozone disinfection on the surface of four dental elastomeric impression materials.
Materials and Methods: Four dental elastomeric impression material brands were used (two vinyl polysiloxane silicones, one polyether, and one vinyl polyether silicone). Total of 32 specimens were fabricated, eight from each impression material. Specimens were immersion (0.525% sodium hypochlorite solution or 0.3% benzalkonium chloride solution) or ozone disinfected or served as controls and examined with SEM.
Results: Surface degradation was observed on several specimens disinfected with 0.525% sodium hypochlorite solution.
Similar wavy-wrinkling surface structures were observed in almost all specimens, when treated either with 0.3% benzalkonium chloride solution or ozone.
Conclusion: The SEM images obtained from this study revealed that both immersion disinfectants and ozone show similar impression material surface alterations. Ozone seems to be non inferior as compared to immersion disinfectants, but superior as to environmental protection

Aims: To examine the effectiveness of low-flow high-ozone concentration disinfection of dental impressions, by means of an automated prototype device.
Methodology: Disc shaped dental addition-cured silicone was inoculated with Klebsiella pneumoniae and Staphylococcus aureus, 10 mm discs were removed and ozone disinfected for different time intervals, immersion disinfected or served as controls.
Disinfection success was examined by using the viable plate count method, while the statistical analysis was conducted via one way-ANOVA (p < 0.05). Results: Significant eradication was observed for selected Gram (+) and Gram (-) bacteria after 3 minutes of ozone exposure, leading to complete disinfection of the samples.
Conclusion: While immersion disinfection of dental impressions is currently the most widely accepted method of disinfecting dental impressions, low-flow high-ozone concentration disinfection provides a quick, efficient, fully automated alternative method, limiting liquid waste generation. Possible alterations of the materials’ physical and chemical properties, like those of immersion disinfection, are not included in the present manuscript. A precise automated method for impression disinfection is established, relieving the dental team of possible cross-contamination.

The aim of this research is to clarify whether the midline axis of the complete upper denture (CUD) is the axis of its torsion during loading, apart from the known bending deflection. Furthermore the present study is intended to estimate the influence of the anterior notches on the torsional deformation of the CUD. Using commercial edentulous molds and standardized procedures, six identical CUDs were fabricated with an initial fraenal notch of 5 mm. Two additional notch conditions were produced by deepening the notch to a total depth of 9 mm and by creating an incisal diastema of 7 mm. Five biaxial (also known as “fish bone”) strain gauges were cemented onto the palatal section of the dentures so that their middle axis coincided with the midline axis of the outer surface of the denture. For the denture specimen used in this study, the specific point of torsion was detected 2 cm from the point of contact of the two artificial central incisors. The presence of a deep fraenal notch and the combination of the deep fraenal notch with the presence of an incisal diastema increased the torsion of the CUD to a significant level (P = 0.006 and P = 0.05, respectively). It was shown that the midline can be the CUD’s axis of torsion. Biaxial strain gauges could be a reliable method of measuring the torsional deformation of the CUD.

The present study determines the stress field in the region of the labial flange of the complete upper denture (CUD).
Using commercial edentulous molds and standardized procedures eight identical CUDs were fabricated with an initial fraenal notch of 5 mm. Three addition notch conditions were produced by deepening the notch two times giving a total depth of the notch of 7 and 9 mm respectively. Finally an incisal diastema of 7 mm was created in every CUD.
Three elements rosette strain gauge was cemented onto the midline of each denture specimen near the fraenal notch, for calculating the two principal stresses and the maximum shear stress.
It is less possible that a failure crack in a CUD will be initiated from the region of the fraenal notch, due to the compressive nature of the principal stresses (they are varied significantly among the four notch conditions with P = 0.035 for σ1 and P = 0.007 for σ2) and the low value of the maximum shear stress. The creation of an incisal diastema significantly decreased the values of the principal stresses σ1 (P = 0.012) and σ2 (P = 0.025). Further investigation is needed to detect the region of the CUD where a failure crack may be initiated.