Larisa Blažić

Technical Quality of Root Fillings Performed by Undergraduate Students: A Radiographic Study

Aim. The aim of this study was to evaluate the radiographic technical quality of endodontic treatment performed by undergraduate students at the School of Dentistry, Faculty of Medicine, University of Novi Sad, Serbia. Materials and Methods. Electronic records of 220 patients treated by final-year undergraduate students during the school year 2011/2012 were examined, and the final sample consisted of 212 patients, 322 teeth, and 565 root canals. The criteria for overall radiographic adequacy of root canal fillings were defined as the presence of adequate length and density and absence of iatrogenic errors (ledge, fractured instrument, untreated canal, and apical transportation). Chi-square test was used to determine statistical significance between different parameters. Results. Adequate root canal fillings were found in 74.22% of the teeth. The percentage of root fillings with adequate length and density was 89.73% and 92.6%, respectively. Fractured instruments and ledges were present in 16 root canals (2.8%), while the presence of missed canal and apical transportation was observed in 2 cases, each (0.3%). Conclusions. Overall, the technical quality of root canal fillings performed by undergraduate students was satisfactory.

Computed-tomography scan-based finite element analysis of stress distribution in premolars restored with composite resin

Mechanical properties of restorative material have an effect on stress distribution in the tooth structure and the restorative material during mastication. The aim of this study was to investigate the influence of restorative materials with different moduli of elasticity on stress distribution in the three-dimensional (3D) solid tooth model. Computed tomography scan data of human maxillary second premolars were used for 3D solid model generation. Four composite resins with a modulus of elasticity of 6700, 9500, 14 100 and 21 000 MPa were considered to simulate four different clinical direct restoration types. Each model was subjected to a resulting force of 200 N directed to the occlusal surface, and stress distribution and maximal von Mises stresses were calculated using finite-element analysis. We found that the von Mises stress values and stress distribution in tooth structures did not vary considerably with changing the modulus of elasticity of restorative material.

Influence of the artificial saliva storage on 3-D surface texture characteristics of contemporary dental nanocomposites

The aim of this study was to analyse the influence of the artificial saliva on a three‐dimensional (3‐D) surface texture of contemporary dental composites. The representatives of four composites types were tested: nanofilled (Filtek Ultimate Body, FUB), nanohybrid (Filtek Z550, FZ550), microfilled (Gradia Direct, GD) and microhybrid (Filtek Z250, FZ250). The specimens were polymerised and polished by the multistep protocol (SuperSnap, Shofu). Their surface was examined, before and after 3 weeks’ exposure to artificial saliva storage. The surface texture was analysed using the atomic force microscope (AFM). The obtained images were processed to calculate the areal autocorrelation function (AACF), anisotropy ratio Str (texture aspect ratio), and structure function (SF). The log–log plots of SF were used to calculate fractal properties, such as fractal dimension D, and pseudo‐topothesy K. The analysis showed changes in surface anisotropy ratio Str values, which became higher, whereas the Sq roughness (root‐mean‐square) reduced after the artificial saliva storage. All the samples exhibited bifractal structure before the saliva treatment, but only half of them remained bifractal afterwards (GD, FZ250), whereas the other half turned into a monofractal (FUB, FZ550). The cube‐count fractal dimension Dcc was found to be material‐ and treatment‐insensitive.

Holographic Measurement of a Tooth Model and Dental Composite Contraction

We have developed a real-time holographic technique to observe deformation induced by dental composite contraction. The standard split beam method was used, in conjunction with in situ holographic plate processing. Experiments were performed on a mechanical model of a human tooth with cavity. A silicone mold was used to manufacture a number of identical casts, using photoactivated composite. A LED lamp was used to induce photo-polymerization reaction in a composite. We have shown that the proposed method is ideal to analyze various polymerization strategies, with the purpose of recommending one which minimizes the polymerization contraction.

Influence of restorative procedures on endodontically treated premolars: Finite element analysis of a CT-scan based three-dimensional model

An endodontically treated tooth with mesial-occlusal-distal (MOD) cavity is often restored with composite resin. Palatal and buccal cusp reduction (MODP, MODPB), and/or fiber-reinforced composite posts (P), are used in an attempt to improve the longevity of the restoration. The aim of this study was to determine the effects of these procedures on von Mises stress values and distribution in dental tissues and restorative materials using finite element analysis. Based on CT scans of an extracted second upper premolar, six 3D endodontically treated tooth models (MOD, MODP, MODPB, MOD+P, MODP+P, MODPB+P) were created. Each model was subjected to a summary force of 150 N on the occlusal surface simulating the normal biting pattern and maximal von Mises stresses were calculated. MODP seems to reduce von Mises stress values in dental tissues and P seems to transfer some of the stresses from dental tissues to the composite filling.

Biomechanical model produced from light-activated dental composite resins: a holographic analysis

Light-activated dental composites, commonly applied in dentistry, can be used as excellent material for producing biomechanical models. They can be cast in almost any shape in an appropriate silicone mold and quickly solidified by irradiation with light in the blue part of the spectrum. In that way, it is possible to obtain any number of nearly identical casts. The models can be used to study the behavior of arbitrary structure under mechanical loads. To test the technique, a simple mechanical model of the tooth with a mesio–occluso–distal cavity was manufactured. Composite resin restoration was placed inside the cavity and light cured. Real-time holographic interferometry was used to analyze the contraction of the composite resin and its effect on the surrounding material. The results obtained in the holographic experiment were in good agreement with those obtained using the finite element method.