Ivan Tanasic

Compressive strains and displacement in a partially dentate lower jaw rehabilitated with two different treatment modalities

BACKGROUND Understanding of the biomechanical consequences of the stresses generated to the supporting bone during occlusal loading is significant for improving the design and clinical planning process in partial edentulism therapy. OBJECTIVE   The aim of this study was to analyse the distribution of strain and displacement on the partially dentate lower jaw rehabilitated with an partial denture (RPD) and to compare it to the strain and displacement distribution on a partially dentate lower jaw rehabilitated with a cantilever fixed partial denture (FPD). MATERIAL AND METHODS The experimental models were a partially dentate mandible with full-arch PFM crowns and RPD and a partially dentate mandible rehabilitated with a full-arch cantilever FPD. Strains and displacement were measured using the Digital Image Correlation Method. RESULTS Displacement values of the first experimental model ranged from 0.31 to 0.54 mm with strains from 1.35 to 2.34%. Analysis of the second experimental model results showed displacement values from 0 to 0.34 mm, while strains were in the range of 0-1.40%. CONCLUSION Higher displacements and strains of bone tissue were observed below the RPD, especially in the region of the distal abutment and distal portion of the free-end saddle. Strains within bone and the bone-denture contact area were mostly influenced by the teeth and denture vertical displacement.

Analysis of the compressive strain below the removable and fixed prosthesis in the posterior mandible using a digital image correlation method

It was the purpose of this study to determine and analyse strains in the bone of posterior mandible below the removable and fixed partial dentures using Digital Image Correlation Method. Dried mandible with shortened dental arch (Kennedy Class 1) was used in the experiment. The mandible model was prepared for accepting two types of restorations for bilaterally missing molars conventional therapy, and removable and fixed partial dentures were manufactured following standard prosthetic protocol. The models with prosthetic restorations placed in situ were subjected to loading of 50–300 N, and photographed using two digital cameras as part of the digital image correlation method equipment. Afterwards, the obtained data for strains within restored mandible during loading ciclus were analysed in the software Aramis and graphically presented. Percentage size of the mandible strains within the line section are from 0.14 to 0.19% for the removable partial denture experimental model and 0–0.14% for the fixed partial denture experimental model. The study has demonstrated that Digital Image Correlation method can be used to measure strain on the mandible surface and replacements during loading and that from biomechanical perspective both therapeutic modalities can be equally useful for the restoration of the mandible with bilaterally distal edentulous spaces.

Prevalence and Clinical Effects of Certain Therapy Concepts among Partially Edentulous Serbian Elderly.

PURPOSE This study was conducted to identify the prevalence of partially edentulous individuals in Serbia and to identify prosthodontic treatment used for their rehabilitation as well as to compare prosthodontic treatment concepts among Serbian elderly participants who answered closed-format questionnaires. MATERIALS AND METHODS The study was conducted at the Clinic for Dental Prosthetics, University of Belgrade, Military Medical Academy and the Department of Prosthodontics of Home Centre Belgrade; the study consisted of 120 participants. A questionnaire with closed-format questions regarding the influence of applied therapy concepts for participants with Kennedy Class I partial edentulism was created. Statistical software SPSS 11.5 was used for data analysis. Chi-square tests were performed, and p-values were calculated for each parameter. RESULTS A total of 1081 people were examined; 730 participants were partially edentulous in at least one jaw. Five hundred forty-one participants wore Kennedy Class I maxillary or mandibular removable partial dentures (RPDs). Ninety percent of the patients were restored with RPDs; 60% of participants were unrestored, had shortened dental arches, and requested alternative therapeutic solutions. Significantly lower needs for new treatments were identified in participants with fixed dental prostheses (7.5%). CONCLUSIONS Kennedy Class I was the most common type of partial edentulism among Serbian elderly, usually treated with RPDs. Elderly participants with the applied shortened dental arch and RPD therapy concepts requested alternative therapeutic solutions more often than those rehabilitated with fixed partial dentures.

Association Between Dentition Status and Malnutrition Risk in Serbian Elders.

PURPOSE The aim of this study was to find the correlation between the number, type, and placement of symmetric functional tooth units and the nutritional status using body mass index (BMI) and Mini Nutritional Assessment (MNA) in patients with both maxillary and mandibular removable partial dentures. MATERIALS AND METHODS A randomized study was conducted at the Clinic for Prosthodontics, School of Dentistry, University of Belgrade, Serbia, followed by determination of number of functional tooth units. After insertion of the prostheses, the nutritional status was assessed, using BMI and MNA form. Nutritional status was reviewed 12 months after prosthetic treatment. Number of teeth and age were analyzed using analysis of variance and t test. For other variables such as BMI baseline, BMI follow-up, MNA baseline, MNA follow-up, change in BMI, and change in MNA, Kruskal-Wallis Test or Mann-Whitney Test were used. RESULTS The results on the MNA changes showed that patients with symmetric natural functional tooth units had significantly higher values (2.9 ± 0.8) compared with patients without natural functional tooth units (1.9 ± 0.6) or with asymmetric natural functional tooth units (1.6 ± 0.4). Patients with asymmetric artificial functional tooth units had significantly lower change in MNA (1.9 ± 0.4) than those with symmetric artificial functional tooth units (2.6 ± 0.9). CONCLUSION The findings of this study suggest that adequate rehabilitation with symmetric positioning of the functional tooth units can improve the nutritional status of partially edentulous patients.

Digital Image Correlation Analysis of Vertically Loaded Cylindrical Ti-Implants With Straight and Angled Abutments

The purpose of this study was to investigate the influence of the abutment angulation upon the strain distribution pattern for the vertical loading situation by means of the digital image correlation (DIC) method. In addition, to find the correlation between acrylic-layer thickness around implant body and surfaces strain induced by vertical loads. Two types of samples consisted of the Straumann® cylindrical dental implant system (4 × 10mm) with the SLActive® surface and the poly-methyl-methacrylate were used in this study. For strain analysis, the DIC system was used, manufacturer GOM. The optical deformation measurement system consists of special set of stereo cameras and lenses, and ARAMIS software (6.2.0, Braunschweig, Germany). Maximum von Mises strain was 0.30% in the sample with the straight abutment and 0.50% in the sample with the angled abutment. Minimum strain measured by Aramis was 0.01%, detected in the 6mm surface layer of the sample with straight abutment. According to results obtained by Aramis data processing, the 4mm surface layer indicated greater overall strain in apical direction with the strains of 0.18–0.50%, depending on the force intensity. Higher strain was noticed in the thinner surface layers. The angulated abutment induced higher strain in both surface layers than the straight abutment did.

Investigation of dental biomaterials under load using a digital image correlation system

The digital image correlation method was used in this study to investigate heat polymerizable acrylic resin, which is the material of choice for prosthesis in edentulous patients. The aim was to analyze and determine the force-induced displacement and strain of a complete denture in the physiological force field of edentulous patients. An acrylic lower complete denture was made for the edentulous mandible, placed on the residual ridge of the macerated mandible bone, lacquered with spray, and exposed to a force of 300 N. The Digital Image Correlation system (DIC) (GOM, Braunschweig, Germany) was used to measure the strain in the complete denture, consisting of two digital cameras and the software ARAMIS (6.2.0, Braunschweig, Germany). Both fields indicated the maximum dimensional changes occurred just below the point of force incidence. The displacement field registered movements in the range from 0.165 to 0.782 mm and the principal strain field showed strain values between 1.25 and 18.94%. In vitro investigation of the dynamic behavior of the lower complete denture under load by using the optical measuring system-DIC demonstrated that the strain/displacement alterations were generally influenced by prosthesis movement toward the residual alveolar ridge.

Analysing Displacement in the Posterior Mandible using Digital Image Correlation Method

Background: Knowing the biomechanical consequences of the stresses generated to the supporting bone during occlusal loading is significant for improving design and clinical planning process in partial edentualism therapy. The objective of this study was to analyze the surface displacement field on partial dentate mandible rehabilitated with removable partial denture and to compare it to displacement field on partial dentate mandible rehabilitated with cantilever fixed partial denture. Material and Methods: The experimental models were partial dentate mandible with full-arch PFM crowns and removable partial denture and partial dentate mandible rehabilitated with full-arch cantilever fixed partial denture. Displacement were measured using Digital Image Correlation Method. Results: Displacement values of the removable partial denture-model were ranging from 0-1.50 mm. Analysis of the fixed partial denture-model results showed displacement values from 0.05-0.69 mm. Conclusion: Higher displacements of bone tissue were observed below the removable partial denture, especially in the region of distal abutment and distal portion of the free-end saddle. Displacements within bone and the bonedenture contact area were mostly influenced by the teeth and denture vertical movements.