Ljiljana Tihacek-Sojic

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.

The effectiveness of oral appliances in elderly patients with obstructive sleep apnoea treated with lorazepam – a pilot study

Obstructive sleep apnoea (OSA) is one of the most common sleep disorders in elderly and represents a special problem for elderly patients. Elderly patients use a large number of drugs that might have an influence on the upper airway structure, anxiolytics or benzodiazepines being the most common. The aim of this study was to examine the effectiveness of mild or moderate OSA treatment with mandibular advance oral appliance in older lorazepam users compared with the age-matched lorazepam-free patients. A total of 40 functionally independent patients with the age of 65-74 were enrolled in the study. All included patients were found to suffer from at least two of the existing OSA symptoms (snoring, sleep fragmentation, daytime sleepiness) and were diagnosed with mild or moderate OSA after nocturnal polysomnography. Patients were divided into two groups. The experimental group consisted of 20 patients who used lorazepam in their daily therapy, and a control group consisted of 20 patients who did not take lorazepam. A mandibular advance appliance was made individually for each patient. Patients involved in the study were not overweight and were suggested to practise sleeping on the side and reduce alcohol consumption during the study. The study has shown that mandibular advance oral appliances were responsible for complete control of the OSA in over 37% of cases (15 patients). Patients have also reported substantial improvement in the symptoms; 80% of them reported that they had snored less, slept better (94%) and have not experienced daytime sleepiness (100%).

Finite element analysis in defining the optimal shape and safety factor of retentive clasp arms of a removable partial denture.

BACKGROUND/AIM Retentive force of removable partial denture (RPD) directly depends on elastic force of stretched retentive clasp arms (RCAs). During deflection RCA must have even stress distribution. Safety factor is the concept which can be applied in estimating durability and functionality of RCAs. This study was based on analyzing properties of clasps designed by conventional clasp wax profiles and defining the optimal shapes of RCAs for stress distribution and safety factor aspects. METHODS Computer-aided-design (CAD) models of RCAs with simulated properties of materials used for fabrication of RPD cobalt-chromium-molybdenum (CoCrMo) alloy, commercially pure titanium (CPTi) and polyacetale were analzed. RESULTS The research showed that geometrics of Rapidflex profiles from the BIOS concept are defined for designing and modeling RCAs from CoCrMo alloys. I-Bar and Bonihard clasps made from CPTi might have the same design as Co-CoCrMo clasp only by safety factor aspect, but it is obvious that CPTi are much more flexible, so their shape must be more massive. Polyacetale clasps should not be fabricated by BIOS concept for CoCrMo alloy. A proof for that is the low value of safety factor. CONCLUSION The BIOS concept should be used only for RCAs made of CoCrMo alloy and different wax profiles should be used for fabricating clasps of other investigated materials. The contribution of this study may be the improve ment of present systems for defining the clasps shapes made from (CoCrMo alloys. The more significant application is the possibility of creating new concepts in defining shapes of RCA made from CPTi and polyacetale.

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.

Identifying enamel diffusion properties in feline teeth affected with resorptive lesions.

Various factors have been suggested in the pathogenesis of feline resorptive lesions, such as periodontal disease, dietary factors, mechanical stress, developmental tooth defects, breed and viral disease, although none of these factors have been definitively proven to be the direct cause. It was recently published that normally enamel in cats is significantly thinner at the cemento-enamel junction, and both enamel and dentine are significantly less mineralized than elsewhere on the tooth. However, it is still unclear what anatomical features of the tooth surface are associated with a predisposition for resorptive lesions, and what is the initiating cause for the clastic activity afterwards. The present study was undertaken with the aim to describe enamel properties of transport and distribution of organic molecules in intact feline teeth and teeth affected with resorptive lesions. The results indicate that damaged enamel is prone to a greater bilateral diffusion process, leading to continuous disruption of the enamel structure. Also, teeth that are subjected to occlusal stress are at greater risk of destruction because micro fractures produce disarrangements in feline dental tissue diffusion homeostasis. The relationship between these features with feline dental resorptive lesions requires further studies.

Biomechanical aspect of feline dental resorptive lesions formation.

Feline dental resorptive lesions affect more than one third of all adult domestic cats and continue to be an enigma in the veterinary dental science although different theories about the pathogenesis of these lesions have been proposed. Recently, a hypothesis was introduced that local mechanical trauma could be an important factor in the initiation of feline dental resorptive lesions and that there is a correlation between the occurrence of resorptive lesions and occlusal trauma in cats. The aim of this study was to analyse stress distribution in feline tooth during occlusal loading in order to accept or reject the hypothesis that dental resorptive lesions in cats might be caused by occlusal trauma. A solid model of feline tooth had to be created in order to perform the investigation. The idea was to gain data for tooth displacement (deformation) and stress and strain distribution under loading generally for any feline tooth using the finite element method. The results of the study contribute to the theory that occlusal overload might be one of the causes in multifactorial resorptive lesions in cats. Succession of tensile and compressive stresses and tooth displacement during occlusal loading might be a contributive factor in the pathogenesis of feline resorptive lesions. However, further research is required to confirm this statement.