Evaluation of early bacterial adhesion on CAD/CAM dental materials: an in situ study.

The aim of this research was to determine if there are differences in early bacterial adhesion among CAD/CAM dental materials after 24 h exposure in the oral environment. One hundred twenty specimens were prepared according to the manufacturer's recommendations and divided into six groups: RBC (resin-based composite), PMMA (polymethyl methacrylate), PEEK (polyether ether ketone), ZP (zirconia polished), ZG (zirconia glazed), and cobalt-chromium alloy (CoCr alloy). Twenty healthy participants were instructed to carry an intraoral device with six specimens, one per group, for 24 h. Thereafter, real-time polymerase chain reaction (qPCR) and scanning electron microscopy (SEM) analyses enabled quantification and 2D view of biofilm formed on the specimens' surfaces. Kruskal-Wallis test and Dunn's post hoc analysis were used for inter-group comparison and data were presented as median (minimum-maximum). RBC specimens accumulated less bacteria, in comparison with ZG (p = 0.017) and PEEK specimens (p = 0.030), that dominated with the highest amount of adhered bacterial biofilm. PMMA, CoCr, and ZP specimens adhered more bacteria than RBC (p > 0.05), and less than ZG (p > 0.05) and PEEK (p > 0.05). The bacterial number varied considerably among participants. The obtained results enable a closer view into the susceptibility of CAD/CAM materials to microorganisms during the presence in the oral environment, which can be beneficial for a proper selection of these materials for a variety of dental restorations.

Biofilm Formation on the Surfaces of CAD/CAM Dental Polymers.

Dental polymers are now available as monolithic materials which can be readily used in computer-aided design and computer-aided manufacturing (CAD/CAM) systems. Despite possessing numerous advantages over conventionally produced polymers, the polymers produced by either of these systems fail to exhibit immunity to surface microbial adhesion when introduced into the oral environment, leading to the development of oral diseases. The aim of this study was to analyze the biofilm formation of six microorganisms from the oral cavity and its correlation to the surface characteristics of CAD/CAM dental polymers. A total of ninety specimens were divided into three groups: resin-based composite, polymethyl methacrylate, and polyether ether ketone. The experimental procedure included surface roughness and water contact angle measurements, colony forming unit counting, and scanning electron microscopy analysis of biofilm formed on the surface of the tested materials. The data were analyzed using the Kruskal-Wallis test, with a Dunn's post hoc analysis, and one way analysis of variance, with a Tukey's post hoc test; the correlation between the measurements was tested using Spearman's correlation coefficient, and descriptive statistics were used to present the data. Despite using the same manufacturing procedure, as well as the identical manufacturer's finishing and polishing protocols, CAD/CAM dental polymers revealed significant differences in surface roughness and water contact angle, and the increased values of both parameters led to an increase in biofilm formation on the surface of the materials. The CAD/CAM resin-based composite showed the lowest number of adhered microorganisms compared to CAD/CAM polymethyl methacrylate and CAD/CAM polyether ether ketone.

Effect of different finishing and polishing procedures on surface roughness and microbial adhesion on highly-filled composites for injectable mold technique.

OBJECTIVE: To evaluate the effect of different finishing and polishing procedures on surface roughness and microbial adhesion and viability of Streptococcus mutans on novel highly-filled composites for injectable mold technique. MATERIALS AND METHODS: One hundred sixty specimens were divided into four material groups: FSF (Filtek Supreme Flowable Restorative), TE (Tetric EvoFlow), GUI (G-aenial Universal Injectable) and GUF (G-aenial Universal Flo). Within each group, specimens were split regarding finishing and polishing (F/P) procedures into: SLD (Sof-Lex Discs), SLS (Sof-Lex Spirals), OG (OneGloss) and PG (PoGo). Surface roughness was analyzed using profilometer (Ra and Rz) and scanning electron microscopy (SEM) and Strep. mutans biofilm formation was analyzed using colony forming unit (CFU) and cell viability assay. Two-way analysis of variance (ANOVA) followed by Tukey's post hoc test were used for comparison among groups, Pearson's coefficient was applied for the correlation between Ra and CFU/ml and all data were presented as mean ± SD. RESULTS: Both materials and F/P procedures affect Ra, Rz and Strep. mutans CFU/ml values (p ≤ 0.05). Considering the Ra and Rz, GUI and GUF revealed lower values, compared to FSF and TE and SLD and SLS revealed lower values, compared to OG and PG. Considering the Strep. mutans CFU/ml and viability, GUI and TE presented lower values, compared to GUF and FSF and SLD and SLS presented lower values, compared to OG and PG. Moderate positive correlation was found between Ra and CFU/ml (r = 0.552). CONCLUSIONS: The smoothest surfaces possess GUI and GUF, among materials and SLD and SLS, among F/P procedures. GUI adhered the lowest amount of Strep. mutans, due to the smoothest surfaces. FSF and GUF revealed the highest amount of Strep. mutans, due to bis-GMA, bis-MEPP and TEGDMA in their composition. CLINICAL SIGNIFICANCE: The findings of the present study may be beneficial for the proper selection of highly-filled composites and an adequate finishing and polishing procedure when performing the injectable mold composite resin veneer technique.

Subjective and Objective Assessment of Chewing Performance in Older Adults with Different Dental Occlusion.

OBJECTIVES: Satisfactory masticatory function is a significant indicator of improved oral health-related quality of life in older adults, either with or without artificial teeth. The purpose of this study was to examine masticatory performance of older adults with different prosthodontic reconstructions and occlusion, as well as to compare subjective and objective assessment of chewing performance. MATERIAL AND METHODS: This study included 100 participants aged 65 and more. The chewing function questionnaire (CFQ) with answers on the Likert scale 0-4 (0 = no difficulties; 4 = maximum difficulties) was used as an indicator of subjective masticatory assessment. The two-color chewing gum test was used as objective assessment of masticatory function (mixing ability), based on the Z-score values. Dental occlusion was assessed using functional teeth units (FTU). RESULTS: The results obtained using the CFQ and the clinical mixing ability test are in compliance with each other (r = 0.742). A decrease in the number of natural teeth, especially posterior teeth, progressively reduced chewing ability and increased difficulties in mastication. Participants with less FTUs, or with FTUs that are a part of removable denture, had greater reduction in masticatory function compared to those with FTUs composed of natural teeth or fixed partial dentures. CONCLUSION: This study revealed a strong positive correlation between the subjective masticatory assessment in older adults using the validated questionnaire and the objective clinical test of the mixing ability of two chewing gums. Our data on influence of the number and the type of FTU on masticatory performance will be valuable when planning prosthodontic therapy.

Microbial adhesion and viability on novel CAD/CAM framework materials for implant-supported hybrid prostheses.

The aim of the study was to investigate the adhesion and viability of Streptococcus oralis and Candida albicans under in vitro conditions on CAD/CAM framework materials for implant-supported hybrid prostheses. Twenty-nine specimens were prepared from each of three different materials: ZR (zirconia), PEEK (polyether ether ketone) and CoCr4 (CoCr4 alloy). The experimental part included surface roughness (SR) and contact angle of water (CAW) measurements, followed by colony forming unit (CFU), cell viability assay and scanning electron microscopy (SEM) analyses of Strep. oralis and C. albicans biofilms on the materials' surfaces. Kruskal-Wallis and one-way analysis of variance (ANOVA) tests were used for differences between materials, and the correlation between measurements was estimated using Spearman's correlation coefficient. PEEK specimens revealed higher SR, CAW and CFU mean values, than ZR and CoCr4 specimens. Strong positive correlation was found between SR and CFU and between CAW and CFU for both microbial species. Cell viability assay revealed similar values for both species across materials. Higher numbers of Strep. oralis and C. albicans on PEEK specimens confirm the impact of the higher surface roughness and contact angle values on the microbial adhesion and describes PEEK as less desirable than ZR and CoCr4 from microbiological aspect.

Study on the surface properties of different commercially available CAD/CAM materials for implant-supported restorations.

OBJECTIVE: To determine if there are any differences in surface characteristics (surface roughness and contact angle) among different CAD/CAM materials indicated for fabricating implant-supported restorations, following all the material preparation protocols provided by the manufacturer. MATERIALS AND METHODS: One-hundred forty-four specimens were divided into six groups: RBC (resin-based composite), PMMA (polymethyl methacrylate), PEEK (polyether ether ketone), ZP (zirconia polished), ZG (zirconia glazed) and CoCr4 (CoCr4 alloy). The experimental part included surface roughness (SR) and contact angle of water (WCA) analyses, fulfilled with Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) view of surface topography. The data were analyzed using Kruskal-Wallis test with a Dunn's post hoc analysis, the correlation between measurements was tested using Spearman's rank correlation coefficient and all data were presented as mean ± SD. RESULTS: ZG specimens were significantly rougher compared to other groups (p ≤ 0.05). The WCA measurements revealed significantly lower mean values in ZG group (p ≤ 0.05), contrary to PEEK and CoCr4 , where significantly higher mean values were observed, compared to other groups (p ≤ 0.05). There exist a moderate negative correlation between the SR and WCA (ρ = -0.41). AFM 3D and SEM 2D images presented more or less heterogeneous surface of all materials. CONCLUSIONS: There were statistically significant differences in surface roughness and contact angle among tested material groups. Moderate negative correlation was found between surface roughness and contact angle of tested material groups. CLINICAL SIGNIFICANCE: The study gives us a better understanding of influence of physicochemical characteristics of investigated materials on their surface properties and provides useful knowledge for future researches in a view of material's behavior under in vivo conditions, when it comes to a question of features related to surface quality, such as microbial adhesion, corrosion, wear, biocompatibility and esthetics.

Salivary VEGF and post-extraction wound healing in type 2 diabetic immediate denture wearers.

OBJECTIVE: Oral wound healing in healthy could be promoted by VEGF in saliva, and immediate denture wearing, but data in type 2 diabetes are lacking. Aims were to investigate the timeline of extraction wound healing in diabetic participants wearing immediate dentures and its correlation to salivary VEGF, as well as to examine the impact of the palatal plate on tissue VEGF during palatal wound healing in rat diabetic model. MATERIAL AND METHODS: Healthy (42) and type 2 diabetic (36) denture wearers, candidates for teeth extractions were included. Extraction wound healing was followed via measurements of socket closure, gingival hyperaemia, pain and presence of necrosis on 3rd, 7th, 14th and on 21st-day post-extraction. Salivary VEGF was measured before and on the 3rd and 21st day after the extraction. In streptozotocin-induced diabetic (30) as well as non-diabetic rats (30), tissue VEGF was measured in palatal wounds healing under or without a palatal plate. RESULTS: Type 2 diabetic prosthetic patients exhibit delayed socket closure, with pronounced hyperaemia, pain and necrosis. Salivary VEGF is increased in diabetes and positively correlates to socket closure while negatively with pain on 21st day after the extraction. Palatal incision induced VEGF increase in non-diabetic and diabetic, but less pronounced in diabetic rats. Wound healing under the palatal plate exhibit higher tissue VEGF. CONCLUSION: Type 2 diabetes-induced increase in salivary VEGF may mitigate diabetes-induced detrimental effects on extraction wound healing. Lack of adequate tissue VEGF response to injury may underly dysregulation of diabetic oral wound healing.

The effect of COVID-19 pandemic on final year dental students' self-confidence level in performing clinical procedures.

BACKGROUND: The outbreak of COVID-19 pandemic in 2020 has dramatically changed teaching approach in dental schools due to the switch to distance learning and the lack of practice training in direct contact with patients with possible impact on clinical skills of students. The aim of the study was to assess the level of the 2020 final year dental students' self-confidence in performing different dental procedures through specially designed questionnaire and compare it to self-confidence of the 2019 final year students. MATERIALS AND METHODS: An anonymous questionnaire consisting of 40 questions regarding self-confidence level in performing 40 different dental procedures and based on five points Likert-like scale was distributed during November 2020 to final year dental students whose studies were disrupted by the COVID-19 pandemic lockdown in one semester. The study group comprised their answers. The comparison was done with the control group that consisted of students' answers on the same questionnaire from previous 2019 year conducted as a part of regular internal educational evaluation. RESULTS: Response rate was 74.2% in study group and 89.3% in control group. Mean level of self-confidence reported by 115 students in study group was significantly lower than that reported by 100 students in control group (3.28±1.08 vs. 3.58±0.88, respectively) and the distribution of self-confidence scores were different in observed groups. Graduates from study group felt less confident than those from control in 8 clinical skills. CONCLUSION: Abrupt changes in teaching modalities caused by COVID-19 pandemic had significant impact on final year dental students' self-confidence indicating additional educational needs in postgraduate period.

Oral Health Status and Nutritional Habits as Predictors for Developing Alzheimer's Disease.

OBJECTIVE: Poor oral health, mainly tooth loss, has been suggested to pose a risk factor for Alzheimer's disease (AD). The nature of this relationship can be explained by mastication deficit and nutritional status. Also, the influence of nutritional parameters on cognitive impairment has been documented. The aim of this study was to investigate whether poor dental status and nutrition habits can be potential separate or associated risk factors for development of the AD. METHODS: The study sample included 116 patients with AD and 63 controls. Sociodemographic variables were investigated as factors potentially associated with AD. Dental examination included recording the number of natural teeth, presence of fixed or removable dentures, and the number of functional tooth units (FTUs). Nutritional status analysis included qualitative nutrition information, body mass index, serum albumin level, food consistency, and need for assistance in feeding. Regression analysis was used to investigate the predictors for development of AD. RESULTS: Variables with significant differences between groups, which were analyzed by using the binary regression analysis, were marital status, residence, number of total FTUs (no matter whether the contacts were between natural teeth or dentures), eating meat/fish and fruits/vegetables, food consistency, and serum albumin level. Logistic regression analysis showed that being single/widowed/divorced, eating more meat/fish or fruit/vegetable, eating blended/mashed/liquid food, having low levels of serum albumin, and having less FTUs were significant predictors for developing dementia. CONCLUSION: Having fewer occlusal contacts, consumption of soft food, and lower serum albumin levels can be considered as associated risk factors for AD.

The use of digital texture image analysis in determining the masticatory efficiency outcome.

The mixture level of gum samples consisting of two colours can be assessed visually, using the electronic colorimetric method, employing digital image processing techniques and specially designed software. The study investigates the possibility of an alternative method called "digital texture image analysis" (DTIA) to assess improvement of masticatory efficiency in denture wearers. The objectives were i) to evaluate whether DTIA discriminates changes in the colour mixing ability within a group over time; ii) to determine whether DTIA can be used to detect improvement in chewing ability; iii) to select the most appropriate DTIA feature that sufficiently describes masticatory efficiency in CDs wearers. The study was designed as an intra-individual evaluation of masticatory efficiency, which was assessed in participants with new dentures in three follow-up times. A set of four texture features was used in the current study. Uniformity, Contrast, Homogeneity and Entropy of the obtained chewing-gum samples were correlated to the degree of gum comminution. A statistically significant difference in masticatory efficiency was observed based on the values of the analysed DTIA variables of gum samples-Uniformity, Contrast, Homogeneity, and Entropy-have changed in the participants during the observation period. The improvement of the masticatory function in relation to the mixing ability of two-coloured chewing gum could be traced by monitoring changes in the values of DTIA variables. The most increasement of masticatory efficiency was observed by monitoring DTIA parameters such as contrast, and homogeneity.

Bleeding Index and Monocyte Chemoattractant Protein 1 as Gingival Inflammation Parameters after Chemical-Mechanical Retraction Procedure.

OBJECTIVE: A widely used chemical-mechanical method of gingival retraction can cause gingival tissue damage. The aim of this study was to test the influence of the chemical-mechanical gingival retraction procedures on the gingival bleeding index (GBI) and the salivary concentration of monocyte chemoattractant protein 1 (MCP-1) as an indicator of inflammatory changes in the gingiva. MATERIALS AND METHODS: The effects of 2 different retraction agents (aluminum chloride and ferric sulfate) were compared, particularly their tissue damaging effect during tooth preparation. Therefore, GBI values and the salivary concentration of MCP-1 were assessed during the chemical-mechanical method of gingival retraction in a homogenous group of respondents. The subjects (n = 60) were divided into 2 experimental groups (G1 and G2) regarding the need for tooth preparing and making artificial crowns. Each group was further divided into 2 subgroups (R1 and R2) according to the type of the gingival retraction agent used (aluminum chloride and ferric sulfate). RESULTS: Compared to the values at the study start, a statistically significant increase in GBI and salivary MCP-1 (p < 0.001) 1 day after gingival retraction agent application was observed in both experimental groups. After 72 h, the values were lower than in the second observation period but still statistically significantly higher compared to the study start (p < 0.001), which indicated the reversibility of the tissue changes. CONCLUSION: Higher values of the investigated parameters were observed in the group of subjects with prepared teeth, and clinical changes were more pronounced after the use of ferric sulfate.

Development and validation of mathematical models for testing antifungal activity of different essential oils against Candida species.

OBJECTIVE: The upward trend in using plant materials introduced essential oils (EOs) as a valuable, novel, bioactive antifungal agent and as an alternative to standard treatment protocol of denture stomatitis caused by Candida species. Therefore, the aim was to evaluate the antifungal activity of different EOs and to present the response surface methodology (RSM) and artificial neural network (ANN) as possible tools for optimizing and predicting EOs antifungal activity. METHODS: Minimum inhibitory concentration (MIC) and Minimum fungicidal concentration (MFC) of the EOs against 3 species Candida spp. (C. albicans, C. tropicalis, C. glabrata) isolated in patients with DS were determined, together with optimization and prediction based on non-terpene and terpene content in EOs, using two mathematical models RSM and ANN-GA. RESULTS: The highest concentrations of EO M. alternifolia inhibited (1.6-2.8 µg/ml) and fungicided (3.5-6.0 µg/ml) all three investigated Candida spp. while the lowest concentrations of EO C. limon inhibited (0.2 - 0.5 µg/ml) and fungicided (0.6-1.1 µg/ml). Among the three types of Candida, C. glabrata was the most sensitive. The RSM modelling proved that MICs and MFCs statistically depend on non-terpene and terpene content in different EOs (<0.0001). Both models showed that a citrus oil (EO C. limon) with 89% content of terpenes and limonene as major constituent was more antifungal efficient. CONCLUSIONS: The investigated EOs showed a broad spectrum of anticandidal activity, also confirmed using the RSM and ANN-GA models. Since EOs can be cytotoxic in higher concentrations, models may be used for qualitative and quantitative dosage predictions of the antifungal activity of EOs.

The severity of denture stomatitis as related to risk factors and different Candida spp.

OBJECTIVES: 1) To select patients with Candida-related denture stomatitis (DS) and to study possible risk factors associated with DS, 2) to evaluate the severity of DS according to Newton's classification, and 3) to investigate the association between the presence of non-albicans Candida spp. (NAC) or mixed Candida spp. and the severity of DS. STUDY DESIGN: Eighty-two patients with Candida-positive DS have undergone 1) filling in the interview questionnaire, 2) clinical examination, and 3) microbiologic examination. RESULTS: A total of 113 Candida spp. isolates were obtained from Candida-positive DS patients: C. albicans (as a single species) in 47/82 (57%) patients (study group A [SG_A]) and NAC/mixed Candida spp. in 35/82 (43%) patients (SG_B). Univariate logistic regression analysis showed that older age, longer age of the mandibular denture, and ex-smoker status were associated with SG_A. A multivariate model revealed no significant predictor of DS severity. Patients from SG_A were 3 times as likely to have DS type I, while patients from SG_B were 4.9 times as likely to have DS type III. CONCLUSIONS: Our results show the association between type III of DS (by Newton's classification) and the presence of NAC or mixed Candida spp. in denture wearers.

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.

Treatment of obstructive sleep apnea patients using oral appliances--our experiences.

BACKGROUND/AIM: Obstructive sleep apnea (OSA) is one of the most prevalent sleep disorders. It is recognized as a serious risk factor for car and workplace accidents due to daytime sleepiness, and factor for coronary heart diseases and stroke. The aim of this study was to examine the effectiveness of oral appliances for mandibular advance in treating mild to moderate OSA. METHODS: A total of 15 patients were included in this study, all diagnosed with mild or moderate OSA. Oral appliances were custom made for each patient in protrusive position at 50% of maximum mandibular advancement. The patients were given instructions not to sleep on their backs and avoid alcohol consumption during the study as these are the factors that can contribute to symptoms progression. RESULTS: Complete and partial treatment success was achieve in 14 of the patients. Apnea-hypopnea index values were significantly lower (p < 0.05) at the end of a 6-month observation period compared to those at the treatment beginning. A great improvement in symptoms was observed, with daytime sleepiness index values significantly reduced already within the first month of the treatment. CONCLUSION: Treatment of obstructive sleep apnea with oral appliances has proven successful. Patients were comfortable using oral appliances and were ready to wear them for prolonged period of time. Use of oral appliances is very common in the world and should not be discarded. They are also very comfortable, practical and affordable comparing to continuous positive airway pressure (CPAP) apparatus, not to mention surgery. Use of oral appliances is safe and very well tolerated, and ought to be offered to patients with OSA.

Finite element analysis of compressive stress and strain of different implant forms during vertical loading.

This study analyzed the influence of platform switching on the stress/strain distribution of vertically loaded implants. Employing finite element analysis, the aim of this study was to determine the distribution of stresses and strains generated by a simulated vertical load on different implant models positioned in the molar region with respect to changes of implant design and biomechanics. Two different implant designs, one with and one without platform switching, with the same length (11.5 mm) and diameter of (3.80 mm) were analyzed. Both virtual implant-bone models were subjected to a load of 500 N. The results showed that the maximum stress/strain in implant-bone samples was located in the area of the implant neck, with stress/strain values decreasing in the apical direction. It was found that the implant design with platform switching developed lower stresses and strains than the implant design without platform switching.

Frequency and quality of root canal fillings in an adult Serbian population.

INTRODUCTION: Estimation of frequency and quality of root canal fillings is the way to evaluate endodontic treatment needs and success/failure rates of performed endodontic procedures. OBJECTIVE: The aim of this study was to determine the frequency and quality of root canal fillings and the frequency of apical periodontitis on endodontically treated teeth in a group of adult patients from Serbia. METHODS: In order to analyze the presence and quality of root canal fillings and the frequency of periapical radiolucencies on endodontically treated teeth, 3526 teeth were examined on orthopantomograms of 153 adult patients. RESULTS: Overall, 12.5% of examined teeth were root filled, and 51.8% of them had radiographic signs of apical periodontitis. The analysis of root fillings quality revealed the presence of more inadequate ones (55.9%). The frequency of apical periodontitis was significantly higher in teeth with inadequate than in those having adequate root canal obturation (72.2% and 25.9%, respectively). CONCLUSION: The frequency of apical periodontitis on root-filled teeth in this group of patients was high, indicating a low success rate of performed endodotic procedures and high endodontic retreatment needs.

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.

Biomechanical behavior of restored and unrestored mandible with shortened dental arch under vertical loading condition.

The aim of this in vitro study was to investigate the strain distribution of the compressed mandible bone under the applied restoration- removable partial denture and to compare with the same but unrestored mandible under vertical (occlusal) load and to find out whether removable partial denture-restored or unrestored mandible causes greater strain effect on supporting tissue. Four mandible models were tested during loading for the purpose of strain measuring. Digital image correlation system (GOM - German Optical Measuring, Braunschweig, Germany), used for measuring strain consists of two digital cameras and software ARAMIS (6.2.0, Braunschweig, Germany). Remaining teeth suffer from greater strain in the mandible model without removable partial denture (7.5-10%). On the contrary, mandible with removable partial denture shows the maximum strain below the denture saddle (3.5%). However, it can be noticed that the marginal bone of the second lower praemolar in both experimental models is deformed whether the mandible model has (2.8%) or has not (10%) replacement. Within the limitations of this study the higher strain is observed in mandible model without replacement and the strain is limited locally, in the bone region that surrounds remaining teeth and mental foramen.

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.