Clasp Arm Research Articles

Finite element analysis of fatigue life of commercially pure titanium clasps additively manufactured with different building orientations.

The geometrical accuracy of additively manufactured pure titanium clasps depends on the building orientation. The aim of this study is to compare the geometrical accuracy and the fatigue lives predicted by finite element analysis (FEA) among three clasps manufactured with different building orientations. Besides, this paper proposed a calculation method of the moment of inertia of area and cross-sectional area along with the arm as the geometrical parameters. One of the clasps manufactured with a cylindrical chucking part for the fatigue test had almost the same geometrical parameters with the CAD design. Also, the authors' fatigue life prediction method using the CAD based FEA was verified through comparison with micro-CT image-based FEA. The other two clasps had larger geometrical parameters than the CAD design, resulting in longer fatigue lives. The results implied the importance of calculating the moment of inertia of the area in the design of the clasp arm.

Impact of the Removable Partial Denture Components on the Prognosis of the Abutment Teeth: An Exploratory Clinical Study

Introduction Partial edentulism is considered one of the challenging topics in dentistry. The main objectives of the patient are to restore function and esthetics. However, the dentist’s main goals are preserving the remaining teeth supporting structures and restoring the patient’s quality of life. A Removable Partial Denture (RPD) design should be considered carefully for each case, as there are clinical and personal variables for each patient that will impact the prognosis of the denture. With the growing need for RPD, design principles require more research to improve the preservation of abutment teeth. This study aims to clinically evaluate the abutment teeth and supporting tissues before and after RPD placement and to correlate these clinical findings with the RPD components. Methods: Patients were recruited from the dental clinic at Schulich Dentistry, Western University in London, Ontario, Canada. Abutment teeth were evaluated for the following clinical parameters: Tooth Mobility (TM), caries, defective restorations, tooth fracture, Probing Depth (PD), Gingival Recession (GR), bleeding on probing (BOP) and Plaque Index (PI). These clinical measurements were collected at the time of RPD insertion and at least two years after. Clinical parameters were analyzed using Kruskal Wallis H, Mann-Whitney U and Chi-Squared tests. Results: 34 participants were recruited, and 40 cast metal RPDs were evaluated. The mean age of participants was 73.8 years, and the mean duration of denture use was 37.6 months. Most frameworks assessed were Kennedy Class III RPDs. Caries were significantly associated with rest type, wherein occlusal rests showed an increased incidence of caries compared to cingulum rests. The retentive clasp arm type was associated with a mean difference in PD, wherein cast circumferential and wrought wire clasp arms had deeper PD after RPD insertion than Infra gingival clasps (I-bars). Conclusion: The results of this study suggest clasp arms and occlusal rests influence dental disease. Larger samples and more clinical studies are needed to confirm the role of specific RPD components on the abutment teeth prognosis.

The optimal design and three-dimensional finite element analysis of CAD/CAM integrated roach attachment

ObjectivesTo investigate the effect of different designs of movable parts and prosthetic materials on the stress distribution of supporting tissues in mandibular free end dentition defects using three-dimensional finite element analysis of digital Roach attachments. Material and methodsA 3D model of a patient with Kennedy class I mandibular edentulous conditions was generated, and twelve prosthesis models were applied, combining two designs of removable parts and six types of CAD/CAM restorative materials with different elastic modulus (conventional zirconia, ultra-translucent zirconia, Polyetheretherketone (PEEK), Lithium disilicate, Nanoceramic resin, and resin composite (Paradigm MZ100, 3 M ESPE)). The stress distribution of abutment periodontal ligament, edentulousmucosa, and junction of attachment were analyzed using finite element analysis. ResultsThe stress value of the buccal neck of the periodontal ligament and the maximum compressive stress of the distal periodontal ligament of the design with clasp arms were higher than those without clasp arms, while the stress on the junction of attachment and the displacement of the mucosa in the edentulous area were smaller. Restorative materials with high elastic modulus, such as conventional zirconia and ultra-translucent zirconia, are recommended to be used as the fixed part of Roach attachment. ConclusionCAD/CAM Roach attachments with clasp arms are recommended for the protection of mucosal soft tissue. Restorative materials with high elastic modulus, such as conventional zirconia and ultra-translucent zirconia, are recommended as the fixed part of Roach attachment for patients with free end defect of mandibular dentition. Clinical significanceThis study provides references for the design with clasp arms and the selection of clinical fixed-movable prosthetic materials. Clinicians should consider the design of attachments and selection of appropriate manufacturing materials carefully to avoid negative impacts on patients' periodontal support tissues.

The Dimensional Changes of Clasp Arm in Removable Partial Denture Frameworks Fabricated Through DMLS and Conventional Lost Wax Technique: An In Vitro Study

AIM: The aim of the present study is to evaluate the effect of CAD designing on the dimensions of the clasp arm. METHODOLOGY: A Kennedy Class III mod I cast was selected as the reference cast. Samples were divided into 2 groups, Group I with DMLS and Group II with Conventional lost wax technique. Three reference points were selected on the clasp arm and the vertical dimensions were measured in the digital design and compared it with the dimensions at the same points in the final framework. RESULTS: There was slight expansion in group 1 (p-value > 0.05) with mean of -0.035 and standard deviation 0.088. And there was decrease in dimensions in the clasp arm in group 2 (p-value < 0.05) with mean of 0.1741 and standard deviation 0.081. CONCLUSION: From the present study, it was concluded that the dimensions of the clasp arm of DMLS framework increased slightly, whereas the there was significant decrease in the clasp arm dimensions in the framework produced through conventional lost wax technique. Both the frameworks had clinically acceptable fit.

Comparison of the Retention and Fit of Polyether Ether Ketone Clasps during Fatigue Circulation Tests

PurposeThe purpose of this study was to evaluate the fit and retention of clasps made of polyether ether ketone (PEEK) or cobalt–chromium alloy (Co–Cr) at different tooth positions in experimental simulations of in vitro wear and removal for 5 years. MethodsStandard crowns of the right mandibular first premolar (44) and first molar (46) were selected, and a circular three-arm clasp was designed, scanned and fabricated. Ten PEEK clasps were used as the experimental group, and 10 Co–Cr clasps were used as the control group. The seating channel was parallel to the side of the abutment base in both groups. The oral environment was simulated, and each clasp was tested in artificial saliva for 7200 cycles while the change in clasp retention force was recorded. The fit before and after the fatigue cycles was measured by the silicone rubber film copying method. Data were statistically analyzed using the independent samples t-test (α = 0.05). ResultsBefore circulation, the retention forces of the clasps at position 44 were 4.61 ± 0.91 N (PEEK) and 47.50 ± 10.59 N (Co–Cr), and the forces at position 46 were 3.38 ± 0.49 N (PEEK) and 28.79 ± 10.99 N (Co–Cr). After circulation, the retention forces of the clasps at position 44 were 4.15 ± 0.91 N (PEEK) and 13.90 ± 6.59 N (Co–Cr), and the forces at position 46 were 2.93 ± 0.25 N (PEEK) and 11.56 ± 3.93 N (Co–Cr). Before circulation, the fit of each clasp at the reference points (clasp tip, clasp arm, and occlusal rest) was between 41.70 μm and 170.29 μm, and after circulation, they were between 64.05 μm and 182.59 μm. The retention force and fit of the PEEK clasps did not undergo statistically significant changes from before to after circulation (P > 0.05). However, there were statistically significant (P < 0.05) decreases in the retention force of the Co–Cr clasps and the fit of the clasp tip during circulation. In addition, there was a sudden and large change in the retention force of the Co–Cr clasps after approximately 360 cycles. ConclusionsThe retention force and suitability of the PEEK clasps met the requirements for clinical use during testing that simulated the in vitro wear and removal procedure for 5 years. Compared with the Co–Cr clasp, the PEEK clasp underwent less fatigue deformation, which makes it feasible for clinical applications.

Research on the Quality of Partially Removable Skeletal Prostheses Made Using Classical Versus Modern Sintering Techniques.

Conventional partially removable skeletal dentures are one of the most common therapeutic solutions offered to edentulous patients worldwide. The present study aims to compare the skeleton of removable dentures realized via classical techniques to that realized via modern techniques, represented by the laser sintering technique, with the comparative aspects being realized through the evaluation of atomic force microscopy (AFM). A total of 20 metal frameworks made of Co-Cr were sectioned, representing the infrastructure of partially removable skeletal dentures, developed using the classical technique versus the laser sintering technique. The infrastructures of partially removable skeletal dentures were designed for both the maxilla and the mandible, with the design of each type of denture being identical, and were developed using both techniques. The roughness values are different depending on the technological method used; for the conventional casting technique, we have higher roughness for the component elements of the partially removable skeletal denture that have more stretch, e.g., the major connector, and for the 3D laser sintering technique, lower roughness is obtained for the component elements that have a lower stretch, e.g., the clasp arms, the minor connector, or the junction between the saddles and the major connector. The clinical implications of the presence of roughness at the level of the active arms or at the level of the connector saddle junction are represented by the risk of fracture, which confers real discomfort to the patient.

Feasibility study and material selection for powder-bed fusion process in printing of denture clasps

Background and objectiveThe retention of selective laser melting (SLM)-built denture clasps is inferior to that of cast cobalt-chromium (Co–Cr) clasps engaging 0.01-in undercuts, which are commonly used in clinical practice. Either the clasps engage in excessively deep undercuts or inappropriate printing process parameters are applied. With appropriate undercut engagement and levels of process parameters, the retention of SLM-built clasps (including Co–Cr, commercially pure titanium [CP Ti], and Ti alloy [Ti–6Al–4V] ones) may be comparable to that of cast Co–Cr clasps. Therefore, this feasibility study aimed to evaluate their retention to guide dentists during material selection for the powder-bed fusion process during the printing of denture clasps. MethodsWe engaged the clasp arm at an appropriate undercut depth (0.01 or 0.02 in), built clasps at the orientation of their longitudinal axes approximately parallel to the build platform, generated square prism support structures at a critical overhang angle of 30°, applied optimized laser parameters (laser power, scan speed, and hatch space), and adopted annealing treatment for Co–Cr, CP Ti, and Ti–6Al–4V clasps. After postprocessing and accuracy measurement, an insertion/removal test of the clasps for 15,000 cycles was performed to simulate 10 years of clinical use, and the retentive force was recorded every 1500 cycles. Permanent deformation of the retentive arms of the clasps was measured. Cast Co–Cr clasps engaging 0.01-in undercuts were designated the control group. ResultsThe initial retentive forces of the SLM-built Co–Cr clasps engaging 0.01-in undercuts and CP Ti and Ti–6Al–4V clasps engaging 0.02-in undercuts were comparable to those of the control group. SLM-built Co–Cr clasps engaging 0.01-in undercuts and Ti–6Al–4V clasps engaging 0.02-in undercuts had similar final retentive force and less permanent deformation compared with those of the control group; SLM-built CP Ti clasps engaging 0.02-in undercuts had lower final retentive force and greater permanent deformation. ConclusionsConsidering the long-term retention and permanent deformation of the retentive arms, Co–Cr and Ti–6Al–4V alloys, except CP Ti, are recommended for printing denture clasps. SLM-built Co–Cr clasps should engage 0.01-in undercuts, and Ti–6Al–4V clasps should engage 0.02-in undercuts.

COMPARATIVE SIMULATION TESTINGWITH FUNCTIONAL LOADING OF TWO DENTURE FRAMEWORK MATERIALS – A PILOT STUDY

Introduction:Simulation tests may significantly decrease the cost and time needed for planning and production of prosthetic restorations, providing both computer simulation as part of the refinement process and experimental testing. Aim: Comparative simulation testing with functional loading of two denture framework materials. Materials and methods: Upper model cast denture forbilateral edentulous areas posterior to the natural teeth (Kennedy Class I) was produced on the "Frasaco" phantom model. The denture was scanned by a 3D optical laboratory scanner. The 3D model was transformed into an STL-file and was processed with "Cinema 4D" software before the application of the program "SOLIDWORKS" v.2018. Parameters of two materials – metal alloy I-MG EKO (Interdent, Slovenia) and injection molded resin Bio Dentaplast (Bredent, Germany) were applied. Simulations were performed by equivalent loading according to the Third strength theory (von Mises stress-test) and loading with deformation and shift at constant force 0.1N/mm2 at a maximal number of 159 181 segmented elements of the 3D object. Tests were held upon unilateral loading on the working side, and support was provided by reciprocal clasp arms on the working and non-working side, denture flanges and major connector. Results and discussion: Results showed insignificant differences between the common reflected load of the two tested materials but with different distribution - on the major connector, it was 0.4N for the alloy and 0.87N for the resin, at the flanges – 2.26N and 5.6N respectively, for the clasps – 5.1N and 5.7N. Conclusion: The tested metal alloy is rigid and resistant material which provides distribution of the reflected load between clasp elements and denture saddle, especially distally, while the the tested injection molded material possesses relatively high flexibility and elasticity, which hides a risk for the teeth bearing clasps.

Performance of Graphene-Based and Polyether-Ether-Ketone Polymers as Removable Partial Denture Esthetic Clasp Materials after Cyclic Fatigue.

The esthetic clasp material is a clinical demand for a satisfactory removable partial denture. The purpose of this study is to assess the mechanical performance of graphene-based polymer (GBP) and polyether-ether-ketone (PEEK) materials as clasp materials. Thirty-two clasps were fabricated by CAD-CAM from two materials, GBP and PEEK. All clasps were tested for retention force after 10,000 cycles of insertion and removal and thermocycling. The clasp arms’ deformation was measured, and areas of stress–strain concentration were explored. The Mann–Whitney U test was used to compare the retentive force of the studied groups, while the independent sample t-test was applied to check the difference in clasp arm deformation at α = 0.5. The results showed a significantly higher retentive force (2.248 ± 0.315 N) in PEEK clasps, at p < 0.001. The deformation of the clasp arm of the GBP clasps was significantly higher than PEEK clasps. Areas of stress–strain concentration were seen at the junction of the retentive arm to the minor connector and at the retentive arm terminal. It could be concluded that PEEK polymer had a better mechanical performance as an esthetic clasp material than the GBP. An optimization study for GBP might be required to check the validity of such an application.

Trueness of 3D printed partial denture frameworks: build orientations and support structure density parameters.

PURPOSEThe purpose of the study was to assess the influence of build orientations and density of support structures on the trueness of the 3D printed removable partial denture (RPD) frameworks.MATERIALS AND METHODSA maxillary Kennedy class III and mandibular class I casts were 3D scanned and used to design and produce two 3D virtual models of RPD frameworks. Using digital light processing (DLP) 3D printing, 47 RPD frameworks were fabricated at 3 different build orientations (100, 135 and 150-degree angles) and 2 support structure densities. All frameworks were scanned and 3D compared to the original virtual RPD models by metrology software to check 3D deviations quantitatively and qualitatively. The accuracy data were statistically analyzed using one-way ANOVA for build orientation comparison and independent sample t-test for structure density comparison at (α = .05). Points study analysis targeting RPD components and representative color maps were also studied.RESULTSThe build orientation of 135-degree angle of the maxillary frameworks showed the lowest deviation at the clasp arms of tooth 26 of the 135-degree angle group. The mandibular frameworks with 150-degree angle build orientation showed the least deviation at the rest on tooth 44 and the arm of the I-bar clasp of tooth 45. No significant difference was seen between different support structure densities.CONCLUSIONBuild orientation had an influence on the accuracy of the frameworks, especially at a 135-degree angle of maxillary design and 150-degree of mandibular design. The difference in the support’s density structure revealed no considerable effect on the accuracy.

Guidelines for the choice of circumferential wrought wire and cast clasp arms for removable partial dentures

PurposeThe aim of this study was to establish guidelines for the selection of cast and wrought-wire clasps for removable partial dentures (RPDs) that would be appropriate for clinically encountered undercuts and facial curvatures. MethodsRandomly selected discarded casts were collected and 30 premolars and 30 molars were surveyed, sectioned to a line representing the clasp and scanned using a flatbed scanner. The average clasp curvature and length for each group was determined and a three-dimensional model printed, to which wrought wire clasps of 0.9- and 1.0-mm diameter were adapted. Standard wax clasp patterns were adapted and cast in a stellite alloy. Each clasp was deformed beyond its proportional limit; and the forces exerted at that limit and at deflections of 0.25 mm, 0.5 mm, and 0.75 mm were measured, and a safety limit was calculated that would ensure elastic deformation at the required undercuts. ResultsA table was produced with guidelines for those clasps that would provide the highest retentive force within the proposed safety limit. The highest forces were provided by cast clasps in a 0.25-mm undercut. Wrought round wire of 1-mm diameter provided the next highest retentive forces, in a 0.25-mm undercut for premolar clasps arms and 0.5-mm for molar clasps. ConclusionsThe results provide valid guidelines for the use of combinations of clasp material and undercut that would exert the maximum retentive force without deformation for both short (premolar) as well as long (molar) clasps, for wrought and cast clasps.

Fitness accuracy and retentive forces of additive manufactured titanium clasp

PurposeLaboratory and clinical assessment of cast titanium dentures were reported, little is known about additive manufacturing (AM) frameworks. This study evaluated in vitro AM titanium alloy clasps for clinical use. MethodsAfter scanning the stainless steel dies to simulate the first molar, an Akers clasp was designed by CAD. AM clasp specimens were manufactured using laser sintering and AM machines from CP titanium grade 2 (CPTi), Ti-6Al-4V (Ti64), and Ti-6Al-7Nb (Ti67) powders. As controls, cast titanium clasps were conventionally made with same three titanium alloys. After nondestructive inspection and surface element analysis, surface roughness, fitness accuracy, initial retentive forces, and changes in retentive forces were measured. ResultsAlthough few porosities and little contamination of AM clasps were confirmed, the AM clasp arm and tip indicated slightly worse fitness accuracy as compared to cast clasps. The initial retentive forces of all titanium clasps showed appropriate retentive forces within the acceptable ranges, AM clasps tended to have lower decreases in retentive forces with up to 10,000 insertion/removal cycles as compared to those of the cast clasps. ConclusionsAM titanium clasps would be acceptable for clinical use similar to that of cast titanium clasps.

Accuracy of removable partial denture framework fabricated by casting with a 3D printed pattern and selective laser sintering

PurposeThe present study aimed to compare the accuracy of removable partial denture (RPD) frameworks fabricated by 3D-printed pattern casting and those fabricated by selective laser sintering (SLS). MethodsA partially edentulous mandibular model was used for the simulation model. Scanning of the model was performed using a dental scanner. The framework was designed by using CAD software. The 3D-printed resin pattern was formed using a 3D printer and casting was performed (AM-Cast framework), and a direct metal laser sintering machine was used for the framework of SLS (SLS framework). 3D scanning of fabricated two types of framework were performed, and these data were overlapped with design data. Fabrication accuracy was verified using the Mann–Whitney U test to compare the discrepancy between the AM-Cast and SLS frameworks. ResultsThe range of differences for the AM-Cast and SLS framework were −0.185±0.138 to 0.352±0.143mm and −0.166±0.009 to 0.123±0.009mm, respectively. Statistically significant differences were observed at the rests, proximal plates, connectors, and clasp arms. Regarding the rests, both lateral and medial displacement in the two types framework was observed in relation to the design data. Large lateral discrepancies of the connectors were observed at the joining area on the tooth-supported side of the lingual bar for the AM-Cast framework. Localized discrepancies were observed at the center of the lingual bar for the SLS framework. ConclusionThe accuracies of RPD frameworks fabricated by AM-Cast and SLS differ depending on the specific structural component of the RPD.

Finite-element analysis and optimization of the mechanical properties of polyetheretherketone (PEEK) clasps for removable partial dentures

PurposePolyetheretherketone (PEEK), a high-strength, aesthetic, and non-allergic thermoplastic polymer, recently became a candidate for replacing metallic components in dental prosthesis. However, as PEEK is flexible, the need for retention presents a key challenge in terms of its clinical application. In this study, clasps prepared using PEEK were optimized and evaluated to provide the mechanical properties required by dentures. MethodsSeventy-two three-dimensional rod-shape models, based on four thickness/width ratios, three base widths, and six taper ratios were created. These models were analyzed using finite-element methods to determine which modified clasp arm shape provided the most appropriate mechanical properties. Three shape-optimized PEEK specimens and one standard-shape Co–Cr alloy specimen were then fabricated. Constant-displacement fatigue testing was performed to calculate load values and deformations after ten years of clinical use. ResultsShape optimization indicated a maximum stress concentration that was consistently located at the base of the specimen, a correlation between mean load values and thickness that was greater than that with the width, and a correlation between taper ratio and mean load values. Fatigue testing showed that although PEEK exhibited significantly lower average load values than the Co–Cr alloy, these were sufficient for clinical use. All specimens exhibited significant deformation during the first period of cycling; however, there was no significant difference in the deformation between the two materials after fatigue testing. ConclusionsPEEK exerts fewer stresses on abutments compared to standard-alloy clasps, provides adequate retention, and satisfy aesthetic demands, indicating that PEEK presents a promising alternative to conventional metal clasps.

The effect of build orientation on the microstructure and properties of selective laser melting Ti-6Al-4V for removable partial denture clasps

Statement of problemSelective laser melting (SLM) Ti-6Al-4V has been used for removable partial dentures, but the impact of SLM Ti-6Al-4V build orientation is not evident. PurposeThe purpose of this in vitro study was to investigate the microstructure and properties of SLM Ti-6Al-4V clasps with different build orientations compared with cast Ti-6Al-4V clasps. Material and methodsForty-eight clasps were made from Ti-6Al-4V alloys—by SLM with 3 different build orientations (SLM0, SLM45, and SLM90) and cast (CAST) as a control. The microstructure was investigated by using a metallographic microscope and a confocal laser scanning microscope. The fit and surface roughness of the clasps were measured, and the physical properties were evaluated. In addition, the von Mises stresses in the clasps were calculated by finite element analysis. All specimens were then subjected to insertion and removal tests in artificial saliva to model 5 years of clinical use. After these tests, 3-point bend tests were used to analyze the fracture surface of the clasp arms, which were observed by using a scanning electron microscope. All data were statistically analyzed (α=.05). ResultsThe microstructure of the Ti-6Al-4V specimens was a comixture of α+β phases. In addition, growth directions of β grains were approximately parallel to the build orientation, with acicular α grains present between β grains. SLM0 and SLM45 had significantly higher roughness than SLM90. Even though the fit was inferior to that of SLM90, SLM0 and SLM45 still performed better than cast specimens (P<.05). The finite element analysis showed that the maximum von Mises stress was located on the middle part of the retainer arms and that the values of the 0.50-mm undercut clasps were much lower than the elastic limit. In addition, the decrease of retentive force in SLM90 clasps was less than that of the CAST group (P<.05). CAST clasps showed brittle fracture, whereas all SLM clasps showed ductile fracture. ConclusionsThe microstructure of SLM Ti-6Al-4V affected the properties of clasps by changing the anisotropy of specimens. Among the tested groups, SLM90 clasps had the best fit, the lowest surface roughness, and the best fatigue resistance. Furthermore, SLM Ti-6Al-4V clasps could be engaged into 0.50-mm undercuts.

Studying the effect of the circumferential clasp arm design on stress distribution using three-dimensional finite element analysis

High stresses which result during functions in the cast clasps arms are the main causes of deformations or fractures. The purpose of the study was to evaluate the stress distribution in three-dimensional finite element analysis models of clasps and to select their preferable design.A three-dimensional finite element analysis was used for the investigations. Preformed clasp wax patterns for circumferential clasps were selected and three parameters namely length, thickness and width at the base and tip were measured to generate purposely designed experimental three-dimensional models. Generated stresses and deformatioans were calculated numerically and plotted graphically.Within the limitations of this study, the preferable cross-sectional shape of the retentive cast circumferential clasp arm was determined as half-round and the taper 0.6 mm.the ideal cross section of the retentive clasp arm was half round with 0.6mm taper diameter.

Retentive force evaluation of cobalt-chromium and gold nanoparticles reinforced flexible clasps in Kennedy class I removable partial denture#

The purpose of this study was to evaluate retentive force of cobalt- chromium (Co-Cr) and nano-gold (AuNps) reinforced flexible clasps in Kennedy class I removable partial denture (RPD). Acrylic model represented Kennedy class I partially edentulous maxillary arch was fabricated and prepared for RPD fabrication. Traditional Co-Cr RPDs with gingivally approaching retentive clasp arm, thermopress flexible polymeric and AuNps reinforced thermopress flexible polymeric RPDs with circumferential retentive clasp arm were fabricated. Retentive force of RPDs were evaluated. The flexible polyamide and reinforced flexible RPDs revealed better preservation of retentive force rather than Co-Cr RPDs that showed a decrease in magnitudes after repetitive cycles.

Comparison of Retention of Clasps Made of Different Materials Using Three-Dimensional Finite Element Analysis.

Retention and esthetics are believed to play a crucial role in deciding the success of removable partial dentures. To compare retention of acetal resin and cobalt-chromium clasps. A finite element model was designed with an edentulous space between mandibular right second premolar and second molar. Occlusal rests were placed on distal fossa of the second premolar and mesial fossa of second molar. An undercut depth of 0.01inch was created on the mesiobuccal surface of the premolar and distobuccal surface of second molar. Three dimensional finite element model of clasp assembly was designed and assigned with the properties of two different materials namely acetal resin and cobalt-chromium in successive steps. A horizontal bar was constructed between the occlusal rests of the prosthesis. Later, variable amount of dislodging force, in increasing order, was applied at the centre of the horizontal bar and the force at which the clasp arm gets dislodged was noted with respect to each of the material. The obtained values were noted and then subsequently analyzed. The amount of force required to dislodge acetal resin and cobalt-chromium clasps was found to be 0.02N and 2N respectively. The results obtained suggested that acetal resin clasp exhibited less retentive force than cobalt-chromium clasps.

Clinical evaluation of removable partial dentures on the periodontal health of abutment teeth: a retrospective study.

The aim of this retrospective study was to evaluate the effect of removable partial dentures in periodontal abutment teeth in relation to the type of denture support and design of RPD in a five-year worn period. Methods : A total of 64 patients with removable partial dentures (RPDs), participated in this study. It were examined ninety-one RPDs. There were seventy-five RPDs with clasp-retained and sixteenth were RPDs with attachments. There were 28 females and 36 males, aged between 40-64 years, 41 maxillary and 50 mandible RPDs. For each subjects the following data were collected: denture design, denture support, and Kennedy classification. Abutment teeth were assessed for plaque index (PI), calculus index (CI), blending on probing (BOP), probing depth (PD), gingival recession (GR), tooth mobility (TM). Level of significance was set at p<0.05. Results : According to denture support of RPD, BOP, PD, PI, GR, CI and TM-index showed no statistically significant difference. Based on the denture design of RPD’s, BOP, PD, PI, CI, and TM-index proved no statistically significant difference. Except GR-index according to denture design confirmed statistically significant difference in RPD with clasp p<0.01. The higher values of all periodontal parameter as BOP, PD, PI, CI and TM were in patients with RPD’s with claps comparing with RPD’s with attachment. Conclusion : RPD’s with clasp increased level of gingival inflammation in regions covered by the dentures and below the clasp arms in abutment teeth.

Forward Kinematics Analysis and Experiment of Small-Caliber Well Rescue System

As for the new designed small-caliber well rescue system for the fallen person in deep well, we made a detailed description about the rescue mechanism, which was composed of framework, anchorage set, stretching arm and clasp arm, and illustrated the function of each mechanical component. Moreover, we deduced the forward kinematics matrices of the clasp arm and the stretching arm, and analyzed and provided the parameters of each degree of freedom. Meanwhile, the experimental prototype of the rescue system was designed and the imitated rescue experiment for a doll was fulfilled. The experimental results show that the rescue system is feasible in small caliber deep well rescue.