Minor Connector Research Articles

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.

Finite Element Analysis of Endocrown and Post-and-Core Abutments for Removable Partial Dentures with Different Framework Materials.

To evaluate the stress distribution in endocrowns and post-and-core crowns used as abutments for a Kennedy Class I removable partial denture constructed with different framework materials. 3D models of a Kennedy Class I mandible were constructed. Cobalt-chromium (Co-Cr) and polyether ether ketone (PEEK) frameworks were simulated for Models 1 and 2, respectively. An endocrown and a fiber post-and-core crown for the mandibular left and right second premolar abutments, respectively, were simulated for both models. Lithium disilicate porcelain was defined for the crowns. A 200-N occlusal force was applied in the vertical and 30-degree oblique directions. The von Mises stresses were evaluated for the abutments and prostheses, and the principal stresses for the cortical bone under vertical and oblique loading. Endocrowns showed lower stress values than post-and-core crowns in both models. Post-and-core crowns generated the highest stress in Model 2 under vertical loading. The PEEK framework caused higher stress values on the abutments than Co-Cr. Compressive stresses were higher than tensile stresses in cortical bone. The highest compressive stress was observed around the left premolar cortical bone area in Model 1 under oblique loading. Oblique loading caused lower stress values than vertical loading, except for on the minor connectors and cortical bone. From a biomechanical perspective, endocrowns may be more advantageous than post-and-core crowns when used as abutments for a Kennedy Class I removable partial denture. In addition, Co-Cr frameworks showed more favorable stress distribution on abutments than PEEK frameworks. Int J Prosthodont 2023;36:203-215. doi: 10.11607/ijp.7269.

Evaluation of PEEK and zirconia occlusal rest designs for removable partial dentures based on finite element analysis.

Purpose We aimed to assess removable partial denture occlusal rests composed of polyether-ether-ketone (PEEK) and zirconia, using finite element analysis.Methods Three-dimensional PEEK and zirconia rest models, including the occlusal rest (1.5 mm thickness at the basal portion, 3.0 mm width) and minor connector (1.5 mm thickness, 6.0 mm height), and rest seat models with mechanical properties of enamel were constructed. The radius of transitional curvature between the rest and minor connector was 0.1-0.5 mm. The rest and rest seat model interfaces were set as frictional contacts (μ = 0.1), and the base of the rest seat model was restrained in all the directions. A 100 N downward load was applied perpendicular to the bottom surface of the minor connector. The maximum value of the first principal stress (Max-S1) was compared to the flexural and fatigue strengths of each material. Occlusal rests with 1.0-2.0 mm thickness, 2.0-3.5 mm width, and 0.5 mm radius of transitional curvature were analyzed.Results Max-S1 was observed at the transitional part and decreased with increasing radius of the transitional curvature, rest width, and thickness. PEEK rests with at least 1.5 mm thicknesses and 3.0 mm widths showed lower Max-S1 than the flexural strength. Max-S1 of all PEEK rests exceeded the PEEK fatigue strength, whereas Max-S1 of the zirconia rests was lower than the zirconia fatigue strength.Conclusions Zirconia occlusal rests with conventional metal rest designs have sufficient fatigue strength. PEEK occlusal rests have insufficient fatigue strength and may not withstand repeated mastication.

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.

Accuracy of Removable Partial Denture Frameworks Fabricated Using Conventional and Digital Technologies.

This study analyzed the fit accuracy of the removable partial denture (RPD) metal frameworks produced using digital and conventional manufacturing technologies. Mandibular RPD metal frameworks (N=15, n=3 per group) were fabricated on a representative clinical case. RPDs were fabricated using one of the following manufacturing procedures: a) conventional lost-wax casting technique (C-LW), b) conventional casting of milled sacrificial patterns (C-M), c) conventional casting of printed sacrificial patterns (C-P), d) selective laser melting (SLM), e) direct metal laser sintering (DMLS) technologies. The fit accuracy of RPD frameworks was analyzed by fabricating replicas with silicone registration material and measuring with a digital microscope. A total of 11 sites and 29 areas in the RPD metal frameworks were considered for the accuracy measurements (μm). Data were statistically analyzed using Wilcoxon signed rank and Friedman test (α=0.05). Before finishing and polishing, C-M method presented overall significantly better (P⟨.001) fit accuracy (118 μm) than those of other methods (195-265 μm). After finishing and polishing, C-M method showed overall significantly better (P⟨.033) fit accuracy (205.7 μm) than C-LW and SLM methods (285.7 μm; 249 μm) and comparable fit accuracy to that of C-P and DMLS methods. Accuracy at the minor and major connector areas of RPDs were affected from the manufacturing technologies. Clinical Implications: When accuracy of RPDs are considered, digital technologies tested presented similar results to those of conventional manufacturing method except for minor and major connector areas which necessitates further improvement.

Castability of a Ti-7.5Mo alloy for fabricating frameworks for removable partial dentures

Statement of problemThe properties of commercially pure titanium are better than those of cobalt chromium alloys in various ways. However, casting pure titanium is challenging because of its high melting point and chemical reactivity. Because of excellent mechanical strength, a titanium alloy, Ti-6Al-4V, has been commonly adopted, but the aluminum and vanadium ions released may be cytotoxic. PurposeThe purpose of the present study was to evaluate a new titanium alloy, Ti-7.5Mo, developed by the National Cheng Kung University for casting removable denture frameworks. The casting success rate, porosity, and guide plane or rest fit were compared among frameworks cast with Ti-7.5Mo alloy and pure titanium for 3 types of edentulism. Material and methodsTi-7.5Mo alloy and pure titanium were used to cast frameworks for Kennedy Class I and II and completely edentulous conditions, with 5 frameworks for each condition. Wax patterns of the frameworks were designed and fabricated by using computer-aided design and computer-aided manufacture (CAD-CAM) technology to ensure their geometrical consistency. They were then invested with aluminum oxide–based material and cast. The castings were examined with microcomputed tomography (μCT) for porosity, and fit was evaluated from the thickness of a vinyl polyether silicone material at the guide plane or the rest by using an optical microscope. The casting was determined to be successful if the frameworks were complete. The porosity and fit were statistically evaluated by using 2-way ANOVA (α=.05). ResultsUsing pure titanium, the casting success rate was 80%, with only 64% of the major connectors in the deficient castings being complete. The μCT images showed that the percentage of casting defects in Ti-7.5Mo castings was one-third of the pure titanium castings. Furthermore, internal voids were detected in the clasps of the pure titanium castings, while the Ti-7.5Mo castings had few defects in the minor connectors and no radiographically detectable defects in the clasps. The fit analysis demonstrated smaller gaps over both guide planes and rests in the Ti-7.5Mo castings. ConclusionsTi-7.5Mo alloy had better castability than pure titanium. Based on the results, Ti-7.5Mo alloy is suitable for dental casting and may provide better performance.

Designing metal framework partial denture

The number of partiallyedentulous adults is increasing, and many patients will require replacement of missing teeth. Although current treatment options also include fixed partial dentures and implants, removable partial dentures (RPDs) can have advant-ages and are widely used in clinical practice. However, a significant need exists to advance materials and fabrication technologies because of the unwanted health consequences associated with current RPDs. The RPDs consists of many components, such as major and minor connector, direct and indirect retainer, also rests. The variety of anatomic considerations related to oral con-ditions may affect selection of these components. The objective of this review is to discuss data related to RPDs design and factors affecting its selection. It was concluded that prosthodontists need to fully understand the basic of RPDs design princi-ples and should be familiar with those structures.

The computer-aided design and rapid prototyping fabrication of removable partial denture framework for occlusal rehabilitation: clinical report

The objective of this case report was to describe the clinical sequence for occlusal vertical dimension (OVD) recovering with the manufacture of removable partial dentures (RPD) produced by computer-aided design and rapid prototyping. The patient presented to the Dentistry Department of the Federal University of Rio Grande do Norte reporting dissatisfaction with the superior RPD. At clinical investigation, a fracture in the minor connector and support at the region of tooth 15 was observed, in addition to severe OVD loss. In this case, after obtaining correct OVD, four more sessions were necessary for RPD fabrication. In the first appointment, intraoral scanning was performed to generate STL files used for path of insertion determination in the CAD software. The need for a guide plane on tooth 15 was observed, thus a preparation guide was designed and 3Dprinted to aid axial tooth reduction. At the second visit, after mouth preparation, another intraoral scanning was performed to acquire virtual working models. The RPD framework was designed and 3D printed in a castable resin pattern and invested for cobalt-chromium alloy melting. In the third visit, clinical evaluation of the framework and teeth and artificial gingiva colors selection were performed. The articulated models were then 3D printed, enabling pre-fabricated teeth to be assembled and acrylized. On the fourth appointment, RPD was installed and the patient received routine instructions. In this sense, the use of CAD/CAM technologies presented as a valuable tool to enhance restoration of OVD by the manufacturing of RPD.

Examination of inter-rater and intra-rater reliability during retentive force measurement of different clasps using the developed small-sized retentive force measurement device

BackgroundThe design process of a removable partial denture (RPD) consists of rests, major connectors, minor connectors, denture base, and retainer. The abutment tooth contour determines the location of the retention portion of the clasp at the retention areas. The load capacity of the clasp depends on various factors such as type, the position of a clasp, tooth position, clasp length, and pullout location. As a general rule, the amount of retention required to dislodge the RPD from the supporting structure should always be the minimum necessary to resist reasonable dislodging forces. Excessive force from the clasps may cause many problems. Although there are many reports on the retentive force of cast clasps using large devices, it has not been possible to measure it using simple devices until now.MethodThe purpose of the present study is to develop a small-sized retentive force measurement device that can easily measure the retentive force of a clasp used for an RPD. It is to examine inter-rater and intra-rater reliability. A small-sized retentive force measurement device that can be easily measured in the laboratory has been developed. Using commercially available hard plaster cast, a skilled dental technician has made 10 types of cast clasps used in clinical practice using conventional techniques. Three assessors measured the retentive force of 10 types of cast clasps. To confirm the reliability, the intra-class correlation coefficients ICC (1,1) and ICC (1,3) of the 3 assessors were calculated, and the reliability within the assessor was examined. The inter-class correlation coefficients ICC (3,1) and ICC (3,3) were calculated, and the reliability of the assessors was examined.ResultThe intra-class correlation coefficients of 3 assessors are as follows: assessor 1 has ICC (1,1) = 0.971, ICC (1,3) = 0.990, assessor 2 has ICC (1,1) = 0.967, ICC (1,3) = 0.989, assessor 3 has ICC (1,1) = 0.962, ICC (1,3) = 0.987. The inter-class correlation coefficients of 3 assessors are as follows: ICC (3,1) = 0.993, ICC (3,3) = 0.998. From the evaluation standard of the intraclass correlation coefficients of reliability value by ICC, it was evaluated as almost perfect and high reproducibility was confirmed.ConclusionThe developed small-sized retentive force measurement device has reproducibility within and between the assessors.

Dimensional Changes in Co-Cr Alloys and Titanium Framework of Removable Partial Dentures Evaluation of the dimensions of the dental clasps

Removable partial denture are prosthetic solutions that replace missing teeth of partially edentulous patients, ensuring stomatognathic system functionality with affordable costs.The purpose of this study is to analyze the dimensional variations caused by the execution errors, which can lead to premature deterioration of the removable partial dentures and to conclude what sizes are deficient and can lead to the deterioration of the prosthetic part. The material involved in the present study was represented by the metal framework of 181 removable partial dentures. Of the total of 181 removable prosthetic parts, 88 were maxillary prostheses and 93 were mandibular prostheses. Measurements were made at the retentive arms, opposing arms, minor connectors, rests and junction areas between the body of the clasps and the active arms and studied compared to the edentulous classes. The results are focused on dimensional changes of both the retentive arms and the opposing arms of the clasps, which are roughly modeled in the first 3 edentulous classes, with a significant difference from those achieved in Kennedy`s 4th class edentulous, where these segments of the clasps are much shorter. Regarding the size of the rests, although their thickness approximates the values indicated in the literature, they do not fit into the occlusal relief of the tooth. The length of the retentive arms varies according to the classes of edentulous, the clinical situation, but also the size and type of the tooth (premolars, molars) on which the clasp is applied. Regarding the opposing arm, the observed differences cannot be correlated with the objective criteria of their achievement because the attention is directed towards the realization of the retentive arm.

Evaluation of the effect of ultraviolet light polymerized clear adhesive on shear and tensile bond strength of heat cure denture base resin to the cobalt-chromium retentive minor connector: An in vitro study.

Aim:The aim of this study is to evaluate the efficacy of new material ultraviolet (UV) light polymerized clear adhesive on shear and tensile bond strength of heat cure denture base resin (Polymethylmethacrylate (PMMA)) to cobalt-chromium (Co-Cr) retentive minor connector.Setting and Design:Comparative evaluation- In-vitro study.Materials and Methods:Sixty samples of Co-Cr plates mimicking minor connectors were fabricated. Thirty samples were coated with new material UV light polymerized clear adhesive and cured under UV light source for 10 min. In gun-metal flask, metal plates were placed in the lower compartment over it. Heat cure acrylic resin was packed in the dough stage with the help of clamps and processed according to the manufacturer's instructions. Samples were kept in artificial saliva for 90 days. Shear and tensile bond strengths were calculated of each sample with a Universal testing machine, and results were statistically analyzed. Type of bond failure was observed for each sample under stereomicroscope.Statistical Analysis Used:Unpaired t test.Results:Tensile bond strength, as well as shear bond strength, showed that 0.93 N and 1.64 N respectively for without application of new adhesive was more as compared to that of samples with the application of new adhesive which is 0.75 N and 1.54 N respectively. Bond failure was found to be an adhesive failure in resin–metal interface.Conclusions:Excellent bonding seen between the new adhesive and acrylic interface but limited effect on the metal interface. To increase bond strength between metal and resin interface, some surface treatment with the metal surface is needed to increase the bonding of the new adhesive to the metal surface.

The Need of Additional Tissue Relief Required under a Minor Connector

The Need of Additional Tissue Relief Required under a Minor Connector

Metallic frames of removable partial denture: a planning proposal

Removable partial denture (RPD) is an important oral rehabilitation resource with an acceptable result even over a very long observation period. However, it is still difficult for many clinicians to make an appropriate RPD. One of the main causes of RPD failure is the missing or incorrect planning of the metal frame. Perhaps, this lack of planning occurs because of the difficulty that clinicians have to choose the components for the metallic frame among the enormous number of possibilities that exist. Thus, the present article aims to propose a simple sequence for the planning of metallic frames of the RPD following five steps: I) Classification of partially edentulous arches; II) Choice of the retainer (direct and indirect, when needed); III) Saddle drawing; IV) Choice of the major connector; and, V) Minor connector drawing.KeywordsDental prosthesis; Planning; Removable partial denture.

Increasing Denture Retention using Compound Denture Technique – A Case Report

Background: Treating missing tooth with denture, in some cases, still leave the patient unfulfilled. Good mastication and retention are the main considerations especially for those who require more retentions. In some cases, combination of partial and fixed denture the best approach to achieve better functional and retention results. Purpose: To report compound denture procedures with good mastication and retention as the main considerations. Case: A 43-year-old male patient reported a complaint of chewing difficulty due to missing right upper front teeth caused by work accident and extracted posterior. Patient wanted to wear partial denture to regain good mastication. Case management: Compound denture was chosen to optimize the remaining teeth for better functional and aesthetic. Zirconia all ceramic fixed dentures were fabricated on 13, 14, 15 with an occlusal rest on 13 and 15. Pontic on the 14 used ridge lap design. Discussion: Compound denture is a combination of removable and fixed denture where a minor connector of a removable denture should involve a fixed denture. Fixed denture shall be fabricated first and then removable denture. Conclusion: The definitive restoration of this case was compound denture, which is a combination of partial denture metal frame and fixed denture to restore the good mastication and retention.

Stress and strain analyses of removable partial denture abutment tooth in relation to the position of the minor connector

Introduction/Objective For optimum loading distribution, the angle formed by the occlusal rest and the vertical minor connector from which it originates should be less than 90?. The objective of the article was to visualize the optimum angle between the occlusal rest and the minor connector in terms of intensity and distribution of occlusal loads using finite element analysis. It was the intention, concerning biomechanical behavior, to document that the optimum angle between the occlusal rest and the minor connector should be less than 90?. Methods Three different virtual models of partial edentulous Kennedy III class were created using the CATIA design computer program with different angles between the occlusal rest and the minor connector. Stress distribution after simulated occlusal loading was analyzed using the finite element method. Results Comparing the results obtained for three models, the highest stress values were seen in model 3 (the angle between the occlusal rest and the small connector is greater than 90?) whether the load is applied in the middle or at the end of the saddle. Conclusion Within limitations and on the basis of the study results, the minimum compressive stress was seen in model 1, where the angle between the occlusal rest and the minor connector was less than 90? whether the load is applied in the middle or at the end of the saddle. It is recommended that obtuse angle between the rest and the minor connector should be avoided due to potential hazardous stress concentration on abutment teeth.

大連結子と小連結子の設計に連結効果以上の機能を期待する

大連結子と小連結子の設計に連結効果以上の機能を期待する

Removable Dental Prosthesis Splint. An Occlusal Device for Nocturnal Bruxing Partial Denture Users

Nocturnal bruxing is a parafunctional activity of the masticatory system that may create problems for removable dental prosthesis (RDP) users. Such problems may include root fractures, increased mobility of abutment teeth, excessive wear of resin denture teeth, minor connector bending, or denture base cracking. This clinical report presents an occlusal device fabricated for an RDP patient. The device used existing ERA attachments for added retention designed with the intended purpose of protecting the definitive fixed and RDP from damage due to nocturnal bruxing activity and providing for even distribution of parafunctional forces.

Finite Element Analysis of an Implant‐Assisted Removable Partial Denture

This study analyzes the effects of loading a Kennedy class I implant-assisted removable partial denture (IARPD) using finite element analysis (FEA). Standard RPDs are not originally designed to accommodate a posterior implant load point. The null hypothesis is that the introduction of posteriorly placed implants into an RPD has no effect on the load distribution. A Faro Arm scan was used to extract the geometrical data of a human partially edentulous mandible. A standard plus regular neck (4.8 × 12 mm) Straumann® implant and titanium matrix, tooth roots, and periodontal ligaments were modeled using a combination of reverse engineering in Rapidform XOR2 and solid modeling in Solidworks 2008 FEA program. The model incorporated an RPD and was loaded with a bilateral force of 120 N. ANSYS Workbench 11.0 was used to analyze deformation in the IARPD and elastic strain in the metal framework. FEA identified that the metal framework developed high strain patterns on the major and minor connectors, and the acrylic was subjected to deformation, which could lead to acrylic fractures. The ideal position of the neutral axis was calculated to be 0.75 mm above the ridge. A potentially destructive mismatch of strain distribution was identified between the acrylic and metal framework, which could be a factor in the failure of the acrylic. The metal framework showed high strain patterns on the major and minor connectors around the teeth, while the implant components transferred the load directly to the acrylic.

Connectors and attachments in oral rehabilitation

Connectors, the term itself indicates connection or something that connects one thing to the other. In fixed Prosthodontics, connector refers to the portion of a fixed partial denture that unites the retainer and pontic. For two things to be joined together there should be a medium for it. In other words, something that will connect them together to make them look as one. In removable Prosthodontics, connectors are the one which unite the components: Major connector - that connects the components from one side of the arch to the other side of the arch. Minor connectors - the connecting link between the major connector or base of removable partial denture and other units of the prosthesis such as clasps, indirect retainer and occlusal rest. Precision attachments are special type of direct retainers used in partial denture construction. By definition, the term precision denotes 'the quality or state of being precise'. They are sometimes said to be a connecting link between the fixed and removable type of partial dentures as it incorporates features common to both types of construction. This article brings a case report of using the connectors and attachment for oral rehabilitation.

Comparison between Acetal Resin and Cobalt-Chromium Removable Partial Denture Clasp Retention: An in vitro Study

ABSTRACT Statement of problem The retention qualities of acetal resin clasps are questionable. Purpose To asses the initial retention and after cycling for 1,200 cycles of acetal resin clasps as compared to cobalt-chromium clasps. Materials and methods Extracted maxillary first premolars and molars were collected. Each tooth was embedded in acrylic block up to the cementoenamel junction. On each block, partial denture model consisted of Akers clasp, minor connector, cobalt-chromium horizontal plate representing the denture base, and a vertical arm on the horizontal plate was constructed. Models were divided into four groups (five each). Group I had acetal resin clasps on premolars. Group II had cobalt-chromium clasps on premolars. Group III had acetal resin clasps on molars. Group IV had cobalt-chromium clasps on molars. Akers clasps were designed to utilize 0.01 inch undercut. Each model was connected to the universal testing machine through the vertical arm. The model was placed in artificial saliva and a tensile load was applied to measure the initial retention. Then retention was measured after cycling for 200, 400, 600, 800, 1,000 and 1,200 cycles. One-way analysis of variance followed by Duncan's multiple range test was used to test the effect of groups and cycling on tensile load required for clasp dislodgment. Results Groups I and III showed no change in retention on cycling up to 1,200 cycles. Group I showed significantly higher retention than group III. Groups II and IV showed significant reduction in retention upon cycling more than 800 cycles. In spite of this reduction in retention, it is still higher than that in groups I and III. Conclusion Cobalt-chromium clasps showed higher retention than acetal resin clasps despite the deformation encountered in the former. Acetal resin clasps showed more retention qualities on premolar teeth than that on molar teeth. Clinical implications Acetal resin clasps can be used to retain Kennedy's class III partial denture. However, when used on molar teeth, it is recommended to increase the thickness of the retentive clasp arm or to use a deeper undercut. How to cite this article Mohamed T, Baraka OA, Badawy MM. Comparison between Acetal Resin and Cobalt-Chromium Removable Partial Denture Clasp Retention: An in vitro Study. Int J Prosthodont Restor Dent 2013;3(2):50-56.