Retentive Arms Research Articles

Modified feeding plate for a one-month-old infant with Pierre Robin sequence: A case report

Pierre robin sequence is characterized by the triad of mandibular micrognathia, ‘U’ shaped cleft palate, and glossoptosis. Infants with this condition usually present with airway obstruction and feeding difficulties. This in turn leads to low weight and nutritional deficiencies which might delay the surgical intervention for the same. This case report describes a one-month-old infant with Pierre Robin sequence presenting with feeding difficulty and nasal regurgitation due to a ‘U’ shaped cleft palate. Elastomeric impression followed by fabrication of feeding plate with auto-polymerizing resin was done. Additional ‘S-shaped’ retentive arms were provided from the intra-oral to extra-oral side wire to provide additional retention and to prevent injury to both the child and parent while feeding. Early insertion of a feeding plate helps to prevent nasal regurgitation, to gain weight, and to guide the growth of the mandible in a child with Pierre Robin Sequence.

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.

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.

Retentiveness comparison of individual clasps made from polyamide, acetate resin and cobalt-chrome for removable partial dentures

Objective: This study aimed to evaluate and compare the retention force of individual clasps made from polyamide, acetate resin and cobalt-chrome for removable partial dentures. Material and methods: Three groups of clasps were fabricated: Cr-Co - 10 conventional chrome-cobalt metal clasps; Ac - 10 clasps with reciprocal arms and occlusal rests in chrome-cobalt and retentive arms in acetate resin; and Poly - 10 clasps with reciprocal arms and occlusal rests in chrome-cobalt and retentive arms in polyamide resin. Through the tensile test, in a universal testing machine, the initial retention force of the specimens was obtained and then clasps were cycled 7200 times, immersed in artificial saliva (60 months of simulated clinical use). After cycling, tensile test was performed. Results: All groups presented a retention decrease after the cycling. Ac presented a large reduction in retentive force (61.43%), followed by Cr-Co (26.5%) and Poly (12.09%). Conclusions: Aesthetic clasps of polyamide can be used in clinical cases where the anterior supporting teeth will not be essential for good retention of the removable partial denture because this clasp showed to be more resistant than the acetate resin.

Effect of acetyl resin retentive arms on the retentive force of circumferential clasps: An in vitro study

PurposeTo compare and to evaluate the stability of the retentive force of cobalt–chromium (Co–Cr) circumferential clasps (control) to those with an acetyl resin retentive arm. MethodsSixteen specimens with a couple of circumferential clasps were made using Co–Cr over a metal model providing 0.25mm undercuts. Eight specimens were fabricated without the anterior retentive arm, which was made later using acetyl resin (Dental D). Insertion and removal simulation test was performed through 7250 cycles. The retentive force was recorded in Newtons (N) for periods corresponding to 0, 1, 2, 3, 4, and 5 years. The data were subjected to ANOVA and Tukey test to compare periods and to Student's t test to compare groups (α=0.05). ResultsMean (SD) is presented for Co–Cr and resin groups, respectively: 8.09(3.05) and 2.79(1.57) in period 0; 10.48(4.25) and 3.32(1.92) in 1 year; 10.09(4.15) and 3.47(1.81) in 2 years; 9.87(4.30) and 3.46(1.87) in 3 years; 9.46(3.93) and 3.27(1.59) in 4 years; 9.63(3.79) and 3.41(1.59) in 5 years. There were significant differences for Co–Cr between periods of 0 and 1 (p<0.001), 0 and 2 (p<0.01) and 0 and 3 (p<0.05). In the resin group, no significant differences were found between periods (p>0.05). Comparisons between the groups showed statistical differences for all tested periods: 0 (p=0.0012), 1 (p=0.0013), 2 (p=0.0019), 3 (p=0.0031), 4 (p=0.0027) and 5 years (p=0.0014). ConclusionsAcetyl resin retentive arms, even if only in the anterior clasps, can significantly reduce the retentive force, but this force remained stable after 5 years of simulated use.

Stress distribution in retentive arms of combination clasps used on premolars

Stresses resulting from cast clasp arms during insertion and the removal of removable partial dentures are the main causes of deformations or fractures. Therefore, achieving clasp designs producing less stress is very important. Retentive clasp arms used for premolars were investigated through the reverse engineering approach. The aim was to determine stress distribution in oval and half-oval clasps cross-sections in order to analyse biomechanical behavior. Purposely designed experimental three-dimensional (3D) models of the clasp arms were constructed on the buccal surface of an upper first premolar, to be used for structural simulations. 3D teeth models obtained after laser scanning were used as a support for retentive clasp arms modeling. Parameters of the clasp arms like length, thickness and cross-section were considered for the simulation of stainless steel wires. A concentrated load of 5 N was applied at the inner tip of the clasp arm. A precise model of the coronal buccal surface of an upper first premolar was generated. This model was a useful tool in designing stainless steel clasp arms of different thickness and cross-section. In all cases, high stress values were located on the inner surface of the clasp arm, in the part located above the height of the contour. A similar bending stiffness was observed between the half-round cross-section design with a diameter of 1 mm and the round cross-section design with a diameter between 0.6 and 0.7 mm. This in vitro study demonstrated that the reverse engineering approach and structural analyses provide a powerful tool for designing clasps and visualizing fracture risk areas and for choosing the adequate cross-section for each case. Within the limitations of this study, it was suggested that, on premolars, the biomechanical performance of half-round cross-sections for the retentive arms may be higher than round sections of clasp arms showing similar mechanical stiffness.

Effect of Arm Design and Chemical Polishing on Retentive Force of Cast Titanium Alloy Clasps

Titanium dentures have recently increased in popularity. A decrease in the retentive force of the titanium clasps has frequently been observed. This study investigated the effect of retentive arm design and chemical polishing of titanium clasps. Four Akers clasps with 0.25-mm and 0.5-mm undercuts were designed so that the retentive arms were placed at 1/2 and 2/3 of the undercut area. Wax patterns were fabricated and invested in phosphate-bonded Al2O3/LiAl SiO6. They were cast with CP Ti Grade 2, CP Ti Grade 3, and Ti-6Al-7Nb using an argon gas-pressure casting unit (Autocast HC-III). After sandblasting, the castings were chemically treated with an HNO3/HF solution. The retentive force (N) was measured up to 10,000 insertion/removal times. The results (n = 5) were analyzed by ANOVA/Tukey's test (alpha= 0.05). The retentive forces significantly decreased with increasing immersion time in the HNO3/HF solution (p < 0.05). The retentive force of the 2/3 undercut was significantly greater than that of the 1/2 undercut (p < 0.05). Excluding the initial insertion/removal period of the 2/3 undercut, there were no significant differences among all the titanium metals tested (p > 0.05). As the number of insertion/removal times increased, the retentive force of the 2/3 undercut greatly decreased. The retentive force of the Ti-6Al-7Nb clasps for the 1/2 undercut decreased the least after 10,000 insertion/removal times. Chemical treatment for titanium clasps should be performed for 1-5 minutes due to the following factors: accuracy, surface roughness, surface structure, initial retention, and stability of retention. To maintain appropriate long-term retentive force, the retentive arms should be placed in the 1/2 undercut area of the abutment tooth.

Finite Element Method Analysis of Stress Distribution to Supporting Tissues in a Class IV Aramany Removable Partial Denture (Part II: Bone and Mucosal Membrane)

One of the most important issues in the design of removable partial dentures (RPD) is the location of retentive arms to provide sufficient support. This is a critical factor in patients with less supporting tissue and abutment teeth. Patients classified as Class IV Aramany need special attention in this area of RPD design to minimize the stress distribution in bone and mucosal membrane. Using the finite element method, the aim of this study was to analyze the distribution stress to supporting tissues when a Class IV Aramany RPD is worn. The data presented in this report are the effects of the stress on bone and mucosal membranes. Results on teeth and the periodontal ligament have been previously reported. Three dimensional finite element models were constructed using normal dimensions. Exact physiology and morphology of teeth and the remaining palate were simulated to that of a maxillectomy patient. Three RPD designs with circumferential cast retainers were examined: buccal retention and palatal reciprocation (P1); palatal retention and buccal reciprocation (P2); and buccal and palatal retention (P3). After completion of the models and remaining palate, each RPD design was loaded under 53N and stress was applied in three different directions: vertical to the posterior teeth (premolar and first molars) of the RPD (F1); at a 33 masculine angle to the posterior teeth (premolar and first molars) of the RPD (F2); and vertically on the anterior teeth (central incisors) of the RPD (F3). The stress distribution in the RPD models on cortical and cancellous bone and the mucosal membrane was analyzed using von Mises criterion. The maximum tension in cortical bone (70.84 Mpa) was observed when a 53N force was applied in a vertical direction to posterior teeth (F2) using buccal and palatal retention (P3). Minimum tension (15.73 Mpa) in cortical bone was observed using the F3 load on the P2 design. Similar results were seen in cancellous bone, with the highest stress (8.01 Mpa) observed using F2 load on the P3 design and the lowest stress (3.04 Mpa) observed using the F3 load on the P2 design. For mucosal membrane, the maximum (3.57 Mpa) and minimum (3.05 Mpa) stress was observed using the F3 load on the P3 design and the F1 load on the P2 design, respectively. The average stress in all RPD designs was 3 Mpa. The design demonstrating the least tension in cortical and cancellous bone and mucosal membrane was the P2 design, a RPD with palatal retention and buccal reciprocation. Palatal retention and buccal reciprocation (P2 design) is recommended for patients with maxillofacial RPDs.

Finite Element Analysis of Thermal Stresses in Circumferential Cast Clasps of Removable Partial Dentures

Several studies evaluated the removable partial dentures by the finite element analysis, but none of them evaluated thermal stresses. The purpose of the study was to explore the influence of thermal oral changes induced by hot/cold liquids and food on the circumferential cast clasps of removable partial dentures. A 3-dimensional finite element method was used to explore the temperature distribution, thermal stress and the influence of thermal changes on stresses and displacements of circumferential clasps during functions. Thermal variations induce stresses in dental clasps, high temperatures having a more aggressive effect than lower one. Cold liquids and food induce high stresses in the retentive clasp arms while hot ones in the occlusal rests of the clasps and for the back action clasp also in the minor connector. The study suggests the importance of consFigureidering thermal variations for stress analyses of the cast clasps.

The curvature of the retentive arm in a circumferential clasp and its effect on the retention: 3D analysis using finite element method

Introduction: Missed teeth are replaced to provide the patients with occlusal stability. Partial removable prosthodontics are still in use among the various applications in this field. Adequate retention is essential for its function. Circumferential clasps are used and the main goal of this study is to assess the importance of the geometry of the retentive arm and its effects on the quality of retention produced. Materials and Methods: Three-dimensional finite element method of analysis was selected to find answer to the questions. Three models were designed with the retentive arms of same lengths and different angular coverages ( α is explained in text). 0.01″ to 0.03″ of displacements were applied and the forces derived. Results: Different amounts of retentive forces were produced, which were assessed in two directions. Conclusion: The greater the curve of a retentive arm, the greater the retention force produced, assuming that the length of retentive arm remains constant.

Framework retention for maxillary obturator prostheses

An in vitro study was done to evaluate the relative effectiveness of clasp placement in specific obturator framework designs. Three commonly encountered defects were studied. These included (1) the antero-hemimaxillectomy, in which the only remaining dental support is from canine to second molar on one side; (2) the hemimaxillectomy, in which the defect extends the length of the midpalate to the mesial surface of the central incisor; and (3) the partial or posterior maxillectomy, in which all six anterior teeth remain along with all posterior teeth on the nondefect side. Three frameworks that demonstrated the following design characteristics were made for each cast: (1) full lingual plate with buccal retentive arms, (2) lingual retention with buccal reciprocation, and (3) buccal and lingual retention.

Construction techniques for wrought-wire retentive clasp arms as related to clasp flexibility

The three standard means of attachment of circumferential wrought-wire retentive arms to removable partial denture frameworks were tested for their influence on component flexibility. A wire retentive arm, adapted after framework construction and soldered to the frame on the base retentive meshwork well away from the minor connector was found to be more flexible than the other common methods of wire attachment. Wire components, attached in this manner, appear to have the same degree of flexibility as unattached wire.