Retentive Undercut Research Articles

A DISTINCTIVE APPROACH TO REHABILITATE PATIENT WITH BILATERAL MAXILLECTOMY DEFECT BY TWO-PIECE HOLLOW OBTURATOR- CASE REPORT

An obturator is a common tool for prosthetic rehabilitation following invasive surgery, particularly in a total maxillectomy case. However, loss of teeth, palatal denture-bearing area, and vestibular retentive undercuts leaves an inadequate anatomic base to construct the definitive prosthesis. This results in compromised retention and stability. The retention problem can be resolved by fabricating an obturator that engages remaining undercuts. But in such acquired large defects, if all undercuts are engaged, the prosthesis may become too heavy, non-retentive, and challenging to insert, particularly in patients with very high and large defects. Therefore, in this case fabrication of two-piece magnet retained hollow obturator was described to make a prosthesis light weight with the use of thermoplastic polyvinyl chloride sheet in first part which provides adequate retention by engaging the desirable undercuts. The second part of the obturator was made hollow by the use of urinary catheter that was removed easily after completion of denture processing. After this, both the parts were attached together with the use of magnets. This technique is economical and easy to use to restore both function and esthetics in patients with bilateral maxillectomy defect.

Retention Assessment of High Performance Poly-etheretherketone Removable Partial Denture Frameworks Constructed by Various Techniques (in vitro Study).

Statement of the Problem: Poly-etheretherketone is a novel material used in the construction of the removable partial dentures frameworks instead of the metal frameworks. This material can be fabricated by various techniques. Most common methods are the injection molding or Computer Aided Design/Computer Aiding Manufacturing (CAD/CAM) milling techniques. The fabrication technique may affect the adaptation of the frameworks by influencing the retention.Purpose: To assess the effect of the processing techniques of high performance Poly-etheretherketone either by injection molding (pressing) or CAD/CAM milling techniques on removable partial denture frameworks retention for rehabilitation of upper class I Kennedy classification.Materials and Method: This in vitro study was performed on one epoxy resin model representing the partially edentulous maxillary arch with natural teeth extending from first premolar to first premolar. First premolars and canines were reduced to receive porcelain fused to metal crowns with 0.50mm mesio-buccal retentive undercuts, distal guiding planes and mesial occlusal rest seat on first premolars and cingulum rest seat on canines. Considering the construction technique of frameworks, twenty samples were divided into two groups. In the group I, ten frameworks were fabricated by injection molding, and in the group II, ten frameworks were fabricated by CAD/CAM. The removal and insertion was carried out at 120, 720 and 1440 cycles for both groups, respectively. The retention values were measured by using Universal Testing Machine before cycling and after each interval.Results: Independent t-test showed significant difference on retention at different simulation cycles between groups. Group II exhibited significantly less retention than group I (p< 0.001), while comparing the retention at different cycles within each group by paired sample t-test exhibited significant decrease of retention till the end of the cycling (p< 0.001).Conclusion: From the retention point of view, high performance poly-etheretherketone frameworks fabricated by injection molding technique provided a promising method over CAD/CAM technique milling method.

Rehabilitation of a patient after a total maxillectomy with a 2-piece magnetically retained obturator: A clinical report

After ablative surgery, especially a total maxillectomy, an obturator is commonly used as a method of reconstruction. However, the loss of a palatal denture-bearing area and vestibular retentive undercuts leaves an anatomically deficient base on which to construct the definitive prosthesis. As a result, retention and stability is compromised. A solution to the retention problem is to construct an obturator that engages undercuts and scar bands. Engagement of all undercuts can lead to a prosthesis that is too cumbersome and difficult to insert, especially in a patient with scars after radiation. In this article, a technique for creating a 2-piece magnetic obturator that engages the nasal scar band is described.

Rehabilitation of Exenterated Right Eye: A Prosthetic Challenge

Background: Facial defects can be acquired or congenital, but irrespective of etiology, any maxillofacial structure if damaged or missing will result in an unaesthetic and unappealing personality of individual. Orbital defects are very evident and effect the appearance and social front of the individual. Many modalities are available to rehabilitate the defect of an orbit but prosthetic rehabilitation with silicone prosthesis is a simple and effective approach. Retention is generally achieved by engaging available undercuts or using mechanical accessories or skin adhesives etc. This case report describes successful rehabilitation of right orbital defect using a non-surgical approach with room temperature vulcanized silicone and skin adhesives. Case Report: A 45 yr old male reported with, chief complaint of missing right orbit and unaesthetic appearance secondary to gunshot wound. Patient was not ready for any more surgical procedures or additional accessories and available retentive undercuts were minimal. Hence, conventional silicone prosthesis was made using stock eye shell and room temperature vulcanized silicone retained with skin adhesives. The approach was simple to a complex problem and gave reliable result in very limited time. Conclusion: With extensive orbital defect, rehabilitation is difficult and complex as retention is compromised and it is difficult to match the shade of the prosthesis.This case represents a simple and predictable approach to a case of exenterated right orbit with conventional roomtemperature vulcanized silicone and silicone skin adhesives.

An Evaluation of Retentive Ability and Deformation of Acetal Resin and Cobalt-Chromium Clasps.

To compare the retentive ability and deformation of Acetal resin with Cobalt-Chromium clasps via Insertion Removal apparatus after subjecting them to stimulate clinical use. Materials used for this study are commercially available Cobalt-Chromium alloy namely Wironit, Bego, Germany and Acetal resin namely Biodentaplast, Bredent, Germany. The test samples were divided into two major groups based on the type of materials used in the study. Each major group is further subdivided into two sub groups based on the retentive undercut depths used to engage the clasps. So a total of 20 specimens were prepared, comprising of 5 specimens in each sub group. Then the specimens were tested for retention force and deformation. The results of this study indicate that acetal resin clasps are resistant to deformation and may offer a clinical advantage over the conventional metal clasps. The retentive force of acetal resin clasps did not decrease over the cycling periods. This would be attributed to the resilient nature of acetal resin. Under the conditions of the present study cobalt chromium clasps lost retentive force within 730 cycles of placement and removal and continued to lose retentive force during the remaining test period. This invitro study demonstrated that retentive force of cobalt chromium clasp is superior to that of Acetal resin for removable partial dentures. As acetal resin clasps exhibits greater flexibility and long term retentive resiliency, it can be used for removable partial dentures where aesthetics or periodontal health is a primary concern.

New Clasp Assembly for Distal Extension Removable Partial Dentures: The Reverse RPA Clasp.

Several clasp types are used in distal extension removable partial dentures. In some cases the terminal abutments have only distal retentive undercuts that can be occupied by bar clasps; however, bar clasps may be contraindicated with no suitable alternative. This article presents a reasonable solution by introducing a new clasp design as a modification to the well-known RPA clasp. The design includes a mesial rest, proximal plate, and buccal retentive arm arising from the rest and extending to reach the distal retentive undercut.

In Vitro Comparative Study of Retention of Maxillary Kennedy Class I Removable Partial Denture Retained with Four Different Designs of Esthetic Clasps

To study the effect of clasp, design, material, and amount of retentive undercut of esthetic clasp on retention of removable partial dentures restoring maxillary Kennedy class I removable partial denture.

Fabricating a Hollow Obturator with Light-Cured Resin System

Tumor resection of a cancer lesion produces maxillary defects that can be easily restored with an obturator to close the defect area. Postsurgical maxillary defects predispose a patient to hypernasal speech, fluid leakage into the nasal cavity, and impaired masticatory function. Therefore, the primary aims of prosthetic rehabilitation in total and partial maxillectomy patients include: separation of oral and nasal cavities to allow adequate deglutition and articulation, possible support of orbital contents and support of soft tissue to restore mid-facial contours. A method of fabricating a simple hollow obturator for maxillectomy patients is described. The use of a relatively long-lasting light cure resin materials in making obturators allows stable, comfortable, and effective obturation. The hollow prosthesis is lightweight and sufficiently flexible to allow relatively simple placement in retentive undercut regions.

Comparison of cast Ti-Ni alloy clasp retention with conventional removable partial denture clasps

Statement of problem The elastic property of Ti-Ni alloy may be a desirable property for cast removable partial dentures. However, little is known about the retentive properties of cast Ti-Ni alloy clasps. Purpose This in vitro study investigated the retentive force of various types of clasps during repeated cycles of placement and removal to determine whether Ti-Ni alloy clasps maintain their initial retentive force under varied conditions, including different retentive undercut depths and clasp size (thickness and width). Material and methods The test models were developed using a mandibular dentiform with a horizontal plane of occlusion. Two complete metal abutment crowns were made for the left second molar, differing only in retentive undercut depths. A total of 98 clasps (n=7) were fabricated, including 14 wrought wire clasps and 28 clasps from each of the following alloys: Co-Cr alloy (Biosil), Type IV gold alloy (Cast-4), and Ti-Ni alloy (TN-10). Clasps were made to engage one of 2 retentive undercut depths (0.25 mm or 0.75 mm) and were made in 2 sizes (0.8 mm or 1.4 mm). Each clasp was radiographically examined for casting defects and porosity. The force (N) required to remove the clasps was measured using a universal testing machine with a crosshead speed of 10 mm/min. After measuring the retentive force, a masticatory simulator was used to cycle the clasps on and off the metal crown 500 times, simulating the insertion and removal of a removable partial denture clasp. The cycling sequence was repeated 10 times, and retention force was measured after each sequence. The internal surface of the clasp arms was examined for evidence of metal fatigue using scanning electron microscopy. Data were subjected to 2-way and 4-way analysis of variance, followed by Scheffe's multiple comparison test (α=.05). Results Co-Cr alloy and gold alloy clasps in the 0.25-mm retentive undercut groups experienced a gradual decrease in retentive force measurements ( P<.001). In contrast, the Ti-Ni alloy clasps maintained a retentive force of approximately 1.8 N and 2.6 N for the 0.8 mm and 1.4 mm clasp groups, respectively. Although Ti-Ni alloy clasps' retentive force was reduced slightly after the first cycling sequence, it was negligible compared with other clasps tested. The wrought wire clasps also retained their retentive force until the final cycling sequence. A similar trend was found in the clasp groups engaging 0.75-mm retentive undercuts. Conclusion Although the end-point retention for all the clasps was similar, there was less change in the retentive force of the cast Ti-Ni alloy clasps after repeated cycling sequences of simulated placement and removal.

Effect of undercut placement on crown retention after thermocycling

The aim of this study was to examine the effect of undercuts in castings and/or tooth structure on the retention of crowns luted with glass ionomer cement. After routine full-crown preparations had been made in 48 human premolars, wax patterns were fabricated for each tooth. Retentive coves were then produced with a round bur in either the tooth structure or the wax patterns, or in both. One group of teeth and patterns did not receive any undercuts; this was the control group. Castings were made in non-precious metal. All crowns were luted with glass ionomer cement. Half of the samples were thermocycled, and the remainder were kept at 37 degrees C. Crowns were removed using tension (0.012 cm min-1) and the mean bond strengths calculated. The differences in retentive strengths were tested for statistical significance using ANOVA and Scheffe's test. The presence of coves in castings and/or tooth structure significantly increased the retentive strength of castings cemented with glass ionomer, as compared with conventional crown preparations without retentive undercuts. The effect of thermocycling on the retentive strength of castings cemented with glass ionomer was not statistically significant.

A study of the flexibility of wrought wire clasps

T he 18-gauge platinum-gold-palladium (PGP) wrought wire clasp arm is often used as a direct retainer for distal-extension removable partial dentures instead of a cast chromium-cobalt clasp arm, when the retentive undercut is on the mesial-buccal part of the abutment tooth. The wrought wire clasp arm can flex in any direction so that stresses caused by movement of the removable partial denture are dissipated. This helps to protect the abutment tooth from harmful forces. The 18-gauge PGP clasp wire has a fusing temperature sufficiently high that it can be safely cast against by gold and some chromium-cobalt alloys and soldered without changing its physical properties. An 18-gauge clasp wire is thick enough to resist breakage and allow tapering for additional flexibility.’ However, clinical observations of some wrought wire clasps on removable partial dentures constructed at the School of Dentistry, University of Washington, have indicated that these clasps may be less flexible than expected. Several reports in the dental literature have documented similar findings.

Single-visit hollow obturators for edentulous patients

A method of fabricating a simple hollow obturator for edentulous patients was described. This procedure can be accomplished in a single office visit using readily available materials. The use of a relatively long-lasting soft reline material for obturators allows stable, comfortable, and effective obturation for many edentulous patients with recently created maxillary defects (Fig. 6). The hollow prosthesis is lightweight and sufficiently flexible to allow relatively simple placement in retentive undercut regions. Direct finger placement of the material insures complete duplication of all desired tissue undercuts. The soft reline material may also serve as a final impression of the defect when fabrication of the definitive prosthesis is undertaken.