|Year : 2016 | Volume
| Issue : 3 | Page : 119-126
Clinical and radiographic comparative study between two different types of clasps materials used in unilateral maxillary Kennedy class II removable partial denture cases
Fatma A Elhadad BSc , Fadel A Abd Elfatah, Nahed A Kashef
Department of Prosthodontics, Faculty of Dentistry, Tanta University, Tanta, Egypt
|Date of Submission||25-Mar-2016|
|Date of Acceptance||27-Mar-2016|
|Date of Web Publication||29-Sep-2016|
Fatma A Elhadad
Department of Prosthodontics, Faculty of Dentistry, Tanta University, Tanta
Source of Support: None, Conflict of Interest: None
Objective: The objective of the present study was to compare between two different clasp materials for the treatment of maxillary class II Kennedy classification clinically, radiographically.
Materials and methods: Twenty male patients were selected for this study. The patients were divided into two groups. Each group consists of 10 patients. For group I each patient have maxillary removable partial denture that was constructed and retained by cobalt–chromium RPI clasp on the maxillary first premolar with cross arch stabilization (using double Aker clasp) on the other side. For group II each patient has the same except that the retentive I bar of RPI clasp was made of acetal resin. Patient satisfaction, clinical, and radiographic evaluations were carried out for every patient at insertion, 3, 6, and 9 months, the data were collected, tabulated, and statistically analyzed using t-test.
Results: Satisfaction for the treatment. Group II patients were more satisfied of the treatment regarding aspects of the patients' comfort and esthetics. No significant difference in the aspects of phonetics, the ability to eat, prosthesis loosening, the gingival health, general satisfaction and food impaction between the two groups were found, also there were insignificant increase in the gingival recession, pocket depth, and plaque index around the abutments tooth in both groups. Radiographically, there was significant decrease in the bone height around the abutments in both groups.
Conclusion: Removable partial denture with acetal resin clasp is better for esthetic and patient comfort. Good periodontal condition of the abutment tooth of both groups is maintained. Acetal resin clasp is the clasp of choice when esthetic is of primary concern to the patient.
Keywords: acetal resin, cobalt–chromium, removable partial denture
|How to cite this article:|
Elhadad FA, Abd Elfatah FA, Kashef NA. Clinical and radiographic comparative study between two different types of clasps materials used in unilateral maxillary Kennedy class II removable partial denture cases. Tanta Dent J 2016;13:119-26
|How to cite this URL:|
Elhadad FA, Abd Elfatah FA, Kashef NA. Clinical and radiographic comparative study between two different types of clasps materials used in unilateral maxillary Kennedy class II removable partial denture cases. Tanta Dent J [serial online] 2016 [cited 2018 Nov 20];13:119-26. Available from: http://www.tmj.eg.net/text.asp?2016/13/3/119/191431
| Introduction|| |
Patient demands a removable partial denture (RPD) for health, anatomic, psychological, or financial reasons. Fabricating an esthetically pleasing RPD while avoiding the unsightly display associated with conventional clasp assemblies often presents a challenge to the dentist . The traditional use of the metal clasp like cobalt–chromium (Co–Cr), gold, stainless steel, and titanium hampers esthetics, since it's obvious display conflicts with patient's prosthetic confidentiality. Methods to overcome this esthetic dilemma include the painting of clasps with tooth-colored resin , use of lingually positioned clasps ,, engagement of mesial rather than distal undercuts , and use of gingival approaching clasps. Unless clasps can be avoided by using precision attachments , some of the RPD framework will be invariably visible.
Several types of metal alloys have been used in RPD construction. Frequently, RPD clasp are made of the same alloy as metal framework. The most common alloys used for clasps are Co–Cr alloy and titanium alloys .
Although the RPI clasp (R=mesial oclusal rest, P=proximal plate, I=I bar retentive arm) was designed to give the denture framework some freedom to move tissue ward under occlussal stresses . Using of metal clasps on teeth may cause esthetic problem. Polyoxymethelene also known as acetal resin has been used as an alternative tooth-colored denture base and denture clasps material since 1986 and was promoted primarily for superior esthetic .
Acetal resins have fracture strength, wear resistance and flexibility in comparison with metals. These characteristics make them usable for preformed clasps, partial denture frameworks, provisional fixed partial dentures, artificial teeth for removable dentures, resin-bonded fixed partial dentures, and orthodontic appliances . Clasps are used as direct retainers for the RPD. The flexible clasp tip engages the undercut of the abutment to provide retention ,. The components of any clasp assembly must satisfy six biomechanical requirements: retention, stability, support, reciprocation, encirclement and passivity ,. In addition, the clasp assembly must ideally not affect esthetics adversely. Careful selection of clasp position on the individual tooth, clasp type, clasps material, clasp location in the dentition and the number of clasps is important. A clasp arm design producing less stress is important for predictable long-term use of an RPD. Three factors which are clasp material, clasp form, and the amount of undercut affect the design of a clasp arm . Clasp form involves the elements of length, curvature, cross-sectional dimension, and taper. Among these, the first two elements are determined by the abutment tooth contour, and the latter two elements are under the control of the dentist or technician. Furthermore, clasp form is associated with stress distribution, which affects fatigue and permanent deformation . Poor fit may cause the decrease of retention and failure of RPD function . However, the mechanical properties of a clasp material are generally determined by the alloy used . Retentive clasp arms must be capable of flexing and returning to their original form and should retain an RPD satisfactorily. The tooth should not be unduly stressed or permanently distorted during service and should provide esthetic results . It is reported that acetal resin have a sufficiently high resilience and modulus of elasticity to allow its use in the manufacture of retentive clasps, connectors, and support elements for RPDs. Retention clasps can be excellent with retainer that lock the remaining dentition, however they may subject abutment teeth to excessive stresses and premature tooth loss. Some clinicians aimed to reduce the weight of the prosthesis to minimize the damage to the abutment teeth, splinting some or all the abutment teeth to dissipate the forces ,.
Fitton tested some physical characteristics of polyoxymethelene (acetal resin) for dental use like the modulus of elasticity in compression, extension, and flexure, stress relaxation, force displacement behavior of clasp forms, impact strength, and glass transition temperature. Results showed that resin clasp may be resilient enough to engage the undercuts for the retention of RPD. But the low flexural modulus requires the resin to be used in greater cross-sectional area than the metal alloys to gain useful retention. This greater bulk has implication for plaque accumulation and maintenance of periodontal health .
| Materials and Methods|| |
Twenty partially edentulous individuals (40–50 years) were selected from the Outpatient Clinic, Prosthetic Department, Faculty of Dentistry, Tanta University. All Patients were informed about the steps of this research and signed a written consent according to the committee of ethics approved by Faculty of Dentistry, Tanta University. They had maxillary unilateral distal free end edentulous area (Kennedy class II) with the first premolar as the last standing tooth. The lower jaw was almost with complete dentition. They were having Angle's class I ridge relationship, sufficient intermaxillary space, and a good oral hygiene. All should have no previous prosthetic management and should be free from any systemic diseases that might affect bone. All individuals were examined clinically and radiographically. Periapical radiographs were made for all abutment teeth and for the edentulous alveolar ridge. Occlusal analysis was also done to detect any premature contact or over-eruption, which was corrected by selective grinding. The patients were randomly divided into two equal groups, 10 in each.
Group 1: For each patient, maxillary RPD was constructed and retained by Co–Cr clasp on the maxillary first premolar with cross arch stabilization (using double Aker clasp) on the other side.
Group 2: For each patient, maxillary RPD was constructed from Co–Cr and retained by RPI clasp (the mesial occlusal rest and the proximal plate of RPI were made of Co–Cr but the retentive I bar was made of acetal resin) on the maxillary first premolar with cross arch stabilization (using double Aker clasp) on the other side.
Construction of metallic removable partial denture
Study casts obtained from alginate impressions (Kromopan; Lascod SPA-Laboratori Scientific Odontoiatria, Firenze, Italy) were surveyed, proper design delineated on the cast, Mouth preparation was done in the patient's mouth as delineated on the primary casts proximal surfaces of the abutment teeth were prepared parallel to the path of insertion to act as guiding planes. Following mouth preparation, final impressions were made using rubber base impression material (Rubber base impression material; Zhermack, Badia Bolesine-RO, Italy) in a custom tray [Figure 1]. Master casts were surveyed, modified and duplicated. For the first group, wax pattern and casting was completed in the conventional manner. For the second group, the master casts were duplicated twice. One of the duplicate casts was made of stone (Moldano stone W. German, Heraeus Kulzer, Bremen, Germany) used for constructing the wax pattern of the acetal resin retentive arm direct retainers. The other duplicate cast was made of investment (Wirovest Special; BEGO Bremer Goldschlägerei Wilh. Herbst GmbH & Co. KG, Bremen, Germany) used to construct the other parts of the direct retainer in Co–Cr in conventional manner. Wax pattern of acetal resin direct retainer were made in a special muffle. After the wax pattern was eliminated, the acetal resin material was softened at 260°C and injected into the mold with a special injection gun. Pressure was maintained till the material cools. Clasp retentive arm was deflected, finished and polished, then seated on the master cast and mechanically attached to the metal framework by self-cure acrylic resin [Figure 2]. The metal framework was tried for both groups. Maxillomandibular relation was recorded, setting up of teeth and denture was tried in the patient's mouth. Lastly at insertion, stress the oral and hygienic measures for each patient [Figure 3].
All patients in both groups were evaluated.
- Clinically concerning: patient satisfactions, gingival recession, the pocket depth, plaque index.
- Radiographically for evaluation bone change occurring in the abutment tooth throughout the periods of follow-up (3, 6, and 9 months).
The patient satisfaction 
The patients were asked to give their perception on the prosthesis therapy and mention aspects of satisfaction using a questionnaire. After informed consent was obtained, each patient was asked to fill out a satisfaction questionnaire regarding aspects of:
Comfort, esthetics, ability to eat, gum shape and color (gingival health), food impaction, phonetics, prosthesis loosening, general satisfaction.
Responses to statements were given on the Likert response scale : 5=strongly agree; 4=agree; 3=neither agree nor disagree; 2=disagree; 1=strongly disagree for each of these parameters.
The distance from the top of the abutment to the gingival margin was measured at the four sides mesial, distal, labial, and lingual the average was calculated for the abutment tooth .
The pocket depth
The pocket depth was measured on the four surfaces of the abutment tooth using a periodontal probe, average was calculated.
Plaque adherent to the tooth was quantified using Mombelli and Lang  plaque index at four surfaces; buccal, lingual, mesial and distal, using a mouth mirror and a dental explorer after air drying of the tooth and gingiva. Each of the four areas was scored 0–3 according to the following criteria.
Serial standardized periapical radiographs were made for all abutment tooth using long cone paralleling technique, this technique describe an accurate and dependable technique of achieving standardized serials of periapical radiographs that enables the observation of bone changes over a long period of time with high degree of accuracy. The Rinn XCP (Rinn Corporation, XCP Elgin Company, Rochester, New York, USA) system was used for achieving standardization of the follow-up periapical radiographs and consist of a standardized aluminum extension arm was fabricated to relate the plastic film holder located intraorally to the X-ray tube, an acrylic template designed to be seated on the occlusal surface of abutment tooth with the neighboring adjacent teeth was constructed to accurately relate the film holder parallel to the natural tooth and plastic bite block made for the abutment tooth. The top part of the plastic bite block was filled with rubber base impression material and inserted in the patient mouth where the patient bite down on it with the acrylic template to record the relation of upper teeth to the template, that make a standardized position on which the patient bite on during all the periods of follow-up.
Rinn XCP film holder (Eastman Kodak Company, Rochester, New York, USA), and radiographic films (Image x system; De Gotzen, Olgiate Olona Va, Italy) in 70 KVP X-Ray equipment. The processing was formed automatically. All radiographs were taken at the Faculty of Dentistry, Tanta University. The radiographs were taken at the following intervals (at time of denture insertion, 3, 6, and 9 months).
The periapical radiographs was digitized to computer by digital camera then the software Image J 1.24 (National Institute of Mental Health, Bethesda, Maryland, USA). was used to measure the linear distance in pixel between two marked points (at the alveolar crest and the root apex) mesial and distal of the abutment [Figure 4]).
|Figure 4: Radiographic evaluation of bone change using software, Image J 1.24.|
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| Results|| |
The patient satisfaction as regards patient comfort, esthetics, ability to eat, gum shape and color (gingival health), food impaction, phonetics, prosthesis loosening, general satisfaction was evaluated. The percentage of the patients agree the treatment was high in group I than in group II ([Table 1]). There was no significant difference between two the groups, as P ≤ 0.005, in all patient questionnaire except patient comfort and esthetics there was significant difference.
There was no significant difference between the two groups at different follow-up intervals [Table 2].
There was no significant difference between the two groups at different follow-up intervals [Table 3].
There was no significant difference between the two groups at different follow-up intervals [Table 4].
|Table 4: Comparison of the mean value and SD of the plaque index at different periods of follow-up between the two groups|
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There was significant difference between the two groups at different follow-up intervals [Table 5].
|Table 5: Mean and SD of bone height for acetal resin and cobalt-chromium groups|
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| Discussion|| |
This research was carried out on 20 partially edentulous patients having maxillary class II Kennedy's classification.
The upper jaw was selected because it could be considered the most difficult case to receive esthetically, satisfactory and comfortable removable denture. Also it has high blood supply when compared with the lower jaw ,,. For all patients the opposing arches were almost dentulous to equalize forces falling on the abutments. Angle class I cases were considered to exclude the effect of different masticatory forces resulting from abnormal teeth relations usually present in Angle class II and III. Also the selected patients had no experience with any previous prosthesis to be sure that the tissue changes are related to the prosthesis under investigation .
The remaining natural teeth were free from any periodontal diseases as the condition of the periodontium is an important factor to prevent the possibility of denture movements under functional load. The healthy abutment and its periodontal ligament help to convert the compressive force on the tooth into tensile force in the bone . The selected patients were systemically free from any diseases which may have an influence on the alveolar bone, the abutment teeth and the surrounding periodontium as diabetes, neutropenia, Down's syndrome .
Diagnostic casts were mounted for the examination of the inter arch relationship of the upper and lower arches. Selection of the direct retainer to be used concerning the crown length, the periodontal support of the abutment and the intermaxillary space .
The RPI clasp was used in this study as it is the clasp of choice used on maxillary first premolars in distal extension bases due to its stress breaking effect and for esthetic reasons, a cross arch stabilization was achieved by double Aker clasp on the first and second molars this was supported by Davenport et al. .
In this study the patients in the first group received (RPI) clasp made from Co–Cr alloy as the metallic framework, Co–Cr alloy has high elastic modulus meaning that it is a rigid material, so partial denture clasps made from Co–Cr alloys are suitable for engaging undercuts of reasonable depth to avoid permanent deformation of the clasp during activity . But in the second group, the I bar retentive arm of RPI clasp was made of acetal resin because it has esthetic character also acetal resin used for elastic denture and clasp as it has 30% elasticity compared with 6% of Co–Cr alloy. Acetal resin is of superior esthetics, which allowed the clasp to better match the color of the abutment tooth. Acetal as a homopolymer has good short-term mechanical properties, but as a copolymer has better long-term stability. Acetal resin is very strong, resists wear and fracturing, and is quite flexible. These characteristics make it an ideal material for preformed clasps for partial dentures, single pressed unilateral partial dentures, partial denture frameworks, provisional bridges, occlusal splints, and even implant abutments ,.
For patient satisfaction
There was a significant difference in the patients' comfort and esthetic between the two groups, which might be attributed to the relative simplicity and tooth colored of acetal resin clasp and these results are in agreement with Bortun et al. , and Arda and Arikan . They describe the esthetic properties of acetal resin and using of nonmetallic clasp to achieve esthetic demand for patient.
According to the ability to eat and a prosthesis loosening, there was no significant difference between the two groups. This may be due to the improved retention and stability of the maxillary metallic partial dentures due to presence of maxillary major connector (mid-palatal plate) and double Aker clasp on the opposite side for cross arch stabilization beside good occlussal adjustment. So improving in retention and stability of RPD increases the ability to eat and decreases prosthesis loosening. These results are in agreement with Carr et al. .
Regarding to the phonetic there was no significant difference between two groups which may be attributed to simplicity of the design and the major connector does not cover the anterior part of the palate and so no trouble or annoyance occurred to the patient during speech. This was supported by Carr et al. .
There was no significant difference in the gingival health and food impaction between two groups which might be attributed to the improved retention and stability of the prosthesis resulting in better healthy condition for the gingival and periodontium of the abutment tooth. These results are in agreement with several authors ,.
Regarding the general satisfaction there was no significant difference between two groups and this may be attributed to simplicity of the design and good retention and stability of the prosthesis in the patient's mouth.
Evaluation of the tissue health of the abutment was carried out using clinical parameters including gingival recession, pocket depth, plaque index and bone height. They were selected as they have shown to be the most definitive criteria to determine the status of the abutment health. Zlataric and colleagues ,.
For the abutment tooth, there was nonsignificant increase in the gingival recession of the abutment teeth between the two groups at the different follow-up intervals and this was in agreement with studies made by Bergman et al. , Petridis and Hampton  who mentioned that RPD did not cause any adverse periodontal reactions provided that the preprosthetic periodontal health has been established and maintained with meticulous oral hygiene.
Regarding the pocket depth, there was no significant difference between two groups at different intervals and this was in agreement with studies made by Schwalam et al.  and Gomes et al. . who reported that there were no significant changes in the pocket depth following a longitudinal study of gingival condition in RPD wearers. This could be explained on the basis that the injury to the gingival tissue due to the presence of plaque leads to gingivitis, the severity of this inflammatory response will depend on the nature of plaque and modified by local or systemic host factor. So, the disease does not necessarily progress to periodontitis leading to increase pocket depth .
Also, there was no significant increase in the plaque index between two groups till the nine months of the denture insertion. This nonsignificant increase were considered a sign of inflammation was in agreement with Abu Elross and colleagues ,. who explained that the presence of intraoral appliance produce alternation in the ecological condition of the surrounding tissue which is caused by plaque accumulation and also coverage of tissue by RPD.
On the other hand there was significant difference in the clinical parameter (gingival recession, pocket depth, and plaque index) within the individual group this finding was in agreement with the study made by Tuominen et al. . who mentioned that the wearing of RPD significantly increase the odds of having periodontal pocket in general as well as the odds of having deep periodontal pocket and plaque accumulation.
For the bone height change, there was significant reduction in the bone height of the abutment tooth between the two groups at the different follow-up intervals, this finding was in agreement with the studies made by Waerhaug , Rissin et al. , Yusuf and Isa  who mentioned that the periodontal condition of the tooth adjacent to the denture were poorer than around those not directly involved in its construction due to food stagnation and difficult in oral hygiene caused by RPD components in addition the RPD may sink into the soft tissue cause bone resorption. The reduction in the bone height measurement in the first group was significantly higher than the second group at different follow-up intervals; this could be due to the fact that the rigid Co–Cr clasp transferred more stresses to the abutment tooth than the flexible acetal resin clasp did, also the acetal resin has 30% elasticity compared with 6% of Co–Cr elasticity ,.
This result was similar to the previous studies made by Arda and Arikan  and Yusuf and Isa  when compared between Co–Cr and acetal resin clasps, stated that a reduction of bone density of the acetal resin group was less than the metallic group due to reduced load distribution over abutment teeth, acetal resin clasp flexibility transmit less stress to the abutment compared with metal clasp and at the same time there was good bracing from the other rigid metallic components of the clasp and the force required to remove acetal clasp was significantly lower than that with Co–Cr clasp. Also, there was high significant decrease in the bone height within the individual group and this is attributed to the effect of partial denture on the abutment tooth which is in agreement with many authors , [Table 6].
| Conclusion|| |
- Acetal resins offer the strength of metal and the flexibility and comfort of plastic; they are an ideal material for the fabrication of dental prostheses, particularly clasps.
- Acetal resin clasp is better regarding the esthetic demand of the patient in maxillary class II Kennedy classification as it eliminate metal display this is due to the tooth-colored properties of acetal resin.
- The elastic and flexible properties of acetal resin added that acetal resin provides a higher standard of function by using the flexibility of the material to balance masticatory forces between the entire supporting ridge and the abutment instead of individual support points.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]