• The Journal of Korean Academy of Prosthodontics
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• v.29 no.1
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• pp.281-287
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• 1991

This study was designed to investigate the influence of the clasp arm length on the change of retentive force with repeated placement or removal. The author measured the retentive force of Akers clasp and I-bar clasp in the depth of undercut 0.5mm, 0.25mm, respectively, varying the length of clasp arm, that is, 10mm, 14mm, 17mm in Akers clasp and 16mm, 18mm, 20mm in I-bar clasp. The retentive force was measured just before the placement of removal, after 100 times repeated placement or removal, after 300 times repeated placement or removal. The obtained results were as follows : 1. The shorter the clasp arm, the greater retention in Akers clasp and I-bar clasp(p<0.05). 2. There was decreased retentive force of Akers clasp and I-bar clasp after 300 times repeated placement or removal(p.<0.005). 3. The decreasing rate of retentive force in Akers clasp with 10mm was higher than that with 17mm, after 300 times repeated placement or removal, but there was no statistica difference(p>0.05).

• The Journal of Korean Academy of Prosthodontics
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• v.30 no.2
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• pp.203-224
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• 1992

The purpose of this study was to evaluate the stress distribution developed in supporting structures by distal extension removable partial denture with 4-types of direct retainer. The direct retainers examined were Akers clasp, RPI clasp, RPA clasp and RPL clasp in bilateral & unilateral free end case. 3-dimensional photoelastic stress analysis was used to record the isochromatic fringe patterns and to calculate the compressive stress at measuring points. The results were as follows. 1. In bilateral free end case, RPI clasp exhibited the similar stress distribution on distal and mesial alveolar crest but Akers clasp exhibited higher stress concentration on distal alveolar crest than mesial alveolar crest. 2. In bilateral free end case, RPA clasp and RPL clasp exhibited the similar stress distribution on distal and mesial alveolar crest and RPL clasp exhibited higher stress concentration on buccal alveolar crest than lingual alveolar crest. 3. Akers clasp produced high stress concentration on residual alveolar ridge distally, but RPI clasp, RPA clasp and RPL clasp produced even stress distribution on residual alveolar ridge. 4. Removable partial denture in unilateral free end case exerted higher stress on abutment tooth root apex than bilateral distal extension removable partial denture.

• The Journal of Korean Academy of Prosthodontics
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• v.28 no.1
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• pp.43-61
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• 1990

The laser reflexion method is a new technique which permits precise contactless measurement and observation of tooth mobility as well as tooth movement. The purposes of this study were to clarify the reliability of the laser reflexion method in clinical application and to measure the abutment tooth movement according to clasp design. This study was designed to determine 1) How much a bending movement of the impression plate stand affects the position of the reflexion pattern and how precise the patient bites into plate 2) Which clasp design causes greater movement of the abutment tooth. Under medium and maximum bite forces, tests were performed on central loading position which was 13mm distal to terminal abutment tooth of distal extension removable partial denture. The movement in the mesiodistal and buccolingual directions was measured. The Duncan's New Multiple-Range test was used to compare the means for the four castings under each direction-load combination; and the paired sample t-test was for medium and maximum bite forces. From this experiment, the following results were obtained. 1. The Roach clasp, the combination clasp, the RPI clasp, and the Akers clasp did not significantly differ in their effects on buccolingual movement of the abutment tooth. 2. The direction of abutment tooth movement was not significantly altered by clasp design and all abutment tooth movements were oriented distobuccally. 3. Under medium bite force, the Akers clasp caused greater distal movement of the abutment tooth than did the combination clasp and the RPI clasp. Under maximum bite force, the Akers clasp caused greater distal movement of the abutment tooth than did the RPI clasp. 4. The testing apparatus and procedures used in this study(laser reflexion method) proved to be reliable in clinical application.

• The Journal of Korean Academy of Prosthodontics
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• v.32 no.4
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• pp.526-552
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• 1994

The extent and direction of movement of removable partial dentures during function are influenced by the nature of the supporting structures and and the design of the prosthesis. Since forces are transmitted to the abutment teeth through occlusal rests, guide planes and direct retainers during functional movements, proper design based on the avaialble research data will maintain the health of abutment teeth and their supporting structures. The purpose of this in vitro study is evaluating stress distribution clinically around the abutment teeth prepared following 4-type clasping systems for unilateral free-end removable partial dentures. Three-Dimensional Photoelastic Stress Analysis method was used because it shows a visual display of stresses of the simulated abutment teeth and residual ridges and reveals stress concentration that can be read at any given points in terms of direction and magnitude. For this study, the author fabricated 4 mandibular photoelastic epoxy models missing left 1st and End molar. Epoxy models were duplicated and 4 unilateral removable partial dentures were construe- ted in accordance with 4-type direct retainers. Unilateral free-end removable partial dentures were positioned on their own models. 6kg force was loaded on the every removable partial dentures of the epoxy model on the central fossa of mandibular left 1st molar vertically by the loading device. After the stress was frozen in a stress freezing furnace, 6 specimens of 6-mm thickness were made from every epoxy model and examined with the circular polariscope. The results were as follows : 1. Generally I-bar clasp revealed the most favorable stress distribution around the abutment teeth. 2. At the end portion of the free-end ridge, Back action clasp showed the highest stress concentration at the bucco-lingual and top portions of the residual alveolar ridge. 3. At the distal area of the abutment teeth, Akers clasp and Roach clasp showed higher stress concentration bucco-lingually and apically than the others. 4. To the abutment tooth, I-bar clasp showed the least stress distribution bucco-lingually but the others showed irregular stress distribution. 5. At the mesial area of the abutment teeth, the order of effective stress distribution was I-bar clasp, Back-action clasp, Akers clasp and Roach clasp. There was big difference of stress distribution between them. 6. At the right 2nd premolar and 1st molar, the stress concentration of Akers clasp was a little high but that of I-bar clasp was low.

• The Journal of Korean Academy of Prosthodontics
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• v.25 no.1
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• pp.17-40
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• 1987

The purpose of this study was to clarify the effect of clasp design on abutment tooth adjacent to a distal extension base under the influence by the location of functional loading. The RPI clasp, the Akers clasp and the combination clasp were selected for evaluation. Tests were performed at 10Kg, 20Kg, 30Kg loads on the buccal, central, lingual, mesial and distal positions of loading platform of each mandibular distal extension partial denture. The laser reflexion method was used for three dimensional measurement of abutment movement, which is possible to measure precisely without contact. The movement in the mesiodistal(X), buccolingual(Y), and occlusoapical(Z) directions and the rotational movement(R) were measured, and in addition, the total movement (SV) as expressed by the three dimensional summation vector independent of direction was calculated. The data were analyzed using Student t-test, p<.05. The following results were obtained from this study; 1. Clasp design did not generally affect the direction of abutment tooth movement except the movement in an undesirable occlusal direction in case of the Akers clasp and the combination clasp. 2. The greater the load on the prosthesis, the greater was the abutment tooth movement, and the direction of abutment tooth movement was affected by positional loading. 3. Each prosthesis was dislodged from the test base under the small amount of load in the distal load position, and the buccal loading showed the greatest abutment tooth movement under the maximum load. 4. RPI clasp was evaluated as the most favorable design.

• The Journal of Korean Academy of Prosthodontics
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• v.37 no.1
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• pp.104-126
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• 1999

The purpose of this study was to compare and evaluate the stress distribution and displacement developed in the abutment teeth and residual ridge area by madibular unilateral distal extension removable partial denture with 2 different retainer designs. The retainers on right and left canine and right 2nd molar were Alters clasp in one model and telescopic crown in the other model. The stress distribution of abutment teeth and residual ridge area on two model were compared and analyzed with 3-dimensional finite element method. 150N and 400N forces were applied vertically, 30 degree and horizontally on the central fossa area of left 1st molar of the removable partial denture, and then stress distribution patterns were analyzed and compared. The results were as follows 1. As the magnitude and angulation of applied force were increased, the magnitude of stress on the right and central residual ridge area and the right canine of the telescopic type increased and comparing to those of the Alters clasp type. 2. As the magnitude and angulation of applied force were increased, the mesial direction of displacement on the right residual ridge area and the right tooth of the telescopic type increased and the distal direction of displacement on left residual ridge area and the left canine increased comparing to those of Akers clasp type. 3. As the vertical force was applied, the distal direction of the displacement of the right tooth were greater and that of the left canine was smaller and the upward displacement of the right canine was greater in telescopic partial denture than those of Akers clasp type. 4. As the 30 degree force was applied, the mesial direction of the displacement of the right tooth were greater and the distal direction of the displacement of the left canine was smaller and the upward displacement of the right canine was greater in telescopic partial denture than those of Akers clasp type. In the horizontal force the results were same in right area tooth but the distal direction of displacement was greater in left canine. 5. In both removable partial dentures, as the magnitude and degree of force were increased, the stress and displacement were increased. The compressive force was dominative than the ten sile force. 6. In both removable partial dentures, the magnitude of stress was greater on mucosal tissue area than that of the alveolar bone area on distal extension residual ridge area but the result was reversed on anterior residual ridge area. The displacement was always greater on mucosal tissue area than that of alveolar bone area.

• 대한치과보철학회:학술대회논문집
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• 1998.11a
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• pp.57-57
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• 1998

• The Journal of Korean Academy of Prosthodontics
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• v.36 no.1
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• pp.150-165
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• 1998

For the purpose of evaluating the effect of both direct retainer design and bony absorption degree around abutment of indirect retainer on the supporting tissue of abutment of indirect retainer, dislodging force was transmitted to unilateral distal extension RPD bases. Analysis of stress distributed within the supporting tissue around abutment of indirect retainer was carried out. Using three-dimensional photoelastic stress analysis method and the conclusion is a follows. 1. According to the extent of force which the direct retainer of the most distal abutment tooth, the amount of force transmitted to the abutment tooth of indirect retainer was small. 2. Of all the cases, Mandibular first premolar which was used abutment tooth of indirect retainer, buccal, mesial and distal sides represented compression stress and lingual side represented tensile stress. 3. The more bone resorption of abutment tooth of indirect retainer, the more distortion of buccal and distal side of abutment tooth was existed and the extent of compression stress which was existed and distal side to abutment tooth was large. 4. When the alveolar bone around the abutment with indircet retainer is normal. The amount of force transmitted on abutment with indirect retainer was small in the order of Akers clasp, RPA clasp, RPI clasp. 5. When the alveolar bone around the abutment with indirect retainer has been absorbed 20% and 30%, the amount of force transmitted on abutment with indirect retainer was small in the order of RPA calsp, RPI clasp, Akers clasp. 6. When denture is displaced, shape of the direct retainer reciprocating abutment affect much the function of indirect retainer.

• The Journal of Korean Academy of Prosthodontics
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• v.19 no.1
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• pp.39-45
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• 1981

Distal-extension removable partial dentures have long been implicated in the increase in mobility and the destruction of the supporting structures of the primary abutment teeth. Various clasping systems have traditionally been used to retain distal extension removable partial dentures, and other designs have been proposed to minimize torquing forces on the abutment teeth. Most recent studies investigating the effects of removable partial dentures on abutment teeth have been performed in it laboratory setting. Results obtained from in vitro research have given dentists insight into removable partial denture design, but laboratory test model cannot be constructed that simulates actual functional or parafunctiona1 movements and forces. The purpose of this study was to clinically evaluate the degree of tooth mobility produced by two clasping systems (suprabulge type and infrabulge type) used for distal extension removable partial dentures. Akers clasp and R.P.I. system were selected for the evaluation, and four patients required a distal extension removable partial denture on the mandibular arch were selected for participation in the study. Two partial dentures were constructed in the same condition expect the design of clasp. All abutments in the study were mandibular first or second premolars. Measurements of mobility were made with a research tool designed by $M\"{u}hlemann$. This instrument, periodontometer, measures tooth mobility in the mouth by means of a dial gauge accurated to 0.01mm when the tooth is stressed with a force meter. Lingual and buccal deflection of abutment tooth was measured using buccal and lingual pressure. The amount of force applied was 500gm. Tooth mobility tests were made at four key stages; 1. Before insertion of the first removable partial denture, baseline mobility was establsihed. 2. After wearing of the first prosthesis, measurement was made at weekly intervals for 4 weeks. 3. The removable partial denture was then taken from the patient, and tooth mobility was measured again at weekly intervals until the patient's established baseline mobility had returned. 4. The second prosthesis of different clasp design was worn for a month and evaluated in the same manner as the first. The sequence of placement of clasping system was alternated between patients. The following results were obtained from this study; 1. The mobility of abutment tooth increased during the initial stage of wear and returned to baseline mobility after removal of removable partial dentures. 2. The mobility of abutment tooth showed no difference between Akers clasp and I-bar clasp during the 4-week test period. 3. All teeth tested showed greater mobility toward the buccal than the lingual direction.

• The Journal of Korean Academy of Prosthodontics
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• v.39 no.5
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• pp.547-555
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• 2001

This study was performed tn investigate the effects of impression method and design of the retainer on the stress of abutment tooth in distal extension RPD. Three different types of direct retainer such as Akers clasp, RPI clasp, and wrought wire clasp were designed. Stress on the abutment tooth was measured and analyzed with strain gauge method. Impressions were anatomic impression technique and functional impression technique. The following conclusions were drawn from this study. 1. The stress at the abutment tooth on all RPD was decreased in functional impression except RPI clasp retained RPD. 2 The stress at the abutment tooth on RPI clasp retained RPD was the most smallest in anatomic Impression. 3. While load is increase the stress at the abutment tooth was increased, but the change of stress at the buccal side of abutment tooth was not too much in functional impression.