{"id":317,"date":"2024-03-19T14:29:04","date_gmt":"2024-03-19T14:29:04","guid":{"rendered":"https:\/\/ekitap.ankara.edu.tr\/dentures\/chapter\/direkt-tutucularin-belirlenmesi\/"},"modified":"2025-10-02T12:40:50","modified_gmt":"2025-10-02T12:40:50","slug":"direkt-tutucularin-belirlenmesi","status":"publish","type":"chapter","link":"https:\/\/ekitap.ankara.edu.tr\/dentures\/chapter\/direkt-tutucularin-belirlenmesi\/","title":{"raw":"Determining the direct retainers","rendered":"Determining the direct retainers"},"content":{"raw":"The retention of a removable partial denture is directly influenced by the position, number, and type of the direct retainer on the arch. The simplest clasp suitable for providing adequate retention should be used. The clasp should offer good stabilization, remain passive until activated by functional stresses, and possess sufficient flexibility to allow limited movement of the denture base without transmitting torque to the abutment tooth.\r\n

Position and number of direct retainer<\/h1>\r\nWhen determining the number and location of direct retainers to be used in a removable partial denture, the retention system and the fulcrum axis must be considered. Direct retainers are primarily placed starting from the posterior region of the arch, and the use of retainers in the anterior region should be avoided whenever possible (Figure 8-9).\r\n\r\n \r\n\r\n[caption id=\"attachment_1865\" align=\"alignnone\" width=\"300\"]\"Figure \u015eekil 8-9.<\/strong> When determining the location of the direct retainer, the retention system and the axis of rotation must be taken into account. In cases where two direct retainers are used, a fulcrum axis is established; therefore, the effect of the direct retainers is enhanced by incorporating an indirect retainer. R: Retainer, IR: Indirect Retainer[\/caption]\r\n\r\nThe ideal approach is to place three retainers in a triangular configuration, spaced as far apart as possible. The third retainer prevents rotation between the other two and enhances the overall stability of the retention system. If the existing undercuts on the abutment teeth are shallow or fewer in number, or if the guide planes are short and limited, additional direct retainers may be required. However, placing more than two retainers on the same plane does not provide a mechanical advantage and may lead to plaque accumulation and increased stress on the abutment teeth. In cases where only two abutment teeth are available, such as in distal extension removable partial dentures, only two direct retainers can be used. Clasp assemblies are not placed on secondary abutment teeth bordering anterior modification spaces due to esthetic concerns.\r\n\r\nIn Kennedy Class I cases, restoring short anterior modification spaces with fixed partial denture may also be considered as a treatment planning option. The same consideration applies to Kennedy Class II and Class III cases.\r\n\r\nThis approach should be evaluated when any of the following conditions are present:\r\n
    \r\n \t
  1. The abutment teeth surrounding the modification space provide adequate support according to the Ante's law,<\/li>\r\n \t
  2. The clinical crown heights of these abutments are suitable for fixed restorations,<\/li>\r\n \t
  3. The abutment teeth present esthetic concerns due to substance loss, existing restorations, malformation, discoloration, or malposition,<\/li>\r\n \t
  4. The abutments have undergone endodontic treatment and require reinforcement with a fixed restoration,<\/li>\r\n \t
  5. When the patient has high esthetic expectations.<\/li>\r\n<\/ol>\r\nShort edentulous spaces in the premolar region that do not give additional support or retention in the treatment plan may also be restored with a fixed partial denture, provided that the above-mentioned criteria are met.\r\n\r\nIn cases where the edentulous spaces are short and the undercuts and guide planes are favorable, two direct retainers placed diagonally may provide sufficient retention. In such situations, occlusal rests placed on teeth without clasps function as indirect retainers, enhancing prosthesis stabilization and supporting the direct retainers.\r\n\r\nExcept in cases where the edentulous spaces are very short and the guide planes are particularly long, the use of a single direct retainer does not provide adequate retention. In these situations, additional support for retention is provided by maximizing tissue coverage, such as through the use of a full palatal plate.\r\n\r\nWhen determining the location of clasp assemblies, their ability to effectively control stress must be taken into consideration.\r\n

    Type of direct retainer<\/h1>\r\nAfter deciding on the position and number of the retainers, the type of direct retainer to be used is selected.\r\n\r\nThe criteria influencing the selection of the direct retainer include:\r\n
      \r\n \t
    1. Condition of the abutment tooth,<\/li>\r\n \t
    2. Amount of required flexibility,<\/li>\r\n \t
    3. Effective use of survey line,<\/li>\r\n \t
    4. Localization of retentive areas,<\/li>\r\n \t
    5. Undercut depth and extent,<\/li>\r\n \t
    6. Presence of soft tissue contour,<\/li>\r\n \t
    7. Esthetics.<\/li>\r\n<\/ol>\r\nCondition of the abutment tooth: <\/strong>If the periodontal support of an abutment tooth is adversely affected by bone loss, placing a retainer on such a tooth should be avoided. If unavoidable, a more flexible retainer (such as a wrought wire clasp) should be selected to limit the load.\r\n\r\nAmount of required flexibility: <\/strong>The required amount of flexibility determines the shape and material of the retainer. Clasps with longer or thinner arms provide greater flexibility. Using wrought wire clasps instead of cast clasps allows for a more flexible clasp design.\r\n\r\nEffective use of survey line: <\/strong>The survey line is important because the rigid, non-flexible parts of the prosthesis should be planned above this line. Within the undercut area below the survey line, only the flexible parts of the prosthesis are designed. The only flexible component of a removable partial denture is the retentive tip of the clasp. When necessary, the path of insertion of the prosthesis can be altered to change the size and location of undercuts (Figure 8-10), or crown restoration of the abutment tooth may be considered to achieve adequate undercuts. Creating an undercut on the enamel of the abutment tooth for clasp placement is also a viable method (<\/span>See. Mouth Preparation; Ch 10<\/a>).<\/span>\r\n\r\n[caption id=\"attachment_293\" align=\"aligncenter\" width=\"235\"]\"Figure<\/a> Figure 8-10. <\/strong> When the path of insertion changes from position \"A\" to position \"B,\" the size and location of the undercut areas are altered.[\/caption]\r\n\r\nLocalization of retentive areas:<\/strong> The localization of the retentive areas (undercuts) is important in the selection of the clasp type. The type of direct retainer is chosen by first identifying the retentive areas on the cast and evaluating the forces of varying magnitude and direction that tend to dislodge the removable partial denture in the occlusal direction.\r\n\r\nUndercut depth and extent: <\/strong>During cast survey, when the contour height of the abutment tooth is determined using a carbon\u00a0 marker, the survey line emerges. The survey line divides the tooth into the \u201cundercut area\u201d (below the line) and the \u201cnon-undercut area\u201d (above the line).\r\n\r\nNey classified survey lines into three categories:\r\n