TYPES bar-retained overdentures 2M*

  1. One of the methods of retention of overdenture is bar attachment.
  2. The typical bar attachment consists of a bar connecting two or more abutments. Joining the two abutments enables splinting
  3. There are two types of bar attachments. 
    1. Bar joints permit rotational movement. 
      1. They are used as a splint connecting the abutments together
    2. Bar units (rigid fixation) permit no movement. 
  4. They are placed as a single unit on the abutment teeth like a stud attachment

REVERSIBLE HYDROCOLLOID = AGAR 2M*

  1. reversible ( gel can change to paste by heating, then can change back to gel by cooling)
  2. a major component is seaweed – comes as collapsible tubes
  3. you boil it at 100° C for 10 mins then store at 65°C for 10 mins then temper at 43-46° C 5-10 mins before you take the impression
  4. agar can be stored at 65°C for 5 days before it has to be reboiled again 

ENAMELOPLASTY 2M**

  1. Simple enameloplasty to reduce the severe curve of spee and adjust supra erupted teeth 
  2. Enameloplasty is defined as a procedure of recontouring a portion of the enamel to obtain the desired morphology
  3. A tapered diamond cylinder stone in a high-speed handpiece with air-water spray is used for the procedure.
  4. After the procedure, fluoride application is done by using plastic mouth guards.

Stress breaker 4m** 2m**

  1. It is defined as a device, which relieves the abutment tooth of all or part of the occlusal forces (GPT) 
  2. In order to minimize the stress in the case of distal extension partial denture, devices like stress breakers are used.
  3. Type I = In this type, a movable joint is placed between the direct retainer and denture base.
  4. Type II  = This type consists of a flexible connection between the direct retainer and the denture base. 
  5. Advantages 
    1. Preservation of the alveolar support of abutment
      tooth due to the reduction of stress on it.
    2. Balanced stress on residual alveolar ridge and
      abutment.
    3. Weak abutment teeth are well splinted even when
      the denture base is moved.
    4. Even if relining is not done properly, abutment
      teeth are not damaged.
    5. Direct retention is less required.
    6. A massaging effect is produced on the soft tissues during the movement of the denture base.
    7. This lessens the need for frequent relining and rebasing.
  6. Disadvantages 
  • Complicated design and expensive.
  • Weak assembly and fractures easily.
  • It distorts due to rough handling.
  • It is difficult to repair.
  • It can counter only the vertical forces on the
    denture.
  • Reduced stability against horizontal forces.
  • Inappropriate relining leads to excessive ridge resorption.
  • Reduced indirect retention.
  • The split major connector tends to collect food
    debris at the area of split.

Soldering 2m**

  1. is defined as joining two components of metal with an intermediate metal whose melting temperature is lower than the parent metal. 
  2. Types of soldering for metal-ceramic restoration 
    • Oven soldering
    • Torch soldering
    • Infrared soldering
    • Laser welding

Tripoding the cast 2m**

  • Tripoding is a procedure where three different widely spaced out points of a single plane are marked on the cast.
  • To allow you to reposition the cast according to the selected path of insertion 
  • These tripod points are used as a reference point and they should not be altered until the treatment is completed.

MINOR CONNECTORS

  • Minor connector: connecting link between the major connector and other components of the RPD
  • MAXILLA = Must extend up to tuberosity 
  • MANDIBLE = must extent up to 2/3rd of the edentulous area or cover retromolar pad
  • Must be rigid to distribute the stress between the linked components, must not impinge on the mucosa, the mucosal surface must be highly polished

Functions of the minor connector : 

  1. Join the denture parts together 
  2. Transfer functional stresses to abutment teeth through the occlusal rest 
  3. Transfer the effect of the retainer, rests, stabilizing components to the rest of the denture 

FOUR TYPES OF MINOR CONNECTORS

  1. Joins the clasp assembly to major connector
    1. Broad B-L and Thin M-D = allow easy placement of prosthetic teeth. 
    2. Triangular cross-section
    3. Lingual embrasure = bulk is not evident 
  1. Joins indirect retainer to major connector
    1. 90 degrees to the major connector but slightly curved as it will decrease the concentration of stress
    2. Should always fit into embrasure areas 
  2. Joins denture base to major connector (draw)
    1. Open lattice 
    2. Mesh or ladder pattern = Require acrylic attachments
    3. Bead, wires, and nail heads = capture acrylic material 
    4. Class III is completely tooth supported = do not reline procedure
    5. Class I and II = are distal extension cases = Relining or rebasing procedure, therefore metal parts should not be in direct contact with tissue = Hence, METAL nail heads and beads come in direct contact with underline tissue.
    6. External and internal finish lines are necessary for class I and Class II situations 
  3. Serves as an approach arm for the vertical projection or bar clasp. 

REST AND REST SEATS

  1. Rest = part of RPD = rigid extension of the RPD – provides support. 
  2. Rest Seat = Prepared on abutment teeth
  3. Functions: 
    1. Directs and distributes occlusal force apically to abutment teeth 
    2. Acts as vertical stop = doesn’t allow RPD to move in the tissue-ward direction
    3. Maintains retentive clasp in position = SUPPORT in RPD
    4. Rest do allow slight movement = dissipates horizontal forces
  4. TYPES
    1. PRIMARY = part of the clasp assembly 
    2. SECONDARY/AUXILLARY = indirect retention

OCCLUSAL 

  1. Shape = ROUNDED TRIANGULAR
  2. Base = Margin of tooth 
  3. Apex = center of tooth
  4. Floor = spoon-shaped
  5. Dimensions = 1/3rd to half of M-D diameter of tooth and ½ of B-L diameter of the entire tooth 
  6. Measured from cusp tip of buccal side to cusp tip of lingual side. (draw)
  7. ACUTE angle = floor is inclined to towards center of tooth and angle is less than 90* = hence, Increases the support (draw)
  8. If an obtuse angle is present, it causes Slippage of the prosthesis = therefore, avoiding the inclined plane effect 
  9. Occlusal rest = 0.5mm thick at the thinnest point 
  10. 1-1.5 mm = when it crosses the marginal ridge
  11. We use diamond or carbide round burs with water and light pressure 
  12. Preparation is done entirely on enamel only
  13. If the rest seat needs to be placed away from the edentulous area→it is not flared to the facial line angle and should be more flared lingually ( to provide space for minor connector)  
  14. Interproximally extended occlusal rest seat:
    1.  Flared more buccally and lingually without affecting the contact area 
    2. U shaped trough that is 1mm wide and 1 mm deep 
    3. Without breaking the contact = Use a shoulder bur to create a 1 mm Buccolingual clearance from the proximal side then use a round bur to create the seat 
  15. In RPA with intracoronal occlusal rest seat
    1. A partial denture that is totally tooth supported by means of cast retainers on all abutment teeth may use intracoronal rests for both occlusal support and horizontal stabilization
    2. Open the margins more and do slight lingual flaring for the minor connector
  16. Extended occlusal seat rest
    1. In Kennedy Class II, modification 1, and Class III situations in which the most posterior abutment is a mesially tipped molar
    2. an extended occlusal rest should be designed and prepared to minimize further tipping of the abutment and to ensure that the forces are directed down the long axis of the abutment.
    3. This rest should extend more than ½  the MD width of the tooth and 1/3 rd the B L width of the tooth
    4. 1mm thickness of metal = the preparation should be rounded with no undercuts or sharp angles 

LINGUAL REST/CINGULUM REST

  1. Only for maxillary canine 
  2. The mandibular canine is avoided as it lacks the bulk of enamel. 
  3. V-shaped = boomerang shape – Cross section view 
  4. Cresant/Half moon shape – Lingual view
  5. Dimensions = 2.5mm M-D to 2mm B-L 
  6. Depth = 1.5mm = as average thickness of enamel is 2 mm

INCISAL REST 

  1. Mandibular canines and rarely incisors 
  2. V-shaped notch = 1.5 – 2mm away from the proximal incisal angle
  3. Purpose = functioning as secondary rest for indirect retention
  4. Dimensions = 1.5mm wide, 1.5 mm deep, and 1.5mm away from the proximal incisal angle
  5. If multiple incisal rests are needed = rests are connected with linguloplate i.e Choice of major connector
  6. Lingual rest are more commonly preferred than incisal= as lingual rest will be very close to the rotational center of tooth = Bear loads in a much better manner than incisal rest
  7. Major problem = Anterior zone are aesthetic zones. Hence, lingual is chosen over incisal. 

EMBRASSURE REST 

  1. B-L = 3-3.5mm wide
  2. Depth = 1.5mm – 2mm deep
  3. If not met = definite chances of fracture of RPD components. It is very difficult to fix it with the same strength of RPD design 

Reciprocation 4m**

  1. Each retentive arm should be opposed by a reciprocal component capable of resisting any orthodontic pressure exerted by the retentive arm 
  2. Functions of reciprocal arm 4m*
    1. It provides stabilization/reciprocation against the action of the retentive arm.
    2. It also stabilizes the denture against horizontal movements.
    3. The reciprocal arm may act as an indirect retainer to a certain extent, i.e. when it rests on a supra-bulge surface of an abutment tooth lying anterior to the fulcrum line.
  3. Design specifications for a reciprocal arm 
    1. It is positioned on the side of the tooth opposite to the retentive arm
    2. The reciprocal arm must be rigid and should not be tapered
    3. It is positioned on a tooth surface that is reasonably parallel to the denture’s path of insertion and withdrawal.
    4. It is ideally located at the junction of the gingival and middle third of the abutment tooth

Some special reciprocal elements 

  1. At times, linguoplate can be used to provide reciprocation.
  2. Sometimes, an occlusal rest positioned on the opposite side of the tooth will provide reciprocation.

Swing-lock dentures 4m***

  1. Swing-lock RPDs are used, when a number of remaining teeth is too few to support a conventional design. 
  2. This denture has a labial bar extending labially all along the arch like a major connector. 
  3. The labial bar is connected to the remaining parts of the denture by a hinge on one side and a lock on the other. 
  4. The labial bar can be unlocked during insertion and locked after insertion. 
  5. Indications 
    1. Missing key abutments 
    2. When the number of remaining natural teeth is less 
    3. When the remaining teeth are too mobile to serve as abutments 
    4. When the soft tissue and the tooth are in unfavorable contours 
    5. Provide retention and stability for maxillofacial prostheses, such as obturators 
    6. For retention of the prosthesis in case of loss of large segments of teeth and alveolar ridge, due to trauma or infection. 
  6. CONTRAINDICATIONS
    1. When the vestibule is shallow 
    2. High labial frenal attachment 
    3. Patient with poor oral hygiene 
  7. Advantages 
    1. The construction is relatively simple and inexpensive. 
  8. Disadvantages 
    1. It is unaesthetic in patients with short lips. 
    2. Tipping is seen in the remaining anterior teeth in the distal extension case. 

Fabrication 

  1. Selection of metal for swing-lock framework
    1. The metal of choice is chrome alloy. 
    2. Gold alloys wear off due to constant movement
  2. Surveying and designing 
    1. The cast is mounted on the surveyor. 
    2. The path of insertion is from a lingual direction with the labial arm open. 
  3. Lingual plate
    1. The lingual plate should be designed to end above the survey line. 
    2. It prevents the tissueward displacement.
  4. Occlusal rest 
    1. helps to prevent tissueward displacement of the denture. 
  5. Major connector 
    1. The mandibular major connector extends above the survey line with scallops extending up to contact points. 
    2. The maxillary major connector is the complete palatal or closed horseshoe with borders extending up to or above the survey line. 
  6. Labial arm design 
    1. The vertical projection of the labial bar should be designed to touch the teeth below the height of contour. 
  7. Conventional design
    1. This consists of a labial bar with metallic vertical I-bar or T-bars attached to it.
    2. Using acrylic resin retention loop 
    3. This is indicated for patients with short lips and where aesthetics is of concern. 
  8. Selection of impression material = Heavy-bodied alginate is best preferred. 
  9. Tray selection = A custom tray should be used for recording maximum labial and buccal vestibular depths.
  10. For the secondary impression, 5–6 mm space should be given between the teeth and the tray when placed in the mouth. 
  11. Making the impression. 
    1. It is similar to conventional dentures. 
    2. Dual impressions may be required for distal extension.
  12. Framework fabrication.
  13. Fitting the framework.
  14. Arranging artificial teeth to occlusion 
  15. Insertion = Lingual path of insertion is done. 
  16. Post insertional care = Oral hygiene should be maintained by the patient. Distal extension RPD has to be frequently relined.