Removable partial denture

REMOVABLE PARTIAL DENTURE RPDs are components of prosthodontics ( branch of Dentistry) pertaining to the restorations and maintenance of oral function, comfort, appearance, and health of the( pt) by replacement the missing teeth and craniofacial tissues with artificial substitute .

The Basic Objectives of prosthodontic Treatment Elimination of oral disease. Preservation of the health and relationship of the teeth, and the health of the oral and para-oral structure. Restoration of oral function (comfort, esthetic, speech).

Consequences of Tooth Loss Aesthetics Speech. Drifting, tilting, over-eruption. Loss of masticatory efficiency. Loss of vertical dimension. Deviation of mandible. Loss of alveolar bone.

P.D may: Give support to periodontally diseased teeth. Restore vertical facial dimension. Prevent T.M.J problems. Prevent tooth drifting or over eruption. Stimulate non-used tissues. Support collapsed structure (muscles of lips and cheeks). Prevent attrition of remaining teeth. Improve oral hygiene by preventing stagnation of food in disused areas.

Classification Of Partially Edentulous Arches The most familiar classification are those proposed by Kennedy, Cummer, and Bailyn, Beckett,… The recent classification has been proposed for partial edentulism that is based on diagnostic criteria.

Requirement Of an Acceptable Method Of Classification It should permit immediate visualization of the type of partially edentulous arch. It should permit immediate differentiation b/w tooth- supported and the tooth and tissue-supported. Universally acceptable.

Kennedy Classification 4 basic classes. Edentulous areas other than those determining the basic classes were designated as modification spaces. Class I : Bilateral edentulous areas located posterior to the natural teeth. Class II : A unilateral edentulous area posterior to the remaining natural teeth.

Kennedy Classification Class III: Unilateral edentulous area with natural teeth remaining both ant and post to it. Class IV : A single, but bilateral (crossing the midline), edentulous area located anterior to the remaining natural teeth.

Principal Advantage It permits immediate visualization of the partially edentulous arch and allows easy distinction b\w tooth-supported versus tooth-tissue supported prostheses.

Applegate's Rules for Applying the Kennedy Classification Rule 1 : The classification should follow, not precede extractions. Rule 2 : If a 3 rd molar is missing and not to be replaced, it is not considered in the classification. Rule 3 : If a3rd molar is present and not to be used as an abutment, it is not considered in the classification.

Applegate's Rules Rule 4 : If a 2 nd molar is missing and not to be replaced, it is not considered in the classification. Rule 5 : The most posterior area always determines the classification. Rule 6 : Edentulous areas other than those determining the classification are referred to as modifications and designated by their No.

Applegate's Rule Rule 7 : The extent of the modifications is not considered, only the No. of additional edentulous areas. Rule 8 : There are no modification in Class IV.

Principal Of Partial Denture Design Stresses acting on RPDs are transmitted to the teeth, and to the tissues of the residual ridges. The stresses, which tend to move the PD in different directions are: Masticatory stress( Tissue ward movt). Gravity( Tissue away movt). Sticky food pull the denture occlusaly (Tissue-away movt).

4. Muscles and tongue tend to displace denture from its foundation. 5. Intercuspation of the teeth may tend to produce horizontal and rotational stresses unless occlusal is adjusted.

Properly Constructed PD Must Have: Support: Resistance to vertical seating forces( provided by teeth and mucosa). Retention: Resistance to vertical displacing forces. Stability( bracing) resistance to horizontal and lateral displacement. All the above should be within the physiological limits of the tissue involved. A

Designing Support a. Tooth support: When abutment teeth available at both ends of the denture base( bounded saddle). It most commonly obtained by occlusal rests. b. Mucosa support: (mucoperiosteum covering residual alveolar bone). It allows varying degree of displacement. The amount of displacement( tissue ward movt) will depend on: The amount of pressure applied. The nature of the mucosa (thickness).

3. Area covered by the denture( the wider the area the less the displacement). 4. Fit of the denture base. 5. Type of impression( anatomical, functional, or selective pressure). c. Tooth-mucosa support: ( Bilateral free end saddle). Posterior tissue support, and anterior tooth support.

Designing Retention Retention should be designed to counter act dislodging forces( sticky food, muscle at periphery of the denture, intercuspation, gravity). Retention is gained by mechanical means 1. direct retainers: a. Intercoronal( clasps). b. intracronal(percision attachment). 2. Indirect retainers.

Physical factors( cohesion, adhesion, atmospheric pressure, surface tension). it play a minor role RBD.

Designing Bracing and Stability Bracing( providing resistance to lateral movt.of RBD). Causes of tipping, rocking and rotation of P.D. Quality of supporting structure.

2. The tissue-ward movt. Of the free end base create an axis of rotation around which this appliance is rotated. This axis of rotation is called a fulcrum line (it is imaginary line extending between the two main abutment.

How to counteract lateral shifting? Bracing the sides of the teeth by means of rigid clasp arms. Use of continuous bar resting on the lingual surfaces of the natural standing teeth.

Components Of RPDs Major connectors. Minor connectors. Rests. Direct retainers. Stabilizing or reciprocal components (part of clasp assembly). Indirect retainers( if prosthesis has distal extension).

Major Connecters Major connector is component of the PD which connect all parts of the prosthesis directly or indirectly. It provides the cross-arch stability to help resist displacement by functional stresses.

Characteristics Of Major Connectors Made from material compatible with oral tissue. It is rigid. Doesn't alter the natural contour of the lingual surfaces of the mandibular alveolar ridge or of the palatal vault. Doesn't impinge on oral tissue in (insertion, withdrawal. Or in function).

6. Cover no more tissue than is absolutely necessary. 7. Doesn't contribute to the trapping of food particles. 8. Has support from other elements of the frame work to minimize rotation in function. 9. Contribute to the support of the prosthesis.

Mandibular Major Connectors Lingual bar. Linguoplate. Sublingual bar. Lingual bar with cingulum bar (continuous bar). Cingulum bar (continuous bar). Labial bar. Lingual bar and Linguopslate are most common used.

Mandibular lingual Bar Indication: Where sufficient space exist b/w elevated alveolar lingual sulcus and the lingual gingival tissue. Location: Half-pear shaped, with bulkiest portion inferiorly. Superior border tapered, located at least 4mm inferior to gingival margin.

4. Inferior border located at site of the alveolar lingual sulcus where the pt ´s tongue is elevated. Finishing line: Butt-type joints with minor connector for retention of denture base.

2. Mandibular Sublingual Bar It is modification of lingual bar used when the existing space not allow placement of lingual bar. The shape remain the same but placement is inferior and posterior to site of lingual bar.

Contraindication: Remaining natural anterior teeth severely tilted toward the lingual. Characteristics and location: Half-pear shaped same like the lingual bar except that the bulkiest portion is located to the lingual and the tapered portion is toward the labial.

2. The superior border of the bar should be at least 3mm from the free gingival margin of the teeth. 3. The inferior border is located at height of the alveolar lingual sulcus when the pt ´s tongue is elevated. 4. Functional impression is most. Finishing line: Butt-type joints with minor connectors for retention of denture base.

3. Mandibular Linguoplate Indication for use: No sufficient space for lingual bar. The residual ridge undergone a vertical resoption which offer minimal resistance to horizontal rotation. Periodontally weakened teeth. When future replacement of one or more incisor teeth will be facilitated.

Characteristics and location: Half-pear shaped with bulkiest portion located. Thin metal apron extending superiorly to contact cingulum of ant. Teeth. Apron extended interproximally to the height of contact points. Inferior border at ascertained height of the alveolar lingual sulcus where the pt ´s tongue is slightly elevated.

4. Mandibular Lingual Bar with Continuous Bar( Cingulum Bar ) Indication for use: When Linguoplate is indicated but the axial alignment of ant. Teeth prevent . When wide diastema b/w mandibular ant. Teeth.

Characteristics and location: Shaped and located same as lingual bar. Thin, narrow(3mm) metal strap located on a cingula of anterior teeth. Scalloped to follow interproximal embrasures. Originated bilaterally from incisal, lingual, or occlusal rests of adjacent principal abutment.

5 . Mandibular Labial Bar Indication for use: When a lingual inclination of remaining MPM and incisors teeth cannot be corrected. Severe lingual tori cannot be removed. Severe tissue undercut.

Characteristics and location: Half –pear shaped with bulkiest portion inferiorly located on the labial and buccal aspect of the mandible. Superior border tapered to soft tissue. Superior border located at least 4mm inferior to labial and buccal gingival margins and more if possible. Inferior border located in the labial buccal vestibule.

Maxillary Major Connectors A. Single palatal strap Characteristics and Location: Anatomic replica form. Ant. Border follow the valleys b/w rugae at right angle to median suture line. Posterior border at right angle to median suture line. Strap should be 8mm wide. Confined with in an area bounded by the four principal rests.

B. Single Broad Palatal Major Connector Indication: Class I. V or U shaped palate. Strong abutments. 6 remaining ant teeth. No interfering tori.

Characteristics and location: Anatomic replica form. Anterior border following valleys of rugae and at right angle to median suture line and extending anterior to occlusal rests or in direct retainer.

3. Posterior border located at junction of hard and soft palate. And extended to pterygomaxillary notches.

C. Anterior-posterior Strap Indication : Class I and II. Long edentulous span class II MOD 1 arches. Class IV. Palatal tori.

Characteristics and location: Parallelogram shaped and open in center portion. Relatively broad(8-10mm) ant. And post. Palatal strap. Lateral palatal strap (7-9mm) parallel to curve of arch. 6mm from gingiva of remaining teeth.

4. Anterior palatal strap; ant border not placed further interiorly than ant rests and never closer than 6mm to lingual gingival cervices.

D. Complete Palatal Coverage Indication for use: Situation in which only some or ant teeth remains. Class II arch with large posterior modification space and some missing anterior teeth.

3. Class I arch with 1-4 PM and some or all ant teeth remaining, abutment support is poor, residual ridge extremely resorbed, direct retention is difficult to obtained 4. No tori.

Characteristics and location: Anatomic replica form supported anteriority by rests seats. Palatal Linguoplate supported anteriorly and designed for the attachment of acrylic resin extension posteriorly. Contact all of the teeth remaining in the arch. Posterior border, terminates at the junction of the hard and soft palate, extended to hasmular notch areas.

D. U-shaped Palatal Major Connector Is used only in which inoperable tori extended to the posterior limit of the hard palate. It is the least favorable design of all palatal major connector( lack rigidity).

Rests and Rest seats Vertical support provided by rests (occlusal, incisal, or cingulum). Rests located on properly prepared tooth surface . The prepared surface of an abutment to receive the rest is called the rest seat.

The primary purpose of the rest is to provide vertical support for PD. It also does the following: Maintain components in planned position. Maintained established occlusal relationship. Prevent impingement of soft tissue. Direct and distribute occlusal loads to abutment teeth.

Form Of Occlusal Rest and Rest Seats The outline form of the occlusal rest should be rounded, triangular shaped with the apex toward the center of occlusal surfaces. It should be as long as it is wide. The base is 2.5mm for M and PM. Reduction in marginal ridge is 1.5mm.

4. It should be concave and spoon shaped (no sharp edges or line angle). 5. The angle formed by the occlusal rest and the vertical minor connector from which its originate should be less than 90 *.

Extended Occlusal Rest In mesially inclined abutment the rest extend more than one half of the mesio-distal width. In severely tilted abutment the extended occlusal rest may take the form of an only to restore the occlusal plane.

Interproximal Occlusal rests. Intra-coronal Rest: It is used for both occlusal support and horizontal stabilization. Horizontal stabilization is derived from the near vertical walls of this type of rest seat. The form of the rest should be parallel to path of placement, slightly tapered occlusaly, and slightly dove-tailed to preve3nt dislodgement proximally.

The main advantages of the internal rest are that it facilitates the elimination of the visible clasp arm.

Direct Retainer It is a clasp or attachments applied to an abutment tooth for the purpose of holding RPD in position. Classification : Extracronal direct retainer ) casted clasp, wrought wire clasp). a/ Occlusaly approaching clasp (circumferential) . b/ Gingivally approaching clasps (Bar clasps)

2. Intracronal direct retainer( attachments): a/ Internal attachment. b/ External attachment. c/ Special attachment. Component parts of the clasp: 1. Retentive terminal 2. Retentive arm 3. Reciprocal arm 4. Occlusal rest 5. Shoulder 6. Body 7. Minor connector

Height of contour: is greatest convexity of tooth. The basic principle of clasp design is encirclement to obtain more than 180 * of continuous contact. Types of cast Circumferential clasps: Simple circlet clasp: widely used, tooth supported PD, approach the undercut from edentulous space. Not used for distal extension.

2 . Reverse clasp. 3. Multiple circlet clasp( combination of two circlet clasps). 4. Embrasure clasp 5. Ring clasp; no buccal undercut. Isolated abutment, lingually tipped molar, from disto- buccal to disto-lingual undercut. 6. Hairpin clasp. when undercut is near to edentulous space. 7 . Combination clasp.

Bar clasp: Composed of two parts ( Gingivally approaching and retentive tip) Approach arm: It is a minor connector. Semi circular in cross section, cross the gingival margin at right angle. Retentive terminal : it should end below undercut.

Advantages: Easy to insert and difficult to remove. More aesthetic, cover less tooth structure. Types of Bar clasps: T-Bar clasp. Y- Bar clasp. I- Bar clasp.

Indirect Retainer Apart of RPD which assists the direct retainers in preventing displacement of distal extension denture base by functioning through lever action on the opposite side of the fulcrum line.

Types of indirect retainer: Auxiliary occlusal rest, most frequently used, located far as possible from distal extension base, placed perpendicular to the mid point of the fulcrum line. If this perpendicular line ends on the incisal area it is a voided, instead it transfers to PM in both sides.

2. Canine extension from occlusal rest, finger like extention(lug seat) from the PM rest is placed on the lingual slope of adjacent canine. 3. Canine rest. 4. Continuous bar retainers and Linguoplate.

Denture Base Denture base defined as that part of a denture which rests on the oral mucosa and to which teeth are attached. Ideal requirements: Accurate tissue adaptation with minimal change in volume. Thermal conductivity. Sufficient strength to resist fracture or distortion under function.

4. Cleansability. 5. Ability to be relined if necessary. 6 Cost effective. 7. Low specific gravity. 8. Ability to achieve a good finish.

Types of denture base: Acrylic Metal. Combination. Acrylic Resin denture base; mainly used for distal extension PD- attached to the frame work by minor connector-with 1.5mm thick to have a adequate strength.

Advantages: Anterior teeth can be replaced at their original position (aesthetic level). Restore the contour of the edentulous ridge. Brings out the normal contour of the lip and cheeks. Can be relined.

Disadvantages: May break on usage. Tend to accumulate mucous deposits and food debris. Soft tissue irritation. Allergy.

Metal denture base: mainly used for tooth supported PD. Advantages: Accurate tissue adaptaion( better retention). Easy to clean. Strong even in thin section. Heat conductivity( physiologic tissue stimulation).

Disadvantage: Difficult to trim and adjust. Over extension can injure the soft tissue. Poor aesthetic. Difficult to reline and rebase.

Removable partial denture

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Removable partial denture