Mid ==================

partial dentures

Prosthodontics : dental specialty pertaining to diagnosis, treatment planning, rehabilitation and the maintenance of all oral functions AND this specialty deal with clinical conditions associated with missing or deficient teeth or maxillofacial tissues.

types of RPD : 1)Interim RPD: they are temporary dentures that placed for a short period of time. made from acrylic.2)Definitive RPD: RPD that are made out of metal , *they are permanents DEFINITIVE mean that we place the RPD as a final stage.

* BIOMECHANICHAL CLASSIFICATION OF RPDs: 1-Tooth Borne : the support of this RPD come from the teeth.2- Tooth – Mucosa Borne: the support of this RPD come from sub tissue .3- Mucosal Borne: the support of this RPD come from mucosa and sub tissue.

▪Recall: partial dentures are made for those patients that are partially dentate/ partially edentulous. (Two terms, same meaning)

▪Kennedy's classification:- Class I: -Bilateral edentulous area located posterior to all teeth. ( 2 missing areas posteriorly)- class II : Unilateral edentulous area located posterior to all teeth.- Class III: Unilateral bounded saddle.- Class IV: single missing area crossing the midline.

*Applegate's Rules:1- Classification should follow rather than precede extraction.2- If 3rd molar is missing & not to be replaced, it is not considered in the classification.3- If the 3rd molar is present and to be used as an abutment or rest, it is considered in the classification.4- If the second molar is missing and not to be replaced (the opposing is not present), it is not considered in the classification.5- The most posterior edentulous area determines the classification.6- Other edentulous areas other than those determining classification are called modification spaces. (In some books or websites they may be called Anterior Space or Posterior space, different terms but they refer to the same thing).7- The extent of the modification is not considered, only the number. (the class 3 with 1 missing tooth space is the same as class 3 with 5 missing teeth space).8- There is no modification space in Class IV.

Temporary RPD

3 types of RPDs : 1.interrim 2.transitional 3.therapeutic or treatment RPD

Temporary RPDs mostly get supported from mucosa only

Treatment options:-No Replacement.-Fixed Partial Denture (FPD),-Removable Partial Denture (RPD).-Implant crowns/FPD.-Extractions & Complete Denture.

easily talking : Whenever a fixed PD is not a choice , you choose a RPD – that’s if the patient chose a replacement - .

*Indications for an interim RPD :- Maintenance of oral health- The sake of appearance- Maintenance of a space- Reestablishing occlusal relationships- Conditioning teeth and residual ridges –since I cant place a definitive crown before bleaching-

*Indications for a transitional RPD :when hopeless teeth need extraction but can not be done at once due to: a. Health b. Psychological reasons (the patient is not expecting extraction )

*Indications for a treatment RPD :A. Vehicle for tissue conditionerB. TMJ problem (clicking , pain, bubbling sounds)C. occlusion modification

Forces in the oral cavity:

- if the forces exceed the ability of tolerance (how much tissue can tolerates/stands), they become potentially destructive which is considered as a pathological change.

- How do forces become harmful? If they change from normal, by changing: 1. Magnitude: is the amount of the force2. Direction: tilted teeth direct the forces in an incorrect direction.3. Duration: is a single force and means how much you keep biting on your teeth, in chewing cycle your teeth touch each other in 0.3 sec only4. Frequency: how much do you eat.

* Un-wanted movement in RPD: Gravity: pulling upper RPD down. Sticky food: pulling both upper and lower dentures away from their seating. Occlusal forces : moving the distal extension bases towards tissue are subject to movement in response.

*support components-resist occlusal forces : 1. Rigid connectors : major and minor connectors.2. Maxillary major connectors incorporate horizontal hard palate coverage.3. Direct retainer designs for control of forces minimize horizontal forces on abutment teeth.4. Rests provide dento-alveolar support

* Stability :1. Any vertically placed components of RPD denture

2. Minor connectors: to get sub- stability from them3. Proximal plates4. Reciprocating arms of clasps5. Lingual plates6. Rest seats designed as intra-coronal boxes (channel rest)7. Residual ridges as in complete dentures, so please revise the lecture in complete denture course.8. get stability from the other side of the arch

Reciprocation : resistance of the minor movement that caused by insertion and removal of the clasp from the abutment teeth and grasping the tooth from the other side .

the reciprocal arm is passive all the time ; it’s always going down not engaging any bulge or undercut. But the retentive arm is active while it’s over the maximal bulge crossing to the undercut of the tooth.

in C-clasp we have the rest on the same side of the guide plane and in I-bar or infra-bulge clasp we place the rest on the opposite side of the guide plane.

- Our final design should: Have good tapered body , they taper up to the last third Have cross section is half circular, because the more round cross section the more flexible it will be. go into the undercut by 0.5 mm

** stainless steel is more flexible than chrome-cobalt.

RPI system : mesial rest , Distal guide plane and I bar

RPA system : where the clasp is made of stainless steel wire.

FINAL ==================

Surveying

-Identify parallel surfaces and maximum contours (teeth and ridges)-

-Graphite marker : The tip level with the gingival margin if not

False survey line

Path of insertion; = path of withdrawal, Single or multiple

-Path of displacement; Variable, 90° at the occlusal plane

– at Initial survey:

-Horizontal occlusal plane, “0” tilt

-Identify undercuts position and amount in relation to the most likely path of displacement

Sufficient undercuts or not-

-At zero tilt:

Path of insertion=path of displacement

-Other tilts:

Path of insertion≠path of displacement

-Undercuts must be present on teeth relative to the horizontal survey(retention)

Resistance along the path of displacement-.

Clasps and guide planes

-Resistance along the path of withdrawal.

Clasps only

-Blockout; Done on the master cast

- Types of blockout; 1-Arbitrary blockout:- Gingival crevices + Undercut areas not crossed by denture,,,2- Shaped blockout:- Clasp arms,, 3- Relief: Over thin tissues + Attachment of resin

Denture base considerations in RPD Design

Acrylic Resin Bases; Most common type-

-Indications; 1-For extension bases.2-When denture base resin is needed to restore anatomic contour and esthetics.3- When there is a need for relining.

4-For long span tooth supported saddle

-The framework is embedded in the base material of at least 1.5 mm acrylic

- Tissue stop should be made for combination of acrylic and metal base- open lattice framework better than mesh patterns

-by tissue stop: 1mm space is provided between the mucosa and the denturebase connectors.

-The outer longitudinal struts are wider than the inner transverse struts in lattice work denture base minor connecter, only the transverse struts should cross the crest of the residual ridge

-Internal & external finish lines should not coincide

-Metal Bases; indecations: 1-For short span tooth borne denture.2-When there is insufficient vertical space for use of resin.

3-When there is a deep vertical overlap of anterior teeth.

Contraindecation; -difficult to reline •Contra-indicated in distal extension RPD

•Contra-indicated immediately after extractions

-What is the indication for using metal base?Small bounded saddle area.If it is large (the missing teeth more than 4) we will use acryl.

-allow some minor vertical movement, so wheneverthe patients bite on the artificial teeth the forces will notdistribute to the abutment.

- like ball and socket , any movement on free end saddle isbroken by the movement of the joint around the ball

-flange extension: Don’t go beyond 2-3 mm buccally and lingualy with metal base but you can with acrylic, unless there is an undercut you can block it or make the flange shorter

-Metal alloy may be cast much thinner than acrylic resin and still have adequate strength and rigidity((Chrome=titanium, < gold))

-all parts of the partial denture framework are rigid except the retentive arm of the direct retainer

-tooth- tissue supported partial dentures should be maximally extended forsupport & retention

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RPD Design

- -it is the dentist who is responsible for the design primarily,

-C clasp "circumferential clasp" or Akers clasp "contains the rest, guide plane, reciprocal and retentive arms , it will be used in the bounded saddle area , on the saddle area we will use open lattice because it is stronger than the mesh, On the free end saddle we will use RPI

system .

-IF we want to get support for our design , we can get support from the rests, so we need to select the size of the rest, and the site of it and if the rest have to be bilateral or not, because if we put one rest on one side we have to put another rest on the opposing side even if there is no missing teeth are there!, this is what we call it cross arch stabilization,

- The Akers clasps are the easiest one to construct, although the best retention comes from the I-bar.

- any plate which is extended to the anterior teeth should have rests on the canines to prevent causing a trauma of the gingiva.

-On the secondary cast , we do some blocking out then we duplicate it by using a refractory material, & we make the metal component on the refractory cast

-The rests must be positioned very well on their seats, we don’t have what we call metal flush, which is an edges of fine metal that is replaced places where we had some wax. so metal flush should be removed.

- the idea of the altered cast; It's a secondary cast but we alter it in a way that we take excellent impression of the free end saddle areas and over that we continue our work.

-----------------------------------Definitions:

-Analyzing rod; study the undercuts without marking

-Graphite marker:; Identify and mark the survey line

- Trimming knife; Used to make sure that the block out is parallel to the path of insertion

• Guide surfaces; Parallel axial surfaces on abutment teeth, Limit the path of insertion

•-Path of insertion; The path followed by the denture from its first contact with the teeth until it is fully seated

•-Path of displacement; It is the direction in which the denture tends to be displaced in function

-denture base considerations in RPD Design: The denture base isthat part of the RPD, which contacts the oral mucosa and in which the artificialteeth are attached.

-finish line: the junction between the acrylic denture base and the major connector or any polished metal surface.

- Internal finish line (IFL): Space between the metal framework andthe tissues surface of the cast is provided by adding relief wax ontothe edentulous ridge on the master cast. The ledge created by themargin of the relief wax in the metal framework should be sharpand definite

-External finish line (EFL): It is the junction between the acrylic and the exposed metal on the external or polished surface.

- Nailheads: like a pen but at the end, it has horizontal piece forbetter retention