designing acrylic rpd

7/29/2019 Designing Acrylic RPD

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Designing Acrylic RPD

1) Anterior edentulous area The labial flange should not extend into bony undercut except

in very long span class IV situations.

2) Posterior edentulous area The buccal flange should not extend into bony undercuts in

class III situations. Mesial and distal edges of the flange should not fall in the shadow of

the proximal surfaces of the abutments and corners should be rounded. Buccal flanges

should extend into undercuts in class I and Class II maxi cases.

3) Disto-palatal extension (Maxillary)

a) Class III and class IV situation Minimum is upto second premolars. With

more missing teeth the plate is extended further back.

b) Class I and class II situations Plate must extend upto junction of hard andsoft palate.

4) Disto-lingual extension (Mandibular)

a) Class III and class IV situations Minimum upto second premolars.

Maximum upto second molars. Should NOT extend into third molar area

because it has severe undercuts.

b) Class I and class II situations Must extend over the retromolar pads and into

retromylohyoid fossa.

5) Antero-palatal extension (Maxillary) This extension applies to class I, class II and class

III situations. Mostly the border ends along the cingulum of the anterior teeth. However,

in some situations, it is required to be taken back along the rugae:

a) Anterior deep bite

b) Reclined incisors

c) Prominent spacing

6)Extension along remaining natural teeth (on lingual/palatal surface)

The plate contacts a number of remaining natural teeth along their palatal

surfaces,lingual surfaces and the proximal surfaces of the abutments. The level at which

the plate contacts these teeth is very critical.

a) Posterior teeth : Edge of the plate should contact these teeth 1mm above the

height of contour. If the edge is kept more gingivally, it will be lying in the


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undercut area of the teeth, which will prevent insertion of the denture. One has

to then grind the edge of the plate where interference to insertion is noted.

Consequently insertion takes place and the tooth, therby causing irritation to

the tongue and food entrapment.

b) Maxillary anterior teeth : The edge of the plate must be well above thecingulum and cover the lingual embrasures. In class I, class II and Class III

situations, the plate must have sufficient strength to prevent warpage or

fracture. It should be rigid and not flexible. The strength and rigidity is

provided by not only thickness but also width of the plate. Hence if necessary

the edge of the plate may be taken closer to the incisal edge of the anterior

teeth to make it wider.

7) A common error :

Based on above guidelines, a very definite and distinct outline of the plate ismarked on the working cast using an indelible pencil (copying pencil) orr a

marker pen.

However, this phase of removable partial denture fabrication is treated very

lightly and carried out without adequate knowledge of the guidelines mentioned

above. The biggest error commonly committed is placing the outline along the

scalloped edge of the gingival. As a result, the plate edge comes to lie in

undercuts thereby preventing insertion. Plate edges ending at the marginal gingiva

can cause severe gingivitis due to which acrylic plate partials got the bad name,

gum strippers.

N. B. In severe lingually inclined teeth especially with heavy occlusal attrition,

the height of contour on lingual surface is at occlusal surface level.

Such cases need recontouring of lingual surface by grinding to lower the

height of contour.

CLASPS :

A) Depending on the condition of the arch, clasps incorporated with acrylic partials will:

i) Increase retention

ii) Be the sole source of retention

iii) Be unnecessary


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Fabricating a clasp and incorporating it into the denture needs much skill and

care. A wrongly designed and in corporate clasp can only create problems during fitting

of the denture. Hence, if survey of the cast indicates that the plate alone is capable of

providing retention, one may as well avoid incorporating the clasp.

For example:

1) Short span class IV condition

2) Short span class III modification condition

Clasps not only provide retention (prevent vertical displacement) they prevent

horizontal shifting or rotation. Hence, they are essential in class I and class III situations.

B) Type of clasp : Invariably, C-clasps are placed on the abutment teeth using stainless

steel wire of 19, 20 or 21 gauge. Higher the gauge figure, smaller is the wire

diameter, hence more flexible. Thicker wires are used when available undercut is

minimal and thinner if undercut is heavy.

C) Location of clasp :

a) Tip of the clasp should lie in undercut.

b) Proximal portion (tagum side) should be in a non-undercut area of the abutment.

c) Entire tagum should in nn-undercut area.

d) Tagum should have one or two bends or a loop at the tip. Straight tagum may

result in displacement of clasp.

e) In mandibular R.P.D. the tagum should be on buccal side or on ridge crest.

Placing it on lingual side will weaken the denture base and it will fracture along

the clasp.

f) Adapt modeling wax on thickness over area where clasp tagum is to be located.

designing acrylic rpd

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