over denture part 2 (2021)

1-Simple Tooth Modification and Reduction
• teeth are merely reshaped to eliminate undercuts
• reduced in vertical height
Indication:
1-good oral hygiene with a low caries index
2-vital pulps must be receded sufficiently
3-partially anadontic patient
4-severe abrasion of teeth
5-sufficient interocclusal distance
2-Tooth Reduction and Cast Coping:
• minimum reduction in the crown: root ratio
• A cast coping are made after reducing the teeth to prevent sensitivity or as caries control
Indicated when the teeth have :
1 – Adequate bony support
2 – Good periodontal prognosis
3 – Adequate interocclusal distance
3-Endodontic Therapy and Amalgam Plug:
• reduced (1-2mm)gingival level
• endodontic therapy
4-Endodontic Therapy and Cast Coping:
• shallow dome shape with the margin slightly supragingival
• recurrent decay on the exposed dentin when there is a history of carious involvement.
• short post .
5-Endodontic therapy with cast coping utilizing some form of attachment:
• patients with a favourable prognosis
b- low caries index
c- proper home care
d- good periodontal health
e- Adequate bony support
f- Available inter-ridge distance
6-Endodontic treated tooth with prefabricated retentive element:
• simple and inexpensive
• temporary fixation of overdentures
• spherical retentive element attached to a threaded post (Dalbo-Rotex system)
7- The telescopic overdenture:
• endodontically treated, reduced slightly
• smoothed and polished.
Impression of the abutment teeth:
One –stage technique with supporting element:
Abutment teeth without root copings, the full-arch impression is made as soon as the abutments are prepared. Root copings without retentive elements , the impression is made after final cementation of the copings. It covers all of the ridge except for any undercut areas near the abutment teeth .
One -stage technique with existing retentive element:
Zinc oxide-eugenol paste or elastomer
Pre-existing retentive elements
Transfer matrices are set in place on the involved retentive elements and picked up in the impression.
RECORD BASES:
Incorporation of the metal bearing in the record base. The shape of the base must correspond to that of the future overdenture, i.e., it should not cover the facial marginal gingiva in the abutment region.
Few select cases the rim can be temporarily fixed to the abutments for greater stability:
1-dowel copings and retentive elements already present from previous treatment.
2- When directly mountable retentive elements have been inserted prior to registering maxillomandibular relations.
Criteria for Designing the Base:
- Not unnecessarily promote plaque accumulate
- Not mechanically traumatize the marginal gingival.
- Not impede the performance of good oral hygiene.
- Not interfere with normal function of the tongue, lips and cheeks.
- Not interfere with esthetics or speech
- Permit modifications and additions with moderate technical effort.
DESIGNS THAT LEAVE THE PERIODONTIUM UNCOVERED:
The base does not cover the gingiva, and the artificial teeth are prepared to fit directly upon the roots or the dowel copings:
1- Bases that are circumdentally open
2- Bases that are facially and proximally open.
Temperatures in the gingival sulcus are significantly higher under closed bases that cover the gingival margin than with open designs . Gingival reaction was always most severe where the denture base covered the gingival margin &least severe in uncovered gingival margins, caused by a reaction in the gingival circulation.

1. Cover as little of the marginal gingiva as possible
2. Border the proximal spaces with metal.
3. The greater the number of abutment teeth and the better their prognosis, the more open the construction may be.
Advantages of a base designed that it does not cover the gingiva :
1-precludes direct mechanical trauma .
2-reduce plaque retention around the abutment.
3-it possible to clean the proximal surfaces of the root coping with interproximal brushes with the prosthesis in place .
4-prevents a suction effect: combined with inadequate coping shape and poor oral hygiene , would lead to hyperplasic proliferation (suction hyper plasia ).
5-prevents undesirable vacuum retention in maxillary overdentures with retentive attachment.
Disadvantages:
1-increased risk of fracture of the base.
2- Unfavourable spatial relationships that do not permit extensive proximal openings.
3- Aesthetic considerations.
4- increased food impaction in the open proximal spaces.
5- Speech problems such as sigmatism .
6- Poor prognosis for the abutment teeth, making probable an early conversion to a CD.
Denture Base Design ,Function and Aesthetics:
The normal position and function of the lips and cheeks as well as their natural relation to the residual ridge, are maintained only when the denture base does not cover the ridge facial to the abutment teeth.
Facially over bulked denture bases may be manifested through:
1- increased food entrapment under the base.
2- Greater difficulty for the cheek muscles to position the food bolus between the teeth.
3 - Interference with lip movement during speech.
DESIGN OF BASE IN EDENTULOUS AREAS:
Modifications:
• Any overextension, that might be tolerated or even indicated in a CD, must be avoided.
• areas the artificial teeth may abut directly against the edentulous ridge for a better aesthetic effect
- In some types of ridges e g, Club-shaped", border extensions are dictated by the path of insertion of the retentive attachments. The base must end at the survey line (height of contour) of the ridge because further extension would allow the trapping of food in the undercut areas.
Cast Reinforcing Frameworks:
• The presence of mechanical attachments and the interruption of the denture flange near abutments reduce the cross sectional area of the denture &increase the danger of fracture.
• This weakness should not be compensated for by:
1- by thickening the acrylic resin.
2- prefabricated metal reinforcers.
CIRCUMDENTALLY OPENED DESIGN:
Advantages:
1- possible to clean the abutments without removing the denture.
2- The base cannot traumatize the gingiva around the abutments.
3- minimal extension of the base.
Disadvantages:
1- very complex
2- The risk of fracture is greater.
3- The possibilities are limited for modifying and adding to the denture when abutment teeth are lost.
Indications:
• abundant space over the abutments .
• a good prognosis .
FACIALLY AND PROXIMALLY OPEN DESIGN:
Have enough rigidity only if they incorporate custom cast reinforcing frameworks.
Advantages:
• less involved technical construction.
• the reduced risk of fracture .
• the ease of modification when an abutment is seldom causes any problem with phonation or food retention.
Disadvantages:
1-difficulty in cleaning
2-The greater extension of the denture base (psychological disadvantage).
Indications:
• Poor prognosis
• speech problems
• extensive tissue loss in the anterior region.
• unfavourable spatial relations .
RECORDING MAXILLOMANDIBULAR RELATIONS:
• Erroneous registration of the horizontal relations will have its first destructive effect on the abutment teeth.
• shearing or lifting forces on the abutments leads to increased tooth mobility and, the loss of the abutment teeth.
TEETH SELECTION:
The posterior tooth form is determined by:
(1) the teeth in the opposing arch and .
(2) the concept of occlusion the dentist desires to use
-Material composition of the artificial teeth:
1-over the abutment teeth should be acrylic resin.
2-opposing arch have gold occlusal surfaces, the occlusal surfaces of the artificial teeth should be either gold or acrylic resin, preferably gold.
3-opposing arch have had the occlusal surfaces restored with porcelain, the artificial teeth preferably should be porcelain.
4-opposing arch are natural teeth not restored with gold or porcelain, acrylic resin artificial teeth are preferred.
Tooth Arrangements:
Overdenture occlusal form corresponds to that of a complete denture:
1-minimize the non-physiologic effects of occlusal forces.
- Position of the artificial teeth within the envelopes of action of tongue, cheeks and lips.
- Harmony between the cuspl inclines and the movements of the mandible.
- Multilocal autonomous stabilizing contact during mastication. (that traumatic occlusion leads to further periodontal destruction)
2-overdenture may have to be converted into a CD when &if the remaining teeth are lost.
TRYING IN THE TEETH:
At this appointment perform the following procedures:
1. Verify the jaw relation records.
2. Make eccentric jaw relation records and adjust the articulator.
3. Assure aesthetic acceptability by the patient.
4. Verify phonetic acceptability.
Mounting the Attachments:
• the amount of space available for an attachment can now be reliably evaluated for the first time.
• Tongue space not be reduced or altered because of the size or location of an attachment.
• A retentive element should be mounted as near the centre of the dowel-coping as possible
• the path of insertion of a rigid element should be approximately parallel to the long axis of the root.



Denture Insertion:
• Use pressure disclosing paste to locate contacts between the female member in the denture base and the male abutments. There should be no contact except between the convex surface of the metal bearing and the concave bearing surface of the coping.
• Evaluate tissue side of the denture base &the borders for pressure areas &overextension.
• Perfect the occlusion by remounting the dentures and selectively grinding the teeth.




PLACEMENT OF OVERDENTUR ATTACHMENTS:
• The traditional technique involves using cold cure acrylic powder and liquid with a brush to place acrylic in the access holes of the overdenture, porosity and voids are discovered when the overdenture is first removed from the mouth.
• quick and reliable method of placing cold cure acrylic and using a disposable syringe when transferring the attachments to the overdenture chair-side.