Components of Removable PartialDentures Denture Bases and Artificial Teeth Mohammad Zakaria Nassani DDS, PhD Al-Farabi College for Dentistry and Nursing Prosthetic Dental Sciences Department
What is a denture base? A denture base is that part of a denture which rests on the foundation areas and to which teeth are attached (The glossary of prosthetic terms. 6th ed. St. Louis, C V Mosby, 1994)
Functions of denture bases1. Attach the prosthetic teeth to the RPD.
Functions of denture bases2. Stress distribution: Transfer occlusal forces to the abutment teeth and, in tooth-tissue supported RPDs, to the denture foundation area.
Functions of denture bases3. Improve esthetics: Replace the missing alveolar tissue in bulk and appearance
Functions of denture bases4. Contribution to bracing, retention and indirect retention of the RPD
Functions of denture bases4. Contribution to bracing, retention and indirect retention of the RPD
Requirements for an ideal denture base material1. Accuracy of adaptation to the tissues, with minimal volume change (Dimensional stability).2. Dense, nonirritating surface capable of receiving and maintaining a good finish3. Thermal conductivity
Requirements for an ideal denture base material4. Lightweight in the mouth5. Sufficient strength; resistance to fracture or distortion6. Easily kept clean
Requirements for an ideal denture base material7. Esthetic acceptability8. Potential for future relining9. Low initial cost
Requirements for an ideal denture base material Such an ideal denture base material does not exist, nor is it likely to be developed in the near future. However, any denture base should come as close to this ideal as possible.
Types of denture bases 1. Acrylic Resin BasesThere are two types of RPD denture bases: 2. Metal Bases
Acrylic Resin Bases Acrylic resin bases are the most common types used in removable partial dentures. The acrylic resin denture bases have the plastic material in contact with the edentulous ridge. They should be routinely used in distal extension cases to allow for relining of the base to maintain mucosal support.
Acrylic Resin Bases Indications1. Tooth-tissue supported edentulous spaces.2. Tooth supported edentulous spaces where bone resorption will necessitate a reline/rebase.
Acrylic Resin Bases Indications3. Where considerable missing alveolar tissue must be replaced.4. Where esthetics is a primary concern.
Acrylic Resin Bases Note: Where protrusive or lateral occlusal guidance will be on the prosthetic teeth, the use of acrylic resin bases can be considered a risk factor for artificial teeth detachment in the corresponding area
Acrylic Resin Bases Advantages1. Can be easily relined.2. Esthetically superior to metal bases3. Easy to fabricate, adjust, finish and polish, and repair.
Acrylic Resin Bases Disadvantages1. Dimensional stability less than metal bases – risk of warpage2. Lower strength than metal Requires more bulk for rigidity than metal Easily abraded. Easily fractured.
Acrylic Resin Bases Disadvantages3. More porous than metal and therefore more difficult to clean.4. Low thermal conductivity
Metal Bases The metal denture base has metal in contact with the edentulous ridge. Prosthetic teeth are attached to the metal base with a plastic base (acrylic resin) or by retentive posts on the metal surface.
Metal BasesRetentive posts can be particularly usefulin anterior regions
Metal Bases Indications Metal bases can be used wherever acrylic resin bases are used.1. A tooth supported edentulous space where further bone resorption is not anticipated.
Metal Bases Indications2. When a facing, tube tooth, metal pontic, or metal reinforced denture tooth is to be used.
Metal Bases Contraindications Tooth-tissue supported edentulous space. Tooth supported edentulous space where bone resorption is expected (in areas where teeth have been removed within 12 months, resorption will still be occurring at an increased rate and relining will be usually be required).
Metal Bases Advantages1. Very rigid2. Very stable form – Maintain their accuracy3. High abrasion resistance4. High thermal conductivity - improved thermal perception may lessen the feeling of the denture as a foreign object.
Metal Bases Advantages5. Less porous than resin and therefore easier to clean. Also this character lessens food, plaque and calculus accumulation, thereby maintaining healthy tissues.6. Minimal weight and bulk - The metal bases can be cast thinner than resin bases while maintaining adequate strength.
Metal Bases Diasadvantages1. Metal not esthetic - the esthetic result can be compromised unless the metal can be veneered with sufficient thickness of acrylic. If an insufficient veneer is used, a greyish hue of the underlying metal becomes visible.2. Metal bases cannot be relined.
Denture Base and flange extension1. Denture bases for tooth-tissue supported partial dentures (Class I and II) should be extended to provide the greatest available surface area for support and retention, without overextension or impingement on movable border tissues.
Denture Base and flange extension2. Tooth supported partial dentures (Class III and IV) need not necessarily be extended maximally, since most of the support for these dentures comes from the teeth.
Denture Base and flange extension2. Tooth supported partial dentures (Class III and IV) The level of extension may be dictated by esthetic considerations
Denture Base and flange extension3. Maxillary distal extension denture bases should terminate in the hamular notches.
Denture Base and flange extension4. Mandibular distal extension denture bases should terminate on the pear-shaped retromolar pads.
Denture Base and flange extension Occasionally, the path of insertion can cause the denture flanges to impinge on the mucosa above undercut portions of the residual ridge, when the partial denture is being seated. In these instances, it is usually preferable to shorten the flange, rather than relieving the internal surface. If the internal surface is relieved significantly, a space will exist between the denture base and the tissues when the denture is fully seated. Food may become trapped in the space and work its way under the partial denture.
Deep lingual undercut Do not relieve internally Shorten flange(difficulty seating, pain) (food trap) (maintain usable undercut) (for retention)
Acrylic resin finish lines Denture bases should have internal and external finish lines which do not coincide. Internal finish lines should be placed furthest from the abutment teeth Offsetting improves the strength at the metal/denture base junction.
Acrylic resin finish lines The purpose of finish lines is to create a distinct resin-metal interface and to prevent the acrylic resin from becoming too thin Because acrylic resin gains its strength with increasing bulk, it should not be finished to a thin edge. If this is attempted, the material may chip or fracture. This can create unhygienic and potentially irritating conditions.
Acrylic resin finish lines Finish lines should be slightly undercut to provide a margin with maximum bulk of resin strength and maximum retention of the resin.
Acrylic resin finish lines The external metal finish line should be located approximately 2 mm lingual to the lingual surface of the replacement denture teeth.
Acrylic resin finish lines Finish line on right is too far toward midline of palate. The location of the finishing line at the junction of the major and minor connector should be based on restoring the natural palatal shape, taking into consideration the location of the replacement teeth.location of finishing lines minimizes bulk ofresin attaching the artificial teeth.Palatal contours are restored, enhancingspeech and contributing to a natural feelingfor the patient
Acrylic resin finish lines If the finishing line is located too far medially, the natural contour of the palate will be altered by the thickness of the junction and the acrylic resin supporting the artificial teeth If, on the other hand, the finishing line is located too far buccally, it will be most difficult to create a natural contour of the acrylic resin on the lingual surface of the artificial teeth.
Partial Denture Replacement Teeth Prosthetic teeth: Artificial teeth used on a denture to substitute for natural teeth.
Partial Denture Replacement Teeth By substituting for the missing natural teeth, prosthetic teeth provide esthetics Function ofProsthetic teeth Prosthetic teeth aid the function of mastication The prosthetic teeth transfer occlusal forces to the denture base and subsequently to the supporting structure (natural teeth and/or edentulous ridges) and thus provide the function of support Prosthetic teeth preserve the stability of the natural dentition
Partial Denture Replacement Teeth Acrylic denture teeth should be used in most instances since they will not wear the opposing dentition to the same degree as porcelain teeth.
Partial Denture Replacement Teeth Porcelain denture teeth cause accelerated wear of the natural dentition, particularly once the surface glaze has been broken. Acrylic teeth are easier to arrange, modify and adjust.
Partial Denture Replacement Teeth Tooth Form The selected tooth form should be selected to harmonize with the opposing teeth.
Partial Denture Replacement Teeth Tooth Form Where the replacement teeth oppose natural dentition with minimal wear, a 30 or 33 tooth form may be indicated.
Partial Denture Replacement Teeth Tooth Form Where the opposing dentition exhibits advanced occlusal wear, a form with more shallow or no cuspal inclinations might be indicated.
Partial Denture Replacement Teeth Tooth Form In almost all instances where the teeth will oppose a natural dentition, adjustment of the occlusal surfaces will be necessary to provide acceptable occlusal contacts.
Partial Denture Replacement Teeth Denture teeth should be selected to harmonize with the shade, shape, length and width of the remaining dentition.
Partial Denture Replacement Teeth Appearance will be most compromised if there is a vast difference in tooth length between the replacement tooth and adjacent natural teeth.
Partial Denture Replacement Teeth In order to improve esthetics, teeth adjacent to the abutment teeth may have to be modified to ensure the proximal plates and other framework components do not interfere with proper positioning of the denture teeth. Replacement teeth may be modified so they can veneer over proximal plates and other framework elements to provide the best possible appearance. Note on the facial surface that the denture tooth slightly overlaps the proximal plate to hide this portion of the framework.
Final anterior denture teeth and waxedAnterior denture teeth ground and denture base conceal metal bar. fitted to metal bar