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VII. Aesthetic requirements for the arrangement of artificial teeth for complete dentures. Cross bite, prognathic and progenic arrangement. VIII. Waxing, flasking, polymerization, cleaning and polishing of the complete dentures.
Aesthetic requirements for the arrangement of artificial teeth for complete
dentures.
• Gerber's (1979) minimum requirements for complete dentures must be met when arranging artificial teeth. They are as follows: "Complete dentures should restore the facial appearance with a personalized and natural look."
• "Complete dentures should preserve the residual tissue structures of the gnathodynamic system."
• "Complete dentures should attempt to ensure adequate masticatory function and enhance clear phonation."
In keeping with Gerber’s requirements, the aesthetic components of the anterior tooth arrangement must not be dissonant with a
patient’s facial appearance.
• Establishing maxillary anterior tooth width can be aided by observing the relative widths of the base (ala) and the bridge of the nose. For tooth selection that is harmonious with a patient’s facial appearance, the incisal width of the central incisor should reflect the width of the base of the nose, and the width of the lateral incisor should reflect the width of the bridge of the nose. That is, when the base of the nose is wide, the width of the maxillary central incisor should be wide. If the bridge of the nose is narrow, the lateral incisors should be narrow.
Selecting Tooth Forms
face with square forms
face with tapered forms
face with oval forms
in harmony with facial forms:
•Square face with square forms
•Oval face with oval forms
•Triangular face with tapered forms
Sagittal and frontal considerations
• The incisive papilla is an invaluable reference point for correct placement of the maxillary anterior teeth and the anterior arch form. The maxillary anterior teeth lie to the facial of the incisive papilla. In the young, the line connecting the tips of the canines transverses the incisive papilla. As the alveolar ridge is increasingly resorbed with increasing years since loss of the teeth, the line moves posteriorly and may eventually pass through the posteriorly extent of the papilla.
• The distance from the middle of the
incisive papilla to the labial surface of the
maxillary central incisor is typically 8
mm. Because this distance is fixed, the
apparent curvature of the anterior arch
form will increase as a person
experiences more alveolar ridge
resorption.
• The labial surface of the canine is
normally 10.5 mm from the lateral aspect
of the anterior rugae.
• The distance between the tips of the canines is the same as the width of the base of the nose.
• Canines are immediately inferior to the side of the nose. They must not be positioned directly at the corners of the mouth when the patient smiles, so the "buccal corridor"—the facial surfaces of the premolars and first molar—can be visualized between the cuspid and the corners of the mouth.
• The width of the central incisor approximates the width of the philtrum.
• First premolars appear at the head of the "buccal corridor" and behind the canine.
Tips of canines = width of nose
Width of centrals = width of
philtrum
• Selecting Tooth Shade, Form, and Alignment
• Selecting tooth shade, form, and alignment is best accomplished prior to setting posterior teeth. Once the anterior teeth have been selected and set, the dentist needs to evaluate the midline in the mouth to ensure acceptable tooth placement.
• The Smile Line Once the midline is established as correct, the length, contour, and position of the incisal edges can be checked. The final evaluation of the anterior arrangement, which will include the gingival contours and margins, will be completed at the last try-in.
• Final evaluation at last try-in In this example, the central incisors appear too short and the canines appear too long.
Orthognathic ratio in the side sections
Medio-posterior shortening of the upper dentition
In retainer upper alveolar ridge-Pelo Weights and
order at the front
Maxillary progeny Malocclusion I
1. Overdeveloped frontal area of the
upper jaw.
2. Highly protruding upper lip
3. Positive lip scale
• Arrangement of the upper teeth
• “ Midline”,
• Anterior elliptic curve
• Bilaterally symmetrical arrangement of
the masticatory teeth,
• Functional masticatory center
• Pillars of the tooth rows
Upper anterior teeth – most Inside, advocated crest of the alveolar ridge OPISTOGNATIC SLOPE
LOWER frontal teeth – from out to the contact with lingual canine surfaces.
HORIZONTAL plane- behind the lingual slope of the upper canines
Not required contact between the front teeth - canines
overdeveloped and protruding lower jaw
1. Overdeveloped frontal area of the mandible.
2. HIGHLY protruding lower lip
3. NEGATIVE ORAL tiered ladder
Progeny of Mandible Malocclusion III
Retention prosthetic area
bilaterally
Remove retainer part of the tuber maxillae
Weakly and strongly developed
Tuber maxillae
Upper Total Denture
Pterygoid processes
Elastic deformation
• Two stabilization pterygoid tuberoses
• Midline incision of the palate plate
• Power decomposition
• 1-1,5 мм
• Gap between the two pterygoid processes
• Prosthetic edges - retention paratuber space
Slightly developed tuber maxillae
Total denture
Two paratuber plastic pellets
Horizontal positioning as
drawer
Highly developed tuberculosis
Elastic impressions
Extended base - plate
Wax Pelo prototypes
Acrylic resin Denture
Pelo are cut in supra tuber
spaces
Rules
Shape of the alveolar
ridge
Type of the atrophy
Intraalveolar spaces
Border occlusions
Occlusal curves
Interalveolar angle under
80°
Changed interjaw
relationships
Masticatory region is changed
• The frontal teeth have to be ordered
• Bilaterally arrangement of the masticatory teeth
• Lower premolar – antagonists lower first and second premolars are
changed their position
• medial segment on vestibular cusp has to overlap the distal
segment of the lower first premolar
• distal segment must go behind the medial segment of the second
premolar
• all subsequent upper teeth come in masticatory furrow of the ower
their antagonists
• Slightly lowering upper vestibular cusps
Cross – bite arrangement
Unilaterally cross- bite
Exchange of the upper teeth with the lower in one side only has to be done in interalveolar angle below 80 ° unilaterally? On the opposite side -
orthognathic order
LONGITUDINAL CENTRAL
FISSURE OF THE LOWER
TEETH
Upper vestibular cusps
Processing the denture
1) Flasking. 2) Wax
elimination.
3) Mixing. 4 ) Packing and curing
5) De - packing
6) Shaping and
Polishing.
Flask: Is a metal case or tube
used in investing procedures.
The flask is made of 3 major parts, (1) lower half (which contains the cast), (2)
upper half and (3) the cover or lid. The lower half may have a round plate, covering a
round hole in the base of the lower half.
Flasking: The process of investing the cast and a waxed denture in a flask to make a
sectional mould used to form the acrylic resin denture base.
• Molding or flasking Techniques:
• 1- Compression technique:
• The stone cast with the record denture base, wax and teeth are secured to the lower half
of the flask with gypsum investment material (plaster or stone). Then the upper half of the
• flask is put in place and gypsum is poured to the occlusal surfaces of the teeth. Finally the
top portion of the flask is poured with investment and the lid is placed on the flask.
1) Flasking:
• It is a complicated procedure requiring special
flask and equipment. In this technique
• the wax pattern is sprued and the material is
injected into the mold. This process allows
• injection of further material during
polymerization to compensate for the
polymerization
• shrinkage.
2- Injection moulding technique:
The procedure of flasking a denture in compression technique is as follows:
• 1) The master cast and the wax dentures are
placed in the flask, to insure that the cast fit in
the flask.
• 2) The Inner surface of the flask is coated with
Vaseline, while the base of the cast is painted with separating medium (cold mold seal). To prevent the investment material (plaster of Paris) from attaching to the cast.
3) The first layer of gypsum investment is
poured in the lower half and the cast is placed on top of the investment.
• 4) After the set of the first gypsum investment
layer, a plaster separating medium is painted on it, to prevent the sticking of the second layer of gypsum investment to the first layer.
5) A mix of dental stone is placed over the surface of the teeth in
the invested trial denture , which is referred to as coring.
• 6) The upper half of the flask is put in place,
then the second mix of gypsum investment is placed on the first layer and covers the wax, denture base and teeth.
• 7) Before the second layer sets the lid or flask cover is put in place and tapped to sit properly allowing the excess gypsum to flow out of the holes in the lid.
2- Wax elimination:
• After the complete set of the gypsum the flask is
ready for the next step which is "Wax
elimination", in which the flask is placed in
boiling water for 4 to 6 minutes. Then it is
removed from the water and opened. Then the
wax is washed away with boiling water. After
that the mold is washed with boiling water
containing detergent, then finally washing it with
clean boiling water.
2- Wax elimination:
• After the stone of the flask is dry, the inner side of the mold and the cast are painted with a separating medium by a camel's hair brush and allowed to dry. The separating medium must not come in contact with the teeth because wax residue on the teeth is
contaminant and causes adhesion failure with the denture resin. A second layer of separating medium is applied on the inside of the mold and the flask is allowed to cool to room temperature.
3- Mixing:
• Acrylic resin dough is made by mixing the powder (polymer) and liquid (monomer) to form 'dough' which is packed into a gypsum mold for curing. The ratio of powder to liquid is important since it controls the workability of the mix as well as the dimensional changes on setting.
• The mixing should be done in a clean jar which should be covered to prevent evaporation of the monomer.
4- Packing:
• It should be done when the mixture reaches dough stage, as the dough is rolled into a rod-like form and placed in the upper half of the flask then polyethelen (nylon sheet) is placed over the dough in the upper half and then the two halves of the flask are closed until they are almost in approximation, this is done to spread the dough evenly throughout the
• mold.
4- Packing:
• Then the two halves of the flask are separated,
the excess material at the borders of the denture
is removed by a wax knife, and additional resin is
added at any places that are deficient. At least
two trial closures are done and before the final
closure a thin layer separating medium is applied
on the cast and the polyethelen sheet is removed
and then the two halves of the flask are closed
under pressure by bench press of about 100
Kg/cm2. Then the flask is put in a spring clamp
and the clamp is closed tightly.
5- Curing:
• It is polymerization of the hot cure acrylic to produce the final denture. The material is cured by heating in a water bath; pressure is applied during curing for the following reasons:
• 1- To decrease the effect of thermal expansion.
• 2- To decrease the polymerization shrinkage.
• 3- To increase the evaporation of monomer thus decreases porosity.
Types of curing cycles for heat
cure acrylic:
• 1- Short curing cycle: The denture is placed in water at room temperature and the curing temperature is programmed to 74 ° C for one and half hour followed by 100 ° C for one hour.
Types of curing cycles for heat cure
acrylic: • 2- Long curing cycle:
• The curing temperature is programmed to 100 oC for 8 hours. Polymerization can occur at any temperature but it is very slow at temperature below 70oC,the best curing cycle is the long curing cycle because most of the conversion of monomer to
• polymer occurs during the period at 70oC and during this time the dough itself may approach
• 100oC because the polymerization reaction exothermic. The monomer boils at 100.3oC so the
• dough must be kept below this temperature to avoid boiling of the monomer; on the other
• hand rapid curing cycle usually results in some gaseous porosity.
6- Deflasking:
• Deflasking is the process of removal of the processed denture from the flask and investment mold. Before deflasking of the processed denture begins the flask is left to cool to room temperature. If not, increased distortion of the acrylic may occur.
Laboratory remount
• The denture should be remounted on the articulator as dictated by the indices with sticky wax. The incisal pin discrepancy should be noted. If the discrepancy is less than 2mm, it is acceptable. If the discrepancy is between 2-5 mm, occlusal correction can be accomplished.
• If the discrepancy is more than 5mm, the entire treatment should by repeated.
7- Shaping and Polishing:
• In this step any excess acrylic is removed from the processed denture by the use of stone wheel burs, stone burs, and steel burs. Care must be taken not to heat the denture during grinding, because this may cause distortion of the denture base. Finally, the denture should be smooth and clean, as no plaster and no deep scratches should remain after the preparation for polishing.
• In polishing a rag wheel with pumice is used for smoothing the denture. Then a final high
• polish is given to the denture with a rag wheel and polishing material (Rouge).