Beading and Boxing of final impressions for the construction of Complete Dentures:

Question 1

Why We Need Beading & Boxing?

Answer 1

Beading and boxing of an impression is done to protect the formed border thickness of an impression, regulate the height & size of the cast, avoid undue trimming of the cast and to eliminate distortion associated with slumping of the gypsum material when an impression is inverted

Question 2

Boxing:

Definition:

Answer 2

Enclosing an impression to produce a base, to preserve the vestibular contours of the final impression, and to create a land area to protect the cast.

• You may use either the wax, the alginate or the Play-Doh techniques to box your final complete dentures. Be sure you are thoroughly familiar with whichever boxing technique you choose to avoid remaking final impressions due to improper boxing.

Question 3

Master cast:

Definition:

Answer 3

A replica of the prepared tooth surfaces (where necessary), residual ridge areas, and/or other parts of the dental arch used to fabricate a dental restoration or prosthesis.

Question 4

Boxing of Final Impression:

Equipment and materials:

Answer 4

1. Wax, beading (red, rod and rope), boxing (red) and baseplate (pink)
2. Knife, Bard Parker No. 6 with sharp No. 25 blade
3. Bunsen burner and matches
4. Wax spatula
5. Plaster spatula f. Knife, laboratory

Question 5

Wax Boxing Technique

Maxillary:

Steps:

Answer 5

1. Remove the disinfected impression from the Ziploc bag. Rinse and dry the impression thoroughly.
2. Flatten a strip of rod wax with your fingers to a thin ribbon shape. Place it below the trimmed margin of the dried final impression and press it into place. Wax will not adhere to a wet tray or rubber base. The wax should extend from the pterygomaxillary notch area of one side to the pterygomaxillary notch area on the other side. It is not placed on the posterior border.
3. Next, starting at the middle of the posterior border, a strip of red rope wax is placed on the distal of the posterior border. It is then continued over the flattened wax and around the impression. The rope wax must not be above the height of the impression along the posterior border. On the buccal and labial surface it should be 4 mm from the crest of the border of the impression. The rope wax is then sealed to the impression with a warmed spatula and wax.
4. Attach a strip of boxing wax around the beading wax, starting at the middle of the posterior border. The beading wax should not be displaced against the border. Remove excess boxing wax with a heated knife blade. Gently press the ends together and seal with a heated spatula.
5. Seal any open areas with a hot spatula and wax. The seal must be complete or stone will leak through when the cast is poured.

Question 6

Wax Boxing Technique:

Mandibular:

Steps:

Answer 6

1. Remove the disinfected impression from the bag. Rinse and dry the impression thoroughly.
2. Place the trimmed lower impression on a sheet of pink baseplate wax. Using a warmed knife, outline the shape of the tongue area in the wax using the impression as a pattern. Cut out the wax and seal it to the lingual area of the impression tray using a wax spatula. The wax should be 2-3 mm from the crest of the border of the impression.
3. Next, rod shaped wax is flattened into a ribbon form and pressed into place along the lower margin of the final impression from one retromolar pad area to the other. A strip of rope wax is placed around the impression over the flattened wax and sealed with a hot wax spatula. Another strip of rope wax may be needed to obtain the desired thickness of the base to avoid fracture.
4. Firmly attach a strip of boxing wax around the beading wax. The beading wax should not be displaced against the border.
5. Seal any open areas with a hot spatula and wax.

Question 7

Beading and Boxing the Final Impressions taken with elastomeric material:

Steps:

Answer 7

1. Apply and seal rods of beading wax to the sticky wax on the impression to form the land
2. Wrap a sheet of red boxing wax around the beading wax to form a container. All joints must be sealed with hot wax to prevent stone from leaking through
3. Prepare a dense mix of yellow stone using your vacuum mixer and vibrate the stone into the boxed impression. Be very careful to avoid entrapment of air bubbles

Question 8

Laboratory procedures:

Separating the Impression from the Master Cast:

Answer 8

1. Wait 1 hour for the stone to set.
2. Immerse the cast-impression into hot water for 5 minutes to soften the compound border molding before separating the cast from the impression
3. Then carefully separate the cast from the impression
4. Carefully remove the impression from the cast using a lab knife. The compound should be soft and allow you to remove the cast with a minimum of force.
5. Flatten the base of the casts using the model trimmer. Make the base of the cast parallel to the average height of the ridge (mean foundation plane). The base of the cast is no thinner than 11-13mm.

Question 9

Laboratory procedures:

Trimming of Master cast:

Answer 9

1. With a model trimmer flatten the base so that the base is parallel to the ridge.
2. The cast should be 12-15 mm thick
3. Trim the sides of the cast so that there is an even 4-6 mm of land around the cast
4. Trim the land with a bur or sharp knife and reduce so that the depth of the periphery roll is 2-3 mm throughout
5. If necessary, the sides of the cast should also be trimmed. Also reduce the height of the land area if it exceeds 2 mm above the depth of the vestibule.

Caution: Do not trim away any part of the impression surface of the cast in the pterygomaxillary notch areas until the posterior limit is established at the next patient visit.

Question 10

Laboratory Procedures:

Protective land-measurments:

Answer 10

• The protective land should be 3-4 mm wide. It should be 4-6 mm wide on the posterior border of the mandibular cast.
• Bevel the land area approximately 30- 45 degree with a lab knife or a rotating instrument.
• The tongue area should be flat and smooth and no more than 3 mm above the depth of the vestibule

Question 11

Laboratory Procedures:

Optimum dimensions of the Maxillary Master Cast:

Answer 11

Question 12

Laboratory Procedures:

Grooves:

Answer 12

• Both the maxillary and mandibular casts are indexed by placing grooves or notches in the base of the cast.
• Using a stone on the lathe and suction, make three V-shaped index grooves in the base of the cast, two grooves in the posterior of the cast, and one in the midline in the anterior of the cast.
• Indexing permits removal and accurate replacement of the casts on the articulator mounting. Alternatively, two grooves extending the length and width of the cast base and intersecting at right angles can be placed using a stone in the lathe for purposes of indexing.
• All grooves should be 3-5 mm deep and approximately 10 mm wide.