A Comprehensive Guide to Dental Casting Waxes and Procedures

Posted on Aug 24, 2024 in Biology

Casting Waxes: A Comprehensive Guide

Casting waxes are compositions containing various waxes with desired properties for making wax patterns to be formulated into metal castings.

Types of Casting Waxes

According to Origin:

According to Use and Application:

• Pattern Waxes: Inlay wax, casting wax, base plate wax, carding wax, blockout wax, white wax
• Processing Waxes: Boxing wax, utility wax, sticky wax
• Impression Waxes: Bite registration wax, corrective wax

Waxing Procedures in Cast Partial Dentures

Requirements:

1. A properly prepared and articulated master cast.
2. A diagnostic cast with a neat and specific design carefully drawn on it.
3. A work authorization order covering all aspects of the desired denture.

Design Transfer:

Design transfer is defined as “Conveying the outline of the proposed prosthesis from the diagnostic cast to the master cast.”

Steps Involved in Design Transfer:

• Marking the height of contour.
• Measuring the undercut.
• Drawing the clasps.
• Drawing the connectors.

Block Out of the Master Cast:

Block out is the “Elimination of the undesirable undercut areas on the cast to be used in the fabrication of the removable partial denture”.

Besides this, block out includes:

1. Those areas not involved that are blocked out for convenience.
2. Ledges on which clasp patterns are to be placed.
3. Relief beneath connectors to prevent tissue impingement.
4. Relief to provide for attachment of the denture base to the framework.

Beading:

Beading denotes the scribing of a shallow groove on the maxillary master cast outlining the palatal major connector exclusive of the rugae area.

Purpose:

1. To transfer the major connector design to the investment cast.
2. To provide a visible finishing line for the casting.
3. To ensure intimate tissue contact.

Mandibular Lingual Bar:

Block Out and Relief of the Master Cast:

1. All tissue undercuts parallel to the path of placement.
2. An additional thickness of 32-gauge sheet wax when the lingual surface of the alveolar ridge is undercut or parallel to the path of placement.
3. No relief is necessary when the lingual surface of the alveolar ridge slopes inferiorly and posteriorly.
4. One thickness of baseplate wax over the basal seat areas.

Mandibular Linguoplate:

Block Out and Relief of Master Cast:

1. All involved undercuts of contacted teeth parallel to the path of placement.
2. All involved gingival crevices.
3. Lingual surface of the alveolar ridge and basal seat areas the same as for a lingual bar.

For the Denture Base Area, Different Procedures…:

1. Beads or nail heads.
2. Open retention without relief.
3. Open retention or mesh with relief.
4. All metal base with or without tube teeth, without relief.

Spruing the Cast:

Three General Rules:

1. The sprues should be large enough.
2. The sprue should lead into the mold cavity as directly as possible.
3. Sprues should leave the crucible at a common point and be attached to the pattern at its bulkier section.

Purpose of Investing (Brumsfield):

1. It provides the strength necessary to hold the forces exerted by the entering stream of molten metal until this metal has solidified into the form of the pattern.
2. It provides a smooth surface.
3. It provides an avenue for the escape of gases.
4. It compensates for the dimensional changes in the alloy.

Investing Procedure:

1. Apply the ring liner.
2. Soak the cast in water for 5 minutes in room temperature water.
3. Dispense correct proportions of the investment material and mix (mechanically or hand mix the investment).
4. Paint the wax pattern and sprues with the debubblizer.
5. Paint the investment.
6. Support the cast until the initial set of the investment.

Pouring the Diagnostic Impression & Making the Diagnostic Cast

• Preliminary care of the impression.
• Pouring the impression.
• Separate the cast & trim the excess.

Ideal Requirements of the Cast:

• Cast surface should be free of voids and nodules.
• Extend sufficiently.
• Land area.
• Base of the cast.

Purpose of Making the Diagnostic Cast:

• To measure the depth & extent of undercuts.
• Determine the path of insertion.
• Plan the preprosthetic surgeries.
• Evaluate size & contour of the arch.

Measuring Depth of Undercut:

• Mounting the cast.
• Tilting the cast to change the path of insertion.
• Mark the height of contour.
• Mark the depth of undercut.
• Mock surgery is done.

Ideal Requirements of the Special Tray:

• Rigid.
• Dimensionally stable.
• Should not react with impression material.
• Simple method of fabrication.
• 2mm in thickness & 2 mm short of the sulcus depth.

Fabrication of Autopolymerizing Resin Special Tray:

Procedure:

• Mark the outline of relief, spacer.
• Adapt relief wax.
• Block out.
• Adapt spacer.
• Apply separating media.
• Sprinkle on or dough method.
• Make handle.
• Trim.

Vacuum Adapted Thermoplastic Resin:

Procedure:

• Spacer.
• Center the cast on the vacuum adapter plate.
• Place the resin sheet in the heating frame & rotate the heating unit into position.
• Heating until sheet sags.
• Lower the frame & resin sheet onto the cast & start vacuum adaptation.
• Trim the excess, remove from the cast & final trim.
• Adapt handle.

Bolouri, Terene, Maynard Gowrylok Technique (1975):

• Pour the plaster base & lightly seat the impression into the plaster leaving the peripheral turn at least 4mm above.
• Trim the excess leaving 5mm wide & 4mm below the impression.
• Adapt modeling clay, plasticine.
• Apply separating media.
• Boxing.

Record Base

Ideal Requirements (Elder):

• Adaptation.
• Border form.
• Rigidity.
• Simple, quick, inexpensive fabrication.
• Means for recording jaw relation, teeth arrangement.

Kenneth added: Not to abrade the cast – Take advantage of undercut – Bond with block out material.

Occlusion Rim:

• Occlusion rim is defined as the “Occluding surfaces built on permanent denture bases for the purpose of making maxillomandibular relation records”.
• Four basic factors to be considered are:
• 1) Relationship of natural teeth to alveolar bone.
• 2) Relationship of occlusion rim to the alveolar bone.
• 3) Fabrication technique.

Mounting on to Hanau Articulator:

Procedure:

• Adjust the horizontal condylar guidance.
• Adjust the incisal pin.
• Attach the mounting plate.
• Face bow record transferred.
• Mounting guide as in twirl bow & spring bow, anterior elevator, transfer jig used with kinematic face bow.
• Attach the cast support to the lower member of the articulator.
• Attach maxillary cast with the plaster.
• Mount the mandibular cast.

Horizontal condylar inclination determined with the protrusive record.

Mounting on to the Whipmix Articulator:

• Adjust the intercondylar distance by removing the condylar elements & using the spacers on the condylar shaft.
• Adjust the horizontal condylar inclination.
• Attach mounting plates & plastic incisal guide table.
• Face bow record transferred.
• Mount the maxillary cast with dental plaster.
• Mount the mandibular cast.

Finishing & Polishing of the Dentures:

• Remove the cast.
• Shell blaster to remove the stone from the interior surface.
• Trim the excess.
• Check for nodules.
• Relieve the frenii.
• Finishing of lingual border & palatal surface.
• Pumice the dentures with rag wheel; in inaccessible areas use prophy cup.
• Polishing the teeth.

Investigations of Cardiovascular System:

• Electrocardiography.
• Radiology.
• Echo-Doppler Echocardiography.
• CT.
• MRI.
• Radionuclide Imaging.
• Coronary Artery Angiogram.
• Plasma Biochemical Markers.

Investigation of Respiratory Disease:

Imaging:

• Chest Radiograph:
  • Bronchial Carcinoma.
  • Pulmonary Tuberculosis.
  • Pulmonary/mediastinal abnormality.
• CT:
  • Determine the size and position of a pulmonary nodule or mass and whether calcification or cavitation was present.

Investigations for Diabetes Mellitus:

Urine Testing:

• Glucose.
• Ketones.
• Proteins.

Blood Testing:

• Glucose.
• Glycated hemoglobin.
• Blood lipids.

Fructosamine Test

The Temporomandibular Joint

Investigations:

• Plain radiography.
• Conventional tomography.
• Computed tomography.
• MRI.
• Arthrography.
• Arthroscopy.

Plain Radiography:

Three Types:

1. O.P.G.
2. Transcranial View.
3. Transorbital View.

Some Radiographic and CT Findings in the TMJ:

• Haziness of the joint space – Acute inflammation of the joint.
• Posterosuperior displacement of the condylar head – Impingement over the posterior wall of fossa.
• Restricted movement of the condyle – Uni/bilateral muscular spasm or beginning of ankylosis.
• Erosion/enlargement/hyper mobility of the condyle – Osteoarthritis/chronic arthritis/subluxation respectively.

Diagnosis of Dental Caries

The Ideal Caries Diagnostic Test Must Be:

• Accurate.
• Sensitive.
• Specific.
• Reproducible.
• Reliable.
• Not transfer S.mutans or other bacteria from affected area to unaffected areas.
• Cost effective.

Investigations for Implant Dentistry:

1. Ridge Mapping: This determines the labio lingual width of the bone.
2. Periapical Radiograph: Exposures must be made with a collimated beam.
3. Occlusal Films: Are sometimes used in the set up for CT examinations in the mandible.
4. Lateral Cephalometric Images: Measures the labiolingual dimensions of alveolar crests and also the alveolar height.
5. Panoramic Radiography: It is used in conjunction with ridge mapping and other diagnostic aids and not as a primary imaging test for implant planning.
6. Computed Tomography: It normally images the entire arch and produces 50 to 60 images.

Diagnostic Approach to the Patient with Salivary Gland Disease:

Salivary Gland Imaging:

• Ultrasonography.
• Sialography.
• Radionuclide imaging.
• Computed tomography.

Methods to Investigate the Attachment Apparatus and Vitality of Teeth

Mobility-Depressibility Testing:

• 1st Degree Mobility: Noticeable movement of the tooth in the socket.
• 2nd Degree Mobility: Movement of a tooth within a range of 1 mm.
• 3rd Degree Mobility: Movement greater than 1mm or when the tooth can be depressed.

Investigations of the Periodontal Status of the Teeth:

DETECTION OF POCKETS: Exploration with a periodontal probe

AMOUNT OF ATTACHED GINGIVA:It is the distance between the mucogingival  junction and the projection on the external  surface of the bottom of the gingival sulcus or periodontal pocket