Wax pattern
53 likes30,179 views
The wax pattern is a precursor to the final cast restoration and must be fabricated precisely. There are two techniques for making wax patterns - direct and indirect. Various waxes are used depending on the type of restoration. For inlay patterns, the wax needs to flow easily when heated but be rigid when cool and carve precisely without distortion. The pattern is stored on the die and invested soon after fabrication. The die is prepared, relieved, and lubricated before pattern fabrication. Patterns are built up by adding wax for the coping, axial contours, emergence profile, occlusal morphology, and refined margins. Cusp-marginal ridge and cusp-fossa occlusal schemes are classified.
Wax pattern
- 1. Wax Pattern • Wax Pattern = precursor of cast restoration • Final restoration can be no better than its wax pattern
- 2. Wax Patterns FABRICATION: 1. Direct technique 2. Indirect technique WAX PATTERNS WAXES: ANSI/ADA Specification No.4 • Type I • Type II = = intraoral, extraoral, melting temp melting temp
- 3. Inlay Waxes Requirements of a good inlay wax: 1. Can flow easily when heated, without chipping, flaking, or loosing its smoothness. 2. Rigid when cool. 3. Can be carved precisely without chipping, distorting or smearing. 4. Color must contrast with the stone die (Blue, red, green). Wax is thermoplastic - distortion !!! - how to control The wax pattern should be stored on the lubricated die and invested as soon as possible after fabrication. Cast and Die Preparation • Working cast and opposing cast are Correctly mounted on an articulator. • Preparation finish line is outlined in Red pencil (Very fine red line). • Die hardening agent is applied to the Finish line area to protect it from Abrasion (Thin layer, less than 10 Micron). • Die relief agent is painted on the preparation portion of the die, 0.5 mm short of the finish line.
- 4. • 2 coast is usually necessary to achieve the desired 20-40 micron relief. • Proximal contact surfaces of the adjacent teeth are lightly scraped and protected with due hardening agent. • Die lubricant coated over the die and allowed to soak for several minutes.
- 5. Wax pattern fabrication 1. 2. 3. 4. 5. Coping fabrication. Axial contours Emergence profile Occlusal morphology Margin finishing Armamentarium 1. 2. 3. 4. 5. 6. Pkt (Thomas) waxing instruments No.s 1 to 5. Wax spatula. Sable brush. Inlay wax Zinc stearate powder Die lubricant
- 6. Coping fabrication The coping is a thin structure closely adapted to the prepared area of the die, and serves as a foundation for the axial contours and occlusal morphology of the wax pattern. The coping can be formed using: 1. 2. 3. 4. Inlay wax Heated resin material Vacuum-adopted polystyrene Pressure-formed polyprophlene Axial contours The proximal contacts (mesial & distal) and the facial and lingual axial contours of the wax pattern, are waxed up onto the finished coping. A) Proximal contacts: • Occlusogingival location: Occlusal third of the other posterior crown. Maxillary first and second molar in the middle third. • Faciolingual location: Facial aspect of the middle of the posterior teeth. Maxillary first and second molar centered faciolingually.
- 7. Axial contours B) Facial and lingual contours In harmony with the normally positioned, adjacent teeth. Axial contour C) Height of contour (Maximum prominence of a surface) • Facial surface of posterior teeth: Occurs in the cervical third. Extends approximately 0.5 mm (beyond the cementoenamel junction) • Lingual surface of maxillary posterior teeth: Occurs in the middle third. Extends approximately 0.5 mm mandibular 1st premolar. Extends approximately 0.75mm on mandibular 2nd premolar. Extends approximately 1 mm on mandibular molars.
- 8. Axial contour d) Emergence profile: • The part of the axial contour which extends from the gingival sulcus to the height of contour. It must be straight profile in the gingival third of the axial surface. • This will assist the cleaning efficiency of the toothbrush and floss. Over contour/Undercontour Occlusal morphology The occlusal morphology of the wax pattern is waxed up when axial contours are essentially complete. The occlusal scheme can be classified by the location of the occlusal contact made by the functional cusp on the opposing tooth in centric relation. Two types: 1. Cusp-fossa. 2. Cusp-marginal ridge.
- 9. Classification of occlusal arranements Type Cusp-Fossa Cusp-Marginal Ridge Location of occlusal contact in opposing teeth Relation withopposing tooth/teeth Advantages Occlusal fossae only Marginal ridges and occlusal fossae Tooth-to-tooth Tooth-to-two teetch Occlusal forces are directed parallel with the long axis of the tooth. These forces are near the centre of the tooth-placing little lateral stress on the tooth. Rarely found in natural occlusion, and so can only be used when restoring several contacting teeth and the teeth which oppose them Full mouth reconstruction Most natural type of occlusion, found in 95% of adults. Ca be used for single cast restorations. Disadvantages Application Food packing and displacement of teeth may arise if a functional cusp wedges into a lingual embrasure. Most cast restoration done in daily practice. Cusp-marginal ridge arrangement MANDIBULAR BUCCAL CUSPS 1st Premolar 2nd Premolar 2nd Premolar Mesiobuccal cusp of 1st molar Distobuccal cusp of 1st molar Distal cusp of 1st molar Mesiobuccal cusp of 2nd molar Distobuccal cusp of 2nd molar Distal cusp of 2nd molar MAXILLARY OCCLUSAL SURFACE Mesial marginal ridge of 1st premolar Distal marginal ridge of 1st premolar Distal marginal ridge of 1st premolar Distal marginal ridge of 2nd premolar and mesial marginal ridge of 1st molar Central fossa of a 1st molar (Usually nonfunctional) Distal marginal ridge of 1st molar and mesial marginal ridge of 2nd molar Central fossa of 2nd molar Usually not present.
- 10. Cusp-marginal ridge arrangement A. B. Cusp-Fossa Cusp-Marginal Ridge Functional waxing of the occlusal morphology • The occlusal morphology of posterior teeth can be waxed up by adding wax in six specific and progressive stages. Wax additive technique Color coded inlay can be sued for visual convenience. • The six stages of functional occlusal waxing are: Cones (cusp positions) PKT NO.1 yellow wax. Marginal & cusp ridges Pkts No.1 Blue wax. Buccal & lingual ridges Pkt No.1 Red wax Axial contours Pkt. No. 1 & 4. Green wax. Triangular ridges Pkt. No.1 Red wax Supplemental anatomy Pkt. No. 1,3 & 5. Green wax. Cusp-marginal ridge for mandibular teeth
- 11. • The iocclusal morphology of the wax pattern is waxed up when axial contours are essentially complete. Cusp-marginal ridge for mandibular teeth. Cones for buccal cusp: Pkt. No.1 Junction of buccal one-third and lingual two-thirds of mandibular teeth. Mesiodistally in line with opposing fossae or marginal ridge. Length of mandibular cus determined by contact in the fossa or on the marginal ridges of the maxillary teeth.
- 12. Cusp-marginal ridge for mandibular teeth. Cones for buccal cusp : Pkt No.1 Junction of buccal one-third and lingual two – thirds of mandibular teeth. Mesiodistally in line with opposing fossae or marginal ridge. Length of mandibular cusp determined by contact in the fossa or on the marginal ridges of the maxillary teeth. Cusp – marginal ridge for mandibular teeth. Buccal ridges: Pkt No.1 Buccal ridges from the tip for the cone to its base and will produced the outline of the final contour of thebuccal surface. Check in centric and lateral excursions and make sure that it is not overcontoured. Cusp marginal ridge for mandibular teeth Mesial and distal cusp ridges: PKT No. 1 Add mesial and distal ridges to the buccal cusp and complete buccal contours by blending these ridges into the buccal surface. Check the inclines of the new ridges for compatibility by moving the articulator through excursions
- 13. Cusp marginal ridge for mandibular teeth Triangular ridges: PKT No.1 Add triangular ridges to the buccal cusp.The base of these triangular ridges should form the central groove of the occlusal surface. The ridges should be convex to insure optimal contact with opposing teeth. Cusp marginal ridge for mandibular teeth Cones for lingual cusp: PKT No. 1 Position the cones for lingual cusp(non functional) Placed as far lingually as possible to prevent working side interferences. The lingual cusp should be shorter than the buccal cusp. Cusp marginal ridge for mandibular teeth Triangular ridges: PKT No. 1 Add ridges to form lingual outline of the lingual contour. Broad based triangular ridges with the PKT No. 1 and will converge slightly toward the central fossa. The contacts formed by each of the opposing cusp should form a tripod configuration Cusp marginal ridge for mandibular teeth Marginal ridges: PKT No. 1
- 14. Form marginal ridges by joining the buccal and lingual cusp ridges. Smooth all grooves and fossae with PKT No. 3. Round and finish the ridges with the PKT No. 5. Cusp marginal ridge for mandibular teeth Margin finishing Remove wax pattern from die and re-lubricate the die Place wax pattern on freshly lubricated die Re-melt the entire margin with hot PKT No. 1. Add wax on the margin and carve precisely upto the margin with PKT No. 4. Check the margin carefully for the following discrepancies: 1. 2. 3. 4. 5. Overwaxed margins Short margins Ripples Thick margins Open margins