IMPRESSION-MAKING-CAST-FABRICATION.pdf

PROSTHODONTICS 1 FIXED PARTIAL PROSTHODONTICS WEEK # 3: Impression Making and Diagnostic Cast Fabrication - Excess mucinous saliva is wiped from the...

PROSTHODONTICS 1 FIXED PARTIAL PROSTHODONTICS WEEK # 3: Impression Making and Diagnostic Cast Fabrication - Excess mucinous saliva is wiped from the palate with a gauze sponge *saliva triggers hypersensitive reaction so least saliva DIAGNOSTIC CAST possible is recommended evaluate soft tissue contour Management of patient with hypersensitive gag vestibular morphology and frenum reflex: attachment - Psychological management bony contour - Topical anesthesia crown length - Pre medication tooth alignment - Distraction pontic space - Controlled tongue position occlusion - Mouth rinse using cold water Topical anesthesia: *soft palate – most sensitive part IRREVERSIBLE HYDROCOLLOID (ALGINATE) Controlled tongue position: *Upward and forward movement of tongue Inexpensive leads to constriction of muscles of soft palate. The tip of tongue must Accurate press the lingual surface of mandibular incisor Easy to manipulate Cold water: *lessens the hypersensitivity gag reflex due to numbness. Does not require custom tray Cold temperature: constricts the salivary gland duct Readily removed from undercut TYPES OF IMPRESSION TRAY *impression is a NEGATIVE reproduction of dentition - Plastic tray (too narrow) *Diagnostic cast is a POSITIVE reproduction of dentition - Perforated metal tray PROPERTIES OF ALGINATE : - Perforated rim lock (recommended) - Rim lock Potassium alginate 15% - Custom made tray calcium sulfate 16% - Stock tray zinc oxide 4% *How to choose the right tray? Through TRIAL INSERTION potassium titanium fluoride 3% diatomaceous earth 60% 1. clearance (4 mm space) sodium phosphate 2% 2. extension (landmarks should be seen: a. maxillary: hamular notch; Spatulation time b. mandibular: retromolar pad - 45 seconds to 1min. with a vigorous figure 8 motion PATIENT’S POSITION Gelation time Lower arch impression - 3 to 4 min. after the beginning of the mix at a - patient is seated at a 45-degree angle to the room temperature floor - 2 mins. Inside the mouth Upper arch impression *The colder (lower) the temperature of the water the longer it takes to set; conversely, the higher the water temperature the faster it - patient is seated in an upright position sets (shorter setting time) DENTIST POSITION 1. Patient preparation 2. Tray selection For lower arch impression 3. Patient’s position - 8 o’ clock position 4. Operator’s position - instruct the patient to bring the tongue up and 5. Manipulation of impression material forward 6. Accuracy of impression For upper arch impression PATIENT PREPARATION - 11 o’ clock position - Patient must be informed about the procedure - Pull lip over the side of the tray (informed consent form) - Mouth preparation - Management of hypersensitive gag reflex - Smooth surface - Well-rounded borders Mouth Preparation - Adequate coverage - Patient is ask to rinse - Detailed anatomic landmarks - Mouth is gently dried WEEK # 3: Impression Making and Diagnostic Cast Fabrication DMD-3-Y2-2 SY: 2023-2024 CARE FOR IMPRESSION BUBBLES (most common mistake) - Impression is immediately rinsed - Disinfect- sprayed with glutaraldehyde Cause: - Dried slightly with gentle air stream - Undue gelation - Poured immediately - Air incorporated during mixing - Poured impression should be covered with wet paper and stored in a humidor for 1 hour. IRREGULARLY SHAPED VOIDS Remove the tray by breaking the seal at the periphery then Cause: giving a quick pull - Moisture or debris on tissue POURING OF STONE ROUGH OR CHALKY STONE CAST If stone is not poured immediately, it will result: Cause: - Syneresis – shrinking of impression material due to - Inadequate cleaning of the impression evaporation of water. (loss of water) - Excess water left on the impression - Premature removal of cast *Imbibition - the uptake by agar or alginate when immersed - Leaving cast in impression too long in water due to absorption. (gain of water) - Improper manipulation of stone DISTORTION - Mucobuccal, mucolabial, and mucolingual folds Cause: - A land area of 2 to 3 mm. - A cast base approximately ¾ inch thick - Impression not poured immediately - Flat lingual area - Movement of tray during gelation - Premature removal from mouth - Improper removal from mouth - Tray held in mouth too long 1. Polysulfide rubber 2. Condensation silicone 3. Polyether 4. Addition silicone Polysulfide rubber - Dimensional stability less than polyether and addition silicone - Less expensive - Long setting time (10 min) - Unpleasant odor - Stain clothing Condensation silicone - Odorless - Dimensional stability less than polysulfide - Short setting time (6 to 8 min) - Hydrophobic GRAINY MATERIAL - By product (alcohol) Cause: Polyether - Improper mixing - Addition polymerization - Prolonged mixing - Low polymerization shrinkage - Undue gelation - Short setting time (5 min) - Water/powder ratio too low - Stiff TEARING - Hydrophobic Cause: - Allergic hypersensitivity - Inadequate bulk Addition silicone - Moisture contamination - Dimensionally stable - Premature removal from the mouth - Delayed pouring - Prolonged mixing - Addition polymerization