Wax Pattern PDF

Wax Pattern The cast restoration is duplicated exactly through fabricating wax pattern that is converted into metal using the lost wax technique & this is summarized in: - Wax pattern >> holding of wax pattern using a sprue form...

Wax Pattern The cast restoration is duplicated exactly through fabricating wax pattern that is converted into metal using the lost wax technique & this is summarized in: - Wax pattern >> holding of wax pattern using a sprue former >> pouring investment around the wax pattern >> burning out of wax pattern >> space (mold) >> casting of molten metal (recently ceramics) through an empty channel (sprue) ‫ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬Wax Pattern ‫ــــــــــــــــــــــــــــــــــــــ‬ ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬1‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬  Requirements of casting wax 1- Flow readily 2- Take the fine details & preserve it till investing 3- Accept addition 4- Can be carved without chipping & flaking 5- Can be burnished & polished 7- Has a minimum rate of stress relaxation after carving & before casting to prevent distortion 8- Evaporate without leaving any debris or residual ashes during burn out 9- Has different color than the used die material 10- Acceptable strength & rigidity after cooling Components of wax pattern A- Paraffin wax or synthetic wax (40-60%) B- Bees wax (carnauba wax) >> to increase melting temperature & gives rigidity C- Dammer resin >> to decrease flakes D- Dies > provide the necessary color contrast Types of wax  Type I >> medium: used for direct technique (inside patient mouth) soften at 37 oc  Type II >> soft wax: used for indirect technique (Outside patient mouth) 25oc Instruments of wax pattern fabrication 1- Heating instrument: Normal or Electric wax instrument (thermojet) which allows accurate control of wax temperature 2- Waxing instrument: (P.K. Thomas kit = Wax dropper (small & large) + Burnisher + Blade carver + Cones carver (small & large) + Wax spatula 3- Wax 4- Separating medium 5- Wax caliper: to measure the thickness of wax 6- Powder: Zinc stearate powder to check the occlusal contact ‫ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬Wax Pattern ‫ــــــــــــــــــــــــــــــــــــــ‬ ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬2‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬  Techniques of wax pattern fabrication I- Direct technique  Inside patient mouth  In case of intra-coronal restorations (inlays or post)  Medium wax is used II- Indirect technique  On Prepared die on a stone cast  Most popular >> high accessibility & time saving  Soft wax is used III- Indirect-direct technique  The pattern is constructed by indirect method > then final adjustment is done intra-orally Methods of Wax pattern construction 1- Dipping method - Done by dipping the die into molten wax to get a thin (0.3 mm), uniform & adapted layer of wax called “coping” 2- Incremental (addition) method - Done by melting the wax & dropping it using hot special instruments then carved by sharp carver - Used to build full anatomical wax patterns N.B: But, multiple addition of wax >> induce stresses >> relaxation >> distortion ‫ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬Wax Pattern ‫ــــــــــــــــــــــــــــــــــــــ‬ ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬3‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬  Steps of wax pattern construction I- Coping construction - Coping is a thin thimble non-anatomical crown (0.3mm) properly adherent to the preparation to get all fine details - Done mainly be dipping technique or using wax dropper II- Wax pattern removal & evaluation - The wax pattern should be allowed to cool before removal from die - A constant light grip is maintained on the pattern by the thumb & fore finger of the other hand which also holds the die.. why?  To ensure it can be removed easily & intact  To ensure it is adapted on the die accurately III- Proximal surfaces A) Axial surface of the pattern cervical to the proximal contact should be straight or slightly concave to allow proper oral hygiene & accommodate the inter-dental papilla (Straight emergence profile) B) Contact area:  In maxillary teeth: Contact areas should be located occlusal & buccal  In mandibular teeth: Contact areas are centrally located N.B: Open contact >> food wedging between teeth leading to caries, bad odor & periodontal diseases N.B: To ensure proper contact, grind (scrap) small amount of stone from the adjacent teeth on the cast before waxing ‫ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬Wax Pattern ‫ــــــــــــــــــــــــــــــــــــــ‬ ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬4‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬  IV- Buccal & Lingual surfaces A) Height of contour - The normal height of contour allows proper protection of gingiva from food impinging & allows soft tissue massaging due to food deflection - Location: in cervical 1\3 EXCPT lingual surfaces of mandibular posterior (middle 1\3) - Height of contour: should not extend more than 1 mm to avoid overcontouring - Height of contour should follow the contour of adjacent teeth N.B: - If over-contoured >> Plaque accumulation & periodontal diseases N.B: - If under-contoured >> food impinging on gingiva >> gingival recession (less significant than overcontouring) B) Straight emergence profile - “It is an imaginary line cervical to the height of contour (between the base of gingival sulcus & height of contour) to allow proper oral hygiene & accommodate the inter- dental papilla” - It should be straight or slightly concave - If convex emergence profile >> food stagnation >> caries & PDL disease V- Occlusal surface A) Functional & non-functional cusps - Palatal cusps of upper teeth & buccal cusps of lower teeth are called functional cusps & used to grind food - While Buccal cusps of upper & lingual cusps of lower are called non-functional cusps & used to prevent overflowing of food & protect buccal mucosa & tongue form biting - Tripoding: each cusp should contact the opposing tooth in 3 points N.B: The occlusal contacts should be at the base of triangular ridge not at the cusp tip to avoid wearing ‫ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬Wax Pattern ‫ــــــــــــــــــــــــــــــــــــــ‬ ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬5‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬  B) Pattern of occlusion 1- Cusp to fossa (tooth to tooth contact) is more favorable because:  Forces are // to long axis >> less tipping & wedging  Efficient chewing  Eliminate the food impaction below marginal ridges  Allow tripoding contact  Less wear of cusp tips >> More stable occlusion 2- Cusp to marginal ridge (tooth to two teeth contact) C) Occlusal anatomy & cusps should follow:  Curve of Spee >> important in protrusive movement  Curve of Wilson >> important in lateral movement N.B: Posterior teeth are disoccluded in all eccentric movements VI- Margination - Margins should be reflowed & refinished immediately before investing to increase margin adaptation which leads to decrease dissolution of luting cement N.B: Wax pattern should be sprued & invested immediately >> because any delay will lead to stress relief >> distortion ‫ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬Wax Pattern ‫ــــــــــــــــــــــــــــــــــــــ‬ ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬6‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬  Wax pattern for veneered crown (PFM): Steps: Usually full anatomical wax pattern should be fabricated >> Cut back should be done (a uniform thickness of wax should be removed to allow uniform thickness of veneering porcelain (0.8-1mm) >> provides better mechanical & esthetic properties) Recent advances - CAD Wax: wax blocks are milled using CAD/CAM machine  Easier & Time saving  Documentation  Accurate ‫ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬Wax Pattern ‫ــــــــــــــــــــــــــــــــــــــ‬ ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬7‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬