class II for amalgam.pdf

CLASS II CAVITY PREPARATION FOR AMALGAM RESTORATION Dr. Ahmed A. Holiel BDs, M.sc, PhD Lecturer of conservative Dentistry Faculty of Dentistry - Alexandria University ‫‪To the memory‬‬ ‫‪of my Brother‬‬ ‫ي ﷺ‪ :‬إذا مات ابنُ آدم انقطع عملُه إال من ثالث‪ :‬صدقة جارية‪ ،‬أو علم يُنتفع به‪،‬‬ ‫يقول...

CLASS II CAVITY PREPARATION FOR AMALGAM RESTORATION Dr. Ahmed A. Holiel BDs, M.sc, PhD Lecturer of conservative Dentistry Faculty of Dentistry - Alexandria University ‫‪To the memory‬‬ ‫‪of my Brother‬‬ ‫ي ﷺ‪ :‬إذا مات ابنُ آدم انقطع عملُه إال من ثالث‪ :‬صدقة جارية‪ ،‬أو علم يُنتفع به‪،‬‬ ‫يقول النب ُّ‬ ‫أو ولد صالح يدعو له‬ ▪ Smooth surface lesion ▪ Occurring on the proximal surfaces of molars and premolars Spread of caries in enamel and dentin ▪ It spreads in enamel and dentin in a conical pattern Classification Simple Compound Complex Class II simple cavity preparation ▪ In cases having enough proximal access due to: ▪ ▪ ▪ ▪ Missing adjacent tooth Wide embrasure (senile gum recession) Teeth spacing Malpositioned or rotated tooth ▪ Ridge is intact and not undermined by caries Slot preparation • Advantages: • Conservative approach • Preserve proximal contact • Does not alter occlusal relationship • Disadvantages: • Injury to adjacent tooth ▪ Carious lesion at least 2.5 mm apical to MR ▪ Entry in occlusal fossa 2 mm away from MR • Advantages: • Conservative approach • Disadvantages: • • • • • Injury to adjacent tooth Limited visual access Not sure of complete caries removal Close proximity to the pulp Weak enamel proximally and weak MR Class II compound or complex cavity is composed of ▪ 1 Occlusal ▪ 2 Isthmus ▪ 3 Proximal Steps of cavity preparation Outline form Occlusal portion The same as occlusal class I cavity Using high speed with air-water spray, using a No. 245 bur INITIAL DEPTH ▪ Initial depth is 1.5 mm from the central pit or 0.5 mm into dentin ▪ Extend towards the marginal ridge of involved proximal surface, stop approximately 0.8 mm (diameter of the bur) Isthmus portion ▪ The isthmus width no wider than ¼ the intercuspal distance ▪ Buccal& lingual walls must extend to the buccal and lingual embrasures (0.3- 0.5 mm clearance) could be checked by passing tip of explorer Reverse or "S" curve is incorporated into the preparation to create a butt joint margin without destroying excessive tooth structure. • However, they are generally necessary on the buccal portion of the proximal box. • In some cases, they not be necessary. ➢ Straight: In case of small contact area. ➢ Uniform: In case of normal sized contact area. ➢ Reverse curve: In case of broad/ wide contact area. Proximal portion PROXIMAL DITCH • Stop approximately mm from MR • Proximal ditch extended gingivally to the desired level of gingival wall • Move bur buccally and lingually including contact area leaving a thin shell of enamel 0.8 • Removing isolated enamel with a spoon excavator Or enamel hatchet to fracture out weakened proximal enamel. • Smoothen the buccal and lingual wall By this technique proximal area is accessed without injury to the neighboring tooth • Wedging to protect gum from injury • A matrix band could be also used to protect the neighboring tooth. ▪ Placing the cavity margins in the embrasures to be in self cleansable areas. ▪ The gingival floor is 0.5 mm below contact area ▪ The axial wall is about 1.5- 2 mm depth to provide enough bulk of the restoration. Proximal box flare Proximal extension CAVITY MARGINS EXTEND BEYOND PROXIMAL CONTACT 0.5 mm Clearance with adjacent tooth buccally, lingually and gingivally (measured by side of probe) Resistance form Isthmus portion • Minimal width of the cavity Bucco lingually about ¼ the inter cuspal distance (1-1.5 mm wide) • Roundation of the axio pulpal line angle • Reverse curve in case of wide proximal contact area will provide maximum conservation of the sound tooth structure Proximal portion • Reverse curve approach • Gingival floor should be smooth, flat and parallel to the pulpal floor and the occlusal plane. • Axial wall parallel to the external proximal tooth surface and depth of 1.5-2 mm, this will provide uniform bulk of the restoration. • Buccal and lingual walls parallel to the direction of the corresponding surfaces. • The axial wall follows the direction of the outer tooth surface convex buccolingually • Slanted toward pulpal floor Retention form • Mechanical undercuts by preparing the cavity walls slightly converging occlusally (functional cusp) • The inverted truncated cone shape of the proximal portion. • Proximal axial grooves (extra means of retention) • Cut in the axio buccal and axio lingual line angles, extended from the gingival floor in occlusal direction up to the level of the pulpal floor (Full length axial wall) • These grooves are prepared using small round bur ¼ or small tapered fissure bur No 169 bur. Convenience form • Cutting an occlusal cavity provides accessibility to the proximal portion • The axial wall should be parallel to the tooth long axis to allow instrumentation up to the depth of the proximal portion • Selection of instruments suitable sized Finishing of enamel wall: • Trim the buccal& lingual walls using enamel hatchet chisel • Gingival wall by gingival margin trimmer to ensure full length enamel rods CHECKLIST MOD preparation Thank you Dr Ahmed Holiel [email protected]