Cavity Preparation (I-V) PDF

Cavity preparation (I-V) Assoc.Prof. Ingrida Pacauskienė  Dear students, listeners, We remind you that information or visual provided by the lecture/seminar may not be copied, recorded, or distributed without the consent of the author.  Preparation rules and recommendations for each cavity clas...

Cavity preparation (I-V) Assoc.Prof. Ingrida Pacauskienė  Dear students, listeners, We remind you that information or visual provided by the lecture/seminar may not be copied, recorded, or distributed without the consent of the author.  Preparation rules and recommendations for each cavity class ( I – V) preparing to fill them with different restorative materials: 1. composite resin, 2. amalgam, 3. and GIC.  Initial teeth preparation skills will be acquired in the phantom class on the clinical simulation unit. Plastic teeth do not provide the same real feel of cutting enamel and dentine, and also composite bonding procedure can’t be performed because of absence of enamel and dentin. So preparation of natural teeth is advisable to form better skills. Natural teeth should be cleaned and placed in sodium hypochlorite 0,5 % in hermetically sealed container. The solution should be changed once every 2 weeks. When natural teeth dry out they become brittle and crack more easily. The preparation cavities on the models follow recommendations and theoretical rules of resistance for remaining tooth and restorative material in order to perform the ideal shape of the cavity. In clinical situations, the shape of the cavity mainly depends on the spread of caries, on previously placed restorations and may differ from that ideal shape. In the models, the carious process/cavity are imaginable, so we follow the theoretical recommendations during the preparation.  Conventional preparation (retention form; special requirements) Conventional with bevels (amalgam restoration is replaced by composite) Modified preparation – for composite resins Minimally invasive preparation for biomimetic restorative technique Class I  During each preparation step (phase): WHAT? WHY? HOW? Opening (outline, resistance, convenience) Cavity excavation( soft dentin) Praparation of enamel margins( britlle enamel, bevel) Outline. Tooth preparation involves removal of carious dentin and unsupported enamel. Sound (healthy) dentin is not removed to create a flat floor (although in the big cavities flat floor increases resistance). Rules for establishing outline form: 1.Extend the preparation margin until sound tooth structure is obtained and no unsupported or weakened enamel remains. 2. Avoid terminating the margin on cusps heights or ridge crests. 3. If the extension from primary groove includes is more than one third (>1/3) of the of the distance between cusp tips, cusp reduction, capping must be considered. 4. When two preparations have less than 0.5 mm between them, they should be joined to eliminate a weak wall, marginal ridge should be 1.5 mm thickness or more. (2) Typical outlines. Outline form corresponds to the shape of fissures, pits and caries extent. Cavity outline should be rounded without sharp angles. Wherever possible, two occlusal cavities should remain separate without removing the transverse ridge between the cusps (> 0.5 mm wall between). Unnecessary removing will weaken the tooth. Extending outline we should consider about convenience form, cavity must have good access for further caries excavation and restoration. (2) Outline on the buccal surface On the palatal (1) Resistance form. 1. If marginal ridge minimum 1.5 mm is not preserved, class I is prepared as a class II then. 2. The depth should be a minimum of 1.5 mm (preparation for amalgam) where there is a direct load from the antagonist. (2) Resistance form. 3. If the faciolingual width of the preparation exceeds 1/3 the distance between the tips of the facial and lingual cusps that can lead to fracture. Cusps should be evaluated for cracs that could lead to fracture, and functional loading to which they will be exposed should be assesed. The design features that enhance primary resistance: relatively flat floor; box shape; preservation of cusps and marginal ridges; rounded internal angles; adequate thickness of restorative material (depth of cavity), reduction of cusps when indicated; inclusion of weakened tooth structure (covering with the restorative material) (2) Correct position of the bur helps prepare strong walls; no unsupported enamel will be left. Depending on the of bur position we can prepare parallel or converging walls. (2)  (2) Correct position of the bur helps prepare strong walls. Depending on the of bur position we can prepare parallel or converging walls. Retention form is achieved through a slight converging of the axial walls occlusally, and flat floor. Preparing retention is important if amalgam restoration is going to be placed Excavation. Removal of carious dentin is carried out with low speed round carbide bur. Dark, but hard dentin can be left. The pulpal wall not necessary flat if cavity is deep. Preparation of enamel margins No occlusal angle (bevel) is indicated, enamel margins, to enhance their ability to resist fracture should be prepared at the angle 90° with enamel rods resting on sound dentin. correct (2) 1. Unsupported enamel will not be resistant. 2. Margins of restorative material will not be resistant. 3. Correct. Class I for resin composite material The preparation should be as narrow as technically possible without any enamel bevel in the occlussal fissure area; unsupported enamel should be removed. General requirements are the same as for the amalgam preparation, but making retention form is not necessary. The bevels on enamel are not recommended, unsupported thin enamel usually is removed. The preparation of small cavities ( if possible), results in fillings where masticatory forces acting on the restoration surface are small. Small fillings will have reduced wear compared to large fillings and longevity of small restorations is increased. Differeces from the amalgam preparation: conservative outline, no retention form. Class II Outline. Proximal + occlusal preparation or slot? Small class II cavities are closed from occlusal side and should be opened through the occlusal surface. Proximal and occlusal preparation enhance retention, but can be made only in the case of caries in the fissures or old restoration. If fissures are free of caries it’s recommended not extent the preparation to oclussal surface – slot preparation should be made; as much sound structure as possible must be preserved. (2) Initial cut is made through the marginal ridge with the narrow bur to penetrate to carious dentin, then the slot is widened facio-lingually. Proximal enamel plate is thinned to facilitate its removal. Tunnel preparation – marginal ridge is preserved; only in minimal cavities; high failure rate, as marginal ridge will be unsupported by thick dentin and may fracture. (2) Proximal surfaces of the adjacent tooth during preparation may be damaged up to 69%, they will be 3 times more likely to become carious. The plate of proximal enamel may be thined and fractured with a hand instrument to prevent damage of adjacent tooth by bur. The fractured margins have been planed with a gingival margin trimmer. (2) Wedge is placed before preparing , it provides tooth separation, it helps prevent damage to the adjacent tooth. Wedge guard or metal matrix strip must be placed on the adjacent tooth to protect it. (4) Direction of the bur. Slot is widened faciolingually until caries free areas are obtained. (2) The final preparation outline will be determined after all carious structure is removed. It should provide for at least minimal (0.5 mm) separation of margins from adjacent tooth (for amalgam). Gingival margin extended apically of the proximal contact provide minimal space; this enhances placement of matrix, finishing of restorative material.Facial and lingual walls separated from adjacent tooth provide better visualization and proper margin preparation, finishing of material. (1)  It is important to observe the height of the gingival floor as soon as the contact area is passed. The gingival margin should preferably be situated supragingivally with as much healthy enamel left as possible. (1) Preparation of gingival wall. Unsupported, demineralised enamel should be removed by gingival margin trimmer or bur. (1) Preparation of occlusal part. If occlussal fisures are demaged by caries, occlussal box preparaed similarly as class I preparation, avoiding to cut ridges and cusps.S shape curve preparation on the premolar helps to save more structure and enhance retention. Ridges are preserved. Resistance form. To resist amalgam fracture at the occlusal/ interproximal box junction, axiopulpal line angle beveled. The cavities should be at least 1.5 mm deep at the isthmus. Extention of occlusal preparation into occlusal surface(but only when caries in the fissures exists) increase retention, but buccolingually : ¼ (and no more 1/3) the distance between the tips of the facial and lingual cusps. Resistance to fractures. Faciolingual width of the preparation should preferably not exceed one third the distance between the tips of the facial and lingual cusps. Next step – cavity excavation, if remaining soft dentin exists. (2) Retention form. Then the cavity includes occlusal fissure preparation it will provide better retention. Parallel margins, walls coverging occlusally, gingival wall directed axially also increase retention Extension without parallel cavosurface margins or slot preparation will not provide the resistance needed to prevent displacement of the proximal amalgam during mastication – retention grooves should be added. (2) Retention form. Secondary retention grooves in the slot preparation. Retention grooves 0.5 mm wide and 0.5 mm deep are directed parallel to the DEJ (magnification recommended) at low speed. Grooves should be located in the dentin. (2) Complex preparations For large cavities as alternative restoration in order to avoid fractures. Occlusal surface is reduced by 2.5 mm corresponding to it’s anatomy. All cusps and occlusal surface is covered by amalgam. (2) Tissue – saving, pear shaped class 2 preparation for composite restorations. More tissue can be saved, more conservative outline. (2) Steps and burs (4) Clinical example Interproximal protection. Prior to preparation rubber dam wedge and /or metal strip, or special WedgeGuards ( for ex. Polodent) should be placed. Separation of teeth with Palodent (Densply) WedgeGuard ( wedge with the metal plate) or retaining ring. (2) (2) Enamel preparation Enamel on buccal or lingual walls can be beveled for composite preparation. (4) Then enamel on the gingival wall is not so close to the cervical line, a bevel can be placed to enhance composite adaptation and seal. (2) Enamel bevels class II (for composite): 1.On the buccal and lingual and gingival walls 2. On the buccal and lingual walls ; there is no adequate enamel on gingival, Excavation of a proximal lesion may result in more gingival extent of the preparation. Refining the preparation to eliminate very thin enamel and prepare an inverse bevel will expose enamel rods and provide better adhesion to the gingival margin. (2) Final preparation for the composite resin (2)  Class III Below contact point, most often in the middle of proximal surface (1) Outline. Initial preparation should be made through the marginal ridge (perpendicular to the palatal surface, often in the middle third of crown), away from the adjacent tooth surface. Separation needed with the wedge and/ or metal matrix, or wedge guard. The cavity is prepared with a facial or lingual approach, depending on the localization of the lesion; lingual approach is more preferable and aesthetic. Extensive lesions may already have cavitated onto the labial surface, in which case direct access may be possible. Soft dentin excavation should be done with the round carbide bur, low speed. Dark dentin can’t be left, because restoration will be not esthetic. (2) Caries extending to the dentin – cementum surface (beyond the cementoenamel junction). Bonding with cementum and dentin is more problematic than to enamel, some studies show that a groove (0.5mm width and depth) placed 0.5 – 0.7 mm from the external surface of the root helps reduce the microleakage between the composite and dentin (technically difficult). The preparation is most likely to receive an adhesive composite restoration, so there is no need to prepare retention form. (2) Enamel bevels enhance aesthetics and retention. Bevel 0.5 mm width can be placed lingually or/and labially. Class III for glass- ionomer cements do not need enamel bevels and grooves. (2) Sequence of burs (4)  flame shape smooth (red, yellow) diamonds - can be used for the enamel bevelling (1) Clinical example Vestibular surface defect may vary to very large Class IV preparation. 1. Fractures – trauma. 2. Class III caries spreading to incisal edge. The preparation demands the presence of sufficient enamel for retention. Fractures often require no preparation other than an enamel bevel 1-2 mm width, 45°. In the case of caries preparation similar to class III, but extending to incisal edge which is prepared, wider bevels on vestibular and palatal sides prepered as well. (2) Class V Class V preparation. The outline should be rounded and limited to the demineralized area. In premolars – kidney shaped; in molars – sausage – shaped. If enamel is missing on the gingival wall some studies show that grooves placed gingivally help to reduce microleakage (and create retention). This technique is difficult to perform, magnification needed also preparing groove on the gingival wall we do not save all healthy dentin tissue. Class V for resin composite should be prepared with the enamel bevel oclusally, then retention form is based on acid etch retention in the enamel. Minimal cavity preparation is needed for glass ionomer cements (no enamel bevel needed ). (1)  Summary Class I composite preparation : the faciolingual width up to 1/3 intercuspal distance; at least 1,5 mm of mesial/distal marginal ridge is preserved; no enamel bevel on the occlusal enamel edge. Class II composite preparation. occlusal surface is prepared in the case of caries or old restoration replacement; the faciolingual width – up to 1/3 intercuspal distance; no enamel bevel on occlusal part; enamel bevel sometimes could be prepared on the enamel of vestibular or oral wall, and if there is adequate enamel – in some cases can be prepared on the gingival wall. Class III – IV. Enamel bevels - on vestibular or oral walls 0,5 – 1,5 mm width. Class V for the GIC - no enamel bevel; for composite – enamel bevel occlusally. References 1. Ritter AV, Boushell LV, Walter R. Sturdevant‘s art and science of operative dentistry. 7th ed. St. Louis, Missouri: Elsevier; 2019. 2. Summitt JB, Robbins JW, Schwartz RS, editors. Fundamentals of operative dentistry: a contemporary approach. 4th ed. Chicago: Quintessence; 2013. 3. I.Pacauskienė, J.Siudikienė, V.Mačiulskienė ir kt. Ikiklinikiniai dantų preparavimo ir plombavimo darbai. Kaunas: LSMU; 2009. 4. Catalogs of the instruments. Dėkoju už dėmesį