Fundamentals of Tooth Preparation PDF

Fundamentals of Tooth Preparation Ronald George, D.D.S. Assistant Professor Midwestern University College of Dental Medicine Illinois © CDMI Objectives: 1. Understand the principles of tooth preparation 2....

Fundamentals of Tooth Preparation Ronald George, D.D.S. Assistant Professor Midwestern University College of Dental Medicine Illinois © CDMI Objectives: 1. Understand the principles of tooth preparation 2. Describe G.V. Black’s classification of carious lesions 3. Explain Operative Dentistry preparation terminology 4. Understand the design differences of tooth preparations 5. Describe the steps in cavity preparation and the components of each This presentation may contain copyrighted material (“Material”), the use of which may not have been specifically authorized by the copyright owner. Midwestern University is making the Material available through this presentation solely and strictly for illustrative purposes, including criticism, comment, and teaching, with the objective of advancing dental education. This use of the Material constitutes a “fair use” of any such copyrighted Material as provided for in Section 107 of the United States Copy Right Law. In accordance with Title 17 U.S.C. § 107, the Material is distributed without profit to those who have research and/or educational interests. Reproduction or dissemination of the Material, including this presentation, in any format or medium is prohibited. All rights reserved. Outline I. Tooth PreparationBone V. Tooth Preparation Definitions VIII. Tooth Preparation Procedure O A. Why? A. Intracoronal tooth preparation A. Rotary Instrument Axis B. Objectives B. Extracoronal tooth preparation B. Occlusal Contact Identification C. Principles VI. Tooth Preparation Terminology C. Step 1 - Initial depth and Outline Form II. Tooth Preparation Classification A. Simple D. Step 2 - Primary Resistance Form A. Class I B. Compound 1. Preserving Cusps B. Class II C. Complex 2. Preserving Marginal Ridges C. Class III D. Walls and Floors E. Step 3 - Primary Retention Form D. Class IV 1. Internal F. Step 4 - Convenience Form E. Class V 2. External G. Step 5 F. Class VI E. Box 1. Removal of defective restorative G. Other F. Angle material 1. Root surface caries 1. Line angle 2. Removal of soft dentin 2. NCCL 2. Point angle H. Step 6 - Pulp Protection III. Naming Tooth Preparations G. Cavosurface I. Step 7 - Secondary Resistance and IV. Tooth Preparation Design 1. Cavosurface angle Retention Forms A. Factors impacting preparation 2. Cavosurface margin J. Step 8 - External Wall Finishing design VII. Tooth Preparation Wall Direction K. Step 9 - Final Procedures 1. Patient factors A. Parallel 1. Debridement 2. Anatomical factors B. Convergent 2. Inspection 3. Procedural factors 1. Direct restoration 4. Lesion/Defect factors C. Divergent 5. Restorative material factors 1. Indirect restoration  Tooth Preparation “Tooth preparation is the mechanical alteration of a defective, injured, or diseased tooth such that placement of restorative material reestablishes normal form (and therefore function) including esthetic corrections, where indicated.” Sturdevant’s Art and Science of Operative Dentistry Tooth Preparation – Why? Caries lesion progression to the point that loss of tooth structure requires restoration Tooth fracture compromising form and function with or without associated pain or sensitivity Congenital malformation or improper position in need of reestablishment of form or function Previous restoration with inadequate occlusal or proximal contact, defective (open) margins, or poor esthetics As part of fulfilling esthetic or other restorative needs Tooth Preparation – Objectives Conserve as much healthy tooth structure as possible Remove all defects while simultaneously providing protection of the pulp–dentin complex Form the tooth preparation so that, under the forces of mastication, the tooth or the restoration (or both) will not fracture and the restoration will not be displaced Allow for the esthetic placement of a restorative material where indicated Tooth Preparation – Principles Before beginning tooth preparation it is essential to have a working knowledge of: Morphology Enamel Dentin Pulp Cariology Biomaterials Amalgam Composite Ceramics Gold Pulp protection Other restorative materials Instrumentation Handpieces Burs Hand instruments  Tooth Preparation Classification Greene Vardiman Black (1836–1915) Greene Vardiman Black Memorial Lincoln Park, Chicago (Chicago Park District) G. V. Black’s classification of carious lesions and tooth preparations coincides with the diseased anatomic area of the tooth and the associated type of treatment. G.V. Black’s Classification System It is used in diagnosis of caries and identification of preparations and restorations. Class I – pit and fissures Occlusal surfaces of premolars and molars Occlusal two thirds of the facial and lingual surfaces of molars (buccal and lingual pits) NOTE: can be multiple surfaces (Example: Maxillary molars – OL, Mandibular molars OB) Lingual surfaces of maxillary incisors Class I Preparation G.V. Black’s Classification System It is used in diagnosis of caries and identification of preparations and restorations. Class II - proximal surfaces of posterior teeth NOTE: Can include multiple surfaces Class II Preparation G.V. Black’s Classification System It is used in diagnosis of caries and identification of preparations and restorations. Class III - proximal surfaces of anterior teeth that do NOT include the incisal edge Class III Preparation G.V. Black’s Classification System It is used in diagnosis of caries and identification of preparations and restorations. Class IV - proximal surfaces of anterior teeth that include the incisal edge Class IV Preparation G.V. Black’s Classification System It is used in diagnosis of caries and identification of preparations and restorations. Class V - gingival third of the facial or lingual surfaces of all teeth Class V Preparation NOTE: May be referred to as smooth surface caries G.V. Black’s Classification System It is used in diagnosis of caries and identification of preparations and restorations. Class VI - incisal edges of anterior teeth or the occlusal cusp tips of posterior teeth Class VI Restorations with a Class II Preparation G.V. Black’s Classification System Class I Class II Class III Class IV Class V Class VI  Additional Carious and Non-carious Lesions Non - GV Black “classifications” Root surface caries - caries on root surface of any tooth Non-Carious Cervical Lesion or “NCCL” occurs from abrasion, erosion, and abfraction  Naming Tooth Preparations * Naming Preparations Preparations named by using first letter (capitalized) of each tooth surface involved and all additional surfaces are capitalized as well O MOB MOD DO MO MOL DL F or L  “Tooth preparation design takes into consideration the Tooth nature of the tooth (the structure of enamel, the structure of dentin, the position of the pulp in the Preparation pulp–dentin complex, the enamel connection to the Design dentin) and the nature of material to be used for restoration of the defect.” Sturdevant’s Art and Science of Operative Dentistry Factors That May Impact Preparation Design Factors That May Impact Preparation Design Enamel Rod Orientation Walls of preparations should provide enamel rods supported by dentin to maintain enamel strength Enamel rods run perpendicular to the outermost layer of dentin The preparation walls should be, at minimum, oriented 90 degrees to the external surface of the enamel to maintain dentinal support. An even more durable wall configuration results when the preparation has full- length enamel rods buttressed by shorter enamel rods on the preparation side of the wall. Unsupported enamel Enamel that does not have dentin support is called unsupported enamel which can fracture and leave an open margin around the restoration * Factors That May Impact Preparation Design Enamel Rod Orientation Enamel rods Enamel rods NOT supported by dentin – supported unsupported/friable/undermined enamel by dentin – prone to fracture  Factors That May Impact Preparation Design Remaining Dentin Thickness (RDT) RDT = the thickness of dentin remaining after tooth preparation  Between the preparation walls and pulp  The greater the RDT the less chance of damage to the pulp from toxins and tooth preparation  Liners and bases may be needed to protect the pulp with reduced RDT  Tooth Preparation Definitions Sturdevant’s Art and Science of Operative Dentistry Intracoronal Tooth Preparation Intracoronal – within the normal contours of the clinical crown of a tooth Preparation described as “boxlike” Does NOT add strength to the tooth NOTE: Goal is maximum conservation of remaining clinical crown Extracoronal Tooth Preparation Extracoronal – outside or external to the crown of a tooth Destruction of the clinical crown is severe Encircle and reinforce remaining tooth structure May include the whole anatomic crown Preparation described as “stumplike” Restoration termed a “crown” NOTE: Less conservative than intracoronal tooth preparation  Tooth Preparation Terminology Sturdevant’s Art and Science of Operative Dentistry Terminology Tooth preparation: Simple – only one tooth surface Compound – two or three surfaces Complex – four or more surfaces Terminology Walls and floors:  Internal wall – prepared surface that does not extend to the external tooth surface  Pulpal wall (Pulpal floor) oriented perpendicular to the long axis of the tooth, occlusal to the pulp  Axial wall – oriented parallel to the long axis of the tooth  External wall – prepared surface that extends to the external tooth surface – takes the name of the tooth surface that it is adjacent to  Vertical - Mesial, Distal, Facial, Lingual  Horizontal – Gingival wall (Gingival floor) NOTE: Pulpal and Gingival walls are also known as floors since they are horizontal Terminology Boxes - The internal aspect of preparations formed by walls and floors Buccal/Facial wall Occlusal Box of occlusal box Buccal/Facial wall of proximal box Proximal Box Class II Terminology Angles – junction of two or more prepared surfaces  Line angle – junction of two surfaces/walls of different orientation  Combine the names of the two surfaces but drop the “al” ending from the first surface and add an “o”. When two Os are adjacent, separate by a hyphen.  Point angle – junction of three surfaces/walls of different orientation  The name of a point angle follows the same rule except there will be three surfaces.  Terminology Cavosurface  Cavosurface margin – actual junction of the prepared/unprepared portion of the tooth  Cavosurface angle – angle formed by the junction of the prepared wall and the external surface ≥90° NOTE: Cavosurface margin = outer edge of the preparation Restoration margin = outer edge of the restoration  Tooth Preparation Wall Direction Convergent Parallel Divergent NOTE: Class II Proximal Boxes  NOTE: the lines are Parallel Walls the same distance apart from the closed Parallel – side by side having the same end to the open end distance continuously between them NOTE: The ability of composite to chemically bond to tooth structure makes preparations with parallel walls feasible  NOTE: the lines Convergent Walls converge toward the open end Convergence - coming closer together Note: Convergence toward the occlusal  Convergent Walls Convergence - coming closer together After tooth preparation a direct restoration can be placed at that time. Amalgam and composite are examples of direct restorations Amalgam is inserted as a plastic mass and then hardens. There is no “reaction” of amalgam with tooth structure, therefore when it hardens it is retained (locked in) solely by the converging walls of the preparation Resin composite is inserted as a moldable mass therefore converging walls are helpful in retaining composite after it is cured/hardened with a light Amalgam Composite  NOTE: the lines Divergent Walls diverge toward the open end Divergence - moving further apart/separation - opposite of convergence Note: Divergence toward the occlusal Divergent Walls Divergence - moving further apart/separation - opposite of convergence For an indirect restoration an impression is made or a scanned image is obtained and the restoration is fabricated outside of the mouth Since indirect restorations are fabricated outside of the mouth they have to be able to be “tried-in” and then removed so cement/bonding can be added to permanently hold them in place There needs to be divergence Gold and ceramic inlays/onlays are examples of indirect restorations  “It is imperative that the end result (i.e., the overall shape/goals of the preparation procedure) be envisioned/considered before the initiation of any step.” Steps of Tooth Preparation Tooth Preparation Procedure The goals of each step in the preparation stages must be thoroughly understood, and each step must be accomplished as precisely as possible if optimal treatment outcomes are to be obtained. Sturdevant’s Art and Science of Operative Dentistry * Rotary Instrument Axis Alignment Occlusal preparation D M Facial or Lingual surfaces Bur is kept perpendicular to occlusal table / parallel to long axis of tooth crown  Pre flight check Occlusal Contact Identification Identify occlusal contacts preoperatively/before rubber dam with articulating paper – close on articulating paper to maximum intercuspation (MI) Essential to prevent the placement of a preparation/restoration margin where an occlusal contact occurs Occlusal contact at the preparation/restoration interface will increase the risk of early failure of the restoration Step 1: Initial depth and outline form “It is essential that the outline form be visualized (i.e., mentally anticipated) as much as possible before any mechanical alteration of the tooth has begun.” Sturdevant’s Art and Science of Operative Dentistry Step 1: Initial depth and outline form Establish the Initial Depth and Outline Form Begin in a carious pit or fissure and establish the initial depth with your bur Initial depth for an occlusal preparation is 0.2 mm internal to the DEJ At that depth the walls of the preparation are extended until the junction between the enamel and supporting dentin is uncompromised (“Sound DEJ” has been reached) Establishment of the ideal depth is always accomplished even when there is a large carious lesion or previous restorative material present The peripheral walls determine the overall outline of the preparation which is the outline form Step 1: Initial depth and outline form Establish the Initial Depth and Outline Form (Continued) Primary anatomy of the tooth (pits, grooves, fossae) influences outline form and will vary depending on the occlusal morphology Ideal outline form is established first Clinically, disease (the extent of the carious lesion) is the primary determinant of the final outline form Other factors influence preparation design including choice of restorative materials Goals include: Preservation of cusp and marginal ridge strength Limitation of the depth of the preparation into dentin Minimization of faciolingual and mesiodistal extensions Step 1: Initial depth and outline form Establish the Initial Depth and Outline Form (Continued) Outline form should remove all unsupported or weakened (friable) enamel, remove all faults, and margins are usually placed in a position that allows inspection and finishing of the subsequent restoration margins Once final outline form is established, it must be reevaluated in terms of size/extent to determine whether cusps or marginal ridges are weakened A decision may be necessary as to whether the direct restoration is best or a more extensive indirect restoration is best to protect the tooth Step 2: Primary resistance form Obtain resistance form Resistance form is the shape and placement of preparation walls/floors that best enables both the remaining tooth structure and restoration to withstand without fracturing, masticatory forces delivered principally along the long axis of the tooth Conserve as much healthy tooth structure as possible to maximize dentinal support and strength for cusps and marginal ridges (resistance to fracture) Floors are prepared to provide a flat level supporting surface for the restoration which allows a broader area for stress distribution. The floors are approximately parallel to the occlusal surface and relatively perpendicular to occlusal forces. Internal line angles are rounded to limit stress concentration in the corresponding intaglio (interior) surface of restorative materials Fracture Allow adequate thickness of restorative material to resist fracture of the restoration (Ex. 1.5mm for amalgam, 2mm for ceramic) Step 2: Primary resistance form Preserving Cusps The isthmus is the narrow part of the preparation between buccal and lingual cusps Isthmus width is the measurement of this narrow part of the preparation and is important in determining cusp strength Intercuspal distance is the distance from cusp tip to cusp tip opposing one another, directly across the occlusal surface A wide isthmus in relation to intercuspal distance is associated with cusp fracture A narrower isthmus shows less incidence of cusp fracture Step 2: Primary resistance form Preserving Cusps When an extensive carious lesion is present, facial or lingual extension of pulpal or gingival walls may require reduction of weak cusps for coverage by the restorative material Step 2: Primary resistance form Preserving Marginal Ridges The walls of the preparations should provide enamel rods supported by dentin to maintain enamel strength and resist fracture Wall direction takes into account the enamel rod direction At the mesial and distal the walls diverge for both direct and indirect restorations to provide supported enamel rods Conserve as much marginal ridge width as possible to maintain Fractured marginal ridge strength  Step 3: Primary retention form Obtain retention form Retention form is the shape of the Converging Diverging walls walls preparation that resists displacement or removal of the restoration from tipping or lifting forces Amalgam restorations are retained by external tooth walls that converge occlusally Composite are primarily retained by micromechanical retention through Retentive Non-retentive bonding Inalys and onlays rely on diverging walls and are cemented/bonded into the tooth Step 4: Convenience form Obtain convenience form “Convenience form is the shape or form that provides adequate observation, accessibility, and ease in the preparation and restoration of the tooth.”Sturdevant’s Art and Science of Operative Dentistry It is especially important to access the carious lesion and allow for removal of caries “Preparation extensions to increase the convenience of various procedures are always accomplished in light of the goal of conserving as much healthy tooth structure as possible.” Sturdevant’s Art and Science of Operative Dentistry  Step 5: Removal of defective restorative material and/or soft dentin Ideal tooth preparation, then removal of remaining caries and defective restorative material Clinical decisions that guide carious tissue removal are based on the relative tactile hardness (firmness) of the dentin associated with the caries lesion. Carious tissue that has been demineralized and structurally damaged feels tactilely soft and is therefore referred to as soft dentin. Soft dentin no longer retains the physical properties necessary to survive in the rigors of the oral environment and is removed. Caries removal in advanced lesions usually is immediately followed by efforts to afford protection to the pulp tissue adjacent to the deepest area of the preparation. NOTE: Spoon excavator used to remove soft dentin Step 6: Pulp protection When necessary STAY TUNED FOR NEXT EPISODE (Fundamentals of Pulp Protection) Step 7: Secondary resistance and retention forms When the external walls of the preparation converge toward each other, as they NOTE: Secondary retention is gained by: approach the external surface of the tooth, Vertical retention grooves (A) in then no additional or “secondary” retention vertical walls Horizontal coves (C) in vertical is required. walls Correctly oriented external walls (walls that C Slots (B) in horizontal walls/floors have proper dentinal support of the enamel) may diverge as they approach the external Complex Preparation Retention grooves surface of the tooth. Preparation walls that diverge will not physically retain a restoration that is not bonded in place. Diverging walls will not resist forces that have the potential to result DEJ in the dislodgement of a restoration. It may be necessary to strategically modify internal aspects of the preparation to 0.2mm mechanically retain the restoration Sturdevant’s Art and Science of Operative Dentistry Step 7: Secondary resistance and retention forms Bevels Composite Provides for greater surface area for enamel bonding Most useful in esthetic region (Class III, IV, V) Allows for blending of composite with tooth structure Cast metal – gold Cast metal - gold provides for an overlapping margin for cast metal – better junctional relationship (marginal seal) between metal and tooth Step 8: External wall finishing Includes walls and cavosurface margins “Proper finishing of the external walls allows the creation of an optimal marginal junction between the restorative material and the tooth structure. When this occurs there is a smooth transition across the marginal junction and both tooth and restorative material have maximal strength.” “It is appropriate, for clinical practicality, to consider that enamel rods are oriented perpendicular to the external tooth surface. Enamel walls that form a 90-degree angle with the cavosurface may be considered to have dentinal support and to be strong. Enamel rods incline slightly apically in the gingival third of the tooth crown and preparation design in this area should be modified so as to ensure strong enamel margins.” “An acute, abrupt change in a preparation wall outline form increases the difficulty of optimal adaptation of the restorative material. The outline form of all preparation walls should have smooth curves or straight lines.” Sturdevant’s Art and Science of Operative Dentistry  Step 9: Final procedures: debridement and inspection Clean the tooth preparation Complete Excess moisture is debridement allows Air/Water syringe is Explorer or cotton removed with a few IMPORTANT NOT TO inspection/assessment used to remove visible pellet may be needed gentle/light bursts of DEHYDRATE TOOTH of the preparation to debri with water to loosen debri air ensure proper/quality preparation design NOTE: Remaining debri can affect the final restoration Saliva, blood, and debri adversely affects bonding Contaminants can stain margins affecting the esthetic result Preparation Assessment ❑ Occlusal outline: Pits, grooves and fossae included, centered on central groove, smooth rounded flowing shape, maintaining a minimum of 1.5mm of remaining marginal ridge ❑ Groove extensions: slightly divergent, extend ½ way up grooves (extensions centered in groove) at a width of 1mm (small condenser fits) ❑ Triangular ridges, cusps and marginal ridges not compromised or undermined ❑ Isthmus width: 1.25mm wide at the cavosurface measured perpendicular to occlusal table ❑ Margins: Cavosurface angle > or = 90°, smooth, continuous, well defined, no unsupported enamel or bevels ❑ Pulpal floor: 1.5mm deep at shallowest point , flat, parallel to occlusal table ❑ B/L Walls: isthmus slightly convergent occlusally to the long axis of the crown ❑ M/D Walls: slightly divergent occlusally to the long axis of the crown ❑ Walls and floors: smooth ❑ Internal line angles: well defined, smooth and rounded ❑ No damage to prepped tooth, adjacent tooth or soft tissue NOTE: Slightly = 3-6° NOTE: KNOW YOUR Critical Errors! Thank You for sharing some time! References: 1. Sturdevant’s Art and Science of Operative Dentistry, Andre V. Ritter, Lee W. Boushell, Ricardo Walter, 7th Edition, Elsevier, 2019 2. Summitt’s Fundamentals of Operative Dentistry: A Contemporary Approach, Thomas J. Hilton, Jack L. Ferracane, James C. Broome, 4th Edition, Quintessence, 2013 3. Thank you to Dr. Geaman & Dr. Babka!