Dental Cavity Preparation and Burs

• A low speed handpiece is optimal for cutting dentin and removing carious tissue.

Black's Principles of Cavity Prep

• Establish the outline form
• Primary resistance form prevents fracture
• Resistance forms requires slightly diverging walls
• Primary retention form prevents movement
• Retention requires slight convergence of occlusal walls
• Convenience form
• Remove remaining carious dentin
• Finish the enamel walls

Burs

• Amalgam preparations necessitate an initial pulpal depth of 0.5 mm into dentin.
• Composite preparations don't need the same depth and may not need uniform penetration.
• Round burs are spherical and are for initial entry, prep extension, retention points, enameloplasty, and caries removal.
• Inverted cone burs are tapered for undercuts in cavity preparations.
• Pear-shaped burs are slightly tapered for cavity prep requiring occlusally converging walls like amalgam.
• Straight fissure burs are elongated cylinders used for deep amalgam cavities with adequate wall retention and curved tip angles are available.
• Tapered fissure burs are slightly tapered cones, small end away from the shank, creating undercut-free preparations for cast restoration seating/removal.
• Enamel hatchets cut enamel and refine proximal walls in Class II preps.
• Gingival margin trimmers bevel gingival enamel margins and round axiopulpal line angles of two-surface preps.
• A distal marginal trimmer has a second number of 90 to 100
• A mesial marginal trimmer has a second number of 85 to 75
• A #245 bur has a 3mm head length and 0.8mm diameter
• A #330 bur is a smaller version of #245 with a 1.2-1.5mm head length.
• Acceptable pulpal floor depth is > 2.0 mm in the area of the cusps because depth into dentin matters most.
• Deepen only areas needing decay removal, and do not flatten the entire floor.
• Class I preps with an isthmus width ¼ the intercuspal distance show minimal fracture strength decrease.

Procedures

• Marginal ridge loss in Class II preps weakens the tooth unlike Class I preps.
• Class II cavity prep requires facial and lingual proximal walls diverge slightly towards the proximal surface
• The top of the handpiece should be parallel to the occlusal plane for a flat pulpal floor.
• Preserve the oblique ridge in maxillary first and second molars unless decay undermines it or less than 1mm tooth structure is present.
• Use a #56 or #57 bur to refine Class I and II preps.
• Measure depth with a perio probe
• Use PLG7081T to measure prep depth, proximal clearance, and isthmus width.
• A #23 explorer is 0.3mm at tip, 0.5mm 5mm from tip, and 0.7mm apex of curve diameter.
• Use a 1.0 mm enamel hatchet to measure the gingival floor.
• Pit and fissure lesions and smooth surface lesions are possible

Decay

• Smooth surface decay cones are apex to base (Class III, Class V)
• Class I decay cones are base to base
• Pit and fissure lesion decay spreads along the DEJ when it reaches it.
• Zinc eugenol is toxic to pulpal tissues at high concentrations.
• Enamel permeability decreases with age.

Black's Classification of Carious Lesions

• Class I: pits and fissures in occlusal, buccal, and lingual molars, occlusal premolars, and lingual incisors/canines.
• Class II: proximal surfaces (mesial/distal) of premolars and molars.
• Class III: surfaces of incisors and canines, minus incisal angles.
• Class IV: proximal surfaces and incisal angles of incisors/canines.
• Class V: gingival third of facial/lingual surfaces of all teeth.
• Class VI: cusp tips of canines, premolars and molars or incisal edges of incisors, not corners.

Lesion Categories

• E1 - hallway into enamel
• E2 - reaching DEJ but not extending into dentin
• D1 - minimally into dentin
• D2 - moderately into dentin
• D3 – extremely advanced into dentin

Deterioration

• Attrition is normal, slow tooth structure loss via occlusal function in opposing arches.
• Abrasion is mechanical wear from forces besides occlusion like tooth brushing.
• Erosion is non-carious dissolution of tooth structure.
• Abfraction involves parafunctional habits causing facial/lingual cervical third of crown.
• Do not detect decay with an explorer because it can damage enamel.
• Use visuals for Class I, radiographs for Class II.
• Caries types are pit/fissure, smooth surface, and root surface caries.
• Visual examination is useful because not all staining is decay.
• Dentin can be primary, secondary, tertiary, reparative, reactionary, and dead tracts.
• Discourage tactile evidence with an explorer, and remove soft dentin.
• Use excavators or round burs to remove decay.
• Remineralization appears radiolucent (dark) at the DEJ.
• Caries dyes detect caries.
• Use spoon excavators or round burs on slow speed handpieces to remove decay. Do not use a sharp explorer because it could result in pulpal penetration
• Caries is slow developing from organisms secreting weak acids, metabolizing carbohydrates, and dissolving minerals
• Surgical intervention is necessary at Temple when enamel surfaces are cavitated and/or decays extends into dentin, and surface sealants are not applied for dentinal caries.
• Smooth, hard, and shiny Class V enamel surfaces are usually non-active remineralized lesions
• Dull enamel surfaces covered in plaque are active lesions.
• Initial lesions are only seen after drying the tooth
• Advancing initial lesions can be seen wet and dry
• Shadowing under the marginal ridge with no visible dentin indicates a moderate lesion needing operative intervention.
• Enamel loss with visible dentin is an extensive lesion

Radiographic Extent of Dental Caries

• E0 - sound
• E1 - lesion in outer half of enamel
• E2 - lesion in inner half of enamel
• D1 - lesion in outer third of dentin
• D2 - lesion in middle third of dentin
• D3 - lesion in inner third of dentin

Classification of Lesions

• Sound
• Lesion present, active non-cavitated
• Lesion present, arrested non-cavitated
• Lesion present, active cavitated
• Lesion present, arrested cavitated

Occlusal Adjustment

• Occlusal adjustment modifies a tooth’s biting surfaces to improve function/morphology
• Occlusal equilibration treats occlusal trauma/irregularities or during full mouth rehabilitation.
• Plan occlusal adjustment on articulated study models prior clinically
• Use cotton rolls/triangle pads to isolate teeth during procedures.
• The Isolite device combines high-speed evacuation with a method to physically isolate teeth and provide moisture control.
• Rubber dams are best for isolating teeth, preventing moisture contamination, protecting the operator, and staff by limiting saliva spray.
• Mastering the handpiece, mirror positioning, and chair positioning is important for good ergonomics.
• The operator's thighs should be horizontal and feet flat on the floor. Their back and neck should be straight but relaxed. The patient's mouth should be approximately 12 to 18 inches from the operator’s eyes.
• Maxillary arch patient should lie supine so that the maxillary occlusal plane is vertical (perpendicular to the floor).
• Mandibular arch patient should be reclined less so that the mandibular occlusal plane is nearly horizontal (parallel to the floor) when mouth is open.
• The operator occupies the 11:00 position when treating the maxillary arch. Direct the task light above the patient’s mouth and reflect light onto the max teeth using a mirror.
• With the mandibular arch, a dentist sits at 8:00 or 9:00, can usually do direct vision, but use the mouthmirror.

More Procedures

• Use a modified pen grasp, palm and thumb grasp for lab procedures, and set finger rest for control
• Use indirect of direct vision and enhanced illumiation
• Most Class II preps cut away the marginal ridge near the diseased surface and prepare a proximal cavity via an occlusal approach.
• Use a matrix or fender wedge to protect adjacent teeth during Class II preps.
• Use a #330 bur to prep a Class I cavity and #245 to drop the box for Class II because #330 is too short for this.
• Buccal, lingual, and gingival Class II cavity prep margins need at least 0.3mm of opening in order for the explorer tip to fit between.
• The gingival wall should be 1.0 mm for premolars and 1.5mm for molars.
• Make an S curve on the occlusal outline to preserve tooth structure and smooth outline
• Remove residual decay with #2, #4, or #6 round bur. Don't deepen the entire pulpal floor or axial wall.
• Preparation of maxillary first molar - If the central groove is intact and ridge support is good, do not complete a single MOD cavity.
• Add a dovetail for retention.
• Class II: external cavosurface margin meets enamel at 90 degrees
• Reduce supporting cusps by 2.0mm and non-supporting by 1.5mm when remaining tooth structure lacks proper resistance and will be prone to fracture.

Composite Restorations

• Depth is determined by decay, rising/falling depending on decay removal. There is no minimal pulpal depth, but 1mm is conventional
• Pulpal depth affects the resistance form of tooth/restoration
• Dentin can be distinguished from enamel by color (more yellow), reflectance, and explorer drag.
• Round axio-pulpal line angles reduce tooth/restoration stress.
• Create flat pulpal and gingival floors perpendicular to the tooth's long axis, specifically those of the mandibular first premolar and the OL preparations of maxillary molars.
• Prepare the prep and restoration to resist fracture from forces along the tooth's axis.
• Extend lateral walls minimally.
• Create a deep pulpal floor that provides adequate strength to the restorative material.
• Create a flat pulpal floor perpendicular to long axis of the tooth
• Preserve adequate marginal ridges.
• Create walls with 90° cavosurface margins.
• Flare 10 degrees to avoid undermining enamel at the marginal ridge if the outline form is closer than 1.6mm from contact point.
• Position occlusal and proximal cavomargins between 80-100 degrees.
• There should be no Unsupported enamel.
• Decay spreads at the DEJ.
• Shape or form of a prepared cavity resists displacement or removal
• Primary retention uses walls parallel or slightly convergent in an occlusal direction.
• Dovetails are necessary with 2-surface restorations where extensioninto the buccal/lingual grooves of molars offers retention that prevents proximal dislodgement. Use them in 3 surface restorations if necessary.
• Secondary retention features are slots, locks, boxes, and pins. Place with round burs, 169, or 34 inverted cones in dentin
• Retention grooves must be placed 0.5mm pulpal to the DEJ regardless of gingival width.
• Shoulders are placed if decay is present in external wall. Mesial/distal proximal boxes should be prepared with the axial wall.

Occlusal Equilibration Steps

• Preliminary grinding
• Correct tooth contacts in centric relation
• Correct protrusive occlusion
• Correct working contacts
• Correct non-working contacts
• Centric relation is maxilla-mandibular relationship where condyles are in the anterior-superior position against the slopes of the articular eminences and doesn't rely on teeth.
• Maximum intercuspation is the complete intercuspation of opposing teeth independent of condylar position
• Centric occlusion is the occlusion of opposing teeth in centric relation but may not coincide with maximum intercuspation
• Adjust the buccal of upper and lingual of lower with the BULL rule for working contacts.
• Avoid adjusting the lingual of upper or buccal of lower teeth because they are centric supporting cusps.
• Several rounds of adjustment are necessary for occlusal equilibration.
• For maxillary crowns: Adjust occlusion by adjusting inner inclines of palatal cusps
• For mandibular crowns: Adjust occlusion by adjusting the inner incline of buccal cusps.

Treating Deterioration

• Non-surgical (medical) treatment addresses decay in enamel.
• Cavitated enamel requires surgical intervention.
• Decay into dentin requires surgical intervention.
• Use a slot preparation when the occlusal approach is difficult.
• Remove axial decay using a round bur for a slot prep.
• First premolar aesthetic concern: Do not remove mesiofacial contact if the decay is located lingually.
• Amalgam can be repaired and can be as effective as replacement.
• Pin placement requires one pin per missing cusp on flat surfaces, interpin distance 3-5 mm, and pins no closer than 1 mm to DEJ and 1.5mm to the external tooth (if below CEJ).
• Cervical 1/3 of molars and premolar pinholes are located near line angles. Do not over enlarge pin holes and keep the handpiece parallel to the occlusal plane.
• After extending the outline form to sound tooth structure, remove any caries or old restorative material remains on the pulpal floor with a round bur or hand instrument.
• If the remaining dentin thickness (RDT) is between 0.5 and 1.5 mm, use a resin-modified glass ionomer (RMGI) base. If the RDT is very small, use a calcium hydroxide liner before RMGI.
• C-factor describes a bonded to unbonded surfaces ratio. A Class I tooth prep has high C-factor of 5/1 (pulpal, facial, lingual, mesial, distal vs. occlusal )
• Higher C-factors increase the the potential for composite polymerization shrinkage stress, as composite shrinkage deformation is restricted by bonded surfaces.
• Incremental insertion and light curing of composite class 1 restorations.
• Place posterior composites incrementally to facilitate proper light curing/anatomy.
• Large posterior composite restorations have similar 12-year survival rates to amalgam restorations, although amalgam is better with high caries risk.

Class II Composite Restorations

• The tooth preparation primary retention is micro-mechanical bonding.
• Remove remaining old restorative material on the axial wall if amalgam (color), caries lesion, or the tooth pulp was symptomatic preoperatively, periphery has deterioration
• A properly contoured and wedged matrix is a prerequisite for a restoration involving the entire proximal contact area, unless the adjacent tooth is missing
• Dark, opaque shades benefit from light exposures.
• Class V tooth preparations are in the gingival one third of the facial/lingual
• Mylar matrix are used Class III and IV preps
• Layering and light curing in increments helps composite polymerization shrinkage, ensuring light curing in remote regions.
• Use hand instruments or syringes to insert the composite, while composites and RMGIs are useful in Class V restorations. Light-cured material is recommended because of the extended procedure.
• Use a flame-shaped carbide finishing bur or diamond to remove excess composite.
• Glass ionomers release fluoride.
• Composite is the choice for Class III and IV restorations and high esthetic demand Class V restorations. Though, composites are difficult to use.

Decay Prevention

• Sealants are the simplest intervention for pit and fissure anatomy. This is a intervention with no tooth structure removal to prevent caries.
• A surgical procedure resulting in decay removal is required if decay appears in the dentin
• The following patients benefit with sealant placement, as long as adequate moisture controls is possible and the sealant adequately seals.
• Patients with deep retentive pits and fissures
• Patients with stained pits and fissures with the appearance of demineralization
• Patients with caries or restorations in other primary or permanent teeth (high caries index) Patients that demonstrate no evidence of proximal dentinal involvement on the teeth to be sealed
• Teeth within 4 years of eruption are most susceptible to decay.
• Glass ionomer sealants are usually the material of choice due to poor retention. A newly erupted tooth with caries formation and moisture compromise is one exception. Place the glass and replace when tooth more erupted.
• Round rather than the pear produces angular adaptation
• For preparations below the CEJ (on root surface) the initial depth for amalgam and 0.75 – 1.0 mm min for the retention feature which is required. Optional for glass ionomer.
• Composite resin can have a butt joint margin or a bevel.
• The outline form for a Class V preparation is determined by decay to sound tooth structure with an initial axial depth of 0.5 mm into dentin (above the CEJ).
• Class V preparations often extend subgingival and require placement of the 212 retraction clamp.

Restorative Differences

• For both amalgam and composite preparations, outline is determined by decay, removal for large composite preps, and axial wall into dentin usually to remove decay
• Composite preparations margins using or flame shaped microleakage
• Amalgam is a better material choice for large preparations on the distal aspect, or the composites are often preferred for esthetics.
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