13 - Class III Preparations and Restorations

class III lingual outline form

located in middle third of proximal surface

• lingual view → shows incisal and gingival walls perpendicular to long axis of tooth

• axial wall → extended to width of marginal ridge, not extending into fossa unless decay is present

• internal line angles are rounded

• facial wall → parallel to long axis of tooth, located just beyond midline of tooth

  • extends to include decay

  • breaks contact to reach decay

• gingival / incisal walls → parallel, perpendicular to long axis of tooth for retention

class III lingual approach

aim for lingual approach

• facial enamel conserved for esthetics

• color matching less critical

• discoloration or deterioration of restoration is less visible

• UNLESS

  • caries facially positioned → access from facial to conserve tooth structure

  • teeth irregularly aligned → access from facial to conserve tooth structure

  • extensive caries extending onto tooth structure

  • faulty restoration on facial needs to be replaced

class III lingual preparation guidelines

outline form for class III is in middle third of proximal surface

• start in middle of contact point and move gingivally

• incisal-gingivally → ≤3.0mm

• mesiodistally → not in lingual fossa, ~1.5mm

• the wall opposite of access, if broken, may extend <1.0mm beyond. contact area

• gingival and facial contacts are broken, incisal contact is not broken

class III lingual preparation steps

• start on lingual surface with #2 round carbide bur in center of outline form and removing enough tooth structure to place #330 bur into preparation

• take #330 bur to enlarge preparation to extent of outline form

  • hold bur perpendicular to long axis of tooth to create incisal and gingival walls in correct orientation

  • end of bur creates facial wall, which must be parallel to long axis of tooth and just beyond midline

  • gingival and facial margins just break contact with adjacent tooth

• use hand instruments to smooth incisal, axial, gingival, and facial walls

• leave axio-gingival and axio-incisal internal line angles rounded

class III restoration

• place a clear mylar matrix and wedge

  • matrix should be between wedge and preparation

  • wedge must be tight to establish strong interproximal contact with restoration

• etch and bond as normal

• while holding matrix band against facial surface of tooth, place and adapt a small amount of composite into retentive areas of preparation

• light cure for 20 seconds

• continue to add composite in layers no greater than 2mm thick, and cure each layer from lingual and facial direction for 20 seconds

  • while curing, hold fingers on both facial and lingual to allow for proper contour

  • recure once fingers are moved

• after placing the final layer, remove excess around margins before curing

  • gently curl matrix around embrasures on both facial and lingual surfaces while curing final addition of composite

• remove matrix and wedge, and check for excess material in embrasure with an explorer

  • if there is excess, remove before polishing

  • contact should be checked with floss

class III polishing

use composite finishing kit to contour and finish restoration

• egg/football carbide bur or diamond to contour and remove any excess material in lingual fossa area

  • maintain convex shape and width of marginal ridge

• use flame-shaped rubber abrasive instrument to polish lingual fossa and marginal ridge area

  • maintain convex shape and width of marginal ridge

• use finishing strips to contour and remove any excess material interproximally

  • coarse then fine abrasive sides

  • create S-shape

• polish lingual surface with polishing paste on a felt tip

when to do facial approach

• when decay (dark grey or brown) can be seen just beneath facial surface

• cavitation from decay can be seen breaking through enamel in area of facial embrasure

class III facial esthetics

• only remove what needs to be removed

• stay where the decay is → don’t make a box/rectangle like in lingual approach

• expand only what is needed → maintain convenience and access form

• no unsupported enamel

class III facial preparation steps

• start preparation with #1 or #2 round carbide bur on proximal surface

• enlarge outline form to obtain clear visualization of internal aspects of preparation

  • facial wall is slightly crescent-shaped when viewed from facial aspect

• extend facial margin until all decay is removed, then bevel facial aspect of the preparation

  • only beveled if it must be extended to facial embrasure due to decay

  • 1mm wide bevel placed on facial margin

bevel

cut an angle that is not a right angle, having a slant

• bevel facial aspect of prep if decay is on facial or extends facially enough that it can be seen from the facial

• increases surface area for bonding at margin, increasing marginal seal

• improves esthetics by gradually transitioning from tooth to restoration

how to create bevel

use flame-shaped diamond to create bevel

• avoid touching adjacent tooth with diamond by using shorter flame bur

facial + lingual approach

combination of facial and lingual approach for removal of extensive decay

• outline form → extends from lingual, through to the facial surface of the tooth

  • lingual cavosurface margin has rectangular shape

  • lingual portion has parallel gingival and incisal walls

  • facial portion has crescent-shaped cavosurface margin

• convenience form → allows for complete removal of decay from facial to lingual

• 1mm bevel on facial cavosurface margin

facial + lingual restoration

• properly place mylar strip and wedge

• add and cure composite in layers no greater than 2mm thick

• make sure that facial bevel is covered completely

• remove excess before curing composite, don’t leave excess interproximally

• check for overhangs after curing with small end of explorer

• facial contour must be convex like natural tooth

• lingual marginal ridge and contact must be restored

• polish tooth

choosing color

color is chosen before rubber dam is placed

• do test amount on facial of tooth without etch and bond

• write down shade selection, then place rubber dam