All-Ceramic Restorations in Prosthodontics

• Clinical Fixed Prosthodontics I is course PRO 222
• The lecture is about all-ceramic restorations
• Dr. Nermeen Nagi is the lecturer, she is an Assistant Professor of Fixed Prosthodontics

Advantages of All-Ceramic Restorations

• Provide superior esthetics and excellent translucency
• Translucency mimics natural teeth
• All-ceramic crowns have high light transmission showing light through the body of the crown when illuminated with a fiber-optic light
• Metal-ceramic restorations illuminated by fiber-optic light can show dark shadows
• It elicits favorable tissue response, even for subgingival margins
• All-ceramic restorations permit more conservative reduction of the facial surface
• The restorations can restore function and give maximum retention
• Demonstrates high color stability
• Demonstrates low conductivity

Disadvantages of All-Ceramic Restorations

• The least conservative preparations compared to metal ceramic crowns because proximal and lingual reduction are less conservative
• Proper preparation design is critical to ensure mechanical success
• A 90-degree cavosurface angle is essential to permit favorable stress distribution, to decrease the risk of fracture
• The strength is reduced because the brittle ceramic is subject to fracture
• Wear of opposing natural teeth on functional cusp can occur
• Laboratory costs are high
• Are more technique sensitive

Indications for All-Ceramic Restorations

• High esthetic requirements exist, and no other conservative restoration is indicated
• Can function as an individual restoration
• Can function as a bridge retainer if using high strength ceramics
• Used for large proximal or facial defects that can't be restored with composite resin
• Intact incisal edges
• Favorable distribution of occlusal load
• Used for Fractured anterior teeth that don't involve more than 1/3 incisogingivally
• Used for discolored anterior teeth because of trauma or root canal treatment
• Indicated for malformed teeth caused by developmental defects
• Indicated for malposed or rotated teeth

Contraindications for All-Ceramic Restorations

• When greater strength is required, PFM may be appropriate
• When esthetic demand is reduced
• A more conservative restoration can be used
• If patients exhibit short clinical crowns
• Liability for fracture is increased as there is insufficient tooth to support the lingual and incisal surfaces of the restoration
• Stress concentration in the labiogingival area of the crown can produce a "Half-moon" fracture in the labiogingival area of the restoration
• Unfavorable distribution of occlusal loads can be a contraindication
• Deep bite and edge to edge bites resulting in a half-moon fracture are contraindications
• Young age with large vital pulp means massive reduction which is a contraindication
• Thin teeth facio-lingually or constricted cervical circumference because pulp might be involved are contraindications
• Individuals engaged in contact sports or hard line jobs represent a contraindication
• Patients with bad habits such as Bruxism are contraindications
• Young careless patients are contraindications

Armamentarium for All Ceramic Crown Preparation

• It includes needle stone, cylinderical with round end, cylindercal with flat angle, round edge wheel, foot ball, tapered with round end

Preparation for All Ceramic Crown Preparation

• Before preparation begins, putty impression material adapts to facial and lingual surfaces of the tooth to be prepared
• The putty should extend to at least one tooth on either side of it
• Putty also serves as a depth-reduction index
• It provides information about the reduction in the distal half of the tooth, and has incisal information
• A facial index is made by sectioning the set putty along its incisal edges of the tooth imprints, then the facial segment is cut into incisal and gingival haves

Preparation Sequence

• Includes incisal reduction, facial reduction, proximal reduction, lingual reduction, and axial wall and shoulder finishing

Incisal Reduction

• A flat-end tapered diamond is used as an instrument
• A clearance of 1.5-2 mm should be achieved to enable superior esthetics and adequate strength of the restoration
• A flat, 45° incisoligual bevel resists forces perpendicularly on the incisal edge and prevent porcelain shearing under shear stress
• Flat-end tapered diamond is used to create depth-orientation grooves
• Done by a rotary instrument of known diameter as the depth of reduction is measured against the untouched enamel
• Three incisal depth grooves of 1.3 mm deep allow more reduction during finishing; diamond should be inclined faciolingually, i.e. 45° incisolingual bevel

Facial Reduction

• A flat-end tapered diamond is used as an instrument
• Approximate reduction to 1 mm
• Prepared in two planes: gingival and incisal
• Gingival part is parallel to the proposed path of insertion, and possess a slight taper with the prepared cingulum (retention form)
• Incisal part is parallel to the incisal 2/3 of the original tooth contour
• The facial surface is therefore reduced in two planes; one nearly parallel with the path of insertion, and one parallel with the incisal two-thirds of the facial surface of the tooth
• Inadequate space of porcelain in the incisal 1/3 of the tooth can result if one plane reduction is parallel with the path of insertion
• The pulp entity can be endangered and the restoration overtapered by one plane reduction, which creates adequate space for the restoration, both in the shoulder and the incisal areas
• Mesio-distally should follow the tooth's original axial contour
• Recommended finish lines include shoulder and deep chamfer
• There should be no lip created on the margin
• Shoulder Margin should be 1.0mm
• The axial-gingival Line Angle should be Rounded
• The axial-gingival Line Angle should be 1.5 - 2.0mm
• Incisal 1/2 of the facial three incisal grooves are done at a depth of 0.8 mm initially to allow more reduction during finishing
• Gingival 1/2 of facial reduction
• Two gingival grooves are prepared on the facial surface, each at the depth of 0.8 mm
• The stone is positioned parallel to the proposed path of insertion

Proximal Reduction

• Needle diamond and flat end tapered stones are used as instruments
• It should be separated from the adjacent teeth
• A approximate reduction of 1 mm prepared in two stages

Lingual Reduction

• Flat-end tapered diamond and wheel or football diamond are used as instruments
• A 1 mm clearance is needed in all mandibular excursive movements
• Prepared in two parts: Cingulum and Fossa
• The cingulum and fossa are parallel to the proposed path of insertion to form a vertical lingual wall of minimum taper for retention and resistance
• Flat-end diamond is used to reduce the cingulum, following the tooth contour with minimal taper with the facial gingival part
• The fossa's concavity should be followed to allow the maximum clearance needed
• A football diamond is used to reduce the lingual fossa
• Errors in lingual reduction include overtapering the prepared cingulum results in lack of resistance and retention
• Over tapered the prepared cingulum can exert wedge like forces on a restoration causing crown fracture
• It's important to reduce stresses
• The canine lingual fossa is carried out without eliminating completely the lingual ridge

Axial Wall and Shoulder Finishing

• Instrument finishing diamond stones and Carbide burs
• Rounding of sharp line and point angles
• Refining the shoulder finish line

Additional Instruments

• Hand cutting instruments (binangle chisel)
• Used to Plannig the surface of the shoulder finish line
• Used to remove loose enamel rods at the cavosurface angle
• A 1.0-mm-wide enamel hatchet is used to plane the surface of the shoulder and to check its width
• Do not forget to recreate the incisal bevel if it's removed during palatal preparation