03 - Indirect Dental Restorations

indirect restorations

restorations fabricated outside the mouth

• includes crowns, bridges, inlays, and onlays

flexural strength

modulus of rupture that is a critical metric because teeth almost never experience pure, isolated forces

• restoration is subjected to compression on its top surface, shear forces along its sides, and tension along its base as it bends under the load

• measures ability to resist deformation and withstand those combined complex forces without snapping

shear forces

unaligned forces pushing one part of a body in one specific direction, and another part of the body in the opposite direction

• cause internal layers of a material to slide laterally past one another

high flexural strength cases

high flexural strength is good for materials that must survive massive chewing forces over a wide or thin structural span without structure failure

• multi-unit posterior fixed partial dentures (bridges) → the longer the span, the more it bends

  • zirconia or metal-ceramic frameworks

• bruxism patients → teeth grinding generate extreme lateral masticatory forces

  • monolithic zirconia or lithium disilicate (Emax)

• thin-profile restorations → for when tooth structure is preserved (ultra-thin posterior onlays or occlusal veneers)

low flexural strength cases

low flexural strength (higher elasticity) are desirable for shock absorption, flexibility, or easy removal

• temporary/provisional restorations → easy to trim with acrylic burs, cheap to fabricate, designed to be brittle enough to section and remove

  • PMMA

• stress-absorbing bases and liners → serve as an elastic buffer zone to subtly flex with the tooth to absorb occlusal shock and reduce stress at adhesive margin

  • flowable resin composites or glass ionomer cements

• orthodontic appliances and nightguards → removable celar aligners or soft occlusal splints that will not fracture teeth or cause immense patient pain

lithium disilicate (IPS, emax)

• pros:

  • highly esthetic → more translucent than zirconia, with high optical properties and translucency like natural teeth

  • 10-year crown survival rate of 96.7%

  • loss of pulp vitality 2% after 5 years → teeth don’t die

• cons:

  • higher enamel abrasion → not good for bruxers, causing loss of vertical dimension due to wear

  • limitations on location → not good for posteriors

  • less strength than zirconia → 360 Mpa milled, 400 Mpa pressed

zirconia (BruxZir)

• pros:

  • biocompatibility, esthetics, less reduction required

  • superior strength → lower wear on opposing teeth, fracture resistance, inhibits crack propagation

    • flexural strength of 850-1000 Mpa

• cons:

  • too opaque in anterior region

• multiple types

  • monolithic is opaquer

  • HT zirconia is more translucent and opalescent with 590-720 Mpa

  • porcelain layered zirconia has good esthetics but only 100 Mpa

resin matrix ceramic (espe lava ultimate)

restorative that mimics both enamel and dentin in esthetics and physical properties, to incorporate advantages of glass ceramics and composites in one material

• types include hybrid ceramics, resin nanoceramics (RNC), resinmatrix ceramics, polymer-infiltrated ceramic networks (PICN), and nanoceramic resin hybrids

• pros:

  • ease of repair, low abrasion of opposing dentition, polishability, lower wear on opposing teeth

• cons:

  • low durability, color instability over time, inferior mechanical properties

  • flexural strength is 850-1000 Mpa

zirconia is not a metal

use of zirconium oxide (ZrO₂), the oxide crystal of zirconium to be a ceramic

• inorganic nonmetallic, mostly crystalline solid

• strong covalent bonds, hard, brittle, wear resistant, thermic insulator, electric insulator, oxidation resistant, no chemical corrosion, non-magnetic

• will ear opposing teeth if not adjusted correctly, making restoration pathologic

  • polished zirconia causes less dental enamel wear than glazed zirconia, while veneering porcelain causes greatest enamel wear

polishing zirconia

final adjustments with fine and super fine diamonds with preferred shape before polishing

• 3-step ceramic polishing system → coarse (blue), medium (pink), fine (grey)

  • optimal soft-tissue adherence → roughness of 0.2 µm, achieved with course or medium polisher

• 2-step polishing system → ZR1, ZR2

  • zirconia is a small grain-sized particle material that can be polished to higher gloss than natural teeth

  • ZR2 used sparingly to get a natural luster

zirconia cementation

zirconia crowns and bridges with proper thickness, good retention, and fit do not need bonding

• use conventional cementation with glass-ionomer cement (GIC), resin-modified glass-ionomer cement (RMGIC), or self-adhesive resin cement (SAC)

  • crown must first be meticulously cleaned; can be dirtied by saliva

1. after try-in, clean restoration in ultrasonic bath in alcohol for 5 minutes, or use zirconia/ceramic cleaner

2. air-particle abrasion with 30-60 µm alumina particles for 5 seconds

3. apply cement in restoration and seat on tooth