CHAPTER 12-13

DIGITAL DENTISTRY / INTRODUCTION TO DENTAL BIOMATERIALS

digital technology (computerized dentistry / digital dentistry)

it allows dentists to deliver esthetic ceramic restorations in a single dental appointment

CAD/CAM technology is used for the fabrication and delivery of permanent restorations for teeth and implants

primary factors include the type of restoration, material choice, desired occlusal relationships, and ability to isolate tooth preparation

treatment planning considerations for CAD/CAM restorations are similar to ceramic restorations with conventional impression materials

3 sequences in CAD/CAM process

intraoral scanner or camera (digital impression)

a proprietary software design program

computer-controlled device

chairside CAD/CAM systems

conceptualized by Dr. Francois Duret in 1973

can produce inlays, onlays, veneers, crowns, short-span fixed partial dentures, and temporary restorations

first prototype introduced in 1980s by Swiss prosthodontist Dr. Werner Mörmann and Italian electrical engineer Marco Brandestini

4 chairside CAD/CAM systems

CEREC 1 (CEREC system) — 1985

E4D dentist system (D4D technologies) — 2008

CEREC omnicam — 2012

CS 3500 (carestream system) — 2013

tooth preparation principle for CAD/CAM restoration

guidelines based on specific geometries and thickness dimensions

undermilling — cannot mill small or detailed areas, leaving extra material

overmilling — removes more restorative material than needed for restoration seating

CAD/CAM crown preparation

follows same principles as laboratory-fabricated crowns

margins should be shoulder, sloped shoulder, or heavy chamfer

reduction (ceramic) — 1mm - 1.2mm, 1.5mm (central fissure area and nonfunctional cusps), 2mm (functional cusps)

CAD/CAM inlay and onlay preparation

isthmus: 2mm

functional cusps: 2mm

central fossa & nonfunctional cusps: 1.5mm

onlay preparations don't require ferrule creation like metal castings

adhesive-style preparations rely on resin cement adhesion to dentin and enamel

chairside restorative materials

Vita Mark I blocks evolved into Vita Mark II

available in various materials, colors, and strengths

attached to mandrels for insertion into specific milling machines

these blocks are industrial-grade, homogeneous, and free from internal flaws

dental material manufacturers produce monolithic materials for chairside CAD/CAM restorations

categories of chairside CAD/CAM materials

composite materials with resin matrix

full-contour zirconia — cemented to tooth

provisional materials for temporary restorations

resilient ceramics — non-required porcelain furnace adhesively bonded to tooth

adhesive ceramics — ethically etched and adhesively bonded to tooth structure

high-strength ceramics — improved strength properties compared to adhesive ceramics

adhesive ceramics

feldspathic, leucite-reinforced

flexural strength: ~100–175 MPa

etched with hydrofluoric acid for better bonding

must be etched and adhesively bonded to the tooth structure

weak physically, so they require adhesive bonding with resin cement

high glass content gives excellent translucency and chameleon effect (blends with natural teeth)

indications:

• veneers

• inlays, onlays

• low-stress anterior crown

high-strength ceramics

stronger than adhesive ceramics

used in both anterior and posterior regions

IPS e.max CAD (lithium disilicate) / Celtra Duo

IPS e.max CAD partially crystallized, fully crystallized in a furnace (from 160 MPa to 500 MPa)

Celtra Duo (zirconia-reinforced lithium silicate) pre-crystallized, reaches up to 370 MPa after glazing

indications:

• crowns, onlays, veneers

resilient ceramics

polymer-infiltrated ceramics / lava ultimate (3M) / cerasmart (GC) / enamic (Vita)

contain resin matrix instead of pure glass

designed to absorb biting forces better without breaking

require no furnace firing—faster and easier workflow

adhesive bonding is a must; sandblasting and total-etch technique recommended

flexural strength:

• Lava Ultimate — 170 MPa (not for crowns)

• Cerasmart — 230 MPa (for crowns)

• Enamic — ~135–150 MPa (more brittle)

composite resin blocks

Paradigm MZ100 (3M) / Brilliant Crios

paradigm MZ100: 85% filled, ~150 MPa

indication — inlays, onlays, and single-unit crowns

processed similarly to direct composites, but more cross-linked and durable

easier control of contact points and occlusion compared to traditional composites

full-contour zirconia / CEREC zirconia

extremely strong: over 900 MPa

suitable for crowns and short-span bridges (FPDs)

cemented with traditional cements (no bonding needed)

requires furnace sintering, which shrinks the restoration ~22–24%

fast production time: ~10–25 mins sintering; optional glazing afterward

CAD software adjusts for shrinkage by enlarging the design before milling

provisional materials

Vita CAD-Temp, Telio CAD

used to make temporary crowns and bridges

come in large blocks for multi-unit provisionals

avoid issues like oxygen inhibition and polymerization shrinkage

accuracy of digital impressions

eliminates material distortions

offers immediate feedback, reducing errors

faster workflow and enhanced patient comfort

high accuracy in capturing tooth morphology and marginal integrity

limitations in subgingival areas require tissue management and isolation

research relative to CAD/CAM system

all systems produced clinically acceptable quadrant impressions

studies show no significant difference in accuracy between conventional and digital devices

in vivo precision of impressions was evaluated using conventional and digital methods

CEREC system, the first chairside CAD/CAM platform, has over 30 years of research supporting its accuracy

PlanFit and CS Solutions systems have limited published research on margin fit and internal adaptation

a systematic review found CAD/CAM restorations had better internal fit than traditional lab-made restorations

Hack and Patzalt measured the ability of six intraoral scanners to accurately capture a single molar abutment tooth in vitro

marginal adaptation

ideal margin gap — ≤ 100 µm

most CAD/CAM systems produce margins between 10–110 µm, with many studies reporting gaps < 80 µm

clinical longevity of CAD/CAM restoration

studies assess relative longevity in oral environment

dental literature varies in independent randomized studies

long-term randomized clinical trials are robust for longevity assessment

adhesive cementation influences clinical survival, maximized with enamel margins

technique sensitivity

refers to how a material success depends on precise handling and correct clinical procedure

amalgam is less sensitive to technique and more forgiving.

4th-gen adhesives require perfect steps for excellent bonds

small errors like contamination, incorrect curing, or poor isolation can lead to weak bonds, sensitivity, microleakage, or early failure, can lead to:

• sensitivity

• weak bonds

• microleakage or early failure

2 things determine success in using a material:

select the right material

• based on the case and on tooth structure, caries risk, restoration type, esthetics

manipulate it correctly

• correct isolation, bonding, layering, and curing.

dimensional change

composites shrink 2.4–2.8%

use incremental layering or bulk-fill with caution

some cements expand → risk for post-cementation fracture

the percent shrinkage or expansion of a material, which usually occurs as a result of the setting reaction

thermal coeficient of expansion (COE)

waxes have the highest COE of all dental materials

different materials expand / contract at different rates

defined as the amount a material expands per unit length if heated 1 degree higher

percolation

with composite — it can lead to decay

with amalgam — it eventually seals itself

the process of fluids entering the microscopic space between a restorative material

thermal conductivity

prevented with liners or bases

amalgam conducts heat → sensitivity

the rate at which thermal changes are conducted through a material

creep

high creep = marginal breakdown

this property is important with silver amalgam

one of the few properties that has a demonstrated ability to predict clinical performance

defined as time dependent plastic deformation of a material under static load or constant stress

solubility

some cements dissolve over time

the relative tendency to dissolve in oral fluids

ZOE cement shouldn’t be used beyond 6 weeks

glass ionomers dissolve early but stabilize after a few months

3 major electrical properties

tarnish

corrosion

galvanism

galvanism

gold crown + amalgam

gold crown + metal-ceramic crown

sudden “electrical shock” sensation and metallic taste

occurs whenever different metals are in contact with one another in the presence of an electrolyte (saliva)

tarnish

gold, platinum, palladium

alloys need ≥45% noble metal to resist tarnish

chromium adds tarnish resistance in base-metal alloys

refers to surface discoloration of metals, no structural damage

corrosion

rare, but may occur in endodontic posts

leads to material degradation and failure

caused by varying pH levels in the mouth

a chemical or electrochemical dissolution of metals in oral fluids

reflection

light bounces off the surface

refraction

light bends as it passes through

absorption & fluorescence

light is taken in and may be re-emitted

transmission

light passes through the material

color

measured by CIE system as ΔL*, Δa*, Δb*

perceived based on how different wavelengths are absorbed or reflected

translucency

important for mimicking natural enamel

affected by material composition and moisture

created by internal light scattering and partial transmission

radiopacity

the ability to absorb x-rays

composites with barium / lithium

important for detecting restorations on radiographs

refractive index affects light path and visual harmony with surrounding tooth structure

compressive strength

resistance to being squashed

tensile strength

resistance to being pulled apart

flexural strength

resistance to bending forces

fracture toughness

resistance to crack growth or propagation

load-to-failure testing

can be very misleading

apply one-time extreme force until the material breaks

does not provide predictive information on clinical performance

fatigue testing

mimics real-world conditions

helps identify how materials fail gradually, not just suddenly

simulates repeated chewing forces over timeepeated stress over time