CHAPTER 8: PART II

7 properties of dental composite

LCTE — linear coefficient of thermal expansion

radiopacity

wear resistance

solubility

water sorption

surface texture

modulus of elasticity

linear coefficient of thermal expansion (LCTE)

measures how much a material expands / contracts with temperature changes

ideal when close to enamel’s LCTE to avoid marginal gaps

composites have ~3× higher LCTE than tooth structure

bonding reduces effects of LCTE mismatch

water sorption

indicates how much water the material absorbs over time

water absorption can degrade the composite’s properties

higher filler content = lower water absorption

wear resistance

affected by filler size, shape, and amount

location in the mouth and occlusion also affect wear

modern composites wear well, approaching amalgam durability

resistance to surface loss from chewing, brushing, and abrasion

surface texture

smoothness of the final restoration surface

important for gingival health when near soft tissues

determined by filler properties and polishability

nanofill & nanohybrid composites — offer smooth, esthetic finishes

radiopacity

needed to distinguish restorations from caries on radiographs

achieved by adding radiopaque fillers (e.g., barium glass)

modulus of elasticity

reflects the stiffness of the material.

high modulus = rigid; low modulus = flexible

microfill composites (more flexible) may suit Class V restorations better

flexibility helps accommodate tooth flexure and protects bond integrity

less critical with improved adhesives unless high occlusal stress exists

solubility

measures material breakdown in oral fluids

composites show no clinically significant solubility under normal conditions

polymerization shrinkage

occurs as composite materials polymerize (harden)

can cause the material to pull away from cavity walls, risking marginal gaps

clinical impact of polymerization shrinkage

gaps may lead to microleakage or recurrent caries

less problematic when margins are entirely on enamel

gaps are more likely when margins extend onto the root surface (dentin/cementum)

preventive techniques of polymerization shrinkage

apply composite in incremental layers

use adhesive bonding to improve retention

consider placing RMGI liner on root surfaces before composite

control placement direction and minimize volume per increment

configuration factor (C-factor)

ratio of bonded surfaces to unbonded (free) surfaces

higher C-factor = greater internal stress during curing

class I (C-factor = 5) = high risk

class IV (C-factor = 0.25) = low risk

minimizing stress in C-factor

use soft-start curing (gradual light intensity)

apply flowable composites or stress-breaking liners

types of composites by shrinkage

typical hybrids (Bis-GMA/UDMA) — 2.4-2.8%

microfills & flowables — higher shrinkage due to lower filler content

silorane-based (e.g., Filtek LS) — 0.7%

2 types of polymerization methods

self-cured composites

light-cured composites

self-cured composites

short working time; more finishing needed

lower color stability (breakdown of amines)

mixed from two components (base + catalyst)

higher risk of air bubbles and internal porosity

shrinkage pulls toward the center, possibly aiding marginal adaptation

light-cured composites

less internal porosity

requires a light source to initiate curing

incremental curing reduces shrinkage stress

allows more working time and better color stability

shrinkage direction influenced by light positioning

precautions needed to protect eyes from light exposure

old methods of light curing systems

quartz-tungsten-halogen (QTH)

plasma arc curing (PAC) — fast but produce more heat and stress

modern standard of light curing systems

blue LED light-curing units

portable, efficient, durable

provide faster, consistent curing with reduced stress

part of the ongoing effort to enhance bond strength, curing speed, and material properties

steps in composite restoration

defective tooth structure is removed

tooth is treated with enamel and dentin adhesive

composite is inserted, shaped, and polished

success depends on proper technique and effective bonding to tooth structure

indications of composite

periodontal splinting

class I–VI restorations

temporary restorations

core buildups/foundations

cement for indirect restorations

sealants and preventive resin restorations

esthetic enhancements (veneers, contouring, diastema closures)

isolation factors

contamination prevents proper bonding

if isolation is not possible, amalgam may be preferable

proper isolation from moisture is essential (rubber dam or cotton rolls)

occlusal factors

composite has less wear resistance than amalgam, but newer materials have improved

for normal occlusion — composite performs well

for bruxism — heavy occlusion or complete

for occlusal contact — amalgam is often better

operator factors

requires greater skill in:

• isolation

• adhesive application

• operator’s technical ability

• precise insertion, contouring, and polishing

contraindications of composite

moisture control is not achievable

all occlusion falls on the restoration

restoration extends onto root surface, risking gap formation

operator is not able or committed to perform detailed bonding techniques

using an RMGI liner may help mitigate gaps and leakage

advantages of composite

highly esthetic

conservative — less tooth structure needs to be removed

insulating — low thermal conductivity, reducing sensitivity

versatile — applicable in many restorative and cosmetic procedures

simpler preparation — uniform depth and mechanical retention often unnecessary

produced when composite bonded to tooth

retention

microleakage prevention

strength of remaining tooth structure

repairable if damaged

disadvantages of composite

risk of gap formation esp at root surfaces

higher LCTE — increases risk of marginal leakage

more difficult and time-consuming to place than amalgam

greater occlusal wear in high-stress areas or when bearing full occlusion

technique-sensitive — strict moisture control and bonding protocol are essential

initial clinical procedures for composite restorations

finalize examination, diagnosis, and treatment plan before operative work (except emergencies)

review medical history, chart, radiographs before starting procedure

local anesthesia

an advantage for patients with too much sensitivity

often necessary for comfort and procedure efficiency

reduces salivation, aiding in moisture control for bonding

cons: patient can’t inform the dentist that there is alr pain if naapil na ang pulp cavity

preparation of the operating site

clean area with pumice to remove plaque and stains

avoid prophy pastes with flavoring, glycerin, or fluoride (can interfere with bonding)

remove calculus if needed

shade selection

select shade before drying teeth because dehydration lightens teeth

consider natural light; avoid prolonged viewing bc it can cause eye fatigue

use manufacturer-specific shade guides with vita guides

check cervical, middle, and incisal thirds for natural color gradation

record chosen shade in the chart

bleaching (if planned) should be done before restoration

optional: apply a small cured composite sample on tooth to verify shade

isolation of the operating site / rubber dam

preferred method for moisture control and access

isolate multiple teeth (esp in proximal restorations)

may require a no. 212 clamp for facial / lingual lesions

use wedge to:

• depress gingiva

• protect tissue and dam

• slightly separate teeth for matrix placement

cotton rolls (w/ or w/o retraction cord)

alternative to rubber dam

requires experienced operator/assistant

cotton roll placement:

• facial vestibule (adjacent to target tooth)

• lingual vestibule (mandibular teeth)

retraction cord for subgingival margins:

• may be soaked in astringent to control bleeding

other pre-operative considerations

assess occlusion before dam placement

consider using sectional matrix systems with separating rings

pre-wedge for proximal restorations—helps with contact re-establishment

identify occlusal contacts on restoration site and adjacent teeth—helps guide occlusal contact adjustment post-restoration

repairing composite restorations on accessible defects

roughen → etch → adhesive → composite → contour & polish

repairing composite restorations on inaccessible defects

prep tooth to expose area → use matrix if needed → apply adhesive & composite

repairing composite restorations on voids immediately after placement

add composite directly if not contoured yet (oxygen-inhibited layer allows bonding)

if contoured, re-etch & re-apply adhesive before adding

common problems in composite restoration

poor retention

inaccurate shade selection

contouring and finishing problems

poor isolation of the operating area

white line or halo adjacent to enamel margin voids

weak or missing proximal contacts (class II, III, IV)

causes of poor isolation of the operating area

careless technique

deep gingival preparation

inadequate cotton roll isolation

no rubber dam or leaking rubber dam

potential solutions of poor isolation of the operating area

use better isolation techniques

use matrix to assist in isolation

repeat bonding if contamination occurs

consider using a material other than composite that does not require bonding

causes of white line / halo adjacent to enamel margin

traumatic contouring / finishing

inadequate etching / bonding

excessive curing intensity

potential solutions of white line / halo adjacent to enamel margin

re-etch, prime, and bond the area

remove defect conservatively and re-restore

use gentle, intermittent finishing and soft-start polymerization

leave as is and monitor for leakage if minor

causes of voids

gaps between increments

mixing of self-cured composite

composite pulling away during insertion

potential solutions of voids

use more careful insertion technique

repair marginal voids by re-preparing and restoring

causes of weak or missing proximal contacts (class II, III, IV)

matrix band too thick

inadequate wedging

poorly contoured matrix band

matrix not contacting adjacent tooth

circumferential matrix when restoring 1 contact

composite pulling from matrix during insertion

potential solutions of weak / missing proximal contacts (class II, III, IV)

proper matrix contouring and placement

use firm wedging pre-op and during insertion

ensure matrix contact with adjacent surface

use a sectional matrix system for single contacts

composite pulling from matrix during insertion

be careful with insertion technique

causes of inaccurate shade selection

poor operator lighting

non-matching shade tab

incorrect shade selected

shade chosen after tooth drying

potential solutions of inaccurate shade selection

use natural or neutral lighting

try cure shade on tooth and remove

select shade before isolating or drying

understand natural shade zones of the tooth

causes of poor retention

inadequate prep form

poor bonding technique

contaminated bonding area

use of incompatible bonding materials

potential solutions of poor retention

maintain strict isolation during bonding

follow manufacturer’s bonding protocol carefully

add bevels, flares, or retention grooves if needed

causes of contouring and finishing problems

ditching cementum

margins hard to visualize

over- or under-contouring

inadequate anatomic form

damage to nearby tooth structure

potential solutions of contouring and finishing problems

use rotary instruments carefully

view from all angles during finishing

match natural anatomy and embrasure form

use appropriate instruments and techniques

use a well-contoured matrix and proper tools

liners / bases under composite

RMGI and flowable composites may improve seal on root surfaces and act as stress breakers

retention in class V restorations

retention grooves often unnecessary with modern bonding agents

wear problems

composite may be used in areas of shared occlusal load; avoid sole load-bearing areas

gap formation

may not affect longevity unless resin layer breaks down early

RMGI liners help resist caries