Dental Composite Lecture – Part 2 Review

Fifty question-and-answer flashcards covering properties, polymerization, clinical techniques, indications, contraindications, and troubleshooting for direct dental composite restorations.

What are the seven key properties of dental composites highlighted in the lecture?

Linear coefficient of thermal expansion (LCTE), radio-opacity, wear resistance, modulus of elasticity, surface texture, water sorption (absorption) and solubility.

Why must a restorative material’s LCTE closely match enamel?

To minimize marginal gaps by ensuring the restoration and tooth expand and contract similarly with temperature changes.

How does the current LCTE of composites compare with enamel’s LCTE?

It is roughly three times higher than enamel, making composites more thermally unstable.

What effect does increasing filler content have on a composite’s water sorption?

Higher filler content lowers water absorption and improves long-term stability.

Which dental material is especially known for high water absorption and discoloration over time?

Acrylic resin used in dentures.

Name two filler-related factors that influence composite wear resistance.

Filler size and filler shape (amount of filler also plays a role).

Why do macrofill composites wear faster than microfill composites?

Large macrofill particles leave bigger voids when lost, accelerating surface loss.

How does restoration location affect wear resistance?

Surfaces under heavy occlusal load (e.g., Class I) wear faster than low-load cervical Class V sites.

Which filler technology produces the smoothest, most polishable composite surfaces?

Nanofill and nanohybrid composites.

Why must direct composites be radio-opaque?

So restorations can be distinguished from radiolucent caries on radiographs.

Which filler additive commonly imparts radio-opacity to composites?

Barium glass.

What does a high modulus of elasticity indicate in a composite?

The material is rigid/stiff.

Which composite type is preferred for Class V restorations subject to abfraction and why?

Microfill composites because their lower modulus provides flexibility to accommodate tooth flexure.

Do composites show clinically significant solubility in saliva under normal conditions?

No, they are essentially insoluble in oral fluids.

Define polymerization shrinkage and its clinical significance.

Volumetric contraction during curing that can pull composite away from cavity walls, creating gaps and microleakage.

What maximum incremental layer thickness is recommended when placing composite?

About 2 mm per increment.

List four strategies to reduce the effects of polymerization shrinkage.

Adhesive bonding, incremental layering, use of RMGI/flowable liners, and controlled placement direction/volume.

What is the configuration factor (C-factor) in composite restorations?

The ratio of bonded surfaces to unbonded (free) surfaces within a cavity.

Which cavity class has the highest C-factor and highest shrinkage stress risk?

Class I cavities (C-factor ≈ 5).

How does soft-start (ramp) curing reduce shrinkage stress?

Light intensity increases gradually, allowing stress relaxation before full polymerization.

How do flowable composites act as stress breakers inside deep cavities?

Their lower filler content and greater flexibility absorb shrinkage stress between tooth and overlying packable composite.

Compare shrinkage of BIS-GMA/UDMA hybrids with silorane-based composites.

Hybrids shrink about 2.4–2.8 %, whereas silorane composites shrink around 0.7 %.

What are the two principal polymerization methods for direct composites?

Self-cure (chemical) and light-cure.

Give two disadvantages of self-cured composites.

Short working time and higher risk of air bubbles/porosity.

Why should light-cured composite be kept away from operatory light until curing?

Ambient light can start premature polymerization, reducing working time.

What protective equipment is mandatory during light curing?

Orange/red protective eyewear for both clinician and patient.

State two advantages of modern blue LED curing units over older QTH/plasma arc lights.

They are portable and provide faster, more consistent curing with less heat and stress.

Why is only defective tooth structure removed when preparing for composite?

Because bonded composites allow conservative preparations without extensive mechanical retention.

List four common indications for using composite resin.

Class I-VI restorations, core buildups, sealants/preventive resin restorations, and aesthetic veneers or diastema closures.

Name two situations in which composite is contraindicated.

Inability to achieve moisture control (e.g., uncooperative child) and a single tooth bearing full occlusal load/high stress.

What is the preferred isolation method when placing composites?

Rubber dam isolation.

When should shade selection be performed and why?

Before tooth desiccation, under natural or neutral light, because dehydration lightens teeth and distorts shade matching.

Which property makes composite an electrical and thermal insulator compared with metal?

It does not conduct heat or electricity, preventing galvanic shock.

Can a new composite layer be bonded over an old composite restoration?

Technically yes, but ethically the old restoration should be removed and replaced.

State one major disadvantage of composite versus amalgam in high-stress posterior sites.

Greater occlusal wear and risk of fracture under heavy load.

Which operator factors critically influence composite success?

Skill in isolation, adhesive technique, incremental insertion, contouring and polishing.

What is a "white liner halo" at the enamel margin and its main causes?

A whitish rim from microcracks/poor bonding caused by over-finishing, inadequate etching/bonding or too-strong curing light.

How can marginal voids be prevented during composite placement?

Use careful incremental insertion and ensure proper adaptation between increments and cavity walls.

How does poor lighting or dried teeth affect shade matching?

It leads to inaccurate shade selection and obvious color mismatch.

What immediate step is required if contamination occurs during bonding?

Re-isolate, re-etch, re-prime/bond and repeat the bonding process.

Why are retention grooves usually unnecessary in modern Class V composites?

Adhesive bonding provides adequate retention without mechanical undercuts.

What is the role of an RMGI liner under composite on root surfaces?

It seals dentin/cementum, absorbs stress and helps prevent recurrent caries.

How does filler particle size affect polishability?

Smaller particles allow easier polishing and produce a smoother surface texture.

When scaling/polishing and composite restoration are done in one visit, what is the correct order?

Scale first, perform the restoration, then polish last to avoid prophy paste contaminating the bonding surface.

What chiefly causes gap formation at root margins, and how can it be limited?

Shrinkage stress on less-mineralized root surfaces; use liners, incremental placement and strong bonding to mitigate.

Why may local anesthesia not always be used for composite placement in the Philippines?

Cost and the diagnostic value of patient sensitivity to indicate depth during preparation.

How can the direction of polymerization shrinkage be influenced during curing?

By directing the curing light toward the composite mass being cured.

What risk arises from failing to replace wet cotton rolls during cotton-roll isolation?

Moisture contamination that weakens bonding and may cause restoration failure.

Which composite type shows greater overall shrinkage and why: microfill/flowable or hybrid?

Microfill/flowable composites, because their lower filler (higher resin) content increases volumetric shrinkage.

Approximately how much contact separation does a green V3 ring provide during Class II placement?

Around 60-80 microns, helping achieve tight proximal contacts.