Application features of pastes and cements in endodontics
Using exclusively setting pastes or cements to fill the root canal has several significant drawbacks. The clinician cannot precisely control the volume of material introduced, there is a high risk of void formation, and the material itself undergoes volumetric shrinkage over time.
There are two main methods for introducing such materials:
- Manual method. The mixed material is introduced using a root canal needle, file, or manual root canal filler. Introduction is performed with pumping motions strictly up to the physiological apex. Important rule: each new portion is introduced to a lesser depth, after which it is condensed with a cotton pellet. The process ends with final condensation at the canal orifice.
- Mechanical method. A rotating root canal filler is used at low speeds. The material is loaded onto the stopped instrument, inserted to the full working length, and then the handpiece is turned on. Instrument extraction is performed only while the motor is running. The procedure is repeated 2–3 times with a gradual decrease in insertion depth.
An alternative is the single (master) cone technique. A plastic sealer (paste) is introduced into the dried canal, followed by a fitted gutta-percha cone coated with the same paste, strictly to the working length. The protruding coronal part of the cone is cut off with a heated instrument.
Assessment of canal obturation quality
After completing endodontic treatment, a radiographic check is mandatory. The ideal result is when the filling mass densely fills the entire canal lumen without voids and terminates exactly at the physiological apex of the root.
Potential clinical errors:
- Underfilling: the material does not reach the apex, leaving the apical space empty. This threatens the development of inflammation.
- Overfilling: excess mass is pushed beyond the root apex directly into the periapical tissues, which can cause an acute reaction and pain.
Copper and silver amalgam: composition and properties
Amalgam is a classical filling material, which is an alloy of metals with mercury.
Copper amalgam features high plasticity, retains its shape exceptionally well, and can be used in conditions of high humidity. It is mainly used in pediatric practice for treating premolars and molars.
Silver amalgam (especially its modern high-copper variant) is used more widely. Its composition includes metal filings (silver 65–66%, tin 29–32%, copper 2–6%, zinc up to 1%) and mercury.
Each component performs its own role:
- Silver provides maximum hardness.
- Tin imparts plasticity and slows down setting.
- Copper improves marginal adaptation and strength.
- Zinc combats oxide formation and reduces brittleness.
Setting phases and the gamma-2 phase problem
The structure of hardened silver amalgam is heterogeneous and consists of three phases:
- γ-phase ($Ag_3Sn$) — original alloy particles, the strongest and most stable part.
- γ1-phase ($Ag_2Hg_3$) — silver-mercury compound.
- γ2-phase ($Sn_7Hg_8$) — tin-mercury compound.
The gamma-2 phase is the weakest link. It is unstable, easily corroded, and has high electrochemical activity. It causes mercurioscopic expansion: free mercury diffuses inward, forms new compounds, the filling expands, and its edges rise and crack under masticatory load, inevitably leading to secondary caries.
To solve this problem, gamma-2-free amalgams (non gamma-2) were created. They contain an increased amount of copper (up to 27%). Copper actively takes mercury away from tin, forming a strong $Cu_6Sn_5$ compound and completely eliminating the appearance of the weak gamma-2 phase.
Working rules and safety precautions
Preparing amalgam requires strict proportions (usually 3–4 parts filings to 1 part mercury). Trituration in a mortar must be thorough: the generated heat helps the filings combine with mercury. If the mass is squeezed through gauze, it should not show cracks. Excess mercury is squeezed out manually strictly in rubber gloves so that mercury does not get into skin pores and sweat does not contaminate the filling.
Sanitary regimen:
- Excess mercury may only be squeezed out into a jar of water (with a ground-glass stopper) placed in an enamel tray.
- It is strictly forbidden to squeeze mercury into an instrument tray or pour it down the drain.
- Spilled droplets are collected with a rubber bulb.
- Frequent ventilation and wet cleaning with a 10% soap solution are necessary in the office.
Briefly: answers to topical questions
What methods of root canal obturation using gutta-percha cones exist?
The following root canal obturation methods using gutta-percha exist:
- Cold lateral compaction of gutta-percha — filling with paste and multiple cones.
- Warm vertical compaction method — introduction of heated gutta-percha from a special syringe followed by compaction in the canal.
- Filling with pre-warmed gutta-percha outside the canal — using the Thermafil system, the OBTURA II injection system, and analogues.
What is the chemical composition of the powder and liquid of classical glass-ionomer cements?
The chemical composition of classical glass-ionomer cements is a two-component system that undergoes an acid-base reaction.
- Powder — ground fluoroaluminosilicate glass containing aluminum, calcium, sodium, and fluoride ions.
- Liquid — an aqueous solution of polyacrylic and tartaric acids. Itaconic and maleic acids may also act as alkenoic monomers.
What types are glass-ionomer cements subdivided into depending on their clinical purpose?
Depending on clinical application, glass-ionomer cements are subdivided into:
- Glass-ionomer luting cements.
- Restorative glass-ionomer cements for permanent fillings, which are divided into aesthetic and reinforced ones.
Strength hierarchy of amalgam phases: from Gamma (strongest, original) to Gamma-2 (weakest, tin-mercury). The higher the number, the worse the strength.
Class and exam questions
Why is it forbidden to add more mercury to amalgam to extend working time?
This is a gross error. Subsequent squeezing of excess mercury from the mass will remove tin and other important metals in unpredictable amounts, which will irreversibly destroy the strength of the future filling.
What is mercuryscopic expansion?
This is a process where, due to gamma-2 phase corrosion, free mercury penetrates deep into the filling, combines with silver, and causes material expansion. As a result, the edges of the filling chip off under masticatory pressure.
What is the advantage of modern spherical-particle amalgams?
They are more plastic, homogeneous, and stronger than old needle-shaped filings. In addition, they do not require excessive force during condensation in the tooth cavity and are easily polished.
What else to study on this topic
- Contraindications to amalgam use: galvanism, radiotherapy, presence of gold crowns.
- Algorithm for drying the root canal with paper points before filling.
- Specifics of mercury-containing waste disposal using potassium permanganate.
- Effect of amalgam triturating time on the increase of the weak $\gamma_2$-phase content.
- Technique of condensing a plastic setting paste in the canal orifice using a cotton pellet.
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Other topics in "Chapter 7. Endodontics"
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