Definition of Zinc Oxide Impression Material
QZN: Is zoe mucostatic or mucocompressive?
Zinc oxide impression material is a paste-based substance composed primarily of metallic oxides. It possesses excellent flow characteristics, allowing it to capture intricate details of oral structures accurately. One of its key features is its non-elastic nature, which means it does not rebound upon removal from the mouth. Additionally, it is considered mucostatic, meaning it records the tissues in their natural position without significant displacement.
Characteristics of Zinc Oxide Eugenol Impression Material
Composition
Zinc oxide impression material consists of two main components: the base paste and the catalyst. The base paste, typically white in color, comprises:
- Zinc Oxide (80%): This is the primary component responsible for the material’s structure and rigidity.
- Inert Oils (15%): Including olive, linseed, and light mineral oil, these act as plasticizers, enhancing the material’s flexibility and flow.
- Hydrogenated Resin: This component acts as an accelerator in the setting reaction, promoting cohesion within the material.
The catalyst paste, usually red in color, contains:
- Eugenol (15%): Derived from oil of cloves, eugenol provides antiseptic properties and aids in the setting process.
- Gum Resin and Oils (65%): These ingredients contribute to the viscosity and consistency of the paste.
- Fillers (Talc and Kaolin) (16%): These additives help to improve the structure and consistency of the material.
- MgCl2 Accelerator or Zn Acetate/Moisture: These compounds accelerate the setting reaction, ensuring timely solidification of the material.
It’s important to note that eugenol, one of the components of Zinc Oxide Eugenol, has notable characteristics. It has a bitter taste and can cause irritation, burning, and stinging sensations. Additionally, it has a distinct odor and may have allergenic potential for a small percentage of the population.
Manipulation Technique
To manipulate Zinc Oxide Eugenol Impression Material (ZOIM), the base and accelerator pastes are mixed in a specific ratio of 2.5 parts base to 1 part accelerator. This ratio ensures the proper setting and consistency of the material. The mixing process involves dispensing equal lengths of both pastes onto an impervious paper pad. Using a mixing spatula, the pastes are spatulated together until they form a homogeneous pink color. It’s crucial to stabilize the paper pad with one hand while mixing to prevent any displacement of the mixture. This process is illustrated below
Table 6.1: Approximate Manipulation Durations of Zinc Oxide Eugenol Impression Material
| Procedure | Time (minutes) |
|---|---|
| Mixing of Pastes | 1-2 |
| Loading to Special Tray | 1-2 |
| Insertion into Mouth | 1-2 |
| Setting Time in Mouth | 3-5 |
| Removal from Mouth | 1-2 |
Note: Times may vary depending on environmental conditions and specific product formulations.
To record the impression, the mixed ZOIM is loaded onto a special tray and inserted into the mouth, ensuring proper coverage of the edentulous arches and fine details. Custom trays, closely fitting the jaws, are typically used to achieve a wash impression of 2-3mm thickness. This impression serves as a final or secondary impression, capturing precise details for accurate fabrication of dental restorations.
Setting Reaction
The setting reaction of Zinc Oxide Eugenol Impression Material is a chemical process triggered by the interaction of the base and accelerator pastes. Water is essential for this reaction and is provided through the rehydration of the powder during manufacturing. Additionally, an increase in temperature accelerates the setting reaction, causing the material to solidify. Consequently, the material in the mouth sets faster than the material on the mixing pad. Figure 6.3 illustrates the chemical structures of eugenol and eugenolate, key components involved in the setting reaction.
Properties of Zinc Oxide Eugenol Impression Material (ZOIM)
ZOIM, a widely used non-elastic impression material, offers several advantageous properties when manipulated correctly:
- Accuracy: ZOIM is capable of recording fine details accurately, with minimal dimensional change (less than 0.1%) during hardening. Impressions made with ZOIM exhibit stability on storage and can be preserved indefinitely.
- Working Time: Adequate working time is provided by ZOIM, allowing clinicians to manipulate the material effectively before it sets.
- Low Viscosity: With low viscosity, ZOIM flows easily and wets the tissues, ensuring good adaptation and impression accuracy. Moreover, its mucostatic nature makes it suitable for capturing accurate impressions.
- Strength: Despite being non-elastic, ZOIM possesses sufficient strength to build borders and withstand repeated insertions in the mouth without fracturing.
- Adhesion: ZOIM adheres well to dried special trays, eliminating the need for separating media between ZOIM and model or die materials, which simplifies the impression-making process.
Disadvantages:
- Non-Elasticity: As a non-elastic material, ZOIM is unable to flex and recover, making it unsuitable for recording undercut areas and prone to distortion or fracture during removal.
- Odour: ZOIM has a characteristic unpleasant odour, primarily due to the presence of eugenol, which can be discomforting for patients and clinicians.
- Stickiness: The material can be excessively sticky, making it challenging to remove from instruments and tissues, leading to potential contamination.
- Patient Sensations: Some patients may experience discomfort, such as burning or stinging sensations, especially those sensitive to eugenol.
- Disinfection: Proper disinfection of ZOIM impressions requires immersion in 2% alkaline glutaraldehyde for a duration of 10 minutes, which adds to the overall processing time.
Applications of Zinc Oxide Eugenol Impression Material
ZOIM finds applications in various dental procedures, including:
- Final (Secondary) Impressions in Complete Denture Fabrication: ZOIM is commonly used to obtain precise impressions of edentulous arches for fabricating complete dentures, ensuring accurate fit and comfort for patients.
- Sealing of Occlusal Rims in Jaw Registration: It is employed to create stable occlusal rims, providing support and stability during jaw registration procedures.
Modifications of Zinc Oxide Eugenol Impression Material
In response to the undesirable biological properties of eugenol, alternative formulations have been developed:
- Substitution of Eugenol: One approach involves replacing eugenol with a carboxylic acid, which reacts with Zn hydroxide to form Zinc carboxylate and water. This modification reduces the irritant potential associated with eugenol.
- Noneugenol Formulations: Another substitute for eugenol is lauric acid, resulting in modified cements known as Noneugenol pastes. These formulations offer similar properties to ZOIM but without the allergenic potential of eugenol.