**Abstract**

Hydrocolloids are complex polysaccharides that disperse or dissolve in aqueous solution to give thickened or vicious effects. Also hydrocolloids possess high molecular weight. Owing to these characteristics, hydrocolloids have been widely used in various applications. In dentistry, for example, most intricate and precise procedures are made of hydrocolloids and are found in its simplest material to the most complex material such as impression making, fillings, separating media, electro-polishing etc. The two common hydrocolloids widely used in dentistry are reversible (agar) and irreversible (alginate) materials. Hence, this chapter bring to the forefront their preparations, uses and storage for optimal results and application.

**Keywords:** agar, alginate, dentistry, hydrocolloids, impression materials

## **1. Introduction**

Hydrocolloids are colloidal systems wherein the colloid particles are hydrophilic polymers dispersed in water and depending on the quantity of water available that can take place in different states, e.g., gel or sol (liquid) It is an intermediate between a solution and a suspension which can be distinguished from solutions using the Tyndall effect [1]. Hydrocolloids materials are available in the form of viscous liquids in the "sol" state or the form of semi-solid substances of a gelatinous consistency. Without a filler, the gel would lack stability and would have a slimy surface covered with synerate exudate [2]. They can be either irreversible (single-state) or reversible hydrocolloids (transiting from gel-sol-gel on the application of heat) [3]. Owing to their unique properties, hydrocolloids have found wide and useful applications in various fields including, dentistry, medicine and the food industries. For instance, hydrocolloids such as Xanthan, gum Arabic, Pectin are added to food as additives due to their gelling, viscosity, and stabilizing properties [4, 5]. The aforementioned hydrocolloids could significantly reduce human appetite in acute settings due to the ability to form gelation in the stomach when ingested. An important rheological property of fibers within the intestine is viscosity, which is thought to account for beneficial physiological responses in relation to appetite regulation, glycemic and lipidemic control [4, 5]. In Medicine, studies have been carried out with different strategies and approaches or a combination of both as hydrocolloid gels have found some potentials in bone regeneration in the delivery of osteo-inductive factors, bone-forming cells, or a combination of both [2].

Recently, hydrocolloid (alginate) gels have also been actively investigated for their ability to mediate the regeneration and tissue engineering of different tissues and organs, including skeletal muscle, nerves, the pancreas, and liver. Current strategies for skeletal muscle regeneration include cell transplantation, growth factor delivery, or a combination of both approaches [6, 7]. Also, Studies within the pharmacological field have demonstrated how alginate-antacid formulations can decrease post-prandial symptoms by neutralizing the acidity of gastric contents by forming a gel-like barrier to displace the "acid pocket" from the oesophagogastric junction and protect the oesophageal and gastric mucosa with controlled released drug products used as model system for mammalian cell culture in biomedical studies [6]. In Dentistry, for example, hydrocolloids are widely used in the fabrication of dental and maxillofacial prostheses impression due to their biocompatibility with the tissues, ease of use, physical properties and hydrophilicity with the oral tissues [8]. Other areas of hydrocolloids applications include orthopaedic structures and stone models in surgical cases [8]. This chapter aims to discuss the different hydrocolloids used in dentistry, their preparations, uses and storage for optimal results and application.
