The Rubber Dam Sheet in Dentistry-Natural Rubber Latex

The legacy of the dentist Sanford C. Barnum was founded on March 15, 1864, when he punched a hole in a sheet of rubber and stretched it over a mandibular molar. That day represented the beginning of the dental rubber dam—a term long used in the construction and shipbuilding industry for the isolation of a cavity from moisture.

The rubber dam remains a simple, quickly applicable, and effective tool in endodontics and other fields of dentistry.

A 15 × 15 cm (6 × 6 in) sheet of rubber is the most frequently used rubber dam for clinical use. The raw material—as with latex gloves—is the sap of the native rubber tree. Chemically, the substance is a cis-1.4 polyisoprene.Natural Rubber Latex Film is mostly made with pure natural rubber latex, a white sap that is harvested from live trees.¹

Hevea brasiliensis, the Pará rubber tree, sharinga tree, seringueira, or, most commonly, the rubber tree or rubber plant, is a flowering plant belonging to the spurge family Euphorbiaceae. It is the most economically important member of the genus Hevea because the milky latex extracted from the tree is the primary source of natural rubber. The tree is native to rainforests in the Amazon region of South America, including Brazil, Bolivia, Peru, Venezuela, Ecuador, and Colombia.

H. brasiliensis is a tall deciduous tree growing to a height of up to 43 m (141 ft) in the wild, but cultivated trees are usually much smaller because drawing off the latex restricts the growth of the tree. The trunk is cylindrical and may have a swollen, bottle-shaped base. The bark is some shade of brown, and the inner bark oozes latex when damaged.. The white or yellow latex occurs in latex vessels in the bark, mostly outside the phloem. These vessels spiral up the tree in a right-handed helix which forms an angle of about 30 degrees with the horizontal, and can grow as high as 45 ft.

In plantations, the trees are generally smaller for two reasons: 1) trees grow more slowly when they are tapped for latex, and 2) trees are generally cut down after only 30 years, because latex production declines as trees age, and they are no longer economically productive.²

Rubber tapping is the process by which latex is collected from a rubber tree. The latex is harvested by slicing a groove into the bark of the tree at a depth of one-quarter inch (6.4 mm) with a hooked knife and peeling back the bark. Trees must be approximately six years old and six inches (150 mm) in diameter in order to be tapped for latex.

Rubber tapping is not damaging to the forest, as it does not require the tree to be cut down in order for the latex to be extracted

Each night a rubber tapper must remove a thin layer of bark along a downward half spiral on the tree trunk. If done carefully and with skill, this tapping panel will yield latex for up to five hours. Then the opposite side will be tapped, allowing this side to heal over. The spiral allows the latex to run down to a collecting cup. The work is done at night or in the early morning before the day's temperature rises,so the latex will drip longer before coagulating and sealing the cut.

Depending on the final product, additional chemicals can be added to the latex cup to preserve the latex longer. Ammonia solution helps prevent natural coagulation and allows the latex to remain in its liquid state. Plastic bags containing a coagulant have replaced cups in many plantations in Malaysia. This form of latex is used as the raw material for latex concentrate, which is used for dipped rubber products or for the manufacture of ribbed smoke sheet grades.

Naturally coagulated latex, sometimes referred to as cup lump, is collected for processing into block rubbers, which are referred to as technically specified rubbers (TSRs). The serum left after latex coagulation is rich in quebrachitol, a cyclitol or cyclic polyol.

Products made from natural rubber latex have many unique properties that make them desirable for a variety of applications. Excellent stretch and recovery is one of the main reasons people use natural rubber latex in their applications. Natural rubber latex products are considered biodegradable because the liquid latex used to manufacture the products is naturally extracted from the Hevea Brasiliensis, or “The Rubber Tree”.

In its natural state the latex sap has many limitations; it is highly affected by temperature, acting soft and sticky in the heat and brittle in the cold. In its natural state it is also easily degraded. With vulcanization, the latex turns into a product that can now be used and will remain firm and flexible in a wide temperature range.

Once all the bark from the available portion of the tree is gone, the latex harvesters must wait 7 years for it to re-grow before they can continue the tapping cycle. In general, tapping on one tree should only last around 28 years. Overall, the trees will remain unharmed as long as the tapping is done properly, which is why this is considered a sustainable process that produces a natural resource.

The finished products produced from natural rubber latex exhibit the properties that are typically associated with very stretchy rubber – they have excellent elongation, tear resistance and recovery.

The processed rubber dam sheet has superior physical properties

Features

• High tensile strength
• High elongation
• Excellent tear resistance
• Exceptionally tight tolerance
• Available in many different thicknesses³

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