injection

Dental needles

The most painful: nasopalatine block injection, followed closely by any of the palatal submucosal infiltration injections. i.e. the ones that you have in the roof of your mouth. Why? Because in this area the tissues are denser and accomodates very little in the way of volume.

The least painful: the maxillary buccal infiltration injection in the molar area. i.e. the ones you have in your cheek for upper back teeth. Why? Because there are few nociceptive nerve endings in this region of loose connective tissue.

Def An injection is an injective function f:X-->Y. That is, given any x and y in X, if we have f(x)=f(y) then this implies that x=y. Equivalently, whenever x and y in X are not equal then f(x) and f(y) are not equal.

If you're not familiar with functions, a function f:X-->Y is a black box that given as input an element from the set X gives as output an element f(x) from the set Y. So to say the function is injective just means that if you have two distinct inputs then the outputs will also be distinct.

An example of an injection is the identity function 1_X:X-->X which takes every element to itself.

Another example (this time not a bijection) is the function f:Z-->Z with f(n)=2n. Here Z denotes the set of all integers.

Here's an example that is not an injection. Consider the function f:Z-->Z with f(n)=n². This time f is not injective because f(-1)=f(1).

In*jec"tion (?), n. [L. injectio : cf.F. injection.]

1.

The act of injecting or throwing in; -- applied particularly to the forcible throwing in of a liquid, or aeriform body, by means of a syringe, pump, etc.

2.

That which is injected; especially, a liquid medicine thrown into a cavity of the body by a syringe or pipe; a clyster; an enema.

Mayne.

3. Anat. (a)

The act or process of filling vessels, cavities, or tissues with a fluid or other substance.

(b)

A specimen prepared by injection.

4. Steam Eng. (a)

The act of throwing cold water into a condenser to produce a vacuum.

(b)

The cold water thrown into a condenser.

Injection cock, ∨ Injection valve Steam Eng., the cock or valve through which cold water is admitted into a condenser. -- Injection condenser. See under Condenser. -- Injection pipe, the pipe through which cold water is through into the condenser of a steam engine.

 

© Webster 1913.