Here are the quotations that have been written in the FCI Standard of 1993.

Teeth: Strong, regular and complete scissor or even bite. Reverse scissor bite acceptable. Missing PM 1 (premolar 1) tolerated.

We will find under the faults section the following quote:

* Missing teeth other than PM 1 (premolar 1)
* Under- or overshot bite.
* Muzzle too short or too long.

Bearing in mind the following quotes a misunderstanding arises about teeth that does effect a big portion of the word TYPE to the Swiss Standard. When a muzzle becomes too short, the teeth become distorted in the lineup or do not appear and in some instances disappear from the jaw altogether. This is the indication of the depletion of the phenotype of skull. In these instances, dogs that show this deformation should never be graded higher than a "Satisfactory". One gets instances where teeth for example on the bottom jaw have disappeared. Judging these type of dogs one must penalize them severely as well. This is the indication of the depletion and alteration of the bottom jaw. Dogs like this again should not be graded higher than "Satisfactory" as these instances are serious genetic faults.

Our Standard, requires 42 teeth in the Saint Bernards mouth. Requirements are met by 20 on the upper jaw and 22 on the bottom jaw, with the excusable missing teeth are the P1 (Pre-molar 1).
When evaluating the teeth of the Saint Bernard and there is no gap where the P1 can come out then the dog should never be graded more than "Very Good". The reason for this is that the dog is now showing the early stages of the depletion of the bottom jaw and muzzle (i.e.. the mouth is becoming too small or too short).

When observing the bottom jaw of an open mouthed Saint Bernard the six incisors should represent a square shape  (i.e. they should all be in a straight or near straight line) and any form of roundness in these teeth indicate the snipiness of the muzzle. The teeth should be of medium size to large. Small teeth should be indicated in a critique of the dog and the breeder should be informed of it. Although the Saint Bernard does not use its jaw for man work, etc., it is important on the bitches to have very strong and correct tooth placement when it comes to the Pre-Molar 4 on both the upper and bottom jaws. The  Pm4 (Pre-Molar 4) is used by the bitch to sever (cut cleanly) the umbilical cord of its pups at birth. The incisors are used top tear open the Placentae while the bitch is licking the pup to resuscitate it. Therefore one can see that if a Saint Bernard has small teeth the natural instinctive traits are being disturbed.

The Saint Bernard Standard does describe the word "Reverse Scissor Bite". This is when the bottom jaw teeth are slightly overlapping the top teeth, the exact opposite of a scissor bite. This is still accepted but  it  must not change the formation image of the muzzle (i.e. It must not look like a Boxer's jaw). A Saint Bernard with this type of "Boxer Jaw" should never be graded an "Excellent". Atypical feature of the Molloso type breeds one must understand that the bottom jaw through its entire life does not stop growing. one could have a dog at two years of age with a perfect scissor bite and the same dog at six years of age could have a level to a reverse scissor bite. This is why the standard has left the tolerance factor for the Saint Bernard. 

when Judging the FCI Saint Bernard the judges must count the dog's teeth and make note on the critique for future evaluation into future generations that might deviate from the phenotype of the Saint Bernard.

Below are diagrams of the jaw of  dogs in general naming and placing all the teeth in the respected positions. Included are over, under, level and scissor bites.