Protruding lower jaw
(under bite)

This is when the lower teeth close in front of the upper teeth. A protruding lower jaw can be unattractive and can cause uneven wear of the front teeth and jaw joint problems.
Read more about a protruding lower jaw 
(Link opens in new window - Australian Society of Orthodontists)

Deep bite

In a deep bite the top teeth bite deeply down over the lower teeth. In severe cases, the upper teeth can cover the lower teeth completely.
Read more about a deep bite
(Link opens in new window - Australian Society of Orthodontists)

How to check: With your teeth closed, look at yourself in the mirror face on and check whether you can see your lower teeth. Normally you would expect to see about one third of your bottom teeth. If you see less than half, you may have a deep bite.
 

Protruded upper teeth

Protruded ('buck')  upper teeth result when the top teeth are positioned further forward than normal. Protruded upper teeth can be unattractive and prone to accidental damage. Often teeth become worn unevenly.

Read more about protruded upper teeth and how they are treated 
(Link opens in new window - Australian Society of Orthodontists)

Crooked, crowded and overlapping teeth

Crooked, crowded and overlapping teeth that don’t fit together, (technically termed malocclusion), can cause a range of oral health problems, including:

• Dental caries (tooth decay) and gum disease – misaligned teeth are harder to clean, particularly if they overlap.
• Injury to the gum – a misaligned tooth may sink into the nearby gum and cause injury.
• Wear and tear – if teeth are misaligned, the action of chewing may grind the teeth unevenly.
• Jaw injury – a bad bite may place stress and strain on the jaw joints.

Read more about problems caused by crowded teeth 
(Link opens in new window - Australian Society of Orthodontists)