たんだ ⇒ てん

As a summary of a few more of the regular particle patterns that change in 関西弁(かんさいべん), we have the following:
んだ becomes ねん (less commonly んや, or にゃ)
たんだ becomes てん
It may seem a little odd to cover both of these in one lesson, but the reason is primarily due to the structures that are being replaced in standard Japanese. Both of which are patterns that contain んだ (the sentence ending expression used to convey new information, or make enquiries).
Let's have a look at these structures in action, and see how they compare to the originals.

• 昨日(きのう)からずっとお腹(なか)が痛(いた)いねん 。
  My stomach has been hurting since yesterday.

Like んだ, ねん regularly appears at the end of sentences, and points out that the thing that was just said is an explanation.

• 先週(せんしゅう)家族(かぞく)でユニバに行ってん。
  Last week, I went to Universal Studio Japan with my family.

Also pointing out an explanation, てん simply means that something 'was' a certain way (incorporating the past tense of だった).ねん and てん are the primary elements to remember here, as やねん is merely a conjugation of ねん that includes や, rather than something that would be considered its own separate grammar pattern. All of these expressions can be thought of as simple replacements for んだ (or のだ).