I have been on trinessa for one year now and have never missed a pill but I was on my tenth pill and

I realize this answer is a bit late... but for the future.

The pill that turned into powder was effectively a missed pill and if you had unprotected sex within 7 days of that missed pill then the chances of becoming pregnant are highly. Generally you have to take the active tablets for at least 7 consecutive days to be safe.

What happens if I miss a dose?

Missing a pill increases your risk of becoming pregnant.

If you miss one "active" pill, take two pills on the day that you remember. Then take one pill per day for the rest of the pack.

If you miss two "active" pills in a row in week one or two, take two pills per day for two days in a row. Then take one pill per day for the rest of the pack. Use back-up birth control for at least 7 days following the missed pills.

Expand this post...

If you miss two "active" pills in a row in week three, or if you miss three pills in a row during any of the first 3 weeks, throw out the rest of the pack and start a new one the same day if you are a Day 1 starter. If you are a Sunday starter, keep taking a pill every day until Sunday. On Sunday, throw out the rest of the pack and start a new one that day.

If you miss three "active" pills in a row during any of the first 3 weeks, throw out the rest of the pack and start a new pack on the same day if you are a Day 1 starter. If you are a Sunday starter, keep taking a pill every day until Sunday. On Sunday, throw out the rest of the pack and start a new one that day.
If you miss two or more pills, you may not have a period during the month. If you miss a period for two months in a row, call your doctor because you might be pregnant.

If you miss any reminder pills, throw them away and keep taking one pill per day until the pack is empty. You do not need back-up birth control if you miss a reminder pill.

http://www.drugs.com/mtm/trinessa.html