[DonaldPShimoda]

Aspiration is a separate phenomenon. English also has unaspirated plosives — they just mostly only occur in word-final positions, like the <t> in "pat", and they are not contrastive with their aspirated versions.

What I was talking about was how the Spanish /t/ has the tip of the tongue just a bit further forward, so that it touches the back of your teeth. English /t/ is, for most people, purely alveolar, so there's no teeth contact.

[leephillips]

Agreed. But some Spanish speakers pronounce t with the tongue quite far forward, between the teeth; that’s what I meant by comparing it to an unaspirated English th. But I think we are getting into regional variations now.

It’s even more crucial with d. An English native speaker who is a beginner in Spanish will pronounce tened in a way that will be interpreted by Spanish speakers as tener.