When /t/ or /d/ is produced, the tip of the tongue is used to touch the upper teeth ridge. So, whether the mouth is open is not so important.
When /t/ or /d/ is produced, the tip of the tongue is used - U 1-2 - 英语语音 - 浙江省高等学校在线开放课程共享平台 | 大学网课搜题引擎