Interdental fricatives and affricates (Lisp)

Within the past several months or years, I've slowly come to a startling
conclusion -- I lisp (and I'm not refering to the programming language!). An
interdental lisp to be precise.

Googling for more information, I found that it usually dissapears around the
age of six or so, but I'm 22! Normally, people seem to understand me just
fine, but once in a very rare while there's an embarassing moment when I try
to pronounce /s/, that people have difficulty understanding. Usually around
people that don't know me very well; since I'm not exactly a socializer,
this doesn't happen often.

For instance, a few years ago in college, another student was asking me to
spell my name |Caleb|.

------------
So I replied: /si ?eI ?El ?i bi/.

What was the first letter? /Ti/?

No, /si/!

/Ti/?!

No! /si/! /si/! Like in cat!
------------

At the time, I didn't even know there was a name for it, and like I said,
I'm generally well-understood, but I never knew alot of kids growing up, so
I was never made fun of. But when I started conlanging, I applied what I had
been reading about phonology to analyze what I was actually doing. It's more
complex then just /s/ -> [T], since /s/ and /T/ are distinct phon(em)es for
me (I pronounce them differently). Here's what I found that I do. I'm not
exactly sure if I'm using the right CXS symbols, so bear with me as I
explain (also, I'll be explaining with unvoiced phonemes, but everything
applies equally well to the voiced versions, /z/ and /D/).

I have two allophones for /s/:

/s/  -> [T], [T-], where
[T]  -> Interdental fricative (this one is the most common by far)
[T-] -> Postdental fricative (tongue touching the inside bottom of the upper
front teeth, air blown through gap between two front teeth.)

But I _do_ distinguish /T/ from /s/. Here's how -- untill the last few years
(when I started conlanging), I had been under the assumption that /T/ was an
affricate (I didn't know the term, but I knew the concept). I even remember
as a kid, when I first learned that |ch| was actually two sounds, /tS/, I
thought "Oh! and for that matter, soft |th| is basically just /ts/, and hard
|th| is just /dz/". And this is how I still pronounce it, give or take.

/T/  -> [t_mT)], where
[t_m] a laminal alveolar stop. (Tongue blade placed on alv. ridge)
[T] The first phone of /s/ above. (Tongue tip is interdental)

But if /T/ is [tT], then you might be wondering how I pronounce /ts/. Quite
simply like this:

/ts/ -> [t+T-], where
[t+] -> A post-dental stop.
[T-] -> The second phone of /s/ given above.
The tongue sort of slides from being directly behind the top of the teeth in
[t+] to being behind the bottom of the teeth. This exposes the gap between
my front teeth which lets air hiss out to form /s/ -> [T-].

The one combination that  really gets me, though, is word-final /Ts/, for
example, in |baths|. This ends up being something like [b&t_mT)T] or even
uglier [b&t_mT).@D] (remember, [D] is my /z/). It's not so difficult in the
middle of a word, where I can break the syllable up.

So my question is twofold. First of all, does anyone know how common lisping
is in adults? I coudn't find much at all about adult lisping on Google. And
secondly, how on earth do you pronounce /s/ and /z/ _correctly_???!! Even
though most people understand me well enough, it would be nice to be capable
of making a "true" /s/, even if only in a pinch.

Can thomebody pleadhe help me?

[t_mT)eINkT],
~Caleb

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