How can it be sacrilege? I’m not sure you can accidentally commit sacrilege.
A sacrilege is any violation or misuse of something sacred. It does not have to be deliberate and therefore it is not always a sin.
I would agree with those who say that this is not a sin because it was not deliberate nor was it neglect of normal care. You normally do not expect to find a fragment of the Sacred Host lodged on your teeth. You try to clear your mouth of all fragments when you consume Holy Communion in the first place and you assume that doing your best is sufficient.
OK, so in the future someone who has found he has gaps where things lodge might try not to allow the host in that part of his mouth, so as to avoid an unintentional repeat. It is objectively desirable, however, to avoid a scrupulous attitude, because this puts a soul in danger of "straining out the gnat but swallowing the camel (Matt 23:24), which is a serious spiritual trap. You only have so much attention to spread over your day and, as Steven Covey put it, “the main thing is to keep the main thing the main thing.”
I think when we find we have unknowingly committed a sacrilege it is better to reflect on how often we unknowingly fail to reverence Our Lord by failing to practice charity or mercy. I’ve always liked this poem in that regard:
The Fool’s Prayer (by Edward Rowland Sill)
The royal feast was done; the King
Sought some new sport to banish care,
And to his jester cried: “Sir Fool,
Kneel now, and make for us a prayer!”
The jester doffed his cap and bells,
And stood the mocking court before;
They could not see the bitter smile
Behind the painted grin he wore.
He bowed his head, and bent his knee
Upon the Monarch’s silken stool;
His pleading voice arose: "O Lord,
Be merciful to me, a fool!
"No pity, Lord, could change the heart
From red with wrong to white as wool;
The rod must heal the sin: but Lord,
Be merciful to me, a fool!
"'T is not by guilt the onward sweep
Of truth and right, O Lord, we stay;
'T is by our follies that so long
We hold the earth from heaven away.
"These clumsy feet, still in the mire,
Go crushing blossoms without end;
These hard, well-meaning hands we thrust
Among the heart-strings of a friend.
"The ill-timed truth we might have kept–
Who knows how sharp it pierced and stung?
The word we had not sense to say–
Who knows how grandly it had rung!
"Our faults no tenderness should ask.
The chastening stripes must cleanse them all;
But for our blunders – oh, in shame
Before the eyes of heaven we fall.
“Earth bears no balsam for mistakes;
Men crown the knave, and scourge the tool
That did his will; but Thou, O Lord,
Be merciful to me, a fool!”
The room was hushed; in silence rose
The King, and sought his gardens cool,
And walked apart, and murmured low,
“Be merciful to me, a fool!”
So…I think when we are guilty of unintended offenses, the thing to do is to ask for mercy and to ask to be given the grace to extend mercy to those whose foolishness wounds us, lest we deserve the penalty due to hypocrites.