DECLARE @a as NVARCHAR(15)
SET @a = '2.18.4.14'

SELECT
    @a = CASE
        WHEN CHARINDEX('.',@a) < 4
            THEN STUFF(@a,1,0,REPLICATE('0',4-CHARINDEX('.',@a,1)))
        ELSE @a
    END
,
    @a = CASE
        WHEN CHARINDEX('.',@a) < 8
            THEN STUFF(@a,5,0,REPLICATE('0',8-CHARINDEX('.',@a, 5)))
        ELSE @a
    END
,
    @a = CASE
        WHEN CHARINDEX('.',@a) < 12
            THEN STUFF(@a,9,0,REPLICATE('0',12-CHARINDEX('.',@a, 9)))
        ELSE @a
    END
,
    @a = CASE
        WHEN LEN(@a) < 15
            THEN STUFF(@a,13,0,REPLICATE('0',15-LEN(@a)))
        ELSE @a
    END

SELECT @a