Filling the gap in teeth will create problem in speaking?

In all of my years of dentistry I have never encountered a problem with bonding a gap between the front teeth and change of speech. Sometimes, when do 4 to 6 veneers, it causes a change in speech and will require a little practice on your part but not big deal to correct. Hope this answers your question and alleviates your fear.

In 35 years in dentistry I've never seen any kind of permanent change in phonetics (speech) with simple closure of the spacing between upper front teeth (called diastemas).  Sometimes after placement of the restoration, the patient will feel a bit awkward because the tongue is used to going into the space to make a seal when swallowing.  However, the human body quickly adapts to this.  Think how many youngsters get braces and then have to wear (and talk) with retainers.  Or how many millions of people around the world have dentures.  If they can adjust to that, you should certainly have no problems with your diastema closure.With crowns or veneers, some issues might exist is if the upper front teeth are too long, making it difficult to say the "v" or "f" sound.  Or, if the lower teeth are too thick or tall, or upper teeth are too thick from the back side of the teeth, saying the "s" sound can be impaired.  But once recognized, this can be easily corrected by the dentist with some simple adjustments to the restorations.