The ideal time to stop your child using a dummy is between 6-12 months. It’s harder to get rid of dummies when your baby becomes a toddler.
Extended use of a dummy can affect your child’s speech, cause dental problems such as open bite and cross bite as well as over development of the muscles at the front of the mouth compared to those at the back of the mouth which may lead to a persistent tongue thrust and further effect placement of the teeth.

Other problems that can occur are excess dribbling and there is an increased risk of middle ear infections.

Some top tips to help you ditch that dummy: 
1. First reduce dummy time during the day. Use distraction techniques or introduce another comforter such as a soft toy to calm your child. Depending on their age explain what’s going to happen and let them be involved; you could use a Star Chart. 
2. Make a little box to keep in the bedroom (your child can help decorate it) so you can make sure you have all the dummies in one place and explain that she/he can only have a dummy for bed. 
3. When stopping the dummy at night you may find a change of routine or introducing a special blanket may help to calm your child. 
4. Some ideas for getting rid of dummies completely include letting your child throw them in the bin or give them away themselves, maybe to the ‘Dummy Fairy’ or to another imaginary character. 

For more information on the above and useful websites please visit 
www.nhs.uk/video/pages/when-should-we-ditch-the-dummy.aspx 
https://www.nhs.uk/conditions/pregnancy-and-baby/helping-your-childs-speech/ 
http://www.talkingpoint.org.uk/parents/speech-and-language/do-dummies-affect-speech