At the end of a long, stressful day, you may want to just fall into your bed and sleep. However, you should not forgo your oral hygiene routine, no matter how tired you feel. Your teeth should be brushed twice a day and flossed once a day. When you skip brushing, especially before you go to sleep, then cavities and other dental problems can begin developing in your mouth.
Plaque decays teeth by producing acids when it processes sugars. Plaque is always present, but you can get rid of it for some time through brushing and flossing. When you do not brush before you go to bed, the plaque not only remains undisturbed, but it has sugar available from the food debris still trapped in your mouth.
When plaque is left undisturbed, it not only freely produces acids, but it can crystallize into calculus (tartar). You cannot brush off calculus with a toothbrush; only a dental hygienist can scrape it off of your teeth through scaling.
When you sleep, your saliva flow reduces significantly. This means that your mouth becomes more susceptible to decay because saliva helps neutralize acids and remineralize tooth enamel. This risk for decay increases even more when you do not brush and floss your teeth.
No one likes morning breath, and you can imagine just how much worse it becomes when you do not brush and floss before sleeping. Food debris has been stinking up your mouth all night long, and oral bacteria create another stench when it processes this food.