Umur 18 bulan memang agak lambat untuk belum ada gigi lagi, biasanya babies start around 6 months, tapi setiap baby beda-beda lah timing dia. A few of my mum friends' babies juga delayed sikit, and turned out fine je, tapi sebaiknya you check with your pediatrician just to make sure, maybe ada nutrient deficiency or other factors yang perlu ditengok. Don't worry lah, doctor dapat assess better and give proper guidance!