A dentist has revealed two common mistakes people make that can lead to yellow teeth. Brushing dry, without first wetting the brush, can make teeth look dull and yellow. Wetting the brush allows the toothpaste to spread evenly, making cleaning more effective. Another mistake is brushing immediately after consuming acidic foods or drinks. This weakens enamel, making teeth more susceptible to yellowing. The dentist recommends waiting at least 30 minutes after consuming acidic items before brushing to allow the enamel to remineralize.