A smile line that is parallel to the horizontal is considered to be most attractive. Sometimes the level of the eye line does not coincide with that of the smile line. Your dental professional should always strive to create the illusion of the horizontal alignment of your smile, even if this is the case. The most attractive smiles all possess one important feature, symmetry. The human eye can easily detect any difference in the size and shape of your front teeth. Making your front teeth the same size and shape, whilst positioning them around the centre of your face, produces the perfect looking smile. The smile line follows the biting edges of your top teeth. In the most attractive smiles, the biting edges of the top teeth gently follow the curve of the lower lip. A flat, straightened smile line suggests aged worn teeth, whilst a curved smile line rejuvenates, making you and your smile look younger. The most attractive smiles have gum lines that follow the upper lip and are symmetrical. The gum line is like a frame to a beautiful painting. It will either significantly enhance the appearance of your smile, or significantly detract from your smile if poor in health and shape. The teeth towards the back of the mouth can always be seen in an attractive smile. In a narrow smile the back teeth are often in shadow. This is called negative space and it creates the appearance of 'black triangles' at the corners of the mouth, and front teeth that protrude. Embrasures are the natural triangular indentations that occur between the tips of the teeth. For a smile to look attractive, the embrasures should be at their smallest between the front teeth, gradually increasing in size towards the back of the mouth. The golden proportion, also known as the divine proportion or golden ratio, is a mathematical relationship that is present throughout nature. The ratio of 1.6 : 1.0 : 0.6 indicates the amount of tooth surface that should be seen when looking directly at a smile. The closer the teeth are to this ratio, the more attractive a smile is. This golden proportion rule is used as a starting point when designing a new smile. In the most attractive smiles there is a certain length to width ratio for the two front teeth. This is usually a ratio of 0.7 : 1. The length of a front tooth should always be greater than its width. Teeth that are shorter in length become more square in their appearance. This has an ageing effect on the smile by giving the impression that the teeth have been worn down and flattened through usage over time. When designing your new smile it is possible to change the shade (colour) of your teeth. Teeth are not pure white, they possess a range of colours and translucencies. A tooth may be divided into three regions:- The cervical third should be more yellow in appearance, even in bright white smiles. - The middle third or body of the tooth will be the prominent shade, generally less yellow and brighter in appearance. - The incisal third possesses varying degrees of translucency and may appear a little blue or grey. The most attractive smiles incorporate all of these features. Without these subtle nuances, teeth look artificial.