An aesthetic dental plan that begins with the teeth tends to produce a result that looks correct on a model and wrong in a face. The reference points sit outside the mouth.
Teeth are only visible in a frame
Nobody sees a tooth in isolation. It is read against the lips, the gum line and the face around it, and those surroundings set the expectations the eye applies.
A central incisor of a given length can look long or short depending on how much of it the upper lip covers at rest and in a full smile.
Planning therefore starts by recording where the lips sit in several positions, because those positions determine which parts of the restoration will ever be seen.
The resting lip line fixes tooth length
With the face relaxed and the lips apart, a small amount of upper tooth is usually visible. That measurement anchors how long the front teeth should be built.
Display at rest changes across a lifetime as facial tissues alter, which is one reason a length that suits one person can look excessive on another of the same build.
Getting this wrong is the most common cause of teeth that read as artificial, because the error shows constantly rather than only when smiling.
Midline and horizon are judged against the face
The line between the two upper front teeth is compared to the centre of the face, not to the centre of the dental arch, since the two often do not coincide.
Small deviations are tolerated well by the eye. A midline that is tilted rather than shifted is far more noticeable, because it breaks the vertical reference the face provides.
Similarly, the plane across the biting edges is checked against the eyes and the horizon, as a canted plane reads as wrong even when every tooth is well made.
The lower lip guides the smile curve
In an unforced smile, the curve across the upper biting edges tends to run roughly parallel to the upper border of the lower lip.
A flat edge line against a curved lip reads as aged or worn, which is often what people are responding to when they describe a smile as tired.
Restoring that curve can change how a smile is perceived more than changing shade does, and it involves no whitening at all.
Why a trial stage exists
Because these judgements are visual, most careful planning includes a stage where the proposed shapes are previewed in the mouth before anything permanent is made.
That preview allows length, curve and midline to be checked while the person speaks and smiles, which no model or photograph fully replaces.
It is also the point at which disagreement is cheap to resolve, and a dentist who offers such a stage is giving the plan its most useful test.