Prosthodontics & Occlusion · patient case with 3 questions

Shade selection for an anterior restoration

Patient: Adult requiring an anterior indirect restoration

Chief complaint: Concerned about the appearance of the definitive crown.

Background: No relevant medical history reported.

Current findings: Shade selection is being carried out against a prepared tooth, using a shade guide.

Question 1

When should the shade be selected?

After drying the teeth thoroughly
Under the operating light at maximum intensity
At the end of the appointment, after preparation
At the start of the appointment, before the teeth are isolated and allowed to dry

Show answer and explanation

Correct answer: D. At the start of the appointment, before the teeth are isolated and allowed to dry

A. This is the very error described. Dehydrated teeth appear falsely light.
B. Intense direct light bleaches perception and obscures the subtleties of value and translucency.
C. By the end of the appointment the tooth is fully dehydrated and the reference tooth may be gone.
D. CORRECT. Shade must be taken FIRST, before isolation and dehydration. Teeth dehydrate rapidly once isolated, becoming lighter and more opaque as enamel loses water and its refractive index changes. A shade taken from a dehydrated tooth will be too light, and the restoration will look conspicuously dark once the tooth rehydrates.

Note: Take the shade at the start, on hydrated teeth, under neutral light, at eye level, in short glances of 5–7 seconds.

The definitive crown returns looking too white. Which dimension of colour is most likely responsible?

Show answer and explanation

Correct answer: A. Value

A. CORRECT. VALUE is lightness or darkness, and is the dimension the eye judges first and most acutely. A restoration that reads as 'too white' is almost always too high in value. Value is also the hardest error to correct, since it is largely determined by the underlying framework and opaquer, and it is the dimension to match first.
B. Chroma is saturation — the 1, 2, 3, 4 of the VITA guide. Low chroma contributes to a washed-out appearance, but 'too white' is primarily a value problem.
C. Excess translucency makes a restoration look greyer and darker, not whiter.
D. Hue is the basic colour family — the A, B, C or D of the VITA guide. An error here would read as the wrong colour, not simply too white.

Note: In the VITA classical guide, the LETTER is hue and the NUMBER is chroma. So in A3, the 3 denotes chroma.

Which error in shade taking would produce a crown that is too white?

Show answer and explanation

Correct answer: C. Taking the shade after the tooth had been isolated and dehydrated

A. Taking the shade before preparation is correct practice, not an error.
B. Neutral, daylight-corrected lighting is the recommended condition.
C. CORRECT. Dehydration lightens the tooth, so the shade recorded is falsely light and the crown is fabricated too white. Once the natural tooth rehydrates and returns to its true darker shade, the mismatch becomes obvious.
D. Eye level is the correct viewing position, using the most colour-sensitive part of the retina.