why is the porcelain fused to metal crown little radiopaque in the panoramic film?

[Toan Phan Van]

I'm sorry about the bad picture. In this picture, there are some area that little radiopaque than others in the crowns. I don't know why it is. Anyone can help me explain it? and is the crown made of titanium more radiolucent than other metals ? thank you very much.

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[THS]

Are you asking why the most radiopaque shape within the crown is a different shape than the tooth? Or why each crown has a smaller radiopaque shape inside of the shape of the clinical crown?

Keep in mind that for PFMs, the metal coping will more or less have the same shape as the prepared tooth. The porcelain will be shaped to look like a natural tooth. There has to be enough material between the porcelain and the metal coping (about 1.0-1.2mm facial/lingual, and about 2.0mm incisal/occlusal) to look natural in the patient's mouth, without the metal showing through the porcelain and giving the tooth an ugly gray color.

 

[Toan Phan Van]

I don't mean that. I want to ask about the little radioulucent area inside the crown where made of metal. in theory it is radiopaque like others because it made of metal??

 

[THS]

I don't mean that. I want to ask about the little radioulucent area inside the crown where made of metal. in theory it is radiopaque like others because it made of metal??

I'm guessing it's because the xrays have to travel through more metal while going through the proximal surfaces of the coping than the center. Just like in a natural tooth, the proximal and occlusal enamel looks radiopaque while the facial and lingual enamel surfaces of the tooth are more RL, since there is less material for the x rays to pass through.