صورة الأشعة السينية واضحة، كما أن طبيب الأسنان يرى تسوس الأسنان.

Because it describes صورة, which is a feminine singular noun meaning image/picture.

So in:

صورة الأشعة السينية واضحة

the adjective واضحة must agree with صورة, not with الأشعة.

• صورة = feminine singular
• واضحة = feminine singular adjective meaning clear

That is why you do not say واضح here.

This is very common in Arabic nominal sentences.

In a sentence like:

صورة الأشعة السينية واضحة

the first part is the subject, and the second part is the predicate. Predicate adjectives are often indefinite in Arabic, even when the subject is definite.

So:

• صورة الأشعة السينية = the X-ray image
• واضحة = clear

Literally, Arabic structures this like:

• The X-ray image [is] clear

This is normal Arabic grammar.

This is an iḍāfa construction, often called a construct phrase.

It is made of:

• صورة = image/picture
• الأشعة السينية = the X-rays / X-ray radiation

Together:

• صورة الأشعة السينية = the image of the X-rays, naturally translated as the X-ray image

A key rule of iḍāfa:

• the first noun usually does not take الـ
• the whole phrase can still be definite because the second part is definite

So صورة الأشعة السينية is definite even though صورة has no الـ.

Because الأشعة is a non-human plural, and in Modern Standard Arabic, non-human plurals usually take feminine singular agreement.

So:

• الأشعة = rays / radiation
• السينية = feminine singular adjective agreeing with a non-human plural

This is why الأشعة السينية is correct for X-rays.

This pattern is very common:

• الكتب الجديدة = the new books
• السيارات السريعة = the fast cars

Even though the nouns are plural, the adjective is often feminine singular when the plural is non-human.

الأشعة السينية means X-rays or X-ray radiation.

The phrase is:

• الأشعة = rays / radiation
• السينية = X-ray, literally the standard adjective used in Arabic for this term

So صورة الأشعة السينية is the standard way to say the X-ray image.

كما أن is a connector that adds another related statement. In this sentence, it means something like:

• and also
• moreover
• furthermore
• in addition

So:

صورة الأشعة السينية واضحة، كما أن طبيب الأسنان يرى تسوس الأسنان.

means that one fact is being added to another:

• the X-ray image is clear,
• and in addition, the dentist can see tooth decay.

It is a slightly more formal connector than just و.

Yes, in many contexts you could say:

صورة الأشعة السينية واضحة، وطبيب الأسنان يرى تسوس الأسنان.

That would simply mean:

• The X-ray image is clear, and the dentist sees tooth decay.

But كما أن gives a slightly more formal and explanatory tone, like moreover or in addition. It helps show that the second clause supports or adds to the first.

Because طبيب الأسنان is another iḍāfa construction:

• طبيب = doctor
• الأسنان = the teeth

Together, it means doctor of the teeth, which is how Arabic says dentist.

In iḍāfa:

• the first noun usually does not take الـ
• the second noun can take الـ

So:

• طبيب الأسنان = the dentist / dentist
• not الطبيب الأسنان

If you want to make the whole phrase clearly definite, Arabic often still leaves it as طبيب الأسنان, because the definiteness comes from the second noun.

يرى is the present tense verb meaning he sees.

It comes from the verb رأى = to see.

So:

• طبيب الأسنان يرى تسوس الأسنان = The dentist sees tooth decay

Because the subject طبيب الأسنان is singular masculine, the verb is also singular masculine:

• يرى = he sees

Both orders are possible in Arabic, but they can sound slightly different in style or emphasis.

Here the sentence uses:

• طبيب الأسنان يرى تسوس الأسنان

This is a subject-first order, which is very common in clear, straightforward Modern Standard Arabic prose.

Arabic can also use verb-first order:

• يرى طبيب الأسنان تسوس الأسنان

Both mean essentially the same thing:

• The dentist sees tooth decay

The version in your sentence may feel a bit more balanced after كما أن.

Because تسوس الأسنان is an iḍāfa construction:

• تسوس = decay / caries
• الأسنان = the teeth

Together:

• تسوس الأسنان = tooth decay or more literally decay of the teeth

In iḍāfa, the first noun usually does not take الـ. The whole phrase can still be definite because the second noun is definite.

So تسوس الأسنان is perfectly normal Arabic.

Arabic often expresses ideas with noun phrases where English might prefer a different structure.

تسوس الأسنان is a very common and natural way to say:

• tooth decay
• dental caries
• sometimes, depending on context, cavities

It is a standard medical or general term. Arabic often prefers this kind of phrase instead of matching English word-for-word.

Because the two phrases serve different functions:

• طبيب الأسنان = dentist
• تسوس الأسنان = tooth decay

Even though الأسنان appears in both, each phrase is an established expression:

• one names the profession,
• the other names the condition.

So the repetition is natural and not awkward in Arabic.

Yes. In the present tense, Arabic usually does not use a separate word for is/am/are.

So:

صورة الأشعة السينية واضحة

literally looks like:

• The X-ray image clear

but it means:

• The X-ray image is clear

This is one of the most important differences from English.

In fully vocalized formal Arabic, yes, the endings would show grammar more clearly:

• صورةُ الأشعةِ السينيةِ واضحةٌ، كما أنَّ طبيبَ الأسنانِ يرى تسوُّسَ الأسنانِ.

These endings show things like subject, object, and iḍāfa relationships.

But in normal everyday writing, these short vowels are usually omitted, so learners commonly see:

صورة الأشعة السينية واضحة، كما أن طبيب الأسنان يرى تسوس الأسنان.

That is completely normal.

In كما أن, the word أن helps introduce a full clause after the connector.

So:

• كما أن طبيب الأسنان يرى تسوس الأسنان = moreover, the dentist sees tooth decay

You can think of كما أن as a set phrase in formal Arabic writing. It is best learned as one expression meaning moreover / and also / in addition.

A careful reading would be approximately:

ṣūratu l-ashiʿati s-sīniyyati wāḍiḥatun, kamā ʾanna ṭabība l-ʾasnān(i) yarā tasawwusa l-ʾasnān.

A few notes:

• صورة becomes ṣūratu in full case pronunciation
• الأشعة السينية is an iḍāfa phrase
• أن in careful speech is ʾanna
• يرى is pronounced yarā
• تسوس is often pronounced tasawwus(a) in full formal reading

In ordinary unvowelled reading, learners usually just focus on the words as written.