One may treat early to prevent a bigger problem; another may monitor.
Time horizon
Planning for five years and for twenty produce different answers.
Restorative philosophy
Conserving tooth structure versus maximising predictability.
What they can see
Different images, different angles, different days.
Your stated priorities
A plan built around cost differs from one built around longevity.
Genuine uncertainty
Some teeth are borderline, and honest clinicians will say so.
How to use a second opinion well
Ask each clinician the same questions: what happens if I do nothing, what are the alternatives, what makes you prefer this one for me. Compare the reasoning rather than the price list.
What should concern you is not disagreement. It is a plan that cannot be explained, or one that will not discuss alternatives.
What we can explain here — and what needs an exam
A page can inform you. It cannot examine you.
We can explain online
Why judgement varies legitimately
What questions to ask both clinicians
What should actually concern you
Determined after an exam
What your specific tooth needs
How much genuine uncertainty exists in your case
What each plan would cost you
What to do next
Bring another plan and we will examine you ourselves and explain what we see. We will not critique a colleague we have not spoken to.