All data taken from 2009 ADA Survey of Dental Practice series:
Average Full-Time General Practice Salary: $215,120
Average Full-Time Periodontist Salary: $263,200
Average age of Dental School Graduate: 28
Average Total Income produced from age 28-65 for GP: $8,174,560
Average Total Income produced from age 31-65 for Periodontist minus extra tution cost:
Total DebtYearlyTotalNetTotal % more than GP over career-200000$28,475.50 $284,755.01 $9,496,755.01 16.17%-150000$21,356.63 $213,566.25 $9,425,566.25 15.30%-100000$14,237.75 $142,377.50 $9,354,377.50 14.43%-50000$7,118.88 $71,188.75 $9,283,188.75 13.56%-25000$3,559.44 $35,594.38 $9,247,594.38 13.13%-100000$14,237.75 $142,377.50 $9,354,377.50 14.43%0$0.00 $0.00 $9,212,000.00 12.69%10000($1,423.78)($14,237.75)$9,197,762.25 12.52%25000($3,559.44)($35,594.38)$9,176,405.62 12.26%50000($7,118.88)($71,188.75)$9,140,811.25 11.82%100000($14,237.75)($142,377.50)$9,069,622.50 10.95%150000($21,356.63)($213,566.25)$8,998,433.75 10.08%200000($28,475.50)($284,755.01)$8,927,244.99 9.21%
*A negative debt means the program is paying you, rather than you paying tuition
Since most perio programs end up costing, all else being equal you are looking at a ~10-12% greater increase in income over your career. Is an extra 3 years of school and limiting your scope really worth only making 10% more over your career? That's a question you will have to answer for yourself, but definetely not for me...
Remember as well that perio salaries have been declining and are continuing in that trend.
Disclaimer: all data is based on published averages, individual situations may very