Under the Company’s amended and restated certificate of incorporation, the Company’s authorized capital stock consists of 500.0 million shares of common stock with a par value of $0.01 per share and 15.0 million shares of preferred stock with a par value of $0.01 per share. No preferred shares were issued or outstanding as of December 31, 2023 and 2022.

Each share of the Company’s common stock entitles the holder to one vote on all matters to be voted upon by common stockholders. The Company’s Board of Directors (the “Board”) is authorized to issue shares of preferred stock in one or more series and has discretion to determine the rights, preferences, privileges and restrictions, including voting rights, dividend rights, conversion rights, redemption privileges and liquidation preferences, of each series of preferred stock. The Board’s authority to issue preferred stock with voting rights or conversion rights that, if exercised, could adversely affect the voting power of the holders of common stock, could potentially discourage attempts by third parties to obtain control of the Company through certain types of takeover practices.


	Year Ended December 31,
	2023	2022	2021
Common stock - shares issued:
Balance, beginning of period	163.7	162.0	160.2
Issuance of common stock	9.6	1.7	1.8
Balance, end of period	173.3	163.7	162.0

The Company adopted the 2019 Omnibus Incentive Plan (the “Stock Plan”) that provides for the grant of stock appreciation rights, restricted stock units (“RSUs”), and performance stock units (‘PSUs”) (collectively, “Stock Awards”), as well as stock options (“Options”). A total of 21.0 million shares of the Company’s common stock have been authorized for issuance under the Stock Plan. Under the Stock Plan, stock-based grants are awarded at a price equal to the fair market value at the date of grant based upon the closing price on that date. Options and Stock Awards generally vest over a period of three to five years. Options expire ten years after the date of grant.

RSUs issued under the Stock Plan provide for the issuance of a share of the Company’s common stock at no cost to the holder. The RSUs granted to employees provide for time-based vesting, generally over a three to five-year period. Prior to vesting, RSUs granted under the Stock Plan do not have dividend equivalent rights, do not have voting rights and the shares underlying the RSUs are not considered issued and outstanding. PSUs issued under the Stock Plan provide for the issuance of a share of the Company’s common stock based on the achievement of various financial performance metric targets and market conditions, which are set at the time of grant.

The Company accounts for stock-based compensation by measuring all RSUs, PSUs and Options at fair value as of the grant date. The Company recognizes the compensation expense over the requisite service period (which is generally the vesting period but may be shorter than the vesting period if the employee becomes retirement eligible before the end of the vesting period). The fair value for RSU awards is calculated using the closing price of the Company’s common stock on the date of grant. The fair value of the Options granted is calculated using a Black-Scholes option pricing model (“Black-Scholes”).

On December 23, 2021 and January 21, 2022, the Company entered into and finalized, respectively, an RSU agreement with Pacific Dental Services (“PDS”) which awarded PDS RSUs with a fair value of $12.5 million, or 273,522 RSUs, based on the Company’s stock price on December 23, 2021. The RSUs vest over approximately four years and contain performance milestones. All of the 273,522 RSUs remained unvested as of December 31, 2023.


	2023		2022		2021
Risk-free interest rate	3.9 – 4.4%		1.9 – 3.1%		1.0 – 1.3%
Weighted average volatility	35.2	%	33.6	%	25.3	%
Dividend yield	—	%	—	%	—	%
Expected years until exercise	6.0		6.0		6.0

The risk-free rate of interest for periods within the contractual life of the awards is based on a zero-coupon U.S. government instrument with a maturity period that approximates the award’s expected term. The weighted average volatility used in the Black-Scholes model to value Options was estimated based on an average historical stock price volatility of a peer group of companies. The dividend yield was 0.0% as the Company does not offer a dividend. To estimate the option exercise timing used in the valuation model, in addition to considering the vesting period and contractual term of the Option, the Company analyzes and considers actual historical exercise experience for previously granted awards.

The amount of stock-based compensation expense recognized during a period is also based on the portion of the awards that are ultimately expected to vest. The Company estimates pre-vesting forfeitures at the time of grant by analyzing historical data and revises those estimates in subsequent periods if actual forfeitures differ from those estimates. The Company has estimated an annual forfeiture rate of 12.0% for the year ended December 31, 2023 and 6.0% for the years ended December 31, 2022 and 2021.

The Company’s stock-based compensation is primarily recognized as a component of selling, general and administrative expenses in the accompanying Consolidated Statements of Operations. As of December 31, 2023, $27.5 million of total unrecognized compensation cost related to Options and RSUs/PSUs is expected to be recognized over a weighted average period of approximately one year.


	Number of Stock Options	Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value
Outstanding as of December 31, 2020	8.1	$	20.08
Granted	1.7	$	38.15
Exercised	(1.3)	$	15.74
Cancelled/forfeited	(0.6)	$	26.74
Outstanding as of December 31, 2021	7.9	$	24.16
Granted	0.5	$	48.23
Exercised	(1.2)	$	18.61
Cancelled/forfeited	(0.7)	$	30.29
Outstanding as of December 31, 2022	6.5	$	26.24
Granted	0.4	$	38.03
Exercised	(0.6)	$	18.87
Cancelled/forfeited	(0.7)	$	35.19
Outstanding as of December 31, 2023	5.6	$	26.90	5.4	$	13.7
Vested and expected to vest as of December 31, 2023	5.5	$	26.76	5.4	$	13.6
Vested as of December 31, 2023	3.9	$	24.26	4.8	$	12.8


	Outstanding				Exercisable
Exercise Price	Number of Stock Options	Average Exercise Price		Average Remaining Life (in years)	Number of Stock Options	Average Exercise Price
$11.35 to $12.81	0.3	$	12.55	1.5	0.3	$	12.55
$12.82 to $19.49	1.3	$	18.45	3.9	1.3	$	18.44
$19.50 to $26.50	2.2	$	24.19	5.4	1.4	$	24.03
$26.51 to $38.25	1.4	$	36.85	7.2	0.7	$	36.16
$38.26 to $48.52	0.4	$	47.91	7.5	0.2	$	47.48

The intrinsic value of Options is calculated as the amount by which the market price of the Company’s stock exceeds the exercise price of the Option. The aggregate intrinsic value of Options exercised during the years ended December 31, 2023, 2022 and 2021 was $9.0 million, $31.0 million and $33.0 million, respectively.

The following summarizes information on unvested RSU and PSU activity related to the Company’s employees and non-employee directors (in millions; except weighted average grant-date fair value):


	Number of RSUs/PSUs	Weighted Average Grant-Date Fair Value




Unvested at December 31, 2020	1.9	$	22.01
Granted	0.5	$	38.76
Vested	(0.5)	$	20.34
Forfeited	(0.2)	$	26.54
Unvested at December 31, 2021	1.7	$	26.82
Granted	0.6	$	47.80
Vested	(0.5)	$	24.85
Forfeited	(0.3)	$	33.62
Unvested at December 31, 2022	1.5	$	34.85
Granted	1.0	$	39.93
Vested	(0.6)	$	30.93
Forfeited	(0.2)	$	39.44
Unvested at December 31, 2023	1.7	$	38.56

The Company recognizes tax benefits for stock compensation in certain jurisdictions, primarily the United States, where tax deductions are based on market value at exercise or release and may exceed the grant-date value. The Company realized such tax benefits of $1.0 million, $4.0 million and $4.0 million in 2023, 2022 and 2021, respectively, related to the exercise of Options and $1.0 million in each of the years ended December 31, 2023, 2022 and 2021, related to the vesting and release of RSUs and PSUs. For all periods presented, the tax benefits were included as a component of income tax expense and as an operating cash inflow in the accompanying Consolidated Financial Statements.

In connection with the exercise of certain Options and the vesting of RSUs and PSUs, a number of shares sufficient to fund statutory minimum tax withholding requirements has been withheld from the total shares issued or released to the award holders (though under the terms of the applicable plan, the shares are considered to have been issued and are not added back to the pool of shares available for grant). During the year ended December 31, 2023, 214.8 thousand shares with an aggregate value of $8 million were withheld to satisfy the requirement. During the year ended December 31, 2022, 192.4 thousand shares with an aggregate value of $9 million were withheld to satisfy the requirement.