This excerpt taken from the XRAY DEF 14A filed Apr 12, 2007.
Change in Control
Immediately upon a Change in Control (as defined in the Equity Incentive Plan), all outstanding Options and Stock Appreciation Rights, whether or not otherwise exercisable as of the date of such Change in Control, will become fully exercisable and all restrictions thereon will terminate in order that optionees may fully realize the benefits thereunder, and all restrictions and conditions on all Restricted Stock and Restricted Stock Units granted to Key Employees or Outside Directors shall lapse upon the effective date of the Change of Control. The Committee may determine in its discretion (but shall not be obligated to do so) that any or all holders of outstanding Options and Stock Appreciation Right Awards which are exercisable immediately prior to a Change of Control (including those that become exercisable upon the Change in Control) will be required to surrender them in exchange for a payment, in cash or Common Stock as determined by the Committee, equal to the value of such Options and Stock Appreciation Rights (as determined by the Committee in its discretion), with such payment to take place as of the date of the Change in Control or such other date as the Committee may prescribe. The acceleration described above also applies if following a reorganization, merger or combination in which new shareholders comprise at least forty-five percent (45%) of the ownership of the Common Stock or voting power in the Company, a Key Employee grantees employment is terminated other than for Cause (as defined in the Plan) or if a Key Employee grantee voluntarily terminates his or her employment in certain circumstances.