Control arrangement for controlling an external computer having a display functionally connected thereto, the external computer being connectable to a dental unit (102, 104) and, when connected, constituting a dental apparatus, comprising said external computer and its display, said dental unit (102, 104), and said control arrangement including control means (112, 116, 117) configured to control functions of at least said external computer and said dental unit (102, 104), wherein said control of functions of said dental unit includes transmitting a control signal to a digital data processing unit of said dental unit (102, 104) with said digital data processing unit being configured to control instruments connected to said dental unit, wherein at least part of the control means configured to control functions of said external computer is arranged in connection with said dental unit (102, 104) and is arranged at least as bi-functional such that it is configured to control said external computer on the one hand and to control at least said dental unit (102, 104) on the other hand, wherein said control means configured to control the external computer is configured such that control information for controlling a cursor to be presented on the display of the external computer are transmitted by said control means, and wherein said control means configured to control the external computer comprise a touch pad having a contact surface, wherein said touch pad is configured to transmit control information for controlling the operation of the cursor presented on the display of the external computer in response to moving and/or touching operations performed with a pointing device on the surface of said touch pad, characterized in that said bi-functionality of the control means is implemented by one of that an operating mode of said touch pad is changeable from computer control mode to dental unit control mode and an area is arranged to the said contact surface, said area being configured to transmit a control signal of change of the operating mode of the control means from computer control mode to dental unit control mode and vice versa, and arranging said control means to comprise a contact surface in which a first area has been arranged for transmitting signals to be used to control the computer and a second area for transmitting signals to be used to control the dental unit (102, 104). said external computer and its display, said dental unit (102, 104), and said control arrangement including control means (112, 116, 117) configured to control functions of at least said external computer and said dental unit (102, 104), wherein said control of functions of said dental unit includes transmitting a control signal to a digital data processing unit of said dental unit (102, 104) with said digital data processing unit being configured to control instruments connected to said dental unit, wherein at least part of the control means configured to control functions of said external computer is arranged in connection with said dental unit (102, 104) and is arranged at least as bi-functional such that it is configured to control said external computer on the one hand and to control at least said dental unit (102, 104) on the other hand, wherein said control means configured to control the external computer is configured such that control information for controlling a cursor to be presented on the display of the external computer are transmitted by said control means, and wherein said control means configured to control the external computer comprise a touch pad having a contact surface, wherein said touch pad is configured to transmit control information for controlling the operation of the cursor presented on the display of the external computer in response to moving and/or touching operations performed with a pointing device on the surface of said touch pad, characterized in that said bi-functionality of the control means is implemented by one of that an operating mode of said touch pad is changeable from computer control mode to dental unit control mode and an area is arranged to the said contact surface, said area being configured to transmit a control signal of change of the operating mode of the control means from computer control mode to dental unit control mode and vice versa, and arranging said control means to comprise a contact surface in which a first area has been arranged for transmitting signals to be used to control the computer and a second area for transmitting signals to be used to control the dental unit (102, 104).