One drop!

In the past, people of a certain generation (mine!) had a phone attached to a land line, and a camera into which a reel of film was inserted upon which to record the images. Incorrect focus or inappropriate directioning of the camera resulted in a wasted film! For the benefit of young readers, illustrations can be seen in Figure 1!

Today, I don't need to tell readers that these functions are combined into one device, the ubiquitous mobile phone – with functions as diverse as phone (obviously!), payment device, clock, alarm, map reader, calculator, game host, music store, text messager, device for watching/downloading videos, and many more.

In the past, dentists of a certain generation thought that a bonding agent was a bottle of unfilled resin (often methylmethacrylate and, later, BisGMA). This bonded to etched enamel, but not to dentine. I recall using an early dentine bonding agent that comprised five different bottles of reagent, to be used in a certain order, but not numbered appropriately. As a result, in those days, the chance of successful bonding (even if the material was efficacious) was low! The early understanding of the smear layer (that layer on the instrumented dentine surface principally containing hydroxyapatite, collagen debris and bacteria) was poor, insofar that manufacturers developed reagents that were good wetting agents, thereby wetting and penetrating the dentine surface, but, alas, they later discovered that the smear layer was not well attached to the underlying dentine, thereby rendering the bond strengths to dentine of this group of early bonding agents suboptimal, very poor being probably being more truthful.