1. Ala'a Otaibi, 2013
2. Category-1: Excessive wear with loss of VDO
   1. In a typical category-1 patient (loss of VDO), the closest speaking space is more than 1 mm and the interocclusal space is more than 4 mm and has some loss of facial contour that includes drooping of the corners of the mouth.
   2. The reliable method to confirm the diagnosis and to determine a physiologic VDO is placement of trial restorations.
      1. At first, a removable splint or partial denture is placed and observed periodically for 6-8 weeks.
      2. Fixed provisional restorations are placed for another 2-3 months before planning permanent restorations. A removable trial restoration cannot be solely relied because the patient may have removed the prosthesis during periods of stress, fatigue, and soreness associated with excessive OVD. Heat-polymerized acrylic resin is satisfactory for provisional restorations.
3. Category-2: Excessive wear without loss of VDO but with space available
   1. Patients in category-2 typically have a long history of gradual wear caused by bruxism, moderate oral habits, or environmental factors. In these patients, the OVD is maintained by continuous eruption. Tooth preparation to establish retention and resistance form may be critical because of shorter crown length. Gingivoplasty may be needed to gain clinical crown length. Enameloplasty of opposing posterior teeth may provide some space for the restorative materia
4. Category-3: Excessive wear without loss of VDO but with limited space
   1. In patients of category-3, there is excessive wear of anterior teeth, which has occurred over a long period, and there is minimal wear of the posterior teeth. Centric relation and centric occlusion are coincidental with a closest speaking space of 1 mm and an interocclusal distance of 2-3 mm. In such cases vertical space must be obtained for restorative materials. This can be accomplished by orthodontic movement, restorative repositioning, surgical repositioning of segments, and programmed OVD modification.