Method and system for finding tooth features on a virtual three-dimensional model
A method and system are disclosed for finding virtual tooth features on virtual three-dimensional models of the teeth of patients. The tooth features comprise marginal ridges, cusp tips, contact points, central groove and buccal groove. Tooth axes system plays a key role in identifying the tooth features. An iterative method is disclosed for improving the accuracy of the tooth axes system. A virtual three-dimension model preferably obtained by scanning the dentition of a patient forms the basis for determining the tooth features. Tooth features are derived for all categories of teeth including molars, premolars, canines and front teeth. Tooth features are very helpful and used in planning orthodontic treatment. The tooth features are determined automatically using the computerized techniques; and can be manually adjusted when necessary.
1. A method of digitally finding one or more ridge points on the occlusal surface of a virtual three-dimensional model of a tooth using a workstation, comprising the steps of:
(a) obtaining a virtual three-dimensional model of a tooth from scanned images of said tooth; wherein said virtual three-dimensional model of said tooth has a mesial direction, a distal direction, a buccal direction, a lingual direction, an occlusal direction, and a gingival direction; wherein said virtual three-dimensional model of said tooth further has an occlusal surface and a bottom, wherein said bottom is opposite said occlusal surface;
(b) defining a tooth axes system (TAS) for said virtual three-dimensional model of said tooth; wherein said TAS comprises an origin, an x-axis in the mesial and distal directions, a y-axis in the buccal and lingual directions and a z-axis in the occlusal and gingival directions;
(c) defining a plane containing said z-axis from said TAS, said plane intersecting the entire surface of said virtual three-dimensional model of said tooth, thereby showing a curve formed along the surface of said three-dimensional model of said virtual three-dimensional model of said tooth; and
(d) tracing said curve from the bottom of said virtual three-dimensional model of said tooth (i) starting on one side of said curve with a moving tangent until said tangent becomes horizontal thereby finding a ridge point on the surface at the location where said tangent touches said curve; and (ii) then starting on the other side of said curve with a moving tangent until said tangent becomes horizontal thereby finding a ridge point on the surface at the location where said tangent touches said curve.
2. The method of claim 1 , after step (d) of claim 1 , further comprising the steps of:
(i) rotating said plane around said z-axis by an angle, said plane intersecting the entire surface of said virtual three-dimensional model of said tooth, thereby forming a curve along the surface of said virtual three-dimensional model of said tooth;
(ii) performing step (d) of claim 1 ; and
(iii) repeating steps (i) and (ii) until the entire surface of said virtual three-dimensional model of said tooth has been explored, thereby finding a family of ridge points for said virtual three-dimensional model of said tooth.
3. The method of claim 2 , further comprising the steps of:
(i) dividing the surface of said virtual three-dimensional model of said tooth into two halves, wherein said virtual three-dimensional model of said tooth has a mesial side in said mesial direction and a distal side in said distal direction, a first half on the mesial side of said virtual three-dimensional model of said tooth, and a second half on the distal side of said virtual three-dimensional model of said tooth;
(ii) identifying a first set of ridge points comprising ridge points located in said first half from said family of ridge points, and a second set of ridge points comprising ridge points located in said second half from said family of ridge points;
(iii) finding a first minimum ridge point from said first set of ridge points, and a second minimum ridge point from said second set of ridge points; and
(iv) identifying two marginal ridges for said virtual three-dimensional model of said tooth wherein said two marginal ridges comprise said first minimum ridge point and said second minimum ridge point.
4. The method of claim 3 , further comprising the step of:
(i) dividing said family of ridge points for said virtual three-dimensional model of said tooth into two subsets, wherein said virtual three-dimensional model of said tooth has a buccal side in said buccal direction and a lingual side in said lingual direction, wherein each subset is bounded by the two marginal ridges, one subset of ridge points at the buccal side of said virtual three-dimensional model of said tooth, and the other subset of ridge points at the lingual side of said virtual three-dimensional model of said tooth;
(ii) finding local maxima of the subset of ridge points at the buccal side of said virtual three-dimensional model of said tooth and local maxima of the subset of ridge points at the lingual side of said virtual three-dimensional model of said tooth; wherein said local maxima has maximal z-coordinate; and
(iii) identifying buccal cusp tips and lingual cusp tips; wherein said buccal cusp tips are defined by the local maxima of the subset of ridge points at the buccal side of said virtual three-dimensional model of said tooth, and said lingual cusp tips are defined by the local maxima of the subset of ridge points at the lingual side of said virtual three-dimensional model of said tooth.
5. The method of claim 1 , wherein said tooth is a molar.
6. The method of claim 1 , wherein said tooth is a premolar.
7. The method of claim 2 , wherein said angle is 15 degrees.