Guide
Misch bone density classification (D1–D4) and Hounsfield units
The Misch classification groups jaw bone into four density classes, D1 (dense cortical) to D4 (fine trabecular), with D5 sometimes added. Ranges often quoted are D1 above 1250 HU, D2 850–1250, D3 350–850 and D4 150–350. On CBCT these numbers are only relative, because CBCT gray values are not calibrated Hounsfield units.
The four classes
| Class | Description (tactile/structural) | Commonly quoted CT range |
|---|---|---|
| D1 | Dense cortical bone | > 1250 HU |
| D2 | Thick porous cortical over coarse trabecular bone | 850–1250 HU |
| D3 | Thin porous cortical over fine trabecular bone | 350–850 HU |
| D4 | Fine trabecular bone, little cortex | 150–350 HU |
| D5 | Very soft, incompletely mineralised bone (sometimes added) | < 150 HU |
The classification was described by Carl E. Misch in the late 1980s and 1990s in the implant dentistry literature, based on tactile and radiographic assessment; the HU ranges were later associated with it using medical CT.
Why CBCT values are not true Hounsfield units
Important: CBCT gray values vary between scanners, exposure settings, field-of-view size and position within the volume, and are affected by scatter and artifacts. They cannot be compared directly with medical CT Hounsfield units or with values from another scanner.
Medical CT is calibrated so that water is 0 and air is −1000. Most CBCT units do not guarantee this calibration across the volume. The same bone can show different values in two scans, or at the centre and edge of one scan. That is why the D-class shown from a CBCT should be read as a relative indication at most.
How Ossidex shows D-class
In Ossidex, the HU probe shows the value under your finger and, as a reading aid, the Misch class that value would fall into using the ranges above. On medical CT the value is a Hounsfield unit derived from the DICOM rescale parameters. On CBCT it is the scanner’s gray value, with the caveats above. Use it to compare regions within the same scan, not as a measured bone quality.
Using density values sensibly
- Compare within one scan, at similar depth and away from metal artifacts.
- Use an ROI (mean over an area) rather than a single pixel, which is noisy.
- Remember that density is only one factor clinicians consider; it does not replace clinical judgement.
Where the classification comes from
Carl E. Misch described bone quality in four main groups (D1–D4) from how bone feels during drilling and how it looks on radiographs, and later linked them to typical Hounsfield ranges measured on medical CT. A fifth group, D5, is sometimes used for very soft, immature bone. The classes are descriptive: they summarise the ratio of dense cortical to porous trabecular bone at a site.
Typical locations
| Class | Description | Where it is often described |
|---|---|---|
| D1 | Dense cortical bone | Anterior mandible, especially in resorbed ridges |
| D2 | Thick porous cortex with coarse trabeculae | Anterior and posterior mandible |
| D3 | Thin porous cortex with fine trabeculae | Anterior maxilla, posterior mandible |
| D4 | Fine trabecular bone, little cortex | Posterior maxilla |
These are general tendencies reported in the literature, not rules for an individual patient.
Reading values with the HU probe
- Open the site on a cross-section. Build the arch (Pro) or use MPR so that the slice runs through the area you want to look at.
- Place the probe. Choose the HU probe in the side menu and touch the bone. The value under your finger appears with the class that value would fall into.
- Sample several points. Values vary between cortex and trabecular bone and from slice to slice. Look at a few points rather than one.
- Compare within the same scan. Relative differences inside one CBCT (for example between two sites) are more meaningful than absolute numbers.
Common pitfalls
- Metal nearby. Crowns, implants and posts create streaks that raise or lower values next to them.
- Edge of the field of view. Values drift towards the edges of a small CBCT volume.
- Different machines. The same bone can read differently on two CBCT units; do not compare numbers across scanners.
- Partial volume. On thin cortical plates a single voxel may mix bone and soft tissue.
Frequently asked questions
What is D2 bone?
In the Misch classification, D2 is thick porous cortical bone over coarse trabecular bone, commonly associated with roughly 850–1250 HU on medical CT.
Can I get Hounsfield units from a CBCT?
You get gray values, which some scanners scale to resemble HU. They are not calibrated like medical CT and should be treated as relative.
Does Ossidex measure bone density?
It displays pixel values and the matching Misch class as a reading aid. It does not calculate bone quality or recommend treatment.
Related pages
DICOM measurements and PDF reports on iPhone and iPad
Measure length, angles and Hounsfield units on CT, CBCT and MRI in Ossidex, annotate the view, and export an image or a one-page PDF report, anonymized.
Reviewing a CBCT before an implant
Before an implant, review CBCT arch views, cross-sections, ridge dimensions, canal and sinus proximity, then plan it in the Ossidex app on iPhone or iPad.
Dental CBCT viewer
Panoramic arch, cross-sections, MPR and 3D for cone beam CT from any scanner.
Dentists
CBCT from any scanner at the chair: arch, cross-sections, MPR, 3D and TMJ MRI.