Buccal Object Rule - A Radiographic Aid in Dental Practice.

In this lecture we explain to you, in simple terms, the buccal object rule or what's known as SLOB rule (same lingual, opposite buccal).
This rule is very helpful radiographic aid, that many clinicians use in daily routine.
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1. Buccal Object Rule

For localizing objects in oral cavity in the buccal and palatal dimentions

[ Iraqi Dental Academy 4 ida_lectures

2. Definition

m Buccal object rule is a a rule that can be used to localize

superimposed objects in radiograph.

m It's used when we have two objects, one behind the other, and

we want to know their relative location (buccal/lingual).

m It's first described by Clark in 1909, when he suggested taking
three radiographs (Central, Mesial, Distal) and comparing them
together. The rule has been redefined and expanded by
Richards in 1953 and again in 1980.

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3. Definition

m Modern Buccal Object Rule uses two radiographs and
sometimes only one. Using some landmarks and tips only one
radiograph is enough to differentiate between mesiobuccal

canal and lingual canal in Endodontics.

m It also known as SLOB Rule (Same Lingual, Opposite Buccal),
Clark's Rule, and Walton's Projection.

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4. Applications

m Ithas many applications in:

» Endodontics (locating roots, canals, calcifications, perforation)
> Orthodontics & Pedodontics (impacted teeth, impacted canine)
» Oral Surgery & Trauma Cases (foreign objects, impacted teeth)
> In any bucco-lingual localization in oral cavity and extraoral

structures.

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5. Concept

m When taking radiograph of two objects one behind other at
straight line, the objects will be superimposed, and radiographic

landmarks can not be distinguished.

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6. Concept

m By tilting the x-ray cone mesially or distally, the radiographic
landmarks will not be superimposed anymore. We can compare
between first and second radiographs to know which one is the

palatal and which one is the buccal.

m The start position of both object is superimposition, so when
titling x-ray cone mesially (or distally) one object will be on

mesial and other will be on distal (no superimposition).

m The object that moved the same as x-ray cone direction is the
(palatal) object and the object that moved on opposite direction

of x-ray cone is the (Buccal) object.

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7. Concept

m This can be memorized by remembering the word SLOB
(same lingual, opposite buccal).
As seen in following photos:

rasta eae

E

distal

1 @ o.

wi due

distal *————— mesial distal *———— mesial

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8. Concept

m The reason for this phenomenon is that the object that is close
to the x-ray cone will be affected much by cone movement,
while the object lies on lingual will be affected very little to
movement because it's very close to the radiographic film

(it's position almost static on radiogrphic film).

m The buccal object will be always on the same direction as x-ray
beam (opposite direction of x-ray cone) (note that x-ray cone
and beam two different concepts, one on the opposite direction
of other. When moving cone mesially we directing x-ray beam

distally, and vice versa.).

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9. BOR in Endodontics

m It has many useful applications in Endodontics:

» Distinguish between normal anatomical landmarks and
pathogens associated with root/tooth.

» Determine the buccal/lingual position of perforation,
radiolucency, and fracture.

» Locating anatomical landmarks in periapical surgery.

» Determine the number, size, shape and direction of

canals/roots.

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10. BOR in Maxillary Arch

m It's most important in locating roots/ canals of maxillary molars.
m These are some rules and tips for Maxillary Molars radiography:
> When taking radiograph at straghit line to maxillary molars

the palatal root will be seen between mesiobuccal and

distobuccal roots

STRAIGHT ON

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11. BOR in Maxillary Arch

» When titling x-ray cone mesially the palatal root will be close
to mesiobuccal root. The palatal root lies in mesial direction and
the mesiobuccal root lies distal to palatal root. As seen in

following photo:

$ B
MESIAL

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12. BOR in Maxillary Arch

> When titling x-ray cone distally the palatal root will be close to
distobuccal root. The palatal root lies in distal direction and the

distobuccal root lies mesial to palatal root.

Y 4
DISTAL

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13. BOR in Maxillary Arch

» Sometimes when the canine is seen in the radiograph of

maxillary molars that's a clue that x-ray cone was mesially titled.

» When teeth contact point overlap on radiograph that's a clue the

cone was titled either mesially or distally but not straight on.

» Many buccal root apices are titled distally, and many palatal
roots apices titled mesially. and most single rooted teeth apices
are titled distally So when taking radiograph with mesial
inclination, the apices of single rooted teeth and buccal roots
will tilt distally (because of elongation)(distal beam and distal

original inclination of apices results in elongation).

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14. BOR in Maxillary Arch

» Zygomatic Process (which lies buccally to teeth) will move in

opposite direct in relation to x-ray cone.

» Because the x-ray was taking from positive vertical angle
(10 to +45), the palatal root will be more elongated than buccal

roots. This rule will be explained more in the next slide

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15. Vertical Angulation

m Most books and literature describe cone movement in horizontal
direction (mesial/distal), but what vertical angle of x-ray cone

has effect on radiographic landmarks?

m Asageneral rule, when titling cone vertically (upward,downward),
the lingual/palatal object will move the same direction, while the

buccal object moves to opposite direction.

m So when using positive angulation (upward) the lingual/palatal

objects moves up, while buccal objects moves down.

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16. Vertical Angulation

m in Maxillary teeth:

» Most maxillary radiographs are taking at positive
angulation (10 to +45).

»- As angle increased, the distortion or elongation is increased.

> if the radiograph was taking from positive angle, the palatal
root will be longer in maxillary teeth. So, the longer root is
the palatal always.

» also the lingual cusp will be shorter by same effect.

> And the lingual portion of rubber dam clamps is the most

apical one.

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17. Vertical Angulation

m in Mandibular Teeth :

» Most mandibular radiographs are taking at negative
angulation (O to 10).

» This give shorter root length (and shorter tooth), especially
in the area of second and third molars.

» Most lower teeth crown is titled toward the tongue, therefore,
a positive vertical angle will give normal length of roots/teeth.

» Also, the ill-defined border of filling in molars will look more

sharp on film now.

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18. BOR in Mandibular Arch

The buccal cusp of premolars is the highest, and will move

opposite direction of x-ray cone.

Sometimes when the canine is seen in the radiograph of
mandibular molars that's a clue that x-ray cone was mesially
titled.

When teeth contact point overlap on radiograph that's a clue the

cone was titled either mesially or distally but not straight on.

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19. BOR in Mandibular Arch

The lingual roots (if any) will move same direction as x-ray cone.

Buccal roots will be opposite.

MESIAL

If the mental foramen is visible, the radiograph was probably
made from the distal.
The lingual portion of rubber dam clamp will move same as x-ray

cone.

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20. Examples

m In this xray of maxillary second premolar, the cone was titled
mesially. Therefore, the palatal canal is mesial, and buccal

canal is distal.

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21. Examples

m Same tooth was taken by x-ray but with distal titled cone.

Therefore, palatal canal is distal, and buccal canal is mesial.

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22. Examples

m In this x-ray of mandibular first molar, the cone was titled
mesially. Therefore, the lingual root is mesial, and the buccal

root is distal.

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23. Examples

m Same tooth was taken by x-ray but with distal titled cone.

Therefore, lingual root is distal, and buccal root is mesial.

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24. Examples

m When denstist took routine dental radiograph he noticed a
foreign body on x-ray. when he moved x-ray cone distally,

foreign object moved mesially. Later he found the foriegn object

in the cheek (buccal)
dE ‘3e

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25. Image Shift Technique

m It's based on the same principle as BOR, but in this technique
two radiograph is taken for the questioned tooth/object
without titling x-ray cone, only changing the position of x-ray

cone.

m We study movement of "the object" in relative to movement of

other objects on x-ray.

m The object in question, if located buccally, will move more in the

radiograph than objects located lingually. See the follwoing
photos:

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26. Image Shift Technique

m As seen in the above photos, the foreign object moved from
1st premolar location to 2nd premolar location, this indicate the

foreign body is located buccally, beacuse it moved too much in
relative to other objects on x-ray film.

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27. References

m A Method of ascertaining, the Relative Position of Unerupted
Teeth by means of Film Radiographs. Charles A. Clark.

m À Simplified Look at the Buccal Object Rule in Endodontics,
Journal of Endodontics, Vol. 13, N- 12, December 1987

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28. Thank You

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