TOPIC: BISECTING LINE ANGLE TECHNIQUE
🌟 IMPORTANT POINTS TO REMEMBER
🔹Bisecting line angle technique is also called short cone technique.
🔹Cieszynski rule: This rule states that two triangles are equal when they share one common side and have two equal angles. The central ray of the X-ray beam and the imaginary bisector result in formation of two congruent right-angled triangles.
🔹Maxillary radiograph: While taking a maxillary radiograph, the head should be positioned downward so that the line drawn from ala of the nose to tragus of the ear (ala–tragus line) is parallel to the floor. This is also called an upper horizontal baseline.
🔹Mandibular radiograph: While taking the mandibular radiograph, the chin should be moved upwards so that the line drawn from the corner of the mouth to the tragus of the ear should be parallel to the floor. This is also called a lower horizontal baseline.
🔹Incisor and canine: The long axis of the film should be placed vertically.
🔹Premolar and molars: The long axis of the film should be placed horizontally.
🔹About 2 mm of the film packet should extend above the incisal or occlusal edge to ensure that the entire tooth appears on the film.
🔹Different film holders used in bisecting line angle technique are Snap-A-Ray film holder, Rinn BAI and patient’s finger as film holder.
🔹Incorrect vertical angulation results in foreshortening (increased vertical angulation, shortening of the image occurs) and elongation (less vertical angulation is given, the image will be elongated).
🔹If the horizontal angulation is incorrect, then there is overlapping in the proximal contact area, leading to difficulty in the detection of initial proximal caries in that area.
🔹Maxillary projection: Horizontal plane – a line drawn from the ala of the nose to the tragus of the ear is used as a reference line, and all the points of entry should fall on this plane only.
🔹Vertical plane – this differs from teeth to teeth. X-ray cone should be positioned at a point where both the vertical and horizontal planes meet each other for the respective tooth.
🔹Mandibular projection: Horizontal plane – the centre of the X-ray cone should be 1 cm above the lower border of the mandible.
🔹Vertical plane – it is the same as that of maxillary projection.
🔹Le Master technique: It is the modification of the bisecting angle technique which is done in the case of prominent malar bone. The cotton roll is fastened in the front side of the film, which rests against the palatal surface of the molars making the mean plane of the film more parallel to the plane of the tooth.
📌 ADVANTAGES AND DISADVANTAGES OF BISECTING LINE ANGLE TECHNIQUE
💡 ADVANTAGES:
🔸Comfortable positioning of film: Positioning of the film packet is comfortable for the patient in all areas of the mouth
🔸Simple method: Positioning is relatively simple and quick. It does not require film holders
🔸Adaptation: It can be adapted according to the shape of most dental arches
🔸No sterilization: No sterilization of holders is required as they are not used
🔸Decreased exposure time: Less exposure time is required as short PID is used
🔸Uncooperative patient: It can be easily undertaken in uncooperative patients as less exposure time is required
🔸If all angulations are assessed correctly, the image of the tooth will be of the same length as that of the tooth itself and of adequate diagnostic purpose
💡 DISADVANTAGES:
🔸Image distortion: The various variables involved in the technique may result in a distorted image. Another reason behind this is that the film and the object are not parallel to each other and X-rays are not perpendicular to the film and the object
🔸Foreshortening and elongation: Incorrect vertical angulations result in foreshortening or elongation of the image. When the projection of the X-ray beam is done from increased vertical angulation, the images appear as foreshortened, and if the X-ray tube head is positioned at decreased vertical angulation, then the resultant image will be elongated
🔸Periodontal bone level: The periodontal bone levels are poorly represented
🔸Overlapping of shadow of zygomatic bone: The shadow of the zygomatic bone is generally superimposed over the roots of the maxillary molars
🔸Angulation problems: The horizontal and vertical angles have to be assessed for every patient and considerable skill is required
🔸Not reproducible: It is not possible to obtain a reproducible view
🔸Cone cutting: Coning off or cone cutting may result if the central ray is not aimed at the centre of the film
🔸Overlapping in proximal area: Incorrect horizontal angulations can result in overlapping of the crowns and roots
🔸Distorted crown: The crown of the teeth is often distorted, thus preventing the detection of proximal caries
🔸Foreshortened buccal roots: The buccal roots of the maxillary premolars and molar appear foreshortened