Year 3 Flashcards
(19 cards)
When is caries seen radiographically?
When at least 40% demineralisation of the proximal surface has occurred
How often should bitewings radiograph be taken in the primary dentition?
Low caries risk: 12-18 months
Moderate caries risk: 12 months
High caries risk: 6 months
How often should bitewings radiograph be taken in the permanent dentition?
Low risk: 24 months
Moderate risk: 12 months
High risk: 6 months
What are the two techniques for periapical radiographs?
- The bisecting angle technique
2. The paralleling technique
Describe the paralleling technique
- A technique where the x-ray film is positioned parallel with the long axis of the teeth/tooth to be imaged
- This enables central Ray of the x-ray beam to pass at right angles to the long axis of the teeth and the plane of the film
Describe the bisecting angle technique
- A technique based on geometric theorem of isometric where the central x-ray beam passes through the root of the tooth at right angles to a plane which is the bisector of angle formed by the long axis of the tooth and plane of the film
- This position allows the x-ray beam to cast a shadow of the tooth
What the features that must be incorporated into a film holder?
- A bite block to stabilise and locate the device correctly
- A rigid backing to prevent bending
- An extra oral arm to ensure correct angulation
How is an endodontic film holder modified from a normal film holder?
The dense bite block is replaced with an open basket design to accommodate the rubber dam clamp and endodontic files
State the advantages and disadvantages of paralleling technique
Advantages
1. Minimal elongation/foreshortening/distortion
2. The increased focus-to-skin (FSD) distance reduced surface dose and the penumbra effect
3. Reduction in distortional effects due to bending of film/image receptor
4. Allows the operator to obtain images that have reproducibility and standardisation
Disadvantages
1. Anatomical limitation such a shallow palate (especially in anterior region) preclude true parallel placement of the film relative to the tooth
2. Film holders are uncomfortable for patient and may not be tolerated
What are essential image characteristic in a periapical radiograph?
- There should be no evidence of bending of the teeth and periapical region of interest in the image
- There should be no foreshortening or elongation of the teeth
- Ideally there should be no horizontal overlap (if present should not obscure pulp/root canals)
- The film should demonstrate all the tooth/teeth of interest
- There should be 3mm of periapical bone visible to enable an assessment of apical anatomy
- The should be good dentistry and contrast between enamel and dentine
How does periapical radiography for endodontic differ?
For all molars and maxillary first premolars, two images must be taken to separate super imposed root canals
- One normal paralleling technique film
- One image with a posterior 20 degrees oblique horizontal beam angle
What are indications for a periapical radiograph?
- Assessment of the periodontium, encompassing the periapical and the periodontal status
- Assessment of apical pathology and other lesions within the alveolar bone
- Pre and post operative assessment of alveolar surgery
- Following trauma to teeth and alveolar bone
- Presence/absence of teeth
- Prior to extraction to assess tooth morphology and the relationship of roots to vital structures (eg: inferior dental canal, the maxillary antrum)
- During endodontic therapy
- Pre operative assessment of teeth considered for crowning or bridge placement
- Pre and post operative assessment of implants
When is a vertical bitewing indicated instead of a horizontal bitewing?
When a patient exhibits bone loss of >6mm
What are essential image characteristics of a bitewing radiograph?
- There should be no evidence of bending of the image of the teeth
- There should be no foreshortening or elongation of the teeth
- Ideally there should be no horizontal overlap (if present it should not obscure more than half of enamel thickness)
- The film should cover the distal surface of the canine teeth and the mesial surface of the most posterior erupted teeth
- The periodontal bone level should be visible and equally imaged in the mandible/maxilla
- There should be good density contrast between enamel and dentine
What is the difference between low energy and high energy x-ray?
- Higher energy x-ray: needed to penetrate the patient and reach the film
- Low energy x-ray: do not contribute to image production but add considerably to skin dose
How do we remove unwanted low energy x-ray?
Using aluminium filter of 1.5mm or 2.5mm fitted over portal of the x-ray set
What is the purpose of collimating?
Collimating removes the most peripheral divergent x-rays thus restricting the beam and reducing the radiation dose. This is achieved by using a rectangular collimation.
What clinical finding prompts you to take a vertical bitewing radiograph?
- BPE code of 4 in the sextant to be examined
2. Significant gingival recession
What are the sizes of film and their uses?
- Size 0: for small children and for use in anterior regions with film holder and paralleling technique
- Size 2: adult bitewing and posterior periapical projection
- Occlusal film: to produce large plan views of the maxilla and mandible
* size 1: not routinely used in UK
