July 1, 2000
by Martin J. Bourgeois DDS, M.Ed., Dip. Oral Rad.
The use of dental implants has increased dramatically over the last decade and is becoming the preferred choice of replacing missing teeth over conventional fixed and removable prosthesis.
There are many factors that play a role in the success of implant dentistry. One key factor is pre-surgical assessment of the alveolar ridge as a potential site.
Radiographs can provide the most accurate means to assess the morphology of the alveolar ridge. There are several imaging modalities available to the clinician. Several imaging objectives should enable the clinician to best select the ideal radiographic system.
These imaging objectives are:
— cross-sectional views of the dental arch for visualization of jaw size, orientation of vertical long axis of jaw and internal anatomy
— accuracy of measurements
— bone quality
— presence or absence of pathoses
— transfer of radiographic and clinical information
— readily available at reasonable cost
— minimal radiation exposure to patient
With these objectives in mind, the role of different imaging modalities in pre-surgical implant planning will be discussed. The main advantages and limitations of each technique are discussed.
A: INTRAORAL TECHNIQUE
(periapical and occlusal) (Fig. 1)
Periapical — Advantages:
— approximate vertical height of alveolar ridge can be determined
— best image detail with minimal image distortion
— location of some critical anatomic structures (eg: mental foramen, inferior dental nerve canal & maxillary sinus)
— some information about bone quality (density, trabecular pattern) and presence/absence of pathoses is revealed
— films readily available to clinician
— low cost to patient
— limited area viewed on a single film
— some distortion
— two-dimentional view
— no buccal-lingual or horizontal dimension of alveolar ridge nor bone volume information is revealed
— no accurate assessment of vertical bone dimension or the “precise” location of anatomic structures.
Occlusal (Fig. 2) — Advantages:
— best image detail
— indication of buccal-lingual dimension of mandible
— determination of jaw size, jaw curve at proposed implant site
— readily accessible to clinician
— low cost to patient.
— only reveals maximum buccal-lingual dimension and not medial and lateral extent of cortical bone
— two dimensional
EXTRAORAL TECHNIQUES: (panoramic, lateral ceph, cross-sectional tomography, computed tomography)
B: PANORAMIC (Fig. 3)
— excellent “screening” film for pre-surgical implant planning
— readily accessible: low cost to patient
— minimal radiation dose
— demonstrates presence/absence of pathoses
— indication of anatomic spatial relationship.
— little or no information about width or ridge inclination
— magnification is not uniform in a vertical or horizontal direction
— poor resolution and presence of artifacts may limit diagnostic accuracy
— image distortion (technique sensitive to patient positioning errors)
— two dimensional image
— inability to modify angulation of central ray.
C: LATERAL CEPH (Fig. 4)
— height/width information is revealed in the anterior mandible/maxilla
— images are cross-sectional images
— low radiation dose; low cost to patient
— image magnification is constant
— limited use (anterior region only)
— superimposition of structures
— reveals only maximum buccal-lingual width and not depression in ridge
D: CROSS-SECTIONAL TOMOGRAPHY (Fig. 5) (eg: Scanora, CommCAT)
— produces cross-sectional images of specific proposed implant sites
— assessment of bone height, width and inclination of ridge
— assessment of bone quality
— determination of anatomic spatial relationship
— exact imaging and detailed view of specific implant site
— little or no superimposition
— selection of varying slice thickness and slice location
— relatively low exposure to patient
— development of treatment planning software for certain imaging systems
— equipment cost
— recommends availability of trained Oral Radiologist to perform imaging and calculate bone dimensions
— time consuming when multiple sites are indicated
— transfer of radiographic information to clinical site may necessitate imaging stent
— variable definition of specific anatomic structures dependent of imaging system and availability
E: COMPUTED TOMOGRAPHY (C.T.) (Fig. 6)
— assessment of bone height, width, ridge inclination, bone quality, anatomic spatial relationship
— less time consuming for multiple sites
— images free from superimposition
— better contrast sensitivity than film tomography
— availability of treatment computer software
— 3-D reformation of images possible with appropriate software.
— degradiation of image by metallic restorative materials (amalgam, crowns, post, pins) known as “scatter”
— patient movement including swallowing results in distortion of image – cost to patient
— difficulty in accessibility (C.T. units usually limited Hospital)
— higher radiation exposure to patient as compared to cross sectional film tomography
In the past, potential implant patients were assessed radiographically with panoramic,intra-oral and cephalometric radiographs. These radiographs revealed to the clinician a gross determination of the hieght of the alveolar ridge and the ability to identify anatomical structures; in particular the inferior dental nerve canal. Accurate measurements were difficult with these techniques. The need for cross sectional visualization of the alveolar ridge, accurate measurements, and the visualization of internal anatomy such as inferior dental nerve canal and the maxillary sinus made the development of specific tomographic units for dental implant imaging more immediate.
Alongside this development was the emergence of a specific dental software system (Dentascan) for Computed Tomograhy (C.T.). Today, the clinician has the availability of advanced dental implant imaging systems as well as specific implant planning software to enable appropriate presurgical planning for implant dentistry. The field of imaging for dental implants is growing as the demand from patients and clinicians is pressing. With new technologies, we are able to better prepare our patients for implant dentistry with less potential risks and complications leading to an increased success and patient satisfaction with implant dentistry.
Dr. Bourgeois maintains a private practice, specializing in Oral & Maxillofacial Radiology in Toronto, ON.
Oral Health welcomes this original article.
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