Cone-beam computed tomography (CBCT) increases the amount of pre-operative information related to condition and position of regional anatomy and key structures. It provides valuable information on alveolar bone volume and shape as well as vital landmarks such as the inferior alveolar nerve or maxillary sinus, which cannot be interpreted to anywhere near the same level of accuracy when 2-D imaging is used.
A CBCT-based classification of dentoalveolar bone
In the context of orthodontic treatment for skeletally mature patients, evaluation of the dentoalveolar bone thickness in both the crestal and the radicular zone can be crucial to minimize the risk for iatrogenic sequelae. According to a CBCT imaging study evaluating nearly 500 patients, average facial bone thickness was determined to be less than 1 mm in 90 % of the patients evaluated (maxillary first molar to maxillary first molar)1 – underscoring the vulnerability and limitations of the periodontium to certain tooth movements.
In 2013, we published a CBCT-based classification system which categorizes crestal and radicular dentoalveolar bone and helps establish risk prior to interdisciplinary dentofacial therapy cases involving tooth movement.2 The system defines two zones (crestal and radicular) and describes four different dentoalveolar bone phenotypes [thick (>1 mm) or thin (<1 mm) by classifying bone thickness in each zone (fig. 1)2:
- a thick crestal zone and a thick radicular zone
- a thin crestal zone and a thick radicular zone
- a thick crestal zone and a thin radicular zone
- a thin crestal zone and a thin radicular zone
The use of this classification system allows a risk assessment to occur prior to orthodontic tooth movement and can help with the decision as to whether the patient is a candidate for conventional orthodontic therapy or whether alternative orthodontic approaches, such as surgically facilitated orthodontic therapy (SFOT), should be considered.
Surgically facilitated orthodontic treatment
It is well known that moving teeth outside the “orthodontic walls” leads to loss of alveolar bone and increases the risk for iatrogenic sequela.3 However, in the management of malocclusions with dentoalveolar bone deficiencies, leaving the teeth inside the native bone envelope can mean that permanent teeth have to be extracted in order to gain space and correct arch forms. Plus retractive orthodontic schemes to correct the crowded/constricted arch form may induce other problems such as alveolar bone loss and/or result in a net loss of oral cavity volume, which is counterproductive for anterior tongue posturing.4
Therefore, surgically facilitated orthodontic therapy enables management of crowding and dentoalveolar bone deficiencies by arch expansion (vs. retraction), which enhances the orthodontic walls through bone grafting (fig. 2). This approach allows orthodontic decompensations to occur for optimal facial esthetics and function as well as optimization of anterior protected articulation parameters and improvement of oral cavity volume (which may have a positive effect on measureable airway parameters during sleep). Corticotomy based SFOT surgery involves corticotomies and dentoalveolar bone decortication as well as bone augmentation to enhance the orthodontic walls.5,6 It is periodontal ligament mediated and dependent.