The Use of Three-Dimensional Reconstructions in the Diagnosis of Impacted Teeth

Introduction

The incidence of fully impacted teeth is reported to vary between 5-20% in the general population (Grover & Lorton L, 1985, Frank, 2000). The overwhelming majority of impacted teeth involve third molars, followed by maxillary canines and mandibular second premolars. While most of the other teeth in the upper and lower jaws can also be affected, the incisors and first molars in the mandible are very rarely impacted (Grover & Lorton L, 1985, Dachi & Howell 1961).

A special category of impacted teeth are supernumerary teeth that can be present in various forms and in any region of the mandible or maxilla, but have a predisposition for the anterior maxilla (Scheiner & Sampson, 1997). The prevalence of supernumerary teeth in the permanent dentition has been reported to be between 0.1% and 3.8% (Rajab & Hamdan, 2002, Schulz et al., 2009). The most widely accepted pathogenetic theory is that the tooth bud splits into two (dichotomy) equal or different-sized parts, developing into two teeth of normal size, or one normal and one dysmorphic type, as a result of local, independent, conditioned hyperactivity of the dental lamina (Taylor, 1972). Supernumerary teeth can occur as single, multiple, unilateral or bilateral entities in one or both jaws and are classified according to location-related, size-related or shape-related characteristics (Ooshima et al., 1996).

Principally, the treatment of impacted teeth is based on four concepts: observation, intervention, relocation or extraction (Frank, 2000, Kokich & Mathews, 1993). Observation implies no treatment for a specific period of time. This time period can be further subdivided in a preimpaction and postimpaction phase. Trained dentist are therefore able to either predict tooth impaction (during the preimpaction observation period) or anticipate pathological sequelae associated with impacted teeth (in the postimpaction observation period). Intervention involves orthodontic procedures to establish adequate space in the dental arch that enables eruption. Theses procedures are often performed in combination with removal of hard- and soft-tissue obstructions form the eruption path of the impacted teeth (Ohman & Ohman, 1980, Shapira et al. 1996). Relocation implies active orthodontic movement of the impacted teeth or even surgical reposition (autotransplantation; Schatz & Joho, 1994). Finally, if impacted teeth cannot be repositioned in the alveolar process using treatment strategies mentioned above, their removal might be indicated.

In orthodontics, three-dimensional (3D) structures have been routinely analyzed using on two-dimensional (2D) imaging. Besides conventional intraoral radiographs, cephalometric imaging and panoramic views were applied on a routine basis for diagnostic and treatment planning purposes (Hechler, 2008). To diagnose and to locate impacted teeth accurately, periapical and occlusal radiographs were the radiographic methods of choice for decades. Orthodontists have used the tube shift technique to compare two periapical radiographs taken at different beam angles to determine the facial/oral position of impacted teeth, and also to base surgical and/or orthodontic treatment planning upon. Although the „same lingual, opposite buccal“ rule is helpful in determining whether the impacted tooth is positioned buccal or oral to the roots of the neighbouring teeth, it has clear limitations when assessing the exact angulation of the impacted tooth and possible crown/root proximities with or without resulting root resorptions. (Jacobs, 1999).