Buccolingual Angulations Of The Alveolar Process Of Jaws Measured By CBCT

Objectives 1) To measure the buccolingual angulation of the alveolar process of jaws based on CBCT images; 2) to investigate prelimilarily the relationship among it and age, sex and tooth loss, in order to help determine the implant angulation in the buccolingual direction at the implant treatment-planning phase.Methods A random sample of 428 CBCT images of patients firstly visiting Department of Stomatology, General Hospital of the Chinese People’s Liberation Army from November 2014 to November 2015, were selected. CBCT images of the maxilla of 98 patients (52 female,46 male) between 18.6 and 68 years of age and of the mandible of 97 patients (53 female,44 male) between 18.3 and 69.7 years of age were included finally. The NewTom 5G CBCT images were reformatted at 0.5-mm thickness and 5-mm spacing, with the inferior border of the regions of interest (ROIs) parallel to the occlusal plane (for the maxilla) or to the inferior border of the mandible (for the mandible). Twenty-four buccolingual cross-sectional images of the alveolar process of each maxilla or mandible were obtained for angulations measurement using NewTom 5G dedicated software NNT version 5.6.Results In the upper jaw, angulations of the alveolar process at cross-section NO.2 and NO.3 being the smallest and at cross-section NO.10 and NO.11 being the greatest, increase statistically from at cross-section NO.4 to NO.10, and then decrease statistically from at cross-section NO.11 to NO.12 (P<0.05). In the lower jaw, angulations of the alveolar process at cross-section NO.2 and NO.3 being the greatest, decrease statistically from at cross-section NO.4 to NO.9 (P<0.05), but the direction the alveolar process at cross-section NO.9 incline is in contrast with that at cross-section NO.9. Angulation of the mandibular alveolar process increase statistically from at cross-section NO.9 to cross-section NO.10 (P<0.05), which is not statistically different from that at cross-section NO.11 and NO.12 (P>0.05). The way in which angulations of the alveolar process change in the left side of the jaws is symmetrical to that of their right counterparts.The proportion of angulations of the buccally inclined alveolar process greater than 30 degrees in the maxillary anterior tooth region varies from 60 percent to 99 percent. The proportion of angulations of the buccally inclined maxillary alveolar process below 20 degrees in the distal part of the premolar region ranges from 58.1 percent to 91.8 percent. Most of the maxillary alveolar process in the molar region inclined buccally within 10 degrees (including 0 degree). The proportion of angulations of the buccally inclined alveolar process below 10 degrees in the mandibular anterior tooth region is over 53 percent. The proportion of angulations of the lingually inclined mandibular alveolar process between 10 and 20 degrees in the distal part of the premolar region is about one half, which is a little bit greater than that of angulations of the mandibular alveolar process below 10 degrees. Most of the mandibular alveolar process in the molar region inclined lingually between 15 and 30 degrees.No statistically significant differences, both between patients younger than 45 and older than 45 and between females and males, were found (P>0.05). Angulations of the mandibular toothless alveolar process are statistically greater than that of the tooth-bearing alveolar process at cross-section NO.3, NO.16 and NO.18 (P<0.05).Conclusions The mean or median buccolingual angulations of maxillary alveolar process decrease from anterior tooth region through the premolar region to the molar region, with the lateral incisor and canine region being the most bucally-inclined and a high proportion of the molar region being nearly vertical. The buccolingual angulations of mandibular alveolar process increase gradually from the anterior tooth region via the premolar region to the second molar region. Most of the mandibular alveolar process cross-sections at the anterior tooth region inclined buccally, while most of those at the premolar region and all of those at the molar region inclined lingually. Known average buccolingual angulations of alveolar process before dental implantation may help the clinician plan the orientation of implants, especially when an implant surgical template is not available.