Influence of bone anatomical morphology of mandibular molars on dental implant based on CBCT

Abstract

Background: To apply CBCT to investigate the anatomical relationship between the mandibular molar and alveolar bone, aimed to provide clinical guidelines for the design of implant restoration.

Methods: 201 CBCT data were reevaluated to measure height of the alveolar process (EF), width of the alveolar process (GH), width of the basal bone (IJ), the angle between the long axis of the first molar and the alveolar bone (∠a) and the angle between the long axis of the alveolar bone and basal bone (∠b). The angle and width were measured to determine the implant-prosthodontic classification of the morphology in the left lower first molar (36) and right lower first molar (46). All measurements were performed on the improved cross-sectional images.

Results: EF, GH and IJ were measured as (10.83 ± 1.31) mm, (13.93 ± 2.00) mm and (12.68 ± 1.96) mm for 36, respectively; and (10.87 ± 1.24) mm, (13.86 ± 1.93) mm and (12.60 ± 1.90) mm for 46, respectively. No statistical significance was observed in EF, GH, IJ, ∠a and ∠b between 36 and 46 (all P > 0.05). The morphology was divided into three categories including the straight (68.7-69.2%), oblique (19.9-20.4%) and concave types (11%). Each type was consisted of two subcategories.

Conclusions: The proposed classification could provide evidence for appropriate selection and direction design of the mandibular molar implant in clinical. The concave type was the most difficult to implant with the highest risk of lingual perforation. The implant length, width, direction required more attention.

Keywords: Alveolar bone morphology; Cone-beam computed tomography; Dental implant; Mandibular molar.

Fig. 1

Determination of the measurement plane. a The horizontal plane was adjusted to the neck of the lower first molar and the cross-sectional plane passed through the midpoint of the tested tooth mesiodistally. b The improved cross-sectional plane aligned along the long axis of the tooth. c The selected measurement plane paralleled the improved cross-sectional plane when the plane showed complete root in the single-rooted molar or the mesial and distal root bifurcations displayed complete mesial root

Fig. 2

Data measurement. a The long axis of the tooth was determined by connecting the apex of the mesial root (point A) and the midpoint of a line drawn from the abrupt point of the buccal counterpart (point B) to the lingual counterpart (point C). b The long axis of the alveolar process (line 2) was marked by bisecting the buccal line of the alveolar process (line Le) and lingual line of the alveolar process (line Lf). The upper internal angle a was formed by L1 and L2. The width GH was between the buccal and lingual alveolar plates at the lowest point of the alveolar bone and perpendicular to L2. KL was between the midpoint of EF and GH. c The long axis of the basal bone (line 3) was marked by bisecting the buccal basal bone surface (line Lg) and lingual basal bone surface (line Lh). The upper internal angle b was formed by L2 and L3. The width IJ was between the buccal and lingual basal plates at the highest point of the basal bone and perpendicular to L3.Distance EF was between the buccal and lingual alveolar crest

Fig. 3

The straight type a I: L2 and L3 were overlapped or nearly overlapped. GH/IJ was small whereas GH was large. b II: L2 and L3 were overlapped or nearly overlapped. Both GH/IJ and GH were small

Fig. 4

The oblique type a I: angle b was positively large, whereas GH/IJ was small. b II: angle b was positively large, whereas GH/IJ was small

Fig. 5

The concave type a I: angle b was negatively large. b II: L2 and L3 were nearly aligned and GH/IJ was large

Fig. 6

The placement of an implant in the straight type of cross-sectional posterior mandibular morphology. a The first subcategory of the straight type. b Cross-sectional CBCT image demonstrating dental implant insertion in the alveolar bone at the first molars. c Cross-sectional CBCT image after the prosthetic rehabilitation

Fig. 7

The placement of an implant in the straight type of cross-sectional posterior mandibular morphology. a The second subcategory of the straight type. b Cross-sectional CBCT image demonstrating dental implant insertion in the alveolar bone at the first molars. c Cross-sectional CBCT image after the prosthetic rehabilitation. A proper implant diameter should be decided based on the width of alveolar bone

Fig. 8

Cross-sectional views showed the buccolingual orientation of implants in the oblique type. a The first subcategory of the concave type after the prosthetic rehabilitation. b The second subcategory of the concave type after the prosthetic rehabilitation. A shorter tapered implant can be selected

Fig. 9

Cross-sectional views showed the buccolingual orientation of implants in the oblique type. a The first subcategory of the concave type after the prosthetic rehabilitation. b The second subcategory of the concave type after the prosthetic rehabilitation. Pay attention to the implant length, width and embedded direction to avoid lingual perforation