The purpose of this study was to measure the depth and location of the sublingual fossa, a potential site of sublingual bleeding/lingual cortical perforation during endosseous implant placement in the mandibular interforaminal region (MIR), to clarify anatomical variation. Using the mandibles of 37 Japanese cadavers, the lingual depth (LD) between the lingual surface and the line perpendicular to the inferior margin of the mandible (IMM), as well as the vertical distance (VD) between the lingual surface and the IMM or the mental foramen (MF) level, were measured at defined points and lines within the MIR. The definite sublingual fossa (SF) was identified by the LD (≥1.0 mm) and the VD, and the depth and location of the SF were determined. The depth ranged between 1.0 mm and 5.8 mm, and the vertical location ranged between 9.2 mm and 15.7 mm from the IMM and between 2.2 mm and 6.1 mm from the MF level. These results revealed certain tendencies in the depth and location of the SF but the variation was substantial. The SF should be identified in each case as accurately as possible by CT before implant placement in the MIR to minimize the risk of the potential complications.
In 1981, Adell et al. reported a procedure for installing endosseous implants (hereafter, implants) in the mandibular interforaminal region (MIR) for edentulous patients. The procedure avoided the mandibular canal during implant placement and was considered to incur relatively few complications. Some life-threatening cases complicated by haemorrhage have been reported during or following the procedure. These complications are likely to occur because drilling or implant placement perforates the lingual cortical bone and damages the submental artery (a branch of the facial artery) or the sublingual artery (a branch of the lingual artery) coursing by the lingual cortical bone. Factors that might be linked to the complications include: size, shape, and length of the implant ; direction of placement ; possible bone pathology ; surgical skill of the operator ; preoperative assessment including imaging ; systemic factors including medical history ; and anatomical variation of the site. Regarding the anatomical variation of the site, Krenkel and Holzner, Mordenfeld et al. and Hofschneider et al. have emphasized the importance of obtaining morphologic information on the sublingual fossa in the MIR. No studies have described the anatomic variation of the sublingual fossa.
The authors attempted to measure the depth and location of the sublingual fossa anatomically in the MIR to investigate the variation, to provide basic morphologic data that may assist virtual measurement by computed tomography (CT).
Materials and methods
37 Japanese cadavers (36 right and 35 left hemi-mandibles; total 71) used in the Department of Anatomy of Saga Medical School were examined under the approval of the Ethics Committee at Saga Medical School. All the cadavers had been stored in 10% neutral formalin solution. Three hemi-mandibles damaged during the gross anatomy course at Saga Medical School were excluded from the study.
22 male (43 hemi-mandibles) and 15 female (28 hemi-mandibles) cadavers were used; the age at the time of death was 45–96 years (mean 74.7 years). The specimens were divided into two age groups for statistical analysis: 45–75 years (19 cadavers; 37 hemi-mandibles); and 76–96 years (18 cadavers; 34 hemi-mandibles). The 71 hemi-mandibles were divided into two groups according to dental status: a dentate group with at least 1 tooth (36 hemi-mandibles); and an edentulous group with no teeth (35 hemi-mandibles).
The mandible was detached from the cadaver and completely exposed. The mandible sample was placed on a flat experimental table and the inferior margin of the mandible (IMM) was defined as the reference plane ( Fig. 1 ). A line (interforaminal line) drawn between the right and left mental foramen (MF) parallel to the IMM was defined on the labial surface of the mandible ( Fig. 1 ). A mid-sagittal plane was defined by connecting the central point of the interforaminal line, the tip of the mental spine, and the centre of the IMM (gnathion; Gn) ( Fig. 1 ). The interforaminal line on the mandibular labial surface was divided into left and right parts from the mid-sagittal plane, each of which was then divided into four equivalent lines ( Fig. 1 ). The vertical lines between the interforaminal line and the IMM on the mandibular labial surface were divided into four equivalent lengths to create a grid-like pattern on the MIR. The vertical lines were designated 1–4 mesially for both sides, and the horizontal lines were designated A–D from the alveolar crest. The intersections (32 points) of the vertical and horizontal lines on the labial cortical surface were defined ( Fig. 1 ).
The points on the lingual cortical surface corresponding to those on the labial cortical surface were defined using callipers (Code-Nr.209-602; Mitutoyo Corporation, Kanagawa, Japan) with a parallel indicator ( Fig. 2 a) as follows: the mandibular bone was placed labiolingually between the callipers and the position was adjusted so that the parallel indicator was parallel with the IMM; with one jaw of the callipers placed at an intersection of the vertical and horizontal lines on the labial cortical surface, the point at which the other jaw was placed was defined as the corresponding point of the lingual cortical surface ( Fig. 2 b); and similar to the labial cortical surface, the vertical (1–4) and horizontal lines (A–D) were defined on the basis of the points defined on the lingual cortical surface ( Fig. 3 ).
The measurements were obtained from the left and right hemi-mandibles. The lines perpendicular to the IMM from the reference points (A1, A2, A3, and A4 (MF level)) were defined, and the lingual depths (LDs) from these lines to the 12 intersection points of the vertical and horizontal lines on the lingual cortical surface (points on the B–D levels) were measured ( Fig. 4 ). The vertical distances (VDs) from the IMM to the horizontal lines (A–D levels) and from horizontal line A (MF level) to horizontal lines B–D were measured ( Fig. 5 ).
A depth gauge (Kohler, Neuhausen, Germany) and callipers (N10S; Mitutoyo Corporation) were used for all measurements. All the measurements were performed by one expert. The measurements for a site were repeated three times, and the average was obtained.
The presence of the sublingual fossa was grossly observed, and the point with the largest LD in the defined 12 points nearest to the sublingual fossa was identified. When the nearest and deepest point in a sample had an LD ≥ 1.0 mm, the point was regarded as the definite sublingual fossa (SF) as shown in Fig. 6 . The depth of the SF was determined as the LD of the deepest point, and the location was determined from the VD between the IMM and the SF and the VD between the MF level and the SF for each sample. The location of the tooth corresponding to the SF was also confirmed. In the edentulous group, the location was determined on the basis of the average mesiodistal diameter of the permanent teeth from the mid-sagittal plane in Japanese adults. The frequency of the presence of SF was calculated as a total of all samples, as well as by gender, age, and dental status.
All statistical analyses were processed using SPSS statistical software (version 11.0J, SPSS, Tokyo, Japan). For comparison of the frequency of the presence of SF by gender, age, and dental status, a χ 2 test was used.
A comparison between the dentate and edentulous groups in the specimens with the SF was performed using an unpaired Student’s t test. P values < 0.05 were considered statistically significant.
SFs were present in 45% of all samples (32/71 hemi-mandibles), 58% of male samples (25/43 hemi-mandibles), 25% of female samples (7/28 hemi-mandibles) ( Table 1 ), 49% of 45–75 year old samples (18/37 hemi-mandibles), 41% of 76–96 year old samples (14/34 hemi-mandibles) ( Table 2 ), 58% of dentate samples (21/36 hemi-mandibles), and 31% of edentulous samples (11/35 hemi-mandibles) ( Table 3 ). The frequency of the presence of SF was statistically significantly higher in the male and/or dentate samples than in the female and/or edentate samples ( P = 0.006 < 0.05 and P = 0.02 < 0.05, respectively) ( Tables 1 and 3 ), whereas the difference was not statistically significant between the 45–75 and the 76–96 year old groups ( P = 0.53 > 0.05) ( Table 2 ).
|With SF||Without SF||Total|
|With SF||Without SF||Total|
|With SF||Without SF||Total|
The ranges and mean ± standard deviation (SD) of the LD of the SF, the VD from the IMM to the SF, and the VD from the MF level to the SF in all samples with the SF are shown in Table 4 . The SF of all 32 hemi-mandibles with SF was vertically located on the B level above the mylohyoid line ( Fig. 4 b). The horizontal location of the SF corresponded to B2, B3, or B4 in all of the 32 hemi-mandibles ( Fig. 4 a). The SF was located in the canine or premolar region in all of the samples.