This study investigated the locational relationship between the sublingual fossa (SF) and the lateral lingual foramen (LLF) in order to gain useful knowledge so that perforation of the lingual cortical bone and damage to the adjacent blood vessels can be avoided when placing an endosseous implant (implant) in the mandibular interforaminal region. The deepest point of the SF (SFP) and the LLF were identified in 38 Japanese cadaver mandibles (20 edentulous and 18 dentate) by computed tomography (CT) and physical measurement. Their locations were measured. In the edentulous cases, the SFP was located approximately 15 mm vertically from the alveolar crest in the direction of the mandibular lower margin in the canine and premolar regions, and the LLF was located within a 5 mm radius from the SFP. Thus, significant attention to the locational relationship between the SFP and the LLF, as seen on preoperative CT, is required when placing an implant ≥3.75 mm in diameter and ≥15 mm in length in this region.
Haemorrhage during or following the installation of endosseous implants (hereafter, implants) in the mandible is reported to cause marked swelling of the floor of the mouth that can result in airway obstruction. This is often caused by either lingual cortical bone perforation from drilling, or the implant itself injuring the adjacent vessels. In a previous study by this group, in which it was noted that the presence of the sublingual fossa (SF) was a factor involved in the perforation of the lingual cortical bone, the SF was located and the depth measured anatomically, and it was found that the deepest point of the SF was located in the canine and premolar regions. This location corresponds to the implant sites in many cases of serious haemorrhage in the floor of the month, suggesting a high probability that the severe haemorrhage reported in these cases was caused by perforation of the lingual cortical bone and then injury to the adjacent vessels or vessels penetrating the lateral lingual foramen (LLF) in the canine and premolar regions.
This study focused on clarifying the locational relationship between the SF and the LLF by computed tomography (CT) and anatomical measurements in order to gain useful preventive knowledge so that such cases of serious haemorrhage can be avoided.
Materials and methods
Thirty-eight Japanese cadavers (76 hemimandibles) were obtained from the Department of Anatomy at Saga Medical School and examined with the approval of the Ethics Committee of Saga Medical School. All of the cadavers were fixed in a 10% neutral formalin solution. Fifteen were male (30 hemimandibles) and 23 were female (46 hemimandibles). The age range at the time of death was 55–96 years (mean 78 ± 10 years). The 38 mandibles (76 hemimandibles) were divided into two groups: an edentulous group (20 mandibles, 40 hemimandibles) and a dentate group with at least one tooth remaining (18 mandibles, 36 hemimandibles).
The 38 mandibles (76 hemimandibles) were scanned with a Multislice CT device (SOMATOM Emotion 16-slice configuration; Siemens AG, Germany). Imaging parameters were the following: tube potential 130 kV, tube current 150 mA, scan time 1 s, gantry tilt 0, slice thickness 0.6 mm, beam pitch 1.0, reconstruction interval 0.6 mm, and reconstruction function H90s. The field of view was 150 mm, and the voxel size was 0.3 mm for the x and y axes and 0.6 mm for the z -axis. The mandible sample was fixed on an acrylic fixture device with the inferior mandibular margin (IMM) plane aligned in parallel with the scanning plane and scanned with the mid-sagittal plane of the sample aligned with the vertical midline of the gantry. The CT data were saved in Digital Imaging and Communications in Medicine (DICOM) format.
The CT data obtained were analyzed with software program Landmark System LAND marker Direct, version 6.11 (iCAT, Osaka, Japan), as described below.
First, among the slices vertical to the dental arch both mesially and distally from the mental foramen (MF), slices with possible SF were selected for measurement; the deepest point of the SF (SFP0) was defined on the lingual surface and the depth of the SF (SFD0) was measured on each slice ( Fig. 1 ). The largest value among SFD0s was defined as the SFD; the corresponding SFP0 was defined as the SFP ( Fig. 2 A) . The vertical distance between the alveolar crest (AC) and the SFP (AC–SFP; Fig. 2 A) and the horizontal distance between the MF and the SFP (MF–SFP; Fig. 2 B) were measured.
The LLF was defined as a foramen on the lateral lingual surface that was different from those around the mental spine on the mandibular midline. The LLF was identified in each sample; the vertical distance between the AC and the LLF (AC–LLF; Fig. 3 A) , the horizontal distance between the MF and the LLF (MF–LLF; Fig. 3 B and C), the vertical distance between the SFP and the LLF (SFP–LLF-Ver; Fig. 4 A) , and the horizontal distance between the SFP and the LLF (SFP–LLF-Hor; Fig. 4 B and C) were measured.
A positive value was assigned to MF–LLF when the LLF was located mesially relative to the MF ( Fig. 3 B), while a negative value was assigned when it was located distally relative to the MF ( Fig. 3 C). In the samples with negative MF–LLF values, the horizontal diameter of the MF was measured ( Fig. 3 C). In the samples with multiple LLFs in a hemimandible, the largest LLF was selected.
Both the SF and the LLF were identified by CT in 24 of the 76 hemimandibles. These samples were cleared of soft tissues to identify the SF and the LLF grossly ( Fig. 5 A and B) . The mandible sample was placed on a flat experimental table and the IMM was defined as the reference plane. Lines (red lines in Fig. 5 A) were drawn vertically to the dental arch on the lingual side of the mandibles in the range in which the SF was present; the deepest point of the SF (SFP0) was defined along each line and the depth of the SF (SFD0) was measured with a mini digital tread depth gauge (MDDG; MonotaRo, Japan). SFP0, corresponding to the longest SFD0 in the SFD0s for the multiple lines (red lines in Fig. 5 A), was defined as the SFP ( Fig. 5 B). Callipers (N10S; Mitutoyo Corporation, Kanagawa, Japan) were used to measure the linear distance between the SFP and the LLF (SFP–LLF, Fig. 5 B).
All CT and physical measurement procedures were performed by one expert examiner.
Identification of the vessel penetrating the LLF
Prior to the removal of soft tissues for physical measurement, the origin of vessels penetrating the LLF was identified grossly in 15 mandibles (30 hemimandibles) selected from the 38 mandibles.
All statistical analyses were conducted using SPSS statistical software, version 11.0J (SPSS Japan, Tokyo, Japan). P -values of <0.05 were considered statistically significant. The χ 2 test was used to compare the frequencies of the presence of SF and LLF in all samples. The range, mean, and standard deviation (SD) of the measurement values related to the location of the SFP and LLF were calculated for all samples and by gender and dental status. The unpaired t -test was used for comparison of the measurement values related to the location of the SFP and LLF, by gender and by dental status.
The frequencies of the SF and the LLF in all samples are presented in Table 1 . The SF was present in 48.7% and the LLF in 52.6%. Both the SF and the LLF were present in 31.6%, the SF only was present in 17.1%, and the LLF only was present in 21.1%. Neither was present in 30.3%. Comparison of the SF and the LLF in frequency reached statistical significance, demonstrating their correlation ( P < 0.05).
|With SF||Without SF||Total|
The CT and physical measurements (range, mean, and SD) of all the samples with the SF and LLF are presented in Tables 2–4 , for the total samples, by gender, and by dental status, respectively. Only one hemimandible among the 40 with the LLF showed a negative value of −2.3 mm for MF–LLF. The horizontal diameter of the MF in that hemimandible was 2.0 mm. The comparison by gender revealed significantly higher values for SFD and AC–LLF in the male group compared to the female group ( P < 0.05). The comparison by dental status revealed a significantly smaller value of AC–LLF in the edentulous group than in the dentate group ( P < 0.01).
|Measurement||Range||Mean ± SD|
|SFD||n = 37||0.4–2.4||1.3 ± 0.6|
|AC–SFP||n = 37||5.9–26.4||15.3 ± 4.4|
|MF–SFP||n = 37||0–12.7||5.3 ± 4.1|
|AC–LLF||n = 40||8.1–34.5||19.3 ± 6.4|
|MF–LLF||n = 40||−2.3 to 14.9||5.3 ± 4.4|
|SFP–LLF-Ver||n = 24||0–9.2||4.9 ± 4.7|
|SFP–LLF-Hor||n = 24||0–8.3||2.7 ± 2.9|
|SFP–LLF||n = 24||0–19.1||6.0 ± 4.8|