Computed tomography and anatomical measurements of critical sites for endosseous implants in the pterygomaxillary region: a cadaveric study

Abstract

The aim of this study was to obtain computed tomography (CT) and physical measurements of the pterygomaxillary region to determine the anatomical and radiographic landmarks that clinicians need for pterygoid implant placement. Seventy-eight hemi-heads with an atrophic posterior maxilla from 46 cadaveric samples were measured using CT. Twenty-one hemi-heads were selected randomly for physical measurements. CT measurements showed that the mean and minimum distance between the maxillary tuberosity point (MT) and the most lateral lowest point of the pterygomaxillary fissure (PF) were 18.7 mm and 10.0 mm, respectively. The mean and minimum distance between the alveolar crest point passing the extended line of the infrazygomatic crest and the PF were 22.7 mm and 14.7 mm, respectively. The mean and minimum distance between the PF and the greater palatine canal were 2.9 mm and 0.2 mm, respectively. Physical measurements showed that the mean and minimum distances between the MT and the descending palatine artery (DPA) were 19.4 mm and 12.7 mm, respectively, and those between the PF and the DPA were 3.7 mm and 0.0 mm, respectively. The results confirmed considerable variation in the values of the pterygomaxillary region measured at the specific sites. Therefore, careful and sufficient consideration is required in each case of pterygoid implant placement.

In the late 1980s, Tulasne introduced the tilted endosseous implant placement procedure from the maxillary tuberosity into the pterygoid process of the sphenoid bone for the treatment of the atrophic edentulous posterior maxilla . Although this procedure has been applied widely since its introduction, it is also challenging .

Both Graves and Venturelli suggested that the implant be directed 45° to the occlusal plane . In 1998, in an anatomical study, Yamaura et al. used a cadaveric maxilla to measure the angles of inclination of possible pillars of bone between the maxillary tuberosity and the pterygoid process . In 2001, Lee et al. measured the pyramidal process of the palatine bone that is related to pterygoid implants in dry skulls .

On the other hand, Rodriguez et al. used clinical data and panoramic radiographic images of pterygoid implants to report that a mesiodistal inclination of a pterygoid implant at 70° to the Frankfort horizontal (FH) plane decreases the non-axial loads of rehabilitation and exhibits good long-term survival . In 2014, Rodriguez et al. used cone beam computed tomography (CBCT) data of 100 cases and placed a virtual pterygoid implant in these; they reported that the mesiodistal inclination relative to the FH plane was 72.5 ± 4.9° and the distance between the maxillary tuberosity and the pterygoid process was 22.5 ± 4.8 mm . In 2016, a third study by Rodriguez et al. used CBCT data of 202 Caucasian adult patients and a virtual implant to report that the mesiodistal inclination relative to the FH plane was 74.19 ± 3.13° and the distance between the maxillary tuberosity and the extremity of the pterygoid process was 22.15 ± 1.56 mm . These studies by Rodriguez et al. provided information from indirect measurements using panoramic radiography and CBCT , while the previous cadaveric studies did not focus on vessel information .

This study aimed to obtain measurements for the branch sites of the maxillary artery using both CT data and cadaveric samples, to identify effective landmarks that clinicians require for pterygoid implant placement.

Materials and methods

Materials

Forty-six Japanese cadavers were obtained from the Department of Anatomy of Saga Medical School and were examined with the approval of the Ethics Committee of Saga Medical School. An atrophic posterior maxilla with all molars missing was chosen for the study (i.e., CT measurement showing ≤10 mm between the alveolar crest and the sinus floor in the molar region), as described by Rodríguez et al. . Thus, 78 hemi-heads were selected (42 hemi-heads from 24 males and 36 hemi-heads from 22 females). The age range at time of death was 65–100 years (mean 81 ± 9.1 years). All the cadavers had been fixed in a 10% neutral formalin solution. Thirteen of the 46 cadavers (21 hemi-heads) were selected randomly for physical measurements. The head was detached from the neck in all cases.

Methods

CT measurements

A multi-slice CT system (SOMATOM Emotion 16-slice configuration; Siemens, Germany) was used for CT measurements. The 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 (FOV) 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 scan was taken between the superior orbital margin and the maxillary alveolar process. The midsagittal plane was aligned with the mid-longitudinal axis of the gantry for scanning via parallel alignment of the scan and FH plane. The CT data were saved as DICOM files (Digital Imaging and Communications in Medicine).

The CT data were analyzed using measurement software (LANDmarker Direct, version 6.11; iCAT, Osaka, Japan). The lowest posterior point of the maxillary tuberosity (MT), the most lateral lowest point of the pterygomaxillary fissure (PF), the central lowest point of the alveolar crest through which the extended line of the infrazygomatic crest passes (A), and the greater palatine canal (GPC) were defined ( Fig. 1 ). The following distances were measured: (1) residual alveolar bone height: linear distance from point A to the maxillary sinus floor on the line perpendicular to the FH plane including point A in sagittal view ( Fig. 1 B); (2) MT–PF: the linear distance between the MT and the PF in panoramic view ( Fig. 2 ); (3) MT–PF angle: the angle between the plane parallel to the FH plane including MT and the MT–PF line in panoramic view ( Fig. 2 ); (4) A–PF: the linear distance between point A and the PF in panoramic view ( Fig. 2 ); (5) A–PF angle: the angle between the plane parallel to the FH plane including point A and the A–PF line in panoramic view ( Fig. 2 ); (6) PF–GPC: the shortest distance between the PF and GPC in axial view ( Fig. 3 ).

Fig. 1
Images of the area between the inferior orbital margin and the maxillary alveolar process: (A) three-dimensional, (B) sagittal, and (C) axial views at the zygomatic arch level. The yellow arrow shows the lowest posterior point of the maxillary tuberosity ‘MT’; the red arrow indicates the most lateral lowest point of the pterygomaxillary fissure ‘PF’; the green arrow shows the central lowest point where the alveolar crest passes through the extended line of the infrazygomatic crest ‘A’; and the white arrow shows the greater palatine canal ‘GPC’. The white horizontal line including point A in Fig. 1 B indicates the plane parallel to the Frankfort horizontal (FH) plane. The white double-headed arrow ( Fig. 1 B) indicates the residual alveolar bone height, i.e. the linear distance from point A to the maxillary sinus floor on the line perpendicular to the FH plane including point A.

Fig. 2
Panoramic view of a slice within the molar region, maxillary tuberosity, and pterygopalatine fossa. ‘MT’ indicates the lowest posterior point of the maxillary tuberosity; ‘PF’ indicates the most lateral lowest point of the pterygomaxillary fissure; ‘A’ indicates the central lowest point of the alveolar crest passing the line extending from the infrazygomatic crest. The white horizontal line indicates the plane including the MT and point A and parallel to the Frankfort horizontal (FH) plane. The linear distance between MT and PF (MT–PF) indicated by the yellow double-headed arrow, and the angle between the yellow double-headed arrow and the white horizontal line (MT–PF angle) were measured. The linear distance between point A and the PF (A–PF) indicated by the green double-headed arrow, and the angle between the green double-headed arrow and the white horizontal line (A–PF angle) were also measured.

Fig. 3
Axial view of a slice with the pterygomaxillary area including the most lateral lowest point of the pterygomaxillary fissure ‘PF’. The red arrow indicates PF and the white arrow indicates the greater palatine canal (GPC). The black double-headed arrow on the right side indicates the midsagittal plane. The shortest distance between the PF and GPC (PF–GPC), shown by the yellow double-headed arrow, was measured.

Physical measurements

Using a lateral approach, a fan-shaped incision was made on the lateral part of the head of each sample to remove the temporal and masseter muscles. The zygomatic arch was then dissected at both ends of the masseter muscle, turned downwards, and removed. The mandibular ramus above the mandibular foramen was dissected, and the temporal muscle was turned upwards to identify the maxillary artery. Then, the vessels within the pterygopalatine fossa that were peripheral to the maxillary artery were identified and dissected, along with the MT and PF. Finally, soft tissues around the pterygopalatine fossa (excluding the vessel peripheral to the maxillary artery) were removed, leaving only the maxillary bone, the palatal bone, and the lateral plate of the pterygoid process of the sphenoid bone. The samples were placed on a flat experimental table with the FH plane parallel to the table surface. The shortest distances between the MT and the descending palatine artery (DPA) (MT–DPA), between the PF and DPA (PF–DPA), and between the alveolar crest and the posterior superior alveolar artery (PSAA) (AC–PSAA) were measured directly using a caliper (N10S; Mitutoyo Corporation, Kanagawa, Japan) ( Fig. 4 ). ‘AC’ in the above ‘AC–PSAA’ indicates the point on the alveolar crest at which the distance between the alveolar crest and the PSAA is shortest. The shortest distance between point A and the DPA, as well as the distance between the PF and the greater palatine artery, could not be measured directly.

Dec 14, 2017 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Computed tomography and anatomical measurements of critical sites for endosseous implants in the pterygomaxillary region: a cadaveric study
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