Posterior superior alveolar artery (PSAA) and lateral wall thickness

The lateral part of the maxillary antrum and the Schneiderian layer overlying the lateral portion of maxillary antrum are supplied by the PSAA, an extension of the maxillary artery. Deep bleeding is a possibility that should be thoroughly assessed during sinus grafting surgeries. There have been reports of excessive bleeding following PSAA damage during augmentation of base of maxillary antrum using the transcrestal approach. On CBCT scans, probability of visualization and detection of PSAA varied from approximately 49% to 92%. PSAA was less common at the outermost region of the antrum lateral wall (5 to 10%), while it was more common beneath the membrane that covers the sinus (13 to 16%) or found intraosseously (29% to 72%).^[12], ^[13], ^[14], ^[15], ^[16], ^[17], ^[18] Because PSAA is minuscule and lies closely on both ends of the maxillary antrum lateral wall without creating a bone depression, it may appear to be absent in CBCT images.^[63], ^[64], ^[65], ^[66], ^[67], ^[68], ^[69], ^[70], ^[71], ^[72], ^[73], ^[74]

In the meantime, CBCT imaging may be used during interventions for augmentation of floor of maxillary sinus to assess the maxillary sinus's lateral wall thickness. The overall average thickness of lateral wall of maxillary antrum was determined to be 1.6 ± 0.8 mm measured at both four millimeters apically and six millimeters apically or superiorly to floor of maxillary antrum in a retrospective examination of 209 individuals presenting with CBCT images.^[19], ^[20], ^[21], ^[22], ^[23], ^[24], ^[25], ^[26], ^[27]

On the other hand, the average lateral wall thickening of the instances with perforation of antrum membrane during the surgery was 2.4 ± 0.6 millimeters at both four millimeters and six millimeters apically to the floor of maxillary antrum, while the non-perforation patients had an average thickness of 1.2 ± 0.4 millimeters. Additionally, it was discovered that the thickness of maxillary antrum lateral wall is significantly linked with leftover ridge height and significantly thicker in individuals with partial edentulism than in circumstances of full edentulism. The thickness of the maxillary antrum lateral wall and the measurement of the diameter of PSAA exhibited a favorable connection.^[28], ^[29], ^[30], ^[31], ^[32]

The frequency of inadvertent maxillary sinus discoveries in orthodontic cone-beam computed tomography (CBCT) pictures was examined by Pazera P et al. in their 33-" study. Of all CBCTs, 65 had incidental abnormalities in the maxillary sinus, accounting for 46.8% of the total. Three types of accidental observations were found: flat mucosal thickening (23.7%), polypoid mucosal thickening (19.4%) and acute sinusitis symptoms (3.6%). Incidental maxillary sinus abnormalities unrelated to the main reason are seen in a significant number of CBCTs performed for orthodontic diagnostic purposes.

Pneumatization

The constant expansion of the paranasal sinuses, a condition known as sinus pneumatization, is a normal physiological function. A person's sinuses make their voice more resonant, help shape their face and even warm and humidify the air that is inspired to a certain extent. Localized alterations in the dimensions of both hard and soft tissues are facilitated by tooth loss. Implant placement at the back of the upper jaw might be challenging due to the presence of maxillary sinus approximation and bone loss. The maxillary sinuses, out of the four paranasal sinuses, are the most relevant to dental care because of their close proximity to teeth. The process of pneumatization occurs when the sinuses cavities are created and filled with air during the development of the maxillary bone.^[34], ^[35], ^[75], ^[36], ^[37], ^[38], ^[39], ^[40], ^[41], ^[42] The most common anatomical area is the alveolar process, however pneumatization also causes the maxillary sinuses to enlarge into neighboring tissues. A lot of people still don't understand the procedure. Genetics, craniofacial traits, bone density, sinus operations, growth hormones, air pressure inside the sinus cavity, natural aging and nasal mucous membrane pneumatization are some of the factors that have been shown to influence maxillary sinus pneumatization in clinical studies.^[43], ^[44], ^[45], ^[46], ^[47], ^[48]

In a population from southern Iran, Shahidi S et al.,(2016)^[49] employed CBCT to determine normal variations of the maxillary sinus. Axillary images were employed to evaluate a range of anatomic anomalies, including anterior pneumatization, exostosis and hypoplasia. The precise positioning of the PSAA and the height and location of the sinus septa were also assessed. The study discovered that there were frequent anatomical variations in the maxillary sinuses in maxilla CBCT. Preoperative CBCT imaging appears to be quite helpful in better analysing the maxillary sinus architecture and PSAA placement prior to surgery. The surgical treatment plan may then be adjusted using this information to get improved results.

A narrative review of the application of cone beam computed tomography (CBCT) in evaluating the architecture and common disorders of the maxillary sinuses was presented by Yeung AWK et al.,(2022).^[68] Information was given on the location, morphometric properties and rate of detection and visualization. Anatomical features of the sinuses that were investigated included pneumatization of the sinuses, hypoplasia, septa, main and auxiliary sinus ostia and the posterior superior alveolar artery. The pathology assessment included antrolith, mucous retention cysts and membrane thickening in periapical/ periodontal lesions. Procedures that include the extraction of teeth, the insertion of implants or the elevation of the sinus floor are all performed in close proximity to the sinus floor, thus it is crucial to observe and evaluate the maxillary sinus before these operations. Periodontal bone loss and other sinus pathologies might be accompanied with odontogenic lesions.

Hypoplasia

Maxillary sinus hypoplasia (MSH) results in a smaller antrum cavity space than sinus pneumatization. This appears to be a favorable situation at first since there is enough space between the sinus floor and the dentoalveolar area. On the other hand, the frequency of sinus mucosal thickness and obstructed ostium was observed to be significantly higher when there is evidence of MSH in CBCT pictures. According to reports, the frequency of MSH ranges from 0.2% to 50%. ^[32], ^[33], ^[34], ^[35], ^[75], ^[36], ^[37], ^[38], ^[39], ^[40], ^[41], ^[42] The majority of patients fell into either type II (26%) having features like poorly defined or missing infundibular tract, hypoplastic uncinate process and moderate MSH or type I (69% having features of patent infundibular tract, normal uncinate process and mild hypoplasia). A minority (5%) with significant sinus hypoplasia and no uncinate process, was explained by type III. In rare cases, aplasia may be discovered accidentally during CBCT imaging. ([Figure 1]) Sinus hypoplasia did not appear to have an impact on the health or functionality of dentoalveolar frameworks, including open bite, facial asymmetry, or swaying of occlusal plane, aside from sinus healthiness. Any substantial mediation at the back of the mouth needs to be done by a professional who has studied the anatomy and physiology of the maxillary sinuses extensively.^[43], ^[44], ^[45], ^[46], ^[47], ^[76] There are two possible times when maxillary sinus hypoplasia (MSH) occurs: during embryological development or as a result of injury, iatrogenic factors, or other underlying conditions. Because the hypoplastic sinus lacks a distinctive ostium, it experiences mucosal thickening due to restricted infundibular entrance. On top of that, MSH makes procedures more difficult by causing the horizontal nasal wall to enlarge at its proximal end.^[48], ^[49], ^[50], ^[51], ^[52], ^[53], ^[54], ^[55], ^[56], ^[57], ^[58], ^[59], ^[60]

Sinus augmentation

A maxillary sinus elevation treatment should be used to enhance the quantity of bone below floor of maxillary antrum in implant situations when the extensively resorbed alveolar bone crest was inadequate to support an implant. Following five to six months of recovery, the volume of the bone graft dropped by 25% on an average, according to recent CBCT studies. There was a mean reduction in graft volume of twenty-eight to forty percent from six months to three years following grafting.^[40], ^[41], ^[42], ^[76], ^[43], ^[44], ^[45], ^[46], ^[47], ^[48], ^[49], ^[50], ^[51], ^[52], ^[53], ^[54], ^[55], ^[56], ^[57], ^[58], ^[59], ^[60], ^[61], ^[62], ^[63] But four to seven months following surgery, no such appreciable decrease in the volume of graft was discovered in one CBCT investigation. For an implantation to be effective, the density of bone minerals is just as crucial as volume of bone. It was discovered that there was a strong association between the gray level evaluated at the insertion sites of dental implants in CBCT images and the actual calcified material content calculated at the implant locations. Furthermore, during four to seven months of subsequent follow-up, the gray level of the regions grated by bovine bone fragments stayed steady.^[52], ^[53], ^[54], ^[55], ^[56], ^[57], ^[58], ^[59], ^[60], ^[61], ^[62], ^[63]

Septa

The maxillary sinus floor is divided into many compartments, called breaks, by the second rate or parallel sinus walls, from which the shape emerges as a converted gothic curve. ([Figure 4]) Anatomist Arthur S. Underwood was the first to study these septa and describe their characteristics; as a result, they are often referred to as Underwood's septa.^[7], ^[8]

Neugebauer J et al.,^[31] performed research to evaluate the need for suitable imaging before sinus floor elevation by retrospectively determining the prevalence of septa in the maxillary sinus using computed tomography (CBCT). With respect to the sinuses, 47% of patients and 33.2% of septa were detected. Regarding age, sex and side, there was no statistically significant variation in prevalence. Although 13.7% of individuals with septa had one in each sinus, 24.6% had one in only one sinus. A small percentage of individuals (8.7%) had additional combinations, with up to three septa per sinus. With 256 septa, the first molar area was the most prevalent location for septa.

Li J et al.,^[76] “analyzed the maxillary sinus septum of Han nationality in the Jiangsu region using cone-beam computed tomography (CBCT) in conjunction with Simplant software to determine the anatomical basis for oral implant surgery following maxillary sinus lifting and to provide surgical instructions for the procedure. The proportion of the occurrence of maxillary sinus septa in 424 subjects was 44.81% and 21.23% of the subjects (n=90) had multiple sinus septa, while 20.52% had bilateral sinus septa (n=87) in total, 848 maxillary sinuses were included for this analysis and 32.67 percent, or 277 sinuses, had septa. Gender, age and tooth presence/absence had no statistically significant correlation with septa prevalence. The median position of septa in the maxillary sinus was the most common, at 59.94%. In the right maxillary sinus, the average height of the sinus septa was 5.90±3.65mm, whereas in the left sinus, it was 5.54±2.87mm. Sinus septa in the right maxillary sinus averaged 8.15±2.40mm in length, whereas those in the left maxillary sinus averaged 7.88±2.73mm.

Orhan K et al.,^[43] used cone beam computed tomography (CBCT) for maxillary sinus surgical procedures to assess the frequency, height, placement and shape of maxillary sinus septa in children with mixed dentition, adults with partial or full dentition and edentulous individuals. Septa involving the maxillary sinus segments were seen in 58% of cases. Septa ranging from totally edentulous (CE) in 13 cases (3.2% of the total), edentate in 198 cases (53.9%) and mixed dentition in 14 cases (3.8%) were seen in the maxillary segments. In terms of septum height, there were no discernible changes according to age or gender. Having said that, compared to edentate and CE individuals, partly edentulous patients had greater maxillary sinus septa. Extensive examination using a suitable radiographic approach was important to minimize any difficulties during sinus surgery, since septa of varying heights and courses occurred in all areas of the maxillary sinus.

Membrane thickening associated with periapical lesions

Thickening of the sinus membrane was frequently observed in teeth with endodontic involvement. Numerous studies have reported on it. In a single research study, the membrane of the sinuses was shown to be much thicker in individuals with concomitant teeth exhibiting apical disease than normal controls.^[22], ^[23], ^[24], ^[25], ^[26], ^[27], ^[28], ^[29], ^[30], ^[31], ^[32] According to an additional research study, the average incidence of membrane thickening was found to be 41.5% in patients with apical periodontitis who had no associated teeth. However, this number rose to approximately 70% in patients who had visible minor modifications in the structure of the bone to an established radiolucent periapical region and it reached 100% in individuals with severe cases of the disease.^[33], ^[34], ^[35], ^[75], ^[36]

A more contemporary study's outcomes supported earlier findings, showing that teeth having periapical lesions were more probable to be related to sinuses with greater than two mm membrane thickening. When periapical lesions are present, the likelihood of membrane thickening might increase up to three times higher than in the absence of periapical lesions. For sinus membrane thickening to occur, the periapical lesion did not always need to come into contact with or penetrate the sinus floor. The degree of thickening was likewise unaffected by the quantity of related root canal treatments.^[37], ^[38], ^[39], ^[40], ^[41], ^[42], ^[76], ^[43]

Membrane thickening associated with periodontal lesions

Membrane thickening appeared to be more common in teeth with more extensive periodontal degeneration, which is similar to periapical lesions. Those with extensive periodontal bone loss had a 4.6-fold higher likelihood of membrane thickening compared to those with minor bone loss. ([Figure 5]) Membrane thickening was 1.6 and 3.5 times greater more common in individuals experiencing class II and class III furcation lesions, respectively, compared to those lacking furcation involvement. Additionally, thickening of maxillary sinus membrane was found to be 2.4–5.6 fold more common when there were any transverse intra-bony pockets than in the absence of such pockets. At four months, the thickening of sinus membrane would completely resolve with the removal of the periodontally affected tooth.^[40], ^[41], ^[42], ^[76], ^[43], ^[44], ^[45], ^[46], ^[47], ^[48], ^[49], ^[50], ^[51], ^[52], ^[53], ^[54], ^[55]

Mucous retention cyst (MRC)

A common location for MRCs is the maxillary sinus; ten percent to thirty percent of the maxillary sinus had MRCs. Within a single sinus, up to four MRCs have been recorded. Rather than on the roof, MRCs were more frequently found at the walls of maxillary antrum and floor. If a tooth had endodontic therapy, periapical lesions, or had significant bone loss, the likelihood of MRCs on the floor of maxillary antrum was increased.^[34], ^[35], ^[75], ^[36], ^[37], ^[38], ^[39], ^[40], ^[41], ^[42], ^[76], ^[43], ^[44], ^[45], ^[46], ^[47], ^[48], ^[49], ^[50], ^[51], ^[52], ^[53], ^[54]

Antrolith

A calcified lump in the maxillary antrum is called an antrolith. Between 0.6% and 8.4% of maxillary antrum had antroliths. They could be amorphous, linear, or punctate. Instead of being in the premolar area, the majority of them were situated on the floor of sinus in the molar area. The highest cross-sectional area estimated based on coronal slices revealed that the measurement of an antrolith ranged from 1 to 91mm². According to another study, the average measurements were 3.5± 2.1mm in height, 4.1± 2.9mm in breadth and 5.6± 4.4mm in length.^[31], ^[32], ^[33], ^[34], ^[35], ^[75], ^[36], ^[37], ^[38], ^[39], ^[40], ^[41], ^[42], ^[76], ^[43], ^[44], ^[45], ^[46], ^[47], ^[48], ^[49], ^[50], ^[51] Although it would seem intuitively that having antroliths would increase the likelihood of membrane perforation after implant placement when sinus floor elevation is occurring at the same time, however study findings did not support this theory.^[21], ^[22], ^[23], ^[24], ^[25], ^[26], ^[27], ^[28], ^[29]

Foreign bodies

Latrogenic entry of foreign bodies into the maxillary sinus can occasionally happen because the dentoalveolar area and the maxillary sinus floor are so close together. CBCT imaging can be used to pinpoint the foreign substances. For instance, one study found that 27 individuals had dental implants, tooth pieces, whole teeth, dental burs, root filling material, dental impression material placed inside their maxillary sinus.^[61], ^[62], ^[63], ^[64], ^[65] During root canal therapy, a perforated root could allow a large amount of root filling material to be forced into the maxillary antrum cavity. In the meantime, even in cases where a substantially atrophic edentulous ridge was present, the majority of dental implant patients that were placed into the sinus did not have a preoperative CBCT exam.^[42], ^[76], ^[43], ^[44], ^[45], ^[46], ^[47], ^[48], ^[49]