Anatomy Respect in Implant Dentistry. Assortment, Location, Clinical Importance (Review Article)

Aims: In this article; we will reviews critically important basic structures routinely encountered in implant therapy. It can be a brief anatomical reference for beginners in the fi eld of dental implant surgeries. Highlighting the clinical importance of each anatomical structure can be benefi cial for fast informations refreshing. Also it can be used as clinical anatomical guide for implantologist and professionals in advanced surgical procedures. Background: Basic anatomy understanding prior to implant therapy; it's an important fi rst step in dental implant surgery protocol specifi cally with technology advances and the popularity of dental implantation as a primary choice for replacement loosed teeth. A thorough perception of anatomy provides the implant surgeon with the confi dence to deal with hard or soft tissues in efforts to restore the exact aim of implantation whether function or esthetics and end with improving health and quality of life. Collection and citation of more than eighty published articles discuss anatomical importance in implant dentistry and reviews the clinical importance of each landmarks can affect the dental implant procedures in different situations. Conclusion: Though knowledge and understanding of the anatomical basics before surgery can reduces unsolicited complications and reducing the success criteria subsequently affect patients satisfactions. However, certain anatomic sites may be challenging concerning treatment plan as maxillary sinus area of inferior alveolar nerve area. Review Article Anatomy Respect in Implant Dentistry. Assortment, Location, Clinical Importance (Review Article) Rawaa Y Al-Rawee1* and Mohammed Mikdad Abdalfattah2 1Department of Oral and Maxillofacial Surgery, Al-Salam Teaching Hospital. Mosul, Iraq 2Post Graduate Student in School of Dentistry, University of Leeds. United Kingdom, Ministry of Health, Iraq Received: 19 August, 2020 Accepted: 31 August, 2020 Published: 01 September, 2020 *Corresponding author: Dr. Rawaa Y Al-Rawee, BDS, M Sc OS, MOMS MFDS RCPS Glasgow, PhD, MaxFacs, Department of Oral and Maxillofacial Surgery, Al-Salam Teaching Hospital, Mosul, Iraq, Tel: 009647726438648; E-mail: ORCID: https://orcid.org/0000-0003-2554-1121


Introduction
In general; there are dozens of studies discussing the dental implants different subjects elaborately; but limited researches focus on clinical importance of anatomical aspect in implants dentistry; in spite of knowing anatomy consider the fi rst step of precise surgeries and is critically important.
Basic anatomy understanding prior to implant therapy; it's an important fi rst step in dental implant surgery protocol specifi cally with technology advances and the popularity of dental implantation as a primary choice for replacement loosed teeth . Implantologist should be familiar with all anatomical landmarks, muscles attachments, vascularization and innervations for both soft tissues and bone. Good knowledge of oral structures will affect patient assessment and enable smooth surgical and prosthetic procedures. Furthermore, careful perception of anatomy provides professionals with the confi dence to deal with hard or soft tissues in efforts to restore the exact aim of implantation whether function or esthetics and end with improving health and quality of life.
Collection and citation of more than eighty published articles discuss anatomical importance in implant dentistry and reviews the clinical importance of each landmarks can affect the dental implant procedures in different situations.
In this review article, we will reviews critically important basic structures routinely encountered in implant therapy.
It can be a brief anatomical reference for beginners in the

Maxillary structures
Gingiva and palatal mucosa thickness: Gingiva and palatal epithelium thickness is 0.3 mm [1]. Lamina propria forming the supporting layer of the gingiva, whereas, mucosal layer with the lamina propria is supporting the palatal epithelium.
surrounding the incisive papilla is essential to avoid splitting nasopalatine canal vessels [5]. Although bisecting the canal will not give a detrimental effect, however, numbness of the anterior palatal tissue will result in frequent cases [6].
According to Artzi [7], when a large canal was present, surgeon can move contents of the canal over without elimination and placed an implant. On the contrary, Rosenquist and Nystrom [8] approach and enucleated the contents, inserted a bone graft, and subsequently placed an implant. We usually angulate the implant and avoid the canal.

Infraorbital foramen
Infraorbital foramen is a signifi cant landmark as it's the emergence point of the infraorbital nerve and blood vessels.
The direct location of the foramen is in the infraorbital ridge 5mm inferiorly under the pupil of the eye, and easily palpable through the skin of the cheek [9]. However, in sever resorbed maxilla cases, alertness needs to be exercised avoiding nerve injuries.

Nasopalatine foramen
Stenson foramen or the more familiar term incisive canals are vital anatomical landmarks forming two lateral canals noticeable in the nasopalatine foramen or incisive foramens [4]. These canals are functioning to transmit descending palatine vessels (anterior branches) and the nasopalatine nerves. In unresorbed ridge nasopalatine foramen situated about 7.4 mm from the labial surface and 4.6 mm wide, mean length 8.1mm as described by Jacobs R [4], exits as the incisive foramen ( Figure 3).
Clinical importance: Incisive canal with its position can form obstacle to implant placement in the anterior region (incisor area). Creation of labial incision on the crest;

Greater palatine foramen
The greater palatine vessels emerge from the foramen and cross the palate in anterior direction and the foramen located in the midway between the crestal bone and the median raphe.
Foramen position is different according to articles, eighty six percent (86%) of cases showed the foramen situated opposite the third molar, in 13% between the 2 nd and 3 rd molar in 13% of cases, and opposite the 2 nd molar in 1% of cases [11]. Other investigators [12] observed that the foramen was positioned opposite the 3 rd molar in 55% of cases, between the between the 2 nd and 3 rd molar in 19% of cases, opposite the 2 nd molar in 12% of cases, and distal to the 3 rd molar in 14% of cases. Wang, [13] stated that 6mm is the mean distance from the center of the greater palatine foramen to the mid-sagittal plane of the hard palate ( Figure 5).

Greater palatine artery
Greater palatine foramen is forming the emergence point of the descending palatine artery when the later navigates anteriorly in a slit present in the medial side of the hard palate ends within the incisive canal [15]. After enters the incisive canal it anastomoses with the nasopalatine branch of the sphenopalatine artery. Monnet-Corti, [16] reported that "the distance from the gingival margin to the greater palatine artery ranged from 12.07 -2.9 mm in the canine area to 14.7 -2.9 mm at the mid-palatal aspect of the second molar level". Reiser GM stated in his article that distance of palatine artery from the cemento-enamel junction can be calculated depends on palatal vault shape as low vault (fl at), average and high vault (U-shaped) respectively (7mm, 12 mm, 17 mm) [17]. The mean palatal vault height for males and females is 14.9 and 12.7 mm, respectively [17].
Clinical importance: With respect to the greater palatine artery, connective tissue graft can be complicated practically if the palatal vault height not assessed precisely. It is advantageous to leave 2 mm distance away from the artery and the end of the surgical incision to perform smooth surgery without causing traumatic injuries to the artery [17].

Spheno palatine artery
The sphenopalatine artery arises from same named foramen pass to insert to the superior meatus of the nose [15,18]. It is branching to posterior and medial lateral nasal arteries. Give supply to conchae, posteromedial and posterior wall of the maxillary sinus.
Clinical importance: In sinus lift surgeries, caution must be exercised to avoid damaging these vessels if the procedure is being extended to the posterior wall of the sinus.

Anterior nasal spine
Sharp bony process formed as forward elongation of the maxillae [19]. It's positioned below the nose at lower margin of the anterior aperture exactly in midline.
Clinical importance: It is used as a landmark for the pre maxilla surgeries in fl ap advancement preparation. Flaps should not extend beyond the spine because the tissue is thin, and it is possible to penetrate through the tissue into the nose ( Figure 7).

Maxillary innervations
Maxillary nerve supply sensation to the palate [20]. Sensory branches are greater palatine nerve supplying the gingiva, mucous membranes, and most of the hard palate glands [20]. Anterior part of the hard plate supplied through nasopalatine on the contrary soft palate innervated by lesser palatine branch [20]. Anterior teeth with the gingival area supplied by infraorbital nerve which also innervate maxillary sinus mucosa, lower eyelid and conjunctiva furthermore supply part of the nose and the superior lip [21]. Maxillary bone posteriorly supplied through posterior superior nerve including sinus, and molar teeth [20] (Figure 8).

Blood supply in the maxilla
The internal maxillary artery ( Figure 6) arises from the external carotid artery behind the neck of the mandible and provides branches to several regions of the face: mandibular, pterygoid, and pterygopalatine [14].

Maxillary sinus
One of most imperative anatomical structure located in maxilla is maxillary sinus which considered as hugest paranasal sinus. It shaped as pyramid. Average dimensions are 36-45mm, 25-35 mm, 38-45 mm respectively (height, width and length) [10]. The sinus known to have opening that situated in the middle meatus of the nose named as the ostium. Ostium is approximately 28.5mm away from the antral fl oor [22].The maxillary sinus is surrounded by six walls (Figure 9) [23]. Maxillary sinus has special characteristic anatomy in some patients which are special underwood's clefts or septa in 31.7% of cases in the premolar area, and they usually do not divide the antrum [24]. Schneiderian membrane is the soft tissue sac of the antrum with thickness (0.3 to 0.80) mm average [25].
Clinical importance: briefl y the surgical anatomical advice is to avoid membrane perforation through sinus fl oor lifting procedures. As well as avoid overfi lling the sinus with graft material more than 15mm to forestall possible obstructing the ostium opening ends with sinusitis. For these two advices; surgeon should proceed in latero-medial direction, because anterior-posterior elevation may be more prone to create a perforation ( Figure 10).    In presences of multiple septa, operator can approach the sinus through more than one lateral window [24]. Beside, septa can be considered as alarm if an osteotomy for sinus fl oor elevation procedure is organized because of fracture diffi culty of subantral fl oor beneath them.
There are numerous other relevant disputes of concern in maxillary sinus area dealing. Bony fenestration presence in diagnostic images whether in the alveolar ridge (inferior wall) or the lateral wall. Fugazzotto state that a split-thickness fl ap needs to be established over these defects avoiding Schneiderian membrane perforations. Consequently, the residual tissue over the bone defects must be pushed into the sinus, because it's diffi cult to separate lodged residual tissues from membrane [26].

Mandibular structures
Mandibular foramen: Mandibular foramen are inferiorly positioned to occlusal plane in 75% among adults in cadaver while at same level seen in about 22.5% and above it in 2.5%, respectively [27]. In another study [28] were 29.4%, 47.1%, and 23.5%, respectively, this can be related to race and cultural difference. Mandibular foramen length is 21mm on cadaver's assessment [29].
Clinical importance: According to these investigations, occlusal plane level of block injection will be not benefi cial it is better to inject 6-10 mm superiorly to occlusal plane [30]. can "drape downward in catenary fashion [curled as hanging between two points]" [33]. The IAN changing direction from lingual to buccal side and at the area of lower 1 st molar located in the middle between bony cortical plates (buccal and lingual) [34]. Usually, the IAN ( Figure 12) divides into the mental and incisive nerves in the premolar molar region [35]. The mental canal form the emergence of the mental nerve, mandibular canal extended anteriorly and end with as incisive canal [36].

Inferior alveolar canal
The mandibular canal can show bifurcations in the superiorinferior plane latero-medial plane in 1% of patients which manifested as more than one mental foramen diffi cult to be diagnosed on panoramic or periapical fi lms. [37]. Denio, et al. [38] evaluated cadavers to determine distance of IAN from the posterior teeth apices. The mean distance to the second molar, fi rst molar, and premolars were 3.7, 6.9, and 4.7 mm, respectively. Similarly, Littner, et al. [39] reported that distance between the upper border of the canal and root apices of fi rst and second molars were 3.5 to 5.4 mm. Other investigators [40] estimate that the canal was in intimate contacts that to the inferior border of the mandible and in some instances to adjacent to the molar teeth apices. Radiographically, Denio, et al. [38] reported that in "28% of patients the mandibular canal could not be clearly identifi ed in the second premolar and fi rst molar region on periapical radiographs". Therefore, panorama is preferable to view the canal than periapical radiographs.
Cone beam tomography or CT scan can be used as indicated [41]. Anderson LC [33] advice that "during Implants drilling, however, clinicians should not rely on tactile feedback to signal the canal is about to be penetrated, because a twist drill can enter the canal with little warning, a sudden decrease in resistance may give an erroneous impression that the canal has been breached". Therefore, it's crucial for precise radiographic distance details to be used, also drill stopper for safety drilling. For precise estimation of the canal radiographically, professionals can use markers of identifi ed dimension when taking radiographs (e.g., 5-mm-diameter ball bearing).

Bucco-lingual direction of implant positioning in relation
to IAN can be unsafe strategy without the support of computed tomography (CT). Canal bifurcations also need to be evaluated before any surgeries in the area [41].

Mental foramen and nerve
Commonly, mental foramen is the emerging point of the mental nerve [36]. Mental nerve are supplying sensation to skin of the mental foramina area, lower lip, chin, mucous membranes, and the gingiva until the 2 nd premolar. In some circumstances it supplies the innervation for the incisor teeth [42]. The mental foramen position differs in both horizontally  and vertically, and these variations can be linked to race, for example, horizontally position can be found white individuals fl anked by the premolar apices [43] and next to the apex of the second mandibular premolar among Chinese subjects [44].
Atypically, the foramen may be situated by the canine or the fi rst molar [44,45].
The position of the foramina also varies in the vertical plane [43]. Pertinently, in study prepared by Fishel D, [43], for detection of mental nerve of fi rst premolar area in 936 patients, he reported that the foramen was "situated coronal to the apex in 38.6% of cases, at the apex in 15.4% of cases, and apical to the apex in 46.0% of cases. The foramen's location, in relation to the second premolar, was coronal to the apex in 24.5% of cases, at the apex in 13.9% of cases, and apical to the apex in 61.6%of cases". Thus, careful maneuver should be employed, especially in immediate implantations procedures in the premolar area, because of coronally positioned foramen seen in 25%to 38% of cases in relation to bicuspid's apex [43].
As we discuss earlier the IAN loops back to emerge from the foramen when it course inferio-anterioly to the mental foramen. This is known as the anterior loop of the mental foramen [46]. Identifying and measuring the size of the anterior loop is vital and can be done by using varied diagnostic methods: Patients panoramic fi lms, cadaver panoramic fi lms with markers, cadaver periapical fi lms, CT scans of patients, and surgical cadaver dissections [47,48] (Figures 13-15).
Clinical importance: Thus, mental nerve exact location should be identifi ed before implant insertion. First, radiographical determination in relation to premolar region should be utilized. In premolar region creation of a vertical incision mesially to the canine and fl ap refl ected. Wet gauze used to permit safe elevation extend apically and expose the mental foramen roof, then gentle pushing of the gauze by periosteal elevator apically; the nerve is exposed [47]. Direct measurement of the distance is take place between the coronal aspect of the foramen and the alveolar crest by use of a periodontal probe; permit 2mm safety distance in choosing correct implant length from the nerve [47,49].
The mental nerve comes out of the mental canal, which is angled upward from the mandibular canal [50]. Therefore, it should be noted that the inferior alveolar nerve is lateral and apical to the mental foramen. It's preferable to provide safe distance more than 2mm anterior to the mental foramen, Anterior loop presence should be detected by CT scan if other diagnostic elements fail to notify correctly. In this regard, assess opening of distal aspect of the foramen by curved probe (e.g., Naber's 2N probe) in gentle and careful manner not to injure the nerve.

Mandibular incisive canal
Mandibular canal continued as incisive canal mesial to the mental foramen ( Figure 16). It can be seen truly in 80% of cases in middle third of mandible [51]. The incisive nerve supplies innervation to the six anterior teeth. It usually narrows with 1.8 -0.5 mm width [52].The nerve typically terminates apically to either lateral incisor or sometimes central incisor [52]. Jacobs [53] evaluate 545 panoramic fi lms for diagnostic appearance of the incisive canal, he notices that 15% of the fi lms show its presence. On the contrary, it's shown on 93% of CT scans.
Clinical importance: Patients can suffer pain or slight discomfort in presence large incisive nerve canal [54] or   in some cases postoperative pain can be sever need implant removal [55].

Lingual foramen and lateral canals
Minute vascular canals with mean diameter 0.7 mm and 0.6 mm are usually present in the midline and lateral to the midline. One to fi ve canals per patient can be seen as described by Gahleitner [56] (Figure 17). In skull dissection research show that foramen noticed in 99% of the mandibles [57]. While radiographically it noticed in only 49% of the periapical fi lms depending on the beam angulations [56].
Clinical importance: Midline insertion of implants can be complicated by bleeding from this site if larger canal exist [59]. Guide pin use can help to complete the operation.

Submental and sublingual arteries
The submental artery originated from facial artery [60] while lingual artery gives off the sublingual artery, the average both artery diameter is 2mm. [61]. The sublingual artery pass to supply the fl oor of the mouth crossing over the mylohyoid muscle [61]. The submental artery often navigates in inferior direction crossing mylohyoid muscle but might pierce the mylohyoid muscle as noticed in 41% of cadavers. These arteries pass in close proximity to lingual plate [62] (Figure 18). Clinical importance: Sublingual or submandibular hematoma in the fl oor of the mouth can be seen if inadvertent penetration of lingual cortical plate during drilling preparations [63]. Swelling and tongue pressure superior and inferior direction can affect airway causing distress [64,65]. Eventually simple implant procedure can ends with aggressive medical and perhaps surgical maneuvers if an airway crisis sustained. Flap refl ection and elevation also can cause arterial injuries in the lingual side, so carful and proper visualization and elevation should be done to avoid unintentional perforations.

Submandibular and sublingual fossae
These two depressions are presented on the mandibular medial surface forming compartments for the salivary glands. Mylohyoid line separates these compartments. Inferiorly to the line submandibular fossa embraces the submandibular gland [66]. On the contrary shallow slit sublingual fossa is positioned superior to the line and contain the sublingual gland [67] (Figure 19). Computerized Tomography Scan (CTS) used to evaluate the depth of these concavities show that 6 mm depth were reported in 2.4% [62].

Lingual and mylohyoid nerves
Lingual nerve is branch arise from mandibular nerve [68].
Give sensory supply to anterior two-thirds of the tongue and the lingual tissues. The lingual nerve is usually "located 3 mm apical to the osseous crest and 2 mm horizontally from the lingual cortical plate" [69]. Yet, in 15% to 20% of cases, can give various positions to be at or above the bone crest in wisdom tooth area [70]. (Figure 20).    mandibular foramen entrance [70]. Also give innervation to the digastric muscle, anterior belly only.
Clinical importance: It can give accessory sensory innervation to mandibular teeth making diffi cult to perform complete anesthesia [71,72]. Lingual side anesthesia in posterior area can give good solution for such problem [72].

Long buccal nerve
Buccal gingiva and check mucosa innervated by long buccal nerve in retromolar area ends in second premolar. Long buccal nerve arise from the infra temporal fossa pass through the heads of pterygoid muscle giving sensory innervation [73].
Clinical importance: Turner's variation presence considered as important complication can face the professional where the nerve emerges from retromolar fossa special foramen so traumatic injury can result in gingiva and mucosa paresthesia [74].

Muscles attached to the mandible
There are 26 muscles attached to the mandible (Figure 21), we discuss the only concerned with dental implants surgeries [75].

Mentalis muscle
Mandibular incisive fossa gives the origin of paired tiny muscles known as mentalis muscle which inserts into the chin [76]. The muscle fi bers control lower lip elevations as the fi bers crosses inferiorly Clinical importance: Full muscular release from its protuberances can affect facial appearance as consequence to disturbed muscular contraction giving the double chin facial appearance (witch's chin). Avoiding this maneuver tow layers suturing technique should followed

Mylohyoid muscle
Two fl at arms serve as sling supporting the fl oor of the mouth and positioned inferior to the tongue [78]. It has long origin extend along the mandibular body medially from the symphysis to the last molar overlying the digastric muscles given fi nal insertion on the hyoid bone. For this signifi cant position it forms imperative anatomic landmarks separating the sublingual fossa which situated superior to the muscle from the inferiorly seated submandibular fossa.

Genial tubercles (genioglossus and geniohyoid muscles)
The genial tubercles are tiny, four bony heights, can be seen in the mandibular bone lingually seated on both side near to inferior border. Genial tubercle forming attachment of the geniohyoid and genioglossus muscles [79]. The two superior tubercles serve as the origin of genioglossus muscle while the inferiorly positioned are serve as geniohyoid muscle origin from the inferior genial tubercles. In the center between these tubercles, lingual foramen can be seen. [80].

Clinical importance:
If there is progressive bone resorption anteriorly, might alter the superior tubercle height in relation to superior level of the ridge. When fl aps elevated surgically for access, avoid complete refl ection of the genioglossus muscle from the tubercles because posterior retraction of the tongue to the throat can occur and the airway obstruction can be complicate the procedure [81].
Clinical importance: In regard to their position it's usual to release them if mental nerve surgeries is needed by using wet gauze pieces to protect the nerve and refl ect the muscles smoothly.

Buccinator and orbicularis oris muscles
Strong submucosal attachment to both to the cheek and lip through buccinator muscle and orbicularis oris muscle [82].

Conclusion
All implantologist seek for high rate success criteria in dental implants; with advanced technology nowadays we can see that dental implant procedures gain more publicity all over the worlds. Though knowledge and understanding of the anatomical basics before surgery can reduces un wanted complications and reducing the success criteria subsequently affect patients satisfactions. However, certain anatomic sites may be challenging concerning treatment plan as maxillary sinus area of inferior alveolar nerve area. For advanced surgeries it's essential and vital to have good anatomical understanding with proper training to perform smooth success implants.