Romanian Journal of Morphology and Embryology 2008, 49(4):485–489
O OR RI IG GI IN NA AL L P PA AP PE ER R
The maxillary sinus floor in the
V. NIMIGEAN1), VANDA ROXANA NIMIGEAN2),
NICOLETA MĂRU1), D. I. SĂLĂVĂSTRU1),
DANIELA BĂDIŢĂ3), MIHAELA JANA ŢUCULINĂ4)
1)Department of Clinical and Topographical Anatomy
2)Department of Oral Rehabilitation
3)Department of Physiology
Faculty of Dental Medicine,
“Carol Davila” University of Medicine and Pharmacy, Bucharest
4)Department of Restorative Odontology,
Faculty of Dental Medicine,
University of Medicine and Pharmacy of Craiova
The aim of this study was to establish the mean distances between the maxillary sinus floor and the roots of the lateral maxillary teeth in
dentate subjects, respectively the mean height of the available bone for oral implant placement in the corresponding area, in edentulous
ones. Material and Methods: We determined the maxillary sinus floor position in relation to morphoclinical alveolodental benchmarks on
50 dry skulls, dentate 30 and edentulous 20, and correlations were performed by use of 40 CT-scans of the targeted area. In addition,
20 human adult cadavers were bilaterally dissected in order to bring topographical evidence at that level. Results: The data we obtained
lead us to define three dentosinusal relations: tangent (close) relation 60.8%; distanced relation 25.6%; penetrating relation: 13.6%; three
subantral classes in edentulous patients, emphasizing the direct relation of the age of the edentulism and the degree of bone resorption.
We discuss the results we obtained from the viewpoint of their application in the field of oral implantology. Conclusions: The maxillary sinus
floor represents the danger zone for the oral implantology.
Keywords: available bone, oral implant, the lateral maxillary teeth, the maxillary sinus floor.
The alveolar process of the maxilla forms the
maxillary sinus floor. If the sinus is of an average size,
it is on a level with the floor of the nose; if the sinus is
large, it reaches below this level. Projecting into the
floor of the antrum are several conical processes,
corresponding to the roots of the first and second molar
teeth; in some cases, the fangs of the teeth perforate the
The close anatomical relationship of the maxillary
sinus with the roots of maxillary molars and premolars
renders this anatomical region susceptible to morbid
situations resulting from damage to, and therapeutic
intervention in the dentoalveolar environment.
The loss of the teeth interrupts the cybernetic
connections of the stomatognatic system, determining
maxillary and mandibular structural changes that
represent signs of inactivity atrophy due to functional
unload. Modifications in the lateral area of the
edentulous maxilla may affect more than 70% of its
height and width.
The present study was performed in order to
establish the mean distances between the maxillary
sinus floor and the roots of the lateral maxillary teeth in
dentate subjects, respectively the mean height of the
available bone for oral implant placement in the
corresponding area, in edentulous ones.
? Material and Methods
Fifty dry skulls, dentate 30 and edentulous 20, were
morphologically and morphometrically investigated for
the study, and correlations were performed by use of
40 CT-scans of the targeted area. We investigated the
dentosinusal relations on 125 teeth. In addition,
20 human adult cadavers were bilaterally dissected in
order to bring topographical evidence at that level.
The results obtained were processed for further use
in the oral implantology. The floor of the maxillary
sinus is oriented inferiorly and laterally toward the
alveolar process of the maxillary bone. At this level, it
can form recesses between the dental roots.
The alveolar recess – in the alveolar process, 52% of
cases, the most frequent sinus extension, facilitates the
violation of the antrum through endodontic or surgical
therapy (Figure 1).
Normally, the sinus floor is placed at an average
distance of 1.5 cm below the floor of the nasal fossa, on
the horizontal line leaving the lower end of ala nasi.
V. Nimigean et al.
Figure 1 – The alveolar recess between
the roots of the premolars
The shape of the sinus floor was concave (rounded),
mono- or two-concave in most of the cases (80%).
In the remaining situations, the sinus floor had an
irregular or a plane aspect. The interradiculo-antral bone
of a uniform lamellar aspect, presents an antral contact
surface in relation with the sinusal mucoperiosteum and
a dental surface in relation with the periapical space.
These limits of the sinusal floor are independent as
orientation and relations between them and, rarely, on
short distances, are parallel.
The relations of the sinus floor and the root
apices in dentate specimens
We investigated the dentosinusal relations on
125 teeth (Table 1) and we set three types of vertical
▪ distanced relation: between the apices and the sinus
floor, there is a thick bony wall;
▪ tangent relation: between the apices and the sinus
floor, there is a very thin bony lamella;
▪ penetrating relation: when the apices are covered
by the sinusal mucosa.
The bony lamella separating the maxillary sinus and
the teeth decreases in thickness from the upper canine
(6.9 mm) to the 2nd molar (1.7 mm) and further
increases to the 3rd molar (2.8 mm).
Table 1 – Dentosinusal relations
Tangent (close) relation under the
Teeth No. Distanced relation to the
Medium thickness of the alveolar
sinusal wall [mm]
Total tangent (close) relation: 76 (60.8%); Total distanced relation: 32 (25.6%); Total penetrating relation: 17 (13.6%).
From the data obtained it results that the second
molar has the most intimate antral relation (the lowest
point of the sinus floor is placed on its level), so 93.9%
of the second molars showed close relations with the
maxillary sinus floor, tangent and penetrating.
Furthermore, from the all teeth having close relations
with the sinus floor, the second molar represented
27.6% (Figure 2).
Figure 2 – Antral relation of the upper 2nd molar:
1 – sinus floor; 2 – apex of the MB root;
3 – sinus cavity
The tangent and penetrating dentosinusal relations
are the dangerous factor in the surgery of the oral
implants applied immediately after the extractions;
neglected, this treatment may be iatrogenic, leading to
chronic maxillary sinusitis due to the implant
penetration into the antrum.
The sinus floor in edentulous specimens
The mechanism of the alveolar crest atrophy is
incompletely elucidated, several theories: functional
unload, ischemia, pressure, and local inflammation,
have been developed.
Misch CE (2005) , defined four subantral classes
in what regards the average height of the available bone
in the edentulous maxilla.
The measurements we performed leaded us to
establish only three subantral classes (SAC 1–3) for the
subantral residual bone, depending on the osseous
height and the age of the edentulism, the latter not being
considered in classifications at this time.
Bone height minimum 10 mm, what allows to apply
an endosseous implant if the bone width is adequate,
minimum 5 mm. We encountered this type in 56% of
the cases, no edentulism being older than five years
Bone height of 5–10 mm, which necessitate either a
sinus lifting if the bone width is adequate, minimum
5 mm, or osseous augmentation if bone width is
The maxillary sinus floor in the oral implantology
2.5–5 mm, to be performed before implant placement.
We encountered this type in 32% of the cases, the
edentulism being 5–10 years old, without prosthetic
treatment (Figure 4).
Bone height of 0–5 mm, making necessary the sinus
lifting / healing period / graft maturation / delayed
implant placement. This type was present in 12% of the
cases, the edentulism being older than 10 years, without
prosthetic treatment (Figures 5 and 6).
Figure 3 – SAC 1. CT. Right upper jaw cross sections with
measurements step 2 mm (yellow – the bone high;
green – the bone width)
Figure 4 – SAC 2. CT. Right upper jaw cross sections with
measurements step 2 mm (yellow – the bone high;
green – the bone width)
Figure 5 – SAC 3. CT. Left upper jaw cross sections with
measurements step 2 mm (yellow – the bone high;
green – the bone width)
Figure 6 – Severe resorption: 1 – subantral bone high;
2 – sinus floor
The anatomical relation between the maxillary sinus
and the teeth is a complex one, due to the variable
extension of the sinus.
The relations between the dental roots apices and the
sinus floor are critical elements for the diagnosis and
surgical treatment of antral pathology. The results
obtained in this study are useful both in endodontics and
in oral surgery. In what concerns the latter field, the
antrum–teeth relations interfere with teeth removal and
immediate placement of dental implants in the lateral
maxillary region. Identification of the distance between
the dental roots apices and the sinus floor and the
establishment of the available bone thickness are
imperative requirements in case of surgical procedures
of this area. This importance is also emphasized by
Yoon HR and Park CS (1998), who described similar
vertical dento-antral relations, but proposed a
complicated classification, with little clinical relevance.
The buccal roots of the second maxillary molar showed
close relations with the sinus in 40.5% of their studied
Several studies have reported the relative positions
of the roots with respect to the sinus [4, 5].
We consider the classification into three types of the
vertical dento-antral relations, simpler and much useful
with regard to oral surgery than the classification of
Kwak HH et al.  that presents five types of these
relations. Kwak HH et al. found that the most frequent
vertical relationship was a sinus floor that did not
contact the dental roots.
The maxillary height in the region of the first
premolar and first molar in our study was significantly
higher in men than in women, and the most lower zone
of the maxillary sinus floor was the most frequently at
the level of the 2nd molar, at 50% in men and 56% in
The frequency of close proximity (0.5 mm or less)
between the roots of the posterior maxillary teeth
and the sinus floor is 45.5% for the second molars,
30.4% for the first molars, and 19.7% for the second
The buccal roots of the molars may present a vertical
or slightly externally oblique, para-sinusal or internal-
antral orientation, and when the variations of length and
radicular direction are superposed with a lower sinus
floor, we frequently evidence penetrating and
perforating relations, more frequent than for the palatal
Koppe T et al. (2005)  found in 50% of the
examined skulls, that the apices of the upper first
and second molars gave rise to prominences on
maxillary sinus floor and Ariji Y et al. (2006) ,
showed that the roots of the maxillary first molar
were close to the sinus floor in 60% of the studied
The smallest thickness of the alveolar sinus wall
was in our study 1.7 mm at the level of the second
molar. The mean high in the region of the antral teeth
was 1.8 mm, the value being depended on the dental
V. Nimigean et al.
Ariji Y et al. (1996) found a medium high of 3.7 mm
for the bone below the sinus . In this study, the value
did not depend on the dental status, but it was
negatively correlated with the antral volume.
Regarding the shape of the sinus floor, Yoon HR
et al. (2001), presents the following frequent shapes:
plane (54.5%) and round (21.2%). Yuichiro S et al.
(2000) found the following shapes of the sinus floor:
mono-concave (37.8%), two-concave (32.3%), three-
concave (16.2%), and four-concave (13.7%) [10, 11].
Takahisa N (2002) showed that the sinus floor could
be round in case of a small antral volume, plane and
irregular in case of a bigger sinus volume, situation
when the distance between the Schneider membrane
and the teeth apices was reduced. He found the
smallest distance at the level of the second molar buccal
These observations demonstrate
anatomical relations between the sinus floor and the
surrounding structures and the importance of their
knowledge in patients’ clinical management. In the
situations with bone septa inside the sinus, the
possibility of antral membrane perforation through sinus
lifting procedures is very high [13, 14].
Variations of the sinus floor’s depth can depend on
sinuses dimensions, their size and pneumatization being
functions of the skull, and a great degree of
pneumatization is accompanied by a closeness of the
lateral teeth apices to the sinus floor. Variations of the
pneumatization of the maxillary alveolar process could
take place due to the craniofacial morphological
modifications through evolution. Sinuses development
is influenced by dentition, chewing force, breathing
movements and craniofacial growth, factors that also
control the pneumatization of the maxillary alveolar
The antral floor depends upon the dental scaffold
that constitutes the main factor during development and
will transform in relation with the normal/pathological
status of the dento-periodontal apparatus.
Together with the antral volume and high, the
surface of the sinus floor can constitute a criterion for
the maxillary sinuses classification .
Relations of the teeth with the sinus floor can be
accurately assessed on bucco-lingual slides obtained
through 3-D CT-scan.
Knowledge of the distances between the sinusal
roots and the sinus floor is useful for evaluation of the
diameter and length of the dental implants, especially
for immediate implant placement.
Wiltfang J et al. (2000), shows that a maintaining
ratio of the subsinus bone of 4–8 mm is very
unfavorable for the prosthetic
Endoscopic and ultrasonographic evaluations of the
sinus floor can reduce the complications after surgical
Radiologically comparing the depth of the sinus
floor, Ohba T et al. (2001) did not observe statistical
differences between the right and the left sides .
In our opinion, the asymmetry between left and right
antrum sides is a demand for the radiological
assessment of each sinus.
Under normal clinical use and without a
standardized method of film positioning, the average
alveolar bone level measurements varied significantly
between conventional radiographs and digital images in
multiple regions of the mouth. In addition, the digital
images revealed a higher number of sites with early-to-
moderate bone loss than did the conventional images.
These findings suggest that evaluation of alveolar bone
loss using intraoral digital radiographs is not comparable
with that of conventional radiological film under normal
The available bone is lost from the inferior
expansion of the sinus after tooth loss, involving the
residual ridge region. The bone density in this area is
the smallest one registered for any mandibular and
maxillary regions and decreases very fast. The width of
the available bone placed below the sinus is important
for the establishment of the diameter of the implant and
for the crestal approach in case of sinus floor lifting,
which is more conservative than the lateral approach.
Woo I and Le BT (2004) also agrees with this
The quantity and quality of the available bone
placed below the sinus and the local topographic
conditions are decisive factors for the implant-prosthetic
treatment in the lateral maxillary region .
The danger of the antral penetration is grater at the
level of the buccal roots of the first and second molars
and of the second premolar – these roots can be
considered sinusal roots.
The lateral maxillary area is the less predictable for
the implant–prosthetic treatment and we consider that
the main factor leading to osseous resorption in this area
is the functional unload determined by the lack of teeth
or lack of prosthetic treatment.
The maxillary sinus floor represents the danger zone
for the oral implantology.
This research was sustained by VIASAN Research
Grant no. 101/2006.
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Victor Nimigean, Professor, MD, PhD, Head of Clinical and Topographical Anatomy Department, Faculty of
Dental Medicine, “Carol Davila” University of Medicine and Pharmacy, 8 Eroilor Sanitari Avenue, 5th sector,
050 474 Bucharest, Romania; Phone +4021–318 08 62, E-mail: firstname.lastname@example.org
Received: September 1st, 2008
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Accepted: October 25th, 2008