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RADIOGRAPHIC SCREENING FOR IMMEDIATE MOLAR IMPLANT PLACEMENT
28
to posterior, while lingual cortical plates decrease in
thickness from anterior to posterior
31,32
(Fig 2-6).
Padhye et al33 examined CBCT scans of 200 mandibular rst molars from patients without radiographic
or clinical evidence of periodontal disease, severe root
resorption, trauma, or periapical lesions. e mean
thicknesses of buccal and lingual buccal bone 2 mm
apical to the crest were 0.84 ± 0.39 mm and 2.71 ±
1.17 mm (P = .003). However, it should be noted that
others have reported that if buccal bone thickness is
1 mm or less, its measurement can be largely inaccurate.34 Careful review of every patient’s CBCT scan
should take these observations into consideration.
Cross-sectional root shapes
Many dierent root morphologies can present with
mandibular molars. However, as already stated, the
most common nding is for a mandibular molar to
have separate mesial and distal roots with a prevalence of 68% and 78% for mandibular rst and second
molars respectively.31 A study by Dunlap and Gher
measured the root surface area of mandibular rst
molars.35 ey reported that the mesial root had a
larger surface area than the distal root (Fig 2-7). erefore, should the operator ever elect to place an IMI
into one of the molar root sockets (eg, for a second
molar where IMIs are being placed at both the rst and
FIG 2-6 e mandibular buccal cortical plate normally thickens from its anterior
to posterior aspects.
FIG 2-7 e distal roots of mandibular molars
generally are smaller in size and surface area than
their mesial roots.
second molar sites) to optimize subsequent prosthetic
restoration, the distal one would be the preferred.
Site-specific considerations
Septal bone present within the furcation area
Achieving primary stability in mandibular molar
extraction sockets can be challenging due to the width
of the socket and anatomical limitations beyond the
root apices, ie, proximity of the IAC.10 erefore, the
IRS bone and the peripheral bony walls of the socket
oer the safest areas for implant stabilization. Smith
and Tarnow classied molar sockets into three types
of IRS.11 Type A sockets are those with wide IRS bone
and are anticipated to house the entire coronal body
of the IMI (Fig 2-8a). Type B molar sockets are those
with sucient IRS bone to stabilize the implant but
not completely encircle its coronal segment (Fig
2-8b). Type C mandibular molar IRS will have little
to no septal bone in which to engage the implant (Fig
2-8c), and therefore to achieve initial stability, a widerdiameter implant will likely be needed in order to make
contact with the socket walls. Alternatively, a longer
implant could be used, but this comes with increased
risk because it would need to engage at least 4 mm of
native bone apically and runs the risk of damaging the
IAN. Of the three categories, type A sockets are the
29
Radiographic Screening for Mandibular IMI Placement
most favorable for IMI placement. However, type B
IRS are the most common in the mandible, while type
C should be considered the most technique-sensitive
and unpredictable if the clinician is inexperienced. Here
a better option would be socket preservation grafting
and delayed implant placement (see chapter 1). Ho et al
recently showed that IRS < 3 mm was found in 76.8%
of second and 44.6% of rst mandibular molars.
27
Root apex to canal distance
Root apex to canal (RAC) distance can be dened as
the distance from the root tips to the superior border
of the IAC36 (Fig 2-9). IAN damage is the prevalent
nerve injury in implant dentistry (64.4%).37 It can
happen during osteotomy preparation (laceration/
trauma) or during implant placement (compression).38
Complications resulting from damage to the IAN
FIG 2-8 (a) As seen in this occlusal CBCT slice, the
typical type A mandibular molar IRS will have sucient
IRS bone in the furcation area to completely house a
standard-diameter dental implant placed as an IMI.
(b) An example of a type B mandibular molar IRS. e
bone available is insucient to completely surround
the coronal aspect of a standard-diameter IMI. e IMI
will likely be without bone cover on its distal aspect. (c)
is example shows an extreme type C IRS. No IRS bone
exists between the roots of the second molar.
a
c
b
FIG 2-9 (a) In this example, the root apices of a mandibular second molar have an RAC of > 2 mm but still possibly insucient to
safely place an IMI secured by 4 mm of apical bone if the implant were to be placed in one of the root sockets instead of the IRS. (b) e
example shown clearly would be taboo for consideration of IMI placement at this second molar type C socket.
a b
4.91 mm
4.95 mm
1.08 mm
1.34 mm
7.04 mm
3.79 mm
4.91 mm
10.04 mm
10.04 mm
2
RADIOGRAPHIC SCREENING FOR IMMEDIATE MOLAR IMPLANT PLACEMENT
30
include temporary or permanent paresthesia or hyperesthesia, which can be debilitating for the patient by
aecting daily activities such as speech, eating, drinking, kissing, and shaving.
36–38
Most instances of IAN
damage during implant placement have been reported
to occur when the RAC distance is less than 2 mm.39
In their assessment of CBCT scans of mandibular rst
molar sites, Padhye et al33 documented that, on aver-
a b c
FIG 2-10 (a) is patient has a large embrasure between the two molars that fulll the desired 1.5 mm needed between implant and
adjacent tooth. (b) is image depicts the typical smaller embrasure space between the mandibular second premolar and rst molar. More
care is needed here in placing an IMI to prevent interproximal bone loss or impingement of the implant onto the distal of the premolar.
(c) In this example, placing the IMI into the IRS will help to maintain the interproximal bone between the implant and second premolar.
FIG 2-11 is mandibular rst molar had acute periapical infection and associated obliteration of the IRS.
It was not managed with an IMI.
age, mesial and distal RACs were 4.31 mm and 4.61
mm, respectively, while Demircan29 measured these
mean RAC distances in males versus females as signicantly higher in the former (5.02 mm for males and
3.49 mm for females). Ho et al recently also showed
the distances from the root apices of mandibular rst
molars to be signicantly greater that those at second
molars. In addition, up to 14.5% of second molar sites
had < 10 mm of vertical bone height between the IAC
and furcation bone crest.
27
Interroot distance between adjacent teeth
e distance between roots of adjacent molar teeth
is an important consideration when placing implants
into fresh extraction sockets. Embrasure spaces
between rst and second mandibular molars range
between 0.8 and 3.2 mm (Fig 2-10a). However, smaller
embrasure spaces (0.2–4.5 mm) exist between second
premolars and rst molars (Fig 2-10b), requiring
strict evaluation and measurement when considering
immediate implants for rst molar sites because 1.5
mm will need to be maintained between the premolar and implant to prevent unwanted interproximal
bone resorption.40 When these distances are less than
1.5 mm, the clinician should consider placing the IMI
more distally within the socket in order to avoid the
3.50 mm
1.86 mm
1.86 mm4.14 mm
31
Radiographic Screening for Maxillary IMI Placement
risk of traumatizing adjacent teeth roots (Fig 2-10c).
Using an implant that allows platform switching also
can assist in situations where the implant-to-tooth
distance is only marginally sucient.41
Pathologic considerations
Presence of periapical pathology
Preexisting infection of molars is a common nding
and often an indication for extraction. e presence of
infection in a fresh extraction socket may have implications for IMIs. Molars with acute infection like that
shown in Fig 2-11 are poor candidates. However, Chen
et al42 showed no statistically signicant dierence
when placing implants immediately into sites with
chronic infection, as long as the residual infected
tissue was removed with the use of degranulating
burs. As long as there is sucient bone remaining to
stabilize an IMI, a favorable outcome in chronically
infected sites can be anticipated (see also chapter 5).
Here the RAC is an important parameter to evaluate.
Radiographic Screening for
Maxillary IMI Placement
When screening for IMIs in the maxilla, parameters
that need consideration include socket measurements,
alveolar recesses in the coronal plane, the relation
ships between sinus and molar apices in the sagittal
plane, IRS bone, distance from molar furcation and
alveolar crest to sinus oor, root intrusion into sinus,
and pathology (Table 2-3).
TABLE 2-3
Risk assessment of anatomical, site-specific, and pathologic considerations for IMI placement in
maxillary molar areas
FAVORABLE UNFAVORABLE
Anatomical parameters
Socket measurements in the coronal plane ≥ 5 mm distance between buccal and palatal roots < 5 mm distance between buccal and palatal roots
Socket measurements in the sagittal plane ≥ 5 mm distance between mesiobuccal and disto-
buccal roots
< 5 mm distance between mesiobuccal and
distobuccal roots
Root apex to sinus floor > 5 mm distance from root apices to sinus floor < 5 mm distance from root apices to sinus floor
Position of alveolar recess relative to
maxillary first molar roots
Type 2 Type 1, 3, 4
Position of the anterior wall of sinus
relative to maxillary first molar roots
Type 2 Type 1, 3
Site-specific parameters
Septal bone presence Type A Type B, C
Root apices intrusion into sinus Nonintruded Intruded
Pathologic parameters
Presence of PA pathology No PA pathology present or after removal of PA
pathology
Acute PA pathology
PA = periapical.
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RADIOGRAPHIC SCREENING FOR IMMEDIATE MOLAR IMPLANT PLACEMENT
32
Anatomical considerations
Socket measurements
Coronal plane. A minimum amount of bone width
is required to achieve primary stability of maxillary
IMIs. e distance between the buccal and palatal
root apices can help to determine whether there is
sucient bone to surround the implant completely.
When placing an IMI of standard diameter (4 mm),
a minimum of 5 mm of IRS bone width is required43
(Fig 2-12a). When there is less than 5 mm of bone
between the roots, it is dicult to achieve primary
stability, and therefore immediate implant placement
may be contraindicated (Fig 2-12b).
Sagittal plane. e distance between the mesiobuccal and distobuccal roots of a maxillary molar under
consideration for an IMI should also be measured in the
sagittal plane. Matsuda et al43 suggested that a minimum distance of 5 mm of bone width between the two
buccal roots of a maxillary molar is required to achieve
primary stability using an IMI of standard diameter.
When this IRS width is less than 5 mm, the prognosis
for IMI placement is likely unfavorable (Fig 2-13).
FIG 2-12 (a) is CBCT coronal slice reveals there to be 8.19 mm width between
the buccal and palatal roots. If the IRS is 5 mm or greater, as it is here, adequate
stabilization of an IMI is likely. (b) e measurement of IRS width in the coronal
plane reveals there to be inadequate bone to stabilize an IMI.
FIG 2-13 e IRS width between
the mesiobuccal and distobuccal
roots of this maxillary rst molar
is only 1.51 mm, making the prognosis for an IMI unfavorable.
FIG 2-14 (a) When the distance from the molar root apices to the sinus
oor is greater than 5 mm, adequate stabilization of an IMI is likely
achievable. (b) In this example, the distances between the molar root
apices and the antral oor were less than 5 mm, making IMI placement
challenging for the inexperienced clinician, as it would likely require
simultaneous indirect sinus oor elevation.
FIG 2-15 Measurements between
sinus oor and the alveolar crest and/
or the molar furcation can be helpful in
planning IMIs. (Courtesy of Dr Maziar
Ebrahimi, Toronto, Ontario.)
8.19 mm
3.08 mm 1.46 mm
6.03 mm
7.60 mm
2.92 mm
1.51 mm
a
a
b
b
33
Radiographic Screening for Maxillary IMI Placement
Root apex distance to sinus oor. e bone available from the root apices of a maxillary molar to the
sinus oor can be utilized to gain primary stability
of an IMI. When distance from the root apex to the
sinus oor is 5 mm or more, adequate primary stability of an IMI is likely achievable
43
(Fig 2-14a). In situations where there is less than 5 mm of this subantral
bone, IMI placement is deemed more technically challenging and may require simultaneous transcrestal
sinus oor elevation or augmentation (Fig 2-14b). In
another recent study, Deporter et al44 measured mean
distances from sinus oor to mesiobuccal, distobuccal,
and palatal root apices to be 2.89 mm, 2.48 mm, and
2.37 mm for maxillary rst molars and 0.93 mm, 2.45
mm, and 2.58 mm for second molars. Other useful
CBCT measurements for planning IMIs in maxillae include the distance from alveolar ridge crest to
sinus oor and distance from molar furcation to sinus
oor (Fig 2-15). Demircan and Çankaya45 reported the
mean distances from alveolar crest to sinus oor to be
approximately 7.50 mm, while Matsuda et al43 calculated the mean distance from molar furcation to sinus
oor to be 6.51 mm (standard deviation of 2.94 mm).
Alveolar recesses in the coronal plane
e maxillary alveolar recess denes the inferior
border of the maxillary sinus and is another important
anatomical landmark when IMIs are being considered
for the maxillary rst molar. Knowing the locations
of alveolar recesses relative to the molar apices allows
for proper implant positioning.45 Alveolar recesses are
measured in the coronal view and can be categorized
into four groups
45
:
• Type 1: e alveolar recess is lateral to both buccal
and palatal roots of the rst maxillary molar (Fig
2-16a).
•
Type 2: e alveolar recess is between the buccal
and palatal roots (Fig 2-16b).
• Type 3: e alveolar recess is medial to both buccal
and palatal roots (Fig 2-16c).
• Type 4: No alveolar recess is present in the location
of the maxillary rst molar (Fig 2-16d).
Relationship between sinus and molar apices
in the sagittal plane
When planning maxillary IMI placement, the root
apices of the molar teeth in the sagittal plane should
be away from the maxillary sinus. Demircan and
Çankaya
45
classied the relationships between the
antrum and the maxillary rst molar using the anterior wall of the sinus as the reference point. ree
categories were described. With type 1 relationships,
the anterior wall of the maxillary sinus was seen to be
FIG 2-16 (a) is coronal view shows the alveolar recess (arrow) to be lateral to both molar roots, a favorable situation for an IMI.
(b) With this molar, the type 2 alveolar recess is located between the buccal and palatal roots, in which case an IMI can be safely placed.
(c) is type 3 alveolar recess is located medially to both the palatal and buccal roots, indicating a poor prognosis for an IMI because of
inadequate bone for stabilization. (d) Coronal view of a type 4 alveolar recess. e lack of a recess makes IMI placement unfavorable.
a b c d
2
RADIOGRAPHIC SCREENING FOR IMMEDIATE MOLAR IMPLANT PLACEMENT
34
FIG 2-17 (a) In the sagittal plane, a type 1 relationship was specied to have the anterior wall of the sinus located between the mesio-
buccal and distobuccal roots of the rst molar. is relationship is considered too dicult for IMI placement as there is a high risk of
sinus oor perforation. (b) e anterior wall of the maxillary sinus is posterior to the distobuccal root of the rst molar, making the
prognosis for an IMI favorable. (c) In this type 3 situation, the anterior wall of the antrum is anterior to the mesiobuccal root of the
rst molar, again making placement of an IMI challenging.
FIG 2-18 (a) A type A maxillary socket after Smith and Tarnow.11 ere is adequate IRS to completely house a standard-diameter
implant. Implant simulation is depicted in the right-hand occlusal CBCT view. (b) With a type B socket, there will be sucient IRS to
stabilize an IMI but not enough to totally house its coronal aspect. Implant simulation predicts the IMI to be contacting all three roots,
resulting in signicant IRS dehiscences. (c) Type C sockets have too little to no IRS for implant stabilization.
FIG 2-19 (a) No root intrusion into the sinus domain makes IMI placement into the IRS favorable. (b) Intrusion of both buccal roots
into the sinus domain can be a contraindication for IMI placement at this rst molar site. (c) e palatal root intrusion would make IMI
placement challenging for the novice implant surgeon. (d) Both buccal and palatal roots intrude into the sinus domain, making this
site unfavorable for IMI placement.
a
a b c d
a
b
b
c
c
5.06 mm5.10 mm
35
Conclusion
between the mesiobuccal and distobuccal roots (Fig
2-17a). With type 2, the anterior wall of the maxillary
sinus was described to be posterior to the distobuccal
root (Fig 2-17b), while with type 3, the anterior antral
wall was anterior to the mesiobuccal root (Fig 2-17c).
Site-specific considerations
IRS bone
Smith and Tarnow11 categorized molar socket IRS into
three types, depending on the degree of diculty in
manipulating them. As stated earlier, type A sockets
are those having adequate IRS bone to contain circumferentially the entire coronal portion of an IMI, and
are the most favorable sites for IMIs (Fig 2-18a). In
contrast, type B sockets were classied as those with
enough septal bone to stabilize an IMI but insucient
to encase its coronal portion fully (Fig 2-18b). Finally,
type C sockets were classied as those with insucient
septal bone to stabilize an IMI. As a result, achieving
stability of an IMI with a type C socket requires that
either a wider-diameter implant be used in order to
contact the socket walls, or a longer implant be used
to go beyond the previous root apices for stability
(Fig 2-18c). Deporter et al44 recently reported on the
dimensions of IRS in maxillary molars. Mean coronalmost buccopalatal/mesiodistal IRS widths were 6.52
mm/7.33 mm for rst molars and 5.85 mm/6.86
mm at second molar sites. In their patient sample,
61.7% of rst molars and 34.0% of second molars had
suciently broad IRS to encase completely a 5-mm-
diameter IMI.
Root intrusion into sinus
When roots intrude into the maxillary sinus, there is
an increased risk of oroantral communication after
tooth extraction. Demircan and Cancaya classied
this occurrence into 4 types45:
1. No intrusion (Fig 2-19a)
2. Buccal root intrusion (Fig 2-19b)
3. Palatal root intrusion (Fig 2-19c)
4. Buccal and palatal root intrusion (Fig 2-19d)
e recent data from Deporter et al44 showed that
palatal roots of maxillary rst molars showed higher
intrusion rates (36.74%) than the two buccal roots,
FIG 2-20 Acute periapical
infection with sinus pene
tration at the rst molar site
precluded IMI placement.
while with second molars, the mesiobuccal roots were
more likely to be intruding into sinus (40%).
Pathologic considerations
Presence of periapical pathology
Similar to mandibular molar sites, where there is
chronic infection in a maxillary molar extraction
socket but sucient bone for implant stabilization
after tooth removal and degranulation, IMI placement
can be considered favorable.42 However, as seen in Fig
2-20, where there is acute infection within the socket,
IMI placement is contraindicated.
Conclusion
With the increasing demand for faster implant treatment by patients, implant placement into fresh
extraction sockets has become a popular treatment
modality. However, the IMI approach should be
considered a technique-sensitive procedure, one critical factor being the need to achieve adequate initial
implant stability. CBCT radiographs are considered the
gold standard for initial implant treatment planning,
and their benets over conventional radiographs have
been discussed in this chapter. Undertaking thorough
assessment of these scans preoperatively with attention being paid to the anatomical, site-specic, and
pathologic parameters described here will allow the
clinician to predict cases as having either a favorable
or unfavorable risk prole. It is important to note
that rarely is there an ideal site with all parameters
favorable. However, accurate and knowledgeable
radiographic screening can be the dierence between
success and failure.
2
RADIOGRAPHIC SCREENING FOR IMMEDIATE MOLAR IMPLANT PLACEMENT
36
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KEY POINTS
• CBCT pretreatment assessment is considered to be the gold standard for planning IMIs.
•
When screening for IMIs, a number of anatomical, site-specific, and pathologic parameters
need to be considered.
•
For mandibular IMIs, ridge morphology, lingual ridge concavities, thicknesses of buccal and
lingual cortices, IRS bone type, and distances from root apices to IAC must be evaluated.
• Mandibular IMIs are ideally placed in IRS if feasible, noting that second molar sites are of
greater risk because of local anatomy.
•
With maxillary IMIs, socket measurements, alveolar recesses in the coronal plane, relationships between sinus floor and molar root apices in the sagittal plane, IRS type, root
intrusions into sinus, and distances from furcation and alveolar crest to sinus floor provide
crucial information.
37
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