Central incisor implant

J Oral Maxillofac Surg
69:142-153, 2011

Classification of Maxillary Central
Incisors—Implications for Immediate
Implant in the Esthetic Zone
Sze Lok Lau, BDS(HK), MDS(OMS)(HK), AdvDipOMS(HK), MOSRCS(Edin),
FHKAM(DS), FCDSHK(OMS),*
James Chow, MBBS(HK), BDS(HK), MDS(OMS)(HK), FHKAM(DS),
FCDSHK(OMS), FDSRCS(Eng), FRCD(C),†
William Li, BDS(HK), MDS(OMS)(HK), AdvDipOMS(Hk), MOSRCS(Edin),
FRACDS, FHKAM(DS), FCDSHK(OMS),‡ and
Lop Keung Chow, BDS(HK), MDS(OMS)(HK), MOSRCS(Edin), FHKAM(DS),
FCDSHK(OMS)§

Purpose: This is the first study to analyze the positions and angulations of the central maxillary incisors
with reference to the alveolus, providing data for clinicians to achieve good esthetic results for immediate
implant placement in the esthetic zone.
Materials and Methods: A total of 300 cone beam images were selected randomly. Five aspects were
measured: the thickness of the palatal and buccal bone at their mid-root and apical level and the apical
bone height. A classification was established according to the positions and angulations of the tooth.
Results: The data from 170 cone beam images were included in the present study. The mean thickness
of the buccal bone at the mid-root level was 0.9 0.4 mm and at the apical level was 2.04 1.01 mm.
The mean thickness of the palatal bone at the mid-root level was 3.76 1.37 mm and at the apical level
was 8.51 2.54 mm. The mean apical bone height was 9.53 2.76 mm. The proportion of incisors
positioned more buccally (type B) was 78.8%, 19.4%, and 1.8% positioned midway (type M) and more
palatally (type P), respectively. Regarding the angulation, 49.9% were classified as type 2 (toward buccal),
34.7% as type 3 (toward buccal, with the long axis anterior to the A point), and 15.4% were categorized
as type 1 (toward palatal or parallel to the alveolus).
Conclusions: We recommend that clinicians appreciate the socket in 3 dimensions to achieve a good
outcome. According to the difficulty of achieving good results, the cases were categorized as levels I to
III and recommendations were given.
© 2011 American Association of Oral and Maxillofacial Surgeons
J Oral Maxillofac Surg 69:142-153, 2011

Throughout the past 40 years, dental implantation has by a dental implant has become the reference stan-
gradually changed our thoughts about the line be- dard. Traditional guidelines have suggested a 2- to
tween saving a tooth and extraction, as well as tooth 3-month healing period after dental extraction to al-
replacement therapy. With rapid advances in grafting low sufficient bone infilling and remodeling before
materials and refinements in the surgical and pros- dental implant placement,1,2 after which, a 3- to
thetic protocols, the restoration of a single tooth gap 6-month healing period should be allowed before the

Received from Branemark Osseointegration Centre, Hong Kong, ter, 99 Queen’s Road Central, Hong Kong, People’s Republic of
People’s Republic of China. China; e-mail: alfred.lau@disc-hk.com
*Specialist in Oral and Maxillofacial Surgery. © 2011 American Association of Oral and Maxillofacial Surgeons
†Specialist in Oral and Maxillofacial Surgery. 0278-2391/11/6901-0020$36.00/0
‡Specialist in Oral and Maxillofacial Surgery. doi:10.1016/j.joms.2010.07.074
§Specialist in Oral and Maxillofacial Surgery.
Address correspondence and reprint requests to Dr Lau: Brane-
mark Osseointegration Centre, Hong Kong, Room 1901, The Cen-

142

LAU ET AL 143

implant is exposed and loaded with a fixed prosthe- thetic results. The thicknesses of the bone at the
sis.1,2 However, the negative effect of tooth extrac- buccal and palatal side were evaluated, as was the
tion on the volumetric hard and soft tissue changes in bone height at the apical tooth region. A new classi-
the buccolingual and vertical dimensions has been fication is introduced to categorize the different tooth
reported extensively in published studies. Using diag- positions and angulations, providing a reference to
nostic casts,3-5 radiographs,6-8 and direct measure- help avoid compromising the buccal bone thickness
ments9 to evaluate the magnitude of bone resorption, and to prevent fenestration and perforation during
it has been reported that during the first 4 months implant placement. Different types of teeth were also
after extraction, the mean bone reduction was 5 to 7 ranked according to their difficulties for achieving
mm buccolingually8,9 and 2 to 4.5 mm vertically.6 good long-term results, and general recommendations
Because such bone resorption will strongly affect the for their management were given.
implant placement and, thus, the esthetics outcome,
clinicians started to insert the implant directly into
Materials and Methods
the extraction socket immediately after extraction,
under the assumption that this would reduce the A series of 300 cone beam (CB) images of the
bone resorption. The first case report of this tech- maxilla taken from April 2006 to August 2006 were
nique was published in 1976.10 Since then, numerous randomly selected from the computer record at the
studies have been published regarding the refinement Dental Implant and Maxillofacial Centre in Hong
of this technique.11-13 Additional clinical research has Kong. All CB images were taken with the same ma-
shown that the outcomes of immediate implant place- chine (I-CAT cone beam volumetric tomography and
ment, delayed implant placement, and implant place- panoramic dental imaging system; Imaging Science
ment in healed socket sites were all comparable.14 International, Hatfield, PA). The head positions were
The multiple advantages of immediate implant place- standardized by aligning the patient’s head with hor-
ment are well known, especially in the esthetic zone, izontal and vertical reference lines, constructed using
such as the maxillary central incisors. These advantages a beam of light. The patient’s head was positioned
include a reduction in the number of surgeries, a reduc- such that the horizontal reference beam was at the
tion of the total treatment time, the preservation of level of the patient’s eyes and the vertical reference
alveolar bone,15-17 the maintenance of a good soft tissue beam was passing through the patient’s facial midline.
profile,18 and the reduction of the patients’ psychologi- Once the ideal head position had been located, the
cal trauma owing to the loss of a front tooth.19 However, patient’s head was fixed with a head frame. The CB
such therapy is not without drawbacks. The greatest images were viewed and measured by the software
problem for clinicians is the unpredictability of the long- provided. Each image was examined to identify a fully
term soft tissue stability. The problem of soft tissue formed, intact, and healthy permanent central upper
recession is usually exacerbated in patients with rela- right incisor (tooth 11) for analysis. If the central
tively thin buccal bone and thin gingival biotypes.20 upper right incisor was missing, the upper left central
Because the gingival biotype cannot be changed, the incisor was selected for analysis. The CB imaging data
critical aspect of achieving esthetic success depends on were excluded if any radiographically detectable
the ideal 3-dimensional implant position21 and the main- enamel or dentine defect, caries, apical pathologic
tenance of adequate buccal bone thickness over the features, periodontal alveolar bone loss, restoration of
implant buccal surface.22 Immediate implant therapy any kind, or fracture was present or when both cen-
has been reported to be very technically demanding14 tral incisors were missing.
and requires an understanding of all these aspects and Landmarks were identified and marked in the com-
more. Failure to do so will result in an adverse outcome, puter before the measurements were done. The sag-
defeating the initial objectives of the therapy itself. Im- ittal section of the chosen incisor was viewed at the
mediate implantation is never easy, especially when the center of its mesial-distal dimension. As shown in
demand for long-term stable esthetic results is high; Figure 1, both the palatal line (line 1) and the buccal
thus, case selection is of the utmost importance. line (line 2) were marked by a line best-fit to the
The criteria for implant success have been chang- palatal alveolar surface and the buccal alveolar sur-
ing, and interest in the esthetic outcome is becoming face, respectively. The alveolar line (line 3) was
a major concern. Implant dentistry has gradually marked by bisecting the palatal and buccal lines. This
evolved from a bone-driven surgical protocol to a indicated the angulation of the alveolar process in the
restorative and biologically driven protocol. The sagittal plane. The angulation of the tooth root was
present study is the first to analyze the positions and indicated by its long axis (line 4), and this axis was
angulations of the central maxillary incisors with ref- marked by the midpoint of a line drawn from the buccal
erence to the alveolar bone. Our results will provide enamel-dentine junction to its palatal counterpart, the
data for clinicians to achieve the best long-term es- apex of the root. The present study involved measure-

144 CLASSIFICATION OF MAXILLARY CENTRAL INCISORS

ward the buccal bone surface. The thickness of the
buccal bone at the mid-root level (measurement I) was
measured from a point at the buccal root surface to the
buccal bone surface along this line. The palatal bone
thickness at the mid-root level (measurement II) was
measured from a point at the palatal root surface toward
the palatal bone along this same line. The thickness of
labial bone at the apical level (measurement III) was
defined as a line perpendicular to the long axis of the
root, from the apex of the root toward the buccal bone
surface. The thickness of the palatal bone at the apical
level (measurement IV) was defined as the distance
of the line perpendicular to the long axis of the root
from the apex of the root toward the palatal bone
surface. The apical bone height (measurement V) was

FIGURE 1. Landmarks for measurement.
Lau et al. Classification of Maxillary Central Incisors. J Oral
Maxillofac Surg 2011.

ment of the residual bone thickness and angulations of
the extraction sockets. The long axis of the tooth root,
instead of the long axis of the whole tooth, was used,
because the range of the crown-root angle is 25.5° for
maxillary central incisors.23 From these reference lines,
4 measurements were performed, using the built-in mea-
suring function of the computer software. The measure- FIGURE 2. Measurements of bone thickness at different aspects
ments are shown in Figure 2. (measurements I to V).
A line was drawn from the mid-point of the long axis Lau et al. Classification of Maxillary Central Incisors. J Oral
of the root perpendicularly from the palatal bone to- Maxillofac Surg 2011.

LAU ET AL 145

measured along the long axis of the root from the root All measurements and classifications were per-
apex toward the superior bone surface. formed by 2 investigators. Reliability tests were also
From the CB measurements, the positions and angu- performed to check the consistency and accuracy
lations of the tooth roots were classified with reference using the Statistical Package for Social Sciences, ver-
to the alveolar process. By comparing the buccal and sion 11.0, software (SPSS, Chicago, IL). Studies of this
palatal bone thickness at the mid-root level, their posi- type are exempt from approval by the local institu-
tions with reference to the mid-alveolar line were de- tional review board.
fined and classified as follows (Fig 3): type B (closer to
the buccal alveolar surface); type M (midway between
Results
the buccal and palatal alveolar surface); and type P
(closer to the palatal alveolar surface). Comparing the The CB imaging data from a series of 300 randomly
angulations of the alveolar process with the long axis of selected patients were accessed initially. The images
the roots, the angulations were classified as follows (Fig were all examined to identify useful data according to
3): type 1 (root apex angulated toward the palatal side the defined inclusion and exclusion criteria. The CB
or parallel to the alveolus); type 2 (root apex angulated imaging data from 170 patients were included in the
toward the buccal side with the long axis passing pos- final analysis. Of the excluded 130 patients, 109 had a
terior to point A); and type 3 (root apex angulated defective incisor (eg, caries, infections, restorations,
toward the buccal side with the long axis passing ante- periodontal bone loss, or fracture) and 21 had both
rior to point A). central incisors missing. The mean patient age was 47

FIGURE 3. Classification according to position and angulation.
Lau et al. Classification of Maxillary Central Incisors. J Oral Maxillofac Surg 2011.


Table 1. MEASUREMENT RESULTS

Thickness at Mid-Root
Level Thickness at Apical Level
Measurement Buccal Bone Palatal Bone Buccal Bone Palatal Bone Apical Bone Height
(mm) (Measurement I) (Measurement II) (Measurement III) (Measurement IV) (Measurement V)

Mean 0.90 3.76 2.04 8.51 9.53
Median 0.89 3.69 1.96 8.40 9.57
Standard deviation 0.40 1.37 1.01 2.54 2.76
Maximum 1.99 10.10 7.72 22.41 17.20
Minimum 0.10 0.50 0.10 2.56 2.15

years (range 13 to 85). Of the 170 patients, 76 (45%) root to the nasal floor, almost one half of the patients
were males and 94 were females (55%). (47.6%) had at least 10 mm of bone height; 97.6% had
The mean thickness of the buccal bone at the 4 mm or more of bone height and 71.2% of patients
mid-root level (measurement I) was 0.9 mm (range had 8 mm or more of bone height (Table 6).
0.1 to 1.99), and the mean thickness of the palatal A classification of the positions and angulations of
bone at the mid-root level (measurement II) was 3.76 the central incisors with reference to the alveolar
1.37 mm (range 0.5 to 10.1). The mean thickness of bone was established. Most of the central incisors
the buccal bone at the apical level (measurement III) (78.8%) were positioned more buccally within the
was 2.04 1.01 mm (range 0.1 to 7.72), and the alveolar bone (type B), 19.4% were positioned in
mean thickness of the palatal bone at the apical level midway (type M), and 1.8% were positioned more
(measurement IV) was 8.51 2.54 mm (range 2.56 to palatally (type P; Table 7). Regarding the incisor an-
22.41). The mean apical bone height (measurement
gulations, almost one half (49.9%) of the central inci-
V) was 9.53 2.76 mm (range 2.15 to 17.2). These
sors were classified as type 2, 34.7% were classified as
measurements are listed in Table 1.
type 3, and 15.4% (26 cases) were categorized as type
Additional analysis of the measurements revealed
that 57% of the patients had a buccal bone thickness 1. An analysis that combined both the position and
at the mid-root level of less than 1 mm (Table 2), and the angulation type showed that most were type B2
62.4% of patients had a palatal bone thickness at the (38.2%). The incidence of type B3 (34.7%) was only
mid-root level of less than 4 mm—up to 86.5% of slightly less than that of type B2, followed by type M2
patients had a thickness of less than 5 mm (Table 3). (11.7%). No type P2, P3, or M3 was found in our
Similarly, the buccal bone at the apical level was patient series. The rest of the types were few and are
much thinner than its palatal counterpart. The buccal listed in Table 7.
bone thickness at the apical level was less than 5 mm A reliability test was done to determine the accu-
in 98.8% of the patients, and more than one half of the racy of the measurements and classifications between
patients (51.8%) had a thickness of less than 2 mm the 2 investigators. The correlation coefficients for
(Table 4). In contrast, 96.5% of patients had a palatal the different measurements are listed in Table 8 and
bone thickness at the apical level of 5 mm or more, reflected the good consistency between the 2 inves-
and more than one half of the patients (55.9%) had a tigators.
thickness of 8 mm or more (Table 5). Regarding the
apical bone height, measured from the apex of the

Table 3. THICKNESS OF PALATAL BONE AT MID-
Table 2. THICKNESS OF BUCCAL BONE AT MID- ROOT LEVEL (MEASUREMENT II)
ROOT LEVEL (MEASUREMENT I)
Thickness (mm) Patients (n)
2 8 (4.7)
0.5 23 (13.5) 3 40 (23.5)
1.0 97 (57) 4 106 (62.4)
1.5 158 (92.9) 5 147 (86.5)
2.0 170 (100) 6 159 (93.5)
Data in parentheses are percentages. Data in parentheses are percentages.
Lau et al. Classification of Maxillary Central Incisors. J Oral Lau et al. Classification of Maxillary Central Incisors. J Oral
Maxillofac Surg 2011. Maxillofac Surg 2011.

LAU ET AL 147

Table 4. THICKNESS OF BUCCAL BONE AT APICAL Table 6. APICAL BONE HEIGHT (MEASUREMENT V)
LEVEL (MEASUREMENT III)
4 166 (97.6)
1 17 (10.0) 6 153 (90.0)
2 88 (51.8) 8 121 (71.2)
3 152 (89.4) 10 81 (47.6)
4 164 (96.5)
5 168 (98.8) Data in parentheses are percentages.
Data in parentheses are percentages. Maxillofac Surg 2011.

evaluate the root position 3 dimensionally before
Discussion placement.
Although it might be worthwhile information, we
The present study aimed to provide data to aid the purposely did not include the measurements of the
treatment planning of immediate implant in the es- buccal and palatal bone thickness at the crestal re-
thetic zone using a CB imaging technique. With rapid gion, because of the uncontrollable high percentage
advances in surgical and imaging techniques, the de- of error owing to its relative thinness. Although mag-
mand for accuracy in 3-dimensional and volumetric nification is possible in the computer, the resolution
measurements is ever increasing. CB imaging has be- will be too low for measurement. Moreover, a beam
come the standard for implant planning, especially in hardening effect is always present over the edge,
the highly esthetically demanding areas. Numerous making measuring the bone thickness at the crestal
studies have been published to support the routine level worthless.
use of CB imaging in implant dentistry, including the As previously mentioned, the main drawback of
advantages of convenience, accuracy, and relatively
immediate implant placement into the extraction
low radiation dosage.24-27 Increasingly, more clini-
sockets has been the lack of predictability of the
cians have been incorporating this into daily practice.
long-term soft tissue profile, especially on the buccal
Only the roots of the maxillary central incisors
aspect. Thus, the position of implant placement is
were evaluated in the present study, instead of the
critical and is a limiting variable. Although it was
whole tooth. Neither were the crown-to-root relation-
previously believed that the bone remodeling and soft
ships measured. This was because it was reported by
tissue recession over an extraction socket would be
Bryant et al23 that only a mean of 1.74° is present
arrested by inserting a dental implant into the socket,
between the long axis of the root and the crown of
recent studies have failed to support this.28-30 It has
normal central maxillary incisors. With priority given
been confirmed that, irrespective of the placement of
to a restorative driven concept, if implants could be
a dental implant, bone resorption after extraction will
placed into the extraction sockets exactly at the same
still occur, leading to a loss of bone volume.28-30 It has
angulations as the roots inside the alveolar bone, it
also been reported that the buccal bone resorbs more
would provide an ideal 3-dimensional position for the
than the lingual or palatal bone after extraction, be-
prosthetic crown and only a simple straight stock
cause it is composed of bundle bone alone. In con-
abutment would be needed. Thus, it is important to
trast, lingual or palatal bone is composed of cortical
bone, at least at the outermost surface; thus, the
resistance to resorption is better.31 The mid-buccal
Table 5. THICKNESS OF PALATAL BONE AT APICAL recession of an immediate implant placed into a fresh
LEVEL (MEASUREMENT IV)
extraction socket has been reported to be 0.55 to
Thickness (mm) Patients (n) 0.75 mm at 1 year of follow-up.32,33 However, long-
term data are still not available to determine whether
5 164 (96.5)
additional resorption occurs. Kohal et al34 have
6 153 (90)
7 126 (74.1) shown that pressure of the inserted implant on the
8 95 (55.9) bony wall can result in microfractures, leading to
9 61 (35.9) crestal bone loss. Therefore, the ideal placement of an
10 38 (22.4) immediate implant should be aimed toward obtaining
Data in parentheses are percentages. maximum bone-to-implant contact to achieve good
Lau et al. Classification of Maxillary Central Incisors. J Oral primary stability and promote greater osseointegra-
Maxillofac Surg 2011. tion.35,36 However, the key to long-term good esthetic


Table 7. CLASSIFICATION

Type
Type B M P Total

1 5.9 (10) 7.7 (13) 1.8 (3) 15.4 (26)
2 38.2 (65) 11.7 (20) 0 (0) 49.9 (85)
3 34.7 (59) 0 (0) 0 (0) 34.7 (59)
Total 78.8 (134) 19.4 (33) 1.8 (3) 100 (170)
Data are presented as parentheses, with numbers in parentheses.

results is to avoid exerting pressure on the crestal giva, thus minimizing mid-buccal recession and
bony wall, particularly on the buccal aspect. shrinkage of the papillae. However, only 7.7% of type
With respect to the classification reported in the M1 were reported (Table 7).
present study, both the position and the angulation Although type P1 is not as perfect as type M1, these
types were categorized into different ranks according types are still good, because they will have enough
to their difficulty for achieving ideal esthetic results in buccal bone to support the overlying soft tissue. Rel-
immediate implant cases. The classification levels are atively less bone will be present at the palatal side;
level I to level III (Fig 4). however, the palatal soft tissue is very thick and the
palatal bone can resist resorption much better. The
LEVEL I recession of palatal tissue will be less significant, if
Level I (M1, P1) indicates that the implant could be any occurs, and the esthetic demand is usually not
placed with the same angulation as the extraction high on the palatal side. Similar to those with type M1,
socket, without compromising the primary stability those with type P1 were in the minority, with only 3
and long-term esthetic outcome because of the com- patients (1.8%) classified as having type P1 (Table 7).
mon features of a relatively thicker buccal bone. Be-
cause no modification of the drilling angle would be LEVEL II
required, a straight stock abutment could be used. Level II (B1, B2, M2, M3, P2, P3) is more technically
These types are the most straightforward for both demanding. The angulation of the implant should be
surgery and its restoration of all the levels. However,
only 9.5% of patients had extraction sockets catego-
rized as this level (Fig 4).
Type M1 should be ideal for immediate implant
cases. This type of tooth lies in the middle of the
alveolar bone and root apex, angulated away from the
buccal wall. When placing an implant into the extrac-
tion socket, enough bone will be present to support
the implant, thereby achieving good primary stability
and enough bone-to-implant contact for good os-
seointegration. Also, the implant angulation will be
perfect for the superstructure. Moreover, enough
buccal bone is present to support the overlying gin-

Table 8. INTERINVESTIGATOR RELIABILITY TEST

Investigation Correlation Coefficients

Measurement I 0.955
Measurement II 0.805
Measurement III 0.830
Measurement IV 0.876
Measurement V 0.898 FIGURE 4. Levels according to difficulty in achieving good long-
Classifications 0.922 term esthetic results for immediate implant.
Lau et al. Classification of Maxillary Central Incisors. J Oral Lau et al. Classification of Maxillary Central Incisors. J Oral
Maxillofac Surg 2011. Maxillofac Surg 2011.

LAU ET AL 149

changed to avoid thinning of the buccal bone to Table 9. APICAL DIMENSIONS OF COMMONLY
maintain a long-term stable esthetic outcome, be- USED IMMEDIATE IMPLANTS IN ESTHETIC ZONE
cause it has the common disadvantage of a relatively
thin buccal plate. The angle of the implant should be Apical Diameter Radius
Implant Brand (mm) (mm)
placed more palatally to avoid compressing or drilling
the buccal bone, minimizing the chance of perfora- Ankylos (A type), Densply
tions and fenestrations. Because a discrepancy exists Friadent 3.5 1.75
between the implant angle to the original tooth, an OsseoSpeed (4.5), Astra Tech
Dental 3.5 1.75
angled abutment should be chosen to obtain good Tapered Internal (3.8 mm),
esthetics. More than one half of the cases (55.8%) BioHorizons 2.8 1.40
were categorized as level II (Table 7). ITI (Bone Level), Straumann 3.5 1.75
Regarding the positions of the maxillary central Replace Tapered Groovy (RP),
incisors, most were type B (78.8%); thus, most of the Nobel Biocare 2.7 1.35
Tapered Screw-Vent (3.7
teeth lie more buccally. Type B1 (5.9%) is not ideal for mmD), Zimmer Dental 3.1 1.55
immediate implantation, because it is close to the
buccal wall, indicating relatively thinner buccal bone. Lau et al. Classification of Maxillary Central Incisors. J Oral
However, type B1 is not the most challenging of this
level because it does not angulate toward the natural
depression of the buccal alveolus. The chance of the side of the implant drill should not be cutting on
additional thinning of the buccal wall or fenestration the buccal plate during osteotomy, especially for type
will be reduced. B, because it is expected to be thinner than other
The least favorable types of maxillary central inci- types. Otherwise, the risk of perforation or thinning
sors for immediate implant are those positioned near down the already thin buccal plate will be high. Table
the buccal wall with the apex pointing toward the 9 provides a reference for the apical radius of com-
buccal side (types B2 and B3; type B3 was categorized monly used implant brands for immediate implant in
as difficult [level III] and was included in the next the esthetic zone, which ranges from 1.35 to 1.75
section). A type B2 tooth would naturally produce a mm. More than one half of the patients had a buccal
thin buccal plate at both the crestal and the apical bone thickness of less than 2 mm at the apical region,
region. For immediate implant placement, good pri- indicating that placing implant drills exactly along the
mary stability is mandatory, especially for those axis of extraction sockets will result in a high risk of
scheduled to have immediate placement of a provi- perforation, especially when placing the implant
sional crown. When achieving good primary stability, deeper toward the apical bone to achieve primary
pressure is almost always present on the buccal bone, stability.
either at the apical region or at both the apical and the The mean thickness of the palatal bone at the apical
crestal regions. Because this type has a thin buccal level (measurement IV) is much greater than its buc-
plate, any pressure exerted on it will significantly cal counterpart. We found an average of 8.51 mm of
increase the risk of bone resorption, leading to the palatal bone at this region, with a maximal thickness
loss of soft tissue in the long term. However, a major of 22.41 mm (compared with an average of 2.04
proportion of patients will have these types (type B2, 1.01 mm). More than one half (55.9%) of the patients
38.2%). This explains the “physiologic” bone and soft had a thickness of 8 mm or more and 96.5% of pa-
tissue loss on the buccal side in some immediate tients had a thickness of 5 mm or more (Table 5). In
implant cases. Although it can be difficult to achieve contrast, the thickness of the palatal bone at the
good primary stability, clinicians will still need to mid-root level (measurement II) had a mean of only
avoid overcompression of the buccal plate in such 3.76 mm, and 76.5% of patients have a bone thickness
cases. This explains why these cases are so technique- of less than 3 mm. This probably resulted from the
sensitive. contour of the palatal vault. Thus, the more apically
Our data suggest that the buccal bone of maxillary placed, the thicker the palatal bone. However, this is
incisors were, on average, thin. The mean thickness not the same for the buccal aspect owing to the
of the buccal bone at the mid-root level (measure- natural depression at point A and, sometimes, the
ment I) was only 0.9 mm, and the buccal bone at the extreme root angulations, such as a type 3 tooth.
apical level (measurement III) was 2.04 mm. More Thus, the implant should be placed more palatally in
than one half of the patients (57%) have a buccal bone the extraction socket, because more bone will be
thickness at the mid-root level of less than 1 mm present in that area to achieve good implant stability
(Table 2), and 51.8% of patients had a buccal bone and to avoid thinning of the buccal wall. However,
thickness at the apical level of less than 2 mm (Table the implant should also be placed more palatally at
4). It is critical not to drill over the buccal area— even the apical area, pivoting around the mid-root level.


This is because the palatal bone is relatively thicker at angulation with reference to the extraction socket,
the apical area than at the mid-root region. Clinicians and in this case, more palatally.
must also be careful not to angulate the apex of the
implant too palatally, otherwise, the coronal part of LEVEL III
the implant will be tilted too buccally. This can lead to The type B3 tooth is the most challenging case with
overcompression, or even perforation, on the buccal respect to achieving good long-term esthetic out-
crestal wall, making the coronal platform point outcomes because it not only will have a very thin buccal
ward buccally and compromising the esthetic out- plate, but also the long axis of the tooth apex will be
come. A recent study confirmed that the buccal-lin- angulated very buccally, passing anterior to the natu-
gual position of the implant shoulder is a very ral contour of the maxillary alveolar bone (Fig 5A).
important factor determining the degree of buccal This type is mostly seen in patients with maxillary
marginal tissue recession.37 It was reported that an alveolar hyperplasia and angle Class II division 2 oc-
implant with a shoulder positioned at, or buccally, to clusion. Because a large difference exists between the
a line drawn between the cervical margin of the angulations of the alveolar bone and the tooth, the
adjacent teeth resulted in 3 times more recession than implant position will be compromised, regardless of
an implant with a shoulder positioned lingually or whether a bone-driven or restorative-driven protocol
palatally to this line.37 If an ideal angulation for good is used (Figs 5A,B). Sometimes, traditional guidelines
apical stability without exerting excessive pressure can be followed for such cases by extracting the
on the buccal wall and without placing the shoulder
buccal to this line cannot be achieved, clinicians can
always consider choosing an implant with a smaller
coronal diameter.
Regarding the apical bone height (measurement V),
it was recorded that 97.6% of patients had a bone
height of 4 mm or more, and 90% of patients had a
bone height of 6 mm or more (Table 6). The general
recommendation for the placement of immediate im-
plant in an extraction socket in the apical dimension
is to engage the implant 3 to 5 mm beyond the apex
of the socket to achieve good primary stability.38,39
The results of the present study have shown adequate
bone is present at the apical area. Even when the
primary stability is not optimal, the implant could
be placed deeper to achieve this, because usually
more than enough bone is present at this region
(almost one half of the patients had 10 mm or more of
apical bone height). However, a suitable implant
length should carefully be chosen, because the apical-
coronal position of the implant shoulder is also an
important factor in determining the long-term soft
tissue profile and the esthetic outcome.21,40,41 The
length of the implant should be optimal, deep enough
to provide good apical stability, without perforation,
and the shoulder positioned with, or slightly apical to,
the buccal marginal bone crest (around 3 to 4 mm
from the buccal gingival margin38,42,43 or 3 mm apical
to the cementoenamel junctions of the periodontally
sound adjacent tooth44).
Unlike type B2, types M2, M3, P2, and P3 have
similar characteristics, including a relatively thicker
buccal plate. However, the root apexes will point
toward the buccal side. If the implant were placed
FIGURE 5. Examples of level III socket. A, Large difference be-
exactly into the extraction socket with the same an- tween angulations of original tooth and future implant. B, Extreme
gulation, the risk of perforation would be very high. angulation requiring traditional treatment or socket transformation.
The general recommendation for all level II cases is Lau et al. Classification of Maxillary Central Incisors. J Oral
that the implants should be inserted with a modified Maxillofac Surg 2011.

LAU ET AL 151

tooth, with or without simultaneous grafting, and supply from the periosteum to the buccal plate during
inserting the implant several months later. As such, the flap raising. For level I cases, inserting the implant
although the advantages of immediate implantation with the same angulation of the socket using a stan-
would not be achieved, the long-term soft tissue sta- dard drilling protocol will be straightforward. For
bility will be more predictable. level II cases, the implant angulation should be
If enough bone is present at the palatal and apical changed to a more palatal aspect at the apical region,
aspects, an attempt could be made by placing the pivoting around the mid-palatal area. It is recom-
implant both palatally and apically to avoid touching mended to first use a round bur to create a step at the
the buccal plate. However, even if primary stability palatal aspect of the apical area of the socket before
can be achieved, the difference will still be large using a straight drill to ensure that the hardness of the
between the angle of the implant and prosthetic cortical bone and natural contour of the socket does
crown. An angled abutment will always be needed. not misguide the operator to drill parallel toward the
One should be familiar with the implant system one apical long axis (Fig 6). The implant should be in-
is using, whether an angulated temporary abutment is serted with good primary stability, without exerting
available, and, if so, the different angles available if pressure on the buccal wall. To ensure the absence of
planning an immediate provisional crown. The final pressure on the buccal bone, the operator can leave a
restoration should also be considered before the im- gap between the implant surface and the buccal
plant is inserted. Most often, for an abutment with a bone, as long as the primary stability is not compro-
relatively big angle, a step of metal will be present on mised. The gap can be treated with grafting materials
the buccal aspect. It can sometimes show through the and/or a barrier membrane to achieve maximum os-
buccal gingiva, compromising the esthetic outcome. seointergration and good soft tissue healing, depend-
Placing the implant further apically can be done to ing on the gap size.12,14,45-48 The implant shoulder
solve this problem. Customized abutments or a ce- should be optimally placed in terms of the depth and
ramic abutment can also be used according to the buccal-palatal dimension. A provisional crown should
position and angulation of the implant. However, the im- be considered whenever possible for soft tissue sup-
plant position will most often be controlled by the port, favoring the long-term esthetic outcome,31 by
bone available for such cases. Thus, type B3 is very selecting an appropriate abutment. For level III cases,
technically demanding for immediate implant, be- extra precautions should be given to the prosthetic
cause it is both a bone-driven and a prosthetic-driven piece owing to its extreme angulations. One should
procedure. be familiar with the different types of abutments avail-
If the demand for a good esthetic outcome and able, as well as their dimensions and shapes. The
immediate provisional restoration is very high, a implant can be placed deeper apically to avoid buccal
socket transformation procedure can be done by showing of the metal margin of an angulated abut-
grafting the buccal wall in the first stage, followed by
extraction of the problematic tooth and a normal
immediate implantation protocol several months
later. Thus, a type B3 (level III) socket could be
transformed iatrogenically to an easier type, such as
type B2 (level II) or, even, type M2 (level II), keeping
the advantages of immediate implant. However, more
evidence is needed to justify the long-term success of
this treatment concept.
In conclusion, the bone availability in all dimen-
sions should be considered to achieve a good implant
esthetic. The angulation and position of the original
tooth should be well appreciated 3-dimensionally dur-
ing the planning stage. This is best performed by
measurement of a CB image. A suitable implant type
and the length and diameter at the apical, mid-body,
and coronal level should be customized to the original
socket as much as possible. Tapered-screw implants
are suggested, because they can fit to the extraction
socket better, and primary stability can be achieved
easily. After an atraumatic extraction, all granulation FIGURE 6. Drilling with a round bur toward palatal aspect.
tissue should be removed. A flapless approach is rec- Lau et al. Classification of Maxillary Central Incisors. J Oral
ommended to minimize the breakdown of the blood Maxillofac Surg 2011.


ment. A traditional protocol can sometimes be fol- comparing different types of serial immediate implantation. Int
J Oral Maxillofac Implants 10:561, 1995
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results with immediate implantation. However, it is peri-implant mucosa: An evaluation of maxillary anterior single
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