The purpose of present article was
to review the classifications suggested for assessment of the jawbone anatomy, to
evaluate the diagnostic possibilities of mandibular canal identification and risk
of inferior alveolar nerve injury, aesthetic considerations in aesthetic zone, as
well as to suggest new classification system of the jawbone anatomy in endosseous
dental implant treatment.
Material and Methods
Literature was selected through a search of PubMed, Embase and Cochrane electronic
databases. The keywords used for search were mandible; mandibular canal; alveolar
nerve, inferior; anatomy, cross-sectional; dental implants; classification. The
search was restricted to English language articles, published from 1972 to March
2013. Additionally, a manual search in the major anatomy and oral surgery books
were performed. The publications there selected by including clinical and human
anatomy studies.
Results
In total
109 literature sources were obtained and reviewed. The classifications suggested
for assessment of the jawbone anatomy, diagnostic possibilities of mandibular canal
identification and risk of inferior alveolar nerve injury, aesthetic considerations
in aesthetic zone were discussed. New classification system of the jawbone anatomy
in endosseous dental implant treatment based on anatomical and radiologic findings
and literature review results was suggested.
Conclusions
The
classification system proposed here based on anatomical and radiological jawbone
quantity and quality evaluation is a helpful tool for planning of treatment strategy
and collaboration among specialists. Further clinical studies should be conducted
for new classification validation and reliability evaluation.
After the loss of
teeth atrophy of the alveolar processes occurs in a vertical as well as a horizontal
plane. The term atrophy is defined in the dictionary as "a wasting away; a diminution
in the size of a cell, tissue, organ, or part" [1]. This process
is starting and continuous throughout life because of the lack of stimuli (disuse
atrophy) seen on alveolar process of the jaws [2].
Dental implants have
become the most popular and reliable treatment option for restoring missing teeth.
Nowadays there is a wide choice of screw-type implant systems. The success of dental
implants depends on the jawbone quantity and quality [3]. Therefore,
it is important to measure the alveolar process precisely so that the proper system
may be chosen [4]. There are number of classifications suggested
for assessment of the degree of atrophy of partially or fully edentulous jaws [5-11].
One of the most popular classification systems for jaw anatomy (jaw shape and quality)
for dental implant treatment was proposed by Lekholm and Zarb in 1985 [12].
However, this classification, like many others, described changes only of jaw shapes
in general and failed to indicate precise measurements [13].
Juodzbalys et al. in 2004 [14] proposed clinical and radiological
classification of the jawbone anatomy for implantation based on edentulous jaw dental
segment (eJDS) anatomy assessment. Nevertheless, this classification fails to assess
mandibular canal anatomy variations and risk degree of inferior alveolar nerve injury.
By means of the advancement of radiographic technology, i.e. development of cone
beam computed tomography (CBCT), diagnostic possibilities are more precise, especially
in the case of mandibular canal assessment [15-17]. In view of
these considerations the purpose of present article was to review the classifications
suggested for assessment of the jawbone anatomy, to evaluate the diagnostic possibilities
of mandibular canal identification and risk of inferior alveolar nerve injury, aesthetic
considerations in aesthetic zone, as well as to suggest new classification system
of the jawbone anatomy in endosseous dental implant treatment.
MATERIAL AND METHODS
Literature was selected
through a search of PubMed, Embase and Cochrane electronic databases. The keywords
used for search were mandible; mandibular canal; alveolar nerve, inferior; anatomy,
cross-sectional; dental implants; classification. The search was restricted to English
language articles, published from 1972 to March 2013. Additionally, a manual search
in the major anatomy and oral surgery books were performed. The publications there
selected by including clinical and human anatomy studies.
RESULTS
Classifications of jawbone anatomy
It was mentioned
above that the most popular classification systems for jaw anatomy (jaw shape and
quality) for dental implant treatment was proposed by Lekholm and Zarb [12].
The quantity of jawbone is divided into five groups, based on residual jaw shape
following tooth extraction. There are presented drawings of the jaws – jaw cross-sections,
accompanied by text, and assessment methods. Similarly Cawood and Howell's [9]
ridge classification presented as alveolar process resorption level jaw cross-sections
and text. During all stages of the alveolar ridge atrophy, characteristic shapes
result from the resorptive process.
The biggest shortcoming
of previous classifications [5-11] is fact, that those classifications
are two-dimensional representations and do not show the three-dimensionality of
atrophic ridges. Nowadays clinician can combine three-dimensional jawbone assessment
and image-guided surgery by means of CBCT. Diagnostic and planning software are
available to assist in implant planning to create diagnostic and surgical implant
guidance stents (e.g., Virtual Implant Placement, Implant Logic Systems, Cedarhurst,
USA; Simplant, Materialise, Belgium; Easy Guide, Keystone Dental, USA) [18].
Misch and Judy [19]
classified available bone into 4 divisions: abundant, barely sufficient, compromised,
and deficient (A-D). Abundant bone requires no augmentation and is greater than
5 mm in width, 10 to 13 mm in height, and 7 mm in length. Barely sufficient bone
is 2.5 to 5 mm in width, greater than 10 to 13 mm in height, and greater than 12
mm in length and can be modified with osteoplasty or augmentation of hard or soft
tissues, depending on the nature of the defect (B-w). Compromised bone necessitates
osteoplasty and some form of hard or soft tissue augmentation depending on the extent
of the defect in height (less than 10 mm, C-h) or width (less than 2.5 mm, C-w).
Deficient bone requires substantial hard tissue augmentation from extraoral sites
and is generally not amenable to implant rehabilitation. Unfortunately, aesthetic
component in this classification is not considered. Implant rehabilitation is no
longer just a vehicle to restore lost masticatory and phonetic function. It has
become an integral part of modern implant dentistry for achieving structural and
aesthetic pleasing outcomes [20]. It is well established that
the soft tissue appearance is largely dependent upon the underlying bone topography
[21]. Hence, it is important to assess hard tissue parameters,
such as horizontal bone deficiency and interproximal bone height.
Current classifications
also fail to assess mandibular canal anatomy variations and risk degree of inferior
alveolar nerve injury. Worthington [22] showed that even after
the accurate measurement of available bone, the nerve injury can occur as the result
of over penetration of the drill owing to low resistance of the spongy bone; this
can lead to slippage of the drill even by experienced surgeons.
Lekholm and Zarb
[12] classify quality of residual alveolar bones into four types:
type 1 = large homogenous cortical bone; type 2 = thick cortical layer surrounding
a dense medullar bone; type 3 = thin cortical layer surrounding a dense medullar
bone; type 4 = thin cortical layer surrounding a sparse medullar bone). According
to Ribeiro-Rotta et al. [23] and Bergkvist et al. [24]
classification of quality of residual alveolar bones indicate a good correlation
with bone mineral content. Trisi and Rao [25] proposed the system
for bone quality assessment with three classes (dense, normal and soft bone).
Some authors proposed
to evaluate jawbone density in presurgical planning [26-28].
It is possible to assess jawbone density using CT values (Hounsfield units: HU)
and bone mineral densities obtained by medical CT. Norton and Gamble [27]
measured the bone density in the posterior mandible using SimPlant software (3D
Diagnostix, Boston, MA, USA) and concluded that the mean CT value was 669.6 HU.
Misch [26] classified cancellous bone density into 5 grades:
D1: > 1250 HU; D2: 850 to 1250 HU; D3: 350 to 850 HU; D4: 150 to 350 HU; and D5:
< 150 HU. In the conversion of CT values (HU), the mean value in the molar region
was 4.5 x 102 (D3): in the first molar region it was 5.2 x 102 (D3), in second molar
region 4.3 x 102 (D3), and in the third molar region it was 0.7 x 102 (D5).
It is interesting
to know that Başa and Dilek [29] assessed the risk of perforation
of the mandibular canal by implant drill using density and thickness parameters.
They investigated whether the resistance of the bone surrounding the mandibular
canal had sufficient density and thickness to avoid perforation by implant drills.
Study of the computed tomography (CT) images of 99 patients, showed that overall,
average bone thickness in the premolar and molar regions was 0.87 ± 0.18 and 0.86
± 0.18 mm, respectively, whereas the bone density in the premolar and molar regions
was 649.18 ± 241.42 and 584.44 ± 222.73 HU, respectively (P < 0.001). It was concluded
that the average density and thickness of the bone that surrounds the mandibular
canal was not sufficient to resist the implant drill. Furthermore, in the posterior
mandible, cancellous bone is more abundant and has bigger intratrabecular spaces
and less dense than in anterior mandible [30,31]. In some cases
with low density bone, the twist drills may drop into intratrabecular spaces during
preparation thus leads to the displacement of the implants deeper than planned [32].
The measurements
of bone density in designed sites are important in presurgical planning when using
CBCT for dental implant treatment. However, the pixel or voxel values obtained from
CBCT images are not absolute values. Naitoh et al. [33] demonstrated
a high-level correlation between voxel values of CBCT and bone mineral densities
of multislice CT (r = 0.965). They concluded that voxel values of mandibular cancellous
bone in CBCT could be used to estimate bone density. In contrast, Nackaerts et al.
[34] and Parsa et al. [35] determined the
grey value variation at the implant site with different scan settings, including
field of view (FOV), spatial resolution, number of projections, exposure time and
dose selections in two CBCT systems and compared the results with those obtained
from a multislice CT system. Authors concluded that grey-level values from CBCT
images are influenced by device and scanning settings.
Radiological examination
The main goals of
radiological jawbone examination are to determine the quantity, quality and angulations
of bone, selection of the potential implant sites, and to verify absence of pathology.
Clinician should choose proper radiographic method which provides sufficient diagnostic
information with the least possible radiation dose.
Periapical radiographs
have been used for many years to assess the jaws pre- and post-implant placement
[36]. Periapical radiographs commonly are used to evaluate the
status of adjacent teeth, remaining alveolar bone in the mesiodistal dimension and
vertical height. The long cone paralleling technique for taking periapical X-ray
is the technique of choice for the following reasons: reduction of radiation dose;
less magnification; a true relationship between the bone height and adjacent teeth
is demonstrated [37]. If the paralleling technique is not used,
periapical radiographs create an image with foreshortening and elongation [38-40].
Nevertheless, the biggest concern of periapical radiographs is in 28% of patients
that mandibular canal could not be clearly identified in the second premolar and
first molar regions [41] and mandibular foramen can be identified
around 47 - 75% cases [42].
When a specific region
(maxillofacial area, including many of the vital structures, such as maxillary sinus,
inferior alveolar nerve and nasal fossa) that is too large to be seen on a periapical
view, panoramic radiograph can be the method of choice. The major advantages of
panoramic images are the broad coverage of oral structures, low radiation exposure
(about 10% of a full-mouth radiographs), and relatively inexpensiveness of the equipment.
The major drawbacks of panoramic imaging are: lower image resolution, high distortion,
and presence of phantom images [43]. For example, Naitoh et al.
[33] found that mandibular canal visibility on panoramic radiographs
in superior and inferior wall was only 36.7%. Similarly, Lindh et al. [44]
reported that the mandibular canal of specimen cadavers was clearly visible in 25%
of panoramic radiographs (range 12 to 86%). Klinge et al. [45]
also reported that the mandibular canal of specimen cadavers was not visible in
36.1% of panoramic radiographs. The location and configuration of mandibular canal
are important in imaging diagnosis for the proper dental implant placement in the
mandible [46-48].
One of the most challenged
regions for implantation in mandible is mental foramen region. This is because there
are many variations with regards to the size, shape, location and direction of the
opening of the mental foramen. After comparison of the anatomical and radiological
assessment of 4 cadaver skulls, Yosue and Brooks [49] concluded
that the panoramic and periapical films reflected the actual position of mental
foramen in the skulls < 50% the time. Furthermore, Sonick et al. [50]
found that the average linear errors occurred during routine bone assessments (n
= 12) for panoramic films were 24% (mean 3 mm; range 0.5 to 7.5 mm), for periapical
films were 14% (mean 1.9 mm; range 0.0 to 5.0 mm) and only 1.8% (mean 0.2 mm; range
0.0 to 0.5 mm) for CT scans. Kuzmanovic et al. [51], Ngeow and
Yuzawati [52] and Jacobs et al. [53] similarly
concluded that panoramic radiograph is not sufficient for anterior loop detection
and presurgical implant planning in the mental region and there is a need for other
additional images.
Even incisive canal
detection is complicated using panoramic radiography. For example, Jacobs with co-workers
[54] reported that the mandibular incisive canal was identified
only in 15% of the 545 panoramic radiographs, with good visibility of only 1%. In
contrast, canal was observed on 93% of CT scans with a good visibility in 22% of
cases.
Peker et al. [55]
showed that the measurements obtained from CT images are more consistent with direct
measurements than the measurements obtained from panoramic radiographic images or
conventional tomographic images. Furthermore, Rouas et al. [56]
reported that the atypical mandibular canal such as bifid mandibular canal, in most
cases can be identified using only three-dimensional imaging techniques. It was
thought that the bifid mandibular canal is often left unrecognized [57].
Therefore, duplication or division of the canal by means of panoramic radiographs
was found in about 1% of patients [58]. Naitoh et al. [59]
reconstructed 122 two-dimensional images of the various planes in mandibular ramus
region to the computer program using three-dimensional visualization and measurement
software. Bifid mandibular canal in the mandibular ramus region was observed even
in 65% of patients.
When the periapical
radiography, panoramic radiography, tomography, or CT were compared for their efficiency
in the identification of the mandibular canal, the CBCT seems to have the most potential
while reduces radiation exposure considerably [60]. Similarly,
CT scans are more accurate than conventional radiographs in mental foramen and anterior
loop detection [45,50,53,61,62].
However, cross-sectional imaging have following limitations: limited availability,
high cost and the need for image interpretation [63,64]. However,
CBCT is often recommended for clinical usage, especially in cases there the vital
structures are difficult to detect due to its high accuracy and low radiation exposure
[65,66,68]. The main advantage of CBCT is a low dose scanning
system, which has been specifically designed to produce three-dimensional images
of the maxillofacial skeleton. Hence, a major difference between CT and CBCT is
how the data are gathered: CT acquires image data using rows of detectors, CBCT
exposes the whole section of the patient over one detector [69,70].
Furthermore, CBCT permits not only diagnosis, it facilitates image-guided surgery
[18].
Inferior alveolar nerve injury risk
Inferior alveolar
nerve injury is a serious complication with incidence ranged from 0 to 40% [71-87].
As a result, many important functions such as speech, eating, kissing, make-up application,
shaving and drinking were affected [77]. This influences patient's
quality of life and often resulted in negative psychological adverse effects [79].
The most common causes of iatrogenic inferior alveolar nerve injuries are discrepancies
of radiographs, surgeon's mistakes, low resistance of mandibular spongy bone and
lack of mandibular canal superior wall.
The most severe types
of injuries are caused by implant drills and implants themselves [22].
Many implant drills are slightly longer, for drilling efficiency, than their corresponding
implants. Implant drill length varies and must be understood by the surgeon because
the specified length may not reflect an additional millimetre so called "y" dimension
[84]. Lack of knowledge about this may cause avoidable complications
[88]. Damage to the inferior alveolar nerve can occur when the
twist drill or implant encroaches, transects, or lacerates the nerve.
Over penetration
of the drill (drill slippage) can be triggered by the low resistance of the spongy
bone [22]. It was mentioned above that Başa and Dilek [29]
assessed the risk of perforation of the mandibular canal by implant drill using
density and thickness parameters. They investigated whether the resistance of the
bone surrounding the mandibular canal had sufficient density and thickness to avoid
perforation by implant drills. The results showed the risk of inferior alveolar
nerve injury can be avoided by accurately determine the bone mass around the canal
and avoid use excessive force when approaching the canal. Furthermore, Wadu et al.
[93], studying mandibular canal appearance on the panoramic radiographs,
found that the number of cases of radio-opaque border was either disrupted or even
absent. The superior border was more prone to disruption than the inferior border.
It is evident that low resistance of the spongy mandibular bone and absence of mandibular
canal superior wall is inauspicious anatomical combination which can lead to inferior
alveolar nerve injury.
Juodzbalys et al.
[87] showed that in 25% cases (n = 4) implant drill was identified
as etiological factor with 2 cases caused by drill slippage during osteotomy preparation.
The inferior alveolar nerve may be affected by perforation of the mandibular canal
during drilling, or positioning the implant close to the canal and the subsequent
formation of an adjacent hematoma that presses against the nerve [89].
Khawaja and Renton [90] indicated that "cracking" of the inferior
alveolar nerve canal roof by its close proximity to preparation of the implant bed
(millimetres) may cause haemorrhage into the canal or deposition of debris which
may compress and cause ischemia of the nerve.
Limited evidence
exists with regard to the proper distance between the implant and the mandibular
canal to ensure the nerve's integrity and physiologic activity. The proper distance
should come from evaluation of clinical data as well as from biomechanical analyses
[91,92]. Sammartino et al. [91] created a
numeric mandibular model based on the boundary element method to simulate a mandibular
segment containing a threaded fixture so that the pressure on the trigeminal nerve,
as induced by the occlusal loads, could be assessed. They found that the nerve pressure
increased rapidly with a bone density decrease. A low mandibular cortical bone density
caused a major nerve pressure increase. In conclusion, they suggested a distance
of 1.5 mm to prevent implant damage to the underlying inferior alveolar nerve when
biomechanical loading was taken into consideration.
Aesthetic considerations
It is generally agreed
that implant success criteria should include an aesthetic component [94].
Although implant success, as measured through fixture osseointegration and restoration
of function, is high, the procedures available to create aesthetic implant "success"
are not always predictable [20]. To ensure optimal aesthetic
implant rehabilitation, the following prerequisites are considered essential: adequate
bone volume (horizontal, vertical, and, contour), optimal implant position (mesiodistal,
apicocoronal, buccolingual, and angulation), stable and healthy periimplant soft
tissues, aesthetic soft tissues contours, and ideal emergence profile [20,95].
The level of bone support and the soft tissue dimensions around the implant-supported
single-tooth restoration are factors suggested to be important for the aesthetic
outcome of implant therapy [96]. It has been demonstrated that
presence or absence of bone crest influences the appearance of papillae between
implants and adjacent teeth [97]. Furthermore, the implant-supported
restoration should be in symmetry with the adjacent dentition [98].
The parameters of
three-dimensional optimal implant position was defined by several authors [20,94,99,100].
Mesio-distal dimension between adjacent teeth should be 6 to 9 mm to ensure minimal
(1.5 mm) distance between implant fixture and adjacent teeth [99,100].
Vela et al.[101] showed that it is possible to place platform-switched
implant 1 mm from teeth while maintaining the bone level adjacent to them. Apicocoronal
implant position should be 2 mm below the adjacent cervicoenamel line [94].
Natural buccal and proximal restorative contour can be ensured by correctly orienting
the implant in a buccolingual position - 3 to 4 mm from outside buccal flange [20].
Minimum 2 mm of space should be maintained on the buccal side in front of the external
implant collar surface.
It is necessary to
mention that recommendations for successful results ideally require at least 1 mm
of bone surrounding each implant [102].
Classification system of the jawbone anatomy in endosseous dental implant treatment and assessments
New classification
system of the jawbone anatomy in endosseous dental implant treatment is suggested
taking into consideration previous Juodzbalys and Raustia [14]
classification and literature review results (Figure 1) (Table 1). Surgical dental implant installation requires understanding of associated
anatomical structures. Planning should be done on three-dimensional edentulous jaw
segment (EJS) pattern (Figure 2). This is because the EJS consists
of alveolar and basal bone. In addition, EJS describes planned implant bed relation
to present anatomical borders such as mandibular or maxillary vital structures.
This is in coincidence with Ribeiro-Rotta et al. [23], they proposed
that each implant site should be assessed and characterized knowing that bone characteristics
vary within the same jaw [103]. All measurements should be obtained
clinically and from CBCT and panoramic radiographic images. It should be done by
identifying and depicting anatomical landmarks and position of important vital structures,
when planning for dental implant operation.
Classification system of the jawbone anatomy in endosseous
dental implant treatment. H = height; W = width; L = length; RVP = Alveolar
ridge vertical position; ME BPH = Mesial interdental bone peak height; DI
BPH = Distal interdental bone peak height; MC = mandibular canal; IAN =
inferior alveolar nerve; MSR = maxillary sinus region (all linear measurements
are expressed in mm).
Edentulous jaw segments (A = maxillary, B and C = mandibular)
that consists of alveolar and basal bone. A = the vertical dimension (H)
of the EJS is determined by the distance between the alveolar ridge crest
and maxillary sinus. B = the vertical dimension (H) of the EJS is determined
by the distance between the alveolar ridge crest and mandibular canal. C
= the vertical dimension (H) of the planned implant is determined by the
distance between the alveolar crestal ridge and mental foramen. The horizontal
EJS dimensions: length (L) in all cases is determined by the distance between
neighbouring teeth or implants and width (W) is determined by the alveolar
process width measured at the level of 3 mm (W1) and 6 mm (W2) from the
crest of alveolar process.
Classification system of the jawbone anatomy in endosseous dental implant treatment
Edentulous jaw segment parameters
Edentulous jaw segment types (risk degree)
Type I
(low risk)
Type II
(moderate risk)
Type III
(high risk)
Non aesthetic zone
Height (mm)
Maxilla
> 10
> 8 to ≤ 10
> 4 to ≤ 10 in
MSR
≤ 8
≤ 4 in
MSR
Mandible
> 10
> 8 to ≤ 10
≤ 8
Width (mm)
> 6
> 4 to ≤ 6
< 4
Length (mm)
≥ 7 or ≤ 12
≥ 6 or ≤ 13
< 6 or > 13
Alveolar ridge vertical position (mm)
≤ 3
> 3 to < 7
≥ 7
Aesthetic zone
Height (mm)
Maxilla
> 10
> 8 to ≤ 10
> 4 to ≤ 10 in
MSR
≤ 8
≤ 4 in
MSR
Mandible
> 10
> 8 to ≤ 10
≤ 8
Width (mm)
Optimal implant diameter + 3
Optimal implant diameter + < 3
Optimal implant diameter + ≤ 0
Length (mm)
Equal to contralateral tooth
Asymmetry with contralateral tooth < 1
Asymmetry with contralateral tooth ≥ 1
Alveolar ridge vertical position (mm)
≤ 1
> 1 to ≤ 3
> 3
Interdental bone peak height (mm)
Mesial
3 to 4
≥ 1 to < 3
< 1
Distal
3 to 4
≥ 1 to < 3
< 1
MC region (IAN injury risk degree)
MC walls identification and jawbonequality typea combination
Identified MC walls/D2
and D3
Unindentified superior
MC wall/D1 and D4
Unindentified MC/D1 and D4
aD = bone quality defined according to Lekholm and Zarb (1985).
MC = mandibular canal; IAN = inferior alveolar nerve; MSR = maxillary sinus region.
Classifications and risk factors identification
There are two zones
distinguished in the new classification system - aesthetic and non aesthetic and
two regions - mandibular canal and maxillary sinus. EJSs are attributed to aesthetic
and non aesthetic mandibular or maxillary zone, because the demands and risks of
aesthetic result achievement differ significantly in aesthetic zone in comparison
with non aesthetic zone. Mandibular canal and maxillary sinus regions are important
because of the risk of injury of inferior alveolar nerve and maxillary sinus and
implant operation planning peculiarities. Furthermore, all EJSs are divided into
types (Types I to III) according to their assessment result and risk degree of planned
surgical treatment success. This is in coincidence with Friberg et al. [104],
they suggested that the justification for assessing jawbone tissue in endosseous
dental implant treatment should be diagnostic tool to assess whether the jawbone
tissue is sufficient for implant treatment and a prognostic tool to predict the
probability of success or failure.
The minimal dimensions
of EJS for proper implantation were estimated according to the principles of threaded
implant insertion.
Non aesthetic zone
The height of the
alveolar process (H): the distance between the crest of the alveolar process and
the important vital structures of the jaws (maxillary sinus, mandibular canal, mental
foramen, anterior loop of mental nerve). Several factors should be considered when
estimating the minimal height of an alveolar process. In some cases the crest of
alveolar process is thin and it is necessary to reduce it, so it can have wider
base for the planned implant installation. In such cases, the heights of EJS will
be shortened by 1 to 3 mm; this reduction had to be considered when calculating
the available bone height [105] (Figure 3).
If the operation is planned according to the orthopantomograph, implantation in
the areas of the mandibular canal mandated that the apices should be at least 2
mm away from those vital structures. A minimum of 1 mm is demanded if the operation
is planned with CBCT [106]. Essentially, the minimal height
of the Type I EJS is > 10 mm (Figures 4A, B). EJS with the less
height of > 8 to ≤ 10 mm (Figure 4C) and > 4 to ≤ 10 mm in maxillary
sinus region (Figure 4D) were considered to be Type II. However,
such height was found to be sufficient to ensure primary stability of implants [14].
Simultaneous implantation with vertical alveolar process augmentation or sinus floor
augmentation is recommended. If EJS height was less than ≤ 8 mm and ≤ 4 mm in maxillary
sinus region was categorized as Type III (Figures 4E, F). These
measurements were considered to be insufficient for 8 mm length implant installation
and primary stability achievement even in maxillary sinus region. Vertical alveolar
process and/or sinus floor augmentation and late implantation are recommended.
Thin crestal ridge was reduced to create wide recipient bed
for planned implant installation. In such cases, the heights of EJSs would
have been shortened by 1 to 3 mm at least.
A = Upper jaw first
right molar EJS on CBCT cross-sectional image is more than 10 mm in height
and classified as Type I with no requirement of vertical alveolar process
bone height augmentation prior endosseous dental implant treatment (all
CBCT images in this article were obtained with I-CAT® (Imaging Sciences
International LLC, Hatfield, PA USA) CBCT, a letter "b" on cross-sectional
CBCT image means buccal side).
B = Type I height
(> 10 mm) of lower jaw first left molar EJS on CBCT cross-sectional image.
C = Type II height
(> 8 to ≤ 10 mm) of lower right first molar EJS on CBCT cross-sectional
image. Simultaneous implantation with sinus floor augmentation are recommended.
D = Type II height
(> 4 to ≤ 10 mm) of upper right first molar EJS on CBCT cross-sectional
image. Simultaneous implantation with vertical alveolar process augmentation
are recommended.
E = Type III height
(≤ 8 mm) of lower left second molar EJS on CBCT cross-sectional image. Vertical
alveolar process augmentation and late implantation are recommended. Mandibular
canal walls have proper identification with D2 bone quality.
F = Type III height
(≤ 4 mm) of upper left premolar EJS on CBCT cross-sectional image. Sinus
floor augmentation and late implantation are recommended.
The width of alveolar
process (W): determined by the alveolar process width measured at the level of 3
mm (W1) and 6 mm (W2) from the crest of alveolar process. The smallest measurement
should be accepted as the width of the EJS. Recommendations for successful results
ideally require at least 1 mm of bone surrounding each implant [102].
Most implant systems require bone widths of 5 to 7 mm [12,102].
We estimated that for proper implantation the minimal width of an EJS (Type I) should
be 6 mm (Figure 5A). Alveolar processes with widths of > 4 to
≤ 6 mm were deemed insufficient (Type II) for proper implantation (Figure
5B). Despite such deficiencies, it is expected that the wider parts of the implants
will be covered by bone after insertion and that primary stability would be achieved.
Simultaneous implantation with alveolar process horizontal augmentation is recommended. EJS which width is less than 4 mm is categorized as Type III (Figure
5C). These measurements are considered to be insufficient for primary stability
of implants. Horizontal alveolar process augmentation and late implantation is recommended.
A = Type I width (> 6 mm) of lower molar EJS
on CBCT cross-sectional image at the level of 3 mm and 6 mm with no requirement
of horizontal alveolar process augmentation prior endosseous dental implant
treatment.
B = Type II width (> 4 to ≤ 6 mm) of lower right molar
EJS on CBCT cross-sectional image. Endosseous dental implant treatment with
simultaneous alveolar process horizontal augmentation are recommended.
C = Type III width
of lower premolar EJS on CBCT cross-sectional image. Horizontal alveolar
process augmentation and late implantation are recommended.
The length of the
EJS (L): is determined by the distance between equators of neighbouring teeth or
implants. The minimal distance between 2 implants should be at least 3 mm [107],
and minimal distances between implants and natural roots should be at least 1.5
mm [108] or in case of platform-switched implant 1 mm [101].
Considering that the optimal recommended diameter of implants in distal jaws segments
is 4 to 5 mm, all EJS of Type I should be ≥ 7 or ≤ 12 mm in length (Figure
6). EJS which length is ≥ 6 or ≤ 13 mm is considered as Type II and < 6 or >
13 mm as Type III. In Type III EJS is impossible to install one or two proper diameter
implants. Orthodontic treatment prior to implant treatment is recommended.
The length of EJS in non aesthetic zones on CBCT image (panoramic
reconstruction): measurement "1" - Type I, measurement "2" - Type II, measurement
"3" - Type III.
Alveolar ridge vertical
position (RVP): the distance between the lowest point of alveolar ridge crest to
the labial/buccal surface cervicoenamel line of the adjacent teeth. This parameter
is important for achieving of favourable implant/crown length ratio and adequate
aesthetic result. Adequate distance for Type I EJS is estimated to be ≤ 3 mm. The
alveolar ridge vertical position > 3 to < 7 mm is defined as Type II EJS. In case
when EJS height is sufficient for implant primary stability achievement, simultaneous
implantation with vertical alveolar process augmentation or sinus floor augmentation
and vertical alveolar process augmentation is recommended (Figure
7). The alveolar ridge vertical position ≥ 7 mm is defined as Type III EJS with
high risk of implant treatment success due to doubtful primary stability achievement.
For Type III EJS vertical alveolar process augmentation and late implantation are
recommended.
Alveolar ridge vertical position in non aesthetic zone: the
distance between the lowest point of alveolar ridge crest to the cervicoenamel
line of the adjacent teeth.
Aesthetic zone
The height of the
alveolar process (H): the distance between the crest of the alveolar process and
the important vital structures of the jaws (nasal sinus floor, mental foramen, anterior
loop of mental nerve). To facilitate a better implant/crown ratio, the minimal dental
implant length in the aesthetic zone is 10 mm [109]. Hence,
the alveolar process height for Type I EJS should be > 10 mm because the recommended
apicocoronal position of the dental implant is 2 mm below the adjacent cementoenamel
junction [94]. A height for the alveolar process of > 8 to ≤
10 mm and > 4 to ≤ 10 mm in maxillary sinus region is defined as Type II EJS. Simultaneous
implantation with vertical alveolar process augmentation or sinus floor augmentation
is recommended. Alveolar process height ≤ 8 and ≤ 4 mm in maxillary sinus region
is defined as Type III EJS. These measurements were considered to be insufficient
for 8 mm length implant installation and primary stability achievement even in maxillary
sinus region. Vertical alveolar process and/or sinus floor augmentation and late
implantation are recommended.
The width of alveolar
process (W): determined by the alveolar process width measured at the level of 3
mm (W1) and 6 mm (W2) from the crest of alveolar process. The smallest measurement
should be accepted as the width of the EJS. It was taken into consideration that
optimal implant diameter indicated for implantation in aesthetic zone can vary depending
on tooth type and measurements. To make presented herein classification system more
universal, it was considered to indicate proper alveolar process width for Type
I EJS, as calculation of optimal implant diameter + 3 mm of the alveolar bone. It
was mentioned above that it should be minimum 1 mm of bone surrounding each implant
[102]. Hence, 3 mm in this case means that implant will be surrounded
by minimum 1.5 mm of bone in buccal and lingual regions. The width of the alveolar
process - optimal implant diameter + < 3 mm is defined as Type II EJS, and optimal
implant diameter + ≤ 0 mm is defined as Type III EJS. For Type II EJS simultaneous
implantation with alveolar process horizontal augmentation is recommended. For Type
III EJS horizontal alveolar process augmentation and late implantation is recommended.
The length of the
EJS (L): is determined by the least distance between neighbouring teeth or implants.
The minimal distance between 2 implants should be at least 3 mm [107],
and minimal distances between implants and natural roots should be at least 1.5
mm [108] or in case of platform-switched implant 1 mm [101].
To ensure optimal aesthetic implant rehabilitation, the implant-supported restoration
should be in symmetry with the adjacent dentition [98]. Consequently,
Type I EJS width must be equal to contralateral tooth. The alveolar process length
characterised as asymmetry < 1 mm in comparison with contralateral tooth is defined
as Type II EJS. Asymmetry ≥ 1 mm in comparison with contralateral tooth is defined
as Type III EJS. In cases of Type II and III EJSs treatment choice depends on patient's
aesthetic demands. If patient wish to have adequate aesthetic result, orthodontic
treatment for EJS length optimisation should be recommended prior to dental implant
surgical placement.
Alveolar ridge vertical
position (RVP): the distance between the lowest point of alveolar ridge crest to
the cervicoenamel line of the adjacent teeth. This parameter is important for achieving
of implant-supported restoration length equability to contralateral tooth (Figure
8). Adequate distance for Type I EJS is estimated to be ≤ 1 mm. The alveolar
ridge vertical position > 1 to ≤ 3 mm is defined as Type II EJS and distance > 3
mm is defined as Type III EJS. Simultaneous implantation with vertical alveolar
process augmentation in case of Type II EJS is recommended. For Type III EJS vertical
alveolar process augmentation and late implantation are recommended.
Alveolar ridge vertical position in aesthetic zone: the distance
between the lowest point of alveolar ridge crest to the cervicoenamel line
of the adjacent teeth.
Mesial and distal
interdental bone peak height (BPH): the distance from the tip of the interdental
bone peak to the alveolar crest midline. Distances of 3 to 4 mm, ≥ 1 to < 3 mm,
and < 1 mm were defined as Types I, II and III, respectively (Figure
9). A study [97] demonstrated that the presence or absence
of a bone crest influences the appearance of papillae between implants and adjacent
teeth.
Type II (measurement "2") and Type III (measurement "3") bone
peak heights of the first upper premolar EJS on CBCT image reconstruction.
Mandibular canal
walls (MCW) and jawbone quality (JBQ) type identification: mandibular canal walls
are depicted on panoramic radiographs or CBCT images as radio-opaque white lines
which are flanking a dark ribbon.The bone quality types are characterised according
to Lekholm and Zarb classification [12] (Figures
10A - D). The combination of identified MC walls and D2 or D3 bone quality types
indicates Type I EJS with low risk of inferior alveolar nerve injury. In case when
it is impossible to identify superior MC wall on X-ray and there is registered D1
or D4 bone quality type, Type II EJS with moderate inferior alveolar nerve injury
risk is defined. The high inferior alveolar nerve injury risk and Type III EJS is
considered when it is impossible to identify MC (Figure 11) and
bone quality is registered as D1 or D4 type.
Bone quality according to Lekholm and Zarb classification.
A = D1 on the CBCT
cross-sectional image (mental region EJS); B = D2 on the CBCT cross-sectional
image (36 tooth EJS); C = D3 in the EJS of upper second molar (CBCT cross-sectional
image); D = D4 in the EJS of 17 tooth on CBCT cross-sectional image.
The part of reconstructed panoramic radiograph with unidentified
superior MC wall in the EJS of 36 tooth (the same CBCT as Figure 10B).
CONCLUSIONS
New classification
system of the jawbone anatomy in endosseous dental implant treatment, based on three-dimensional
edentulous jaw segment pattern, is suggested. It is evident that the demands and
risks of aesthetic result achievement differ significantly in aesthetic zone in
comparison with non aesthetic zone. Mandibular canal and maxillary sinus regions
are important anatomical vital structures of the jaws, because of the risk of injury
of inferior alveolar nerve and maxillary sinus and implant operation planning peculiarities.
In a result, two zones - aesthetic and non aesthetic and two regions - mandibular
canal and maxillary sinus are distinguished in the new classification system. Finally
edentulous jaw segments are divided into three types (Types I to III) according
to their assessment result and risk degree of planned surgical treatment success.
The classification system proposed here based on anatomical and radiological jawbone
quantity and quality evaluation is a helpful tool for planning of treatment strategy
and collaboration among specialists. Further clinical studies should be conducted
for new classification validation and reliability evaluation.
ACKNOWLEDGMENTS AND DISCLOSURE STATEMENTS
The authors report no conflict of interest related to the present study.
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