A 5-year Follow-up for Implant Placement Immediately Following the Lateral
Approach of the Trap Door Window Procedure to Create a Maxillary Sinus
Lift Without Bone Grafting of 80 Implants in 44 Patients
I-Ching Lin*, Anne Margaret Gonzalez*, Hsin-Ju Chang**, Shou-Yen Kao◎, Ta-Wei Chen#
* I-Ching Lin, DDS & Anne Margaret Gonzalez, DDS, MS, Residents, Oral and Maxillofacial
Surgery, Dept. of Stomatology, Taipei-Veterans General Hospital (VGH), Taipei, Taiwan.
** Hsin-Ju Chang, DDS, Attending Dr., Prosthodontic Dentistry, Kaoshiung-VGH
◎
Shou-Yen Kao, DDS, MHA, DMSc, Professor and Head, Department of Stomatology, Taipei-
VGH; School of Dentistry, National Yang-Ming University (NYMU), Taipei, Taiwan.
#
Ta-Wei Chen, DDS, Clinical professor, Oral & Maxillofacial Surgery, Department of
Stomatology, Taipei- VGH; School of Dentistry, NYMU, Taipei, Taiwan.
Correspondence and reprint request to Dr. Ta-Wei Chen, (e-mail: 52599881990@yahoo.com.tw)
& Dr. Shou-Yen Kao, (e-mail: sykao@vghtpe.gov.tw) No. 201, Sec. II, Shih-Pai Road, Oral and
Maxillofacial Surgery, Department of Stomatology, Taipei-VGH, Taipei, Taiwan, ROC.
Tel: 886-2-28757013, Fax: 886-2-28742375
Running title: Immediate implant placement with lateral approach sinus lift without graft
Keywords: Graft, Implant, Lateral approach, Sinus lift, Survival
1
A 5-year Follow-up for Implant Placement Immediately Following the Lateral Approach of the
Trap Door Window Procedure to Create a Maxillary Sinus Lift Without Bone Grafting of 80
Implants in 44 Patients
Abstract
Purpose: The study was to evaluate the 5-year status of immediately placed implants subjected
to a maxillary sinus lift without graft.
Materials and Methods: Eighty implants were placed in 44 patients from 2004 to 2005. A
minimum of 3-mm retained bone height (RBH) was required. All implants were placed with
sinus lifting through a lateral approach by the trap-door, open-window method without
placement of any graft. Patients underwent oral hygiene instruction, periodontal charting, yearly
panoramic radiographs, and cone beam computed tomographic (CT) scan during the regular
follow-up. The gained bone height (GBH) in maxillary sinus, peri-implant sulcus depth and
marginal bone loss were statistically analyzed by student t-test. The implant survival was defined
when the prosthesis had been delivered without infection, pain, or mobility.
Results: Forty-four patients (16 males, 18 females) having an average age of 58 years old, with a
total of 80 fixtures were followed for 5 years after prosthesis delivery. No patients developed
sinusitis or other complications leading to loss of implant. The average RBH was 5.06±1.51 mm
and the average endosinus implant length was 7.77±1.7 mm. The 2-year and 5-year survival rates
of fixtures were both 100%. The GBH in sinus ranged from 3 to 12 mm with an average of
2
7.24±1.83 mm at 2-year follow-up & 7.44±1.94 mm at 5-year follow-up (P>0.05). The average
peri-implant sulcus depths were 2.5±0.4 mm at 2-year follow-up & 3.1±0.5 mm at 5-year followup (p<0.05). The mean peri-implant marginal bone loss was 1.3±0.3 mm at 2-year and 2.1±0.5
mm at 5-year follow-up (p<0.05).
Conclusions: Endosinus new bone formation was confirmed with a good survival of implants
with maxillary sinus lift by the lateral approach without graft was observed at the 5-year followup. Attention should still be focused on the oral hygiene maintenance to warrant the stability of
the peri-implant gingival health.
Keywords: graft, implant, lateral approach, maxillary sinus, survival
3
Introduction
Pneumatization of maxillary sinus and resorption of alveolar ridge after loss of premolars
and molars often lead to insufficient bony support for implant placement over atrophic posterior
maxilla. Boyne first described the elevation of maxillary sinus floor for bone grafting in the
severely resorbed maxilla. He further reported on sinus augmentation using autogenous iliac
bone chips placed via lateral approach at the first stage surgery followed by the second stage
wherein blade type implants were placed at the augmented area to support fixed or removable
prosthesis.1-2 The lateral approach of maxillary sinus augmentation is the classic and more
commonly performed technique for the past 30 years and is done by creating a lateral trap-door
window for the elevation of the sinus membrane and grafting with autogenous bone or various
alloplastic bone graft substitutes.1-2 In 2008, Pjetursson BE et al reported a 90.1% 3-year implant
survival rate after lateral approach sinus augmentation through a meta-analysis on 48 studies
with 12020 implants in 4000 patients.1-2 The other method, internal sinus membrane lifting with
osteotome, also known as transalveolar technique, was first described by Summers in 1994.3-4
Various filling materials have been used for sinus augmentation, including autografts, xenografts,
allografts and synthetic bone grafts.5-8 Tan WC et al similarly reported in 2008 a 92.8% 3-year
implant survival rate after transalveolar sinus augmentation on 19 studies with 4388 implants in
2830 patients.9 The transalveolar technique may be considered easier and less invasive and was
reported to have a lower sinus perforation rate than the lateral approach. Yet, the lateral approach
4
seems to provide a more direct vision of any sinus perforation and a higher capacity to receive
bone grafts or substitutes than the transalveolar procedure. While both techniques demonstrated
their own unique advantages, the guidelines for choice of grafts in these two approaches based
on the retained bone height have been fully discussed in a sinus consensus conference.10 On the
other hand, experimental data interestingly demonstrated a potential of sinus bone regeneration
by membrane elevation without placing any bone graft.11-13 Clinical evidence of sinus floor
elevation with simultaneous implant placement without any graft was first described by Bruschi
et al in 1998.15 A limited period of follow-up for no more than 2 years were consequently
reported in several articles from 2004 to 2007.13-19 Nedir further reported a 3-year prospective
study in his follow-up using osteotome technique without graft in 2009.19 As far as we reviewed,
there was no report of a longer period of case series in this regard. We continued to prospectively
observe our cases extended from our previously published cohort study19 in an attempt to help
formulate successful strategies for maxillary sinus floor augmentation. The present study was
undertaken to measure the height of new bone formation in the maxillary sinus through the use
of conventional panoramic films assisted by cone bean computerized tomography (CT) in
patients whose implants were inserted into the maxillary sinus without additional grafting
material after sinus membrane elevation.
Materials & Methods
5
- Patients & pre-surgical evaluation Forty-four patients who were treated with implant rehabilitation as well as sinus lifting
without graft from 2004 to 2005, were prospectively followed and evaluated for 5 years after
prosthesis delivery. All patients were physically healthy and free of any systemic problems that
could interfere with the wound healing process. They also denied having any medical history of
diseases contraindicated for sinus or implant surgery. In this study, inclusion criteria were as
follows: 1. Patients required implant treatment in the posterior maxilla. 2. Primary stability of the
implant was obtained. 3. There were no signs of sinusitis before the surgery. Study models of the
patients were transferred to articulators for analysis and fabrication of surgical stents for guiding
the position and axis of implant fixtures. Patients were informed of the potential unfavorable
conditions for implant rehabilitation. They were given necessary information about the
procedure, including its prognosis, need for regular radiographs in follow-ups, potential hazards
and complications after the diagnosis. A treatment plan was then decided.
- Surgery The operations were carried out with the patients under either local or general anesthesia.
Prophylactic antibiotics (10 mg dexamethasone, 3,000,000 U crystal penicillin and 80 mg
gentamicin intravenously, 30 minutes prior to surgery or 2 g amoxicillin or 600 mg clindamycin,
1 hour prior to surgery) were given. A surgical stent was prepared and transferred from a
simulated augmented ridge from the study model of the patient’s maxilla. Under local anesthesia,
6
full-thickness flaps were elevated carefully following a mid-crestal incision. A mesiovertical
releasing incision was made as necessary. The sharp and thin alveolar ridge and the lateral wall
of the maxillary sinus were exposed. Extreme care was taken to radically elevate the sinus
membrane from the trap-door window opened by using an electric-motor drill with adequate
water-cooling. The floor, lateral wall and posterior wall of the sinus membrane were detached,
pushed upward and medially allowing the placement of dental implants into the bone chamber.
The implant fixture was positioned from the crestal bone and extended into the space with a
primary stabilization provided by the retained alveolar bone (minimal initial bone height was 3
mm and shortest implant length was 12 mm). Two 1-stage implant systems (ITI; Straumann,
Waldenburg, Switzerland, and SwissPlus; Centerpulse Dental, Carlsbad, CA) were used in
patients with focal edentulous areas. A 2-stage implant system (Friate-2; Friadent GmbH,
Mannheim, Germany) was used for submerged healing beneath the gingiva after the implant was
inserted. Instead of placing autogenous bone or allogeneic bone substitute into the sinus space as
fillers, the space was created by the elevation of sinus membrane with or without an attached
maxillary cortical plate, which was then supported by the fixture. No membrane was used to
cover the lateral wall. For 1-stage implant, the healing abutment ontop of the fixture was exposed
(Fig 1. A-D). The wound was further closed with 4-O Vicryl suture and was covered by
periodontal dressing material (Coe-Pack; Coe Laboratories Inc, Chicago, IL). Six months after
surgery, the second-stage operation was carried out to expose the implanted 2-stage system
7
fixtures. A labially positioned palatal flap was used to ensure sufficient keratinized gingiva at the
buccal side of the fixture. A minimum of 1 month was required for the healing of the flap and
peri-implant tissues. The referring prosthodontists carried out the prosthetic rehabilitation of both
1-stage and 2-stage systems at 7 to 8 months and with initial force loading at about 9 months
after sinus lifting-combined implant surgery (Fig. 2A-D). All patients received a strict and
periodic plaque control program to maintain peri-implant tissue health.20
- Analysis of radiographsPreoperative, 6-month and annual postoperative panoramic radiographs were taken in all
cases (Fig. 2A-D). A single radiographic unit was used to obtain all panoramic films at
standardized parameters, which were determined by the manufacturer to minimize possible
distortions. The pre-operative metal rod and the length of the implant were used to calibrate the
amount of magnification for each radiograph. A cone beam computed tomographic (CT) scan or
conventional CT scan taken at 2-3 year follow-up was used to observe the regeneration of bone
after maxillary sinus lifting procedure (Fig. 2E-G).16, 21-23 Panoramic radiographs at 2- & 5-year
follow-ups were used for calculation and analysis (Fig. 3). The retained bone height (RBH) was
measured at 1 mm adjacent to the implants, from the maxillary sinus floor to the edentulous
ridge crest. The amount of gained bone height (GBH) and the remodeling bone height were then
calculated from these readings (Fig. 4).21 The outcome of the implant was defined as “survival”
8
accordingly when the prosthesis was still functioning by the implant support with no signs of
continued pain, uncontrolled peri-implant tissue infection.
Results
Forty-four patients including 18 females and 26 males with a mean age of 58.1±12.3
years, ranging from 25 to 86 years of age, were analyzed in this cohort study. A total of 80
implant fixtures that were immediately placed through the lateral approach of the trap-door
window procedure to create a maxillary sinus lift without bone grafting from 2004 to 2005 were
followed for more than 5 years after prosthesis delivery. 15 patients received one implant, 22
patients received two implants, and 7 patients received three implants. All implants were 12 to
15 mm in length and protruded more than 4 mm (range 4-11mm) into the sinus cavity. The
surgical sites were upper first molar region (no=37, 46%), followed by upper second molar
(no=27, 34%) and premolar regions (no=16, 20%) respectively. None of the patients developed
sinusitis or other complications leading to loss of an implant subsequent to performance of the
sinus lifting-combined immediate implant surgery. All 80 fixtures healed well, no uncontrolled
infection or implant mobility was observed on initiation of loading force from the prosthetic
components from 9 months after implant surgery to a minimum of post-delivery 5-year followup. The initial RBH between the edentulous ridge crest and the sinus floor was 3 to 8 mm with
an average of 5.06±1.51 mm. The average endosinus implant length was 7.771.69 mm. The
GBH in the sinus ranged from 3 to 12 mm with an average of 7.24±1.83 mm at 2-year-period
9
observation and an average of 7.44±1.94 mm at 5-year-period observation (P>0.05). The periimplant soft tissue was evaluated during the course of the study using visual examination and
measurement of peri-implant sulcus depth. With the periodic plaque control program, the periimplant soft tissue health can be effectively maintained in our patients. Visual examination
revealed no obvious plaque accumulation or soft tissue inflammation around most implants.
Averages of peri-implant sulcus depth at 2-year and 5-year follow-ups were 2.5±0.4 mm and
3.1±0.5 mm (p<0.05), and there was no evidence of bleeding on probing in most of implant sites.
The mean peri-implant marginal bone loss was 1.3±0.3 mm at 2-year and 2.1±0.5 mm at 5-year
follow-up (p<0.05). 18 cases had reversible peri-implant mucositis and were managed by
endorsed oral hygiene instruction (OHI) program to maintain peri-implant tissue health. 3 cases
with 8 fixtures developed peri-implantitis with angular bony destruction more than 3 mm during
the follow-up (Fig. 3); a flap surgery for maintenance of peri-implant tissue health was
performed in these 3 cases. The principles of the Cumulative Interceptive Supportive Therapy
(CIST) protocol were employed in the treatments.24 Through a minimum follow-up of 5 years in
44 patients with 80 fixtures, the fixture survival was 100% and the function and stability of these
fixtures was judged to be good (Table 1).
Discussion
While clinical interests still focused on abundant covariates regarding the success of sinus
lifting for dental implants,9, 25 the observation of bone regeneration in the sealed bone chamber in
10
several animal studies had already highlighted a new clue to the increase of bone by sinus lifting.
Earlier report by Boyne PJ in 1993 using an animal model in monkeys revealed that implants
protruding into the maxillary sinus following elevation of the sinus membrane without grafting
material exhibited spontaneous bone formation below the sinus membrane.11 At the same time,
Linde et al reported using an osteopromotive membrane technique to successfully create new
bone without graft on the calvarium of rats and demonstrated that the osteogenesis depends on
the stiffness of membrane for space maintenance and healing time.12 A comparative
histomorphometric observation by Haas et al in an animal study in sheep further demonstrated
that the new bone formation after membrane elevation without graft could be from the
periosteum at the cervical part of implant and bone proper from other part of bone chamber with
a more bone-implant contact in a longer time of healing.13
The experimental results were further evidenced by a series of clinical observations. Winter
first used osteotome technique for local management of posterior maxillary sinus membrane with
simultaneous implant without graft in 58 implants of 34 patients with a mean RBH of 2.87 mm
and reported a success rate of 91.4% in a period of 22 months follow-up.26 Lundgren S et al first
used lateral approach in his 12 months short-term observation after functional loading in 10
patients for 12 maxillary sinus floor augmentations of 19 implants with lengths of 10-15 mm and
a longer mean RBH of 7 mm (range, 4-10 mm) and reported that there is a great potential for
bone formation in the maxillary sinus without the use of additional bone grafts or bone
11
substitutes. The excluded compartment created by the elevated sinus membrane, implants, and
replaceable bone window allowed bone formation according to the principle of guided tissue
regeneration.15 In 2007, at the same time that Thor A et al27 reported bone formation at the
maxillary sinus floor following simultaneous elevation of the mucosal lining and implant
installation without graft material in 20 patients with 44 Astra Tech implants, we also reported a
successful implant placement immediately after the lateral approach trap-door window procedure
to create a maxillary sinus lift without bone grafting in a 2-year observation of 47 implants in 33
patients.18 Creation of the sinus space with the trap-door, open window method results in an
enclosed chamber walled by the periosteum on the flap side laterally, the sinus membrane
periosteum with a cortical plate superiorly, and the maxillary bone in other aspects. The dental
implant provides a vertical stop for the upwardly positioned cortical bone on the elevated
membrane such that the space is maintained with clotted blood. A 3-year observation report
using osteotome sinus floor elevation technique without grafting material was recently proposed
by Nedir R et al.19 Jeong et al recently evaluated 9 patients with a total of 10 implants (10-12 mm)
that were inserted into the maxillary sinus 4-6 mm after sinus membrane elevation without bone
grafting. The mean endosinus bone gain was 3.5 mm and 2-year postoperative CT images
showed tent-like bone formation around the implants in their short-term clinical follow-up.28 The
above limited number of articles all concluded that elevation of the sinus membrane without the
addition of a bone grafting material still led to a satisfactory result. Findings of these reports
12
regarding the immediate placement of implants without the use of autogenous bone grafts or
other alloplastic bone substitute materials challenge the utility of the conventional approach
involving placement of filling materials into a sinus space created either by the trap-door window
method or by osteotome sinus floor elevation. 18
We further prospectively conducted this long-term 5-year observation of implants in
patients subjected to a maxillary sinus lift and immediate implant placement without bone
grafting through a lateral trap-door window procedure. Through a minimum follow-up of 5 years
in 44 patients with 80 fixtures, the fixture survival was 100% and the function and stability of
these fixtures was judged to be good. Additionally, sinus elevation from the lateral approach
ensured a highly tented sinus membrane and space for bone regeneration maintained by the
synchronously placed implant. It should be noted that this approach differs from that involving
the greenstick fracture created with the osteotome technique wherein undetected perforation of
the sinus membrane might create a potential problem.
Findings of various reports disagree greatly with regards to the minimal bone height of
the residual ridge needed for sinus lifting; however, in this study, an average of 5 mm (range 3-8
mm) RBH below the lowest part of the sinus floor was present in all cases to provide primary
stability of the implant fixtures. Primary stabilization is of particular importance in implants
placed in the lifted sinus since any constant micromovement of the implant would invite
untoward or complicated inflammation which may lead to a fibrous healing around the implant
13
resulting to a failure in osseointegration. While previous articles suggested the importance of
maintaining the tented membrane by the implant with grafts to allow an appropriate period of 912 months for bone regeneration and a slightly gradual decrease of GBH due to remodeling
around the apex of implants.2,27-29 Our analysis revealed there were no significant changes on the
GBH between 2-year (7.24±1.83 mm) and 5-year (7.44±1.94 mm) follow-ups. This nonsignificant increase did not conflict with a slight decrease with time in GBH mentioned in other
articles.22-24, 27-29 Although a primary stability of all our implants was provided by the retained
bone support during operation, an initial force loading in these cases was not conducted until 9
months after surgery to wait for bone formation around implants. This denotes a valued potential
that our procedure using a radical dissection for lifting the sinus membrane to expose the
endosinus bony wall from the lateral to the posterior and medial endosinus compartment may
provide an advantageous environment for bone regeneration.34,35
Compared with a mean 3-year implant survival rate of 90.1% in a systematic review of
implants in combination with sinus floor elevation by lateral approach with inclusion of various
graft materials,15, 29-30 a good survival of 100% in our case series conceivably evidenced the
success of the procedure to gain new bone formation with only membrane elevation in the sinus.
The bone formation was indirectly demonstrated in the post-operative radiographic images of
panoramic films and cone beam CT. While our study revealed no significant difference in the
GBH between 2-year and 5-year follow-ups, significant differences (p<0.05) between results at
14
2-year and 5-year follow-ups in the average peri-implant sulcus depths (2.6±0.4 mm vs 3.1±0.5
mm) and the mean peri-implant marginal bone loss (1.3±0.3 mm vs 2.1±0.5 mm) were observed.
The significant differences should be attributed to several cases who developed reversible periimplant mucositis or peri-implantitis. This further highlights the importance of the periodic
plaque control program to effectively maintain peri-implant soft tissue health in cases.
Conclusion
Long-term follow-up confirmed the success of the procedure of elevation of the sinus
membrane and simultaneous placement of implants. This study shows that there is great potential
for new bone formation in the maxillary sinus without the use of additional bone grafts. However,
strict oral hygiene was significant in the maintenance of peri-implant health.
Acknowledgement: This study was supported by grants VGH99C1-093, V99S1-004 and
V99E1-006, Taipei-VGH, Taipei, ROC. We appreciate for the contribution from Professor YuLin Lai, Chair of Periodontics Division, Taipei-VGH in support to this clinical study.
Correspondence and reprint refer to Dr. Ta-Wei Chen, (e-mail: 52599881990@yahoo.com.tw)
& Dr. Shou-Yen Kao, (e-mail: sykao@vghtpe.gov.tw) No. 201, Sec. II, Shih-Pai Road, Oral and
Maxillofacial Surgery, Department of Stomatoloy, Taipei-VGH, Taipei, Taiwan. Tel: 886-228757013, Fax: 886-2-28742375
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Table 1. Clinical features of 80 implant fixtures in 44 patients
Average age (year)
Gender
Male
Female
Classification of implant location
Premolars
First molar
Second molar
Length of fixtures (mm)
12
13
14
15
58.1±12.3
26
18
16
37
27
35
33
3
9
18
Table 2. Analysis of 80 implant fixtures at 2- & 5-year follow-ups
Average RBH (mm), range 3-8mm
Average endosinus implant length (mm)
GBH at 2-year follow-up (mm)
GBH at 5-year follow-up (mm)
2-year peri-implant sulcus depth (mm)
5.06±1.51
5-year peri-implant sulcus depth (mm)
2-year peri-implant marginal bone loss (mm)
3.1±0.5*
1.3±0.3
5-year peri-implant marginal bone loss (mm)
2.1±0.5*
7.771.69
7.24±1.83
7.44±1.94
2.5±0.4
* Significant difference (p<0.05) between 2-year and 5-year follow-ups
Figure 1
19
B
A
C
D
E
F
G
Figure 2
20
Figure 3
21
Figure 4
22
Legends of Figures
Figure 1. This panel demonstrated the frontal sections of the right maxillary atrophic edentulous
ridge with a low maxillary sinus floor, prepared for a 1-stage implant surgery to combine with
sinus membrane lifting procedure. A. A full-thickness muco-periosteal flap was raised following
a mid-crestal incision. A mesiovertical releasing incision was made in convenience to expose the
buccal cortical plate at the lateral wall of the maxillary sinus. The trap-door bone window,
locating above the retained alveolar bone, was created by an electric-motor drill with adequate
water-cooling. B. Extreme care should be taken to radically elevate the sinus membrane from the
lateral wall, floor to the posterior and medial walls of the sinus cavity. C. The implant fixture
was positioned from the crestal bone and extended into the space with a primary stabilization
provided by the retained alveolar bone. The tented space below the elevated sinus membrane
allowing for bone regeneration is maintained or supported by the fixture tip within the maxillary
sinus. D. Without placing either autogenous bone or allogeneic bone substitutes into the sinus
space as fillers, the wound was further closed with 4-O Vicryl suture. No membrane was used to
cover the lateral bone window underneath the mucoperiosteal flap. The healing abutment ontop
of the 1-stage implant fixture was exposed.
Figure 2. A 50-year-old male patient presenting a low sinus floor & edentulous ridge in the right
maxilla was prepared for receiving three 2-stage implants. A. Preoperative panoramic radiograph
showed a severely atrophic maxilla with missing of 2nd premolar, 1st & 2nd molars. Arrows
23
indicated the positions of the retained alveolar bone between the sinus floor and the edentulous
ridge crest. B. A lateral approach of the trap-door window procedure was performed to create a
maxillary sinus lift without bone grafting over right posterior maxilla, with simultaneous
placement of 3 implants. C. Implants and bone window was covered by new bone when a labial
positioned palatal flap was raised at 6 months after implant surgery. D. 9 months post-operative
panoramic radiograph showed elevated sinus floor & endosinus new bone around three implants
with temporary restoration on the fixture abutments. Arrows indicated the augmented bone levels
between the lifted sinus floor and ridge crest at 1mm adjacent to apices or necks of implants. EG. Cone beam CT at 2-year follow-up showed the endosinus new bone formation around each
implant.
Figure 3. A 55-year-old female patient presenting a low sinus floor & full edentulous ridge in
the right maxilla was prepared for implant surgery. A. Preoperative panoramic radiograph of
showed a severely resorbed alveolar ridge in the right maxilla with low sinus floor. B. 6 months
post-operative panoramic radiograph showed new bone regenerating within the created sinus
space around two implants. C. 2-year post-operative panoramic radiograph showed the obvious
endosinus GBH around implants & a minimum of less than 1 mm peri-implant marginal bone
loss. D. 5-year post-operative panoramic radiograph showed stable endosinus GBH with an
obvious 3-mm peri-implant marginal bone loss around cervical area of implants indicated by
arrows.
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Figure 4. Schematic drawing of parameters measured from the panoramic radiograph. The
magnification was calibrated based on the length of the implant. A indicating the retained bone
height (RBG) which was defined as the vertical bone height at 1 mm adjacent to the implants,
from the maxillary sinus floor to the edentulous ridge crest. B indicating the gained bone height
(GBH) which was defined as the vertical height at 1 mm adjacent to the implants, between the
original sinus floor and elevated sinus floor. C indicating the remodeling bone height which was
defined as the distance at 1 mm adjacent to the implants, between the apex of the implant and
lifted maxillary sinus floor. B+C was equivalent to the endosinus implant length.
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