|Year : 2015 | Volume
| Issue : 1 | Page : 31-38
Bench surgery training for sinus lift procedures by modeling the sinus lining with an eggshell membrane: A technical report
Rampalli Viswa Chandra, Kura Srikanth, Aravind Kumar, Anumala Naveen
Department of Periodontics, SVS Institute of Dental Sciences, Mahabubnagar, Telangana, India
|Date of Web Publication||2-Apr-2015|
Rampalli Viswa Chandra
Department of Periodontics, SVS Institute of Dental Sciences, Mahabubnagar, Telangana
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Context: Simple low-fidelity process models can be constructed using anatomically similar or analogous materials and can be equivalent to the use of high-fidelity, animal or cadaveric models.
Aim s: The objective of the present report is to describe the construction and learning experience of a low-fidelity model for sinus lift procedures.
Settings and Design: An anatomic model was constructed using a dried human skull into which, an eggshell membrane (ESM) was affixed to mimic the sinus membrane.
Subjects and Methods: Totally, 17 implantology instructors were asked to perform a direct and an indirect sinus lift technique on each of the two halves of the prepared maxilla. Following the procedure, the participants completed a feedback questionnaire to ascertain their impressions on the characteristics of ESM and the suitability and handling of the model.
Statistical Analysis Used: Descriptive data were generated and the Mann-Whitney U-test was used to compare the opinions on direct sinus lift versus indirect sinus lift and validity of the model versus ESM behavior respectively.
Results: A majority of the participants felt that the model is an effective educational tool for teaching sinus lift procedures. The participants agreed/strongly agreed that ESM showed a strong visual resemblance to sinus membrane and demonstrated excellent tear resistance during surgery.
Conclusions: The model can be used for education on the practical aspects of sinus lift surgery and allows residents to learn and practice sinus lift procedures before they take on real patients.
Keywords: Anatomical model, education, low-fidelity model, simulation, sinus lift surgery
|How to cite this article:|
Chandra RV, Srikanth K, Kumar A, Naveen A. Bench surgery training for sinus lift procedures by modeling the sinus lining with an eggshell membrane: A technical report. J Dent Implant 2015;5:31-8
|How to cite this URL:|
Chandra RV, Srikanth K, Kumar A, Naveen A. Bench surgery training for sinus lift procedures by modeling the sinus lining with an eggshell membrane: A technical report. J Dent Implant [serial online] 2015 [cited 2019 Jun 26];5:31-8. Available from: http://www.jdionline.org/text.asp?2015/5/1/31/154428
| Introduction|| |
In sinus lift procedures, the maintenance of membrane integrity is extremely important to allow for the placement and confinement of bone regenerative materials.  During sinus lift procedures, membrane perforation is the most common intraoperative complication and is associated with subsequent unpleasant postoperative sequelae such as bleeding, acute or chronic sinusitis, expectoration of graft material into the sinus and loss of the sinus function itself.  Sinus membrane perforations can occur at any stage of the procedure,  are independent of the surgical method used  and the presence and size of perforation may , or may not  influence subsequent implant survival. In the event of membrane perforation, a growing body of evidence suggests continuing the procedure in cases of minor perforations and vice versa. 
With the existing evidence being extremely varying, the best recourse is to understand and minimize the factors responsible for sinus membrane perforations. In the training phase, familiarity with the various anatomic,  pathologic  and technical factors  leading to sinus perforations and an experience with the surgical procedure itself will ensure that residents can successfully perform a sinus lift without causing an untoward damage to the sinus membrane. The ethical issues about learning on human subjects,  the cost issues in procuring and maintaining live and deceased animals  and the scarcity of cadavers  have all hindered this crucial integration between surgical knowledge and surgical practice. A way to bridge this gap is to utilize a "low-fidelity" model,  which captures the essence of the surgery and replicates the anatomic and the procedural aspects as well.
As for all surgical procedures, the importance of precise anatomical knowledge and the level of the operator experience are key contributors in preventing potential complications during sinus lift procedures.  This knowledge and experience can be acquired from models,  which can mimic current protocols in sinus lifts and capture the conditions leading to sinus membrane perforations. From an implantology point of view, the model is expected to be anatomically accurate, simple to construct and should be able to replicate the clinical behavior of the sinus membrane during the direct and indirect sinus lift procedures.
The objective of the present report is to describe the construction and learning experience of an anatomically accurate, straightforward, low-fidelity model of the maxillary sinus into which, an eggshell membrane (ESM) was affixed to mimic the sinus membrane.
| Subjects and methods|| |
Harvesting the eggshell membrane
Unfertilized Asiatic class chick eggs were ordered and maintained in a 4-6°C environment. The eggs were immersed in a water bath that was brought to a boiling temperature in 1 min. The temperature was reduced to 60°C for 12 min, and the eggs were allowed to cool on a bench at room temperature. The eggshell was cracked at the region over the air space, and care was taken to obtain separated shells in toto. Before harvesting the ESM, eggshells were sprayed with 1.6 g/ml hyperosmotic xylitol solution (Herboveda® , Noida, India) to dehumidify the membrane and facilitate its easy removal. The loosened ESM was gently separated from the shell by lifting it with a pair of forceps [Figure 1] and the extracted membranes were stored in a water bath at 6-8°C until further use. Freshly extracted ESM shows a characteristic and distinct white tinge [Figure 2]. However, ESM is an excellent adsorbent of dyes  and for this model, a characteristic deep pink color was obtained by staining it with Cochineal Red A, which is a normal constituent of a commercially available mouthwash (Eludril® , Win Medicare, New Delhi, India).
|Figure 1: Gentle separation of the eggshell membrane from the shell by lifting it with a pair of forceps|
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|Figure 2: Freshly extracted eggshell membrane shows a characteristic white tinge; the membranes used in the anatomical model were stained with Cochineal Red A to contrast and highlight the membrane during fixation and surgery|
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Fixation of the eggshell membrane
The complete right and left halves of the maxilla from 17 dried adult human skulls without gross anatomical deformities were procured from a medical school. The posterior part of the palatine process and parts of the medial wall of the maxillary sinus were removed to provide access and visibility to the floor and the anterior/posterior walls of the sinus [Figure 3]. In models for direct sinus lift procedures, the location and the extent of the bony window was identified and marked with a pencil. The rehydrated ESMs were placed corresponding to this window in the maxillary sinus and were then stabilized with four 2.5 mm × 6 mm screws (Dynamic Ortho Industries, Mumbai, India) placed at distance of at least 1 cm from the center of bony window. The tips of the screws protruding through the external surface of the maxilla were then sheared off. Another 2.5 mm × 6 mm screw was then placed through the center of the bony window and membrane for "holding" the window after its separation and elevation from the sinus wall [Figure 4]. In models for indirect sinus lift procedures, after identifying the surgical site, the rehydrated ESMs were placed on the sinus floor were then stabilized with three 2.5 mm × 6 mm screws placed at a minimum distance of 1 cm from the site [Figure 5]. The tips of the screws protruding through the alveolar process or through the medial wall were then sheared off.
|Figure 3: The posterior part of the palatine process and parts of the medial wall of the maxillary sinus (shaded areas) were removed to provide access and visibility to the floor and the anterior/posterior walls of the sinus|
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|Figure 4: In models for direct sinus lifts, rehydrated eggshell membranes were placed corresponding to the bony window in the maxillary sinus and were then stabilized with four plate fixation screws|
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|Figure 5: In models for indirect sinus lifts, rehydrated eggshell membrane were placed on the sinus floor and then stabilized with three plate fixation screws placed at a minimum distance of 1 cm from the surgical site|
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Evaluation of the model
Totally, 17 relatively experienced implantology instructors, who have previously performed >25 sinus lift surgeries were asked to assess the anatomical model. Every participant was asked to perform a direct (lateral window technique for sinus augmentation  ) and an indirect sinus lift technique (bone-added osteotome sinus floor elevation  ) on each of the two halves of the prepared maxilla as per the standard protocols. Care was taken to maintain an optimum hydration of the ESM during surgical procedures to further promote its adhesion to the underlying bony surface. Following the procedure, the participants completed a feedback questionnaire to ascertain their impressions on the characteristics of ESM and the suitability and handling of the model on a 14-item questionnaire [Table 1] based on the 5-point Likert scale (1 = Strongly disagree, 2 = Disagree, 3 = Undecided, 4 = Agree, 5 = Strongly agree). If they felt necessary, participants were also invited to comment on the model at each step of the survey questionnaire, and these were reviewed. Descriptive data were generated and the Mann-Whitney U-test was used to compare the opinions on direct sinus lift versus indirect sinus lift and validity of the model versus ESM behavior respectively using a commercially available software program (SPSS version 17.0, SPSS Inc., Chicago, IL, USA).
|Table 1: Summary of survey results for all participants on the educational effectiveness, suitability for learning surgical skills and the ability of the model to simulate a realistic surgical experience as pertaining to direct and indirect sinus lift procedures|
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| Results|| |
[Table 1] summarizes the survey results for all participants on the educational effectiveness, suitability for learning surgical skills and the ability of the model to simulate a realistic surgical experience as pertaining to direct and indirect sinus lift procedures. A rating of 4-5 was given by 69% of the participants indicating that they agreed/strongly agreed that the model is an effective educational tool for teaching sinus lift procedures. The remaining participants felt that the model was oversimplified and modeling the gingiva and the alveolar mucosa as well can serve as complements to the existing model. In assessing the suitability of the present model for learning the technique of sinus lifts, 76% of the participants gave a rating of 4-5 and felt that the basic surgical protocols were simulated adequately in a visually appealing way. The remainder felt that the inability to replicate procedures such as flap management and suturing might limit its usefulness as a surgical benchmark model.
For direct sinus lift procedures, 93% of the participants overwhelmingly agreed that the preparation and appearance of the bony window [Figure 6] and the dissection of the ESM from the sinus wall was comparable to the original surgical technique. However, 47% of the operators were not able to elevate the bony window with a hinge osteotomy and had to resort to a complete 360° osteotomy to separate and elevate the window superiorly [Figure 7]. The participants felt that the method of ESM fixation into the sinus wall restricted its mobility to a greater degree. The bony window also had a tendency to collapse inferiorly though it did not impact subsequent bone graft placement. ESM damage or loosening was not seen in any of the models [Figure 8], and the subsequent radiographic evidence of the increase in the floor height was considered as realistic by all the operators [Figure 9].
|Figure 6: The participants felt that the dissection and the elevation of eggshell membrane from the sinus wall were highly realistic|
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|Figure 7: Probably because of slightly restrictive eggshell membrane fixation, the participants felt that it was difficult to perform a hinge osteotomy and preferred a complete 360° osteotomy of the bony window|
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|Figure 8: The membrane retained its orientation, flexibility and structural integrity throughout the direct sinus lift procedure|
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|Figure 9: Comparison between preoperative and postoperative radiographs showing graft material (arrows) and an increase in floor height|
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About 81-91% of the participants agreed/strongly agreed that the model was able to capture and recreate the surgical aspects of indirect sinus lift procedures. ESM tear was not seen in any model; though in one case [Figure 10], osteotome entered the sinus cavity lifting the membrane without compromising its integrity. For each individual sub-steps, the average ratings were higher for the sinus floor elevation (SFE) procedure and radiographic features [Figure 11] (4.11 and 4.35 respectively). While the majority agreed/strongly agreed that the drilling sequence (87%) and behavior of the osteotomes (81%) were realistic, the remaining participants stated that the bone of the maxilla felt brittle and they experienced bone splintering during the procedure.
Two characteristics of ESM were assessed; visual resemblance and flexibility. All the participants agreed/strongly agreed that ESM showed a strong visual resemblance to sinus membrane and demonstrated excellent tear resistance during surgery. About 87% of the participants felt that the membrane demonstrated flexibility comparable to sinus membrane.
|Figure 10: In one situation, the osteotome seemed to have entered the sinus cavity lifting the membrane without compromising its integrity|
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|Figure 11: Comparison between preoperative and postoperative radiographs showing condensation of graft material (arrows) around the second molar area|
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As shown in [Table 2], when the overall scores between the direct and indirect sinus lift procedure and the ESM behavior and validity of the model were compared to each other, there was statistically significant differences (P ≤ 0.001). In the model, indirect sinus lift procedure had a higher overall mean Likert score (4.17 vs. 3.87) when considering all the factors indicating that this model depicts indirect sinus lift procedure more realistically than the direct sinus lift procedure. While ESM was highly acceptable as a substitute to sinus lining to most of the operators, a significant difference was seen when the overall ESM scores were compared to the validity scores (3.79 vs. 3.96).
|Table 2: Comparison of the total scores between direct sinus lift versus indirect sinus lift procedure and the ESM behavior versus validity of the model|
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| Discussion|| |
A bench model for any surgical procedure should function within the traditional operative paradigm.  Surgery is a complex procedure, and the introduction of a new simulation model requires a design strategy that should take into account all the relevant factors that contribute toward the acquisition of surgical skills. , Knowledge of proper surgical technique and development of adequate skills  before embarking on "actual" sinus lifts may prevent future iatrogenic errors that can cause substantial harm to the patient. 
For sinus lifts, there are several surgical simulation models, ranging from commercially available 3D software (Implant3D® , Media Lab Srl, Trieste, Italy), to low fidelity sinus lift teaching models (Sinus-Teach® , Salvin Dental Specialties, Charlotte, USA), through to higher fidelity animal  and cadaver  models. In simulation models, "fidelity" refers to degree to which a model can accurately achieve the level of realism.  High fidelity cadaveric and animal models are the "most realistic" to learn surgical skills as they accurately mimic the hard and soft tissues encountered in surgery. ,, However, rigid country-of-origin ethical , guidelines, portability and availability issues,  inability to repeat procedures , and high maintenance costs  greatly limit their adoption in surgical training. Additionally, when compared to low fidelity models, the gains are generally nonsignificant and modest. 
Keeping the above principles in mind, we were able to construct an inexpensive, low-fidelity, anatomically correct model designed to improve the core knowledge and skills that form an integral part of sinus lift procedures. Low fidelity models are classically made of commonly available materials and suffer from the lack of depiction of tissue consistency and active physiologic processes (such as bleeding).  Human maxillae were used as they can accurately recreate the anatomy and consistency of hard tissues encountered in sinus lifts. After completion of the indirect sinus lift procedure, participants observed that bone of the maxilla felt brittle. In contrast to fresh bone, preserved dry bone is relatively brittle and inflexible  but bone quality seemed to have no effect on overall scores for the procedure. Unfertilized chick egg ESM was preferred as a substitute for sinus lining primarily because they are considerably less expensive to obtain and maintain  than animals or cadavers and no clearance from the animal ethics committee is required.  Overall, chick ESM  (50-140 μm) is thinner than sinus membrane  (130 μm− 1 mm ) but demonstrates a comparable resistance to rupture or tearing.  A study that used hen's eggs as a surrogate sinus to test the effect of hydraulic pressure stated that 50% of the membrane can be predictably detached from the eggshell without membrane dehiscence.  This was evident in the study as ESM damage or loosening was not seen during the surgical procedure in any of the models.
Until very recently, printed manuals, nonanatomic educational models and even web based videos  have been taking the role of an "informal" mentor to provide basic surgical technical skills and knowledge in oral implantology. In this study, the participants felt that the present low-fidelity model is an effective teaching tool for sinus lift procedures and is suitable for learning the surgical technique of sinus lifts. A previous study on elevation of the maxillary sinus floor with hydraulic pressure, which likened the sinus cavity to that of the interior of a hen's egg, successfully transferred the didactic knowledge gained by injecting normal saline solution under hydraulic pressure from eggshells to high fidelity cadaver and human-surgery models.  Another study that evaluated a high fidelity model for SFE stated that surgical bench models are essential educational tools; but supervised clinical practice should always precede autonomous SFE on real patients.  For fidelity based surgery to carve a niche for itself, an effort should be made to demonstrate that these modalities are as good as traditional media for surgical training. Bridging the gap in knowledge transfer between simulation and actual surgery would ensure their approval as alternatives for teaching surgical skills.
The study has some limitations. Conventional surgical positioning was not implemented as the models were hand-held during surgery with the operator remaining in gross control of the model and the tools as well. This may as well account for the higher mean likert scores for the indirect sinus lift technique where osteotome placement and angulation often determines the success and failure of the procedure. , However, this limitation is less concerning as the use of osteotomes, the feel of the sinus floor "lifting" the preparation and elevation of the bony window require a specific tactile feedback with unmistakable confirmation that is more dependent on operator skill than patient positioning.  While the chief investigator was aware of the overall level of training of the residents who took part in the study, specific information about their earlier or current experience was not studied as the investigator was satisfied with the quality of surgery performed on the models. While the participants overwhelmingly felt that ESM is a good substitute for sinus lining, substantial intergroup differences existed when the ESM behavior was compared to the overall validity of the model. However, elevation of the sinus lining is only one aspect of sinus lift management, and factors such as bone quality or operator experience may also influence the quality of sinus lift surgery. , Lastly, the sample size was limited by the number of Likert items as increasing the sample size or widening the Likert response scale would yield different results.
Simple low-fidelity process models can be constructed using anatomically similar or analogous materials and can be equivalent to the use of high-fidelity, animal or cadaveric models. The anatomical model described herein can enable the flexible enactment of surgical procedures and skills learnt are transferable to the "real" patient. However, further validation studies are necessary before the model can be used on a regular basis with respect to training efficiency and subsequent clinical impact.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11]
[Table 1], [Table 2]