## 4 Discussion  
With a mean elevation height of 10.6 mm, no membrane lacerations could be found during gross and microscopic examinations. The mean pressure during maxillary sinus augmentation was therefore assumed to be below the soft tissue tear point for this animal model. However, the results of the balloon experiment should be interpreted with caution, as they were obtained from an ex vivo animal model and changes in tissue resistance and stability due to post-mortem degradation and dehydration of proteins cannot be ruled out. Pig heads are a well-established animal model in implantology research due to their similarity with human anatomy [32; 33; 34]. Nevertheless, the mucosa of the maxillary sinus of the pig is known to be thicker than that of humans [35; 36]. This can lead to increased adhesion and elastic tensile forces.  
In pigs, there is a greater number of Underwood septa. However, the Underwood septa in the region of the lifting procedure did not show a significant influence (\(p=0.096\)) on the lifting process or the lifting force required in this study. Therefore, it is assumed that this anatomical variation may have no influence on sinus elevation procedures where a balloon system is used. Similar results were noted by [PERSON] et al. in their study of pressure and resilience with the Meisinger system [31].  
Due to the pronounced crestal bone height found in this animal model, the lateral surgical approach through the maxillary sinus wall was chosen. In this area, the bone  
Figure 4: (**a**) General distribution of maximum pressure in the maxillary sinus. (**b**) Distribution of mean maximum pressure in the maxillary sinus with and without a septum. (**c**) Mean pressure distribution in the maxillary sinus membrane with and without a septum.  
level in the pig would not exceed 2-3 mm, reflecting the situation found in a patient with an atrophied maxillary alveolar process [36; 37]. All other steps of the procedure were performed and assessed analogous to a crestal approach. However, the lateral accessed may have influenced the pressure values obtained, as the thickness of the lateral sinus mucosa may be different to that of the sinus floor. The thickness of healthy sinus membrane in humans has been shown to vary depending on the region of the maxillary sinus which is being studied (0.99 to 2.58 mm), as well as between individuals [38; 39].  
The mean pressure needed to elevate the mucosa of the maxillary bone floor was calculated to be 344.5 mmHg, a considerably lower value than that obtained in the pressure and resilience measurement study by [PERSON] et al., where the balloon elevation system (Meisinger) was used on ex vivo bisected pig heads, giving a pressure of 748 mmHg [31].  
Histological images did not reveal ruptures or lacerations of the membranes in any of the samples. Thin layers of collagen were observed in the bone, which may be interpreted as periosteum or parts of it, in agreement with the study by [PERSON] et al. which compared various methods of indirect elevation in an ex vivo experimental study.  
Despite the above limitations, the preliminary results of this study with an experimental set-up based on the author's patented sinus floor elevation kit with an inflatable balloon demonstrate that the measuring configuration is appropriate for directly and reliably determining the pressures which occurred in the sinus during the elevation procedure. The possible transfer of this procedure to a clinical environment has therefore been proven, along with a demonstration of the general applicability of this technical configuration for future clinical trials.