Bone Quality Obtained in Sinus Lifting with Anorganic Bovine Bone. A CBCT Study

Author(s): Martínez Soledad Melisa, Ibañez Maria Constanza* and Ibañez Juan Carlos Objective: Quantitatively assess bone density in maxillary sinus lifting with ABB (Bio-Oss®), using Cone-Beam computed tomography 6 months after surgery. Material and methods: A retrospective observational study was conducted between February 2018 and February 2019 on 33 Cone-Beam tomographic studies of 29 adult patients of both genders, with maxillary sinus floor li ... Abstract View Full Article View DOI: 10.17352/2455-4634.000045


Introduction
Sinus lifting technique and implant placement have been successfully used when vertical height available in the posterior maxilla is reduced [1,2].
Although ABB particle size indicated for use in sinus fl oor elevation is "large" [8], it would also be possible to use small particles, and even mix both sizes. These modifi cations in the selection of particle size could produce different results in the fi nal density of the graft.
On the other hand, it is important to note that the area where the highest density of the graft is needed would be the most occlusal part of it, because that is where the implants will be placed. Furthermore, due to the improvements in ultramicrotopography, currently shorter fi xations are used, and there is no need for long implants [9][10][11][12][13][14][15][16].
One of the possible ways to assess the effect of particle size on the fi nal graft could be by measuring the bone density obtained at 6-8 months after the healing of the bone fi lling, at which time the implants could also be placed [17,18].
The present research was proposed to determine the bone quality obtained 6 months after performing maxillary sinus lifting with lateral window open using piezo surgery and fi lled with Bio-Oss® with different particle sizes, especially in the middle inferior portion of the graft, through measure density in CBCT scans.

Material and methods
A retrospective observational study was carried out between

Surgical protocol
The surgeries were carried out during the regular courses of the Career of Specialization in Oral Implantology of the Catholic University of Cordoba, Argentine. Each patient was treated by different operators, although they were instructed exactly under the same protocol.
Measurement of bone density in tomographic studies.
CBCT were studied before and after 6 months of sinus surgery. DICOM images were taken by a Kodak 9000 tomographer. (Kodak-Carestream Health, CS 9300, NY, USA) in a digital dental diagnostic center (Córdoba, Argentina) and were analyzed with Blue Sky Plan 3 software (Blue Sky Bio, USA).
All the measurements were performed by the same operator.
In pre-surgical tomographies, the measurement of the maxillary residual bone was taken at the point of lowest height in the affected areas in a sagittal section (Figure 1a Three HU measurements were taken for each sector; that is to say, a total of 9 measurements were made moving the measurements apically 1.2 mm from the fi rst measurement and 1.2mm apically again ( Figure 2).
Finally, the residual bone height was measured again in three different points.
All these measurements were transcribed in a spreadsheet taking the average values of each group.  The variables analyzed were the following: -Particle sizes, thickness of remnant bone, age, gender, and distance to remnant bone.

Statistical analysis of the data
Tomographic density contrasts according to the categories were carried out using parametric tests (Student test, one-way ANOVA and repeated measures ANOVA and Tukey post hoc test) and non-parametric tests (Mann-Whitney) according to distribution type for each evaluated factor: particle size, remnant bone thickness, age and gender. The Pearson correlation test was used to analyze the correlation between radiographic density and distance to remnant bone. For all tests the level of statistical signifi cance was set at 0.05.

Results
The average tomographic density of the grafted sinuses was 586 ± 238 HU (mean ± standard deviation). This value corresponds to Type II -III bone considering the classifi cation proposed by Lekholm and Zarb [26], (500-850 HU) and Type II considering Norton's and Gamble's [27], classifi cation. Table 1 shows the results in relation to particle sizes. The cases grafted with mixed particles of both sizes (small and large) recorded the higher radiographic density. The differences obtained were signifi cant.

Tomographic density according to the residual bone
Residual bone was dived into two groups: <= 2mm and > 2mm. Values were similar in both groups. As seen in the box diagram of Figure 3, there were two outliers values, one for each category, which correspond to cases of grafts performed with mixed particles (small and large). The results did not show signifi cant differences.

Tomographic density according to patient's age
When comparing the density values considering only the age factor, the differences were signifi cant (Mann-Whitney test: p = 0.015; p <0.05) Table 2.

Tomographic density according to patient's gender
The results were considered without taking into account the infl uence of mixed particle cases, since the 3 mixed particle cases corresponded to women. No signifi cant differences were obtained Figure 4.

Tomographic density according to distance to residual bone
Distance of the measure to the remnant bone was divided into three groups as Table 3 and Figure 2 show. The distributions were very similar, with no signifi cant differences between the three groups (ANOVA: p = 0.879; p> 0.05).

Discussion
The average radiographic density of the grafted sinus was 586 ± 238 UH (mean ± standard deviation), a value that corresponds to Type II-III bone considering the classifi cation proposed by Lekholm and Zarb [26], (500-850 UH) and Type II according to Norton and Gamble [27]. Seiler, et al. [18], after comparing two fi lling materials (Osteodens vs Bio-Oss) at 6-8 months after regeneration, obtained an average bone density value of 625.0 UH for Bio-Oss®, result which is similar to the one obtained in this study. Soardi, et al. [19], found similar values but using different biomaterials (Puros and Biomend) and they confi rm the results using biopsies. Besides in another study [28], they performed CBCT scans for each patient in the maxillary region following this sequence: before surgery, after sinus augmentation, immediately after implant insertion (6 months), and consecutively after 10 and 18 months and reported similar results to the present study.     [19,28].
As it can be seen in the present study, most of the measurements were performed in the lower portion of the grafted sinus, not higher than 8 mm. The reason for this decision was that most of the implants used nowadays are not too long due the improvements in their microtopography [9][10][11][12][13]. The use of short implants is as effective as using longer implants [12,15,16,[31][32][33][34]. Moreover, Shi, et al. [35] showed similar results between 6 and 8mm long implants and 10mm implants in combination with sinus lifting. In addition, the 1 to 9 mm lower portion of a grafted sinus would have greater vascularization, as shown in the work done by Wong, et al. [36], The results of these last two investigations may be related to the fi ndings of the present research.

Conclusion
The bone density obtained after grafting maxillary sinuses using lateral window technique with ABB as a bone graft and collagen membrane as barrier , and measuring Hounsfi eld Units in CBCTs, shows quantitative values similar to those of a bone type II -III, providing a high degree of predictability for implant placement 6 months after the sinus intervention.