Comparison of calcium sulfate and tricalcium phosphate in bone grafting after sinus lifting for dental implantation: A randomized controlled trial

Background. Maxillary sinus grafting is considered the most common surgical technique to secure a sufficient bone height for placing dental implants. It is carried out either by making a bony window in the lateral wall of the maxillary sinus (the external procedure) or through the alveolar entrance technique by using alveolar osteotomes (the internal procedure), depending on the quality and quantity of the remaining bone. Objectives. The aim of the present study was to compare radiologically the amount of bone gain (an increase in bone dimensions) and bone reduction (the loss of the graft volume) obtained by using tricalcium phosphate (TCP) and calcium sulfate (CS) grafts mixed with advanced platelet-rich fibrin (A-PRF).


Introduction
Bone height in the maxillary posterior edentulous area may be insufficient for dental implant placement due to the pneumatization of the maxillary sinus after the ex traction of the teeth. 1 Maxillary sinus grafting is the most commonly used surgical technique for securing bone height sufficient for dental implantation in such cases. 2he operation is carried out using one of the 2 basic techniques, i.e., making a bony window in the lateral wall of the maxillary sinus (the external sinus lift) or through the alveolar approach with the use of alveolar osteotomes (the internal sinus lift). 3any types of bone grafts have been used, though auto genous bone has always been considered the gold stan dard due to superior osteoconduction, osteoinduction and osteogenesis. 4However, there are some disadvan tages connected with the process of acquiring it, includ ing the limited amount of bone obtained from the inside of the oral cavity and the need for an additional surgical procedure, which leads to an increase in the surgery time.These factors have led to increasing interest in the search for alternative graft materials. 5Tricalcium phosphate (TCP) is a bone substitute that promotes bone growth 4 and is considered one of the preferred grafts for maxil lary sinus lifting due to its suitable absorption nature and volume stability. 6alcium sulfate (CS) occupies a unique position in the field of regenerative materials, as it has a long history of clinical usage as compared to other currently available biomaterials and is widely recognized as a welltolerated material with applications in bone regeneration.It under goes virtually complete resorption in vivo, without eliciting a significant inflammatory response, [7][8][9] which is critical in this procedure, as the positioning of implants seems to be even more delicate.In particular, recent stu dies have highlighted extremely high levels of periimplant tissue inflammation as compared to the natural tooth, which promotes longterm bone remodeling and resorp tion.Using drugs that contain inflammationmoderating components may also enhance the properies of the bone. 8tudies have investigated mixing alloplastic grafts with plateletrich fibrin (PRF) to reduce the amount of graft and promote osteogenesis in the grafted area.The texture resulting from such mixing facilitates clinical handling, increases the stability of the graft and improves the out comes. 10,11his study aimed to evaluate and compare the benefits of using CS and TCP as graft materials for the twostage maxillary sinus lifting procedure in cases of high bone re sorption, using the radiological analysis of bone gain and bone reduction.

Study design
This was a randomized (1:1), splitmouth clinical trial (randomized controlled trial -RCT) (No.Faculty of Dentistry/RCTs758) comparing the use of CS and TCP in bone grafting for external sinus lifting for dental implantation.
The Consolidated Standards of Reporting Trials (CONSORT) statement was used as a guide for this study. 12The study was conducted in the laboratory of the Maxillofacial Surgery Hospital and the Department of Implantology at the Faculty of Dentistry of Damascus University, Syria (Fig. 1).
Informed consent was obtained from the partici pants, and the ethics board at the Faculty of Dentistry of Damascus University, Syria, approved the study (FMD185).

Participants
The sample was selected from among the patients who sought implant treatment at the Department of Oral and Maxillofacial Surgery at the Faculty of Dentistry of Damascus University, Syria.Data was collected from February 2018 to January 2021.

Sample size calculation
The sample size was calculated using the G*Power 3.1.3program (https://www.psychologie.hhu.de/arbeitsgruppen/allgemeinepsychologieundarbeitspsychologie/ gpower), based on a study power of 80% with a signifi cance level at p = 0.05, and the effect size data (0.83) from a study by Călin et al. 13 Considering sample dropout led to the addition of 2 maxillary sinuses to each group to give a total sample size of 20 maxillary sinuses.The sample size for each group was 20 maxillary sinuses (10 patients).

Randomization
The maxillary sinuses were randomly allocated using Microsoft Excel 2010 to either the CS group (the inter vention group) or the TCP group (the control group).Therefore, there were 10 maxillary sinuses per group.
The inclusion criteria comprised good oral health, bi lateral edentulism in the maxilla, age between 45 and 70 years, and the bone height of the alveolar ridge be tween the alveolar crest and the bottom of the maxillary sinus ranging from 0.5 to 5 mm.
The exclusion criteria were as follows: metabolic diseases that affect normal bone metabolism, such as hyper para thyroidism or osteoporosis; being treated with drugs that cause bone metabolic disorders, such as corticosteroids, oral contraceptives, hormonal or chemical treatment, without ever having undergone radiotherapy to the head and neck region; general systemic diseases, such as diabetes, cardiovascular disorders, leukemia, hyper tension, and coagulation disorders; autoimmune diseases; and any local contraindications, including the inflammation of the maxillary sinuses.

Primary stage
A conebeam computed tomography (CBCT) image was taken before the commencement of the surgical pro cedure.This phase was considered as time zero (T0).The dental scaling of the jaws with the use of chlorhexidine (0.12%) rinses was performed 2 or 3 days prior to surgery.The medication (a 750 mg Levoflox (levofloxacin) tablet) was prescribed 24 h before surgery and 9 days post surgery.

Second stage
Immediately before the surgical procedure, advanced plateletrich fibrin (APRF) was prepared by aspirating 60-80 mL of blood from the patient's basilar vein in the elbow fold, using 20milliliter syringes or 24gauge intra venous catheters when a larger volume was required.The aspirated blood was placed in special APRF tubes and centrifuged immediately at 1,500 rpm for 14 min. 14

Surgical method
The mouth was disinfected with 0.12% chlorhexidine rinses, the skin around the mouth was disinfected with a polyvidone iodine solution and the surgical area was isolated using sterile surgical scrubs.Local (buccal and palatal) anesthesia utilized 2% lidocaine hydrochloride (HCl) and epinephrine (1:80,000) (Fig. 2).A trapezoid shaped, fullthickness mucoperiosteal buccal flap was then created (Fig. 3).
Using a piezosurgical device with appropriate saline ir rigation, a bony window with rounded corners was creat ed to reduce perforation during lifting.It had dimensions of 12-15 mm in length and 10 mm in height based on the size of the area to be grafted.A CBCT radiograph indi cates the thickness of the bony window, which facilitates its preparation; 2-3 mm above the bottom of the maxil lary sinus to enable sufficient vision during work and re duce the tension of the sinus membrane in the initial lift ing phase.However, the window should not be enlarged much, as the surrounding walls aid bone healing (Fig. 4).
The sinus membrane was elevated with a sinus lift tool -the Dentium Advanced Sinus Kit (DASK) (Dentium, Cypress, USA), and for the grafting of the maxillary sinus, the mixture of CS or TCP with APRF was used (Fig. 5).When using the TCP/APRF compound, we placed a collagen membrane on the bony window (Fig. 6).The CS/APRF compound does not require any membrane, as a catalyst is added to the CS graft to harden fast.As such, the CS graft replaces the membrane due to its hardening and slow absorption properties. 15g. 2. Bilaterally edentulous maxilla before surgery and after anesthesia Interrupted suturing employed 40 Prolene sutures and a reverse cutting needle (Ethicon US, Cincinnati, USA) (Fig. 7).The patients received postsurgery instructions and a medical prescription, and had a followup appointment to remove the sutures (Fig. 8).

Radiological study method
Three CBCT radiographs were performed for each patient with the use of the PaXi3D Green imaging system (Vatech, Hwaseong, South Korea).All scans were conducted in the same radiology center to standardize the characteristics of the radiographs, with the same position being repeated preop (T0), immediately postop (T1) and 6 months postop (T2), i.e., before the 2 nd surgical operation (implantation).
The radiographs were examined using the OnDe mand3D program (https://www.ondemand3d.com/en),which enabled standardization by merging the 2 radio graphs (taken at T0 and T1) to ensure the measurements of the same site on both scans, and to avoid any changes that could be caused by altering the position of the pa tient's head (Fig. 9).
The 1 st image (T0) allowed the measurement of bone height before the maxillary sinus lift, using points in the sagittal view.The 3 rd image (T2) was used to measure the amount of lifting at the same sites.
Bone height was measured on the 1 st image (T0) at 5 lo cations in the coronal view, where each point in the coro nal view matched the corresponding point in the sagittal view, using the 'ruler' tool.Bone height was also measured on the 3 rd image (T2) at 5 locations in the coronal view.Using the same method, we measured bone height in the sagittal and coronal views on the 2 nd image (T1).

Statistical analysis
The IBM SPSS Statistics for Windows software, v. 25.0 (IBM Corp., Armonk, USA) was used to perform all statisti cal analyses, and a pvalue of 0.05 was considered statistically significant.The Shapiro-Wilk test determined the normal ity of data distribution, and the independent t test evaluated differences between the 2 groups at T0, T1 and T2.
The null hypotheses were as follows: -There is no statistical difference between T0 and T2 in bone height in the TCP group (1).-There is no statistical difference between T0 and T2 in bone height in the CS group (2).-There is no statistical difference between the TCP and CS groups when comparing bone gain (3).-There is no statistical difference between the TCP and CS groups when comparing bone reduction (4).

Error of the method
A total of 25% of the measurements were randomly se lected and repeated a month after the 1 st measurement by the same examiner (MAA).Systematic and random errors were calculated by comparing the 1 st and 2 nd mea surements with the use of the paired t test.No statistically significant differences were found between the 1 st and 2 nd measurements for any variable (p > 0.05).

Results
Figure 1 shows the CONSORT flow diagram.The study included 20 maxillary sinuses in 10 patients, though 1 pa tient was excluded from the sample after refusing to at tend the radiographic followup.Therefore, a complete followup was done for 9 patients (18 maxillary sinuses), and the statistical analysis was conducted.The descriptive statistics of bone height in both groups at each time stage are shown in Table 1.
The results presented in Tables 2 and 3 indicate that bone height increased significantly in the TCP and CS groups between T0 and T1 and between T0 and T2, and decreased significantly between T1 and T2 (p < 0.05).
Table 4 shows that there were no significant differ ences, at a confidence interval (CI) of 95%, in the amount of bone gain (p = 0.693) or bone reduction (p = 0.678) be tween the 2 groups.The mean bone gain in the CS graft  was higher than in the TCP graft, with a minor difference recorded (0.43 mm).Also, the mean bone reduction in the TCP graft was slightly greater than in the CS graft, with a 0.44 mm difference between the two.

Discussion
Maxillary sinus lifting is a still evolving procedure, necessary to increase bone height for dental implants.However, performing the procedure requires extended knowledge of maxillary sinus anatomy and its variations, as there may occur difficulties in window preparation, causing the perforation of the Schneiderian membrane.Before sinus lift surgery, CBCT should be conducted to discover the prevalence of septa. 16any studies have investigated the optimal bone graft for sinus lifting, although autogenous bone grafts are con sidered the gold standard, as they provide osteoconduc tion, osteoinduction and osteogenesis -the 3 essential elements for bone regeneration. 16However, the additional surgical site created to obtain an autograft increases the procedure time and causes more pain to the patient. 16,17hese factors have led to increasing interest in the search for alternative graft materials, mixing autografts with other types of bone grafts or completely replacing them with other grafts. 9here is increased interest in using alloplastic bone grafts to facilitate surgical procedures.However, the large amounts of materials required in cases of high maxillary sinus bone absorption increase expense.Therefore, stu dies have investigated mixing alloplasts with APRF to reduce the amount of graft needed and promote bone graft osteogenesis.Advanced PRF is an autologous graft material that eliminates any risk of disease transmission.In addition, its gelatinous consistency improves clot and graft stability, as it reduces the time required to ossify. 11ased on the current literature, the present research aimed to investigate the effectiveness of the CS/APRF compound in the grafting procedure after a maxillary sinus lift.Calcium sulfate is readily available, provides acceptable results, is easy to use, and helps to reduce surgical costs.Also, unlike other bone substitutes, 18,19 it can be used with out absorbable and nonabsorbable membranes. 18o verify the CS graft results, it was compared with TCP, as it is the same class of alloplast, it is reliable and is frequently used in the grafting procedure, 6 and pro vides a resorbable scaffold for bone growth. 9Both grafts were mixed with APRF to accelerate and increase new bone formation, and reduce the amount of graft material used. 11Since there are no previous studies in the literature comparing these 2 grafts, this study aimed to compare CS/APRF with TCP/APRF in the external sinus lift pro cedures, using the radiographic measurements of bone gain and bone reduction after 6 months.
The study sample included 20 maxillary sinuses of 10 patients who had a bilaterally edentulous posterior maxilla, were aged 45-70 years, had bone height between the alveolar bone crest and the bottom of the maxillary sinus ranging from 0.5 mm to 5 mm (class SA4 according to Misch classification), did not suffer from any system ic diseases affecting the surgical procedure, and did not suffer from any health problems in the nose and sinuses that are considered a contraindication for sinus lifting.One patient was excluded from the sample, because he refused to attend the radiographic followup.Therefore, the sample consisted of 18 maxillary sinuses (9 patients) randomly distributed into 2 groups, with 9 sinuses in the CS group and 9 sinuses in the TCP group.A splitmouth technique was used, where the CS/APRF graft was ap plied to one maxillary sinus, and the TCP/APRF graft was applied to the other side.
The lateral approach technique was followed to lift the maxillary sinus, since this method is indicated for maxil lary sinus elevating in class SA4 cases and the delayed im plantation excludes other methods, such as the alveolar approach (the internal sinus lift). 20In addition, the im plant success rate is higher in the twostage method than in the onestage technique in SA4 cases. 21n ultrasonic system was used for window preparation, similar to other studies, 22 as it reduces the incidence of the perforation of the maxillary sinus membrane to 7% from the 25% experienced with rotary instruments.The method also reduces pain, discomfort and edema after surgery, and generally helps to protect soft tissues, including the maxillary sinus membrane and the mandibular nerve. 23fter maxillary sinus grafting, the bony window was covered with an absorbable collagen membrane on the side grafted with the TCP/APRF compound, which helps to prevent the surrounding connective tissue cells from entering the bone graft material and increases vital bone formation. 24No membrane was used for the CS/APRF compound, and the window was covered only with the CS graft material.The material can be used as a membrane due to its physical properties, 15 which reduces the finan cial cost and the surgical procedure time.
The radiological study used CBCT images, which are accurate and sufficient for determining reference points, and threedimensional (3D) measurements can be made with ease.Three radiographs were performed for each pa tient to study bone gain and bone reduction in the grafted area, 25 with the 1 st one taken preop (T0), the 2 nd imme diately postop (T1) and the 3 rd 6 months postop (T2).
The CS/APRF graft material proved to be useful and safe for the twostage external maxillary sinus lifting  26 reported that CS grafts promoted implant stability and new bone forma tion after its absorption.However, a study that followed up 2 years after the 1 st surgery found a greater reduction than the current study (1.0-3.5 mm), perhaps due to the difference in the observation period (2.5 years). 15he use of TCP/APRF as a grafting material after ex ternal sinus lifting helped to secure a sufficient amount of bone for implantation, where the average bone height at T0 was 3.859 ±1.728 mm and it increased immediately to the size of the graft at T1 (14.185 ±3.025 mm).After 6 months, bone height decreased to 11.391 ±0.934 mm, resulting in a gain of 7.532 ±1.150 mm and a reduc tion of 2.794 ±2.310 mm.Oba et al. recorded a gain of 3.11 ±1.35 mm, which is less than in this study, perhaps because their study used the osteotome sinus lifting tech nique, 27 which does not allow to achieve a high bone gain as compared to the lateral lifting method. 25Okada et al. also found a reduction of 0.73 ±1.33 mm, which was due to the differences in the radiological and surgical meth ods, where the implants were placed at the same time as grafting. 28hen comparing the 2 study groups, we did not find significant differences in the amount of bone gain or bone reduction, and no clinical or radiological complications were observed during the 6month followup period.

Conclusions
Both grafts can be used for maxillary sinus lifting with the delayed implantation.The properties of CS are nega tively affected by moisture, so the graft must be applied with a pasty texture in addition to isolating the receiving area, and it is better to apply the material in layers to re duce shrinkage.The APRF material helped to increase the graft size, reduced costs and promoted bone forma tion, while it also helped to increase TCP graft bonding.

Table 1 .
Mean bone height values [mm] in both groups at each time stage M -mean; SD -standard deviation; min -minimum, max -maximum.

Table 3 .
Changes in bone height at different time stages in the calcium sulfate (CS) group (paired t test)

Table 2 .
Changes in bone height at different time stages in the tricalcium phosphate (TCP) group (paired t test)

Table 4 .
Comparison of the amount of bone gain and bone reduction in the 2 study groups (independent t test) 8and Tarnow et al.