{'fraction_non_alphanumeric': 0.03248526663791864, 'fraction_numerical': 0.019836136265631736, 'mean_word_length': 4.9875215146299485, 'pattern_counts': {'":': 0, '<': 1, '<?xml version=': 0, '>': 1, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Histological and dimensional changes of the alveolar ridge following tooth extraction when using collagen matrix and collagen‐embedded xenogenic bone substitute: A randomized clinical trial

Abstract Aim To assess the horizontal and vertical dimensional changes of the alveolar ridge when using a collagen matrix in combination with collagen embedded xenogenic bone substitute, in comparison with natural healing after tooth extraction. Methods Patients that required extraction in non‐molars areas were included. Test group‐15 sockets were treated with deproteinized bovine bone mineral containing 10% collagen (DBBM‐C), covered by a procaine collagen membrane (CMXs). Control group‐15 sockets left for spontaneous healing. We used a custom‐made acrylic stent as a reference for alveolar ridge measurements. Six‐month postoperative, a single implant was placed in the experimental site. A core biopsy was taken from the site, using a trephine bur. Histomorphometric analysis assessed bone area, connective tissue, bone marrow, and residual bone graft. Results Six months later, horizontal ridge width at −3 mm showed a significant (p < 0.05) reduction in both groups albeit smaller in the test group 1.19 ± 1.55 mm, compared with the control 2.27 ± 1.52 (p = 0.087). At −5 mm sub‐crestally, statistically non‐significant reduction was noted in both groups, 1.61 ± 1.53 and 1.96 ± 1.52 mm for the test and control groups, respectively (p = 0.542). Vertical changes were smaller in the test group (0.14 ± 1.84 mm) compared with control (0.98 ± 1.49 mm). Keratinized tissue (KT) width was 7.3 ± 2.13 and 7.5 ± 3.49 mm in the test and control groups, respectively. Newly formed bone occupied 33.79 ± 17.37% and 51.14 ± 23.04% in the test and control groups, respectively, (p = 0.11). Connective tissue volume was 33.74 ± 13.81% and 30.12 ± 18.32% in the test and control groups, respectively (p = 0.65). Bone marrow occupied 19.57 ± 10.26% and 18.74 ± 17.15% in the test and control groups, respectively (p = 0.91). Residual graft occupied 12.9 ± 9.88% in the test group. Conclusion Alveolar ridge preservation using DBBM‐C resulted in reductions of the vertical and horizontal dimensions albeit not reaching statistical significance. The larger than anticipated standard deviation and smaller inter‐group differences might account for this phenomenon.

larger than anticipated standard deviation and smaller inter-group differences might account for this phenomenon.

K E Y W O R D S
alveolar ridge dimensions, alveolar ridge preservation, collagen embedded xenogenic bone substitute, core biopsy, non-molars area

What is known
Ridge preservation after tooth extraction is a well-known and documented procedure in the dental scientific literature. There is a wide variety of grafting materials and surgical methods.
Hence, the decisions about material and way of usage should be based on clinical and histological research.

What this study adds
This study is the first randomized controlled clinical trial, which collected both clinical and histological data on alveolar ridge preservation combined therapy in humans, using DBBM-C covered by a procaine collagen membrane (CMXs).

| INTRODUCTION
Alveolar ridge preservation (ARP) is a well-documented surgical procedure associated with tooth extraction designed to attenuate ridge volume diminution. 1 Alveolar bone resorption following tooth extraction was already documented in 1967. 2 Later, Osburn in 1974 introduced the idea that teeth roots can maintain ridge volume beneath removable dentures, hence the term ridge preservation was introduced. 3 The usage of bone grafts in fresh sockets for ARP was introduced in the 1980s. 4 With time, different ARP procedures evolved, using different bone substitutes, as allografts, 5 alloplasts, 6 and xenografts 7 and xenografts embedded in collagen. 8 Free autogenous connective tissue grafts are sometimes used to seal the extraction sites; while this procedure is considered beneficial, it is somewhat unpredicted. 9 On the other hand, coronal flap advancement to achieve primary closure of the grafted socket does not yield better results over a flapless approach. 10 Likewise, Oghli and Steveling 11 reported no difference between atraumatic extraction and socket seal surgery.
Collagen matrix is a barrier material, which can be left exposed to the oral cavity, while sealing the grafted socket, results in good re-epithelialization during 6-month healing period. 12 Using this kind of material, makes the procedure easier and safer, as there is no need in harvesting connective tissue graft. It was also found beneficial for minimizing ridge resorption and maintaining the soft tissue. 13 We therefore hypothesize that combining collagen matrix with bone graft will improve the results of ridge preservation.
The purpose of this study was to assess the post-extraction horizontal and vertical dimensional changes of the alveolar ridge treated with collagen embedded xenogenic bone substitute covered with collagen matrix and compare it to natural healing.

| METHODS
The study was designed as a prospective randomized controlled clinical trial. This study has been independently reviewed and approved by the Rambam Health Care Campus Research Ethics Committee (approval IRB no. 0507-17-RMB) and registered prior to commencement on clinicalTrials.gov NCT# 03395145.
All participants provided written informed consent prior to enrolment in the study.

| SAMPLE SIZE AND POWER CALCULATION
Power calculation based on the detection of estimated alveolar ridge reduction, 6 months post-extraction, of 3.2 mm in mean in the control group and 2 mm in the test group, with a standard deviation of 1.1 mm, 14 with an alpha error defined to 0.05 and beta error to 0.20 (power 80%), revealed that 13 subjects in each treatment group were required. Assuming a dropout of 15%, a total of 30 patients were recruited.

| Study population
Patients were recruited at the department of periodontology, school of dentistry at Rambam health care campus, from May 2018 to August 2020. Patients who required extraction and implant installation in non-molars areas, were initially recruited to the study using the following criteria: at least 18 years old and in need for tooth extraction in the premolar, canine or incisor area with no/minimal (up to 4 mm) bone dehiscence limited to one bony wall only.
Patients were excluded if they were pregnant, lactating or demonstrated incapacity to complete or understand the informed consent process. Also excluded were patients who used medications that affected bone metabolism, heavy smokers (>10 cigarettes a day), patients with dental conditions which might affect the treated site and patients with allergy to collagen.
Prior to the study, all patients underwent clinical and radiographic examination and received periodontal treatment as needed.
After tooth extraction, a single operator (EG) assessed the extraction socket for intact socket walls to determine final eligibility.
Patients then signed an informed consent and were randomly allo- Patients remained blinded to the procedure and were not informed for their allocation all along the research period.
Clinical and histological data were collected by another researcher, who remained blinded to patients allocation till opening end.

| Surgical procedure
Patient received 2 g amoxicillin (600 mg of clindamycin for patients allergic to penicillin) prior to the procedure. Under local anesthesia, the tooth was extracted without flap elevation, attempting to minimize damage to the socket walls.
The following measurements were performed using a custom- In test group, the surgeon filled the socket with DBBM-C and covered it with CMXS. 5-0 nylon sutures were used to secure the CMXS and get complete seal of the grafted socket ( Figure 1). In the control group, the socket margins were sutured in order to stabilize the blood clot; no attempt was made to get a primary socket closure ( Figure 2).

| Postoperative protocol
Patients were instructed to use a chlorhexidine 0.2% mouthwash twice daily after tooth brushing for 14 days. Additional antibiotics were prescribed for 7 days (amoxicillin 1.5 g/day or clindamycin 600 mg/day) and analgesics as necessary. Sutures were removed after 10-14 days.

| Implant placement
Six-months postoperative, a CBCT was obtained and a single implant was installed in the experimental site. All implant surgeries were performed by the same clinician (EG).
After signing informed consent for surgical procedure, patient received antibiotic preoperative as described above. KT width was measured at the post-extraction site. A muco-periosteal flap was elevated and intraoperative measurement were repeated at the same site, using the same stent. All measurements were performed by a single examiner (EM).
Next, a core biopsy from the center of the site was taken using a 2.2 mm diameter trephine. The bone samples were processed for histological evaluation of percentage of vital bone, connective tissue, and residual bone graft. Sites were further prepared, using the surgical kit drills, and a bone level titanium alloy implant were installed. Implant insertion torque was measured with a dental implant torque wrench ratchet (in N/cm 2 ). Resonance frequency analysis (RFA) was measured using Osstell IDx (Osstell, Göteborg, Sweden). Three successive measurements were reordered for each implant and the mean calculated and recorded ( Figure 3). Finally, periapical orthoradial X-rays were taken.
Postoperatively, patients were instructed to rinse with 0.2% chlorhexidine for 10 days twice daily, continue their antibiotics for 7 days and use analgesics as needed. Sutures were removed after 10-14 days. Adverse events (AE) and severe adverse events (SAE) cases were monitored and recorded throughout the study. Final restorations were delivered 3-6 months postoperative.

| Histologic and histomorphometric analysis
All specimens were fixed in 4% paraformaldehyde for 2 days, decalcified in 10% EDTA, for 4 weeks. Samples were dehydrated and washed with ethanol baths in increasing concentrations, in order to remove residual water, afterwards Xylol (hydrophobic agent) was used to remove alcohol remains. Samples were infiltrated with paraffin wax and were F I G U R E 2 Thirty patients, who needed a tooth extraction in a non-molars area, were initially recruited to the study according to the inclusion and exclusion criteria (T0). Patients were randomly allocated into test/control group and the procedure was carried out accordingly (T1). During follow-up of 6 months, two patients were withdrawn from the study (one from each group). At T6, implants were placed; clinical measurements and trephine biopsies were taken. CM, collagen membrane; DBBM-C, deproteinized bovine bone mineral containing 10% collagen      (Table 4).

| DISCUSSION
The present study was designed to explore the use of DBBM-C and collagen matrix for ARP following tooth extraction. As mentioned, according to our inclusion criteria, we included sockets with no/minimal (up to 4 mm) bone dehiscence limited to one bony wall.
The rational of combining both DBBM-C and CMXS was to allow a flapless ARP procedure with minimal heterogeneity, which is possible only in well containing sites. When performing ARP in severely compromised socket, raising partial 15 or full thickness flaps 16 will be needed, such a procedure might be considered as a ridge augmentation procedure, rather than ARP. A meta-analysis of six studies with ARP in compromised buccal wall sites, reported a high degree of heterogeneity. 17 In the current study, we focused on sites with atraumatic extraction with minimal soft tissues manipulation. CMXS served as a durable barrier between the grafted socket and the oral cavity for the initial 30 days healing period. 18 The socket sealing was essential to perform a flapless procedure, without any soft tissue manipulation and KT preservation. Meloni et al. 19  pain score in the test group may be explained by the pressure applied while inserting the DBBM-C into the socket, as it was previously found that mechanical pressure may be represented by VAS pain score. 34 Yet in both groups pain scores were in the mild pain range. Likewise, mild pain scores (2.8 VAS) were reported when DBBM and hemostatic gelatin sponge were used for ARP. 35 However, these higher pain scores did not affect patients' satisfaction, as the VAS scores for satisfaction were similarly high in both groups in both time points.

| CONCLUSION
ARP using DBBM-C and collagen matrix resulted in a small reduction of the vertical and horizontal dimensions. These changes were consistently smaller than those for the control, however they did not reach statistical significance. The larger than anticipated standard deviation and smaller inter-group differences might account for this phenomenon.

ACKNOWLEDGMENTS
The study was funded, and material supported by Geistlich Pharma AG, Wolhusen, Switzerland. Mrs. Liron Eliezer, the research coordinator of the Department of Periodontology and Implant dentistry, was supervising patients' recruitment process, allocation according to randomization, data collection and scheduling appointments.

AUTHOR CONTRIBUTIONS
Eran Gabay designed, performed all the surgeries, drafted and approved the article, and critically revised. Anat Katorza collected and analyzed the data, drafted and approved the article. Hdar Zigdon-Giladi contributed to histology, data analysis, critical revision, and approval of article.
Jacob Horwitz contributed to data analysis, critical revision, and approval of article. Eli E. Elyahu Machtei contributed to design, clinical measurements, statistics, critical revision, and approval of the article.

DATA AVAILABILITY STATEMENT
The data that support the findings of this study are available from the corresponding author upon reasonable request.