ARP versus SH

Extraction of the teeth in the posterior region of the mandible may be an indication for the placement of dental implants. However, after extraction of the teeth, the alveolar ridge undergoes changes due to resorption (Van der Weijden et al., 2009). Resorption is most pronounced on the buccal side and might complicate implant placement as is could lead to proximity issues with the inferior alveolaris nerve of the mandible (Pietrokovski & Massler, 1967; Tonetti et al., 2019). 

Alveolar ridge preservation (ARP) is commonly performed technique aimed at preserving available bone after tooth extraction. It facilitates delayed implant placement, reducing morbidity and providing optimal esthetic outcomes for implant placement (Avila-Ortiz et al., 2020). This procedure is performed using autogenous bone grafts, bone substitutes such as xenografts or allografts or a mixture of both. Also, membranes can be used to direct the growth of new bone. 

A thin buccal bone wall is an indicator for bone loss that may compromise the integrity of the buccal bone and lead to biologic and esthetic complications (Avila-Ortiz et al., 2020; Monje et al., 2023). When the buccal bone wall has a width of < 1.5mm, it is considered an indication for ARP (Darby et al., 2008). 

ARP is found to be effective in reducing bone loss and facilitating implant placement after extraction in the anterior region and for multi-rooted sides (Atieh et al., 2022; Avila-Ortiz et al., 2019; Jonker, Strauss, et al., 2021). However, most available evidence including RCTs, involves patients with at least 50% of buccal bone intact. Consequently, it is uncertain whether the efficacy ARP is also applicable in situations involving damaged sockets (buccal bone loss >50%). 

To assess and compare ARP to spontaneous healing in damaged sockets (>50% buccal bone loss) in the posterior mandible regarding the additional need for bone augmentation either prior to or during implant placement 4-6 months after tooth extraction

Randomized controlled trial (RCT)

Intake
Patients will be seen by an experienced surgeon (JP) and a treatment plan will be set up in close cooperation with the referring dentist. Before the surgical procedure, a periapical x-ray picture as well as an intra-oral scan (IOS) is made to address the baseline situation. Patients must complete a patient questionnaire to address the current situation and expectations. 

Extraction

Pre-operative protocol consists of 2g amoxicillin 1 hour pre-operative according to the clinical guideline. A-traumatic flapless extraction by an experienced surgeon (JP) using elevators and forceps will take place under local anaesthesia. After extraction, the buccal defect will be measured by a periodontal probe. 

The measurements will be performed in three dimensions (Figure 1): 

• Buccal bone height (a) 
  • The height from the most apical part of the alveole to the most coronal part of the alveole
• Width in mesiodistal direction (b)
  • The width from the mesial crest to the distal crest
• Width in buccolingual direction (c)
  • The width from the lingual crest to the buccal crest with the lingual crest as a reference for the height. 

Patients will be included it there is >50% buccal height bone loss 

Randomization to either the XG-group, AG-group or control group will take place.

In the XG-groep, ARP is performed by using a XG (Cerabone® plus, botiss biomaterials GmbH, Zossen, Germany) and coverage by a membrane (Jason® membrane, botiss biomaterials GmbH, Zossen, Germany) . The same procedure will take place in the AG-group, however ARP is performed by using an AG (Maxgraft granules, botiss biomaterials GmbH, Zossen, Germany). In the control group, the wound is left for spontaneous healing. The wound is closed by a suture (4-0 Ethilon, Ethicon) in all groups. A CBCT-scan and IOS will be performed (baseline) to evaluate the defect. Post surgical protocol consists of rinsing with 0.2% chlorhexidine solution twice a day, and NSAID’s (according to individual requirements). 

Check-up
Two weeks after extraction, patients will be seen for a routine check-up. At this appointment, surgical complications will be scored (swelling, dehiscence, haemorrhage and infection) and a patient questionnaire will take place.

Check-up and assessment  Two weeks before the planned implant placement, the situation is assessed based on a CBCT-scan and an IOS. A digital planning is set up using coDiagnostiX (Dental Wings GmbH, Chemnitz, Germany) and the necessity for additional augmentation before or during the implant placement is assessed independently by two researchers (JP, NN). This decision will be made based on the clinical guideline as set up by Yu et al (Yu et al., 2023). 

Implant placement
After the healing period of 4-6 months, guided implant placement will be performed. 2g of amoxicillin will be administered orally one hour before the implant surgery, The procedure is performed under local anaesthesia. After raising the mucoperiostal flap at the top of the alveolar process the exact position of the implants will be determined using a surgical template. The initial burrhole will be created using a trephine burr, which is also employed for the biopsy. Tissue Level implants (Straumann® Tissue Level SLA, Basel, Switzerland) 4.1 mm implants will be placed guided. In case of a thin buccal plate (<3mm) or buccal dehiscense, GBR is performed (see guided bone regeneration) The post-operative protocol includes rinsing with a 0.2% chlorhexidine solution twice daily, and NSAID medication (according to individual requirements). Implants will heal submerged. 

Guided bone regeneration
As described earlier, prior to implant placement, the possibility of placing the implant is assessed. If, based on the assessment by the two independent researchers, GBR is necessary this will be performed using AB, locally harvested by a bone scraper or from the mandibular ramus. The frequency of GBR and the use of either locally harvested bone or a block from the mandibular ramus will be scored. 

Check-up
Two weeks after implant placement, patients will be seen for a routine check-up. At this appointment, surgical complications will be scored (abnormal swelling, dehiscence, haemorrhage and infection) and a patient questionnaire will take place. 

Second phase surgery
4-6 months after implant placement, a small stab incision is made and healing abutments are placed. The patient is referred back to the referring dentist. 

Prosthetic protocol
The implants will be loaded 4-6 months after implant placement. The construction of the suprastructure is taken care of by the referring dentist. 

Follow-up
Follow-up will be performed 1-4 weeks after placement of the crown. A periapical radiograph will be taken and the clinical indices KMW, PPD and BOP will be measured. Also, a digital photograph, IOS and a patient questionnaire is performed. 
Follow up will also take place after 1, 3, 5 and 10 years of loading and the clinical indices KMW, PPD and BOP will be measured. Also, a CBCT-scan, digital and X-ray photographs, IOS are taken and patient questionnaires are performed. 

The measurements performed in this research are clinical and radiological analyses of the peri-implant bone and soft tissues. Participation in this research is not dangerous and the patients are not at risk. The radiographs (before extraction and after implant placement) are taken, whether or not the patient is participating in this research. The CBCT-scans (after extraction and before implant placement) are part of the standard pre-implant procedure to determine the available bone volume. The health of the patients is not at risk. Given that the treatments have been performed for many years we expect no complications. In case of pregnancy the treatment is not performed, but postponed until after pregnancy. Withdraw from this research is possible at all times without giving a reason. In consultation with the patient one of the two treatment options will be chosen. If a withdrawal occurs after ARP had already been performed implant treatment will be identical to protocol. However, the collected measurements will not be used for this research project.