All patients referred to the Department of Oral and Maxillofacial Surgery (University of Groningen, University Medical Hospital), from January 2016 to July 2017, for single-tooth implant therapy in the maxillary and mandibular posterior region were considered for inclusion. The following inclusion criteria were applied:

One failing first or second molar in the maxilla or mandible;

Sufficient bone volume, with an intact buccal and lingual wall, to insert a dental implant of at least 7 mm in length;

Implant site is free from infection;

Adequate oral hygiene as expressed by the modified plaque index and the modified sulcus bleeding index from Mombelli et al. [16];

Sufficient mesio-distal, bucco-lingual, and interocclusal space for the placement of an anatomic restoration;

The patient is capable of understanding and giving informed consent.

Patients were excluded from the experimental protocol when at least one of the following exclusion criteria was met:

Medical and general contra indications for the surgical procedures;

Presence of active and uncontrolled periodontal disease;

Bruxism;

An active smoker;

History of local radiotherapy to the head and neck region.

Patients fulfilling all the inclusion and none of the exclusion criteria were informed verbally and in writing about the study and signed the informed consent form.

The Medical Ethical Committee of the University Medical Center Groningen considered this case series study was not subject to the Medical Research Involving Human Subjects Act (Number M15.184100). The study was registered at the Netherlands Trial Register (Number NL8117).

The surgical and prosthetic treatments were performed at the Department of Oral and Maxillofacial Surgery, University Hospital Groningen. One oral surgeon, experienced in implant dentistry, executed the surgical treatments and two experienced prosthodontists performed the restorative procedures. All the laboratory procedures were carried out in a single dental laboratory.

The patients had a failing molar at the time of the intervention (Fig. 1). Antibiotic prophylaxis (2 g amoxicillin or, if allergic to penicillin, 600 mg clindamycin) was given 1 h pre-operatively as was a 0.2% chlorhexidine mouthwash (two times daily for 10 days) for oral disinfection. The first step of the surgical procedure, which was performed under local anaesthesia, involved carefully detaching the periodontal ligament from the failing tooth by an incision in the sulcus. Periotomes were used to extract the failing molar atraumatically. No mucoperiosteal flap was raised. The interradicular bone of the alveolus was prepared for the implant following the manufacturer’s protocol using a surgical template based on the ideal position of the prospective implant crown. The final twist drill was placed in the prepared socket. The remaining space between the drill and bone walls was augmented with a 1:1 mixture of autogenous bone, harvested from the retromolar or tuberosity area using a bonescraper (Bonescraper, Biomet 3i, Warsaw, Indiana, USA), and a bone substitute (Bio-Oss®, Geistlich Pharma AG, Wolhusen, Switzerland). The drill was carefully removed and a regular diameter implant (NobelActive, Nobel Biocare AB, Goteborg, Sweden) was placed, according to the manufacturers’ protocol. Regarding the corono-apical position of the implant, the shoulder of the implant was placed at a depth of 3 mm apical to the most apical aspect of the prospective clinical crown, with the help of a surgical template. The implant diameters were 4.3 mm, and the lengths varied from 8.5 mm to 10 mm, depending on the available bone height at the implant site. The primary implant stability was > 45 Ncm, measured with a manual torque wrench (NobelBiocare AB). A cover screw (NobelBiocare AB) was placed and the extraction socket closed with a mucosa graft, which was harvested from the tuberosity region. The wound was closed with Ethilon 5-0 nylon sutures (Johnson & Johnson Gateway, Piscataway, NJ, USA). One week after implant placement, a follow-up visit was scheduled for suture removal and to review the healing process. After 3 months, the implant was uncovered and a healing abutment (NobelBiocare AB) was installed.