Osseodensification Effective for Immediate Molar Replacement

Immediate implant placement can offer significant advantages to patients such as reduced treatment time and less discomfort. This treatment approach has been used primarily for the replacement of anterior teeth and posterior single-rooted teeth. Molar tooth replacement, however, is the most common indication for implant dentistry in dental practice, as many adults present with heavily restored molars that eventually become unrestorable. Other common reasons for molar tooth loss are difficult endodontic therapy and fractures.

Although, to reiterate, immediate implant placement is a well-established treatment modality for anterior and single-rooted teeth, clinicians are often reluctant to use this method of treatment to immediately replace molar teeth. There are several reasons for this, including the technical challenge of creating an implant osteotomy in a fresh extraction socket of a multi-rooted tooth, the proximity to important anatomic structures such as the mandibular canal and the maxillary sinus, and the difficulty in achieving adequate implant stability since the distance between the implant and socket walls is typically much greater than it is when an implant is placed in the socket of a single-rooted tooth.

The aim of this article is to describe and illustrate a simplified and predictable technique for immediate molar replacement based on the principles of osseodensification.

Indications, Contraindications, Site Assessment

Several factors must be considered when evaluating the potential for immediate implant placement in molar sites. Common indications include but are not limited to tooth extraction due to root fracture, endodontic lesions, extensive caries, and coronal fracture. Post-extraction the site must present intact socket walls, a thick gingival phenotype, sufficient bone apical to the socket, and sufficient septum width.¹

Potential contraindications for immediate implant placement in molar sites may include but are not limited to history of smoking, radiation therapy, uncontrolled diabetes, history of RANKL inhibitors, and bruxism.^2,3

Regarding site assessment, Smith and Tarnow classified molar sockets into three categories based on post-extraction status of the molar septum⁴:

type A: sufficient bulk and width of septal bone to stabilize and house the implant

type B: sufficient bulk and width of septal bone to stabilize but not fully house the implant

type C: insufficient bulk and width of septal bone to stabilize or house the implant

Radiographic Evaluation

Mandible: Preoperative cone-beam computed tomography (CBCT) scanning is an essential diagnostic tool to assess socket anatomy, estimate post-extraction socket type, and reduce the risk of damaging the mandibular canal or perforating the lingual plate. Froum et al suggested that at least 4 mm of apical bone must be engaged to enhance implant primary stability; therefore, the distance from the socket apex to the mandibular canal must be a minimum of 6 mm.⁵ This prerequisite is not always available and is a consideration mostly in type B and type C sockets. An anatomical cross-sectional CBCT analysis study by Lin et al demonstrated that a 6 mm distance between the root apex and mandibular canal is safe for immediate mandibular molar implant placement utilizing the septum. The authors demonstrated through 237 CBCT samples that the distance available in first molar sockets is 7 mm ± 2.9 mm and 4.3 mm ± 2.7 mm in second molar sockets.⁶ Thus, more mandibular nerve complications are likely to occur in mandibular second molar extraction site placement (70%) compared to mandibular first molar sites (35%).

Lingual concavity perforation is another risk factor in immediate implant placement in mandibular molar sockets. This risk is higher in mandibular second molar sites (62.3%) compared to mandibular first molar sites (57%). The risk is related to the distance between the molar root apex and the mandibular canal and is reduced by 34% for every 1 mm increase in this distance.⁷

Maxilla: Low bone quality and limited vertical quantity due to the proximity of the maxillary sinus presents several complex surgical challenges that may directly affect implant stability and subsequent osseointegration in maxillary molar extraction sockets.⁸ Hence, anchoring the implant onto the floor of the maxillary sinus in combination with elevation of the Schneiderian membrane of the maxillary sinus may optimize implant primary stability. A distance of at least 5 mm from the top of the septum to the sinus floor is required to stabilize an immediately placed dental implant.⁸

Minimally Traumatic Exodontia

When performing exodontia in molar sites, gentle root separation with minimal or no buccal flap reflection should be utilized to minimize the disruption of the periosteal blood supply, which, in turn, will reduce the risk of crestal bone loss and enhance the chances for success. Ragucci et al in a systematic meta-analysis reported a success rate of 93.3% of a total sample of 1,106 immediate implants placed in molar sites. Marginal bone loss was 1.29 mm ± 0.24 mm after 1 year. More marginal bone loss was evident with the use of flap reflection and extra-wide implants with immediate placement versus delayed placement, especially in thin scalloped cases.⁷

Implant Position and Size

The implant platform for immediately placed implants in molar sockets should be at the level of 1 mm to 2 mm below the buccal bone crest.^9,10 Subcrestal implant placement has been reported to result in less long-term crestal bone loss and increased bone-to-implant contact. Grafting the gap around the implant was emphasized as a beneficial step for predictable healing. Grafting the gap and loading protocols have shown to affect both the survival and success rates of immediately placed implants in molar sites.^11-13

Implant diameteris usually narrower than the diameter of the molar extraction socket; this may lead to a gap between the implant and socket wall. In cases where the distance between the implant and extraction socket is less than 2 mm, spontaneous bone healing can be expected without additional grafting procedures.¹⁴ If, however, this distance is larger than 2 mm, bone grafting is indicated. Grafting of extraction socket gaps is well established in the literature with the accompanying use of barrier membranes.^15-17 Regular-diameter (4.1 mm) implants placed in molars sockets showed higher failure rates than wide-diameter (5 mm to 6 mm) implants. Higher failure rate was also reported with ultra-wide-diameter (7 mm to 9 mm) implants when compared to wide-diameter (5 mm to 6 mm) implants.^9,18-20 Ultra-wide-diameter implant placement in molar sites was reported with variable success due to technical difficulties and complications associated with site instrumentation related to significant drill chatter and implant seating requirements.²¹

Site Instrumentation

Site instrumentation is a crucial factor for producing the required stability for sufficient osseointegration. The septum width plays a key role in achieving adequate implant stability. Septum mesiodistal width of 3 mm or more has been reported as necessary for successful expansion of the septum and adequate implant placement.^22,23 Therefore, the preservation and expansion of the septal bone is an important factor for the osseodensification treatment modality. Historically, rotary expanders, osteotomes, and specialized ultrasonic instruments have been utilized to expand the septum in mandibular and maxillary molar extraction sites and to lift the Schneiderian membrane with a crestal approach and graft the sinus prior to placing implants. Several factors govern the outcome of immediate implant placement in multirooted extraction sockets, as outlined in the following paragraphs.

First, the molar socket anatomy is considered a significant predetermining factor that may govern both site instrumentation and the implant placement position in favor of one root socket. This may negatively affect the restorative outcome. Therefore, precise 3-dimensional implant placement in the septum is highly desirable to achieve both predictable implant primary stability and a favorable restorative outcome.

Second, high implant primary stabilityis a prerequisite to reduce implant micromotion during the healing process and allow for adequate secondary stability and subsequent osseointegration. Implant initial stability can be unpredictable and is usually lower in immediate versus delayed implant placement, especially in molar extraction sockets. Maxillary sites produce lower insertion torque than mandibular sites. Low implant initial stability in molar extraction sockets dictates the need for primary full closure to promote predictable healing.²⁴

Third, the gap between the implant and socket walls should be grafted to enhance the healing outcome if this distance is greater than 2 mm.²⁵

Osseodensification Protocol

The osseodensification protocol (presented in Figure 1 through Figure 9) begins by separating molar roots at the furcation without compromising the integrity of the septum (Figure 1). The pilot drill is then used in clockwise mode, reaching a depth that is 1 mm deeper than the planned implant length (Figure 2). Following the manufacturer's corresponding densifying reference guide, the subsequent densifying burs (Densah^®, Versah, versah.com), which are progressively wider, are then used in smaller increment increases with constant irrigation to expand the osteotomy and increase bone plasticity. The osteotomy is expanded such that the last Densah bur diameter is equal to or slightly larger than the planned implant major diameter. As the bur diameter increases, the bone expands to reach the final osteotomy diameter (Figure 3).

Implant placement should be either at the level of the osseous crest or subcrestal, depending on the connection type (Figure 4). The gap is then filled with a bone allograft if needed (Figure 5). This is followed by connecting a healing abutment to the implant and approximating the buccal and lingual flaps with single interrupted sutures (Figure 6).

Results of the case presented are shown in Figure 7 through Figure 9.

Various techniques to overcome the challenges of immediate molar replacement have been proposed over the years. Immediate molar replacement with dental implants is now considered a predictable therapeutic approach, with survival rates comparable to implants placed in healed ridges.^26,27 An 11-year retrospective study of 300 implants immediately placed in molar extraction sockets reported an overall survival rate of 97.3%.²⁸ Success of immediate molar replacement was directly related to preservation of molar socket anatomy with minimally traumatic extraction techniques, as well as careful and precise osteotomy preparation to achieve adequate implant position and primary stability.²⁹ Hence, predictability of immediate molar replacement requires bone instrumentation methods that not only promote precision in the irregular molar socket anatomy, but also increase bone density within the osteotomy to optimize primary stability of the dental implant.

A novel universal bone drilling protocol known as osseodensification has been developed and used in contemporary implant dentistry.³⁰ The dynamic, nonsubtractive bone instrumentation method is aimed at enhancing bone density through compaction autografting. Osseodensification has been shown to cause a controlled plastic deformation of bone due to rolling and sliding contact with the densifying burs.^31-33 The drills operate in both clockwise and counterclockwise directions and have been compared to standard drills during osteotomy preparation.³⁰ In both clockwise and counterclockwise directions, densifying burs demonstrated significant bone compaction toward the walls of the osteotomy sites when compared to standard drills.^30,34 Bone compaction has been reported as a method to improve early fixation stiffness and strength of implants.^33,35 Compaction autografting achieved with densifying drills supplements the basic bone compression effect to further densify the inner walls of the osteotomy creating a density crust along the entire depth of the osteotomy, resulting in a well-adapted bone-to-implant surface. The improved early fixation strength is a result of both greater bone volume in the proximity of the implant and compressive forces of the compacted bone, also known as "spring-back effect."^36-41 Bone compaction not only improves implant primary stability, but also reduces the level of implant micromotion and enhances the process of intramembranous bone formation around the implant body.^42,43

These unique characteristics of densifying drills offer high precision during implant osteotomy preparation and can be utilized to overcome anatomic alveolar bone challenges, such as the irregularity of molar extraction sockets. Furthermore, due to the lateral and apical bone compaction effects of this nonsubtractive bone drilling method, alveolar bone can be expanded laterally and apically. A clinical study demonstrated a 93% survival rate in osseodensification-expanded alveolar ridges.³³ Osseodensification has also been reported to facilitate implant placement in conjunction with crestal elevation of the floor of the maxillary sinus graft with high success rates.⁴⁴ Hence, application of the principles of osseodensification in immediate molar replacement procedures provides unique advantages over conventional drilling methods, including superior control and precision, ability to expand the molar septum for superior implant adaptation and contact with native bone, and crestal sinus floor elevation when indicated.⁴⁵

Osseodensification facilitates immediate molar replacement by allowing molar septum expansion, enhancing bone density and subsequent implant primary stability, and combining crestal sinus floor elevation on maxillary molar sites. Future studies with larger cohorts are necessary to further validate this technique.

Dr. Huwais has a financial affiliation with Versah, the manufacturer of the osseodensification drills discussed in this article.

Samvel Bleyan, DDS
Private Practice, Moscow, Russia

Salah Huwais, DDS
Adjunct Clinical Assistant Professor, University of Illinois, College of Dentistry, Chicago, Illinois; Adjunct Assistant Professor, Department of Periodontics, University of Pennsylvania School of Dental Medicine, Philadelphia, Pennsylvania; Director, Academy of Osseodensification, Chicago, Illinois

Rodrigo Neiva, DDS, MS
Chairman and Clinical Professor, Department of Periodontics, University of Pennsylvania School of Dental Medicine, Philadelphia, Pennsylvania