Immediate Load Protocol for Anterior Maxilla With Cortical Bone From Mandibular Ramus

Abstract

Objective: 

To evaluate the concept of a nonfunctional immediate load protocol with single implants placed in the anterior maxilla that has been bone grafted with autogenous, block cortical grafts harvested from the ramus of the mandible.

Methods: 

There were 19 hydroxyapatite-coated dental implants surgically placed in 19 patients, and immediately loaded between 48 hours and 3 days later with a custom acrylic provisional restoration that was placed out of functional occlusion. After 12 weeks, the definitive ceramo metal restoration was cemented to the custom abutment.

Results: 

Over a 1-year observation period, all implants continue to function.

Conclusion: 

The preliminary results of this clinical study indicate that immediate, nonfunctional load with single implants is a predictable protocol in the bone grafted anterior maxilla in select cases.

Successful formation of a direct bone-to-implant interface is the goal in implant therapy. The 2-stage surgical protocol established by Brånemark¹ and Adell et al² consisted of a healing phase of 3 months in the mandible and 6 months in the maxilla to allow for the formation of mineralized tissue at the interface of dental implants before functional restoration. It was theorized that early or immediate loading would promote fibrous tissue formation around the implants rather than bone.³ Because of improved surgical instrumentation, implant design and surface topography, this concept has been challenged. Human clinical^4–7 and animal^8–11 experimental studies have shown that implants that are immediately loaded develop bone at the implant interface and are able to tolerate occlusal forces. Implants placed in the totally edentulous anterior mandible that are cross-arch stabilized with a rigid bar or fixed (splinted) restoration have shown successful osseointegration comparable to success rates of conventionally loaded implants using the Brånemark protocol.^5,6,12–14

The protocol for immediate or delayed loading of the edentulous single implant restoration in the anterior maxilla continues to evolve. The few reports in the literature describe immediate or delayed loading without functional occlusion and implant survival rates on implants placed immediately in a fresh extraction or healed extraction site.^15–18 To date, and to our knowledge, there are no reports in the dental implant literature describing immediate load of implants placed in the compromised maxilla that required grafting using autogenous, cortical block grafts harvested from the posterior mandibular ramus before implant surgery. This prospective study presents a single-tooth implant protocol in the anterior maxilla without splinted implants. The purpose of this study was to evaluate the clinical response and concept of a nonfunctional, immediate load protocol in the block grafted anterior maxilla through evaluation of implant survival after 12 months.

In 1938, Dr. Alvin Strock¹⁹ was the first clinician to document the success of placing a single endosseous implant into an extraction site to support a restoration that lasted more than 10 years. It was not until 1989 that a clinical series of implants placed in an extraction site that was immediately loaded with a provisional restoration was published. Lazzara²⁰ was the first to describe his experience of immediate implant placement in postextraction sites. In 1998, Lindh et al²¹ showed that the 1-year survival rate for single implants was 97.2% when placed in the anterior maxilla. In 1998, Wohrle²² reported a 100% success rate of 14 implants placed in the anterior maxilla that was immediately loaded using the natural tooth as the provisional restoration. The crown of the extracted tooth was sectioned from the root, and hollowed internally to fit passively over the fabricated abutment and cemented. The crown was placed out of occlusion and used for a period of 6 months before the definitive restoration was placed on to the implant.

Malo et al²³ reported a 2-year survival rate of 96% when implants were immediately loaded in the aesthetic zone of both the maxilla and mandible. In a multicenter study, 58 implants were placed in a 1-stage procedure to replace 1 or 2 teeth in the anterior maxilla and restored 3 weeks later with a provisional restoration. Of the 58 implants placed, 2 failed, resulting in a 96.2% survival rate.²⁴ In this study, the significance was that all implants were freestanding and not splinted together. Chaushu et al¹⁵ compared the success rates of immediately loaded implants in fresh extraction and healed extraction sites. A total of 28 implants were placed, including 19 in fresh extraction and 9 in healed extraction sites. The survival rate was 100% for implants immediately loaded and placed in healed extraction sites. However, for implants immediately loaded in implants placed in fresh extraction sites, the success rate was 82.4%. The failure rate of 17.6% was similar to that in the study by Ericsson et al,²⁵ which documented a 15% failure rate when implants were immediately loaded in fresh extraction sites. In contrast, when implants were staged, there was a 100% survival rate.

Anderson et al²⁶ reported a 100% survival rate after 5 years of 8 implants placed in the anterior maxilla in 8 patients. Acrylic provisional restorations were placed 1 week after implant placement and placed out of occlusion. After 6 months in function, the provisional restorations were replaced with the final restorations.

Terminology

Until recently, there was no clear consensus as to the precise definition of immediate load and early load. As a result, considerable confusion existed as to when these terms should be applied. In 2004, The Immediate Function Consensus Conference²⁷ was conducted to resolve this issue, and terminology regarding immediate load and its guidelines were developed. Using the terminology adopted from this conference, all 19 cases included in this study were defined as a nonfunctional immediate restoration. In each case, the implant prosthesis in a patient who is partially edentulous was delivered within 2 weeks of implant insertion, with no direct occlusal load. The 19 cases also satisfied the criteria to be included in early occlusal loading, which is defined as occlusal load to an implant prosthesis between 2 weeks and 3 months after implant placement.

Bone Graft Physiology

A basic review in the stages of healing and revascularization of bone is important in implant dentistry to obtain predictable results in implant survival and loading protocols. At the macroscopic level, the skeleton consist of 2 types of bone: a dense cortical and spongy cancellous tissue. At the microscopic level, there are 4 types of bone observed: woven, composite, lamellar, and bundle bone.²⁸ Autogenous bone grafts are considered the gold standard for reconstructing acquired defects of the oral and maxillofacial region, and the review pertains only to this type of graft.

For the graft to survive, the host tissues must have a sufficient vascular supply to provide nutrients to the transplanted bone. After the graft is stabilized to the host site with rigid fixation screws, hematoma formation occurs as a result of surgical trauma to the surrounding hard and soft tissues.²⁸ A hypervascular response is observed as the avascular cortical graft, which has few viable cells on its surface, is infiltrated with capillary buds and is slowly being replaced with new bone by endosteal osteoblasts recruited during angiogenesis.^29,30 As the inflammatory phase continues by the second week, a dense fibrovascular network is observed around the graft, which continues to recruit osteoblasts and osteoclasts into the area.^30,31 It is these cells that will produce individual islands of osteoid that will eventually replace the graft. The existing bone graft will continue to act as a scaffold for the deposition of new bone. Islands of osteoid will coalesce to consolidate the graft to the host bone.³² The biologic process of bone resorption and remodeling will continue until the immature, woven bone is replaced by mature, lamellar bone, which is more mineralized and structurally organized.²⁸

Revascularization and deposition of new bone in cortical grafts can take 3–6 months, starting from the periphery and advancing to the interior of the graft.³³ Because of the density of lamellar bone, revascularization of cortical bone is incomplete, which limits vascular penetration only through the Haversian and Volkman canals.³⁴ Because of incomplete revascularization, cortical bone grafts will have regions of necrotic bone surrounded by viable dense lamellar or woven bone. Studies by Ozaki and Buchman,³⁵ and Chen et al³⁶ have shown that revascularization to the interior region of the graft is observed between 8 and 16 weeks after transplantation.

Materials and Methods

Patient Enrollment

In this prospective clinical study, 19 implants were placed in 19 patients with block grafts, who ranged in age from 16 to 56 years, with a mean age of 37 years. Provisional acrylic resin restorations were placed on the implants from 48 to 72 hours after implant surgery. There were 7 patients who received the provisional restoration 48 hours after surgery, while the remaining 12 received the restoration 3 days later. The decision to place the provisional restoration on the implant was made at the time of implant surgery, when bone density could be evaluated.

Bone density was evaluated during implant surgery and defined according to the classification as described by Lekholm and Zarb.³⁷ Type I bone is described as dense, types II and III as normal, and type IV as soft. Patients were included in the study if they fulfilled the following criteria: (1) atrophy in the labiolingual dimension, which prevents implant placement; (2) autogenous block grafting is indicated to reconstruct the atrophic labial cortical plate; and (3) replacement of a missing maxillary canine, lateral, or central incisor. All patients were informed of the newly established protocol, and informed consents were obtained. Exclusion criteria were: (1) parafunctional habits such as bruxism and clenching, including abnormal movement of the mandible in lateral and protrusive directions; (2) pregnancy; (3) use of tobacco; (4) therapeutic irradiation to the maxillofacial region; and (5) medical conditions that were a contraindication to implant treatment.

Surgical Protocol

Presurgical treatment planning consisted of a diagnostic waxup of both arches using a semi-adjustable articulator, fabrication of a acrylic surgical template, photographs, radiographs, and computerized tomography (CT) (Fig. 1). All 19 patients who participated in the study completed autogenous bone grafting of the anterior maxilla to correct the existing atrophy or osseous defect in the labiolingual dimension under local anesthesia. There were 11 autogenous block grafts harvested from the ascending ramus of the mandible, as described by Misch,^38,39 using a fissure bur in a high-speed handpiece under cool water irrigation. The remaining 8 block grafts were procured using the Waterlase laser (Biolase Technology, Inc., San Clemente, CA) according to the technique, as described by Lee.⁴⁰

Fig. 1.: A, Saggital view. Preoperative CT of anterior maxilla. In-office CT shows atrophy in the labiolingual dimension. Less than 5.0 mm of bone width is available for implant placement. More than 15.0 mm of vertical bone height is available for implant placement. B, Saggital view. Postoperative CT of bone grafted anterior maxilla. Width of bone grafted maxilla is now more than 8.0 mm, which will permit implant placement. Note the use of rigid fixation screws to stabilize block cortical graft to maxilla.

Before receiving the block graft, all graft recipient sites were contoured to receive the block graft, but not decorticated or perforated. Each block graft was adjusted passively to the dimensions of the future implant site and stabilized to the maxilla with mini-rigid fixation screws using 2-point fixation (Fig. 2). After 12 weeks of healing time, observation revealed that each block graft was well consolidated with the maxilla. Rigid fixation screws were then removed and tapered, and internally hexed hydroxyapatite-coated dental implants (Screwvent; Zimmer Dental, Carlsbad, CA) were selected and surgically placed according to the manufacturer's recommendations under aseptic conditions and local anesthesia. Initial primary implant stability, evaluated as an insertion torque of 30 Ncm, was required if the implant was to be immediately loaded.

Fig. 2.: Autogenous, block graft harvested from the posterior ramus stabilized to the maxilla using 2 rigid fixation screws.Fig. 3. A, Provisional acrylic restoration placed 48 hours after implant surgery. B, Definitive restoration cemented to custom abutment 12 weeks after implant placement showing excellent soft tissue contours for pleasing aesthetic result. Note regeneration of papillae.

The length and diameter of each implant varied according to bone quality and proximity to anatomical structures. Implant length was selected based on proximity to vital anatomical structures, such as the maxillary sinus and nasal cavity. Implant width was determined according to proximity to vital anatomical structures such as the incisive canal, and its neurovascular bundle and the thickness of the reconstructed labial cortical plate.

Prosthetic Protocol

After each implant was surgically placed in the maxilla using the template as a guide, implant position was immediately indexed by the surgeon with the closed tray technique using the impression coping provided by the implant manufacturer and a polyvinylsiloxane impression material to facilitate the fabrication of the provisional acrylic resin restoration. The Screwvent dental implant is supplied with a premounted titanium abutment that serves as the fixture mount, temporary abutment, and impression coping for indexing to transfer the position of the surgically placed implant to the master cast. The decision to place the provisional restoration 48 hours to 3 days later was determined by the limited time available for this procedure following surgery between the surgeon, patient, and dental laboratory. The custom abutment and provisional restoration were fabricated by the dental laboratory and returned to the surgeon. The provisional restoration was adjusted chairside and cemented with temporary cement out of occlusion (Fig. 3A). Twelve weeks later, the restorative dentist obtained final impressions, and the definitive ceramometal restoration was fabricated and delivered to the patient (Fig. 3B). All patients were advised to avoid loading of the implant restoration for a total of 3 months after implant placement and to maintain good oral hygiene.

Criteria for Implant Success

All implants with the provisional and definitive restorations were determined to be successful if the following criteria were observed up to 1 year after implant placement: (1) no implant mobility, (2) no complaint of pain around the implant, (3) no evidence of infection associated with the implant, and (4) no neurosensory deficits reported by the patient.

Results

There were 19 patients who participated in the study, with 19 implants placed in the grafted anterior maxilla. Table 1 shows implant position and size of implants placed in each patient. All implants were loaded with nonfunctional, provisional acrylic restorations within 48 hours to 3 days after implant surgery. The definitive restoration was delivered to the patient 12 weeks later and observed for a period of 1 year. There were no implant failures observed from the time of implant surgery to delivery of the final restoration. In all but 1 patient, soft tissue anatomy was considered satisfactory. In this patient, a subepithelial connective tissue graft was used to provide an adequate zone of attached tissue around the implant. In-office CT (Imaging Sciences Int., Hatfield, PA) was obtained immediately after cementation of the definitive ceramometal restoration and at the 1-year observation visit (Fig. 4). CT allows for the observation of implant position in the grafted maxilla and assessment of bone loss around the implants in all 3 dimensions.

Table 1: Implant Position and Size in the Block Grafted Anterior Maxilla

Fig. 4.: Saggital view. In-office CT showing implant with ceramometal restoration osseointegrated in consolidated block grafted anterior maxilla. Definitive restoration was placed on implant 12 weeks after implant surgery.

Discussion

The early reports by Brånemark¹ and Adell et al² recommended an occlusal-free submerged healing time of 6 months for implants surgically placed in the maxilla to allow for successful osseointegration. This traditional implant protocol continues to be modified because of advances in implant technology and clinical experience of the implant team. Bone quality from the ascending ramus of the mandible is type I bone, and grafting the anterior maxilla from the ramus effectively changes the osseous macrostructure from type III to type I bone. As many immediate loading studies have documented, type I bone of the anterior mandible can be successfully and predictably loaded immediately after implant placement.^5,6,12–14

The ramus grafted anterior maxilla shares these same characteristics and is most likely a result of the favorable, primary stability of the implants placed in dense, type I bone. From bone physiology studies, revascularization to the interior of the graft has been observed as early as 8 weeks and deposition of new bone complete as early as 12 weeks.^35,36 Therefore, successful early remodeling and consolidation of the graft to the native maxilla could be the most important reason implants can be surgically placed and immediately loaded 3 months after the grafting procedure instead of 6 months, as recommended by the conventional Brånemark protocol.

In the esthetic zone of the anterior maxilla, the challenge is to maintain or recreate the soft tissue contours of the interproximal papillae and gingival profile.⁴¹ Compared to a stock healing abutment, the shape of the provisional restoration should allow for guided soft tissue healing to maintain the scalloped architecture of the gingiva. Of the 19 patients, 18 did not require soft tissue augmentation because there was an adequate zone of attached tissue to withstand the functional stresses of mastication, and the natural soft tissue contours were determined to be esthetically pleasing to the patient. Therefore, the provisional restoration provides an important role early in the course of treatment before the patient receives the final definitive restoration.

Implant design and surface characteristics should be seriously considered in esthetic situations. All tapered implants surgically placed in this series were internally hexed and coated with hydroxyapatite. The Zimmer Dental Screwvent implant has a 1.5-mm deep internal hex that distributes forces deeper in the implant, protecting the retention screw from excessive loading and loosening. This specific feature not only decreases screw loosening but also creates a low profile at the implant-abutment interface, which allows for a more natural emergence profile.⁴² Surface topography is also important in achieving primary stability. Improving the surface roughness of the implant promotes osteogenesis by increasing the osteoblastic metabolic activity and cellular adhesion, stabilizing the fibrin scaffold and increasing the available surface area for bone attachment.⁴³ Experimental studies have shown a direct relationship between push-out failure load and surface roughness.⁴⁴ Hydroxyapatite-coated implants had higher removal torques compared to other implants.^45,46 Histologically, the hydroxyapatite coating increases surface area that allows for increased bone apposition, which facilitates osseointegration.⁴⁴

Conclusion

The preliminary clinical results of this study suggest that a nonocclusal immediate loading protocol in the reconstructed anterior maxilla should be considered as an alternative treatment option compared to the traditional Brånemark protocol. The 100% survival of implants placed in the grafted anterior maxilla and immediately loaded within 48 hours to 3 days can be attributed to changing the osseous macrostructure from type III to type I bone and use of rough surfaced, internally hexed tapered dental implants. With this immediate loading protocol and use of a provisional restoration, natural soft tissue contours can be successfully maintained or recreated. Although we have routinely included this loading protocol into our surgical practice, additional clinical studies of longer duration are needed to confirm the encouraging results of this study.

Disclosure

The authors claim to have no financial interest in any company or any of the products mentioned in this article.