Placing implants when the bone is limited or when there is irregular patterns of bone resorption could require bone grafting or bone remodelling before implant insertion. In these case studies, bone remodelling is selected for patients with a mandible that has a crest with ‘pyramid’ morphology, classified as a Misch B-w Division bone.
The bone crest would be remodelled into a Misch A division with minimal osteoplasty.1 Implant insertion would be set according to the crest after remodelling. These procedures can be done either with free handed or with computer guided surgery. However, free handed implant placement will be surgically driven, as for computer guided surgery; it will be prosthetically driven with a higher accuracy.2,3
CT scan imaging along with the SimPlant (Materialise Dental, Leuven, Belgium) parametric software were used to virtually plan the bone remodelling and the teeth extraction in order to set the position of the implants according to the prosthetic plan.
A stereolothographic model, Immediate Smile® (Materialise Dental, Leuven, Belgium) was ordered for the second case to allow for better planning of restorative and surgical phases, since an immediate load is anticipated.2
A bone reduction guide and surgical templates were fabricated in order to accurately transfer the simulated plan to the patient.4,5
The use of bone reduction guide during surgery eliminates the arbitrary removal of osseous structure and helps ensure the mandibular crest is reduced in prescribed dimensions,6 eliminating only the sharp edge of the knife ridge.
The implants can be placed with guided surgery exactly in the desired location where the bone has been reduced horizontally to increase its crest width.
With this surgical approach, sufficient bone volume and primary retention for the implants are optimized for a better prognosis.
CASE 1
Complete Mandibule Rehabilitation Involving Bone Reduction Guide
A 74-year-old male patient, socially involved as a past mayor, requests a mandible prosthesis supported by implants. He is complaining about an ill-fitting lower partial denture.
Diagnosis
This patient has been wearing a conventional upper maxillary complete removable prosthesis and a lower partial prosthesis for over 50 years. He has three teeth and residual roots in his mandible. In addition, parodontisis, ill-fitting upper and lower prosthesis, malocclusion and aesthetic unappealing prosthesis were observed (Fig. 1). For the purpose of this study, the mandibule rehabilitation will be detailed.
PHASE I
Planning and Surgery
A two-phase treatment plan was established. Phase I includes the extraction of the residual roots and decayed teeth, in order to eliminate the parodontisis in the projected implant site. Phase II, the implant placement is done in a healed site where keratinised soft tissue is promoted allowing for a good prognosis of immediately loaded prosthesis. The panoramic radiography of the edentulous mandible revealed uneventful healing with sufficient bone height. No sign of pathology or teeth fragments were observed after teeth and root extractions. A scanographic template for a CT SimPlant protocol was prepared according to the prosthetic plan. The patient was then sent for a CBCT scan wearing the scanographic template.
3D Diagnosis
Bone thickness and density were evaluated for the anticipated osteoplasty and immediate implant loading procedures (Fig. 2).
Study of the CBCT reconstruction radiography reveals the following:
• Residual root tips in the anterior mandible are identified with the density tool. Those roots were not visible on the panoramic radiography;
• The morphology of the bone in the pre-mandible is of a pyramid morphology, corresponding to a div B-w Misch-Judy.
• Unfavourable bone density for immediate load in implant positions A and E.7
• Sufficient bone width between both mental foramen to fit five implants.8
• Favourable bone height for a good implant to prosthesis ratio.
PHASE II
Planning and Surgery
Mandible osteoplasty for a conversion of a div B-w to a div A was planned with SimPlant software. The horizontal bone reduction line between both foramens is determined to achieve optimal bone coverage for implant placement (Fig. 3). Five implants of 4 mm in diameter are planned in the anterior mandible. Angulations and emergence profile were guided by the radiographic template9 (Fig. 4). Overall bone density indicates a four-month healing period before proceeding with the prosthetic protocol.
A bone reduction guide, along with the corresponding stereolithographic model of the reduced mandible section was ordered. Stereolithographic surgical guides were ordered to fit on the completed osteotomy.
Surgery is performed with local anaesthesia. The first procedure is to raise a full thickness flap that will expose the bone crest where the bone reduction guide will be installed (Figs. 5, 6).
After bone reduction completion, fitting of the surgical guide is checked for intimate contact with the crest. The bone supported surgical guide was secured with two fixation screws. A D1-D2 osteotomy protocol was performed with a set of three surgical guides and implants (Maestro, Bio Horizon, Birmingham U.S.A) were placed as planned to sub-millimetre precision (Fig. 7).
Voids of bone around implants A and E are identified; they would be filled with minor autogenous bone grapht collected from the osteoplasty reduction (Fig. 8). A low torque resistance of 10 Newton/cm was recorded for implants A and E. These low torque values can have a 90 percent failure after immediate load,10 therefore, a two stage approach will be required to avoid loading the implants and achieve a successful osseointegration of the implants.
At second stage surgery, an open tray impression was made at the implants’ level and a 3i hybrid fixed titanium bar (Biomet 3I, Fl., USA) was CAD-CAM milled for this case (Fig. 9). The final prosthesis was installed on the implants, according to the precise initial treatment plan.
CASE 2
Immediate Loaded Implants, Virtual Extractions and Bone Reduction Guide
In this case study, the patient’s concern was to have her teeth replaced with no time period spent with missing teeth after extraction. Implant dentistry has progressed allowing the replacement of patient’s teeth with immediate implants and loaded prosthesis, in many cases.
In the literature studies presented successful use of an immediate placement approach in conjunction with full-arch restorations.11-14 However, multiple factors are critical to implant placement, such as; bone density around the implant, torque resistance to implant placement,15 resonance frequency analysis,16 implant size, numbers and shape,1 tissue biotype17 and occlusion pattern. These reveal to be key factors in immediate implant placement and loading, and must be evaluated accurately prior to surgery.
Diagnosis
A 52-year-old female patient has a maxilla with complete conventional removable prosthesis and a mandible with partial removable prosthesis for her posterior bilateral edentate’s areas (Fig. 10).
In this case, only the mandibule restoration is detailed. She has a posterior bilateral advanced vertical bone resorption. Her remaining anterior incisors had biomechanical compromises, bone loss and soft tissue inflammation revealed a parodontisis disease. The prognosis for her remaining mandible teeth was poor. Dentofacial compromises are present due to the absence of teeth needed to support her facial soft tissues (Fig. 11).
After being informed of her treatment options, she elected to have her remaining mandib
le teeth removed and replaced with implants to be immediately loaded.
Planning and Surgery
The treatment planning protocol for this case study was to acquire a CBCT scan, an optical impression scan of her mandible and merge those scans onto the parametric software. Merging both scans replaces a scanning template for this case study.18 Computer implant planning was carried on to replace her existing teeth with an immediate transitional prosthesis.
Virtual teeth extraction, virtual bone reduction (Figs. 12, 13) and implant placement were implemented to the plan. The curvature of the mandible had a restricted anterior-posterior ratio (AP). Five implants were planned for this case with two distal tilted implants to achieve an increased AP ratio (Fig. 14). At completion of this plan, a stereolithographic surgical guide and a Nobel Guide compatible (Materialize Dental), were ordered along with both a bone reduction guide, as well as an Immediate Smile® stereolithographic model (Fig. 15). This later model is produced with sockets, to receive the implant analogues that replicated the positions of the proposed implant placement sites (Fig. 16).
Once the stereolithographic model is received, it is mounted onto an articulator, and all mandible teeth are removed from the model exactly like the virtual extraction plan. Implant analogues are secured into the model’s sockets and temporary implant abutments are screwed on the implant analogues (Fig. 17). A laboratory acrylic prosthesis is prepared on those abutments and is designed without any cantilever (Fig. 18). The abutments receptacles are hallowed out, creating a space between the abutments and the prosthesis, which was filled with cold cure resin, after implant placement.
Surgical Phase
Infiltration and bloc anesthesia of the mandibular nerve were conducted. All remaining teeth were extracted, the bone reduction guide was set on the mandible and osteotomy was achieved with success, in accordance to the proposed plan (Figs. 19, 20). As the bone reduction guide is removed, the receptor site is now set to receive the stereolithographic surgical guide. The surgical guide for implant placements was then secured to the mandibule along with two-bone fixation screws (Fig. 21).
A D2 Misch osteotomy protocol was carried on. All implants (Nobel Replace, Nobel Biocare Canada Inc., Richmond Hill, Ontario) had primary fixation of over 45 Ncm (Fig. 22) and socket voids were filled with autologous bone harvested from the bone reduction osteotomy (Figs. 24, 25). A dermal acellular matrix (Alloderm, Birmingham, AL, USA) was inserted between the particulated bone autograph and the transitional prosthesis, to allow bone guide regeneration and adequate soft tissue coverage (Fig. 26). Implant abutments were screwed at 35 Ncm. The immediate transitional prosthesis was set on the abutments and relined with an acrylic cold cure resin. Before occlusion assessment, abutment access holes were closed with composites. The patient was relieved and an uneventful healing was achieved (Fig. 27).
Four months later, definitive prosthetic procedure had been undertaken. Radiographic analysis, radio frequency analysis and reverse torque test at 20 Ncm were done.19 All these evaluations were favorable (Fig. 28). A computer milled titanium bar, covered with acrylic was delivered (Fig. 29) and then, screwed onto the five implants. A new maxillary complete prosthesis, harmonized with the mandibule, was simultaneously made to improve function and esthetics (Figs. 30, 31).
CONCLUSION
Planning for an immediate load case with CT scan imaging, can be difficult if the bone height or width is irregular. In order to achieve accurate implant placement, it is necessary to know in advance the relationship between the desired teeth position and the underlying bone. To overcome planning obstacles, parametric software and stereolithographic guides are an adjunct for a better prognosis. Bone reduction guides are useful to level the bone crest in order to reduce its surface irregularity. Achieving homogeneous bone morphology with a reduction guide will help planning for an ideal implant placement. But this approach has its limitations. Based on a finite element analysis, when reducing the bone horizontally, cancellous bone can be exposed significantly. Placing the implants within that type of bone along with immediate load will increase bone strain around the implant.20 Reduction of the alveolar bone may redistribute and decrease the stress. Based on the results of that study, taking into consideration the wide variation in bone morphology and cortical bone thickness among individuals, it may be impossible to draw a definitive conclusion regarding the limit to which the crestal region can be reduced, without causing considerable increase in the resultant stresses.
Therefore, selecting a case for a bone reduction and immediate loaded implant would be based on a multifactorial evaluation of several parameters, such as bone density, implant torque resistance, resonance frequency analysis, implant size, number and design, implant position, tissue biotype, prosthesis design and occlusion pattern.
Stereolithographic bone reduction guide and stereolithographic drill guides facilitate the bone osteoplasty and enables the surgeon to place the implants according to the prosthetic plan. This technology allows for a true prosthetically driven implantology.
Being able to assess the bone volume in relation to the prosthetic design will enable ideal implant placement and increase predictability and precision of surgical procedures. Achieving predictable prosthetics will increase patient’s satisfaction. Also, reducing the operatory time through the use of surgical guides, contribute to minimizing the time the flap and bone surface is exposed. These factors will contribute to a shorter healing period and increased post operatory comfort.
Some of the advantages of virtual extractions and stereolithographic models are to allow the patient to retain his/her teeth until the day of surgery, have a pre-surgical prosthesis built in advance and achieve prosthetic results, as per initial treatment plan.OH
Dr. Gilbert Tremblay is the Founding President of the Quebec Dental Implantology Institute, dedicated to the professional training and development of implant rehabilitation. As Founding President, he oversees the activities in support of the goals and mission of the Institute, in sharing his clinical knowledge adapted to today’s realities. Dr. Gilbert Tremblay, B.Sc., D.M.D., Dipl. ABOI/ID; Fellow & Dipl. ICOI; Fellow AAID; Fellow MIII; Fellow Pierre Fauchard Academy; Founding President of the Quebec Dental Implant Institute.
www.dentalimplant3D.com
Acknowledgements:
The author would like to thank Therese Lanciault, B.Sc., M.Sc., and Director of the Quebec Dental Implant Institute, for her guidance, support and assistance with this manuscript, as well as Anas Raffoul, Certified Technician, R&B Laboratories and Thomas Kuun from Materialise Dental for their technical support.
Oral Health welcomes this original article.
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