Ultra-narrow diameter implants for the treatment of mandibular anterior external resorption

Dr. Paul Mozer discusses guided implant surgery with narrow diameter implants

Successful implant surgery is in large measure reliant upon the accurate position of the implant and its prosthetic components.^1,2 The overloading of the implant body or its prosthetics have been considered by several studies that specifically addressed the concerns that arise from poor implant positioning. Weinberg, et al., in 1995 articulated the force magnifiers that resulted from improper implant placement and described the concepts of cuspal inclination, implant inclination, horizontal implant offset, and apical implant offset.³ Directional displacement of the implant away from its intended position resulting from variations in vertical, horizontal, and depth positioning resulted in substantial increases in force transmitted to the implant and its prosthetics. These increased forces can lead to premature prosthetic component wear, prosthetic failure, bone loss, and implant loss.³

Historically, clinicians used two-dimensional panoramic X-rays, bone mapping using ridge calipers, and open-flap measurements, among other techniques to measure the width and height of the residual ridge before and during implant placement. Most often final implant size and position were determined chairside with the surgical site flapped open. These approaches alone or in combination all yielded significant gaps in critical clinical information since these methods all lacked the appreciation of the three-dimensionality of bone.^4,5,6

Many studies have described the challenges of freehand implant surgery under normal conditions. Hoffman, et al., performed a model-based study in which the mean angle deviation between planned implants and final implant placement was 11 degrees with a range from 4.1 to 25.3 degrees.⁷ A malpositioned implant with an 11-degree angulation would have potentially significant and long-lasting consequences on the implant and its prosthetics.

Three-dimensional cone beam imaging has opened the door for clinicians to assess bone density and volume before performing the implant procedure.^5,6 Computer-aided design and manufacturing (CAD/CAM) can be utilized to plan ideal implant positions in implant software and bring those ideal surgical plans to the patient using static stereolithographic (STL) static surgical guides.^7,8 Surgical guides allow clinicians to increase the predictability of implant placement⁸ while limiting the negative outcomes of implant malposition and force multipliers. Guided surgery drill kits provided by the implant manufacturer restrict the drill path by engaging the guide sleeve within the STL surgical guide.¹³

Studies by Hoffman, et al., and Choi, et al., show a 50% or greater improvement in implant position accuracy utilizing static surgical guides over freehand methods. The advantages of guided surgery become critical in complicated cases where bone volume or bone density require precision that can be difficult to achieve with freehand implant placement.^7,14

Edentulous areas with a narrow ridge that is deficient in width and/or height have traditionally undergone a bone augmentation procedure prior to implant placement. Augmentation with bone blocks, bone plates, or ridge-splitting procedures are technique-sensitive, costly, and can result in comorbidities such as a second surgical site dehiscence or a final implant site with a remaining width deficiency.¹¹ Narrow interdental edentulous spaces such as maxillary lateral incisors and mandibular incisors are unique in that except for orthodontic arch expansion, the adjacent teeth prevent bone grafting as a solution to gain more space for a larger implant diameter. As implant material science has advanced, narrow diameter two-piece implant designs have allowed clinicians and patients to set aside traditional grafting techniques and utilize narrow (3.0 mm-3.25 mm) and ultra-narrow (2.75 mm) diameter implants with measurable success. A systematic review by Schiegnitz and a study by Grandi both show the success of ultra-narrow diameter 2.75 mm implants to be between 94.7 and 97.6%, results that are consistent with the success of more traditional sized implants.^16,17

Clinical case

The patient presented with the diagnosis of unrestorable external resorption of teeth Nos. 25, 26, 27 in the anterior mandible. A cone beam image was taken using the i-CAT™ FLX (Imaging Sciences, Hatfield, Pennsylvania). Analysis showed very thin bone surrounding the existing teeth with a density of 1243-1383 Hounsfield units, suggesting very dense Type I bone. Treatment-planning options for a narrow ridge included the options of onlay block grafting with delayed implant placement and the disadvantages of a second surgical site, comorbidities, and technique-sensitive surgical procedures. The traditional prosthetic dental options of a lower partial denture and fixed bridge were alternatives that were less than desirable for the patient. The patient ultimately opted for implant placements.

In this case, the ultra-narrow platform Adin Touareg CloseFit™ 2.75mm diameter implants (Adin Implants Afula, Israel) were treatment planned for guided surgery using 360Imaging™ (Atlanta, Georgia) surgical guides. The workflow included a three dimensional cone beam image taken at the consultation appointment along with physical polyvinyl siloxane impressions (3M™, St. Paul, Minnesota) for interim prosthesis fabrication and a digital impression of the clinical arch (Cerec Omnicam, Dentsply Sirona, Salzburg, Austria) for surgical guide planning. The collected data was sent to 360Imaging through its online courier service for analysis and treatment planning. Treatment planning was performed collaboratively between the clinician and the dentist treatment planners at 360Imaging via Zoom (San Jose, California) and screenshare technology. The teeth were digitally extracted, and the final implant positions were planned in 360dps software (360Imaging, Atlanta, Georgia). Static STL surgical guides were fabricated and delivered to the clinician’s practice within a few days.

The day of the procedure, consent was obtained, amoxicillin 2G was given to the patient before the procedure and 2.5 carpules of articaine 4% 1:100k epinephrine local anesthetic was administered (Septodont, Lancaster, Pennsylvania). The affected teeth were extracted as atraumatically as possible using forceps. The positive seating of the surgical guided was verified clinically, and three Adin Touareg CloseFit 2.75 mm ultra-narrow diameter implants were immediately placed using the static surgical guides and Adin’s keyless guided surgery kit (Adin Implants, Afula, Israel). Cover screws were placed and torqued to 15Ncm, and particulate bone grafts with BioOss^® (Geistlich, Wolhusen, Switzerland) were placed with aPRF and iPRF using the Choukroun Duo Quattro PRF™ Centrifuge (Advanced Platelet Rich Fibrin, Choukroun Centrifuge Nice, France). A BioGide^® cross-linked collagen membrane (Geistlich, Wolhusen, Switzerland) was placed over the grafted site and tension-free PGA (polyglycolic acid) sutures were placed. Hemostasis was observed. The previously fabricated temporary removable prosthesis was adjusted chairside and delivered to the patient, making sure that there was no positive pressure on the ridge from the interim prosthesis. The patient was placed on a postoperative regimen of Ibuprofen 800mg every 4 hours for the first 24 hours and Amoxicillin 500mg 3 times daily, warm salt water rinses 5-6 times per day, and 0.12% Chlorhexidine rinses twice daily for 7 days. The patient was seen for suture removal 10 days after the procedure, and oral hygiene instructions were reinforced.

After 4 months of healing, the site was uncovered, healing abutments placed for tissue contouring, and an open tray impression was taken with Impregum™ (3M™, St. Paul, Minnesota). Three splinted screw-retained crowns were inserted and torqued to 35Ncm. The lingual screw accesses were covered with PTFE Teflon tape, resin restorations were placed, and the occlusion was adjusted where necessary. Oral hygiene was reviewed, and the patient was seen 3 weeks later for an occlusal reassessment.

In a freehand implant placement surgical approach, obtaining optimal positioning in Type I bone can be clinically challenging for a single implant. In this particular case, the patient presented with a narrow mandibular anterior edentulous space that required precision placement of three implants in narrow and dense bone. The ability to achieve the ideal placement required for multiple placements of ultra-narrow implants with screw-retained crowns would have proven very difficult. As indicated in Figure 7B, screw access was through the cingulum on the lingual aspect of the prosthetics. Static-guided implant surgery utilizing the Adin’s ultra-narrow 2.75 mm implants allows implant placements in dense thin bone to be as predictable as 5.0 mm implants in a wide edentulous ridge.