Replacement of congenitally missing lateral incisors can pose challenges that can lead to clinical complications.
These are related to several factors, including angulation of the premaxilla (triangle of bone) and depression of the facial plate due to lack of development related to the missing permanent tooth. Traditional radiographs lack the information necessary to understand the anatomy in the facial–palatal dimension, and this can lead to dehiscence of the facial aspect of the implant when placed freehand using a flapless technique. A flap can be elevated prior to osteotomy preparation so that visualisation of the osseous anatomy can be achieved, allowing the osteotomy to be angled to prevent dehiscence. Clinically, freehand, non-guided site preparation has the risk that the practitioner may overcompensate for the facial defect and angle of the premaxilla, creating an osteotomy that is angled too far to the facial aspect, creating restorative challenges in the aesthetic zone.
3D evaluation by CBCT provides greater information on the dimensions of the edentulous site to allow implant planning and utilisation of a flapless technique while ensuring that the osteotomy does not create a dehiscence and the implant when placed is surrounded by bone. A guided approach to osteotomy preparation allows a flapless approach for implant placement, making healing for the patient easier and less traumatic. Additionally, an osteotomy is planned that is ideal for the site’s osseous anatomy, simplifying the restorative aspect of treatment and yielding a natural aesthetic end result of replacing the congenitally missing incisor.
The article will discuss a case wherein replacement of bilateral congenitally missing lateral incisors was planned utilising a diagnostic guide for a CBCT scan, virtual planning of the implants and correction of the guide for a surgical guide fabricated in-office. The accuracy of this technique has previously been described regarding the accuracy of the geometric approach to guided surgery in an in vitro model.
A 17-year-old female patient presented for consultation on replacement of the bilateral missing maxillary lateral incisors with implants (Fig. 1). The patient had undergone orthodontic treatment and the roots of the canines and central incisors bilaterally were parallel, providing spacing for possible implant placement. Examination noted that a facial defect on the ridge was present at both lateral sites related to the lack of development of permanent lateral incisors and loss of the primary lateral incisors prior to orthodontic treatment. Evaluation of the preliminary radiographs confirmed adequate space between the roots of the canine and central incisor to accommodate a narrow-diameter implant while maintaining the recommended distance between the natural root and implant on the mesial and distal sides (Fig. 2).
Components of the Guide Right system (DePlaque) would be utilised to create the diagnostic guide to be used for the CBCT scan and the subsequently corrected surgical guide that would be utilised for osteotomy creation (Figs. 3a–c). Preliminary impressions were taken and casts fabricated. A hole was made in the cast at the planned implant sites with a 2.38 mm drill in a laboratory handpiece, placing each in the ideal prosthetic position centred in the edentulous site at the estimated position and trajectory based on the orientation to the tooth mesial and distal to the missing tooth. A diagnostic guide post was inserted into the hole in the cast, and a 2 mm guide sleeve was placed over the post with its retention element (cleat) oriented to the palatal aspect (Fig. 4).
A two-piece guide post upper removable part (URP) with cap was positioned over the 2 mm guide post and then a 2 mm guide sleeve was placed on the URP. This narrower 2 mm guide sleeve provided more accuracy for the radiographic diagnosis. The palatal and occlusal surfaces of the cast were lubricated to prevent resin adherence when the guide was fabricated. A lightpolymerised resin (primopattern LC gel, primotec) was expressed on the cast over the cleat (Fig. 5a), and primosplint resin (primotec) was placed on the adjacent teeth to create a stabiliser for the diagnostic guide when inserted intraorally, and these were light polymerised (Fig. 5b).
The guide posts were removed from the sleeves, completing the diagnostic guide. The diagnostic guide was inserted intra-orally, and a CBCT scan was taken to evaluate the ideal placement of the implant platform in relation to the osseous anatomy. The patient returned for a CBCT scan with the diagnostic guide. The guide was inserted intra-orally and the CBCT taken. The scan was imported into the implant planning software (Carestream). The metal sleeve is visible on the scan and its radiolucent centre length allows a trajectory to demonstrate the facial–palatal orientation of the implant if the long axis or position of the original sleeve has been used to guide the implant drills in creating the osteotomy. CBCT tangential and cross-sectional views at both sites were evaluated in the planning software. The right lateral incisor site, based on the site dimensions, would accommodate a tapered bone-level implant (3.3 mm × 12.0 mm, Roxolid, SLActive; Straumann). It was noted that an offset of 0.5 mm and an angle correction of 6° to the palatal aspect would be necessary (Figs. 6a & b). Additionally, owing to the facial–palatal width of the ridge at mid-height crestally and apically, ridge augmentation would be required to eliminate a dehiscence at the time of surgical placement of the implant. Evaluation of the left lateral incisor site also determined that an implant of the same type and specifications would be accommodated by the site. The tangential view determined that no linear correction was needed (Fig. 7a), but in the cross section, it was determined that an angular correction of 6° to the palatal aspect would be required (Fig. 7b). No offset would be necessary on the left site. Like with the bilateral site, because of the facial–palatal width of the ridge at mid-height crestally and apically, ridge augmentation would be required at or prior to the time of surgical placement of the implant.
On the cast, an offset guide post (0.5 mm) was placed into the right site and a straight (no offset) guide post placed into the left site (Fig. 8).
A URP was placed over both guide posts, and the cast was coated with metatouch (primotec) to prevent the resin that would be added for fabrication of the surgical guide from adhering to the cast (Fig. 9). A 3.9 mm guide sleeve was placed over both URPs, the cleat positioned to the palatal side of the cast (Fig. 10).
Like with fabrication of the diagnostic guide, primopattern gel was placed over the cleat on each guide sleeve (Fig. 11a) and then a 2.5 cm length of primotec splint resin was applied to the palatal side of the cast (Fig. 11b).
The splint resin was adapted to the cleats and palatal and occlusal/incisal aspects of the adjacent teeth on the cast to create the surgical guide and then light-polymerised (Fig. 12a). Coverage of the occlusal/incisal aspect of the adjacent teeth with slight extension on to the buccal aspect of the teeth creates a guide that will be stable intra-orally during osteotomy preparation. The URPs were removed from the cast, allowing removal of the surgical guide from the cast (Fig. 12b).
The patient presented for the surgical appointment, and the consent forms were reviewed and signed by the patient’s parent. Local anaesthetic was administered to the sites in the buccal vestibule and palatally. A #15 scalpel blade was utilised to make an incision from the midfacial aspect of the right central incisor in the sulcus and continued to the mesial aspect of the distal papilla of the canine, and a full-thickness flap was elevated to expose the facial aspect of the ridge at the right lateral incisor site (Fig. 13a). The cortical plate was perforated at multiple points at the facial ridge defect with a surgical bur. An OsteoGen Block (Impladent) was hydrated with the INFUSE XX SMALL KIT (Medtronic), hydrated with 0.7 ml sterile water, divided into halves and placed over each defect on the facial aspect of the ridge (Fig. 13b). OsteoGen is a bioactive, resorbable non-ceramic calcium apatite crystal that is similar to human bone and is carried by a bovine collagen created from the Achilles tendon, allowing adaption to the defect as a malleable material. INFUSE, a recombinant bone morphogenetic protein-2, has been shown to enhance the maturation of the graft it is combined with, accelerating guided bone regeneration with an increase in graft–bone contact. Combination of the two materials allows maintenance of the grafted space as host angiogenesis occurs and stimulation of conversion to host bone. The graft is placed in enough volume to be equal to the ridge contour of the adjacent teeth. The procedure was repeated on the left incisor site (Figs. 14a & b). The flaps were closed with #6/0 nylon sutures in an interrupted pattern and the patient dismissed.
The patient returned four months after the graft placement, and a CBCT scan was taken to evaluate the graft and ridge contours in cross section (Figs. 15a & b).
Local anaesthetic was again administered into the buccal vestibule and palatal aspects of the ridge at both planned surgical sites. The surgical guide that had previously been fabricated in office was inserted intra-orally. A flapless surgical approach would be utilised. A 2.2 mm depth stop drill for the 3.9 mm guide sleeve of the appropriate length for the implant that was planned at each site was run through the surgical guide to depth. The surgical guide was removed, and a 2.0 mm direction indicator (DePlaque) was placed into each osteotomy and a periapical radiograph taken to confirm the planned osteotomy in relation to the adjacent teeth (Figs. 16a & 17a). The surgical guide was reinserted intra-orally, and the osteotomies were enlarged with consecutive 1.5–2.2 mm tapered depth stop drills of increasing lengths—6.0, 8.0, 10.0, 11.5, 13.0 and 15.0 mm—and then the next largerdiameter drill series was repeated with 2.0–2.8 mm depth stop drills and finally a 2.8 mm diameter drill was taken to 15.0 mm. The extra length was used to accommodate the 3 mm depth of the soft tissue using a flapless protocol. The two implants were placed utilising the guide sleeves to position them. The guide was removed, and 2 mm healing abutments were placed on both implants. A periapical radiograph was taken of both sites to document the depth and direction of the osteotomy prior to implant placement in relation to the adjacent teeth as well as the depth of the osteotomy in relation to the ridge crest (Figs. 16b & 17b). The patient was dismissed to allow for implant osseointegration.
A post-surgical CBCT scan was taken and imported into the planning software. The virtual planned implant cross section was overlaid on to the cross section at the right lateral incisor to verify that the surgical guide had been able to achieve the planned position in relation to the osseous anatomy (Fig. 18). Both the planned position of the right lateral incisor and actual implant position were identical, demonstrating that the in-office surgical guide was accurate regarding the virtual planned position. Additionally, the facial aspect of the ridge where the graft had been placed eight months prior demonstrated sufficient thickness of bone for long-term implant maintenance. Evaluation of the left lateral site made similar findings, demonstrating the accuracy of the surgical guide in replicating the virtual planning (Fig. 19). Implant healing and integration were complete, and the restorative phase of treatment could be initiated.
CBCT scans increase the information available when planning implant placement by views that are not provided with traditional 2D radiographs. Utilisation of a diagnostic guide to take the CBCT scan increases the accuracy in the implant planning software, as it provides references to where the implants may be placed in the space that can be coordinated with the osseous anatomy. Corrections can then be made in in-office fabrication of the surgical guide that will be created on the cast used to create the diagnostic guide. Congenitally missing lateral incisors pose challenges due to the limited facial–palatal dimensions of the ridge related to lack of development that would normally occur with tooth development at the site. CBCT planning allows cross-sectional viewing of the intended site to assess whether the width of the ridge will allow implant placement or supplemental grafting will need to be performed. Often in lateral sites with congenitally missing teeth, insufficient width is present, and grafting will need to be performed either in conjunction with implant placement or as a precursor to implant site osteotomy preparation. The case presented involved a ridge that would not allow initial implant stability at the sites, necessitating osseous grafting to improve the ridge dimensions and site healing before implant site preparation could be performed. The corrected surgical guide allowed planning in order to position the implant ideally for the anatomy, taking into consideration the triangle of bone in the premaxilla.