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Mandibular Incisor Replacement With Narrow-Diameter Implants
An alternative to fixed prostheses involving natural teeth in sites with limited space for conventional implants
Eugene Kim, DDS | Gregori Kurtzman, DDS
The use of implants to replace single lost or failing incisors in the anterior region of the mandible can be clinically challenging due to the narrow dimensions of those natural teeth. Anterior crowding may complicate this, further decreasing the dimensions of the space for a planned implant. To avoid encroaching upon the periodontal ligament space of the adjacent teeth and facilitate maintenance of the interproximal bone over time, there needs to be sufficient bone width and space between an implant and the adjacent teeth. The literature has recommended that a minimum of 1.5 mm is required to meet that goal.1-3 In addition, after implant placement, a minimum of 1 mm of bone needs to be present between the implant and the exterior aspect of both the buccal and lingual osseous plates.4,5 Bone density is also a factor in placement. Denser bone is typically found on the mandibular buccal and lingual plates, and the maxillary palatal plate is more stable in thinner thicknesses than the lesser dense bone found in the buccal plate of the maxilla.6 Therefore, implant placement in mandibular sites with limited volume, as is found in the incisor sites, has a more forgiving nature than implant placement in volumetrically similar sites in the maxilla. The anterior region of the mandible also allows for the placement of longer implants due to the lack of anatomical structures (eg, nerves, blood vessels) between the anterior loops of the mental nerve bilaterally.
Narrow-Diameter Implants
Frequently, a standard diameter implant (3.5 mm to 4.2 mm) cannot be utilized in a mandibular incisor position due to the insufficient dimensions of the space to receive it because this would compromise the adjacent teeth or lead to dehiscence upon placement. One-piece, small-diameter implants (2.5 mm to 3.4 mm in diameter) or mini implants (1.8 mm to 2.5 mm in diameter), which do not create microgaps as a result of their design, are ideally suited to facilitate implant placement in these limited volume spaces. When treatment planning small-diameter implants, the use of cone-beam computed tomography (CBCT) is invaluable in determining the dimensions of the available space in 3D so that the correct diameter can be selected. Should the virtually planned position create a dehiscence upon placement, simultaneous osseous grafting can be performed to ensure that the implant will be completely surrounded by adequate bone following healing.
One-piece, small-diameter implants, which are also referred to as narrow-diameter implants, have been reported to have high long-term success rates of approximately 96% and should be considered when treatment planning single incisor sites.7,8 These success rates have been reported to be comparable to those of standard diameter implants.9
Because the smaller diameter of narrow-diameter implants will not permit a two-piece design that would be strong enough at the implant-abutment connection to resist fracture under function, they are designed to be single-piece and, thus, require a transitional restoration during the period of time in which they undergo initial osseointegration and the soft tissue is allowed to mature or a provisional restoration if an acceptable initial insertion torque value is achieved. For implants to be immediately loaded, it is recommended that they achieve an insertion torque value of greater than 35 Ncm.10
The anterior region of the mandible offers benefits not found in other areas of the arches, such as a lack of anatomical structures and significant available bone height where the other anterior teeth are present. Therefore, the use of longer implants that the height will accommodate can yield greater bone-implant contact, increasing the insertion torque and improving primary stability as well as functional load distribution during the early healing phase of treatment. In addition to being longer than a standard implant, the narrow-diameter implant used in the following case report has a neck that is narrower apical to the widest part of the restorative head, which results in thicker soft tissue for better stability of the gingiva long term, aids in maintaining the crestal position in relation to the implant on the vertical axis, and helps prevent gingival recession over time.
When an immediately placed anterior narrow-diameter implant is provisionalized, the temporary restoration should be kept out of occlusal contact, and the patient should be advised not to chew with his or her anterior teeth and to maintain a soft diet during the osseointegration period. Impressions for the final prosthesis can be performed after the soft tissue has been allowed to mature sufficiently to match the emergence profile of the implant and its provisional restoration. Typically, a period of 3 months is allowed for this and complete osseointegration to be achieved.
Case Report
A healthy 66-year-old male patient with a recently exfoliated left mandibular central incisor (ie, tooth No. 24) presented for a consultation for implant placement to replace the missing tooth. The patient indicated that the tooth had "fallen out" while he was showering. Prior to presenting, he had received treatment consultations at two other dental practices. The first dentist had recommended the extraction of tooth No. 25, followed by socket grafting and the placement of one standard implant between the edentulous sites of teeth Nos. 24 and 25. This area would then be restored with a 2-unit fixed prosthesis on the single implant. The other dentist had recommended extraction of the remaining mandibular incisors (ie, teeth Nos. 23, 25, and 26), followed by socket grafting, a 4-month healing period, and then placement of two implants at sites Nos. 23 and 26. These implants would then be restored with a 4-unit fixed prosthesis. The patient expressed that these two treatment plans that had initially been presented to him seemed extreme because they required the extraction of additional healthy teeth that demonstrated no mobility or clinical issues that he was aware of.
Examination and Treatment Planning
During the clinical examination, a narrow space of 3.5 mm was noted between the mandibular left lateral incisor (ie, tooth No. 23) and the right central incisor (ie, tooth No. 25) cervically. A CBCT scan was acquired to further evaluate the dimensions of the edentulous site. Using cross-sectional, coronal, and panoramic views of the site, it was determined that there was 4.5 mm between the buccal and lingual osseous limits of the space (Figure 1 and Figure 2). The adjacent incisors exhibited normal mobility, probing depths that were within normal limits, and no restorative issues. Following clinical examination and evaluation of the CBCT scan, a treatment plan was recommended that involved placing a one-piece, narrow-diameter implant that the space would accommodate, immediately placing a provisional restoration, and then fabricating and delivering a final restoration after a 4-month healing period to allow for osseointegration and soft-tissue maturation around the implant and provisional restoration. As an alternative treatment option, the patient was informed that a conventional 3-unit fixed prosthesis utilizing the adjacent natural teeth for support was also a possibility.
The current clinical findings and recommendations as well as the treatment recommendations of the prior two practices were reviewed with the patient. He agreed to implant therapy with a single narrow-diameter implant at the lost central incisor site that would not involve treatment of the adjacent teeth, and he was scheduled for implant placement with immediate provisionalization. Before the appointment ended, an impression of the patient's mandibular arch was acquired in order to fabricate a stent that would aid in the fabrication of the immediately placed provisional restoration at the surgical appointment.
Surgery and Provisionalization
The patient was instructed to premedicate with 2 g of amoxicillin 30 minutes prior to the surgical appointment. When the patient presented for the appointment, a consent form was reviewed and signed. Prior to the administration of a local anesthetic, the patient was instructed to rinse with a 0.12% chlorhexidine gluconate solution for 1 minute. Two cartridges of lidocaine hydrochloride 2% with epinephrine 1:100,000 were administered into the buccal vestibule to the left and the right of the planned surgical site and also into the lingual gingiva.
Once profound anesthesia was achieved, a 1.5-mm diameter lance pilot drill (HM Kit, Hiossen Implant) was used in a surgical handpiece with irrigation to create an initial osteotomy centered in the space mesiodistally and buccolingually to a depth of 13 mm (Figure 3). A 1.8-mm diameter twist drill (MH Kit, Hiossen Implant) was then used to depth to complete the osteotomy (Figure 4). Prior to implant insertion, a guide pin was inserted into the osteotomy, and a periapical radiograph was acquired to confirm that adequate bone was present between the osteotomy and the adjacent teeth (Figure 5). A one-piece implant with a 2.5-mm diameter and 13-mm length (MS SA Narrow Ridge, Hiossen Implant) was selected for this case and inserted utilizing the driver on the surgical handpiece until the unit torqued out at the set value of 40 Ncm (Figure 6). When the handpiece driver was removed from the mouth, it was noted that the implant was not fully in the osteotomy and that the cervical constriction below the abutment margin was positioned supracrestally (Figure 7). A hand wrench with a fixture driver was utilized to place the implant to the correct depth, positioning the abutment head's crown margin 1-mm to 2-mm subgingivally (Figure 8). A periapical radiograph was then acquired to document the implant's position and angulation relative to the anatomy and adjacent teeth as well as the position of the crown margin on the abutment head relative to the labial gingival margin.
To prevent the provisional restoration from locking onto the site during fabrication, a temporary filling material (Cavit™ W, 3M) was placed on the proximal, buccal, and lingual surfaces of both of the adjacent teeth to block out any undercuts (Figure 9). A composite instrument was utilized to develop the contour of the temporary material. Next, a vacuum-formed stent, which was made on a model created from the impression taken at the initial appointment with a denture tooth to fill the missing central incisor space, was filled with provisional acrylic resin (Protemp™, 3M) and inserted over the implant and adjacent teeth (Figure 10). Upon setting, the vacuum-formed stent was removed from the mouth and then the provisional restoration was removed from the stent. The temporary filling material was removed from the adjacent teeth utilizing a scaler.
To complete the fabrication of the provisional crown extraorally, it was seated on an implant analog, and a flowable composite resin (Revolution™ Formula 2, Kerr Corporation) in a matching shade was added to the cervical area to create a proper emergence profile with the crown margin of the abutment head (Figure 11). An acrylic bur was used to remove the proximal excess resin and develop the contours, and then after further contouring and polishing were performed, tints (Shade Modification Kit, SDI North America) were applied to the provisional restoration to esthetically blend it with the adjacent natural teeth, which were dark and affected by recession that had resulted in root exposure (Figure 12 and Figure 13). The provisional restoration was then tried in to verify complete seating over the abutment head portion of the one-piece implant. Following adjustments to ensure that the provisional restoration had light proximal contacts and was completely out of occlusion, it was cemented to the implant with provisional cement (Temp-Bond ™, Kerr Corporation). The excess marginal cement was removed with a scaler, and the occlusion was given a final check. Esthetically, the replication of the root contour and the custom staining on the provisional restoration allowed it to blend well with the adjacent teeth (Figure 14).
Restoration and Follow-up
After a 3-month period to allow the implant to osseointegrate and the soft tissue to mature to match the emergence of the implant abutment and provisional restoration, the patient was recalled to the practice. Radiographs were acquired to confirm integration, and the patient indicated that he hadn't experienced any sensation associated with the implant since placement. The provisional restoration was removed from the implant, and once any residual provisional cement was removed from the head of the implant, a plastic impression cap was seated onto it, and an impression was made of the full arch using medium and light body vinyl polysiloxane impression materials (Aquasil®, Dentsply Sirona). Next, an analog replicating the implant was inserted into the impression, and a soft-tissue material was injected around the cervical aspect of the analog to fabricate a soft-tissue model (Figure 15). The case was then sent to the laboratory for fabrication of a porcelain-fused-to-metal (PFM) final restoration with light occlusion.
When the final restoration was finished, the patient returned to the practice, and the provisional restoration was removed so that the final restoration could be tried in. The occlusion was checked, and the restoration was luted with a resin-reinforced glass-ionomer cement (GC Fuji PLUS®, GC America). With the aid of photographs that were sent along with the impressions, the laboratory was able to create crown esthetics that blended well with the adjacent teeth (Figure 16). A posttreatment CBCT scan was acquired to document the condition of the bone surrounding the implant, and sufficient bone was noted in all dimensions (Figure 17).
Subsequently, the patient was seen for routine recall appointments. A CBCT scan acquired 3 years after placement and restoration demonstrated maintenance of the crestal and buccolingual bone when compared with the levels at placement (Figure 18). At 10 years postplacement and restoration, a periapical radiograph demonstrated maintenance of the bone crestally with no observable change in the bone level in relation to the implant's neck when compared with the initial radiograph at the time of placement (Figure 19). The adjacent teeth also did not exhibit any bone loss following the 10-year period since implant placement. Regarding the esthetics, slight further recession was noted as well as minor darkening of the exposed root surfaces when compared with the simulated root recession of the implant restoration (Figure 20). The patient expressed that he was satisfied with the esthetics because his lip line prevented the cervical area of his anterior mandibular teeth from being visible during eating or talking. Despite the recession, the gingival tissue demonstrated an absence of inflammation, no bleeding upon probing was noted, and the area remained within normal limits.
Conclusion
The replacement of a single mandibular incisor with a conventional implant-supported restoration can be challenging due to the limited space available in the mesiodistal dimension. As an alternative to fixed prostheses involving the adjacent natural teeth, the use of a one-piece narrow-diameter implant that allows for sufficient spacing and surrounding bone should be considered to enable a fixed implant-supported approach. When the protocol demonstrated in the case report is followed as presented, the long-term stability of an implant-supported restoration in the anterior mandible as well as its associated hard and soft tissues can be achieved.
About the Authors
Eugene Kim, DDS
Private Practice
Buena Park, California
Gregori Kurtzman, DDS
Master
Academy of General Dentistry
Diplomate
International Congress of Oral Implantologists
Private Practice
Silver Spring, Maryland
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