CC

The patient states, “I need to have two teeth on the lower right evaluated for possible removal and implants.”

HPI

The patient is a 66-year-old female with stable moderate periodontitis. Previously treated with periodontal therapy, she is now managed by her general dentist and home care. Despite this management, her disease has progressed on the teeth on the lower right (teeth #29 and #30) and have become mobile. Her general dentist has deemed the prognosis for these teeth to be hopeless and has recommended removal with replacement with two dental implant–supported prostheses.

PMHX/PDHX/medications/allergies/SH/FH

The patient has a noncontributory medical history, including an unremarkable heart murmur, osteoarthritis, osteoporosis, and osteopenia. She denies the administration of a bisphosphonate or receptor activator of nuclear factor-κB ligand (RANKL) inhibitors. There is no history of smoking or bruxism or parafunctional habits. The only medications that she takes are supplements (calcium, vitamin D ₃ , and collagen peptides). She is allergic to latex and codeine.

Examination

Clinical examination revealed no associated temporomandibular joint dysfunction. Intraoral examination of the posterior mandible grossly demonstrates good ridge form buccolingually, which is rounded and wide (6–8 mm). However, a composite hard and soft tissue defect was appreciated consistent with vertical bone loss, which was later noted on imaging. A periodontal evaluation showed probing depths measured at 1 to 2 mm with moderate dental mobility (class I/II) of both teeth, and a class 2 furcation defect was clinically appreciated on tooth #30. Dental tissue loss was noted as toothbrush abrasion and attributed to aggressive hygiene techniques and root surface exposure. A sound opposing dentition and a level occlusal plane were noted. The anteroposterior (AP) ridge space is adequate for placement of two implants to replace the lower right second bicuspid and first molar. This is determined by consideration of the following biologic parameters for dental implant placement. The distance from an implant to an adjacent natural tooth and between adjacent implants at the coronal–crestal aspect should be 2 mm and 3 mm, respectively. Planning should allow for buccal bone thickness of least 2 mm and lingual bone thickness of 1 mm (implant diameter + 3 mm). Greater buccal bone is desirable because of greater resorption patterns on the buccal aspect. To maintain a margin of safety, the apical extent of the implant should be planned no closer than 2 mm from the inferior alveolar nerve (IAN). No other soft tissue or bony abnormalities are noted, and the patient opens 45 mm. (Restricted mouth opening can pose a problem for implant placement.) Diagnostic casts or stereolithographic models can aid in determining arch relationship, occlusal discrepancies, occlusal plane curves, tooth position, and adequacy of vertical and horizontal space for prosthetic components.

Imaging

The preoperative planning radiography shows that the proposed implant sites as 8.5 mm wide in the buccolingual dimension ( Fig. 32.1 ) with the apex of the implant placement approximately 7 mm above the inferior alveolar neurovascular bundle and the center of the implant in line with functional cusp of the opposing tooth ( Fig. 32.2 ). The distal implant (site #30) is planned slightly mesial to maintain a distance from the vertical defect on tooth #31. There is 3.44 mm of interimplant distance planned ( Fig. 32.3 ). The AP space availability measures at 19.82 mm, which allows comfortable placement of two 5-mm diameter implants when all other parameters are accounted for ( Fig. 32.4 ). The bone quality is type II ( Box 32.1 ).

Preoperative cone-beam computed tomography scan (coronal cut) showing an alveolar width of 8.5 mm in the buccolingual dimension at the proposed implant site.

Preoperative cone-beam computed tomography scan (coronal cut) showing a distance of 7 mm between the apex of the proposed implant and the inferior alveolar canal cortex. The proposed implant is also aligned with the functional cusp of the opposing tooth.

Preoperative cone-beam computed tomography scan (sagittal cut) showing appropriate placement of both implants in the mesiodistal dimension with maintenance of the appropriate interimplant distance and accounting for the vertical bony defect mesial to tooth #31.

Preoperative cone-beam computed tomography scan (axial cut) showing an anteroposterior distance of 19.82 mm and thus allowing for appropriate placement of two 5-mm-diameter implants.

These data can be used for surgical guide fabrication or for intraoperative measurements if a free-handed approach is used. A surgical guide can be generated from the data contained in the cone-beam computed tomography (CBCT) if the surgeon thinks it is necessary, and instrumentation keyed to this guide can be applied for precision placement; otherwise, a surgical guide is prepared on the study models. Panoramic two-dimensional (2D) radiography and bone mapping can be used in situations in which the tip of the implant is estimated to be greater than 1 mm from the IAN canal provided that the canal is radiographically identifiable, patient positioning is correct, and the magnification rate is known and accounted for.

Labs

No laboratory testing is indicated for implant placement unless dictated by the medical history or anesthesia concerns.

Assessment

A 66-year-old female with osteopenia and osteoarthritis presents with moderate periodontal disease with severe abrasion lesions necessitating removal of the lower right second bicuspid and first molar. Treatment options discussed include no replacement versus fixed partial denture versus dental implant therapy with osseous grafting for ridge regeneration.

Treatment

The patient elected to undergo extraction of the two teeth with site regeneration with corticocancellous allograft. Guided bone regeneration was accomplished with amnion–chorion membrane and a collagen plug. This was allowed to heal for a period of 14 weeks at which time the patient returned for a repeat computed tomography scan and implant placement. Local anesthesia was delivered, and a bite block was used to maintain adequate opening and provide support for the temporomandibular joint (TMJ) and masticatory muscles. A crestal full-thickness mucoperiosteal incision was made from the mesial of tooth #31 to the distal of tooth #28 and then in the intrasulcular space buccally to the interdental papilla between the canine and first bicuspid. A full-thickness flap was reflected sufficient to visualize the bony ridge and appreciate the buccal and lingual cortices. A vacuum-formed template of an anatomic wax-up was used to ensure that the spacing of the implants would correspond to the clinical crowns. Spacing and paralleling of the implants was accomplished using a paralleling guide pin system, which allowed for control of spacing in addition to paralleling. The osteotomies were performed using manufacturer specific protocols under irrigation with normal saline. Type 2 (D2) bone was encountered in the posterior mandible. Tissue-level implants were used to position the abutment implant interface away from the bone margin to minimize future crestal bone loss. Closure screws were placed on the implants, and the tissue was closed around the neck of the implant using 3-0 chromic gut suture. Postoperative radiography with a periapical radiograph was taken to verify spacing and positioning of the implant. The patient was sent home with instructions to use over-the-counter pain medication for postoperative pain management and amoxicillin 875 mg twice a day for 7 days as a prophylactic measure. The patient returned to the office in 3 months for uncovering of the implants, and verification of osseointegration was accomplished with a torque challenge to 50 Ncm of torque. A periapical radiograph was taken at this time to identify any osseous abnormalities or marginal bone loss that may have occurred.

Surgical complications

The success of an endosseous dental implant is dictated by several factors, including its stability, functionality, and esthetics. In the era of three-dimensional (3D) imaging, virtual surgical planning, and guided implant surgery, the success rate for implant placement is high. Despite these advances, complications can still occur, and it is important to be aware of the pitfalls and know how to manage them.

Early implant failure is often associated with a lack of primary stability, which may occur either at the time of surgery because of poor placement (e.g., insufficient bone stock) or over the ensuing postoperative days because of early loading protocols, surgical trauma (e.g., overheating of the osteotomy site), or infection. Most infections can be managed conservatively with antibiotics, debridement, or incision and drainage. Implant removal should be reserved as a last resort.

Late implant failure is most frequently a result of occlusal overburden and peri-implantitis. Other complications that may occur independent of the site of placement include fibrous integration, buccal cortex dehiscence, and damage to adjacent teeth and implants. Aspiration or swallowing of implant components is also a procedural concern; the use of floss ligatures and oral packings can help to minimize this risk.

The posterior mandible poses unique challenges for implant placement based on its anatomy, proximity to vital structures, and relatively difficult access. Understanding the anatomy and accounting for all dimensions during placement are crucial for obtaining excellent outcomes.

The foremost limiting factor for placement of implants in the posterior mandible is the available height of bone above the inferior alveolar canal (IAC). Impingement of the IAN can lead to hypoesthesia or anesthesia. It is generally agreed that 2 mm or more should remain between the implant and cortical border of the canal. If a patient experiences neurosensory changes immediately within the postoperative period (after local anesthesia has subsided), the implant should be backed out as soon as possible or removed and replaced with a smaller implant. In questionable cases, CBCT can be used to assess the distance between the implant and IAC to determine the need for intervention. Panoramic radiography is not sensitive enough to rule out spacing issues because of distortion and superimposition of nearby structures.

The inferior alveolar artery also resides within the IAC and is typically positioned superior to the namesake nerve. Damage to the artery alone may lead to a hematoma within an enclosed space and subsequent damage to the IAN. It is important to remember that damage to the IAC and its contents can be caused by the osteotomy drill or by the implant itself if submerged too apically. Implant guides and drill stops are useful tools for controlling the depth of the osteotomy. If there is an insufficient height of bone to support an implant, ridge augmentation or nerve repositioning could be considered, although these procedures also carry a risk of neurosensory changes. Providers must also be cognizant of the path of the lingual nerve and ensure minimal or careful elevation of the lingual tissue in the posterior mandible.

Another anatomic feature of the posterior mandible complicating implant placement is the presence of a lingual undercut. This lingual concavity varies in severity but is present in most of the general population, with the highest frequency occurring in the second molar region. Also, the edentulous posterior mandible tends to resorb in a buccal-to-lingual fashion. Both anatomic constraints require that the apex of the osteotomy be angulated buccally. Failure to consider these factors may lead to perforation of the lingual cortex with the potential for subsequent hemorrhage, salivary gland injury, and infection. An extruded implant can also act as a source of constant tissue irritation. Shorter tapered implants can be helpful in avoiding perforations while also ensuring that the implant is not excessively angulated, thus complicating restoration and function.

Discussion

A number of factors need to be considered before placement and restoration of a mandibular implant. A problem-focused examination, highlighted in this chapter, focuses on the area of interest. However, an examination of the entire oral cavity should be performed to identify patterns for failure or the presence and extent of disease processes. A comprehensive clinical examination includes the clinician considering TMJ function, evidence of parafunctional behavior, periodontal status, and occlusion.

Both the quality and quantity of bone must be considered for successful implant placement. Historically, implant surgery has been planned using 2D panoramic radiography with a surgical planning template coupled with bone-mapping techniques. A far simpler and more accurate methodology involves CBCT. The advent of cone-beam technology affords the clinician accurate 3D data with minimal distortion and is currently the imaging of choice for implant planning and placement. Surgical planning software may be used to simulate implant and restoration position to verify adequate bone volume restorative requirements in the preoperative workup.

Beginning with the end in mind will help to identify potential pitfalls before they occur. Hence, prosthetically driven surgery should be in the forefront of the clinician’s mind when beginning any implant treatment plan. Surgical guide options are operator dependent. A vacuum-formed template created over an anatomic wax-up was used in this case. This can be accomplished with diagnostic models and a wax-up of the proposed locations of the teeth. A vacuum-formed template can be created over this and then used intraoperatively to position the implants relative to the proposed locations of the crowns. Although a surgical guide is not essential, it does help to idealize the placement of the implant with respect to the digitally planned position of the crown. Similarly, a static printed surgical guide with or without metal guide sleeves, dynamic navigation, and robotic-assisted surgery may also be used.

Marginal bone loss on implants is a common phenomenon. To minimize bone loss on adjacent structures, a minimal distance from implant to adjacent structure should be maintained. A minimum distance of 3.0 mm from implant to implant and 2.0 mm from implant to natural adjacent tooth at the ridge crest are recommended for optimal hard and soft tissue preservation.

Interarch space requirements (osseous ridge to opposing occlusal surface) should be considered as well with the optimal vertical restorative space being 9 to 10 mm in the posterior regions. Restorative space should consider soft tissue thickness, as well as abutment height and prosthetic crown space requirements. Factors such as dental attrition, which can result in loss of vertical dimension of occlusion, and supereruption of the opposing tooth should be considered in the examination because they may encroach on vertical restorative space and result in restorative complications. If interarch restorative space is limited, restorative challenges may be mitigated by selecting a bone-level restorative platform instead of a tissue-level restorative platform to increase the amount of space available for the abutment–crown complex.

The severity of periodontal disease influences implant survival. Chronic stable periodontitis is not a contraindication to dental implant therapy; however, a maintenance program for the patient must be considered to maintain disease control especially if disease persists in areas adjacent to the implant sites.

Implant reconstruction in the posterior mandible is often complicated by the angulation of the body of the mandible or loss of alveolar housing, which can cause an excessive lingual or buccal angulation of the implant. Socket grafting of the site restores the alveolar contours, and prosthetically guided surgery can aid in placing the screw channels in the central fossa of the mandibular teeth, eliminating the loss of cuspal anatomy. Another complicating factor is the positioning of the IAN and the emergence of the mental nerve, which may cause an implant to be placed in a suboptimal position to avoid this structure. These situations are compensated for by overcontouring the crown to maintain contacts; however, excessive cantilevers are to be avoided to maintain healthy peri-implant tissues and prevent material fractures or screw loosening. Placing the implant too deep or shallow compared with the alveolar margin to avoid the IAN can pose restorative challenges as well. Implants that are placed too apically can be restored with an elongated abutment to compensate for this; however this comes at the risk of a possible misfit at the implant-abutment interface and bone loss. Implants placed too coronally likewise risk excessive loss of marginal bone because of the contact of the soft tissue with the roughened surface of the implant.

Materials commonly used for posterior fixed reconstruction are ceramo-metal or zirconia-based alternatives. Both materials exhibit the strength and esthetics to adequately restore posterior single or multiple teeth cases and allow for a well-fitting screw retained restoration to manufacturer supplied abutments. An alternative is a customizable abutment with a machined implant contact and customizable coronal portion that can be used for screw-retained or cementable crowns.

Host factors such as smoking are known to increase the risk of failure of dental implants. Smoking provides an anaerobic environment that facilitates the growth of periodontal pathogens and contributes to attachment loss. Consequently, smokers have a greater than twofold increase in marginal bone loss, postoperative infections, and implant failure compared with nonsmokers.

Immune cell function plays a vital role in integration and maintenance of implanted medical devices. Vitamin D is a potent immunomodulator. Vitamin D supplementation in patients who are known to be vitamin D deficient can reduce the risk of failure because low vitamin D levels have been correlated with early implant failure. This patient with a history of osteopenia and osteoporosis is currently supplementing her vitamin D with oral daily intake, a favorable step towards successful implant treatment.

There are no standardized protocols for prescribing antibiotics in the pre- or postoperative period for dental implant surgery. Antibiotic resistance and other complications related to disruption of gut flora must be considered when determining the duration and type of antibiotic to be used. Based on recent data, there have been shown to be improved clinical outcomes, specifically lower implant failure rates, when patients are administered a single preoperative dose of antibiotics. Although penicillin and penicillin derivatives are the most administered antibiotics for dental implant surgery, the data are inconclusive about which antibiotic provides the most benefit.