Congenital absence of one or more teeth (hypodontia) is the most common developmental dental anomaly in humans. The prevalence of hypodontia has been reported to range from 2.3% to 10.1%.1 As early as 1936, Werther and Rothberg found 2.3% of 1,000 schoolchildren to be missing 1 or 2 teeth.1 In their study, the maxillary lateral incisor was most frequently absent. More recent studies have indicated the prevalence of hypodontia to be approximately 5%, with the maxillary lateral incisor being the second most common missing tooth (the mandibular second premolar was most often absent).1 It is also noteworthy that missing teeth occur more frequently in females.2 At present, the etiology of this condition, as well as any genetic and environmental influences, are not known.2
This paper will review the available treatment options to replace congenitally missing maxillary lateral incisors and present a case report to illustrate a therapeutic approach.
TREATMENT OPTIONS FOR CONGENITALLY MISSING PERMANENT LATERAL INCISORS
Fixed Partial Dentures
Conventional crown and bridge treatment offers many advantages as a therapeutic choice for tooth replacement. In reference to an implant approach, a fixed partial denture does not require an implant surgical phase. Therefore, the treatment time is considerably less than what is required for implant-based treatment. Further, this approach can be comparatively cost-effective, unless replacement of the prosthesis is required at a later date. With the advent of pressed glass and hybrid bridges, patients can expect excellent aesthetic results.
However, there are disadvantages. If the proximal teeth have not previously been restored, the preparation of such teeth is of concern. The preparation of unaffected teeth invites a multitude of future periodontal and endodontic problems. One study that followed the periodontal and pulpal condition of abutment teeth over an 8-year period found that teeth that had received full crown restorations demonstrated both higher plaque indices and probing depths than non-crowned teeth.3
In a 15-year clinical and radiographic follow-up of dental bridges, Valderhaug and Ellingser revealed that caries was present in 10% of cases at 10 years, and there was an increased frequency of damage to periodontal tissues when compared to pretreatment indices.4 Bergenholtz and Nyman reported that up to 15% of abutment teeth lost their vitality 8 to 11 years after receiving dental bridges.3 Therefore, evidence indicates that preparing virgin teeth for fixed replacement increases the risk for caries, pulpal involvement, and periodontal pathology when compared to unprepared teeth. Although conventional crown and bridge has many clinical applications, there are significant disadvantages associated with its use to restore missing maxillary lateral incisors where the space is bounded by virgin teeth. In addition, if only one lateral incisor is missing, acceptable aesthetics of a unilateral fixed partial denture presents a challenge to the clinician.
Resin-Bonded Fixed Partial Dentures
Resin-bonded fixed partial dentures (RBFPD) date back to 1973. These prostheses consisted of 1 or 2 porcelain or acrylic teeth held in place by at least 2 metal wings chemically bonded to the lingual surface of the adjacent teeth. The literature reveals 2 distinct categories of clinical trials involving RBFPDs: those with original designs and more recent studies on improved or modified designs. A study of 203 resin-bonded bridges over a 5-year period found 47 dislodgements and 30 pontic fractures.5 One of the advantages of a resin-bonded bridge is that the restoration can be rebonded. However, a study by Creiger revealed that rebonded resin-bonded bridges were more susceptible to dislodgement than original bonded resin-bonded bridges; 57% dislodged within 3.7 years.5 Common problems with the early designs include debonding, poor aesthetics, and technique sensitivity. Recent clinical trials have indicated a need for a retentive preparation of the abutment teeth.6
The use of nonprecious alloys, which are more amenable to chemical bonding with some resin cements, has improved the survival rate.6 An overall success rate of 75% to 80% at 6 years has been reported.7 A study by Leibrock and colleagues examined 120 RBFPDs. They found that the preparation of retentive grooves and pinholes resulted in a 95% survival rate after 10 years.7 The retentive preparation form in this study consisted of at least one proximal seating groove and a pinhole at least 1.0-mm deep in each abutment tooth.
In the case of resin-bonded retainers, an argument can be made for their use when replacing missing maxillary lateral incisors. If the use of pins and grooves are employed, they can be considered as preferred over fixed partial dentures. Nevertheless, the best results reveal a 95% success rate over 10 years. Most patients with congenitally missing lateral incisors seek definitive treatment in their late teenage years. Recent statistics reveal the average life expectancy in the United States is 78 years.8 This would imply 3 to 6 additional restorations over a patient's lifetime—all containing pins and grooves if maximum success is desired.
Fiber-reinforced composite bridges. During the past decade, fiber-reinforced composite bridges have emerged as an alternative for tooth replacement. Advantages include excellent aesthetics, minimal wear of the opposing dentition, and relatively conservative tooth preparation. The materials used for these restorations consist of glass fibers that are either preimpregnated with a resin matrix (eg, Targis Vectris, Ivoclar Vivadent or Sculpture Fibrekor, Pentron Laboratory) or nonimpregnated utilizing a substructure of either a polyethylene weave (Ribbon Connect, Kerr) or a glass weave (Glass Span).
A recent study by Frelich, et al9 reviewed 39 fiber-reinforced composite bridges and found that 95% of the prostheses survived a mean of 3.75 years. The 5% that didn't survive either debonded or sustained a fracture of either the veneer or the framework. Here, the authors noted that one indication for fiber-reinforced composite bridges is when the abutment teeth have minimal or no restorations. Although it is clear that fiber-reinforced composite bridges can provide a desirable aesthetic outcome, and cause minimal wear of the opposing dentition, the disadvantage is that tooth structure is sacrificed for a restoration that will last an average of 3.75 years.
Orthodontic Space Closure
Orthodontic space closure is another possible treatment modality for missing maxillary lateral incisors. This approach has both advantages and disadvantages.
The most obvious advantage of this approach is eliminating the need for lifelong maintenance of a fixed restoration as well as the aforementioned consequences of preparing unrestored abutment teeth. Implant surgery is also not needed. Other advantages include the permanent nature of the completed treatment and the avoidance of interim provisional partial dentures.
There are also disadvantages of orthodontic treatment. Following treatment, there is a tendency for the space between the anterior teeth to reopen.10 When the occlusion permits, this is treated with palatally bonded retaining wire. In addition, cuspid-protected occlusion is eliminated, thus placing forces on the shorter and thinner roots of the first premolar.11 The major disadvantage of this treatment approach relates to the positioning of the maxillary cuspid tooth in the lateral incisor position. Cuspids have many forms, from blunt trapezoid to conical shapes.12 Sometimes the cuspid tooth requires only minor adjustment, and an aesthetic result can be achieved. However, other times adjustment of the shape of the cuspid tooth is not sufficient, and adjacent teeth require either veneers or bonded restorations. There is also a color difference among maxillary cuspids, maxillary central incisors, and mandibular incisors
Despite these disadvantages, orthodontic space closure is second to implant therapy as the preferred approach in the treatment of missing maxillary lateral incisors. Furthermore, orthodontic therapy is often beneficial in conjunction with subsequent implant therapy.
Osseointegrated implants have revolutionized the restoration of edentulous and partially edentulous patients, including individuals who are congenitally missing maxillary lateral incisors. There have been many studies of single-tooth implants. A series of reports from 1991 through 1996 revealed a success rate of 97.2% at 5 years.13
The advantages of this approach have previously been discussed. They include longevity, preservation of adjacent teeth, aesthetics, and cost of the treatment if assessed over time.
However, there are contraindications to implant treatment for replacement of congenitally missing maxillary lateral incisors. A common complication is malpositioned roots of the proximal teeth. This often requires that orthodontic treatment be performed before im-plant placement. Ideally, to ac-commodate the implant a mesiodistal distance of 6 mm between the roots of the maxillary central incisor and cuspid is needed. Consequently, smaller-diameter implants are often used, requiring overcontouring of the facial emergence profile.14
Time is also a factor when considering implant therapy, since it may take 5 to 7 months to place and restore the implant. In response, current studies and reports are investigating immediate loading of implants, which would shorten treatment time. Another drawback to implant therapy often not considered is that the consequences of failure are greater than for a conventional crown and bridge approach. Implant failure often results in bone loss, necessitating bone grafting and retreatment at significant additional cost.
Despite the shortcomings of implant therapy, it has emerged as a conservative and predictable method for replacing missing congenital lateral incisors. The following case report illustrates this treatment.
|Figure 1. Pretreatment condition.|
A 17-year-old female patient with no medical contradictions presented for replacement of the maxillary left lateral incisor (Figure 1). The patient had recently completed orthodontics, and the adjacent teeth were in ideal position. There was 7.0 mm between the left central incisor and cuspid. An implant was selected to replace the lateral incisor.
|Figures 2 and 3. Panoramic radiograph and preoperative model.|
Preoperative models were mounted and a panoramic radiograph was taken (Figures 2 and 3). The adjacent teeth were evaluated for tooth and root alignment and the position of the cementoenamel junction (CEJ). Ideally, the implant would be placed to a point 0.5 mm above the osseous crest; this bone level would be 1 to 2 mm below the facial CEJ of the adjacent teeth.15
An antibiotic regimen of amoxicillin 500 mg, 1.5 mg dexamethasone, and 600 mg ibuprofen was prescribed to be taken an hour before implant surgery.
In a young person, proper timing of implant placement is important. There is a danger in placing implants too early in development. Unlike teeth, implants are not capable of compensatory eruption and actually behave like ankylosed teeth.16 If growth of the maxillary and mandibular arches occurs after implant placement, infraocclusion of the implant will result, with concurrent soft-tissue complications such as chronic inflammation. There is general agreement that implant placement should be delayed until after puberty, when growth and skeletal development are complete.17
Flapless Versus Conventional Flap Access
When placing implants, one consideration is whether to gain access using a mucoperiosteal flap. Under traditional implant guidelines, the soft tissue is reflected first and the bone is then prepared to receive the implant, with consideration of implant length and width. Flapless surgery involves no elevation of soft tissue. Rather, a punch is utilized at each planned implant site. Using a single-stage approach, implants are placed so that either a healing cap or a temporary abutment with an immediate provisional crown emerges from the soft tissue. A second surgical exposure is not required. If patient selection and surgical technique are appropriate, flapless surgery has a number of inherent advantages. Leaving the periosteum intact on the buccal and lingual aspects of the ridge maintains a better blood supply to the site, thus reducing the likelihood of resorption.18 In addition, the procedure requires less time, eliminates the need for sutures, and there is less postoperative discomfort. In a 10-year retrospective analysis, the cumulative success rate for flapless, single-stage surgery improved from 74.1% in 1990 to 100% in 2000.19
The 17-year-old patient in this study was an excellent candidate for flapless surgery. The quantity and morphology of the bone were assessed preoperatively using a panoramic radiograph, digital palpation, and bone sounding. The ridge should be evaluated at both the top of the ridge and at the apex. If undercuts greater than 15° are present, traditional flap reflection is recommended.20 Also lending support to the flapless approach was the fact that the patient had significant keratinized tissue. At least 5.0 mm of tissue is desired, since the flapless procedure results in removal of a portion of the attached gingiva.20
|Figures 4 and 5. Tissue punch and 15c Bard-Parker blade used to remove keratinized plug.||Figure 5.|
|Figure 6. Osteotomy with flapless surgery.||Figure 7. Directional indicator.|
|Figure 8. Final placement of the implant is 0.5 mm above the aveolar crest.||Figure 9. 3.5 x 16.0-mm Replace Select tapered implant.|
|Figure 10. Radiograph following implant placement.|
This patient had no undercuts of the alveolar ridge. After administering local anesthesia (lidocaine HCL with 2% epinephrine 1:100,000), a tissue punch was employed along with a 15c Bard-Parker blade and a curette to remove the soft-tissue plug (Figures 4 and 5). An osteotomy was performed using a No. 3 round bur, a pilot drill, and a 3.5 implant drill (Figure 6). In an effort to prevent a perforation or impingement of the adjacent root structures, a directional indicator was used prior to the final implant drill (Figure 7). The implant was then inserted 0.5 mm above the osseous crest (Figure 8). The implant was a 16-mm 3.5 Hacoated Replace Select tapered implant (Nobel Biocare, Figure 9). A postoperative panoramic radiograph was taken to verify proper implant placement and to assess the relationship of the implant to surrounding structures (Figure 10).
The patient was instructed to rinse with chlorhexidine for 30 seconds twice a day for 2 weeks.
Immediate Loading Versus 2-Stage Therapy
One consideration in implant therapy is when to load the implant being placed.
The traditional 2-stage surgical approach to implant therapy separates placement and loading of the implant by 3 to 6 months. The reasons cited for this approach include the following: (1) to minimize bacterial infection, (2) to prevent apical migration of oral epithelium, and (3) to reduce early implant loading during bone remodeling.21
Patients with missing anterior teeth have aesthetic considerations. Most of these patients present with some form of tooth replacement, ranging from resin-bonded bridges to a removable prosthesis. It would clearly be beneficial to these patients if they could leave the implant placement visit with a provisional crown. This provisional restoration often can be a problem. From debonded resin bridges to poor aesthetics associated with a removable prosthesis, the patient in this case had not been happy with the temporary restorative options.
In recent years, several studies on immediate loading of implants have demonstrated that it is possible to achieve success comparable to the classic 2-stage approach. One study re-ported a survival rate of 95.7% of immediate loading of implants placed in the aesthetic zone.22 Another study revealed a 96% survival rate at 1 and 2 years. All failures occurred in fresh extraction sites.23 Combined data from 6 studies with a total of 1,046 immediately loaded implants demonstrated a survival rate of 98.0%.24 It is noteworthy that the implants in these studies were only evaluated from 1 to 3 years. The early findings suggest that once immediately loaded implants integrate, they appear to have long-term bone loss and soft-tissue stability comparable to conventionally loaded im-plants.24 There remains a paucity of long-term data on immediately loaded implants. All studies recommended maximization of implant stability by using longer implants and eliminating occlusal contact in centric and excursive movements.24
Several requisites for immediate load have emerged. Specifically, the candidate must have the following:
• excellent bone quality—D225 (dense to porous cortical bone on crest and coarse trabecular bone within)
• adequate width and height of the implant, ideally 13 to 16 mm in length and 3.8 mm in diameter
• sufficient keratinized soft tissue
• adjacent teeth that can absorb occlusal forces and protect the healing implant during function.20
|Figure 11. Preprepared temporary abutment.||Figure 12. Provisional restoration at 10 days.|
All of these requirements were present in this case. Following implant placement, an appropriate implant abutment was selected and prepared outside the mouth, and an acrylic provisional restoration (Luxatemp, DMG) was fabricated using a Nobel Biocare temporary abutment (Figures 11 and 12).
Impression and Final Restoration
Eight weeks were allowed before taking a final impression. The implant was clinically and radiographically evaluated for osseointegration and absence of soft-tissue complications. A proper emergence profile had been developed by the provisional restoration.
|Figure 13. Lava zirconia abutment.|
The impression was made using a polyether material (Impregum, 3M ESPE) in a custom closed tray. A custom abutment was fabricated using Procera Scanned Zirconia (Nobel Biocare, Figure 13). A coping was fabricated with Lava Zirconia (3M ESPE) and layered with porcelain (Noritake).
Cement Retention Versus Screw Retention
|Figure 14. Final restoration.|
There are different opinions concerning how to retain the implant crown. Clinicians who favor screw-retained crowns compromise occlusion and aesthetics for retrievability.26 As the survival rate of implants has dramatically risen, the issue of retrievability has become less important. The absence of screw holes with a cemented prosthesis increases the strength of the porcelain, resulting in fewer fractures.26 Occlusion can be developed with greater attention to function. Furthermore, a cemented prosthesis costs less, is less complex from the laboratory perspective, and is more accessible for cleansing (Figure 14).
It has been demonstrated that an increase in surface area and height increase retention and resistance forms.27 On occasion, the clinician encounters limited abutment height due to limited interocclusal space. This compromises surface area and consequently the effectiveness of the cement, and can be a contraindication to a cement-retained implant crown.
There are several treatment modalities available to replace missing maxillary lateral incisors. Each of them has inherent advantages and disadvantages. All should be considered when evaluating a patient.
In general, 3 pretreatment conditions require consideration when treatment planning the replacement of maxillary lateral incisors.
Proximal Teeth That Are Heavily Restored
When the clinician is faced with multiple pre-existing restorations on adjacent teeth, the use of conventional fixed partial dentures or orthodontic space closure would emerge as favored treatment modalities.
Proximal Teeth With Minimal Restorations
In this situation, the use of RBFPD (with pins and grooves) or hybrid bridges would be prudent.
Proximal Teeth With No Restorations
Minimal invasion of unrestored teeth to accomplish tooth replacement is a treatment goal of all practitioners. Therefore, orthodontic space closure or implant therapy would receive first consideration as treatment options.
In addition to proximal tooth conditions, patient-specific conditions will influence treatment planning. For example, patients with unrestored proximal teeth may not approve a surgical procedure or may decline pretreatment orthodontic therapy to align converging roots. Conversely, a patient who may seem well-suited for a 3-unit bridge may oppose splinted teeth of any kind and choose implant therapy. Therefore, there will be instances where a clinician could recommend 2 different treatment plans for identical clinical scenarios due to nonclinical factors. For this reason, when treatment planning for missing teeth, the pretreatment work-up should be thorough and fully documented.
The predictability of implant therapy has revolutionized how clinicians treat a wide array of tooth replacement situations, including the problem of a congenitally missing maxillary lateral incisor. Although a number of therapeutic alternatives should be considered, treatment with implants allows the clinician to avoid the preparation of adjacent teeth and provides a predictable and enduring solution to the clinical problem.
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25. Misch CE. Contemporary Implant Dentistry. 2nd ed. St Louis, Mo: Mosby; 1999:113.
26. Hebel KS, Gajjar RC. Cement-retained versus screw-retained implant restorations: achieving optimal occlusion and esthetics in implant dentistry. J Prosthet Dent. 1997;77:28-35.
27. Kaufman EG, Coelho DH, Colin L. Factors influencing the retention of cemented gold castings. J Prosthet Dent. 1961;11:487-502.
The author would like to acknowledge the contributions of Steve Hedquist, Tauni Jansen, and Pete Hemstock from Valley Dental Laboratory.
Dr. Rasner is a general practitioner in Bridgeton, NJ. He can be reached at (800) 337-8435 or realizing-the-dream.com.