|Year : 2014 | Volume
| Issue : 1 | Page : 58-62
The mandibular two-implant overdenture
Abu-Hussein Muhammad1, Azzaldeen Abdulgani2, Musa Bajali3, Chlorokostas Giogrges4
1 Visiting Professor, Napoli University, Italy and University of Athens, Greece
2 Department of Conservative Dentistry, AlQuds University, Jerusalem, Palestine
3 Department of Periodontology, AlQuds University, Jerusalem, Palestine
4 Implantogist, Private Dentistry, Athens, Greece
|Date of Web Publication||6-May-2015|
Dr. Abu-Hussein Muhammad
123 Argus Street, 10441 Athens, Greece
Source of Support: None, Conflict of Interest: None
Successful treatment with the two-implant overdenture has been documented with multiple implant designs (e.g., hexagonal, Morse taper, internal connection) and many implant systems. Clinicians may select implants for retention of the two-implant overdenture according to personal experience and preference with confidence that treatment success will not be determined by the selection made. This is due primarily to the anatomy and density of the bone in the anterior mandible. The aim of this case report is to demonstrate the concept of immediate functional loading in the mandible using unsplinted implants to support a locator attachment supported overdenture.
Keywords: Freestanding implants, immediate loading, locator, mandibular overdenture
|How to cite this article:|
Muhammad AH, Abdulgani A, Bajali M, Giogrges C. The mandibular two-implant overdenture. J Dent Allied Sci 2014;3:58-62
|How to cite this URL:|
Muhammad AH, Abdulgani A, Bajali M, Giogrges C. The mandibular two-implant overdenture. J Dent Allied Sci [serial online] 2014 [cited 2020 Jan 29];3:58-62. Available from: http://www.jdas.in/text.asp?2014/3/1/58/156537
| Introduction|| |
Dental implants are prosthetic devices, made of alloplastic materials that are inserted into the oral cavity to provide retention and support to removable and fixed dental prostheses. , The concept of using implants to replace teeth is age old. In fact, in ancient history thousands of years ago, ivory teeth were used as implants in Egyptian mummies. However, the era of modern dental implantology began much later, in the 1940's, with the discovery of screw type implants by Formiggini et al. , The introduction of the concept and the biology of osseointegration, by Brånemark et al., added another milestone in the history of dental implantology.  Over the years, this field has significantly evolved and emerged as an extensively used treatment modality for oral rehabilitation.
The first clinical outcome of surgical procedure is the primary stability of the implant. Primary stability is rigid fixation and lack of micro motion of the implant into the bone cavity. ,, The absence of stability can lead to excessive mobility and cause fibrous tissue formation around the implants inhibiting osseointegration. , Primary stability depends on the surgical technique, implant design, and the implant site. ,,
Bone tissue is arranged in two macro architectural forms, trabecular or cancellous and cortical or compact. Leckholm and Zarb (1985) have classified bone types in the oral cavity, depending on the relative proportions of cancellous and cortical bone:
- Class I: Predominantly cortical.
- Class II: Thick layer of compact bone surrounding a dense cancellous core.
- Class III: Thin layer of compact bone surrounding a cancellous core.
- Class IV: Very thin compact layer around a low-density trabecular bone.
Sennerby et al. compared implants placed in rabbit cortical versus cancellous bone and established that cortical bone has a higher modulus of elasticity, is harder to deform and provides greater resistance to the motion.  Hence, Class I and Class II bone would facilitate higher primary stability.
The original protocol for loading, as described by Brånemark et al., involved waiting for 3 months (for mandible) to 6 months (for maxilla) after implant placement. Such a delayed loading protocol was aimed at allowing undisturbed healing and complete osseointegration before implants could be loaded. For a long time, it was assumed that premature loading would limit peri-implant osteogenesis and induce fibrous tissue formation. ,
Schnitman et al. introduced the concept of immediate loading, which has been described as attachment of the prostheses within 24 h to 1-week after implant placement. , Some of the advantages of immediate loading are shortened treatment time and early functional, physiological and psychological rehabilitation of the patient. In addition, there have been some claims made about a biologic advantage in the form of enhanced osteoblastogenesis with immediate loading. An in-vivo study by Qi et al., evaluated the response of mesenchymal stem cells to mechanical strain and their consequent gene expression patterns.  Their results suggested that the mechanical strain might act as a stimulator to induce differentiation of stem cells into osteoblasts.  Indeed, cyclic tensile strain has been shown to increase osteoprotegrin synthesis and decrease soluble receptor activator of nuclear factor kappa-B ligand, thus favoring bone formation.  This theory was tested in an rabbit model by Duyck et al., who concluded that mechanical loading stimulated bone formation and led to a higher bone fraction. ,
Treatment of complete edentulism: Implant overdentures
An overdenture is defined as any dental prosthesis that covers and rests on one or more remaining natural teeth, the roots of natural teeth, and/or dental implants.  The concept of overdentures is age old. Ledger as early as 1856, suggested utilizing natural teeth to stabilize removable prostheses and after a whole century Miller introduced the concept of tooth retained overdentures.  The downside of these prostheses was the frequent failure of abutments caused by periodontal disease, periapical lesions, caries and fracture of teeth. 
The introduction of osseointegrated implants and implant-retained prostheses led to a paradigm shift for the management of edentulism. This is true especially for mandibular edentulism, where the problem of advanced alveolar resorption and difficulty in providing stable, retentive and functionally comfortable prostheses seemed to represent a major challenge. 
A number of randomized controlled trials (RCTs) have demonstrated increased patient satisfaction and reduced negative impact on the quality of life with implant retained overdentures as opposed to conventional dentures in the mandible.  Other studies have reported an improvement in chewing ability, bite force and in serum nutritional and anthropometric parameters (such as skinfold thickness, waist hip ratio and body mass index). , The long-term efficacy of implant-supported overdentures has been established in many retrospective and longitudinal trials. ,,
Implant overdentures are used in conjunction with attachments, and there are many different attachments provided by a large number of manufacturers around the world. The attachments currently available can be broadly divided into two major categories:
- Splinted/bar attachments - Dolder bar and hader bar are examples of splinted attachments
- Nonsplinted/solitary/stud attachments - Ball attachments, magnets and locators exemplify solitary attachments.
Loading of implant overdentures
A fairly recent systematic review by Gallucci et al. (2009) presented the strength of evidence available for different loading protocols (conventional, early and immediate loading) in completely edentulous patients. Their search led to a conclusion that the highest level of scientific and clinical validation was available for conventional loading with mandibular overdentures. However, immediate loading of mandibular dentures was clinically well documented but not scientifically validated.  Clinical documentation of immediate loading can be exemplified by various prospective trials that have been conducted using this protocol for mandibular dentures. For example, a longitudinal study with 3-8 years of follow-up by Chiapasco and Gatti looked at success and survival of immediately loaded implants supporting a mandibular overdenture. Four implants were placed per patient, connected by a splinted bar attachment. A cumulative success rate of 88.2% and survival rate of 96.1% was seen after a mean follow-up period of 62 months.
The authors concluded that, for about 3 years after immediately loading the implants, the success and survival were the same as that documented for delayed loading. However, with a longer follow-up it became evident that immediately loaded implants had a moderate decrease in success rate.  Similar results were reported by Kronstrom et al., wherein he advised caution in using immediate loading due to a low survival rate of 81.8% at 1-year follow-up.  Other investigators have, however, reported higher rates of success and survival using an immediate loading protocol. A cohort study by Gatti and Chiapasco has shown a cumulative survival rate of 100% and minimal bone level changes (0.5-0.9 mm) around immediately loaded implants.  Alfadda et al. used historical controls with delayed loading in a prospective cohort study and compared it to immediate loading. At 5 years, they found identical success, survival, satisfaction and impact on the quality of life between the two groups. 
Randomized clinical controlled trials are considered as the most reliable (level I) form of validation in the hierarchy of scientific evidence, essentially because they reduce spurious causality and bias. In order to prove the efficacy and safety of an immediate loading protocol, Chiapasco et al. performed a RCT comparing an immediate and a delayed protocol for four splinted implants supporting a mandibular overdenture. They found no difference in cumulative survival rate, bone loss, clinical and radiographic parameters at 2 years between the two groups. 
Review paper by Gallucci et al. (2009) and 10 years clinical trial by Meijer et al., among many others, have shown that there is no difference in the clinical and radiographic performance of two or four implants supporting a mandibular overdenture. , Hence, having established that immediately loaded four implants supporting a mandibular overdentures are comparable to delayed loaded implants, it would be interesting to see if these results can be replicated when two-implants were used in conjunction with unsplinted attachments such as locators.
| Case Report|| |
A 58-year-old female patient without any medical contraindication for implant therapy presented with an ill-fitting, lower complete denture that she had been wearing for 4 years. The clinical and radiographic findings revealed slight to moderate mandibular ridge resorption with an ill-fitting lower denture [Figure 1] and [Figure 2]. The patient was given the option of placing two-implants to support her existing lower denture. The treatment plan was accepted and included an immediate functional loading using a locator attachment-supported mandibular overdenture.
|Figure 1: Mandible at the time of implant placement with moderate bone resorption|
Click here to view
At the surgical appointment, following the administration of local anesthetic, a mid-crestal incision was performed, and a full-thickness flap was reflected. In addition, osteotomies were prepared in type II bone. Bone taps were used to countersink the sites, after which two ITI tapered implants Strauman 3.3 mm × 14 mm were placed with the hand piece and hand ratchet. The implants were torqued to 35 N [Figure 3] and [Figure 4]. Immediately after implant surgery, the mandibular denture was seated in the patient's mouth and adjusted to provide clearance in the area of the locator(s). Two locators (4 mm in length) were torqued to 30 N [Figure 5] and [Figure 6]. Following the suture of the flap with 4-0 vicryl, the processing rings were placed over the locators and were picked up directly in the mouth using hard self-curing acrylic [Rebase II, Tokuyama; [Figure 8]]. The patient was given postoperative instructions, including the use of 0.12% chlorhexidine gluconate 3 times a day.
She was furthermore prescribed 500 mg of amoxicillin (to be taken every 6 h for 7 days). The patient was then informed that the implant-supported overdenture was to be left in place for 48 h. Two days later, she was seen for a follow-up visit, and the healing process was uneventful. The black processing rings were switched to blue rings 10 weeks after the placement. After 6 months, the patient returned for another follow-up visit and all two locators were torqued to 30 N [Figure 5] and [Figure 6]. It was determined that all two-implants had achieved full integration. Currently, the patient is on a 6 months recall to ensure the proper maintenance of the implants and the prosthesis [Figure 7], [Figure 8], [Figure 9] and [Figure 10]. The last maintenance visit was 24 months postplacement and all implants have maintained healthy soft tissue and a stable bone level.
|Figure 7: Panoramic radiograph immediately after locator implant placement|
Click here to view
| Conclusion|| |
In conclusion, within the limits of this interim report, immediate loading of two-implants supporting a locator retained mandibular overdenture seems to be a suitable treatment option. The marginal bone level changes around immediately loaded implants are comparable to those seen around implants loaded with a torque do not effect peri-implant bone loss. Implant survival of immediately loaded implants may be lower than those loaded with a delayed protocol, but this needs to be confirmed in future investigations with a larger sample size. Elayed protocol, at 6 months postsurgery. Implant length and peak insertion.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]