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Twenty-four patients were treated with 71 IMZ implants, between 1987 and 1991 at Tufts University School of Dental Medicine by senior dental students. Soft tissue, marginal bone height and prostheses were evaluated. Inflammation was noted around 70% of the implants, and marginal bone loss around 13% of the implants exceeded 2 mm. Prosthodontic complications included broken screws, broken dentures, broken intramobile elements (IMEs), porcelain fracture, and IMZ clip replacement. All 71 implants are immobile. (J Prosthet Dent 1995;74:56-9.)

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Dental implant use by American dentists increased by 70% between 1986 and 1990(1). At the 1988 National Institute of Health(NIH) Development Conference on Dental Implants, it was predicted that the demand for dental implant treatment would continue to increase(2). Given the public demand for these services, training dentists in implant diagnosis, treatment planning, and procedures is most critical.

Dental school deans have become aware of the need to increase the implant curriculum. Before December 1991, surveys demonstrated that few dental schools were training their predoctoral and postdoctoral students in implant dentistry(3). In December of 1991, curriculum guidelines were published for predoctoral implant dentistry. These guidelines required students to receive exposure to implant procedures(4).

The success rate of dental implants is judged by criteria from the National Institute of Health Conference in1988(5). These criteria were further detailed by Smith and Zarb in 1989(6). Complications previously recorded for the Branemark Implant (Nobelpharma, USA, Chicago, Ill.) include screw fracture,(7-13) inflammation around implants,(7,12-18) loose components,(7-15) and broken dentures.(13,16,17) Minimal published data exist that describe the complications associated with the IMZ implant system (Interpore International, Irvine, California).(19)

The IMZ implant is a two-stage, cylindrical implant. Unique features include the Transmucosal Implant Extension(TIE) and the Intramobile Element (IME). The IME is intended to mimic the resiliency of the periodontal ligament. The system is indicated for splinting to natural teeth, freestanding fixed partial dentures (FPDs), and clip bar prostheses for edentulous patients.

This article describes the results of patients treated with the IMZ implant system at Tufts University School of Dental Medicine from 1987 to 1991 by senior dental students. Criteria used to evaluate these patients are similar to those described by Smith and Zarb.(6)

Twenty-four patients, 17 woman and seven men, were given restorative dental treatment with 71 IMZ implants from 1987 to 1991 at Tufts University School of Dental Medicine. Six patients were followed for five years, eight patients for four years, nine patients for three years and one patient for two years. Patients were between 26 and 74 years old with the mean age being 58. All recall examinations were done by one examiner. All implants were placed by one surgeon. There were 26 maxillary and 45 mandibular implants restored by senior predoctoral dental students.

Table I shows the different treatment types, number of patients and number of implants per treatment type. Mandibular overdentures represent the largest treatment group. Three (3) patients had o-ring (Implant SupportSystems, Irvine, California) attachments, 3 patients had IMZ clip attachments, and 5 patients had Hader bar-clip attachments (APM Sterngold, Attleboro, Massachusetts). Patients receiving fixed partial dentures (FPD) were differentiated between those FPD's attached to teeth or freestanding. Information collected prior to Stage II surgery focused on the use of interim prostheses. If patients wore prostheses covering the surgical site, the opposing occlusion and soft tissue complications were recorded.

Information collected after prosthodontic treatment described the soft tissue response, marginal bone height changes and mechanical complications. Soft tissue inflammation was detected by bleeding on probing. Attachment levels were recorded instead of pocket depth. The technique for measuring attachment level required measuring from a fixed point on the implant or superstructure to the bottom of the sulcus where the soft tissue attaches to the implant, as described by Newman and Flemming.(20)

Marginal bone height and peri-implant bone quality were evaluated radiographically. An effort was made to standardize the radiographic technique by trying to keep the film and implant parallel and the X-ray beam perpendicular to both. Changes in bone height of 1 mm or more were recorded. Peri-implant bone quality was determined to be inadequate when there was radiolucency at the bone implant interface.

Mechanical complications were also recorded. These complications included IMZ clip replacement, denture fracture, broken IME's, broken prosthetic retention screws and porcelain fracture. Data were collected at prosthetic placement, 3 months, 6 months, one year and bi-annually thereafter for 2-5 years.

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Thirteen (13) patients of the 24 wore interim overdenture prostheses covering 36 implants. Four (4) implants became exposed to the oral cavity prior to Stage II surgery. Pre-Stage II exposures did not lead to failures. No difference in marginal bone height could be seen around any of the 36 implants covered with interim prostheses during the healing period as compared to those without interim prostheses.

Soft tissue inflammation was noted around 20 of the 26 implants in the lower overdenture group. Soft tissue hypertrophy was also seen around 5 implants in two patients. Five implants in 4 patients showed marginal bone loss greater than 2 mm. Three of these implants demonstrated bone loss on one side to the apex (lingually).

Table II shows that a common mechanical complication was IMZ clip replacement. The IMZ clip was replaced 9 times in 3 patients and caused 2 dentures to fracture. The Hader clipwas replaced once for each of two patients. O-rings were replaced every six months. Patients who had o-rings were forced to comply with their recall visits because they noticed a loosening of their denture.

All FPD treatments were grouped together. Twenty-four implants in seven patients showed the presence of inflammation. Four implants in 3 patients showed bone loss greater than 2 mm. Bone loss did not reach the apex around any of these implants.

Mechanical complications, as shown in Table III, included 9 broken IME's, 3 broken screws and 2 porcelain fractures. In some of the first recall visits, some screws were found to be loose. Once tightened, however, they were not found to be loose at future recall examinations.

The maxillary overdenture group included two patients with eight implants. There were no mechanical complications. Inflammation was present around six of the eight implants and bone loss did not exceed 2 mm.

Table IV refers to the overall presence of inflammation and bone loss greater than 2 mm. for all patients treated. Inflammation was present around 70% of the implants. Bone loss greater than 2 mm. was seen around 13% of the implants. All prostheses, however, are still functioning and all implants remain immobile.

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Four implants became exposed to the oral cavity prior to Stage II surgery. Early perforation has been described before in which a flap was mobilized and resutured.(7,8) Active surgical measures were not taken on the implants in this study. In all cases, the denture was relieved in the area of the implant after it was exposed. Early perforation might have been avoided if more frequent attention was paid to the interim prosthesis such as routine changing of the tissue conditioning liner. Faculty members attempt to work closely with students during the healing phase to minimize this complication.

Inflammation of between 50-70% around implant overdenture abutments has been documented.(18) In this study, inflammation was present around almost 80% of the implants in the lower overdenture group. Additionally, hypertrophy was found, while in previous publications, recession was reported.(17,18) Both inflammation and hypertrophy might be explained by inadequate oralhygiene. Plaque and calculus were present at nearly all recall visits. Recall and maintenance including reinforcement of oral hygiene instruction by a faculty member is felt to be necessary. Students should participate in recall visits before they are allowed to treat a patient. This should provide the graduating dentist an understanding of the longterm maintenance commitment needed to treat patients with dental implants.

Bone loss greater than 2 mm was recorded around 5 implants in 4 patients for the lower overdenture group. This degree of bone loss is greater than previous reports describe.(7,17,18) When initiating a new program, there is a learning curve for the surgeon and the restorative dentist. Diagnostic radiographic techniques have improved since this program began. It is quite possible that some of the implants were placed too far lingually resulting in bone loss reaching the apex lingually. The predoctoral implant program now requires use of surgical guides and ideal placement is attempted. Restorative faculty and students are present during implant placement.

Marginal bone loss is generally described for the first year of loading and then annually thereafter. Bone loss of 1mm or less the first year and 0.1 mm per year thereafter is acriterion for success.(6) Bone loss greater than 2 mm has not been described. Two mm bone loss was chosen because this degree of change is easily detected radiographically. The IMZ implant is cylindrical, not screwlike, making exact measurement difficult. Radiographic stents for each patient were not fabricated. It was not possible to view the implant in the same dimension in each radiograph.

Clip replacement and broken prostheses have been documented in previous reports.(17) The IMZ clip required more than routine maintenance. It was replaced much more frequently than Hader clips and because of its size, caused 2 denture fractures. Denture fracture might have been avoided by treatment planning a different attachment because of insufficient interarch space. The IMZ clip is expensive compared to Hader clips or the elastic portion of the o-ring attachment. The o-ring attachment seemed to give the best results for patients included in the study. It is simple to replace, it is inexpensive and because it wears after approximately six months, it reinforces patient recall compliance. Also, because there is no bar, it is more easily cleaned.

When examining FPD's, inflammation and bone loss did not seem as common as for the lower overdenture group. This finding may not be significant because the study sample was small and statistical analysis was not performed. Complications for FPD patients resembled previous reports.(7-15) The IME, unique to the IMZ system, is plastic and will fracture. In 8 of the 9 fractures, the IME was more than one year old. The manufacturer suggests replacement annually. Fracture can be detected clinically by noting instability in the prosthesis. In some cases this is difficult to detect and the prosthesis must be removed.

The attachment level, as described by Newman and Flemming(21) proved to be an excellent diagnostic tool. An increase in attachment level between visits suggests anapical migration of the bone. When the difference between visits was 2 mm or more, radiographs were taken to see if bone loss could be detected. In seven of the nine cases where bone loss exceeded 2 mm change in attachment level suggested this finding. Upon radiographic confirmation of bone loss, patients were scheduled more frequently and pressed for improved oral hygiene. The only disadvantage to accurately recording attachment level is that often the prosthesis must be removed and is therefore time consuming.

Several types of treatment were included in this study. With the exception of the lower overdenture group, other treatment groups had, at most, four patients. This approach was used to determine what type or types of treatment seemed most appropriate for teaching undergraduate students. Although no specific type of FPD led to failure, all too often the faculty had to perform most of the work. Full arch FPD's and FPD's attached to teeth were difficult for students to comprehend. Simple treatment planning, lower overdentures with o-ring attachments and two to four unit, free standing implant FPD's seemed most appropriate for pre-doctoral students.

All prostheses are still functioning and all implants are still immobile. The pre-doctoral implant program has matured from this experience. Students and restorative faculty are now present at time of insertion, second stage surgery, and recall examinations. Patient selection for the IMZ system is now limited to lower overdentures and two to four unit freestanding fixed partial dentures.

In order to provide the highest quality implant services to the public, dental schools must remain committed to providing the necessary education to future dentists through the pre-doctoral implant curriculum.

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Twenty-four patients were restored with 71 IMZ implants by senior predoctoral dental students at Tufts University School of Dental Medicine and followed-up for 5 years. Treatment types included maxillary and mandibular overdentures, fixed partial dentures, freestanding implant restorations, and implant restorations attached to restored natural teeth. Findings included tissue inflammation, marginal bone loss, and technical complications.

Inflammation occurred in approximately 80% of the implants used for mandibular overdentures. Twenty percent of the implants that had bone loss greater than 2 mm were placed too far lingually. IMZ clips required more frequent replacement and were associated more frequently with denture fracture. O-ring attachments improved patient compliance because of loosening of the denture and were cost-efficient to replace.

Inflammation occurred in approximately 60% of the implants for FPDs. Approximately 10% showed bone loss greater than 2 mm. Although this group demonstrated fewer complications, full-arch FPDs and FPDs attached to teeth were technically difficult for students to complete and for faculty to take the necessary time to monitor.

All prostheses are still functioning. Undergraduate students can restore implant, but caution should be taken to ensure close faculty supervision, simple prosthodontic procedures, and excellent recall system with both instructor and student involvement.

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