Prospective clinical implementation of optional implant treatment into pregraduate dental education—mini implants for retention and support of mandibular overdentures

Dental implant therapy (DIT) needs proper knowledge and training that should be implemented into dental academic education. In accordance, DIT is mostly prevalent during the last 2 years of academic training [1]. There is a variety of programs and methods relating to preclinical DIT such as jaw models and drilling simulators [2, 3], but direct patient care remains the most beneficial instructional method [1]. Though, even if DIT has been incorporated into most pregraduate academic dental institutions in the USA and Europe, it has been taught markedly conservative when compared to other treatment modalities [1]. Nevertheless, there is evidence that dental implants that were provided by pregraduate students (undergraduate students in the clinical part at dental school)—under work standardization, strict guidance, and proper patient selection—show high survival and success rates, even in the esthetic zone [4‐6]. Also, implementation of implant-restorative programs in undergraduate dental curricula resulted in a high students’ satisfaction [7]. Besides, single-tooth implant and implant overdenture therapies promote the standard of care at general dentist level and are described to be feasible at pregraduate level as well [8].

Implant-supported overdentures are considered to be the treatment of choice for rehabilitation of the edentulous mandible [9, 10]. Even so, standard implant placement protocols often need bone grafting procedures before implant insertion. Here, chronic systemic diseases and medications such as anticoagulation may hamper advanced surgical methods [11, 12]. Together with a certain healing period before prosthetic loading, placement of conventional implants may also increase patients’ morbidity and discomfort [13]. Even if the considerable costs of standard-width implants are no issue, especially older patients refuse to undergo implant placement procedures due to anticipated pain and associated complications [14]. Mini dental implants (MDIs; ≤ 2.5 mm diameter [15]) for immediate loading of a mandibular overdenture offer a less invasive and cost-effective alternative to standard-width implants [16‐18]. They may be indicated in patients dissatisfied with conventional overdentures and with limitations or contraindications for placement of conventional implants. In a recent systematic review, Lemos et al. analyzed the results of 2330 MDIs in the lower and 164 MDIs in the upper jaw. Here, a cumulative survival of 92% after 6–7 years (significant more failures in the maxilla when compared to the mandible) could be shown. Survival values of MDI > 10 mm in length were similar to those obtained by standard implants. In the mandible, the reported peri-implant bone loss accounted for less than 1.5 mm. In terms of patient-reported oral health-related quality of life, a significant increase in terms of retention, stability, chewing, speaking, comfort, esthetics, satisfaction, and social life/quality of life was proven [19]. For retention of mandibular overdentures, four MDIs are commonly used, showing higher rates of success and masticatory ability when compared to less MDIs [19, 20]. For four implants supporting mandibular overdentures, a 1-year survival rate of 96–97% [16, 21] and of 96% after 3 years [22] was seen. However, restauration of implant overdentures via mandibular overdentures is included in a paucity of predoctoral programs only [23], and there is no report on planning and insertion of MDIs as well as providing MDI-stabilized overdentures by dental students in the literature yet.

Therefore, the aim of the study was to develop and evaluate an optional pregraduate, academic teaching course including fabrication of overdentures and MDI planning and placement as well as chair-side incorporation of the respective restauration. As patient-related outcomes are of pivotal importance and receive high emphasis in health care assessment, primary research parameter was implant survival and prosthodontic maintenance. Secondary parameters of interest were students’ as well as patients’ perceptions before and after the course as well as other implant related data.

In dental implant therapy (DIT), lack of experience or technical skills may result in disadvantageous results or even serious complications [2], and there is increasing interest in providing adequate DIT-related education for dental students, even if with variable content and duration [6]. Dental and surgical simulators may allow familiarizing with a variety of procedures before performing them on a patient, but only live procedures on real patients will give the student an overview of the treatment situation. Also, actual clinical outcomes may be the best measurement for assessing overall effectiveness of the respective training [6, 8]. Therefore, the present study evaluated an optional pregraduate DIT-course consisting of simple prosthodontic and surgical tasks. Here, after a follow-up of 1 year, an implant survival of 96.25% was seen. Two implants fractured during insertion and one implant was lost after 3 months. These values are in accordance to the literature on treatments performed by postgraduate residents, and implant loss after 1 year is rarely reported [16, 19, 21, 22, 26, 27], though a high need of prosthodontic maintenance could be seen and it seems that prosthetic complications of MDI-retained overdentures are frequent [27]. In accordance, Lemos et al. summarized a mean overdenture-related survival of 91%, and most fractures occurred in the area of metal housing but could be repaired easily. Interestingly, most of these failures occurred in the maxilla (32% versus 5% in the mandible) [19]. Schwindling and Schwindling also experienced an incidence of overdenture fractures of 24% as well as the need for minor maintenance that should not be under-estimated [28, 29]. In total, maintenance rates in the literature are similar to those reported in the study at hand. It has to be discussed if relining of an implant-retained overdenture or change of retention rings should be interpreted as a complication or rather a part of the treatment concept [30, 31]. In conclusion, the present study supports data obtained by others showing that undergraduates will receive acceptable clinical outcomes of implant-related treatments [32‐36] even if data on MDI-related restorations from students—let alone in a prospective clinical study—are not available yet. In cases of MDI, special care should be undertaken at time of implant insertion as they are prone to fracture as described in the literature as well [28, 37]. In accordance, when compared to standard implants, the insertion torque has to be significantly reduced and strict bone-preconditioning via drilling is recommended [28, 38].

In the past, students reported a lack of preparedness in providing routine DIT [26, 39]. This is analog to the present study as the majority of students also deemed themselves to be not prepared for DIT. In brief, 11/20 wrote that they had at least insufficient knowledge on implant surgery and 17/20 that their knowledge was at least insufficient in terms of implant prosthodontics. After participation, all students quoted a gain of practical knowledge by following the course. This is comparable to other pregraduate courses on DIT reported in the literature [7]. Besides, all students thought of carrying out DIT with MDIs in their own private practice. Analog to this, it was reported that graduates who actively participated in formal as well as preclinical and clinical implant education conduct significantly more often DIT at general practice level, i.e., restore significantly more implants and refer more patients to surgical specialists when compared to others with a lack of such an implant curriculum [40, 41]. In accordance, an implant program such as presented in the present study may increase students’ awareness that dental implants are a treatment option and are beneficial for suitable patients.

There are several patient-related factors influencing and defining the characteristics and the number of implants to be inserted. First, the choice of implant strongly depends on the quantity and quality of bone tissue available. Here, in case of a low bone thickness, MDIs are an alternative rehabilitation option for the edentulous mandible. As bone augmentation techniques are not needed and a flapless approach is possible in selected cases, MDI will decrease postoperative morbidity and therefore increase patients’ acceptance [42]. Whereas in most of the studies MDI were inserted in a flapless approach [29, 42], in the present analysis, small flaps were raised due to the narrow alveolar ridges in order to prevent accidental lingual perforation. This bias results in the teaching environment and in order to overcome limitations of the flapless approach such as limited visibility and the lack of water cooling. Besides, Ribero et al. could not find significant differences in terms of pain and postoperative morbidity when comparing flapless and flap technique in cases of standard implants [42].

As expensive specific retention systems are not needed, MDI may also be a good choice for patients with limited finances that do not want to give up the benefits of retained overdentures. Besides, the prosthodontic technique of incorporating an MDI into a pre-existing overdenture is an approach that can be learned easily and seems suitable for pregraduates getting in touch with DIT. Also, the manufacturing of new dentures is mainly based on standard techniques for conventional overdentures.

Lower scores of the Oral Health Impact Profile (OHIP; ranging from 0 to 56) represent a better oral-related quality of life and well-being. In brief, patients’ OHIP-reported satisfaction significantly increased in comparison to the old, non-MDI-supported dentures after 4 weeks and 3 and 12 months such as seen in the literature [20]. This clearly strengthens the weak existing evidence [43] that MDI-retained overdentures achieve favorable results in terms of patient perceptions. In general, it could be shown that OHIP-scores of patients with four MDIs are comparable or even superior with those of patients obtaining overdentures retained by conventional implants [20, 27, 43].

In the literature, bleeding on probing was positive in 33% of implants after three weeks, followed by 33% and 39% after 6 and 12 months [20] that is in accordance to the present study. As a drawback, peri-implant marginal bone level was not measured as routine radiological assessment at follow-up examinations as it was not approved by the local ethics committee.

In the study at hand, not only the prosthodontic part and the planning—as reported by others [4, 7]—but also part of the surgical procedure was conducted by pregraduate students resulting in an interdisciplinary DIT approach in a comparable safe learning environment. Nevertheless, it should be mentioned that such a program needs a high student/teacher relation and therefore a comparable high manpower. For implementation into the dental curriculum, it may also require previous theoretical and laboratory training as well as changes in the course contents and additional resources, instructors with specific expertise, and a long-term patient support structure. In accordance, a necessary change of academic dental curricula towards dental implant therapy may be a demanding and long process that sometimes does not meet the current pace of innovation [23]. In the past, directors of predoctoral programs on dental implant therapy have been predominantly affiliated with restorative dentistry as DIT is considered to be a restorative treatment approach supported by surgical protocols [1, 8]. Even so, as DIT continues to become more pervasive, an increase of surgical expertise may be predicted [44]. In accordance, the present course was conducted interdisciplinary, being held by a prosthodontic and a surgical university department. Even so, as the present study is a pro-post survey including implant survival, prosthodontic maintenance as well as patient- and student-reported outcome only, its impact on several educational aspects for further integration into the dental pregraduate curriculum may be limited.

Patient-related outcomes are an interesting and promising way to assess pregraduate training programs rather than assessment of an individual student. The present study gives evidence that dental implant therapy planned and performed by pregraduate students yields comparable results in terms of survival rates as well as patients’ satisfaction to those published in the literature. Besides, the course was unanimously rated as positive, productive, and valuable for the future work. Next to pregraduates’ satisfaction, patients’ perception was positive and even increased over the time of follow-up. Therefore, it may be suggested that the use of this strictly guided incremental learning system will result in not only positive patient-related outcomes but also student-related outcomes.