Aesthetics in Removable Partial Dentures: Modification of the Proximal Plate and Retentive Lamellae in Kennedy's Second Classes

1. Introduction

Despite the constant evolution of digital technologies and the extensive development of implant techniques in dentistry, the removable partial denture (PPD) continues to play a significant role in clinical practice. This type of prosthesis, which has deep historical roots in the field of dental prosthetics, remains a valuable and versatile treatment option for patients with partial edentulism or missing multiple teeth. Its usefulness is supported by a series of advantages ranging from the preservation of residual dental tissue to aesthetic and functional customization [1,2,3]. While the dental landscape has witnessed notable advancements in digital technologies and the widespread use of dental implants to restore edentulous spaces, removable partial dentures continue to meet specific clinical needs for patients who may not be adequately rehabilitated with other solutions. Their removable nature allows for flexible management of ever-changing oral conditions, making corrections and modifications easier when needed. Furthermore, removable partial dentures offer a less invasive alternative to implant procedures, making them particularly appropriate for patients who may not be ideal candidates for dental implants. The versatility of removable partial dentures is also manifested in their ability to be adapted to patients' individual preferences and needs. Thanks to modern computer-aided design (CAD) and computer-aided manufacturing (CAM) techniques, it is possible to create highly customized and comfortable removable partial dentures, which integrate harmoniously with the oral morphology and improve the patient's aesthetics [4,5,6,7,8]. The correct insertion of the skeletonized prosthesis and periodontal health ensure that these prostheses have a long life if carefully maintained; in other cases the presence of destructive cavities, large reconstructed teeth and periodontally compromised teeth lead the patient to undergo dental extractions with consequent modification of the prosthesis and in some cases also the movement of the hook to another tooth, increasing the blemish even further [9,10,11]. This research has focused attention on a new design which involves the modification of the proximal plate through the addition of two functionally equivalent extensions to the hooks, with the aim of giving greater retention to the proximal plate while also increasing the aesthetics of the skeletonized prosthesis [12,13]. The new design used mainly in the third Kennedy classes in our experimentation was used in the second Kennedy classes evaluating the efficiency, aesthetics and retention of the prosthesis.

2. Materials and Methods

For the evaluation of removable partial dentures with lamellar retentions in the second classes of Kenney, 4 freelance dentists in the Lombardy hinterland were selected, who gave their availability while respecting anonymity, to mainly carry out the branch of dental prosthetics, and at each dentist was asked to: a) select 4 patients, 2 men and 2 women; b) to create removable partial dentures in Kennedy class II edentulous cases for the upper arch with the new design where possible; c) to anonymously fill out (respecting privacy) 4 questionnaires, the first upon delivery of the prosthesis (questionnaire 1), the second after 1 month, the third at 6 months and the fourth at 12 months from delivery (questionnaire 2, 3,4). In total, a sample of 16 patients was selected, aged between 65 and 85 (patients considered elderly) who should have performed rehabilitation in the upper arch with a removable partial prosthesis. All the selected patients were not willing to undergo implant-prosthetic rehabilitation or rehabilitation with a fixed prosthesis, all the patients chose mobile rehabilitation both for economic and anatomical reasons (lack of bone). All selected patients signed the informed consent. The choice of only the upper arch for the evaluation of the parameters is mainly due to aesthetic reasons, as the more visible upper arch affects people's smiles during social relationships [14,15,16,17]. Each dentist selected the patients, 2 men and two women, according to inclusion and exclusion criteria.

The inclusion criteria were:

• presence of partial edentulism classifiable as Kennedy class II;
• absence of tori that could affect the adaptability of the prosthesis;
• non-inclined residual elements (excessive undercut);
• absence of para-functions;
• presence of stable soft tissues not affected by periodontal disease or mucogingival lesions;
• adequate depth of the roots of the abutment teeth;
• informed consent of the patient and acceptance of the therapeutic rehabilitation plan with partial removable prosthesis and compliance with the dentist's instructions.
• age between 65 and 85 years.

Patients who met the following exclusion criteria were excluded from the study:

• poor oral hygiene and lack of patient compliance;
• smoking habits (>10 cigarettes/day);
• subjects suffering from oral pathologies;
• active periodontal disease;
• anomalies in the anatomy of the labial frenulum (which can interfere with the insertion and adaptability of the removable prosthesis);
• drug addictions;
• psychiatric pathologies;
• subjects disbarred less than 5 years ago;
• subjects on bisphosphonate therapy;
• deep bite;
• failure to consent to prosthetic rehabilitation and to comply with the dentist's instructions.

The selected patients were numbered from 1 to 16 in order to respect anonymity and privacy (Table 1).

Questionnaire n. 1 administered to patients upon delivery of the prosthesis

Questionnaire administered to patients 1, 6, 12 months after delivery of the prosthesis

All dentists were asked to speak with the dental technician for the design of the retentions and the proximal plate in order to have adequate retention and aesthetics. The dental technician was provided with a drawing and wax-up of the project in the study model in order to replicate the same with the removable partial denture (Figure 1 a-d).

3. Results

The results are based on the information obtained from the questionnaires filled out at each check-up by the patients taken as a sample considering a follow-up period of 12 months (Table 2, Table 3 and Table 4), Table 5 expresses the reference values. Some aspects such as satisfaction, stability, retention and aesthetics were taken into consideration. The results were evaluated by averaging the values ​​to have an immediacy of any critical issues, while for the last questionnaire the standard deviation was also calculated to evaluate any differences in the values ​​of each observation compared to the average after 12 months. of the variables.

During the checks, no patient underwent treatment on the abutment teeth and no clinically evident cavities were found in any element. No patient discontinued use of the skeleton due to lack of retention or stability. At the first check-up, one month after delivery, the patient identified with number 13 expressed a low score (2 out of 4) for three parameters (retention, aesthetics and satisfaction), while the patient identified with number 15 expressed a low score for all parameters.

At the six-monthly checks only in a single case (Questionnaire 2 - patient identified with number 8) was a fracture of a resin element found. Once the element was replaced, the patient was satisfied with the result and at the subsequent check-up the skeleton was found to be perfectly suitable. Patients identified with numbers 13 and 15 expressed low scores. The last questionnaire, at 12 months, was completed by only 14 patients, the patients identified with numbers 2 and 7 did not show up for the check-up. Interviewed by telephone on the same day, using the same parameters, they reported having no problems of any kind and that they were very satisfied. For our investigation, both patients were assigned the maximum value of 4 in all sections. The patient identified with the number 13, despite the checks and attention, did not feel satisfied because he did not accept the idea of ​​having a mobile prosthesis, the patient identified with the number 15, despite the prosthesis being stable and aesthetic, did not feel satisfied .

The two most appreciated parameters among those evaluated in the questionnaires were aesthetics and stability, obtaining a score of 3.56 out of 4. Ten patients (62.5%) expressed a score of 4 out of 4 in the aesthetics and in the stability boxes. A detail found by the dentists during the checks was that no patient requested the activation of the lamellae retentions to improve retention and only two patients identified with the numbers 9 and 5 used the adhesive paste for dentures, only on the occasions of social dinners , for fear that the prosthesis might move. Another important fact is that in no case was it necessary to reline the prosthesis after some time (12 months).

4. Discussion

Edentulism still represents a very important problem to solve for dentists today, dental caries and periodontal diseases are the main causal factors of tooth loss and, if not treated adequately, lead to edentulism [18,19,20,21]. The aesthetic judgment of patients, often negative regarding the removable partial denture, is very high due to the vision of the clasps, the retention, furthermore after the delivery of the prosthesis there are subsequent adjustments or modifications to the prostheses in the following years also due to periodontal problems [22,23,24]. The progress of the different techniques that use the new Cad/Cam technologies have allowed operators to use design software also using different materials to find increasingly comfortable and aesthetic solutions for the patient [25,26,27,28,29,30,31]. The results of this study highlight how the lamellar retentions in the edentulous areas interspersed in Kennedy's II classes had a good evaluation for the parameters examined. In these edentulous areas we tried to exploit the modification of the proximal plate by designing it a few tenths of a millimeter per below the undercut of the tooth so as to be more retentive, furthermore if we consider the forces that insist on an inclined plane we can say that the friction force during the removal of the prosthesis represents the value of the angle between the tooth and the proximal plate. From a practical point of view, the inclined plane is used to move bodies using less effort than that necessary for their vertical lifting; in prosthetic terms, the more adherent the proximal plate is, the greater the effort will be to remove the prosthesis. Of the 16 patients selected, 7 patients (43.75%) considered themselves very satisfied with the therapeutic choice, 7 patients (43.75%) considered themselves satisfied and only 2 patients (13.5%) did not consider themselves satisfied. Examining the standard deviation values ​​obtained for 4 parameters 0.68 for satisfaction, 0.60 for stability, 0.61 for retention and 0.60 for aesthetics, we can say that the data are relatively homogeneous and coherent, with little significant variation between data points. This may indicate some stability or uniformity within the phenomenon or process being sampled.

In practical terms, low values ​​of standard deviation suggest that the measurements or observations are very similar to each other and that there are few significant fluctuations. However, it is important to consider the sample size which is small. The design of the skeletonized prosthesis with lamellar retentions, in Kennedy class III edentulism, was introduced in the 2000s. In the first study of 2003 the concept of "lamellae" is described, in particular the modification of the proximal plate of the skeleton by applying two extensions having the same functions as a hook, in the year following 2004 with the collection of a sample of 31 patients with Kennedy class III partial edentulism, the stability, retention, integrity, hygiene of the prosthesis and conditions of the elements were checked teeth adjacent to the edentulous area, evaluating the presence of caries, mobility of the residual elements [12,13]. The search for aesthetics by modifying the hooks to make them increasingly aesthetic has been an objective pursued by researchers [32,33]. The design of the modified retentive devices are very aesthetic as they do not have a supraequatorial portion, their occlusal and lateral stability is maintained by the large secondary joint and the primary support designed distally (Figure 2). Clearly the information and indications that the dentist must provide to the technician must be as precise as possible, especially on the health of the periodontium [34,35,36,37].

In light of the results obtained in previous studies and the following study, it is demonstrated that the design of the skeletonized prosthesis with lamellar retentions is not harmful to the periodontal structures of the residual teeth if the level of oral hygiene is maintained good and professional checks are constant.

5. Conclusions

In conclusion, we can state that the lamellar retentions designed in Kennedy's second classes have shown good satisfaction in selected patients. The dialogue between the dentist and dental technician during the design of the prostheses was fundamental for the aspects of retention and aesthetics by not altering the occlusion. In light of the results obtained, we can confirm that even in non-implant-prosthetic cases, the skeletonized partial prosthesis can represent a valid solution for patients, especially if lamellar retentions are designed in the intercalated areas. This study could be continued with a longer follow-up at 2 and 3 years to also evaluate the periodontal appearance and the mobility index of the abutment teeth.