The use of articial teeth in a pre-clinical xed prosthodontics post-core undergraduate teaching program

Background The use of articial teeth in pre-clinical simulation clinic teaching of post-core techniques has clear educational benets for students and staff. This study explored the reasons for selection and direct student experiences with articial teeth in a recently conducted pre-clinical xed prosthodontics post-core technique teaching program. An online anonymous survey was delivered to fourth year undergraduate dental students who had completed the xed prosthodontics pre-clinical program seeking information on the choice of articial or natural teeth and direct experiences. Quantitative data was summarised and qualitative data was clustered into topics.


Introduction
Pre-clinical teaching Fixed prosthodontics teaching in undergraduate dental curricula has traditionally included pre-clinical courses covering theory and practical techniques in crown preparation and post-core procedures. The importance of pre-clinical dental education has been demonstrated as a key factor in facilitating a smooth transition to the clinical setting. 1 There is an established positive correlation of pre-clinical grades with clinical grades in operative dentistry and xed prosthodontics. 2 Dental simulation clinic teaching has established itself as a mainstay in pre-clinical teaching for students to develop practical skills. 3 Simulation clinic teaching has been used extensively in both pre-clinical and end-point xed prosthodontics teaching modalities where students typically complete a sequence of formative practical exercises culminating in a summative practical assessment. 4 In some curricula, dental simulation clinic teaching has signi cantly replaced clinical practice.
Post-core restorations Post-core restorations facilitate the reconstruction of endodontically treated teeth and present advantages over extraction and tooth replacement enabling patients to retain natural teeth for longer. 5 In the modern era of dentistry with an ever-increasing placement of dental implants, post-core procedures may be thought of as a forgotten art, however they have an important role in restorative dentistry and prosthodontics particularly with adults retaining more teeth for longer. 6,7 Typically, teeth requiring postcore restorations have minimal remaining sound tooth structure and require assessment of the volume of remaining tooth structure, location of remaining tooth structure, and adequate ferrule prior to consideration for post-core restoration. 8 The normal purpose of a post is to retain the coronal restoration. 9,10 The coronal restoration may comprise a core that provides adequate coronal structure through key principles of retention and resistance form for an arti cial crown 9 or may be a stand-alone restoration in itself. The core can be constructed in conjunction with the post as in the case of a traditional cast post-core, or, may be constructed separately and chemically and/or mechanically retained by the post.
Historically, cast post-cores were constructed using the direct (intraoral) resin pattern then casting by means of the lost wax system. Today, there is a myriad of options, post types and materials available in the marketplace including prefabricated, cast, metallic, non-metallic, active, passive, bonded, cemented, direct and indirect varieties. 10,11 Most available post-systems can be used provided certain principles are followed. 12 Despite the provision of guidelines, post selection can be challenging and requires guidance at the beginner level as there are a multitude of factors that require consideration. 13 Furthermore, the mechanisms of post failure should also be known and can be quite speci c to the post type. 14,15,16 Postcore procedures are complex and require a high level of skill. It is therefore imperative undergraduate dental students are trained accordingly.
Simulation clinic teaching of post-core techniques Traditionally, extracted natural teeth have been sourced for pre-clinical simulation clinic teaching of xed prosthodontics and post-core techniques. In recent years, limitations have been encountered such as ethical barriers, cross-infection requirements, sourcing teeth with appropriate tooth structure, and sourcing teeth with appropriate root canal anatomy. The nature of variations in natural teeth limit the standardisation, repeatability and consistency of teaching and can result in a diverse range of student experience of learning.
The bene ts of using arti cial teeth in simulation teaching in xed prosthodontics include standardisation of teeth, standardisation of techniques, life-like appearance, facilitation of repeatable practical demonstrations that are directly applicable to the student's tooth, and being readily available. The known shortcomings are limitations in the anatomical simulation of natural teeth, different surface textures compared to natural teeth, and the cost involved in obtaining teeth, models and manikins.
As education philosophes and technology have evolved, the bene ts of teaching alternative and modernised techniques in xed prosthodontics have been established resulting in quality gains evidenced by students producing closer to ideal crown preparations. 17,18 Dental simulation teaching has expanded beyond the traditional manikin model to encompass virtual reality technologies. 3,19 Recent developments have been directed at 3D technologies associated with the creation of layered arti cial teeth. 20,21,22 Arti cial endodontic teeth have been produced and used in endodontic pre-clinical teaching with promising initial results 23 but there have not yet been any reports for post-core teaching.

Study Aim
Although extracted natural teeth provide a high-delity experience, the dominant challenges in using natural teeth for post-core pre-clinical xed prosthodontics procedures have been sourcing appropriate teeth and when sourced the compromised restorative state. Research speci cally focussed on undergraduate pre-clinical education in post-core techniques is scarce. More speci cally there remains a dearth of evidence on the use of arti cial teeth in the education of undergraduate students speci cally in post-core exercises.
The aim of this study was to explore the reasons for selection and direct student experiences with arti cial teeth in a recently conducted pre-clinical xed prosthodontics post-core technique teaching program using a survey of student experience.

Ethical considerations
Ethics approval was obtained from the Human Research Ethics Committee at The University of Adelaide (H-2020-106).

Context
Fourth year undergraduate dental students undertaking the xed prosthodontics pre-clinical program at the Adelaide Dental School, The University of Adelaide were presented with an option to source extracted natural teeth or purchase arti cial teeth ( Fig. 1) at A$25 per tooth prior to the post-core component of the program. A total of six teeth were required for all post-core exercises. Any combination of arti cial and natural teeth was permissible, all of which could be used in the same acrylic base model tted to the manikin head. The teeth were manufactured using conventional moulding techniques, not threedimensional (3D) layering. The use of the teeth for the set exercises followed a comprehensive xed prosthodontics didactic program and was conducted in a dental simulation clinic.

Survey Development
Two surveys were developed according to whether students used arti cial teeth (Survey 1) or natural teeth (Survey 2) for the post-core exercises in the xed prosthodontics pre-clinical program ( Table 1)

Results
A 100% response rate was received. Of the 70 respondents, 25 (36%) chose to use one or more arti cial teeth for the post-core exercises in the pre-clinical program, with 17 (68%) of these respondents choosing three or less of the possible six arti cial teeth. 45 (64%) respondents chose not to use arti cial teeth, choosing to use only natural teeth.

Survey 1 (Arti cial Teeth)
For the 25 respondents who used at least one arti cial tooth, the reasons for choosing arti cial teeth were dominated by di culty in sourcing appropriate natural teeth (59% of responses) compared 13% reasoning an educational bene t (Fig. 2).
When the direct student experiences of using arti cial teeth were examined with open ended questions, 'ease of use' was established as a dominant positive aspect accounting for 52% of 71 responses. The main negative aspect was 'unrealistic simulation of natural teeth' representing 50% of 64 responses.
When compared with natural teeth, 28% (n = 7) found arti cial teeth to have the same surface texture using a high speed bur whereas 44% (n = 11) found the arti cial teeth a little harder; 56% (n = 14) found the canals were a little easier to locate; and 36% (n = 9) found the same ease of deviating or perforating from the obturated canal compared with natural teeth.
Two of the 25 respondents reported perforating the arti cial teeth.

Survey 2 (Natural Teeth)
Of the 45 respondents who chose only natural teeth for post-core exercises, 49% of 79 responses reported the selection was due to 'arti cial teeth cost too much' (Fig. 3). If given the choice again, 23 (51%) of the respondents would choose arti cial teeth at the same cost.
For the 45 respondents who did not use any arti cial teeth, if they were to use arti cial teeth in the future the perceived bene ts were dominated by 'ease of use' (45% of 118 responses) (Fig. 4) whereas the perceived negative aspects focussed on 'unrealistic simulation of natural teeth' (48%) and 'cost ' (27% of 118 responses) (Fig. 5).
The average cost that the same respondents were willing to pay in the future for arti cial teeth was A$6.43 per tooth with 73% of respondents willing to pay A$6 or less per tooth (n = 45).

Direct ndings
The study found a range of reasons for the selection of arti cial teeth for post-core pre-clinical exercises but was predominantly explained by di culty in sourcing appropriate natural teeth. Beyond ethical considerations, obtaining appropriate tooth types (single rooted, multiple rooted) with appropriate root anatomy, in a restorable state, in large numbers, and for large numbers of students is a challenge that obtaining arti cial teeth from a dispensing machine overcomes.
For the 36% of respondents who used arti cial teeth, cost was not reported as a major drawback. The dominant direct bene cial experiences of students who used arti cial teeth was the ease of use and the main negative aspect was unrealistic simulation of natural teeth, which are somewhat contradictory. Further investigation is required but could in theory be reasoned by the pristine unrestored nature of the arti cial teeth compared with the frequently heavily restored, diseased or broken-down natural teeth. Arti cial teeth were judged by respondents who used the teeth as similar to natural teeth in surface texture and ease of deviating from the obturated canal but slightly easier to locate the canal which reinforces the appropriateness of using arti cial teeth in post-core pre-clinical programs.
Contrastingly, it was apparent that cost served as an initial barrier to choosing arti cial teeth over sourcing natural teeth as demonstrated by the 64% of respondents who chose not to use any arti cial teeth. Students already have signi cant educational expenses and when posed with a decision to outlay further, they predominantly chose to source natural teeth at their own individual time and effort expense. Students have choices, their opinions can be in uenced by a variety of factors, and in practical terms it may have been a relatively simple decision of cost outweighing convenience.
The 64% of respondents who did not use arti cial teeth perceived future potential bene ts as ease of use but were concerned with the potential unrealistic simulation of natural teeth more than cost. Surprisingly, educational bene t did not feature highly in the responses. Students may have a different perspective to that of teaching staff, focussing more on the practicalities of sourcing teeth, associated costs and ease of use rather than educational bene t. The ability to use standardised simulation teaching resources has clear educational bene ts, where a consistent educational experience can be provided and repeated for all students in the class at different points in time. Students may perceive cost as a barrier to gaining educational bene t.

Comparative research
There has been no known previous research in this speci c eld of the use of arti cial teeth in post-core teaching of undergraduate students, as such direct comparisons are limited. Overarching surveys of curriculum structure, techniques taught, and materials used in undergraduate prosthodontics courses (that include xed prosthodontic components) have been conducted at various points in time 24,25,26,27 and have fuelled recommendations and publication of curriculum guidelines. 28 Surveys of student experiences have been performed in the broader prosthodontics educational context including self-report of con dence in undergraduate removable prosthodontic education 29 and effectiveness of preclinical courses in preparing students for patient treatment. 30 More speci c research has focussed on student experiences in xed prosthodontics such as using 3D scanner technologies to more objectively assess student crown preparations 31 teaching different crown preparation techniques 32 and evaluating the effectiveness of different teaching methodologies using digital and real time technologies. 18 Each has proposed educational bene ts.
An underpinning principle of successful pre-clinical xed prosthodontics education is that simulation teeth should have an accurate and realistic representation of natural teeth while ideally circumventing the educationally limiting complexities in post-core technique teaching such as ne, blocked and curved canals. In the present study, arti cial teeth were predominantly reported to have the same or a little harder surface texture as natural teeth when using a high speed bur which tends to agree with a comparative study where the majority (71.1%) of the students thought there was not much difference in the tactile sense between natural teeth and the typodont teeth, notwithstanding the unknown brand of tooth used in the comparative study. 33 When coupled with the present study's nding that it was a little easier to locate the canals on arti cial teeth than natural teeth, the initial use of arti cial teeth for post-core teaching appears to suggest a bene cial educational experience for students especially at the commencement level.
The limitations of using natural teeth for endodontic pre-clinical teaching have previously been recognised 34 and their use may not represent a completely bene cial educational experience at the beginner level considering the intricacies of the root canal system. The use of arti cial teeth for endodontic pre-clinical procedures has been associated with promising initial results using traditionally mould-formed teeth 23 and 3D printed teeth 35 but the tooth hardness has been criticised. Clearly, further research and development is required in this area.

Arti cial tooth development
The development of arti cial teeth for use in simulation teaching has rapidly advanced in recent years.
3D printing of teeth with different layers may present reduced cost and manufacturing time bene ts and their use has been found to have a positive impact on the educational experience of students performing post preparations. 21 However, the hardness of the teeth has received initial criticism 21 with new materials proposed to address this issue. The hardness of 3D printed teeth has not been widely analysed speci cally in post-core procedures and requires further re nement.
This was the rst time arti cial teeth had been included as an option in the post-core component of this study's pre-clinical program, therefore no preceding student experiences were available. The manufacturing company of the arti cial teeth proposed user bene ts of a natural root form tooth model with anatomical pulp cavity, radiographic imaging ability, and a difference in cutting feel between the enamel and the dentin material similar to natural teeth. 36 The range of teeth is at present limited and being further developed.
Clinical applications and the importance of post-core education Extensive clinical research has been published in the eld of post-core materials and techniques including reviews of the founding principles 8 and systematic reviews and meta-analyses that claim high success rates in anterior and posterior teeth. 37 The cumulative survival rate of post-core restorations has been reported at 86% at 10 years 38 with summary rates of root fracture of less than 2% 39 but dependent on the post material and modulus of elasticity. However, the path to success is multi-factorial and especially in uenced by the selected post system. 37,40 Clinical practice has been reported as the key to competence and undergraduates' perceived competence in prosthodontics has been directly related to the number of treatments performed. 41 Pre-clinical education, as the precursor to clinical experience, is an essential component in the undergraduate dental curriculum. In this context of performing a complex procedure usually due to the substantial loss of coronal tooth structure, and with a myriad of post systems available in the marketplace, it is critical graduating dental students have a grounding in the mainstream post-core systems. The teaching of post-core exercises still represents a key component of the undergraduate xed prosthodontics programs in training dental students to be competent dentists.

Limitations
The 100% response rate was an excellent result and has been reported in other studies of similar type 29 and location 42 involving student participants. Although representative of this particular student cohort, the study was conducted at a single dental school and the results may not be generalisable to students in other programs. The responses were taken at a single point in time after the completion of the pre-clinical program and gathered retrospective data. The demographic of gender distribution was not investigated and the study included a relatively small number of students who chose to use a relatively small number of arti cial teeth. The results have a distinct educational focus and cannot be applied clinically. Nevertheless, in the context of limited previous research in this area, the present study's ndings are encouraging and should serve as a sound precedent for further research.

Recommendations
Based on the current available research, the author's proposal for future teaching of post-core techniques in a xed prosthodontics pre-clinical program is to use arti cial teeth for initial training leveraging the bene ts of simplicity and standardisation to build initial skills. When initial skills have been formed, proceed to further pre-clinical training on extracted natural teeth utilising their realistic properties of surface texture and the unique features frequently encountered in natural teeth before progressing to the clinical setting. Natural teeth still have a role to play in the pre-clinical simulation clinic teaching of postcore techniques.

Conclusions
Within the limitations of this study, arti cial teeth provided an appropriate and realistic simulation compared to extracted natural teeth and were easier to source for the post-core exercises of the preclinical xed prosthodontics program. More widespread use of arti cial teeth was limited by cost. There was a sole author who produced this work