Introduction: This article presents possibilities regarding how orthodontists and prosthodontists can cooperate together to create conditions for an esthetically pleasing and functionally oriented treatment result. When planning the prosthetic treatment of anterior gaps, the gaps can be adjusted in advance by means of orthodontic treatment so that they can subsequently be treated in the best possible esthetic and functional manner.
Material and Methods: Adhesive bridges represent a suitable treatment option in adolescents for congenitally missing lateral incisors or after anterior tooth loss due to trauma. When designed with one wing, adhesive bridges can be used before the completion of jaw bone development and, if necessary, they can be orthodontically positioned together with the abutment tooth. Prior to complex prosthetic rehabilitation in the esthetic area, malpositioned abutment teeth can be orthodontically positioned or aligned to generate space for an ideal restoration design. Moreover, orthodontic extrusion provides the possibility of achieving sufficient abutment heights in the case of deeply destroyed or fractured teeth, thus permitting the adequate treatment of these critical teeth according to prosthetic guidelines. Oftentimes, in the case of tilted, protruded or retruded teeth, an orthodontic intervention previous to tooth preparation is useful for tooth substance conservation and maintaining the vitality of abutment teeth.
Conclusion: It can be concluded that a specific combination of orthodontic and prosthetic treatment measures can achieve a better restorative treatment result in terms of function, esthetics and long-term stability. Often, this is accompanied by a reduction in treatment duration and costs.
Clinic for Prosthodontics, Center for Implantology, Medical Center of RWTH Aachen University: Dr. Karin Groß; Prof. Dr. Stefan Wolfart
Translation from German: Christian Miron
Citation: Groß K, Wolfart S: Interfaces between orthodontics and prosthodontics: interdisciplinary possibilities and “innovations”. Dtsch Zahnärztl Z Int 2020; 2: 160–167
Peer-reviewed article: submitted: 13.03.2020, revised version accepted: 07.06.2020
In order to achieve esthetically pleasing and functionally optimized treatment results in complex treatment cases, close cooperation between the orthodontist and prosthodontist is often advisable. In ideal circumstances, this teamwork extends from treatment planning to joint treatment implementation and is rewarded by satisfied patients and high-quality treatment results. The overlap, or interface, between the two disciplines is multifaceted. This article discusses 4 of these interfaces and presents clinical examples to illustrate them:
- If individual teeth are missing, the question of which specialty domain should have pre-eminence, and accordingly the responsibility, often arises: Should an existing dental gap be orthodontically closed, or be restored by prosthetic means, such as a bridge, adhesive bridge or implant? Each of these approaches has advantages and disadvantages; they can best be discussed in a joint consultation between the dentist, orthodontist and patient.
- In the case that a dental gap is to be treated by prosthetic means, it is necessary to first check the gap size and decide whether or not it is acceptable, as corrective orthodontic treatment may be required beforehand for an esthetically pleasing or functionally reasonable solution. The same applies for the restoration of multiple teeth in the esthetic zone. Often, this is only useful if the abutments are spaced at a distance that allows esthetically pleasing length-width ratios to be anticipated for each individual restoration and between adjacent anterior teeth.
- For the crowning of teeth, it is necessary to have adequate abutment height and sufficient healthy tooth structure after tooth preparation. If this is not the case due to biological width considerations and a high degree of destruction, an orthodontic extrusion can be considered.
- Following a crowning procedure, approximately 15 % of teeth show a negative response to sensitiv- ity testing after 10 years . A remaining dentin thickness of 0.5 mm should be aimed for in order to reduce the risk of pulp damage . Therefore, it is important to remove as little healthy tooth structure as possible during preparation. Currently, preparation designs which preserve tooth substance have gained in importance. In this respect, the position and axial inclination of teeth play a decisive role. In clinical situations where the prospective abutment teeth require a common insertion path, but differ greatly in their axial inclinations, a conservative tooth preparation design is not attainable. In these cases, in order to avoid exceedingly invasive tooth preparations, orthodontically active components can be used in combination with interim dentures. By combining the temporary prosthetic phase with orthodontic dental alignment, a lower amount of tooth substance removal can be facilitated.
First interface: missing teeth
Anterior region gaps are most frequently caused by the congenital absence of teeth, especially maxillary lateral incisors, or traumatic loss. Around one quarter of young people experience front tooth trauma by the age of 14 and about 7 % of these front teeth are lost . Circa 1.5–1.8 % of people in Germany are affected by upper lateral incisor agenesis . Hence, it can be assumed that approximately 3–3.5 % of young people aged 14 years old are missing anterior teeth . A number of treatment options can then be chosen. If the lateral incisors are congenitally missing, patients, or rather their parents, are often presented with the options of either an orthodontic gap closure or an implant-supported restoration. Orthodontists often favor gap closure by means of canine mesialization. Gap closure not only has functional implications, but also esthetic ones. This is because canines differ noticeably from lateral incisors, in both shape and color, as canines usually appear darker than incisors. Consequently, in the majority of cases, the treatment is not fully complete after orthodontic gap closure due to esthetic reasons; for a natural appearance, canines then require corrective treatment to imitate the appearance of lateral incisors. This implicates adapting the tooth’s shape and color by means of applying a veneer, preparation of the enamel or whitening of the enamel by bleaching [18, 20, 26]. Particularly in the case of unilateral agenesis, asymmetrical tooth positions may lead to esthetic impairments. For this reason, the symmetrical alignment of the front teeth should always be an important objective.
Implant-supported restorations are contraindicated in adolescence. Nevertheless, even after transversal bone growth and canine eruption have been completed, vertical bone growth may continue into adulthood [21, 22]. Implants which are placed too early are often located in an infra position after a few years, which not only results in step formation at the incisal edges, but also in poor red-white esthetics in the area of the gingival line. Especially in the case of a high smile line, the timing for implant placement should be carefully considered. Adhesive bridges are often overlooked, or are solely considered a more or less temporary solution, until the age is reached when implants can be inserted. Lately, however, very good long-term results have been reported when using adhesive bridges. One-wing adhesive bridges have proven to be more reliable than two-wing bridges [2, 4, 10, 19, 24]. The clinical survival rate of one-wing adhesive bridges made of aluminum or zirconium oxide ceramics is between 95.4 and 98 % after 10 years [6, 9]. Thus, the survival rates of implant-supported crowns and one-wing adhesive bridges can therefore be regarded as being equivalent .
With reference to legally consistent patient education, the law governing the improvement of patients‘ rights, anchored in the Federal Law Gazette 2013, specifies that the patient should be completely informed regarding all possible treatment options . Accordingly, adhesive bridges must definitely be discussed as a treatment option. This necessity is also underlined by the fact that adhesive bridges are listed as a standard care procedure in the service catalogue of statutory health insurance companies since 2016. The key advantages of one-wing adhesive bridges are the minimally invasive preparation design which is only confined to the enamel and the fact that the restoration can be applied regardless of the stage of jaw bone development. The requirement is the presence of a completely erupted, caries-free neighboring tooth which borders the gap, having an adhesive surface in the enamel of at least 30 mm2, as well as, sufficient space relative to the antagonist jaw for the purpose of being able to design a connector with a height of at least 3 mm . Additionally, sufficient space should be generated for wing insertion in the case of maxillary adhesive bridges. For this purpose, the corresponding abutment tooth is protruded by approximately 0.7 mm using an aligner or multiband therapy. This creates sufficient space to attach the wing of the bridge without the need to perform any occlusal adjustments by grinding of antagonist teeth in the antagonist jaw. These necessary space conditions should be taken into consideration early on when planning an orthodontic treatment.
If only one incisor is missing, the contralateral tooth in the same jaw determines the size and shape of the intended restoration. A timely consultation with the prosthodontist is helpful here. Thus, a wax-up/set-up can be prepared at an early stage in order to model a suitable tooth. A try in of the tooth wax-up can be made, which is thereafter converted into composite. The model tooth is fixed in the dental arch in order to give the orthodontist the chance to adjust the dental gap exactly to the desired size and position for the subsequent esthetic restoration. A similar procedure is useful if both lateral incisors are missing (Fig. 1). In this case, too, an ideal situation can be created through precise prosthetic planning before, or at the latest, during orthodontic treatment (Fig. 2). Above all, the ideal width of the lateral incisors must be carefully considered. When the width of the lateral incisors is between 50 and 74 % of that of the central incisors, they are perceived as being esthetic  (Fig. 3). However, if the gaps are set-up as being too small or too large, the dental restoration can either
- then be too narrowly or too widely designed,
- arranged in an overlapping position,
- be fitted in, but with a remaining gap
- or orthodontic measures must be carried out once again after the prosthetic treatment.
Directly after the removal of the multiband appliance, a retention splint must be worn; it is essential to ensure that the patient wears it continuously until the adhesive bridge is introduced. Otherwise, there is a risk that the teeth could move in the short time it takes for the adhesive bridge to be finished. Directly after the adhesive bridge is cemented, a retainer must be applied, as is common for all orthodontic treatments. The splinting together of the two adhesive wings can take over this function (Fig. 4).
Second interface: setting ideal tooth spaces before beginning with the restoration
Provided that several teeth in the esthetic zone must be restored with crowns, or veneers, it is always useful to prepare a wax-up in advance to check if the ideal length-width ratios and proportions of the teeth with respect to each other can be achieved. In the abrasive dentition shown here, conspicuous diastemas existed between all anterior teeth. Given the tooth positions, it was not possible to close the spaces and make sufficient vertical bite correction, and yet, still be able to create esthetically pleasing anterior esthetics (Fig. 5–7). For this purpose, anterior tooth lengths averaging 11.7 mm for the central incisors, 9.5 mm for the lateral incisors and 10.8 mm for the canines are desirable . Additionally, a harmonious anterior overjet, a length-to-width ratio of the central incisors corresponding to 75–85 %, and a cen-tral to lateral incisor width ratio between 50 and 74 % should be present . In order to achieve this, a gap closure by means of mesialization and a gap expansion in the premolar region took place. Based on this orthodon-tic pre-treatment, which lasted about 1 year, an esthetically pleasing and functionally appropriate prosthetic restoration could be created (Fig. 8–11).
Third interface: orthodontic extrusion for tooth preservation
The extrusion of roots often makes it possible to preserve and restore fractured or deeply destroyed teeth [3, 5]: The background behind this has to do with the planned/existing dental post in non-vital teeth having to be surrounded by at least 2 mm of healthy hard substance (adequate ferrule design). For vital abutment teeth, however, a remaining abutment height of at least 3 mm is required. Furthermore, an adequate biological width must be maintained around the abutment teeth. In the existing case, the ceramic crown on tooth 21 was paragingivally fractured. The remaining abutment did not fulfill the conditions just described for a new crown which would have a favorable long-term prognosis. The neighboring teeth 11 and 22 displayed adequate restorations. Surgical crown lengthening was not an option due to esthetic reasons, as the previous gingival profile showed a harmonious appearance. In order to preserve the tooth, the root was extruded with the help of magnets. For this purpose, a magnet with flowable composite was attached to the vital abutment tooth. The magnet had to be reduced in size beforehand so that it matched the remaining abutment tooth (Fig. 12). Using a 1 mm thick placeholder, a second magnet was positioned on top of the first magnet and fixed to a previously fabricated Miniplast splint (Fig. 13). The supracrestal periodontal fibers were additionally cut with a scalpel under local anesthesia. In one to two weeks, the root was orthodontically extruded to the desired millimeter using magnetism. By moving the magnet twice inside the splint, with a renewed adjustment of 1 mm space between the magnets, the root could be extruded approximately 3 mm over a period of 6 weeks. The costs of this preliminary measure are not included in the service catalogue of the statutory health insurance companies, and must therefore, like any other orthodontic treatments in adulthood, be covered by the patients themselves. Subsequent to this procedure, a core build-up with composite, preparation of the abutment and fabrication of a temporary crown ensued (Fig. 14). In order to prevent the tooth from migrating again, the temporary crown was fixed to the adjacent teeth with retainer wire for 4 months. After the retention period, the definitive zirconia crown could be fabricated with vestibular veneering and adhesively bonded to the abutment. Figure 15 shows the restoration half a year after placement. The tooth continues to react positively to the cold sensitivity test.
Another method to mobilize teeth is through forced extrusion using rubber bands. For this purpose, if required, bars are fixed occlusally to the adjacent teeth [14, 16]. The abutment itself is fitted with a dumbbell-shaped device in the oro-vestibular direction. Elastic bands can then be hooked in with varying amounts of force (Fig. 16–18), so that the tooth root usually extrudes within a few weeks. The supracrestal separation of the gingival fibers prevents the fixed gingiva from moving with the root. When a coronal displacement of the soft tissue is also desired, the supracrestal fibers are not cut . This applies to all extrusions, regardless of the procedure.
Fourth interface: conservative preparation by uprighting teeth before crown preparation
A well-known procedure and typical example includes the classical uprighting of a molar that is inclined towards a mesial gap. We would like to present the case of an innovative, simple, and patient-oriented approach for aligning two canines. A 67-year-old patient with a remaining dentition consisting of 33, 43, and 44 in the lower jaw required a new prosthetic restoration. Owing to the inclination of the canines, the patient could hardly insert and remove the existing clasp-retained removable partial denture (Fig. 19). Besides this, the patient no longer wished for the new restorative treatment to have visible clasps. After a detailed consultation, he chose a telescopic denture. In order to have achieved a common insertion path during the preparation of the 3 abutment teeth, the canines should have been devitalized. A treatment alternative was represented by the uprighting of the two teeth in a mesial direction. The orthodontic appliance could be integrated into the already existing interim denture by applying orthodontic elements into its structure. Also, in this case, the orthodontic treatment had to be privately covered by the patient and an additional private agreement for the treatment and cost plan was created, which contained just the orthodontic measures. In order to use the time to test the new vertical bite position by means of the interim denture, a guide groove for the elastic band was prepared in cooperation with the department of orthodontics on the canines in the distal, lingual and vestibular areas. In addition, the denture teeth 31 and 41 each received a knob vestibularly to avoid protrusion or retrusion. In this way, the patient was able to attach elastics on his own, which he changed daily (Fig. 20 and 21). After 3 months, the two canines were upright enough so that their preparation could be successfully accomplished, while maintaining a common insertion path and the vitality of the pulp (Figs. 22 and 23). The retention of the two teeth was ensured by the telescopic restoration. Figure 24 shows the patient after 3 years. The two canines still respond positively to sensitivity testing.
In summary, a purposeful combination of prosthetic and orthodontic treatment measures can achieve better esthetics and function in many cases. This is often accompanied by a reduction in treatment duration and costs. For optimal treatment outcomes, coordinated treatment planning between the orthodontist and prosthodontist is recommended before beginning treatment.
Conflicts of Interest
The authors declare that there is no conflict of interest as defined by the guidelines of the International Committee of Medical Journal Editors.
- Gesetz zur Verbesserung der Rechte von Patientinnen und Patienten. Bundesgesetzblatt 2013; 9: 277–282
- Botelho MG, Chan AW, Leung NC, Lam WY: Long-term evaluation of cantilevered versus fixed-fixed resin-bonded fixed partial dentures for missing maxillary incisors. J Dent 2016; 45: 59–66
- Brawek P, Schley J, Wolfart S: Zahnerhalt durch forcierte Magnetextrusion – eine Falldarstellung. Dtsch Zahnärztl Z 2013; 68: 456–462
- Djemal S, Setchell D, King P, Wickens J: Long-term survival characteristics of 832 resin-retained bridges and splints provided in a post-graduate teaching hospital between 1978 and 1993. J Oral Rehabil 1999; 26: 302–320
- Harder S, Mehl C, Kern M: Behandlungsmöglichkeiten bei tief frakturierten Pfeilerzähnen. Quintessenz 2010; 61: 1485–1494
- Kern M: Fifteen-year survival of anterior all-ceramic cantilever resin-bonded fixed dental prostheses. J Dent 2017; 56: 133–135
- Kern M: Einflügelige Adhäsivbrücken. Kieferorthopädie 2018; 32: 123–134
- Kern M: Adhäsivbrücken: Minimalinvasiv – ästhetisch – bewährt. Quintessenz, Berlin 2018
- Kern M, Passia N, Sasse M, Yazigi C: Ten-year outcome of zirconia ceramic cantilever resin-bonded fixed dental prostheses and the influence of the reasons for missing incisors. J Dent 2017; 65: 51–55
- Kern M, Sasse M: Ten-year survival of anterior all-ceramic resin-bonded fixed dental prostheses. J Adhes Dent 2011; 13: 407–410
- Kern M, Wolfart S: Kontrovers diskutiert: Versorgung von Frontzahnlücken bei Jugendlichen nach Abschluss der kieferorthopädischen Therapie. Dtsch Zahnärztl Z 2018; 73: 330–337
- Kerschbaum T: Das Risiko des Vitalitätsverlustes nach Überkronung. DGZMK Statement 1998
- Magne P, Gallucci GO, Belser UC: Anatomic crown width/length ratios of unworn and worn maxillary teeth in white subjects. J Prosthet Dent 2003; 89: 453–461
- Mörig G, Svoboda R, Podolsky L: Forcierte Extrusion – ein Behandlungskonzept für bisher ausweglose Fälle. ZMK-aktuell 2017; 33: 42–50
- Murray PE, Smith AJ, Windsor LJ, Mjor IA: Remaining dentine thickness and human pulp responses. Int Endod J 2003; 36: 33–43
- Neumeyer S: Extrusions- und Implantationstechniken. Grundlegende Aspekte des Tissue Master Concepts (TMC) – ein biologisches Gewebemanagement. BZB 2013; November: 54–60
- Polder BJ, Van‘t Hof MA, Van der Linden FP, Kuijpers-Jagtman AM: A meta-analysis of the prevalence of dental agenesis of permanent teeth. Community Dent Oral Epidemiol 2004; 32: 217–226
- Priest G: The treatment dilemma of missing maxillary lateral incisors-Part I: Canine substitution and resin-bonded fixed dental prostheses. J Esthet Restor Dent 2019; 31: 311–318
- Saker S, El-Fallal A, Abo-Madina M, Ghazy M, Ozcan M: Clinical survival of anterior metal-ceramic and all-ceramic cantilever resin-bonded fixed dental prostheses over a period of 60 months. Int J Prosthodont 2014; 27: 422–424
- Schneider U, Moser L, Fornasetti M, Piattella M, Siciliani G: Esthetic evaluation of implants vs canine substitution in patients with congenitally missing maxillary lateral incisors: Are there any new insights? Am J Orthod Dentofacial Orthop 2016; 150: 416–424
- Thilander B: Dentoalveolar development in subjects with normal occlusion. A longitudinal study between the ages of 5 and 31 years. Eur J Orthod 2009; 31: 109–120
- Thilander B, Odman J, Jemt T: Single implants in the upper incisor region and their relationship to the adjacent teeth. An 8-year follow-up study. Clin Oral Implants Res 1999; 10: 346–355
- Tuli T, Hachl O, Rasse M, Kloss F, Gassner R: [Dentoalveolar trauma. Analysis of 4763 patients with 6237 injuries in 10 years]. Mund Kiefer Gesichtschir 2005; 9: 324–329
- van Dalen A, Feilzer AJ, Kleverlaan CJ: A literature review of two-unit cantilevered FPDs. Int J Prosthodont 2004; 17: 281–284
- Wolfart S, Thormann H, Freitag S, Kern M: Assessment of dental appearance following changes in incisor proportions. Eur J Oral Sci 2005; 113: 159–165
- Zachrisson BU, Rosa M, Toreskog S: Congenitally missing maxillary lateral incisors: canine substitution. Point. Am J Orthod Dentofacial Orthop 2011; 139: 434, 436, 438 passim