Commentary: A Translational Medicine Approach to Tooth Transplantation

Translational approach to tooth autotransplantation: A 27-year case study

BACKGROUND

The aim of this case report was to present a translational approach to tooth autotransplantation using jiggling forces to enlarge the periodontal ligament (PDL) space before autotransplantation, with the goal of improving treatment success and long-term survival.

METHODS

A 23-year-old patient, undergoing orthodontic therapy and with an unrestorable maxillary first molar, was proposed to have a healthy and fully-erupted maxillary third molar transplanted in the socket of the first molar. Jiggling forces were applied to the third molar to enlarge the PDL space and facilitate the preservation of PDL fibers on the root surfaces during the extraction.

RESULTS

Jiggling forces induced hypermobility and widened PDL space of the third molar. The autotransplantation was successful and the patient was followed regularly over a 27-year period. At the 27-year visit, the patient showed optimal chewing function, oral plaque control, and absence of gingivitis. The transplanted molar exhibited periodontal health and absence of mobility. Probing depth of 5 mm and radiographic external root resorption was noted on a localized area of the transplanted tooth which had experienced traumatic and unintentional removal of PDL fibers during the extraction.

CONCLUSIONS

A translational approach was proposed by integrating knowledge from the fields of orthodontics, trauma from occlusion, and replantation. It validated the crucial importance of maintaining healthy PDL fibers on the root surface and demonstrated clinically the successful autotransplantation of a fully formed third molar into the socket of a first molar with a retention of 27 years.

KEY POINTS

Why is this case new information? This case provided evidence of successful autotransplantation of a molar with complete root formation. It reported the longest-term follow-up (27 years) present in the literature. Most importantly, it used a translational medicine approach to apply concepts from the fields of orthodontics and traumatic occlusion to improve the success of the autotransplantation procedure. What are the keys to the successful management of this case? Jiggling forces induced tooth hypermobility and increased the PDL space of the tooth planned for autotransplantation. In turn, they facilitated the atraumatic extraction and preservation of the PDL fibers on the transplanted tooth, improving the success of the reattachment of periodontal fibers. What are the primary limitations to success in this case? Traumatic extraction resulting in the unintended removal of PDL fibers from the tooth planned for autotransplantation, or intentional removal of PDL fibers with root planing are expected to decrease the success rate of the autotransplantation procedure. This is due to the lack of viable PDL cells necessary for reattachment.

Numerical simulation of optimal range of rotational moment for the mandibular lateral incisor, canine and first premolar based on biomechanical responses of periodontal ligaments: a case study

OBJECTIVES

The objective of this study was to investigate the optimal range of rotational moment for the mandibular lateral incisor, canine and first premolar to determine tooth movements during orthodontic treatment using hydrostatic stress and logarithmic strain on the periodontal ligament (PDL) as indicators by numerical simulations.

MATERIAL AND METHODS

Teeth, PDL and alveolar bone numerical models were constructed as analytical objects based on computed tomography (CT) images. Teeth were assumed to be rigid bodies, and rotational moments ranging from 1.0 to 4.0 Nmm were exerted on the crowns. PDL was defined as a hyperelastic-viscoelastic material with a uniform thickness of 0.25 mm. The alveolar bone model was constructed using a non-uniform material with varied mechanical properties determined based on Hounsfield unit (HU) values calculated using CT images, and its bottom was fixed completely. The optimal range values of PDL compressive and tensile stress were set as 0.47-12.8 and 18.8-51.2 kPa, respectively, whereas that of PDL logarithmic strain was set as 0.15-0.3%.

RESULTS

The rotational tendency of PDL was around the long axis of teeth when loaded. The optimal range values of rotational moment for the mandibular lateral incisor, canine and first premolar were 2.2-2.3, 3.0-3.1 and 2.8-2.9 Nmm, respectively, referring to the biomechanical responses of loaded PDL. Primarily, the optimal range of rotational moment was quadratically dependent on the area of PDL internal surface (i.e. area of PDL internal surface was used to indicate PDL size), as described by the fitting formula.

CONCLUSIONS

Biomechanical responses of PDL can be used to estimate the optimal range of rotational moment for teeth. These rotational moments were not consistent for all teeth, as demonstrated by numerical simulations.

CLINICAL RELEVANCE

The quantitative relationship between the area of PDL internal surface and the optimal orthodontic moment can help orthodontists to determine a more reasonable moment and further optimise clinical treatment.

Dynamic measurement of orthodontic force using a tooth movement simulation system based on a wax model

BACKGROUND

Orthodontic force is often statically measured in general, and only the initial force derived from appliances can be assessed.

OBJECTIVE

We aimed to investigate a technological method for measuring dynamic force using tooth movement simulation.

METHODS

Tooth movement was simulated in a softened wax model. A canine tooth was selected for evaluation and divided into the crown and root. A force transducer was plugged in and fixed between the two parts for measuring force. Forces on this tooth were derived by ordinary nickel-titanium (Ni-Ti) wire, hyperelastic Ni-Ti wire, low-hysteresis (LH) Ti-Ni wire and self-made glass fibre-reinforced shape memory polyurethane (GFRSMPU) wire. These forces were measured after the tooth movement.

RESULTS

The canine tooth moved to the desired location, and only a 0.2 mm deviation remained. The changing trends and magnitudes of forces produced by the wires were consistent with the data reported by other studies. The tooth had a higher moving velocity with ordinary Ni-Ti wires in comparison to the other wires. Force attenuation for the GFRSMPU wire was the lowest (40.17%) at the end of the test, indicating that it provided light but continuous force.

CONCLUSIONS

Mimicked tooth movements and dynamic force measurements were successfully determined in tooth movement simulation. These findings could help with estimating treatment effects and optimising the treatment plan.