Envelope of Discrepancy in Orthodontics: Enhancing Precision in Treatment
- 1. ENVELOPE OF DISCREPENCY PRESENTED BY – DR. POOJA PGT 3rd YEAR GUIDED BY- DR. DEEPAK SINGH DR. DIVYA SWAROOP DR. ARCHANA KUMARI DR. SHREYA SHARMA
- 2. CONTENTS • INTRODUCTION • ENVELOPE OF DISCREPENCY IN MAXILLA • ENVELOPE OF DISCREPENCY IN MANDIBLE • LIMITATIONS OF ENVELOPE OF DISCREPENCY • Expanding the Scope of Envelop of Discrepancy with TAD • REVISED ENVELOPE OF DISCREPENCY • SHOULD THE “ENVELOPE OF DISCREPENCY” BE REVISED IN THE ERA OF THREE- DIMENSIONAL IMAGING? CONCLUSION • REFERENCES
- 3. INTRODUCTION • One of the most important concepts for a beginning orthodontic resident to grasp is the range of tooth movement that can be accomplished within the biological limits of the system. • One way to describe the theoretical boundaries of the potential range of tooth movement is the “Envelope of Discrepancy”. • The envelope of discrepancy is an essential component of treatment planning, not only for appropriate positioning of the anterior and posterior teeth in the alveolar bone, but also for restoring stable occlusion. • Proffit and Ackerman (1994) introduced the concept of the envelope of discrepancy to graphically illustrate how much change can be produced by various types of treatment. • It was developed from cephalometric data and thus uses tooth movement relative to the underlying jaw and jaw relationships relative to the cranial base.
- 4. For any characteristic of malocclusion, four ranges of correction exist: (1) the amount that can be accomplished by orthodontic tooth movement alone; (2) a larger amount that can be accomplished by orthodontic tooth movement aided by absolute anchorage (bone anchors); (3) an additional amount that can be achieved by functional or orthopedic treatment to modify growth; and (4) a still larger amount that requires surgery as part of the treatment plan.
- 5. • The envelope can be imagined as an elastic 3D, asymmetric closed container. • It portrays the limitations of the range for the maxillary and mandibular teeth during - orthodontic treatment (inner envelope), orthodontic treatment combined with growth modification (middle envelope), and orthognathic surgery (outer envelope)
- 7. • The inner envelope for the upper arch suggests that maxillary incisors can be brought back a maximum of 7 mm by orthodontic tooth movement alone to correct protrusion • It can be moved forward only 2 mm. • The limit for retraction is established by the lingual cortical plate and is observed in the short term • the limit for forward movement is established by the lip and is observed in long-term stability or relapse. • Upper incisors can be extruded 4 mm and intruded by 2 mm, with the limits being observed in long-term stability rather than as limits on initial tooth movement.
- 8. • 5 mm of growth modification in the AP plane to correct Class II malocclusion is the maximum that should be anticipated, whether occlusion is achieved by acceleration of mandibular growth or restriction of maxillary growth. • The outer envelope suggests that 10 mm is the limit for surgical maxillary advancement or downward movement, although the maxilla can be retracted or moved up as much as 15 mm • the mandible can be surgically set back 25 mm but can be advanced only 12 mm.
- 9. • Clinicians must develop an envelope of discrepancy concept for the transverse dimension as well. • The transverse dimension can be crucial to long-term stability, periodontal health, and frontal dentofacial aesthetics. • Camouflaging the transverse skeletal deficiency by only moving the teeth may cause periodontal problems, mainly buccal gingival recession and instability of the occlusal scheme. The orthodontic and surgical envelopes can be viewed separately for the upper and lower arches, but the growth modification envelope is the same for both
- 11. Envelope of discrepancy tells us that- There is more potential for retraction than protraction. More potential for extrusion than intrusion More potential to setback than to advance maxilla or mandible Orthodontic and growth modification treatment can create larger sagittal (anteroposterior) corrections than in the vertical or transverse planes of space. Greater change is produced by growth modification orthodontic tooth movement (in growing child) than produced by teeth movement alone Greater change is produced orthognathic surgery than by orthodontic tooth movement (in adult patients)
- 12. • Since growth of the maxilla cannot be modified independently of the mandible, the growth modification envelope for the two jaws is the same. • These numbers are merely guidelines and may underestimate or overestimate the possibilities for any given patient; however, they help place the potential of the three major treatment modalities in perspective • The timing of treatment is a factor in the amount of change that can be produced. • The amount of tooth movement that is possible is about the same in children as it is in adults. • However, the growth modification range diminishes steadily as a child matures and disappears after the adolescent growth spurt, so some Class II and Class III conditions that could have been treated in a growing child with growth modification and tooth movement would require surgery if treated later on.
- 13. LIMITATIONS • These limitations were initially established based on visibility in conventional two-dimensional cephalometric images. • The detailed three-dimensional morphology of some structures cannot be determined using conventional imaging methods as these structures such as the incisive canal and maxillary sinus may limit maxillary tooth movement. • It reflects only hard tissue limitations • Soft tissue limitations are not reflected in the envelope of discrepancy which are major factor in the decision for orthodontic or surgical-orthodontic treatment
- 14. Expanding the Scope of Envelop of Discrepancy with TAD • Previously the orthodontic movements that were regarded to be difficult and that should be addressed within the limitations of the envelop of discrepancy are now attainable due to bone anchoring devices. • These device does not speed up movement of tooth, but they provide with the most bone-borne anchoring, resulting in more effective mechanics for movement of teeth • Another benefit is the use of mechanics that do not rely on patient compliance. • TADs have enhanced the efficiency of therapeutic results and made it possible to treat patients more effectively. • TADs can be used to address surgical problems without the need for surgery. • As a result, temporary anchorage devices are expanding the envelope of discrepancy.
- 15. REVISED ENVELOPE OF DISCREPENCY
- 17. • The different colored zones describe the range of potential tooth movement. • The arrows designate the direction of the movement in the diagram. • The pink zone represents the envelope for orthodontics alone, • the yellow zone depicts orthodontics plus orthopedics, • the green zone shows skeletal anchorage, • the blue zone any combination of the above with orthognathic surgery. The reason the green zone is shown in “fuzzy” fashion is that there is only sufficiently reliable data to make estimates at this point • The same limitation is the reason there is not a figure depicting the mandibular transverse envelope.
- 19. Should the “envelope of discrepancy” be revised in the era of three-dimensional imaging? He did a study to highlight the importance of understanding the mutual relationship between the roots of the maxillary teeth and structures i.e. incisive canal and maxillary sinus for diagnosis and treatment planning, as well as potential need to revise the envelope of discrepancy.
- 20. Cone-beam computed tomography (CBCT) has recently been used to obtain three- dimensional images of the craniofacial skeleton and teeth. Thus, CBCT has clarified the three-dimensional morphology/configurations of structures that cannot be appropriately visualized using conventional imaging (i.e., cephalometric and panoramic radiographs). These structures include the incisive canal and maxillary sinus. Structures such as the incisive canal and maxillary sinus may limit maxillary tooth movement. In this review, he highlighted the importance of understanding the mutual relationship between the roots of the maxillary teeth and these structures for diagnosis and treatment planning, as well as potential need to revise the envelope of discrepancy.
- 21. The shape of the incisive canal is known to vary among patients. The canal has two openings: one at the inferior nasal cavity and the other at the superior oral cavity. Because it is surrounded by thick cortical bone and contains arteries, veins, and nerves, root resorption of the maxillary anterior teeth can occur on contact with the cortical bone of the incisive canal. Takashi Ono in his case report observed unilateral root resorption in an incisor that was in contact with the incisive canal, whereas the contralateral incisor that lacked contact with the incisive canal remained intact. Sice the incisive canal is hardly visible on two-dimensional images (i.e., lateral cephalometric radiographs), careful attention to these details was not possible until the introduction of CBCT
- 22. An adult male patient with protrusion of the maxillary incisors and mandibular retrusion exhibited a Class II molar relationship, deep overbite, large overjet, and missing lower lateral incisors. Pretreatment CBCT images revealed that the incisive canal was large, and that the distance between the incisive canal and maxillary incisors was small. Two treatment options were proposed to the patient. The first option was an orthodontic treatment, including extraction of the maxillary first premolars and mandibular third molars on both sides, followed by orthognathic surgery due to the severe Class II skeletal relationship. Second option was Orthodontic treatment with TADs following extraction of the maxillary first premolars and mandibular third molars. The patient chose the latter option. During orthodontic treatment using TADs, CBCT revealed contact between the roots of the maxillary central incisors and the incisive canal. Thus, the treatment plan was changed to orthognathic surgery to close the remaining space in the premolar area via Le Fort I and Wunderer osteotomies. Acceptable occlusion was established at the end of active treatment. Root resorption of the maxillary central incisors did not progress after switching the treatment plan.
- 23. • Indeed, numerous reports have documented root resorption in the maxillary incisors following posterior movement. • Whether this occurred owing to contact between the root and incisive canal is controversial, as two-dimensional imaging provided incomplete visualization of the size and position of the canal. • • Till date, no studies have demonstrated that remodeling of the cortical bone of the incisive canal occurs following contact with the tooth root. • Therefore, the incisive canal can be the boundary on three-dimensional CBCT imaging to reconsider the envelope of discrepancy, if complete retraction of the maxillary incisors is attempted. • So, the envelope of discrepancy should be revised based on evidence obtained via newer imaging modalities such as CBCT.
- 24. CONCLUSION • Envelope of discrepancy is an essential component of treatment planning that describes the theoretical boundaries of the potential range of tooth movement • As it estimates the range of tooth movement that can be accomplished within the biological limits of the system. Thus, we as an orthodontist should consider it before deciding the treatment modalities for our patient.
- 25. REFERENCES • Proffit William R, Ackerman James L. Diagnosis and Treatment Planning in Orthodontics (Chapter 1). In: Graber Thomas M, Vanarsdall Robert L, editors. Orthodontics: Current principles and Techniques. 2nd. St. Louis, MO, USA: Mosby; 1994. p. 3e95. • Ono T. Should the "envelope of discrepancy" be revised in the era of three-dimensional imaging? J World Fed Orthod. 2020 Oct;9(3S):S59-S66. doi: 10.1016/j.ejwf.2020.08.009. Epub 2020 Sep 30. PMID: 33023734. • Mayuri Chinnawar, Pallavi Diagavane, Rizwan Gilani, Ranjeet Kamble, Expanding the Scope of Envelop of Discrepancy with Tad– A Review, J Res Med Dent Sci, 2022, 10 (10): 172-176. • Graber LW, Vanarsdall RL, Vig KWL. Orthodontics : Current Principles & Techniques. 5th ed. Elsevier/Mosby; 2012. .