Mechanical stress generated by orthodontic forces on apical root cementum: a finite element model.

OBJECTIVES: 1) To determine the mechanical stress generated at the root apex during different types of tooth movement using a finite element model of an ideal, human maxillary central incisor. 2) To determine the relationship of thickness of cementum and the magnitude of mechanical stress at the root apex. DESIGN: Computer simulation. SETTING AND SAMPLE POPULATION: Not applicable, computer simulation. EXPERIMENTAL VARIABLES: Tooth and investing tissue layers (enamel, dentin, cementum, pulp, periodontal ligament, and alveolar bone). OUTCOME MEASURE: Von Mises and maximum principal stresses. RESULTS: Increasing the apical thickness of cementum increases the amount of mechanical stress. CONCLUSION: A finite element model incorporating all layers of a human maxillary central incisor has been developed. This model was used to determine the location and magnitude of mechanical stress generated for all regions of the tooth, PDL, and enclosed alveolar bone, when orthodontic forces are applied to the tooth. Mechanical stresses were found to increase at the root apex with increasing thickness of apical cementum.

Characteristics of patients with severe root resorption.

OBJECTIVES: The purpose of this study was to compare a group of patients in whom all four maxillary incisors were resorbed at least 20% with a matched group. MATERIALS AND METHODS: Retrospective, case-control. Root resorption was measured on pre- and post-treatment periapical radiographs collected from 868 patients treated in private practices in southern California. Diagnostic and treatment factors were recorded, and vertical and horizontal apical movement calculated from cephalometric films. Root shape was assessed with a six-object non-parametric rating system. From this patient population, 25 patients were found who had >20% root resorption on all four maxillary incisors. A case control group without severe root resorption matched by sex, treating office, age at start, ethnicity, and duration of treatment was created with two controls for each severe case. RESULTS: There were no statistically significant differences found for extractions, use of Class II and finishing elastics, transverse treatments, overjet, overbite, vertical, tooth length, habits, and root shape. Higher estimated risk was found for abnormal root shape for both maxillary incisors, and tongue thrust. Horizontal apical displacement was not significantly different (p = 0.07) but severely resorbed incisors were retracted an average of one millimeter further. CONCLUSIONS: Twenty-five of 868 patients were found to have over 20% of all four of their maxillary incisors resorbed. This is <3% of the total patients. Matching this group by sex, ethnicity, office, treatment time, and age greatly reduced the number of factors that would differentiate these patients from 50 who did not get severe root resorption. We conclude that horizontal root displacement, tongue thrust, and abnormal root shape may have higher estimated risk but interoffice variability and treatment time cannot be underestimated.

Assessment of root resorption and root shape: periapical vs panoramic films.

A radiographic examination is an essential part of the diagnostic process in orthodontics. However, what radiographs are needed to properly evaluate root shape and position? Most clinicians order panoramic or periapical radiographs in addition to the cephalometric radiograph. The purpose of this study was to find out whether one type of film is more accurate than the other in the pretreatment evaluation of root shape and the posttreatment computation of apical root resorption. Pretreatment and posttreatment panoramic films and full-mouth periapical films from 42 patients who completed fixed orthodontic treatment were assessed for tooth length and root shape. Panoramic films showed significantly greater average apicaL root resorption than periapical films for the 743 teeth surveyed. The greatest differences were found in the lower incisors, the least in the maxillary incisors. Classification of root shape was significantly different between the 2 types of radiographs. Root dilacerations and other abnormal shapes, clearly visible on periapical films, often appeared normal on panoramic films. The findings strongly suggest that root shape is much harder to assess on panoramic films. We conclude that, in cases where the apices are obscured or other factors are present that might suggest higher risk for root resorption or vertical bone loss, periapical films should be ordered. The use of panoramic films to measure pre- and posttreatment root resorption may overestimate the amount of root loss by 20% or more.

Predicting and preventing root resorption: Part I. Diagnostic factors.

The purpose of this study was to determine whether it would be possible to identify pretreatment factors that will allow the clinician to predict the incidence, location, and severity of root resorption before the commencement of orthodontic treatment. The records of 868 patients who were treated with full, fixed edgewise appliances were obtained from 6 private offices; full-mouth periapical radiographs were used to accurately assess apical root resorption from first molar to first molar in both arches. The results showed that resorption occurs primarily in the maxillary anterior teeth, averaging over 1.4 mm. The worst resorption was seen in maxillary lateral incisors and in teeth with abnormal root shape (pipette, pointed, or dilacerated). Adult patients experienced more resorption than children did in the mandibular anterior segment only. Asian patients were found to experience significantly less root resorption than white or Hispanic patients. Increased overjet, but not overbite, was significantly associated with greater root resorption. There was no difference in either the incidence or severity of root resorption between male and female patients.

Predicting and preventing root resorption: Part II. Treatment factors.

The main objective of this study was to determine which treatment factors are most clearly identified with external apical root resorption that is detectable on periapical radiographs at the end of orthodontic treatment. The records of 868 patients who completed fixed, edgewise treatment from experienced clinicians in private practice were examined. The horizontal and vertical displacement of the root apex of the maxillary central incisor was measured on cephalometric radiographs. Patients who underwent first premolar extraction therapy had more resorption than those patients who had no extractions or had only maxillary first premolars removed. Duration of treatment and the horizontal (but not vertical) displacement of the incisor apices were significantly associated with root resorption. No differences were found for slot size, archwire type, use of elastics, and types of expansion. However, there was considerable variation among the 6 offices that were surveyed; 1 office averaged nearly a full millimeter more of resorption per anterior tooth than the office with the least amount of root resorption. We conclude that the clinician should exercise caution with those patients in whom extraction therapy is planned for overjet correction that requires above average treatment time. Finally, each clinician should be aware that the root resorption seen in one practice may be different from the root resorption found in another practice.

A finite element model of apical force distribution from orthodontic tooth movement.

This study was undertaken to determine the types of orthodontic forces that cause high stress at the root apex. A 3-dimensional finite element model of a maxillary central incisor, its periodontal ligament (PDL), and alveolar bone was constructed on the basis of average anatomic morphology. The maxillary central incisor was chosen for study because it is one of the teeth at greatest risk for apical root resorption. The material properties of enamel, dentin, PDL, and bone and 5 different load systems (tipping, intrusion, extrusion, bodily movement, and rotational force) were tested. The finite element analysis showed that purely intrusive, extrusive, and rotational forces had stresses concentrated at the apex of the root. The principal stress from a tipping force was located at the alveolar crest. For bodily movement, stress was distributed throughout the PDL; however, it was concentrated more at the alveolar crest. We conclude that intrusive, extrusive, and rotational forces produce more stress at the apex. Bodily movement and tipping forces concentrate forces at the alveolar crest, not at the apex.

Facial growth in adulthood after primary periosteoplasty or primary bone grafting in UCLP.

OBJECTIVE: The primary research aim of this study was to compare long-term differences in craniofacial morphology at adulthood between two groups of unilateral cleft lip and palate (UCLP) patients: one operated by primary periosteoplasty and the other by primary bone grafting. DESIGN: The two groups were followed longitudinally at 5-year intervals; this study examined the 15- to 20-year age range. SETTING: University hospital/center located in Prague, Bohemia, Czech Republic. PATIENTS: 17 men with primary bone grafting, 29 men with primary periosteoplasty. INTERVENTIONS: Primary bone grafting or periosteoplasty. METHODS: Serial cephalometric radiographs. MAIN OUTCOME MEASURES: Conventional cephalometric and finite element measures. RESULTS: The mandibular symphysis was larger in the bone-grafted group. The periosteoplasty group displayed a more horizontal growth of the mandible with less rotation than the bone-grafted group. There were no other significant differences. CONCLUSIONS: We conclude that the original outcomes differences observed in childhood and adolescence were masked by skeletal and dental compensations in adulthood. These observations can be attributed to both natural growth and clinical intervention.

Accuracy of video imaging for predicting the soft tissue profile after mandibular set-back surgery.

The purpose of this study was to compare the accuracy of two video-imaging programs for predicting the soft tissue outcomes of mandibular set-back surgery for patients with skeletal class III malocclusion. The sample consisted of 30 previously treated, nongrowing, white patients who had undergone isolated mandibular set-back surgery. An objective comparison was made of each program's cephalometric prediction using a customized analysis, as well as a subjective comparison of the predicted images as evaluated by a panel of six raters. The results showed that both programs produced similar cephalometric and video image predictions. The cephalometric visual treatment objective predictions were found to be most accurate in the horizontal plane; approximately 30% of cases showed errors greater than 2.0 mm, whereas in the vertical plane, the error rate was greater (50%). The resulting video image predictions were judged by the panel as being in the "fair" category. A particular problem was noted when significant vertical compression of the soft tissue images was required. Video imaging was suitable for patient education but not accurate enough for detailed diagnosis and treatment planning.

The role of computerized video imaging in predicting adult extraction treatment outcomes.

The purpose of this study was to evaluate the accuracy of computerized video imaging in predicting the soft tissue outcome of extracting four premolars in adults. The pretreatment and posttreatment cephalometric and facial photographic records of 31 previously treated, nongrowing patients were digitized and computer-generated cephalometric VTOs and video images were compared with the known outcomes. The results showed that both the VTOs and video images were accurate enough to be used for patient education and communication, as well as for diagnosis and treatment planning. While lay people found that the predicted video images adequately resembled the actual outcomes, orthodontists were more critical, particularly of the lower lip area where variable soft tissue responses to treatment were noted.

The long-term stability of LeFort I maxillary downgrafts with rigid fixation to correct vertical maxillary deficiency.

This study evaluated the long-term stability of LeFort I maxillary downgrafts with rigid fixation in 28 patients with vertical maxillary deficiency. Preorthodontic, presurgical, immediate postsurgical, and an average of 16 months postsurgical cephalometric radiographs were evaluated. The results indicated that overall vertical maxillary stability after downgraft was good with 80% of the cases showing superior relapse of 2 mm or less. The mean amount of postoperative relapse represented 28% of the surgical downgraft. No correlation was found between the amount of the maxillary downgraft and the subsequent postsurgical vertical stability of the maxilla. No difference was found in the vertical stability of the maxilla comparing one-jaw and two-jaw procedures. It was also found that there was no difference in the vertical stability of the maxilla between single-segment and multiple-segment maxillary procedures, and also when comparing standard and high LeFort I osteotomy techniques. In addition, occlusal plane rotation of surgery, as well as the type of presurgical orthodontic movement, were both found to have no influence on postoperative stability of the maxilla.

Predicting soft tissue changes in mandibular advancement surgery: a comparison of two video imaging systems.

The purpose of this study was to evaluate the accuracy of two video imaging systems, Prescription Portrait and Orthognathic Treatment Planner, in predicting the soft tissue profiles of 39 patients who underwent mandibular advancement surgery. Presurgical cephalograms and profile photographs were entered into a computer. Computerized cephalometric line and video image predictions were generated and compared with the actual postsurgical results. The results indicate that both programs were equally accurate clinically in their line drawing and video image predictions. In the line drawings, clinically acceptable accuracy was shown in approximately 80% of the upper lip and chin predictions and in less than 50% of the lower lip predictions. The video images produced by both programs received fair to good ratings from a panel of professional and lay judges. Orthodontists and surgeons rated all aspects of the images similarly, while lay people were most critical of the chin and submental areas and least critical in their overall evaluation.

Predicting soft tissue changes in maxillary impaction surgery: a comparison of two video imaging systems.

The purpose of this retrospective study was to investigate the accuracy of two video imaging systems, Orthognathic Treatment Planner (OTP) and Prescription Portrait (Portrait), in predicting soft tissue profile changes after maxillary impaction surgery. Computer-generated line drawing predictions were compared with actual postsurgical profiles. Neither program was very accurate with vertical measures and lower lip contour. Portrait was more accurate at pronasale, inferior labial sulcus, and pogonion in the y-axis direction (P < 0.05). Video image predictions produced from the presurgical photographs were rated by orthodontists, surgeons, and lay people, who compared the predictions with the actual postsurgical photographs using a visual analog scale. Portrait's prediction images were scored higher than OTP's for five of eight areas. Orthodontists were most critical of the lips and the overall appearance. Lay people were most critical of the chin and submental areas.

The accuracy of video imaging for mixed dentition and adolescent treatment.

The purpose of this study was to evaluate the accuracy of computerized video imaging in predicting the soft tissue outcome of growth modification treatment for skeletal Class II malocclusions. Pretreatment and posttreatment cephalometric and facial photographic records of 22 mixed dentition (8 to 10 years old) and 20 adolescent (12 to 14 years old) patients were digitized, and the known outcomes were compared with computer-generated VTOs and video images. The predicted video images were found to be reasonably accurate for the mixed dentition group, but unacceptable for the adolescent group. When graded by a panel of judges, orthodontists were far more critical of the findings than their lay counterparts. These results emphasize the potential of video imaging as a communication medium, rather than as a diagnostic tool for growing patients.

Facial growth after primary periosteoplasty versus primary bone grafting in unilateral cleft lip and palate.

A cephalometric evaluation of long-term changes resulting from two different surgical techniques for the correction of unilateral cleft lip and palate (UCLP) was undertaken on a sample of 19 males with primary bone grafting, and 42 males with primary periosteoplasty from the Science Academy of the Czech Republic, Prague. Lateral cephalometric radiographs collected at approximately 10 and 15 years of age were traced, digitized, and analyzed using the finite-element method. Facial growth and development between the two groups were compared. Significant differences between the two groups were found in the upper face, the posterior part of the maxilla, the anterior bony chin, and nasal bone areas. The periosteoplasty group demonstrated significantly greater vertical development between anterior cranial base and the maxilla. The bony chin was larger and a greater inferior displacement of the posterior palate were found in the periosteoplasty group. An increased proclination in the nasal bone was observed in the bone graft group. This investigation both confirms the findings of a previous study of these sample populations, and provides additional important details regarding the differences between the groups.

Finite element-based cephalometric analysis.

The finite element method has proven to be a useful tool for morphometric analysis in craniofacial biology. However, few attempts have been made to adapt this method for routine use by clinicians. The CEFEA program incorporates the advanced features of the finite element method but bypasses the detailed understanding of the engineering and mathematics previously required to interpret results. The program uses the color graphics display of common personal computers to show size change, shape change, and angle of maximum change. These are pictured as colored triangles of clinically relevant regions between pre- and mid- or posttreatment lateral headfilms. The program is designed to have features of interest in both clinical practice and research.