Bony Chin Research Articles

3D analysis of facial asymmetry in subjects with juvenile idiopathic arthritis

To investigate and compare facial asymmetry in subjects with JIA with unilateral, bilateral or no TM joint (TMJ) involvement. Eighty-one subjects with JIA: 22 with unilateral TMJ involvement (Group 1), 15 with bilateral TMJ involvement (Group 2) and 44 with no TMJ involvement (Group 3). Panoramic X-rays and three-dimensional (3D) photographs (surface scans) were obtained for all subjects. Panoramic X-rays were rated for severity of TMJ involvement. For each individual, a spatially detailed facial asymmetry map was created from the 3D photograph. Mean and variability of asymmetry were calculated for each of the three groups and compared. Distinct patterns of asymmetry were found in Groups 1 and 2. With mean asymmetry values up to 3.5 mm, Group 1 exhibited a significantly greater amount of asymmetry in a broad band along the lower jaw extending from the region of the condyle to the chin than Group 2. The mean facial asymmetry (1 S.D.) for each JIA group was 2.3 (0.9), 2.0 (0.7), 1.7 (0.5) mm for Groups 1, 2 and 3, respectively. JIA subjects with TMJ involvement displayed patterns of facial asymmetry consistent with the destruction of the condylar growth centre, leading to mandibular asymmetry with displacement of the bony chin. Facial asymmetry quantification was found to be an effective method for assessing both the amount and the localization and spatial extent of asymmetry in all 3Ds.

Soft-Tissue Changes Related to Mandibular Advancement Surgery

This retrospective study assessed the relationship between the soft-tissue contours of the lower lip and chin and the underlying hard tissues consequent to surgical advancement of the mandible in the endeavour to enhance prediction in treatment planning. Cephalometric head films of 25 cases, 7 of which had advancement genioplasties, were available at presurgical, early postsurgical, intermediate, and long-term stages. Nineteen cephalometric landmarks were located and the data measured relative to X-Y coordinates constructed on the head films and were recorded on a Kontron video plan computer (Kontron Messgerate, GmbH, Image-analysis-systems, Eching/Munchen, West Germany). The data were organized and tabulated with Statgraphics version 4.0 software and statistically analyzed at the Institute of Medical Biostatistics, University of the Witwatersrand. No significant differences were found in the data between the patients who had undergone advancement genioplasties and those who had not. The soft-tissue chin advanced in a 1:1 ratio with the bony chin and a significant correlation was found between the horizontal change at labrale inferius relative to the lower incisor tip with a ratio of 0.77:1, but only marginally improved when tissue thickness was incorporated into a multiple regression analysis. Vertical changes of the lower lip did not show significant correlations with any hard tissue changes. Only when presurgical tissue thickness was included into a multiple regression analysis did the vertical change at labrale inferius demonstrate a fairly good correlation with the vertical change at menton. No significant changes occurred in the upper lip, and there was no significant relapse recorded at a minimum of 12 months after surgery.

Class II Treatment in Adults: Comparing Camouflage Orthodontics, Dentofacial Orthopedics and Orthognathic Surgery – A Cephalometric Study to Evaluate Various Therapeutic Effects*

It was the aim of this clinical study to compare the skeletal and dentoalveolar effects as well as those on the profile of three different treatment approaches in Class II patients (camouflage orthodontics, dentofacial orthopedics, and combined orthodontic and surgical treatment). Our study cohort consisted of 60 young adults presenting a skeletal Class II, Division 1 malocclusion: 20 patients whose overjet was reduced by camouflage following premolar extraction, 20 patients whose occlusions were corrected by placement of a fixed functional orthopedic appliance, and 20 who underwent orthognathic surgery (bilateral sagittal split osteotomy of the mandible without genioplasty). We documented the therapeutic progress using cephalometry. Each patient group achieved a reduction in overjet via their respective treatment. While no treatment-related changes in the maxillary area were assessable, the effects on the mandible differed. We observed advancement of the bony chin and an increase in mandibular length in the sagittal-diagonal dimension in the surgical and functional orthopedic groups. However, the extent of the treatment-related changes was significant only in the group of patients that had undergone orthognathic surgery. Only the surgical group presented changes in vertical relationships. Incisor repositioning as an outcome of the respective treatments differed fundamentally, with those in the surgical group revealing significant protrusion of the upper incisors. The maxillary incisors were retruded and mandibular incisors proclined in the functional orthopedic group, whereas the upper and lower incisors both retruded significantly in the extraction group. Soft-tissue remodeling bore no linear relationship to treatment-induced skeletal and dental effects. Still, orthognathic surgery led to the most marked profile changes. Treatment using fixed functional orthopedic appliances reduced the convexity of the soft-tissue profile at least moderately. Camouflage orthodontics, on the other hand, resulted in an increase in the nasolabial angle. In young adults fixed functional appliances are a treatment alternative to extraction therapy but to a lesser extent to orthognathic surgery. Because of their limited skeletal effects and minor changes in the profile they are indicated only in patients with a moderately severe Class II malocclusion. Pre-treatment proclined mandibular incisors limit the scope of indications for fixed functional appliances, as they can cause an increase in lower incisor proclination. Significant reductions in profile convexity are achievable only by combined orthodontic and surgical treatment of the malocclusion. When performing camouflage orthodontics in conjunction with maxillary premolar extractions in adults, an increase in the nasolabial angle, which is often esthetically undesirable, has to be discussed as a potential side effect and has to be taken into account when considering the different therapeutic approaches.

Craniofacial and dental phenotype of Smith–Magenis syndrome

The aim of this study was to assess and characterize dental and craniofacial findings in individuals with a confirmed diagnosis of Smith-Magenis syndrome (SMS). Extraoral and intraoral examination including dental and craniofacial radiographs and three-dimensional facial photoimaging were performed for 15 cases between ages 4 and 19 years old. Tooth agenesis (13/15 cases) affecting primarily the mandibular second premolars and taurodontism (13/15 cases) were common findings. Dilaceration of the tooth roots was present in one-third of the cases. At least one dental anomaly was present in each case. These findings occur with greater frequency than in the general population (P < 0.001). An age-related increase in decayed and restored teeth was found. Poorer oral hygiene, increased dental plaque, and increased gingival inflammation progressed from childhood to teenage years. Radiographic findings suggest the prognathic appearance is not caused by excessive mandibular growth. Other findings including protrusion of the mandibular anterior teeth, increased bony chin size, and macroglossia were noted, which may contribute to the prognathic appearance. The high prevalence of dental anomalies (>90%) further expands the phenotype and indicates that dental evaluation may aid in the diagnosis of SMS.

O.110 The need for autogenous blood donation in bimaxillar orthognathic surgery: An analysis of 79 consecutive cases

During facial growth, the maxilla and mandible translate downward and forward. Although the forward displacement of the maxilla is less than that of the mandible, the interarch relationship of the teeth in the sagittal view during growth remains essentially unchanged. Interdigitation is thought to provide a compensatory (tooth movement) mechanism for maintaining the pattern of occlusion during growth: the maxillary teeth move anteriorly relative to the maxilla while the mandibular teeth move posteriorly relative to the basilar mandible. The purpose of this study was to investigate the hypothesis that the human chin develops as a result of this process.Twenty-five untreated subjects from the Iowa Facial Growth Study with Class I normal occlusion were randomly selected based on availability of cephalograms at T1 (mean = 8.32 yr) and T2 (mean = 19.90 yr). Measurements of growth (T2 minus T1) parallel to the Frankfort horizontal (FH) for the maxilla, maxillary dentition, mandible, mandibular dentition, and pogonion (Pg) were made.Relative to Pg (a stable bony landmark), B-point moved posteriorly, on average 2.34 mm during growth, and bony chin development (B-point to Pg) increased concomitantly. Similarly, the mandibular and maxillary incisors moved posteriorly relative to Pg 2.53 mm and 2.76 mm, respectively. A-point, relative to Pg, moved posteriorly 4.47 mm during growth.Bony chin development during facial growth occurs, in part, from differential jaw growth and compensatory dentoalveolar movements.

Computergestützte Kaukraftanalyse bei Patienten mit Unterkieferkontinuitätsresektionen

Surgical treatment of tumors of the oral cavity often requires a segmental resection of the mandible. This always implies a considerable loss in function and aesthetics. The aim of the present study was to measure the chewing force obtained by patients after mandibular resection. In a group of 20 patients (twelve males, eight females, average age 59 years), chewing force were registered by means of a computerized measurement device. In 16 patients, the defect was bridged by a reconstruction plate, in three with an iliac bone graft stabilized by miniplates, and in one patient with only two miniplates. The maximum value in the molar region was 186 N und the minimum was 28 N. The average bite force in the molar region reached 81.1 N (+/-46.1) with 42.9 N (+/-35.7) in the front region. The highest value was registered in a patient with an iliac bone graft without soft tissue defect. The lowest was found in patients with bony chin defects. Based on these results, a reduction of 76% in the molar region and 59% in the incisor region was observed. These values might be helpful in providing a more realistic definition of the functional loadings found in patients after mandibular resection, which in turn may help in the development of new reconstruction devices.

Dental arch width in Class II Division 2 deep-bite malocclusion

A severe phenotype of Angle's Class II Division 2 (II/2) malocclusion with extremely deep overbite has been called cover-bite, or “Deckbiss” in its early German descriptions. This distinctive occlusal variation is characterized by skeletofacial hypodivergence, mandibular dentoalveolar retrusion, excessive bony chin projection, reduced mesiodistal tooth size, maxillary incisor retroclination, and at least 100% overbite, covering at least 1 mandibular incisor in occlusion. In this study, maxillary and mandibular dental arch widths measured at the first molars and the canines were recorded from dental casts of 23 subjects with II/2 cover-bite malocclusions. The data were compared with a control-reference sample of 46 orthodontic patients matched for age and gender. In the cover-bite group, the intermolar widths in both arches and the intercanine width in the maxilla were comparable with those in the control sample. However, mandibular intercanine width in the II/2 cover-bite group was significantly less than that of the controls (P =.01). These findings suggest that II/2 deep overbite malocclusion is characterized by normalized and relatively compatible transverse dimensions in the maxilla and in the mandibular posterior segments. The transverse underdevelopment that this study identified in the mandible from canine to canine is probably responsible for mandibular incisor compression and crowding—natural sequelae of the deep overbite in II/2 cover-bite. Thus, a reasonable orthodontic treatment plan for the mandibular dentoalveolar compensation often seen in II/2 deep-bite patients would be anterior expansion of the mandibular arch width, usually reducing the need for orthodontic tooth extractions and increasing the desirability of fixed retention. (Am J Orthod Dentofacial Orthop 2002;122:608-13)

Mandibular setback osteotomy: facial soft tissue behavior and possibility to improve the accuracy of the soft tissue profile prediction with the use of a computerized cephalometric program: Quick Ceph Image Pro: v. 2.5.

In part I, to derive ratios of soft to hard tissue profile changes after mandibular setback surgery and to report postoperative changes in soft tissue thickness at the lip and chin areas and, furthermore, to test the hypothesis that soft tissue thickness can act as one of the predictors of soft tissue response after surgery. In part II, to compare the predicted profile lines, using either the customized or the pre-programmed ratios, with the actual postsurgical outcomes. A retrospective study with the sample divided into two groups for different purposes. Department of Orthodontics and Department of Oral and Maxillofacial Surgery at Göteborg University, Sweden. Forty-one Caucasian subjects in need of mandibular setback surgery only. Hard and soft tissue movements and changes in soft tissue thickness after surgery were calculated using a customized analysis. Comparisons of the predicted profile outcomes with the actual postsurgical outcomes were carried out with another customized analysis. Distance measurements of certain landmarks in relation to constructed reference lines, both in horizontal and vertical planes, were calculated. The upper lip thickness decreased and the lower lip thickness increased after surgery. The hypothesis that the soft tissue thickness at the lip and chin areas could act as predictors of the ratios of soft to hard tissue changes after surgery, was not supported. Ratios for the lower lip of about 83% of the horizontal and 14% of the vertical movement of the PM point on the bony chin were found in Part I. In Part II, these ratios were introduced and the predicted profile moved significantly closer to the actual postsurgical outcome than if using the pre-programmed ratios (p < 0.05). Being able to customize the ratios of soft to hard tissue changes after a particular type of orthognathic surgery will enhance the accuracy of a patient's predicted profile outcome. These ratios should be pre-programmed in future versions of the software.

Class II Division 2 malocclusion: a heritable pattern of small teeth in well-developed jaws.

Angle's designation of the Class II Division 2 (II/2) malocclusion recognizes a unique combination of overbite, incisor retroclination, and sagittal discrepancy. A very severe II/2 phenotype, characterized by concealment of the mandibular incisors in occlusion, has been called Deckbiss in German, or cover-bite. In this report, the cover-bite malocclusion is studied to identify morphological factors associated with Angle's II/2 occlusal discrepancy. Selected X-ray cephalometric and odontometric measurements were recorded for 23 subjects (M14; F9) with II/2 cover-bite malocclusion. Data were compared with those from a control-reference sample of 537 individuals. Cephalometrically, the II/2 cover-bite sample showed a pattern of strong vertical posterior development of the mandible with forward-rotation and skeletofacial hypodivergence (p < 0.0001). Anteroposteriorly, the maxillomandibular dentoalveolar relationship was relatively normal, and the basal bone region of the mandibular corpus appeared significantly well developed anteriorly, accounting for excessive bony chin projection (p < 0.0001). Dentally, mesiodistal tooth diameters for the maxillary and mandibular incisors of the II/2 cover-bite sample were significantly smaller than those of the reference sample (p < 0.002), pointing to systematically reduced tooth-size as a trait associated with II/2 malocclusion. These findings of a characteristic pattern of heritable skeletal and tooth-size features in II/2 cover-bite malocclusion indicate the presence of strong genetic influences in the formation of Angle's II/2 deep-bite discrepancy.

Sliding osteotomies in mandibular reconstruction

There are several indications for resecting the bony chin, such as squamous cell carcinoma, sarcoma, or benign tumors of the jaw such as ameloblastoma. Several techniques for reconstruction of the bony chin, such as the use of metal plates and also revascularized free bone grafts of the iliac crest, fibula, or scapula, are common. In the case of poor vascular supply, however, alternative techniques may be necessary. In this report, a new technique is described using pedicled bone flaps from both sagittally split mandibular stumps following chin resection. These flaps were pedicled on the mylohyoid muscles and advanced to restore the continuity of the mandible. An advantage of this procedure was minimization of the soft tissue defect, making repair easier. Morbidity of the resection and reconstruction was thus reduced, and recovery of the patient was very quick.

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.

Skeletal change at surgery as a predictor of long-term soft tissue profile change after mandibular advancement

Purpose: This study examined the time course of hard and soft tissue changes after mandibular advancement surgery and the association between skeletal changes as a result of surgery and subsequent soft tissue changes. Patients and Materials: Subjects were enrolled in a randomized clinical trial of rigid versus wire fixation after sagittal split ramus osteotomy, with cephalometric data obtained before orthodontics, immediately before surgery and at 8 weeks, 6 months, 1 year, and 2 years postsurgery. This early report describes changes in 20 Caucasian female subjects who had completed all phases of the study; these were not segregated by fixation method. Cephalometric changes were referenced to a cranial base coordinate system. Differences in soft and hard tissue changes among time intervals were examined using analysis of variance; the associations between immediate surgical change in chin landmarks and subsequent short- and long-term soft and hard tissue changes were examined using linear regression analysis. Results: Soft and hard tissue mandibular structures were positioned anteriorly and inferiorly during surgery; the horizontal and vertical hard tissue mandibular changes were stable for 2 years after surgery ( P > .30), as were the vertical soft tissue changes ( P > .08). There was horizontal relapse of the lower lip and the inferior sulcus ( P < .03) by 8 weeks; no horizontal relapse was detected in soft tissue chin points for up to 2 years after surgery. The time course of changes in osseous pogonion was more strongly predicted by the amount of surgical osseous chin change than were changes in soft tissue chin projection. Conclusions: Prediction of changes in soft tissue chin projection after mandibular advancement surgery is less certain as time from surgery increases and less certain than the prediction of changes in bony chin projection.

Hard and soft tissue predictability with advancement genioplasties

Variability in soft tissue response to genial advancements has been noted in the literature. Although many factors may influence the results, little attention has been paid to bony vertical movement in conjunction with the bony horizontal movement of the chin and its effect on horizontal soft tissue movement. Eighteen patients who underwent isolated genial advancements were studied preoperatively and for at least 6 months after surgery. It was noted that the further the chin was advanced the less the soft tissue followed the advancement. In addition, vertical movement of the chin greatly influenced the overall result. The more the bony chin is shortened, the thicker the soft tissue chin becomes; the reverse is true when it is lengthened. Finally, horizontal resorption/stability appears to be influenced by the amount of dissection rather than the amount of advancement.

A Surgical System for the Correction of Bony Chin Deformity

Because the chin, like the nose, occupies a prominent position in the face, it must also be assessed in planning any changes in the facial profile. For example, a large nose associated with a microgenia does not appear as large when the chin is augmented. A chin increased in the vertical dimension confers an excessively long appearance to the face. Finally, a microgenia is associated with the stereotype of a sluggish personality, and a large chin in women connotes a masculine personality. The authors provide guidelines for assessing these variables and including them in surgical plan.

Use of preformed hydroxylapatite blocks for grafting in genioplasty procedures

Dense hydroxylapatite is a synthetic, biocompatible, immunologically inert material that can establish a chemical union with bone when placed in intimate contact in histologic studies. The following is a preliminary report of the use of preformed dense, non-resorbable hydroxylapatite blocks as a grafting material for use in advancement and vertical lengthening of the bony chin associated with orthognathic surgical procedures. In rare instances where an autogenous bone graft would be required for vertical lengthening without any advancement of bony pogonion, the need is obviated by utilization of the hydroxylapatite solid block.

Sagittal genioplasty: a new technique of genioplasty

A new technique for performing genioplasties is described. Antero-posterior and vertical deformities of the chin can be corrected and because a large surface area of bone remains in contact under compression following the osteotomy, a stable osteosynthesis is achieved. Access for fixation, using either wires or leg screws, is good and this feature, combined with the mechanical advantage obtained from the osteotomy cuts, contributes to great stability. The technique is safe, since there is minimal periosteal stripping; the bone cuts avoid the mental nerves and the mobilised bony chin retains a vascularised muscle pedicle.

A soft-tissue cephalometric analysis and its use in orthodontic treatment planning. Part II

To summarize, the soft-tissue profile can vary in many ways and still be in balance and harmony. There is a wide range of acceptability regarding soft-tissue chin position in the profile. Both the lips and the chin should line up near the H line, but we need to look at the upper lip from a different perspective or in its relation to a line perpendicular to the Frankfort plane and tangent to the vermilion border to be certain that we are planning the best possible lip support for the case at hand. The H angle, allowing a few degrees for soft-tissue thickness variability, must increase as the basic skeletal convexity increases, and as the convexity increases, the lower incisors will need to be left farther forward than in a straight or concave skeletal profile. A thick integumental covering in the chin area can also effectively align the lower facial profile where lower incisors are farther forward than we are accustomed to seeing them. This principle can also be applied by surgically moving the bony chin forward until the three key soft-tissue points line up. Because there are wide variations in skeletal convexity, standardizing the position of the lower incisor to its apical base support as measured in the Frankfort mandibular incisor angle fails to recognize that upper incisors can be retracted too far, leaving a “streamlined” upper lip which is not esthetically pleasing. Locating the lower incisor in relation to the expected point A to pogonion line is somewhat better but still fails to recognize the wide range of variability in the thickness of the lips and soft-tissue chin. We must also guard against “dishing” those cases having good facial balance with quite normal skeletal convexity and only 5 mm or 6 mm of lower arch length discrepancy.Finally, it is completely practical as a treatment-planning procedure to approach the proposed orthodontic changes from a soft-tissue analysis perspective, making changes only to the point where the best possible soft-tissue profile is established, and then compute the tooth movement necessary to develop ideal profile relationships. The visualized treatment objective, or VTO, is the vehicle that I use to accomplish this.

Cephalometric guidance for the positioning of the lower incisors.

Lateral cephalometric radiographs of 67 German adults with ideal occlusion and good facial harmony were measured to establish the position of the lower incisors relative to the NB-line, and the configuration of the face and of the bony chin. These data were used to test an equation to establish a norm for the position of the lower incisors. The principle of a guiding multiple linear equation was confirmed and the following equation was found to be applicable to the German population:

Floating norms as guidance for the position of the lower incisors.

1. The incisor position should be evaluated in relation to the sagittal and vertical configurations of the face, as well as to the shape of the bony chin. 2. A floating norm for the positioning of the lower incisors is established based upon the guiding variables ANB, ML-NL and the N angle with the introduction of a multiple regression equation. The anticipated values for the guiding variables at the end of the treatment are used in the calculation.

The human chin and its relationship to mandibular morphology.

This study evaluated the proportion of the external chin (protuberantia mentalia) in relation to the total symphyseal area in normal jaws and those with a diverse morphology. A sample of 60 cases was randomly selected and divided into three groups of 20 each on the basis of normal growth, horizontal growth and vertical growth with an open bite. Tracings of lateral dn frontal radiographs were used to describe general mandibular form and to determine the percentage of external/total symphyseal area. Dental casts were also examined to determine a basal arch form ratio. The results of this study indicate that the amount of bony chin present is related to certain morphologic features of the mandible. The most significant findings illustrate: 1. The chin increases in size as the mandibular type varies from a vertical type, to a normal type, to a horizontal type of growth pattern. 2. With dental "hypofunction" in combination with an exaggerated vertical development of the mandible, a smaller proportion of the protruding chin is present. 3. The chin increases in size as the mandibular basal arch form varies from a tapered shape for the vertical cases to a more square form in the horizontal cases. 4. The degree of lateral ramal flair does not appear to influence the proportion of protruding chin present. Several models have been presented which attempt to explain protuberantia mentalia variation. The evidence in this study supports the concept that mandibular morphology is the result of the action of compensative adaption in a developing structure. There appears to be an implied polygenic influence on symphyseal morphology operating from the cartilaginous cranial base and mandibular basilar bone. This may be manifested in the relative proportion of mandibular basal bone to cranial base width, and to the vector of cranial base growth. The ultimate proportion of the bony chin is viewed to be the result of mandibular adaption to a functional musculoskeletal balance in the craniofacial complex. The extreme variability of chin form in man may be considered to be the result of compensative growth developing in response to the most structurally efficient jaw form, the contiguous soft and hard tissue environment, and the intrinsic genotype of the mandible.