The mandibular dental arch: part III. Buccal expansion.

The tendency toward relapse in intercuspid width has been examined with those cases having final intercuspid width less than 27 mm showing significantly less relapse than those cases with final intercuspid width of 28 mm or more. The point of contact between the cuspid and first premolar has been introduced as a key point on the arch, determining arch width. An individualized norm has been derived for this measurement as a function of the patient's tooth size, facial pattern, and other variables based upon stable normal occlusions in treated cases. Those cases expanded to a dimension exceeding the norm by more than 1 mm showed a greater propensity toward relapse. The group following the norm was significantly more stable than the over- and underexpansion groups at the .025 significance level. An individual norm for intermolar width based upon the patient's facial pattern (using frontal and lateral X-rays) has been established. Cases showing relapse showed considerably less space between the lower molar and the JAG plane, and greater lower face height than stable cases. The results show that the space available for the permanent dentition can be estimated in advance of treatment based on the patient's own skeletal measurements, thus minimizing unnecessary extractions, relapse, and extended treatment time due to errors in diagnosis.     

Stability of dental arch expansion in the deciduous dentition

Thirteen patients with deciduous dentition and more than 3mm intercuspid arch length deficiency are expanded and followed, with controls, for 6 years. Arch perimeter and width at permanent cuspids and bicuspids appear to be slightly greater, and lower incisors are positioned somewhat more forward on the mandible.     

Correlation between transverse expansion and increase in the upper arch perimeter after rapid maxillary expansion

The purpose of the present study was to assess the correlation between transverse expansion and the increase in upper arch perimeter, after maxillary expansion. Dental casts of eighteen patients were obtained before treatment and again five months after maxillary expansion. Measurements of intermolar width, intercanine width, arch length and arch perimeter were made with a digital caliper on photocopies taken from the dental casts. After assessment of the method error, a multiple regression model was developed following the identification of the best subset of variables. The resulting equation led to the conclusion that the increase in arch perimeter is approximately given by the addition of 0.54 times the intercanine expansion, and 0.87 times the arch length alteration.     

Longitudinal assessment of vertical and sagittal control in the mandibular arch by the mandibular fixed lingual arch.

The purpose of this investigation was to determine and quantify vertical changes in the position of the mandibular molars while maintaining arch perimeter with a fixed lingual arch. Twenty-three patients with a mean age of 10.4 +/- 0.6 years were selected to receive fixed lingual arch treatment as the only appliance in the mandibular arch. Average treatment time was 18.3 +/-+/- 0.6 months. Longitudinal records for 12 and 24 months of 24 individuals matched by ethnic origin, age, gender, and mandibular plane inclination were used as controls. Pretreatment and posttreatment cephalograms were used to determine positional changes. Statistically significant differences between the fixed lingual arch and control groups were found. The results of this investigation indicated that the mandibular fixed lingual arch is a useful tool to control the vertical development of the mandibular molars.     

下颌舌侧半固定扩弓矫治器的制作及临床应用

下颌舌侧半固定扩弓矫治器由下颌磨牙带环、栓道和扩弓簧组成,将扩弓簧两末端的栓销插入栓道内可对下牙弓进行扩弓。对25例下牙弓狭窄患者的扩弓矫治表明,下颌舌侧半固定扩弓矫治器的扩弓效果良好。     

An experimental study on mandibular expansion: increases in arch width and perimeter

The purpose of this study was to estimate the increase in arch perimeter associated with mandibular lateral expansion. The mandibular expansion was simulated using a three-dimensional (3D) finite element method (FEM) and a computer graphics technique (3D simulation). The centre of rotation of molars during movement accompanied by lateral expansion was calculated using 3D FEM. The geometry of the model was determined using the mandibular bone of an East Indian skeletal specimen and 1 mm computer tomogram (CT) slices. The 3D set-up simulation was then conducted using 3D computer graphics instead of performing a manual set-up. Rotational movement was induced in the buccal segment, from the first premolar to second molar, in the 3D set-up model around the location of the centre of rotation (4.5 mm below the root apex of the first molar) derived from the FEM. According to 3D simulation, the model showed an opening space of 1.43 mm between the canine and first premolar, and thus a change in arch perimeter of 2.86 mm. The tip of the mesio-lingual cusp of the first molar moved 3.88 mm laterally, resulting in a change in inter-molar width of 7.76 mm. These values mean that a 1 mm increase in arch width resulted in an increase in arch perimeter of 0.37 mm. This result would be of value clinically for prediction of the effects of mandibular expansion.     

Orthodontic correction of transverse arch asymmetries.

The purpose of this study was to determine whether asymmetries in the transverse dimension are corrected after orthodontic treatment and to determine differences between age-group responses in the correction of transverse asymmetries. Sixty orthodontically treated subjects with transverse asymmetries in arch width were grouped by age, treatment modality, and arch location. Casts were analyzed to assess the correction of arch asymmetry. Lateral cephalometric analysis was performed to assess vertical change differences between age groups, and to detect correlations between vertical and arch-width changes. After orthodontic treatment, it was found that the arch width between the 2 halves of the arch still showed significant differences (P < .05); it was also found that arch-width changes between pretreatment and posttreatment showed significant differences (P < .05) for nonextraction treatment and for the anterior region in extraction treatment. Analysis of lateral cephalograms showed significant differences (P < .05) in vertical-dimension changes between growing and nongrowing subjects. The Pearson product moment correlation test showed no significant correlation at the P < .05 level between vertical and arch-width changes. We concluded that, for this sample, asymmetry in transverse dimension was not corrected, and there was no difference between growing and nongrowing individual responses in transverse asymmetry correction.     

Stability of the transverse dimension of the maxilla after surgically assisted rapid expansion

The aim of this study was to evaluate the behavior of the transverse dimension of the maxilla after surgically assisted rapid expansion with and without using a transpalatal arch fixed retention. Sixty cast models of the maxilla and 60 posteroanterior radiographs from 30 adult subjects, 16 male subjects and 14 female subjects, were evaluated. The subjects were 18.1 to 53.2 years old (mean age, 27.3 years), had been submitted to surgically assisted rapid maxillary expansion, and were using the expansion appliance for four months. The subjects were randomly assigned into two groups of 15 subjects. One group, called the group with retention, received a transpalatal arch fixed retention and another group, which received no retention, was called the group without retention. The assessments were performed at two time points: at the removal of the expansion appliance (T1) and 6 months after the removal of the expansion appliance (T2). In the cast models, interpremolar distances (A-A1) and intermolar distances (B-B1) were measured and in the posteroanterior radiographs, maxillomandibular discrepancy was used. A reduction in the distances A-A1 (-0.76 mm) and B-B1 (-1.54 mm) was observed among the time points studied in the group without retention and this difference was statistically significant. In the group with retention, the difference between the time points T1 and T2 was not statistically significant. The assessment of the maxillomandibular difference showed an increase between the time points T1 and T2 in the group with retention (1.54 mm) and the group without retention (0.84 mm), which means a reduction in the maxillary width in the posteroanterior radiograph. In the comparison between the groups, the assessment of the cast models and the assessment of the posteroanterior radiograph showed no statistically significant difference in any of the variables studied.     

下颌扩弓结合固定矫治后牙弓和WALA嵴宽度的变化

目的 应用下颌改良扩弓器,结合MBT直丝弓矫治技术治疗处于生长发育高峰期或末期中重度牙列拥挤伴牙弓狭窄的青少年患者,探讨矫治前后下颌牙弓和WALA嵴宽度的变化.方法 对29例10～15岁中重度牙列拥挤伴牙弓狭窄的青少年进行下颌扩弓,下颌为改良式网状支架扩弓器,运用直丝弓矫治技术完成矫治.矫治前后制取模型,采用Andrews关于牙弓,WALA嵴的定点方法测量下颌牙弓及WALA嵴宽度,并对治疗前后的测量结果进行配对t检验.结果 矫治完成后,下颌牙弓和WALA嵴宽度均不同程度增加(P＜0.05).均以第二前磨牙区扩大最多,其次是第一前磨牙区、磨牙区,而尖牙区最小,矫治效果良好.结论 下颌改良扩弓器结合固定矫治对下颌中重度拥挤伴牙弓狭窄青少年患者的矫治效果良好.     

Spontaneous mandibular arch response after rapid palatal expansion: a long-term study on Class I malocclusion.

The purpose of this study was to investigate the spontaneous mandibular arch response to rapid palatal expansion as the sole orthodontic intervention. Particular attention was paid to clinically significant effects and long-term (mean age, 11.3 years) posttreatment stability in 30 Class I malocclusion patients treated during the early and mid mixed dentition. Measurements were made directly on 120 dental casts obtained at 4 assessment stages: pre-expansion (A1), short-term follow-up (A2), progress (A3), and long-term follow up (A4). Comparisons between A1 and A2 showed statistically significant (P < .001) increases for intermolar widths (lingual and occlusal values). During the transition to the permanent dentition, a significant (P < .001) decrease occurred in arch length and arch perimeter. There was a 25% intermolar width (occlusal value) decrease from the initial net gain, whereas the lingual values remained unchanged. Comparisons between A2 and A4 showed an intermolar width (occlusal value) net gain of 50% and a significant (P < .001) decrease for the arch length and arch perimeter. There was remarkable stability in intermolar width (lingual value) and intercanine width (occlusal value), indicating that the increase in the mandibular arch width dimension was in response to the orthopedic effects of rapid palatal expansion in the early and mid-mixed dentition and that the stability was maintained until adulthood.     

A reassessment of the mandibular transverse horizontal axis therory.

1. Within the limits of accuracy imposed by individual operators, equipment, and patient variations, a single transverse horizontal axis can usually appear to be located. 2. Location of a kinematic axis is worthwhile clinical procedure to transfer an arc of rotation in the sagittal plane from the patient to an articulator. 3. Past experiments have been useful, but none have proved or disproved the presence of colinear or noncolinear condyle arcs. Only the arc of the rigid clutch and its associated mechanism is located. Such an apparent arc may result from the resolution of compound condylar movements. 4. The right angle-nonright angle concept is misleading and generally is not applicable to clinical procedures. 5. The anatomic asymmetries of the axis transfer procedure may result in cast dislocations that may produce undesirable alterations in esthetic tooth positions. 6. The single transverse horizontal axis as a fact in articulating instruments and as a theory in the human craniomandibular complex. 7. The terms "transverse horizontal mandibular axis" and "intercondylar axis" should not be confused or used as synonyms. The term "transverse horizontal mandibular axis" ("hinge axis") should be used instead of "condylar" or "intercondylar" axis.     

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近年来,许多正畸医生对安氏Ⅱ1错畸形伴下颌前牙轻度唇向倾斜的患者多倾向于不拔牙治疗而运用唇挡这一功能性矫治器进行治疗,这一技术受到人们越来越多的关注。本文就唇挡的作用原理、制作要求、矫治效果及效果的稳定性等几方面加以综述。     

Unilateral expansion of a narrow mandibular dental arch combined with bimaxillary osteotomies in a patient with hypoglossia

A 23-year-old female with hypoglossia, who had a narrow mandibular dental arch, was treated using the gradual expansion technique. Three lower incisors were missing and the right molar occlusion showed a scissor bite. Her speech was acceptable. Gradual unilateral expansion of the mandibular alveolar bone was performed. Orthodontic tooth alignment was performed prior to surgical treatment. A tooth-borne expander was devised using a hyrax-type screw to move the inclined right alveolar bone into an upright position. Alveolar bone osteotomies were performed under general anesthesia and the expander was placed in the mandibular dental arch. After a 5-day latency period, the screw was activated for 21 days. After expansion, the width of the mandibular dental arch increased by 10 mm at the first molar region and the right molars were moved to an upright position. After a consolidation period of 7 days, simultaneous two-jaw surgery that combined Le Fort I osteotomy and intraoral vertical ramus osteotomies was performed to obtain a stable occlusion. After post-surgical orthodontic and prosthodontic treatment, her occlusion improved without deterioration of her speech. The results indicate that this technique is useful for unilateral expansion of distorted mandibular alveolar process.     

Increase in arch perimeter due to orthodontic expansion.

A mathematical model was developed to compare quantitatively the effects of various types of orthodontic expansion on mandibular arch perimeter. Mandibular arch form was modeled with spline interpolation to fit a smooth curve between assigned molar, canine, and incisor positions. Starting with average arch dimensions, intermolar width, intercanine width, and midline arch length were increased individually and in combination in millimeter increments up to 5 mm, and the consequent changes in arch perimeter were measured. Increasing midline arch length by incisor advancement was nearly four times as effective in increasing arch perimeter as was molar expansion; canine expansion had an intermediate effect. Arch perimeter increments increased slightly with successive amounts of expansion for the molar, canine, and incisor. Combinations of molar-canine and canine-incisor expansion yielded results comparable to the total effects achieved by expansion of those teeth individually. Combined molar-canine expansion created increases in arch perimeter that were only slightly less than those generated by incisor advancement alone.