| Bimaxillary protrusion is more common in orthodontic clinic with the protrusion ofmaxillary, mandibular, alveolar bone and teeth which will severely affect the patients’profile and periodontal tissue. The most common therapy for this malocclusion involvesextracting the4premolars and then retracting the incisors to improve the profile and gotthe normal occlusion. However there is a disagreement about whether the alveolar bonemorphology of bimaxillary protrusion is consistent with individual normal occlusion, andwhether the thinner alveolar bone of anterior can meet the long distance movement.Excessive retraction might cause iatrogenic bone loss. There are lots of studies showingthat the capacity of the alveolar bone reconstruction can not compensate for the bone loss.The morphology of the alveolar bone in the anterior incisor region had traditionally beenevaluated with X-ray radiographs, which also did not distinguish the growth and type ofmalocclusion. But the insufficient of the two-dimensional view, the effect of growth andmalocclusion could effect the veracity and objectivity of the result. With CBCT technology, this study can acquire the accurate radiographic images to investigate thecharacteristics of morphology alveolar bone in the region of incisors and the change afterretraction.ObjectiveThis clinical study aims to compare the thickness and structure of the incisorsalveolar bone in untreated adult patients with bimaxillary protrusion forward with those ofthe normal occlusion, and compare the changes of the alveolar bone before and after theincisor retraction.MethodsExperime nt1: Eighteen cases with bimaxillary protrusion(8men,10women, age:19-30years) and fifteen cases (7men,8women, age:20-30years) with individual normalocclusion were selected randomly. Lateral cephalograms and CBCT scans were made. Allthickness of the labial and lingual alveolar bone of the8incisors in both groups weremeasured, and analyzed. Comparison between two groups was done with independentsample T-test and correlation analysis.Experime nt2: Sixteen adult patients with bimaxillary protrusion (4men,12women,age:20-32years) treated by extracting the4first premolars were evaluated with lateralcephalograms and CBCT. Cephalograms and CBCT scans were made before treatmentand3months after retraction. For all maxillary and mandibular incisors, we assessed thelabial and the lingual alveolar plates at crest level, midroot level, and apical level forbone-thickness changes during retraction of the maxillary and mandibular anteriorsegments. Linear measurements of the central incisors were also evaluated on lateralcephalograms to determine the amount of lingual movement. Paired t tests were used toevaluate the changes of alveolar bone that occurred as a result of incisor retraction.Results1The comparison between the adult with Class Ι bimaxillary protrusion malocclusionand the normal occlusion samples showed:①The total width of alveolar process at theroot apical level of maxillary and mandibular incisors in bimaxillary protrusion decreasedsignificantly than those in normal occlusion (P<0.05);②Labial thickness of alveolar bone at the crest and root midpoint showed significant decrease, but there were nosignificantnt difference in lingual.2Changes in alveolar bone thickness due to retraction of anterior teeth shows:①Labial thickness of alveolar bone at root midpoint showed increase except maxillarycentral incisor(P<0.05). Labial thickness of alveolar bone at root apical level of maxillaryincisors showed significant decrease after retraction;②The thickness of alveolar boneat P1, P2lever showed significant decrease after retraction;③The total width of alveolarbone at the root apical level of maxillary and mandibular central incisors showedsignificant decrease (P<0.05);④The amount of lingual movement of incisal margin wasgreater than that of the root apical.ConclusionsThe incisors′alveolar thickness of adult patients with Class Ι bimaxillary protrusionwas thinner than norm occlusion. There were statistically significant decreases in lingualbone width in both arches after retracting the incisors. Therefore, we should focus on theprocess of making plan and treatment to avoid negative iatrogenic effects．... |
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