| Comparing with Angle Ⅰ, Ⅲ malocclusion patients, Angle Ⅱ malocclusion patients have a higher incidence of temoporamandibular disorders(TMD). Special occlusal features of Angle Ⅱ malocclusion which is one of the most common malocclusion in GuangDong area are related to TMD, e.g.(deep overbite,overjet, less teeth contact).Centric relation (CR)means the lower jaw position relative to the upper jaw or the skull when condyle is seated more anterior and upper. CR is none of occlusion’s business. In CR, the condyle is located in the back of articular tubercle’s posterior inclined plane and articular disc position is moderate and stable. What’s more, lower jaw position relative to the upper jaw is the most stable and comfortable position too which also can be repeated easily. Centric occlusion(CO) means upper and lower teeth bite together and have the most extensive and close contact.Premature contact means that there are few teeth contact in CR. In order to avoid the premature contact,the lower jaw slides to CO from CR under the nervous system regulation, the lower jaw deviates from the normal track and condylar position changes too. The difference between CO and CR is a common phenomenon and the difference may lead to condylar position change. And in CR, there is premature contact. It’s worth studying whether patients who have different premature contact in CR always have different condylar position. Knowing about the disharmony between malocclusion and mandibular position, the difference between CO and CR, condylar position changes between CO and CR, premature contact in CR, can help orthodontist make correct diagnosis and treatment plan.Objective:To explore the premature contact in CR of Angle II malocclusion patients without and with TMD, condylar position in CO, changes of condylar position and malocclusion between CO and CR, and offer the theoretic basis for this kind of patients before the orthodontic treatment.Method:1. This study selectd 23 Angle II malocclusion patients who have healthy temporomandibular joints and 23Angle II malocclusion patients with TMD at the Orthodontics Dept of Stomatology Hospital of Guangdong Province during 2013-2014, who first visit and accept orthodontic treatment or clinical examination, and they are 12-32 years old.The 23 Angle II malocclusion patients who have healthy temporomandibular joints are classified as control group, the average age is 15.7 years old, while 23Angle II malocclusion patients with TMD are classified as experimental group, and the average age is 20.1 years old. Inclusion criteria:(1) Up to the diagnostic criteria for Angle II malocclusion, no orthodontic history; (2) The second molars have already erupted and all patients have full teeth arrangement; (3) Patients can cooperate with clinical practice,such as taking dental impression, recording occlusion by biting wax, transferring facial arch and taking CBCT. (4) TMD patients:Up to the diagnostic criteria for TMD study (RDC/TMD). Exclusion criteria:(1) 1 or more tooth loss and cusps had decay. (2) Limited mouth opening, the range of mouth opening motion was less than 3cm; (3) Patients had traumatic history or operation history of maxillofacial region and temoporaomandibular joint(TMJ). (4) Patients with cleft lip and palate. (5) Patients with psychological problem and systemic diseases (Rheumatoid, tumor, epilepsy and so on). Study content2.1 Clinical functional examination of the Friction’s TMJ and masticatory musclesFriction temporomandibular disorders index was calculated to assess the health status of temporomandibular joint of all patients.Fricton craniomandibular index includes TMJ dysfunction index (dysfunction index, DI) with palpation index (palpation index, PI), dividing for Fricton craniomandibular index (craniomandibular index, CMI) equally DI and PI.2.2 Cephalometry films analysisAll patients should take cephalometry films. Winceph7.0 software was used to measure ∠SNA, ∠SNB, ∠ANB, which can reflect information about upper and lower jaw.2.3Occlusal changes between CO and CR2.3.1 Determination of CO:Red bite registration sheet wax were used to record occlusion of CO.2.3.2Determination of CR:Patients were asked to do small range of mouth opening motion, at the same time, doctor’s right hand thumb put on the-patient’s pogonion, forefinger and middle finger on the left and right sides of angle incisure of the mandible angle and applied anterosuperior force, then the condyle would be induced to CR. Next,blue bite registration sheet wax were used to record occlusion of CR. Transfer the occlusion to the dental cast. We can measure the changes of overbite, overjet, left and right molars and canines position between CO and CR.2.4Examination of premature contactWe used Delar wax to record occlusion of CR, transfer the facebow, and shift the occlusion of CR to articulator. Then using red occluding paper and silver paper to examine premature contact.2.5Analysis of condylar position2.5.1 Measurement of temporomandibular joint spaceCone beam computer temography(CBCT)were performed to scan bilateral temporomandibular joint and the images were input into NNT software for reconstruction. Selected the maximum cross-sectional diameter of condylar, and made paralle line and vertical line of condyle long axis to measure anterior space, posterior sapce,lateral space, superior space and mesial space of temporomandibular joint.2.5.2Assessment of condylar positionCalculation of InP/A:InP/A was greater than 0.25, anterior condylar position was defined. Centric condylar position was defined if InP/A between-0.25 and 0.25; and posterior condylar position was indicated for value InP/A less than-0.25.Calculation of LR(LR=(P-A)/(P+A)*100):If LR was greater thanl2, anterior condylar position was defined. Centric condylar position was defined if LR between-12 and 12. And posterior condylar position was indicated for value LR less than-12 (A and P represent anterior space and posterior space of temporomandibular joint respectively).2.6Measures condyle displacement(MCD) recordBy transferring facebow, we can shift the patients’occlusion of CR to articulaor, and use the MCD tracing paper to record the condylar position of CO and CR respectively.Results1. Results of Fricton’s CMIThe score of mandibular movement (MM), joint noise (JN), joint palpation (JP), dysfunction index (DI), craniomandibular index (CMI) and palpation index (PI) of control group was zero; while the score of MM(1.435±1.237), JN(1.562±1.308), higher than the control group’s,and the difference was statistically significant. The score of PI(0.006+0.018)of experimental group was greater than the the control group’s, but it was no significant difference.2. Measurement result of celphalometry filmsThe mean value of SNA angle,SNB angle, ANB angle of control group of 23 patients was 81.404±3.239°,77.314±3.166°,4.127±1.892°espectively, while the mean value of SNA angle, SNB angle, ANB angle of experimental group of 23 patients was 80.971±3.901°,75.640±4.183°,5.374±2.318°respectively. The ANB angle of the control group is smaller than the experimental group’s, but it was no statistical difference (P> 0.05)3. Changes of occlusion between CO and CR3.1 Changes of overbite and overjet between CO and CRFrom CO to CR, the average decrease of ovebite of control group was 0.84+ 0.89mm, the average increase of overjet of control group was 1.39+1.18mm, the difference was statistically significant (P<0.05); the average decrease of ovebite of experimental group was 1.13±0.54mm, the average increase of overjet of experimental group was 1.94±1.40mm, the difference was statistically significant(P <0.05); while the overbite and overjet changes of experimental group were larger than the control group’s, but the difference between the two groups was not significant (P>0.05).3.2Changes of the molars and canines position between CO and CRFrom CO to CR, the average value of distal movement of the left and right molars of control group was 0.935±0.919mm,1.034±0.679mm respectively, the average value of distal movement of the left and right canines of control group was 1.780Q1.477mm,1.733±1.481mm respectively; while the average value of distal movement of the left and right molars of experimental group was 1.780±1.477mm, 1.733±1.481mm respectively, the average value of distal movement of the left and right canines of experimental group was 1.654±1.371mm,1.567±1.334mm respectively. The average value of distal movement of the left molars, left canines, right molars of experimental group was larger than the control group’s, and the difference was statistically significant (P<0.05).4. Location and distribution regularity of premature contactIn CR, eighty-six point nine percentage of premature contacts of control group patients located in posterior teeth,while percentage of posterior premature contacts of experimental group reached to ninety-five point six. In CR, premature contacts of experimental group tended to the more distal tooth of the denture.5.Analysis of condylar position in CO5.1 Measurement result of temporomandibular joint spaceFor all patients’ joint spaces, there was no difference between left and right sides (P>0.05). Anterior space (2.268±0.602mm) of control group was smaller than the experimental group’s anterior space (2.584±0.728mm), mesial space (2.683 ±0.789mm) of control group was larger than the experimental group’s mesial space (2.342±0.804mm), which also had statistically significant difference (P<0.05). Posterior joint space, lateral joint space and superior joint space showed no statistically significant difference (P>0.05)5.2 Analysis of condylar positionCentric condylar position of control group was sixty point nine percentage (LR)and sixty-three point one percentage(InP/A). While fifty-two point two percentage of condyles of experimental group were seated more posteriorly.6. MCD records6.1 Intra-group comparisonIn the control group, the vertical difference of left condyle and the sagittal difference of the right condyle between CO and CR were statistically significant(P< 0.05); in the experimental group, sagittal and vertical differences of left condyle were statistically significant(P<0.05).6.2 Comparison between the two groupsCondyle changes between CO and CR of the experimental group patients in the sagittal direction:left side (1.196±0.705mm), right side (1.339±0.896mm); in the sagittal direction:right side (1.339±0.860mm), were larger than the control group’s, and it was statistically significant (P<0.05). Condyle changes between CO and CR in the transversal direction:the average change of the control group was 0.426± 0.326mm, while the average change of the experimental group was 0.487+ 0.255mm, but there was no statistically significant difference between the two groups (P>0.05)6.3 Analysis result of MCDMCD records showed that most anteroinferior position of the left condyle of the two groups patients in CO, while for the right condyle, most posteroinferior position. Most patients’ left condylar position of CR located on the posterosuperior part of CO, right condylar position of CR located on the anterosuperior part of CO.Conclusion1. Dentist found that Fricton’s CMI of Angle Ⅱ malocclusion patients with TMD was higher than the AngleⅡmalocclusion patients’, who had healthy temporomandibuar joint, so in the clinical work orthodontists should pay more attention to TMJ examination.2. Compared with the ANB angle of Angle Ⅱ malocclusion patients with TMD, the ANB angle of AngleⅡ malocclusion patients with healthy temporomandibular joint was much smaller. And it suggests that the greater difference between upper and lower jaw position is probably one of the TMD inducing factors.3. In CR, Angle II malocclusion patients had a higher incidence of premature contact. The study selected forty-six Angle Ⅱ malocclusion patients and all the patients had premature contacts in CR. Premature contacts of AngleⅡmalocclusion patients with TMD tended to the more distal tooth of the denture.4. The greater differences between CO and CR may play an important role in TMD.5. Most condyles of AngleⅡmalocclusion patients with TMD were posteriorly positioned in the glenoid fossa, before designing treatment plan, posterior condylar position should be restored to normal position. |
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