Orthopedic dentistry and dental prosthetics
In the present conditions, with life expectancy increasing, the demand for prosthodontics, especially of complete denture prosthosis in our country will also tend to increase in the coming years. A complete denture prosthosis that ensures function and aesthetic has great influence for the quality of life. However, the complete denture fabrication has always been a challenge, even for the experienced clinicians.
On the other hand, according to several studies in recent years, the prevalence of the temporomandibular joint disorders seems to be increasing steadily, particularly for people with high quality of life caused a big concern as well as many other issues for the diagnosis.
Thus, the knowledge of the parameters of condyle is an urgent demand of clinicians. Because of objectivity and sensitivity of the recognizing the parameters of temporomandibular joint, the study of axiography is one of urgent requirement in order to improve the quality of prosthodontics as well as diagnosing, monitoring and evaluating the treatment results of the temporomandibular joint. With the aim of initially using the axis recorder and commenting the characteristics in axiography of normal people, we conducted a study entitled “The survey of Bennett angle and the condylar inclination of Vietnamese group, aged 18-25 using axiograph Quick-Axis”, with the following objectives:
- Determining the average values on the axiography: the depth and length of maximum opening movement; the length of protrusive movement and maximum lateral movement.
- Identifying the principal parameters for transferring information from people to articulator: Bennett angle, the angle of condylar inclination, immediate side shift.
- SUBJECTS AND METHODS
The study was conducted on 100 students (18-25 years old) of Hanoi Medical University. All of them have enough 28 teeth; class I of Angle’s classification of maloclusion; without symstoms of temporomandibular joint disorder and history of maxillofacial trauma as well as history of orthodontic treatment. All participants had no tooth that deviates from arch; and agreed to participate in this research.
Exclusion criteira: facial deformities; history of maxillofacial trauma; history of orthodontics and prosthedontics treatment; history of temporomandibular joint disorder.
Study design: cross sectional study.
Materials: An axiograph Quick-Axis of F.A.G.Dentaire-France; Mitutoyo’s digital caliper; Examination instruments: tray; mirror, tweezers, probe.
|Fig 1 An axiograph Quick – Axis|
|Fig 2 Mitutoyo Digimatic Caliper CD-6” CSX|
– Placement of para-occlusal clutch: a metal tray was affixed on the mandibular arch using a quick-setting plaster. The transverse bar holding an axiograph stylus was connected to mandible via this tray.
|Fig 3.1: Placement of para-occlusal clutch.||Fig 3.2 Placement of recording graph paper.|
– Placement of recording graph paper: the recording graph paper was fixed on head.
– Placement of transverse bar: the transverse bar holds a stylus
Fig 3.3 Placement of transverse bar
– After mounting transverse bar on the para-occlusal clutch and adjusting the stylus in the direction of the graph paper correctly, participants were asked to hold the clutch in the centered position. The position of mandible was determined in the centric relation position while the stylus was adjusted to the origin of the axes.
Fig 3.4 Placement and adjustment of the stylus
– Recognizing the following parameters: recording the condylar pathways of the opening movement; maximum protrusive movement and maximum lateral (both side) movements.
– The mandible was guilded from the posterior border to maximum opening. At that time, the stylus was moved out the origin of the axes on the graph paper.
– Similarly, the mandible was guilded to the maximum protrusive position, maximum lateral (both side) positions from the centric relation position. The tracings of axiograph were created on the graph paper. Each movement was performed several times.
|Fig 3.5 Recording the condylar pathways ||Fig 3.6 Measurement of Bennett angle |
The condylar inclination angle was defined as an angle created by a horizontal axis with line segment connects the origin point of the axes and the intersection of condylar tracing and the circle has center at origin and a radius of 5mm.
The lateral condylar inclination angle (Bennett angle = B angle): replacing the stylus with a micrometre device. The mandible was guilded to the opposite side ultil the stylus pointing the first circle on graph paper. The micrometre device moved a line segment and the value of Bennett angle that corresponding to this line segment was transferred to the articulator.
- Research ethics:
- All subjects agreed to participate voluntarily in this study.
- This study was accepted by Research and Ethics Council of Hanoi Medical University before performing.
- The research subjects could quit the study anytime they want.
- The confidentiality of personal information of participants are ensured.
- This study just aims to improve the oral health care, without any other purpose.
- Data processing methods:
Coding and entering the data into the IBM SPSS statistics version 19.0
- Errors and solutions:
- Subjective errors:
- The stylus was not perpendicular to the graph paper.
- The micrometre device did not contact to the graph paper
- The error during measuring the values on the graph paper
Solution: checking carefully during setting the axiograph and recording. Using the magnifying glass and digital caliper while measuring the values on the graph paper.
- Objective errors:
- The error of digital caliper
Khắc phục: Kiểm tra bản ghi. Đo trên bản ghi nhiều lần.
Solution: Checking the standard of graph paper. Measuring multiple times.
- The characteristics of the tracing on graph paper of axiograph Quick-Axis
|Fig 3.8 The tracings for male participant (D: Right; G: Left)|
|Fig 3.9 The tracings for female participant|
The tracing on graph paper in opening movement of mandible (red tracing) is a continuous curve comes from the origin point of the axes and runs downward and forward. The tracing starts as a short, downward sloping, and then runs as a horizontal line. The tracings for male and female participants have the same shape.
The tracing on graph paper in maximum protrusive movement (black tracing) also comes from the origin point of the axes and runs downward and forward. This tracing coincides with the tracing in maximum opening movement during the first 5mm of movement. Then, this tracing runs downward more than the tracing in maximum opening movement so that two tracings are separated.
The tracing on graph paper in lateral movement (blue tracing) also comes from the origin point of the axes and runs downward and forward. This tracing coincides with the tracings in maximum opening movement and maximum protrusive movement, and then separates from them.
The tracings for male and female participants have the same shape.
- Length values of the tracings on graph paper
Table 1 The average () and the standard deviation (σ) of tracings on graph paper for male and female participants
|The depth of maximum opening movement (mm)||Male||R||3,05||0,75||> 0,05||< 0,05|
|Male & Female||R||2,83||0,74|
|The length of maximum opening movement (mm)||Male||R||12,54||2,45||> 0,05||> 0,05|
|Male & Female||R||12,20||2,47|
|The length of protrusive movement (mm)||Male||R||8,69||1,61||> 0,05||< 0,05|
|Male & Female||R||8,13||1,52|
|The length of lateral movement (mm)||Male||R||11,96||2,47||> 0,05||> 0,05|
|Male & Female||R||11,57||2,55|
P: the differences between males and females / R: right –/ side L: left side
There were significant differences between males and females in average values for the length of maximum opening movement on left side and the length of protrusive movement on left side.
- Value of condylar parameters
Condylar inclination angle: On graph paper, identifying, reading and recording the condylar inclination angle: drawing a line segment from the origin point of the axes to the intersection of tracing in maximum opening movement and the circle has center at origin and a radius of 5mm. The angle made by the horizontal axis and this line segment are defined as condylar inclination angle.
Bennett angle: When the participants were asked to move their mandible to the working side, the needle of Micrometre device was in contact with the circle has a radius of 3mm on the graph paper. The value of tracing on Micrometre device was recorded and converted according the conversion table of manufacturer.
Immediate side shift: The right hand is used to supporting the mandible and the thumb touches the ramus of mandible. The left hand is used to holding the head. Making a lateral pressure that is parallel to the hinge axis to the mandible. The value of tracing on Micrometre device corresponds to the length (mm) that need for transferring to the articulator according the conversion table of manufacturer.
These parameters were recorded. The average and standard deviation for males, females and both of them were calculated and presented in Table 3.2.
Table 2 The average () and the standard deviation (σ) of condylar parameters for male and female participants
|Condylar inclination angle (degree)||Male||R||33,57||13,0||> 0,05||> 0,05|
|Bennett angle (degree)||Male||R||5,71||1,81||> 0,05||> 0,05|
|Immediate side shift (mm)||Male||R||0,50||0||> 0,05||> 0,05|
P: the differences between males and females / R: right –/ side L: left side
There were no significant differences between males and females in any average values of condylar parameters.
- Characteristics of the study
All research samples are the students of Hanoi Medical University aged 18 to 25 years old that satisfy the inclusion/exclusion criteria. After screening examination, 31 students include 14 males and 17 females were selected.
The study design was cross-sectional study, which is a type of observational study that are widely used in medical research.
The axiograph Quick-Axis of F.A.G.Dentaire-France records the condylar movements on both sides. Because this axiograph does not have any supporting or assistance of machines, the process of recording parameters may be occurred errors due to many different causes. Because of realizing this problem, we have had some solutions for maximum fixing the errors and avoiding the misleading results during performing our study.
On the graph paper, the tracings in the vertical plane were overlapped during the first 5mm of movement. Then, they are separated and differ in the level and shape. The tracing in maximum opening movement was the longest tracing.
The average and standard deviation of tracings of the condylar pathway of Vietnamese group were identified. They include the length of maximum opening movement (Right: 12,20 2,47 mm; Left: 12,432,74mm); the depth of maximum opening movement (Right: 2,830,74mm; Left: 2,970,93mm); the length of lateral movement (Right: 11,572,55m; Left: 11,362,77mm); and the length of protrusive movement (Right: 8,131,52mm; Left: 8,401,95mm)
If the average of tracing on graph paper for both males and females was taken as a standard, we could see the differences between the average for both of them and the average for each gender on the right and left side of condyle. These were shown in the Chart 4.2 and 4.3.
The average and standard deviation of condylar parameters of Vietnamese group also were identified. They include Bennett angle (Right: 5,65o1,70o; Left: 5,32o1,25o); condylar inclination angle (Right: 30,65o14,67o; Left: 34,10o14,07o); and the immediate side shift (Right: 0,530,12mm; Left: 0,520,09mm).
Recording the condylar movement using the axiograph allows evaluating the characteristics of condyle-disk assembly. The axiograph also provides the accurate parameters of the temporomandibular joint, that transferring to the articulator.
This is a relatively simple method which can be used in clinical practice for diagnosis and application of articulator in order to perform the restoration and treatment for the temporomandibular joint disorders.
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