Al-Noor University College Dentistry Department 4th Class Orthodontic Lecture Lecture 9 PDF

Al-Noor University College- Dentistry Department- 4Th Class-Orthodontic Lecture Lecture 9 ETIOLOGY OF MALOCCLUSION Part two: Classification of etiological factors November, 25 , 2024 Monday 1 Assistance Professor Dr....

Al-Noor University College- Dentistry Department- 4Th Class-Orthodontic Lecture Lecture 9 ETIOLOGY OF MALOCCLUSION Part two: Classification of etiological factors November, 25 , 2024 Monday 1 Assistance Professor Dr. Hakam H. Alfahkry PhD Orthodontics Etiology of malocclusion is the study of its causes. WHAT CAUSES A MALOCCLUSION? This question has to be answered correctly before any decision can be taken regarding its prevention or correction. Researches have grouped the common etiologic factors associated with malocclusions and presented various classifications. The various classifications proposed are: White and Gardiner’s classification Salzmann’s classification Moyer’s classification Graber’s classification. The final form of the occlusion and position of the teeth exhibits a wide range of variation.  The most commonly referred classifications are listed by Graber who divided the etiologic factors as general or local factors. 1 The General Factors: which have general effect on the occlusion and play a part in the development of every occlusion. 2 The Local Factors: which do not necessarily appear in everyone but they may be the main cause in producing a malocclusion in an individual. A given case of malocclusion may be a result of either a single or multiple local or general factors or be caused by a combination of local and general factors.  General Factors affecting Occlusal Development (where the variations were expected to arise):  Skeletal Factors (general factors): The size, shape and relative positions of the upper and lower jaws.  Soft tissue or muscle Factors (general factors): The form and function of the muscles which surround the teeth, i.e. the muscles of the lips, cheeks and tongue.  Dental Factors (general and local factors): The size of the dentition in relation to the size of the dental arches. General Factors (Skeletal Factors) : Excluding any pathological condition, the teeth are supported by the alveolar bone, which in turn is based on the basal bone of the jaws, therefore jaw bone can be subdivided into alveolar bone and basal bone, although both of them are belonged to the same bone. General Factors (Skeletal Factors) :  As the teeth are set in the jaws, the relationship of the jaws to each other will influence the relationship of the dental arches.  Jaw relationship can be considered as: A) Jaws in Relation to the Cranial Base:  Jaws are part of the head therefore each jaw may vary in its positional relationship to other structures of the head.  Such variation can occur in sagittal, lateral and vertical planes.  In orthodontic diagnosis it is usual to relate the position of upper and lower jaws to the anterior cranial base and each jaw can vary independently in its relation to the cranial base. General Factors (Skeletal Factors) : B) Jaws in Relation to Each Other: The relationship of the jaws to each other can also vary in sagittal, lateral and vertical planes, and variation in any plane can affect the occlusion of the teeth. The sagittal or antero-posterior relationship of the upper and lower jaws to each other called the skeletal relationship or skeletal pattern which can be: General Factors (Skeletal Factors) : B) Jaws in Relation to Each Other:  Skeletal class I:  In which the jaws are in ideal antero- posterior relationship in occlusion with the bones of the face and jaws being in harmony with one another and with the rest of the head.. General Factors (Skeletal Factors) : B) Jaws in Relation to Each Other:  Skeletal class II: in which the lower jaw in occlusion is positioned further back in relation to the upper jaw. General Factors (Skeletal Factors) : B) Jaws in Relation to Each Other:  Skeletal class III: in which the lower jaw in occlusion is positioned further forward in relation to the upper jaw. General Factors (Skeletal Factors) : CL I CL II CL III General Factors (Skeletal Factors) : Variation in the skeletal relationship results from: Variation in the size and position of the jaw: In the sagittal plane if one jaw is excessively small or large in relation to the other in antero-posterior dimension the development of skeletal class II or class III relationship may result. Also if one jaw is set further back or further forward than the other in relation to the cranial base, again skeletal class II or class III relationship may result. General Factors (Skeletal Factors) : C) Alveolar bone in relation to basal bone: although the alveolar bone is supported by the basal bone, the relationship between the upper and lower bones is not necessarily the same as that between the upper and lower basal bones. The alveolar bone supports the teeth and will therefore match tooth position rather than basal bone position. Antero-posterior skeletal relationship General Factors (Skeletal Factors) : Variation in the skeletal relationship results from:  In lateral plane, if the jaws match in size then the occlusion of buccal teeth in transverse relation is correct. However, if one jaw is wider than the other it may result in buccal cross bite, when lower jaw wider, or scissor bite, when the upper jaw is wider.  In the vertical plane, the effect is mostly seen with the variation in the shape of the lower jaw at the gonial angle. When this angle increased the vertical dimension of the face increased and vice versa. General Factors (Soft tissue Factors) : The teeth erupt into an environment of functional activity governed by the muscles of face, mastication and tongue. The muscles of tongue, lips and cheeks are of particular importance in guiding the teeth into their final position and variation in muscle form and function can affect the position and occlusion of the teeth. All muscles exert their influence by their sites of origin and insertion. Since the origins of these muscles are mainly on the basal bone therefore the position of the jaws must affect the position and action of the muscles which function on the teeth. General Factors (Soft tissue Factors) : The lips: The several muscles of the lip work as one functional unit; their effect on occlusion development depends on their form, size and function. General Factors (Soft tissue Factors) : The lips  Vertical Relationship: In the ideal lip form the lips meet together at rest position this condition called lip competence. General Factors (Soft tissue Factors) : The lips  Vertical Relationship: If the lips do not meet in rest position a condition due to short upper lip and lips seal achieved only by active contraction of the orbicularis oris and mentalis muscles called lip incompetence. General Factors (Soft tissue Factors) : The lips  Vertical Relationship: Sometimes lip seal is prevented due to malocclusion for example the protruding maxillary incisors despite normally developed lips called potentially competent lips. General Factors (Soft tissue Factors) : The lips  Lips are usually brought together during swallowing and speech movements.  If they are of sufficient size to be together at rest then lip closure will not place extra force on the teeth.  If the lips at rest are apart, then muscular contraction will be required to bring them together during swallowing and speech, which in turn will impose extra forces on the erupting teeth.  The effect of these forces on the erupting teeth depends on the sagittal relationship of the lips. General Factors (Soft tissue Factors) : The sagittal relationship:  it is determined by the relationship of the basal bone of the jaw to which they are attached.  For example the lower lip tends to be further back in class II and further forward in class III, CL I CL II CL III which increase the difficulty to put the lips together and may cause the lower lip to modify the eruptive path of the incisors. General Factors (Soft tissue Factors) : The lips  In skeletal class II the lower lip may function completely or partially behind the upper incisors.  For example In not severe case the lower lip may procline the upper incisors resulting in more severe class II than skeletal relationship.  In more sever skeletal discrepancy the lower lip may function behind the upper incisors without causing them to be proclined. General Factors (Soft tissue Factors) : The lips The lower lip may cause retroclination of the lower incisors during swallowing, speech or smiling activities. General Factors (Soft tissue Factors) : The lips In other skeletal class II the lower lip function entirely in front of upper incisors causing them to be retroclined into the class II division 2 incisor relationship. General Factors (Soft tissue Factors) : Lip line  The level at which the lips meet together in normal function.  The ideal lip line is approximately at the center of the crowns of the upper incisors with the lower lip in front of the upper incisors. 2.7 is the connector space General Factors (Soft tissue Factors) : Lip line  If it is low, part of the lower lip may function behind the upper incisors causing proclination, if it is completely behind upper incisors there will be no lip line as in class II.  It is high in class II division 2 causing retroclination of upper incisors. General Factors (Soft tissue Factors) : The tongue functioning, in conjunction with the lips and cheeks, in guiding the erupting teeth, and this affected by its size, its resting posture and its function. The size of the tongue is mainly related to the size of the lower jaw. If the lower jaw is larger than the upper jaw, the tongue is too large to fit within the upper arch, therefore tongue finds space between upper and lower arches and prevents full vertical development of the dentoalveolar structures resulting in open bite. General Factors (Soft tissue Factors) : The resting position of the tongue is ideally within the dental arches, filling the space enclosed by the teeth. Sometimes the tongue takes up an adaptive postural position, slightly protruded between teeth to touch the lower lip which will prevent the full vertical development of the incisal segment resulting in incomplete over bite. This is produced to seal the front of the mouth to allow nasal breathing (tongue lower lip anterior oral seal instead of lips oral seal) when there is difficulty to hold the lips together due to vertical or sagittal lip discrepancy. General Factors (Soft tissue Factors) : The function of the tongue is concerned with mastication, swallowing and speech. Its effect on the dentition is mostly related to swallowing (on average you swallow 580 times a day). After the food mastication is completed, the swallowing of food and saliva take place in sequence as: a) Closure of the lips. b) Teeth in light occlusal contact. c)Tongue elevated to the palate. d) Momentary clenching of the teeth as food pass into the pharynx. General Factors (Soft tissue Factors) : Variation of normal swallowing are also seen which may be described as tongue thrust: Tongue thrusting may develop as a complication of thumb sucking habit. Sometimes tongue thrusting develops as a compensatory mechanism for existing open –bite (adaptive tongue thrust ). Or may developed due to hereditary factor (endogenous or primary tongue thrust) Genetically predetermined pattern of oral behavior (the persistence of an infantile swallow pattern). endogenous or primary tongue thrust is rare, but it is difficult to distinguish it from an adaptive tongue. General Factors (Soft tissue Factors) : Variation of normal swallowing are also seen which may be described as: 1- Adaptive Swallowing: involves positioning of the tongue between teeth during swallowing and may be carried out with the buccal teeth apart (tongue positioned between teeth, effect the muscle and air pressures within the upper arch lead to narrow arch and buccal cross bite also prevents the full vertical development of the anterior dento-alveolar segment result in incomplete over bite), or buccal teeth together (lead to incomplete overbite or anterior open bite due to forward position of tongue). General Factors (Soft tissue Factors) : 2- Swallowing With Endogenous Tongue Thrust: Involves positioning of the tongue between teeth during swallowing and may be carried out with the buccal teeth apart. swallowing activity is accomplished by an anterior thrust of the tongue which is a basic neuromuscular mechanism. It sometimes associated with anterior lisp during speech. It prevents the full vertical development of the anterior dento-alveolar segments resulting in an incomplete over bite or anterior open bite. General Factors (Soft tissue Factors) : Variation of normal swallowing are also seen which may be described as tongue thrust: These two variations have somewhat similar effects on developing occlusion however, they respond differently to orthodontic treatment designed to reposition the teeth. The adaptive tongue will be changed if the teeth are moved but the endogenous tongue not and will reproduce the original tooth position if these are altered.  Neutral Zone  The fact that the lips and cheeks function outside and the tongue within the dental arches has led to the concept of a neutral zone existing between the inner and outer perimeters of the dental arches, where the forces of lips and cheeks on one hand and of the tongue on the other are balanced and within which the teeth are positioned.  This zone should be considered not only in relation to muscle forces but also in relation to intra oral air pressures which are induced by mandibular positions and movements, and to occlusal contacts and the periodontal ligament.  It is important to keep the teeth in the neutral zone at the end of the orthodontic treatment otherwise they will move to take up other positions.