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INDIAN DENTAL ACADEMY Leader in continuing dental education

Role of occlusion in maintaining aesthetics and function of dentofacial complex: Term occlusion is derived from Latin word occlusio defined as the relationship between all the components of the masticatory system in the normal function dysfunction and parafunction

Occlusion is an anatomic and physiologic complex present when the opposing teeth are in contact. It consists of positional relations , the stresses directed to the supporting structures their resistance to the stresses , the form and arrangement of the teeth , the influencing parts of the components of the TMJ & the neuromuscular mechanism responsible for mandibular movements.

The development of dentition is closely associated with the morphology & growth of the face & the way in which the functions of the orofacial region are exercised. The size of the two jaws , their anteroposterior relationship , the vertical dimension as well as the changes occurring during growth in these components play an essential role in the development of the dentition

Why 2 sets of teeth? The possession of 2 sets of teeth in mammals imparts the advantage of equipping the young in a short time , with the teeth capable of cutting crushing & grinding , while the much larger , more durable & slowly formed permanent teeth are being constructed & erupted.

The deciduous or temporary dentition is gradually shed & followed by a permanent or succedaneous dentition . This is a mechanism that adjusts the size of dental battery to the growing face and jaws. Since teeth once formed cannot increase in size a second dentition consisting of larger & more teeth is required for the larger jaws of the adult

Factors that cause the resorption of deciduous dentition: The physiologic process resulting in the elimination of the deciduous dentition is called shedding or exfoliation. The pressure generated by the growing and erupting permanent tooth dictates the pattern of deciduous tooth resorption.

Cells responsible - odontoclasts. Histochemically characteristic feature - alkaline phosphatase. Alk phosphatase activity occurs with in the vacuoles.

found - on surfaces of roots in relation to advancing permanent teeth. Also found in root canals & pulp chambers of resorbing teeth lying against the predentin origin - same as osteoclasts.( monocytes circulating in the blood originally gives rise to all the different tissue macrophages.)

Sequence of events in resorption of dental lamina: pressure

If succesional tooth germ is missing , shedding of deciduous teeth is delayed

Followed by extracellular dissolution of organic matrix

osteoclast Alk phosphatase activity

Initial removal of mineral

Experimental removal of permanent tooth germ delays but not prevents shedding of deciduous teeth Forces of mastication applied to the deciduous teeth are capable of initiating the resorption. As the individual grows , the muscles of mastication increase in size & exert forces on the deciduous teeth greater than its periodontal ligament can with stand. This leads to trauma to the ligament & the initiation of resorption

Stages of dental development The first local changes occurring in tooth development occurs as early as the 6th week of prenatal life. The oral epithelium in the upper & lower jaw thickens , forming the dental lamina from which local buds arise at each point where a tooth will form.

Individual tooth formation proceeds by means of mitotic activity ,particularly in the inner enamel epithelium , until the ameloblasts & odontoblasts are differentiated. The stages of dental development are bud stage, cap stage, bell stage The tooth is an example of typical vertebrate organ starting as an epithelial bud & undergoing complex morphogenesis ,

It has become evident that developmental regulatory genes have been conserved to a great degree during evolution & that similar gene network s regulate the development of teeth as of other vertebrate organs. 5 families of signaling molecules are found to be responsible for tooth development. They are BMP ( bone morphogenic protein) TNF alpha Hedge hog WnT

S.M are released from oral ectoderm & they bind to the receptor on ectomesenchymal cells & activate the transcription factors . They enter the nucleus & regulate the expression of genes. The homeobox genes are Msx – 1 & Pax – 9. They again act on oral epithelium & these are responsible for invagination of oral epithelium & development of tooth buds. From cap stage onwards

Path of eruption of permanent dentition: The word eruption refers to cutting of the tooth through the gum.( in Latin erumpere means “to break out�.) permanent incisors & canines first develop lingual to the deciduous tooth germs at the level of their occlusal surfaces & in the same bony crypt.

As their deciduous predecessors erupt they move to a more apical position & occupy their own bony crypts. Premolars begin their development lingual to the predecessors at the level of their occlusal surfaces & in the same bony crypt. They also shift so that they are eventually situated in their own crypts beneath the divergent roots of the deciduous molars.

The permanent molars which have no deciduous predecessors also move considerably from the site of their initial differentiation. For ex the upper permanent molars which develop in the tuberosity of the maxilla , at first have their occlusal surfaces facing distally & swing around only when the maxilla has grown sufficiently to provide the necessary space.

Mandibular molars develop with their occlusal surfaces inclined mesially & only become upright as room becomes available . All these movements are related to jaw growth and may be considered as movements positioning the tooth & its crypts with in the jaws preparatory to tooth eruption

The neuromuscular & osseous movements influencing the eruption of teeth: Pre-emergent eruption Post-emergent eruption juvenile occlusal equilibrium adult occlusal equilibrium.

Pre emergent eruption: Labial or buccal drift Eruptive movement begins soon after root begins to form Processes necessary for pre-emergent eruption resorption of bone & primary tooth overlying the crown of erupting tooth. eruption mechanism. Ex: cleidocranial dysplasia.

Rate of bone resorption & the rate of tooth eruption are not controlled physiologically by the same mechanism. Ex : expts on dog & child Follicle of erupting tooth signals bone resorption Nature of signal – unknown .

Mechanism of eruption: Cross linking of collagen fibers contribute to elasticity of periodontal ligament. Contractions & relaxations of these fibers leads eruption force. Proved by animal expts.

Other possibilities: Localized variations in BP Forces delivered from contraction of fibroblasts. Alterations in the extra cellular ground substances of the PL similar to those that occur in thixotropic gels.

Post emergent eruption: Once tooth emerges into oral cavity it continues till it approaches the occlusal level & is subjected to the forces of mastication. Post emergent spurt.

Juvenile occlusal equilibrium: Phase of very slow eruption Rate of eruption parallels rate of jaw growth. Disturbance in coordination between these two leads to orthodontic problems. Since the rate of eruption parallels the rate of jaw growth pubertal spurt in eruption of teeth accompanies the spurt in jaw growth.

Adult occlusal equilibrium When pubertal growth spurt ends , a final phase in tooth eruption called the adult occlusal equilibrium is achieved. During adult life , teeth continue to erupt at a n extremely slow rate.

If its antagonist is lost at any age , a tooth can again erupt at more rapidly , demonstrating that eruption mechanism remains active and capable of producing significant tooth movement even late in life. Occlusal wear of teeth is compensated by eruption of teeth.

If severe occlusal wear occurs – cannot be compensated by eruption hence lower facial height decreases. In few cases any wear of teeth is compensated by additional eruption & facial height remains constant or even increases slightly in 4th 5th & 6th decades of life

Neonatal line: Despite the physical adaptations that facilitate it, birth is a traumatic process. For a short period growth ceases & there may be a small decrease in weight during first 7 – 10 days of life.

Such an interruption in growth produces a physical effect in skeletal tissues that are forming at that time, because the orderly sequence of calcification is disturbed – noticeable line across bones & teeth that are forming at that time.

Natal tooth: First primary teeth do not erupt until approximately 6 months of age. The natal tooth may be a supernumerary one formed by an aberration in the development of the dental lamina, but usually is merely a very early but otherwise normal central incisor.

Eruption of primary teeth: Development of incisors & canines precedes that of the structures that contain them – this explains the overlapping of incisors & canines before birth. This extra space needed is provided by the jaw growth after birth in first 6- 8 months after birth. The extensive early transverse development of both jaws can be realized mainly because of the presence of suture in the median plane of the maxilla & of a synchondrosis in the mandible.

As synchondrosis in the mandible calcifies at about 6 months of age , the potency for transversal growth in the lower jaw is eliminated . In contrast with the situation of the mandible maxilla maintains its rapid median growth potency. Maxillary median suture remains until the development of the two dental arches become coordinated.

The first vertical support associated with interdigitation – the interlocking of maxillary & mandibular posterior teeth occurs when the first deciduous molar attains contact. As rule , those teeth are not centered over each other in such a position that no transverse or sagittal translation will be required to reach correct interdigitation.

In most instances , the large palatal cusp of the maxillary 1st molar arrives with its cone shape with in the crater formed by the occlusal anatomy of the mandibular one. The crater will function as a funnel by which both teeth are directed towards each other in the proper position.

 A required movement of the teeth will be involved will be derived more from a displacement of the maxilla than of the mandibular molar as the structures in the mandible favor such a movement less than those in the maxilla.  The occlusion in the posterior region is established when the deciduous 1st molars have settled.

There after the relation between the two dental arches will stabilize in the transverse & sagittal direction. The deciduous dentition is complete after all the 2nd deciduous molars have attained occlusion, usually at around 2.5 years of age. Diastemata is present between all teeth particularly in the anterior region.

Mandibular teeth occlude slightly lingual with the maxillary ones. The terminal plane of deciduous dentition will be flush. Little changes take place in the deciduous dentition from 2.5 to 5 years. Superiorly & lingually to the deciduous teeth the formation of their successors continues in the maxilla. The permanent molars are formed posterior to the dental arches.

First transitional period: Emergence of 1st permanent molar & the transition of the incisors. The anteroposterior relation between the two opposing molars after emergence depends on their positions previously occupied with in the jaws, the sagittal relation between the mandible & maxilla & the ratio of mesiodistal crown dimensions of the mandibular & maxillary deciduous 2 nd molars

If the crown dimensions of the max & mand deciduous second molars are same , the sagittal relation between corresponding M & D surfaces will be similar. A mesial shoulder will be present anteriorly at the mesial surfaces & posteriorly at the D surfaces of the teeth. The terminal plane will have a M step. Baume (journal of dental research, 1950 ) classified the relationships of primary teeth into straight terminal plane, mesial step & distal step.

If the mand 2nd deciduous molar is considerably larger than the maxillary one then the distal surfaces will lie in one plane. Under these occlusal conditions a flush terminal plane is present. One month or more may pass between the emergence of corresponding left & right incisors in one jaw.

Early mesial shift In pts with spaced primary dentition & st terminal plane relationship of molars , the permanent molars will erupt at around 6 yrs of age & move the primary molars mesially , close the space distal to the primary canines, convert the st terminal plane to mesial step , reduce the arch length in mand dentition & allow the permanent molars to emerge in class I relationship.

Late mesial shift: In pts with closed primary dentition & st terminal plane the permanent max &mand 1st molars emerge into a cusp to cusp relationship as no space exists. At approximately 11 yrs the primary mand 2nd molars are exfoliated & the permanent mand 1st molars migrate mesially into the excess lee- way space provided by the diffs in the mesiodistal dimensions of the primary second molars & the permanent second premolar teeth. Again this reduces arch length ,converts the st terminal plane into a mesial step & provides for a class I relationship of 1st molars. It has been referred to as the late shift.

Incisor liability:(Warren Mayne 1969) Mesiodistal width of permanent incisors are more compared to deciduous incisors. This space is gained by the labial & distal movement of canines thus enhancing the intercanine distance(secondary spacing). The incisor liability is about 1.6 mm on each side.

Safety valve mechanism: During the period of permanent incisor eruption notable amounts of intercanine arch width development occur in both the max & mand dentition. In mand the increase occurs between 6 &9 years for boys & between 6&8 yrs for girls. In maxilla it increases longer to 16 yrs in boys & 12 yrs in girls. This is called safety valve mechanism.

According to Moorrees ( J dent res 1965) the average increase in the mandibular dentition of boys & girls is approximately 3mm ,in maxilla it is approximately 4.5 mm. according to Mayne ( current orthodontic concepts & techniques 1969) permanent incisors erupt labial to the deciduous incisors.Baume estimated that the permanent incisors are 2.2 mm forward of primary incisors in maxilla & 1.3 mm in the mandible.

A small opening in the bony alveolar process is present on the lingual aspect of each deciduous incisor in the upper & lower jaws. This opening forms the oral aspect of gubernacular canal which runs to the crypt of the successor. Gubernacular canal contains the gubernacular cord which which consists of epithelium of the dental lamina. The epithelium dissolves & a C.T strand remains ,which subsequently disintegrates further

The opening of the gubernacular canal on the oral side increases in size with the approach of the associated permanent tooth. The gubernacular canal probably plays a role in the guidance of the direction of eruption of incisors through the bone & in the determination of the spot of emergence.

Inter transitional period: The inter transitional period presents itself in a growing child as a rather stable phase with little changes in the dentition.when only the intraoral picture is considered. However with in the jaws resorption of the deciduous roots & reduction in the cervically surrounding bone takes place.

Root formation of the already emerged incisors & molars continues. The roots of permanent canines, premolars, & 2nd molars gradually increase in length. The space needed for that purpose is is provided by the concomitantly increase in height of the alveolar processes in both jaws. In the inter transitional period the mandible & maxillary dental arches consists of sets of deciduous & permanent teeth.

Between the 4 permanent incisors & right & left first permanent molars , the deciduous canines & & 1st & 2nd deciduous molars are located on each side of the dental arch. Maxillary incisors are labially inclined . A central diastema is present. Frequently no contact exists between centrals & laterals. Like wise a diastema is often present in the maxillary dental arch mesial to the deciduous canine.

Ugly duckling stage:( 9 - 12 yrs) During the eruption of permanent canines, the crowns of permanent canines hit the roots of lateral incisors leading to their distal tipping . It is a self correcting anomaly. Once the permanent canine erupts, the diastema will be closed as the erupting canines apply a mesial force on the incisors.

In mandible the incisors are less labially inclined than in the maxilla. A diastema is seldom present between the mandibular central incisors. All incisor crowns are usually in contact with each other & laterals touch the deciduous canines.

Second transitional period: At approximately 10 yrs of age the 1st deciduous tooth in the post region usually a mand canine sheds. This happens more than 1.5 years after the maxillary LI has emerged & about 1 yr after it has reached the level of the occlusal plane.

During formation maxillary canine & 1st premolar are in close proximity of with each other& overlap vertically. The already calcified distal corner of the permanent canine is directly adjacent to the forming mesial cervical region of the 1st PM. Accordingly max 1st PM shows a concavity on the M surface at the cementoenamel junction.(fossa canina). The premolar erupts first.

A comparable M concavity is absent or present only in reduced form at the maxillary 2nd premolar whose crown morphology strongly resembles that of the maxillary 1 st premolar. Sequence of emergence of posterior permanent teeth in mandible – canine,1st PM, 2nd PM. Maxilla – 1st PM,2nd PM,canine.

Variations may occur in the sequence of emergence with a restriction that as a rule the 1st PM precedes the permanent canine in eruption. In majority of cases the 2nd permanent molar emerges after all the deciduous teeth have been lost& replaced. The transition in lower jaw usually runs ahead of that in the upper

During the replacement of deciduous canines & molars by premolars, leeway space is utilized. The deciduous 1st & 2nd molars are wider in mesiodistal dimension compared to premolars. This leeway space is around 2.5 mm in upper arch & 1.5 mm in lower arch.

Abnormalities in dental arches The most frequently occuring abnormality in the dental arches is a discrepancy between the needed & the available dental arch perimeter. Concerning the individual teeth , abnormalities in size shape number & position.

Deviation in the number of teeth in the deciduous dentition is rare.they are regularly encountered in the permanent dentition. Agenensis occurs quite often. The sequence of diminishing frequency in agenesis is 3rd molars , max lateral incisor, mand 2nd PM, mand incisor, max 2nd PM.

Supernumerary teeth can be encountered in the dental arches & particularly in the mand & max incisor region. most frequently a supernumerary tooth occurs between two max central incisors. May form at any time before birth or at 10 –12 years of age. Most commonly found in maxilla.

Anomalies in size MD width is more in males compared to females & it is more pronounced in permanent teeth. Anomalies are more common in mand 2nd PM region. One or more teeth fuse with neighbouring teeth.

Anomalies in shape: Peg shaped lateral Cingulum quite prominent Sharp marginal ridges (particularly Japanese) Extra lingual cusp on mand 2nd PM

Developmental defects like amelogenesis imperfecrta, hypoplasia, gemination, dens in dente, odontomas, fusion, congenital syphilitic aberrations such as hutchinsons incisors & mulberry molars

Diastema: Midline diastema & presence of fibrous tissue attachment provides excellent chicken & egg routine for controversy. Faustin weber noted the following as causative factors. They are Microdontia, Macrognathia, Supernumerary teeth(mesiodens), peg shaped lateral, missing laterals.

Heavy occlusion against the lingual surface of the maxillary incisors, habits such as thumb sucking, tongue thrusting, lip biting, lip sucking, midline cysts.

Premature loss of deciduous teeth Primary teeth are organs of mastication, space savers, maintain opposing teeth at occlusal level. When there is generalized lack of space, primary canines exfoliate faster to give space for erupting incisors. This is often a clue for guided extraction of deciduous teeth & possible removal of 1st PM.

If primary second molar exfoliates early _ 2 nd PM is blocked out. If maxillary molar drifts mesially, the mesiobuccal cusp rotates lingually. If mandibular molar drifts rotation is less but it tips mesially. Permanent 1st molar is lost in many children due to caries. It leads to shortening of arch length on that side ,tipping of contiguous teeth, over eruption of opposing teeth, periodontal implications

Prolonged retention & abnormal resorption of deciduous tooth: Dentist should maintain the tooth shedding timetable at about the same level for each of the 4 buccal segments. If dental developmental age is abnormally advanced or retarded a check into endocrine history should be made.

Hypo thyroidism – delayed developmental pattern, prolonged retention of deciduous teeth Increased gonadotropic harmone – dental dev markedly accelerated because maturation occurs early ,crowding is mandatory. Cortisone & other steroids are frequently used in treatment of a variety of general dev pattern may become abnormal. Hence medication may be the ultimate cause.

Retained root fragments of deciduous tooth: Deflect permanent tooth Prevent proper contact between permanent teeth Serve as foci for cysts ocassionally Rupture of periodontal membrane at one or more points establishing a bony bridge between tooth and lamina dura preventing normal eruption

Delayed eruption of permanent teeth: Endocrine disorders – hypothyroidism Congenital absence Supernumerary tooth Deciduous root Mucosal barrier – if erupting force is not vigorous , the mucosa can effectively stop the erupting tooth for a considerable period of time

Bony crypt occasionally forms in line of eruption of permanent teeth . A check of timetable in other segments should be made before deciding to curette bone barrier.

Abnormal eruptive path Secondary manifestation of primary disturbance. A blow is a possible Early ortho intervention of class II cases trying to move maxillary dentition back can cause maxillary 2nd molar to erupt in cross bite or can impact 3rd molar.

Coronal cyst 3rd molars are impacted due to abnormal path of eruption Ectopic eruption. Sign of arch length deficiency indicate the need of surgical or guided extraction.

Ankylosis : 6 – 12 years May be due to injury Part of PL is perforated & bony bridge is formed joining the laminadura & cementum Accidents or trauma Endocrine conditions Congenital conditions like cleidocranial dysostosis

Dental caries: Premature loss of teeth both primary & secondary Abnormal axial inclination Over eruption Bone loss Not only to prevent infection & loss of teeth but to maintain integrity of dental arches

Improper dental restorations: Over extended proximal restorations cause irregular mandibular incisors . Tight contact causes elongation of tooth being restored or approximating teeth. Loose contact permits easy packing of food in the interdental area leading to caries. Leader in continuing dental education

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