Development Of Dental Occlusion PDF

DEVELOPMENT OF DENTAL OCCLUSION AND CONCEPTS OF NORMAL OCCLUSION DEPARMENT OF ORTHODONTICS AND DENTOFACIAL ORTHOPEDICS INDEX ▪ INTRODUCTION ▪ PERIODS OF OCCLUSAL DEVELOPMENT PRE-DENTAL PERIOD DECIDUOUS DENTITION PERIOD...

DEVELOPMENT OF DENTAL OCCLUSION AND CONCEPTS OF NORMAL OCCLUSION DEPARMENT OF ORTHODONTICS AND DENTOFACIAL ORTHOPEDICS INDEX ▪ INTRODUCTION ▪ PERIODS OF OCCLUSAL DEVELOPMENT PRE-DENTAL PERIOD DECIDUOUS DENTITION PERIOD MIXED DENTITION PERIOD PERMANENT DENTITION PERIOD ANDREWS SIX KEYS TO OCCLUSION CONCLUSION OCCLUSION ANGLE defined occlusion as the normal relation of the occlusal inclined planes of the teeth when the jaws are closed. SALZMAN has defined occlusion in orthodontics as the changing interrelationship of the opposing surfaces of the maxillary and mandibular teeth which occurs during movements of the mandible and terminal full contact of the maxillary and mandibular dental arches. WHEELERS when the tooth in the mandibular arch come into contact with the maxillary arch in any functional relation are said to be in occlusion. STAMP CUSP AND SHEARING CUSP The cusp which goes into the fossa of the opposing teeth is called stamp cusp. Example: lingual cusp of upper teeth buccal cusp of lower teeth. Shearing cusp is the opposite of stamp cusp which mainly helps in cutting of the food. Example: buccal cusp of upper teeth lingual cusp of lower teeth IDEAL OCCLUSION An ideal occlusion is the perfect interdigitation of the upper and lower teeth, which is a result of developmental process consisting of the three main events, jaw growth, tooth formation and eruption. Simpler terms : esthetically and physiologically good. NORMAL OCCLUSION Angle’s class 1 is considered normal where the mesiobuccal cusp of the maxillary 1st molar occludes in the mesiobucall groove of mandibular 1st permanent molar.  IDEAL OCCLUSION NORMAL OCCLUSION A coincident midline Some deviations from ideal No crowding , spacing ,rotation. Overjet 2-4mm Correct crown angulation and inclination Class 1 molar and canine relation A flat curve of spee MALOCCLUSION Any deviation from ideal that may be considered aesthetically or functionally unsatisfactory is called malocclusion BALANCED OCCLUSION CENTRIC RELATIONSHIP TRAUMATIC OCCLUSION THERAPEUTIC OCCLUSION  STATIC OCCLUSION: Is the study of contacts between the teeth when the jaw is not moving.The contacts are points(seen as dots when articulating paper is used). DYNAMIC OCCLUSION: Is the study of the contacts that teeth make when the mandible is moving ,contacts when the jaw moves sideways , forward, backwards or at an angle. The contacts are not points they are lines. Pre-dental Period/ Gum Pads Stage It extends from birth until the eruption of first primary tooth. It usually lasts for six months. Usually, a lower central incisor erupt around 6 or 7 months of age. GUM PADS Alveolar processes at time of birth. Pink, firm and covered by dense layer of fibrous periosteum.  The gum pad soon gets segmented by a groove called transverse groove, & each segment is a developing tooth site The pads get divided into ‘labio- buccal’ & ‘lingual portion’, by a dental groove. The groove between the canine and the 1st molar region is called the lateral sulcus, useful for judging the inter arch relationship at a very early stage.  The upper gum pad is horse shoe shaped & shows: Gingival groove: separates gum pad from the palate. Dental groove: starts at the incisive papilla, extends backward to touch the gingival groove in the canine region & then moves laterally to end in the molar region. Lateral sulcus.  The lower gum pad is ‘U’ shaped and rectangular, characterized by: Gingival groove: lingual extension of the gum pads. Dental groove: joins gingival groove in the canine region. Lateral sulcus. Relationship of Gum Pads Mandibular lateral sulci lies posterior to maxillary lateral sulci. Mandibular functional movements are mainly vertical, and to a little extent antero-posterior. Lateral movements are absent. When viewed from above maxilla is larger than mandible. Status of dentition at birth The neonate is without teeth for about 6 months of life. At birth: The gum pads are not suffciently wide to accommodate the developing incisors which are crowded in their crypts. During the first year of life: The gum pads grow rapidly permitting the incisors to erupt in good alignment. A precise bite‟ or jaw relationship is not yet seen. Therefore, neonatal jaw relationship cannot be used as a diagnostic criterion for reliable prediction of subsequent occlusion in the primary dentition.  Very rarely teeth are found to have erupted at the time of birth. NATAL TEETH NEONATAL TEETH. The natal & neonatal teeth are mostly located in the mandibular incisor region. They show a familial tendency. Pre erupted teeth Natal/neonatal teeth Classification Hebling (1997) classified natal teeth into 4 clinical categories: 1. Shell-shaped crown poorly fixed to the alveolus by gingival tissue and absence of a root; 2. Solid crown poorly fixed to the alveolus by gingival tissue and little or no root; 3. Eruption of the incisal margin of the crown through gingival tissue 4. Edema of gingival tissue with an unerupted but palpable tooth.  Gender Predilection for females Kates et al (1984) reported a 66% proportion for females against a 31% proportion for males. Etiology It has been related to several factors, such as:- Superficial position of the germ Infection or malnutrition Eruption accelerated by febrile incidents or hormonal stimulation, Hereditary transmission of a dominant autosomal gene Osteoblastic activity inside the germ area related to the remodeling phenomenon and hypovitaminosis Associated syndromes Hallerman-Streiff Ellis-Van Creveld Craniofacial dysostosis Multiple steatocystoma Congenital pachyonychia Sotos Syndrome. complications Interference with feeding. Risk of aspiration. Trauma to baby’s tongue and to maternal breast. Riga fede disease Early eruption of teeth causes Ulceration on the ventral surface of the tongue by sharp edges of the tooth.  Diagnosis A radiographic verification of the relationship between a natal and/or neonatal tooth and adjacent structures, nearby teeth, and the presence or absence of a germ in the primarytooth area would determine whether or not the tooth belongs to the normal dentition ( AlmeidaCM et al 1997) Most natal and neonatal teeth are primary teeth of the normal dentition and are not supernumerary teeth ( Brandt Sk et al 1983) Correspond to teeth of the normal primary dentition in 95% of cases, while 5% are supernumerary (Hawkins C 1932) Treatment If the erupted tooth is diagnosed as a tooth of the normal dentition -- maintenance of these teeth in the mouth is the first treatment option, unless this would cause injury to the baby (Chow MH 1980, Roberts MW 1992) When well implanted-- these teeth should be left in the arch and their removal should be indicated only when they interfere with feeding or when they are highly mobile, with the risk of aspiration (Toledo AO 1996) Reasons for removal -- The risk of dislocation and consequent aspiration, traumatic injury to the baby‟s tongue and/or to the maternal breast, (Kates GA et al 1984) Cleaning of gum pads Started with the first week of birth. The parent can be instructed to lay the baby down with his/her head in your lap & feet pointing away. Take a small gauze between thumb and forefinger & wipe vigorously over the gum pad. Deciduous dentition PERIOD (6 months to 6 YEARS) Chronology of primary dentition Overbite Overbite is the amount of vertical overlap between the maxillary and mandibular central incisors. This relationship can be described either in millimeters or more often as a percentage of how much the upper central incisors overlap the crowns of the lower incisors. Edge to edge or zero bite. The overbite in the primary dentition normally varies between 10% and 40%.  Foster in a study of 100 British children between 2 and 3 years of age described the overbite relationship as ideal (19%), reduced (37%), open bite (24%), and excessive overbite (20%). The fact that more than 60% of the children in this population have a reduced overbite or an open bite is attributed to the effects of the various oral habits (finger or pacifier sucking) that are common in this age group. Overjet Overjet is the horizontal relationship or the distance between the most protruded maxillary central incisor and the opposing mandibular central incisor. This relationship is expressed in millimeters. The normal range of overjet in the primary dentition varies between 0 and 4.0 mm. underjet  In the same study by Foster , the overjet was ideal in 28% of the cases and excessive in 72% of the children. Again, the presence of excessive overjet was attributed to the effects of the oral habits. Spacing In the primary dentition stage a child may have generalized spaces between the teeth, localized spaces, no spaces, or a crowded dentition. The presence of spacing in the primary dentition stage is a common occurrence. According to Foster, generalized spacings occur in almost 2/3 of the individuals in the primary dentition stage. B)primate / simian / anthropodial / baume space Seen mesial to maxillary canines and distal to mandibular canines. Utilized during early mesial shift of molars from end on to class 1 relation. A tooth size-arch length discrepancy (TSALD) in the form of crowding is less common and occurs in approximately 3% of the children in the primary dentition stage. AT AROUND 5-6 YEARS There are 48 teeth/parts of teeth present in the jaw. It is at this time that there are more teeth in the jaws than at any other time. CANINE RELATIONSHIP The relationship of the maxillary and mandibular deciduous canines is one of the most stable in primary dentition. Class I: mandibular canine interdigitates in embrasure between the maxillary lateral and canine. Class II: mandibular canine interdigitates distal embrasure. MOLAR RELATIONSHIP FLUSH TERMINAL PLANE- Upper primary second molar occludes with lower second primary molar, a tangent line drawn vertically touches the distal surface of both upper and lower primary molar.(37%) MESIAL STEP Mandibular cusp ahead of maxillary cusp in mesial direction.(49%) Distal step Maxillary cusp will be ahead of mandibular cusp in mesial direction giving distal step.(14%) Unfavorable relation Indicates developing class 2 molar relation. Natural space maintenance Natural tooth is the best space maintainer– functional , correct size and exfoliates appropriately. Restoration of proximal contact Save tooth even if pulp treatment required. Effects of premature loss of a tooth Loss of arch circumference Accelerated eruption of succedaneous teeth. MIXED DENTITION PERIOD (6-12Years)  The period where both deciduous and permanent teeth are present in the oral cavity. Most watchful period of development of normal dentition and occlusion. This is important because the growth spurts of maxilla and mandible coincides with the mixed dentition stage. Alveolar process is most actively adaptable during this period and thus ideal time for most orthodontic interventions. Divided in two stages Early mixed dentition late mixed dentition 6-9years 9-12 years FIRST TRANSITION PHASE(6-9years) Emergence of first permanent molar. Eruption of permanent incisors MOLAR RELATION:-4mm forward movement of lower molar for smooth transition to class1 molar relation , and space is provided by:- 1)Differential growth of lower jaw 2)Physiological and leeway spaces  Early mesial shift:-eruption of first permanent molar exerts a mesial force on deciduous dentition anterior to it. Primate spaces are closed Occurs Class1 relation from end on relation. LATE MESIAL SHIFT:-due to lack of primate spaces , when deciduous second molar exfoliates permanent molar drifts mesially. Incisor liability The difference in the mesiodistal dimensions of the deciduous incisors and their succedaneous permanent incisors(Warren mayne,1969). In maxilla:- 7.6mm In mandible:-6mm  Change in incisor inclination:-primary incisor are more upright than permanent incisors. Decreases in angle from 150 to 123 degrees. Safety valve mechanism Natural mechanism by which the maxilla and mandible maintain proper occlusion. The intercanine width of maxilla acts as a safety valve. Mismatch in the horizontal(sagittal) growth of maxilla and mandible postnatally. The intertransitional phase(8-10years) More stable period of mixed dentition Deciduous canine are present in between permanent molars and incisors. Ugly duckling stage Self correcting malocclusion seen in maxilary incisor region between 8-10years of age. Seen during eruption of the upper permanent canines. Children exhibit midline diastema along with distal flaring of the incisors.  Described by Brodbent as the ugly duckling stage as children tend to look ugly during this phase. Erupting flared incisors tend to look like the walking of a ducking. Features include: -Maxillary midline diastema -Distal tilting and flaring of incisor crowns Second transitional phase(10-12 years) Exchange of primary canines and premolars to permanent canine molars Leeway space of nance Term “leeway” means “more room”. Combined mesiodistal width of the permanent canine and premolars is lesser than the combined width of deciduous canine, first molar and second molar. In maxilla-1.8mm per arch or 0.9mm per quadrant In mandible-3.4mm per arch or 1.7mm per quadrant Importance of leeway space: Permits the mesial movement of lower molar and shift of the flush terminal plane mesially to establish normal occlusion Dimisional changes of arch:- Decrease in arch perimeter:- due to growth of mandible Decrease in arch length:- due to uprighting of incisors and loss of leeway space by the mesial movement of first permanent molar. Increases in intermolar width:- average increase is 2.2mm in maxillary arch width between 8-13 years. Permanent dentition stage Period begins with shedding of the last primary tooth. Growth of jaw bones slows and stops eventually. Eruption sequence o Maxillary arch 6-1-2-4-3-5-7 or 6-1-2-3-4-5-7 o Mandibular arch(knott and meredith) 6-1-2-3-4-5-7 or 6-1-2-4-3-5-7 ❑The permanent incisors develop lingual to the deciduous incisors and move labially as they erupt. ❑The premolars develop below the divergent roots of the deciduous molars. ❑At approximately 13 years of age all permanent teeth except third molars are fully erupted ❑Vertical overbite of about one third the clinical crown height of the mandibular central incisors. ❑Overjet and overbite decreases throughout the second decade of life due to greater forward growth of the mandible OCCLUSAL PLANE THE DEVELOPMENT OF THE CONCEPTS OF OCCLUSION The development of concept of occlusion can be traced through fictional, hypothetical and factual approach. The fictional approach was a convenient arrangement of a series of observation and thoughts more or less logically arranged. The hypothetical approach was based on provisional acceptance of certain logical entities. Fact is a truth known by actual experience or observation. Both the fictional and hypothetical approach are necessary for the establishment of fact.  ANDREWS 1972 gave six keys to occlusion thus providing a guidance for exact positioning for each tooth on all 3 planes. ROTH 1981 in an excellent series of articles later added to the static occlusion keys, which relate occlusal function and orthodontic mechanics. Thus made it possible for us to attain gnathological goals orthodontically.  He stated that evaluation of each case on articulator for optimum function should be one of the treatment objectives. This leads to the fundamental aspect of orthodontic correction the needs to co-ordinate tooth position and jaw function. The goal of modern orthodontics according to Proffit is “the creation of best possible occlusal relationship within the framework of acceptable facial aesthetics and stability of result”.  Dental occlusion varies among individuals according to tooth size and shape, tooth position, timing and sequence of eruption, dental arch size and shape and pattern of craniofacial growth. The position of the teeth within the jaws and the mode of occlusion are determined by developmental processes that interact on the teeth and their associated structures during the period of formation, growth and postnatal modification SIX KEYS TO NORMAL OCCLUSION LAWRENCE F.ANDREWS(1972) Collection of 120 models of teeth with naturally excellent occlusion Criteria for selection 1. Had never undergone orthodontic treatment 2. Were straight & pleasing in appearance 3. Had a bite which looked generally correct 4. In his judgement, would not benefit from orthodontic treatment  Key I – Molar relationship MB cusp of the max 1st molar falls into the mesiobuccal groove of the mand 1st molar and that the distal surface of the DB cusp of the upper first permanent molar should make contact and occlude with mesial surface of the MB cusp of the lower second molar.  Key II Crown angulation (Tip) The angulation of the facial axis of every clinical crown should be positive The gingival portion of the long axis of the all crowns must be distal than the incisal portion.  Key III Crown inclination In upper incisors, the gingival portion of the crown‟s labial surface is lingual to the incisal portion. In all other crowns, including lower incisors, the gingival portion of the labial or buccal surface is labial or buccal to the incisal or occlusal portion.  Key IV – Rotations The fourth key to normal occlusion is that the teeth should be free of undesirable rotations. Key V – Tight contacts contact points should be tight (no spaces). In absence of abnormalities such as genuine tooth size discrepancies, contact point should be tight.  Key VI – Occlusal plane or curve of spee ▪ The curve of Spee should have no more than a slight arch. ▪ Intercuspation of teeth is best when the plane of occlusion is relatively flat. ▪ A deep curve of spee results in a more contained area for the upper teeth, making normal occlusion impossible. ▪ A reverse curve of spee results in excessive room for upper teeth.  Key VII – Correct tooth size or the bolton’s ratio Bennett and McLaughlin in 1993 gave seventh key to normal occlusion. i.e. the upper and lower tooth size should be correct. Roth (1981) added some functional keys to the previous six keys to normal occlusion by Andrew: a) Centric relationship and centric occlusion should be coincident. b) In protrusion, the incisors should disclude(seperate) the posterior teeth, with the guidance provided by the lower incisal edges passing along the palatal contour of the upper incisors. c) In lateral excursions of the mandible, the canine should guide the working side whilst all other teeth on that and the other side are discluded. d) When the teeth are in centric occlusion, there should be even bilateral contacts in the buccal segments.