Development of occlusion Presented by- Kritika Sarkar B.D.S Final year
Introduction• Salzmann & Gregory defined occlusion as:“The changing interrelationship of the opposing surfaces of the maxillary & mandibular teeth which occur during movements of the mandible & terminal full contact of the maxilla & mandibular arches.”• According to Angle: “Occlusion is the normal relation of the occlusal inclined planes of the teeth when jaws are closed”.
• Occlusion is the sum total of many factors such as: – Genetic – Environmental – Muscle pressure – Changes with: • Development • Maturity • Aging.
Periods of tooth development Pre-dental Stage (0-6months) Deciduous dentition (6 months-6 years) Mixed dentition (6-12 years) Permanent dentition
Pre-dentate stage •Pre dentate stage refers to the period from birth to the eruption of first deciduous tooth in the oral cavity. •Ideally ranges from birth to 6 months but a delay in eruption of first deciduous teeth by 4-10 months is considered normal.
• Aka neonate’s mouth or gum pad stage.• The alveolar arches at the time of birth are called gum pads.• The form of arches is determined in the intra-uterine life.• Leighton has outlined the various factors that determine the size of gum pads as follows: – The state of maturity of infant at birth. – The size at birth as expressed by birth weight. – Size of developing primary teeth. – Genetic factor
• Maxillary gum pad is horse shoe shaped & the gum pads extend labially & buccaly beyond those in the mandible.• They develop in 2 parts: – Labio-buccal (differentiates former to the lingual) – Lingual.• Mandibular gum pads U-shaped and are anteriorly everted.
Maxillary gum pad Gingival groove- Separates gum pads from palate. Dental groove- Extends from the incisive papilla, backwards to touch the gingival groove in the canine region & continues forward in the molar region. Transverse grooves- Depressions between the 10 segments of the gum pads. Lateral sulcus- Transverse groove between the canine & molar sac region.
Mandibular gum pad • Like the upper arch, there are 10 segments but are less demarcated. • The gingival groove demarcates the lingual extent. • The dental groove runs backwards, and laterally in the canine region.
Relation of gum padsAt rest:• An anterior open bite is present.• Contact at the molar area only.• Tongue is interposed between the space.• Maxillary gum pads is wider than mandibular & there is total overlapping of maxillary gum pad. It lies in a class II type relation, where the upper gum pad is forwardly placed. This is a transient &self correcting.• The gum pads grow rapidly during the 1st year of life & the growth is more in the transverse direction.• Length increases, mostly in the posterior direction.
Studied under Development of primary Development of primary teeth teeth occlusionCalcification Eruption Terminal Relation of Type of Spaces plane anterior dentition relations teeth
Development of deciduous teethCalcification:• The factors that control primary teeth’s calcification include: – Genetic factors. – Sexual dimorphism (calcification begins earlier in females and hence the eruption is earlier).
• Eruption starts when root formation of primary teeth begin.• A>B>D>C>E.
Types of primary dentitionOpen type:• Primary teeth with spaces.Closed type:• Primary teeth without spaces due to larger teeth of small arch length.
Development of primary occlusion• Inter-dental Spacing.• Physiologic spacing: – This is present due to antero-posterior growth of jaws. – In maxilla it is 4 mm & in mandible it is 3mm. – It is preferable since the chances of crowding in the succedenous dentition is minimal.• Primate space: – Aka Simian/Anthropoid space (also seen in monkeys). – Present between: • Lateral incisor & canine in the maxilla • Canine & first molar in the mandible
• By 21/2 years of age, deciduous dentition is usually complete & in function. And by 3 years of age the roots of all the deciduous teeth are complete.• The crowns of permanent first molars are fully developed & the roots are starting to form.• The crypts of the 2nd molar are now definite and occupy the space formerly occupied by the 1st molar.• By 3rd-6th year of age the development of the permanent teeth continues, with the incisors most advanced.• From 5-6 years, just before shedding of the deciduous incisors, there are more teeth in the jaws than any other time.• Developing permanent teeth shift closer to the alveolar border. Very little bone remains b/w permanent teeth & there crypts and the front line of the deciduous teeth.
Features• Deep bite: when the primary incisors erupt, the overbite is deep. This might be due to vertical inclination of the incisors. This is gradually corrected by: – Eruption of primary 1st molars. – Rapid attrition of incisors.• Overjet: initially it is more in primary dentition. By movement of whole arch, the overjet decreases gradually. Generally it is 1-2 mm for primary dentition.
The concept of bite opener• According to Schwarz; there are 3 periods of physiologic raising of the bite, with the eruption of: – 1st permanent molar @ 6 years – 2nd permanent molars @ 12 years – 3rd permanent molar @18.
6-7 yearsEruption of first permanent molars:• The 1st molars erupt, the pad of tissue overlying them creates a premature contact.• Propioceptive responses conditions the child against biting on the natural “bite opener”, & thus the deciduous teeth anterior to the 1st permanent molar erupt, reducing the overbite.• The upper and the lower molars show different paths of eruption. – Maxillary: buccal and distal – Mandibular: lingual and mesial.
Early mesial shift• In children with open primary dentition, the mandibular 1st molars close the primate space distal to canine.• Thereby, the flush terminal plain gets converted into a mesial step.• This allows the permanent maxillary first molars to erupt into class 1 molar relationship.• This is called “early mesial shift”.
Eruption of Incisors &Incisor liability• The size of the permanent incisors is greater than there deciduous counterparts, hence they need more space for proper alignment. This difference in the space required and available is known as incisor liability. (Described by Warren Mayne, in 1969).• Incisor liability for – Maxilla is 7.6mm – Mandible is 6mm.• How is the space discrepancy is compensated?• It is compensated by: – Increased inter-canine distance (3-4mm) – Inter-dental spacing. – Labial eruption of the incisors.
8 to 9 years-The “Ugly duckling” stage• About this time, the deciduous central incisors are lost & their permanent successors start their eruptive path toward contact with the incisors of the opposing arch.• Usually the mandibular central incisors erupt first.• They erupt lingual to there deciduous counterparts.• Around the age of 8 yrs a physiologic midline diastema is commonly seen in the upper arch. It is also known as Broadbent’s phenomena.
9-10 years• The apices of the deciduous canines & molars begin to resorb.• At this time in the mandible, the combined width of deciduous- cuspid, 1st & 2nd molar is approximately 1.7 mm. And in maxillary it averages to 0.9 mm.• This differential for each of the arches in the buccal segment id known as “Leeway space” (as described by Nance).M-D width of: C+D+E> 3+4+5Leeway space = (C+D+E )-(3+4+5)
• It is this temporary increase in the arch length, often prevents the inter-digitation of the permanent 1st molars.• They maintain an end to end relation until the 1st & 2nd primary molars are lost.• The flush terminal plane is eliminated & the correct cusp & fossa inter-digitation occurs only after the exchange of deciduous molars & canines for there succedenous counterparts.• The late mesial drift of the lower molars takes up the greater leeway space that is present in the lower arch.• If there is a distal step instead of flush terminal then a developing Class II malocclusion is likely.• A mesial step, may mean a developing Class III malocclusion.
10 to 12 years• This stage involves replacement of primary canines & molars by permanent canines and premolars.• In maxilla first bicuspid erupts before canine. The canine and second premolar erupt at almost same time.• There is decrease in arch length, in both the arches, as the first molars shift mesially which enable the establishment of full cusp Class I relationship from flush terminal. This is known as the “Late mesial shift” of molars.
• Eruption of 2nd molar teeth occurs shortly after the appearance of the 2nd bicuspid.• The gingival pads overlying the 2nd molar contact prematurely again, blocking open the bite anteriorly, allowing the eruption of teeth anterior to the 2nd molars. (This is the 2nd bite opener as stated by Schwarz).• The reduction in the overbite is minimal and variable.
Features:1. Overlap- in Class I occluding dentition, the maxillary teeth are labial or buccal to the mandibular teeth.2. Angulation- bucco-lingual & mesio-distal.3. Occlusion- with the exception of central incisors and third molars, each tooth occludes with 2 teeth.4. Arch curvature- a) Antero-posterior curvature of the mandible= Curve of Spee.
b) Corresponding curve in the maxillary arch is called compensating curve.c) Bucco-lingual curve from one side to the other is called Monson’s curve.5. Overbite: the normal overbite expressed in terms of % in adult dentition is 10-30%.6. Molar relationship: class I mesio-buccal cusp of maxillary 1st molar occludes on the mesio-buccal grove of the permanent mandibular 1st molar.7. Dimensional changes: a) Basal arch-this corresponds to the basal bone of maxilla & mandible. b) Alveolar arch-joins the tooth to the basal arch. c) Dental arch-joins the combined mesio-distal widths of the teeth.
8. During the growth the dimensional values of basal & alveolar arches change but the dental arch remains constant.9. There is reduction in arch circumference with aging & it is more pronounced in mandible.
Bibliography• Graber’s Textbook of orthodontics.• Textbook of cranio-facial growth by Sridhar Premkumar.• Evaluation, diagnosis & treatment of occlusal problems by Peter E Dawson.• Wheeler’s dental anatomy, physiology & occlusion (8th Edition).• Pediatric dentistry-Clinical approach by Goran Koch.• www.google.co.in• www.slideshare.com• www.authorstream.com• www.docstock.com