Eruption and Arch Development

Period of the mixed dentition 6 to 12 years of age Mixed dentition.

Shedding of primary teeth Causes of shedding of primary teeth. Resorption pattern of anterior and posterior primary teeth.

Shedding of teeth A result of the progressive resorption of the roots of teeth and their supporting tissues. Accomplished by multinuclear odontoclasts. Highly specialized cells that are identical to osteoclasts. Periods of rest and repair. In the end, resorption predominates.

Shedding of teeth Causes Pressure from the erupting successional tooth plays a major role.

Shedding of teeth When a successional tooth germ is missing, shedding of the deciduous tooth is delayed but not stopped. The deciduous tooth is eventually lost.

Shedding of teeth Causes Forces of mastication that are greater than the periodontal ligament of a deciduous tooth can withstand. Trauma to the periodontal ligament and initiation of resorption.

Resorption pattern of anterior teeth Permanent teeth undergo complex movements before they reach the position from which they will erupt. ‘Pre-eruptive movement’ Permanent incisors and canines first develop lingual to the deciduous tooth germs. As their deciduous predecessors erupt, they move to a more apical position and occupy their own bony crypts.

Resorption pattern of anterior teeth Resorption of the roots of the deciduous incisors and canines begins on their lingual surfaces. Later these developing teeth occupy a more apical position.

Resorption pattern of anterior teeth

Resorption pattern of posterior teeth Permanent premolars begin their development lingual to their predecessors. Shift so they are situated in their own crypts beneath the divergent roots of the deciduous molars.

Resorption pattern of posterior teeth This change in position provides the growing premolars with adequate space for their continued development. Premolars erupt in the position of deciduous molars

Resorption pattern of posterior teeth

Eruption of permanent teeth

Eruption of permanent teeth Chronology of eruption. Sequence of eruption, variations. Rhythm of eruption.

Chronology of Eruption (Years)

Premature loss of primary molars Eruption of the premolar teeth is delayed in children who lose primary molars at 4 or 5 years of age and before. If extraction occurs after the age of 5 years there is a decrease in the delay of premolar eruption. At 8, 9, and 10 years of age, premolar eruption resulting from premature loss of primary molars is greatly accelerated. Posen, 1965

Sequence of eruption

Sequence of eruption (6-1)-2-3-4-5-7-8 most common in mandible. 6-1-2-4-5-3-7-8 most common in maxilla. Eruption timing in girls generally precedes that in boys by an average of 5 months.

Sequence is Important! Alteration of sequence of eruption alerts the practitioner to potential problems. Always count the teeth!

Variations in the sequence of eruption No clinical significance to the eruption of incisors before first molars. It is desirable that the mandibular canine erupts before the first and second mandibular premolars. This aids in maintaining adequate arch length and in preventing lingual tipping of the incisors.

Variations in the sequence of eruption If the mandibular second permanent molar erupts before the second premolar, a deficiency in arch length can occur. Due to mesial migration and tipping of the first molar & encroachment on the space needed for the second premolar.

Variations in the sequence of eruption Untimely loss of primary molars in the maxillary arch may allow the first permanent molars to drift and tip mesially, resulting in the permanent canine being blocked out of the arch.

rhythm of eruption

Rhythm of eruption of permanent teeth Two stages: Incisors and first permanent molars erupt first. Early mixed dentition.

Rhythm of eruption of permanent teeth Premolars, canines & second molars erupt. Late mixed dentition. Teeth erupt symmetrically in both jaws, simultaneously and in pairs. Third stage: third molars.

The rule of ‘Four’ for permanent tooth development At birth, four first molars have initiated calcification. At 4 years of age, all crowns have initiated calcification. At 8 years of age, all crowns are complete. At 12 years of age, all crowns have emerged. At 16 years of age, all roots are complete.

Permanent tooth development Crown formation completed at least 3 years before eruption. Roots completed around 3 years after eruption. Teeth erupt when 2/3 to ¾ root development.

Hard tissue formation starts At birth or slightly before Upper 1s and 3s Lower 1s 2s and 3s 3-6 months of age Upper 2s 10-12 months of age Upper and lower premolars and second molars 1 ½ - 3 years of age Upper and lower third molars 7-10 years of age

Enamel completed 6s 2 ½-3 years of age 1s, 2s and 4s 4-6 years of age

Eruption of Permanent teeth

Eruption of Permanent teeth Lingual eruption of mandibular incisors. Ankylosed primary molars. Eruption sequestrum. Ectopic eruption of 6s. Incisor liability. Leeway space. Late mesial shift.

Lingual eruption of mandibular permanent incisors A cause of concern for parents. Seen both in patients with an obvious arch length inadequacy and in those with a desirable amount of spacing in the primary dentition.

Lingual eruption of mandibular permanent incisors Primary teeth may be mobile and held only by soft tissue. Or they may not have undergone normal resorption & thus stay solidly in place.

Lingual eruption of mandibular permanent incisors Position will improve over several months. In some cases, there is justification for removal of corresponding primary tooth. Extraction of other primary teeth in the area is not recommended.

Lingual eruption of mandibular permanent incisors The tongue and continued alveolar growth seem to play an important role into influencing the permanent incisors into a more normal position with time. The situation will resolve on its own

Lingual eruption of mandibular permanent incisors If the condition is identified before 7 1⁄2 years of age it is unnecessary to subject the child to the trauma of removing the primary teeth because the problem is almost always self-correcting within a few months. Gellin et al

Lingual eruption of mandibular permanent incisors In an older child and when the radiograph shows no root resorption of the primary teeth, self-correction has not been achieved and the corresponding primary teeth should be removed. Gellin et al

Lingual eruption of mandibular permanent incisors Labial migration occurs naturally with or without extraction of the primary incisor (Gellin & Haley, 1982) Removal of a tooth during the first dental visit may not be the best introduction to the dental surgery.

Lingual eruption of mandibular permanent incisors Still, some parents are alarmed by seeing a double row of teeth & extracting the offending incisor may lay the problem to rest.

ankylosed primary molars

Ankylosed primary molars Also referred to as: Submerged teeth. Teeth in infraocclusion.

Ankylosed primary molars The ankylosed tooth is in a state of static retention. In the adjacent areas, eruption and alveolar growth continue.

Ankylosed primary molars Mandibular primary molars are most commonly affected.

Ankylosed primary molars Cause is unknown: Familial. Observation of ankylosis in several members of the same family.

Ankylosed primary molars Absence of a permanent successor. There is a suggested relationship between congenital absence of permanent teeth and ankylosed primary teeth. Brown et al

Ankylosed primary molars Normal resorption involves periods of rest. A solid union may develop between the primary tooth and bone.

Ankylosed primary molars Diagnosis: Opposing molars are out of occlusion. Tapping with a blunt instrument. Solid vs. cushioned.

Ankylosed primary molars Diagnosis: The ankylosed tooth is not mobile even in cases of advanced root resorption. Radiograph will show a break in the continuity of the periodontal ligament.

Ankylosed primary molars Management: Keep the tooth under observation. The tooth may undergo root resorption later on and be normally exfoliated.

Ankylosed primary molars Management: In ankylosed primary molars with missing successors, establish functional occlusion with SSC or bonded restorations.

Ankylosed primary molars Management: High caries rate or loss of arch length. Eventual treatment may include surgical removal.

ERUPTION SEQUESTRUM

Eruption Sequestrum Seen occasionally in children at the time of the eruption of the first permanent molar.

Eruption Sequestrum A tiny spicule of nonviable bone overlying the crown of an erupting permanent molar just before or immediately after the emergence of the tips of the cusps through the oral mucosa. Starkey et al

Eruption Sequestrum The sequestra may develop from either osteogenic or odontogenic tissue.

Eruption Sequestrum Generally overlying the central fossa of the associated tooth, embedded, and contoured within the soft tissue.

Eruption Sequestrum Some of these sequestra spontaneously resolve without noticeable symptoms. It may easily be removed if it is causing local irritation.

Eruption Sequestrum The base of the sequestrum is often still well embedded in gingival tissue when it is discovered.

Eruption Sequestrum Application of a topical anesthetic or infiltration of a few drops of a local anesthetic may be necessary to avoid discomfort during removal.

Ectopic eruption of first permanent molars

Ectopic eruption of first permanent molars 6s may be positioned too far mesially in their eruption path with resultant ectopic resorption of the distal root of the second primary molar.

Ectopic eruption of first permanent molars Two types of ectopic eruption—reversible and irreversible.

Ectopic eruption of first permanent molars In the reversible type, the molar frees itself and erupts into normal alignment with the second primary molar remaining in position.

Ectopic eruption of first permanent molars Most permanent molars in children with reversible patterns free themselves by 7 years of age.

Ectopic eruption of first permanent molars In the irreversible type, the maxillary first molar remains unerupted and in contact with the cervical root area of the second primary molar.

Ectopic eruption of first permanent molars By the age of 7 and 8 years, any ectopic eruption of a permanent first molar should be considered irreversibly locked.

Ectopic eruption of first permanent molars Prevalence low, around 3%. Seen more frequently in boys than in girls. Occurrence in more than one quadrant is frequent. Most often observed in the maxilla . 47 Young et al

Ectopic eruption of first permanent molars Two thirds of ectopic molars erupted into their essentially normal position without corrective treatment (reversible). 47 Young et al

Ectopic eruption of first permanent molars Children with irreversible ectopic eruption patterns had : Significantly larger permanent first molars, A more pronounced mesial angle path of eruption, A tendency toward a shorter maxilla in relation to the cranial base. Bjerklin and Kurol, 1983

Ectopic eruption of first permanent molars No significant differences in these variables were found between sides with reversible ectopic eruption and sides with normal eruption. Ectopic molars also show a significant familial tendency with a prevalence of 19.8% in affected siblings versus the overall 2% to 3% general occurrence. Bjerklin and Kurol

Ectopic eruption of first permanent molars A frequent occurrence rate of ectopic first permanent molars at 25% in cleft lip and cleft palate children. Possibly caused by maxilla positioning and basal arch size.

Ectopic eruption of first permanent molars Irreversible ectopic molars that remain locked, if untreated, can lead to Premature loss of the E with a resultant decrease in quadrant arch length, Asymmetric shifting of the upper first molar toward class II positioning,

Ectopic eruption of first permanent molars Irreversible ectopic molars that remain locked, if untreated, can lead to : Supraeruption of the opposing molar with distortion of the lower curve of Spee and potential occlusal interferences.

Ectopic eruption of first permanent molars If detected at 5 to 6 years of age, an observation approach of “watchful waiting” with appropriate monitoring is indicated. With self-correction being unlikely approaching 7 years of age, continued “locking” of the first molar with advanced resorption of the primary second molar usually warrants intervention.

Ectopic eruption of first permanent molars Another timing clue is that when the opposing molar reaches the level of the lower occlusal plane, intervention is indicated to establish proper vertical control and prevent supraeruption. Because the anomaly often occurs bilaterally in conjunction with a tooth mass discrepancy, the finding should result in careful examination of other areas for similar conditions.

Ectopic eruption of first permanent molars Approaches include: Separators. Distalizing appliances.

Ectopic eruption of first permanent molars Orthodontic elastic separators are the first choice if access is sufficient to allow insertion for engagement in the contact areas of entrapment.

Ectopic eruption of first permanent molars Progressive use of larger separators facilitates this approach.

Ectopic eruption of first permanent molars Separating springs can also be used provided sufficient eruption for insertion between the contact areas.

Ectopic eruption of first permanent molars Brass ligature wire threaded between the contact areas of the affected teeth may facilitate distal movement of the permanent molar. Periodic tightening of the looped wire every 3-5 days is indicated as a separating force.

Ectopic eruption of first permanent molars Treatment with any of the separator techniques requires that only a minimal lock be evidenced and that minimal resorption of the primary second molar has occurred.

Ectopic eruption of first permanent molars Distally directed forces from the second primary molars may be needed to disengage and allow eruption of the first permanent molar. Ortho appliances may be used to distalize the first permanent molar.

Incisor liability

Incisor liability Permanent incisors are larger than primary incisors. How does the body create enough room for the larger permanent incisors?

Incisors Interdental spacing of primary incisors. Intercanine arch width growth. Labial positioning of the permanent incisors. Favorable size ratio between the primary and permanent incisors.

Interdental spacing of primary incisors. Good interdental spacing of the primary incisors allows for better positioning of the permanent incisors.

Arch length prediction from alignment of primary teeth Primary alignment Permanent outcome Crowding Almost certain extraction No spacing Possible extraction Fair spacing Mild to moderate crowding Good spacing No or mild crowding Excess spacing No crowding/excess

Intercanine arch growth Width growth creates more room for the permanent incisors. Mandibular intercanine growth occurs mostly during permanent incisor eruption. Maxillary intercanine growth occurs during incisor eruption, and continues. Unpredictable.

Labial positioning of the permanent incisors Permanent incisors erupt to a more labial position Permanent incisors are angled more labially. The above creates more arch length

Favorable size ratio between the primary and permanent incisors Size ratio between the primary and permanent incisors may be favorable or unfavorable. Favorable: large primary, small permanent. Unfavorable: small primary, large permanent.

Leeway space

Leeway space The amount by which the combined size of the primary canine and molar teeth exceeds the combined mesiodistal widths of the permanent canine and premolar teeth.

Leeway space Sum of (C-D-E) greater than sum of (3-4-5) This allows more space for 3,4,5. Averages 1.5 mm in the upper arch and 2.5 mm in the lower arch.

Occlusal changes in the mixed dentition Distal step Flush terminal plane Mesial step Class II ETE Class I Class III